Central Catecholaminergic Neurons Research Articles

Role of Glial Cell Line-Derived Neurotrophic Factor in the Maintenance of Adult Mesencephalic Catecholaminergic Neurons.

The glial cell line-derived neurotrophic factor has a potent neuroprotective action on mesencephalic dopamine neurons, which are progressively lost in Parkinson's disease. Intrastriatal administration of this factor is a promising therapy for Parkinson's disease. Glial cell line-derived neurotrophic factor is naturally produced in restricted cerebral regions, such as the striatum, septum, and thalamus; however, its effects in the adult brain remain under debate. We sought to clarify the physiologic role of endogenous glial cell line-derived neurotrophic factor in the survival of catecholaminergic neurons of the substantia nigra pars compacta and the locus coeruleus in adult mice. We used 2 new Cre recombinase-based mouse models to delete a floxed-glial cell line-derived neurotrophic factor gene. The first model had Cre expression in the parvalbumin expressing interneurons, as these cells represent the major source of striatal glial cell line-derived neurotrophic factor. The second model was an estrogen receptor 2-based inducible Cre triggered by tamoxifen at 2 months of age. We found that the floxed-glial cell line-derived neurotrophic factor gene was resilient to ablation by Cre-induced recombination and that parvalbumin-driven Cre was particularly inefficient to do so. The inducible-Cre model allowed an average 70% to 80% reduction in glial cell line-derived neurotrophic factor messenger ribonucleic acid and protein in striatum and septum with moderate significant loss of catecholamine neurons in the nigrostriatal pathway and, more markedly, in the locus coeruleus. This was accompanied with mild locomotor decline. Our data support qualitatively the view that brain glial cell line-derived neurotrophic factor is needed for the maintenance of adult central catecholaminergic neurons. © 2020 International Parkinson and Movement Disorder Society.

Neuroprotective Effects of Intranasal IGF-1 against Neonatal Lipopolysaccharide-Induced Neurobehavioral Deficits and Neuronal Inflammation in the Substantia Nigra and Locus Coeruleus of Juvenile Rats

Neonatal lipopolysaccharide (LPS) exposure-induced brain inflammation resulted in motor dysfunction and brain dopaminergic neuronal injury, and increased the risks of neurodegenerative disorders in adult rats. Our previous studies showed that intranasal administration of insulin-like growth factor-1 (IGF-1) protects against LPS-induced white matter injury in the developing rat brain. To further examine whether IGF-1 protects against LPS-induced brain neuronal injury and neurobehavioral dysfunction, recombinant human IGF-1 (rhIGF-1) at a dose of 50 µg/pup was administered intranasally 1 h following intracerebral injection of LPS (1 mg/kg) in postnatal day 5 (P5) Sprague-Dawley rat pups. Neurobehavioral tests were carried out from P7 to P21, and brain neuronal injury was examined at P21. Our results showed that LPS exposure resulted in disturbances of motor behaviors in juvenile rats. Moreover, LPS exposure caused injury to central catecholaminergic neurons, as indicated by a reduction of tyrosine hydroxylase (TH) immunoreactivity in the substantia nigra (SN), ventral tegmental area (VTA) and olfactory bulb (OB), and brain noradrenergic neurons, as indicated by a reduction of TH immunoreactivity in the locus coeruleus (LC) of the P21 rat brain. The LPS-induced reduction of TH+ cells was observed at a greater degree in the SN and LC of the P21 rat brain. Intranasal rhIGF-1 treatment attenuated LPS-induced central catecholaminergic neuronal injury and motor behavioral disturbances, including locomotion, beam walking test and gait analysis. Intranasal rhIGF-1 administration also attenuated LPS-induced elevation of IL-1β levels and numbers of activated microglia, and cyclooxygenase-2+ cells, which were double labeled with TH+ cells in the SN, VTA, OB and LC of the P21 rat brain. These results suggest that IGF-1 may provide protection against neonatal LPS exposure-induced central catecholaminergic neuronal injury and motor behavioral disturbances, and that the protective effects are associated with the inhibition of microglia activation and the reduction of neuronal oxidative stress by the suppression of the neuronal cyclooxygenase-2 expression.

