Expression of c-fos-like protein as a marker for neuronal activity following noxious stimulation in the rat

Ginsenoside Rh2 Ameliorates Neuropathic Pain by inhibition of the miRNA21-TLR8-MAPK axis

Ginsenoside Rh2 is one of the major bioactive ginsenosides in Panax ginseng. Although Rh2 is known to enhance immune cells activity for treatment of cancer, its anti-inflammatory and neuroprotective effects have yet to be determined. In this study, we investigated the effects of Rh2 on spared nerve injury (SNI)-induced neuropathic pain and elucidated the potential mechanisms. We found that various doses of Rh2 intrathecal injection dose-dependently attenuated SNI-induced mechanical allodynia and thermal hyperalgesia. Rh2 also inhibited microglia and astrocyte activation in the spinal cord of a murine SNI model. Rh2 treatment inhibited SNI-induced increase of proinflammatory cytokines, including tumor necrosis factor-α, interleukin (IL)-1 and IL-6. Expression of miRNA-21, an endogenous ligand of Toll like receptor (TLR)8 was also decreased. Rh2 treatment blocked the mitogen-activated protein kinase (MAPK) signaling pathway by inhibiting of phosphorylated extracellular signal-regulated kinase expression. Finally, intrathecal injection of TLR8 agonist VTX-2337 reversed the analgesic effect of Rh2. These results indicated that Rh2 relieved SNI-induced neuropathic pain via inhibiting the miRNA-21-TLR8-MAPK signaling pathway, thus providing a potential application of Rh2 in pain therapy.

Functional correlates of immediate early gene expression in mouse visual cortex

During visual development, response properties of layer 2/3 neurons in visual cortex are shaped by experience. Both visual and visuomotor experience are necessary to co-ordinate the integration of bottom-up visual input and top-down motor-related input. Whether visual and visuomotor experience engage different plasticity mechanisms, possibly associated with the two separate input pathways, is still unclear. To begin addressing this, we measured the expression level of three different immediate early genes (IEG) (c-fos, egr1 or Arc) and neuronal activity in layer 2/3 neurons of visual cortex before and after a mouse's first visual exposure in life, and subsequent visuomotor learning. We found that expression levels of all three IEGs correlated positively with neuronal activity, but that first visual and first visuomotor exposure resulted in differential changes in IEG expression patterns. In addition, IEG expression levels differed depending on whether neurons exhibited primarily visually driven or motor-related activity. Neurons with strong motor-related activity preferentially expressed EGR1, while neurons that developed strong visually driven activity preferentially expressed Arc. Our findings are consistent with the interpretation that bottom-up visual input and top-down motor-related input are associated with different IEG expression patterns and hence possibly also with different plasticity pathways.

Efficient spatially targeted gene editing using a near-infrared activatable protein-conjugated nanoparticle for brain applications

Spatial control of gene expression is critical to modulate cellular functions and deconstruct the function of individual genes in biological processes. Light-responsive gene-editing formulations have been recently developed; however, they have shown limited applicability in vivo due to poor tissue penetration, limited cellular transfection and the difficulty in evaluating the activity of the edited cells. Here, we report a formulation composed of upconversion nanoparticles conjugated with Cre recombinase enzyme through a photocleavable linker, and a lysosomotropic agent that facilitates endolysosomal escape. This formulation allows in vitro spatial control in gene editing after activation with near-infrared light. We further demonstrate the potential of this formulation in vivo through three different paradigms: (i) gene editing in neurogenic niches, (ii) gene editing in the ventral tegmental area to facilitate monitoring of edited cells by precise optogenetic control of reward and reinforcement, and (iii) gene editing in a localized brain region via a noninvasive administration route (i.e., intranasal).

Spatial control of gene expression allows precise control over biological processes. Here, the authors develop an efficient light-responsive formulation based on upconversion nanoparticles, and demonstrate on-demand genetic manipulation in deep brain tissue.

Embryonic medial ganglionic eminence cells survive and integrate into the inferior colliculus of adult mice

Acoustic overexposure can lead to decreased inhibition in auditory centers, including the inferior colliculus (IC), and has been implicated in the development of central auditory pathologies. While systemic drugs that increase GABAergic transmission have been shown to provide symptomatic relief, their side effect profiles impose an upper-limit on the dose and duration of use. A treatment that locally increases inhibition in auditory nuclei could mitigate these side effects. One such approach could be transplantation of inhibitory precursor neurons derived from the medial ganglionic eminence (MGE). The present study investigated whether transplanted MGE cells can survive and integrate into the IC of non-noise exposed and noise exposed mice. MGE cells were harvested on embryonic days 12-14 and injected bilaterally into the IC of adult mice, with or without previous noise exposure. At one-week post transplantation, MGE cells possessed small, elongated soma and bipolar processes, characteristic of migrating cells. By 5 weeks, MGE cells exhibited a more mature morphology, with multiple branching processes and axons with boutons that stain positive for the vesicular GABA transporter (VGAT). The MGE survival rate after 14 weeks post transplantation was 1.7% in non-noise exposed subjects. MGE survival rate was not significantly affected by noise exposure (1.2%). In both groups the vast majority of transplanted MGE cells (>97%) expressed the vesicular GABA transporter. Furthermore, electronmicroscopic analysis indicated that transplanted MGE cells formed synapses with and received synaptic endings from host IC neurons. Acoustic stimulation lead to a significant increase in the percentage of endogenous inhibitory cells that express c-fos but had no effect on the percentage of c-fos expressing transplanted MGE cells. MGE cells were observed in the IC up to 22 weeks post transplantation, the longest time point investigated, suggesting long term survival and integration. These data provide the first evidence that transplantation of MGE cells is viable in the IC and provides a new strategy to explore treatment options for central hearing dysfunction following noise exposure.

CXCR4/CX43 Regulate Diabetic Neuropathic Pain via Intercellular Interactions between Activated Neurons and Dysfunctional Astrocytes during Late Phase of Diabetes in Rats and the Effects of Antioxidant N-Acetyl-L-Cysteine

Growing evidence suggests that the interactions between astrocytes and neurons exert important functions in the central sensitization of the spinal cord dorsal horn in rodents with diabetes and neuropathic pain (DNP). However, it still remains unclear how signal transmission occurs in the spinal cord dorsal horn between astrocytes and neurons, especially in subjects with DNP. Chemokine CXC receptor 4 (CXCR4) plays critical roles in DNP, and connexin 43 (CX43), which is also primarily expressed by astrocytes, contributes to the development of neuropathy. We thus postulated that astrocytic and neuronal CXCR4 induces and produces inflammatory factors under persistent peripheral noxious stimulation in DNP, while intercellular CX43 can transmit inflammatory stimulation signals. The results showed that streptozotocin-induced type 1 diabetic rats developed heat hyperalgesia and mechanical allodynia. Diabetes led to persistent neuropathic pain. Diabetic rats developed peripheral sensitization at the early phase (2 weeks) and central sensitization at the late phase (5 weeks) after diabetes induction. Both CXCR4 and CX43, which are localized and coexpressed in neurons and astrocytes, were enhanced significantly in the dorsal horn of spinal cord in rats undergoing DNP during late phase of diabetes, and the CXCR4 antagonist AMD3100 reduced the expression of CX43. The nociceptive behavior was reversed, respectively, by AMD3100 at the early phase and by the antioxidant N-acetyl-L-cysteine (NAC) at the late phase. Furthermore, rats with DNP demonstrated downregulation of glial fibrillary acidic protein (GFAP) as well as upregulation of c-fos in the spinal cord dorsal horn at the late phase compared to the controls, and upregulation of GFAP and downregulation of c-fos were observed upon treatment with NAC. Given that GFAP and c-fos are, respectively, makers of astrocyte and neuronal activation, our findings suggest that CXCR4 as an inflammatory stimulation protein and CX43 as an intercellular signal transmission protein both may induce neurons excitability and astrocytes dysfunction in developing DNP.

Effects of a psychedelic 5-HT2A receptor agonist on anxiety-related behavior and fear processing in mice

Psychedelic-assisted psychotherapy gained considerable interest as a novel treatment strategy for fear-related mental disorders but the underlying mechanism remains poorly understood. The serotonin 2A (5-HT2A) receptor is a key target underlying the effects of psychedelics on emotional arousal but its role in fear processing remains controversial. Using the psychedelic 5-HT2A/5-HT2C receptor agonist 2,5-dimethoxy-4-iodoamphetamine (DOI) and 5-HT2A receptor knockout (KO) mice we investigated the effect of 5-HT2A receptor activation on emotional processing. We show that DOI administration did not impair performance in a spontaneous alternation task but reduced anxiety-like avoidance behavior in the elevated plus maze and elevated zero maze tasks. Moreover, we found that DOI did not block memory recall but diminished fear expression in a passive avoidance task. Likewise, DOI administration reduced fear expression in an auditory fear conditioning paradigm, while it did not affect retention of fear extinction when administered prior to extinction learning. The effect of DOI on fear expression was abolished in 5-HT2A receptor KO mice. Administration of DOI induced a significant increase of c-Fos expression in specific amygdalar nuclei. Moreover, local infusion of the 5-HT2A receptor antagonist M100907 into the amygdala reversed the effect of systemic administration of DOI on fear expression while local administration of DOI into the amygdala was sufficient to suppress fear expression. Our data demonstrate that activation of 5-HT2A receptors in the amygdala suppresses fear expression but provide no evidence for an effect on retention of fear extinction.

