Time course of phosphorylated CREB and Fos-like immunoreactivity in the hypothalamic supraoptic nucleus after salt loading

Effects of physical training on hypothalamic neuronal activation and expressions of vasopressin and oxytocin in SHR after running until fatigue

To assess the influence of physical training on neuronal activation and hypothalamic expression of vasopressin and oxytocin in spontaneously hypertensive rats (SHR), untrained and trained normotensive rats and SHR were submitted to running until fatigue while internal body and tail temperatures were recorded. Hypothalamic c-Fos expression was evaluated in thermoregulatory centers such as the median preoptic nucleus (MnPO), medial preoptic nucleus (mPOA), paraventricular nucleus of the hypothalamus (PVN), and supraoptic nucleus (SON). The PVN and the SON were also investigated for vasopressin and oxytocin expressions. Although exercise training improved the workload performed by the animals, it was reduced in SHR and followed by increased internal body temperature due to tail vasodilation deficit. Physical training enhanced c-Fos expression in the MnPO, mPOA, and PVN of both strains, and these responses were attenuated in SHR. Vasopressin immunoreactivity in the PVN was also increased by physical training to a lesser extent in SHR. The already-reduced oxytocin expression in the PVN of SHR was increased in response to physical training. Within the SON, neuronal activation and the expressions of vasopressin and oxytocin were reduced by hypertension and unaffected by physical training. The data indicate that physical training counterbalances in part the negative effect of hypertension on hypothalamic neuronal activation elicited by exercise, as well as on the expression of vasopressin and oxytocin. These hypertension features seem to negatively influence the workload performed by SHR due to the hyperthermia derived from the inability of physical training to improve heat dissipation through skin vasodilation.

Integrating network pharmacology and experimental verification to explore the mechanism of puerarin against oliguria in acute alcoholism

Purpose: This study was designed to evaluate the pharmacological mechanisms of puerarin against oliguria in acute alcoholism via network pharmacology analysis combined with experimental verification.

Methods: First, this study established an acute alcoholism rat model, compared the changes in urine volume in each group, and observed the therapeutic effect of puerarin by H&E staining, biochemical, RT-qPCR, and immunohistochemical analyses. Second, puerarin-related targets were searched in TCMS, PubChem, CNKI, Wanfang, PubMed, and GeenMedical Academic databases. Also, potential disease targets were obtained from the GeneCards, MalaCards, and NCBI-gene databases and genes with puerarin target gene intersections were screened out. The interaction network for co-predicted targets was obtained using the STRING database, and the core targets were imported into Cytoscape for visualization using DAVID Bioinformatics Resources 6.8. The essential genes were subjected to the Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) pathway enrichment analyses to predict related biological processes and significant signaling pathways. Finally, molecular docking was used to examine the interaction of puerarin with key targets, and the core targets were validated further by RT-qPCR and Western blotting.

Results: Compared to the model group, the urine volume of the rats was significantly increased after puerarin treatment, and the levels of anti-diuretic hormone (ADH) and aquaporin 2 (AQP2) expression were decreased. Searching the intersection of puerarin and acute alcoholism targets yielded 214 potential targets, 837 biological processes, and 185 signaling pathways involved. The molecular docking results indicated a good affinity between puerarin and key targets (cyclic adenosine monophosphate (cAMP), protein kinase A (PKA), cAMP-response element-binding protein (CREB), and c-Fos). RT-qPCR and Western blotting further verified that puerarin could down-regulate the expression of cAMP/PKA/CREB/c-Fos.

Conclusion: This study identified the potential targets of puerarin against oliguria in rats with acute alcoholism using network pharmacology and animal experiments. The mechanism may be closely related to the cAMP signaling pathway.

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.

Contextual Fear Conditioning Alter Microglia Number and Morphology in the Rat Dorsal Hippocampus

Contextual fear conditioning is a Pavlovian conditioning paradigm capable of rapidly creating fear memories to contexts, such as rooms or chambers. Contextual fear conditioning protocols have long been utilized to evaluate how fear memories are consolidated, maintained, expressed, recalled, and extinguished within the brain. These studies have identified the lateral portion of the amygdala and the dorsal portion of the hippocampus as essential for contextual fear memory consolidation. The current study was designed to evaluate how two different contextual fear memories alter amygdala and hippocampus microglia, brain derived neurotrophic factor (BDNF), and phosphorylated cyclic-AMP response element binding (pCREB). We find rats provided with standard contextual fear conditioning to have more microglia and more cells expressing BDNF in the dentate gyrus as compared to a context only control group. Additionally, standard contextual fear conditioning altered microglia morphology to become amoeboid in shape – a common response to central nervous system insult, such as traumatic brain injury, infection, ischemia, and more. The unpaired fear conditioning procedure (whereby non-reinforced and non-overlapping auditory tones were provided at random intervals during conditioning), despite producing equivalent levels of fear as the standard procedure, did not alter microglia, BDNF or pCREB number in any dorsal hippocampus or lateral amygdala brain regions. Despite this, the unpaired fear conditioning protocol produced some alterations in microglia morphology, but less compared to rats provided with standard contextual fear conditioning. Results from this study demonstrate that contextual fear conditioning is capable of producing large alterations to dentate gyrus plasticity and microglia, whereas unpaired fear conditioning only produces minor changes to microglia morphology. These data show, for the first time, that Pavlovian fear conditioning protocols can induce similar responses as trauma, infection or other insults within the central nervous system.

Suckling induced activation pattern in the brain of rat pups

OBJECTIVES

The aim of the study was to understand the effects of suckling on the brain of the pups by mapping their brain activation pattern in response to suckling.

METHODS

The c-fos method was applied to identify activated neurons. Fasted rat pups were returned to their mothers for suckling and sacrificed 2 hours later for Fos immunohistochemistry. Double labeling was also performed to characterize some of the activated neurons. For comparison, another group of fasted pups were given dry food before Fos mapping.

