Detection of estrogen receptor alpha and beta messenger ribonucleic acids in adult gonadotropin-releasing hormone neurons

The behavior of the gonadotropin-releasing hormones (GnRH) neurons controlling fertility is dependent upon cyclic fluctuations in circulating concentrations of estrogen. However, the nature of estrogen action upon these cells has remained controversial due to their dispersed distribution within the brain, and evidence indicating that they do not express nuclear estrogen receptors (ERs) in vivo. We report here an acute brain slice preparation that enables individual living GnRH neurons to be identified within the mouse brain and show, using single cell multiplex RT-PCR, that the greater than 50% of GnRH neurons in adult and prepubertal females contain ERalpha messenger RNA. Approximately 10% of GnRH neurons contained ERbeta transcripts that were always coexistent with ERalpha. Single cell RT-PCR analysis of nonGnRH cells located in the medial preoptic area revealed a similar coexpression pattern of ERalpha and ERbeta transcripts. In contrast, single striatal cells were not found to contain ERbeta despite ERalpha being present in approximately 25% of cells. The analysis of single GnRH neurons in cycling female mice revealed that the detection of ERalpha and ERbeta transcripts was lowest on proestrus (ERalpha, 18% of all GnRH neurons; ERbeta, 0%) compared with diestrus (44% and 6%) and estrus (75% and 19%, respectively). Using a novel approach that enables single cell RT-PCR analysis of GnRH neurons, we present here evidence for the cyclic expression of ERalpha and ERbeta messenger RNAs within prepubertal and adult female GnRH neurons.

Localization of estrogen-receptive neurons projecting to the GnRH neuron-containing rostral preoptic area of the ewe

Estrogen exerts important feedback effects upon the biosynthetic and secretory behavior of gonadotropin-releasing hormone (GnRH) neurons to control reproductive functioning. The mechanism of estrogen action upon these neurons is unclear and seems likely to involve the transsynaptic regulation of GnRH neurons. The objective of the present study was to identify the estrogen-receptive neural populations which project to the general vicinity of the GnRH perikarya in the rostral preoptic area and diagonal band of Broca (rPOA/DBB) of the ewe. Intact breeding-season ewes received an injection of the retrograde tracer fluorogold (FG) into the rPOA/DBB, and their hypothalami and brainstems examined for the presence of FG and estrogen receptor alpha (ERalpha) immunocytochemistry. Retrogradely labeled neurons were identified principally within the lateral septum (LS), lamina terminalis, bed nucleus of the stria terminalis, POA, arcuate nucleus (ARN), ventromedial nucleus (VMN) and median eminence. Smaller numbers of FG-immonoreactive cells were found in the caudal brainstem where they resided mostly in the ventrolateral medulla (VLM). Dual-labeled cells exhibiting both FG and ERalpha staining were prominent in the POA, LS and at all rostrocaudal levels of the VMN and ARN. Small numbers of dual-labeled cells were found in the VLM. These observations indicate that a number of distinct ERalpha-expressing neural populations project to the rPOA/DBB where the majority of the GnRH perikarya are found in the ewe. Although it is not possible to determine the direct connectivity of these projections with GnRH neurons, the findings provide an initial neuroanatomical framework through which the transsynaptic actions of estrogen on ovine GnRH neurons may be tested.

Control of REM sleep: an aspect of the regulation of physiological homeostasis

Since REM sleep is characterized by a suspension of the hypothalamic integration of homeostatic regulations, it has been assumed that the duration of both REM sleep episodes and of the time interval between the end of one episode and the beginning of the following episode may be regulated according to sleep related processes and the homeostatic needs of the organism. A series of studies performed on the rat has shown that REM sleep episodes occur as two basic types: single REM sleep episodes, that are separated by intervals > 3 min and sequential episodes, that are separated by intervals < or = 3 min and appear in a cluster. Moreover, it has been observed that, in this species, a change in REM sleep occurrence is caused by a modification in the number of episodes and not in their duration. With respect to this, sleep deprivation and recovery are characterized by a decrease and an increase, respectively, in the number of sequential REM sleep episodes, but the number of single episodes tends to be kept constant. The central aspects of this kind of regulation have been examined biochemically in the preoptic-anterior hypothalamus, an area involved in the control of autonomic and sleep related processes. The results show that the accumulation of adenosine 3':5'-cyclic monophosphate (cAMP) is impaired, in this region, during sleep deprivation and appears to return to the control levels, during the recovery, with a rate inversely related to the degree of the previous deprivation. Moreover, it has been observed that the systemic administration of DL-propranolol and LiCl reduces cAMP accumulation mainly in the preoptic-anterior hypothalamus; this condition is concomitant with a reduction in REM sleep occurrence.

