Fos-immunoreactive Neurons Research Articles

Fos-containing neurons in medulla and pons after unilateral stimulation of the afferent abdominal vagus in conscious rabbits

Vagal afferents originating in abdominal viscera initiate numerous centrally-mediated responses, including behavioural, cardiovascular and hormonal changes associated with satiety, and nausea and vomiting. The present work was undertaken to map the pontomedullary distribution of neurons expressing Fos immunoreactivity following unilateral electrical stimulation of abdominal vagal afferents in conscious unanaesthetized rabbits. After 2 h of stimulation of the anterior trunk of the abdominal vagus nerve (20 Hz, 0.5mA, 0.5 ms duration, 4.5 min on, 0.5 min off), Fos-positive neurons were found in the area postrema, the nucleus tractus solitarius, the spinal nucleus of the trigeminal nerve, the caudal and the rostral ventrolateral medulla, the locus coeruleus, the subcoeruleus and the lateral parabrachial nucleus. In all these regions, more than 70% of Fos-containing neurons occurred on the ipsilateral side. In control animals only occasional Fos-immunoreactive neurons were observed, usually very faintly labelled. Simultaneous staining for both Fos and tyrosine hydroxylase revealed Fos immunoreactivity in catecholamine neurons, including A1, A2, C1, A5, subcoeruleus and locus coeruleus (A6) groups. Our findings complement functional studies in the rabbit, identifying A1 neurons as part of the central pathway by which afferent abdominal vagal stimulation increases plasma vasopressin, and C1 neurons as part of the central pathway, whereby afferent abdominal vagal stimulation increases arterial pressure.

Electrical stimulation of the central nucleus of the amygdala induces fos-like immunoreactivity in the hypothalamus of the rat: a quantitative study

The effect of electrical stimulation of an important forebrain autonomic structure, the central nucleus of the amygdala (CNA), on c- fos expression in three hypothalamic nuclei was studied in rat with immunocytochemistry to reveal the protein (Fos) encoded by the immediate early gene (IEG). Image analysis was used to quantify the Fos immunoreactive neurons within the supraoptic (SON), paraventricular (PVN), and arcuate (AN) nuclei. Stimulation for 60 min induced a statistically significant increase of the number of Fos immunoreactive neurons in all three nuclei ipsilateral to the CNA stimulation site. Double immunocytochemical staining (Fos and vasopressin or Fos and oxytocin) was employed to evaluate the participation of different subpopulations of neurons within the SON and PVN in response to CNA stimulation. In the SON, the increased number of Fos immunoreactive nuclei following the stimulation was observed in the vasopressin and oxytocin-secreting cells within this nucleus. In the PVN, the increase in the number of Fos immunoreactive neurons was predominantly within the parvocellular compartment. These studies demonstrate that IEG expression in hypothalamic neurons can be evoked as a result of afferent stimulation from the CNA. Activation of peptide- and hormone-containing neurons within the SON, PVN and AN, through mono- or multisynaptic pathways, may play a role in hormonal and autonomic responses.

Differences in the induction of Fos protein in cat visual cortex during and after the critical period

The aim of this study was to compare the inducibility of Fos protein, in terms of magnitude and laminar distribution in visual cortex, between young (5-week-old) and adult cats. Immunohistochemical methods were used to detect Fos protein in visual and frontal cortex of young and adult cats who experienced brief (1 or 4 h) visual experience after a 1 week period of total darkness. In the 5-week-old kittens, densely stained Fos-immunoreactive neurons were found throughout all visual cortical layers as a result of 1 h of visual experience. In the adults, immunoreactive cells were concentrated in supra- and infragranular layers and only very faint labeling was found in layer IV. Immunoreactivity in young kittens persisted at much greater dilutions of primary antibody than in adults, suggesting a difference in the magnitude of induction between ages. The inductions were markedly greater in visual than in frontal cortex, where only scattered immunopositive cells were seen at the highest antibody concentration. The induction of Fos protein in visual cortex was transient and largely disappeared by 4 h at both ages. The differences between ages, both in the magnitude and laminar distribution of immunoreactivity, are inconsistent with a simple explanation of Fos inductions in terms of neural activity level. Rather, these results suggest a relation between Fos inducibility and the level of plasticity in visual cortex.

