Coexistence of FMRFAMIDE-like and LHRH-like immunoreactivity in the terminal nerve and forebrain of the big brown bat, Eptesicus fuscus

The coexistence of molluscan cardioexcitatory neuropeptide (FMRFAMIDE) and luteinizing hormone-releasing hormone (LHRH) was studied in the nervous system of the big brown bat, Eptesicus fuscus, with immunocytochemistry. Within mammals, this is the first report of the coexistence of these neuropeptides in the terminal nerve. In juvenile and adult bats, both neuropeptides are distributed identically throughout the terminal nerve (tn), and they coexist in many parts of the prosencephalon from the olfactory bulb as far caudally as the interpeduncular nucleus. Peripherally, on the basal surface of the forebrain, fibers and a few perikarya, which may belong to the tn, form a loose plexus. Within the brain wall, regions of maximal immunoreactivity (ir) are the habenula, medial preoptic area, arcuate nucleus, and the infundibulum. Whereas in most areas of the prosencephalon (e.g., stria terminalis and bed nuclei, amygdaloid complex) fibers show stronger immunoreactivity to FMRFAMIDE, labeling of fibers in the habenula and infundibulum is largely identical for both neuropeptides. The arcuate nucleus contains a large number of perikarya and is the major source of both FMRFAMIDE- and LHRH-ir within the forebrain. A number of fibers run along the ependyma of the ventricular system and seem to terminate here; this is particularly evident in the median eminence and infundibular stalk. In the big brown bat, there seems to exist a continuum of FMRFAMIDE- and LHRH-ir throughout the tn and those structures of the forebrain that are known to be engaged in the control of mating behavior, reproduction, and rhythmicity. Concerning the hypothalamo-hypophyseal-gonadal axis, the arcuate nucleus may serve as a central hub between the olfactory/terminal input and superior areas including the limbic system. In contrast to LHRH immunoreactivity, FMRFAMIDE-like ir extends throughout the brainstem and cervical spinal cord. This system may also be involved in the processing and modulation of autonomic input via the parabrachial and solitary nuclei, the rhombencephalic central gray, and its projection into the hypothalamus (paraventricular nucleus), thus facilitating feed-back of gonadotropic influences of the terminal nerve and prosencephalon.

The distribution of cells containing estrogen receptor-alpha (ERalpha) and ERbeta messenger ribonucleic acid in the preoptic area and hypothalamus of the sheep: comparison of males and females

We have used in situ hybridization to compare the distributions of estrogen receptor alpha (ERalpha) and ERbeta messenger RNA (mRNA)-containing cells in the preoptic area and hypothalamus of ewes and rams. Perfusion-fixed brain tissue was collected from luteal phase ewes and intact rams (n = 4) during the breeding season. Matched pairs of sections were hybridized with sheep-specific, 35S-labeled riboprobes, and semiquantitative image analysis was performed on emulsion-dipped slides. A number of sex differences were observed, with females having a greater density of labeled cells than males (P < 0.001) and a greater number of silver grains per cell (P < 0.01) in the ventromedial nucleus for both ER subtypes. In addition, in the retrochiasmatic area, males had a greater (P < 0.05) cell density for ERalpha mRNA-containing cells than females, whereas in the paraventricular nucleus, females had a greater density (P < 0.05) of ERalpha mRNA-containing cells than males. There was a trend (P = 0.068) in the arcuate nucleus for males to have a greater number of silver grains per cell labeled for ERalpha mRNA. In both sexes, there was considerable overlap in the distributions of ERalpha and ERbeta mRNA-containing cells, but the density of labeled cells within each nucleus differed in a number of instances. Nuclei that contained a higher (P < 0.001) density of ERalpha than ERbeta mRNA-containing cells included the preoptic area, bed nucleus of the stria terminalis, and ventromedial nucleus, whereas the subfornical organ (P < 0.001), paraventricular nucleus (males only, P < 0.05), and retrochiasmatic nucleus (females only, P < 0.05) had a greater density of ERalpha than ERbeta mRNA-containing cells. The anterior hypothalamic area and supraoptic nucleus had similar densities of cells containing both ER subtypes. The lateral septum and arcuate nucleus contained only ERalpha, whereas only ERbeta mRNA-containing cells were seen in the zona incerta. The sex differences in the populations of ER mRNA-containing cells in the ventromedial and arcuate nuclei may explain in part the sex differences in the neuroendocrine and behavioral responses to localized estrogen treatment in these nuclei. Within sexes, the differences between the distributions of ERalpha and ERbeta mRNA-containing cells may reflect differential regulation of the actions of estrogen in the sheep hypothalamus. Low levels of ERbeta mRNA in the preoptic area and ventromedial and arcuate nuclei, regions known to be important for the regulation of reproduction, suggest that ERbeta may not be involved in these functions.