A Central Catecholaminergic Circuit Controls Blood Glucose Levels during Stress

Stress-induced hyperglycemia is a fundamental adaptive response that mobilizes energy stores in response to threats. Here, our examination of the contributions of the central catecholaminergic (CA) neuronal system to this adaptive response revealed that CA neurons in the ventrolateral medulla (VLM) control stress-induced hyperglycemia. Ablation of VLM CA neurons abolished the hyperglycemic response to both physical and psychological stress, whereas chemogenetic activation of these neurons was sufficient to induce hyperglycemia. We further found that CA neurons in the rostral VLM, but not those in the caudal VLM, cause hyperglycemia via descending projections to the spinal cord. Monosynaptic tracing experiments showed that VLM CA neurons receive direct inputs from multiple stress-responsive brain areas. Optogenetic studies identified an excitatory PVN-VLM circuit that induces hyperglycemia. This study establishes the central role of VLM CA neurons in stress-induced hyperglycemia and substantially expands our understanding of the central mechanism that controls glucose metabolism.

A brain-sparing diphtheria toxin for chemical genetic ablation of peripheral cell lineages

Conditional expression of diphtheria toxin receptor (DTR) is widely used for tissue-specific ablation of cells. However, diphtheria toxin (DT) crosses the blood–brain barrier, which limits its utility for ablating peripheral cells using Cre drivers that are also expressed in the central nervous system (CNS). Here we report the development of a brain-sparing DT, termed BRAINSPAReDT, for tissue-specific genetic ablation of cells outside the CNS. We prevent blood–brain barrier passage of DT through PEGylation, which polarizes the molecule and increases its size. We validate BRAINSPAReDT with regional genetic sympathectomy: BRAINSPAReDT ablates peripheral but not central catecholaminergic neurons, thus avoiding the Parkinson-like phenotype associated with full dopaminergic depletion. Regional sympathectomy compromises adipose tissue thermogenesis, and renders mice susceptible to obesity. We provide a proof of principle that BRAINSPAReDT can be used for Cre/DTR tissue-specific ablation outside the brain using CNS drivers, while consolidating the link between adiposity and the sympathetic nervous system.

Exaggerated phosphorylation of brain tau protein in CRH KO mice exposed to repeated immobilization stress

Neuroendocrine and behavioral stress responses are orchestrated by corticotropin-releasing hormone (CRH) and norepinephrine (NE) synthesizing neurons. Recent findings indicate that stress may promote development of neurofibrillary pathology in Alzheimer's disease. Therefore, we investigated relationships among stress, tau protein phosphorylation, and brain NE using wild-type (WT) and CRH-knockout (CRH KO) mice. We assessed expression of phosphorylated tau (p-tau) at the PHF-1 epitope and NE concentrations in the locus coeruleus (LC), A1/C1 and A2/C2 catecholaminergic cell groups, hippocampus, amygdala, nucleus basalis magnocellularis, and frontal cortex of unstressed, singly stressed or repeatedly stressed mice. Moreover, gene expression and protein levels of tyrosine hydroxylase (TH) and CRH receptor mRNA were determined in the LC. Plasma corticosterone levels were also measured. Exposure to a single stress increases tau phosphorylation throughout the brain in WT mice when compared to singly stressed CRH KO animals. In contrast, repeatedly stressed CRH KO mice showed exaggerated tau phosphorylation relative to WT controls. We also observed differences in extent of tau phosphorylation between investigated structures, e.g. the LC and hippocampus. Moreover, CRH deficiency leads to different responses to stress in gene expression of TH, NE concentrations, CRH receptor mRNA, and plasma corticosterone levels. Our data indicate that CRH effects on tau phosphorylation are dependent on whether stress is single or repeated, and differs between brain regions. Our findings indicate that CRH attenuates mechanisms responsible for development of stress-induced tau neuropathology, particularly in conditions of chronic stress. However, the involvement of central catecholaminergic neurons in these mechanisms remains unclear and is in need of further investigation.

Is the catecholaminergic (CA) System an important mechanism for respiratory regulation during hypercapnia and hypoxia in newborn rats (P7‐8)?