Fos induction by nerve growth factor in the adult rat brain

The distribution of Fos, the protein product of the immediate early gene c- fos, was studied with immunocytochemistry in the adult male rat brain after nerve growth factor (NGF) administration. NGF was injected in the lateral cerebral ventricle through a previously implanted cannula. The total number of Fos-immunoreactive (ir) neurons in the brain was 2–3 times higher after NGF administration than in control animals (untreated or injected with cytochrome c). With respect to control rats, in the NGF-treated cases Fos-ir cells were more numerous in the anterior olfactory nucleus, in the medial prefrontal and anterior cingulate cortices, in the basal forebrain, in the preoptic and ventromedial nuclei of the hypothalamus, as well as interior hypothalamic area, in the thalamic midline nuclei, and in some brainstem structures, such as the parabrachial nucleus. The relative quantitative increase of Fos-ir neurons varied in the different structures. In addition, Fos-ir neurons were evident after NGF administration in areas devoid of immunopositive cells in control animals. These included: frontoparietal and occipital cortical fields, the hypothalamic arcuate nucleus, and many brainstem structures, such as the dorsal nucleus of the lateral lemniscus, posterodorsal tegmental, medial and lateral vestibular, ventral cochlear, and prepositus hypoglossal nuclei. These findings demonstrate that the intracerebroventricular administration of NGF can induce c- fos expression in neurons in vivo. The distribution of Fos-ir neurons indicates that NGF can induce activation of functionally and chemically hetergeneous neuronal subsets in the brain.

Corticotropin-releasing factor activates c-fos, NGFI-B, and corticotropin-releasing factor gene expression within the paraventricular nucleus of the rat hypothalamus.

Studies examining the regulation of hypothalamic CRF biosynthesis have provided substantial information regarding the relevance of this peptide in neuroendocrine homeostasis. However, the consequences of elevated CRF levels within the mammalian central nervous system on regulation of CRF production within the paraventricular nucleus (PVN) of the hypothalamus remain unclear. The expression of the immediate early gene c-fos has been used and validated as a marker for neural systems activated by a variety of extracellular stimuli and has been especially useful when examining activation of central neuroendocrine systems such as those involved in the response to stressful stimuli. The present study investigates the effects of injecting CRF into the lateral ventricle of conscious rats, firstly on the expression of two separate immediate early genes, c-fos and NGFI-B within the hypothalamic PVN, and secondly on the expression of CRF mRNA itself, as determined by quantitative in situ hybridization. Expression of Fos protein was also examined by immunohistochemical techniques. Intracerebroventricular (icv) injection of CRF increased the gene expression of both c-fos and NGFI-B in the parvocellular division of the PVN 30 min after injection. Fos immunoreactivity increased in this same region between 30-60 min, whereas expression of the CRF gene itself increased 2-fold 60 min after injection and remained elevated 2 h after treatment. A positive hybridization signal for CRF was observed over Fos-immunoreactive neurons within the parvocellular division of the PVN. Finally, we observed that all CRF-induced changes in gene expression were abolished by pretreatment with the competitive CRF antagonist alpha-helical CRF-(9-41). The time-related changes in expression of the genes measured imply that the expression of both c-fos and NGFI-B occurs before a significant increase in the expression of CRF. The results also suggest that CRF may act in a positive manner to regulate its own biosynthesis.

Hyperthermia induces c- fos expression in the preoptic area

To identify thermosensitive areas of brain, we exposed rats to warm or cool environments and used the expression of the protein Fos as a marker of neuronal activity. In hyperthermic, heat-exposed rats, the median preoptic nucleus, and the medial and lateral preoptic areas had significantly more Fos immunoreactive neurons than control or cold-exposed animals. These observations add to the physiologic evidence that neurons of the preoptic area participate in thermoregulation and provide a means to identify the neurotransmitter systems involved.

