The luteinizing hormone-releasing hormone (LH-RH) neuronal networks of the guinea pig brain. I. Intra- and extra-hypothalamic projections

Intercellular communication within the rat anterior pituitary: XIV electron microscopic and immunohistochemical study on the relationship between the agranular cells and GnRH neurons in the dorsal pars tuberalis of the pituitary gland

Although numerous investigators in 1970s to 1980s have reported the distribution of LH-RH nerve fibers in the median eminence, a few LH-RH fibers have been shown to be present in the pars tuberalis. The significance of the finding remains to be elucidated, and there are few studies on the distribution of LH-RH neurons in the pars tuberalis, especially in the dorsal pars tuberalis (DPT). Adult male Wistar-Imamichi rats were separated into two groups: one for electron microscopy and the other for immunohistochemistry to observe LH-RH and neurofilaments. Pituitary glands attached to the brain were fixed by perfusion, and the sections were prepared parallel to the sagittal plane. The typical glandular structure of the pars tuberalis was evident beneath the bottom floor of the third ventricle, and the thick glandular structure was present in the foremost region. Closer to the anterior lobe, the glandular structure changed to be a thin layer, and it was again observed at the posterior portion. Then the pituitary stalk was surrounded with the dorsal, lateral, and ventral pars tuberalis. LH-RH and neurofilaments fibers were noted in the bottom floor, and some of them vertically descended to the gland. Adjacent to the glandular folliculostellate cells in the pars tuberalis, Herring bodies with numerous dense granules invading into the gland were present between the pituitary stalk and DPT. It was postulated that the "message" carried by LH-RH might have been transmitted to the cells in the DPT to aid in the modulation of LH release.

Calcium influx and DREAM protein are required for GnRH gene expression pulse activity

Recent evidence using GT1-7 cells indicates that GnRH pulsatility depends on exocytotic-release and gene transcription events. To determine whether calcium or DREAM may play a role in linking these processes, we used an L-type Ca(2+)-blocker (nimodipine) and found that not only GnRH gene expression (GnRH-GE) pulse activity was abolished but also that binding of proteins to OCT1BS-a (essential site for GnRH-GE pulses) was reduced. We further found that only EF-hand forms of DREAM were expressed in GT1-7 and that DREAM was part of the complex binding to OCT1BS-a. Finally, microinjection of DREAM antibody into cells abolished GnRH-GE pulses demonstrating its importance in pulsatility. These results reveal that calcium and DREAM may bridge cytoplasmic and nuclear events enabling temporal coordination of intermittent activity. Expression of DREAM in various cell types coupled with the universal role of calcium raise the possibility that these factors may play similar role in other secretory cells.

Highly selective localization of leukotriene C4 synthase in hypothalamic and extrahypothalamic vasopressin systems of mouse brain

While leukotriene C4 (LTC4) was originally identified as a potent bronchoconstrictor, the compound has versatile biological activities besides inflammatory reactions. Although the high content of LTC4 has been reported in the hypothalamus and median eminence, the precise localization of the compound remained obscure. To elucidate its possible functions in the neuroendocrine systems, we determined immunohistochemical localization of LTC4 synthase, a key enzyme to produce LTC4 using mouse brains. Light microscopy and confocal laser scanning microscopy showed that LTC4 synthase was selectively localized in the vasopressinergic magnocellular neurons of the hypothalamic paraventricular, supraoptic and suprachiasmatic nuclei and in the retrochiasmatic area, as well as in axons that emanated from these neurons to the pars nervosa of the pituitary gland. At subcellular level, however, LTC4 synthase and arginine vasopressin appeared to localize differently within individual neurons. LTC4 synthase immunoreactivity was also observed in the axons of the extrahypothalamic system including the bed nucleus of the stria terminalis, lateral habenular nucleus, midbrain central gray, medial amygdaloid nucleus and ventral septal area, although this immunoreactivity was relatively minor. The other brain regions did not contain LTC4 synthase immunoreactivity. The distribution of LTC4 synthase did not overlap with that of either oxytocin or luteinizing hormone releasing hormone. Therefore, LTC4 is considered to be involved in neural functions of the brain magnocellular vasopressinergic system such as water retention. LTC4 may also be involved in extrahypothalamic vasopressinergic neural functions including the regulation of learning and memory, social recognition memory, sexual and aggressive behavior, etc.

