c-Fos Immunoreactivity Research Articles

Effect of relative social rank within a social hierarchy on neural activation in response to familiar or unfamiliar social signals

Competent social functioning of group-living species relies on the ability of individuals to detect and utilize conspecific social cues to guide behavior. Previous studies have identified numerous brain regions involved in processing these external cues, collectively referred to as the Social Decision-Making Network. However, how the brain encodes social information with respect to an individual’s social status has not been thoroughly examined. In mice, cues about an individual’s identity, including social status, are conveyed through urinary proteins. In this study, we assessed the neural cFos immunoreactivity in dominant and subordinate male mice exposed to familiar and unfamiliar dominant and subordinate male urine. The posteroventral medial amygdala was the only brain region that responded exclusively to dominant compared to subordinate male urine. In all other brain regions, including the VMH, PMv, and vlPAG, activity is modulated by a combination of odor familiarity and the social status of both the urine donor and the subject receiving the cue. We show that dominant subjects exhibit robust differential activity across different types of cues compared to subordinate subjects, suggesting that individuals perceive social cues differently depending on social experience. These data inform further investigation of neurobiological mechanisms underlying social-status related brain differences and behavior.

Female rats display higher methamphetamine-primed reinstatement and c-Fos immunoreactivity than male rats

Methamphetamine (meth) dependence is often characterized by persistent and chronic relapse (i.e., return to drug use). Previous work suggests females may be at greater risk to relapse. In this study, we extended this limited evidence and identified sex-dependent neural substrates related to meth-triggered reinstatement. Male and female Sprague-Dawley rats were implanted with indwelling jugular catheters. Half of the rats were then trained to self-administer meth (0.05 mg/kg/inf); the other half self-administered saline during 21 daily sessions (2 h). Rats were then given 12 extinction sessions. Twenty-four hours after the last extinction session, rats received reinstatement testing. Half of the rats received a meth-prime (0.3 mg/kg, IP) injection and the remaining rats received a saline injection. This design resulted in 4 separate groups for each sex, allowing for careful investigation of brain regions related to meth-triggered reinstatement. Brains were harvested following the reinstatement session and c-Fos immunoreactivity was measured in multiple brain regions. Meth triggered reinstatement in both sexes and this effect was more robust in females compared to males. Significant sex differences were detected. Females showed greater c-Fos immunoreactivity in the cingulate cortex area 1, lateral orbitofrontal cortex, prelimbic cortex, caudate-putamen, nucleus accumbens core and shell, and central nucleus of the amygdala following meth-primed reinstatement.

The PGE2 receptor EP3 plays a positive role in the activation of hypothalamic-pituitary-adrenal axis and neuronal activity in the hypothalamus under immobilization stress

BackgroundProstaglandin E2 (PGE2) binds to four receptor subtypes (EP1, EP2, EP3 and EP4) and plays an important role in response to stress. However, the identity of the receptor(s) responsible for PGE2 regulation of neuronal activity and signaling through activation of the hypothalamic-pituitary-adrenal (HPA) axis under immobilization stress is unknown. PurposeThe present study aimed to investigate the role of the hypothalamic PGE2 receptors in the activation of the HPA axis and neuronal activity in a rat model of stress. MethodsStress was induced by immobilization of the animals, after which the stress-induced profile of PGE2 receptor signaling in the rat hypothalamus was determined by real-time polymerase chain reaction and immunohistochemistry. The effect of a selective EP3 receptor antagonist on corticosterone concentrations and c-Fos immunoreactivity was measured. ResultsExpression of EP2 and EP3 receptor genes, but not EP1 and EP4, was increased following immobilization stress. The EP3 receptor was localized to the paraventricular nucleus (PVN) of the hypothalamus, and the integrated density of the EP3 receptor was increased after immobilization stress. Rats given L-798,106, a selective antagonist of the EP3 receptor, showed significant attenuation of stress-increased serum corticosterone levels. EP3 antagonist also significantly suppressed the increase in the gene expression of c-Fos and the number of c-Fos-immunoreactive cells in the PVN of the hypothalamus following immobilization stress. ConclusionsThese results suggest that immobilization stress may result in increased activation of the HPA axis and neuronal activity through regulating the function of the EP3 receptor.