RESULTS

After suckling, we found an increase in the number of Fos-immunoreactive neurons in the insular and somatosensory cortices, central amygdaloid nucleus (CAm), paraventricular (PVN) and supraoptic hypothalamic nuclei, lateral parabrachial nucleus (LPB), nucleus of the solitary tract (NTS), and the area postrema. Double labeling experiments demonstrated the activation of calcitonin gene-related peptide-ir (CGRP-ir) neurons in the LPB, corticotropin-releasing hormone-ir (CRH-ir) but not oxytocin-ir neurons in the PVN, and noradrenergic neurons in the NTS. In the CAm, Fos-ir neurons did not contain CRH but were apposed to CGRP-ir fiber terminals. Refeeding with dry food-induced Fos activation in all brain areas activated by suckling. The degree of activation was higher following dry food consumption than suckling in the insular cortex, and lower in the supraoptic nucleus and the NTS. Furthermore, the accumbens, arcuate, and dorsomedial hypothalamic nuclei, and the lateral hypothalamic area, which were not activated by suckling, showed activation by dry food.

DISCUSSION

Neurons in a number of brain areas are activated during suckling, and may participate in the signaling of satiety, taste perception, reward, food, and salt balance regulation.

Rasd1, a small G protein with a big role in the hypothalamic response to neuronal activation

Background

Rasd1 is a member of the Ras family of monomeric G proteins that was first identified as a dexamethasone inducible gene in the pituitary corticotroph cell line AtT20. Using microarrays we previously identified increased Rasd1 mRNA expression in the rat supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the hypothalamus in response to increased plasma osmolality provoked by fluid deprivation and salt loading. RASD1 has been shown to inhibit adenylyl cyclase activity in vitro resulting in the inhibition of the cAMP-PKA-CREB signaling pathway. Therefore, we tested the hypothesis that RASD1 may inhibit cAMP stimulated gene expression in the brain.

Results

We show that Rasd1 is expressed in vasopressin neurons of the PVN and SON, within which mRNA levels are induced by hyperosmotic cues. Dexamethasone treatment of AtT20 cells decreased forskolin stimulation of c-Fos, Nr4a1 and phosphorylated CREB expression, effects that were mimicked by overexpression of Rasd1, and inhibited by knockdown of Rasd1. These effects were dependent upon isoprenylation, as both farnesyltransferase inhibitor FTI-277 and CAAX box deletion prevented Rasd1 inhibition of cAMP-induced gene expression. Injection of lentiviral vector into rat SON expressing Rasd1 diminished, whereas CAAX mutant increased, cAMP inducible genes in response to osmotic stress.

Conclusions

We have identified two mechanisms of Rasd1 induction in the hypothalamus, one by elevated glucocorticoids in response to stress, and one in response to increased plasma osmolality resulting from osmotic stress. We propose that the abundance of RASD1 in vasopressin expressing neurons, based on its inhibitory actions on CREB phosphorylation, is an important mechanism for controlling the transcriptional responses to stressors in both the PVN and SON. These effects likely occur through modulation of cAMP-PKA-CREB signaling pathway in the brain.

Transcription factor CREB3L1 mediates cAMP and glucocorticoid regulation of arginine vasopressin gene transcription in the rat hypothalamus

BACKGROUND

Arginine vasopressin (AVP), a neuropeptide hormone that functions in the regulation of water homeostasis by controlling water re-absorption at kidneys, is synthesised in supraoptic nucleus and paraventricular nucleus of the hypothalamus. An increase in plasma osmolality stimulates secretion of AVP to blood circulation and induces AVP synthesis in these nuclei. Although studies on mechanism of AVP transcriptional regulation in hypothalamus proposed that cAMP and glucocorticoids positively and negatively regulate Avp expression, respectively, the molecular mechanisms have remained elusive. Recently, we identified CREB3L1 (cAMP-responsive element binding protein 3 like 1) as a putative transcription factor of Avp transcription in the rat hypothalamus. However the mechanism of how CREB3L1 is regulated in response of hyperosmotic stress in the neurons of hypothalamus has never been reported. This study aims to investigate effect of previously reported regulators (cAMP and glucocorticoid) of Avp transcription on transcription factor CREB3L1 in order to establish a molecular explanation for cAMP and glucocorticoids effect on AVP expression.

RESULTS

The effect of cAMP and glucocorticoid treatment on Creb3l1 was investigated in both AtT20 cells and hypothalamic organotypic cultures. The expression of Creb3l1 was increased in both mRNA and protein level by treatment with forskolin, which raises intracellular cAMP levels. Activation of cAMP by forskolin also increased Avp promoter activity in AtT20 cells and this effect was blunted by shRNA mediated silencing of Creb3l1. The forskolin induced increase in Creb3l1 expression was diminished by combined treatment with dexamethasone, and, in vivo, intraperitoneal dexamethasone injection blunted the increase in Creb3l1 and Avp expression induced by hyperosmotic stress.

CONCLUSION

Here we shows that cAMP and glucocorticoid positively and negatively regulate Creb3l1 expression in the rat hypothalamus, respectively, and regulation of cAMP on AVP expression is mediated through CREB3L1. This data provides the connection between CREB3L1, a newly identified transcription factor of AVP expression, with the previously proposed mechanism of Avp transcription which extends our understanding in transcription regulation of Avp in the hypothalamus.

The use of protein-DNA, chromatin immunoprecipitation, and transcriptome arrays to describe transcriptional circuits in the dehydrated male rat hypothalamus

The supraoptic nucleus (SON) of the hypothalamus is responsible for maintaining osmotic stability in mammals through its elaboration of the antidiuretic hormone arginine vasopressin. Upon dehydration, the SON undergoes a function-related plasticity, which includes remodeling of morphology, electrical properties, and biosynthetic activity. This process occurs alongside alterations in steady state transcript levels, which might be mediated by changes in the activity of transcription factors. In order to identify which transcription factors might be involved in changing patterns of gene expression, an Affymetrix protein-DNA array analysis was carried out. Nuclear extracts of SON from dehydrated and control male rats were analyzed for binding to the 345 consensus DNA transcription factor binding sequences of the array. Statistical analysis revealed significant changes in binding to 26 consensus elements, of which EMSA confirmed increased binding to signal transducer and activator of transcription (Stat) 1/Stat3, cellular Myelocytomatosis virus-like cellular proto-oncogene (c-Myc)-Myc-associated factor X (Max), and pre-B cell leukemia transcription factor 1 sequences after dehydration. Focusing on c-Myc and Max, we used quantitative PCR to confirm previous transcriptomic analysis that had suggested an increase in c-Myc, but not Max, mRNA levels in the SON after dehydration, and we demonstrated c-Myc- and Max-like immunoreactivities in SON arginine vasopressin-expressing cells. Finally, by comparing new data obtained from Roche-NimbleGen chromatin immunoprecipitation arrays with previously published transcriptomic data, we have identified putative c-Myc target genes whose expression changes in the SON after dehydration. These include known c-Myc targets, such as the Slc7a5 gene, which encodes the L-type amino acid transporter 1, ribosomal protein L24, histone deactylase 2, and the Rat sarcoma proto-oncogene (Ras)-related nuclear GTPase.