Immunolocalization of androgen receptors and aromatase enzyme in the adult musk shrew brain

In the brain and other tissues, estrogens are produced by aromatization of androgens. Biochemical data suggest that aromatase enzyme is regulated by the androgen receptor (AR). Neurons that contain either AR or aromatase (AROM) enzyme reside in many of the same brain regions. In this report, we examined the codistribution of AR- and AROM-enzyme-immunoreactive (-ir) neurons in several regions of the adult male and female musk shrew brain. Data were collected from the intermediate nucleus of the lateral septum (LS), medial anterior (BNSTMA) and medial posterointerior (BNSTMP) divisions of the bed nucleus of the stria terminalis, medial preoptic area (mPOA), ventromedial nucleus of the hypothalamus (VMN), medial (MeA), cortical and central nuclei of the amygdala. Males had significantly more AR-ir neurons in the BNSTMP, mPOA, VMN and LS as compared to females. With the exception of the BNSTMA and LS, males had more AROM-ir neurons in each region than females. Furthermore, males had significantly more double-labeled neurons than females in the BNSTMP, mPOA, VMN, LS and MeA. The percentage of AROM-ir neurons that also contained AR immunoreactivity ranged from 13 to 82% depending on sex and region. The highest percentage of dual-labeled neurons (79% in females and 82% in males) was found in the VMN. Taken together, these data show that there is extensive cellular colocalization of AR and AROM enzyme in specific regions of the musk shrew brain. We propose that in both sexes, androgen receptors may act as transcription factors to regulate AROM enzyme.

Rhythms in Fos expression in brain areas related to the sleep-wake cycle in the diurnal Arvicanthis niloticus

Most mammals show daily rhythms in sleep and wakefulness controlled by the primary circadian pacemaker, the suprachiasmatic nucleus (SCN). Regardless of whether a species is diurnal or nocturnal, neural activity in the SCN and expression of the immediate-early gene product Fos increases during the light phase of the cycle. This study investigated daily patterns of Fos expression in brain areas outside the SCN in the diurnal rodent Arvicanthis niloticus. We specifically focused on regions related to sleep and arousal in animals kept on a 12:12-h light-dark cycle and killed at 1 and 5 h after both lights-on and lights-off. The ventrolateral preoptic area (VLPO), which contained cells immunopositive for galanin, showed a rhythm in Fos expression with a peak at zeitgeber time (ZT) 17 (with lights-on at ZT 0). Fos expression in the paraventricular thalamic nucleus (PVT) increased during the morning (ZT 1) but not the evening activity peak of these animals. No rhythm in Fos expression was found in the centromedial thalamic nucleus (CMT), but Fos expression in the CMT and PVT was positively correlated. A rhythm in Fos expression in the ventral tuberomammillary nucleus (VTM) was 180 degrees out of phase with the rhythm in the VLPO. Furthermore, Fos production in histamine-immunoreactive neurons of the VTM cells increased at the light-dark transitions when A. niloticus show peaks of activity. The difference in the timing of the sleep-wake cycle in diurnal and nocturnal mammals may be due to changes in the daily pattern of activity in brain regions important in sleep and wakefulness such as the VLPO and the VTM.

Calbindin-D28k immunoreactivity is a marker for a subdivision of the sexually dimorphic nucleus of the preoptic area of the rat: developmental profile and gonadal steroid modulation

Calbindin-D28k (calbindin) is a 28 kilodalton calcium binding protein which potentially plays a role in neuroprotection. We report here the normal development and gonadal steroid modulation of a sexually dimorphic group of calbindin immunoreactive cells within the sexually dimorphic nucleus of the preoptic area (SDN) which we call the calbindin-immunoreactive SDN or CALB-SDN. Beginning on PN2, a faintly immunoreactive CALB-SDN is present, however, the volume is not sexually dimorphic. On PN4, the staining of the CALB-SDN appears more robust but the volume is still not sexually dimorphic. By PN8 and extending through PN12 and PN26, the latest age analysed, the volume of the CALB-SDN is larger in males by two- to fourfold. Cresyl violet counterstain reveals a similar developmental profile of the SDN as well as clusters of darkly staining calbindin immunonegative cells which lie around the CALB-SDN. Castration of males on PN0 decreases the volume of the CALB-SDN by PN12 and administration on the day of birth and PN1 of either testosterone propionate or oestradiol benzoate, but not dihydrotestosterone propionate to females increases the volume of the CALB-SDN by PN12. By demonstrating the sexual dimorphism and gonadal steroid modulation of the CALB-SDN, we hereby establish that calbindin is a specific marker of a subdivision of the SDN and can be used as such in future studies.

The two thyroid hormone receptor genes have opposite effects on estrogen-stimulated sex behaviors

The two genes coding for thyroid hormone receptors (TR) alpha 1 and beta have opposite effects on female sex behaviors. Deletion of TRalpha 1 reduced them, whereas deletion of TRbeta actually increased them. These results could not be attributed to altered levels of hormones in the blood, general alterations in estrogen responsiveness or altered general activity. Instead, they indicate a previously unknown molecular mechanism upon which the two TR genes exert opposite influences.

