Locus Coeruleus Lesions Research Articles

Banisteriopsis caapi extract: Implications for neuroinflammatory pathways in Locus coeruleus lesion rodent model

Ethnopharmacology relevanceAyahuasca is a beverage obtained from the decoctions of Banisteriopsis caapi (Spruce ex Griseb.) Morton and Psychotria viridis Ruiz & Pav., used throughout the Amazon as a medicinal beverage for healing and spiritual exploration. The Banisteriopsis caapi extract consists of harmine, harmaline, and tetrahydroharmine (THH); which inhibit the isoforms of monoamine oxidase A and B. In the central nervous system (CNS), it can increase the norepinephrine (NE) concentration, produced in the Locus coeruleus (LC), reducing inflammation that is associated with some neurological disease, such as Parkinson's disease and Alzheimer's disease. Aim of the studyevaluate the effects of treatment with B. caapi extract on the neuroinflammatory profile in animals with selective LC lesions. Material and methodsmale Wistar rats with LC lesions induced by 6-hydroxydopamine were treated with B. caapi extract. Subsequently, behavioral tests were conducted, including the elevated plus maze, rotarod, and open field. Tyrosine hydroxylase positive (TH+) neurons and IBA-1 positive microglia were quantified from the LC inflammatory markers and free radical products were assessed. ResultsBoth 6-Hydroxydopamine hydrochloride and the Banisteriopsis caapi extract causes reduction of LC neurons, at the concentration and frequency used. The LC depletion and the treatment of B. caapi extract interfere with locomotion. B. caapi extract and the LC lesion increased the number and activation of inflammatory cells, such as microglia. B. caapi extract decreases IL-10 in the hippocampus and BDNF gene expression. ConclusionThis study suggests that B. caapi extract (at the concentration and frequency used) promotes noradrenergic neuron depletion and creates a proinflammatory environment in the CNS.

Role of the Locus Coeruleus Arousal Promoting Neurons in Maintaining Brain Criticality across the Sleep-Wake Cycle.

Sleep control depends on a delicate interplay among brain regions. This generates a complex temporal architecture with numerous sleep-stage transitions and intermittent fluctuations to micro-states and brief arousals. These temporal dynamics exhibit hallmarks of criticality, suggesting that tuning to criticality is essential for spontaneous sleep-stage and arousal transitions. However, how the brain maintains criticality remains not understood. Here, we investigate θ- and δ-burst dynamics during the sleep-wake cycle of rats (Sprague-Dawley, adult male) with lesion in the wake-promoting locus coeruleus (LC). We show that, in control rats, θ- and δ-bursts exhibit power-law (θ-bursts, active phase) and exponential-like (δ-bursts, quiescent phase) duration distributions, as well as power-law long-range temporal correlations (LRTCs)-typical of non-equilibrium systems self-organizing at criticality. Furthermore, consecutive θ- and δ-bursts durations are characterized by anti-correlated coupling, indicating a new class of self-organized criticality that emerges from underlying feedback between neuronal populations and brain areas involved in generating arousals and sleep states. In contrast, we uncover that LC lesion leads to alteration of θ- and δ-burst critical features, with change in duration distributions and correlation properties, and increase in θ-δ coupling. Notably, these LC-lesion effects are opposite to those observed for lesions in the sleep-promoting ventrolateral preoptic (VLPO) nucleus. Our findings indicate that critical dynamics of θ- and δ-bursts arise from a balanced interplay of LC and VLPO, which maintains brain tuning to criticality across the sleep-wake cycle-a non-equilibrium behavior in sleep micro-architecture at short timescales that coexists with large-scale sleep-wake homeostasis.

Behavioral effects of 6-hydroxydopamine-induced damage to nigro-striatal pathway and Locus coeruleus as a rodent model of Parkinson’s disease

Parkinson's disease (PD) is a chronic and progressive neurodegenerative disorder characterized by the loss of dopaminergic neurons in the Substantia nigra pars compacta (SNpc), which leads to motor and non-motor symptoms (NMS). NMS can appear many years before the classical motor symptoms and are associated with the neurodegeneration of several nuclei; in this work, we highlight the neurodegeneration of Locus coeruleus (LC) in PD. The aim was to investigate the effects of depleting SNpc and LC catecholaminergic neurons on behavioral and neurobiological endpoints. Here we used 6-hydroxydopamine (6-OHDA) in order to induced neurotoxic damage in three independent experimental groups: SNpc lesion group, which 6-OHDA was injected into CPu (CPu-6-OHDA), LC lesion group, which 6-OHDA was injected directly on LC to selectively caused a damage on this nucleus (LC-6-OHDA), and the combined SNpc and LC lesion group (CL-6-OHDA). Next, the behavioral studies were performed using the Morris water maze (MWM), open field (OF), and elevated plus maze (EPM). After stereotaxic surgeries, the animals showed a loss of 67% and 77% of Tyrosine hydroxylase (TH) reactive neurons in the SNpc and LC, respectively. The behavioral analysis showed the anxiety-like behavior in CL-6-OHDA group in the EPM test; in the MWM test, the combined lesions (CL-6-OHDA) showed an impairment in memory acquisition and spatial memory; and no changes were observed in locomotor activity in all the tests. Furthermore, our investigation demonstrating the effects of depleting SN and LC catecholaminergic neurons on behavioral and neurobiological parameters. All these data together lead us to believe that a bilateral PD model including a LC bilateral degeneration is potentially a more accurate model to evaluate the NMS in the pathological development of the disease in rodents.

