Brain Of Adult Male Rats Research Articles

Neurons of the superior nucleus of the medial habenula and ependymal cells express IL-18 in rat CNS

The habenular–interpeduncular pathway is involved in the modulation of several functions including neuroendocrine and stress responses. Interleukin-18 (IL-18) is a pro-inflammatory cytokine predominantly studied as a modulator of immune functions and also produced in the adrenal cortex following activation of the hypothalamic–pituitary–adrenal axis. In the central nervous system, IL-18 was demonstrated to induce sleep and to influence long-term potentiation and was proposed to mediate local inflammatory reactions. The present study investigated the localization of IL-18 and its expression following either acute or chronic restraint stress in the brain of adult male Wistar rats. Using immunocytochemistry and in situ hybridization we report the unprecedented localization of IL-18 in the neurons of the superior part of the medial habenula (MHbS), their projections to the interpenducular nucleus and its expression in the ependymal cells surrounding the third and the lateral ventricles. In addition, acute (2 h) or chronic (6 h/day for 3 weeks) restraint stress induced a strong elevation of IL-18 immunostaining in the MHbS but not in ependymal cells. The present data suggest that IL-18 may participate in the modulation of stress responses in the MHbS. They also suggest that ependymal cells may be the source of IL-18 previously reported in the cerebrospinal fluid (CSF). The role of IL-18 in the ependyma and the CSF remains to be elucidated.

Distribution and differences of estrogen receptor beta immunoreactivity in the brain of adult male and female rats

Studies have shown that estrogen plays important roles in regulating neural structure and function in the brain, but the mechanism remains unclear. The actions of estrogen were thought to be mediated by a single estrogen receptor until the identification of another estrogen receptor, namely estrogen receptor-β (ER-β). Here we report a comprehensive study of the localization of ER-β immunoreactivity and differences in the brains of adult male and female rats on the basis of a nickel ammonium sulfate-enhanced immunocytochemical method using a polyclonal antiserum sc-8974. The results of these studies revealed: (1) ER-β immunoactive material was mainly localized in the neuronal nucleus, but it was also detectable in the cytoplasm and neuronal processes; (2) in both male and female rats, high levels of ER-β immunopositive signals were detected in the anterior olfactory nucleus, cerebral cortex, Purkinje cells, vertical limb of the diagonal band, red nucleus, locus ceruleus, and motor trigeminal nucleus. Moderate levels were found in the medial septum, lateral amygdaloid nucleus, substantia nigra, and central gray. Weak signals were localized in other subregions of the hypothalamus and amygdaloid complex; (3) there was an obvious difference of ER-β immunoreactivity between male and female rats, and its intracellular distribution also showed a sex difference. The above results provide the first detailed evidence that ER-β protein is widely distributed in both male and female rat brains, but that distinctive sex differences also exist. Estrogen may exert its function in different brain regions in a gender-specific manner.

Subchronic Dermal Application of N,N-Diethyl m-Toluamide (DEET) and Permethrin to Adult Rats, Alone or in Combination, Causes Diffuse Neuronal Cell Death and Cytoskeletal Abnormalities in the Cerebral Cortex and the Hippocampus, and Purkinje Neuron Loss in the Cerebellum