Transcription factor CREB3L1 regulates vasopressin gene expression in the rat hypothalamus

Arginine vasopressin (AVP) is a neurohypophysial hormone regulating hydromineral homeostasis. Here we show that the mRNA encoding cAMP responsive element-binding protein-3 like-1 (CREB3L1), a transcription factor of the CREB/activating transcription factor (ATF) family, increases in expression in parallel with AVP expression in supraoptic nuclei (SONs) and paraventicular nuclei (PVNs) of dehydrated (DH) and salt-loaded (SL) rats, compared with euhydrated (EH) controls. In EH animals, CREB3L1 protein is expressed in glial cells, but only at a low level in SON and PVN neurons, whereas robust upregulation in AVP neurons accompanied DH and SL rats. Concomitantly, CREB3L1 is activated by cleavage, with the N-terminal domain translocating from the Golgi, via the cytosol, to the nucleus. We also show that CREB3L1 mRNA levels correlate with AVP transcription level in SONs and PVNs following sodium depletion, and as a consequence of diurnal rhythm in the suprachiasmatic nucleus. We tested the hypothesis that CREB3L1 activates AVP gene transcription. Both full-length and constitutively active forms of CREB3L1 (CREB3L1CA) induce the expression of rat AVP promoter-luciferase reporter constructs, whereas a dominant-negative mutant reduces expression. Rat AVP promoter deletion constructs revealed that CRE-like and G-box sequences in the region between -170 and -120 bp are important for CREB3L1 actions. Direct binding of CREB3L1 to the AVP promoter was shown by chromatin immunoprecipitation both in vitro and in the SON itself. Injection of a lentiviral vector expressing CREB3L1CA into rat SONs and PVNs resulted in increased AVP biosynthesis. We thus identify CREB3L1 as a regulator of AVP transcription in the rat hypothalamus.

Possible involvement of neuropeptide Y in photo-induced suppression of growth hormone pulses

It is well established that growth hormone (GH) is secreted in a pulsatile manner. Although the GH pulse-generating mechanism is not fully understood, we have previously reported that neuropeptide Y (NPY) profiles in the cerebrospinal fluid were negatively correlated with serum GH pulses. In addition, it is known that photic stimulation suppresses GH pulses for a certain period of time. In the present study, to investigate the involvement of NPY in regulating GH pulse generation, NPY gene expression in the arcuate nucleus (ARC) of the hypothalamus in rats was analyzed at around the lights on. First, we confirmed that GH pulses did not occur for around 1.5 hr after the start of the light phase. Then, we analyzed the activity of neurons and expression of NPY mRNA 1 hr before and 0.5 and 2 hr after lights on. Both the activity of neurons, which was evaluated by immunohistochemical detection for phosphorylated-cAMP response element binding protein (pCREB), and NPY mRNA levels in the caudal ARC were higher at 0.5 hr after lights on than the other two time points, while pCREB-positive cell numbers in the rostral ARC remained unchanged throughout the experimental period. In addition, NPY immunoreactivity in the periventricular nucleus (PeVN) was also higher at 0.5 hr after lights on than the other time points. These results suggest that NPY neurons in the caudal ARC projecting to the PeVN play a role in inhibiting GH pulses at the commencement of the light phase.

Reactive oxygen species are required for the hypothalamic osmoregulatory response

Free radicals, or reactive oxygen species (ROS), are highly reactive byproducts of oxygen degradation. They are well known for their cellular toxicity, but few studies have analyzed their potential role in homeostatic processes. We investigated ROS production and function during the arginine vasopressin (AVP) hypothalamic response to hyperosmolarity. Six-week-old male C3H/HeJ mice were subjected to salt loading for 2 or 8 d. The osmotic axis was progressively activated and reached a new steady-state status at 8 d as demonstrated by monitoring of plasmatic osmolality and c-Fos and AVP expression in the supraoptic nucleus (SON). Free radicals, visualized by dihydroethidine staining and measured by 2'-7'dichlorofluorescein diacetate assays, were detected after 2 d of salt loading. The activity and expression of superoxide dismutase 2 and catalase were concomitantly up-regulated in the SON, suggesting that free radicals are detoxified by endogenous antioxidant systems, thereby avoiding their deleterious effects. The early phase of the osmoregulatory response has been investigated using an acute hyperosmotic model; free radicals were produced 45 min after an ip injection of 1.5 m NaCl. This was followed by an increase in c-Fos and AVP expression and an increase in superoxide dismutase 2 and catalase activities. α-Lipoic acid, a ROS scavenger, administrated during the 3 d before the hypertonic ip injection, abolished the increase of AVP. These findings establish that hyperosmolarity causes ROS production in the SON, which is essential for AVP increase. This demonstrates the importance of free radicals as physiological signaling molecules in the regulation of body-fluid balance.

Activation and role of the medial prefrontal cortex (mPFC) in extinction of ethanol-induced associative learning in mice

Although the medial prefrontal cortex (mPFC) has been shown to be integrally involved in extinction of a number of associative behaviors, its role in extinction of alcohol (ethanol)-induced associative learning has received little attention. Previous reports have provided evidence supporting a role for the mPFC in acquisition and extinction of amphetamine-induced conditioned place preference (CPP) in rats, however, it remains unknown if this region is necessary for extinction of ethanol (EtOH)-induced associative learning in mice. Using immunohistochemical analysis of phosphorylated and unphosphorylated cAMP response element-binding protein (CREB), the current set of experiments first showed that the prelimbic (PL) and infralimbic (IL) subregions of the mPFC exhibited dynamic responses in phosphorylation of CREB to a Pavlovian-conditioned, EtOH-paired cue. Interestingly, CREB phosphorylation within these regions was sensitive to manipulations of the EtOH-cue contingency-that is, the cue-induced increase of pCREB in both the PL and IL was absent following extinction. In order to confirm a functional role of the mPFC in regulating the extinction process, we then showed that electrolytic lesions of the mPFC following acquisition blocked subsequent extinction of EtOH-CPP. Together, these experiments indicate a role for the PL and IL subregions of the mPFC in processing changes of the EtOH-cue contingency, as well as in regulating extinction of EtOH-induced associative learning in mice.