Braak‐stage II atrophy links lower locus coeruleus – medial temporal lobe connectivity to cognitive decline in preclinical AD

AbstractBackgroundIn preclinical human Alzheimer’s disease (AD), novelty‐related functional connectivity of the locus coeruleus (LC) with the medial temporal lobe (MTL) (ConnLC‐MTL) predicted beta‐amyloid (Aβ)‐related longitudinal cognitive decline. In animals, LC lesions in AD models led to dwindling LC projections to the hippocampus, hippocampal atrophy, and cognitive impairment. Following these observations, we investigated the contribution of cross‐sectional and longitudinal atrophy in early Braak stages as a potential mechanism underlying this relationship.MethodWe included 128 participants of the Harvard Aging Brain Study (HABS) with baseline Pittsburgh Compound‐B Positron Emission Tomography – Distribution Volume Ratio (PiB PET, DVR; 36 Aβ+), as well as baseline functional and longitudinal structural MRI (ntot = 372; ∼ every 3 years; follow‐up 5±3.4 years) and yearly cognitive assessments (PACC5 = Preclinical Alzheimer’s Cognitive Composite; ntot = 874; follow‐up 6.5±3.3 years) (Table 1). ConnLC‐MTL values were derived voxel‐wise and averaged across significant clusters. FreeSurfer‐estimated cortical thickness and hippocampus/amygdala volume (adjusted for intracranial volume) were z‐scored and averaged in two variables (THV2/THV3), encompassing regions associated with Braak stage II and III respectively (Table 1). Baseline associations were evaluated with linear models, longitudinal relationships between ConnLC‐MTL and THV2/THV3 with mixed‐effects models (random intercept and slope). Mediation of ConnLC‐MTL and PACC5 slopes (year 5‐13) by THV2/THV3 slopes (year 0‐5) was calculated (n = 79; bootstrapped n = 1000; Table 1). All models contained age, sex and education as covariates.ResultAt baseline, ConnLC‐MTL positively associated with THV2 (p = 0.005) and with PACC5 (p = 0.045), but not with THV3 (p = 0.26; Figure 1A‐C). Longitudinally, ConnLC‐MTL did not predict changes in THV2 nor THV3. However, we observed faster cortical atrophy with lower ConnLC‐MTL at higher levels of neocortical PiB (THV2: p = 0.02; THV3: p<0.001; Figure 1D‐E). Finally, THV2, but not THV3, mediated the relationship between ConnLC‐MTL and PACC5 decline (p = 0.024) and this effect was stronger in PiB+ individuals compared to PiB‐ (p = 0.026; Figure 2).ConclusionWorse LC‐MTL connectivity was associated with downstream atrophy in the target Braak‐stage II areas, which impacted cognitive performance in preclinical AD. Given that in similar previous animal findings activation of the norepinephrine LC system reversed memory deficits, maintaining optimal ConnLC‐MTL may be a promising intervention target to delay disease progression.

Early loss of locus coeruleus innervation promotes cognitive and neuropathological changes before amyloid plaque deposition in a transgenic rat model of Alzheimer's disease.

The locus coeruleus (LC) is the main source of noradrenaline (NA) in the mammalian brain and has been found to degenerate during the initial stages of Alzheimer's disease (AD). Recent studies indicate that at late stages of the amyloid pathology, LC-pathological alterations accelerate AD-like pathology progression by interfering with the neuromodulatory and anti-inflammatory properties of NA. However, the impact of LC degeneration at the earliest stages of amyloidosis on the AD-like pathology is not well understood. The LC was lesioned in wild-type and McGill-R-Thy1-APP transgenic (APP tg) rats by administering N-(2-chloroethyl)-N-ethyl-bromo-benzylamine before amyloid plaque deposition. Cognitive deficits and AD-like neuropathological changes were measured after the LC lesion. Four months post-treatment, rats displayed a decrease in brain noradrenergic innervation. The LC lesion in APP tg-treated rats enhanced cognitive deficits and decreased hippocampal cholinergic innervation and neurotrophin expression. In addition, the APP tg-treated rats displayed an increased microglial and astroglial cell number in close vicinity to hippocampal amyloid-beta burdened neurons. The recruited microglia showed cellular alterations indicative of an intermediate activation state. Our results indicate that early LC demise aggravates the early neuroinflammatory process, cognitive impairments, cholinergic deficits and neurotrophin deregulation at the earliest stages of the human-like brain amyloidosis.