N,N-Diethyl m-toluamide (DEET) and permethrin have been implicated as potential neurotoxic agents that may have played an important role in the development of illnesses in some veterans of the Persian Gulf War. To determine the effect of subchronic dermal application of these chemicals on the adult brain, we evaluated histopathological alterations in the brain of adult male rats following a daily dermal dose of DEET (40 mg/kg in 70% ethanol) or permethrin (0.13 mg/kg in 70% ethanol) or a combination of the two for 60 days. Control rats received a daily dermal dose of 70% ethanol for 60 days. Animals were perfused and brains were processed for morphological and histopathological analyses following the above regimen. Quantification of the density of healthy (or surviving) neurons in the motor cerebral cortex, the dentate gyrus, the CA1 and CA3 subfields of the hippocampus, and the cerebellum revealed significant reductions in all three treated groups compared with the control group. Further, animals receiving either DEET or permethrin exhibited a significant number of degenerating (eosinophilic) neurons in the above brain regions. However, degenerating neurons were infrequent in animals receiving both DEET and permethrin, suggesting that neuronal cell death occurs earlier in animals receiving combined DEET and permethrin than in animals receiving either DEET or permethrin alone. The extent of neuron loss in different brain regions was similar among the three treatment groups except the dentate gyrus, where neurodegeneration was significantly greater with exposure to DEET alone. The neuron loss in the motor cerebral cortex and the CA1 subfield of all treated groups was also corroborated by a significant decrease in microtubule associated protein 2-immunoreactive elements (15–52% reduction), with maximal reductions occurring in rats receiving DEET alone; further, the surviving neurons in animals receiving both DEET and permethrin exhibited wavy and beaded dendrites. Analysis of glial fibrillary acidic protein immunoreactivity revealed significant hypertrophy of astrocytes in the hippocampus and the cerebellum of all treated groups (24–106% increase). Thus, subchronic dermal application of DEET and permethrin to adult rats, alone or in combination, leads to a diffuse neuronal cell death in the cerebral cortex, the hippocampal formation, and the cerebellum. Collectively, the above alterations can lead to many physiological, pharmacological, and behavioral abnormalities, particularly motor deficits and learning and memory dysfunction.

Estrogen receptor (ER)alpha, but not ERbeta, gene is expressed in growth hormone-releasing hormone neurons of the male rat hypothalamus.

GH synthesis and release from pituitary somatotropes is controlled by the opposing actions of the hypothalamic neuropeptides, GH-releasing hormone (GHRH), and somatostatin (SS). There is a striking sex difference in the pattern of GH secretion in rats. Early reports indicate that gonadal steroids have important imprinting effects during the neonatal period. Recently, our laboratory and others have reported that the GH secretory pattern is altered by short-term gonadal steroid treatment in adult rat, suggesting that gonadal steroids are also important determinants of the pattern of GH secretion during adult life. However, the site of action of gonadal steroids in the adult rat hypothalamus is still unknown. In this study, we used in situ hybridization in the adult male rat brain to determine whether GHRH neurons and/or SS neurons coexpress estrogen receptor alpha (ERalpha) and ERss genes. In the medial basal hypothalamus of adult male rat, the ERalpha messenger RNA (mRNA) was located in medial preoptic area (MPA) and arcuate nucleus (ARC), whereas ERss mRNA was detected in MPA, supraoptic nucleus, and paraventricular nucleus. From studies using adjacent sections, the distribution of ERalpha mRNA-containing cells appeared to overlap in part with those of GHRH and SS expressing cells only in the ARC. On the other hand, the distribution of ERss mRNA-containing cells does not appear to overlap with GHRH cells or SS cells. The double label in situ hybridization studies showed that in the ARC, 70% of GHRH neurons contain ERalpha mRNA, whereas less than 5% of SS neurons expressed the ERalpha gene. These results indicated that GHRH neurons are direct target cells for estrogens, and estrogens may act directly on GHRH neurons through ERalpha during adult life to modify GH secretory patterns.

Estrogen Receptor (ER) , But Not ER , Gene Is Expressed in Growth Hormone-Releasing Hormone Neurons of the Male Rat Hypothalamus