Fos proteins are not prerequisite for osmotic induction of vasopressin transcription in supraoptic nucleus of rats

While it is well known that osmotic stimulation induces the expression of Fos family members in the supraoptic nucleus (SON), it is unclear whether the induced protein products are involved in the regulation of the gene transcription of arginine vasopressin (AVP). In the present study, we examined the in vivo correlation between changes in AVP gene transcription and expression of the various Fos family members in the SON after acute osmotic stimuli. The data demonstrated that the peak of AVP transcription (measured by intronic in situ hybridization) observed 15min after an injection of hypertonic saline preceded the expression of Fos proteins, which became detectable at 30min and peaked at 120min. Electrophoretic mobility shift assay showed that the expressed Fos proteins bound to the composite AP-1/CRE-like site in the AVP promoter. These data suggest that Fos proteins in the SON induced by acute osmotic stimuli could affect AVP gene transcription by binding to the AVP promoter, but they are not prerequisite for the induction of AVP gene transcription.

Heterogeneous distribution of basal cyclic guanosine monophosphate within distinct neuronal populations in the hypothalamic paraventricular nucleus

The supraoptic (SON) and the paraventricular (PVN) hypothalamic nuclei constitute major neuronal substrates underlying nitric oxide (NO) effects on autonomic and neuroendocrine control. Within these nuclei, constitutively produced NO restrains the firing activity of magnocellular neurosecretory and preautonomic neurons, actions thought to be mediated by a cGMP-dependent enhancement of GABAergic inhibitory transmission. In the present study, we expanded on this knowledge by performing a detailed anatomical characterization of constitutive NO-receptive, cGMP-producing neurons within the PVN. To this end, we combined tract-tracing techniques and immunohistochemistry to visualize cGMP immunoreactivity within functionally, neurochemically, and topographically discrete PVN neuronal populations in Wistar rats. Basal cGMP immunoreactivity was readily observed in the PVN, both in neuronal and vascular profiles. The incidence of cGMP immunoreactivity was significantly higher in magnocellular (69%) compared with preautonomic ( approximately 10%) neuronal populations (P < 0.01). No differences were observed between oxytocin (OT) and vasopressin (VP) magnocellular neurons. In preautonomic neurons, the incidence of cGMP was independent of their subnuclei distribution, innervated target (i.e., intermediolateral cell column, nucleus tractus solitarii, or rostral ventrolateral medulla) or their neurochemical phenotype (i.e., OT or VP). Finally, high levels of cGMP immunoreactivity were observed in GABAergic somata and terminals within the PVN of eGFP-GAD67 transgenic mice. Altogether, these data support a highly heterogeneous distribution of basal cGMP levels within the PVN and further support the notion that constitutive NO actions in the PVN involve intricate cell-cell interactions, as well as heterogeneous signaling modalities.

Water-deprivation-induced expression of neuronal nitric oxide synthase in the hypothalamic paraventricular nucleus of rat

This study was conducted to define the molecular mechanism by which dehydration induces expression of neuronal nitric oxide synthase (nNOS) in the hypothalamic paraventricular nucleus (PVN). Rats were deprived from water for 48 hr and then sacrificed immediately or 1 hr after ad libitum access to water. Another group of rats had free access to food and water and was included as euhydrate control group. The PVN sections fixed with 4% paraformaldehyde were processed for nNOS immunohistochemistry and NADPH-diaphorase (NADPH-d)/pCREB or NADPH-d/c-Fos double staining. nNOS-ir neurons significantly increased with water deprivation and decreased with rehydration, both in the posterior magnocellular (pM)- and the medial parvocellular (mP)-PVN. Most NADPH-d histostained neurons in the PVN appeared to exhibit pCREB-ir as well. Water deprivation markedly increased, and rehydration decreased, NADPH-d/pCREB neurons both in the pM- and in the mP-PVN. Gel shift assay demonstrated that dehydration may promote CREB binding to nNOS promoter in the PVN neurons. Significant amounts of NADPH-d-stained neurons in the PVN of water-deprived rats (67-68% in both the mP and the pM) exhibited c-Fos-ir. NADPH-d/c-Fos neurons in the pM-PVN were increased by water deprivation but not changed by rehydration. NADPH-d/c-Fos double-stained neurons in the mP-PVN did not significantly change depending on different water conditions. These results suggest that pCREB may play a role in dehydration-induced nNOS gene expression in the PVN neurons, and c-Fos might not be implicated in the regulatory pathway.

Gene regulation system of vasopressin and corticotropin-releasing hormone

The neurohypophyseal hormones, arginine vasopressin and corticotropin-releasing hormone (CRH), play a crucial role in the physiological and behavioral response to various kinds of stresses. Both neuropeptides activate the hypophysial-pituitary-adrenal (HPA) axis, which is a central mediator of the stress response in the body. Conversely, they receive the negative regulation by glucocorticoid, which is an end product of the HPA axis. Vasopressin and CRH are closely linked to immune response; they also interact with pro-inflammatory cytokines. Moreover, as for vasopressin, it has another important role, which is the regulation of water balance through its potent antidiuretic effect. Hence, it is conceivable that vasopressin and CRH mediate the homeostatic responses for survival and protect organisms from the external world.

A tight and elaborate regulation system of the vasopressin and CRH gene is required for the rapid and flexible response to the alteration of the surrounding environments. Several important regulatory elements have been identified in the proximal promoter region in the vasopressin and CRH gene. Many transcription factors and intracellular signaling cascades are involved in the complicated gene regulation system. This review focuses on the current status of the basic research of vasopressin and CRH. In addition to the numerous known facts about their divergent physiological roles, the recent topics of promoter analyses will be discussed.