Effect of interleukin-1beta on gonadotropin-releasing hormone (GnRH) and GnRH receptor gene expression in castrated male rats

Increasing evidence suggests that interleukin-1beta (IL-1beta) regulates luteinizing hormone (LH) release primarily through modulation of the gonadotropin-releasing hormone (GnRH) neuronal activity. This study was undertaken to elucidate the effect of IL-1beta on GnRH as well as GnRH receptor (GnRHR) gene expression in the preoptic area. IL-1beta (100 ng/rat) or saline was administered into the lateral ventricle of castrated rats. RNA samples were isolated from micropunches of the preoptic area and mediobasal hypothalamus from individual brain slices and GnRH mRNA levels in the preoptic area and GnRHR mRNA levels in the mediobasal hypothalamus were determined by competitive reverse transcription-polymerase chain reaction (RT-PCR) protocols. Serum LH concentrations were decreased from 1 h to 3 h after IL-1beta treatment, but rebounded at 5 h, while serum concentrations of follicle-stimulating hormone (FSH) and prolactin were not altered. There were no significant changes in GnRH mRNA levels from the micropunched preoptic area, while GnRHR mRNA levels from the preoptic area and mediobasal hypothalamus micropunch samples, but not in the anterior pituitary, showed a pattern similar to the serum LH profile following i.c.v. administration of IL-1beta. We then examined the effect of IL-1beta on the translational efficiency of the GnRH mRNA. After the separation and fractionation of polyribosome-associated cytoplasmic RNA from the hypothalamic fragments containing the preoptic area-anterior hypothalamic area of control (saline-treated) and IL-1beta-treated group 3 h after administration, GnRH transcript levels were examined from the each fraction. IL-1beta decreased the translational efficiency of the transcribed GnRH mRNA. These results clearly demonstrate that central administration of IL-1beta suppresses the translational activity of GnRH mRNA. Moreover, GnRHR may play an important role in the modulation of GnRH neuronal activity through GnRHR-expressing neurones (or glia) in the hypothalamus.

Differential distribution of gonadotropin-releasing hormone-immunoreactive neurons in the stingray brain: functional and evolutionary considerations

Gonadotropin-releasing hormone (GnRH) is a neuropeptide that occurs in multiple structural forms among vertebrate species. Bony fishes, amphibians, reptiles, birds, and mammals express different forms of GnRH in the forebrain and endocrine regions of the hypothalamus which regulate the release of reproductive gonadotropins from the pituitary. In contrast, previous studies on bony fishes and tetrapods have localized the chicken GnRH-II (cGnRH-II) nucleus in the midbrain tegmentum and, combined with cladistic analyses, indicate that cGnRH-II is the most conserved form throughout vertebrate evolution. However, in elasmobranch fishes, the neuroanatomical distribution of cGnRH-II and dogfish GnRH (dfGnRH) cells and their relative projections in the brain are unknown. We used high-performance liquid chromatography and radioimmunoassay to test for differential distributions of various GnRH forms in tissues from the terminal nerve (TN) ganglia, preoptic area, and midbrain of the Atlantic stingray, Dasyatis sabina. These experiments identified major peaks that coelute with cGnRH-II and dfGnRH, minor peaks that coelute with lamprey GnRH-III (lGnRH-III), and unknown forms. Immunocytochemistry experiments on brain sections show that dfGnRH-immunoreactive (-ir) cell bodies are localized in the TN ganglia, the caudal ventral telencephalon, and the preoptic area. Axons of these cells project to regions of the hypothalamus and pituitary, diencephalic centers of sensory and behavioral integration, and the midbrain. A large, discrete, bilateral column of cGnRH-II-ir neurons in the midbrain tegmentum has sparse axonal projections to the hypothalamus and regions of the pituitary but numerous projections to sensory processing centers in the, midbrain and hindbrain. Immunocytochemical and chromatographic data are consistent with the presence of lGnRH-III and other GnRH forms in the TN that differ from dfGnRH and cGnRH-II. This is the first study that shows differential distribution of cGnRH-II and dfGnRH in the elasmobranch brain and supports the hypothesis of divergent function of GnRH variants related to gonadotropin control and neuromodulation of sensory function.

Phytoestrogens decrease brain calcium-binding proteins but do not alter hypothalamic androgen metabolizing enzymes in adult male rats

Phytoestrogen [plant estrogenic-like molecule(s)] research has grown rapidly in recent years due to their potential health benefits. However, little is known about phytoestrogen's effects on the CNS. Androgen metabolizing enzymes are known to regulate neuroendocrine functions and reproductive behaviors, while calcium-binding proteins are associated with protecting against neurodegenerative diseases. Therefore, we examined aromatase and 5alpha-reductase enzyme activities in the medial basal hypothalamic and preoptic area (mbh-poa) and characterized mbh-poa and amygdala (amy) calbindin and calretinin levels (via Western analysis) from animals fed a phytoestrogen-free (P-free) vs. a phytoestrogen-containing diet [(P-600); that had 600 microg/g of phytoestrogens]. After approximately 5 weeks on the diets, the male rats were killed at 105 days. P-600 plasma phytoestrogen levels were 78-fold higher than the P-free values and the mbh-poa phytoestrogen content was 8-fold higher than the P-free group, demonstrating the passage of phytoestrogens into brain. In general, brain aromatase or 5alpha-reductase activity levels were not significantly altered by the experimental diets. However, independent of brain site (i.e., mbh-poa or amy) the abundance of calbindin from male P-600 rats was significantly lower than P-free animals. Conversely, for calretinin there were no significant alterations in the mbh-poa tissue site, while in the amy a similar pattern of expression was seen to that of the calbindin results. These data suggest that consumption of phytoestrogens via a soy diet for a relatively short interval can significantly: (1) elevate plasma and brain phytoestrogens levels and (2) decrease brain calcium-binding proteins without altering brain androgen metabolizing enzymes.