GH synthesis and release from pituitary somatotropes is controlled by the opposing actions of the hypothalamic neuropeptides, GH-releasing hormone (GHRH), and somatostatin (SS). There is a striking sex difference in the pattern of GH secretion in rats. Early reports indicate that gonadal steroids have important imprinting effects during the neonatal period. Recently, our laboratory and others have reported that the GH secretory pattern is altered by short-term gonadal steroid treatment in adult rat, suggesting that gonadal steroids are also important determinants of the pattern of GH secretion during adult life. However, the site of action of gonadal steroids in the adult rat hypothalamus is still unknown. In this study, we used in situ hybridization in the adult male rat brain to determine whether GHRH neurons and/or SS neurons coexpress estrogen receptor α (ERα) and ERβ genes. In the medial basal hypothalamus of adult male rat, the ERα messenger RNA (mRNA) was located in medial preoptic area (MPA) and arcuate nucleus (ARC), whereas ERβ mRNA was detected in MPA, supraoptic nucleus, and paraventricular nucleus. From studies using adjacent sections, the distribution of ERα mRNA-containing cells appeared to overlap in part with those of GHRH and SS expressing cells only in the ARC. On the other hand, the distribution of ERβ mRNA-containing cells does not appear to overlap with GHRH cells or SS cells. The double label in situ hybridization studies showed that in the ARC, 70% of GHRH neurons contain ERα mRNA, whereas less than 5% of SS neurons expressed the ERα gene. These results indicated that GHRH neurons are direct target cells for estrogens, and estrogens may act directly on GHRH neurons through ERα during adult life to modify GH secretory patterns.

Progesterone receptor isoforms expression in the prepuberal and adult male rat brain

Progesterone receptor (PR) isoforms expression was determined in several regions of the prepuberal and adult male rat brain by using reverse transcription coupled to polymerase chain reaction. Rats under a 14:10-h light–dark cycle, with lights on at 0600 h were used. We found that in the hypothalamus of prepuberal animals the expression of both PR isoforms was similar, whereas PR-A expression was higher than that of PR-B in adults. In the cerebellum PR-B expression was predominant in both prepuberal and adult rats. In both ages PR-A and PR-B exhibited a non-significant tendency to be predominant in the hippocampus and the preoptic area respectively. In the frontal cortex and the olfactory bulb PR isoforms were expressed at a similar level. These results indicate a differential expression pattern of PR isoforms in the male rat brain and suggest that the tissue-specific expression of PR-A and PR-B is important for the appropriate response of each cerebral region to progesterone.

Prenatal exposure to morphine differentially alters gonadal hormone regulation of δ-opioid receptor binding in male and female rats

The present study tested the hypothesis that exposure to morphine on gestation days 11–18 differentially alters δ-opioid receptors in the brain of adult male and female rats. In Experiment 1, the binding characteristics of δ-opioid receptors were examined in membrane homogenates from six brain regions, including the hypothalamus (HYP), preoptic area, frontal cortex (CX), ventral tegmental area, striatum (STR) and cerebellum of adult male and female rats. In Experiment 2, the density of δ-opioid receptors was assessed in the CX and STR using receptor autoradiography. Prenatal morphine exposure has no effects on δ-opioid receptors in the brain of gonadally intact, adult male rats regardless of methodology. However, when male rats were gonadectomized in Experiment 2, morphine-exposed males have fewer δ-opioid receptors than controls in the CX but not in the STR. These reductions in cortical δ-opioid receptors are restored by testosterone replacement, demonstrating that prenatal morphine exposure alters testosterone regulation in the CX of male rats. In ovariectomized (OVX) female rats, prenatal morphine exposure increases the density of δ-opioid receptors in the frontal CX. Interestingly, this up-regulation of δ-opioid receptors is not present when the CX is investigated by autoradiography. Moreover, progesterone given alone or in combination with estrogen reduces the density of δ-opioid receptors in the CX and STR of both saline- and morphine-exposed, OVX females. Thus, mid to late gestational morphine exposure differentially alters the influence of adult gonadal hormones on δ-opioid receptors in the CX, decreasing the sensitivity in females and increasing it in males. This is also the first report to demonstrate that gonadal hormones regulate δ receptor densities in brain regions other than the HYP of OVX females.