Distribution of estrogen receptor-beta messenger ribonucleic acid in the male sheep hypothalamus

As a first step in determining possible influences of the newly discovered estrogen receptor (ER)-beta on reproduction, we have localized mRNA for ER-beta within the male sheep hypothalamus using in situ hybridization and a rat ER-beta cRNA probe. Highest amounts of hybridization signal were observed in the preoptic area (POA), bed nucleus of the stria terminalis, paraventricular nucleus, and supraoptic nucleus. Relatively moderate amounts of hybridization signal were observed in the retrochiasmatic area (RCH), anterior hypothalamic area, dorsomedial hypothalamus, and lateral hypothalamus. Only a low level of hybridization signal was observed in the ventromedial hypothalamus, suprachiasmatic nucleus, and arcuate nucleus. The presence of ER-beta mRNA in several areas of the male sheep hypothalamus suggests multiple functions for this receptor. The distribution of ER-beta in the ovine hypothalamus was similar to that described for the rat, suggesting a high degree of functional conservation across species. A role for ER-beta in influencing reproduction is suggested by its presence in the POA and RCH, regions of the hypothalamus that control reproduction.

Corticotropin releasing factor in the brain of the gymnotiform fish, Apteronotus leptorhynchus: immunohistochemical studies combined with neuronal tract tracing

The expression of corticotropin-releasing factor (CRF) has been studied by immunohistochemistry in the brain of the gymnotiform fish, Apteronotus leptorhynchus. Labeled somata were found exclusively in the posterior subdivision of the nucleus preopticus periventricularis and in the hypothalamus anterioris, where these cells form a continuous cluster of neurons. Combination of anti-peptide immunohistochemistry with an in vitro tract-tracing technique confirmed that at least some of these neurons project to the pituitary. Additional terminal fields were present in the following areas of the telencephalon and the diencephalon: ventral subdivision of the ventral telencephalon, supracommissural subdivision of the ventral telencephalon, anterior subdivision of the nucleus preopticus periventricularis, inferior subdivision of the nucleus recessus lateralis, central posterior/prepacemaker nucleus, hypothalamus dorsalis and lateralis, medial subdivision 2 of the nucleus recessus lateralis, and in the region between the dorsal edge of the nucleus tuberis anterior on the one side and both the glomerular nucleus and the central nucleus of the inferior lobe on the other side. It is likely that the projection of CRF-expressing neurons of the posterior subdivision of the nucleus preopticus periventricularis/hypothalamus anterioris to the pituitary provides, similarly as in other fishes, the neural substrate for the activation of the hypothalamo-pituitary adrenal axis through CRF. In addition to this function, CRF may be involved in the regulation of several other processes, including neural control of communicatory behavior exerted by neurons of the central posterior/prepacemaker nucleus.

Effects of a D1 antagonist and of sexual experience on copulation-induced Fos-like immunoreactivity in the medial preoptic nucleus

The medial preoptic nucleus (MPN) of the medial preoptic area (MPOA) and the medial amygdala are two brain regions in which male rat sexual behavior increased Fos-like immunoreactivity (Fos-Li). Dopamine is released in the MPOA during male rat sexual behavior and facilitates copulation. Psychostimulants, which increase dopamine levels, induce Fos-Li in the striatum through D1 receptors. We examined whether copulation-induced Fos-Li in the MPN was also mediated through D1 receptors. In Experiment 1, sexually inexperienced male rats that received the D1 antagonist Schering 39166 prior to their first sexual experience had fewer Fos-Li cells in the MPN than did those that received vehicle. In Experiment 2, no significant effect of the D1 antagonist was observed on copulation-induced Fos-Li in male rats that had received repeated sexual experiences prior to the drug test day. Sexual experience increases copulatory efficiency; the mechanisms by which this improvement occurs are unclear. In Experiment 3, copulation by highly experienced male rats led to greater Fos-Li in the MPN than did copulation by sexually naive males. Although there were no differences between groups in amygdala Fos-Li in these studies, in several groups Fos-Li in the medial amygdala was positively correlated with the post-ejaculatory interval. These experiments indicate that (1) stimulation of D1 receptors may contribute to the transient copulation-induced increase in Fos-Li in the MPN, and (2) repeated sexual experiences enhanced copulation-induced Fos-Li in the MPN, which may represent a marker of altered responsiveness of neurons in the MPN to sexual or conditioned stimuli.