In vivo brain-derived neurotrophic factor release and tyrosine kinase B receptor expression in the supraoptic nucleus after osmotic stress stimulus in rats

Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophin family involved in plasticity and neuroprotective processes. In recent years, we have reported the presence of BDNF mRNA in the supraoptic nucleus (SON) as well its sensitivity to osmotic stress. The rat SON is a relatively homogenous nucleus mainly consisting of magnocellular soma with their dendritic processes. BDNF may be released from dendrites to the extracellular space to stimulate tyrosine kinase (Trk) B receptors which are hypothetically present on these subcellular SON compartments. The main goal of this work was thus to study the presence and the in vivo BDNF-IR release from SON using the push-pull perfusion technique following systemic (i.p.) or local (within the SON) osmotic stimulation. BDNF was detected by immunocytochemistry and its release was measured by immunological assay (ELISA). Likewise, TrkB receptor localization in the SON-mRNA and their respective proteins-were studied by in situ hybridization and immunohistofluorescence techniques, respectively. Phosphorylation of CREB was detected by immunohistofluorescence. We present here direct evidence of in vivo dendritic BDNF release from SON which is highly sensitive to osmotic stress. The osmotic response latency period clearly depends on the mode of stimulus application (210 min for i.p. route vs. 15 min for intra-SON administration). The fact that BDNF is released as a very rapid peak when osmotic stimulation is locally applied is strong evidence in favor of an intra-SON origin of this secretion. Osmotic stress also increased phosphorylated cAMP response element binding protein immunoreactivity in the SON. In addition, we show in control rats that truncated forms of tyrosine kinase B receptor 2 mRNA represent the most abundant messenger in the SON as compared with brain-derived neurotrophic factor full-length catalytic receptor or truncated forms of tyrosine kinase B receptor 1 mRNA. In conclusion, it is likely that BDNF and their receptors are involved in neuronal plasticity changes induced by osmotic stress in the SON.

Distribution of transcription factor inducible cyclicAMP early repressor (ICER) in rodent brain and pituitary

In morphogenetic dynamics of neurons, and in adaptive physiology of brain function, transcription factors of the cyclicAMP signaling pathway, such as activator cyclicAMP responsive element binding protein (CREB) and inhibitor inducible cyclicAMP early repressor (ICER), play an important role. In particular, the presence of the transcription factor ICER in neurons or neuroendocrine cells suggests the need for the gating of an up-regulated gene expression. Little is known, however, about the natural distribution of the inhibitory transcription factor ICER. We, therefore, mapped the rodent brain and pituitary for an ICER immunoreaction and found a nuclear staining for this transcription factor. ICER-positive glial cells were found throughout the brain. ICER-positive neurons were found in sensory input centers, like the olfactory bulb, or sensory brain stem nuclei, and in hypothalamic nuclei involved in central neuroendocrine control. In addition, neuroendocrine/endocrine transducers, like the pituitary and the pineal gland showed a high basal presence of ICER. Our data show that a basic ICER level is required by many cell systems and can be seen as an anticipatory and/or a protective measure in systems with superior reactive dynamics.

Neural activity protects hypothalamic magnocellular neurons against axotomy-induced programmed cell death

Axotomy typically leads to retrograde neuronal degeneration in the CNS. Studies in the hypothalamo-neurohypophysial system (HNS) have suggested that neural activity is supportive of magnocellular neuronal (MCN) survival after axotomy. In this study, we directly test this hypothesis by inhibiting neural activity in the HNS, both in vivo and in vitro, by the use of tetrodotoxin (TTX). After median eminence compression to produce axonal injury, unilateral superfusion of 3 microM TTX into the rat supraoptic nucleus (SON), delivered with the use of a miniature osmotic pump for 2 weeks in vivo, produced a decrease in the number of surviving MCNs in the TTX-treated SON, compared with the contralateral untreated side of the SON. In vitro application of 2.5 microM TTX for 2 weeks to the SON in organotypic culture produced a 73% decrease in the surviving MCNs, compared with untreated control cultures. Raising the extracellular KCl in the culture medium to 25 mM rescued the MCNs from the axotomy- and TTX-induced cell death. These data support the proposal that after axotomy, neural activity is neuroprotective in the HNS.

Sodium chloride regulation of the alpha epithelial amiloride-sensitive sodium channel (alphaENaC) gene requires syntheses of new protein(s)

The epithelial amiloride-sensitive sodium channel (ENaC) plays a central role in sodium homeostasis and blood pressure control. The molecular effect of high sodium intake on the ENaC gene is not well known. This study examined the effects of high salt (HS) intake on alphaENaC gene transcription in rat kidney. Rats were injected intraperitoneally with hypertonic (1.5M NaCl) or normal saline solution (three rats per group). The serum sodium concentration of rats injected with hypertonic saline increased significantly 30 min after injection (158 +/- 2 mM versus 140 +/- 1 mM for normal saline injected rats and 139 +/- 1 mM for uninjected rats). At 3 h after injection, serum sodium decreased (144 +/- 1 mM) but remained above the control values (139 +/- 1 mM for normal saline injected rats, 139 +/- 1 mM for uninjected rats). The serum aldosterone decreased 1.5 and 3 h after the hypertonic saline injection (217 +/- 10 and 139 +/- 23 pg/ml for hypertonic saline injected rats, 358 +/- 2 pg/ml for uninjected rats). The kidney cortex was dissected macroscopically and total RNA was isolated at 1.5 and 3 h after treatment. Semi-quantitative RT-PCR studies revealed that following hypertonic saline treatment, alphaENaC mRNA levels were dramatically downregulated, compared with controls, as early as 1.5h. Western blot analysis showed similar patterns of protein downregulation. Inhibition of protein synthesis by cycloheximide (CHX) blocked the sodium chloride-induced alphaENaC mRNA downregulation, 3h after treatment. This indicates that synthesis of new, uncharacterized protein(s) is required for sodium chloride-mediated inhibition of alphaENaC gene transcription.

