Differential regulation of c-Fos and FosB in the rat brain after amygdala kindling

Integrated analysis of circRNA- related ceRNA network targeting neuroinflammation in medial temporal lobe epilepsy

BACKGROUND

medial temporal lobe epilepsy (mTLE) is among the most common types of temporal lobe epilepsy (TLE) ，it is generally resistant to drug treatment, which significantly impacts the quality of life and treatment. Research on novel therapeutic approaches for mTLE has become a current focus. Our study aims to construct and analyze a competing endogenous RNA (ceRNA) network that targets neuroinflammation using publicly available data, which may offer a novel therapeutic approach for mTLE.

METHODS

we utilized the R package to analyze GSE186334 downloaded from Gene Expression Omnibus database, subsequently constructing and identifying hub network within the ceRNA network using public databases. Lastly, we validated the expressions and interactions of some nodes within the hub ceRNA network in Sombati cell model.

RESULTS

our transcriptome analysis identified 649 differentially expressed (DE) mRNAs (273 up-regulated, 376 down-regulated) and 36 DE circRNAs (11 up-regulated, 25 down-regulated) among mTLE patients. A total of 23 candidate DE mRNAs associated with neuroinflammation were screened, and two ceRNA networks were constructed. A hub network was further screened which included 3 mRNAs, 22 miRNAs, and 11 circRNAs. Finally, we confirmed the hsa-miR-149-5p is crucial in the regulatory effect of hsa_circ_0005145 on IL - 1α in the hub network.

CONCLUSIONS

In summary, our study identified a hub ceRNA network and validated a potential circRNA-miRNA-mRNA axis targeting neuroinflammation. The results of our research may serve as a potential therapeutic target for mTLE.

A companion to the preclinical common data elements and case report forms for neuropathology studies in epilepsy research. A report of the TASK3 WG2 Neuropathology Working Group of the ILAE/AES Joint Translational Task Force

The International League Against Epilepsy/American Epilepsy Society (ILAE/AES) Joint Translational Task Force initiated the TASK3 working group to create common data elements (CDEs) for various aspects of preclinical epilepsy research studies, which could help improve the standardization of experimental designs. This article addresses neuropathological changes associated with seizures and epilepsy in rodent models of epilepsy. We discuss CDEs for histopathological parameters for neurodegeneration, changes in astrocyte morphology and function, mechanisms of inflammation, and changes in the blood-brain barrier and myelin/oligodendrocytes resulting from recurrent seizures in rats and mice. We provide detailed CDE tables and case report forms (CRFs), and with this companion manuscript, we discuss the rationale and methodological aspects of individual neuropathological examinations. The CDEs, CRFs, and companion paper are available to all researchers, and their use will benefit the harmonization and comparability of translational preclinical epilepsy research. The ultimate hope is to facilitate the development of rational therapy concepts for treating epilepsies, seizures, and comorbidities and the development of biomarkers assessing the pathological state of the disease.

Protective Effects of PACAP in a Rat Model of Diabetic Neuropathy

Pituitary adenylate cyclase-activating peptide (PACAP) is a neuropeptide with a widespread occurrence and diverse effects. PACAP has well-documented neuro- and cytoprotective effects, proven in numerous studies. Among others, PACAP is protective in models of diabetes-associated diseases, such as diabetic nephropathy and retinopathy. As the neuropeptide has strong neurotrophic and neuroprotective actions, we aimed at investigating the effects of PACAP in a rat model of streptozotocin-induced diabetic neuropathy, another common complication of diabetes. Rats were treated with PACAP1-38 every second day for 8 weeks starting simultaneously with the streptozotocin injection. Nerve fiber morphology was examined with electron microscopy, chronic neuronal activation in pain processing centers was studied with FosB immunohistochemistry, and functionality was assessed by determining the mechanical nociceptive threshold. PACAP treatment did not alter body weight or blood glucose levels during the 8-week observation period. However, PACAP attenuated the mechanical hyperalgesia, compared to vehicle-treated diabetic animals, and it markedly reduced the morphological signs characteristic for neuropathy: axon–myelin separation, mitochondrial fission, unmyelinated fiber atrophy, and basement membrane thickening of endoneurial vessels. Furthermore, PACAP attenuated the increase in FosB immunoreactivity in the dorsal spinal horn and periaqueductal grey matter. Our results show that PACAP is a promising therapeutic agent in diabetes-associated complications, including diabetic neuropathy.

