Sympathetic Noradrenergic Innervation Research Articles

Cardioselective peripheral noradrenergic deficiency in Lewy body synucleinopathies.

ObjectiveLewy body (LB) synucleinopathies such as Parkinson’s disease (PD) entail profound cardiac norepinephrine deficiency. The status of sympathetic noradrenergic innervation at other extracranial sites has been unclear. Although in vivo neuroimaging studies have indicated a cardioselective noradrenergic lesion, no previous study has surveyed peripheral organs for norepinephrine contents in LB diseases. We reviewed 18F‐dopamine (18F‐DA) positron emission tomographic images and postmortem neurochemical data across several body organs of controls and patients with the LB synucleinopathies PD and pure autonomic failure (PAF) and the non‐LB synucleinopathy multiple system atrophy (MSA).Methods 18F‐DA–derived radioactivity in the heart, liver, spleen, pancreas, stomach, kidneys, thyroid, and submandibular glands were analyzed from 145 patients with LB synucleinopathies (112 PD, 33 PAF), 74 controls, and 85 MSA patients. In largely separate cohorts, postmortem tissue norepinephrine data were reviewed for heart, liver, spleen, pancreas, kidney, thyroid, submandibular gland, and sympathetic ganglion tissue from 38 PD, 2 PAF, and 5 MSA patients and 35 controls.ResultsInterventricular septal 18F‐DA–derived radioactivity was decreased in the LB synucleinopathy group compared to the control and MSA groups (P < 0.0001 each). The LB and non‐LB groups did not differ in liver, spleen, pancreas, stomach, or kidney 18F‐DA–derived radioactivity. The LB synucleinopathy group had markedly decreased apical myocardial norepinephrine, but normal tissue norepinephrine in other organs. The MSA group had normal tissue norepinephrine in all examined organs.InterpretationBy in vivo sympathetic neuroimaging and postmortem neurochemistry peripheral noradrenergic deficiency in LB synucleinopathies is cardioselective. MSA does not involve peripheral noradrenergic deficiency.

32-LB: Early Selective Loss of CGRP Sensory Innervation to Cutaneous Arterioles May Be an Early Prediabetic Feature Developing prior to the Onset of Overt Type 2 Diabetes (T2D) in Rhesus Monkeys and Humans Instead of Being a Consequence

Vasculopathy complications of T2D cause limited tissue perfusion, ulcers, and often amputation. Mechanisms underlying T2D vasculopathy remain ambiguous. Compare to normal controls, multi-molecular immunofluorescence of glabrous hand and foot skin biopsies from 12T2D monkeys and 35 humans revealed a consistent depletion of CGRP containing sensory innervation (CGRPsens) that normally mediates local vasodilatation of cutaneous resistance arterioles. By contrast, arteriole vasoconstricting noradrenergic sympathetic innervation (NAsymp) remained largely intact. Thus, a vasoconstrictive imbalance could potentially impede arteriole blood flow contributing to hypertension and reduced capillary perfusion. Further analyses of monkeys indicated that this neurovascular pathology may begin during prediabetic metabolic syndrome. Surprisingly, the NAsymp and a separate set of CGRPsens to precapillary arterioles and capillaries initially remained intact in the T2D monkeys and humans and may even be increasing. This may be a maladaptive response to dilate and increase capillary perfusion to compensate for a reduced arteriole supply. As such, dilatation of the capillaries may increase their blood volume, but inadvertently reduce the rate of blood flow resulting in anoxia. In advanced T2D, a de novo superficial shunt pathology appears and capillaries begin to deteriorate. In contrast to this neurovascular pathology occurring early or before overt T2D onset, we and others have non-painful and painful T2D neuropathies involving other types of tactile sensory innervation typically occur after T2D hyperglycemia is well established. Thus, the early stage neurovascular pathology may be a direct contributor to the onset of 2TD instead of being a consequence of TD2 hyperglycemia, and may be a potential target for early detection and pre-emptive treatment. Disclosure F. Rice: None. G. Houk: None. B.C. Hansen: None. X. Tigno: None. P. Albrecht: None.

Alpha-Synuclein Deposition Within Sympathetic Noradrenergic Neurons Is Associated With Myocardial Noradrenergic Deficiency in Neurogenic Orthostatic Hypotension.