GABAergic interneurons' feedback inhibition of dorsal raphe-projecting pyramidal neurons of the medial prefrontal cortex suppresses feeding of adolescent female mice undergoing activity-based anorexia

Anorexia Nervosa (AN) is characterized by voluntary food restriction, excessive exercise and extreme body weight loss. AN is particularly prevalent among adolescent females experiencing stress-induced anxiety. We used the animal model, activity-based anorexia (ABA), which captures these characteristics of AN, to reveal the neurobiology underlying individual differences in AN vulnerability. Dorsal raphe (DR) regulates feeding and is recruited when coping inescapable stress. Through chemogenetic activation, we investigated the role of mPFC pyramidal neurons projecting to DR (mPFC→DR) in adolescent female mice's decision to eat or exercise following ABA induction. Although the DREADD ligand C21 could activate 44% of the mPFC→DR neurons, this did not generate significant group mean difference in the amount of food intake, compared to control ABA mice without chemogenetic activation. However, analysis of individuals' responses to C21 revealed a significant, positive correlation between food intake and mPFC→DR neurons that co-express cFos, a marker for neuronal activity. cFos expression by GABAergic interneurons (GABA-IN) in mPFC was significantly greater than that for the control ABA mice, indicating recruitment of GABA-IN by mPFC→DR neurons. Electron microscopic immunohistochemistry revealed that GABAergic innervation is 60% greater for the PFC→DR neurons than adjacent Layer 5 pyramidal neurons without projections to DR. Moreover, individual differences in this innervation correlated negatively with food intake specifically on the day of C21 administration. We propose that C21 activates two antagonistic pathways: (1) PFC→DR pyramidal neurons that promote food intake; and (2) GABA-IN in the mPFC that dampen food intake through feedback inhibition of mPFC→DR neurons.

Chemogenetic Activation of Astrocytes in the Basolateral Amygdala Contributes to Fear Memory Formation by Modulating the Amygdala–Prefrontal Cortex Communication

The basolateral amygdala (BLA) is one of the key brain areas involved in aversive learning, especially fear memory formation. Studies of aversive learning in the BLA have largely focused on neuronal function, while the role of BLA astrocytes in aversive learning remains largely unknown. In this study, we manipulated the BLA astrocytes by expressing the Gq-coupled receptor hM3q and discovered that astrocytic Gq modulation during fear conditioning promoted auditorily cued fear memory but did not affect less stressful memory tasks or induce anxiety-like behavior. Moreover, chemogenetic activation of BLA astrocytes during memory retrieval had no effect on fear memory expression. In addition, astrocytic Gq activation increased c-Fos expression in the BLA and the medial prefrontal cortex (mPFC) during fear conditioning, but not in the home cage. Combining these results with retrograde virus tracing, we found that the activity of mPFC-projecting BLA neurons showed significant enhancement after astrocytic Gq activation during fear conditioning. Electrophysiology recordings showed that activating astrocytic Gq in the BLA promoted spike-field coherence and phase locking percentage, not only within the BLA but also between the BLA and the mPFC. Finally, direct chemogenetic activation of mPFC-projecting BLA neurons during fear conditioning enhanced cued fear memory. Taken together, our data suggest that astrocytes in the BLA may contribute to aversive learning by modulating amygdala–mPFC communication.

Age-Dependent FOSB/ΔFOSB Response to Acute and Chronic Stress in the Extended Amygdala, Hypothalamic Paraventricular, Habenular, Centrally-Projecting Edinger-Westphal, and Dorsal Raphe Nuclei in Male Rats

FOS proteins are early-responding gene products that contribute to the formation of activator protein-1. Several acute and chronic stimuli lead to Fos gene expression, accompanied by an increase of nuclear FOS, which appears to decline with aging. FOSB is another marker to detect acute cellular response, while ΔFOSB mirrors long-lasting changes in neuronal activity upon chronic stress. The notion that the occurrence of stress-related mood disorders shows some age dependence suggests that the brain's stress sensitivity is also a function of age. To study age-dependent stress vulnerability at the immediate-early gene level, we aimed to describe how the course of aging affects the neural responses of FOSB/ΔFOSB in the acute restraint stress (ARS), and chronic variable mild stress (CVMS) in male rats. Fourteen brain areas [central, medial, basolateral (BLA) amygdala; dorsolateral- (BNSTdl), oval- (BNSTov), dorsomedial-, ventral- (BNSTv), and fusiform- (BNSTfu) divisions of the bed nucleus of the stria terminalis; medial and lateral habenula, hypothalamic paraventricular nucleus (PVN), centrally-projecting Edinger-Westphal nucleus, dorsal raphe nucleus, barrel field of somatosensory cortex (S1)] were examined in the course of aging. Eight age groups [1-month-old (M), 1.5 M, 2 M, 3 M, 6 M, 12 M, 18 M, and 24 M] of rats were exposed to a single ARS vs. controls. In addition, rats in six age groups (2, 3, 6, 12, 18, and 24 M) were subjected to CVMS. The FOSB/ΔFOSB immunoreactivity (IR) was a function of age in both controls, ARS- and CVMS-exposed rats. ARS increased the FOSB/ΔFOSB in all nuclei (except in BLA), but only BNSTfu, BNSTv, and PVN reacted throughout the examined lifespan. The CVMS did not increase the FOSB/ΔFOSB in BLA, BNSTov, BNSTdl, and S1. PVN showed a constantly maintained FOSB/ΔFOSB IR during the examined life period. The maximum stress-evoked FOSB/ΔFOSB signal was detected at 2-3 M periods in the ARS- and at 6 M, 18 M in CVMS- model. Corresponding to our previous observations on FOS, the FOSB/ΔFOSB response to stress decreased with age in most of the examined nuclei. Only the PVN exerted a sustained age-independent FOSB/ΔFOSB, which may reflect the long-lasting adaptation response and plasticity of neurons that maintain the hypothalamus-pituitary-adrenal axis response throughout the lifespan.

Research progress of the paraventricular thalamus in the regulation of sleep-wake and emotional behaviors

The paraventricular thalamus (PVT) is a major component of the midline structure of the thalamus. It is one of the nonspecific nuclei of the thalamus, which plays a great role in the regulation of cortical arousal. PVT, an important node in the central nervous system, sends widespread outputs to many brain regions and also accepts plentiful inputs from many brain regions to modulate diverse functions, including sleep-wake state, attention, memory, and pain. Recently, with the increasing prevalence of sleep disorders and mood disorders, people pay great attention to PVT, which was implicated in arousal and emotional behaviors. Therefore, the main purpose of this review is to illustrate the characteristic of PVT to provide a reference for future research.

Deletion of the homeodomain gene Six3 from kisspeptin neurons causes subfertility in female mice

The homeodomain transcription factor SIX3 is a known regulator of eye, nose, and forebrain development, and has recently been implicated in female reproduction. Germline heterozygosity of SIX3 is sufficient to cause subfertility, but the cell populations that mediate this role are unknown. The neuropeptide kisspeptin is a critical component of the reproductive axis and plays roles in sexual maturation, ovulation, and the maintenance of gonadotropin secretion. We used Cre-Lox technology to remove Six3 specifically from kisspeptin neurons in mice to test the hypothesis that SIX3 in kisspeptin neurons is required for reproduction. We found that loss of Six3 in kisspeptin neurons causes subfertility and estrous cycle irregularities in females, but no effect in males. Overall, we find that SIX3 expression in kisspeptin neurons is an important contributor to female fertility.

Neural Hyperactivity Is a Core Pathophysiological Change Induced by Deletion of a High Autism Risk Gene Ash1L in the Mouse Brain

ASH1L is one of the highest risk genes associated with autism spectrum disorder (ASD) and intellectual disability (ID). Our recent studies demonstrate that loss of Ash1l in the mouse brain is sufficient to induce ASD/ID-like behavioral and cognitive deficits, suggesting that disruptive ASH1L mutations are likely to have a positive correlation with ASD/ID genesis. However, the core pathophysiological changes in the Ash1l-deficient brain remain largely unknown. Here we show that loss of Ash1l in the mouse brain causes locomotor hyperactivity, high metabolic activity, and hyperactivity-related disturbed sleep and lipid metabolic changes. In addition, the mutant mice display lower thresholds for the convulsant reagent-induced epilepsy and increased neuronal activities in multiple brain regions. Thus, our current study reveals that neural hyperactivity is a core pathophysiological change in the Ash1l-deficient mouse brain, which may function as a brain-level mechanism leading to the Ash1l-deletion-induced brain functional abnormalities and autistic-like behavioral deficits.

