Hypovolemia induces Fos-like immunoreactivity in neurons of the rat supraoptic and paraventricular nuclei.

Immunoreactivities to Fos proteins were detected in numerous neurons in the supraoptic, paraventricular and accessory neurosecretory nuclei 1 h following withdrawal of 4-5 cc of blood from the rat femoral arteries. Few or no positive cells were observed in the same nuclei in sham-operated or control animals. It is concluded that hypovolemia induces c-fos expression in hypothalamic neurons known to be associated with blood volume/pressure regulation.     

Hemorrhage induces c-fos immunoreactivity in spinally projecting neurons of cat subretrofacial nucleus.

Neuronal expression of c-fos product in the cat rostral ventrolateral medulla was studied by immunohistochemistry. Spinally projecting neurons of the subretrofacial (SRF) nucleus were pre-labeled by retrograde transport of fluorescent latex microspheres from the lumbar cord. In 3 animals which were bled by approximately 25% blood volume from a carotid cannula, 48-62% of SRF-spinal neurons expressed c-fos immunoreactivity. In 2 control animals, the corresponding values were 2% and 4%. The data show that bulbospinal neurons of presumed vasomotor function express c-fos in response to hemorrhage.     

Intracerebroventricular carbachol induces FOS immunoreactivity in lamina terminalis neurons projecting to the supraoptic nucleus

Central application of the non-selective cholinergic receptor agonist, carbachol, induces water intake, vasopressin (VP) release and an acute increase in arterial blood pressure. Forebrain sites, particularly those located along the lamina terminalis (LT) (i.e. the subfornical organ (SFO), organum vasculosum (OV) and the median preoptic nucleus (MePO)) and in the hypothalamus, have been proposed as the major targets for producing the effects induced by intracerebroventricular (i.c.v.) carbachol injections. However, the functional and neuroanatomical relationship among carbachol-activated cells along the LT and hypothalamic areas such as the supraoptic nuclei (SON), is unclear. The present study investigated the i.c.v. carbachol-induced activity of the soma of LT projections which descend from the SFO, OV and MePO and terminate in the region of the SON. Cells along the LT were retrogradely labeled from SON-targeted injections of fluoro-gold, and FOS-immunoreactivity (FOS-ir) was used to assess activation. A significant number of cells in the SFO, OV and MePO were double-labeled for both FOS-ir and fluoro-gold. The FOS labeling in the cells of the LT-associated structures was significantly reduced by pretreatment with the i.c.v. muscarinic antagonist, atropine. Taken together, the results indicate that neurons located in structures located along the LT and projecting to the region of the SON are activated by i.c.v. carbachol and that these receptors are likely to be muscarinic.     

Cardiovascular regulation of vasopressin neurons in the supraoptic nucleus

This paper reviews the regulation of hypothalamic vasopressin and oxytocin neurosecretory cells in the neural response to plasma volume expansion. Many questions remain unanswered regarding how an increase in volume affects neurohypophysial hormone secretion, what receptors are important in mediating this response, and which neural pathways are responsible for conveying the signal from those receptors to the hypothalamus. Plasma volume expansion activates regions of the central nervous system associated with inhibition of vasopressin release, oxytocin secretion, and inhibition of sympathetic nerve activity. Cardiac receptors, not arterial baroreceptors, are primarily responsible for activation of the regions associated with regulation of vasopressin secretion and sympathetic outflow. Other stimuli that as yet are undefined account for activation of oxytocin-secreting neurons. Electrophysiology experiments have measured the inhibition of vasopressin-secreting magnocellular neurons in the supraoptic nucleus by select stimulation of cardiac receptors in the caval-atrial junction. Further experiments suggest that the perinuclear zone, a population of neurons surrounding the supraoptic nucleus, is a necessary part of the pathway by which caval-atrial stretch decreases the excitability of vasopressin neurons. The perinuclear zone is also a necessary synapse for arterial baroreceptor-mediated inhibition of vasopressin neurons. This suggests that the neural pathways that inhibit vasopressin release in response to an increase in blood pressure and an increase in blood volume may overlap at the perinuclear zone of the supraoptic nucleus. Finally, the integration of various neural pathways activated by multiple receptors to ultimately determine the activity of magnocellular neurons and vasopressin secretion is discussed.     