Lewy body diseases involve neurogenic orthostatic hypotension (nOH), cardiac noradrenergic deficiency, and deposition of the protein AS (alpha-synuclein) in sympathetic ganglion tissue. Mechanisms linking these abnormalities are poorly understood. One link may be AS deposition within sympathetic neurons. We validated methodology to quantify AS colocalization with TH (tyrosine hydroxylase), a marker of sympathetic noradrenergic innervation, and assessed associations of AS/TH colocalization with myocardial norepinephrine content and cardiac sympathetic neuroimaging data in nOH. Postmortem sympathetic ganglionic AS/TH colocalization indices and myocardial norepinephrine contents were measured in 4 Lewy body and 3 rare non-Lewy body nOH patients. Sixteen Lewy body and 11 non-Lewy body nOH patients underwent in vivo skin biopsies and thoracic 18F-dopamine positron emission tomographic scanning, with cutaneous colocalization indices expressed versus cardiac 18F-dopamine-derived radioactivity. Ganglionic AS/TH colocalization indices were higher and myocardial norepinephrine lower in Lewy body than non-Lewy body nOH ( P=0.0020, P=0.014). The Lewy body nOH group had higher AS/TH colocalization indices in skin biopsies and lower myocardial 18F-dopamine-derived radioactivity than did the non-Lewy body nOH group ( P<0.0001 each). All Lewy body nOH patients had colocalization indices >1.5 in skin biopsies and 18F-dopamine-derived radioactivity <6000 nCi-kg/cc-mCi, a combination not seen in non-Lewy body nOH patients ( P<0.0001). In Lewy body nOH, AS deposition in sympathetic noradrenergic nerves is related to postmortem neurochemical and in vivo neuroimaging evidence of myocardial noradrenergic deficiency. These associations raise the possibility that intraneuronal AS deposition plays a pathophysiological role in the myocardial sympathetic neurodegeneration attending Lewy body nOH.

Aging of Bone Marrow Microenvironment Promotes Myeloid Bias of Hematopoietic Progenitors and Is a Target in Age-Related Myeloproliferative Neoplasms

Background: BM HSC accumulate during aging but are functionally impaired; however, it remains debated whether this aging results from HSC-intrinsic and/or -extrinsic mechanisms. Myeloid malignancies are more frequent in the elderly, but whether the aged microenvironment predisposes to these malignancies is unclear. Myeloid-biased HSC and especially platelet-primed HSC expand in aged mice. However, both platelet-primed and unprimed old HSCs exhibit myeloid bias, possibly suggesting a microenvironmental participation. Moreover, some hallmarks of murine hematopoietic aging (like increased platelets) are present in premature aging (Hutchinson-Gilford progeria syndrome, HGPS) and are exacerbated in age-related myeloproliferative neoplasms (MPN), where we found that niche heterogeneity can influence disease progression (ASH abstract ID 113495). Given that aging increases myelopoiesis in physiology, HGPS and MPN (despite their heterogenous genetic background), we hypothesized that shared microenvironmental alterations influence HSC lineage bias during agingResults: HSCs, perisinusoidal megakaryocytes (Mk) and myelopoietic cytokines increase in the BM of HGPS mice, resembling normally aged mice. However, WT recipients of HGPS BM cells do not reproduce myeloid bias, indicating that premature aging affects hematopoiesis in HGPS in a non-HSC-autonomous manner. We have investigated niche contributions to lineage bias during physiological aging because HGPSmice do not tolerate myeloablation. Consistently with recent findings (Nat Med 2018;24:782-91) HSC niches decrease near bone (endosteal BM) and expand further from bone in aged mice, but we observed different vascular changes mainly consisting of halved endosteal transition zone vessels with associated Nes-GFP+ cells and 4-fold-increased non-endosteal capillaries with Nes-GFP+ cells. However, contrasting the afore mentioned study but in agreement with other reports, we found aging-related increase of BM noradrenergic innervation, which promotes megakaryopoiesis in WT mice, but not in mice lacking β2 and β3 adrenergic receptors (ARs). Yet, these receptors exhibit opposite effects on microenvironmental regulation of myelopoiesis. β2-AR-agonist promotes Mk differentiation from human CD34+ HSCs co-cultured with MS-5 cells or in WT (but not IL-6 KO) primary murine BM culture. Consequently, adult β2-AR KO mice exhibit decreased Mk-lineage cells, which correlated with reduced BM IL-6. In contrast, adult β3-AR KO mice exhibit increased mature Mk near sinusoids, which correlated with tripled Cxcl12 mRNA expression in non-endosteal BM. Mechanistically β3-AR regulates Cxcl12-dependent HSPC and megakaryocyte localization, nitric oxide (NO) production and expression of myelopoietic cytokines. In vitro, β3-AR-agonist-treated stromal cells decrease human and murine HSPC differentiation into Mk. This effect requires Nos1-dependent NO production, since Nos1-/- mice have high circulating platelets and β3-AR agonist specifically increases lymphoid-biased HSCs in primary BM cultures in a Nos1-dependent manner. Finally, Mk increased in β3-AR KO mice transplanted with MPN BM cells, whereas Mk decreased in MPN mice treated with β3-AR agonist. To test the clinical relevance of our findings, we measured plasma nitrates and myelopoietic cytokines in MPN patients (median age=62) chronically treated only with β3-AR agonist, who show improved myelofibrosis correlated by rescued nestin+ niches (Blood 2016;128:3108), which is consistent with previous results in mice (Nature 2014;512:78-81). We found inverse correlations between the concentration of nitrates and myelopoietic cytokinesConclusions: microenvironmental aging promotes myeloid bias through similar cytokines (e.g. IL1β, IL6) during premature or physiological aging. In the latter, HSC supporting niches decrease near bone but expand further from bone. Increased BM sympathetic noradrenergic innervation promotes β2-AR-IL-6-dependent myeloid bias. Reduction of endosteal niches decreases β3-AR-NO-dependent inhibition of myelopoietic cytokines. However, chronic treatment with β3-AR-agonist does not rejuvenate overall hematopoiesis but decreases exacerbated megakaryopoiesis in mice and humans with MPNs. Therefore, niche aging promotes myeloid bias and might represent a therapeutic target in age-related myeloproliferative disorders DisclosuresNo relevant conflicts of interest to declare.