Evidence for Bell-Shaped Dose-Response Emetic Effects of Temsirolimus and Analogs: The Broad-Spectrum Antiemetic Efficacy of a Large Dose of Temsirolimus Against Diverse Emetogens in the Least Shrew (Cryptotis parva)

Temsirolimus is a prodrug form of sirolimus (rapamycin). With its analogs (everolimus, ridaforolimus, and rapamycin), it forms a group of anticancer agents that block the activity of one of the two mammalian targets of rapamycin (mTOR) complexes, mTORC1. We investigated the emetic potential of varying doses (0, 0.5, 1, 2.5, 5, 10, 20, and 40 mg/kg, i.p.) of temsirolimus in the least shrew. Temsirolimus caused a bell-shaped and dose-dependent increase in both the mean vomit frequency and the number of shrews vomiting with maximal efficacy at 10 mg/kg (p < 0.05 and p < 0.02, respectively). Its larger doses (20 or 40 mg/kg) had no significant emetic effect. We also evaluated the emetic potential of its analogs (5, 10, and 20 mg/kg, i.p.), all of which exhibited a similar emetic profile. Our observational studies indicated that temsirolimus can reduce the shrew motor activity at 40 mg/kg, and subsequently, we examined the motor effects of its lower doses. At 10 and 20 mg/kg, it did not affect the spontaneous locomotor activity (distance moved) but attenuated the mean rearing frequency in a U-shaped manner at 10 mg/kg (p < 0.05). We then determined the broad-spectrum antiemetic potential of a 20 mg/kg (i.p.) dose of temsirolimus against diverse emetogens, including selective and nonselective agonists of 1) dopaminergic D2/3 receptors (apomorphine and quinpirole); 2) serotonergic 5-HT3 receptors [5-HT (serotonin) and 2-methyl-5-HT]; 3) cholinergic M1 receptors (pilocarpine and McN-A-343); 4) substance P neurokinin NK1 receptors (GR73632); 5) the L-type calcium (Ca2+) channel (LTCC) (FPL64176); 6) the sarcoplasmic endoplasmic reticulum Ca2+ ATPase inhibitor, thapsigargin; 7) the CB1 receptor inverse agonist/antagonist, SR141716A; and 8) the chemotherapeutic cisplatin. Temsirolimus prevented vomiting evoked by the aforementioned emetogens with varying degrees. The mechanisms underlying the pro- and antiemetic effects of temsirolimus evaluated by immunochemistry for c-fos expression demonstrated a c-fos induction in the AP and NTS, but not DMNX with the 10 mg/kg emetic dose of temsirolimus, whereas its larger antiemetic dose (20 mg/kg) had no significant effect. Our study is the first to provide preclinical evidence demonstrating the promising antiemetic potential of high doses of temsirolimus and possibly its analogs in least shrews.

Paradoxical effects of posterior intralaminar thalamic calretinin neurons on hippocampal seizure via distinct downstream circuits

Epilepsy is a circuit-level brain disorder characterized by hyperexcitatory seizures with unclear mechanisms. Here, we investigated the causal roles of calretinin (CR) neurons in the posterior intralaminar thalamic nucleus (PIL) in hippocampal seizures. Using c-fos mapping and calcium fiber photometry, we found that PIL CR neurons were activated during hippocampal seizures in a kindling model. Optogenetic activation of PIL CR neurons accelerated seizure development, whereas inhibition retarded seizure development. Further, viral-based circuit tracing verified that PIL CR neurons were long-range glutamatergic neurons, projecting toward various downstream regions. Interestingly, selective inhibition of PIL-lateral amygdala CR circuit attenuated seizure progression, whereas inhibition of PIL-zona incerta CR circuit presented an opposite effect. These results indicated that CR neurons in the PIL play separate roles in hippocampal seizures via distinct downstream circuits, which complements the pathogenic mechanisms of epilepsy and provides new insight for the precise medicine of epilepsy.

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PIL CR neurons are activated during hippocampal seizures

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Optogenetic control of PIL CR neurons bidirectionally modulates seizure development

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LA-projecting and ZI-projecting CR circuits present opposite effects in seizure modulation

Early social isolation stress increases addiction vulnerability to heroin and alters c-Fos expression in the mesocorticolimbic system

RATIONALE

Adverse psychosocial factors during early childhood or adolescence compromise neural structure and brain function, inducing susceptibility for many psychiatric disorders such as substance use disorder. Nevertheless, the mechanisms underlying early life stress-induced addiction vulnerability is still unclear, especially for opioids.

OBJECTIVES

To address this, we used a mouse heroin self-administration model to examine how chronic early social isolation (ESI) stress (5 weeks, beginning at weaning) affects the behavioral and neural responses to heroin during adulthood.

RESULTS

We found that ESI stress did not alter the acquisition for sucrose or heroin self-administration, nor change the motivation for sucrose on a progressive ratio schedule. However, ESI stress induced an upward shift of heroin dose-response curve in female mice and increased motivation and seeking for heroin in both sexes. Furthermore, we examined the neuronal activity (measured by c-Fos expression) within the key brain regions of the mesocorticolimbic system, including the prelimbic cortex (PrL), infralimbic cortex (IL), nucleus accumbens (NAc) core and shell, caudate putamen, and ventral tegmental area (VTA). We found that ESI stress dampened c-Fos expression in the PrL, IL, and VTA after 14-day forced abstinence, while augmented the neuronal responses to heroin-predictive context and cue in the IL and NAc core. Moreover, ESI stress disrupted the association between c-Fos expression and attempted infusions during heroin-seeking test in the PrL.

CONCLUSIONS

These data indicate that ESI stress leads to increased seeking and motivation for heroin, and this may be associated with distinct changes in neuronal activities in different subregions of the mesocorticolimbic system.

Identification of Brain Regions Activated by Sevoflurane and Propofol and Regional Changes in Gene Expression

General anesthetics have different efficacies and side effect incidences based on their mechanism of action. However, detailed comparative studies of anesthetics are incomplete. In this study, target brain regions and gene expression changes in these brain regions were determined for sevoflurane and propofol to understand the mechanisms that cause differences among anesthetics. Rats were anesthetized with sevoflurane or propofol for 1 hr, and brain regions with anesthesia-induced changes in neuronal activity were examined by immunohistochemistry and in situ hybridization for c-Fos. Among the identified target brain regions, gene expression analysis was performed in the habenula, the solitary nucleus and the medial vestibular nucleus from laser microdissected samples. Genes altered by sevoflurane and propofol were different and included genes involved in the incidence of postoperative nausea and vomiting and emergence agitation, such as Egr1 and Gad2. GO enrichment analysis showed that the altered genes tended to be evenly distributed in all functional category. The detailed profiles of target brain regions and induced gene expression changes of sevoflurane and propofol in this study will provide a basis for analyzing the effects of each anesthetic agent and the risk of adverse events.

Antinociceptive Actions of Botulinum Toxin A1 on Immunogenic Hypersensitivity in Temporomandibular Joint of Rats

Botulinum neurotoxin type A1 (BoNT-A) reduces the peripheral peptide and cytokine upregulation in rats with antigen-evoked persistent immunogenic hypersensitivity (PIH) of the temporomandibular joint (TMJ). Herein, we examined the effects of two preparations of BoNT-A, abobotulinumtoxinA (aboBoNT-A; Dysport) and onabotulinumtoxinA (onaBoNT-A; Botox), on spontaneous and evoked nociceptive behaviors, as well as on central neuronal and astroglial activation. The antigen-evoked PIH was induced in rats via repeated systemic and unilateral intra-articular (i.a.) injections of methylated bovine serum albumin (mBSA). Rats were subsequently injected with unilateral i.a. aboBoNT-A (14 U/kg), onaBoNT-A (7 U/kg), or the vehicle (saline). After i.a. treatments, spontaneous and mechanically evoked nocifensive behaviors were assessed before and after the low-dose i.a. formalin (0.5%) challenge. The central effects of BoNT-A were assessed by an immunohistochemical analysis of cleaved synaptosomal-associated protein 25 (cSNAP-25) presence, c-Fos, GFAP, and CGRP expression in the trigeminal nucleus caudalis (TNC). Both BoNT-A preparations similarly reduced the formalin-induced spontaneous pain-related behaviors and mechanical allodynia of the hypernociceptive rats. Likewise, their effects were associated with the central occurrence of cSNAP-25 and reduction of c-Fos and GFAP upregulation in the TNC. BoNT-A antinociceptive activity on the PIH is associated with the toxin axonal transport to trigeminal sensory areas and reduction of neuronal and glial activation in central nociceptive regions.

Intense Acute Swimming Induces Delayed-Onset Muscle Soreness Dependent on Spinal Cord Neuroinflammation

Unaccustomed exercise involving eccentric contractions, high intensity, or long duration are recognized to induce delayed-onset muscle soreness (DOMS). Myocyte damage and inflammation in affected peripheral tissues contribute to sensitize muscle nociceptors leading to muscle pain. However, despite the essential role of the spinal cord in the regulation of pain, spinal cord neuroinflammatory mechanisms in intense swimming-induced DOMS remain to be investigated. We hypothesized that spinal cord neuroinflammation contributes to DOMS. C57BL/6 mice swam for 2 h to induce DOMS, and nociceptive spinal cord mechanisms were evaluated. DOMS triggered the activation of astrocytes and microglia in the spinal cord 24 h after exercise compared to the sham group. DOMS and DOMS-induced spinal cord nuclear factor κB (NFκB) activation were reduced by intrathecal treatments with glial inhibitors (fluorocitrate, α-aminoadipate, and minocycline) and NFκB inhibitor [pyrrolidine dithiocarbamate (PDTC)]. Moreover, DOMS was also reduced by intrathecal treatments targeting C-X₃-C motif chemokine ligand 1 (CX₃CL1), tumor necrosis factor (TNF)-α, and interleukin (IL)-1β or with recombinant IL-10. In agreement, DOMS induced the mRNA and protein expressions of CX₃CR1, TNF-α, IL-1β, IL-10, c-Fos, and oxidative stress in the spinal cord. All these immune and cellular alterations triggered by DOMS were amenable by intrathecal treatments with glial and NFκB inhibitors. These results support a role for spinal cord glial cells, via NFκB, cytokines/chemokines, and oxidative stress, in DOMS. Thus, unveiling neuroinflammatory mechanisms by which unaccustomed exercise induces central sensitization and consequently DOMS.