UVB irradiation induces contralateral changes in galanin, substance P and c-fos immunoreactivity in rat dorsal root ganglia, dorsal horn and lateral spinal nucleus

The selection of control group is crucial, as the use of an inadequate group may strongly affect the results. In this study we examine the effect on contralateral tissue protein levels, in a model of unilateral UVB irradiation, as the contralateral side is commonly used as a control. Previous studies have shown that UVB irradiation increases immunoreactivity for inflammatory regulated neuropeptides.Unilateral UVB irradiation of rat hind paw was performed and corresponding contralateral spinal cord and dorsal root ganglia (DRG) were collected 2–96 h after and investigated for changes in galanin, substance P and c-fos immunoreactivity. Control tissue was collected from naïve rats. Measurement of skin blood flow from contralateral heel hind paws (Doppler), revealed no change compared to naïve rats. However, UVB irradiation caused a significant reduction in the contralateral proportion of galanin immunopositive DRG neurons, at all-time points, as well as an increase in the contralateral spinal cord dorsal horn, around the central canal and in the lateral spinal nucleus (2–48 h). The contralateral proportion of SP positive DRG neurons and dorsal horn immunoreactivity was unchanged, whereas the lateral spinal nucleus area showed increased immunoreactivity (48 h). UVB irradiation also induced a slight contralateral upregulation of c-fos in the dorsal horn/central canal area (24 and 48 h). In summary, unilateral UVB irradiation induced contralateral changes in inflammatory/nociceptive neuropeptides in spinal cord and afferent pathways involved in pain signaling already within 24 h, a time point when also ipsilateral neurochemical/physiological changes have been reported for rats and humans.

Sexually dimorphic effects of prolactin treatment on the onset of puberty and olfactory function in mice

The onset of puberty is associated with the psychophysiological maturation of the adolescent to an adult capable of reproduction when olfactory signals play an important role. This period begins with the secretion of the gonadotropin-releasing hormone (GnRH) from GnRH neurons within the hypothalamus. This is regulated by kisspeptin neurons that express high levels of transmembrane prolactin receptors (PRLR) that bind to and are activated by prolactin (PRL). The elevated levels of serum PRL found during lactation, or caused by chronic PRL infusion, decreases the secretion of gonadotropins and kisspeptin and compromised the estrous cyclicity and the ovulation. In the present work, we aimed to evaluate the effects of either increased or decreased PRL circulating levels within the peripubertal murine brain by administration of PRL or treatment with cabergoline (Cab) respectively. We showed that either treatment delayed the onset of puberty in females, but not in males. This was associated with the augmentation of the PRL receptor (Prlr) mRNA expression in the arcuate nucleus and decreased Kiss1 expression in the anteroventral periventricular zone. Then, during adulthood, we assessed the activation of the mitral and granular cells of the main (MOB) and accessory olfactory bulb (AOB) by cFos immunoreactivity (ir) after the exposure to soiled bedding of the opposite sex. In the MOB, the PRL treatment promoted an increased cFos-ir of the mitral cells of males and females. In the granular cells of male of either treatment an augmented activation was observed. In the AOB, an impaired cFos-ir was observed in PRL and Cab treated females after exposure to male soiled bedding. However, in males, only Cab impaired its activation. No effects were observed in the AOB-mitral cells. In conclusion, our results demonstrate that PRL contributes to pubertal development and maturation of the MOB-AOB during the murine juvenile period in a sex-dependent way.

Early life sleep disruption is a risk factor for increased ethanol drinking after acute footshock stress in prairie voles.