Differential modulation of the anterior cingulate and insular cortices on anxiogenic-like responses induced by empathy for pain

Mice cohabiting with a conspecific in chronic pain display anxiogenesis in the elevated plus-maze (EPM). Given that the anterior cingulate (ACC) and insular (InC) cortices play a role in the modulation of anxiety, pain, and emotional contagion, we investigated (a) the FosB activation in both brain areas and (b) the effects of intra-ACC or -InC injection of cobalt chloride (CoCl₂, a synaptic blocker), on the anxiety of mice cohabiting with a cagemate suffering pain. Twenty-one days after birth, male Swiss mice were housed in pairs for 14 days to establish familiarity. On the 14th day, mice were divided into two groups: cagemate sciatic nerve constriction (CNC; i.e., one animal of each pair was subjected to sciatic nerve constriction), and cagemate sham (CS; i.e., a similar procedure but without suffering nerve constriction). After that, both groups were housed again with the same pairs for the other 14 days. On the 28th day, mice had their brains removed for the immunoassays analyses (Exp. 1). For experiments 2 and 3, on the 23rd day, the cagemates received guide cannula implantation bilaterally in the ACC or InC and, on the 28th day, they received local injections of saline or CoCl₂, and then were exposed to the EPM. Results showed that cohabitation with a conspecific with chronic pain decreases and increases neuronal activation (FosB) within the ACC and InC, respectively. Intra-ACC or InC injection of CoCl₂ reversed the anxiogenic effect in those animals that cohabited with a conspecific in chronic pain. ACC and InC seem to modulate anxiety induced by emotional contagion in animals cohabitating with a conspecific suffering pain.

c-Fos and FosB/ΔFosB colocalizations in selected forebrain structures after olanzapine, amisulpride, aripiprazole, and quetiapine single administration in rats preconditioned by two different mild stressors sequences

OBJECTIVE

Olanzapine (OLA), amisulpride (AMI), aripiprazole (ARI), and quetiapine (QUE) belong to antipsychotics, which administration represents still most reliable way for the treatment of schizophrenic and bipolar disorders. The intention of the present study was to explore whether the acute administration of a particular antipsychotic, indicated by the presence of c-Fos, will: a) stimulate neurons already activated by a long lasting homogeneous or heterogeneous stress preconditioning, indicated by the FosB/ΔFosB (ΔFosB) expression, or b) have a stimulatory effect only on a not activated, so called silent neurons. The pattern of ΔFosB and c-Fos spatial relationship was investigated in three forebrain structures, including the septal ventrolateral nucleus (seVL), the striatal dorsolateral area (stDL), and the shell of the nucleus accumbens (shell).

METHODS

The rats were divided into 10 groups and exposed to two types of stressors. Half of them was exposed to a sequence of homogeneous stressor - handling (HDL) and the other half to a heterogeneous stressor (CMS) daily for 20 days. CMS consisted of five types of stressors: crowding, air-puff, wet bedding, predator stress, and forced swimming applied in an unexpected order. On the 21st day of the experiment, the rats were free of the stress exposure and on the 22nd day, both groups of animals receive a single intraperitoneal injection of vehicle (4% DMSO in saline, 0.1 ml/100 g) or OLA (5 mg/kg), AMI (20 mg/kg), ARI (10 mg/kg), and QUE (15 mg/kg). 90 min after the drugs administration the animals were transcardially perfused, brains removed, cut into 30 µm thick coronal sections, and double stained: first with ΔFosB antibody linked with Alexa488 fluorescent dye and second with c-Fos antibody linked to Alexa596 one. Quantitative evaluation of ΔFosB and c-Fos colocalizations was performed on fluorescence photomicrographs transformed into a final picture containing only yellow, green, and red colored circles.