Equivalent Levels of Mating-Induced Neural c-fos Immunoreactivity in Castrated Male Rats Given Androgen, Estrogen, or No Steroid Replacement1

The nuclear protein product (FOS) of the immediate-early gene, c-fos, was visualized immunocytochemically in the brains of male rats after they either achieved 8 intromissions with an estrous female or were left alone in a test arena. Mating induced equivalent increments in the number of FOS immunoreactive (IR) neurons present in the medial preoptic area (mPOA), the bed nucleus of the stria terminalis (BNST), and the medial amygdala in groups of males that were gonadally intact or had been castrated and treated for 7 days with either testosterone propionate, dihydrotestosterone propionate, estradiol benzoate (EB), or oil vehicle. Equivalent, low numbers of FOS-IR neurons were seen in these brain regions in additional groups of castrated males that received either EB or oil vehicle but were not paired with a female before being killed. Circulating sex steroids apparently contribute little to the mating-induced stimulation of c-fos gene expression, even in brain regions known to contain high levels of androgen and estrogen receptor.

Differential activation of c-fos in spinal neurones by distinct classes of noxious stimuli.

The laminar distribution of spinal cord neurones expressing immunoreactivity to the Fos protein was evaluated in the rat following chemical, thermal or mechanical noxious stimulation of the skin for 2 h. After stimulation by 20% or 5% formalin, Fos-immunoreactive neurones prevailed in lamina I where they accounted for 64% and 59%, respectively, of the entire population of Fos-immunoreactive spinal cells. Values in the remaining laminae were low (2-10%). Following thermal stimulation by radiant heat at 65 degrees C or 58 degrees C, Fos cells were concentrated in laminae I and IIo, amounting to 57% and 62%, respectively, in lamina I, and to 26% and 29% in lamina IIo. Values were lower than 10% in the remaining laminae. Following mechanical stimulation by pinching or needle prick, Fos-positive cells were regularly distributed throughout laminae I-V amounting to 25-26% in lamina I, and 10-20% in each of the remaining laminae. These findings suggest that the spinal neuronal groups upon by prolonged noxious stimulation differ according to the nature of the stimulus.

Mating activates androgen receptor-containing neurons in chemosensory pathways of the male Syrian hamster brain

Fos-immunoreactivity is induced during mating in the male Syrian hamster in limbic areas that relay chemosensory information and contain receptors for gonadal steroid hormones. The induction of Fos is an index of neuronal activation. After mating, c- fos expression is greatest in subnuclei of the medial amygdaloid nucleus (Me), bed nucleus of the stria terminalis (BNST), and medial preoptic area (MPOA). The present study determined if individual neurons in these activated subnuclei contain androgen receptors. We aim to understand how essential chemosensory and hormonal signals are integrated to control copulation Adult male hamster ( n = 6) were allowed to mate with a sexually receptive female for 30 min. They were perfused 1 h later with 4% paraformaldehyde and 40 μm frozen sections were processed for immunocytochemistry using antisera against Fos (Cambridge Research Biochemicals) and the androgen receptor (G.S. Prins). The brains of three non-mated males were also processed for Fos immunocytochemistry. Mating significantly increased the number of Fos-immunoreactive neurons within subnuclei of Me, BNST, and MPOA relative to non-mated males ( P < 0.05). These nuclei contained abundant androgen receptors. In the corticomedial amygdala, 20–40% of Fos-immunoreactive neurons in mated hamsters expressed androgen receptors. Although few androgen receptors are found in the anteromedial and postero-intermediate subdivisions of the BNST, these areas exhibited 26% and 47% co-localization, respectively. In posteromedial BNST, which contains large numbers of steroid receptor-containing neurons, androgen receptors were identified in 48% of Fos-immunoreactive neurons. In the MPOA, 54% of Fos-immunoreactive neurons expressed the androgen receptor throughout the rostrocaudal extent of the medial preoptic nucleus (MPN). The largest percentage of co-localized Fos neurons (70%) was found in the magnocellular subdivision of MPN. These results provide the first direct evidence that androgen receptor neurons are activated by mating behavior, suggesting that such neurons may be incorporated in the neural circuitry underlying copulation. Further, they show that mating selectively and differentially activates androgen receptor cells.