Early postnatal experiences are important for shaping the development of the stress response and may contribute to the later emergence of alcohol use disorders. We have previously found that early life sleep disruption impairs social development and alters GABA neurons in the brain of adult prairie voles, a socially monogamous rodent that displays natural ethanol preference in the laboratory. However, it is unclear whether these effects on social behavior are due, in part, to overall anhedonia and/or altered behavioral response to stress. To address this question, litters containing prairie vole pups were sleep disrupted by gentle cage agitation for 7 consecutive days from postnatal days (P) 14 to 21 (early life sleep disruption, or ELSD group) or allowed to sleep undisturbed (Control). Adult voles underwent a 2-bottle choice ethanol drinking procedure integrated with a single session of footshocks. Ethanol intake after footshock was measured as well as c-Fos immunoreactivity in the lateral and central amygdala. ELSD animals showed increased ethanol consumption and increased neural activity in these amygdala regions after footshock compared to control animals. There were no differences in baseline ethanol drinking prior to exposure to a stressor. These results suggest that early life sleep disruption in prairie voles does not produce anhedonia but can have long-lasting effects on stress reactivity. In addition to shaping species-typical social behavior, early life sleep may be important in the development of stress induced ethanol consumption and the activation of limbic pathways associated with stress. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Neonatal overnutrition programming impairs cholecystokinin effects in adultmale rats

Overfeeding and rapid weight gain during early life are risk factors for the development of obesity in adulthood. This metabolic malprogramming may be mediated by endocrine disturbances during critical periods of development. Cholecystokinin (CCK) acts on the central nervous system by elevating thermogenesis and the activity of anorectic neurons, modulating overall energy balance. Therefore, we tested the hypothesis that postnatal overfeeding impaired CCK effects. Pups were raised in either a litter of three (neonatal overnutrition/small litter group) or 12 (controls/normal litter group) pups per dam to study the effects of postnatal overfeeding on the central and peripheral CCK systems in adulthood. Rats raised in small litters became overweight during lactation and remained overweight as adults, with increased adiposity and plasma levels of lipids, glucose, insulin, and leptin. Neonatally over-nourished rats showed attenuation of gastric emptying and anorexigenic response to CCK, suggesting that offspring from the SL group may present CCK resistance as adult male rats. Consistent with this idea, overweight rats displayed impaired central response in c-Fos immunoreactivity on the nucleus tractus solitarius, area postrema, paraventricular nucleus, central amygdala, arcuate nucleus, and dorsomedial hypothalamus in response to peripheral CCK at adulthood. The small litter group of adult male rats also exhibited reduced norepinephrine- and CCK-stimulated thermogenesis. Unresponsiveness to the effects of CCK may contribute to overweight and metabolic dysfunctions observed in postnatally over-nourished adult rats. Thus, the involvement of an impaired CCK system, among other neurohormonal failures, may contribute to the development of obesity.

Medullary tyrosine hydroxylase catecholaminergic neuronal populations in sudden unexpected death in epilepsy.

Sudden unexpected death in epilepsy (SUDEP) is mechanistically complex and one probable cause is seizure‐related respiratory dysfunction. Medullary respiratory regulatory nuclei include the pre‐Bötzinger complex (pre‐BötC) in the ventrolateral medulla (VLM), the medullary raphé nuclei (MR) and nucleus of solitary tract in the dorsomedial medulla (DMM). The region of the VLM also contains intermingled tyrosine hydroxylase (TH) catecholaminergic neurones which directly project to the pre‐BötC and regulate breathing under hypoxic conditions and our aim was to evaluate these neurones in SUDEP cases. In post‐mortem cases from three groups [SUDEP (18), epilepsy controls (8) and non‐epilepsy controls (16)] serial sections of medulla (obex + 2 to + 13 mm) were immunolabeled for TH. Three regions of interest (ROI) were outlined (VLM, DMM and MR) and TH‐immunoreactive (TH‐IR) neurones were evaluated using automated detection for overall labeling index (neurones and processes) and neuronal densities and compared between groups and relative to obex level. C‐fos immunoreactivity was also semi‐quantitatively evaluated in these regions. We found no significant difference in the density of TH‐IR neurones or labeling index between the groups in all regions. Significantly more TH‐IR neurones were present in the DMM region than VLM in non‐epilepsy cases only (P < 0.01). Regional variations in TH‐IR neurones with obex level were seen in all groups except SUDEP. We also identified occasional TH neurones in the MR region in all groups. There was significantly less c‐fos labeling in the VLM and MR in SUDEP than non‐epilepsy controls but no difference with epilepsy controls. In conclusion, in this series we found no evidence for alteration of total medullary TH‐IR neuronal numbers in SUDEP but noted some differences in their relative distribution in the medulla and c‐fos neurones compared to control groups which may be relevant to the mechanism of death.