RESULTS

The data of this investigation demonstrate that ΔFosB and c-Fos colocalizations occurred in each of the three areas investigated, i.e. seVL, stDL, and shell ones, in both HDL as well as CMS preconditioned rats. The levels of ΔFosB and c-Fos colocalizations varied in the individual forebrain areas studied. From the total 22 areas measured, level of c-Fos colocalization prevailed over ΔFosB in 18 ones. However, neither c-Fos nor ΔFosB reached 100% level of colocalization in any of the forebrain areas investigated.

CONCLUSION

The present findings indicate that ΔFosB and c-Fos colocalizations occurred in each of the three areas investigated, i.e. seVL, stDL, and shell, in both HDL and CMS preconditioned rats, whereas the parallel occurrence of free c-Fos as well as c-Fos colocalized with ΔFosB might speak out for a possible involvement of the c-Fos activated by antipsychotics applied in dual, i.e. short- and long-lasting, functions.

Single prolonged stress alters neural activation in the periacqueductal gray and midline thalamic nuclei during emotional learning and memory

Clinical and preclinical studies that have examined the neurobiology of persistent fear memory in posttraumatic stress disorder (PTSD) have focused on the medial prefrontal cortex, hippocampus, and amygdala. Sensory systems, the periaqueductal gray (PAG), and midline thalamic nuclei have been implicated in fear and extinction memory, but whether neural activity in these substrates is sensitive to traumatic stress (at baseline or during emotional learning and memory) remains unexplored. To address this, we used the single prolonged stress (SPS) model of traumatic stress. SPS and control rats were either subjected to fear conditioning (CS-fear) or presented with CSs alone (CS-only) during fear conditioning. All rats were then subjected to extinction training and testing. A subset of rats were euthanized after each behavioral stage and c-Fos and c-Jun used to measure neural activation in all substrates. SPS lowered c-Jun levels in the dorsomedial and lateral PAG at baseline, but the elevated c-Jun expression in the PAG during emotional learning and memory. SPS also altered c-Fos expression during fear and extinction learning/memory in midline thalamic nuclei. These findings suggest changes in neural function in the PAG and midline thalamic nuclei could contribute to persistent fear memory induced by traumatic stress. Interestingly, SPS effects were also observed in animals that never learned fear or extinction (i.e., CS-only). This raises the possibility that traumatic stress could have broader effects on the psychological function that are dependent on the PAG and midline thalamic nuclei.

RNA-seq analysis of blood of valproic acid-responsive and non-responsive pediatric patients with epilepsy

Epilepsy is the most common chronic neurological disorder, affecting ~70 million individuals worldwide. However, approximately one-third of the patients are refractory to epilepsy medication. Of note, 100% of patients with genetic epilepsy who are resistant to the traditional drug, valproic acid (VPA), are also refractory to the other anti-epileptic drugs. The aim of the present study was to compare the transcriptomes in VPA responders and non-responders, to explore the mechanism of action of VPA and identify possible biomarkers to predict VPA resistance. Thus, RNA-seq was employed for transcriptomic analysis, differentially expressed genes (DEGs) were analyzed using Cuffdiff software and the DAVID database was used to infer the functions of the DEGs. A protein-protein interaction network was obtained using STRING and visualized with Cytoscape. A total of 389 DEGs between VPA-responsive and non-responsive pediatric patients were identified. Of these genes, 227 were upregulated and 162 were downregulated. The upregulated DEGs were largely associated with cytokines, chemokines and chemokine receptor-binding factors, whereas the downregulated DEGs were associated with cation channels, iron ion binding proteins, and immunoglobulin E receptors. In the pathway analysis, the toll-like receptor signaling pathway, pathways in cancer, and cytokine-cytokine receptor interaction were mostly enriched by the DEGs. Furthermore, three modules were identified by protein-protein interaction analysis, and the potential hub genes, chemokine (C-C motif) ligand 3 and 4, chemokine (C-X-C motif) ligand 9, tumor necrosis factor-α and interleukin-1β, which are known to be closely associated with epilepsy, were identified. These specific chemokines may participate in processes associated with VPA resistance and may be potential biomarkers for monitoring the efficacy of VPA.