Galanin-Like Peptide (GALP) mRNA Expression Is Restricted to Arcuate Nucleus of Hypothalamus in Adult Male Rat Brain

Galanin-like peptide (GALP) is a novel 60-amino acid neuropeptide, isolated from porcine hypothalamus and subsequently identified in rats and humans, which has reported selectivity for the Gal-R2 galanin receptor [Ohtaki T et al: J Biol Chem 1999; 274: 37041–37045]. In the current study, the regional and cellular distribution of GALP mRNA in rat brain has been investigated by in situ hybridization of [³⁵S]-labelled oligonucleotide probes. In a thorough screening of adult male rat brain, GALP mRNA expression was detected only throughout the rostrocaudal extent of the arcuate nucleus (ARC) with the most abundant hybridization signal in the posterior, periventricular zones. GALP mRNA-positive neurons were mostly localized in the ventromedial division of the ARC, with many closely adjacent to the wall of the third ventricle. Smaller numbers of labelled neurons were also found in ventrolateral areas. The distribution of GALP mRNA was somewhat complementary to that for galanin (GAL) mRNA in the ARC, but contrasted with the broad distribution of this transcript throughout the hypothalamus. GAL mRNA was also distributed along the rostrocaudal extent of the ARC, but was most abundant in the anterior to middle levels and in ventrolateral regions. Interestingly, somatostatin mRNA expression appeared to overlap the distribution of GALP mRNA in posterior, ventromedial regions of the ARC. Thus, in adult rat brain GALP mRNA expression was restricted to a discrete subpopulation of neurons in the ARC, with a unique localization pattern unlike GAL or many other known peptide- and transmitter-containing cells in this region. GALP could, however, be co-expressed in sub-populations of other neuronal phenotypes (e.g. somatostatin neurons) or within cells that express Gal-R2 receptors. In view of the established anatomy and function of the ARC and the restricted localization of GALP mRNA, this novel peptide is likely to play a role in regulation of anterior pituitary hormone secretion, or in regulation of other hypothalamic peptide and transmitter systems.

Molecular cloning and expression of novel sulphotransferase-like cDNAs from human and rat brain

The sulphotransferase (SULT) gene family is involved with the conjugation of many small drugs, xenobiotics and endogenous compounds. In this report, we describe the cloning and expression of novel cDNAs from human and rat brain, which are structurally related to the SULTs. These cDNAs have been termed 'brain sulphotransferase-like' (BR-STL), because of their similarity to the SULTs and their selective expression in brain tissue. The proteins encoded by the human and rat BR-STL cDNAs (hBR-STL-1 and rBR-STL cDNA respectively), denoted as hBR-STL and rBR-STL, are 98% identical and 99% similar in sequence. The hBR-STL-1 cDNA contains an 852-nt open reading frame encoding a 284-amino-acid protein with a calculated molecular mass of 33083 Da. Northern-blot analyses of RNA isolated from eight human tissues indicate that the hBR-STL message is selectively expressed in brain. Characterization of different brain regions showed that message levels were highest in cortical brain regions. rBR-STL message levels were relatively low in brains of 1-day-old male and female rats, but increased to adult levels in RNA from 7-day-old rats, and remained at that level in adult animals. The hBR-STL and rBR-STL cDNAs were expressed in both Escherichia coli and Sf9 insect cells in the presence or absence of an N-terminal histidine-affinity tag (His-tag). Polyclonal antibodies were raised in chickens against purified His-tagged hBR-STL, and were used to detect the presence of rBR-STL in adult male and female rat brain cytosol. The high degree of sequence conservation, and the selective localization of the BR-STL message in brain, suggest an important function in the central nervous system.

Role of neuronal nitric oxide in methamphetamine neurotoxicity and protection by nNOS inhibitor

Abstract Methamphetamine (METH) is a potent psychostimulant known to produce neurotoxicity. The dopaminergic pathway is particularly sensitive to METH. Recent studies showed that 7-nitroindazole (7-NI), a selective inhibitor of neuronal nitric oxide synthase (nNOS), provided protection against METH neurotoxicity both in vitro and in vivo. The present studies were conducted to determine the nNOS activity in various regions of the brain of young adult male Sprague-Dawley rats treated with different doses of METH. Rats were injected ip with 5, 10, 20, and 40 mg/kg and 24 h after the rats were sacrificed and the brain regions (hippocampus, frontal cortex, and cerebellum) were quickly dissected. The cytosolic fractions were prepared, and the nNOS activity was determined using the 3H-citrulline assay. The results showed that nNOS activity was significantly increased in all three brain regions of rats treated with METH. The increase was dose dependent reaching a maximum of 40-100% over the control values. Rats treated with 7NI 30 min prior to METH injection provided protection against the toxicity and also showed a reduction of nNOS activity. The activation of nNOS is known to increase the synthesis of NO which is involved in the regulation of several neurotransmitter pathways including catecholaminergic system. Reducing the METH-induced production of NO by pretreatment with selective inhibitor of nNOS, 7-NI, provided protection against METH neurotoxicity.