Maternal separation: hypothalamic-preoptic area and hippocampal calbindin-D28K and calretinin in male and female infantile rats

Calcium-binding proteins (CaPs) potentially play important roles in neurogenesis and neuronal survival. Calbindin-D28K (CALB) and calretinin (CALRET) in the medial basal hypothalamic (and preoptic area) (MBH) and hippocampus (HIPPO) from control and maternally separated male and female infantile rats were examined by Western analysis. Significantly greater levels of the CaPs in the MBH vs. the HIPPO may suggest enhanced or decreased neuroprotection, respectively, during the stress hyporesponsive period (SHRP). Male infantile rats separated from their mother's from postnatal day 2-10 displayed significant changes in CALB and CALRET for the MBH (decrease) and HIPP (increase) brain sites suggesting possible modified (negative feedback) mechanism(s) in HPA dysfunction observed during postnatal life.

Catecholaminergic and neuropeptide Y-immunoreactive synaptic inputs onto median preoptic nucleus neurons projecting to the ventrolateral medullary catecholaminergic area in the rat

Median preoptic nucleus (POMe) neurons are innervated by catecholaminergic and neuropeptide Y (NPY)-immunoreactive nerve terminals originating from the catecholamine area of the ventrolateral medulla (VLM). The possibility that such POMe neurons project to the VLM catecholamine area was investigated in the rat. Immunoelectron microscopy revealed synaptic contacts of tyrosine hydroxylase- and NPY-immunoreactive axon terminals onto POMe neurons retrogradely labeled from the VLM catecholamine area, suggesting the existence of bidirectional connections between these two regions.

Postembryonic neural proliferation in the zebrafish forebrain and its relationship to prosomeric domains

Large gaps of knowledge exist regarding postembryonic brain morphogenesis of the zebrafish Danio rerio (Cyprinidae, Teleostei). The zebrafish represents together with the frog (Xenopus), chick and mouse--one of four major models for the genetic study of early brain development. Here, we used normal silver-stained Bodian material and immunohistochemical material stained with a monoclonal antibody against the proliferating cell nuclear antigen (PCNA, cyclin) to study the morphogenetic appearance and location of proliferation zones of the zebrafish brain between day 1 and day 10, focussing on the forebrain at day 5 postfertilization. Our results directly demonstrate that the dorsal telencephalic proliferation zone (i.e. the pallium) extends--consistent with the process of eversion--some distance laterally on top of the telencephalon. The subpallial telencephalic proliferation consists of dorsal and ventral zones. The preoptic region also includes dorsal and ventral proliferation zones. In the diencephalon proper, separate proliferation zones are present in the habenula, and in the periventricular cell masses of the dorsal thalamus, the ventral thalamus, and the pretectum. More ventrocaudally, the latter three massive proliferation zones appear to be replaced each by thinner, but distinct proliferation zones. Two of them represent ventrocaudal continuations of the dorsal and ventral thalamus and lie in the region referred to as the posterior tubercular area in adult teleostean neuroanatomy. The third lies in the region of the nucleus of the medial longitudinal fascicle. In addition, several hypothalamic proliferation zones are present. The data for the diencephalon are largely in agreement with the neuromeric model of brain organization of Puelles and Rubenstein (1993), which is mostly based on amniote data. Generally, the understanding of the prosomeric origin of teleostean prosencephalic cell masses may be regarded as pivotal for their comparative interpretation.

Glucocorticoid receptor immunoreactivity in neurons and pituitary cells implicated in reproductive functions in rainbow trout: a double immunohistochemical study

In order to identify the nature of the glucocorticoid receptor (GR)-expressing neurons and pituitary cells that potentially mediate the negative effects of stress on reproductive performance, double immunohistochemical stainings were performed in the brain and pituitary of the rainbow trout (Oncorhynchus mykiss). To avoid possible cross-reactions during the double staining studies, combinations of primary antibodies raised in different species were used, and we report here the generation of an antibody raised in guinea pig against the rainbow trout glucocorticoid receptor (rtGR). The results obtained in vitellogenic females showed that GnRH-positive neurons in the caudal telencephalon/anterior preoptic region consistently exhibited rtGR immunoreactivity. Similarly, in the anterior ventral preoptic region, a group of tyrosine hydroxylase-positive neurons, known for inhibiting gonadotropin (GTH)-2 secretion during vitellogenesis, was consistently shown to strongly express GR. Finally, we show that a large majority of the GTH-1 (FSH-like) and GTH-2 (LH-like) cells of the pituitary exhibit rtGR immunoreactivity. These results indicate that cortisol may affect the neuroendocrine control of the reproductive process of the rainbow trout at multiple sites.