C-Fos mapping and EEG characteristics of multiple mice brain regions in pentylenetetrazol-induced seizure mice model

Purpose: To confirm different local brain activities characterized in pentylenetetrazol (PTZ)-induced seizure model. Methods: we induced seizure response by a single dose of PTZ injection (45 mg/kg, i.p.). Local activity was recorded in different brain regions by EEG in time and c-Fos staining at different time points (0.5 h, 1 h, 2 h, 4 h) after PTZ treatment. Results: EEG recordings showed distinctive features of activation in different brain areas. With the aggravation of behavioral manifestations of seizures, the frequency and amplitude of the discharges on EEG were increasing gradually. The epileptic response on EEG immediately ended after reaching the maximum stage of seizures, followed by a short period of suppression. The labeling of c-Fos was enhanced in the medial prefrontal cortex, the piriform cortex, the amygdala, hippocampal CA1, CA3 and dentate gyrus, but inapparent in the striatum. The most potent changes in c-Fos were observed in cortex, amygdala nuclei, and dentate gyrus. EEG and c-Fos immunolabeling in neuronal activation showed discrepancies in the striatum. For each brain region, the maximum c-Fos labeling was observed at 2 h after injection and diminished at 4 h. The level of c-Fos immunoreactivity was even lower than the control group, which was accompanied by increased labeling of parvalbumin neurons (PVNs). Conclusions: These findings validated PTZ-induced seizure as a seizure model with a specific spatial-temporal profile. Neuronal activity was enhanced and then subsequently inhibited during seizure evolution. Abbreviations: AEDs: anti-epileptic drugs; AF: Alexa Fluor; CA1: Cornu Ammonis area 1; CA3: Cornu Ammonis area 3; DAB, 3: 3P-diaminobenzidine; DAPI: 4',6-diamidino-2-phenylindole; DG: dentate gyrus; EEG: electroencephalogram; GABA: gamma-aminobutyric acid; IEG: immediate early gene; mPFC: medial prefrontal cortex; NAc: nucleus accumbens; PB: phosphate buffer; PBS: phosphate buffered saline; PBST: phosphate buffered saline with Tween; PFA, paraformaldehyde; PTZ: pentylenetetrazol; PVN: parvalbumin neuron; ROI: regions of interest; SE: status epilepticus.

Using c-Jun to identify fear extinction learning-specific patterns of neural activity that are affected by single prolonged stress

Neural circuits via which stress leads to disruptions in fear extinction is often explored in animal stress models. Using the single prolonged stress (SPS) model of post traumatic stress disorder and the immediate early gene (IEG) c-Fos as a measure of neural activity, we previously identified patterns of neural activity through which SPS disrupts extinction retention. However, none of these stress effects were specific to fear or extinction learning and memory. C-Jun is another IEG that is sometimes regulated in a different manner to c-Fos and could be used to identify emotional learning/memory specific patterns of neural activity that are sensitive to SPS. Animals were either fear conditioned (CS-fear) or presented with CSs only (CS-only) then subjected to extinction training and testing. C-Jun was then assayed within neural substrates critical for extinction memory. Inhibited c-Jun levels in the hippocampus (Hipp) and enhanced functional connectivity between the ventromedial prefrontal cortex (vmPFC) and basolateral amygdala (BLA) during extinction training was disrupted by SPS in the CS-fear group only. As a result, these effects were specific to emotional learning/memory. SPS also disrupted inhibited Hipp c-Jun levels, enhanced BLA c-Jun levels, and altered functional connectivity among the vmPFC, BLA, and Hipp during extinction testing in SPS rats in the CS-fear and CS-only groups. As a result, these effects were not specific to emotional learning/memory. Our findings suggest that SPS disrupts neural activity specific to extinction memory, but may also disrupt the retention of fear extinction by mechanisms that do not involve emotional learning/memory.