Differential Role of Anterior Cingulate Cortical Glutamatergic Neurons in Pain-Related Aversion Learning and Nociceptive Behaviors in Male and Female Rats.

Pain is comprised of both sensory and affective components. The anterior cingulate cortex (ACC) is a key brain region involved in the emotional processing of pain. Specifically, glutamatergic transmission within the ACC has been shown to modulate pain-related aversion. In the present study, we use in vivo optogenetics to activate or silence, using channelrhodopsin (ChR2) and archaerhodopsin (ArchT) respectively, calmodulin-kinase IIα (CaMKIIα)-expressing excitatory glutamatergic neurons of the ACC during a formalin-induced conditioned place aversion (F-CPA) behavioral paradigm in both female and male adult Sprague-Dawley rats. Expression of c-Fos, a marker of neuronal activity, was assessed within the ACC using immunohistochemistry. Optogenetic inhibition of glutamatergic neurons of the ACC abolished F-CPA without affecting formalin-induced nociceptive behavior during conditioning. In male rats, optogenetic activation of ACC glutamatergic neurons decreased formalin-induced nociceptive behavior during conditioning without affecting F-CPA. Interestingly, the opposite effect was seen in females, where optogenetic activation of glutamatergic neurons of the ACC increased formalin-induced nociceptive behavior during conditioning. The abolition of F-CPA following optogenetic inhibition of glutamatergic neurons of the ACC was associated with a reduction in c-Fos immunoreactivity in the ACC in male rats, but not female rats. These results suggest that excitatory glutamatergic neurons of the ACC play differential and sex-dependent roles in the aversion learning and acute sensory components of pain.

Brief stress impairs recognition memory through amygdalar activation in animals with medial prefrontal cortex lesions

The medial prefrontal cortex (mPFC) is thought to exert inhibitory control over stress-induced activation of the amygdala and neurocognitive effects. As evidence to support this, we examined how exposure to either a brief or prolonged stress affected on amygdalar c-Fos levels and recognition memory of animals with mPFC chemical lesions. mPFC-lesioned and sham-operated animals were subjected to either a brief 20-min restraint+20 tailshocks or a prolonged 60-min restraint+60 tailshocks. Post-stress performances in the object recognition memory and c-Fos immunoreactivity in the amygdala were then assessed. In sham-operated animals, the object recognition memory was reliably impaired following the prolonged, but not following the brief stress exposure. On the other hand, in mPFC-lesioned animals, the brief stress significantly impaired recognition memory and enhanced c-Fos expression in the amygdala. Present findings of loss of mPFC activity exacerbating stress effects provide causal evidence that the mPFC exerts inhibitory control on stress.

Prefrontal cortex activity patterns during taste neophobia habituation in adult and aged rats

Age-related memory decline has been associated with changes in the medial prefrontal cortex (mPFC) function. In order to explore the role of mPFC in taste recognition memory, we have assessed mPFC c-Fos immunoreactivity in adult (5-month-old) and aged (24-month-old) male Wistar rats during the first (Novel), second (Familiar I), and sixth (Familiar II) exposure to a cider vinegar solution. Adult brains showed higher c-Fos expression in the ventral but not the dorsal region of mPFC during the second taste exposure. Interestingly, old brains exhibited an altered activity pattern selectively in the dorsal peduncular cortex (DP) which can be associated with a delayed attenuation of vinegar neophobia in this group. These results support the involvement of this area in the formation of safe taste memory. Further research is needed for understanding the role of DP in taste recognition memory and the impact of aging on it.

