Serotonergic mechanisms associated with experimental models of hypoxia: A systematic review.

PURPOSE: The aim of this systematic review was to explore and discuss the literature concerning the effects of hypoxia or anoxia during the perinatal period on the serotoninergic network in rodents, through mechanisms that lead to changes in serotonergic neurons, levels, segments of central nervous system affected, 5-HT transporter, and 5-HT receptor. METHODS: Literature searches were performed in Embase, Medline (PubMed), Web of Science, and SCOPUS, from April to July 2021, with a total of 1045 published studies found. Using a predefined protocol, as registered on the CAMARADES website, 10 articles were included in this review. The PRISMA statement was used for reporting this systematic review. The internal validity was assessed using the SYRCLE's risk of bias tool. RESULTS: Our main findings show that hypoxia in the first days of postnatal life led to a disturbance in the serotonergic system with reduced in 5-HT fibers, reduced brain levels of 5-HT and 5-HIAA, reduced SERT protein expression, and reduced receptor 5-HT7 . Putative mechanisms involving damage in the serotoninergic system include retrograde cell death resulting from primary damage mainly in forebrain areas, which impairs remote areas including serotonergic raphe nuclei. Other probable mechanisms associated with the serotoninergic network damage may be triggered by excitotoxic lesion and neuroinflammation. CONCLUSION: Hypoxia at the beginning of an animal's life leads to modification of the serotonergic components associated with putative mechanisms that include cell damage and neuroinflammation.

Abnormal connectivity model of raphe nuclei with sensory-associated cortex in Parkinson's disease with chronic pain.

BACKGROUND AND OBJECTIVE: There are indicates that raphe nuclei may be involved in the occurrence of chronic pain in Parkinson's disease (PD). In the study, we investigated the functional connectivity pattern of raphe nuclei in Parkinson's disease with chronic pain (PDP) to uncover its possible pathophysiology. METHODS: Fifteen PDP, who suffered from pain, lasted longer than 3 months, sixteen Parkinson's disease patients with no pain (nPDP) and eighteen matched normal health controls (NCs) were recruited. All subjects completed the King's Parkinson's Pain Scale (KPPS) besides Parkinson-related scale and demographics. We performed a seed-based resting-state analysis of functional magnetic resonance imaging to explore whole-brain functional connectivity of the raphe nuclei. Multiple regression model was used to explore the related factors of pain including disease duration, disease severity, Hamilton Depression Rating Scale, age, sex, levodopa equivalent dose and the strength of network functional connectivity. RESULTS: Compared with the nPDP, the PDP group showed stronger functional connectivity between raphe nuclei and pain-related brain regions, including parietal lobe, insular lobe, cingulum cortex and prefrontal cortex, and the functional connectivity values of those areas were significantly positively correlated with KPPS independent of the clinical variables. Compared with NCs, the combined PD groups showed decreased functional connectivity including prefrontal cortex and cingulum cortex. CONCLUSIONS: Abnormal functional connectivity model of raphe nuclei may be partly involved in pathophysiological mechanism of pain in PD.

Serotonin neurons in the median raphe nucleus bidirectionally regulate somatic signs of nicotine withdrawal in mice.

In chronic smokers, nicotine withdrawal symptoms during tobacco cessation can lead to smoking relapse. In rodent models, chronic exposure to nicotine elicited physical dependence, whereas acute antagonism of nicotinic acetylcholine receptors (nAChRs) immediately precipitated withdrawal symptoms. Although the central serotonergic system plays an important role in nicotine withdrawal, the exact serotonergic raphe nuclei regulating these symptoms remain unknown. We used transgenic mice expressing archaerhodopsinTP009 or channelrhodopsin-2[C128S] exclusively in the central serotonergic neurons to selectively manipulate serotonergic neurons in each raphe nucleus. Nicotine withdrawal symptoms were precipitated by an acute injection of mecamylamine, a nonspecific nAChR antagonist, following chronic nicotine consumption. Somatic signs were used as measures of nicotine withdrawal symptoms. Acute mecamylamine administration significantly increased ptosis occurrence in nicotine-drinking mice compared with that in control-drinking mice. Optogenetic inhibition of the serotonergic neurons in the median raphe nucleus (MRN), but not of those in the dorsal raphe nucleus (DRN), mimicked the symptoms observed during mecamylamine-precipitated nicotine withdrawal even in nicotine-naïve mice following the administration of acute mecamylamine injection. Optogenetic activation of the serotonergic neurons in the MRN nearly abolished the occurrence of ptosis in nicotine-drinking mice. The serotonergic neurons in the MRN, but not those in the DRN, are necessary for the occurrence of somatic signs, a nicotine withdrawal symptom, and the activation of these neurons may act as a potential therapeutic strategy for preventing the somatic manifestations of nicotine withdrawal.