Repeated 6-Hz Corneal Stimulation Progressively Increases FosB/ΔFosB Levels in the Lateral Amygdala and Induces Seizure Generalization to the Hippocampus

Exposure to repetitive seizures is known to promote convulsions which depend on specific patterns of network activity. We aimed at evaluating the changes in seizure phenotype and neuronal network activation caused by a modified 6-Hz corneal stimulation model of psychomotor seizures. Mice received up to 4 sessions of 6-Hz corneal stimulation with fixed current amplitude of 32 mA and inter-stimulation interval of 72 h. Video-electroencephalography showed that evoked seizures were characterized by a motor component and a non-motor component. Seizures always appeared in frontal cortex, but only at the fourth stimulation they involved the hippocampus, suggesting the establishment of an epileptogenic process. Duration of seizure non-motor component progressively decreased after the second session, whereas convulsive seizures remained unchanged. In addition, a more severe seizure phenotype, consisting of tonic-clonic generalized convulsions, was predominant after the second session. Immunohistochemistry and double immunofluorescence experiments revealed a significant increase in neuronal activity occurring in the lateral amygdala after the fourth session, most likely due to activity of principal cells. These findings indicate a predominant role of amygdala in promoting progressively more severe convulsions as well as the late recruitment of the hippocampus in the seizure spread. We propose that the repeated 6-Hz corneal stimulation model may be used to investigate some mechanisms of epileptogenesis and to test putative antiepileptogenic drugs.

Altered Expression of Intersectin1-L in Patients with Refractory Epilepsy and in Experimental Epileptic Rats

Epilepsy is a common neurological disorder. Because its underlying mechanisms remain incompletely understood, current treatments are not adequate for all epilepsy patients, and some patients progress to refractory epilepsy. Under physiological conditions, excitatory and inhibitory neurons function in a dynamic balance. Epilepsy develops when this balance is disrupted. Intersectin1-L is a major scaffold protein in the central nervous system that contains multiple functional domains, and it is the long form of intersectin1. Recent studies have shown that intersectin1-L plays an important role in the process of neurotransmitter release. In this study, we investigated the expression pattern and distribution of intersectin1-L in patients with refractory epilepsy, in a rat model of pilocarpine-induced epilepsy, and in a rat model of amygdala-kindled epilepsy by immunohistochemistry, immunofluorescence, and Western blotting. The purpose of this study was to explore the relationship between epilepsy and intersectin1-L. The results showed that the intersectin1-L protein was primarily expressed in neurons in brain tissue. Its expression was remarkably increased in patients with refractory epilepsy and in epilepsy model rats. These results suggest that the abnormal expression of the intersectin1-L protein in epileptic brain tissue may play an important role in epilepsy, especially refractory epilepsy.

c-FOS expression after hippocampal deep brain stimulation in normal rats

OBJECTIVES

We studied the effects of Hip-deep brain stimulation (DBS) on the expression of the inducible transcription factor c-FOS in the brain of normal rats.

MATERIALS AND METHODS

Ten Wistar rats were anesthetized, and nine were implanted with epidural and hippocampal electrodes for brain activity recording; one animal was used as sham. Bipolar stimulating electrodes were implanted in the left hippocampus. Three animals were used as control (implanted but not stimulated), one as sham (not implanted, not stimulated), and six as the study group. Stimulation was carried out using square wave pulses with 0.8V, 300 μsec, and 130 Hz (∼25μC/cm2) on the left hippocampus through the implanted bipolar hippocampal lead. Three animals were submitted to a one-hour and three to a six-hour stimulation session. Immunohistochemistry was employed to visualize c-FOS distribution in the rat's brain. The presence of seizures and electrocorticographic findings also were observed.