Differences in autonomic innervation to the vertebrobasilar arteries in spontaneously hypertensive and Wistar rats.

Essential hypertension is associated with hyperactivity of the sympathetic nervous system and hypoperfusion of the brainstem area controlling arterial pressure. Sympathetic and parasympathetic innervation of vertebrobasilar arteries may regulate blood perfusion to the brainstem. We examined the autonomic innervation of these arteries in pre-hypertensive (PHSH) and hypertensive spontaneously hypertensive (SH) rats relative to age-matched Wistar rats. Our main findings were: (1) an unexpected decrease in noradrenergic sympathetic innervation in PHSH and SH compared to Wistar rats despite elevated sympathetic drive in PHSH rats; (2) a dramatic deficit in cholinergic and peptidergic parasympathetic innervation in PHSH and SH compared to Wistar rats; and (3) denervation of sympathetic fibres did not alter vertebrobasilar artery morphology or arterial pressure. Our results support a compromised vasodilatory capacity in PHSH and SH rats compared to Wistar rats, which may explain their hypoperfused brainstem. Neurogenic hypertension may result from brainstem hypoperfusion. We previously found remodelling (decreased lumen, increased wall thickness) in vertebrobasilar arteries of juvenile, pre-hypertensive spontaneously hypertensive (PHSH) and adult spontaneously hypertensive (SH) rats compared to age-matched normotensive rats. We tested the hypothesis that there would be a greater density of sympathetic to parasympathetic innervation of vertebrobasilar arteries in SH versus Wistar rats irrespective of the stage of development and that sympathetic denervation (ablation of the superior cervical ganglia bilaterally) would reverse the remodelling and lower blood pressure. Contrary to our hypothesis, immunohistochemistry revealed a decrease in the innervation density of noradrenergic sympathetic fibres in adult SH rats (P<0.01) compared to Wistar rats. Unexpectedly, there was a 65% deficit in parasympathetic fibres, as assessed by both vesicular acetylcholine transporter (α-VAChT) and vasoactive intestinal peptide (α-VIP) immunofluorescence (P<0.002) in PHSH rats compared to age-matched Wistar rats. Although the neural activity of the internal cervical sympathetic branch, which innervates the vertebrobasilar arteries, was higher in PHSH relative to Wistar rats, its denervation had no effect on the vertebrobasilar artery morphology or persistent effect on arterial pressure in SH rats. Our neuroanatomic and functional data do not support a role for sympathetic nerves in remodelling of the vertebrobasilar artery wall in PHSH or SH rats. The remodelling of vertebrobasilar arteries and the elevated activity in the internal cervical sympathetic nerve coupled with their reduced parasympathetic innervation suggests a compromised vasodilatory capacity in PHSH and SH rats that could explain their brainstem hypoperfusion.

Reduced Noradrenergic Signaling in the Spleen Capsule in the Absence of CB1 and CB2 Cannabinoid Receptors.

The spleen is a visceral organ that contracts during hypoxia to expel erythrocytes and immune cells into the circulation. Spleen contraction is under the control of noradrenergic sympathetic innervation. The activity of noradrenergic neurons terminating in the spleen capsule is regulated by α2-adrenergic receptors (AR). Interactions between endogenous cannabinoid signaling and noradrenergic signaling in other organ systems suggest endocannabinoids might also regulate spleen contraction. Spleens from mice congenitally lacking both CB1 and CB2 cannabinoid receptors (Cnr1 -/- /Cnr2 -/- mice) were used to explore the role of endocannabinoids in spleen contraction. Spleen contraction in response to exogenous norepinephrine (NE) was found to be significantly lower in Cnr1 -/- /Cnr2 -/- mouse spleens, likely due to decreased expression of capsular α1AR. The majority of splenic Cnr1 mRNA expression is by cells of the spleen capsule, suggestive of post-synaptic CB1 receptor signaling. Thus, these studies demonstrate a role for CB1 and/or CB2 in noradrenergic splenic contraction.

Survival in synucleinopathies: A prospective cohort study.