Phosphorylated cyclic AMP response element binding protein expression induced in the periaqueductal gray by predator stress: its relationship to the stress experience, behavior and limbic neural plasticity

Electrophysiological studies in cats and recently in rats implicate neuroplasticity in the periaqueductal gray (PAG) and its afferents in stressor-induced increases in fearful behavior and anxiety-like behavior (ALB). Such increases may model aspects of affective changes following traumatic stress in humans. The present study explored the role of neuroplasticity in PAG and its connection with the central nucleus of the amygdala (ACE) in male rodent anxiety-like response to predator stress. In the first of two studies, the effects of predator stress on the induction of phosphorylated cyclic AMP response element binding protein (pCREB) were investigated. pCREB expression in the PAG and ventromedial hypothalamus (VMH) was examined immunohistochemically. Predator stress increased the degree of pCREB expression in PAG cells (measured densitometrically) but did not increase the number of cells expressing pCREB (measured stereologically). Moreover, predator stress-specific increase in pCREB-like immunoreactivity (lir) was restricted to the right lateral column of the PAG. In addition, pCREB lir in the right lateral column likely reflects aspects of the stress experience because the stressor (cat behavior) and the response to the stressor (rat defensive behavior) are highly predictive of degree of pCREB expression. There was no effect of predator stress on pCREB lir in the VMH. Because pCREB expression has been associated with long-lasting potentiation (LLP) of neural transmission, we examined the effects of predator stress on transmission in the ACE-PAG pathway in a second study. Predator stress elevated evoked potential measures of ACE-PAG transmission in the right hemisphere but not in the left hemisphere 11-12 days after predator stress. This finding is consistent with the longer-lived effects of pharmacological stress on amygdalo-PAG transmission in the right hemisphere but not in the left hemisphere in cats. Of interest is the fact that the same aspects of the stressor experience and reaction to it, which are predictive of the degree of pCREB expression, are also highly predictive of the degree of potentiation of measures of ACE-PAG transmission. Behavioral analyses revealed that the most consistent effects of predator stress are on behavior in the plus maze (open arm exploration and risk assessment) and on startle. In addition, covariance analysis suggests that ACE-PAG potentiation mediates some but not all of the changes in ALB produced by predator stress. Because pCREB expression may be a precursor to neuroplastic changes in certain forms of memory and LLP, the present findings complement studies in the cat, showing that neuroplastic changes in the PAG underlie changes in affect following stress. Furthermore, these findings suggest that neuroplastic changes in PAG may be important mediators of predator stress-induced changes in affective behavior in rodents. Finally, consistent with cat and human studies, the right hemisphere appears particularly important in long-term response to stress.

Sustained increases in activating transcription factor-2 and activator protein-2 in the rat supraoptic nucleus during water deprivation

During increases in plasma osmolality, extrinsic and intrinsic stimuli converge on the neuroendocrine cells within the supraoptic nucleus (SON) and paraventricular nucleus and evoke the release of vasopressin (VP). This release is accompanied by an increase in VP synthesis, but the signal transduction pathways that coordinate these two processes are still poorly understood. Several transcription factors have been suggested to be intermediates in this process, but their expression is often transient in spite of continued VP synthesis. Transcription factor expression during chronic neuroendocrine cell stimulation has rarely been examined. In an effort to identify sustained increases, we examined the expression of several transcription factors in the SON of normal rats and rats deprived of water for 44 h. Alpha and beta isoforms of activator protein-2 (AP-2 alpha; AP-beta), activating transcription factor-2 (ATF-2), the phosphorylated form of cyclic AMP response element binding protein and phospho-cJun were all expressed in the rat SON under basal conditions. Increases in AP-2 alpha and ATF-2 were sustained throughout the SON during water deprivation, suggesting that these transcription factors could play a role in the maintenance of VP and oxytocin gene transcription in response to dehydration.

Anatomical markers of activity in neuroendocrine systems: are we all 'fos-ed out'?

It has now been nearly 15 years since the immediate early gene, c-fos, and its protein product, Fos, were introduced as tools for determining activity changes within neurones of the nervous system. In the ensuing years, this approach was applied to neuroendocrine study with success. With it have come advances in our understanding of which neuroendocrine neurones respond to various stimuli and how other central nervous system components interact with neuroendocrine neurones. Use of combined tract-tracing approaches, as well as double-labelling for Fos and transmitter markers, have added to characterization of neuroendocrine circuits. The delineation of the signal transduction cascades that induce Fos expression has led to establishment of the relationship between neurone firing and Fos expression. Importantly, we can now appreciate that Fos expression is often, but not always, associated with increased neuronal firing and vice versa. There are remaining gaps in our understanding of Fos in the nervous system. To date, knowledge of what Fos does after it is expressed is still limited. The transience of Fos expression after stimulation (especially if the stimulus is persistent) complicates design of experiments to assess the function of Fos and makes Fos of little value as a marker for long-term changes in neurone activity. In this regard, alternative approaches must be sought. Useful alternative approaches employed to date to monitor neuronal changes in activity include examination of (i) signal transduction intermediates (e.g. phosphorylated CREB); (ii) transcriptional/translational intermediates (e.g. heteronuclear RNA, messenger RNA (mRNA), prohormones); and (iii) receptor translocation. Another capitalizes on the fact that many neuroendocrine systems show striking stimulus-transcription coupling in the regulation of their transmitter or its synthetic enzymes. Together, as we move into the 21st Century, the use of multiple approach to study activity within neuroendocrine systems will further our understanding of these important systems.

Gene regulation in the magnocellular hypothalamo-neurohypophysial system

The hypothalamo-neurohypophysial system (HNS) is the major peptidergic neurosecretory system through which the brain controls peripheral physiology. The hormones vasopressin and oxytocin released from the HNS at the neurohypophysis serve homeostatic functions of water balance and reproduction. From a physiological viewpoint, the core question on the HNS has always been, "How is the rate of hormone production controlled?" Despite a clear description of the physiology, anatomy, cell biology, and biochemistry of the HNS gained over the last 100 years, this question has remained largely unanswered. However, recently, significant progress has been made through studies of gene identity and gene expression in the magnocellular neurons (MCNs) that constitute the HNS. These are keys to mechanisms and events that exist in the HNS. This review is an inventory of what we know about genes expressed in the HNS, about the regulation of their expression in response to physiological stimuli, and about their function. Genes relevant to the central question include receptors and signal transduction components that receive and process the message that the organism is in demand of a neurohypophysial hormone. The key players in gene regulatory events, the transcription factors, deserve special attention. They do not only control rates of hormone production at the level of the gene, but also determine the molecular make-up of the cell essential for appropriate development and physiological functioning. Finally, the HNS neurons are equipped with a machinery to produce and secrete hormones in a regulated manner. With the availability of several gene transfer approaches applicable to the HNS, it is anticipated that new insights will be obtained on how the HNS is able to respond to the physiological demands for its hormones.