Progesterone, but not progesterone-independent activation of progestin receptors by a mating stimulus, rapidly decreases progestin receptor immunoreactivity in female rat brain

Recent studies suggest that progestin receptors may be activated in vivo by neurotransmitters in the absence of ligand. More specifically, vaginal-cervical stimulation (VCS) can influence sexual behavior by activating progestin receptors in the absence of progesterone. Another way to test if progestin receptors are influenced by particular stimuli is to examine progestin receptor immunostaining. We report that progestin receptor immunoreactivity is decreased in the forebrain of estradiol-primed ovariectomized (OVX) rats within 1 h after a subcutaneous injection of progesterone, a time by which rapid down-regulation of progestin receptors does not seem to have occurred. In estradiol-primed OVX rats, VCS also decreased progestin receptor immunoreactivity within 1 h in the medial preoptic area, but not in any other area examined. To determine if the decrease in immunoreactivity by VCS was due to adrenal secretions or by ligand-independent activation of progestin receptors, we repeated the experiment in estradiol-primed OVX/adrenalectomized rats. Prior removal of the adrenal glands blocked the rapid decrease in progestin receptor immunoreactivity, even though data from other experiments suggest that progestin receptors are activated by VCS at this time. These studies suggest the possibility that progestin receptors may be affected differentially by progesterone-dependent or by progesterone-independent pathways. This raises the possibility that activation of progestin receptors by these two distinct pathways may lead to different neuronal consequences.

Gonadotropin-releasing hormones in the brain and pituitary of the teleost, the white sucker

The present study investigated GnRH forms within the brain of a representative of the order Cypriniformes, the white sucker, Catostomus commersoni, using HPLC, RIA, and immunocytochemistry. Several immunoreactive (ir) GnRH forms were identified in the brain of the white sucker by chromatography and radioimmunoassay, including ir-salmon GnRH, ir-lamprey GnRH-I and -III, and ir-chicken GnRH-II. Results from immunocytochemical studies were consistent with multiple GnRH forms distributed in different patterns, particularly for fibers. Neuronal perikarya containing ir-salmon GnRH and ir-lamprey-like GnRH were found laterally within the preoptic area and rostral hypothalamus. Cells containing exclusively ir-salmon GnRH appeared slightly more rostrally, but in the same region. Fibers containing ir-salmon GnRH and ir-lamprey-like GnRH were seen throughout the caudal telencephalon and extended into the diencephalon, toward the pituitary. Fibers containing ir-chicken-II-like GnRH were also seen in the caudal telencephalon, but were concentrated more dorsally in the diencephalon. Within the pituitary, fibers containing ir-salmon GnRH and ir-lamprey-like GnRH entered the neurohypophysis, but differed in their destinations. Fibers containing ir-salmon GnRH remained within the neurohypophysis, while fibers containing ir-lamprey-like GnRH targeted adenohypophyseal tissue. These findings are consistent with the hypothesis that multiple GnRH forms with multiple functions exist within the brain and pituitary of teleosts and provide further evidence of a lamprey-like GnRH within an early evolved teleost species.

Expression of mu-opioid receptor mRNA in the medial preoptic area of juvenile rats

Previous studies indicate that the latency to initiate parental behavior in both male and female rats increases with age; weanling (21 days old) rats display parental behavior 0-2 days after exposure to newborn pups, while older juveniles (30 days old) require 5-6 days of pup exposure before they express the behavior. Furthermore, activation of mu-opioid receptors inhibits parental behavior in juvenile and adult rats. We hypothesized that the age-related increase in behavioral latency could be modulated by the induction of mu-receptor expression in the medial preoptic area (MPOA), a region in which mu-receptors regulate parental behavior. In situ hybridization histochemistry was used to measure mu-receptor mRNA expression in the MPOA of male and female Sprague-Dawley rats that were 21, 24, 27, 30, or 33 days old. Using autoradiographic film analysis, we observed that neurons within part of the MPOA expressed very dense mu-receptor mRNA. Comparison of mRNA distribution with histological boundaries indicated that neurons within the medial preoptic nucleus (MPN), excluding the central part, exhibited the highest density of mu-receptor mRNA within the MPOA. High densities of mu-receptor mRNA extended dorsolaterally and caudally from the MPN toward the bed nucleus of the stria terminalis. MPN mu-receptor mRNA expression was not altered with age and no sex difference was observed. The dense presence of mu-receptor mRNA in the MPN suggests that ample substrate exists on which mu-receptor ligands could modulate the latency to begin parental behavior in juvenile rats, but such behavioral expression apparently is not mediated by a change in mu-receptor mRNA production.

Oestrogen receptor alpha is essential for female-directed chemo-investigatory behaviour but is not required for the pheromone-induced luteinizing hormone surge in male mice