Parkinson disease (PD), multiple system atrophy (MSA), and pure autonomic failure (PAF) involve cytoplasmic deposition of α-synuclein and are considered to be synucleinopathies. Approximately 40% of patients with PD, most patients with MSA, and all patients with PAF have neurogenic orthostatic hypotension (OH). This study compared long-term survival in these synucleinopathies. In this prospective cohort study, survival data were obtained for 97.6% of 206 referred patients evaluated between 1994 and 2014 (47 PD + OH, 54 PD no OH, 15 cerebellar MSA [MSA-C], 57 parkinsonian MSA [MSA-P], 28 PAF). Individual diagnoses were confirmed by clinical criteria and results of pharmacologic, neurochemical, and neuroimaging tests of sympathetic noradrenergic innervation. The Cox proportional hazard model was used to calculate hazard ratios (HRs) from symptom onset and from time of evaluation to death. Patients with MSA-C or MSA-P had shorter survival from symptom onset than did patients with PD + OH (age- and sex-adjusted HR = 6.1, 5.6; p < 0.0001 each), PAF (HR = 10.8, 9.9; p < 0.0001 each) or PD no OH (HR = 14.9, 13.6; p < 0.0001 each). Among parkinsonian patients who died, median times from motor onset to death were 7.5 years in MSA-P, 11.6 years in PD + OH, and 15.8 years in PD no OH. Probabilities of survival for 10 years from onset of relevant symptoms were 0.39 in MSA-C, 0.33 in MSA-P, 0.74 in PD + OH, 0.87 in PAF, and 0.93 in PD no OH. In synucleinopathies, survival depends on the particular disease, with the risk of death greater in MSA-P than in PD + OH and in PD + OH than in PD no OH.

Selective modulation of lymphoproliferation and cytokine production via intracellular signaling targets by α1- and α2-adrenoceptors and estrogen in splenocytes

The mechanistic implications of the presence of sympathetic noradrenergic innervation in lymphoid organs in synaptic association with lymphocytes open to the influence of hormonal fluctuations throughout reproductive age in females has not been investigated yet. The aim of the present study is to investigate the role of alpha-adrenoceptors (α-ARs) and estrogen in modulating immune responses in the spleen through intracellular signaling targets such as ERK 1/2, CREB, Akt, NF-κB. Splenocytes from young Sprague-Dawley rats were incubated with α1- and α2- AR specific agonists, phenylephrine and clonidine, without and with 17b-estradiol or specific antagonists prazosin and idazoxan to examine their effects on proliferation, cytokine production, nitric oxide production, and intracellular signaling molecules. α1-AR stimulation inhibited lymphocyte proliferation and IFN-g production and enhanced IL-2, p-ERK and p-CREB expression. Co-stimulation using estrogen enhanced cytokine production and suppressed p-Akt expression. α1-AR blockade reversed agonist-induced IL-2 production alone. α2-AR stimulation inhibited lymphocyte proliferation, p-ERK and p-CREB expression, and increased p-NF-kB and p-Akt expression. Co-stimulation with estrogen increased IL-2 and suppressed p-CREB expression. α2-AR Idazoxan prevented IL-2 production in the absence and presence of estrogen, and reversed clonidine-induced increase in NO production and p-ERK and p-Akt expression in the presence of estrogen. These results suggest that the cell-mediated immune responses are selectively modulated depending upon the subtypes of α-AR and further, these effects are differentially regulated in the presence of estrogen mediated through selective alteration in the intracellular signaling pathways involving ERK, CREB, Akt, and NF-κB.

Prevention of Mammary Tumor Development through Neuroimmunomodulation in the Spleen and Lymph Nodes of Old Female Sprague-Dawley Rats by L-Deprenyl

Background: Development of mammary tumors is an age-associated phenomenon that is likely due to deficits in the neuroendocrine-immune interactions. Previously, we demonstrated that <smlcap>L</smlcap>-deprenyl, a monoamine oxidase-B (MAO-B) inhibitor, can enhance immune responses and restore noradrenergic (NA) innervation in the spleens of rats with carcinogen-induced and spontaneously developing mammary tumors. Objectives: To investigate whether (1) treatment of early middle-aged female rats would prevent the spontaneous development of mammary tumors accompanied by restoration of immunity in the spleen and draining lymph nodes (DLN) and sympathetic NA innervation in the spleen and (2) deprenyl can influence the proliferation of estrogen receptor (ER)-positive (MCF-7 and T47D) and ER-negative (MDA-MB-231 and Hs 578T) human breast cancer cells. Methods: Early middle-aged (8- to 9-month-old) female Sprague-Dawley rats were treated with 0, 1.0 or 2.5 mg of deprenyl/kg body weight (BW) daily i.p. for 12 months. Cells of ER-positive (ER+) and ER-negative (ER-) human breast cancer cell lines were incubated with media or 10^-3 to 10^-8<smlcap>M</smlcap> deprenyl for 1, 2, 4 or 6 days to examine the proliferation of cells. Results: Tumor incidence increased in saline-treated old female rats, while deprenyl treatment significantly reduced the incidence of mammary tumors in these rats. Saline-treated tumor-bearing rats exhibited reduced splenic NA innervation and norepinephrine (NE) content, splenic interleukin (IL)-2 and interferon (IFN)-γ levels and NK cell activity as well as DLN IL-2 and IFN-γ levels compared to young female rats without tumors. In contrast, treatment with 2.5 mg/kg of deprenyl enhanced IL-2 and IFN-γ production in both the spleen and DLN as well as splenic natural killer (NK) cell activity. Deprenyl treatment also increased concanavalin A (Con A)-induced proliferation of T lymphocytes in the DLN. Deprenyl-induced changes in immune responses were accompanied by enhanced NA innervation and NE content in the spleen. In vitro incubation of various concentrations of deprenyl with ER+ human breast cancer cell lines partly inhibited the proliferation of cells, while it had no effect on the ER- breast cancer cells. Conclusions: These results suggest that (1) development of mammary tumors is mediated through the loss of immunity and sympathetic NA nerve fibers accompanied by reduced NE levels in the spleen, (2) the prevention of mammary tumor development by deprenyl may involve the reversal of the tumor-associated decline in sympathetic NA activity and cell-mediated immune responses in the spleen and DLN and (3) the antitumor effects of deprenyl may be partially mediated through ER-dependent intracellular signaling pathways.

