Detecting steroidal effects on immediate early gene expression in the hypothalamus

Context-Dependent Role of Glucocorticoid Receptor Alpha and Beta in Breast Cancer Cell Behaviour

Background. The dual role of GCs has been observed in breast cancer; however, due to many concomitant factors, GR action in cancer biology is still ambiguous. In this study, we aimed to unravel the context-dependent action of GR in breast cancer. Methods. GR expression was characterized in multiple cohorts: (1) 24,256 breast cancer specimens on the RNA level, 220 samples on the protein level and correlated with clinicopathological data; (2) oestrogen receptor (ER)-positive and -negative cell lines were used to test for the presence of ER and ligand, and the effect of the GRβ isoform following GRα and GRβ overexpression on GR action, by in vitro functional assays. Results. We found that GR expression was higher in ER- breast cancer cells compared to ER+ ones, and GR-transactivated genes were implicated mainly in cell migration. Immunohistochemistry showed mostly cytoplasmic but heterogenous staining irrespective of ER status. GRα increased cell proliferation, viability, and the migration of ER- cells. GRβ had a similar effect on breast cancer cell viability, proliferation, and migration. However, the GRβ isoform had the opposite effect depending on the presence of ER: an increased dead cell ratio was found in ER+ breast cancer cells compared to ER- ones. Interestingly, GRα and GRβ action did not depend on the presence of the ligand, suggesting the role of the "intrinsic", ligand-independent action of GR in breast cancer. Conclusions. Staining differences using different GR antibodies may be the reason behind controversial findings in the literature regarding the expression of GR protein and clinicopathological data. Therefore, caution in the interpretation of immunohistochemistry should be applied. By dissecting the effects of GRα and GRβ, we found that the presence of the GR in the context of ER had a different effect on cancer cell behaviour, but independently of ligand availability. Additionally, GR-transactivated genes are mostly involved in cell migration, which raises GR's importance in disease progression.

Neuronal aromatase expression in pain processing regions of the medullary and spinal cord dorsal horn

In both acute and chronic pain conditions, women tend to be more sensitive than men. This sex difference may be regulated by estrogens, such as estradiol, that are synthesized in the spinal cord and brainstem and act locally to influence pain processing. To identify a potential cellular source of local estrogen, here we examined the expression of aromatase, the enzyme that catalyzes the conversion of testosterone to estradiol. Our studies focused on primary afferent neurons and on their central targets in the spinal cord and medulla as well as in the nucleus of the solitary tract, the target of nodose ganglion-derived visceral afferents. Immunohistochemical staining in an aromatase reporter mouse revealed that many neurons in laminae I and V of the spinal cord dorsal horn and caudal spinal trigeminal nucleus and in the nucleus of the solitary tract express aromatase. The great majority of these cells also express inhibitory interneuron markers. We did not find sex differences in aromatase expression and neither the pattern nor the number of neurons changed in a sciatic nerve transection model of neuropathic pain or in the Complete Freund's adjuvant model of inflammatory pain. A few aromatase neurons express Fos after cheek injection of capsaicin, formalin, or chloroquine. In total, given their location, these aromatase neurons are poised to engage nociceptive circuits, whether it is through local estrogen synthesis or inhibitory neurotransmitter release.

Hypothalamic L-Histidine Decarboxylase Is Up-Regulated During Chronic REM Sleep Deprivation of Rats

A competition of neurobehavioral drives of sleep and wakefulness occurs during sleep deprivation. When enforced chronically, subjects must remain awake. This study examines histaminergic neurons of the tuberomammillary nucleus of the posterior hypothalamus in response to enforced wakefulness in rats. We tested the hypothesis that the rate-limiting enzyme for histamine biosynthesis, L-histidine decarboxylase (HDC), would be up-regulated during chronic rapid eye movement sleep deprivation (REM-SD) because histamine plays a major role in maintaining wakefulness. Archived brain tissues of male Sprague Dawley rats from a previous study were used. Rats had been subjected to REM-SD by the flowerpot paradigm for 5, 10, or 15 days. For immunocytochemistry, rats were transcardially perfused with acrolein-paraformaldehyde for immunodetection of L-HDC; separate controls used carbodiimide-paraformaldehyde for immunodetection of histamine. Immunolocalization of histamine within the tuberomammillary nucleus was validated using carbodiimide. Because HDC antiserum has cross-reactivity with other decarboxylases at high antibody concentrations, titrations localized L-HDC to only tuberomammillary nucleus at a dilution of ≥ 1:300,000. REM-SD increased immunoreactive HDC by day 5 and it remained elevated in both dorsal and ventral aspects of the tuberomammillary complex. Our results suggest that up-regulation of L-HDC within the tuberomammillary complex during chronic REM-SD may be responsible for maintaining wakefulness.

The Importance of Titrating Antibodies for Immunocytochemical Methods

When using immunocytochemistry, investigators may not know how to optimize staining or how to troubleshoot the method when staining fails. Lacking are guides for comparing techniques and applying information derived from one staining method to another. Newer methods amplify signal detection, but will not necessarily work at the same primary antibody concentrations used for less sensitive reactions. Recommendations of optimal titers are often not accurate and are not usually accompanied by information on the method used to test those antibodies or the specifics of the assay. When the staining does not work, the investigators do not know how to determine if the antiserum is bad, the tissue is bad, or the method is inappropriate for their staining. This unit describes detailed procedures for determining optimal staining and applying that information to three common immunofluorescence methods. Lastly, a formula is provided for converting among the different methods. © 2016 by John Wiley & Sons, Inc.

Activation of neurokinin 3 receptors in the median preoptic nucleus decreases core temperature in the rat

Estrogens have pronounced effects on thermoregulation, as illustrated by the occurrence of hot flushes secondary to estrogen withdrawal in menopausal women. Because neurokinin B (NKB) gene expression is markedly increased in the infundibular (arcuate) nucleus of postmenopausal women, and is modulated by estrogen withdrawal and replacement in multiple species, we have hypothesized that NKB neurons could play a role in the generation of flushes. There is no information, however, on whether the primary NKB receptor [neurokinin 3 receptor (NK(3)R)] modulates body temperature in any species. Here, we determine the effects of microinfusion of a selective NK(3)R agonist (senktide) into the rat median preoptic nucleus (MnPO), an important site in the heat-defense pathway. Senktide microinfusion into the rat MnPO decreased core temperature in a dose-dependent manner. The hypothermia induced by senktide was similar in ovariectomized rats with and without 17β-estradiol replacement. The hypothermic effect of senktide was prolonged in rats exposed to an ambient temperature of 29.0 C, compared with 21.5 C. Senktide microinfusion also altered tail skin vasomotion in rats exposed to an ambient temperature of 29.0 but not 21.5 C. Comparisons of the effects of senktide at different ambient temperatures indicated that the hypothermia was not secondary to thermoregulatory failure or a reduction in cold-induced thermogenesis. Other than a very mild increase in drinking, senktide microinfusion did not affect behavior. Terminal fluorescent dextran microinfusion showed targeting of the MnPO and adjacent septum, and immunohistochemical studies revealed that senktide induced a marked increase in Fos-activation in the MnPO. Because MnPO neurons expressed NK(3)R-immunoreactivity, the induction of MnPO Fos by senktide is likely a direct effect. By demonstrating that NK(3)R activation in the MnPO modulates body temperature, these studies support the hypothesis that hypothalamic NKB neurons could be involved in the generation of menopausal flushes.

Comparison of the temporal programs regulating tyrosine hydroxylase and enkephalin expressions in TIDA neurons of lactating rats following pup removal and then pup return

Dopamine (DA) and enkephalin (ENK) release from the tuberoinfundibular dopaminergic neurons (TIDA) into the hypophysial portal circulation is fundamentally different under non-lactating and lactating conditions. The aim of this experiment was to compare the effect of a brief interruption then resumption of suckling on the temporal program of tyrosine hydroxylase (TH; rate-limiting enzyme of dopamine synthesis) and ENK regulation in dams. On post partum day 10, pups were removed for a 4-h period from a group of the dams then returned for 4- and 24-h periods. It was examined whether such a brief interruption of suckling provokes full up-regulation of TH and down-regulation of ENK, and whether reinitiation of suckling limits the extent to which TH up- and ENK down-regulate. At the end of experiment, the animals were decapitated. In situ hybridization was used to examine the expression of TH and ENK mRNA in the arcuate nucleus where TIDA neurons reside. The results showed that, on one hand, the removal of pups induced TH up-regulation, on the other hand, ENK expression also increased 8 h after removal of pups and then started to slowly decline. In dams whose sucklings were reinitiated both TH and ENK mRNAs were up-regulated at least for a day. ENK expression responded more slowly to the removal of pups than expression of TH, and after reinitiation of suckling, the temporal program of regulation of both TH and ENK expressions ran parallel in the first 24 h.