5-HT7 receptor activation rescues impaired synaptic plasticity in an autistic-like rat model induced by prenatal VPA exposure.

Autism spectrum disorder (ASD) is a severe life-long neuropsychiatric disorder. Alterations and imbalance of several neurochemical systems may be involved in ASD pathophysiology, of them, serotonergic neurotransmission dysfunction and deficiency may underlie behavioral abnormalities associated with ASD. However, the functional importance of serotonergic receptors, particularly 5HT7 receptors in ASD pathology remains poorly defined. Serotonin receptor subtype 7 (5-HT7R) plays a direct regulatory role in the development and also for the mature function of the brain, therefore, further studies are necessary to elucidate the role of these receptors in the etiology of autism. To address this issue, we combined here behavioral, electrophysiological methods to further characterize the contribution of 5-HT7Rs in the prenatal valproic acid (VPA) exposure-induced impairment in synaptic plasticity and their impact on the associated behavioral changes. This may help to unravel the underlying cellular mechanisms involved in ASD and can lead to new treatment and/or prevention therapies based on the role of the serotonergic system for autism. Findings revealed that compared to control, autistic-like offspring showed increased anxiety-like behavior, reduced social interaction, decreased locomotor activity, and impaired identification of the novel object. However, administration of 5-HT7Rs agonist, LP-211, for 7 consecutive days before testing from postnatal day 21 to 27 reversed all behavioral deficits induced by prenatal exposure to VPA in offspring. Also, both short-term depression and long-term potentiation were impaired in the autistic-like pups, but activation of 5-HT7Rs rescued the LTP impairment in the autistic-like group so that there was no significant difference between the two groups. Blockade of 5-HT7Rs caused LTP impairment following HFS in the autistic-like group. Besides, there was a significant difference in LTD induction following SB-269970 application between the control and the autistic-like groups measured at first 10 min following TPS. Moreover, both the number and the size of retrograde fast blue-labelled neurons in the raphe nuclei were reduced. Overall, these results provide for the first time, as far as we know, functional evidence for the restorative role of 5-HT7Rs activation against prenatal VPA exposure induced behavioral deficits and hippocampal synaptic plasticity impairment. Therefore, these receptors could be a potential and promising pharmacotherapy target for the treatment of autism.

Olfactory bulbectomy and raphe nucleus relationship: a new vision for well-known depression model.

Background/aim: The olfactory bulbectomy (OBX) technic is a well-known animal model for depression. According to serotonin hypothesis of depression, one of the possible explanations to this mechanism is the destroying effect of OBX on raphe nuclei which especially include serotonergic neurons. In this study, we aimed to explore histopathological findings in raphe nuclei in OBX rats.Materials and methods: Forty-eight rats (8 control group, 10 sham group, and 30 as the study group) were used. No procedure was applied to the control group. Only frontal burr holes were performed at the level of olfactory bulbs (OBs) on the sham group. Mechanical OBX by compression was applied to 20 rats and the OBs of 10 rats were cauterized. Their OBs, olfactory cortices, raphe nuclei were extracted, tissue specimens were taken than examined by using histopathological methods including hematoxylin and eosin, S-100, and TUNEL staining. Physical dissector method was used to evaluate the number of living and apoptotic neurons in the raphe nuclei.Results: Prominent neuronal loss and morphological changes in the dorsal raphe nuclei were detected in study groups.Conclusion: Raphe nuclei degeneration, related alterations in neurotransmitter system activities and functional brain connectivity might be related to neurobiology of depression.

Tau and Amyloid-ß Pathology in Japanese Forensic Autopsy Series Under 40 Years of Age: Prevalence and Association with APOE Genotype and Suicide Risk.

