Fos-like expression and nuclear size in osmotically stimulated supraoptic nucleus neurons

Anatomical Markers of Activity in Hypothalamic Neurons

The scientific community has searched for years for ways of examining neuronal tissue to track neural activity with reliable anatomical markers for stimulated neuronal activity. Existing studies that focused on hypothalamic systems offer a few options but do not always compare approaches or validate them for dependence on cell firing, leaving the reader uncertain of the benefits and limitations of each method. Thus, in this article, potential markers will be presented and, where possible, placed into perspective in terms of when and how these methods pertain to hypothalamic function. An example of each approach is included. In reviewing the approaches, one is guided through how neurons work, the consequences of their stimulation, and then the potential markers that could be applied to hypothalamic systems are discussed. Approaches will use features of neuronal glucose utilization, water/oxygen movement, changes in neuron-glial interactions, receptor translocation, cytoskeletal changes, stimulus-synthesis coupling that includes expression of the heteronuclear or mature mRNA for transmitters or the enzymes that make them, and changes in transcription factors (immediate early gene products, precursor buildup, use of promoter-driven surrogate proteins, and induced expression of added transmitters. This article includes discussion of methodological limitations and the power of combining approaches to understand neuronal function. © 2020 American Physiological Society. Compr Physiol 10:549-575, 2020.

Proteasome inhibition induces DNA damage and reorganizes nuclear architecture and protein synthesis machinery in sensory ganglion neurons

Bortezomib is a reversible proteasome inhibitor used as an anticancer drug. However, its clinical use is limited since it causes peripheral neurotoxicity. We have used Sprague-Dawley rats as an animal model to investigate the cellular mechanisms affected by both short-term and chronic bortezomib treatments in sensory ganglia neurons. Proteasome inhibition induces dose-dependent alterations in the architecture, positioning, shape and polarity of the neuronal nucleus. It also produces DNA damage without affecting neuronal survival, and severe disruption of the protein synthesis machinery at the central cytoplasm accompanied by decreased expression of the brain-derived neurotrophic factor. As a compensatory or adaptive survival response against proteotoxic stress caused by bortezomib treatment, sensory neurons preserve basal levels of transcriptional activity, up-regulate the expression of proteasome subunit genes, and generate a new cytoplasmic perinuclear domain for protein synthesis. We propose that proteasome activity is crucial for controlling nuclear architecture, DNA repair and the organization of the protein synthesis machinery in sensory neurons. These neurons are primary targets of bortezomib neurotoxicity, for which reason their dysfunction may contribute to the pathogenesis of the bortezomib-induced peripheral neuropathy in treated patients.

Nuclear calcium signalling in the regulation of brain function

Synaptic activity initiates biochemical processes that have various outcomes, including the formation of memories, increases in neuronal survival and the development of chronic pain and addiction. Virtually all activity-induced, long-lasting adaptations of brain functions require a dialogue between synapses and the nucleus that results in changes in gene expression. Calcium signals that are induced by synaptic activity and propagate into the nucleus are a major route for synapse-to-nucleus communication. Recent findings indicate that diverse forms of neuroadaptation require calcium transients in the nucleus to switch on the necessary genomic programme. Deficits in nuclear calcium signalling as a result of a reduction in synaptic activity or increased extrasynaptic NMDA receptor signalling may underlie the aetiologies of various diseases, including neurodegeneration and cognitive dysfunction.

Acute hyperosmotic stimulus-induced Fos expression in neurons depends on activation of astrocytes in the supraoptic nucleus of rats

Acute hyperosmolarity induced a time-dependent expression of Fos protein in both neurons and astrocytes of the rat supraoptic nucleus, with peak Fos expression occurring at 45 min in astrocytes and at 90 min in neurons after hypertonic stimulation in vivo. To determine whether the two cell types were activated separately or in an integrated manner, animals were pretreated with fluorocitrate, a glial metabolic blocker or carbenoxolone, a gap junction blocker followed by an acute hypertonic stimulation similar to that of the controls. Antibodies against glial fibrillary acidic protein, connexin 43, vasopressin, and oxytocin were used in serial sections to identify the cellular elements of the supraoptic nucleus. It was found that interruption of astrocyte metabolism with fluorocitrate significantly reduced Fos protein expression in both astrocytes and neurons, whereas blockage of gap junctions with carbenoxolone clearly reduced Fos protein expression in neurons, but not in astrocytes. These results indicate that both neurons and astrocytes in the rat supraoptic nucleus are involved in regulating osmolarity. Astrocytes are activated first, whereas connexin 43 functional hemichannels in SON astrocytes are required for the subsequent activation of the neurons.

Synaptic activity induces dramatic changes in the geometry of the cell nucleus: interplay between nuclear structure, histone H3 phosphorylation, and nuclear calcium signaling

Synaptic activity initiates many adaptive responses in neurons. Here we report a novel form of structural plasticity in dissociated hippocampal cultures and slice preparations. Using a recently developed algorithm for three-dimensional image reconstruction and quantitative measurements of cell organelles, we found that many nuclei from hippocampal neurons are highly infolded and form unequally sized nuclear compartments. Nuclear infoldings are dynamic structures, which can radically transform the geometry of the nucleus in response to neuronal activity. Action potential bursting causing synaptic NMDA receptor activation dramatically increases the number of infolded nuclei via a process that requires the ERK-MAP kinase pathway and new protein synthesis. In contrast, death-signaling pathways triggered by extrasynaptic NMDA receptors cause a rapid loss of nuclear infoldings. Compared with near-spherical nuclei, infolded nuclei have a larger surface and increased nuclear pore complex immunoreactivity. Nuclear calcium signals evoked by cytosolic calcium transients are larger in small nuclear compartments than in the large compartments of the same nucleus; moreover, small compartments are more efficient in temporally resolving calcium signals induced by trains of action potentials in the theta frequency range (5 Hz). Synaptic activity-induced phosphorylation of histone H3 on serine 10 was more robust in neurons with infolded nuclei compared with neurons with near-spherical nuclei, suggesting a functional link between nuclear geometry and transcriptional regulation. The translation of synaptic activity-induced signaling events into changes in nuclear geometry facilitates the relay of calcium signals to the nucleus, may lead to the formation of nuclear signaling microdomains, and could enhance signal-regulated transcription.

Time course of c-fos, vasopressin and oxytocin mRNA expression in the hypothalamus following long-term dehydration

1. This study presents a time course analysis of the messenger RNA (mRNA) levels of c-fos, vasopressin (VP), and oxytocin (OT) in the paraventricular (PVN) and supraoptic nucleus (SON), following acute and chronic dehydration by water deprivation. 2. Male Wistar rats were separated into five groups: nondehydrated (control group) and dehydrated for 6, 24, 48 and 72 h. Following water deprivation, animals were decapitated, their blood was collected for hematocrit, osmolality, and plasma sodium measurements, and brains were removed for dissection of both PVN and SON. 3. As expected, the hematocrit, osmolality, plasma sodium, and weight loss were increased after water deprivation. In SON, a significant increase in both VP and OT mRNA expression was observed 6 h after dehydration reaching a peak at 24 h and returning to basal levels of expression at 72 h. In the PVN, an increase in both VP and OTmRNA expression occurred 24 h after dehydration. At 72 h the VP and OT mRNA expression levels had decreased but they were still at higher levels than those detected in control animals. 4. These results suggest that SON is the first nucleus to respond to the dehydration stimulus. Additionally, we also observed an increase in c-fos mRNA expression in both PVN and SON 6 h after water deprivation, which progressively decreased 24, 48, and 72 h after the onset of water deprivation. Therefore, it is possible that c-fos may be involved in the modulation of VP and OT genes, regulating the mRNA expression levels on a temporally distinct basis within the PVN and SON.