RESULTS

In animals submitted to both one-hour or six-hour unilateral hippocampal stimulation sessions, there was a significant bilateral overexpression of c-FOS in the hippocampus proper, dentate gyrus, and hylus. In the CA1 and CA3 regions, although activation was bilateral, c-FOS hyperexpression prevailed at the stimulated side over time; this was not true for the hilar and dentate gyrus regions where a more symmetric activation occurred over time. A significant c-FOS activation occurred after one hour of Hip-DBS in the ipsilateral amygdala; there was no contralateral amygdala activation, and by six hours, no amygdala activation was noted. No c-FOS activation was noted in other brain areas.

DISCUSSION

Our data showed that unilateral Hip-DBS was able to cause widespread and persistent bilateral activation of the normal rat limbic system, although in some, nuclei activation prevailed over the stimulated side. Cortical activation outside the limbic system was not noted. Our data represent a first approach to study the mechanistic paradigm involved in Hip-DBS.

Knockdown of tyrosine hydroxylase in the nucleus of the solitary tract reduces elevated blood pressure during chronic intermittent hypoxia

Noradrenergic A2 neurons in nucleus tractus solitarius (NTS) respond to stressors such as hypoxia. We hypothesize that tyrosine hydroxylase (TH) knockdown in NTS reduces cardiovascular responses to chronic intermittent hypoxia (CIH), a model of the arterial hypoxemia observed during sleep apnea in humans. Adult male Sprague-Dawley rats were implanted with radiotelemetry transmitters and adeno-associated viral constructs with green fluorescent protein (GFP) reporter having either short hairpin RNA (shRNA) for TH or scrambled virus (scRNA) were injected into caudal NTS. Virus-injected rats were exposed to 7 days of CIH (alternating periods of 10% O2 and of 21% O2 from 8 AM to 4 PM; from 4 PM to 8 AM rats were exposed to 21% O2). CIH increased mean arterial pressure (MAP) and heart rate (HR) during the day in both the scRNA (n = 14, P < 0.001 MAP and HR) and shRNA (n = 13, P < 0.001 MAP and HR) groups. During the night, MAP and HR remained elevated in the scRNA rats (P < 0.001 MAP and HR) but not in the shRNA group. TH immunoreactivity and protein were reduced in the shRNA group. FosB/ΔFosB immunoreactivity was decreased in paraventricular nucleus (PVN) of shRNA group (P < 0.001). However, the shRNA group did not show any change in the FosB/ΔFosB immunoreactivity in the rostral ventrolateral medulla. Exposure to CIH increased MAP which persisted beyond the period of exposure to CIH. Knockdown of TH in the NTS reduced this CIH-induced persistent increase in MAP and reduced the transcriptional activation of PVN. This indicates that NTS A2 neurons play a role in the cardiovascular responses to CIH.

Resilience to audiogenic seizures is associated with p-ERK1/2 dephosphorylation in the subiculum of Fmr1 knockout mice

Young, but not adult, fragile X mental retardation gene (Fmr1) knockout (KO) mice display audiogenic seizures (AGS) that can be prevented by inhibiting extracellular signal-regulated kinases 1/2 (ERK1/2) phosphorylation. In order to identify the cerebral regions involved in these phenomena, we characterized the response to AGS in Fmr1 KO mice and wild type (WT) controls at postnatal day (P) 45 and P90. To characterize the diverse response to AGS in various cerebral regions, we evaluated the activity markers FosB/ΔFosB and phosphorylated ERK1/2 (p-ERK1/2). Wild running (100% of tested mice) followed by clonic/tonic seizures (30%) were observed in P45 Fmr1 KO mice, but not in WT mice. In P90 Fmr1 KO mice, wild running was only present in 25% of tested animals. Basal FosB/ΔFosB immunoreactivity was higher (P < 0.01 vs. WT) in the CA1 and subiculum of P45 Fmr1 KO mice. Following the AGS test, FosB/ΔFosB expression consistently increased in most of the analyzed regions in both groups at P45, but not at P90. Interestingly, FosB/ΔFosB immunoreactivity was significantly higher in P45 Fmr1 KO mice in the medial geniculate body (P < 0.05 vs. WT) and CA3 (P < 0.01). Neurons presenting with immunopositivity to p-ERK1/2 were more abundant in the subiculum of Fmr1 KO mice in control condition (P < 0.05 vs. WT, in both age groups). In this region, p-ERK1/2-immunopositive cells significantly decreased (–75%, P < 0.01) in P90 Fmr1 KO mice exposed to the AGS test, but no changes were found in P45 mice or in other brain regions. In both age groups of WT mice, p-ERK1/2-immunopositive cells increased in the subiculum after exposure to the acoustic test. Our findings illustrate that FosB/ΔFosB markers are overexpressed in the medial geniculate body and CA3 in Fmr1 KO mice experiencing AGS, and that p-ERK1/2 is markedly decreased in the subiculum of Fmr1 KO mice resistant to AGS induction. These findings suggest that resilience to AGS is associated with dephosphorylation of p-ERK1/2 in the subiculum of mature Fmr1 KO mice.