A mouse model of the fragile X premutation: effects on behavior, dendrite morphology, and regional rates of cerebral protein synthesis

Carriers of FMR1 premutation alleles have 55-200 CGG repeats in the 5' untranslated region of the gene. These individuals are at risk for fragile X associated primary ovarian insufficiency (females) and, in late life, fragile X associated tremor and ataxia syndrome (males, and to a lesser extent, females). Premutation carrier status can also be associated with autism spectrum disorder, attention deficit hyperactivity disorder, and some cognitive deficits. In premutation carriers, FMR1 mRNA levels are often higher than those with normal sized alleles. In contrast, in subjects with full mutation alleles, (>200 repeats) the FMR1 gene is silenced and FMR1 mRNA and its product, FMRP, are absent. We have studied a male knock-in (KI) mouse model of the fragile X premutation (120-140 repeats) during young adulthood. In comparison to wild type, KI mice were hyperactive, exhibited less anxiety in both the open field and the elevated zero maze, were impaired on the passive avoidance test, and showed some subtle deficits on a test of social interaction. Motor learning as assessed by the rotarod test was normal. Dendritic arbors were less complex and spine densities and lengths increased in medial prefrontal cortex, basal lateral amygdala, and hippocampus compared with wild type. Regional rates of cerebral protein synthesis measured in vivo in KI mice were increased. KI mice also had elevated levels of Fmr1 mRNA and decreased levels of FMRP. Our results highlight similarities in phenotype between KI and Fmr1 knockout mice and suggest that the decreased concentration of FMRP contributes to the phenotype in young adult KI mice.

Expression of fos and in vivo median eminence release of LHRH identifies an active role for preoptic area kisspeptin neurons in synchronized surges of LH and LHRH in the ewe

We tested the working hypothesis that Fos will identify the critical population of kisspeptin neurons that accompanies the LHRH surge using a synchronized follicular phase model in intact cycling ewes. The model generates an LH surge that starts within a defined 2-h window in a 20-d synchronized cycle. With a modified push-pull cannula in vivo LHRH release from the median eminence was sampled in luteal phase ewes, ewes undergoing an LH surge for 2-4 h, and postsurge animals whose LH surge peaked 10-12 h earlier. In vivo release of LHRH was lower in the luteal and follicular phases than in animals undergoing an LH surge (P < 0.01); it fell to presurge levels after the LH surge. Ewes killed 2-4 h after the surge started, expressed Fos in a large portion of preoptic area (POA) kisspeptin (53.90 ± 4.69%, P < 0.01) and LHRH neurons (48.20 ± 4.49%, P < 0.0001) compared with animals euthanized at any of the other times tested (under <5% of the cells activated). Little Fos activation (under 5%) was observed during any of the times sampled in arcuate (Arc) kisspeptin neurons. The relationship between the number of LHRH neurons and the POA kisspeptin neurons stimulated showed a striking positive correlation with r(2) = 0.68, P = 0.0003, reinforcing the evidence that POA kisspeptin neurons actively participate in the stimulation of LHRH surges.

A direct neuronal connection between the subparafascicular and ventrolateral arcuate nuclei in non-lactating female rats. Could this pathway play a role in the suckling-induced prolactin release?

The neuronal pathways, through which prolactin secretion is regulated during lactation, have still not been fully explored. Studies indicate that the suckling stimulus travels through the spinal cord, the brain stem, and then reaches the hypothalamus. The focus of this present experiment is to further explore the neuronal connections between the brain stem and the arcuate nucleus that may be involved in suckling-induced prolactin release. Ante- and retrograde tracing techniques were used. To chemically characterize the explored neurons neuropeptide immunohistochemistry was applied. Previous studies have indicated that the peripeduncular nucleus is a relay of the suckling stimulus in the midbrain, conveying the information to the hypothalamus. In our experiments, we have found an additional cell group in the subparafascicular parvocellular nucleus located just behind the posterior thalamus that projects to the arcuate neurons. The injection of the retrograde tracer into the ventrolateral part of the arcuate nucleus labeled cells in the lateral subdivision of the subparafascicular parvocellular nucleus. Anterograde tracing from the subparafascicular parvocellular nucleus resulted in fiber labeling in the arcuate nucleus in close apposition with dynorphin immunopositive neurons. Double labeling revealed that a subpopulations of the subparafascicular parvocellular neurons projecting to the arcuate nucleus contained tuberoinfundibular peptide of 39 residues or calcitonin gene-related peptide. The presented findings suggest that the ascending fibers from the subparafascicular parvocellular nucleus might be in the pathway involved in the suckling-induced prolactin release.

The importance of titrating antibodies for immunocytochemical methods

When using immunocytochemistry, investigators may not know how to optimize staining or how to troubleshoot the method when staining fails. Lacking are guides for comparing techniques and applying information derived from one staining method to another. Newer methods amplify signal detection, but will not necessarily work at the same primary antibody concentrations used for less sensitive reactions. Recommendations of optimal titers are often not accurate and are not usually accompanied by information on the method used to test those antibodies or the specifics of the assay. When the staining does not work, the investigators do not know how to determine if the antiserum is bad, the tissue is bad, or the method is inappropriate for their staining. This unit describes detailed procedures for determining optimal staining and applying that information to three common immunofluorescence methods. Lastly, a formula is provided for converting among the different methods.

Blockade of NK3R signaling in the PVN decreases vasopressin and oxytocin release and c-Fos expression in the magnocellular neurons in response to hypotension

Tachykinin neurokinin 3 receptor (NK3R) signaling has a broad role in vasopressin (VP) and oxytocin (OT) release. Hydralazine (HDZ)-induced hypotension activates NK3R expressed by magnocellular neurons, increases plasma VP and OT levels, and induces c-Fos expression in VP and OT neurons. Intraventricular pretreatment with the specific NK3R antagonist, SB-222200, eliminates the HDZ-stimulated VP and OT release. NK3R are distributed in the central pathways conveying hypotension information to the magnocellular neurons, and the NK3R antagonist could act anywhere in the pathways. Alternatively, the antagonist could act at the NK3R expressed by the magnocellular neurons. To determine whether blockade of NK3R on magnocellular neurons impairs VP and OT release to HDZ, rats were pretreated with a unilateral PVN injection of 0.15 M NaCl or SB-222200 prior to an intravenous injection of 0.15 M NaCl or HDZ. Blood samples were taken, and brains were processed for VP/c-Fos and OT/c-Fos immunohistochemistry. Intravenous injection of 0.15 M NaCl did not alter plasma hormone levels, and little c-Fos immunoreactivity was present in the PVN. Conversely, intravenous injection of HDZ increased plasma VP and OT levels and c-Fos expression in VP and OT magnocellular neurons. Intra-PVN injection of SB-222200 prior to an intravenous injection of HDZ significantly decreased c-Fos expression in both VP and OT neurons by approximately 70% and attenuated plasma VP and OT levels by 33% and 35%, respectively. Therefore, NK3R signaling in magnocellular neurons has a critical role for the release of VP and OT in response to hypotension.

Temporal and spatial regulation of CRE recombinase expression in gonadotrophin-releasing hormone neurones in the mouse

Gonadotrophin-releasing hormone (GnRH) neurones located within the brain are the final neuroendocrine output regulating the reproductive hormone axis. Their small number and scattered distribution in the hypothalamus make them particularly difficult to study in vivo. The Cre/loxP system is a valuable tool to delete genes in specific cells and tissues. We report the production of two mouse lines that express the CRE bacteriophage recombinase in a GnRH-specific manner. The first line, the GnRH-CRE mouse, contains a transgene in which CRE is under the control of the murine GnRH promoter and targets CRE expression specifically to GnRH neurones in the hypothalamus. The second line, the GnRH-CRETeR mouse, uses the same murine GnRH promoter to target CRE expression to GnRH neurones, but is modified to be constitutively repressed by a tetracycline repressor (TetR) expressed from a downstream tetracycline repressor gene engineered within the transgene. GnRH neurone-specific CRE expression can therefore be induced by treatment with doxycycline which relieves repression by TetR. These GnRH-CRE and GnRH-CRETeR mice can be used to study the function of genes expressed specifically in GnRH neurones. The GnRH-CRETeR mouse can be used to study genes that may have distinct roles in reproductive physiology during the various developmental stages.