Involvement of interferon-alpha in the regulation of apoptosis of cells of the hypothalamo-hypophyseal-adrenocortical system of aged mice in oxidative stress

The aim of this study was to identify the involvement of interferon-alpha (IA) in controlling apoptosis of cells of the hypothalamo-hypophyseal-adrenocortical system (HHACS) in young and aged mice in conditions of hyperoxia. Oxidative stress led to increases in the numbers of cells synthesizing the proapoptotic protein c-fos in the paraventricular nucleus in mice of both age groups. However, the protective actions of IA in stress were more marked at the earlier stage of apoptosis in young mice. Thus, the level of involvement of IA in controlling programmed cell death of hypothalamic cells depends on the age of the animals. In the fascicular zone of the adrenals in young mice, the number of dying cells was significantly greater after administration of IA, but remained at the control level in conditions of hyperoxia alone and in combination with IA. The proportion of apoptotic cells in the adrenals of aged mice was no different from that in young mice and did not change in response to any of the treatments used.

Dynamical study of tyrosine hydroxylase expression and its correlation with vasopressin turnover in the magnocellular neurons of the supraoptico-posthypophysial system under long-term salt loading of adult rats

Using immunocytochemistry, in situ hybridization and image analysis, we attempted to compare the dynamical expression of tyrosine hydroxylase (TH) and vasopressin (VP) mRNAs and proteins in the magnocellular neurons of the supraoptic nucleus in rats drinking 2% NaCl for 1, 2 and 3 weeks. Three stages in the reaction of VPergic neurons have been distinguished. The initial stage (first week) showed a synchronous activation of TH and VP mRNAs and protein expression as well as an increased number of TH-immunoreactive neurons. The next stage (second week) was characterized by a further increase in the number of TH-immunoreactive neurons. The number of VPergic neurons also increased significantly. Although the TH and VP mRNAs levels fell during the second week of osmotic stimulation, the TH content increased significantly, and the VP content remained at the same level. During the last stage (third week), TH-immunoreactive neurons increased in number and were as numerous as VP-immunoreactive neurons in intact rats. These data suggest that, finally, all the VPergic neurons begin to synthesize TH. The concentrations of VP and TH mRNAs did not change during the third week of osmotic stimulation, while the VP and TH contents increased. Thus, our study shows that there is a correlation between TH expression and VP expression and suggests similar mechanisms for the regulation of VP and TH gene expression and synthesis during long-term osmotic stimulation.

Structural and functional compartmentalization of the cell nucleus in supraoptic neurons

It is well-established that the neuronal cell nucleus is organized in discrete compartments involved in transcription and RNA processing. The main nuclear compartments in neurons include the chromosome territories, the nucleolus, nuclear speckles of splicing factors, Cajal bodies, and nuclear rodlets. The supraoptic nucleus (SON) neurons provide a powerful model in vivo to study the organization of these nuclear compartments in response to variations of cellular activity. The upregulation of transcription in SON neurons under chronic hyperosmolar conditions is associated with 1) nuclear and nucleolar enlargement, 2) dispersion of chromatin, 3) reduction in the size of nuclear speckles, 4) increase in the number of Cajal bodies implicated in the maturation of splicing small nuclear ribonucleoproteins, and 5) proliferation of the fibrillar centers of the nucleolus, the sites of nucleolar transcription of ribosomal genes. These changes revert after the cessation of the activation by rehydration of animals. Under conditions of neuronal stress induced by hypertonic saline injection, SON neurons exhibit an early response of downregulation of transcription. This is accompanied by chromatin condensation, redistribution of splicing factors, reduction in the number of Cajal bodies, and microsegregation of the fibrillar and granular components of the nucleolus and disruption of its fibrillar centers, all of which are associated with a transitory expression of c-Fos. These changes progressively revert and at 24 hours after the stress induction a rebound upregulation of transcription is observed. These findings illustrate the transcription-dependent organization and behavior of nuclear compartments in the neuronal model of magnocellular neurosecretory cells of the hypothalamus.

Space flight affects magnocellular supraoptic neurons of young prepuberal rats: transient and permanent effects

Effects of microgravity on postural control and volume of extracellular fluids as well as stress associated with space flight may affect the function of hypothalamic neurosecretory neurons. Since environmental modifications in young animals may result in permanent alterations in neuroendocrine function, the present study was designed to determine the effect of a space flight on oxytocinergic and vasopressinergic magnocellular hypothalamic neurons of prepuberal rats. Fifteen-day-old Sprague-Dawley female rats were flown aboard the Space Shuttle Columbia (STS-90, Neurolab mission, experiment 150) for 16 days. Age-matched litters remained on the ground in cages similar to those of the flight animals. Six animals from each group were killed on the day of landing and eight animals from each group were maintained under standard vivarium conditions and killed 18 weeks after landing. Several signs of enhanced transcriptional and biosynthetic activity were observed in magnocellular supraoptic neurons of flight animals on the day of landing compared to control animals. These include increased c-Fos expression, larger nucleoli and cytoplasm, and higher volume occupied in the neuronal perikaryon by mitochondriae, endoplasmic reticulum, Golgi apparatus, lysosomes and cytoplasmic inclusions known as nematosomes. In contrast, the volume occupied by neurosecretory vesicles in the supraoptic neuronal perikarya was significantly decreased in flight rats. This decrease was associated with a significant decrease in oxytocin and vasopressin immunoreactive levels, suggestive of an increased hormonal release. Vasopressin levels, cytoplasmic volume and c-Fos expression returned to control levels by 18 weeks after landing. These reversible effects were probably associated to osmotic stimuli resulting from modifications in the volume and distribution of extracellular fluids and plasma during flight and landing. However, oxytocin levels were still reduced at 18 weeks after landing in flight animals compared to controls. This indicates that space flight during prepuberal age may induce irreversible modifications in the regulation of oxytocinergic neurons, which in turn may result in permanent endocrine and behavioral impairments.

Time course of Fos and Fras expression in the hypothalamic supraoptic neurons during chronic osmotic stimulation

The Fos family comprises Fos and several subtypes of Fos-related proteins (Fras) such as FosB, Fra-1, Fra-2, DeltaFosB, and chronic Fras. Changes in the expression of Fos family proteins with time are not well elucidated, particularly during chronic stimulation. In the present experiments, we investigated quantitatively the time course changes in Fos, FosB and Fras immunoreactivity in the magnocellular neurons of the supraoptic nucleus (SON) during acute and chronic osmotic stimulation. A small number of Fos- and FosB-positive neurons were observed in the SON of control rats, while many Fras-positive neurons were seen in control animals. Significant increases in the numbers of Fos-, FosB-, and Fras-positive neurons were observed 2 h after acute osmotic stimulation by intraperitoneal (i.p.) injection of 3% NaCl solution. Although the number of Fos-positive neurons returned to the control level 4 h after i.p. injection, a significant number of FosB- and Fras-positive neurons were still observed 8 h after i.p. injection. During chronic osmotic stimulation by giving 2% NaCl solution for 2 and 5 days, a large number of Fos-positive neurons were observed, but the cessation of chronic osmotic stimulation by normal water drinking immediately decreased the number of Fos-positive neurons to the control level within 2 h. The number of FosB-positive neurons was increased with period of chronic osmotic stimulation, and a significant number were observed 2-8 h after the cessation of the stimulation. The number of Fras-positive neurons was also significantly higher during chronic osmotic stimulation, and this number was significantly high 2-8 h after the cessation of the stimulation. RT-PCR analysis demonstrated the persistent expression of c-fos mRNA in the SON during chronic osmotic stimulation. These results suggest that c-fos mRNA and Fos protein are constitutively elevated during chronic osmotic stimulation and the time course changes in Fos are different from those seen in FosB and Fras.