L-Deprenyl Reverses Age-Associated Decline in Splenic Norepinephrine, Interleukin-2 and Interferon-γ Production in Old Female F344 Rats

Aging in female rats is associated with cessation of reproductive cycles, development of mammary cancer, and increased incidence of autoimmune diseases. Previously, we demonstrated an age-related decline in sympathetic noradrenergic (NA) innervation in the spleen and lymph nodes of female F344 rats accompanied by significantly reduced natural killer cell activity, interleukin (IL)-2 and interferon (IFN)-γ production, and T- and B-cell proliferation, suggesting possible links between sympathetic activity and immunosenescence. Objectives: The aim of this study is to investigate the effects of <smlcap>l</smlcap>-(–)-deprenyl, a monoamine oxidase-B inhibitor, on the sympathetic nervous system and cell-mediated immune responses in old female rats. Methods: Low doses of <smlcap>l</smlcap>-deprenyl (0.25 or 1.0 mg/kg body weight, BW) were administered intraperitoneally to 19- to 21-month-old female F344 rats for 8 weeks. To assess the stereoselectivity of the effects of deprenyl on splenic sympathetic activity and immune responses, the <smlcap>d</smlcap>-enantiomer (<smlcap>d</smlcap>-(+)-deprenyl; 1.0 mg/kg BW) was also included in the studies. Norepinephrine (NE) concentration and content, and mitogen-induced T-cell proliferation and cytokine production were assessed in the splenocytes after deprenyl treatment. Results: Treatment with <smlcap>l</smlcap>-deprenyl reversed the age-related decrease in NE concentration and content and IFN-γ production, and increased IL-2 production in the spleen while <smlcap>d</smlcap>-deprenyl did not affect the age-associated reduction in splenic NE levels or cytokine production. Conclusions: These findings demonstrate that <smlcap>l</smlcap>-deprenyl exerts neurorestorative and immunostimulatory effects on the sympathetic nervous system and cell-mediated immune responses during aging and provides evidence for a causal relationship between some aspects of immunosenescence and the age-related decline in sympathetic nerves in the spleens of female F344 rats.

167. Long-term effects of total body irradiation on sympathetic innervation of the murine spleen

Previous studies in mice have shown that total body irradiation (TBI) leads to splenic atrophy, acute reductions in splenic leukocyte populations, and changes in phagocytic function. We also reported that many TBI-induced changes in splenic phagocytic populations were mitigated by chlorisondamine, a non-selective nicotinic blocker, suggesting sympathetic control. To characterize the long-term effects associated with TBI on the noradrenergic sympathetic innervation of the spleen, female, 9–10 week-old C57BL/6J mice were irradiated with Co-60 gamma-rays (0–2 Gy) and euthanized 6 months later. Sucrose–potassium phosphate–glyoxylic acid (SPG) histofluorescence staining and HPLC were used to examine splenic noradrenergic innervation and neurochemical concentration of catecholamines, respectively. All samples of the spleen were taken distal to the hilus. Fluorescence histochemistry for catecholamines revealed no change in the distribution of fluorescent nerves in the splenic white pulp in irradiated mice compared with controls. However, the density of sympathetic nerves coursing along the central arterioles and extending into the periarteriolar lymphatic sheath was greater in mice irradiated at 2 Gy compared with non-irradiated controls. The white pulps also appeared to be reduced in spleens from this group. While norepinephrine concentrations did not differ from control values, dopamine concentrations were reduced. Collectively, these findings suggest maintained nerve distribution in a reduced volume of white pulp in irradiated mice, and increased norepinephrine release and availability for target cells of the immune system.

Clinical Methods to Assess Cardiac Sympathetic Innervation and Function

Physiological, pharmacologic, neurochemical, and neuroimaging methods enable evaluation of cardiac sympathetic noradrenergic innervation and function in humans. This lecture provides examples of each approach. Low frequency power of heart rate variability, adjusted for total or high frequency power, has been used to examine cardiac sympathetic “tone” or “sympathovagal balance” but seems related more closely to baroreflex modulation of autonomic outflows than to the outflows themselves. Effects drugs on cardiac contractility can separate pre‐ from post‐ganglionic noradrenergic lesions. Measurement of norepinephrine and its main neuronal metabolite during infusion of tracer‐labeled norepinephrine provides a means to examine key aspects of cardiac sympathetic function in heart failure. Cardiac sympathetic imaging is very powerful for detecting dysfunction or loss of cardiac sympathetic nerves. Using this technology we described cardiac sympathetic denervation in Parkinson disease and obtained evidence for decreased vesicular uptake of intra‐neuronal catecholamines in Lewy body diseases. Clinical laboratory evaluation therefore can provide important clues to the pathophysiology of neurocardiologic disorders.