Acute ethanol induces c-fos immunoreactivity in GABAergic neurons of the central nucleus of the amygdala

The central nucleus of the amygdala (CNA) is a component of the brain reward pathway which is believed to represent an anatomical substrate for drugs of abuse. Previous studies have shown that acute ethanol administration induces the expression of c-fos in the CNA of rat brains. We report here, that over 70% of these c-fos immunoreactive neurons are GABAergic. This observation provides the first anatomical evidence that GABAergic neurons of the CNA are responsive to acute ethanol exposure and suggest that the GABAergic system of the CNA is a key neuronal substrate for ethanol actions on the central nervous system.     

Lateral hypothalamic region excites the activity of vasopressin neurons in the supraoptic nucleus through subfornical organ neurons

In urethane-anesthetized male rats, microinjection of angiotensin II into the lateral hypothalamic area excited the activity of about half (N = 7) of subfornical organ neurons (N = 15) antidromically identified as projecting to the hypothalamic supraoptic nucleus. Microinjection of angiotensin II also excited the activity of approximately one-quarter (N = 8) of putative vasopressin-secreting neurons (N = 28) in the hypothalamic supraoptic nucleus and these excitatory responses of putative vasopressin-secreting neurons were blocked (N = 3) or attenuated (N = 3) by pretreatment with the angiotensin II antagonist saralasin, but not by isotonic saline (N = 2), in the subfornical organ.     

Oxytocin neurons in the rat hypothalamus exhibit c-fos immunoreactivity upon osmotic stress

In order to evaluate the responses to osmotic stress of oxytocinergic neurons in vivo, we have studied oxytocin (OXY) and c-fos protein expression in the brain by means of double-immunostaining. C-fos immunoreactivity was detected in a subset of OXY neurons, as well as in other neurons non-immunoreactive for OXY, as early as 90 min after intraperitoneal injection of a hypertonic saline solution. C-fos expression was found in approx. 70% of OXY-immunoreactive neurons in the supraoptic (SON), lateral subcommisural (LSN) and paraventricular (PVN) nuclei, and not in OXY neurons in other hypothalamic areas. The expression of c-fos may be used as a means to map the circuitry by which osmotic stimulation activates OXY-containing neurons, and thus provide further insights into the functions with which OXY may be associated.     

Heat shock induces c-fos protein-like immunoreactivity in glial cells in adult rat brain

Heat shocking of anesthetized rats lead to a massive increase in c-fos protein-like immunoreactivity (FOS-IR) in glial-like cells in white and gray matter regions of the brain. Neuronal FOS-IR was not detectibly altered by heat shock. This induction of FOS-IR was present 1 h, but not 10 min or 24 h, after heat shock. These results demonstrate that c-fos protein is expressed in glial cells following thermal stress.     

Magnocellular neurosecretory neurons with ferritin-like immunoreactivity in the hypothalamic supraoptic and paraventricular nuclei of the rat.

Immunohistochemistry for rat liver ferritin (FRT) revealed an intensive labeling in some structures of the rat brain. In the supraoptic (SON) and paraventricular (PVN) hypothalamic nuclei, almost all neurosecretory neurons with vasopressin (AVP)-like immunoreactivity were immunostained with FRT. After water deprivation, a marked enlargement of cell body and an immunoreactivity to transferrin receptors were found in AVP-, FRT- and double (AVP+FRT)-labeled neurons in the SON and PVN.     