BACKGROUND: Aggregation of abnormal phosphorylated tau in brain stem areas may be a possible early pathological manifestation of Alzheimer's disease (AD). OBJECTIVE: This study aimed to explore the prevalence of cases with AD-related pathology in subjects <40 years of age and to explore the association of such pathology, neuropsychiatric symptoms, and APOE genotype. METHOD: We conducted brain immunohistochemistry for 189 cases <40 years of age (mean±standard deviation age 25.3±13.1 years). Tau positive cases were then assessed for the distribution of tau pathology in the locus ceruleus (LC), raphe nucleus (RN), and entorhinal cortex (ErC), and the distinction between neuronal threads and cellular inclusions. Apolipoprotein E (APOE) genotype was also examined. RESULTS: Tau pathology was detected in 135 cases (71.4%; 13-39 years; only LC, 23 cases; only RN, 4 cases; only ErC, 35 cases; LC+RN, 3 cases; LC+ErC, 57 cases; all three regions, 10 cases). The prevalence of thread pathology was higher than that of cellular inclusions. Significantly higher prevalence of the APOEɛ2 allele were found in 10-39 years of age natural death cases (p < 0.05). Amyloid-ß deposition was found in only 7 cases, along with a significantly high frequency of the ɛ4 allele (p < 0.05). While a past history of psychiatric disease was a significant risk factor for suicide, AD-related pathology was not associated with suicide. CONCLUSIONS: Both the brain stem and entorhinal cortex was the initial site of tau pathology in many younger subjects. AD-related pathology may not be a significant accelerating factor for suicide in younger subjects.

Hypoechogenicity of brainstem raphe correlates with depression in migraine patients.

BACKGROUND: Brainstem raphe (BR) hypoechogenicity in transcranial sonography (TCS) has been depicted in patients with major depression (MD) and in depressed patients with different neurodegenerative diseases. But, up to date, the association of BR alterations in TCS with depression in migraineurs has never been reported. This study was to investigate the possible role of BR examination via TCS in migraineurs with depression. METHODS: Forty two migraine without aura (MwoA) patients and 40 healthy controls were recruited. Echogenicity of lentiform nuclei (LN), caudate nuclei (CN), substantia nigra (SN) and brainstem raphe (BR) and width of the frontal horns of the lateral ventricles and the third ventricle were assessed with TCS. The diagnosis of depression was based on the criteria of the Diagnostic and Statistical Manual of Mental Disorders IV (DSM -IV), and the severity of depression was measured by Hamilton Rating Scale for Depression (HAM-D) and Hospital Anxiety and Depression Scale depression subscale (HADS-D). RESULTS: There were no significant differences between migraineurs and controls in the width of frontal horn of the lateral ventricle (p = 0.955), width of third ventricle (p = 0.129) as well as in the echogenicity of SN (p = 0.942), CN (p = 0.053), LN (p = 0.052) and BR (p = 0.677). Here, it seems that more migraineurs were detected with increased echogenecity of CN and LN compared with controls (33.3% versus 15.0% for CN, 19.0% versus 5.0% for LN) though they had no statistical significance. Patients with hypoechogenic BR had significantly higher HAM-D and HADS-D scores than those with normal BR signal (p = 0.000 for both HAM-D and HADS-D), and most (83.33%) migraineurs with depression exhibited hypoechogenic raphe but none (0.00%) of the migraineurs without depression exhibited hypoechogenic raphe (p = 0.000). CONLUSIONS: TCS signal alteration of BR can be a biomarker for depression in migraine but it is not associated with migraine headache itself. LN and CN alterations in TCS may reflect a potential role of them in the pathogenesis of migraine, which needs to be further elucidated.

Perturbed Developmental Serotonin Signaling Affects Prefrontal Catecholaminergic Innervation and Cortical Integrity.

Proper development of the medial prefrontal cortex (mPFC), crucial for correct cognitive functioning, requires projections from, among others, the serotonergic (5-HT) and catecholaminergic systems, but it is unclear how these systems influence each other during development. Here, we describe the parallel development of the 5-HT and catecholaminergic prefrontal projection systems in rat and demonstrate a close engagement of both systems in the proximity of Cajal-Retzius cells. We further show that in the absence of the 5-HT transporter (5-HTT), not only the developing 5-HT but also the catecholaminergic system, including their projections towards the mPFC, are affected. In addition, the layer identity of the mPFC neurons and reelin-positive interneuron number and integration are altered in the absence of the 5-HTT. Together, our data demonstrate a functional interplay between the developing mPFC 5-HT and catecholaminergic systems, and call for a holistic approach in studying neurotransmitter systems-specific developmental consequences for adult behavior, to eventually allow the design of better treatment strategies for neuropsychiatric disorders.