Site-specific induction of Fos immunoreactivity in preoptic and hypothalamic NADPH-positive neurons during glucoprivation

Neuronal nitric oxide synthase, e.g. NADPH diaphorase (NADPH-d), catalyzes formation of the free radical, nitric oxide (NO), and occurs within brain structures that have functional significance for energy fuel homeostasis. The following studies examined whether populations of NADPH-d-positive neurons in the hypothalamus and nearby preoptic area express immunoreactivity for the nuclear transcription factor, Fos, in response to glucose substrate imbalance. Eight days after bilateral ovariectomy (OVX) and subcutaneous implantation of silastic capsules containing 30 microgram estradiol benzoate/ml, female rats were injected i.p. with the glucose antimetabolite, 2-deoxy-D-glucose (2DG; 400 mg/kg), or the vehicle, saline. The animals were sacrificed by transcardial perfusion 2 h after these treatments. Sections at 150-micrometer intervals throughout preoptic area and anterior and tuberal regions of the hypothalamus were processed for dual cytoplasmic NADPH-d enzyme activity and nuclear Fos-immunoreactivity (-ir). The glucose antimetabolite elicited expression of nuclear Fos-ir by NADPH-d-positive neurons in several neural structures, including the medial preoptic area, median preoptic nucleus, anterior commissural, periventricular magnocellular supraoptic nucleus, paraventricular nucleus, and medial part of the bed nucleus of the stria terminalis. In contrast, the extensive populations of NADPH-d-positive neurons in the ventromedial hypothalamic nucleus and lateral hypothalamic area showed very little immunolabeling for Fos in response to glucoprivation. This demonstration of nuclear immunoreactivity for Fos suggests that cellular glucopenia elicits the transcriptional activation, via AP-1 regulatory sites, of multiple populations of hypothalamic neurons characterized by the functional capacity to generate NO, and thus that this gaseous neurotransmitter may fulfill a role(s) in central neural mechanisms governing regulation of compensatory motor responses to metabolic imbalance.

Fos expression in the sleep-active cell group of the ventrolateral preoptic area in the diurnal murid rodent, Arvicanthis niloticus

The ventrolateral preoptic area (VLPO) of the nocturnal laboratory rat receives direct input from the retina and is active during sleep; however, nothing is known about VLPO function in day-active (diurnal) species. In the first study, we used 24-h videotaping of Arvicanthis niloticus, a diurnal murid rodent, to estimate the distribution of sleep and wakefulness across a 12:12 light-dark cycle. Based on behavioral data, A. niloticus were perfused at a time when the animals are inactive (zeitgeber time (ZT) 20) or at a time when they are awake and active (ZT 23). The brains were processed for immunocytochemistry for Fos, an immediate early gene product used as an index of neural activity. Animals had more Fos-immunoreactive (Fos+) cells in the VLPO at ZT 20 than at ZT 23. The pattern of change in Fos expression seen in this area suggest that the VLPO serves the same function in A. niloticus as in rats. Eye injections of cholera toxin (beta subunit) were used to identify the retinal inputs to the VLPO of A. niloticus. In these animals, the VLPO had only very sparse retinal inputs compared to the rat. Together, these results raise the possibility that inputs from the suprachiasmatic nucleus (SCN) or the retina affect neuronal activity in the VLPO differently in rats and A. niloticus, thereby, contributing to differences in their sleep/wake patterns.