Forced Abstinence From Alcohol Induces Sex-Specific Depression-Like Behavioral and Neural Adaptations in Somatostatin Neurons in Cortical and Amygdalar Regions.

Forced abstinence (FA) from alcohol has been shown to produce a variety of anxiety- and depression-like symptoms in animal models. Somatostatin (SST) neurons, a subtype of GABAergic neurons found throughout the brain, are a novel neural target with potential treatment implications in affective disorders, yet their role in alcohol use disorders (AUD) remains to be explored. Here, we examined the neuroadaptations of SST neurons during forced abstinence from voluntary alcohol consumption. Following 6 weeks of two-bottle choice alcohol consumption and protracted forced abstinence, male and female C57BL/6J mice exhibited a heightened, but sex-specific, depressive-like behavioral profile in the sucrose preference test (SPT) and forced swim test (FST), without changes in anxiety-like behaviors in the elevated plus maze (EPM) and open field test (OFT). FST-induced cFos expressions in the prefrontal cortex (PFC) and ventral bed nucleus of the stria terminalis (vBNST) were altered in FA-exposed female mice only, suggesting a sex-specific effect of forced abstinence on the neural response to acute stress. SST immunoreactivity in these regions was unaffected by forced abstinence, while differences were seen in SST/cFos co-expression in the vBNST. No differences in cFos or SST immunoreactivity were seen in the lateral central nucleus of the amygdala (CEA) and the basolateral amygdala (BLA). Additionally, SST neurons in female mice displayed opposing alterations in the PFC and vBNST, with heightened intrinsic excitability in the PFC and diminished intrinsic excitability in the vBNST. These findings provide an overall framework of forced abstinence-induced neuroadaptations in these key brain regions involved in emotional regulation and processing.

The anorexigenic effect of vasoactive intestinal polypeptide in Japanese quail is associated with molecular changes in the arcuate and dorsomedial hypothalamic nuclei

Vasoactive intestinal polypeptide (VIP) is involved in gastric smooth muscle relaxation, vasodilation, and gastric secretions. It is also associated with appetite regulation, eliciting an anorexigenic response in mammals, birds, and fish; however, the molecular mechanism mediating this response is not well understood. The aim of the present study was thus to investigate hypothalamic mechanisms mediating VIP-induced satiety in 7-d old Japanese quail. In experiment 1, chicks that received intracerebroventricular (ICV) injection of VIP had reduced food intake for up to 180 min after injection and reduced water intake for 90 min. In experiment 2, VIP-treated chicks that were food restricted did not reduce water intake. In experiment 3, there was increased c-Fos immunoreactivity in the arcuate (ARC) and dorsomedial (DMN) nuclei of the hypothalamus in VIP-injected quail. In experiment 4, ICV VIP was associated with decreased neuropeptide Y mRNA in the ARC and DMN and an increase in corticotropin releasing factor mRNA in the DMN. In experiment 5, VIP-treated chicks displayed fewer feed pecks and locomotor behaviors. These results demonstrate that central VIP causes anorexigenic effects that are likely associated with reductions in orexigenic tone involving the ARC and DMN.

The effects of Topiramate on isolation-induced aggression: a behavioral and immunohistochemical study in mice.