The ventrolateral medulla and medullary raphe in sudden unexpected death in epilepsy.

Sudden unexpected death in epilepsy (SUDEP) is a leading cause of premature death in patients with epilepsy. One hypothesis proposes that sudden death is mediated by post-ictal central respiratory depression, which could relate to underlying pathology in key respiratory nuclei and/or their neuromodulators. Our aim was to investigate neuronal populations in the ventrolateral medulla (which includes the putative human pre-Bötzinger complex) and the medullary raphe. Forty brainstems were studied comprising four groups: 14 SUDEP, six epilepsy controls, seven Dravet syndrome cases and 13 non-epilepsy controls. Serial sections through the medulla (from obex 1 to 10 mm) were stained for Nissl, somatostatin, neurokinin 1 receptor (for pre-Bötzinger complex neurons) and galanin, tryptophan hydroxylase and serotonin transporter (neuromodulatory systems). Using stereology total neuronal number and densities, with respect to obex level, were measured. Whole slide scanning image analysis was used to quantify immunolabelling indices as well as co-localization between markers. Significant findings included reduction in somatostatin neurons and neurokinin 1 receptor labelling in the ventrolateral medulla in sudden death in epilepsy compared to controls (P < 0.05). Galanin and tryptophan hydroxylase labelling was also reduced in sudden death cases and more significantly in the ventrolateral medulla region than the raphe (P < 0.005 and P < 0.05). With serotonin transporter, reduction in labelling in cases of sudden death in epilepsy was noted only in the raphe (P ≤ 0.01); however, co-localization with tryptophan hydroxylase was significantly reduced in the ventrolateral medulla. Epilepsy controls and cases with Dravet syndrome showed less significant alterations with differences from non-epilepsy controls noted only for somatostatin in the ventrolateral medulla (P < 0.05). Variations in labelling with respect to obex level were noted of potential relevance to the rostro-caudal organization of respiratory nuclear groups, including tryptophan hydroxylase, where the greatest statistical difference noted between all epilepsy cases and controls was at obex 9-10 mm (P = 0.034), the putative level of the pre-Bötzinger complex. Furthermore, there was evidence for variation with duration of epilepsy for somatostatin and neurokinin 1 receptor. Our findings suggest alteration to neuronal populations in the medulla in SUDEP with evidence for greater reduction in neuromodulatory neuropeptidergic and mono-aminergic systems, including for galanin, and serotonin. Other nuclei need to be investigated to evaluate if this is part of more widespread brainstem pathology. Our findings could be a result of previous seizures and may represent a pathological risk factor for SUDEP through impaired respiratory homeostasis during a seizure.

Visualization of Altered Hippocampal Connectivity in an Animal Model of Alzheimer's Disease.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by cognitive decline and neurodegeneration in the hippocampus. Despite the pathological importance of the hippocampal degeneration in AD, little topographical evidence exists of impaired hippocampal connectivity in patients with AD. To investigate the anatomical connections of the hippocampus, we injected the neurotracer 1,1'-dioctadecyl-3,3,3'3,3'-tetramethyl-indocarbocyanine perchlorate (DiI) into the hippocampi of 5XFAD mice, which were used as an animal model of AD. In wild-type controls, DiI-containing cells were found in the entorhinal cortex, medial septum, locus coeruleus, dorsal raphe, substantia nigra pars compacta, and olfactory bulb. Hippocampal inputs were decreased in multiple brain regions in the 5XFAD mice compared to wild-type littermate mice. These results are the first to reveal alterations at the cellular level in hippocampal connectivity in the brains of 5XFAD mice. These results suggest that anatomical mapping of hippocampal connectivity will elucidate new pathogenic mechanisms and therapeutic targets for AD treatment.

Prevalence of depressive symptoms and their association with brainstem raphe echogenicity in patients with Parkinson's disease and non-PD controls.

Despite advances in diagnostics and clinical recognition, depressive symptoms in Parkinson's disease (PD) exceeding normal limits remain effectively untreated. In this study, we report on the prevalence and severity of depressive symptoms as well as their association with brainstem raphe echogenicity in patients with PD and non-PD controls. The study included 266 Estonian PD patients and 168 age- and education-matched controls. Demographic and clinical data was documented. Brainstem raphe (BR) was visualized by transcranial sonography (TCS). The prevalence of depressive symptoms in the patient sample was found to be significantly higher than in controls. BR echogenicity in both patients and controls was directly related to their total BDI score, although we found a significantly greater reduction of BR echogenicity in patients with PD and depressive symptoms compared to depressed non-PD controls. The present results corroborate the hypothesis that morphological alteration of the BR is involved in the pathogenesis of depressive disorders. TCS of BR could be used as a non-invasive biomarker to improve detection of depressive symptoms in early PD stages where clinicians may not recognize affective disturbances in the context of PD phenomena.