Expression and immunohistochemical localization of vesicular glutamate transporter 2 in the migratory pathway from the rat olfactory placode

The localization of vesicular glutamate transporter 2 (VGLUT2) was examined by immunohistochemistry and in situ hybridization histochemistry in the developing rat olfactory region with special relation to the spatiotemporal location of NCAM, a neural cell adhesion molecule expressed in differentiated neurons, and the calcium-binding protein calbindin D-28k, a marker of neurons migrating from the vomeronasal organ anlage (Y. Toba et al. (2001) J. Neuroendocrinol., 13, 683-694). Both VGLUT2 and NCAM immunoreactivities were first detected at embryonic day 11.5 (E11.5) in the neuronal cell mass beneath the telencephalic vesicle. After E12.5, VGLUT2-immunoreactive cells were detected in the migratory pathways from both medial and lateral olfactory pits, anlagen of the vomeronasal organ and olfactory epithelium. Between E15.5 and E19.5, moderate to intense VGLUT2 immunoreactivity was observed in cell clusters situated along NCAM-bearing vomeronasal nerves, and frequently colocalized with calbindin D-28k immunoreactivity. Using in situ hybridization histochemistry, VGLUT2 mRNA signals were detected in the clustered cells as well as in cells of the vomeronasal and olfactory epithelium. After E20.5, migrating cells gradually decreased in number and VGLUT2 immunoreactivity attenuated in the clustered cells, although calbindin D-28k immunoreactivity in these residual cells was still intense. The presence of intense VGLUT2 immunoreactivity in neurons actively migrating from the olfactory placode suggests that this transporter is involved in the migratory process of these neurons.

Lead-induced cell signaling cascades in GT1-7 cells

The effects of lead on the signal transduction pathways that may be involved in the release of gonadotropin-releasing hormone (GnRH) from neurons in the hypothalamus have not been well defined. Using the GT1-7 cell line, an in vitro model for GnRH-secreting neurons, we examined signal transduction pathways directly affected by lead. We found that lead-induced phosphorylation of extracellular signal-regulated kinase 1 and 2 (ERK1 and ERK2), as well as p90RSK and cAMP response element-binding protein (CREB), but did not induce IkappaB degradation. MEK1/2 inhibitor (PD98059) suppressed lead-induced ERK and p90RSK activation. Neither PKC inhibitors (Go6983, Go6976) nor CaMKII inhibitor (KN-62) had a pronounced effect on lead-induced ERK1 and ERK2 phosphorylation. However, MEK1/2 inhibitor, CaMKII inhibitor, and PKC inhibitor significantly suppressed lead-induced CREB phosphorylation. These results indicate that lead-activated PKC, CaMKII and MEK/ERK/p90RSK pathways simultaneously, all of which contributed to CREB phosphorylation. Our results also indicate that lead-induced p90RSK and CREB activation does not alter expression of early response genes like c-fos. We conclude that lead activates PKC, CaMKII or MEK-ERK-p90RSK pathways in GT1-7 cells, leading to CREB phosphorylation and modulation of gene expression.

alpha(1)-adrenergic receptors mediate LH-releasing hormone secretion through phospholipases C and A(2) in immortalized hypothalamic neurons

Norepinephrine has long been known to stimulate the pulsatile and preovulatory release of LH-releasing hormone (LHRH). In vivo and in vitro studies indicate that these effects are mediated primarily through alpha(1)-adrenergic receptors (alpha(1)-ARs). With the immortalized hypothalamic LHRH neurons, we have found that alpha(1)-adrenergic agents directly stimulate the secretion of LHRH in a dose-dependent manner. Ligand binding and RNA studies demonstrate that the GT1 cells contain both alpha(1A)- and alpha(1B)-ARs. Competition binding experiments show that approximately 75% of the binding is due to alpha(1B)-ARs; the remainder is made up of alpha(1A)-ARs. Receptor activation leads to stimulation of PLC. PLC beta 1 and PLC beta 3 are expressed in GT1 neurons, and these PLCs are probably responsible for the release of diacylglycerol and IP as well as the increase in intracellular calcium. The mobilization of cytoplasmic calcium is sufficient to stimulate cytosolic PLA(2) (cPLA(2)) and release arachidonic acid. A dissection of the contributions of the phospholipases to LHRH secretion suggests that cPLA(2) acts downstream of PLC and that it significantly augments the PLC-stimulated LHRH secretory response. Inasmuch as the alpha(1)-ARs are known to play a critical role in LHRH physiology, we propose that both PLC and cPLA(2) are critical in regulating and amplifying LHRH release.