Topiramate, an antiepileptic drug, has been found to be useful for the treatment of aggression in clinical populations. Most preclinical studies related to Topiramate have been focused exclusively on the quantitative aspects of the aggressive behavior between mice. However, there is still limited knowledge regarding the effects of Topiramate on neuronal mechanisms occurring in aggressive mice. The present work aims to understand further the effects of the antiepileptic drug Topiramate on aggressive behaviors, and on the neural correlates underlying such behaviors. To achieve this, we combined the resident-intruder model of isolation-induced aggression in mice with two drug regimens of Topiramate administration (30.0 mg/kg; acute and sub-chronic treatments). Our data showed that both acute and subchronic treatments decreased the intensity of agonistic encounters and reinforced social behavior. By using C-fos immunoreactivity, we investigated the neuronal activation of several brain regions involved in aggressive behavior following subchronic treatment. We found that Topiramate produced activation in several cortical areas and in the lateral septum of resident brain mice compared with their controls. However, Topiramate induced inhibition in the medial nucleus of the amygdala, the dorsomedial nucleus of the periaqueductal gray, and especially in the anterior hypothalamic nucleus. Finally, we performed microinfusion of Topiramate (0.1 and 0.3 mM) into the lateral septum and anterior hypothalamus on offensive behaviors in isolation-induced-aggression paradigm. Interestingly, the microinfusion of Topiramate into the lateral septum has the capacity to alleviate aggressive behavior, without affecting social behavior. However, the microinfusion of Topiramate into the anterior hypothalamus decreased aggressive behavior and slightly reinforced social behavior. Our observations supported that the dose of 0.1 mM of Topiramate appeared more efficacy to treat aggression in adult mice. These pharmacological characteristics may account for Topiramate efficacy on aggressive symptoms in psychiatric patients.

Modified in situ Hybridization Chain Reaction Using Short Hairpin DNAs.

The visualization of multiple gene expressions in well-preserved tissues is crucial for the elucidation of physiological and pathological processes. In situ hybridization chain reaction (HCR) is a method to visualize specific mRNAs in diverse organisms by applying a HCR that is an isothermal enzyme-free nucleotide polymerization method using hairpin DNAs. Although in situ HCR is a versatile method, this method is not widely used by researchers because of their higher cost than conventional in situ hybridization (ISH). Here, we redesigned hairpin DNAs so that their lengths were half the length of commonly used hairpin DNAs. We also optimized the conjugated fluorophores and linkers. Modified in situ HCR showed sufficient fluorescent signals to detect various mRNAs such as Penk, Oxtr, Vglut2, Drd1, Drd2, and Moxd1 in mouse neural tissues with a high signal-to-noise ratio. The sensitivity of modified in situ HCR in detecting the Oxtr mRNA was better than that of fluorescent ISH using tyramide signal amplification. Notably, the modified in situ HCR does not require proteinase K treatment so that it enables the preservation of morphological structures and antigenicity. The modified in situ HCR simultaneously detected the distributions of c-Fos immunoreactivity and Vglut2 mRNA, and detected multiple mRNAs with a high signal-noise ratio at subcellular resolution in mouse brains. These results suggest that the modified in situ HCR using short hairpin DNAs is cost-effective and useful for the visualization of multiple mRNAs and proteins.

Oxyntomodulin induces satiety and activates the arcuate nucleus of the hypothalamus in Japanese quail

Oxyntomodulin (OXM) is a proglucagon-derived peptide that suppresses hunger in humans. There are some differences in its food intake-inhibitory effects among species. The central mechanisms are unclear and it is unknown if OXM is more efficacious in a gallinaceous species that has not undergone as much selection for growth as the chicken. The objective was thus to determine the effects of OXM on food and water intake and hypothalamic physiology in Japanese quail. At 7 days post-hatch, 6-h-fasted quail were injected intracerebroventricularly (ICV) or intraperitoneally (IP) with 0.32, 0.65, or 1.3 nmol of OXM. All doses decreased food intake for 180 min post-ICV injection. On a cumulative basis, water intake was not affected until 120 min, with the lowest and highest doses decreasing water intake after ICV injection. The two highest doses were anorexigenic when administered via the IP route, whereas all doses were anti-dipsogenic starting at 30 min post-injection. In hypothalamic samples collected at 1-h post-ICV injection, there was an increase in c-Fos immunoreactivity, an indicator of recent neuronal activation, in the arcuate nucleus (ARC) and dorsomedial nucleus (DMN) of the hypothalamus in OXM-injected individuals. Results suggest that quail are more sensitive than chickens to the satiety-inducing effects of OXM. The central mechanism is likely mediated through a pathway in the ARC that is conserved among species, and through activation of the DMN, an effect that is unique to quail. Such knowledge is critical for facilitating the development of novel, side effect-free anti-eating strategies to promote weight-loss in obesity.