Organizational effects of estrogens on brain vasotocin and sexual behavior in quail

Reproductive behavior is sexually differentiated in quail: The male-typical copulatory behavior is never observed in females even after treatment with high doses of testosterone (T). This sex difference in behavioral responsiveness to T is organized during the embryonic period by the exposure of female embryo to estrogens. We showed recently that the sexually dimorphic medial preoptic nucleus (POM), a structure that plays a key role in the activation of male copulatory behavior, is innervated by a dense steroid-sensitive network of vasotocin-immunoreactive (VT-ir) fibers in male quail This innervation is almost completely absent in the female POM and is not induced by a chronic treatment with T, suggesting that this neurochemical difference could be organizational in nature. This idea was tested by injecting fertilized quail eggs of both sexes on day 9 of incubation with either estradiol benzoate (EB) (25 microg, a treatment that suppresses the capacity to show copulatory behavior in adulthood) or the aromatase inhibitor R76713 (10 microg, a treatment that makes adult females behaviorally responsive to T), or with the solvents as a control (C). At 3 weeks posthatch, all subjects were gonadectomized and later implanted with Silastic capsules filled with T. Two weeks later, all birds were perfused and brain sections were processed for VT immunocytochemistry. Despite the similarity of the adult endocrine conditions of the subjects (all were gonadectomized and treated with T Silastic implants providing the same plasma level of steroid to all subjects), major qualitative differences were observed in the density of VT-ir structures in the POM of the different groups. Dense immunoreactive structures (fibers and a few cells) were observed in the POM of C males but not females; EB males had completely lost this immunoreactivity (and lost the capacity to display copulatory behavior); and, conversely, R76713 females displayed a male-typical VT-ir system in the nucleus (and also high levels of copulatory behavior). Similar changes in immunoreactivity were seen in the nucleus of the stria terminalis and in the lateral septum (VT-ir fibers only in this case) but not in the magnocellular vasotocinergic system. These neurochemical changes closely parallel the effects of the embryonic treatments on male copulatory behavior. The vasotocinergic system of the POM can therefore be considered an accurate marker of the sexual differentiation of brain circuits mediating this behavior.

Immunohistochemical demonstration of serotonin-containing axons in the hypothalamus of the white-footed mouse, Peromyscus leucopus

The wild white-footed mouse, Peromyscus leucopus, is commonly used for photoperiod studies utilizing physiological, behavioral, and other biological measures indicative of hypothalamic functions. Indoleamines, like melatonin and serotonin, are implicated in regulating these hypothalamic functions. Although neurochemical analyses of hypothalamic serotonin and its receptors have been reported for this species, the relevant neuroanatomy of the serotonin system within mouse hypothalamus has not been studied. A sensitive immunohistochemical method was used to detect serotonin within axons of coronal sections of formaldehyde fixed forebrain from P. leucopus. Large, medium and small diameter serotonin axons were evaluated in most regions, or nuclei, of the hypothalamus rostral to the mammillary region. A fourth type of serotonin axon was observed to have morphology characteristic of terminal arbors. The density of serotonin axons ranged from no staining to very high density similar to other species for which reports exist, i.e., rat, cat, and monkey. The ventromedial hypothalamic nucleus had distinctively lesser density of serotonin axons in this mouse than other species. Evidence of terminal arborization in hypothalamic nuclei and regions was evident. Neuroendocrine, autonomic, and behavioral functions of the hypothalamus are suggested to be regulated by input from serotonin terminals in this wild species of mouse, in correlation with receptor localization as reported by others.

Diurnal rhythmicity of gonadotropin-releasing hormone gene expression in the rat

The release of the decapeptide gonadotropin-releasing hormone (GnRH) from neuroterminals in the median eminence varies depending upon the stage of development, time of day, reproductive season, and day of the ovarian cycle. With respect to the biosynthetic events responsible for such alterations in GnRH release, we have reported that increases in GnRH mRNA occur concomitantly with or precede the proestrous GnRH/LH surge in female rats, and the pubertal increase in GnRH. Because a hallmark of puberty is the development of nocturnal increases in gonadotropin/GnRH release, in the present study, we examined whether a rhythm in GnRH gene expression occurs that may be responsible for this rhythm of neurosecretion. Additionally, we extended the previous finding of diurnal rhythms of GnRH gene expression in cycling females to adult male rats. The mechanism for these changes, i.e. GnRH gene transcription, RNA processing or a posttranscriptional mechanisms was also elucidated. In experiment I, GnRH gene expression was measured in female rats at different stages of puberty [P25 (juvenile); approximately P37 (day of vaginal opening); and P45 (postpubertal)] at 10.00, 14.00, 18.00, 22.00, 2.00 and 6.00 h. GnRH mRNA levels increased significantly during pubertal development, independent of any changes in GnRH gene transcription or RNA processing, indicating a posttranscriptional mechanism. GnRH mRNA levels did not vary with time of day in these pubertal rats, indicating that the diurnal rhythm of GnRH release that develops during puberty is probably a posttranslational event. In experiment II, GnRH gene expression was measured in adult male rats at the same 4-hour intervals. GnRH mRNA levels varied significantly with time of day: they increased from 10.00 to 14.00 h, remained elevated through 22.00 h, then decreased significantly to the nadir at 10.00 h. The mechanism for these changes appears to involve processing or stability of the GnRH mRNA in the nucleus. These results indicate that GnRH mRNA levels are regulated differentially with time of day depending upon age and gender.