Hemorrhage induces Fos immunoreactivity in rat medullary catecholaminergic neurons

In urethane anesthetized rats one hour after lowering the systolic blood pressure to 70–75 mmHg by withdrawing 3–4 ml of blood, Fos immunoreactivity (Fos-IR), confined to the cell nucleus, was detected bilaterally in numerous cells of the nucleus of the solitary tract (NTS) and ventrolateral medulla (VLM). A few Fos-IR neurons were observed in the lateral reticular nucleus, dorsal medullary reticular nucleus, spinal trigeminal nucleus, medial inferior olive, interfasciculus hypoglossi and paramedian rostral medulla. In sham-operated animals, a much smaller number of Fos-IR neurons were scattered in the NTS, VLM and other nuclei mentioned above. Double labeling with antisera to tyrosine-hydroxylase (TH) andphenylethanolamine- N-methyltransferase (PNMT) showed that 60% of TH-positive neurons in the NTS contained Fos-IR, and 70–80% of TH-positive neurons in the caudal VLM and 50–60% of PNMT-positive neurons in the rostral VLM expressed Fos-IR. Only a few TH- or PNMT-positive neurons in the C2, C3 (paramedian rostral medulla) areas and within the medial longitudinal fasciculus were Fos-IR. About 40% of PNMT/Fos-IR neurons in the rostral VLM contained the retrograde tracer fluorogold, which was injected (< 1 μl) into the white matter dorsolateral to the intermediolateral cell column of T2-T3 segments 2 to 3 days prior to hemorrhagic experiments. Very few TH-positive neurons in the caudal VLM contained fluorogold. Finally, clusters of Fos-IR neurons, which also labeled with antisera to choline acetyltransferase, were detected in the intermediolateral cell column of the spinal cord. The results indicate that during hemorrhage aminergic neurons in the caudal and rostral VLM and in the NTS are activated insofar as c- fos expression is concerned. As a corollary, the monoaminergic neurons in the medulla constitute an essential component in the ascending as well as descending reflex pathway involved in the adjustment of cardiovascular dynamics during hemorrhage.

Long‐term induction of c‐jun mRNA and jun protein in rabbit retinal ganglion cells following axotomy or colchicine treatment

The expression of the c-jun, c-fos, and NGFI-A genes was studied in the rabbit retina after optic nerve crush (ONC) or an intravitreal injection of colchicine. By Northern blotting, the basal expression of c-fos and NGFI-A mRNAs were undetectable, whereas c-jun mRNA showed a low basal expression in sham-operated control retinas. Very few or no Jun- or Fos-immunoreactive nuclei were seen in control retinas. From 1 to 95 days after ONC a marked induction of JUN- but not FOS-immunoreactive neurons was seen in the ganglion cell layer peaking at 3 and 7 days. Jun-positive neurons also accumulated immunoreactive phosphorylated neurofilaments, indicating that they were ganglion cells. Northern blots demonstrated that retinal levels of c-jun mRNA, but not of c-fos or NGFI-A mRNAs, were increased 3 and 7 days after ONC. An intravitreal injection of colchicine also induced Jun-immunoreactivity within 24 hr in most of the neurons in the ganglion cell layer, but not in the inner nuclear and outer nuclear layers. The results indicate that axonal damage induces a specific pattern of IEG expression including a long-term induction of the c-jun gene in CNS neurons.

Stress-induced c-fos expression in the rat brain: activation mechanism of sympathetic pathway

To clarify which brain regions are activated by stress, we used expression of the proto-oncogene, c-fos, as a marker. An increased number of neurons expressing Fos-like immunoreactivity in their nuclei was observed in discrete brain regions, such as the lateral septum, midline nuclei of the thalamus, paraventricular hypothalamic nucleus, brain stem catecholaminergic, and serotonergic neurons, in response to pain or immobilization stress. Distribution patterns of Fos-like immunoreactive neurons were quite similar in animals subjected to pain or immobilization. Whether or not neurons projecting to the spinal cord to activate the sympathetic pathway express Fos-like immunoreactivity was examined by means of fluorescent double-labeling using fluoro-gold (FG) as a tracer. In the PVH, Fosimmunoreactive neurons were localized in the dorsal medial parvocellular part, although those projecting to the spinal cord were localized dorsally and ventrally. Less than 1% of Fos-positive neurons in this nucleus was colocalized with FG. Among fos-like immunoreactive catecholaminergic and serotonergic neurons in the brain stem, those in the A5 region and raphe pallidus projected to the spinal cord.