Inducible and constitutive transcription factors in the mammalian nervous system: control of gene expression by Jun, Fos and Krox, and CREB/ATF proteins

This article reviews findings up to the end of 1997 about the inducible transcription factors (ITFs) c-Jun, JunB, JunD, c-Fos, FosB, Fra-1, Fra-2, Krox-20 (Egr-2) and Krox-24 (NGFI-A, Egr-1, Zif268); and the constitutive transcription factors (CTFs) CREB, CREM, ATF-2 and SRF as they pertain to gene expression in the mammalian nervous system. In the first part we consider basic facts about the expression and activity of these transcription factors: the organization of the encoding genes and their promoters, the second messenger cascades converging on their regulatory promoter sites, the control of their transcription, the binding to dimeric partners and to specific DNA sequences, their trans-activation potential, and their posttranslational modifications. In the second part we describe the expression and possible roles of these transcription factors in neural tissue: in the quiescent brain, during pre- and postnatal development, following sensory stimulation, nerve transection (axotomy), neurodegeneration and apoptosis, hypoxia-ischemia, generalized and limbic seizures, long-term potentiation and learning, drug dependence and withdrawal, and following stimulation by neurotransmitters, hormones and neurotrophins. We also describe their expression and possible roles in glial cells. Finally, we discuss the relevance of their expression for nervous system functioning under normal and patho-physiological conditions.

Water-deprived white-footed mice express c-fos on a day/night cycle graded according to the duration of deprivation

Mammals respond to electrolyte and water imbalance by a variety of neural and endocrine mechanisms that regulate water and salt intake and loss. We used the expression of c-fos and Fos-related antigens to indicate neuronal activation in hypothalamic neurons of members of an outbred laboratory population of white-footed mice (Peromyscus leucopus) deprived of water for biologically reasonable periods of time (6-18 h). We examined Fos-like immunoreactivity (Fos-LIR) in the supraoptic nucleus (SON) and paraventricular nucleus (PVN). During the dark period, when these animals are normally active, 6 h of water deprivation produced near-maximal increases in the number of cells positive for Fos-LIR in the SON and PVN. In contrast, during the light period, when these mice are normally inactive and do not have access to water, 6 h of water deprivation only slightly affected Fos-LIR. During the day, it required as much as 12 h of water deprivation to produce increases in Fos-LIR cells approaching those achieved at night. Plasma osmolarity was directly related to the number of Fos-LIR cells. In addition, mice lost weight more rapidly at night than during the day when water-deprived, and also recovered that lost weight more rapidly when access to water was returned. Our results show (1) that biologically reasonable levels of water restriction (and resulting changes in blood osmolarity) induce changes in Fos-LIR in this wild mouse species, and (2) that these mice have a daily cycle of sensitivity to water deprivation that is demonstrated by both behavioral, psychological and immunohistological assessment of reactions to water deprivation.

Comparison of the expression of c-fos, nur77 and egr1 mRNAs in rat hypothalamic magnocellular neurons and their putative afferent projection neurons: cell- and stimulus-specific induction

Hypothalamic magnocellular neurons and their afferent inputs provide a model system in which to study the regulation of inducible transcription factors in the brain in vivo. Osmotic stimulation of rats produced by graded infusions of saline at different tonicities was found to lead to the induction of c-fos, nur77 and egr1 mRNAs in magnocellular neurons, as well as in putative afferent neurons, including those in structures of the forebrain (subfornical organ, median preoptic nucleus and organum vasculosum of the lamina terminalis). The results presented suggest that stronger levels of osmotic stimulation recruit additional afferents from the forebrain and brainstem that can act on magnocellular neurons via alternative receptors. A single systemic injection of the peptide cholecystokinin produced robust induction of c-fos and nur77 mRNAs in afferent neurons of the brainstem nucleus tractus solitarii and in magnocellular neurons. Despite the fact that these two neuronal populations are clearly electrically active, egr1 was not induced by this stimulus, providing examples of cell- and stimulus-specificity of its expression. This study re-emphasizes that the induction of transcription factors is largely dependent on the nature of the afferent input and does not correlate necessarily to the electrical activity of the neuron.

Daily cycle of fos expression within hypothalamic POMC neurons of the male rat

The activity of hypothalamic pro-opiomelanocortin (POMC) neurons is known to display a circadian cycle. We hypothesized that the existence of a c-Fos responsive element (AP-1 site) within the POMC gene sequence might reflect the ability of POMC neurons to express c-fos proto-oncogene during circadian increase of their neuronal activity. To this aim, adult male rats previously kept under a controlled 12 h light/12 h dark schedule were sacrificed every 4 h throughout the 24 h cycle and their brains processed for Fos and/or POMC immunocytochemistry. Here we show that, specifically during the dark period of the cycle, the mediobasal hypothalamic area spontaneously exhibits a strong Fos immunoreactivity, whereas very low Fos labelling was detected during the light period. As postulated, the simultaneous visualisation of both Fos and POMC antigens allowed us to show that this nocturnal induction of Fos occurs almost exclusively at the nuclear level of POMC-producing neurons. These results not only highlight the mechanisms underlying the physiological functioning of the hypothalamic POMC system, but also demonstrate the feasibility of using c-fos expression as a useful tool to assess the pharmacological effect of drugs on the activity of POMC neurons as is the case for many other neuronal systems. Such drugs might be relevant in the treatment of psychosis since an alteration of POMC-related peptide transmission has been reported in the brains of both schizophrenic and depressive patients.

Cyclophosphamide cystitis as a model of visceral pain in rats: minor effects at mesodiencephalic levels as revealed by the expression of c-fos, with a note on Krox-24