Impairments in laterodorsal tegmentum to VTA projections underlie glucocorticoid-triggered reward deficits.

Ventral tegmental area (VTA) activity is critical for reward/reinforcement and is tightly modulated by the laterodorsal tegmentum (LDT). In utero exposure to glucocorticoids (iuGC) triggers prominent motivation deficits but nothing is known about the impact of this exposure in the LDT-VTA circuit. We show that iuGC-rats have long-lasting changes in cholinergic markers in the LDT, together with a decrease in LDT basal neuronal activity. Interestingly, upon LDT stimulation, iuGC animals present a decrease in the magnitude of excitation and an increase in VTA inhibition, as a result of a shift in the type of cells that respond to the stimulus. In agreement with LDT-VTA dysfunction, we show that iuGC animals present motivational deficits that are rescued by selective optogenetic activation of this pathway. Importantly, we also show that LDT-VTA optogenetic stimulation is reinforcing, and that iuGC animals are more susceptible to the reinforcing properties of LDT-VTA stimulation.

Construct and face validity of a new model for the three-hit theory of depression using PACAP mutant mice on CD1 background.

Major depression is a common cause of chronic disability. Despite decades of efforts, no equivocally accepted animal model is available for studying depression. We tested the validity of a new model based on the three-hit concept of vulnerability and resilience. Genetic predisposition (hit 1, mutation of pituitary adenylate cyclase-activating polypeptide, PACAP gene), early-life adversity (hit 2, 180-min maternal deprivation, MD180) and chronic variable mild stress (hit 3, CVMS) were combined. Physical, endocrinological, behavioral and functional morphological tools were used to validate the model. Body- and adrenal weight changes as well as corticosterone titers proved that CVMS was effective. Forced swim test indicated increased depression in CVMS PACAP heterozygous (Hz) mice with MD180 history, accompanied by elevated anxiety level in marble burying test. Corticotropin-releasing factor neurons in the oval division of the bed nucleus of the stria terminalis showed increased FosB expression, which was refractive to CVMS exposure in wild-type and Hz mice. Urocortin1 neurons became over-active in CMVS-exposed PACAP knock out (KO) mice with MD180 history, suggesting the contribution of centrally projecting Edinger-Westphal nucleus to the reduced depression and anxiety level of stressed KO mice. Serotoninergic neurons of the dorsal raphe nucleus lost their adaptation ability to CVMS in MD180 mice. In conclusion, the construct and face validity criteria suggest that MD180 PACAP HZ mice on CD1 background upon CVMS may be used as a reliable model for the three-hit theory.

Depressive disorder may be associated with raphe nuclei lesions in patients with brainstem infarction.

BACKGROUND: Depression is a common symptom after stroke, but its neural substrates remain unclear. The ascending serotonergic system originates from the raphe nuclei in the brainstem. We hypothesized that depressive disorder due to brainstem infarction is associated with damage to the raphe nuclei. METHODS: We prospectively enrolled 19 patients who had the first-ever acute isolated brainstem infarction in an observational cross-sectional study. All patients were evaluated by using the Montgomery Åsberg Depression Rating Scale (MADRS), the clinician-rated version of Apathy Evaluation Scale (AES-C) and Mini-Mental State Examination (MMSE). Depressive disorder was diagnosed according to DSM-5 and MADRS score of 12 or greater. Diffusion tensor imaging and proton density-weighted images were used to identify damage in the raphe nuclei. Accordingly, patients were classified into either the raphe-nuclei-damaged or intact group. Prevalence of depressive disorder and the MADRS, AES-C, and MMSE scores were compared between the two groups. RESULTS: Depressive disorder was more frequent in the damaged group (n=6) than in the intact group (n=13) (83% vs. 15%; P=0.01). MADRS scores were higher in the damaged group than in the intact group (mean±1 SD, 17.5±7.9 vs. 7.0±4.4; P=0.002), whereas the AES-C and MMSE scores did not differ between groups. LIMITATIONS: We did not assess the damage to the ascending projection fibers from the raphe nuclei. CONCLUSIONS: Our results suggest that damage to the raphe nuclei underlies depressive disorder due to brainstem infarction, possibly via serotonergic denervation.