Chronic intermittent hypoxia sensitizes acute hypothalamic-pituitary-adrenal stress reactivity and Fos induction in the rat locus coeruleus in response to subsequent immobilization stress

Obstructive sleep apnea (OSA) is associated with several pathophysiological conditions, including hypertension, obesity, insulin resistance, hypothalamic-pituitary-adrenal (HPA) dysregulation, and other endocrine and metabolic disturbances comprising the "metabolic syndrome." Repeated episodes of hypoxia in OSA may represent a chronic intermittent stress, leading to HPA dysregulation. Alterations in HPA reactivity could then contribute to or exacerbate other pathophysiological processes. We showed previously that another metabolic stressor, chronic intermittent cold stress, enhanced noradrenergic facilitation of acute HPA stress reactivity. In this study, we investigated whether chronic intermittent hypoxia (CIH), a rat model for the arterial hypoxemia that accompanies OSA, similarly sensitizes the HPA response to novel acute stress. Rats were exposed to CIH (alternating cycles of normoxia [3 min at 21% O(2)] and hypoxia [3 min at 10% O(2)], repeated continuously for 8 h/day during the light portion of the cycle for 7 days). On the day after the final CIH exposure, there were no differences in baseline plasma adrenocorticotropic hormone (ACTH), but the peak ACTH response to 30 min acute immobilization stress was greater in CIH-stressed rats than in controls. Induction of Fos expression by acute immobilization stress was comparable following CIH in several HPA-modulatory brain regions, including the paraventricular nucleus, bed nucleus of the stria terminalis, and amygdala. Fos induction was attenuated in lateral hypothalamus, an HPA-inhibitory region. By contrast, acute Fos induction was enhanced in noradrenergic neurons in the locus coeruleus following CIH exposure. Thus, similar to chronic cold stress, CIH sensitized acute HPA and noradrenergic stress reactivity. Plasticity in the acute stress response is important for long-term adaptation, but may also contribute to pathophysiological conditions associated with states of chronic or repeated stress, such as OSA. Determining the neural mechanisms underlying these adaptations may help us better understand the etiology of such disorders, and inform the development of more effective treatments.

Normoxic ventilatory resuscitation following controlled cortical impact reduces peroxynitrite-mediated protein nitration in the hippocampus

OBJECTIVES

Ventilatory resuscitation with 100% O2 after severe traumatic brain injury (TBI) raises concerns about the increased production of reactive oxygen species (ROS). The product of peroxynitrite-meditated tyrosine residue nitration, 3-nitrotyrosine (3-NT), is a marker for oxidative damage to proteins. The authors hypothesized that posttraumatic resuscitation with hyperoxia (100% fraction of inspired oxygen [FiO2] concentration) results in increased ROS-induced damage to proteins compared with resuscitation using normoxia (21% FiO2 concentration).

METHODS

Male Sprague-Dawley rats underwent controlled cortical impact (CCI) injury and resuscitation with either normoxic or hyperoxic ventilation for 1 hour (5 rats per group). Twenty-four hours after injury, rat hippocampi were evaluated using 3-NT immunostaining. In a second experiment, animals similarly underwent CCI injury and normoxic or hyperoxic ventilation for 1 hour (4 rats per group). One week after injury, neuronal counts were performed after neuronal nuclei immunostaining.

RESULTS

The 3-NT staining was significantly increased in the hippocampi of the hyperoxic group. The normoxic group showed a 51.0% reduction of staining in the CA1 region compared with the hyperoxic group and a 50.8% reduction in the CA3 region (p < 0.05, both regions). There was no significant difference in staining between the injured normoxic group and sham-operated control groups. In the delayed analysis of neuronal survival (neuronal counts), there was no significant difference between the hyperoxic and normoxic groups.

CONCLUSIONS

In this clinically relevant model of TBI, normoxic resuscitation significantly reduced oxidative damage to proteins compared with hyperoxic resuscitation. Neuronal counts showed no benefit from hyperoxic resuscitation. These findings indicate that hyperoxic ventilation in the early stages after severe TBI may exacerbate oxidative damage to proteins.

Effects of congenital hydrocephalus on the hypothalamic gonadotrophin-releasing hormone system

Object

Despite the investigations that have linked hydrocephalus to reproductive system abnormalities, no researchers have attempted to identify the pathophysiological mechanism of this relationship. Because the role of the hypothalamic gonadotrophin-releasing hormone (GnRH) system in the regulation of reproductive functions is well established, the authors used immunohistochemical and radioimmunoassay (RIA) techniques to determine the morphological and biochemical effects of hydrocephalus on the hypothalamic GnRH system.

Methods

Hypothalamic GnRH levels, fiber density, and cell types were studied in 21- and 50-day-old control and congenitally hydrocephalic Texas rats. Results of RIA indicated a significant (8.4%) increase in GnRH in 21-day-old hydrocephalic rats (9.17 ± 0.64 pg/ng total protein) compared with that in controls (0.97 ± 0.74 pg/ng total protein). In addition, the 50-day-old hydrocephalic animals had a significantly higher level of GnRH compared with age-matched controls (20.4 pg/ng compared with 1.88 ± 2.1 pg/ng total protein). This increase was accompanied by changes in the fiber appearance and a shift from low GnRH producing cells to high GnRH producing cells in the hydrocephalic animals; however, there was no significant difference in the fiber density between the control and hydrocephalic animals at 21 days. In addition, poor neurological scores correlated with the severity of hydrocephalus.

Conclusions

These results demonstrated that hypothalamic GnRH levels are significantly affected by fetal-onset hydrocephalus and that the mechanisms responsible for these effects may take place at the cellular rather than the gross structural level. Furthermore, they suggest that impairments in the GnRH system may be protracted in neonates and infants with hydrocephalus, and thus may be overcome by relatively early treatment with ventricular diversion. However, the clinical implications of GnRH perturbations in shunt-dependent patients must await a forthcoming study in shunted animals.

Regional FMRP deficits and large repeat expansions into the full mutation range in a new Fragile X premutation mouse model

Carriers of FMR1 alleles with 55-200 repeats in the 5' UTR are at risk for Fragile X associated tremor and ataxia syndrome. The cause of the neuropathology is unknown but is thought to be RNA-mediated. Maternally transmitted premutation alleles are also at risk of expansion of the repeat tract into the "full mutation" range (>200 repeats). The mechanism responsible for expansion is unknown. Full mutation alleles produce reduced amounts of the FMR1 gene product, FMRP, which leads to Fragile X mental retardation syndrome. We have developed a murine model for Fragile X premutation carriers that recapitulates key features seen in humans including a direct relationship between repeat number and Fmr1 mRNA levels, an inverse relationship with FMRP levels and Purkinje cell dropout that have not been seen in a previously described knock-in mouse model. In addition, these mice also show a differential deficit of FMRP in different parts of the brain that might account for symptoms of the full mutation that are seen in premutation carriers. As in humans, repeat instability is high with expansions predominating and, for the first time in a mouse model, large expansions into the full mutation range are seen that occur within a single generation. Thus, contrary to what was previously thought, mice may be good models not only for the symptoms seen in human carriers of FMR1 premutation alleles but also for understanding the mechanism responsible for repeat expansion, a phenomenon that is responsible for a number of neurological and neurodevelopmental disorders.

Taste-evoked Fos expression in nitrergic neurons in the nucleus of the solitary tract and reticular formation of the rat

The current investigation used double labeling for NADPHd and Fos-like immunoreactivity to define the relationship between nitric oxide synthase-containing neural elements and taste-activated neurons in the nucleus of the solitary tract (NST) and subjacent reticular formation (RF). Stimulation of awake rats with citric acid and quinine resulted in significant increases in the numbers of double-labeled neurons in both the NST and RF, suggesting that some medullary gustatory neurons utilize nitric oxide (NO) as a transmitter. Overall, double-labeled neurons were most numerous in the caudal reaches of the gustatory zone of the NST, where taste neurons receive inputs from the IXth nerve, suggesting a preferential role for NO neurons in processing gustatory inputs from the posterior oral cavity. However, double-labeled neurons also exhibited a preferential distribution depending on the gustatory stimulus. In the NST, double-labeled neurons were most numerous in the rostral central subnucleus after either stimulus but had a medial bias after quinine stimulation. In the RF, after citric acid stimulation, there was a cluster of double-labeled neurons with distinctive large soma in the parvicellular division of the lateral RF, subjacent to the rostral tip of NST. In contrast, in response to quinine, there was a cluster of double-labeled neurons with much smaller soma in the intermediate zone of the medial RF, a few hundred micrometers caudal to the citric acid cluster. These differential distributions of double-labeled neurons in the NST and RF suggest a role for NO in stimulus-specific gustatory autonomic and oromotor reflex circuits.