The expression of normal masculine sexual behaviour requires testosterone. Testosterone can bind to androgen receptors, either in its native form, or after reduction to other androgen metabolites. In addition, testosterone can be aromatized to oestrogen, and bind to oestrogen receptor alpha and/or beta. Male copulatory behaviour is deficient in mice lacking functional oestrogen receptor alpha gene (ERalphaKO mice). We sought to determine which aspect(s) of masculine sexual behaviour is compromised in the ERalphaKOs. Specifically, we asked whether ERalphaKO males have reduced motivation and/or an inability to recognize oestrous females. We found significant differences between mice of different genotypes in the amount of chemo-investigatory behaviour displayed and in the target of their investigation. Wild-type males spent more time investigating ovariectomized, oestradiol-treated females, than either males, or ovariectomized females that had not received hormone priming. ERalphaKO males spent little time investigating any of the stimulus mice and showed no preferences. To test the hypothesis that this lack of chemo-investigatory behaviour is due to the inability of ERalphaKO males to detect and respond to female pheromones, we exposed males to chemosensory cues (soiled bedding) from females. Males resided in clean, or female-soiled, cage bedding for 60 min. Next, blood was collected and plasma luteinizing hormone (LH) assayed. We also assessed Fos-like immunoreactivity (Fos-ir) in several neural regions involved in processing chemosensory cues. Despite the fact that male ERalphaKOs spend little time engaged in chemo-investigation of females, their neuroendocrine responses to female-soiled bedding were similar to those seen in wild-type males. Our data suggest that the normal coupling between the neuroendocrine response to females and the generation of sexual behaviour is disrupted in ERalphaKO mice. Responses to female pheromones do not require ERalpha. However, normal male sexual performance requires the ERalpha gene.

The negative feedback action of progesterone on luteinizing hormone release is not associated with changes in GnRH mRNA expression in the Ewe

Progesterone is the ovarian hormone that times events in the ovine reproductive cycle. When elevated, this ovarian hormone acts centrally to inhibit both the tonic and surge modes of gonadotrophin releasing hormone (GnRH) release. Two studies were performed to address the underlying neural mechanisms. The first tested the hypothesis that the rapid rise in GnRH release, that results from an acute fall in progesterone concentrations (such as occurs following luteolysis), is temporally associated with a rapid rise in the cellular content of GnRH mRNA. Three groups of ovariectomised (OVX) ewes were treated with exogenous progesterone for 10 days, while one remained steroid free (OVX, n=7). To determine the effects of acute progesterone (P) withdrawal, ewes were killed on day 10 while implants were still in place (OVX+P, n=6) or 4 (OVX-P4, n=7) or 12 h (OVX-P12, n=7) after progesterone removal. Coronal sections through the rostral portion of the medial preoptic area (rPOA) were processed for cellular in-situ hybridization for GnRH mRNA. An increase in progesterone concentrations markedly suppressed luteinizing hormone (LH) release, while removal of the implants caused progesterone concentrations to fall (P<0.01) within 1 h and LH pulse frequency to increase (P<0.05) within 4 h. Despite these progesterone-induced changes in LH/GnRH release there were no differences in the cellular content of GnRH mRNA among the four groups. In the second study, three groups of ovariectomised ewes were used to determined whether the inhibitory actions of early (EL; n=8) and mid-luteal (ML; n=8) phase concentrations of progesterone on LH release are accompanied by a decrease in GnRH mRNA expression. P inhibited the secretion of LH in a dose dependant manner; pulses of LH were virtually absent in the ML group. Despite this marked inhibitory steroid action, there was no significant difference in the cellular content of GnRH mRNA among the OVX, OVX (EL) and OVX (ML) groups. Thus, both the negative feedback actions of physiological concentrations of progesterone on GnRH release and the rapid escape from progesterone-inhibition are independent of changes in the cellular content of GnRH mRNA. These data suggest that the mechanism by which progesterone controls the timing of events in the ovine oestrous cycle is primarily by altering the secretion of GnRH rather than GnRH biosynthesis.

Effects of orchidectomy on levels of the mRNAs encoding gonadotropin-releasing hormone and other hypothalamic peptides in the adult male rhesus monkey (Macaca mulatta)

The testicular regulation of luteinizing hormone (LH) secretion in the adult rhesus monkey is mediated by an indirect action of testosterone to decelerate pulsatile gonadotrophin releasing hormone (GnRH) release. Whether this negative feedback action of testosterone involves regulation of GnRH gene expression is unknown. Therefore, the effect of bilateral orchidectomy on hypothalamic levels of the mRNA encoding this hypophysiotropic factor was examined. The feedback action of testosterone is generally considered to be mediated through non-GnRH cells, and the present experiment provided the opportunity to also examine testicular influences on mRNAs encoding putative hypothalamic factors implicated in the testicular regulation of LH secretion. Adult male rhesus monkeys were orchidectomized (n=5) or sham-orchidectomized (n=5) and killed 6 weeks later, after a castration-induced hypersecretion of LH was established. Separate preoptic and mediobasal hypothalamus containing areas were collected, and levels of GnRH mRNA, as well as those of mRNAs encoding pro-opiomelanocortin (POMC), the gamma-aminobutyric acid (GABA) synthesizing enzymes (glutamic acid decarboxylase 65 and 67; GAD65 and GAD67, respectively), neuropeptide Y, galanin and transforming growth factor (TGF)alpha, were quantified using RNase protection assay. Values were expressed in terms of optical density relative to that of cyclophilin mRNA levels. Bilateral orchidectomy produced a significant increase in GnRH mRNA levels that was restricted to the mediobasal hypothalamus and that was associated with a significant decrease in POMC, GAD65 and GAD67 mRNA levels in this region of the hypothalamus. In contrast, neuropeptide Y, galanin and TGFalpha mRNA levels were not affected by castration. These results indicate that, in the monkey, the deceleration of pulsatile GnRH release that is imposed by the testis, and presumably mediated by testosterone, is associated with a concomitant down regulation of GnRH gene expression in the mediobasal hypothalamus. They also support the notion that this hypothalamic feedback action may be mediated by POMC-and GABA-producing neurones in the mediobasal hypothalamus.