Effect of Neural Stem Cells Transplantation on the Paradoxical Sleep in the Rat

Introduction: Nowadays a lot of research is being done on neural stem cell (NSCs) transplantation to repair brain damage. Neural stem cells are found in the nervous system. These cells can differentiate interneurons, astrocytes, and oligodendrocytes. Noradrenergic cells in the locus coeruleus (LC) play an important role in paradoxical sleep (PS). The purpose of this study was the assessment of NSCs transplantation on paradoxical sleep in the unilateral lesion of LC. Methods: Forty adult male Wistar rats (225-250 gr), were categorized into four groups (Control, Lesion, experimental 1 (intravenous transplantation of NSCs), and experimental 2 (intravenous transplantation of NACs). NSCs were obtained from the subventricular zone (SVZ) of newborn rat brains. NSCs were differentiated into NACs in neurobasal medium, B-27, GDNF (30 ng/ ml) and BDNF (50 ng/ ml) for 5 days. We used 3,000,000 cells for cell transplantation. The animals received unilateral lesion of LC by injection of 6_hydroxydopamine. For paradoxical sleep recording, 2EMG and 3 EEG electrodes were placed in the neck and skull muscles, respectively. Results: In this study Tyrosine Hydroxylase (TH) was detected in NACs. A significant increase in paradoxical sleep was seen in the lesion group in comparison with the control group. After NSCs and NACs transplantation, a significant decrease in PS was seen in experimental groups in comparison with the lesion group. Conclusion: The results show that NSCs and NACs transplantation improve PS after unilateral lesion of LC.

Transcutaneous Vagus Nerve Stimulation in Humans Induces Pupil Dilation and Attenuates Alpha Oscillations

Vagus nerve stimulation (VNS) is widely used to treat drug-resistant epilepsy and depression. While the precise mechanisms mediating its long-term therapeutic effects are not fully resolved, they likely involve locus coeruleus (LC) stimulation via the nucleus of the solitary tract, which receives afferent vagal inputs. In rats, VNS elevates LC firing and forebrain noradrenaline levels, whereas LC lesions suppress VNS therapeutic efficacy. Noninvasive transcutaneous VNS (tVNS) uses electrical stimulation that targets the auricular branch of the vagus nerve at the cymba conchae of the ear. However, the extent to which tVNS mimics VNS remains unclear. Here, we investigated the short-term effects of tVNS in healthy human male volunteers (n= 24), using high-density EEG and pupillometry during visual fixation at rest. We compared short (3.4 s) trials of tVNS to sham electrical stimulation at the earlobe (far from the vagus nerve branch) to control for somatosensory stimulation. Although tVNS and sham stimulation did not differ in subjective intensity ratings, tVNS led to robust pupil dilation (peaking 4–5 s after trial onset) that was significantly higher than following sham stimulation. We further quantified, using parallel factor analysis, how tVNS modulates idle occipital alpha (8–13Hz) activity identified in each participant. We found greater attenuation of alpha oscillations by tVNS than by sham stimulation. This demonstrates that tVNS reliably induces pupillary and EEG markers of arousal beyond the effects of somatosensory stimulation, thus supporting the hypothesis that tVNS elevates noradrenaline and other arousal-promoting neuromodulatory signaling, and mimics invasive VNS.SIGNIFICANCE STATEMENTCurrent noninvasive brain stimulation techniques are mostly confined to modulating cortical activity, as is typical with transcranial magnetic or transcranial direct/alternating current electrical stimulation. Transcutaneous vagus nerve stimulation (tVNS) has been proposed to stimulate subcortical arousal-promoting nuclei, though previous studies yielded inconsistent results. Here we show that short (3.4 s) tVNS pulses in naive healthy male volunteers induced transient pupil dilation and attenuation of occipital alpha oscillations. These markers of brain arousal are in line with the established effects of invasive VNS on locus coeruleus–noradrenaline signaling, and support that tVNS mimics VNS. Therefore, tVNS can be used as a tool for studying how endogenous subcortical neuromodulatory signaling affects human cognition, including perception, attention, memory, and decision-making; and also for developing novel clinical applications.

Alzheimer's disease pathology: pathways between central norepinephrine activity, memory, and neuropsychiatric symptoms.