Normoxic resuscitation after cardiac arrest protects against hippocampal oxidative stress, metabolic dysfunction, and neuronal death

Resuscitation and prolonged ventilation using 100% oxygen after cardiac arrest is standard clinical practice despite evidence from animal models indicating that neurologic outcome is improved using normoxic compared with hyperoxic resuscitation. This study tested the hypothesis that normoxic ventilation during the first hour after cardiac arrest in dogs protects against prelethal oxidative stress to proteins, loss of the critical metabolic enzyme pyruvate dehydrogenase complex (PDHC), and minimizes subsequent neuronal death in the hippocampus. Anesthetized beagles underwent 10 mins ventricular fibrillation cardiac arrest, followed by defibrillation and ventilation with either 21% or 100% O2. At 1 h after resuscitation, the ventilator was adjusted to maintain normal blood gas levels in both groups. Brains were perfusion-fixed at 2 h reperfusion and used for immunohistochemical measurements of hippocampal nitrotyrosine, a product of protein oxidation, and the E1alpha subunit of PDHC. In hyperoxic dogs, PDHC immunostaining diminished by approximately 90% compared with sham-operated dogs, while staining in normoxic animals was not significantly different from nonischemic dogs. Protein nitration in the hippocampal neurons of hyperoxic animals was 2-3 times greater than either sham-operated or normoxic resuscitated animals at 2 h reperfusion. Stereologic quantification of neuronal death at 24 h reperfusion showed a 40% reduction using normoxic compared with hyperoxic resuscitation. These results indicate that postischemic hyperoxic ventilation promotes oxidative stress that exacerbates prelethal loss of pyruvate dehydrogenase and delayed hippocampal neuronal cell death. Moreover, these findings indicate the need for clinical trials comparing the effects of different ventilatory oxygen levels on neurologic outcome after cardiac arrest.

Distribution of hypothalamic, hippocampal and other limbic peptidergic neuronal cell bodies giving rise to retinopetal fibers: anterograde and retrograde tracing and neuropeptide immunohistochemical studies

In our present work utilizing the retrograde or anterograde transport of tracers (biotinylated dextran amine and Fluorogold, respectively) we have provided direct evidence for the cells of origin of the limboretinal pathway in rats and their termination in the retina using light microscopic approach. Administration of biotinylated dextran amine into the vitreous body resulted in nerve cell body labeling in several structures: the supraoptic and paraventricular nuclei, the hippocampus (CA1, CA3), the dentate gyrus, the indusium griseum, the olfactory tubercle, and the medial habenula, all of them belong to the limbic system. We estimated that the total number of retrogradely labeled cells is 1495+/-516. We have seen fiber labeling in the retinorecipient suprachiasmatic nucleus and in the primary visual center, the lateral geniculate body, but labeled nerve cell bodies in these structures were never seen. Iontophoretic application of Fluorogold into the hippocampal formation, where the major part of the biotinylated dextran amine-labeled cell bodies was observed, resulted in labeled fibers in the optic nerve and in the retina indicating that the retrogradely labeled cells in the hippocampus and the dentate gyrus among others are the cells of origin of the centrifugal visual fibers. Sections showing biotinylated dextran amine labeling were stained for vasoactive intestinal polypeptide, pituitary adenylate cyclase activating polypeptide or luteinizing hormone-releasing hormone immunoreactivity using immunohistochemistry. Some biotinylated dextran amine-labeled cells also showed vasoactive intestinal polypeptide, pituitary adenylate cyclase activating polypeptide or luteinizing hormone-releasing hormone immunoreactivity. We conclude that the limboretinal pathway exists and that the cells of origin are partially vasoactive intestinal polypeptide, pituitary adenylate cyclase activating polypeptide or luteinizing hormone-releasing hormone immunoreactive.

Changes in hypothalamic corticotropin-releasing hormone, neuropeptide Y, and proopiomelanocortin gene expression during chronic rapid eye movement sleep deprivation of rats

Chronic rapid eye movement (paradoxical) sleep deprivation (REM-SD) of rats leads to two conspicuous pathologies: hyperphagia coincident with body weight loss, prompted by elevated metabolism. Our goals were to test the hypotheses that 1) as a stressor, REM-SD would increase CRH gene expression in the hypothalamus and that 2) to account for hyperphagia, hypothalamic gene expression of the orexigen neuropeptide Y (NPY) would increase, but expression of the anorexigen proopiomelanocortin (POMC) would decrease. Enforcement of REM-SD of adult male rats for 20 d with the platform (flowerpot) method led to progressive hyperphagia, increasing to approximately 300% of baseline; body weight steadily declined by approximately 25%. Consistent with changes in food intake patterns, NPY expression rapidly increased in the hypothalamic arcuate nucleus by d 5 of REM-SD, peaking at d 20; by contrast, POMC expression decreased progressively during REM-SD. CRH expression was increased by d 5, both in mRNA and ability to detect neuronal perikaryal staining in paraventricular nucleus with immunocytochemistry, and it remained elevated thereafter with modest declines. Taken together, these data indicate that changes in hypothalamic neuropeptides regulating food intake are altered in a manner consistent with the hyperphagia seen with REM-SD. Changes in CRH, although indicative of REM-SD as a stressor, suggest that the anorexigenic actions of CRH are ineffective (or disabled). Furthermore, changes in NPY and POMC agree with current models of food intake behavior, but they are opposite to their acute effects on peripheral energy metabolism and thermogenesis.

Estrogen and progesterone do not activate Fos in AVPV or LHRH neurons in male rats

In rodents, females but not males, in response to escalating levels of estrogen, express a luteinizing hormone (LH) surge that is prompted by a surge in luteinizing hormone-releasing hormone (LHRH). It cannot take place if estrogen-sensitive afferents located in the anteroventral periventricular nucleus (AVPV) are either absent or disabled. Males appear to lack the ability to exhibit an LH surge, but it is unclear what level of the CNS contributes to this dimorphic response. This study was conducted to determine whether estrogen followed by progesterone treatment (E + P) of gonadectomized males evokes Fos activation in LHRH and AVPV neurons as it does in females. The results indicated that, consistent with the males' inability to express an LH surge in response to E + P treatment, LHRH and AVPV neurons in males failed to show increased Fos activation. Examination of neuron nuclear antigen (NeuN, a neuron-specific marker), estrogen receptor (ERalpha) and progesterone receptor (PR) neurons in AVPV neurons indicated that, while essentially all the neurons of the caudal AVPV in males and females are steroid responsive, the male possessed half the number of steroid responsive neurons within the caudal AVPV (where activation of Fos is maximal in females) compared to the female. Together, these data indicate that the male lacks a substantial population of steroid receptive AVPV neurons and is unable to respond to the presence of E and P and activate either AVPV or LHRH neurons.

The effects of osmotic stimulation and water availability on c-Fos and FosB staining in the supraoptic and paraventricular nuclei of the hypothalamus

We studied the effects of osmotic stimulation on the expression of FosB and c-Fos in the supraoptic nucleus (SON) and paraventricular nucleus (PVN). Adult male rats were divided into two groups that were injected with lidocaine (0.1-0.2 ml sc) followed by either 0.9% or 6% NaCl (1 ml/100 g bw sc). After the NaCl injections, the rats were anesthetized and perfused 2, 6, or 8 h after the injections. Their brains were prepared for immunocytochemistry and stained with FosB and c-Fos antibodies. The number of c-Fos-positive cells was significantly increased only at 2 h in the SON and PVN. In contrast, the number of FosB-positive cells was significantly increased at 6, and 8 h in both the SON and PVN. In a second experiment, the effect of water availability on FosB staining 8 h after injections of 6% NaCl was tested in 3 groups of rats: water ad libitum, rats that had no access to water, and rats that were given water 2 h prior to perfusion. FosB staining was significantly reduced in both the SON and the PVN of rats that had ad libitum water compared to the two water-restricted groups. In the third experiment, rats were injected with either 0.9% NaCl or 6% NaCl and were either given ad libitum access to water or water restricted for 6 h after the injections and perfused 24 h after the saline injections. FosB staining was not increased when water was available ad libitum. FosB staining was significantly increased at 24 h in the rats injected with 6% NaCl when water was restricted. Thus, FosB may continue to influence protein expression in the SON and PVN for at least 24 h following acute osmotic stimulation.

Quinine and citric acid elicit distinctive Fos-like immunoreactivity in the rat nucleus of the solitary tract

The present experiment investigated Fos-like immunoreactivity (FLI) in the nucleus of the solitary tract (NST) after intraoral infusions of 0.1 M citric acid, 0.3 M NaCl, and 0.3-30 mM quinine monohydrochloride (QHCl) in awake, behaving rats. Increases in QHCl concentration produced increases in the numbers of FLI-labeled neurons in the rostral part of the intermediate (i(r)) and rostral (r) NST, but the topographic distribution of FLI was consistent across QHCl concentrations and distinctive compared with effects of citric acid. Quinine elicited FLI concentrated in the medial third of the nucleus; acid elicited more broadly distributed FLI concentrated farther laterally. Surprisingly, in contrast to QHCl and citric acid, NaCl produced FLI that was indistinguishable from that produced by water. Although the functional significance of these patterns is unknown, citric acid and QHCl are nonpreferred stimuli but produced different oromotor behaviors. QHCl (30 mM) elicited approximately 3.2 times as many gapes as citric acid (0.1 M), and acid elicited more ingestive responses. Parallel differences in FLI expression suggest that different NST regions may have distinctive roles in triggering oromotor behaviors.