Neural circuits regulating pulsatile luteinizing hormone release in the female guinea-pig: opioid, adrenergic and serotonergic interactions

We studied three neurotransmitters involved in the regulation of pulsatile luteinizing hormone (LH) release: opioid peptides, serotonin and norepinephrine, using the ovariectomized guinea-pig. This is an attractive animal model due to the regularity of its LH pulses, enabling any disruptions to be clearly ascertained. In all experiments, a specific agonist or antagonist was administered, either alone or serially to enable detection of interactions, and effects on mean LH concentrations, pulse amplitude and interpulse interval were determined by PULSAR analysis. In the ovariectomized guinea-pig, catecholamines are stimulatory (acting through the alpha1 and alpha2 but not beta receptors, unlike other species), opioids inhibitory and serotonin permissively stimulatory to pulsatile LH release. Stimulatory effects of the opiate antagonist were not blocked by pretreatment with an alpha1- or alpha2-adrenergic antagonist. Similarly, pretreatment with the opiate antagonist did not prevent the suppression of LH release by alpha1 and alpha2 antagonists. This suggests that, in the guinea-pig, effects of opiates and catecholamines on LH release are exerted by independent pathways to luteinizing hormone releasing hormone (LHRH) neurones. For the opiate-serotonin interactions, pretreatment with the serotonergic antagonist did not block the stimulatory effect of the opiate antagonist on LH release. However, pretreatment with the opiate agonist could not be overcome by the serotonergic agonist. This suggests that the effects of the serotonin system on LHRH release may be indirectly mediated by opioid neurones. Taken together, these studies demonstrate that the three neurotransmitter systems studied are critically involved in normal pulsatile LH release in the female guinea-pig, and demonstrate novel functional relationships between the opioid and the adrenergic and serotonergic systems.

Crystalline dihydrotestosterone implants in the lateral septum of male rats. A positive effect on LH and FSH

Previous investigations in our laboratory have shown that testosterone implanted into the lateral septum in male rats increases LH and FSH secretion. However, it was unclear whether the effect of testosterone was direct via androgen receptor, or indirect via the estrogen receptor after conversion by aromatization to estradiol. To answer this question, we implanted either testosterone or the non-aromatizable androgen 5 alpha-dihydrotestosterone (DHT), into the lateral septum of adult male rats and measured plasma levels of LH and FSH by radioimmunoassay 2 days after implantation. Both testosterone and DHT significantly increased the plasma LH and FSH concentrations. Mean concentration of LH in control animals was 0.21 +/- 0.06 ng/ml, a figure that increased to 0.7 +/- 0.12 and 0.55 +/- 0.1 ng/ml after DHT or testosterone implantation respectively. Mean concentration of FSH in control animals was 1.5 +/- 0.3 ng/ml; this figure increased to 3 +/- 0.3 and 2.9 +/- 0.3 ng/ml after DHT or testosterone implantation. Neither plasma DHT (64.0 +/- 5.6 vs. 52 +/- 5 ng/100ml) nor plasma testosterone levels (4.1 +/- 0.38 vs. 3.3 +/- 0.18 ng/ml) were significantly affected by the implants. We conclude that androgens independently of conversion to estrogen acting in the lateral septum facilitates the release of LH and FSH.

Effects of female pheromones on gonadotropin-releasing hormone gene expression and luteinizing hormone release in male wild-type and oestrogen receptor-alpha knockout mice