Biomarkers, Mechanisms, and Treatment of Autonomic Failure in Parkinson Disease and Related Disorders

Parkinson disease (PD) in one of the most common chronic neurodegenerative diseases of the elderly, and it is likely that as populations age PD will become even more prevalent and more of a public health burden. The movement disorder in PD is characterized by and likely results from severe depletion of dopaminergic neurons of the nigrostriatal system. By the time PD manifests clinically, most of the nigrostriatal dopaminergic neurons are already lost. Identifying laboratory measures—biomarkers—of the disease process is therefore crucial for advances in treatment and prevention. PD is often attended by signs or symptoms of impaired autonomic regulation of the circulation. This lecture comprehensively reviews and updates the field of autonomic cardiovascular abnormalities in PD and related disorders. About 30–40% of PD patients have orthostatic hypotension (OH). PD+OH is consistently associated with failure of both the cardiovagal and sympathoneural limbs of the arterial baroreflex, regardless of levodopa treatment. Most PD patients without OH have more subtle baroreflex abnormalities. Plasma levels of the sympathetic neurotransmitter norepinephrine (NE) and of dihydroxyphenylglycol, the main neuronal metabolite of NE, are lower in PD+OH than in PD without OH, indicating a relatively smaller overall complement of sympathetic nerves in PD+OH; however, patients with pure autonomic failure (PAF) have even lower NE and dihydroxyphenylglycol levels than do PD+OH patients, suggesting more extensive extra-cardiac noradrenergic denervation in PAF than in PD+OH. All patients with PD+OH have markedly reduced sympathetic noradrenergic innervation of the left ventricular myocardium. The cardiac neuroimaging findings in PD+OH contrast with those in multiple system atrophy (MSA), which can be difficult to distinguish from PD+OH, in that MSA usually entails intact sympathetic innervation of the heart. In PD patients with localized myocardial denervation there is earlier or more prominent involvement of the inferolateral wall than of the anterobasal septum, consistent with a retrograde, centripetal pathogenetic process. Cardiac sympathetic denervation occurs independently of striatal dopaminergic denervation across individual PD patients. Therefore, although cardiac sympathetic denervation invariably progresses over time in PD and can come on years before the motor disorder, the denervation can also be a late finding. Other non-motor manifestations such as olfactory dysfunction in PD are more closely associated with cardiac noradrenergic than with striatal dopaminergic denervation. PD and PAF feature not only decreased neuronal catecholamine uptake but also accelerated intra-neuronal catecholamine loss, which seems to reflect decreased vesicular uptake via the vesicular monoamine transporter. MSA patients have normal values for these parameters. In summary, baroreflex failure and cardiac and extra-cardiac noradrenergic denervation characterize OH in PD. These abnormalities occur independently of striatal dopamine depletion. Cardiovascular autonomic variables may provide biomarkers of pre-motor PD in some patients. Understanding mechanisms of cardiac sympathetic dysfunction and denervation in PD may also help elucidate bases of central catecholaminergic lesions in a variety of neurodegenerative diseases. In particular, Lewy body forms of alpha-synucleinopathy seem to be associated with decreased vesicular sequestration of cytosolic catecholamines, and since cytosolic catecholamines are toxic, decreased vesicular recycling may be part of a final pathogenetic pathway in the catecholaminergic denervation that characterizes these diseases.

Age-associated alterations in sympathetic noradrenergic innervation of primary and secondary lymphoid organs in female Fischer 344 rats

Normal aging processes, as well as, psychological stress affect the immune system; each can act alone, or interact with each other, to cause dysregulation of immune function substantially altering physical and mental health. The sympathetic nervous system (SNS), a major mediator of stress effects on immune function, is significantly affected by normal aging process, and stress can affect aging of the SNS. Previously, we have shown age-associated changes in sympathetic noradrenergic (NA) innervation of lymphoid organs in male rodents that affect immune regulation. The purpose of this study was to investigate sympathetic innervation of lymphoid organs and associated alterations in immune responses in young and aging female Fischer 344 (F344) rats. Histofluorescence and immunocytochemistry for NA innervation, and neurochemistry for norepinephrine (NE) levels were performed in the thymus, spleen, and mesenteric lymph nodes (MLN) isolated from 3-month-old young (normal estrous cycle), 8- to 9-month-old (onset of irregular estrous cycling), and 24–25month, and 30–31month female F344 rats (acyclic) at diestrus based on vaginal smears. Age-related alterations in natural killer (NK) cell activity, interleukin-2 (IL-2) and interferon-γ (IFN-γ) production, T and B lymphocyte proliferation were examined in splenocytes. Sympathetic NA innervation and NE levels increased with aging in the thymus, declined in spleen and MLN, and was accompanied by significant reductions in NK cell activity, IL-2 and IFN-γ production, and T and B cell proliferation in old female rats. In 8–9mo rats, NE levels in the hilar region of the spleen and IFN-γ production were unaltered, while NE levels in the end region of the spleen and IL-2 production were reduced. Collectively, these results suggest that aging is characterized by significant alterations in sympathetic NA innervation in the thymus, spleen, and MLN associated with immunosuppression, and that there is a marked shift in NA activity and immune reactivity occurring during middle-aged female rats.