The evoked expression of the immediate-early gene-encoded proteins c-Fos and Krox-24 was used to study activation of mesodiencephalic structures as a function of the development of cyclophosphamide (CP) cystitis in behaving rats. This article is the third of a series and completes previously published data obtained at both spinal and hindbrain levels. CP-injected animals received a single dose of 100 mg/kg i.p. under transient volatile anesthesia and survived for 1-4 h in order to cover the entire postinjection period during which the disease develops. Survival times longer than 4 h were not used owing to ethical considerations. Results from CP-injected groups are compared with those from either noninjected controls or saline-injected animals having survived for the same times as CP-injected ones. Quantitative results come from c-fos expression. At mesodiencephalic levels a high and widespread basal c-fos expression was observed in control animals; maximum staining was observed at the midthalamic level. Four groups of nuclei were identified with regard to the density of staining. The first group included nuclei showing clustered, intensely labeled cells; these areas were restricted in extent and related to the maintenance of circadian rythms (intergeniculate leaf, suprachiasmatic nucleus, dorsal parts of either paraventricular thalamic nuclei or central gray), sleep-arousal cycle (supramamillary nucleus), or changes in arterial pressure (laterodorsal tegmental nucleus). The second group included nuclei showing scattered, moderately labeled cells; these areas were widespread at all rostrocaudal levels and related to either autonomic/neuroendocrine regulations (central gray, lateral habenula, hypothalamus) or motor behavior, orienting reflex and oculomotor coordination (unspecific subdivisions of both colliculi and their adjoining mesencephalic regions, zona incerta dorsal). The third group included nuclei with evenly distributed, faintly labeled cells; these areas, which, with few exceptions, covered almost the entire diencephalon, mainly concerned nuclei of multisensory convergence having functions in either discriminative tasks (laterodorsal and lateroposterior thalamic nuclei) or emotional responses (intralaminar and midline thalamic nuclei). The fourth group included nuclei free of labeling; these were areas that received the bulk of unimodal sensory/motor inputs (central inferior colliculus, pretectal optic nuclei, ventral medial geniculate nucleus, ventral anterior pretectal nucleus, dorsal lateral geniculate nucleus, ventrobasal complex; zona incerta ventral, parafascicular thalamic nucleus) and are thus the most discriminative regarding specific modalities. Variations in staining were of the same magnitude in both saline- and CP-injected animals. A sequential study spanning every postinjection hour revealed maximum staining at 1 h postinjection, which was followed by a progressive, time-related decrease. Increases in the number of labeled cells 1 h postinjection were significant in only a restricted number of nuclei showing low basal expression (Edinger-Westphal nucleus and paraventricular, supraoptic, and lateral hypothalamic nuclei); time-related reductions in staining that were correlated to sleep or quiescence behaviors finally resulted in staining equal to or below that seen in control animals. No structures showed significantly increased staining in relation to the full development of cystitis, i.e., with the increase of visceronociceptive inputs. Comparing the present results with those previously obtained at more caudal levels, it appears that subtelencephalic levels primarily driven by visceronociceptive inputs, i.e., those that increase and/or maintain their activity in parallel with the degree of nociception, are confined to brainstem-spinal cord junction levels and only comprise certain subdivisions of the nucleus of the solitary tract (nucleus medialis, nucleus commissuralis, and ventralmost part of area po

Differential effects of haloperidol and two anxiolytic drugs, buspirone and lesopitron, on c-Fos expression in the rat striatum and nucleus accumbens

We have studied the effects of the neuroleptic haloperidol and the non-benzodiazepine anxiolytics buspirone and lesopitron on the expression of c-Fos immunoreactivity in the rat forebrain. Haloperidol and buspirone administration resulted in a significant quantitative increase in the number of Fos-immunoreactive neurons in the lateral striatum and a presumable qualitative increase in the nucleus accumbens. In contrast, lesopitron did not lead to a significant increase in the c-Fos expression in the striatum. The induction of c-Fos immunoreactivity by buspirone is compatible with an interaction of this compound with D2 dopamine receptors, as documented for haloperidol. The lack of effects after lesopitron administration suggests that, in contrast with buspirone, this compound has no dopaminergic blocking activity.

Fos immunoreactivity in the rat brain following consummatory elements of sexual behavior: a sex comparison

In the present study a comparison was made between the distribution of Fos immunoreactivity in the brain of female and male rats following successive elements of sexual behavior. The distribution of Fos immunoreactivity following either mounting, eight intromissions or one or two ejaculations was compared with that in control animals. In both females, Fos immunoreactivity was induced in the medial preoptic nucleus, posteromedial part of the bed nucleus of the stria terminalis, posterodorsal part of the medial amygdala, and the parvicellular part of the subparafascicular thalamic nucleus. In addition, Fos immunoreactivity in females was induced in the ventrolateral part and the most caudoventral part of the ventromedial nucleus of the hypothalamus and in the premammillary nucleus. Differences between females and males were detected in the phases of sexual activity that resulted in Fos immunoreactivity in these brain areas, allowing more insight in the nature of the sensory and hormonal stimuli leading to the induction of Fos immunoreactivity. The posteromedial bed nucleus of the stria terminalis appears to be involved in chemosensory investigation, while specific distinct subregions are only activated following ejaculation. In addition, the parvicellular subparafascicular nucleus and the lateral part of the posterodorsal medial amygdala appear to be involved in the integration of viscero-sensory input. The neural circuitries underlying sexual behavior in males and females appear to be similar in terms of integration of sensory information. In males the medial preoptic nucleus may be regarded as the brain area where the integration of sensory and hormonal stimulation leads to the onset of male sexual behavior, while in females the ventrolateral part of the ventromedial hypothalamic nucleus appears to have this function. In addition, Fos immunoreactivity was distributed in distinct clusters in subregions with various brain areas in males and females. This was observed especially in the posteromedial bed nucleus of the stria terminalis and posterodorsal medial amygdala, but also in the parvicellular subparafascicular nucleus, ventromedial hypothalamic nucleus and ventral premammillary nucleus. It appears that relatively small subunits within these nuclei seem to be concerned with the integration of sensory and hormonal information and may play a critical role in sexual behavior.

Effect of AV3V lesions on Fos expression and cell size increases in magnocellular neurons of the rat hypothalamus during chronic dehydration

The effects of osmotic stimulation on Fos expression and cell size increase in the supraoptic nucleus were evaluated in intact, sham-operated, and AV3V-lesioned rats. Fos-positive neurons were found mainly in the AV3V regions and the hypothalamic magnocellular neurons in the forebrain in dehydrated intact rats. Intraperitoneal injection of hypertonic saline and chronic dehydration induced a significant increase in number of Fos-positive neurons in the supraoptic nucleus of intact and sham-operated rats. AV3V lesions completely abolished the expression of Fos in SON neurons of rats that were intraperitoneally injected with hypertonic saline and were chronically dehydrated. Chronic dehydration increased significantly cell size of the OXT and AVP magnocelluar neurons in intact and sham-operated rats. However, there was no increase in cell size of those in the AV3V-lesioned rats. These results demonstrate that neural input derived from AV3V regions plays a significant role in causing Fos expression and structural changes such as cell size increase in the hypothalamic magnocellular neurons with osmotic stimulation.

AP-1 DNA binding activity induced by hyperosmolality in the rat hypothalamic supraoptic and paraventricular nuclei

Immediate early gene products (c-fos, c-jun and their cognates) act as transcription factors coupling physiologically relevant stimuli to long-term responses by binding to the AP-1 site in the promoter region of target genes. The induction of c-fos has been identified in the paraventricular (PVN) and supraoptic (SON) hypothalamic magnocellular nuclei after hyperosmotic stimulation by using in situ hybridization and immunocytochemistry. In this study, AP-1 DNA binding activity, an indicator of the functional form of the c-fos transcription factor, was examined in nuclear extracts prepared from these brain regions using an electrophoretic mobility shift assay and a labeled oligonucleotide containing the AP-1 consensus sequence. Two hours after hypertonic saline injection (i.p.), rats were killed and nuclear proteins were extracted from tissue punches of brain regions to assess AP-1 binding activity. Hyperosmolality induced an increase of AP-1 binding activity in nuclear protein from SON and PVN, but not striatum. This binding was competitively displaced by excess unlabeled AP-1 oligonucleotide whereas addition of increasing amounts of unlabeled SP-1 oligonucleotide (promoter site on housekeeping genes for the ubiquitous SP-1 transcription factor) did not decrease the binding. The binding protein was shown to contain c-Fos/Fra and c-Jun since addition of c-Fos/Fra antiserum formed a supershift of the DNA, protein and antibody complex, and c-Jun antibody blocked the protein DNA binding. These data suggest that hyperosmolality leads to a selective and specific increase in AP-1 DNA binding activity which may be responsible for regulating secondary target gene expression in the hypothalamic SON and PVN.