Large somal size is associated with the expression of galanin but not with neuronal birthdate in the sexually dimorphic male nucleus of ferret's preoptic area/anterior hypothalamus

Using Nissl and Golgi stains, a sexually dimorphic male nucleus (MN) comprised of a cluster of large cells with large dendritic arbors has been identified in the dorsal preoptic area/anterior hypothalamus (POA/AH) of male ferrets. The MN-POA/AH is formed only in males by the action of estradiol derived from the neural aromatization of testosterone during the last quarter of a 41-day gestation. The ferret's dorsal POA/AH is also characterized by a sex difference in the expression of the neuropeptide galanin which first arises in males around embryonic day (e) 34. We asked whether the male-typical phenotype of large somal size is related to birthdate and/or the capacity of dorsal POA/AH neurons to express galanin. In experiment 1 we labeled cohorts of cells born on E20, E24, or E28 by injecting the amniotic sacs of individual fetuses with the thymidine analogue bromodeoxyuridine (BrdU). On postnatal day 20, BrdU-immunoreactive cells were visualized immunohistochemically, counterstained with cresyl violet, and their somal sizes were measured. BrdU-immunoreactive cells were significantly larger in the males' MN-POA/AH than in a comparable region of females, regardless of when they were born between E20 and E28. In experiment 2 galanin-immunoreactive cells in the dorsal POA/AH of adult ferrets were visualized immunohistochemically, and their somal sizes were measured. Somal areas of galanin-immunoreactive cells were significantly larger in the MN-POA/AH of intact, breeding, or castrated and testosterone-treated males than in the corresponding area of females. Our results suggest that cells in the males' MN-POA/AH are more likely to be larger than cells in females' corresponding region, regardless of birthdate. Finally, in adulthood the male-typical phenotype of large Nissl-stained somal areas of MN-POA/AH cells may, in part, reflect their increased galanin expression.

Developmental sex differences in estrogen receptor-beta mRNA expression in the mouse hypothalamus/preoptic region

Estrogens play a significant role during mammalian brain development and are required for the masculinization of neuronal circuits involved in sex-specific behaviors and neuroendocrine functions. Cellular estrogen signalling is transmitted through nuclear estrogen receptors (ER) which are divided into two subforms: the ER-alpha as well as the recently cloned ER-beta have been demonstrated in the hypothalamus. In the present study, we have analyzed the sex-specific expression of ER-beta mRNA in the pre- and postnatal mouse hypothalamus/preoptic region (Hyp/POA) by semiquantitative RT-PCR. The ER-beta mRNA was detectable as early as embryonic day (E) 15 in the diencephalon of both sexes. In males, levels of mRNA expression in the Hyp/POA increased until birth and remained high throughout postnatal (P) development, whereas in females, such an increase was not observed. Significantly higher mRNA levels were detected in the male Hyp/POA from E17 until P15. Perinatal sex differences in ER-beta mRNA expression coincide with higher estrogen-forming rates in the male Hyp/POA. At present, no direct evidence is available which demonstrates that estrogen signalling through ER-beta is involved in brain development. However, data from our and other studies suggest a potential role for this signal transduction pathway for brain differentiation.

Testosterone differentially regulates expression of GnRH messenger RNAs in the terminal nerve, preoptic and midbrain of male tilapia

The purpose of the present study was to examine the regulation of three molecular variants of gonadotropin-releasing hormone (GnRH)-encoding mRNAs by testosterone in the male tilapia Oreochromis niloticus. Tilapias castrated for two weeks were injected intraperitoneally with sesame oil or 5 microgram/g testosterone for 7 days. In situ hybridization histochemistry was performed using 35S-labelled 30-mer antisense oligonucleotide probes complementary to exon two (bases 1-30) of salmon-, seabream-, and chicken II-GnRH. Computerized image analysis was performed to quantify GnRH mRNA expression in the terminal nerve ganglia (nucleus olfactoretinalis) and in individual cells of the preoptic area and the midbrain tegmentum. Testosterone treatment significantly elevated terminal nerve salmon-GnRH mRNA, reduced preoptic seabream-GnRH mRNA but had no effect on midbrain chicken II-GnRH mRNA levels. The total number and size of preoptic and midbrain GnRH mRNA-containing neurons or the total volume of the terminal nerve ganglia in testosterone-treated animals did not differ significantly from oil-treated animals. The midbrain chicken II-GnRH neurons are not targets of testosterone. These results demonstrate for the first time differential regulation of subpopulations of GnRH neurons with molecular diversity and different topography.