Sleep-inducing effects of adenosine microinjections into the medial preoptic area are blocked by flumazenil

Microinjection of a wide range of sedative agents, including triazolam, pentobarbital, ethanol and adenosine, into the medial preoptic area has been shown to increase sleep, suggesting that it is an important (though not necessarily the only) anatomic site mediating hypnotic effects of these compounds. The mechanism by which adenosine increases sleep at this site is not clear, but one possibility is that this is related to its effects on the GABA(A)-benzodiazepine receptor complex. In order to assess this possibility, this paper describes the administration of adenosine, alone and in combination with the benzodiazepine receptor blocker flumazenil, into the MPA. It was found that 12.5 and 25 nM of adenosine significantly reduced sleep latency and increased total sleep time. The sleep-inducing effect was blocked by flumazenil. Flumazenil caused a modest increase in total sleep, and prevented the increase in total sleep induced by the higher dose of adenosine. These data suggest that at least one aspect of the hypnotic properties of adenosine is mediated by a direct or indirect action on the GABA(A)-benzodiazepine receptor complex.

Changes in brain gonadotropin-releasing hormone- and vasoactive intestinal polypeptide-like immunoreactivity accompanying reestablishment of photosensitivity in male dark-eyed juncos (Junco hyemalis)

In seasonally breeding, photoperiodic birds, the development of photorefractoriness is associated with decreased brain expression of gonadotropin-releasing hormone-like immunoreactivity (GnRH-li ir) and increased expression of vasoactive intestinal polypeptide-like immunoreactivity (VIP-li ir). Dissipation of photorefractoriness and reestablishment of photosensitivity are associated with increased GnRH-li ir brain production, but concurrent changes in VIP-li ir expression have not been investigated. To address this question, we compared the expression of VIP-li ir in the infundibulum (INF) of adult male dark-eyed juncos (Junco hyemalis) that were made photorefractory (PR) by prolonged exposure to long days with that of birds that were not photostimulated (PS), but had regained photosensitivity by exposure to short days for 5 (short-term-PS, ST-PS) or 13 (long-term-PS, LT-PS) consecutive months. Photosensitive males had smaller INF VIP-li ir cell bodies than PR males, but the numbers of INF VIP-li ir cells were independent of photoperiodic condition. Changes in infundibular VIP-li ir were correlated with changes in preoptic area (POA) GnRH-li expression. Specifically, photosensitive males had more and larger POA GnRH-li ir cells and more GnRH-li ir fibers in this region than PR males. Further, LT-PS males had more GnRH-li ir POA fibers and larger testes than ST-PS juncos. Thus, induction of photorefractoriness is associated with increased VIP and decreased GnRH brain expression whereas dissipation of photorefractoriness concurs with decreased VIP and increased GnRH brain expression. These results suggest a physiological role for VIP in the control of changes in GnRH expression as a function of the photosensitive condition.

Activation of gene expression of the gamma-aminobutyric acid rather than the glutamatergic system in the preoptic area during the preovulatory gonadotropin surge of the rat

There is increasing evidence that in the rat prior to and during the preovulatory LH surge, release rates of GABA in the preoptic area (POA) are decreased while no such changes occurred in the mediobasal hypothalamus (MBH). In addition, GnRH release appears to be facilitated by an increased preoptic excitation of glutamate (GLU). To investigate whether such changes of secretory activity of intrahypothalamic GABA or GLU neurons are associated with altered gene expression of biosynthetic enzymes or transporter proteins characteristic for either neuronal system, we determined mRNA levels of the two forms of the GABA-synthesizing enzyme glutamate decarboxylase (GAD65 and GAD67), the glutamate-synthesizing enzyme glutaminase (GLS), the GABA transporter type 1 (GAT-1) and the glutamate-aspartate transporter type 1 (GLAST). Competitive RT-PCRs using mutant cRNAs as internal standards were conducted with mRNA extracted from microdissected tissue of POA and MBH from diestrous, proestrous, and estrous rats. Proestrous animals were subgrouped according to their endocrine status as follows: 'prior to', on the 'ascending' or on the 'descending' limb of the LH peak, and 'after the LH surge (post)'. During the preovulatory LH surge, mRNA concentrations of GAD67 and GAT-1 in the POA were significantly increased compared to those observed on diestrous (2.8-fold for GAD67 and 2.5-fold for GAT-1, p < 0.01), while in the MBH the amount of both mRNAs remained constant. The expression levels of GAD65, GLS and GLAST were without any changes in the POA as well as in the MBH. These findings support the hypothesis that in rats induction of the preovulatory LH surge is controlled at the level of GnRH perikarya, and suggest that altered activities of intrapreoptic GABA neurons at both transcriptional and secretory levels are pivotal for the preovulatory activation of GnRH neurons.