Age-related changes in the sympathetic innervation of cerebral vessels and in carotid vascular responses to norepinephrine in the rat: in vitro and in vivo studies

We hypothesized that the density of sympathetic noradrenergic innervation of cerebral arteries and vasoconstrictor responses evoked in carotid circulation by norepinephrine (NE) increase with maturation and age. In rats of 4-5, 10-12, and 42-44 wk of age (juvenile, mature, middle aged), glyoxylic acid applied to stretch preparations showed the density of noradrenergic nerves in basilar and middle cerebral arteries was greater in mature than juvenile or middle-aged rats. In anesthetized rats, infusion of NE (2.5 mug/kg iv) increased mean arterial pressure (ABP) to approximately 180 mmHg in mature and middle-aged but to only approximately 150 mmHg in juveniles rats. Concomitantly, carotid blood flow (CBF) decreased in mature and middle-aged rats but remained constant in juveniles because carotid vascular conductance (CVC) decreased more in mature and middle-aged than juvenile rats. We also hypothesized that nitric oxide (NO) blunts cerebral vasoconstrictor responses to NE. Inhibition of NO synthase with l-NAME (10 mg/kg iv) induced similar increases in baseline ABP in each group, but larger decreases in CVC and CBF in mature and middle-aged than juvenile rats. Thereafter, the NE-evoked increase in ABP was similar in juvenile and mature but accentuated in middle-aged rats. Concomitantly, NE decreased CVC in juvenile and mature, but not middle-aged rats; in them, CBF increased. Thus, in juvenile rats, sparse noradrenergic innervation of cerebral arteries is associated with weak NE-evoked pressor responses and weak carotid vasoconstriction that allows autoregulation of CBF. Cerebral artery innervation density increases with maturation but lessens by middle age. Meanwhile, NE-evoked pressor responses and carotid vasoconstriction are stronger in mature and middle-aged rats, such that CBF falls despite the evoked increase in ABP. We propose that in juvenile and mature rats, NO does not modulate NE-evoked pressor responses, cerebral vasoconstriction, or CBF autoregulation, but by middle age, NO limits pressor responses and prevents breakthrough of CBF in the upper part of the autoregulatory range.

Adrenal Pheochromocytoma with Surrounding Brown Fat Stimulation

AJR:192, January 2009 chromocytomas induce hypertension through the production of catecholamines, primarily epinephrine, and, less commonly, norepinephrine. Pheochromocytomas are typically sporadic and solitary neoplasms [1]. Only a small percentage of patients with hypertension have a pheochromocytoma, but in those who do, complete resection of the functional tumor provides cure. Cross-sectional imaging such as CT or MRI is an excellent study for showing adrenal masses. Brown fat is normally present in fetuses and infants and diminishes in adults to account for only 1% of the total body mass. Brown fat may have a metabolic or a thermoregulatory function. Remnants of brown fat in the adult are usually found in the neck, mediastinum, axilla, retroperitoneum, and abdominal wall [2]. Brown adipose tissue has much more sympathetic noradrenergic innervation than white adipose tissue [3]. Norepinephrine also has a regulatory function in brown fat. Catecholamine stimulation increases the number of brown fat cells, stimulates lipolysis and glucose transport, and uncouples protein-1 expression in brown fat cells, resulting in heat production [3]. Brown fat is frequently an incidental finding on FDG PET that may result in falsepositive findings [4]. Careful correlation with coregistered CT images should be performed to exclude any masses in areas of brown fat uptake. After injection of the radiotracer, as patients wait to be imaged, controlled room temperature is important to prevent thermogenesis and increased brown fat stimulation. In patients with adrenergic stimulation due to excess catecholamine production, brown adipose tissue may be more abundant than in normal adults. The localization of FDG in areas of excess brown fat in these patients likely results from increased glucose transport related to norepinephrine excess [3, 5]. Adrenal Pheochromocytoma with Surrounding Brown Fat Stimulation

Modulation of rat parasympathetic cardiac ganglion phenotype and NGF synthesis by adrenergic nerves