Sex differences in estrogenic regulation of preproenkephalin mRNA levels in the medial preoptic area of prepubertal rats

Opioids have been implicated in sexual differentiation of the brain and in the regulation of reproductive behavior and endocrinology of mammals. Previous studies have indicated that estrogen administration in adults regulates preproenkephalin MRNA levels in several hypothalamic brain nuclei. We have determined preproenkephalin mRNA levels in estrogen-treated juvenile male and female rats to investigate the developmental pattern of estrogenic regulation of enkephalinergic neurons in the medial preoptic area. Rats were treated with estradiol benzoate (20 microgram/kg/day) or oil from day 21 to 23. Sections of the medial preoptic area (mPOA) were studied by in situ hybridization histochemistry at the single cell level and quantified with the assistance of an image analysis system. Our data indicate that males contain higher levels of preproenkephalin mRNA per neuron than females. In addition, our results indicate that estrogen causes an upward shift in the amount of mRNA expressed per cell, females demonstrating a greater response to estrogen than males. An increase in soma cell area following estrogen treatment was observed only in female mPOA enkephalinergic neurons. Taken together, these results indicate a sex difference in total preproenkephalin levels and in estrogenic regulation of preproenkephalin mRNA in the POA of juvenile rats. These results are discussed in relation to the differential role opioids may play in male and female reproductive physiology.

Androgen-dependent modulation of calbindin-D28K in hypothalamic tissue during prenatal development

We examined the influence of androgens on fetal medial basal hypothalamic and preoptic area (MBH-POA) calbindin-D28K levels (via Western analysis) by treating pregnant rats with testosterone or flutamide, (an androgen receptor blocker). MBH-POA calbindin-D28K levels were significantly decreased in flutamide-treated male fetuses, whereas, MBH-POA calbindin-D28K levels were significantly increased in testosterone-treated female fetuses compared to controls. These results suggest that MBH-POA calbindin-D28K is modulated during prenatal development by androgens.

Monoamines, amino acids and acetylcholine in the preoptic area and anterior hypothalamus of rats: measurements of tissue extracts and in vivo microdialysates

A microbore column high-performance liquid chromatography (HPLC) system was used to measure neurotransmitters in tissue extracts and in vivo microdialysates obtained from the preoptic area (PO) and anterior hypothalamus (AH) of rats. The extracts contained norepinephrine, epinephrine, 3,4-dihydroxyphenylacetic acid (DOPAC), dopamine, 5-hydroxyindoleacetic acid (5-HIAA), homovanillic acid (HVA), 5-hydroxytryptamine (5-HT), aspartate, glutamate, GABA, acetylcholine (ACh) and choline. The microdialysates obtained from the PO and AH of freely moving rats contained all of these substances except for norepinephrine, epinephrine, dopamine, and 5-HT. During collection of microdialysate from the PO and AH, core body temperature and locomotor activity were simultaneously measured by means of telemetry. The locomotor activity and body temperature increased during the night. This was accompanied by increased levels of 5-HIAA. The results suggest that serotonergic neuronal mechanisms in the PO and AH may be involved in hypothalamic regulation of spontaneous behaviors and body temperature.

Preoptic AVT immunoreactive neurons of a teleost fish with alternative reproductive tactics

Recent reports have implicated an important role for arginine vasotocin (AVT) in the socially mediated sexual differentiation of fishes. This study focuses on the plainfin midshipman (Porichthys notatus) which exhibits two male morphs, type I and type II, differing in a suite of behavioral, neurobiological, and endocrine traits. Immunocytochemical techniques were used to detect neurons containing AVT-like peptide in the forebrain of juveniles, adult females, and type I and type II males. AVT immunoreactive (ir) somata were localized to three regions: the terminal nerve ganglion, the preoptic area (POA), and the pineal stalk. The profile area, or size, of AVT-ir POA neurons differed across the four classes of midshipman and was strongly correlated to differences in body size among the groups. By contrast, the number of AVT-ir cells in the POA exhibited no difference across the classes of midshipman. The number of POA cells containing AVT is therefore likely to be set early in development and not to change with the growth of the animal. An analysis of AVT-ir cell number normalized by body mass revealed that the larger morphs, type I males and females, have fewer cells per gram body mass than type II males and juveniles. Therefore, type II males have a juvenile-like AVT POA phenotype with smaller cells and more numerous cells per unit body mass than type I males. Type II males also exhibit more variability in the number of AVT-ir cells found in the POA compared to type I males.