The distribution of brain-stem and spinal cord nuclei associated with different frequencies of electroacupuncture analgesia

Immunocytochemical localization of the c- fos primary gene protein, Fos, was used to identify spinal cord and brain-stem sites activated by either 4-Hz or 100-Hz electroacupuncture (EA) applied to the Zusanli acupuncture points of both hind limbs in lightly anesthetized Sprague-Dawley rats. The number and distribution of Fos-immunoreactive neurons in the brain stem and spinal cord of 4-Hz and 100-Hz EA-treated rats were compared with these in anesthesia and room control rats. Compared to non-stimulated control rats or rats in which EA was applied to a non-acupuncture point, both 4-Hz and 100-Hz EA-treated groups exhibited a significantly greater number of Fos-labeled neurons in the dorsal horn of the L2 spinal cord segment, lateral parabrachial nucleus, substantia nigra, nucleus raphe pallidus, dorsal raphe, locus coeruleus, posterior pretectal nucleus, and the lateroventral periaqueductal gray. In the 4-Hz-treated group, significant increases in Fos labeling were also observed in the cuneiform nucleus, dorsal and laterodorsal subdivisions of the periaqueductal gray, habenular nucleus, arcuate hypothalamic nucleus, and the lateroventral and lateral hypothalamic nuclei as compared to non-stimulated controls. The only brain-stem nucleus that exhibited significantly increased Fos-immunoreactive neurons in 100-Hz but not 4-Hz EA was the rostolateroventral nucleus of the medulla. These results indicate that many brain-stem regions are activated by both 4-Hz and 100-Hz EA but additional brain-stem regions are selectively activated by 4-Hz EA which may relate to the opiate sensitivity of 4-Hz EA. In sum, these data identify several distinct brain-stem nuclei that may play a role in acupuncture-mediated analgesia.

Colocalization of peptide- and tyrosine hydroxylase-like immunoreactivities with Fos-immunoreactive neurons in rat central amygdaloid nucleus after immobilization stress

The central amygdaloid nucleus (ACe) is part of the amygdaloid body, and it has been shown to participate in several stress related reactions. The ACe is densely innervated by tyrosine hydroxylase- (TH), corticotropin releasing factor- (CRF), calcitonin gene-related peptide- (CGRP), neurotensin- (NT), somatostatin- (SOM), enkephalin- (ENK), substance P- (SP), vasoactive intestinal polypeptide- (VIP) and cholecystokinin- (CCK) immunoreactive (IR) nerve terminals. In addition, the ACe contains numerous CRF-, NT-, SOM-, ENK-, and SP-IR perikarya. In previous studies it has been shown that stress stimulates the expression of the immediate early gene c- fos in the ACe. The aim of this study was to demonstrate the colocalization of the Fos-IR neurons with the peptide- and TH-IR structures using an immunocytochemical double staining technique. In intact animals the ACe contained only a few Fos-IR neurons. After immobilization stress about 100 Fos-IR neurons were seen per section. They were mainly located in the area, which was enriched by peptide- and TH-IR nerve terminals. The close contacts observed between the Fos-IR neurons and the peptide- and TH-IR nerve endings suggest that the Fos-IR neurons were innervated by these nerve terminals. Furthermore, several NT-, ENK-, SOM- and CRF-IR neurons were observed and the vast majority of these cells exhibited Fos-like immunoreactivity. These results suggest that stress enhances the synaptic activity of the ACe, which stimulates the expression of c- fos. Subsequently, Fos may regulate the expression of the NT, ENK, SOM and CRF genes and thus affect the peptidergic efferents from the ACe.

Sex difference in the effect of mating on c-fos expression in luteinizing hormone-releasing hormone neurons of the ferret forebrain.