Galanin contributes to monoaminergic dysfunction and to dependent neurobehavioral comorbidities of epilepsy.

Status epilepticus (SE) in rats, along with chronic epilepsy, leads to the development of behavioral impairments resembling depressive disorder and/or attention deficit/hyperactivity disorder (ADHD), thus reflecting respective comorbidities in epilepsy patients. Suppressed neurotransmitter tone in the raphe nucleus (RN)-prefrontal cortex (PFC) serotonergic pathway and in the locus coeruleus (LC)-PFC noradrenergic pathway underlies depressive- and impulsive-like behavioral deficits respectively. We examined possible mechanisms leading to the monoamine dysfunction in brainstem efferents, namely modulatory effects of the neuropeptide galanin on serotonin (5-HT) and norepinephrine (NE) signaling. SE was induced in young adult male Wistar rats by LiCl and pilocarpine. Epileptic rats were categorized vis-à-vis behavioral deficits as not impaired, "depressed" and "impulsive". Depressive- and impulsive-like behaviors were examined in the forced swimming test (FST). The strength of serotonergic transmission in RN-PFC and of noradrenergic transmission in LC-PFC was analyzed using in vivo fast scan cyclic voltammetry. Galanin receptor type 1 (GalR1)/type 2 (GalR2) antagonist M40, and a preferential GalR2 antagonist M871 were administered over 3days locally into either RN or LC by means of ALZET osmotic minipumps connected to locally implanted infusion cannulas. Intra-RN injection of M40 improved serotonergic tone and depressive-like behavior in epileptic "depressed" rats. Intra-LC injection of M40 improved noradrenergic tone and impulsive-like behavior in epileptic "impulsive" rats. The effects of M40 were only observed in impaired subjects. The treatment did not modify neurotransmission and behavior in naïve and epileptic not impaired rats; in "depressed" rats the effects were limited to serotonergic transmission and immobility, while in "impulsive" rats - to noradrenergic transmission and struggling behavior. Intra-RN administration of M871 exacerbated depressive-like behavior, but had no effects on any other of the examined parameters in any category of animals. These findings suggest that endogenous galanin, acting through GalR1 may be involved in the pathophysiology of epilepsy-associated depression and ADHD via inhibiting RN-PFC serotonergic and LC-PFC noradrenergic transmissions respectively.

A pilot study on predictors of brainstem raphe abnormality in patients with major depressive disorder.

BACKGROUND: Hypo/anechogenicity of the brainstem raphe (BR) structures has been suggested as a possible transcranial parenchymal sonography (TCS) marker associated with depression. AIM: The aim of this study was to analyze possible association of the abnormal BR echogenicity in patients with major depression when compared to healthy controls, and to evaluate its clinical and genetic correlates. METHODS: TCS was performed in 53 patients diagnosed as major depressive disorder (MDD) without psychotic symptoms and in 54 healthy matched controls. RESULTS: The TCS detected BR abnormalities were significantly more frequent in MDD patients (35 out of 53; 66%) in comparison to matched controls (5 out of 56; 9%). The prevalence of short allele (s) homozygocity in the length polymorphism of the promoter region of the serotonin transporter gene (5-HTTLPR) was significantly higher in MDD patients relative to those with normal BR echogenicity. A stepwise statistical discriminant analysis revealed statistically significant separation between MDD patients with and without BR abnormalities groups based on the four predictors combined: the Hamilton Anxiety Rating Scale item 5 ("difficulty in concentration, poor memory"), presence of social phobia, s allele homozygocity of the 5-HTTLPR polymorphism, and presence of generalized anxiety disorder. LIMITATIONS: Cross-sectional design and heterogenous treatment of depressed patients. CONCLUSIONS: Reduced BR echogenicity in at least a subgroup of MDD patients may reflect a particular phenotype, characterized by more prevalent comorbid anxiety disorders, associated with particular genetic polymorphisms and neurotransmitter(s) deficits, most probably altered serotonergic mechanisms.

Medullary neuronal loss is not associated with α-synuclein burden in multiple system atrophy.