Manganese scavenges superoxide and hydroxyl radicals: an in vitro study in rats

The present study was designed to investigate the role of manganese (Mn) as an antioxidant element. In vitro experiments have been conducted to evaluate the ability of Mn in scavenging oxygen free radicals. Superoxide (O ·−) and hydroxyl (OH ·−) radicals were generated in vitro by using xanthine and xanthine oxidase system and fenton reactions respectively. Different concentrations of Mn (II) and Mn (III) were used in the reaction mixture to evaluate free radical scavenging ability of Mn. The results indicated that Mn scavenged superoxide radicals at nanomolar concentrations whereas hydroxyl radicals were scavenged at micromolar concentrations. In addition, Mn-superoxide dismutase (SOD) activity was measured in different regions of brain in adult male rats treated with MnCl 2. The results showed that Mn-SOD activity increased in Mn treated animals. Therefore, the data support the hypothesis that Mn is one of the essential elements which can protect against oxidative damage, however, at higher concentrations Mn can be neurotoxic by generating the free radicals.

Sexually dimorphic expression of sst1 and sst2 somatostatin receptor subtypes in the arcuate nucleus and anterior pituitary of adult rats.

The pattern of growth hormone (GH) secretion and rate of somatic growth are markedly sexually dimorphic, but the underlying neuroendocrine mechanisms are far from clear. In the present study, we tested the hypothesis that the sexual dimorphism of GH secretion may be due to gender-related differences in the transduction of somatostatin's actions in brain and/or pituitary. To accomplish this, we compared the distributional pattern and level of expression of two somatostatin receptor subtypes, sst1 and sst2, in the brain and pituitary of adult male and female rats by in-situ hybridization using 35S-labelled antisense riboprobes. In the brain, the hybridization pattern and labelling density of sst1 and sst2 mRNA-expressing cells, as revealed by computer-assisted image analysis, in areas including the cerebral cortex, medial habenula (MHb) and ventromedial hypothalamic nucleus (VMN), were similar in male and female rats. In contrast, there was a marked sex-related difference in sst1 expression in the arcuate nucleus of the hypothalamus; both the number and labelling density of sst1 mRNA-expressing cells were two- to threefold greater in males than in females and this significant increase was homogenous throughout the rostrocaudal extent of the nucleus. No gender-related differences in arcuate sst2 mRNA levels were found. At the level of the anterior pituitary, the labelling density of sst2 mRNA in males was significantly higher than that of females. No sex-related difference in pituitary sst1 mRNA was observed. These results demonstrate a sexual dimorphism in the expression of two somatostatin receptor subtypes, sst1 and sst2, at the level of the arcuate nucleus and anterior pituitary, respectively. Such dimorphism suggests a differential involvement of sst1 and sst2 in GH regulation with respect to gender, and may imply roles for sst2 and sst1 in transducing somatostatin's actions on pituitary somatotrophs and GH-releasing hormone-containing arcuate neurones, respectively, to generate the lower basal and higher GH pulse levels characteristic of the male rat.

Perinatal Δ9-tetrahydrocannabinol exposure reduces proenkephalin gene expression in the caudate-putamen of adult female rats