Endogenous µ-opioid receptor activity in the lateral and capsular subdivisions of the right central nucleus of the amygdala prevents chronic postoperative pain

Tissue injury induces a long-lasting latent sensitization (LS) of spinal nociceptive signaling that is kept in remission by an opposing µ-opioid receptor (MOR) constitutive activity. To test the hypothesis that supraspinal sites become engaged, we induced hindpaw inflammation, waited 3 weeks for mechanical hypersensitivity to resolve, and then injected the opioid receptor inhibitors naltrexone, CTOP or β-funaltrexamine subcutaneously, and/or into the cerebral ventricles. Intracerebroventricular injection of each inhibitor reinstated hypersensitivity and produced somatic signs of withdrawal, indicative of LS and endogenous opioid dependence, respectively. In naïve or sham controls, systemic naloxone (3 mg/kg) produced conditioned place aversion, and systemic naltrexone (3 mg/kg) increased Fos expression in the central nucleus of the amygdala (CeA). In LS animals tested 3 weeks after plantar incision, systemic naltrexone reinstated mechanical hypersensitivity and produced an even greater increase in Fos than in sham controls, particularly in the capsular subdivision of the right CeA. One third of Fos+ profiles co-expressed protein kinase C delta (PKCδ), and 35% of PKCδ neurons co-expressed tdTomato+ in Oprm1Cre ::tdTomato transgenic mice. CeA microinjection of naltrexone (1 µg) reinstated mechanical hypersensitivity only in male mice and did not produce signs of somatic withdrawal. Intra-CeA injection of the MOR-selective inhibitor CTAP (300 ng) reinstated hypersensitivity in both male and female mice. We conclude that MORs in the capsular subdivision of the right CeA prevent the transition from acute to chronic postoperative pain.

Combined In Silico, Ex Vivo, and In Vivo Assessment of L-17, a Thiadiazine Derivative with Putative Neuro- and Cardioprotective and Antidepressant Effects

Depression associated with poor general medical condition, such as post-stroke (PSD) or post-myocardial infarction (PMID) depression, is characterized by resistance to classical antidepressants. Special treatment strategies should thus be developed for these conditions. Our study aims to investigate the mechanism of action of 2-morpholino-5-phenyl-6H-1,3,4-thiadiazine, hydrobromide (L-17), a recently designed thiadiazine derivative with putative neuro- and cardioprotective and antidepressant-like effects, using combined in silico (for prediction of the molecular binding mechanisms), ex vivo (for assessment of the neural excitability using c-Fos immunocytochemistry), and in vivo (for direct examination of the neuronal excitability) methodological approaches. We found that the predicted binding affinities of L-17 to serotonin (5-HT) transporter (SERT) and 5-HT₃ and 5-HT_1A receptors are compatible with selective 5-HT serotonin reuptake inhibitors (SSRIs) and antagonists of 5-HT₃ and 5-HT_1A receptors, respectively. L-17 robustly increased c-Fos immunoreactivity in the amygdala and decreased it in the hippocampus. L-17 dose-dependently inhibited 5-HT neurons of the dorsal raphe nucleus; this inhibition was partially reversed by the 5-HT_1A antagonist WAY100135. We suggest that L-17 is a potent 5-HT reuptake inhibitor and partial antagonist of 5-HT₃ and 5-HT_1A receptors; the effects of L-17 on amygdaloid and hippocampal excitability might be mediated via 5-HT, and putatively mediate the antidepressant-like effects of this drug. Since L-17 also possesses neuro- and cardioprotective properties, it can be beneficial in PSD and PMID. Combined in silico predictions with ex vivo neurochemical and in vivo electrophysiological assessments might be a useful strategy for early assessment of the efficacy and neural mechanism of action of novel CNS drugs.

Compulsive Eating in a Rat Model of Binge Eating Disorder Under Conditioned Fear and Exploration of Neural Mechanisms With c-fos mRNA Expression

Compulsive eating is the most obstinate feature of binge eating disorder. In this study, we observed the compulsive eating in our stress-induced binge-like eating rat model using a conflicting test, where sucrose and an aversively conditioned stimulus were presented at the same time. In this conflicting situation, the binge-like eating prone rats (BEPs), compared to the binge-like eating resistant rats (BERs), showed persistent high sucrose intake and inhibited fear response, respectively, indicating a deficit in palatability devaluation and stronger anxiolytic response to sucrose in the BEPs. We further analyzed the neuronal activation with c-fos mRNA in situ hybridization. Surprisingly, the sucrose access under conditioned fear did not inhibit the activity of amygdala; instead, it activated the central amygdala. In the BEPs, sucrose reduced the response of the paraventricular hypothalamic nucleus (PVN), while enhancing activities in the lateral hypothalamic area (LHA) to the CS. The resistance to devaluating the palatable food in the BEPs could be a result of persistent Acb response to sucrose intake and attenuated recruitment of the medial prefrontal cortex (mPFC). We interpret this finding as that the reward system of the BEPs overcame the homeostasis system and the stress-responding system.

Optogenetically controlled human functional motor endplate for testing botulinum neurotoxins

Background

The lack of physiologically relevant and predictive cell-based assays is one of the major obstacles for testing and developing botulinum neurotoxins (BoNTs) therapeutics. Human-induced pluripotent stem cells (hiPSCs)-derivatives now offer the opportunity to improve the relevance of cellular models and thus the translational value of preclinical data.

Methods

We investigated the potential of hiPSC-derived motor neurons (hMNs) optical stimulation combined with calcium imaging in cocultured muscle cells activity to investigate BoNT-sensitivity of an in vitro model of human muscle-nerve system.

Results

Functional muscle-nerve coculture system was developed using hMNs and human immortalized skeletal muscle cells. Our results demonstrated that hMNs can innervate myotubes and induce contractions and calcium transient in muscle cells, generating an in vitro human motor endplate showing dose-dependent sensitivity to BoNTs intoxication. The implementation of optogenetics combined with live calcium imaging allows to monitor the impact of BoNTs intoxication on synaptic transmission in human motor endplate model.

Conclusions

Altogether, our findings demonstrate the promise of optogenetically hiPSC-derived controlled muscle-nerve system for pharmaceutical BoNTs testing and development.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02665-3.

Spinal Cord Injury Increases Pro-inflammatory Cytokine Expression in Kidney at Acute and Sub-chronic Stages

Accumulating evidence supports that spinal cord injury (SCI) produces robust inflammatory plasticity. We previously showed that the pro-inflammatory cytokine tumor necrosis factor (TNF)α is increased in the spinal cord after SCI. SCI also induces a systemic inflammatory response that can impact peripheral organ functions. The kidney plays an important role in maintaining cardiovascular health. However, SCI-induced inflammatory response in the kidney and the subsequent effect on renal function have not been well characterized. This study investigated the impact of high and low thoracic (T) SCI on C-fos, TNFα, interleukin (IL)-1β, and IL-6 expression in the kidney at acute and sub-chronic timepoints. Adult C57BL/6 mice received a moderate contusion SCI or sham procedures at T4 or T10. Uninjured mice served as naïve controls. mRNA levels of the proinflammatory cytokines IL-1β, IL-6, TNFα, and C-fos, and TNFα and C-fos protein expression were assessed in the kidney and spinal cord 1 day and 14 days post-injury. The mRNA levels of all targets were robustly increased in the kidney and spinal cord, 1 day after both injuries. Whereas IL-6 and TNFα remained elevated in the spinal cord at 14 days after SCI, C-fos, IL-6, and TNFα levels were sustained in the kidney only after T10 SCI. TNFα protein was significantly upregulated in the kidney 1 day after both T4 and T10 SCI. Overall, these results clearly demonstrate that SCI induces robust systemic inflammation that extends to the kidney. Hence, the presence of renal inflammation can substantially impact renal pathophysiology and function after SCI.

Direct measurement of neuronal ensemble activity using photoacoustic imaging in the stimulated Fos-LacZ transgenic rat brain: A proof-of-principle study

Measuring neuroactivity underlying complex behaviors facilitates understanding the microcircuitry that supports these behaviors. We have developed a functional and molecular photoacoustic tomography (F/M-PAT) system which allows direct imaging of Fos-expressing neuronal ensembles in Fos-LacZ transgenic rats with a large field-of-view and high spatial resolution. F/M-PAT measures the beta-galactosidase catalyzed enzymatic product of exogenous chromophore X-gal within ensemble neurons. We used an ex vivo imaging method in the Wistar Fos-LacZ transgenic rat, to detect neuronal ensembles in medial prefrontal cortex (mPFC) following cocaine administration or a shock-tone paired stimulus. Robust and selective F/M-PAT signal was detected in mPFC neurons after both conditions (compare to naive controls) demonstrating successful and direct detection of Fos-expressing neuronal ensembles using this approach. The results of this study indicate that F/M-PAT can be used in conjunction with Fos-LacZ rats to monitor neuronal ensembles that underlie a range of behavioral processes, such as fear learning or addiction.

Functional Convergence of Motor and Social Processes in Lobule IV/V of the Mouse Cerebellum

Topographic organization of the cerebellum is largely segregated into the anterior and posterior lobes that represent its "motor" and "non-motor" functions, respectively. Although patients with damage to the anterior cerebellum often exhibit motor deficits, it remains unclear whether and how such an injury affects cognitive and social behaviors. To address this, we perturbed the activity of major anterior lobule IV/V in mice by either neurotoxic lesion or chemogenetic excitation of Purkinje cells in the cerebellar cortex. We found that both of the manipulations impaired motor coordination, but not general locomotion or anxiety-related behavior. The lesioned animals showed memory deficits in object recognition and social-associative recognition tests, which were confounded by a lack of exploration. Chemogenetic excitation of Purkinje cells disrupted the animals' social approach in a less-preferred context and social memory, without affecting their overall exploration and object-based memory. In a free social interaction test, the two groups exhibited less interaction with a stranger conspecific. Subsequent c-Fos imaging indicated that decreased neuronal activities in the medial prefrontal cortex, hippocampal dentate gyrus, parahippocampal cortices, and basolateral amygdala, as well as disorganized modular structures of the brain networks might underlie the reduced social interaction. These findings suggest that the anterior cerebellum plays an intricate role in processing motor, cognitive, and social functions.