Reporter gene assays for algal-derived toxins

We have modified the cell-based directed cytotoxicity assay for sodium channel and calcium channel active phycotoxins using a c-fos-luciferase reporter gene construct. In this report we describe the conceptual basis to the development of reporter gene assays for algal-derived toxins and summarize both published and unpublished data using this method. N2A mouse neuroblastoma cells, which express voltage-dependent sodium channels, were stably transfected with the reporter gene c-fos-luc, which contains the firefly luciferase gene under the transcriptional regulation of the human c-fos response element. The characteristics of the N2A reporter gene assay were determined by dose response with brevetoxin and ciguatoxin. Brevetoxin-1 and ciguatoxin-1 induced c-fos-luc with an EC50 of 4.6 and 3.0 ng ml(-1), respectively. Saxitoxin caused a concentration-dependent inhibition of brevetoxin-1 induction of c-fos-luc with an EC50 of 3.5 ng ml(-1). GH4C1 rat pituitary cells, which lack voltage-dependent sodium channels but express voltage-dependent calcium channels, were also stably transfected with the c-fos-luc. GH4C1 cells expressing c-fos-luciferase were responsive to maitotoxin (1 ng ml(-1)) and a putative toxin produced by Pfiesteria piscicida. Although reporter gene assays are not designed to replace existing detection methods used to measure toxin activity in seafood, they do provide a valuable means to screen algal cultures for toxin activity, to conduct assay-guided fractionation and to characterize pharmacologic properties of algal toxins.

Loss of luteinizing hormone surges induced by chronic estradiol is associated with decreased activation of gonadotropin-releasing hormone neurons

Chronic exposure of young ovariectomized rats to elevated circulating estradiol causes loss of steroid-induced LH surges. Such LH surges are associated with cFos-induced activation of GnRH neurons; therefore, we hypothesized that chronic estradiol treatment abolishes LH surges by decreasing activation of GnRH neurons. Regularly cycling rats were ovariectomized and immediately received an estradiol implant or remained untreated. Three days or 2 or 4 wk later, the estradiol-treated rats received vehicle or progesterone at 1200 h, and 7 hourly blood samples were collected for RIA of LH. Thereafter, all rats were perfused, and the brains were examined for immunocytochemical localization of cFos and GnRH. The GnRH neurons from untreated ovariectomized rats rarely expressed cFos. As reported, LH surges induced by 3 days of estradiol treatment were associated with a 30% increase in cFos-containing GnRH neurons, and progesterone enhanced both the amplitude of LH surges and the proportion of cFos-immunopositive GnRH neurons. As hypothesized, the abolition of LH surges caused by 2 or more weeks of estradiol was paralleled by a reduction in the percentage of cFos-containing GnRH neurons, and this effect was delayed by progesterone. These results suggest that chronic estradiol abolishes steroid-induced LH surges in part by inactivating GnRH neurons.

Intact osmoregulatory centers in the preterm ovine fetus: Fos induction after an osmotic challenge

We previously demonstrated a functional systemic dipsogenic response in the near-term fetal sheep (128-130 days; 145 days = full-term) with swallowing activity stimulated in response to central and systemic hypertonic saline. Preterm fetal sheep (110-115 days) do not consistently demonstrate swallowing in response to hypertonic stimuli, and it is unclear whether this is due to immaturity of osmoreceptor mechanisms or neuronal pathways activating swallowing motor neurons. To determine whether osmoreceptive regions in the preterm fetus are activated by changes in plasma tonicity, we examined Fos expression with immunostaining in these neurons in response to an osmotic challenge. Nine preterm fetal sheep [five hypertonic saline-treated fetuses (Hyp) and four isotonic saline-treated fetuses (Iso)] were prepared with vascular and intraperitoneal catheters. Seventy-five minutes before tissue collection, hypertonic (1.5 M) or isotonic saline was infused (12 ml/kg) via an intraperitoneal catheter to fetuses. Brains were examined for patterns of neuronal activation (demonstrated by Fos protein expression). Hyp demonstrated increases in plasma osmolality (~10 mosmol/kg H(2)O) and Na concentrations (5 meq/l). Increased Fos expression was detected in Hyp in the organum vasculosum of the lamina terminalis (OVLT), subfornical organ (SFO), median preoptic nucleus (MnPO), supraoptic (SON), and paraventricular nuclei (PVN) compared with Iso animals. Neuronal activation within the OVLT, SFO, and MnPO indicates intact osmoregulatory mechanisms, whereas activation of the SON and PVN suggests intact fetal neural pathways to arginine vasopressin neurons. These results suggest that preterm fetal swallowing insensitivity to osmotic stimuli may be due to immaturity of integrated motor neuron pathways.

Parallel declines in Fos activation of the medial anteroventral periventricular nucleus and LHRH neurons in middle-aged rats

The middle-age decline in reproductive function is manifested by reduced LHRH release, resulting in a decreased magnitude and delay of onset of the LH surge. Earlier studies suggested that the reductions in LHRH neural activation in middle-aged rats resulted from deficits in the afferent drive to the LHRH neurons. One critical afferent to the LHRH neurons lies in the anteroventral periventricular preoptic area (AVPv) nucleus. The neurons of the medial AVPv are synchronously activated to express Fos with LHRH neurons at the time of an LH surge in young adult animals. The present study examined whether, in middle age, reductions in the activation of AVPv neurons accompany the reduction in Fos activation in LHRH neurons. Young (3- to 4-month-old) and middle-aged (10- to 12-month-old) spontaneously cycling and ovariectomized steroid-replaced rats were killed during peak and early descending phase of the LH surge, and their brains were examined for Fos in LHRH and AVPv neurons. Young animals had a characteristic increase in Fos expression in both LHRH and AVPv neurons. In middle-aged rats, the proportion of LHRH neurons expressing Fos at the time of an LH surge was reduced by approximately 50%, irrespective of whether surges were spontaneous or induced by exogenous steroids. A similar reduction in the number of Fos+ cells (by approximately 50%) was noted in the medial AVPv. Linear regression analysis of the relationship between the extent of Fos activation in LHRH and AVPv neurons revealed a strong positive correlation (r(2) = 0.66; P < 0.01), suggesting that changes in the AVPv's drive to LHRH neurons underlie the decrease in LHRH activity in middle age. A second series of experiments examined whether decreased input from the AVPv could account for reduced Fos activation in LHRH neurons seen in middle-aged animals. When the medial AVPv was lesioned, LHRH neurons failed to express Fos on the side ipsilateral to the lesion. Animals with lesioned medial AVPv also had significantly lower LH values than animals with an intact medial AVPv. Taken together, these data suggest that a principal deficit in middle-aged rats is the ability of the medial AVPv to stimulate LHRH neurons.

Suckling stimulus suppresses messenger RNA for tyrosine hydroxylase in arcuate neurons during lactation

Tyrosine hydroxylase (TH) mRNA in tuberoinfundibular dopamine (TIDA) neurons is suppressed during lactation but rebounds upon pup removal. A time course of TH mRNA changes after pup removal revealed three phases: (1) a nuclear phase (evident 1.5 hours after pup removal, maximal at 3 hours) with TH mRNA appearing in 1 or 2 nuclear loci with little or no change in cytoplasmic mRNA; (2) a cytoplasmic phase (noted 6 hours after pup removal, peaked 12-24 hours) with a significant increase in total TH mRNA levels mainly in the cytoplasm; and (3) a stabilization phase (24-48 hours after pup removal) when nuclear signals were low and cytoplasmic RNA showed a slight decline with extension of RNA clusters into the cell dendrites. In rats whose pups could suckle only on one side, TH was up-regulated only on the side contralateral to nipple blockade. These data indicate that after suckling terminates, TH up-regulation is evident at 1.5 hours, but 6 hours is needed before the cells transport sufficient mRNA into the cytoplasm. The rapid signaling of TH up-regulation stems from the fact that the TIDA neurons respond to neural signals from termination of suckling.

Differential distribution of Fos expression within the male rat preoptic area and hypothalamus in response to physical vs. psychological stress

Recent studies on stress-induced adrenal glucocorticoid secretion have demonstrated quantitatively different effects of individual stress stimuli on hormone release, suggesting that the hypothalamic-pituitary-adrenal axis exhibits discriminative, rather than ubiquitous responses to such challenges, particularly psychological vs. physical stressors. The immediate-early gene, cfos, is expressed by central nervous system neurons in response to numerous physiological stimuli, including stress. The following study investigated whether the distribution and/or intensity of immunolabeling for Fos in the preoptic area and hypothalamus differ after imposition of stressors of variable intensity. Groups of male rats were sacrificed by transcardial perfusion 2 h after (1) transfer to a novel environment (NE stress), (2) confinement within a restraint tube (REST stress), or (3) immobilization (IM) stress. Nonstressed controls remained undisturbed in their home cages. Whereas the NE-stress group exhibited Fos immunoreactivity (ir) only within anterior and lateroanterior hypothalamus, both physical stressors induced immunostaining for Fos in the lateral preoptic area, median preoptic, paraventricular, arcuate, dorsomedial hypothalamic nuclei, and lateral hypothalamus, while numbers of Fos-ir-positive neurons were generally greater in the IM vs. REST stress group. In the IM-stressed rats, additional Fos-ir was observed in the supraoptic and suprachiasmatic nuclei. These studies show that neurons expressing Fos-ir in response to the relatively mild stress of novel environment are distributed differently than those that are transcriptionally activated by more aversive stressors. Findings that Fos-ir occurs in several common sites following exposure to REST or IM stress suggest that local neuron populations may comprise a common neural pathway(s) that is activated by intense forms of stress.