Brainstem CA neurons play an important role in the maturation and modulation of respiration. In adult mammals, CA system modulates the hypoxic and hypercapnic drive to breath. We evaluated the role of central CA neurons of male and female neonatal rats (P7-8) in the hypercapnic and hypoxic ventilatory response (HCVR/HVR) by specifically lesioning CA neurons using antidopamine beta-hydroxylase-saporin (DBH-SAP, 42ng / 100nL) injected into the 4th ventricle. Minute ventilation (VE) was recorded by pressure-plethysmography from the body chamber during normoxia, hypercapnia (7%CO2) and hypoxia (10%O2). The HCVR was significantly reduced in male (53%) and female (58%) lesioned neonatal rats (male- control group: 204.7±6.1 vs. lesioned group: 151.1±7.6, p<0.001; female- control group: 210.5±13.9 vs. lesioned group: 152.6±9.1, p<0.001; all values relative to % of baseline). In Addition, a similar reduction was observed in the HVR (male- control group: 169.3±7.1 vs. lesioned group: 109.6±6.9 , p<0.001; female- control group: 163.7±3.8 vs. lesioned group: 129.2±4.7, p<0.001; all values relative to % of baseline). These results suggest that central CA neurons exert an important excitatory modulation in CO2 and O2 chemosensitivity in neonates (P7-8). Financial support: FAPESP and CNPq

Catecholaminergic (CA) neurons modulate hypoxic ventilatory response in newborn rats (P7‐8) (LB737)

CA neurons are involved in autonomic and respiratory regulation during low O2 conditions in adult mammals. We evaluated the participation of central CA neurons of neonate male and female rats (P7‐8) in the hypoxic ventilatory response (HVR) by specifically lesioning them with antidopamine beta‐hydroxylase‐saporin (DBH‐SAP, 42ng / 100nL) injected via the 4th ventricle. Minute ventilation (VE) of newborn was recorded by pressure‐plethysmography from the body chamber during normoxia and hypoxia (10%O2). HVR was reduced significantly (~23%) in male and female lesioned newborn rats (male‐ control group: 137.6±6.4 (% of baseline) vs lesioned group: 104.3±1.4 (% of baseline), p&lt;0.01; female‐ control group: 131±1.0 (% of baseline) vs lesioned group: 102.6±2.6 (% of baseline) p&lt;0.02). These results suggest that catecholaminergic neurons exert an excitatory modulation in newborn rats in O2 chemosensitivity.Grant Funding Source: Fapesp and CNPq

GDNF and protection of adult central catecholaminergic neurons

Neurotrophic factors are small proteins necessary for neuron survival and maintenance of phenotype. They are considered as promising therapeutic tools for neurodegenerative diseases. The glial cell line-derived neurotrophic factor (GDNF) protects catecholaminergic cells from toxic insults; thus, its potential therapeutic applicability in Parkinson's disease has been intensely investigated. In recent years, there have been major advances in the analysis of GDNF signaling pathways in peripheral neurons and embryonic dopamine mesencephalic cells. However, the actual physiological role of GDNF in maintaining catecholaminergic central neurons during adulthood is only starting to be unraveled, and the mechanisms whereby GDNF protects central brain neurons are poorly known. In this study, we review the current knowledge of GDNF expression, signaling, and function in adult brain, with special emphasis on the genetic animal models with deficiency in the GDNF-dependent pathways.

The effects of age and lipopolysaccharide (LPS)-mediated peripheral inflammation on numbers of central catecholaminergic neurons

Parkinson's disease (PD), an age-related movement disorder, is characterized by severe catecholaminergic neuron loss in the substantia nigra pars compacta (SN(PC))-ventral tegmental area (VTA) and locus coeruleus (LC). To assess the stability of these central catecholaminergic neurons following an acute episode of severe inflammation, 6 to 22 month old C57/Bl6 mice received a maximally tolerated dose of lipopolysaccharide (LPS) followed by euthanasia 2 hours later to assay peak levels of peripheral and central cytokines; and, 14 weeks later for computerized stereology of tyrosine hydroxylase-immunopositive (tyrosine hydroxylase-positive [TH+]) neurons in the SN(PC)-VTA and LC. Two hours after LPS, cytokine levels varied in an age-related manner, with the greatest peripheral and central elevations in old and young mice, respectively. Severe inflammation failed to cause loss of TH+ neurons in SN(PC)-VTA or LC; however, there was an age-related decline in these TH+ neurons in LPS-treated and control groups. Thus, unknown mechanisms in the B6 mouse brain appear to protect against catecholaminergic neuron loss following an acute episode of severe inflammation, while catecholaminergic neuron loss occurs during normal aging.