Identification of osmoresponsive neurons in the forebrain of the rat: a Fos study at the ultrastructural level

The aims of this study are twofold. The first is to describe the ultrastructural morphology of putative osmoreceptors concentrated in the ventral aspect of the lamina terminalis in the rat forebrain. The second is to determine whether or not these neurons lie within an area which lacks a blood-brain barrier, i.e. the organum vasculosum lamina terminalis. The results describe a compact population of neurons in the ventral part of the lamina terminalis which both respond to an osmotic challenge and project directly to the supraoptic nucleus. Injection of horseradish peroxidase into the circulation, as a marker to define areas of the brain without a blood-brain barrier, indicates that these neurons are in the dorsal aspect of the organum vasculosum of the lamina terminalis. An ultrastructural analysis of the neurons in this area, which respond to an osmotic challenge with an elevation of Fos protein, show them to have no specific morphological characteristics which differentiate them from other, non-responsive neurons in the organum vasculosum of the lamina terminalis. However, one possible exception is that osmotically sensitive neurons have a less indented nucleus, suggesting that they are in a more active state than their non-osmotically sensitive neighbours. It is concluded that neurons in this region of the brain are candidate structures for the "receptors" which mediate vasopressin release in response to an osmotic challenge. The response of only a subset of neurons in the organum vasculosum of the lamina terminalis to an osmotic stimulus, despite an apparent morphological homogeneity and the ability of blood borne agents to reach all parts of the structure suggests that osmoresponsiveness is conferred by unique membrane properties or intracellular processing events. The presence of synaptic input to osmoresponsive cells indicates a potential for integration of other inputs at this level.

Differential responses of oxytocin and vasopressin neurons to the osmotic and stressful components of hypertonic saline injections: a Fos protein double labeling study

Expression of Fos protein, detected immunocytochemically, was used to assess the relative responses of supraoptic nucleus (SON) oxytocin- (OX) and vasopressin- (VP) containing neurons to the osmotic vs. the osmotic plus stressful components of intraperitoneal hypertonic saline injections. The percentage of SON neurons showing Fos-like immunoreactivity (Fos-ir) was quantified for rats receiving general anesthesia only, anesthesia 1 h prior to either isotonic or hypertonic saline injection or no anesthesia prior to hypertonic injection. Hypertonic saline injection with and without anesthesia induced Fos-ir in 66% and 77% of SON neurons, respectively, whereas isotonic saline with anesthesia and anesthesia alone resulted in 15% and 13%, respectively, of cells showing Fos-ir. Double labeling for Fos-ir and either OX-ir or VP-ir resulted in quantitatively different responses to hypertonic injections with and without anesthesia in OX-ir and VP-ir neurons. The VP-ir neuronal response was similar under the two conditions: 49% and 48% of VP cells displaying Fos-ir with and without prior anesthesia, respectively. By contrast, a higher percentage of OX-ir neurons was found to exhibit Fos-ir without (68%) than with (53%) anesthesia. Thus, a greater percentage of neurons was induced to express Fos-ir when the stressful components of the hypertonic injection were unattenuated by anesthesia, and this difference was entirely due to increased numbers of responding OX neurons. These data indicate that, under these experimental conditions, SON OX neurons respond in larger numbers to the osmotic components of hypertonic saline injections and have a greater responsiveness than do VP neurons to the stressful components.

Alteration of dynorphin and secretogranin II in the prolactin immunoreactive neurons of the rat lateral hypothalamus upon osmotic stimulation

The prolactin immunoreactive neurons of the rat lateral hypothalamus were previously reported to express the dynorphin and secretogranin II genes. In the present study, the response of these neurons to osmotic challenge was immunocytologically investigated by using prolactin, dynorphin, secretogranin II and c-Fos antisera. In addition, the mRNA levels for secretogranin II and dynorphin were compared by in situ hybridization in controls and salt-loaded rats. For this model of chronic hyperosmolality, the prolactin and c-Fos immunoreactivities were not stimulated by salt drinking, but dynorphin and secretogranin II immunoreactivities as well as mRNA levels for dynorphin and secretogranin II significantly increased in the lateral hypothalamus. We suggest that the prolactin-immunoreactive neurons may be involved in the regulation of water homeostasis.

Effect of lesions of forebrain circumventricular organs on c-fos expression in the central nervous system to plasma hypernatremia

Experiments were carried out on conscious adult male Wistar rats to investigate the effect of selective ablation of the subfornical organ (SFO), and/or the anteroventral third ventricular (AV3V) region on the induction of Fos in central structures in response to plasma hypernatremia. Fos induction, detected immunohistochemically, was used as a marker for neuronal activation. Intravenous infusions of hypertonic saline resulted in dense Fos-like immunoreactivity in several forebrain (paraventricular nucleus of the hypothalamus (PVH), supraoptic nucleus (SON), median preoptic nucleus (MnPO), medial preoptic nucleus, organum vasculosum of the laminae terminalis and (SFO) and brainstem (nucleus of the solitary tract, ventrolateral medulla, and parabrachial nucleus) structures. Intravenous infusions of the hypertonic saline solution into animals with lesions of either the SFO, the AV3V or both resulted in a decreased number of Fos-like immunoreactive neurons in the MnPO, PVH and SON. In addition, the number of Fos-labeled neurons in the SON after lesions of both the SFO and the AV3V was significantly greater than that observed in isotonic saline infused controls. Finally, lesions of the forebrain circumventricular structures did not alter the Fos labeling in brainstem structures as a result of the infusion of the hypertonic solution. These data suggest that changes in plasma osmolality and/or concentration of sodium alter the activity of SON and brainstem neurons in the absence of afferent inputs from the SFO and AV3V.

Basal expression of 35 kDa fos-related antigen in olfactory bulb

Recently, there have been a number of reports showing a long-term increased expression of fos-related antigens (fra), molecular weight of 35 kDa, after brain injury or chronic treatment of rats with various drugs. We report elevated basal levels of this transcription factor in the olfactory bulb relative to other brain regions. The expression of this protein is further enhanced in the olfactory bulb as long as 3 months after a single injection of kainate, an effect similar to that we previously observed in the hippocampus. The AP-1 DNA binding activity in olfactory bulb from kainate-treated rats contains fra and jun immunoreactivity suggesting that the 35 kDa fra dimerizes with jun protein, probably junD, to bind to AP-1 sites. Elevated basal levels of this transcription factor in the olfactory bulb appear to be related to the constant reinnervation and synaptogenesis which occurs in this brain region. The 35 kDa fra may be involved in long-term genomic program changes required to adapt to an altered biochemical environment.

Age-induced hypertrophy of astrocytes in rat supraoptic nucleus: a cytological, morphometric, and immunocytochemical study

BACKGROUND

In the adult rat, neuron-astroglia interactions in the supraoptic nucleus (SON) are characterized by the structural and functional plasticity of astrocytes in response to several physiological and experimental conditions. This study has analyzed the plasticity of the supraoptic nucleus astrocytes in response to the age-induced changes in neuronal activity.

METHODS

The study was performed in 5-, 12-, 18- and 24-month-old rats. The cytology and organization of astrocytes in the SON were examined using glial fibrillary acidic and vimentin immunocytochemistry and ultrastructural and morphometric analysis.

RESULTS

No significant age-related variations in the total number of neurons and astrocytes in the SON were detected, although a few degenerating neurons were found in old rats. An age-dependent increase in GFAP immunoreactivity was observed at the ventral glial lamina, perivascularly and between neuronal perikarya. Vimentin overexpression was also detected in ventral lamina astrocytes with advancing age. At the cell nucleus level, we observed an age-associated increase in nuclear size and in the number of coiled bodies, nuclear bodies, and "cleared" nucleoplasmic areas, as well as changes in the nucleolar organization. At the cytoplasmic level, characteristic ultrastructural features in astrocytes of old rats were the hypertrophy of intermediate filament bundles and the formation of an extensive network of Golgi stacks interlinked by tubulovesicular elements. Glial filaments were often associated with the nuclear envelope and polyribosomes.