Electrophysiological evidence that noradrenergic afferents selectively facilitate the activity of supraoptic vasopressin neurons

The functional role of the ascending projection from A1 noradrenergic neurons of the caudal ventrolateral medulla to the supraoptic nucleus of the hypothalamus was investigated by examining the effects of electrical stimulation of the A1 region on the activity of supraoptic neurons deemed to be vasopressinergic or oxytocinergic on the basis of basal firing patterns and responsivity to baroreceptor activation. A1 stimulation enhanced the activity of all putative vasopressin-secreting supraoptic neurons tested. This effect appeared to be selective in that no putative oxytocin-secreting neurons were excited by A1 stimulation. Destruction of the supraoptic noradrenergic terminal plexus by local application of the neurotoxin 6-hydroxydopamine abolished the facilitatory effects of A1 stimulation but did not noticeably alter basal activity patterns, nor the influence of baroreceptor inhibitory pathways. These findings suggest a facilitatory role for noradrenergic afferents in regulating the activity of neurohypophysially-projecting vasopressin neurons of the supraoptic nucleus.     

Arginine vasopressin induces the expression of c-fos in the mouse septum and hippocampus

Arginine vasopressin is a neuropeptide that has been shown to modulate functional ethanol tolerance and memory processes. These actions of vasopressin in the CNS have been shown by us and others to be mediated by V1 receptors. Intracerebroventricular injection of vasopressin in mice resulted in a substantial increase in mRNA for the proto-oncogene c-fos in septum and hippocampus, but no increase in cerebral cortex. A V1-selective agonist also increased septal c-fos mRNA levels, while a V2-selective agonist was less effective. Similarly, the response to vasopressin was more effectively blocked by a V1- than a V2-selective antagonist. These results indicate that vasopressin acts specifically at V1 receptors in mouse septum and hippocampus to increase c-fos mRNA. The vasopressin metabolite, AVP(4-9), also increased c-fos mRNA levels in septum and hippocampus, while the response to oxytocin, which has different effects from vasopressin on memory and tolerance, was greater in hippocampus than in septum. Nerve growth factor, in contrast to the other peptides, had a more pronounced effect on c-fos mRNA levels in cerebral cortex than in the other brain areas. Increased c-fos expression has been hypothesized to play a role in neuroadaptation, and these results suggest that modulation of septal c-fos expression could be important for vasopressin effects on ethanol tolerance and/or memory.     

Rolipram induces c-fos protein-like immunoreactivity in ependymal and glial-like cells in adult rat brain

We tested the effects of the cyclic AMP-dependent phosphodiesterase inhibitor 4- (3-cyclopentyloxy-4-methoxyphenyl)-2-pyrrolidone (rolipram) on c-fos protein-like immunoreactivity (FOS-IR) in adult rat brain. Rolipram (25-100 mg/kg, i.p.) did not detectability alter basal FOS-IR in neurons but induced FOS-IR in glial-like cells scattered in white matter regions and in ependymal cells lining the lateral and third ventricles. This induction was observed at 1 and 4 h after injection but was not detectable 10 min or 24 h after rolipram injection.     

Intravenous CDP-choline activates neurons in supraoptic and paraventricular nuclei and induces hormone secretion