Area-Specific Differences in Transmitter Release in Central Catecholaminergic Neurons of Spontaneously Hypertensive Rats

The link among blood pressure, sympathetic output, and brain neurons producing catecholamines is well documented. Nevertheless, their intrinsic properties and any alterations in signaling characteristics between normotensive and hypertensive phenotypes remain unknown. Here, we directly compared neurophysiological properties of catecholamine release of C1 and A2 neurons of the spontaneously hypertensive rat and Wistar rat in organotypic slices. C1 and A2 areas were studied because both are widely implicated in the pathophysiology of hypertension. Catecholaminergic neurons were visualized using viral vectors to express green fluorescent protein. Microamperometry revealed that C1 axonal varicosities of spontaneously hypertensive but not normotensive Wistar rats release a transmitter predominantly (approximately 86%) in very large quanta, comparable in catecholamine load to adrenal chromaffin granules. Because quantal size affects the spread of transmitter in the extracellular space, this may enhance the impact of C1 varicosities on their downstream targets and increase sympathetic drive in the hypertensive rat. Electrophysiological properties and Ca2+ handling were studied using patch clamp and confocal imaging. Although overall electrophysiological characteristics of C1 and A2 neurons were comparable between strains, the characteristic angiotensin-II-induced Ca2+ mobilization was reduced in A2 neurons of the spontaneously hypertensive rat. Because A2 neurons are a part of a homeostatic antihypertensive circuit, this could reduce their restraining influence on blood pressure. Thus, we have revealed an increased quantal size in C1 varicosities and a reduced responsiveness of A2 neurons of the spontaneously hypertensive rat to angiotensin II. Both effects could contribute to elevated sympathetic activity and blood pressure in the spontaneously hypertensive rat.

Noradrenergic neurones in rat brainstem release noradrenaline from axonal varicosities and cell bodies in vitro

Central catecholaminergic neurones, in particular in areas A2 (nucleus of the solitary tract) and C1 (rostral ventro-lateral medulla) play important roles in various autonomic functions including blood pressure regulation. In order to understand the mechanisms regulating noradrenaline (NA) release in the brain, we investigated vesicle fusion events in central noradrenergic (NAergic) neurones.

Bee Venom Injection Significantly Reduces Nociceptive Behavior in the Mouse Formalin Test via Capsaicin-Insensitive Afferents

Peripheral bee venom (BV) administration produces 2 contrasting effects, nociception and antinociception. This study was designed to evaluate whether the initial nociceptive effect induced by BV injection into the Zusanli acupoint is involved in producing the more prolonged antinociceptive effect observed in the mouse formalin test, and whether capsaicin-sensitive primary afferents are involved in these effects. BV injection into the Zusanli point increased spinal Fos expression but not spontaneous nociceptive behavior. BV pretreatment 10 minutes before intraplantar formalin injection dose-dependently attenuated nociceptive behavior associated with the second phase of the formalin test. The destruction of capsaicin-sensitive primary afferents by resiniferatoxin (RTX) pretreatment selectively decreased BV-induced spinal Fos expression but did not affect BV-induced antinociception. Furthermore, BV injection increased Fos expression in tyrosine hydroxylase immunoreactive neurons in the locus caeruleus, and this expression was unaltered by RTX pretreatment. Finally, BV’s antinociception was blocked by intrathecal injection of 10 μg idazoxan, and this effect was not modified by RTX pretreatment. These findings suggest that subcutaneous BV stimulation of the Zusanli point activates central catecholaminergic neurons via capsaicin-insensitive afferent fibers without induction of nociceptive behavior. This in turn leads to the activation of spinal α 2-adrenoceptors, which ultimately reduces formalin-evoked nociceptive behaviors. Perspective This study demonstrates that BV acupuncture produces a significant antinociception without nociceptive behavior in rodents, which is mediated by capsaicin-insensitive afferents and involves activation of central adrenergic circuits. These results further suggest that BV stimulation into this acupuncture point might be a valuable alternative to traditional electrical or mechanical acupoint stimulation.