The locus coeruleus (LC) supplies norepinephrine to the brain, is one of the first sites of tau deposition in Alzheimer's disease (AD) and modulates a variety of behaviors and cognitive functions. Transgenic mouse models showed that norepinephrine dysregulation after LC lesions exacerbates inflammatory responses, blood-brain barrier leakage (BBB), and cognitive deficits. Here, we investigated relationships between central norepinephrine metabolism, tau and beta-amyloid (Aβ), inflammation, BBB-dysfunction, neuropsychiatric problems, and memory in-vivo in a memory clinic population (total n = 111, 60 subjective cognitive decline, 36 mild cognitively impaired, and 19 AD dementia). Cerebrospinal fluid (CSF) and blood samples were collected and analyzed for 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG), CSF/plasma albumin ratio (Q-alb), Aβ, phosphorylated tau, and interleukins. The verbal word learning task and the neuropsychiatric inventory assessed memory functioning and neuropsychiatric symptoms. Structural equation models tested the relationships between all fluid markers, cognition and behavior, corrected for age, education, sex, and clinical dementia rating score. Our results showed that neuropsychiatric symptoms show strong links to both MHPG and p-tau, whereas memory deficits are linked to MHPG via a combination of p-tau and inflammation-driven amyloidosis (30-35% indirect effect contribution). These results suggest that the LC-norepinephrine may be pivotal to understand links between AD pathology and behavioral and cognitive deficits in AD.

How to demix Alzheimer-type and PSP-type tau lesions out of their mixture -hybrid approach to dissect comorbidity-

Neurofibrillary tangles (NFTs), are shared between progressive supranuclear palsy (PSP) and Alzheimer disease (AD). Histological distinction of PSP and AD is possible based on the distribution of NFTs. However, neuropathologists may encounter diagnostic difficulty with comorbidity of PSP and AD. In this study, we tried to circumvent this difficulty by analyzing five autopsied brains harboring both PSP and AD pathology. Tau-positive lesions were sorted based on their cell type (neuron versus glia), and tau isoforms: three-repeat (3R) versus four-repeat (4R) tau. 16 regions were selected to map these lesions throughout the brain. 4R-tau lesions were present in all areas examined. Among them, 3R-tau lesions were absent in some areas. These 4R selective (4R+/3R-) areas dictate prototypic distribution of PSP, not usually found in AD, such as pontine nucleus, red nucleus, inferior olivary nucleus, dentate nucleus, globus pallidus and putamen, each contained both glial and neuronal lesions. In contrast, additional 3R-tau lesions were found in hippocampal formation to neocortex, where 3R immunoreactivity (IR) was predominant over the 4R counterpart mainly in neurons as found in AD but not in PSP. Although tau lesions in central grey matter, substantia nigra and locus coeruleus are found in both AD and PSP, 4R-selectivity with glial component suggests PSP origin. Even if the presence of 3 R IR in these areas suggests AD pathology, it does not exclude the involvement of PSP-type lesion because distinction of 4R IR into PSP or AD is not yet possible. Further demixing may be possible if biochemical difference of 4R tau between PSP and AD is identified.

Temporal development of behavioral impairments in rats following locus coeruleus lesion induced by 6-hydroxydopamine: Involvement of β3-adrenergic receptors

Noradrenergic degeneration in the locus coeruleus (LC) seems a convergent neuropathological marker of different neurodegenerative diseases. Herein, we investigated the temporal development of apoptotic signaling activation in the LC, noradrenergic dysfunction and behavioral impairments in rats following the noradrenergic lesion of the LC. For this purpose, the dopamine reuptake inhibitor nomifensine was administered 1 h before the stereotaxic bilateral injections of 6-hydroxydopamine (6-OHDA; 5, 10 or 20 μg/hem) into the LC. The behavioral and neurochemical analyses were performed at 7, 21 and 42 days after 6-OHDA injections. All doses of 6-OHDA induced neuronal death in LC, but only the highest dose (20 μg/hem) disrupted the motor function. 6-OHDA (5 μg/hem) injection induced short-term memory deficits in all periods, olfactory discrimination and long-term memory impairments at 7 days, and depressive-like behaviors at 21 and 42 days after injection. Moreover, 6-OHDA infusion increased Bax/Bcl2 ratio and caspase 3 levels, and decreased the dopamine β-hydroxylase immunocontent in the LC. Noradrenergic neurotransmission dysfunction was observed in the LC, olfactory bulb, prefrontal cortex, hippocampus and striatum. The intranasal (i.n.) noradrenaline (NA) infusion restored the impairments in the olfactory discrimination, short-term memory and depressive-like behavior of 6-OHDA-lesioned rats. In addition, these effects were blocked by the prior i.n. infusion of the β3-adrenergic receptor antagonist SR59230A. These findings indicate that the 6-OHDA injection into the LC induced the apoptosis signaling activation, noradrenergic neurotransmission dysfunction and behavioral impairments that were restored via β3-adrenergic receptors activation mediated by the i.n. NA administration.

Locus Coeruleus Ablation Exacerbates Cognitive Deficits, Neuropathology, and Lethality in P301S Tau Transgenic Mice.