Recurrent hypoglycemia alters hypothalamic expression of the regulatory proteins FosB and synaptophysin

A limiting factor to the clinical management of diabetes is iatrogenic hypoglycemia. With multiple hypoglycemic episodes, the collective neuroendocrine response that restores euglycemia is impaired. In our animal model of recurrent hypoglycemia (RH), neuroendocrine deficits are accompanied by a decrease in medial hypothalamic activation. Here we tested the hypothesis that the medial hypothalamus may exhibit unique changes in the expression of regulatory proteins in response to RH. We report that expression of the immediate early gene FosB is increased in medial hypothalamic nuclei, anterior hypothalamus, and posterior paraventricular nucleus of the thalamus (THPVN) of the thalamus following RH. We identified the hypothalamic PVN, a key autonomic output site, among the regions expressing FosB. To identify the subtype(s) of neuronal populations that express FosB, we screened candidate neuropeptides of the PVN for coexpression using dual fluorescence immunohistochemistry. Among the neuropeptides analyzed [including oxytocin, vasopressin, thyrotropin-releasing hormone, and corticotropin-releasing factor (CRF)], FosB was only identified in CRF-positive neurons. Inhibitory gamma-aminobutyric acid-positive processes appear to impinge on these FosB-expressing neurons. Finally, we observed a significant decrease in the presynaptic marker synaptophysin within the PVN of RH-treated vs. saline-treated rats, suggesting that rapid alterations of synaptic morphology may occur in association with RH. Collectively, these data suggest that RH stress triggers cellular changes that support synaptic plasticity, in specific neuroanatomical sites, which may contribute to the development of hypoglycemia-associated autonomic failure.

Late expression of FosB transcription factor in 4-aminopyridine-induced seizures in the rat cerebral cortex

In this study, the immunolocalization of FosB transcription factor was investigated in acute and chronic experimental models of seizures induced by 4-aminopyridine. Wistar rats were injected intraperitoneally daily with 5mg/kg 4-aminopyridine for 1, 4, 8 and 12 days and sacrificed 24h after the last injection. Corresponding control groups received the solvent of 4-aminopyridine. Immunohistochemistry revealed an increase in FosB immunolabelling in the frontal cortex in 4-aminopyridine-treated animals compared to controls, both in acute and chronic time course groups. The dentate gyrus displayed elevated FosB immunopositivity only after repeatedly applied convulsant (4-aminopyridine), i.e. following 4, 8 and 12 days of treatment, but no significant immunolocalization was observed in the hippocampus proper. The neuronal localization of FosB after 12 days of 4-aminopyridine-induced convulsions was analysed by means of FosB-parvalbumin double immunolabelling. The increased number of double-labelled cells was significant in the frontal cortex, hilum of the dentate fascia and region CA1 of the hippocampus. We conclude that the studied neocortical and allocortical areas showed a different pattern of FosB immunolocalization, which suggests a relative deficiency of transcriptional regulation in the Ammon's horn and may be responsible for distinct response to seizure-induced cellular insult.