Monoamine metabolism and sympathetic nervous activation following subarachnoid haemorrhage: Influence of gender and hydrocephalus

Subarachnoid haemorrhage is a serious condition, often accompanied by cerebral vasospasm and hydrocephalus, which may result in delayed cerebral ischaemia and neurological deterioration. While the mechanisms responsible remain unknown, activation of the sympathetic nervous system, leading to elevated levels of circulating catecholamines is, at least in part, implicated. In this study, we sought to examine the importance of sympathetic nervous activation and its relation to brain monoaminergic neurotransmission in 25 patients following subarachnoid haemorrhage by examining plasma and cerebrospinal fluid levels of the catecholamines noradrenaline, adrenaline and dopamine, and their metabolites. Total body sympathetic activity was concurrently assessed using isotope dilution methodology. In the early phase following subarachnoid haemorrhage patients exhibited markedly elevated rates of spillover of noradrenaline to plasma (9.11±1.12 vs. 3.39±0.26 nmol/min, p<0.01), with rates being higher in those patients in whom hydrocephalus developed (11.15±1.40 vs. 7.90±1.41 nmol/min, p=0.05). The degree of sympathetic nervous activation tended to be higher in females compared with males. Lower cerebral perfusion pressures were observed in those patients in whom cerebrospinal fluid concentrations of noradrenaline and dopamine metabolites were high. A marked sympathetic nervous activation, more pronounced in women and in those with hydrocephalus, occurs following subarachnoid haemorrhage. The diminished cerebral perfusion seen following subarachnoid bleeding may occur as a result of activation of central catecholaminergic neurones.

Co-transmitter function of ATP in central catecholaminergic neurons of the rat

Intracellular recordings were made in a mid-pontine slice preparation of the rat brain containing the nucleus locus coeruleus. Focal electrical stimulation evoked biphasic synaptic potentials consisting of early depolarizing (d.p.s.p.) and late hyperpolarizing (i.p.s.p.) components. The α 2-adrenoceptor antagonist idazoxan inhibited the i.p.s.p. without altering the d.p.s.p. All of the following experiments were carried out in the presence of kynurenic acid and picrotoxin to block the glutamatergic and GABAergic fractions of the d.p.s.p., respectively. Guanethidine, which is known to inhibit noradrenaline and ATP release from nerve terminals of postganglionic sympathetic nerves, depressed both the d.p.s.p. and the i.p.s.p. in a concentration-dependent manner. Damage of catecholaminergic nerve terminals by 6-hydroxydopamine also decreased both the d.p.s.p. and the i.p.s.p. The P2 receptor antagonist pyridoxal-phosphate-6-azophenyl-2′,4′-disulphonic acid (PPADS) depressed the d.p.s.p., whereas the i.p.s.p. remained unaffected. The further application of PPADS did not increase the depression of the d.p.s.p. by guanethidine. Superfusion with the mixed α-adrenoceptor agonist noradrenaline or the selective P2 receptor agonist adenosine 5′- O-(2-thiodiphosphate) inhibited both the d.p.s.p. and the i.p.s.p. The inhibitory effects of these agonists were prevented by the respective antagonists idazoxan or suramin. In the presence of suramin noradrenaline failed to inhibit the residual d.p.s.p. Superfused noradrenaline potentiated rather than inhibited responses to pressure-applied α,β-methylene-ATP; superfused adenosine 5′- O-(2-thiodiphosphate) did not interact with pressure-applied noradrenaline. In conclusion, we present electrophysiological evidence for the co-release of ATP and catecholamines in the CNS. At the cell somata of neurons in the locus coeruleus, noradrenaline and ATP activate inhibitory α 2-adrenoceptors and excitatory P2 receptors, respectively. In addition, inhibitory presynaptic autoreceptors of the α 2 and P2 types appear to regulate release of the two co-transmitters.