CONCLUSIONS

The increased GFAP and vimentin immunoreactivity and the morphometric and cytological changes in rat SON astrocytes may reflect a sustained upregulation of cellular activity with age, resulting in hypertrophy of glial perikarya and cell processes. Several factors that are known to influence the expression of the astrocytic phenotype, such as signals produced by degenerating neurons and activated microglia, as well as variations in neuronal activity are considered possible causes of the age-associated changes in SON astrocytes.

Implications of prolonged expression of Fos-related antigens

The AP-1 transcription factors are composed of the Fos and Fos-related antigens as well as Jun and related proteins. These factors have been extensively studied in many diverse paradigms using acute stimuli. Recent attention has focussed on long-term elevation of Fos-related antigens in the CNS, and this is discussed by Keith Pennypacker, Jau-S. Hong and Michael McMillian. Repeated or chronic treatment elevates Fos-related antigen levels for days in many different brain regions. Both direct and indirect stimulation are responsible for the protracted increase in Fos-related antigen-immunoreactive proteins, which may modulate late onset genes involved in neuroplasticity. Understanding the role of these factors in long-lasting or permanent disease states may provide insight into potential therapeutic strategies to treat chronic CNS disorders.

Regional suppression by lesions in the anterior third ventricle of c-fos expression induced by either angiotensin II or hypertonic saline

Angiotensin II (250 pmol) infused into the cerebral ventricles of male rats induces the expression of c-fos in the subfornical organ, supraoptic and paraventricular nuclei of the hypothalamus, as well as in the lateral parabrachial nucleus, locus coeruleus and the nucleus of the solitary tract in the brainstem. Electrolytic lesions of the anteroventral third ventricle, principally the subcommissural (ventral) median preoptic nucleus, inhibited the dipsogenic response to i.c.v. angiotensin II and also suppressed c-fos expression in supraoptic nucleus, paraventricular nucleus, lateral parabrachial nucleus, locus coeruleus and nucleus of the solitary tract but not in the subfornical organ or dorsal median preoptic nucleus. The stimulating effect of i.c.v. angiotensin II on corticosterone was also reduced. Median preoptic nucleus lesions also suppressed the expression of c-fos following i.v. infusions of 6 micrograms angiotensin II in supraoptic nucleus and paraventricular nucleus but not in subfornical organ, dorsal median preoptic nucleus, lateral parabrachial nucleus, locus coeruleus and nucleus of the solitary tract. Median preoptic nucleus lesions reduced the dipsogenic effects of an intragastric infusion of hypertonic (1.5 M) saline and suppressed c-fos expression in supraoptic nucleus and paraventricular nucleus compared to sham-lesioned rats. However, c-fos expression was unaltered in subfornical organ, dorsal median preoptic nucleus lesions had no effect on the increased corticosterone induced by hypertonic saline. Subfornical organ lesions did not alter dipsogenic responses to i.c.v. angiotensin II, nor was the i.c.v. angiotensin II-induced expression of c-fos suppressed in the basal forebrain. These experiments show that the ventral median preoptic nucleus (but not the subfornical organ), part of the anteroventral third ventricle, is critical for the expression of c-fos in more caudal areas of the brain following i.c.v. angiotensin II. c-fos expression in supraoptic nucleus and paraventricular nucleus following i.v. angiotensin II is also dependent on an intact median preoptic nucleus, suggesting that supraoptic nucleus and paraventricular nucleus activation may be dependent on the median preoptic nucleus, and that suppression following i.c.v. infusions is not due to mechanical obstruction to infused peptide. However, there is a clear separation of the effects of i.c.v. and i.v. angiotensin II on brainstem structures. The median preoptic nucleus (but not the subfornical organ) seems essential for activation following the former but not the latter, suggesting alternative mechanisms for the effect of i.v. angiotension II on the brainstem.(ABSTRACT TRUNCATED AT 400 WORDS)

Activation and desensitization of Fos immunoreactivity in the rat brain following ethanol administration

The expression of the Fos proto-oncogene protein has been used as an anatomical marker of activated brain areas. Detection of Fos immunoreactivity can provide information about the sites of action of various stimuli at the level of single cell resolution. Following intraperitoneal injection of ethanol (16% w/v), Fos immunoreactivity was induced in several rat brain areas including the bed nucleus of the stria terminalis, paraventricular hypothalamic nucleus, the central nucleus of amygdala, Edinger-Westphal nucleus, locus coeruleus nucleus and parabrachial nucleus. The induction was dose dependent, and the length of activation time was different in each nucleus. Fos immunoreactivity in the supraoptic nucleus appeared only when a higher concentration of ethanol was injected. Repeated administration of ethanol twice daily for 17 or 24 days resulted in a desensitization of Fos immunoreactivity in these nuclei. These data suggest that induction of Fos immunoreactivity can be used to determine the sites at which ethanol acts on the brain, and may provide important information about the mechanisms underlying the tolerance and physical dependence of alcohol usage.

Expression of histone H1 (zero) in transcriptionally activated supraoptic neurons

This study has analysed by immunocytochemistry the expression pattern of histone H1 zero after the osmotically induced activation of transcription in supraoptic nucleus neurons of the rat. In control rats, histone H1 zero was constitutively expressed in neuronal and glial cell nuclei of supraoptic nucleus. After chronic neuronal stimulation by intermittent salt-loading, the majority of neuronal cell nuclei exhibited a marked reduction of immunostaining, which was confirmed by densitometric analysis of immunoreactivity. This effect was reversible, since optical density values returned to control levels when the stimulation of supraoptic neurons was suppressed by rehydration. Ultrastructural immunocytochemistry of histone H1 zero showed that immunogold particles specifically decorated chromatin fibers, with the highest accumulation of particles being on the condensed inactive chromatin. These results indicate that transcriptional activation in supraoptic neurons is accompanied by a depletion of the chromatin-associated histone H1 zero, and also suggest that this transcription-dependent expression of histone H1 zero may be involved in regulating chromatin condensation and gene expression in mature neurons that constitutively express this protein.

Basal expression of the inducible transcription factors c-Jun, JunB, JunD, c-Fos, FosB, and Krox-24 in the adult rat brain

Jun, Fos, and Krox proteins are inducible transcription factors contributing to the control of gene expression. The elucidation of their individual expression patterns in the nervous system provides new insights into the ability of neurons to react with changes of gene expression to external stimulation under physiological or pathological conditions. The expression of c-Jun, JunB, JunD, c-Fos, FosB, and Krox-24 was investigated in the brain of untreated male Sprague-Dawley and female BDIX rats by immunocytochemistry using specific antibodies. JunD immunoreactivity (IR) labeled the highest number of neurons, being present in almost all neurons of the brain. JunD was expressed at high levels in those areas that also exhibit c-Jun, JunB, c-Fos, and FosB-IR, such as locus coeruleus, periolivary nuclei (ncl.), pontine and central gray, lateral lemniscal ncl., inferior and superior colliculi, leaflet of geniculate ncl., midline nuclei of thalamus, dorsomedial and paraventricular ncl. of hypothalamus, ncl. supraopticus, dorsolateral part of caudate putamen and lateral septal ncl. In contrast to the high number of JunD-positive neurons, c-Jun, JunB, c-Fos, and FosB proteins were detected in rather low numbers of neurons in these brain areas; the rank of the number of immunopositive neurons was c-Fos > JunB > c-Jun > FosB. Particularly high levels of expression were observed for c-Jun in medullary motoneurons, medial geniculate ncl., arcuate ncl., and dentate gyrus, and for JunB in the CA-1 area of the hippocampus and islands of Calleja. The zinc finger protein Krox-24 was expressed in many neurons of these brain areas, with only discrete Jun- and Fos-IR; additionally, many intensely labeled nuclei were present in spinal ncl. of the trigeminal ventromedial ncl. of the hypothalamus and the CA-1 area of the hippocampus. In the cerebellum, nuclear labeling was detected only for c-Jun, JunD, and Krox-24 in granule cells. JunD-IR was also found in glial cells of gray matter and fiber tracts, whereas glial c-Jun-IR was observed only in fiber tracts. Apart from a weak JunD-IR, some areas did not express Jun, Fos, and Krox proteins such as cuneate and gracile ncl., venterobasal complex of thalamus, globus pallidum, and Purkinje cells of the cerebellum. Our data indicate that inducible transcription factors of the fos, jun, and krox gene families show patterns of individual expression in untreated animals, thereby reflecting different mechanisms and/or thresholds for induction under physiological conditions.