Alterations of AP-1 and CREB protein DNA binding in rat supraoptic and paraventricular nuclei by acute and repeated hyperosmotic stress

Electrophoretic mobility shift assays were used to analyze Fos and CREB protein-DNA-interactions in the rat hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei. After intraperitoneal administration of normal saline, PVN (but not SON) extracts exhibited a significant 183% increase in binding to the activational protein-1 (AP-1) canonical DNA binding sequence. Hypertonic saline treatment resulted in a approximately 2.5-fold increase in binding by tissue samples from both regions. AP-1 binding by SON extracts after two hypertonic saline injections caused a 307% increase in binding that was significantly greater than binding by PVN extracts (207%). Fos binding was equal in the SON after one and two hypertonic saline injections, but the PVN exhibited less of an increase after two injections. Binding to the canonical cyclic adenosine monophosphate regulatory element (CRE), and phosphorylated CREB (pCREB) supershift binding, indicated pCREB is constitutively expressed. Any experimental treatment (handling and an injection) caused an elevation in binding in the PVN. AP-1 protein complex DNA binding was increased after osmotic stimulation, and SON and PVN exhibit differences in AP-1 DNA binding kinetics, after repeated hypertonic saline stress. Changes in PVN tissue samples were subtle, and may reflect the fact that magnocellular and parvocellular neurons mediate, respectively, fluid homeostasis and stress responses.

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.

Identification of phosphorylated form of cAMP/calcium response element binding protein expression in the brain stem nuclei at early stage of vestibular compensation in rats

The present study was aimed at evaluating the time-dependent expressions of phosphorylated forms in the cAMP/calcium response element binding protein (pCREB) known to be one of transcription factors for immediate early genes in the brain stem nuclei of Sprague-Dalwey rats. Animals received surgical ablation of right peripheral vestibular labyrinth through a ventral approach. Immunohistochemical staining and digital image analysis systems were used to observe pCREB expressions in neuronal cells of the brain stem nuclei. The number of pCREB labeling neurons were increased with time, and peaked in the vestibular nuclear complex (VNC) bilaterally 1 h after unilateral labyrinthectomy (UL). In addition, high levels of phosphorylated CREB-like immunoreactivity (pCREB-LI) were also observed in bilateral cerebellum, olivary nuclear complex, and medullary nuclei. There was a rapid reduction of pCREB-LI in contralateral VNC but a slow reduction in the ipsilateral side 2 h after UL, causing an asymmetric number of pCREB labeling neurons between bilateral VNC (P<0.05). Thereafter pCREB-LI in bilateral VNC decreased to a very low level and returned to basal level 24 h after UL. These results suggest that the activation of the cAMP/calcium response element binding protein plays a role in the initial events of vestibular compensation in rats.

Brain mechanisms of mammalian fluid homeostasis: insights from use of immediate early gene mapping

A comprehensive review of the literature through mid-1997 is presented on the application of immediate early gene mapping to problems related to brain mechanisms of fluid homeostasis and cardiovascular regulation in mammals. First, the basic mechanisms of fluid intake and the principles and pitfalls of immediate early gene mapping are briefly introduced. Then, data from several principal paradigms are reviewed. These include fluid deprivation and intracellular dehydration, both of which are associated with thirst and water intake. The contributions of peripheral sodium receptors, and of both hindbrain and forebrain integrative mechanisms are evaluated. Extracellular dehydration, and associated aspects of both thirst and sodium appetite are then reviewed. The contributions of both structures along the lamina terminalis and the hypothalamic magnocellular neurosecretory groups figure prominently in most of these paradigms. Effects of hypotension and hypertension are discussed, including data from the endogenous generation and the exogenous application of angiotensin II. Lastly, we summarize the contribution of the early gene mapping technique and consider briefly the prospects for new advances using this method.

Differential stimulation of c-fos expression in hypothalamic nuclei of the rat brain during short-term heat acclimation and mild dehydration

Activation of central nervous structures involved in the perception and integration of thermo- and osmoregulatory signals was investigated in the Sabra rat. Male rats were either non-treated (C-E), water-deprived for 24 h (C-D), short-term acclimated to 34 degrees C for two days (STHA-E) or subjected to both stimuli (STHA-D). Immunoreactivity for c-Fos protein (Fos-IR) as marker for neuronal activation was quantified in (extra-)hypothalamic structures: organum vasculosum laminae terminalis (OVLT); subfornical organ (SFO); medial (MPA), ventromedial preoptic (VMPO) and lateral hypothalamic (LHA) areas; median preoptic (MnPO), magnocellular supraoptic (SON) and paraventricular (mPVN) nuclei; limbic lateral septal (LS) and thalamic paraventricular (PV) nuclei. Compared to C-E rats, dehydration markedly increased Fos-IR exclusively in neurons of the OVLT, SFO and MnPO known to be involved in osmoreception, in the mPVN and SON, and to a minor extent in the VMPO. The VMPO, MPA, LHA and LS-important (extra-)hypothalamic sites for the perception and integration within the thermoregulatory control circuit-exhibited intense elevation of Fos-IR upon short-term heat acclimation. Of all (extra-)hypothalamic structures involved in central osmoregulation, only the MnPO revealed heat-induced Fos-IR in numerous cells located preferentially in its rostral component. Thus, the MnPO proved to be activated during both thermal and osmotic stimulations applied separately. Subjected to the combined stress (STHA-D), most brain structures investigated showed striking Fos-IR due to thermally enhanced osmotic stimulation, with additive effects demonstrated in the MnPO. The data support differential central activation of c-fos expression due to thermal or osmotic stimulations, with the MnPO acting as putative integrative center for both autonomic control circuits.

Patterns of neuronal activation during development of sodium sensitive hypertension in SHR

The effects of regular (RNa) or high (HNa) sodium diet for 3, 7, and 14 days on Fra-like immunoreactivity (Fra-LI) in the brains of Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) were examined using an antibody that recognizes all known members of the Fos family (Fos, Fos-B, Fra-1, and Fra-2). Two weeks of HNa significantly exacerbated hypertension in SHR but had no effects in WKY. On RNa, compared with WKY, SHR showed higher Fra-LI in the median preoptic nucleus, supraoptic nucleus, both parts of the paraventricular nucleus, nucleus of the solitary tract, and central gray. Fra-LI in the subfornical organ did not differ between the two strains. On RNa, Fra-LI in the anterior hypothalamic area could be detected only in WKY. In osmoregulatory areas, HNa diet increased Fra-LI in both SHR and WKY to comparable extents, but in the median preoptic nucleus, Fra-LI was increased to a greater extent in SHR. HNa produced smaller increases in the subfornical organ of SHR compared with WKY. In both the parvocellular and magnocellular paraventricular nuclei, increases in Fra-LI by HNa were more pronounced in SHR than in WKY. In the anterior hypothalamic area, Fra-LI could no longer be detected in WKY on HNa, whereas it appeared in SHR. HNa increased Fra-LI in the NTS and central gray to similar levels in WKY and SHR. These results indicate that WKY and SHR differ in the pattern of neuronal activation accompanying maturation on RNa. HNa activates neurons in a number of brain areas, and the pattern of these changes also differs between WKY and SHR.