Development of catecholaminergic neurons in the pond snail, Lymnaea stagnalis: I. Embryonic development of dopamine-containing neurons and dopamine-dependent behaviors.

The embryonic development of the catecholaminergic system of the pond snail, Lymnaea stagnalis, was investigated by using chromatographic and histochemical methods. High performance liquid chromatography suggested that dopamine was the only catecholamine present in significant concentrations throughout the embryonic development of Lymnaea. Dopamine first became detectable at about embryonic stage (E) 15 (15% of embryonic development) and then increased in amount during early development to reach about 120-140 fmol per animal by around E40. Dopamine content remained stable during mid-embryogenesis (E40-65), increased slowing for the next couple of days, and then increased rapidly to culminate at about 400 fmol per animal by hatching. The detection of aldehyde- and glyoxylate-induced fluorescence and of tyrosine hydroxylaselike immunoreactivity indicated that the first catecholaminergic cells appeared in the late trochophore or early veliger stage of embryonic development (E32-35). The paired perikarya of these transient apical catecholaminergic (TAC) neurons were located beneath the apical plate, remained outside of the central ganglia during embryogenesis, and no longer contained detectable catecholamines close to hatching. TAC neurons bore cilia on the ends of short processes that penetrated the overlying epithelium; their long processes branched repeatedly under the ciliated apical plate. Several smaller catecholaminergic cells first appeared in the anterior margin of the foot at a stage when the embryos began to metamorphose from the veliger form (E55). Similar bipolar cells later appeared in the tentacle and lips. The axons of all of these small peripheral cells projected centrally and terminated within the neuropil of different central ganglia. Central catecholaminergic neurons, including RPeD1, differentiated only after metamorphosis was complete (E75). Development of locomotor, respiratory, and feeding behaviors correlated with maturation of catecholaminergic neurons, as indicated by histology and chromatography.

Development of catecholaminergic neurons in the pond snail, Lymnaea stagnalis: II. Postembryonic development of central and peripheral cells.

Catecholamines have long been thought to play important roles in different mollusc neural functions. The present study used glyoxylate- and aldehyde-induced histofluorescence to identify central and peripheral catecholaminergic neurons in the snail Lymnaea stagnalis. The majority of these cells were also found to react to antibodies raised against tyrosine hydroxylase. A minority of the catecholaminergic neurons, however, exhibited no such immunoreactivity. The number of central catecholaminergic neurons nearly doubled (from about 45 to about 80 cells) during the first 2-3 days of postembryonic development. Thereafter, catecholaminergic neurons again doubled in number and generally grew by about 100-200% in soma diameter as the snails grew by 1,000% in overall linear measurements. In contrast to the relatively meager addition of central catecholaminergic neurons, several thousand catecholaminergic somata were added to different peripheral tissues during postembryonic development. These small, centrally projecting neurons were particularly concentrated in the lips, esophagus, anterior margin of the foot, and different regions of the male and female reproductive tracts. Chromatographic analyses indicated that dopamine was the major catecholamine present in the central ganglia, foot, and esophagus, although detectable levels of norepinephrine (approximately 20% of dopamine levels) were also found in the ganglia. The total content but not the concentration of dopamine increased within the tissue samples during postembryonic development. The companion study (Voronezhskaya et al. [1999] J. Comp. Neurol. 404:285-296) and the present study furnish a complete description of central and peripheral catecholaminergic neurons from their first appearance in early embryonic development to adulthood.

Distribution of central catecholaminergic neurons: a comparison between ungulates, humans and other species.