Sarco/endoplasmic reticulum Ca2+ -ATPase 2b mediates oxidation-induced endoplasmic reticulum stress to regulate neuropathic pain

BACKGROUND AND PURPOSE

Neuropathic pain is a widespread health problem with limited curative treatment. Decreased sarco/endoplasmic reticulum Ca²⁺ -ATPase (SERCA) expression has been reported in dorsal root ganglion (DRG) of animals suffering from neuropathic pain. We aimed to establish the relationship between SERCA expression and the pain responses and to elucidate the underlying molecular mechanism.

EXPERIMENTAL APPROACH

Neuropathic pain was modeled using rat chronic constriction injury (CCI). Ca²⁺ imaging and current clamp patch-clamp were used to determine cytosolic Ca²⁺ levels and action potential firing, respectively. Western blots, immunofluorescence staining and RT-PCR were used to quantitatively assess protein and mRNA expression, respectively. H&E staining and coupled enzyme assay were used to evaluate the nerve injury and SERCA2b activity, respectively.

KEY RESULTS

SERCA2b is the predominant SERCA isoform in rat DRG and its expression is decreased after CCI at mRNA, protein and activity levels. Whereas inhibiting SERCA with thapsigargin causes neuronal hyperexcitation, nerve injury, ER stress, satellite glial cell activation and mechanical allodynia, activating SERCA by CDN1163 or overexpressing SERCA2b in DRG after CCI produces long-term relief of mechanical and thermal allodynia with accompanied morphological and functional restoration through alleviation of ER stress. Furthermore, the downregulation of DRG SERCA2b in CCI rats is caused by increased production of reactive oxygen species (ROS) through Sp1-dependent transcriptional inhibition.

CONCLUSION AND IMPLICATIONS

Our findings reveal a novel pathway centering around SERCA2b as the key molecule underlying the mechanism of development and maintenance of neuropathic pain, and SERCA2b activators have the potential for therapeutic treatment of neuropathic pain.

Separation from a bonded partner alters neural response to inflammatory pain in monogamous rodents

Pain experience is known to be modified by social factors, but the brain mechanisms remain unspecified. We recently established an animal model of social stress-induced hyperalgesia (SSIH) using a socially monogamous rodent, the prairie vole, in which males separated from their female partners (loss males) became anxious and displayed exacerbated inflammatory pain behaviors compared to males with partners (paired males). In the present study, to explore the neural pathways involved in SSIH, a difference in neuronal activation in pain-related brain regions, or "pain matrix", during inflammatory pain between paired and loss males was detected using Fos immunoreactivity (Fos-ir). Males were paired with a female and pair bonding was confirmed in all subjects using a partner preference test. During formalin-induced inflammatory pain, both paired and loss males showed a significant induction of Fos-ir throughout the analyzed pain matrix components compared to basal condition (without injection), and no group differences in immunoreactivity were found among the injected males in many brain regions. However, the loss males had significantly lower Fos-ir following inflammatory pain in the medial prefrontal cortex and nucleus accumbens shell than the paired males, even though base Fos-ir levels were comparable between groups. Notably, both regions with different Fos-ir are major components of the dopamine and oxytocin systems, which play critical roles in both pair bonding and pain regulation. The present results suggest the possibility that pain exacerbation by social stress emerges through alteration of signaling in social brain circuitry.

Posterodorsal Medial Amygdala Regulation of Female Social Behavior: GABA versus Glutamate Projections

Social behaviors, including reproductive behaviors, often display sexual dimorphism. Lordosis, the measure of female sexual receptivity, is one of the most apparent sexually dimorphic reproductive behaviors. Lordosis is regulated by estrogen and progesterone (P4) acting within a hypothalamic-limbic circuit, consisting of the arcuate, medial preoptic, and ventromedial nuclei of the hypothalamus. Social cues are integrated into the circuit through the amygdala. The posterodorsal part of the medial amygdala (MeApd) is involved in sexually dimorphic social and reproductive behaviors, and sends projections to hypothalamic neuroendocrine regions. GABA from the MeApd appears to facilitate social behaviors, while glutamate may play the opposite role. To test these hypotheses, adult female vesicular GABA transporter (VGAT)-Cre and vesicular glutamate transporter 2 (VGluT2)-Cre mice were transfected with halorhodopsin (eNpHR)-expressing or channelrhodopsin-expressing adeno-associated viruses (AAVs), respectively, in the MeApd. The lordosis quotient (LQ) was measured following either photoinhibition of VGAT or photoexcitation of VGluT2 neurons, and brains were assessed for c-Fos immunohistochemistry (IHC). Photoinhibition of VGAT neurons in the MeApd decreased LQ, and decreased c-Fos expression within VGAT neurons, within the MeApd as a whole, and within the ventrolateral part of the ventromedial nucleus (VMHvl). Photoexcitation of VGluT2 neurons did not affect LQ, but did increase time spent self-grooming, and increased c-Fos expression within VGluT2 neurons in the MeApd. Neither condition altered c-Fos expression in the medial preoptic nucleus (MPN) or the arcuate nucleus (ARH). These data support a role for MeApd GABA in the facilitation of lordosis. Glutamate from the MeApd does not appear to be directly involved in the lordosis circuit, but appears to direct behavior away from social interactions.SIGNIFICANCE STATEMENT Lordosis, the measure of female sexual receptivity, is a sexually dimorphic behavior regulated within a hypothalamic-limbic circuit. Social cues are integrated through the amygdala, and the posterodorsal part of the medial amygdala (MeApd) is involved in sexually dimorphic social and reproductive behaviors. Photoinhibition of GABAergic neurons in the MeApd inhibited lordosis, while photoactivation of glutamate neurons had no effect on lordosis, but increased self-grooming. These data support a role for MeApd GABA in the facilitation of social behaviors and MeApd glutamate projections in anti-social interactions.

Gene expression in the dorsolateral and ventromedial prefrontal cortices implicates immune-related gene networks in PTSD

Studies evaluating neuroimaging, genetically predicted gene expression, and pre-clinical genetic models of PTSD, have identified PTSD-related abnormalities in the prefrontal cortex (PFC) of the brain, particularly in dorsolateral and ventromedial PFC (dlPFC and vmPFC). In this study, RNA sequencing was used to examine gene expression in the dlPFC and vmPFC using tissue from the VA National PTSD Brain Bank in donors with histories of PTSD with or without depression (dlPFC n = 38, vmPFC n = 35), depression cases without PTSD (n = 32), and psychopathology-free controls (dlPFC n = 24, vmPFC n = 20). Analyses compared PTSD cases to controls. Follow-up analyses contrasted depression cases to controls. Twenty-one genes were differentially expressed in PTSD after strict multiple testing correction. PTSD-associated genes with roles in learning and memory (FOS, NR4A1), immune regulation (CFH, KPNA1) and myelination (MBP, MOBP, ERMN) were identified. PTSD-associated genes partially overlapped depression-associated genes. Co-expression network analyses identified PTSD-associated networks enriched for immune-related genes across the two brain regions. However, the immune-related genes and association patterns were distinct. The immune gene IL1B was significantly associated with PTSD in candidate-gene analysis and was an upstream regulator of PTSD-associated genes in both regions. There was evidence of replication of dlPFC associations in an independent cohort from a recent study, and a strong correlation between the dlPFC PTSD effect sizes for significant genes in the two studies (r = 0.66, p < 2.2 × 10⁻¹⁶). In conclusion, this study identified several novel PTSD-associated genes and brain region specific PTSD-associated immune-related networks.

Protein lactylation induced by neural excitation

Lactate has diverse roles in the brain at the molecular and behavioral levels under physiological and pathophysiological conditions. This study investigates whether lysine lactylation (Kla), a lactate-derived post-translational modification in macrophages, occurs in brain cells and if it does, whether Kla is induced by the stimuli that accompany changes in lactate levels. Here, we show that Kla in brain cells is regulated by neural excitation and social stress, with parallel changes in lactate levels. These stimuli increase Kla, which is associated with the expression of the neuronal activity marker c-Fos, as well as with decreased social behavior and increased anxiety-like behavior in the stress model. In addition, we identify 63 candidate lysine-lactylated proteins and find that stress preferentially increases histone H1 Kla. This study may open an avenue for the exploration of a role of neuronal activity-induced lactate mediated by protein lactylation in the brain.

Peripheral viral challenge increases c-fos level in cerebral neurons

Peripheral viral infection can substantially alter brain function. We have previously shown that intraperitoneal (i.p.) injection of a viral mimetic, polyinosinic-polycytidylic acid (PIC), engenders hyperexcitability of cerebral neurons. Because neuronal activity is invariably associated with their expression of the Cfos gene, the present study was undertaken to determine whether PIC challenge also increases neuronal c-fos protein level. Female C57BL/6 mice were i.p. injected with PIC, and neuronal c-fos was analyzed in the motor cortex by immunohistochemistry. PIC challenge instigated a robust increase in the number of c-fos-positive neurons. This increase reached approximately tenfold over control at 24 h. Also, the c-fos staining intensity of individual neurons increased. AMG-487, a specific inhibitor of the chemokine receptor CXCR3, profoundly attenuated the accumulation of neuronal c-fos, indicating the activation of CXCL10/CXCR3 axis as the trigger of the process. Together, these results show that the accumulation of c-fos is a viable readout to assess the response of cerebral neurons to peripheral PIC challenge, and to elucidate the underlying molecular mechanisms.