The aim of the present study was to assess the effects of intravenous (i.v.) cytidine-5'-diphosphate (CDP)-choline administration on the activation of oxytocin and vasopressin neurons in the supraoptic (SON) and paraventricular nuclei (PVN), using the immunohistochemical identification of c-Fos expression as a marker of neuronal activation and to correlate this with the plasma hormone levels. Rats were catheterized under sevofluorane anesthesia and experiments were conducted 24h later. Blood samples were withdrawn from arterial catheter at 2, 5, 10, 20, 40 and 60 min after CDP-choline (0.5, 1.0 and 2.0 g/kg; i.v.) or saline (1.0 ml/kg; i.v.) for the measurement of plasma oxytocin and vasopressin levels by radioimmunoassay. Animals were sacrificed 90 min after CDP-choline administration for dual immunohistochemistry which was performed on paraformaldehyde-fixed vibratome sections. Dual immunohistochemistry for c-Fos and oxytocin or vasopressin revealed that CDP-choline activates these neurons in a dose-dependent manner. Light microscopic analyses showed that, about 41%, 75% or 87% of the oxytocin neurons and about 18%, 46% or 82% of the vasopressin neurons in SON express c-Fos, thus activated, by the dosages of 0.5, 1.0 or 2.0 g/kg CDP-choline, respectively. Increases in c-Fos expression were about 29%, 62% or 81% for the oxytocin neurons and about 38%, 70% or 78% for the vasopressin neurons in PVN with the dosages of 0.5, 1.0 or 2.0 g/kg CDP-choline, respectively. When compared to the control groups (8% and 7% oxytocin or 2% and 5% vasopressin neuronal activation in SON or PVN, respectively), these increases were found to be statistically significant (p<0.05). In the PVN most of the magnocellular neurons were activated while less number of parvocellular neurons expressed c-Fos in response to CDP-choline challenge. In correlation with c-Fos data, CDP-choline increased plasma oxytocin and vasopressin levels both dose- and time-dependently. Results of the present study suggested that peripheral administration of CDP-choline is able to increase plasma oxytocin and vasopressin levels while activating the respective neurons.     

Activation of vasopressin neurons in the human supraoptic and paraventricular nucleus in senescence and senile dementia

A recent study has shown that vasopressin (AVP) cells in the human supraoptic (SON) and paraventricular (PVN) nuclei increase in size after 60 years of age, suggesting that AVP production is increased in senescence. In the present study, the same brain material was used for the determination of nucleolar size in immunocytochemically identified AVP and oxytocin (OXT) neurons as an additional parameter for peptide production.A strong correlation was found between nucleolar size and cell size, both in AVP and OXT neurons. Nucleolar size of AVP but not of OXT neurons increased significantly in senescence. Observations in brains from patients with senile dementia of the Alzheimer type (SDAT) were commensurate with their ages. These results strongly support the hypothesis that AVP neurons in the SON and PVN are activated in old age.     

Cholecystokinin induces c-fos expression in hypothalamic oxytocinergic neurons projecting to the dorsal vagal complex.

Systemic administration of cholecystokinin (CCK) decreases gastric motility and stimulates pituitary secretion of oxytocin (OT). Although peripheral OT does not affect gastric function, increasing evidence suggests that central OT secretion acting within the dorsal vagal complex (DVC) can alter gastric motility. To evaluate whether systemically administered CCK is capable of activating oxytocinergic neurons projecting to the DVC, we utilized fluorogold retrograde labeling from the DVC in combination with c-fos and OT immunocytochemical staining to quantitatively analyze paraventricular nucleus (PVN) neurons of rats following injection of CCK at a dose known to cause maximal pituitary OT secretion (100 micrograms/kg i.p.). Our results showed that 2320 +/- 63 PVN neurons were retrogradely labeled from the DVC; 146 +/- 21 (6.3%) of these contained OT, and these cells were predominantly located in the medial parvocellular subdivision of the PVN. Of all retrogradely labeled cells, 671 +/- 112 (28.9%) expressed c-fos after CCK stimulation, and 68 +/- 14 of these (10.1%) contained OT. Approximately 50% of the OT-containing neurons retrogradely labeled from the DVC stained positively for c-fos. Many magnocellular OT neurons in the PVN that were not retrogradely labeled from the DVC also expressed c-fos after CCK stimulation. These results demonstrate that parvocellular OT neurons projecting to the DVC are co-activated along with magnocellular OT neurons projecting to the pituitary following administration of a large dose of CCK, and lend support to a possible functional role for OT as a central neurotransmitter that modulates vagal efferent traffic to the gastrointestinal tract.     