Pheromones are an important class of environmental cues that affect the hypothalamic-pituitary-gonadal axis in a variety of vertebrate species, including humans. When male mice contact female-soiled bedding, or urine, they display a reflexive luteinizing hormone (LH) surge within 30 min. Aside from the requirement that males have gonads to show this response, the physiological mechanisms that underlie this pituitary response are unknown. In this experiment, we asked if female pheromones acted at the level of gonadotropin-releasing hormone (GnRH) gene expression to affect this hormone response. In addition, we also examined the contribution of one of the oestrogen receptors (ERalpha) by studying this neuroendocrine reflex in wild-type and oestrogen receptor-alpha knockout (ERalphaKO) males. Both ERalphaKO and wild-type males showed the expected LH surge, 45 and 90 min after contact with female pheromones. Males housed in clean bedding or bedding soiled by another adult male did not display the LH elevation. Interestingly, this dramatic change in LH concentrations was not accompanied by any alterations in GnRH mRNA expression or levels of primary transcript in the preoptic area-anterior hypothalamus. The one exception to this was a significant increase in GnRH mRNA expression in tissue collected from wild-type males exposed to bedding from another male. This is particularly intriguing since LH was not elevated in these males. These data replicate and extend our previous finding that ERalphaKO males do exhibit an LH surge in response to female pheromones. Thus, this neuroendocrine response is regulated by a steroid receptor other than ERalpha and does not require alterations in GnRH mRNA expression.

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.

Immunocytochemical localization of prostaglandin EP3 receptor in the rat hypothalamus

A rabbit antibody against an N-terminal portion of rat prostaglandin EP3 receptor (EP3R) was produced to examine the distribution of EP3R in the rat hypothalamus. The antibody specifically recognized EP3R proteins in rat brain extract, in membrane fractions of rat kidney, and in membrane fractions of EP3R-expressing culture cells. Intense EP3R-like immunoreactivity was observed in the median preoptic nucleus, medial preoptic area, parastrial nucleus, compact part of the dorsomedial hypothalamic nucleus, and dorsal part of the premammillary nucleus. These results suggest that prostaglandin E2 mediates various actions in the hypothalamus, such as fever induction in the preoptic area, through EP3R.

Preoptic area grafts implanted in mammillary bodies of hypogonadal mice: patterns of GnRH neuronal projections

Gonadotropin-releasing hormone (GnRH) axons project to the median eminence, where the peptide is released to stimulate pituitary gonadotrophs. Hypogonadal mice (hpg) do not synthesize GnRH due to a deletion in the gene. When neonatal preoptic area (POA) tissue from normal mice containing GnRH neurons is transplanted into the third ventricle of hpg mice, GnRH axons exit the graft and specifically project to the median eminence, where the release of GnRH in the portal circulation induces the stimulation of the pituitary-gonadal axis. To test the hypothesis that the median eminence region is critical to targeting, we placed POA grafts in the region of the mammillary bodies, which never contains GnRH cell bodies, but is nevertheless close to the median eminence. Control mice received bilateral grafts into the anterior hypothalamus. GnRH axons innervated the median eminence in animals with grafts in the mammillary bodies and posterior hypothalamus. Mice with such grafts for 4-5 months had gonadal development, while those with grafts for shorter periods did not. Anterior hypothalamic grafts merged into the third ventricle and, consistent with previous studies, this resulted in GnRH innervation of the median eminence and gonadal development. However, when grafts were located within dorsal regions such as the thalamus, no median eminence innervation was seen. In these cases, GnRH axons borrowed other bundles of fibers to travel within the host brain. The pattern of innervation from grafts within ventro-caudal regions of the hypothalamus vs. that from dorsal regions supported the hypothesis that the median eminence releases diffusible substances directing GnRH outgrowth.

Immortalized hypothalamic luteinizing hormone-releasing hormone (LHRH) neurons: a new tool for dissecting the molecular and cellular basis of LHRH physiology