The brainstem locus coeruleus (LC) supplies norepinephrine to the forebrain and degenerates in Alzheimer's disease (AD). Loss of LC neurons is correlated with increased severity of other AD hallmarks, including β-amyloid (Aβ) plaques, tau neurofibrillary tangles, and cognitive deficits, suggesting that it contributes to the disease progression. Lesions of the LC in amyloid-based transgenic mouse models of AD exacerbate Aβ pathology, neuroinflammation, and cognitive deficits, but it is unknown how the loss of LC neurons affects tau-mediated pathology or behavioral abnormalities. Here we investigate the impact of LC degeneration in a mouse model of tauopathy by lesioning the LC of male and female P301S tau transgenic mice with the neurotoxin N-(2-chloroethyl)-N-ethyl-bromobenzylamine (DSP-4) starting at 2 months of age. By 6 months, deficits in hippocampal-dependent spatial (Morris water maze) and associative (contextual fear conditioning) memory were observed in lesioned P301S mice while performance remained intact in all other genotype and treatment groups, indicating that tau and LC degeneration act synergistically to impair cognition. By 10 months, the hippocampal neuroinflammation and neurodegeneration typically observed in unlesioned P301S mice were exacerbated by DSP-4, and mortality was also accelerated. These DSP-4-induced changes were accompanied by only a mild aggravation of tau pathology, suggesting that increased tau burden cannot fully account for the effects of LC degeneration. Combined, these experiments demonstrate that loss of LC noradrenergic neurons exacerbates multiple phenotypes caused by pathogenic tau, and provides complementary data to highlight the dual role LC degeneration has on both tau and Aβ pathologies in AD.SIGNIFICANCE STATEMENT Elucidating the mechanisms underlying AD is crucial to developing effective diagnostics and therapeutics. The degeneration of the LC and loss of noradrenergic transmission have been recognized as ubiquitous events in AD pathology, and previous studies demonstrated that LC lesions exacerbate pathology and cognitive deficits in amyloid-based mouse models. Here, we reveal a complementary role of LC degeneration on tau-mediated aspects of the disease by using selective lesions of the LC and the noradrenergic system to demonstrate an exacerbation of cognitive deficits, neuroinflammation, neurodegeneration in a transgenic mouse model of tauopathy. Our data support an integral role for the LC in modulating the severity of both canonical AD-associated pathologies, as well as the detrimental consequences of LC degeneration during disease progression.

Participation of locus coeruleus in breathing control in female rats

Several evidences indicate that the locus coeruleus (LC) is involved in central chemoreception responding to CO2/pH and displaying a high percentage of chemosensitive neurons (>80%). However, there are no studies about the LC-mediated hypercapnic ventilation performed in females. Therefore, we assessed the role of noradrenergic LC neurons in non-ovariectomized (NOVX), ovariectomized (OVX) and estradiol (E2)-treated ovariectomized (OVX+E2) rats in respiratory response to hypercapnia, using a 6-hydroxydopamine (6-OHDA) – lesion model. A reduction in the number of tyrosine hydroxylase (TH) immunoreactive neurons (51–90% in 3 animals of NOVX group, 20–42% of lesion in 5 animals of NOVX females, 61.3% for OVX and 62.6% for OVX+E2 group) was observed seven days after microinjection of 6-OHDA in the LC. The chemical lesion of the LC resulted in decreased respiratory frequency under normocapnic conditions in OVX and OVX+E2 group. Hypercapnia increased ventilation in all groups as consequence of increases in respiratory frequency (fR) and tidal volume (VT). Nevertheless, the hypercapnic ventilatory response was significantly decreased in 6-OHDA-NOVX>50% rats compared with SHAM-NOVX group and with females that had 20–42% of LC lesion. In OVX and OVX+E2 lesioned groups, no difference in CO2 ventilatory response was observed when compared to SHAM-OVX and SHAM-OVX+E2 groups, respectively. Neither basal body temperature (Tb) nor Tb reduction in response to hypercapnia were affected by E2 treatment, ovariectomy or LC lesion. Thus, our data show that LC noradrenergic neurons seem to exert an excitatory role on the hypercapnic ventilatory response in female rats, as evidenced by the results in NOVX animals with LC lesioned more than 50%; however, this modulation is not observed in OVX and OVX+E2 rats. In addition, LC noradrenergic neurons of OVX females seem to provide a tonic excitatory drive to maintain breathing frequency in normocapnia, and this response may not to be functionally influenced by E2.