Neural activation in photosensitive brain regions of Atlantic salmon (Salmo salar) after light stimulation

Photoreceptive inputs to the teleost brain are perceived as image of the visual world and as photo-modulation of neuroendocrine and neuronal signals. The retina and pineal organ are major receptive organs with projections to various parts of the brain, but in the past decades deep brain photoreceptors have emerged as candidates for photoreceptive inputs, either independent or in combination with projections from light sensory organs. This study aimed to test the effects of narrow bandwidth light using light-emitting diodes technology on brain neural activity through putative opsin stimulation in Atlantic salmon. The expression of c-fos, a known marker of neural activity, was compared in situ between dark-adapted salmon parr and following light stimulation with different wavelengths. c-fos expression increased with duration of light stimulation and the strongest signal was obtained in fish exposed to light for 120 minutes. Distinct and specific brain regions were activated following dark to light stimulation, such as the habenula, suprachiasmatic nucleus, thalamus, and hypothalamus. The c-fos expression was overlapping with photoreceptors expressing melanopsin and/or vertebrate ancient opsin, suggesting a potential direct activation by light. Interestingly in the habenula, a distinct ring of vertebrate ancient opsin and melanopsin expressing cells is overlapping with c-fos expression after neural activation. Salmon exposed to different spectra had neural activation in similar brain regions. The most apparent difference was melanopsin expression in the lateral cells of the lateral tuberal nuclus in the hypothalamus, which appeared to be specifically activated by red light. Light-stimulated neuronal activity in the deep brain was limited to subpopulations of neurons, mainly in regions with neuronal modulation activity, retinal and pineal innervations and known presence of nonvisual photoreceptors. The overlapping expression patterns of c-fos and nonvisual opsins support direct light stimulation of deep brain photoreceptors and the importance of these systems in light induced brain activity.

Spaced training enhances memory and prefrontal ensemble stability in mice

It is commonly acknowledged that memory is substantially improved when learning is distributed over time, an effect called the "spacing effect". So far it has not been studied how spaced learning affects the neuronal ensembles presumably underlying memory. In the present study, we investigate whether trial spacing increases the stability or size of neuronal ensembles. Mice were trained in the "everyday memory" task, an appetitive, naturalistic, delayed matching-to-place task. Spacing trials by 60 min produced more robust memories than training with shorter or longer intervals. c-Fos labeling and chemogenetic inactivation established the involvement of the dorsomedial prefrontal cortex (dmPFC) in successful memory storage. In vivo calcium imaging of excitatory dmPFC neurons revealed that longer trial spacing increased the similarity of the population activity pattern on subsequent encoding trials and upon retrieval. Conversely, trial spacing did not affect the size of the total neuronal ensemble or the size of subpopulations dedicated to specific task-related behaviors and events. Thus, spaced learning promotes reactivation of prefrontal neuronal ensembles processing episodic-like memories.

Effects of Long-Term Exposure to L-Band High-Power Microwave on the Brain Function of Male Mice

Currently, the impact of electromagnetic field (EMF) exposure on the nervous system is an increasingly arousing public concern. The present study was designed to explore the effects of continuous long-term exposure to L-band high-power microwave (L-HPM) on brain function and related mechanisms. Forty-eight male Institute of Cancer Research (ICR) mice were exposed to L-HPM at various power densities (0.5, 1.0, and 1.5 W/m²) and the brain function was examined at different time periods after exposure. The morphology of the brain was examined by hematoxylin-eosin (HE) and deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) staining. Furthermore, cholinergic markers, oxidative stress markers, and the expression of c-fos were evaluated to identify a “potential” mechanism. The results showed that exposure to L-HPM at 1.5 W/m² can cause generalized injuries in the hippocampus (CA1 and CA3) and cerebral cortex (the first somatosensory cortex) of mice, including cell apoptosis, cholinergic dysfunction, and oxidative damage. Moreover, the deleterious effects were closely related to the power density and exposure time, indicating that long-term and high-power density exposure may be detrimental to the nervous system.

Anesthesia in mice activates discrete populations of neurons throughout the brain

The brain undergoes rapid, dramatic, and reversible transitioning between states of wakefulness and unconsciousness during natural sleep and in pathological conditions such as hypoxia, hypotension, and concussion. Transitioning can also be induced pharmacologically using general anesthetic agents. The effect is selective. Mobility, sensory perception, memory formation, and awareness are lost while numerous housekeeping functions persist. How is selective transitioning accomplished? Classically a handful of brainstem and diencephalic "arousal nuclei" have been implicated in driving brain-state transitions on the grounds that their net activity systematically varies with brain state. Here we used transgenic targeted recombination in active populations mice to label neurons active during wakefulness with one reporter and neurons active during pentobarbital-induced general anesthesia with a second, contrasting reporter. We found 'wake-on' and 'anesthesia-on' neurons in widely distributed regions-of-interest, but rarely encountered neurons labeled with both reporters. Nearly all labeled neurons were either wake-on or anesthesia-on. Thus, anesthesia-on neurons are not unique to the few nuclei discovered to date whose activity appears to increase during anesthesia. Rather neuronal populations selectively active during anesthesia are located throughout the brain where they likely play a causative role in transitioning between wakefulness and anesthesia. The widespread neuronal suppression reported in prior comparisons of the awake and anesthetized brain in animal models and noninvasive imaging in humans reflects only net differences. It misses the ubiquitous presence of neurons whose activity increases during anesthesia. The balance in recruitment of anesthesia-on versus wake-on neuronal populations throughout the brain may be a key driver of regional and global vigilance states. [Correction added on September 22, 2021, after first online publication: Due to a typesetting error, the abstract text was cut off. This has been corrected now.].

Identifying c-fos Expression as a Strategy to Investigate the Actions of General Anesthetics on the Central Nervous System

Although general anesthetics have been used in the clinic for more than 170 years, the ways in which they induce amnesia, unconsciousness, analgesia, and immobility remain elusive. Modulations of various neural nuclei and circuits are involved in the actions of general anesthetics. The expression of the immediate-early gene c-fos and its nuclear product, c-fos protein, can be induced by neuronal depolarization; therefore, c-fos staining is commonly used to identify the activated neurons during sleep and/or wakefulness, as well as in various physiological conditions in the central nervous system. Identifying c-fos expression is also a direct and convenient method to explore the effects of general anesthetics on the activity of neural nuclei and circuits. Using c-fos staining, general anesthetics have been found to interact with sleep- and wakefulness-promoting systems throughout the brain, which may explain their ability to induce unconsciousness and emergence from general anesthesia. This review summarizes the actions of general anesthetics on neural nuclei and circuits based on a c-fos expression.

Formation of a novel supraspinal-spinal connectome that relearns the same motor task after complete paralysis

Having observed that electrical spinal cord stimulation and training enabled four patients with paraplegia with motor complete paralysis to regain voluntary leg movement, the underlying mechanisms involved in forming the newly established supraspinal-spinal functional connectivity have become of great interest. van den Brand et al. (Science 336: 1182-1185, 2012) subsequently, demonstrated the recovery, in response to spinal electro-neuromodulation and locomotor training, of voluntary stepping of the lower limbs in rats that received a lesion that is assumed to eliminate all long-descending cortical axons that project to lumbosacral segments. Here, we used a similar spinal lesion in rats to eliminate long-descending axons to determine whether a novel, trained motor behavior triggered by a unique auditory cue learned before a spinal lesion, could recover after the lesion. Hindlimb stepping recovered 1 mo after the spinal injury, but only after 2 mo, the novel and unique audio-triggered behavior was recovered, meaning that not only was a novel connectivity formed but also further evidence suggested that this highly unique behavioral response was independent of the recovery of the circuitry that generated stepping. The unique features of the newly formed supraspinal-spinal connections that mediated the recovery of the trained behavior is consistent with a guidance mechanism(s) that are highly use dependent.NEW & NOTEWORTHY Electrical spinal cord stimulation has enabled patients with paraplegia to regain voluntary leg movement, and so the underlying mechanisms involved in this recovery are of great interest. Here, we demonstrate in rodents the recovery of trained motor behavior after a spinal lesion. Rodents were trained to kick their right hindlimb in response to an auditory cue. This behavior recovered 2 mo after the paralyzing spinal cord injury but only with the assistance of electrical spinal cord stimulation.

Transcriptomic Analysis of HCN-2 Cells Suggests Connection among Oxidative Stress, Senescence, and Neuron Death after SARS-CoV-2 Infection

According to the neurological symptoms of SARS-CoV-2 infection, it is known that the nervous system is influenced by the virus. We used pediatric human cerebral cortical cell line HCN-2 as a neuronal model of SARS-CoV-2 infection, and, through transcriptomic analysis, our aim was to evaluate the effect of SARS-CoV-2 in this type of cells. Transcriptome analyses revealed impairment in TXN gene, resulting in deregulation of its antioxidant functions, as well as a decrease in the DNA-repairing mechanism, as indicated by the decrease in KAT5. Western blot analyses of SOD1 and iNOS confirmed the impairment of reduction mechanisms and an increase in oxidative stress. Upregulation of CDKN2A and a decrease in CDK4 and CDK6 point to the blocking of the cell cycle that, according to the deregulation of repairing mechanism, has apoptosis as the outcome. A high level of proapoptotic gene PMAIP1 is indeed coherent with neuronal death, as also supported by increased levels of caspase 3. The upregulation of cell-cycle-blocking genes and apoptosis suggests a sufferance state of neurons after SARS-CoV-2 infection, followed by their inevitable death, which can explain the neurological symptoms reported. Further analyses are required to deeply explain the mechanisms and find potential treatments to protect neurons from oxidative stress and prevent their death.