Effects of chronic nicotine exposure on Δ9-tetrahydrocannabinol-induced locomotor activity and neural activation in male and female adolescent and adult rats

RationaleHigh rates of comorbid tobacco and cannabis use in adolescents and young adults may be related to functional interactions between the nicotinic cholinergic and cannabinoid systems in the brain during development. This study examined the effects of chronic exposure to nicotine (the psychoactive component in tobacco) on acute exposure to delta-9-tetrahydrocannabinol (THC) (the psychoactive component of cannabis). MethodsMale and female adolescent and adult Sprague-Dawley rats (N = 112) were injected daily with nicotine (1 mg/kg, i.p.) or vehicle for 14 days, followed by a 14-day drug-free period. On test day, rats were injected with THC (5 mg/kg, i.p.) or vehicle, locomotor activity was recorded for 2 h, and brains harvested for c-Fos immunoreactivity (IR). ResultsLocomotor activity and c-Fos IR changes induced by THC challenge were altered by nicotine pre-exposure and modified by age and sex. THC-induced suppression of locomotor activity was attenuated by nicotine pre-exposure in adult but not adolescent males. THC-induced suppression of locomotor activity was potentiated by nicotine pre-exposure in female adolescents, with no effects of THC or nicotine observed in female adults. THC increased c-Fos IR in the caudate, nucleus accumbens, stria terminalis, septum, amygdala, hypothalamus, and thalamus. Nicotine pre-exposure potentiated this effect in all regions. Several brain regions showed age and sex differences in c-Fos IR such that expression was greater in adults than adolescents and in females than males. ConclusionsChronic nicotine pre-exposure produces lasting effects on cannabinoid-mediated signalling in the brain and on behaviour that are mediated by age and sex. Funding supportNSERC.

Gene expression analysis in the mouse brainstem identifies Cart and Nesfatin as neuropeptides coexpressed in the Calbindin-positive neurons of the Nucleus papilio.

Study Objectives: The brainstem contains several neuronal populations, heterogeneous in terms of neurotransmitter/neuropeptide content, which are important for controlling various aspects of the rapid eye movement (REM) phase of sleep. Among these populations are the Calbindin (Calb)-immunoreactive NPCalb neurons, located in the Nucleus papilio, within the dorsal paragigantocellular nucleus (DPGi), and recently shown to control eye movement during the REM phase of sleep. Methods: We performed in-depth data mining of the in situ hybridization data collected at the Allen Brain Atlas, in order to identify potentially interesting genes expressed in this brainstem nucleus. Our attention focused on genes encoding neuropeptides, including Cart (Cocaine and Amphetamine Regulated Transcripts) and Nesfatin 1. Results: While nesfatin 1 appeared ubiquitously expressed in this Calb-positive neuronal population, Cart was coexpressed in only a subset of these glutamatergic NPCalb neurons. Furthermore, an REM sleep deprivation and rebound assay performed with mice revealed that the Cart-positive neuronal population within the DPGi was activated during REM sleep (as measured by c-fos immunoreactivity), suggesting a role of this neuropeptide in regulating some aspects of REM sleep. Conclusions: The assembled information could afford functional clues to investigators, conducive to further experimental pursuits.

Selective Disruption of Inhibitory Synapses Leading to Neuronal Hyperexcitability at an Early Stage of Tau Pathogenesis in a Mouse Model.