The pulsatile secretion of LH was previously found to rise in female ferrets after receipt of an intromission, whereas in males that achieved an intromission, both LH and testosterone secretion were either reduced or unchanged. We sought to determine whether this sexually dimorphic pattern of LH secretion reflects a sex difference in the effect of mating on the activity of forebrain neurons that secrete LHRH. Immunocytochemical methods were used to localize the nuclear protein product of the immediate early gene, c-fos, as an index of increased neuronal activity after mating. Nuclear FOS immunoreactivity (FOS-IR) was monitored in LHRH-IR neurons as well as other non-LHRH forebrain neurons. In confirmation of previous reports, LHRH-IR perikarya in ferrets of both sexes were located medially along the base of the brain at rostral, medial, and caudal levels of the preoptic-hypothalamic continuum. In each of these regions a significantly higher percentage of LHRH-IR neurons was colabeled with nuclear FOS-IR in mated than in unpaired females. By contrast, an equivalent low percentage of LHRH-IR neurons was colabeled with FOS-IR in mated and unpaired male ferrets. Significantly more FOS-IR neurons (not colabeled with LHRH) were detected in the bed nucleus of the stria terminalis, the medial preoptic area, the dorsal-medial hypothalamus, and the medial amygdala (MA) of mated vs. unpaired females. By contrast, mating significantly augmented FOS-IR only in the MA of male ferrets. The results suggest that the sexually dimorphic pattern of LH secretion that occurs in ferrets after mating reflects a selective activation of LHRH neurons in the female forebrain. This sex-specific increase in the responsiveness of LHRH neurons to mating may depend on input from a limbic circuit which includes the medial amygdala, bed nucleus of the stria terminalis, and medial preoptic area.

Expression of c-fos protein in the medulla oblongata of conscious rabbits in response to baroreceptor activation

Neuronal expression of c-fos protein (Fos) in the medulla in response to baroreceptor activation was studied in conscious rabbits. Raising arterial pressure resulted in a marked increase, compared to control animals, in Fos immunoreactivity in the nucleus tractus solitarius, area postrema and ventrolateral medulla (VLM). Fos-immunoreactive neurons in the VLM extended from the level just rostral to the obex to 3 mm more caudal. Only a small proportion of these neurons showed tyrosine hydroxylase immunoreactivity. The results indicate that baroreceptor activation induces Fos expression in circumscribed medullary regions which have previously been shown to receive excitatory baroreceptor inputs.

Tonotopic Order in the Adult and Developing Auditory System of the Rat as Shown by c-fos Immunocytochemistry.

Immediate early genes such as the proto-oncogene c-fos can be expressed in neurons following synaptic excitation by sensory stimulation. C-fos immunocytochemistry has subsequently been shown to be a very sensitive marking technique for neuronal activity. Here, antibodies against the c-fos protein product Fos were used to map the tonotopic organization in the auditory system of adult and developing rats. After stimulating adult rats with pure-tone pulses, bands of Fos-immunoreactive neurons revealed the frequency representation in seven brainstem nuclei: all three subdivisions of the cochlear nucleus, the lateral superior olive, the medial nucleus of the trapezoid body, the ventral nucleus of the trapezoid body, the rostral periolivary nucleus, the dorsal nucleus of the lateral lemniscus and the inferior colliculus. With the exception of the dorsal cochlear nucleus and the inferior colliculus, tonotopicity has not been previously demonstrated in the brainstem nuclei of the rat. During development two striking results were obtained. First, beginning at postnatal day 14 (i.e. approximately 2 days after physiological hearing begins in rats), not only low but also high frequencies were able to induce strong Fos immunoreactivity, indicating that gradual recruitment of formerly unresponsive high-frequency sites does not occur in the rat. Second, a gradual age-related shift of the position of isofrequency bands was not seen in any of the nuclei, suggesting that changes in frequency - place code do not occur after 2 weeks postnatally. These results indicate that the rat's auditory brainstem nuclei achieve their adult-like tonotopic organization early on, implying a somewhat different developmental time course than is found in other mammalian species.

Fos-like immunoreactivity in the brain of homozygous diabetes insipidus Brattleboro and normal Long-Evans rats.