Neurotranscriptomic changes associated with chick-directed parental care in adult non-reproductive Japanese quail

For many species, parental care critically affects offspring survival. But what drives animals to display parental behaviours towards young? In mammals, pregnancy-induced physiological transformations seem key in preparing the neural circuits that lead towards attraction (and reduced-aggression) to young. Beyond mammalian maternal behaviour, knowledge of the neural mechanisms that underlie young-directed parental care is severely lacking. We took advantage of a domesticated bird species, the Japanese quail, for which parental behaviour towards chicks can be induced in virgin non-reproductive adults through a sensitization procedure, a process that is not effective in all animals. We used the variation in parental responses to study neural transcriptomic changes associated with the sensitization procedure itself and with the outcome of the procedure (i.e., presence of parental behaviours). We found differences in gene expression in the hypothalamus and bed nucleus of the stria terminalis, but not the nucleus taeniae. Two genes identified are of particular interest. One is neurotensin, previously only demonstrated to be causally associated with maternal care in mammals. The other one is urocortin 3, causally demonstrated to affect young-directed neglect and aggression in mammals. Because our studies were conducted in animals that were reproductively quiescent, our results reflect core neural changes that may be associated with avian young-directed care independently of extensive hormonal stimulation. Our work opens new avenues of research into understanding the neural basis of parental care in non-placental species.

Gabra6100Q allele Sprague-Dawley rats have a higher sensitivity to hypnosis induced by isoflurane and ethanol than the wild type rats

BACKGROUND

The neurobiological mechanisms underlying how general anesthetics render a patient's unconsciousness (hypnosis) remains elusive. The role of the cerebellum in hypnosis induced by general anesthetics is unknown. Gabra6^100Q allele Sprague-Dawley (SD) rats have a naturally occurring single nucleotide polymorphism in the GABA_A receptor α6 subunit gene that is expressed exclusively in cerebellum granule cells.

METHODS

We examined the loss of righting reflex (LORR) induced by isoflurane, and ethanol in Gabra6^100Q rats compared with those in wild type (WT) SD rats. We also examined the change of c-Fos expression induced by isoflurane exposure in cerebellum granule cells of both mutant and WT rats.

RESULTS

Gabra6^100Q rats are more sensitive than WT rats to the LORR induced by isoflurane and ethanol. Moreover, isoflurane exposure induced a greater reduction in c-Fos expression in cerebellum granule cells of Gabra6^100Q rats than WT rats.

CONCLUSIONS

Based on these data, we speculate that cerebellum may be involved in the hypnosis induced by some general anesthetics and thus may represent a novel target of general anesthetics.

Mutual Interactions Between GnRH and Kisspeptin in GnRH- and Kiss-1-Expressing Immortalized Hypothalamic Cell Models

Kisspeptin and gonadotropin-releasing hormone (GnRH) are central regulators of the hypothalamic-pituitary-gonadal axis and control female reproductive functions. Recently established mHypoA-50 and mHypoA-55 cells are immortalized hypothalamic neuronal cell models that originated from the anteroventral periventricular nucleus (AVPV) and arcuate nucleus (ARC) regions of the mouse hypothalamus, respectively. mHypoA-50 or mHypoA-55 cells were stimulated with kisspeptin-10 (KP10) and GnRH, after which the expression of kisspeptin and GnRH was determined. Primary cultures of fetal rat brain cells were also examined. mHypoA-50 and mHypoA-55 cells expressed mRNA for Kiss-1 (which encodes kisspeptin) and GnRH as well as receptors for kisspeptin and GnRH. We found that Kiss-1 mRNA expression was significantly increased in mHypoA-50 AVPV cells by KP10 and GnRH stimulation. Kisspeptin protein expression was also increased by KP10 and GnRH stimulation in these cells. In contrast, GnRH expression was unchanged in mHypoA-50 AVPV cells by KP10 and GnRH stimulation. In mHypoA-55 ARC cells, kisspeptin expression was also significantly increased at the mRNA and protein levels by KP10 and GnRH stimulation; however, GnRH expression was also upregulated by KP10 and GnRH stimulation in these cells. KP10 and estradiol (E2) both increased Kiss-1 gene expression in mHypoA-50 AVPV cells, but combined stimulation with KP10 and E2 did not potentiate their individual effects on Kiss-1 gene expression. On the other hand, E2 did not increase Kiss-1 gene expression in mHypoA-55 ARC cells, and the KP10-induced increase of Kiss-1 gene expression was inhibited in the presence of E2 in these cells. KP10 and GnRH significantly increased c-Fos protein expression in the mHypoA-50 AVPV and mHypoA-55 ARC cell lines. In primary cultures of fetal rat neuronal cells, KP10 significantly increased Kiss-1 gene expression, whereas GnRH significantly increased GnRH gene expression. We found that kisspeptin and GnRH affected Kiss-1- and GnRH-expressing hypothalamic cells and modulated Kiss-1 and/or GnRH gene expression with a concomitant increase in c-Fos protein expression. A mutual- or self-regulatory system might be present in Kiss-1 and/or GnRH neurons in the hypothalamus.

Early and late visual deprivation induce hypersensitivity to mechanical and thermal noxious stimuli in the ZRDBA mouse

BACKGROUND

Visual deprivation leads to behavioural adaptations. Early visual deprivation has greater effects on sensory systems compared with late visual deprivation. Although this has been well studied, the impact of visual deprivation on pain sensitivity has scarcely been investigated. In humans, one study indicates that pain sensitivity is increased in early, but not late-onset blindness. In animals, one study indicates that sensitivity to noxious stimulation is increased in anophthalmic mice, but the impact of late visual deprivation on sensitivity remains unknown. The aim of this behavioural study was to examine sensitivity to noxious stimulation in mice with early and late visual deprivation. We hypothesized that visual deprivation would have different effects on sensitivity to noxious stimulation depending on its onset.

METHODS

In Experiment 1, mechanical and thermal sensitivity was examined in four ZRDBA mouse groups: sighted mice, anophthalmic mice, dark-reared sighted mice and adult sighted mice deprived of vision for one week. In Experiment 2, mechanical and thermal sensitivity was examined in adult sighted ZRDBA mice deprived of vision for two months.

RESULTS

Anophthalmic and dark-reared mice showed mechanical and thermal hypersensitivity, while the one-week visual deprivation did not alter sensitivity. The two-month deprivation also resulted in mechanical and thermal hypersensitivity.

CONCLUSIONS

These results indicate that early visual deprivation, regardless of the integrity of the visual system, induces hypersensitivity. Moreover, the present findings indicate that late visual deprivation may induce mechanical and thermal hypersensitivity, although this depends on visual deprivation duration. These results have implications for the biological significance of pain in the blind.

SIGNIFICANCE

Sensory deprivation induces behavioural adaptions. For most sensory systems, the extent of these adaptations generally depends on the stage of cerebral development. In contrast, the present results indicate that for the nociceptive system, both early and late visual deprivation have similar effects. Anophthalmic, dark-reared mice and adult mice deprived of vision for two months showed thermal and mechanical hypersensitivity. This shows a clear interaction between visual and nociceptive systems and has implications for the biological significance of pain in the blind.

Nanophase surface arrays on poly (lactic-co-glycolic acid) upregulate neural cell functions

Nerve guidance channels (NGCs) promote cell-extracellular matrix (ECM) interactions occurring within the nanoscale. However, studies focusing on the effects of nanophase topography on neural cell functions are limited, and mostly concentrated on the sub-micron level (>100 nm) surface topography. Therefore, the aim of this study was to fabricate <100 nm sized structures on poly lactic-co-glycolic acid (PLGA) films used in NGC applications to assess the effects of nanophase topography on neural cell functions. For this purpose, nanopit surface arrays were fabricated on PLGA surfaces via replica molding method. The results showed that neural cell proliferation increased up to 65% and c-fos protein expression increased up to 76% on PLGA surfaces having nanophase surface arrays compared to the control samples. It was observed that neural cells spread to a greater extend and formed more neurite extensions on the nanoarrayed surfaces compared to the control samples. These results were correlated with increased hydrophilicity and roughness of the nanophase PLGA surfaces, and point toward the promise of using nanoarrayed surfaces in NGC applications.

In Vivo Wireless Brain Stimulation via Non-invasive and Targeted Delivery of Magnetoelectric Nanoparticles

Wireless and precise stimulation of deep brain structures could have important applications to study intact brain circuits and treat neurological disorders. Herein, we report that magnetoelectric nanoparticles (MENs) can be guided to a targeted brain region to stimulate brain activity with a magnetic field. We demonstrated the nanoparticles' capability to reliably evoke fast neuronal responses in cortical slices ex vivo. After fluorescently labeled MENs were intravenously injected and delivered to a targeted brain region by applying a magnetic field gradient, a magnetic field of low intensity (350-450 Oe) applied to the mouse head reliably evoked cortical activities, as revealed by two-photon and mesoscopic imaging of calcium signals and by an increased number of c-Fos expressing cells after stimulation. Neither brain delivery of MENs nor the magnetic stimulation caused significant increases in astrocytes and microglia. Thus, MENs could enable a non-invasive and contactless deep brain stimulation without the need of genetic manipulation.