Regional distribution of gonadotropin-releasing hormone-like, beta-endorphin-like, and methionine-enkephalin-like immunoreactivities in the central nervous system of the goat

Regional distribution of gonadotropin-releasing hormone (GnRH)-like-, beta-endorphin (beta-end)-like-, and methionine-enkephalin (met-enk)-like-immunoreactivity was quantified across various regions of the central nervous system (CNS) of male and female goats by using highly specific radioimmunoassays. All the animals were sacrificed during the months of March through June (non-breeding season). Although the distribution of these three neuropeptides was similar to other mammalian species, species-specific gender differences in the levels of neuropeptides were noticed in the goat CNS. Highest levels of GnRH-like immunoreactivities were found in the hypothalamus. The hypothalamus of male goats exhibited significantly higher levels of GnRH-like immunoreactivities compared to female goats. Other regions exhibiting GnRH-like immunoreactivities included olfactory bulbs, preoptic and supraoptic regions, and mamillary bodies. Both beta-end- and met-enk immunoreactivities were detected in all selected regions of goat CNS, but highest levels of these opioid peptide-like immunoreactivities were limited to the forebrain regions of the goat. The supraoptic area of the female goats contained significantly higher levels of beta-end-like immunoreactivities than that of the male goats. Met-enk-peptide-like immunoreactivity also exhibited gender-specific differences in its content in some regions of the CNS. The male goats exhibited significantly higher levels of met-enk-like immunoreactivity in both the striatal and hypothalamic regions of the brain.

Characterization and distribution of somatostatin binding sites in goldfish brain

Somatostatin (SRIF) binding sites were characterized in goldfish brain. Binding of (125)I-[Tyr(11)]-SRIF-14 to a brain membrane preparation was found to be saturable, reversible, and time-, temperature-, and pH-dependent. Binding was also displaceable by different forms of SRIF. Under optimal conditions (22 degrees C, pH 7.2), the equilibrium binding of (125)I-[Tyr(11)]-SRIF-14 to goldfish brain membranes was achieved after 60 min incubation. Analysis of saturable equilibrium binding revealed a one-site model fit with K(a) of 1.3 nM. SRIF-14, mammalian SRIF-28, and salmon SRIF-25 displaced (125)I-[Tyr(11)]-SRIF-14 binding with similar affinity, whereas other neuropeptides, e.g., substance P, were unable to displace (125)I-[Tyr(11)]-SRIF-14. Autoradiography studies demonstrated that (125)I-[Tyr(11)]-SRIF-14 binding sites are found throughout the goldfish brain. A high density of (125)I-[Tyr(11)]-SRIF-14 binding sites was found in the forebrain, including the nucleus preopticus, nucleus preopticus periventricularis, nucleus anterioris periventricularis, nucleus lateralis tuberis, nucleus dorsomedialis thalami, nucleus dorsolateralis thalami, nucleus ventromedialis thalami, and nucleus diffusus lobi inferioris. In midbrain, (125)I-[Tyr(11)]-SRIF-14 binding sites were found in the optic tectum. The facial and vagal lobes and the mesencephalic-cerebellar tract were found to have a high density of binding sites. This study provides the first characterization and distribution of specific binding sites for SRIF in a fish brain.

Effects of N-methyl-D-aspartate on luteinizing hormone release and Fos-like immunoreactivity in the male White-crowned sparrow (Zonotrichia leucophrys gambelii)

Seasonal breeding is terminated in the White-crowned sparrow by the onset of absolute photorefractoriness, a condition in which the reproductive system is switched off indefinitely until it is dissipated by short day lengths. Absolute photorefractoriness is controlled by the central nervous system; however, the mechanisms underlying GnRH quiescence in photorefractory birds have yet to be elucidated. Using the excitatory amino acid glutamate agonist N-methyl-D-aspartate (NMDA), plasma LH levels in White-crowned sparrows were significantly elevated regardless of the reproductive or photoperiodic condition. NMDA also significantly induced Fos-like immunoreactivity (FLI) within the infundibular nucleus and median eminence, regions previously shown to express FLI after a photoperiodically driven LH rise. NMDA did not induce FLI within GnRH I neurons; instead, it significantly activated cells within the organum vasculosum of the lamina terminalis in close proximity to GnRH I perikarya. These findings provide the first evidence that photorefractoriness is not due to depletion of GnRH stores, as LH and presumably GnRH were secreted in response to excitatory amino acid stimulation. NMDA activation of FLI in the region of the organum vasculosum of the lamina terminalis and the basal tuberal hypothalamus suggests that seasonal reproductive neuroendocrine control may be mediated via cells in the region of the GnRH I perikarya and terminals.

Elevated Fos-like immunoreactivity in the brains of postpartum female prairie voles, Microtus ochrogaster

This study investigated the expression of the protein product of the immediate early gene c-fos in the brains of female prairie voles (Microtus ochrogaster) in association with pregnancy and postparturient activities including maternal behavior, lactation and postpartum estrus. Fos expression was assessed in female voles that were late in pregnancy, nonpregnant or at one of three different times postpartum (0-8, 12-24, and 24-48 h, respectively). A significant increase in the number of cells displaying Fos immunoreactivity (Fos-ir) was observed during the 0-8 h and 12-24 h postpartum time periods in the accessory olfactory bulbs, medial preoptic area, hypothalamus (specifically, the supraoptic nucleus, ventro-medial hypothalamus, and paraventricular nucleus), lateral septum, bed nucleus of the stria terminalis, and primary somatosensory area of the brain. The number of Fos-ir cells decreased after 24 h postpartum. There were no significant changes in Fos-ir cell numbers in the primary olfactory bulbs, hippocampus, or caudate putamen. The neural activation of the medial preoptic area, accessory olfactory bulbs, hypothalamus, and bed nucleus is consistent with reports in rats of Fos induction associated with the onset of maternal behavior. In voles postpartum estrous behavior begins and ends 0-12 h after parturition. Maternal behavior, including lactation, is initiated at the same time but persists for several weeks. The highest Fos-ir cell numbers reported here coincide with the timing of postpartum estrous behavior in this species.