The role of alpha-2 receptors in the medial preoptic area in the regulation of sleep-wakefulness and body temperature

The study was conducted on 48 free-moving male rats to find out the role of the medial preoptic alpha2 receptors in the regulation of sleep and body temperature. Recording electrodes for assessment of sleep-wakefulness, and injector cannulae for injection of drugs in the medial preoptic area were chronically fixed on the skulls of the animals. The noradrenergic fibres projecting to the medial preoptic area were destroyed in 24 rats by administration of 6-hydroxydopamine at the ventral noradrenergic bundle. Though arousal was produced in normal rats by the injection of the alpha2 adrenergic agonist, clonidine, at the medial preoptic area, it induced sedation in rats with noradrenergic fibre lesion. Clonidine did not alter the rectal temperature in normal rats but it induced hypothermia in lesioned rats. Injection of alpha2 antagonist, yohimbine, at the medial preoptic area induced sleep in rats with intact noradrenergic fibres. However, the sleep inducing effect of this drug was very much attenuated in the lesioned animals. There was no significant change in body temperature, in both these groups of animals, after yohimbine administration. The study indicates the role of presynaptic alpha2 adrenergic receptors in arousal response and indirectly supports the contention that the alpha1 postsynaptic receptors at the medial preoptic area are involved in hypnogenesis. It also suggests that the thermal changes induced by adrenergic system are mediated through alpha1 postsynaptic receptors. But the thermal changes do not contribute towards the induced alterations in sleep-wakefulness. It is proposed that there should be separate sets of noradrenergic terminals for regulation of sleep and body temperature.

Potential role of maternal progesterone in the sexual differentiation of the brain

In rats, fetal testosterone directs sexual differentiation of the brain. However, fetuses are also exposed to maternal progesterone. Here we report that progestin receptor immunoreactivity in the medial preoptic nucleus (MPN) of fetal and neonatal rats is high in males but virtually absent in females. The MPN is one of the most sexually dimorphic structures in the rat brain and mediates several sexually differentiated behaviors. This suggests that progesterone may play a previously overlooked role in the development of sex differences in the brain and behavior. Henceforth, a novel function of the mother in the sexual differentiation of the CNS must be considered.

Fos-immunoreactivity within the extended amygdala is correlated with the onset of sexual satiety

We hypothesized that c-fos expression in the medial amygdala (Me), the bed nucleus of the stria terminalis (BNST), and the medial preoptic area (MPOA) of the male Syrian hamster brain correlated with sexual satiety. To address this hypothesis, males were mated for 4 consecutive days. Experiment 1 determined whether the number of Fos-immunoreactive (Fos-ir) nuclei was equivalent in two groups of males mated to sexual satiety, one group of rested males (9.67 +/- 0.80 ejaculations) and a second group mated for 4 consecutive days (3.50 +/- 0.56 ejaculations). Fos-ir was increased within the caudal posterodorsal Me (cMePD), the anterodorsal and posteroventral subdivisions of the posteromedial BNST [BNSTpm(ad) and BNSTpm(pv)], the dorsolateral MPOA, and the medial preoptic nucleus of all males mated to sexual satiety compared to nonmated controls. In addition, Fos-ir "clusters" within the cMePD and BNSTpm(ad) were present in males mated to satiety regardless of the number of ejaculations. However, all males achieved multiple ejaculations. Therefore, Experiment 2 examined whether two groups of males stopped at one ejaculation exhibit different patterns of Fos-ir depending on proximity to sexual satiety. Brains of consecutively mated males, closer to satiety than rested males, showed greater BNSTpm(pv) Fos-ir and 5/6 males, but no rested male, exhibited cMePD Fos-ir clusters. These results support the hypothesis that cMePD and BNSTpm(pv) neuronal activation is associated with satiety and may constitute a discrete circuit to terminate mating.