Cardiac function is regulated by interactions among intrinsic and extrinsic autonomic neurons, and the mechanisms responsible for organizing these circuits are poorly understood. Parasympathetic neurons elsewhere synthesize the neurotrophin NGF, which may promote postganglionic axonal associations where parasympathetic axons inhibit sympathetic transmitter release. Previous studies have shown that parasympathetic NGF content and neurochemical phenotype are regulated by sympathetic innervation. In this study we assessed contributions of sympathetic input on cardiac ganglion neuronal phenotype and NGF expression. Because cardiac ganglia are reported to contain putative noradrenergic neurons, we eliminated sympathetic input both surgically (extrinsic) and chemically (extrinsic plus intrinsic). In controls, most cardiac ganglion neurons expressed vesicular acetylcholine transporter, frequently colocalized with vesicular monoamine transporter, but lacked catecholamine histofluorescence. Most cardiac ganglion neurons expressed NGF transcripts, and 40% contained mature and 47% proNGF immunoreactivity. Guanethidine treatment for 7 days decreased numbers of neurons expressing vesicular acetylcholine transporter, NGF transcripts and NGF immunoreactivity, but did not affect proNGF or vesicular monoamine transporter immunoreactivity. Stellate ganglionectomy had comparable effects on neurochemical phenotype and mature NGF immunoreactivity, but proNGF expression was additionally reduced. These findings show that individual cardiac ganglion neurons display markers of both cholinergic and noradrenergic transmission. Sympathetic noradrenergic innervation maintains levels of cholinergic but not noradrenergic marker protein. Sympathetic innervation also promotes cardiac ganglion neuronal NGF synthesis. Because chemical blockade of all noradrenergic transmission is no more effective than extrinsic sympathectomy, local intrinsic noradrenergic transmission is not a factor in regulating ganglion neuron phenotype.

Nerve Growth Factor Decreases Potassium Currents and Alters Repetitive Firing in Rat Sympathetic Neurons

The sympathetic nervous system is an essential regulator of the cardiovascular system and interactions with target tissue regulate sympathetic neuronal properties. The heart produces nerve growth factor (NGF), which promotes sympathetic noradrenergic innervation of cardiac tissue and affects sympathetic synaptic strength. Neurotrophins, including NGF, are important modulators of synaptic plasticity and membrane electrical properties. Here we show that acute application of NGF causes a change in the repetitive firing pattern of cultured sympathetic neurons of the rat superior cervical ganglion. Neurons fire fewer action potentials in NGF, but with increased frequency, demonstrating an NGF-dependent change from a tonic to a phasic firing pattern. Additionally, NGF decreases the spike time variance, making spikes more tightly time locked to stimulus onset. NGF causes a decrease in the amplitude of both calcium-dependent and -independent potassium currents, and inhibition of calcium-dependent potassium currents using CdCl(2) reproduces some, but not all, of the firing properties induced by NGF. This study suggests that NGF release from cardiac tissue may act to modulate the repetitive firing properties of sympathetic neurons to tune their output to meet the physiological needs of the organism.

Catecholamines and 5-Hydroxytryptamine in Tissues of the Rabbit Exocrine Pancreas

Norepinephrine (NE), dopamine (DA), epinephrine (Epi), and 5-hydroxytryptamine (5-HT) all modulate pancreatic exocrine secretion, yet their concentrations in specific tissues of the exocrine pancreas are unknown. Concentrations of catecholamines and 5-HT in rabbit pancreatic ganglia, acini, ducts and ampullae, and arteries and veins were measured using HPLC. Concentrations of NE in ganglia from the head/neck region were significantly higher than those from the body (1620 +/- 220 vs. 778 +/- 179 pmol/mg protein). Acini contained little NE, DA, or 5-HT (9 +/- 2, 0.9 +/- 0.2, 13 +/- 5 pmol/mg protein). Ducts and ampullae contained NE (314 +/- 74 and 156 +/- 24 pmol/mg protein), DA (43 +/- 14 and 13 +/- 4 pmol/mg protein), Epi (63 +/- 29 and 39 +/- 6 pmol/mg protein), and 5-HT (696 +/- 151 and 3563 +/- 288 pmol/mg protein). Arteries and veins contained the highest concentrations of NE (1962 +/- 463 and 736 +/- 80 pmol/mg protein, respectively). Pancreatic ganglia and blood vessels, rather than acini, are the main sites of noradrenergic sympathetic innervation of the rabbit exocrine pancreas. These nerves preferentially target ganglionic transmission in the head/neck versus the body. Serotonergic nerves provide little or no innervation of rabbit pancreatic ganglia or acini.

Sympathetic cholinergic target innervation requires GDNF family receptor GFRα2

Many cholinergic parasympathetic and enteric neurons require neurturin signaling through GDNF family receptor GFRα2 for target innervation. Since a distinct minority of sympathetic neurons are cholinergic, we examined whether GFRα2 is important for their development. We detected GFRα2 in neonatal sympathetic cholinergic neurons and neurturin mRNA in their target tissues, sweat glands in footpads, and periosteum. Lack of GFRα2 in mice did not affect the number of sympathetic cholinergic neurons, but their soma size was decreased in comparison to wild types. In adult and in 3-week-old GFRα2 knockout mice, the density of sympathetic cholinergic innervation was reduced by 50–70% in the sweat glands, and was completely absent in the periosteum. Sympathetic noradrenergic innervation of blood vessels in the footpads was unchanged. The density of sympathetic axons in sweat glands was unaffected at postnatal day P4 reflecting successful growth into the target area. Our results indicate that the cholinergic subpopulation of sympathetic neurons requires GFRα2 signaling for soma size and for growth or maintenance of target innervation. Thus, neurturin may be a general target-derived innervation factor for postganglionic cholinergic neurons in all parts of the autonomic nervous system.