Localization of agmatine in vasopressin and oxytocin neurons of the rat hypothalamic paraventricular and supraoptic nuclei

Agmatine (decarboxylated l-arginine), an endogenous ligand of imidazoline and alpha(2) adrenoreceptors, is particularly enriched in the rat hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei. The present study utilized light and electron microscopic immunocytochemical methods to determine the distribution and extent of colocalization of agmatine relative to subpopulations of vasopressin- (VP) and oxytocin- (OT) producing neurons in PVN and SON nuclei. By light microscopy, agmatine-immunoreactive perikarya were found in both the magnocellular and the parvocellular neuronal subdivisions of PVN and SON. Confocal and electron microscopy revealed that agmatine-immunoreactivity (I) within neuronal perikarya was associated with the nuclear membrane as well as mitochondria, Golgi complexes, endoplasmic reticula, and plasmalemma. Additionally, agmatine-I was identified in both axons and axonal terminals, which were enriched in large dense-core vesicles. Dual and triple immunocytochemical labeling experiments also demonstrated that agmatine coexists with VP or OT in most PVN and SON magnocellular neurons. Combinations of iontophoretic injections of Fluorogold into the dorsomedullary complex with immunocytochemical labeling revealed that many retrogradely labeled neurons in the parvocellular region of the PVN contained agmatine-I and either VP or OT. These findings provide evidence that agmatine may function as a modulator of both hypothalamically mediated neuroendocrine and autonomic responses.     

Axotomy induces nerve growth factor receptor immunoreactivity in spinal motor neurons

Expression of the nerve growth factor receptor (NGF-R) mRNA in adult motor neurons is increased by axonal injury. The present study was designed to examine, by immunocytochemistry, the onset, course, and specificity of NGF-R up-regulation following distal or proximal crush of the sciatic nerve. Lesions at both levels induced the appearance of NGF-R-like immunoreactivity in motor neurons beginning on day two postaxotomy. NGF-R-like immunoreactivity was present exclusively in axotomized neurons, as verified by the near complete colocalization of immunoreactive NGF-R with a fluorescent retrograde tracer injected at the crush site. NGF-R expression was closely linked with disconnection of cells from the target; one week after muscle reinnervation, NGF-R immunoreactivity was no longer detectable in animals with distal injuries. These results extend the previous findings of axotomy-induced expression of NGF-R mRNA to the level of the receptor. Furthermore, our observations are consistent with the hypothesis that target-derived factors participate in the regulation of NGF-R gene expression in adult motor neurons.     

Global ischemia induces NMDA receptor-mediated c-fos expression in neurons resistant to injury in gerbil hippocampus.

The induction of c-fos protein-like immunoreactivity (CFPLI) was examined in the hippocampus of gerbils at several time points after transient global ischemia. c-Fos protein induction was largely confined to the dentate gyrus, CA3 and CA4 regions from 2 to 8 h after transient bilateral carotid occlusion. Little CFPLI was seen in the CA1 subfield, which is disproportionately sensitive to injury after global ischemia. c-Fos induction was completely blocked by pretreatment with MK-801 (3 mg/kg). Our results show that c-fos expression after global ischemia is NMDA receptor mediated, and mainly found in hippocampal neurons resistant to ischemic injury.     

Histamine-caused itch induces Fos-like immunoreactivity in dorsal horn neurons: effect of morphine pretreatment.

It is well known that cutaneous pain causes c-fos gene expression in the dorsal horn neurons. The present study examined whether or not an itching sensation had the same effect on these neurons. In order to produce an itching sensation, cotton balls soaked in histamine solutions of different concentrations were applied to the lower limbs of rats and then the treated area was scratched with the tip of a pair of forceps. After 2 h, the number of neurons showing Fos-like immunoreactivity was significantly increased in a dose-dependent manner in the ipsilateral dorsal horn when compared to saline-treated and scratched controls. When scratching with the forceps was omitted, the number of these neurons was reduced to one-third, but was still significantly higher than in controls treated only with saline. Expression of Fos-like immunoreactivity in these animals was markedly reduced by morphine pretreatment (10 mg/kg, i.p.), suggesting that the transmission of both itch and pain is blocked by morphine.