Synaptic dysfunction provoking dysregulated cortical neural circuits is currently hypothesized as a key pathophysiological process underlying clinical manifestations in Alzheimer's disease and related neurodegenerative tauopathies. Here, we conducted PET along with postmortem assays to investigate time course changes of excitatory and inhibitory synaptic constituents in an rTg4510 mouse model of tauopathy, which develops tau pathologies leading to noticeable brain atrophy at 5-6 months of age. Both male and female mice were analyzed in this study. We observed that radiosignals derived from [11C]flumazenil, a tracer for benzodiazepine receptor, in rTg4510 mice were significantly lower than the levels in nontransgenic littermates at 2-3 months of age. In contrast, retentions of (E)-[11C]ABP688, a tracer for mGluR5, were unaltered relative to controls at 2 months of age but then gradually declined with aging in parallel with progressive brain atrophy. Biochemical and immunohistochemical assessment of postmortem brain tissues demonstrated that inhibitory, but not excitatory, synaptic constituents selectively diminished without overt loss of somas of GABAergic interneurons in the neocortex and hippocampus of rTg4510 mice at 2 months of age, which was concurrent with enhanced immunoreactivity of cFos, a well-characterized immediate early gene, suggesting that impaired inhibitory neurotransmission may cause hyperexcitability of cortical circuits. Our findings indicate that tau-induced disruption of the inhibitory synapse may be a critical trigger of progressive neurodegeneration, resulting in massive neuronal loss, and PET assessments of inhibitory versus excitatory synapses potentially offer in vivo indices for hyperexcitability and excitotoxicity early in the etiologic pathway of neurodegenerative tauopathies.SIGNIFICANCE STATEMENT In this study, we examined the in vivo status of excitatory and inhibitory synapses in the brain of the rTg4510 tauopathy mouse model by PET imaging with (E)-[11C]ABP688 and [11C]flumazenil, respectively. We identified inhibitory synapse as being significantly dysregulated before brain atrophy at 2 months of age, while excitatory synapse stayed relatively intact at this stage. In line with this observation, postmortem assessment of brain tissues demonstrated selective attenuation of inhibitory synaptic constituents accompanied by the upregulation of cFos before the formation of tau pathology in the forebrain at young ages. Our findings indicate that selective degeneration of inhibitory synapse with hyperexcitability in the cortical circuit constitutes the critical early pathophysiology of tauopathy.

The vagus nerve is necessary for the rapid and widespread neuronal activation in the brain following oral administration of psychoactive bacteria

There is accumulating evidence that certain gut microbes modulate brain chemistry and have antidepressant-like behavioural effects. However, it is unclear which brain regions respond to bacteria-derived signals or how signals are transmitted to distinct regions. We investigated the role of the vagus in mediating neuronal activation following oral treatment with Lactobacillus rhamnosus (JB-1).Male Balb/c mice were orally administered a single dose of saline or a live or heat-killed preparation of a physiologically active bacterial strain, Lactobacillus rhamnosus (JB-1). 165 min later, c-Fos immunoreactivity in the brain was mapped, and mesenteric vagal afferent fibre firing was recorded. Mice also underwent sub-diaphragmatic vagotomy to investigate whether severing the vagus prevented JB-1-induced c-Fos expression. Finally, we examined the ΔFosB response following acute versus chronic bacterial treatment.While a single exposure to live and heat-killed bacteria altered vagal activity, only live treatment induced rapid neural activation in widespread but distinct brain regions, as assessed by c-Fos expression. Sub-diaphragmatic vagotomy abolished c-Fos immunoreactivity in most, but not all, previously responsive regions. Chronic, but not acute treatment induced a distinct pattern of ΔFosB expression, including in previously unresponsive brain regions.These data identify that specific brain regions respond rapidly to gut microbes via vagal-dependent and independent pathways, and demonstrate that acute versus long-term exposure is associated with differential responses in distinct brain regions.