Sleep deprivation-induced c-fos and junB expression in the rat brain: effects of duration and timing

Expression of the immediate-early genes (IEGs) c-fos and junB in the rat brain was studied in response to sleep deprivation (SD) starting at four time points during the light phase of a 12:12 light:dark cycle. Animals were confined to slowly rotating wheels for 3 or 6 h in order to prevent sleep. The numbers of c-Fos- and JunB-immunoreactive cells were assessed in seven brain regions previously reported to respond to SD with increased c-fos expression (medial preoptic area (MPA), cortex, anterior and posterior paraventricular thalamic nuclei, amygdala, caudate-putamen, and laterodorsal tegmental nucleus). While c-Fos was induced by SD in all regions studied, there were differences in levels of induction depending on the duration of deprivation and on the timing of the deprivation period during the light phase. The most robust induction occurred in most regions in response to 3-h deprivation periods beginning 3 h into the light phase. A similarly timed peak of induction was observed in the MPA and cortex after 6 h of SD. In two regions, the posterior paraventricular thalamic nucleus and amygdala, 6 h of deprivation induced greater c-Fos immunoreactivity than did 3 h of deprivation, collapsed across all phases tested. Increased JunB immunoreactivity in response to either duration of deprivation was more limited and was significant only in the MPA, cortex, caudate-putamen and amygdala. c-Fos and JunB immunoreactivity in the paraventricular hypothalamic nucleus was low and similar in control and deprived animals. These results indicate that both duration of prior wakefulness and time of day influence the extent of IEG expression differentially in brain regions responsive to SD. The results also suggest that the posterior paraventricular thalamic nucleus and amygdala might be primarily responsive to length of wakefulness (sleep drive), while the MPA and anterior paraventricular thalamic nucleus might integrate input related to both homeostatic sleep drive and circadian clock influences on sleep regulation.

Effects of selective sinoaortic denervations on phenylephrine-induced activational responses in the nucleus of the solitary tract

Intravenous administration of phenylephrine provokes a pattern of cellular activation in the nucleus of the solitary tract that resembles the central distributions of primary baroreceptor afferents supplied by the carotid sinus and aortic depressor nerves. Transganglionic transport and denervation methods were used in an experimental setting to test the dependence of phenylephrine-induced Fos immunoreactivity on the integrity of buffer nerve afferents, and to identify the subregions of the nucleus of the solitary tract supplied by each. Cholera toxin B-horseradish peroxidase injections into either or both nerves revealed terminal labeling concentrated in, but not restricted to, the dorsal commissural part of the nucleus of the solitary tract at the level of the apex of calamus scriptorius, and extending into the dorsal subnucleus at the level of the area postrema. Preferential ramifications of carotid sinus and aortic depressor nerve afferents at the levels of the commissural part of the nucleus and the area postrema, respectively, were reflected in the extent to which labeled fibers comingled with neurons exhibiting phenylephrine-induced Fos in dual labeling experiments. Complete sinoaortic denervation reduced by 90% the number of neurons exhibiting drug-induced Fos expression. Selective carotid and aortic sinus denervations effected partial reductions manifest preferentially in the caudal and rostral foci of the distribution, respectively. Reduced activational responses at the level of the area postrema of aortic sinus-denervated rats were accompanied by a reduction in cellular nicotinamide adenine dinucleotide phosphate-diaphorase activity in this region. Animals killed 30 days after complete sinoaortic denervation displayed no evidence of recovery of phenylephrine-induced Fos, while the strength and distribution of the response in rats that received selective carotid sinus denervation were indistinguishable from those seen in controls. These findings (i) support the dependence of phenylephrine-induced Fos expression on the integrity of carotid sinus and aortic depressor nerve afferents, (ii) provide anatomical and functional evidence that the two buffer nerves distribute differentially within the nucleus of the solitary tract, and (iii) implicate central reorganization as a likely basis for functional recovery of baroreflex mechanisms following partial sinoaortic denervation.

Paradoxical activational effects of a corticotropin-releasing factor-binding protein "ligand inhibitor" in rat brain

The corticotropin-releasing factor-binding protein is distinct from known corticotropin-releasing factor receptors, but can bind the peptide and neutralize its biological actions. Recent interest has centered about the therapeutic potential of "ligand inhibitors" of binding protein action, synthetic corticotropin-releasing factor fragments which are inactive at corticotropin-releasing factor receptors, but can displace the peptide from the binding protein, thereby increasing levels of free corticotropin-releasing factor. To identify sites of action of such ligands, the distribution of Fos expression seen following intracerebroventricular administration of rat/human corticotropin-releasing factor(6-33) (5-50 microg) was charted in relation to corticotropin-releasing factor-binding protein and receptor expression. It was expected that Fos induction would mimic aspects of the distribution of the two known corticotropin-releasing factor receptors, but the far greater correspondence was seen with that of the binding protein itself. This included neurons in the isocortex, the olfactory system, amygdala and a number of discrete brainstem cell groups; many Fos-immunoreactive neurons in each were found to co-express corticotropin-releasing factor-binding protein messenger RNA. Subsets of activated neurons co-expressed Type 1 corticotropin-releasing factor receptor messenger RNA, though these were largely limited to cell groups that also express the corticotropin-releasing factor-binding protein, and where binding protein immunoreactivity and Type 1 receptor transcripts were found to co-exist. Responsive neurons displaying Type 2 corticotropin-releasing factor receptor message were seen reliably only in the lateral septal nucleus. These findings support only a limited capacity of the ligand inhibitor to activate neurons bearing corticotropin-releasing factor receptors. The more pervasive activation seen among neurons that express the corticotropin-releasing factor-binding protein may be indicative of an unexpected role for this protein in signaling by corticotropin-releasing factor-related peptides.

Divergent effects of putative anxiolytics on stress-induced fos expression in the mesoprefrontal system of the rat

Previously, we reported that R(+)HA-966, a weak partial agonist for the glycine/NMDA receptor, and guanfacine, a noradrenergic alpha2 agonist, have anxiolytic-like actions on the biochemical activation of the mesoprefrontal dopamine neurons and fear-induced behaviors. Here, we examined these two putative anxiolytic agents, both with primary actions independent of GABAergic systems, for their ability to alter stress-induced Fos-like immunoreactivity in the mesoprefrontal cortex and in tyrosine hydroxylase-stained, presumed dopaminergic, neurons in the ventral tegmental area. The benzodiazepine agonist, lorazepam, and partial agonist, bretazenil, were also tested in this footshock paradigm [10 x 0.5 sec, 0.8 mA paired with a 5-sec tone]. In saline-treated rats, footshock resulted in an increase in Fos-li in the prelimbic and infralimbic cortices and tyrosine hydroxylase-labeled cells in the ventral tegmental area. Treatment with lorazepam or bretazenil prevented the stress-induced activation in Fos-li nuclei in all regions of the medial prefrontal cortex and in dopaminergic neurons in the ventral tegmental area. In contrast, the actions of the novel anxiolytic-like agents on stress-induced Fos-li were different than those observed with benzodiazepine agonists. Both putative anxiolytics, R(+)HA-966 and guanfacine, did not reduce, but significantly enhanced the stress-induced Fos-li in the prelimbic region of the medial prefrontal cortex. Additionally, treatment with R(+)HA-966 completely blocked, while guanfacine attenuated, the stress-induced increase in the number of Fos-li, TH-li cells in the ventral tegmental area. These results indicate that the putative anxiolytics, R(+)HA-966 and guanfacine, have actions on the stress-sensitive mesoprefrontal system which appear distinct from those of traditional anxiolytics.