Loss of cGMP-dependent protein kinase II alters ultrasonic vocalizations in mice, a model for speech impairment in human microdeletion 4q21 syndrome

Chromosome 4q21 microdeletion leads to a human syndrome that exhibits restricted growth, facial dysmorphisms, mental retardation, and absent or delayed speech. One of the key genes in the affected region of the chromosome is PRKG2, which encodes cGMP-dependent protein kinase II (cGKII). Mice lacking cGKII exhibit restricted growth and deficits in learning and memory, as seen in the human syndrome. However, vocalization impairments in these mice have not been determined. The molecular pathway underlying vocalization impairment in humans is not fully understood. Here, we employed cGKII knockout (KO) mice as a model for the human microdeletion syndrome to test whether vocalizations are affected by loss of the PRKG2 gene. Mice emit ultrasonic vocalizations (USVs) to communicate in social situations, stress, and isolation. We thus recorded ultrasonic vocalizations as a model for human speech. We isolated postnatal day 5-7 pups from the nest to record and analyze USVs and found significant differences in vocalizations of KO mice relative to wild-type and heterozygous mutant mice. KO mice produced fewer calls that were shorter duration and higher frequency. Because neuronal activation in the arcuate nucleus in the hypothalamus is important for the production of animal USVs following isolation from the nest, we assessed neuronal activity in the arcuate nucleus of KO pups following isolation. We found significant reduction of neuronal activation in cGKII KO pups after isolation. Taken together, our studies indicate that cGKII is important for neuronal activation in the arcuate nucleus, which significantly contributes to the production of USVs in neonatal mice. We further suggest cGKII KO mice can be a valuable animal model to investigate pathophysiology of human microdeletion 4q21 syndrome.

Central and peripheral emetic loci contribute to vomiting evoked by the Akt inhibitor MK-2206 in the least shrew model of emesis

Akt (protein kinase B) signaling is frequently activated in diverse cancers. Akt inhibitors such as perifosine and MK-2206 have been evaluated as potential cancer chemotherapeutics. Although both drugs are generally well tolerated, among their most common side-effects vomiting is a major concern. Here we investigated whether these Akt inhibitors evoke emesis in the least shrew model of vomiting. Indeed, both perifosine and MK-2206 induced vomiting with maximal efficacies of 90% at 50 mg/kg (i.p.) and 100% at 10 mg/kg (i.p.), respectively. MK-2206 (10 mg/kg, i.p.) increased c-Fos immunoreactivity both centrally in the shrew brainstem dorsal vagal complex (DVC) emetic nuclei, and peripherally in the jejunum. MK-2206 also evoked phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) in both the DVC emetic nuclei and the enteric nervous system in the jejunum. The ERK1/2 inhibitor U0126 suppressed MK-2206-induced emesis dose-dependently. We then evaluated the suppressive efficacy of diverse antiemetics against MK-2206-evoked vomiting including antagonists/inhibitors of the: L-type Ca2+ channel (nifedipine at 2.5 mg/kg, subcutaneously (s.c.)); glycogen synthase kinase 3 (GSK-3) (AR-A014418 at 10 mg/kg and SB216763 at 0.25 mg/kg, i.p.); 5-hydroxytryptamine 5-HT3 receptor (palonosetron at 0.5 mg/kg, s.c.); substance P neurokinin NK1 receptor (netupitant at 10 mg/kg, i.p.) and dopamine D2/3 receptor (sulpride at 8 mg/kg, s.c.). All tested antagonists/blockers attenuated emetic parameters to varying degrees. In sum, this is the first study to demonstrate how pharmacological inhibition of Akt evokes vomiting via both central and peripheral mechanisms, a process which involves multiple emetic receptors.

Voluntary running exercise after focal cerebral ischemia ameliorates dendritic spine loss and promotes functional recovery

Cerebral infarction causes motor, sensory, and cognitive impairments. Although rehabilitation enhances recovery of activities of daily living after cerebral infarction, its mechanism remains elusive due to the lack of reproducibility and low survival rate of brain ischemic model animals. Here, to investigate the relationship between rehabilitative intervention, motor function, and pathophysiological remodeling of the tissue in the ipsilateral hemisphere after cerebral infarction, we took advantage of a highly reproducible model of cerebral infarction using C.B-17/Icr-^+/+Jcl mice. In this model, we confirmed that voluntary running exercise improved functional recovery after ischemia. Exercise did not alter the volume of infarction or survived cortex, or the number of NeuN-labeled cells in the peri-infarct cortex. In mice who did not exercise, the number of basal dendritic spines of layer 5 pyramidal cells decreased in the peri-infarct motor cortex, whereas in mice who exercised it remained at the normal level. The voluntary exercise intervention maintained basal dendritic spine density within the peri-infarct area, which may reflect an adaptive remodeling of the surviving neural circuitry that might contribute to promoting the recovery of activities of daily living.

Cerebellum-Specific Deletion of the GABAA Receptor δ Subunit Leads to Sex-Specific Disruption of Behavior

Granule cells (GCs) of the cerebellar input layer express high-affinity δ GABA_A subunit-containing GABA_A receptors (δGABA_ARs) that respond to ambient GABA levels and context-dependent neuromodulators like steroids. We find that GC-specific deletion of δGABA_A (cerebellar [cb] δ knockout [KO]) decreases tonic inhibition, makes GCs hyperexcitable, and in turn, leads to differential activation of cb output regions as well as many cortical and subcortical brain areas involved in cognition, anxiety-like behaviors, and the stress response. Cb δ KO mice display deficits in many behaviors, but motor function is normal. Strikingly, δGABA_A deletion alters maternal behavior as well as spontaneous, stress-related, and social behaviors specifically in females. Our findings establish that δGABA_ARs enable the cerebellum to control diverse behaviors not previously associated with the cerebellum in a sex-dependent manner. These insights may contribute to a better understanding of the mechanisms that underlie behavioral abnormalities in psychiatric and neurodevelopmental disorders that display a gender bias.

Rudolph et al. show that deletion of the neuromodulator and hormone-sensitive δGABA_A receptor subunit from cerebellar granule cells results in anxiety-like behaviors and female-specific deficits in social behavior and maternal care. δGABA_A deletion is associated with hyperexcitability of the cerebellar input layer and altered activation of many stress-related brain regions.

The HCN Channel Blocker ZD7288 Induces Emesis in the Least Shrew (Cryptotis parva)

Subtypes (1-4) of the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are widely expressed in the central and peripheral nervous systems, as well as the cells of smooth muscles in many organs. They mainly serve to regulate cellular excitability in these tissues. The HCN channel blocker ZD7288 has been shown to reduce apomorphine-induced conditioned taste aversion on saccharin preference in rats suggesting potential antinausea/antiemetic effects. Currently, in the least shew model of emesis we find that ZD7288 induces vomiting in a dose-dependent manner, with maximal efficacies of 100% at 1 mg/kg (i.p.) and 83.3% at 10 µg (i.c.v.). HCN channel subtype (1-4) expression was assessed using immunohistochemistry in the least shrew brainstem dorsal vagal complex (DVC) containing the emetic nuclei (area postrema (AP), nucleus tractus solitarius and dorsal motor nucleus of the vagus). Highly enriched HCN1 and HCN4 subtypes are present in the AP. A 1 mg/kg (i.p.) dose of ZD7288 strongly evoked c-Fos expression and ERK1/2 phosphorylation in the shrew brainstem DVC, but not in the in the enteric nervous system in the jejunum, suggesting a central contribution to the evoked vomiting. The ZD7288-evoked c-Fos expression exclusively occurred in tryptophan hydroxylase 2-positive serotonin neurons of the dorsal vagal complex, indicating activation of serotonin neurons may contribute to ZD7288-induced vomiting. To reveal its mechanism(s) of emetic action, we evaluated the efficacy of diverse antiemetics against ZD7288-evoked vomiting including the antagonists/inhibitors of: ERK1/2 (U0126), L-type Ca2+ channel (nifedipine); store-operated Ca2+ entry (MRS 1845); T-type Ca2+ channel (Z944), IP3R (2-APB), RyR receptor (dantrolene); the serotoninergic type 3 receptor (palonosetron); neurokinin 1 receptor (netupitant), dopamine type 2 receptor (sulpride), and the transient receptor potential vanilloid 1 receptor agonist, resiniferatoxin. All tested antiemetics except sulpride attenuated ZD7288-evoked vomiting to varying degrees. In sum, ZD7288 has emetic potential mainly via central mechanisms, a process which involves Ca2+ signaling and several emetic receptors. HCN channel blockers have been reported to have emetic potential in the clinic since they are currently used/investigated as therapeutic candidates for cancer therapy related- or unrelated-heart failure, pain, and cognitive impairment.

Postnatal Fluoxetine Treatment Alters Perineuronal Net Formation and Maintenance in the Hippocampus

Elevation of serotonin via postnatal fluoxetine (PNFlx) treatment during critical temporal windows is hypothesized to perturb the development of limbic circuits thus establishing a substratum for persistent disruption of mood-related behavior. We examined the impact of PNFlx treatment on the formation and maintenance of perineuronal nets (PNNs), extracellular matrix (ECM) structures that deposit primarily around inhibitory interneurons, and mark the closure of critical period plasticity. PNFlx treatment evoked a significant decline in PNN number, with a robust reduction in PNNs deposited around parvalbumin (PV) interneurons, within the CA1 and CA3 hippocampal subfields at postnatal day (P)21 in Sprague Dawley rat pups. While the reduction in CA1 subfield PNN number was still observed in adulthood, we observed no change in colocalization of PV-positive interneurons with PNNs in the hippocampi of adult PNFlx animals. PNFlx treatment did not alter hippocampal PV, calretinin (CalR), or Reelin-positive neuron numbers in PNFlx animals at P21 or in adulthood. We did observe a small, but significant increase in somatostatin (SST)-positive interneurons in the DG subfield of PNFlx-treated animals in adulthood. This was accompanied by altered GABA-A receptor subunit composition, increased dendritic complexity of apical dendrites of CA1 pyramidal neurons, and enhanced neuronal activation revealed by increased c-Fos-positive cell numbers within hippocampi of PNFlx-treated animals in adulthood. These results indicate that PNFlx treatment alters the formation of PNNs within the hippocampus, raising the possibility of a disruption of excitation-inhibition (E/I) balance within this key limbic brain region.