Resetting the biological clock: mediation of nocturnal CREB phosphorylation via light, glutamate, and nitric oxide

Synchronization between the environmental lighting cycle and the biological clock in the suprachiasmatic nucleus (SCN) is correlated with phosphorylation of the Ca2+/cAMP response element binding protein (CREB) at the transcriptional activating site Ser133. Mechanisms mediating the formation of phospho-CREB (P-CREB) and their relation to clock resetting are unknown. To address these issues, we probed the signaling pathway between light and P-CREB. Nocturnal light rapidly and transiently induced P-CREB-like immunoreactivity (P-CREB-lir) in the rat SCN. Glutamate (Glu) or nitric oxide (NO) donor administration in vitro also induced P-CREB-lir in SCN neurons only during subjective night. Clock-controlled sensitivity to phase resetting by light. Glu, and NO is similarly restricted to subjective night. The effects of NMDA and nitric oxide synthase (NOS) antagonists on Glu-mediated induction of P-CREB-lir paralleled their inhibition of phase shifting. Significantly, among neurons in which P-CREB-lir was induced by light were NADPH-diaphorase-positive neurons of the SCN's retinorecipient area. Glu treatment increased the intensity of a 43 kDa band recognized by anti-P-CREB antibodies in subjective night but not day, whereas anti-alpha CREB-lir of this band remained constant between night and day. Inhibition of NOS during Glu stimulation diminished the anti-P-CREB-lir of this 43 kDa band. Together, these data couple nocturnal light, Glu, NMDA receptor activation and NO signaling to CREB phosphorylation in the transduction of brief environmental light stimulation of the retina into molecular changes in the SCN resulting in phase resetting of the biological clock.

CREB phosphorylation in the nucleus of the solitary tract and parabrachial nucleus is not altered by peripheral cholecystokinin that induces c-Fos

Ca ++/cAMP response element binding protein (CREB), phosphoCREB, and c-Fos-like (c-FL) immunoreactivity (IR) were examined in the nucleus of the solitary tract (NTS) and parabrachial nucleus (PBN) after peripheral cholecystokinin (CCK). c-FLIR was observed only after CCK, but CCK did not alter high basal levels of CREB-IR and phosphoCREB-IR. PhosphoCREB may be necessary but is not sufficient to induce c-Fos after CCK injection.

Expression of activating transcription factor-2 (ATF-2), one of the cyclic AMP response element (CRE) binding proteins, in Alzheimer disease and non-neurological brain tissues

Cyclic AMP response element (CRE) is a specific DNA sequence which mediates transcriptional activation in the response to the cyclic AMP-activated and protein kinase A dependent signaling pathway. We examined the localization of one of the CRE binding proteins which is preferentially expressed in the brain, activating transcription factor-2 (ATF-2), by immunohistochemistry and Southwestern histochemistry, using the brains of neurologically normal and Alzheimer disease (AD) cases. In all brains, the anti-ATF-2 antibody stained white matter microglial cells. In AD, the cytoplasm of some cortical neurons was also positively stained, but no such staining was seen in the neocortex in non-neurological cases staining. However, both the nuclei and cytoplasm of some hippocampal neurons were positive in non-neurological brain tissues. In AD, except for severely damaged areas such as CA1, positive neuronal staining was seen. Southwestern histochemistry gave the same results as immunohistochemistry. These data suggest that the localization of ATF-2 in cortical neurons in AD may reflect early pathological changes characteristic of AD, and that these histochemistrical methods may allow one to differentiate between healthy and mildly damaged neurons.

Pontine cholinergic neurons show Fos-like immunoreactivity associated with cholinergically induced REM sleep

Recently, we showed c-fos expression in pontine nuclei in association with cholinergically induced REM sleep (REMc). Pontine cholinergic mechanisms have been implicated in the orchestration of the phasic and tonic events underlying REM sleep. Therefore, in the present study, we examined whether pontine cholinergic neurons demonstrate Fos-like immunoreactivity (Fos-LI) following cholinergically induced, sustained rapid-eye movement (REMc) sleep in cats. Microinjections (0.25 microliter) of vehicle (n = 2) or carbachol (n = 3; 2.0 micrograms/0.25 microliter) were made into the medial pontine reticular formation. Carbachol produced a state with all the signs of natural REM sleep, and with durations ranging from 27 to 40.1 min. Animals were killed immediately after the end of REMc. Compared to vehicle treated animals (0.9% saline), the animals with REMc showed a significantly higher number of Fos-LI cells in pontine regions implicated in REM sleep generation. More importantly, 11.2% (SEM +/- 0.83) of cholinergic neurons in the lateral dorsal tegmental (LDT) and pedunculopontine tegmental (PPT) nuclei were determined to be also Fos-LI positive. In the vehicle treated animals very few Fos-LI cells were found and none of these were found to be cholinergic. These findings indicate that during REMc a transcriptional cascade involving c-fos occurs in a subpopulation of pontine cholinergic neurons.

Activation of ventrolateral preoptic neurons during sleep

The rostral hypothalamus and adjacent basal forebrain participate in the generation of sleep, but the neuronal circuitry involved in this process remains poorly characterized. Immunocytochemistry was used to identify the FOS protein, an immediate-early gene product, in a group of ventrolateral preoptic neurons that is specifically activated during sleep. The retrograde tracer cholera toxin B, in combination with FOS immunocytochemistry, was used to show that sleep-activated ventrolateral preoptic neurons innervate the tuberomammillary nucleus, a posterior hypothalamic cell group thought to participate in the modulation of arousal. This monosynaptic pathway in the hypothalamus may play a key role in determining sleep-wake states.