Modulation of experimental arthritis by vagal sensory and central brain stimulation

Articular inflammation is a major clinical burden in multiple inflammatory diseases, especially in rheumatoid arthritis. Biological anti-rheumatic drug therapies are expensive and increase the risk of systemic immunosuppression, infections, and malignancies. Here, we report that vagus nerve stimulation controls arthritic joint inflammation by inducing local regulation of innate immune response. Most of the previous studies of neuromodulation focused on vagal regulation of inflammation via the efferent peripheral pathway toward the viscera. Here, we report that vagal stimulation modulates arthritic joint inflammation through a novel “afferent” pathway mediated by the locus coeruleus (LC) of the central nervous system. Afferent vagal stimulation activates two sympatho-excitatory brain areas: the paraventricular hypothalamic nucleus (PVN) and the LC. The integrity of the LC, but not that of the PVN, is critical for vagal control of arthritic joint inflammation. Afferent vagal stimulation suppresses articular inflammation in the ipsilateral, but not in the contralateral knee to the hemispheric LC lesion. Central stimulation is followed by subsequent activation of joint sympathetic nerve terminals inducing articular norepinephrine release. Selective adrenergic beta-blockers prevent the effects of articular norepinephrine and thereby abrogate vagal control of arthritic joint inflammation. These results reveals a novel neuro-immune brain map with afferent vagal signals controlling side-specific articular inflammation through specific inflammatory-processing brain centers and joint sympathetic innervations.

Reply: the early pathological process in sporadic Alzheimer’s disease

[7] was designated NFT stage I [8]. Gallyas-negative AT8immunopositive pretangles, described by Bancher et al. [5] and Braak et al. [6], were included in a revised staging protocol for AD [13], but subcortical and cortical “pretangle stages” (a–c, 1a, 1b) as such have been proposed only recently [10, 11, 14]. The LC is not routinely examined at autopsy for the presence of aggregated tau or other proteinopathies in children or young and middle-aged persons. We performed such a study on 42 cases under the age of 30 using AT8 immunohistochemistry and found tau aggregates in LC neurons of 38/42 (90 %) individuals [10]. The tau pathology was located only in dorsal portions of the LC that contain cortically projecting neurons [27, 43]. 41 out of 42 (98 %) cases lacked cortical Aβ deposition [10]. In a larger autopsy-based study, elobeid et al. [23] reported AT8-immunopositive tau in the LC of 25/83 (30 %) young and middle-aged cases, all without concomitant cortical Aβ deposits and all without aggregated tau in the transentorhinal region. If, as Mann and Hardy [41] speculate, the LC lesions in some of the young subjects were driven by acute lethal head injury [10], we also should have encountered at least some Aβ deposition in the brains of these individuals, inasmuch as head trauma studies performed in humans have reported the presence of transient Aβ deposits [26, 54]. Yet, this was not the case. performance of 3r and 4r immunohistochemistry can allay (or confirm) the reservations expressed by Mann and Hardy [41] regarding the absence of evidence for the different isoforms of phospho-tau in such cases. However, the presence of AT8-immunopositive tau aggregates in the LC of both relatively young cohorts makes it unlikely that all or most of the lesions seen there represent prodromal (“incidental”) pathology associated with rare non-AD tauopathies, such as corticobasal degeneration (CBD) or We are inclined to think that the riddle of the chicken or the egg (i.e., the chicken egg or simply an egg?) is too problematic to help illustrate the problem of tau and amyloid-β (Aβ). However, one can summarize our respective viewpoints in the form of “either/or” propositions: Either Aβ is present in the extracellular space at cortical predilection sites and, from there, causes tau to aggregate within coeruleus neurons, as postulated by Mann and Hardy [41]— the authors do not mention how extracellular cortical Aβ reaches the locus coeruleus (LC) to influence nerve cells there (e.g., by means of retrograde axonal transport)—“the undiscerning ‘locus chicken’ eagerly pecks at” the “bad egg (Aβ deposition).” Or involved projection cells (i.e., nerve cells containing aggregated tau) in the LC and in other nonthalamic nuclei with diffuse cortical projections [10, 29, 31, 50] cause via anterograde axonal transport the release of Aβ into the cortical extracellular space [46], where it can aggregate at local diffusion zones into diffuse amyloid plaques, as we have recently postulated [12]. In our view, the pathological process underlying sporadic Alzheimer’s disease (AD) develops over the course of a lifetime [11, 14]. The original staging protocol was based on the topographical distribution patterns of (1) Gallyasstained neurofibrillary changes (tangles, neuropil threads, dystrophic neurites of neuritic plaques) across six stages (NFT I–VI) and (2) Campbell–switzer-stained Aβ plaque deposition (stages A–C) in the cerebral cortex [8]. The earliest stage of cortical neurofibrillary pathology in the superficial entorhinal layer pre-α of the transentorhinal region

Transitory Activation of the Central and Ovarian Norepinephrine Systems During Cold Stress‐Induced Polycystic Ovary in Rats