Water deprivation induces the production of the transcription factor Fos in neurons of the neurohypophysial system. These neurons, which are located primarily in the hypothalamic paraventricular (PVN) and supraoptic nuclei (SON), produce the antidiuretic hormone vasopressin. The present immunocytochemical study has analyzed the distribution of Fos in brain regions involved in osmoregulation and compared the extent of Fos immunoreactivity (Fos-IR) in vasopressin-deficient Brattleboro and normal Long-Evans rats under stimulated and non-stimulated conditions. Rats were osmotically challenged by means of a single intraperitoneal injection of 1.5 M/L NaCl. Since Fos may be induced by the stress of handling of animals, non-injected and isotonic saline-injected rats were used as controls. Faint nuclear Fos immunostaining was found in the organum vasculosum of the lamina terminalis (OVLT), the median preoptic nucleus (MnPO), subfornical organ (SFO), and SON of non-injected and isotonic saline-injected Brattleboro but not Long-Evans rats. Hypertonic saline injection specifically induced Fos-IR in neurons located in the SFO, OVLT, MnPO, PVN, SON, hypothalamic accessory nuclei (including the nucleus circularis), and arcuate hypothalamic nucleus (Arc) in both Long Evans and Brattleboro rats. No differences in distribution of the induced immunostaining were found between the strains. Stress of handling and (isotonic saline) injection induced Fos-IR in the lateral septal nuclei, central amygdaloid nuclei, medial amygdaloid nucleus, medial preoptic area, the bed nucleus of the stria terminalis, cingulate- and piriform cortex, the lateral hypothalamic area, ventromedial hypothalamic nucleus, and the habenular nucleus. The data are consistent with a role for Fos in the regulation of vasopressin gene expression during acute hyperosmotic stimulation. In addition, this study demonstrated that during chronic osmotic stimulation, as experienced by homozygous Brattleboro rats, Fos-IR is limited but apparently present constantly and that it increased in these animals following acute osmotic challenge. Our observations suggest that c-fos regulatory controls in homozygous Brattleboro rats are different from those in Long-Evans rats.

Mating behavior induces selective expression of Fos protein within the chemosensory pathways of the male Syrian hamster brain.

The effect of mating behavior on the expression of Fos protein was analyzed within the chemosensory pathways of the male Syrian hamster brain. Following a single mating test, the number of Fos-immunoreactive (Fos-ir) neurons increased within the amygdala, bed nucleus of the stria terminalis and medial preoptic area. The mating-induced pattern of Fos expression within these brain regions shows a strong correlation with the sites of lesions that eliminate or alter mating behavior. In addition, Fos expression was increased within the paraventricular nucleus of the hypothalamus. These results provide the first demonstration of a dynamic and selective pattern of neuronal activity within specific nuclei known to be essential for mating behavior in the male Syrian hamster.

Medullary CO2 chemoreceptor neuron identification by c-fos immunocytochemistry.

In a search for CO2 chemoreceptor neurons in the brain stem, we used immunocytochemistry to monitor the expression of neuronal c-fos, a marker of increased activity, after 1 h of exposure to CO2 in five groups of Sprague-Dawley rats (294 +/- 20 g): five air breathing controls, three breathing 10% CO2, three breathing 13% CO2, three breathing 15% CO2, and three breathing 15% CO2 and treated with morphine (10 mg/kg sc). After exposure the rats were anesthetized with pentobarbital sodium and perfused intracardially with 4% paraformaldehyde. The brain stem was removed and cryoprotected, and then 50-microns frozen sections were cut and immunostained for the fos protein. Brain stem fos-immunoreactive neurons were plotted and counted in the superficial 0.5 mm of the ventral medullary surface. Thirteen to 15% CO2 evoked fos-like immunoreactivity (FLI) in 321 +/- 146 neurons/rat. Significant CO2-induced labeling was confined within the superficial 150 microns: 67% of identified cells were less than 50 microns below the surface, greater than 90% between 1.0 and 3.0 mm from the midline, and approximately 60% in the rostral half of the medulla. Thirteen to 15% CO2 also evoked FLI in the area of the nucleus tractus solitarius but not in other medullary regions. Morphine (10 mg/kg sc) did not suppress high CO2-evoked FLI in either the ventral medullary surface or the nucleus tractus solitarius, although it eliminated excitement and hyperventilation. We suggest that respiratory CO2 chemoreceptor neurons can be identified in rats by their expression of c-fos after 1 h of hypercapnia.(ABSTRACT TRUNCATED AT 250 WORDS)