1. Two LHRH neuronal cell lines were developed by targeted tumorigenesis of LHRH neurons in vivo. These cell lines (GN and GT-1 cells) represent a homogeneous population of neurons. GT-1 cells have been further subcloned to produce the GT1-1, GT1-3, and GT1-7 cell lines. While considerable information is accumulating about GT-1 cells, very little is currently known about the characteristics and responses of GN cells. 2. By both morphological and biochemical criteria, GT-1 cells are clearly neurons. All GT-1 cells immunostain for LHRH and the levels of prohormone, peptide intermediates, and LHRH in the cells and medium are relatively high. 3. GT-1 cells biosynthesize, process, and secrete LHRH. Processing of pro-LHRH appears to be very similar to that reported for LHRH neurons in vivo. At least four enzymes may be involved in processing the prohormone to LHRH. 4. LHRH neurons are unique among the neurons of the central nervous system because they arise from the olfactory placode and grow back into the preoptic-anterior hypothalamic region of the brain. Once these neurons reach this location, they send their axons to the median eminence. With respect to the immortalized neurons, GN cells were arrested during their transit to the brain. In contrast, GT-1 cells were able to migrate to the preoptic-anterior hypothalamic region but were unable correctly to target their axons to the median eminence. These problems in migration and targeting appear to be due to expression of the simian virus T-antigen. 5. While GT-1 cells are a homogeneous population of neurons, they are amenable to coculture with other types of cells. Coculture experiments currently under way should help not only to reveal some of the molecular and cellular cues that are important for neuronal migration and axonal targeting, but they should also highlight the nature of the cellular interactions which normally occur in situ. 6. GT-1 cells spontaneously secrete LHRH in a pulsatile manner. The interpulse interval for LHRH from these cells is almost identical to that reported for release of LH and LHRH in vivo. GT-1 cells are interconnected by both gap junctions and synapses. The coordination and synchronization of secretion from these cells could occur through these interconnections, by feedback from LHRH itself, and/or by several different compounds that are secreted by these cells. One such compound is nitric oxide. 7. GT-1 cells have Na+, K+, Ca2+, and Cl- channels.(ABSTRACT TRUNCATED AT 400 WORDS)

Immunocytochemical demonstration of neuropeptide Y and luteinizing hormone-releasing hormone-immunoreactive structures in the organum vasculosum laminae terminalis of juvenile gilts

Immunocytochemical investigations on the immature gilt organum vasculosum laminae terminalis showed extensive neuropeptide Y- and luteinizing hormone-releasing hormone-immunoreactive innervation of the organ. The luteinizing hormone-releasing hormone-containing varicose fibers ran along the organum vasculosum laminae terminalis in close association with blood vessels. The nerve processes originating from well-stained luteinizing hormone-releasing hormone-immunoreactive perikarya were distributed around the organum vasculosum laminae terminalis. The matrix of the organum vasculosum laminae terminalis was abundantly supplied by neuropeptide Y-immunoreactive varicose fibers. Numerous neuropeptide Y-immunoreactive terminals seemed to penetrate the ependymal lining of the organ. From these observations, it is concluded that there are favorable morphological conditions for secretion of neuropeptide Y into the cerebrospinal fluid of the third ventricle and release of luteinizing hormone-releasing hormone into fenestrated capillaries of the organ.

Developmental study of GnRH neuronal projections to the medial basal hypothalamus of the male Djungarian hamster

The present study in the male Djungarian hamster determined the neuroanatomical distribution and morphology of gonadotropin-releasing hormone (GnRH) neurons which innervate the medial basal hypothalamus during sexual maturation. Prepubertal, peripubertal, and postpubertal males were perfused, brains were removed, and crystals of the fluorescent tract tracer, DiI, were implanted directly into the median eminence of the brain. Eight weeks later, brains were sectioned and processed for GnRH immunofluorescence. At all ages, GnRH cell bodies were bipolar or unipolar; both subtypes were labeled with DiI in proportion to their respective numbers in each brain region. GnRH perikarya were distributed in a diffuse ventromedial continuum from the septum through the anterior hypothalamus. In prepubertal males, DiI was present in the majority of GnRH neurons (54% of total) that were located in brain regions rostral to and including the medial preoptic area. In lateral and caudal brain areas, fewer GnRH perikarya contained DiI (28% of total or less). With sexual maturation, fewer GnRH somata were labeled with DiI in areas rostral to the hypothalamus. The data suggest that bipolar and unipolar GnRH neurons in the forebrain, rostral to the preoptic area, are major contributors to the GnRH innervation of the median eminence in the male Djungarian hamster. With the onset of puberty, the finding that decreasing numbers of GnRH perikarya directly project to the medial basal hypothalamus suggests that fewer GnRH neurons constitute the final common pathway that controls gonadotropin secretion.