The Oct-2 POU domain gene in the neuroendocrine brain: a transcriptional regulator of mammalian puberty

POU homeodomain genes are transcriptional regulators that control development of the mammalian forebrain. Although they are mostly active during embryonic life, some of them remain expressed in the postnatal hypothalamus, suggesting their involvement in regulating differentiated functions of the neuroendocrine brain. We show here that Oct-2, a POU domain gene originally described in cells of the immune system, is one of the controlling components of the cell-cell signaling process underlying the hypothalamic regulation of female puberty. Lesions of the anterior hypothalamus cause sexual precocity and recapitulate some of the events leading to the normal initiation of puberty. Prominent among these events is an increased astrocytic expression of the gene encoding transforming growth factor-alpha (TGF alpha), a tropic polypeptide involved in the stimulatory control of LHRH secretion. The present study shows that such lesions result in the rapid and selective increase in Oct-2 transcripts in TGF alpha-containing astrocytes surrounding the lesion site. In both lesion-induced and normal puberty, there is a preferential increase in hypothalamic expression of the Oct-2a and Oct-2c alternatively spliced messenger RNA forms of the Oct-2 gene, with an increase in 2a messenger RNA levels preceding that in 2c and antedating the peripubertal activation of gonadal steroid secretion. Both Oct-2a and 2c trans-activate the TGF alpha gene via recognition motifs contained in the TGF alpha gene promoter. Inhibition of Oct-2 synthesis reduces TGF alpha expression in astroglial cells and delays the initiation of puberty. These results suggest that the Oct-2 gene is one of the upstream components of the glia to neuron signaling process that controls the onset of female puberty in mammals.

Fos-like immunoreactivity in the brain stem following oral quinine stimulation in decerebrate rats

The present study compared the distribution of Fos-like immunoreactivity (FLI) following intraoral stimulation with quinine monohydrochloride (QHCl) in awake intact rats to the pattern obtained in chronic supracollicular decerebrate (CD) rats. Because the behavioral rejection response to QHCl is evident in the CD rat, it was hypothesized that the pattern of FLI in the lower brain stem should be similar in both groups. Overall, the distribution of FLI in the brain stem was quite similar in both intact and CD groups, and QHCl stimulation increased FLI in the rostral (gustatory) nucleus of the solitary tract, the parabrachial nucleus (PBN), and the lateral reticular formation (RF) compared with an unstimulated control group. The CD group differed from the intact group, however, with a trend toward less FLI in the RF and a shift in the pattern of label away from the external subdivision of the PBN. CD rats also had increased FLI in the caudal nucleus of the solitary tract, with or without intraoral infusions. The distribution of QHCl-induced FLI in the brain stem of intact rats thus indicates both local sensorimotor processing as well as the influence of forebrain structures.

GABA-mediated inhibition of raphe pallidus neurons regulates sympathetic outflow to brown adipose tissue

Sympathetic nerve activity to brown adipose tissue (BAT) regulates adipocyte metabolism of its stored lipid fuel and thus the thermogenesis in BAT. To determine if the discharge of neurons in the rostral raphe pallidus (RPa) can influence BAT thermogenesis, changes in sympathetic nerve activity to BAT were recorded after microinjection (60 nl) of the GABAA receptor antagonist bicuculline (500 microM) into the RPa in chloralose-urethan-anesthetized, ventilated rats. Bicuculline caused a large, rapid rise in the sympathetic nerve activity to BAT (which had also increased during acute hypothermia) from very low, normothermic control levels to maximum values (mean: 1,949 +/- 604% control; n = 13) after 4-6 min. The sympathetic nerve discharge to BAT had a mean burst frequency (3. 5 +/- 0.3 Hz) that was significantly less than the heart rate (7.3 +/- 0.2 beats/min), and it was not inhibited during baroreceptor reflex activation. Bicuculline-stimulated increases in the sympathetic nerve activity to BAT and cold-evoked increases in neuronal fos expression were localized to the RPa at the level of the caudal half of the facial nucleus. This dramatic increase in sympathetic nerve activity to BAT after disinhibition of neurons in rostral RPa is consistent with a major role for RPa neurons, perhaps as sympathetic premotoneurons for BAT, in medullary control of BAT thermogenesis.

Central Fos expression in fetal and adult sheep after intraperitoneal hypertonic saline

We hypothesized that neural structures, involved in sensing extracellular body fluid composition in adult animals during an osmotic challenge, would show similar patterns of activation in fetal sheep. Eight adult sheep [4 hypertonic saline-treated adults (HYP-A), 4 isotonic saline-treated adults] and six near-term fetal sheep [3 hypertonic saline-treated fetuses (HYP-F), 3 isotonic saline-treated fetuses; 130 days gestation] were prepared with vascular and intraperitoneal catheters. Seventy-five minutes before tissue collection, hypertonic (1.5 M) or isotonic saline was infused via an intraperitoneal catheter to adult (18 ml/kg) or fetal sheep (6 ml/kg). Brains were examined for patterns of neuronal activation (demonstrated by Fos protein expression). HYP-A and HYP-F demonstrated similar acute increases in plasma osmolality ( approximately 10 mosmol/kgH2O) and comparable patterns of Fos expression within the organum vasculosum of the lamina terminalis (HYP-A, 67 +/- 2 vs. HYP-F, 63 +/- 6; means +/- SE) and hypothalamic supraoptic (SON; HYP-A, 107 +/- 8 vs. HYP-F, 102 +/- 7) and paraventricular nuclei (PVN; HYP-A, 71 +/- 18 vs. HYP-F, 124 +/- 19). Fewer activated neurons were detected in HYP-A vs. HYP-F within the subfornical organ (HYP-A, 33 +/- 8 vs. HYP-F, 91 +/- 17) and median preoptic nucleus (HYP-A, 33 +/- 5 vs. HYP-F, 70 +/- 6). In adults and fetuses, counterstaining for arginine vasopressin revealed that neurons within the SON and PVN respond to osmotic challenge. These findings demonstrate that central osmoregulatory centers in adult and near-term fetal sheep are similarly activated by osmotic challenge.

Periventricular preoptic area neurons coactivated with luteinizing hormone (LH)-releasing hormone (LHRH) neurons at the time of the LH surge are LHRH afferents

Earlier studies demonstrated coactivation of the periventricular preoptic area (pePOA) with LHRH neurons at the time of an induced or spontaneous LH surge, suggesting that the pePOA might regulate LHRH neurons. To investigate this hypothesis, studies were conducted to determine the temporal pattern of pePOA Fos activation during the rat estrous cycle and establish the connections of the pePOA neurons with LHRH neurons. Fos activation within LHRH and pePOA neurons showed the same temporal pattern. Both were absent during diestrous I, diestrous II, and the morning of proestrus. Fos was induced in the pePOA and LHRH neurons beginning on the afternoon of proestrus (4 h before lights off), with a decline 8 h later on proestrous evening. Tract-tracing studies then established the relationship between LHRH and pePOA neurons. Retrograde labeling with fluorogold determined that a portion of the Fos-positive pePOA neurons present at the time of the LH surge sent a projection to regions that contain LHRH cells. Anterograde tracer (neurobiotin) injections established that the pePOA neurons sent axons to the LHRH cells. Taken together, these data indicate that the pePOA provides direct input to LHRH neurons that is likely to stimulate LHRH neurons at the time of the LH surge.

The renal afferent pathways in the rat: a pseudorabies virus study

Retrograde tract tracing studies have indicated that dorsal root ganglion cells from T8 to L2 innervate the rat's left kidney. Electrophysiology studies have indicated that putative second-order sympathetic afferents are found in the dorsal horn at spinal segments T10 to L1 in laminae V-VII. Here, the spread of pseudorabies virus through renal sensory pathways was examined following 2-5 days post-infection (PI) and the virus was located immunocytochemically using a rabbit polyclonal antibody. Two days PI, dorsal root ganglion neurons (first-order sympathetic afferents) were infected with PRV. An average of 1.2, 0.8, 2.1 and 4.4% of the infected dorsal root ganglion neurons were contralateral to the injected kidney at spinal segments T10, T11, T12 and T13, respectively. Four days PI, infected neurons were detected within laminae I and II of the dorsal horn of the caudal thoracic and upper lumbar spinal cord segments. The labeling patterns in the spinal cord are consistent with previous work indicating the location of renal sympathetic sensory pathways. The nodose ganglia were labeled starting 4 days PI, suggesting the involvement of parasympathetic sensory pathways. Five days PI, infected neurons were found in the nucleus tractus solitarius. In the present study, it was unclear whether the infected neurons in the nucleus tractus solitarius are part of sympathetic or parasympathetic afferent pathways or represent a convergence of sensory information. Renal denervation prevented the spread of the virus into the dorsal root ganglia and spinal cord. Sectioning the dorsal roots from T10-L3 blocked viral spread into the spinal cord dorsal horn, but did not prevent infection of neurons in dorsal root ganglion nor did it prevent infection of putative preganglionic neurons in the intermediolateral cell column. The present results indicated that renal afferent pathways can be identified after pseudorabies virus infection of the kidney. Our results suggest that renal afferents travel in sympathetic and parasympathetic nerves and that this information may converge at the NTS.