Perinatal Δ 9-tetrahydrocannabinol ( Δ 9-THC) exposure in rats affects several behavioral responses, such as opiate self-administration behavior or pain sensitivity, that can be directly related to changes in opioidergic neurotransmission. In addition, we have recently reported that the administration of naloxone to animals perinatally exposed to Δ 9-THC produced withdrawal responses, that resemble those observed in opiate-dependent rats. The purpose of the present study was to examine the basal opioid activity in the brain of adult male and female rats that had been perinatally exposed to Δ 9-THC. To this aim, proenkephalin mRNA levels were measured, by using in situ hybridization histochemistry, in the caudate-putamen, nucleus accumbens, central amygdala and prefrontal cingulate cortex. The results showed a marked reduction in proenkephalin mRNA levels in the caudate-putamen of Δ 9-THC-exposed females as compared to oil-exposed females, whereas no changes were observed between Δ 9-THC- and oil-exposed males. There were no differences in proenkephalin mRNA levels in the nucleus accumbens, central amygdala and prefrontal cingulate cortex between males and females perinatally exposed to Δ 9-THC and their respective controls, although a certain trend to decrease was observed in Δ 9-THC-exposed females. In summary, perinatal exposure to Δ 9-THC exposure decreased proenkephalin gene expression in the caudate-putamen of adult rats, although this effect exhibited a marked sexual dimorphism since it was only seen in females. This result is in agreement with a previous observation from our laboratory that females, but not males, that had been perinatally exposed to Δ 9-THC, self-administered more morphine in adulthood. This suggests that low levels of proenkephalin mRNA may be used as a predictor of greater vulnerability to opiates.

Dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulfate (DHEAS) as neuroactive neurosteroids.

The observation was made that dehydroepiandrosterone (DHEA), as the unconjugated steroid, and its sulfate ester (DHEAS) are present in the brain of adult male rats (1). This finding was unforeseen because the rodent steroidogenic glands, including the adrenals, do not secrete significant amounts of DHEA (2). It led to the discovery of a steroid biosynthetic machinery in the nervous system, in charge of producing neurosteroids.

Intracerebral transplantation of testis-derived sertoli cells promotes functional recovery in female rats with 6-hydroxydopamine-induced hemiparkinsonism.

Recently, we demonstrated amelioration of behavioral deficits associated with 6-hydroxydopamine-induced hemiparkinsonism by transplanting rat testis-derived Sertoli cells into adult male rat brains. In the present study, we used adult female hemiparkinsonian rats to investigate whether the beneficial effects of transplantation of Sertoli cells may be differentially affected by gender of the animal transplant recipient. At 1 month posttransplantation, animals transplanted with Sertoli cells showed functional recovery as revealed by significant reductions in apomorphine-induced rotational behavior and asymmetrical elevated body swing behavior. Control animals that received medium alone did not display any visible behavioral recovery. These results suggest that transplantation of Sertoli cells is not male hormone-dependent and further support the use of these cells as a graft source for Parkinson's disease and other neurological disorders.

Maternal Exposure to Δ9-Tetrahydrocannabinol (Δ9-THC) Alters Indolamine Levels and Turnover in Adult Male and Female Rat Brain Regions

Perinatal exposure to Δ9-THC has been shown to produce effects on brain development. In this study we evaluated the changes induced by maternal exposure to Δ9-THC (5 mg/kg per day) from gestational day 5 to postnatal day 24 in eight discrete brain areas on the central serotoninergic system in both adult male and female rats. These result show that maternal exposure to Δ9-THC from gestational day 5 to postnatal day 24 affects development of the various central indoleaminergic system of the offsprings brain. Perinatal exposure to Δ9-THC decreased the levels of 5-HT in hypothalamus and rostral neostriatum in exposed males, and also decreased the levels of 5-HT in ventral hippocampus, septum, and midbrain raphe nuclei in both exposed males and females. Perinatal exposure to Δ9-THC increased the levels of 5-HIAA in dorsal hippocampus, hypothalamus, septum, midbrain raphe nuclei, and rostral neostriatum in exposed males and females. We have also found differences between nonexposed males and females in several brain regions. Our results confirm a regional and sexual specificity in endogenous levels of indoleamine after perinatal Δ9-THC treatment, being the midbrain raphe nuclei the most affected area.

The effect of hypophysectomy and growth hormone replacement on sst1 and sst2 somatostatin receptor subtype messenger ribonucleic acids in the arcuate nucleus.