Regional suppression by water intake of c-fos expression induced by intraventricular infusions of angiotensin II

Intracerebroventricular (i.c.v.) infusions of angiotensin II (AII) reliably induced c-fos expression in the supraoptic (SON) and paraventricular (PVN) nuclei, as well as other areas of the basal forebrain including the OVLT, subfornical organ (SFO), and bed nucleus (BNST). Double-labelling showed that AII-induced c-fos was observed in both vasopressin (AVP-) and oxytocin (OXY)-containing neurons of the SON and PVN in male rats. Allowing rats to drink water after AII infusions suppressed c-fos expression both AVP- and OXY-stained magnocellular neurons. Intragastric infusions of water were also effective, showing that oro-pharyngeal stimuli were not critical. Maximal suppression occurred in rats in whom water had been infused intragastrically about 5 min before i.c.v. AII infusions, suggesting that changes in osmolarity were responsible. i.c.v. AII also induced c-fos expression in a number of brainstem structures, including the solitary nucleus (NTS), lateral parabrachial nucleus (LPBN), locus coeruleus (LC), and the area postrema (AP). These results indicate that AVP and OXY-containing neurons in the magnocellular parts of the SON and PVN alter their immediate-early gene response to AII after water intake, and that this does not depend upon oro-pharyngeal factors. Furthermore, AII can induce c-fos expression in a number of brainstem nuclei associated with autonomic function, and these do not respond to water intake.

Effects of cycloheximide on the structural organization of the nucleolus and the coiled body in normal and stimulated supraoptic neurons of the rat

This study was designed to determine the effects of cycloheximide, a protein synthesis inhibitor that interferes with rRNA synthesis and processing, on the nucleoli and coiled bodies of supraoptic nucleus neurons from normally-hydrated and osmotically-stimulated rats. The number of nucleoli and the nucleolar size were estimated on smear preparations of previously silver-impregnated supraoptic nucleus. No significant differences were registered in the mean number of nucleoli per cell in cycloheximide-treated rats. The number of nucleoli per neuron remained constant, at about 1.3, in all animal groups, suggesting that the nucleoli number is strictly regulated in differentiated neurons. By contrast, a significant reduction in the average nucleolar volume of supraoptic nucleus neurons was detected in cycloheximide-treated groups of rats in comparison with their equivalent non-treated groups. By electron microscopy, most nucleoli and coiled bodies of supraoptic nucleus neurons exhibited cycloheximide-induced alterations in their fine structure and configuration. Nucleolar changes included the occurrence of a few large fibrillar centres, the formation of microspherules and small intranucleolar vacuoles or dilated interstices, and the partial segregation of nucleolar components coupled with the transformation of reticulated nucleoli--a nucleolar configuration characteristic of supraoptic nucleus neurons of non-cycloheximide-treated rats--into compact ones. The redistribution of nucleolar components might reflect the interference with rDNA transcription, and also supports the hypothesis that the normal assembly of these components into the nucleolus depends upon ongoing nucleolar transcription. Concerning coiled bodies, most of them revealed ultrastructural alterations, particularly segregation of the amorphous matrix, compactation of coiled threads and formation of coiled body-derived dense bodies of fibrillar nature. Moreover, cycloheximide also induced the formation of smaller dense bodies--here referred to as dense microbodies--which presumably represent a distinct nuclear entity different from coiled bodies. Ultrastructural silver staining of nuclear bodies showed a selective silver reaction on the dense fibrillar component of normal and altered coiled bodies, as well as on the dense microbodies. The possible relationship between the nucleolus and both coiled bodies and dense microbodies is discussed.

Dehydration induces Fos, but not increased vasopressin mRNA in the supraoptic nucleus of aged rats

Dehydration induces Fos expression and increases the length of the vasopressin (VP) mRNA poly-A tail and the content of VP mRNA in the supraoptic (SON) and paraventricular nuclei (PVN) of the hypothalamus. The current studies were performed to evaluate the effect of aging on these responses. Fischer 344 rats of 4, 14, and 28-30 months of age were either water deprived for 72 h or allowed ad libitum access to water. Fos induction in the SON and PVN was examined by immunocytochemistry in order to provide an index of cellular activation. VP mRNA content and size was examined in SON by Northern analysis as an index of VP synthetic capacity. Dehydration induced the expected increase in plasma osmolality in all three ages, however, serum VP was only increased in the 4- and 14-month-old rats. The increase in serum VP was accompanied by a decrease in VP content of the posterior pituitary (PP) in the dehydrated 4- and 14-month-old rats. PP VP content was reduced in both the hydrated and dehydrated old rats relative to the other ages (P = 0.0007). Fos was induced in both SON and PVN of all water deprived rats regardless of age. The density of Fos staining was increased in both nuclei following dehydration (SON, P = 0.002; PVN, P = 0.0001). There was also a significant increase in the number of cells expressing Fos in both nuclei in the dehydrated animals (SON, P = 0.002; PVN, P = 0.0056). There was no significant effect of age on the density of Fos staining. In contrast, dehydration failed to elicit the expected increase in VP mRNA size and content in the SON of the aged dehydrated rats although both of these parameters were increased in the 4- and 14-month-old rats (P < 0.05). Thus, the inability of old Fischer rats to increase serum VP during chronic dehydration is not caused by decreased activation of the neurons (as indicated by Fos induction), but apparently reflects depletion of PP stores of VP due to an inability to increase the amount of VP mRNA available for translation.

Double immunofluorescence staining of Fos and Jun in the hypothalamus of the rat

The nuclear factor Fos participates in the transcriptional regulation of genes that contain a functional AP-1 binding site. Hyperosmotic stress induces Fos-like immunoreactivity in neurons of the hypothalamus. Fos appears to depend on the co-expression of the nuclear factor Jun, with which it dimerizes, to complete its regulatory role. The immunocytochemical co-localization of both peptides, however, has not been reported. The present study was designed to analyze the distribution of Fos and Jun by double immunofluorescence staining in Long-Evans rats that were osmotically challenged by a single intraperitoneal injection of 1.5 M NaCl. Non-injected and isotonic saline-injected animals were used as controls. Hypertonic saline injection induced Jun immunoreactivity in cell nuclei in the supraoptic nucleus, paraventricular nucleus, and median preoptic nucleus. The immunofluorescence for Jun was strong in the supraoptic and paraventricular nuclei, but weak in the median preoptic nucleus. The immunofluorescence for Fos in all 3 nuclei followed a similar pattern to that for Jun. Double immunofluorescence staining revealed co-localization of Jun with Fos in 87.4% of the cells of the supraoptic nucleus. Neither Jun nor Fos immunofluorescence was detected in control animals. The data support a role for Jun in transcriptional regulation of genes in hypothalamic neurons during acute hyperosmotic stress. Moreover, the findings are compatible with the suggestion that Fos and Jun act cooperatively in the regulation of gene transcription in neuroendocrine systems involved in the control of water balance during acute hyperosmotic stimulation.