Lesions to the medial preoptic area affect singing in the male European starling (Sturnus vulgaris)

The aromatization of testosterone (T) in the medial preoptic nucleus (POM) is known to regulate male courtship and sexual behaviors expressed prior to, and in anticipation of, copulation. Singing in male European starlings is used to attract mates prior to physical sexual contact, suggesting that the POM might be involved. The present study was performed to examine the effects of lesions targeting the POM on singing and courtship behavior in reproductively active male starlings. A significant decrease in song output and the gathering of green nest materials was observed in males with lesions to the POM compared to males with damage to brain areas outside of the POM. Lesions did not affect a male's tendency to remain near a female or to occupy a nestbox, suggesting that the effects of POM lesions were specific to courtship behaviors. Behavioral differences were not related to testis mass or volume, and GnRH immunoreactivity was observed within the hypothalamus and median eminence for each male, suggesting that the effects of POM lesions were related specifically to POM involvement in song expression rather than to a disruption of the GnRH axis. These results suggest a general role for the POM in the expression of behaviors related to sexual arousal or anticipation, including song.

Perinatal developmental changes in expression of the neuropeptide genes preoptic regulatory factor-1 and factor-2, neuropeptide Y and GnRH in rat hypothalamus

The preoptic regulatory factor genes, PORF-1 and PORF-2, are expressed in the rat brain in a regional-, age- and gender-dependent fashion. They are also expressed in the testis, where PORF-2 mRNA localizes to dividing germ cells while PORF-1 mRNA is associated with newly differentiated sperm. This suggests that PORF-1 and PORF-2 may play distinct roles in cell growth and differentiation. Moreover, the two preoptic regulatory factors are also highly expressed in the immature and mature rat hypothalamus, and their expression is modulated by gonadal hormones. Therefore, in the present study we investigated the expression of these two factors in neuroendocrine regions of the developing rat brain by addressing the following questions. First, are PORF-1 and PORF-2 mRNAs expressed during perinatal development in the preoptic area-anterior hypothalamus (POA-AH) and medial basal hypothalamus (MBH), and how do their levels vary? Second, are there gender differences in their expression? We also compared expression of the PORF mRNAs with those of neuropeptide Y (NPY) and gonadotropin-releasing hormone (GnRH), which play critical neuroendocrine roles, in these brain regions. PORF-1, PORF-2, and NPY mRNAs in the POA-AH and MBH, and GnRH mRNA in the POA-AH, were quantified by RNase protection assay at embryonic day (E) 18-19, and postnatal days (P) 0, 5, 10 and 15 in male and female rats. The results show that the four neuropeptide genes are regulated differentially during the perinatal-prepubertal period. PORF-1 mRNA shows age-related increases in expression from E18-E19 to P15 in POA-AH and MBH, without significant gender differences. In contrast, PORF-2 mRNA shows both age and gender differences in expression in these brain regions, with decreases occurring during the same time period in development. NPY mRNA increases similarly in males and females with age in POA-AH and MBH during this period. GnRH mRNA does not change during this period. Taken together with previous studies, the results suggest possible roles for PORF-1 and NPY in the pubertal process, since their expression is maximal from the prepubertal to the early pubertal period. The observation of highest levels of expression of PORF-2 in embryonic neuroendocrine tissues suggests a possible involvement of this neuropeptide in prenatal/neonatal developmental events.

Androgen-metabolizing enzymes show region-specific changes across the breeding season in the brain of a wild songbird

The Lapland longspur (Calcarius lapponicus) is an arctic-breeding songbird that shows rapid behavioral changes during a short breeding season. Changes in plasma testosterone (T) in the spring are correlated with singing but not territorial aggression in males. Also, T treatment increases song but not aggression in this species. In contrast, in temperate-zone breeders, song and aggression are highly correlated, and both increase after T treatment. We asked whether regional or temporal differences in androgen-metabolizing enzymes in the longspur brain explain hormone-behavior patterns in this species. We measured the activities of aromatase, 5alpha-reductase and 5beta-reductase in free-living longspur males. Aromatase and 5alpha-reductase convert T into the active steroids 17beta-estradiol (E(2)) and 5alpha-dihydrotestosterone (5alpha-DHT), respectively. 5beta-Reductase deactivates T via conversion to 5beta-DHT, an inactive steroid. We examined seven brain regions at three stages in the breeding season. Overall, aromatase activity was high in the hypothalamus, hippocampus, and ventromedial telencephalon (containing nucleus taeniae, the avian homologue to the amygdala). 5beta-Reductase activity was high throughout the telencephalon. Activities of all three enzymes changed over time in a region-specific manner. In particular, aromatase activity in the rostral hypothalamus was decreased late in the breeding season, which may explain why T treatment at this time does not increase aggression. Changes in 5beta-reductase do not explain the effects of plasma T on aggressive behavior.