Although considerable evidence indicates that somatostatin (SRIF) exerts direct actions on GH-releasing hormone-containing arcuate neurons within the hypothalamus to modulate hypophyseal GH secretion, the underlying mechanism(s) remains to be elucidated. We recently demonstrated high levels of expression of the messenger RNAs (mRNAs) coding for two prototypic receptors of the recently cloned SRIF receptor (sst) family, sst1 and sst2, in the arcuate nucleus of the rat hypothalamus. However, information on the biological roles of these receptor subtypes and the factors regulating their expression is lacking. In the present study, we hypothesized that perturbations in GH would influence sst mRNA levels in cells of the arcuate nucleus in vivo. To test this hypothesis, we examined the effects of hypophysectomy (HPX) and HPX with GH replacement, on sst1 and sst2 mRNA levels in the brains of adult male rats by in situ hybridization using 35S-labeled antisense riboprobes. The number of labeled cells and the density of silver grains per cell were quantified using a computer-assisted image analysis system. Two weeks after HPX, there was a 50-60% reduction in both the number and labeling density of sst1 and sst2 mRNA-expressing cells in the arcuate nucleus compared to those in sham-operated control rats. Administration of recombinant human GH (200 micrograms/day for 7 days by continuous sc infusion using osmotic minipumps) to HPX rats augmented both the cell number (P < 0.05) and labeling density (P < 0.01) of sst1 mRNA in the arcuate nucleus, but did not significantly alter sst2 mRNA levels compared to those in HPX rats infused with H2O. There were no significant changes in sst1 and sst2 mRNA levels in extra-arcuate areas, including the cerebral cortex and medial habenula, or in suprachiasmatic, medial preoptic, and magnocellular preoptic nuclei after either HPX or GH replacement. These results indicate that the expression of both sst1 and sst2 SRIF receptor subtypes in brain is under the regulatory influence of pituitary hormones. They further suggest that GH may participate in the regulation of its own secretion by influencing the expression of the sst1 receptor gene on arcuate neurons. Such a mechanism may be important in the feedback regulation of GH secretion by the arcuate nucleus.

Distribution and steroid hormone regulation of aromatase mRNA expression in the forebrain of adult male and female rats: a cellular-level analysis using in situ hybridization.

Many of the effects of gonadal steroid hormones in the male brain are due to the actions of the testosterone metabolite estradiol, which is synthesized by the actions of the P450 enzyme aromatase. Aromatase activity is present in regions of the preoptic area, hypothalamus, and limbic system. Levels of aromatase activity in the brain are highly dependent on gonadal steroid hormones in many brain regions, but not all. We examined the distribution of aromatase mRNA in adult male and female rat brains as well as the regulation of the levels of aromatase mRNA in the brains of males by gonadal steroid hormones using in situ hybridization. This method was performed using a 35S-labelled cRNA probe, transcribed in vitro from the rat ovarian aromatase cDNA. In the adult male, many heavily labelled cells were found in the encapsulated bed nucleus of the stria terminalis (BNST), the medial preoptic nucleus (MPN), the ventromedial nucleus (VMN), the medial amygdala (mAMY), and the cortical amygdala (CoAMY). The regional distribution of aromatase mRNA was similar in females, but females tended to have a lower number of aromatase mRNA expressing cells in each region compared to males. Aromatase mRNA levels in the BNST, MPN, VMN, and mAMY tended to be lower in castrated males than in intact males, whereas aromatase mRNA levels were unaltered by castration in the CoAMY. The degree of reduction in mean levels of aromatase mRNA following castration does not simply account for the large changes measured in activity following castration. Examination of the entire population of individual cells expressing aromatase mRNA in castrated males suggests that aromatase mRNA may be regulated by steroid hormones differentially in specific populations of neurons within regions where activity is known to decrease following castration.