Cold stress-induced ovarian sympathetic activation is associated with the development of ovarian cysts in rats. Although we have hypothesised that polycystic ovary (PCO) features induced by cold stress, as prevented by lesion of the noradrenergic nucleus locus coeruleus (LC), were a result of the increased activity of the ovarian norepinephrine (NE) system, this was not evident after 8 weeks of stress. In the present study, we investigated the temporal changes in LC and ovarian NE activities and steroid secretion in rats exposed to single (SS) or repeated (RS) cold stress. SS and 4 week (4W)-RS but not 8 week (8W)-RS increased c-Fos expression in the LC and ovarian NE release. Plasma oestradiol, testosterone and progesterone levels tended to increase in 4W-RS and were elevated in 8W-RS rats, which displayed PCO morphology. β-adrenergic receptor agonist increased steroid hormone release from the ovary of unstressed (US) but not from 8W-RS rats. To determine whether increased activity of noradrenergic system during the initial 4 weeks of RS would be sufficient to promote PCO, rats were exposed to 4 weeks of cold stress and kept in ambient temperature for the next 4 weeks (4W-RS/4W-US). Accordingly, PCO morphology, increased steroid secretion and decreased ovulation rate were found in 4W-RS/4W-US rats, strengthening the hypothesis that the initial increase in NE release triggers the development of PCO. The correlated activity of LC neurones and ovarian noradrenergic terminals and the induction of PCO in 4W-RS/4W-US rats provide functional evidence for a major role of NE in disrupting follicular development and causing the long-lasting endocrine abnormalities found in stress-induced PCO.

Roles of the Locus Coeruleus and Adrenergic Receptors in Brain-Mediated Hypothalamic-Pituitary-Adrenal Axis Responses to Intracerebroventricular Alcohol

Alcohol activates the hypothalamic-pituitary-adrenal (HPA) axis through its actions in both the periphery and the central nervous system (CNS). The studies presented here were designed to test the CNS-specific noradrenergic mechanisms by which alcohol stimulates HPA activity in the male rat. We used an experimental paradigm in which a small, nontoxic amount (5μl) of alcohol was slowly microinfused intracerebroventricularly (icv). Alcohol was administered icv to animals with lesions of the locus coeruleus (LC) or in animals pretreated with α- or β-adrenergic receptor antagonists. Hormonal HPA activation was determined by measuring secretion of the pituitary stress hormone adrenocorticotropin (ACTH). Neuronal activation was determined by quantification of the expression of the transcription factor c-fos (Fos). As expected, icv alcohol stimulated ACTH secretion from the pituitary and Fos expression in the paraventricular nucleus of the hypothalamus (PVN). Bilateral electrolytic LC lesions blocked the ability of icv alcohol to stimulate ACTH secretion. Pretreatment with icv propranolol increased basal ACTH secretion levels, but icv alcohol did not increase this effect. Propranolol also blunted icv alcohol-induced PVN Fos expression. A low dose of phenoxybenzamine, an α-adrenergic receptor antagonist, did not affect the ability of icv alcohol to stimulate ACTH release. However, a higher dose of the drug was able to block the ACTH response to icv alcohol. Despite this, phenoxybenzamine did not inhibit alcohol-induced Fos expression. Icv pretreatment with corynanthine, a selective α-1 adrenergic receptor antagonist, modestly raised basal ACTH levels and blocked the icv alcohol-induced secretion of this hormone. These results indicate that the LC and norepinephrine play important roles in HPA activation caused by icv alcohol administration, but that the specific adrenergic receptor subtypes involved in this phenomenon still need to be identified.

Neuroanatomical substrates for recurrent epileptic limbic seizures

Epilepsy is a neurological disorder characterized by the recurrence of spontaneous, unprovoked epileptic seizures. Mesial temporal lobe epilepsy (more briefly, MTLE) is a very common form of epilepsy which is featured by the occurrence of focal limbic seizures, and associated to a specific neuropathological alteration, the so-called Ammon’s horn sclerosis, whose main features are a selective loss of the CA1 and CA3/4 section of the Ammon’s horn (CA, from Latin Cornu Ammonis, abbreviated as CA), a selective cell loss of inhibitory interneurons in the hilus of the dentate gyrus (DG), and the abnormal sprouting of granule cells mossy fibers (the so called mossy fiber sprouting, MFS). The onset of spontaneous seizures (SRS) is the hallmark of a good model of epilepsy. For temporal lobe epilepsy (TLE), the most used models consist in administering systemically chemoconvulsants inducing limbic status epilepticus (i.e. seizures lasting for more than 30’, SE) and evaluating the occurrence of SRS. However, in these models, the widespread involvement of different structures which complicates the interpretation of experimental findings: limbic seizures and status epilepticus (SE) can be triggered by focal infusion of chemoconvulsants within anterior piriform cortex (abbreviated as APC) This brain region is densely innervated by noradrenergic fibers arising from the locus coeruleus (LC), and we recently showed that a lesion of LC (induced by a selective neurotoxin, DSP-4, i.p.), induces SE. LC plays a critical role in modulating several models of seizures, and it plays a critical role in plastic mechanisms and neuroprotection in the brain. Thus, we compared the group DSP-4+bicuculline and cyclothiazide+bicuculline, to evaluate whether the focal SE evoked from the APC is capable of inducing SRS and AHS, and whether LC plays a significant role in this phenomena. We found that: the loss of LC induced: (i)a higher incidence of SRS; (ii) cell loss in the hippocampal DG hilus and CA3 (iii)the loss of parvalbumin-positive neurons. In conclusion, our study confirms that focal induction of SE from the APC represents a good model of TLE, and that NE released from the fibers originating from the LC plays a significant role both in the hippocampal damage occurring after SE, and in the incidence of SRS.