Proto-oncogene c-fos and the regulation of vasopressin gene expression during dehydration

Secretion of the antidiuretic hormone (ADH) vasopressin is increased when body fluid homeostasis is disturbed by dehydration. Associated with this increased secretion is an elevation of vasopressin mRNA in magnocellular hypothalamic neurons projecting to the posterior pituitary. The proto-oncogene c-fos codes for a nuclear phospho-protein Fos which binds to specific DNA elements and acts as a transcriptional regulator coupling short-term extracellular stimuli to long-term responses by altering secondary target gene expression. This study in rats examined the time courses of dehydration induced c-fos expression and the change of vasopressin gene expression in the magnocellular neurons of the hypothalamus. Immunocytochemical and in situ hybridization study demonstrated that c-fos was induced by acute intracellular dehydration in the hypothalamic magnocellular nuclei of paraventricular (PVN), supraoptic (SON), and accessory groups such as nucleus circularis. Double-label immunocytochemical study co-localized Fos and vasopressin-neurophysin immunoreactivity in the same magnocellular neurons in the SON and PVN. In situ hybridization analysis after acute dehydration revealed a rapid and transient c-fos induction followed by a persistent increase in vasopressin mRNA for up to 2 days even after rehydration. Furthermore, prevention of c-fos translation by pretreatment with protein synthesis inhibitor cycloheximide attenuated this dehydration induced increase in vasopressin mRNA. This study demonstrated that an increase in vasopressin transcription after acute dehydration is dependent on an early phase of protein synthesis.

Nuclear Fos domains in transcriptionally activated supraoptic nucleus neurons

This study has analysed by light and electron microscopy immunolocalization the nuclear pattern of distribution of Fos-related proteins in supraotic neurons. Two experimental models of transcriptional activation have been used: sustained, global transcriptional activation, at relatively near physiological conditions, by six days of chronic intermittent salt loading; and superinduction of c-fos gene by this salt loading regime plus cycloheximide treatment for 4 h. In the first condition, the ultrastructural analysis showed a distribution of Fos-like immunoreactivity on the reticular network of dispersed chromatin that extends between the nucleolar surface and the nuclear envelope, whereas the Fos-negative adjacent interchromatin spaces appeared rich in interchromatin granules by using a cytochemical staining for ribonucleoproteins. The nucleolus associated heterochromatin, fibrillar centers of the nucleolus and coiled bodies were free of immunoreactivity. This immunoelectron pattern seems to indicate that active genes containing activator protein-1 and cyclic AMP response element recognition sites are extensively distributed in euchromatin regions and suggests that the Fos-positive nuclear domains correspond to the actively transcribing chromatin regions, at least in supraoptic neurons. It also suggests that these Fos-positive transcription domains are complementary to adjacent ribonucleoprotein-rich interchromatin spaces which are involved in the processing and splicing of pre-messenger RNA. Moreover, the absence of immunoreactivity on the fibrillar centers, the sites of pre-ribosomal RNA synthesis, suggests that the Fos protein complexes are not involved in regulating the expression of ribosomal RNA genes. Following superinduction of c-fos gene by osmotic stimulation plus cycloheximide treatment, a conspicuous Fos-like immunoreactivity was detected in dispersed chromatin regions, whereas the heterochromatin masses, nucleoli and coiled bodies showed no immunoreaction. Moreover, this treatment induced the formation of nuclear "dense bodies" of a fibrillar nature which were free of immunolabelling. Since Fos proteins are known to be short-lived, the expression of these nuclear constituents, under conditions of protein synthesis inhibition induced by the cycloheximide, suggests the stabilization of chromatin-bound Fos complexes or, alternatively, a preferential synthesis of Fos proteins.

Response of neurons in the solitary tract nucleus, area postrema and lateral parabrachial nucleus to gastric load of hypertonic saline

c-Fos was induced in the solitary tract nucleus (NTS), area postrema (AP) and lateral parabrachial nucleus (LPB) by the intragastric injection of hypertonic saline. The effect was bilateral and most dramatic in the NTS caudal to the facial nucleus and the AP, the areas receiving dense vagal afferent projection from the subdiaphragmatic structures. At least a part of these Fos-LI is considered to have been induced by the activation of the visceral osmoreceptors.

Reactive astroglia-neuron relationships in the human cerebellar cortex: a quantitative, morphological and immunocytochemical study in Creutzfeldt-Jakob disease

In order to investigate the role of neuron-glia interactions in the response of astroglial to a non-invasive cerebellar cortex injury, we have used two cases of the ataxic form of Creutzfeldt-Jakob disease (CJD) with distinct neuronal loss and diffuse astrogliosis. The quantitative study showed no changes in cell density of either Purkinje or Bergmann glial cells in CJ-1, whereas in the more affected CJ-2 a loss of Purkinje cells and an increase of Bergmann glial cells was found. The granular layer in both CJD cases showed a similar loss of granule cells (about 60%) in parallel with the significant increase in GFAP+ reactive astrocytes. GFAP immunostaining revealed greater reactivity of Bergmann glia in CJ-2 than in CJ-1, as indicated by the thicker glial processes and the higher optical density. Granular layer reactive astrocytes were regularly spaced. In both CJD cases there was strict preservation of the spatial arrangement of all astroglial subtypes--Fañanas cells, Bergmann glia and granular layer astrocytes. Reactive Fañanas and Bergmann glial cells and microglia/macrophages expressed vimentin, while only a few vimentin+ reactive astrocytes were detected in the granular layer. Karyometric analysis showed that the increase in nuclear volume in reactive astroglia was directly related with the level of glial hypertrophy. The number of nucleoli per nuclear section was constant in astroglial cells of human controls and CJD, suggesting an absence of polyploidy in reactive astroglia. Ultrastructural analysis revealed junctional complexes formed by the association of macula adherens and gap junctions. In the molecular layer numerous vacant dendritic spines were ensheathed by lamellar processes of reactive Bergmann glia. Our results suggest that quantitative (neuron/astroglia ratio) and qualitative changes in the interaction of neurons with their region-specific astroglial partners play a central role in the astroglial response pattern to the pathogenic agent of CJD.

Osmotic stimulation induces changes in the expression of beta-adrenergic receptors and nuclear volume of astrocytes in supraoptic nucleus of the rat

The influence of osmotic stimulation on the density of beta-adrenoceptor binding sites in the rat supraoptic nucleus (SON) was studied by quantitative autoradiography using 125I-cyanopindolol (ICYP). Increased density of beta-adrenoceptor binding sites was observed in osmotically stimulated rats and also after the suppression of neuronal activation by rehydration of animals. This was mainly due to a significant increase in the concentration of beta 2 binding sites. The overexpression of beta-adrenoceptors occurred concomitantly with nuclear expansion in SON astrocytes. Moreover, the higher concentration of beta-adrenoceptors observed in the ventral portion of the SON largely coincided with the area that showed intense GFAP-immunostaining. These results provide indirect evidence of an astrocytic location of beta-adrenoceptors and also of beta-adrenergic mediation in the structural and functional changes of SON astrocytes.