Distribution and steroid hormone regulation of aromatase mRNA expression in the forebrain of adult male and female rats: A cellular‐level analysis using in situ hybridization

Many of the effects of gonadal steroid hormones in the male brain are due to the actions of the testosterone metabolite estradiol, which is synthesized by the actions of the P450 enzyme aromatase. Aromatase activity is present in regions of the preoptic area, hypothalamus, and limbic system. Levels of aromatase activity in the brain are highly dependent on gonadal steroid hormones in many brain regions, but not all. We examined the distribution of aromatase mRNA in adult male and female rat brains as well as the regulation of the levels of aromatase mRNA in the brains of males by gonadal steroid hormones using in situ hybridization. This method was performed using a 35S-labelled cRNA probe, transcribed in vitro from the rat ovarian aromatase cDNA. In the adult male, many heavily labelled cells were found in the encapsulated bed nucleus of the stria terminalis (BNST), the medial preoptic nucleus (MPN), the ventromedial nucleus (VMN), the medial amygdala (mAMY), and the cortical amygdala (CoAMY). The regional distribution of aromatase mRNA was similar in females, but females tended to have a lower number of aromatase mRNA expressing cells in each region compared to males. Aromatase mRNA levels in the BNST, MPN, VMN, and mAMY tended to be lower in castrated males than in intact males, whereas aromatase mRNA levels were unaltered by castration in the CoAMY. The degree of reduction in mean levels of aromatase mRNA following castration does not simply account for the large changes measured in activity following castration. Examination of the entire population of individual cells expressing aromatase mRNA in castrated males suggests that aromatase mRNA may be regulated by steroid hormones differentially in specific populations of neurons within regions where activity is known to decrease following castration. © 1996 Wiley-Liss, Inc.

Influence of corticotropin-releasing hormone on electrophysiological activity of locus coeruleus neurons

These experiments examined the effects of corticotropin-releasing hormone (CRH) on single-unit electrophysiological activity of locus coeruleus (LC) neurons. As has been reported previously, infusion of CRH into the ventricular system of the brain (i.c.v.) of halothane-anesthetized adult male rats increased spontaneous discharge rate of LC neurons while producing no increase, and possibly a decrease, in sensory-evoked activity. However, when i.c.v. CRH was given to female rats or immature male rats, which had not been studied previously, LC activity was not altered. To attempt to understand this sex and age difference, potential mechanisms by which i.c.v. CRH elevates LC spontaneous activity in adult male rats were examined; in that i.c.v. CRH activates the pituitary-adrenal axis and autonomic nervous system, these response systems were manipulated. Adrenalectomy (with or without corticosterone replacement by pellet) did not affect the ability of i.c.v. CRH to increase LC spontaneous activity in adult male animals, but blockade of sympathetically-mediated autonomic responses, either by chlorisondamine or the beta adrenergic receptor blocker timolol, blocked this increase, indicating that afferent feedback from peripheral autonomic responses was critical for activating LC neurons following i.c.v. CRH. To determine whether CRH neurotransmission might play a role in this feedback pathway, the CRH antagonist alpha-helical CRH (α-hCRH) was microinjected into several brain regions including LC prior to i.c.v. CRH. α-hCRH microinjected into LC reduced the increase in LC activity caused by i.c.v. CRH; however, blockade of this increase was total when α-hCRH was microinjected into the lateral parabrachial nucleus ipsilateral to the LC recording site, suggesting that increased LC activity following i.c.v. CRH is mediated by CRH acting in the parabrachial region. During these studies, it was also observed that microinjection of α-hCRH into LC increased LC spontaneous discharge rate; consequently, CRH was microinjected into LC, and produced a dose-dependent decrease in LC spontaneous activity in both male and female rats, which could be blocked by microinjection of α-hCRH — these data indicated that the direct influence of CRH on LC neurons is to decrease their spontaneous activity. To reconcile this with the original report that CRH applied to LC neurons increases their activity, one possibility suggested is that the CRH microinjection procedure used in the present study stimulated inhibitory receptors on LC dendrites whereas the original study stimulated excitatory receptors on LC cell bodies. It is concluded that an inhibitory influence of CRH on LC activity is consistent with recent data indicating that decreased LC activity increases anxiety and stress-related responses, but that direct influences of CRH appear rather minor in determining LC neuronal activity in comparison to other inputs to LC such as are seen after i.c.v. CRH infusion.