Noradrenergic lesion of the locus coeruleus increases the firing activity of the medial prefrontal cortex pyramidal neurons and the role of α 2-adrenoceptors in normal and medial forebrain bundle lesioned rats

Degeneration of noradrenergic neurons in the locus coeruleus (LC) and dysfunction of the prefrontal cortex were regarded as playing a specific role in the occurrence of non-motor symptoms in Parkinson's disease. The present study examined the spontaneous firing rate and firing pattern of medial prefrontal cortex (mPFC) pyramidal neurons, and effects of α 2-adrenoceptor agonist UK-14,304 and antagonist yohimbine on the neuronal activity in rats with 6-hydroxydopamine lesions of the LC, medial forebrain bundle (MFB) and with combined MFB and LC lesions. The firing rate of mPFC pyramidal neurons in rats with lesions of the LC and with combine LC and MFB lesions is significantly higher than that of normal and MFB-lesioned rats and the firing pattern of these neurons in rats with lesions of the LC and with combine LC and MFB lesions also changed significantly towards more regular compared with normal and MFB-lesioned rats. The local administration of UK-14,304 in the mPFC inhibited the firing activity of the pyramidal neurons in normal rats and rats with lesions of the LC, MFB and with combined LC and MFB lesions, while yohimbine increased the firing activity of the pyramidal neurons. These results indicate that the lesions of the LC lead to hyperactivity of mPFC pyramidal neurons in normal and MFB-lesioned rats, and the postsynaptic α 2-adrenoceptors may partially mediate the inhibitory effects of LC-noradrenergic system on the firing activity of pyramidal neurons in the mPFC, suggesting that LC-noradrenergic system plays an important role in the functional disorders of mPFC in Parkinson's disease.

Noradrenergic lesion of the locus coeruleus increases apomorphine-induced circling behavior and the firing activity of substantia nigra pars reticulata neurons in a rat model of Parkinson's disease

The role of noradrenergic depletion of the locus coeruleus (LC) in the pathophysiology of Parkinson's disease (PD) is still unclear. In the present study, apomorphine-induced circling behavior and extracellular firing activity of substantia nigra pars reticulata (SNr) neurons were examined in rats with unilateral 6-hydroxydopamine lesions of the LC, substantia nigra pars compacta (SNc) and with combined SNc and LC lesions. A moderate contralateral circling was observed in rats with LC lesions after apomorphine. Moreover, the circling behavior was obviously increased by further lesions of LC in SNc-lesioned rats. Extracellular recordings indicated that the firing rate of SNr neurons increased significantly and the firing pattern of these neurons also changed towards more irregular and bursty after SNc lesioning as compared to sham-lesioned rats, while the firing rate and pattern were unaffected in rats with simple lesions of the LC. However, the firing rate of SNr neurons in rats with combined LC and SNc lesions increased significantly when compared to that of rats with simple lesions of the SNc, although the firing pattern was not altered. Furthermore, SNc lesions in rats increased the firing rate of SNr neurons with irregular firing pattern, and additional LC lesions in SNc-lesioned rats increased the firing rate of SNr neurons with regular and irregular firing pattern. These results indicate that lesions of the LC intensify apomorphine-induced circling behavior and lead to a further hyperactivity of SNr neurons in a rat model of PD, suggesting that LC-noradrenergic system is involved in the motor dysfunction of PD.

Noradrenergic Control of Associative Synaptic Plasticity by Selective Modulation of Instructive Signals

Synapses throughout the brain are modified through associative mechanisms in which one input provides an instructive signal for changes in the strength of a second coactivated input. In cerebellar Purkinje cells, climbing fiber synapses provide an instructive signal for plasticity at parallel fiber synapses. Here, we show that noradrenaline activates alpha2-adrenergic receptors to control short-term and long-term associative plasticity of parallel fiber synapses. This regulation of plasticity does not reflect a conventional direct modulation of the postsynaptic Purkinje cell or presynaptic parallel fibers. Instead, noradrenaline reduces associative plasticity by selectively decreasing the probability of release at the climbing fiber synapse, which in turn decreases climbing fiber-evoked dendritic calcium signals. These findings raise the possibility that targeted presynaptic modulation of instructive synapses could provide a general mechanism for dynamic context-dependent modulation of associative plasticity.