Immunohistochemical localization of caffeine-induced c-Fos protein expression in the rat brain

Although caffeine is the most widely used central nervous system stimulant, the neuronal populations and pathways mediating its stimulant effects are not well understood. Using c-Fos protein as a marker for neuronal activation, the present study investigated the pattern of c-Fos induction at 2 hours after low locomotor-stimulant doses (1, 5, 10, and 30 mg/kg, i.p.) of caffeine and compared them with those after a higher dose (75 mg/kg, i.p.) or saline injection in adult male rats. Fos-immunoreactive neurons were counted in selected nuclei across the entire brain. Caffeine induced an increase in locomotor activity in a dose-dependent manner up to doses of 30 mg/kg and a decline at 75 mg/kg. Quantitative analysis of Fos-immunoreactive neurons indicated that no structures showed significant Fos expression at doses below 75 mg/kg or a biphasic pattern of Fos expression, as in locomotion. In contrast, caffeine at 75 mg/kg induced a significant increase compared with the saline condition in the number of Fos-immunoreactive neurons in the majority of structures examined. The structures included the striatum, nucleus accumbens, globus pallidus, and substantia nigra pars reticulata and autonomic and limbic structures including the basolateral and central nuclei of the amygdala, paraventricular and supraoptic hypothalamic nuclei, periventricular hypothalamus, paraventricular thalamic nuclei, parabrachial nuclei, locus coeruleus, and nucleus of the solitary tract. The locomotor-enhancing effects of low doses of caffeine did not appear to be associated with significant Fos expression in the rat brain.

Metabolic inhibition increases feeding and brain Fos-like immunoreactivity as a function of diet

Whether administration of 2,5-anhydro-D-mannitol (2,5-AM) or methyl palmoxirate (MP) elicits eating behavior in rats depends on the composition of the maintenance diet. To assess whether specific brain sites are involved in triggering the eating responses to these metabolic inhibitors, we measured food intake and Fos-like immunoreactivity (Fos-li) in rats maintained on either a low-fat/high-carbohydrate (LF/HC) or high-fat/low-carbohydrate (HF/LC) diet. Rats fed the LF/HC diet increased food intake after administration of 2,5-AM (200 mg/kg ip) but not after treatment with MP (10 mg/kg po), whereas rats maintained on the HF/LC diet increased food intake in response to MP administration but not after 2,5-AM injection. The effects of these inhibitors on brain Fos-li in several specific brain nuclei paralleled those on feeding behavior; that is, the number of cells showing Fos-li increased only under dietary conditions in which 2,5-AM or MP stimulated eating. These results suggest that the eating response to metabolic inhibition is tied to increased neuronal activity in brain regions that process vagal afferent signals.

Injection of corticotropin-releasing hormone into the locus coeruleus or foot shock increases neuronal Fos expression

Previous research suggests that corticotropin-releasing hormone can act in the locus coeruleus to increase the firing of locus coeruleus neurons and elicit physiological responses resembling those associated with stress. The present study used immunocytochemical detection of Fos as a measure of neuronal activation to identify brain areas that were activated by bilateral injections of corticotropin-releasing hormone into the locus coeruleus of rats. Injection of corticotropin-releasing hormone into the locus coeruleus increased the expression of Fos in the locus coeruleus as compared with injection of vehicle into the locus coeruleus or injection of corticotropin-releasing hormone into neighbouring pontine sites. The pattern of Fos expression throughout the brain after injections of corticotropin-releasing hormone into the locus coeruleus was generally consistent with the anatomical organization of efferent projections arising from the locus coeruleus; increased Fos expression was observed in many brain areas including the ventral lateral septum, septohypothalamic nucleus, bed nucleus of the stria terminalis, the central amygdaloid nucleus, the dorsomedial nuclei of the hypothalamus, and the thalamic paraventricular and rhomboid nuclei. Foot shock also increased Fos expression in the locus coeruleus and the other brain regions that expressed Fos after corticotropin-releasing hormone injections into the locus coeruleus. A few brain regions, most notably the hypothalamic paraventricular nucleus, expressed Fos in response to foot shock but not corticotropin-releasing hormone. These results indicate that local injection of corticotropin-releasing hormone into the locus coeruleus stimulates the activity of the locus coeruleus neurons. However, the pattern of Fos expression throughout the brain evoked by injection of corticotropin-releasing hormone into the locus coeruleus does not fully replicate the effects of foot shock.

Infant cold exposure changes Fos expression to acute cold stimulation in adult hypothalamic brain regions

It is known that cold exposure as an infant results in a permanent cold tolerance which is accompanied by a reduced rate of colonic temperature decline and increased metabolic heat production to cold stimulation. The present study was aimed to elucidate the central mechanism of cold tolerance of adult rats with cold exposure as infants. Newborn infants were exposed to cold ambient (4 degrees C) daily for 2 weeks, and when they were 15-weeks old, Fos expression to acute cold stimulation (10 degrees C) in whole brain regions was investigated using quantitative immunohistochemistry. Acute cold stimulation induced a significant increase of Fos-positive neurons in many nuclei of whole brain areas in adult rats both with and without cold exposure as infants. However, the number of Fos-positive neurons was significantly less in the rats with cold exposure than without cold exposure as infants, particularly in the hypothalamic nuclei such as the lateral septal nucleus (LS), preoptic area (POA), parvocellular paraventricular nucleus (pPVN0, ventromedial hypothalamic nucleus (VMH) and supramammillary nucleus (SuM). However, there was no significant difference in the number of Fos-positive neurons in the extra-hypothalamic regions between the rats with and without cold exposure as infants. These results suggest that the central mechanism of cold tolerance with cold exposure as infants is due to metabolic changes of the hypothalamic brain regions.

Immunocytochemical localization of Fos in perfused nonhuman primate brain tissue: fixation and antisera selection

Immunocytochemical localization of immediate early gene proteins, such as Fos, provides a powerful tool with which to demonstrate activated neuronal populations in response to specific stimuli. In contrast to studies using rat brain tissue that consistently show good Fos detection with a variety of antisera, studies using brain tissue from other species yield variable Fos detection. This may be partly due to differences in Fos protein sequences among species or to perfusion and fixation methods. To determine the ability of various Fos antisera to detect neuronal activation in nonhuman primate tissue, we tested nine Fos antisera and compared these antibodies under conditions of intense or physiological stimulation. Monkey brain tissue was either perfused and postfixed with 4% paraformaldehyde or perfused with 4% paraformaldehyde and postfixed with 2.5% acrolein in 4% paraformaldehyde. In rat tissue, stained for comparison, several antisera resulted in good to excellent Fos detection. However, few antisera tested in monkey tissue resulted in excellent Fos staining. We demonstrate that detection of Fos in monkey brain tissue perfused with 4% paraformaldehyde can be improved by postfixation in a dilute acrolein solution. Our findings emphasize the importance of choosing appropriate antisera and perfusion-fixation procedures to optimize Fos detection in nonhuman primate tissue.

Methyl palmoxirate increases eating behavior and brain Fos-like immunoreactivity in rats

Administration of methyl palmoxirate (MP), an inhibitor of fatty acid oxidation, stimulates eating behavior in rats. Fos immunohistochemistry was used to determine neural pathways that may play a role in the eating response to MP. The number of cells showing Fos-like immunoreactivity (Fos-li) was quantified by computerized image analysis. MP treatment, at a dose that increased food intake (10 mg/kg, p.o.), induced Fos expression in the nucleus of the solitary tract, area postrema, lateral parabrachial nucleus, central lateral nucleus of the amygdala, dorsal lateral bed nucleus of the stria terminalis, and the paraventricular nucleus of the hypothalamus. The results suggest that MP activates an afferent pathway projecting from the hindbrain to the forebrain, which may be involved in the eating response after MP treatment.

2,5-Anhydro-D-mannitol induces Fos-like immunoreactivity in hindbrain and forebrain: relationship to eating behavior

Injection of the fructose analogue, 2,5-anhydro-D-mannitol (2,5-AM), stimulates eating behavior in rats. Previous studies have shown that administration of 2,5-AM in doses that elicit eating induces Fos-like immunoreactivity (Fos-li) primarily in hindbrain structures, including the nucleus of the solitary tract (NTS), area postrema (AP), and lateral parabrachial nucleus (PBN). To more closely assess the relationship between neural activation and the eating response to 2,5-AM treatment, we measured food intake and brain Fos-li in rats given a range of doses of 2,5-AM. The numbers of neurons showing Fos-li were quantified by computerized image analysis. Doses of 2,5-AM that reliably stimulated food intake induced Fos-li in both the hindbrain and forebrain, including in the NTS, AP, lateral PBN, central lateral nucleus of the amygdala, dorsal lateral bed nucleus of the stria terminalis (BNSTdl), anterior paraventricular nucleus of the thalamus, supraoptic nucleus, subfornical organ, and paraventricular hypothalamic nuclei. A low dose of 2,5-AM that did not elicit eating increased Fos-li marginally only in the AP, PBN, and BNSTdl. The results suggest that 2,5-AM treatment activates a vagal afferent pathway projecting from the hindbrain to forebrain that is involved in initiating the eating response to the fructose analogue.