In ungulates and primates, the distribution of central catecholaminergic neurons identified using antibodies raised against catecholamine synthesizing enzymes and catecholamines themselves, shows many differences if compared to rats. Catecholaminergic neurons are more loosely clustered in ungulates and primates than in rat. In the medulla oblongata, the density of noradrenergic/adrenergic neurons is lower in ungulates than in other species and, particularly in sheep, the adrenergic group C1 is not observed. The noradrenergic neurons of the locus coeruleus are present in a larger area in ungulates than in rodents. In the hypothalamus, the density of dopamine neurons is lower in ungulates and primates than in rodents. In the rostral hypothalamus of ungulates, the dorsal part of the group A14 is missing, and these species present only the ventral part of the group A15. In primates the group A15 extends into the supraoptic and paraventricular nuclei which have large tyrosine hydroxylase-immunoreactive (TH-IR) neurons not observed in other species. In addition, in all studies species, not all cells expressing catecholamine synthesizing enzymes also express catecholamines, as found in some TH-IR neurons in the arcuate nucleus, thereby demonstrating the necessity of using different markers to ascertain the true catecholaminergic nature of labeled neurons. These anatomical differences between species show the difficulty in extrapolating the distribution of catecholamine neurons from one species to another and may be related to adaptative physiological differences between mammals.

Localization of α 2c-adrenergic receptor immunoreactivity in catecholaminergic neurons in the rat central nervous system

Given the importance of α 2-adrenergic receptors in the regulation of catecholaminergic transmission, we analysed the distribution of immunoreactivity corresponding to the C-subtype of α 2-adrenergic receptor in central catecholaminergic neurons using double-label immunohistochemistry with antibodies directed against a,c-adrenergic receptors and tyrosine hydroxylase. Cells exhibiting both α 2c-adrenergic receptor and tyrosine hydroxylase immunoreactivity were found in most areas containing catecholaminergic cell groups. However, the percentage of double-labelled cells varied in a region-specific manner. In the medulla, α 2c-adrenergic receptor immunoreactivity was characteristic of only a minority of cells exhibiting tyrosine hydroxylase immunoreactivity (40–43% in area A1/C1, 27–36% in area A2/C2, 35% in area C3) while a larger percentage of double-labelled cells was observed in the pons (65% in A5, 92% in locus coeruleus, 68% in A7). In the midbrain, α 2c-adrenergic receptor immunoreactivity was detected in most tyrosine hydroxylase-immunoreactive cells in dopaminergic regions (63% in the retrorubral field, 77–83% in substantia nigra, 67% in ventral tegmental area). These results suggest that α 2c-adrenergic receptors may act as autoreceptors on some central adrenergic and noradrenergic neurons. In addition, the colocalization of α 2c-adrenergic receptor and tyrosine hydroxylase immunoreactivity in dopaminergic cell groups suggests that reported effects of α 2-adrenergic receptor agonists in these areas may be mediated by the C-subtype.

Colchicine Differentially Induces the Expressions of Nitric Oxide Synthases in Central and Peripheral Catecholaminergic Neurons

This study was aimed at elucidating differences in nerve injury induced expression of nitric oxide synthases (NOS) between the peripheral and central catecholaminergic neurons. Colchicine was used to disrupt chemically the neuronal cytoskeletal integrity. A marked increase in the expression of neuronal NOS-IR and NADPH-diaphorase activity, a marker of neuronal NOS (nNOS), was seen in distinct populations of postganglionic sympathetic neurons of the superior cervical ganglion after intraganglionic colchicine injection. Similarly, immunoreactivity for the inducible form of NOS (iNOS) was induced in some sympathetic neuron somata. However, this immunoreactivity did not coincide with nNOS-IR. In contrast to the sympathetic neurons, hypothalamic arcuate and periventricular dopaminergic neurons did not show NOS-IR or NADPH-DA either in intact animals or in animals treated with an intracerebroventricular injection of colchicine. Immunoreactivity for the inducible form of NOS revealed no neuronal staining in the hypothalamic neurons in either group, while a large number of glia-resembling cells around the third ventricle showed slight expression of iNOS-IR. The present results show that expression of both neuronal and inducible forms of NOS may be induced by colchicine in some catecholaminergic neurons. It is suggested that these inductions are specific to certain catecholaminergic neuronal systems, like the sympathetic neurons, rather than a general property of catecholaminergic neurons.

Prenatal development of the central catecholaminergic neurons in human embryos and fetuses

Prenatal development of the central catecholaminergic neurons in human embryos and fetuses