BACKGROUND: Accumulation of α-synuclein in multiple system atrophy (MSA) affects medullary autonomic and respiratory control areas, including the rostral ventrolateral medulla and raphe nuclei. Relative neuronal vulnerability and its relationship to α-synuclein accumulation in these areas are unknown. The aim of this study was to determine the extent of loss of adrenergic neurons in the rostral ventrolateral medulla and serotonergic neurons in the ventrolateral medulla and raphe nuclei and its relationship with α-synuclein accumulation. METHODS: Medullary sections from 7 MSA and 6 control subjects were processed for tyrosine hydroxylase, tryptophan hydroxylase, and α-synuclein immunoreactivity. Neuronal counts were performed stereologically, whereas α-synuclein burden in oligodendrocytes and neurons was quantified using object detection density (area/mm2). RESULTS: All MSA cases had orthostatic hypotension; 5 had laryngeal stridor. There was marked neuronal loss in the rostral ventrolateral medulla and medullary raphe in all cases. Most severely affected were tyrosine hydroxylase ventrolateral medulla (C1) neurons (83% reduction), followed by tryptophan hydroxylase neurons in the ventrolateral medulla (70%), raphe obscurus (56%), pallidus (57%), and magnus (47%). α-Synuclein accumulation occurred predominantly as glial cytoplasmic inclusions with rare α-synuclein accumulation occurring within the remaining neurons. Density of α-synuclein did not correlate with neuronal loss in any of the areas analyzed, and there was no correlation between α-synuclein density and disease duration for any regions of interest. CONCLUSIONS: These findings indicate that in MSA adrenergic neurons are more susceptible than serotonergic neurons in the medulla. Further, loss of medullary monoaminergic neurons may progress independently from α-synuclein accumulation in MSA. © 2016 International Parkinson and Movement Disorder Society.

Combined treatment with subchronic lithium and acute intracerebral mirtazapine microinjection into the median raphe nucleus exerted an anxiolytic-like effect synergistically.

Although preclinical and clinical studies have established the efficacy of lithium augmentation of antidepressant drugs, the mechanism of action of lithium augmentation is not fully understood. Our previous study reported that subchronic lithium treatment enhanced the anxiolytic-like effect of systemic mirtazapine. In the present study, we examined the effect of subchronic lithium in combination with acute local intracerebral injection of mirtazapine on fear-related behaviors in a contextual fear conditioning test in rats to clarify the target brain region of lithium augmentation of mirtazapine. After conditioning by footshock, diet (food pellets) containing Li2CO3 at a concentration of 0.2% was administered for 7 days. Ten min before testing and 7 days after conditioning, mirtazapine (3µg/site) in a volume of 0.5µl was acutely injected into the median raphe nucleus (MRN), hippocampus or amygdala. The combination of subchronic lithium and acute mirtazapine microinjection into the MRN but not the hippocampus or the amygdala reduced fear expression synergistically. These results suggest that intra-MRN mirtazapine treatment with subchronic lithium exerts the anxiolytic-like effect through the facilitation of the MRN-5HT pathway.

α-Synuclein induced toxicity in brain stem serotonin neurons mediated by an AAV vector driven by the tryptophan hydroxylase promoter.

We studied the impact of α-synuclein overexpression in brainstem serotonin neurons using a novel vector construct where the expression of human wildtype α-synuclein is driven by the tryptophan hydroxylase promoter, allowing expression of α-synuclein at elevated levels, and with high selectivity, in serotonergic neurons. α-Synuclein induced degenerative changes in axons and dendrites, displaying a distorted appearance, suggesting accumulation and aggregation of α-synuclein as a result of impaired axonal transport, accompanied by a 40% loss of terminals, as assessed in the hippocampus. Tissue levels of serotonin and its major metabolite 5-HIAA remained largely unaltered, and the performance of the α-synuclein overexpressing rats in tests of spatial learning (water maze), anxiety related behavior (elevated plus maze) and depressive-like behavior (forced swim test) was not different from control, suggesting that the impact of the developing axonal pathology on serotonin neurotransmission was relatively mild. Overexpression of α-synuclein in the raphe nuclei, combined with overexpression in basal forebrain cholinergic neurons, resulted in more pronounced axonal pathology and significant impairment in the elevated plus maze. We conclude that α-synuclein pathology in serotonergic or cholinergic neurons alone is not sufficient to impair non-motor behaviors, but that it is their simultaneous involvement that determines severity of such symptoms.