Gonadotropin-releasing hormone neurons and pathways in the brain of the female mink (Mustela vison)

The distribution of gonadotropin-releasing hormone-immunoreactive neurons and processes was mapped in the female mink brain using coronal, horizontal and sagittal sections. Perikarya were found along a ventral continuum including the olfactory tubercle, the diagonal band of Broca, the lateral septum, the preoptic and anterior hypothalamic area and the mediobasal hypothalamus; 80% of the perikarya were counted in the mediobasal hypothalamus. Fibres were mainly observed in the organum vasculosum of the lamina terminalis and the median eminence. A few processes terminated in the ependymal cells lining the third and lateral ventricles. The total number of immunoreactive perikarya was the highest in the brains of females sacrificed in July; it then significantly decreased until December. This variation is discussed in relation to the annual breeding cycle.

Further Evidence that Most Luteinizing Hormone-Releasing Hormone Neurons are not Directly Estrogen-Responsive: Simultaneous Localization of Luteinizing Hormone-Releasing Hormone and Estrogen Receptor Immunoreactivity in the Guinea-Pig Brain

Gonadotropin secretion from the pituitary is regulated in large part by steroid action on the brain. An important question concerns whether luteinizing hormone-releasing hormone (LHRH) neurons themselves transduce steroid signals, or whether, alternatively, steroid-sensitive interneuronal populations regulate their activity. A previous study in the rat employing steroid autoradiography combined with LHRH immunocytochemistry revealed that only an exceedingly small percentage of LHRH-immunoreactive (ir) neurons was estrogen concentrating. This study has examined the relationship of estrogen receptive and LHRH-ir cells in the male and female guinea-pig brain with double label immunocytochemistry. Since estrogen receptor-ir, as demonstrated with antibody H222, is known to be confined predominantly to the cell nucleus, whereas LHRH-ir is localized mainly in the cytoplasm, single cells can be double-labeled. Diaminobenzidine tetrahydrochloride was used for localization of LHRH-ir while nickel-enhanced diaminobenzidine tetrahydrochloride was used for localization of estrogen receptor-ir. The results revealed that there were many brain nuclei that contained both LHRH and estrogen receptor-positive cells, including the preventricular periventricular nucleus, the anterior subcompact nucleus of the medial preoptic nucleus (MPNa), the remainder of the medial preoptic nucleus, the retrochiasmatic area, and the anterior, dorsomedial, ventrolateral and arcuate nuclei. However, of a total of 2,604 LHRH-ir cells that were examined, we observed only 5 double-labeled cells (<0.2%). The double-labeled cells were not restricted to a single nucleus; they were present in the MPNa, the retrochiasmatic area and the arcuate nucleus. Moreover, at the light microscopic level, LHRH cells quite frequently appeared to be apposed to estrogen receptor-positive cells (8.8% in the female), especially in the MPNa. These results lend further support to the notion that estrogen-mediated regulation of the LHRH system is achieved primarily through estrogen receptive interneurons. However, due to the existence of LHRH-LHRH synaptic interactions, the possibility also exists that a small population of estrogen-sensitive LHRH neurons could contribute to generalized activation of the LHRH system.

Immunocytochemical localization of luteinizing hormone-releasing hormone (LHRH) in the nervus terminalis and brain of the big brown bat, Eptesicus fuscus

Little is known about the immunohistochemistry of the nervous system in bats. This is particularly true of the nervus terminalis, which exerts strong influence on the reproductive system during ontogeny and in the adult. Luteinizing hormone-releasing hormone (LHRH) was visualized immunocytochemically in the nervus terminalis and brain of juvenile and adult big brown bats (Eptesicus fuscus). The peripheral LHRH-immunoreactive (ir) cells and fibers (nervus terminalis) are dispersed along the basal surface of the forebrain from the olfactory bulbs to the prepiriform cortex and the interpeduncular fossa. A concentration of peripheral LHRH-ir perikarya and fibers was found at the caudalmost part of the olfactory bulbs, near the medioventral forebrain sulcus; obviously these cells mediate between the bulbs and the remaining forebrain. Within the central nervous system (CNS), LHRH-ir perikarya and fibers were distributed throughout the olfactory tubercle, diagonal band, preoptic area, suprachiasmatic and supraoptic nuclei, the bed nuclei of stria terminalis and stria medullaris, the anterior lateral and posterior hypothalamus, and the tuber cinereum. The highest concentration of cells was found within the arcuate nucleus. Fibers were most concentrated within the median eminence, infundibular stalk, and the medial habenula. The data obtained suggest that this distribution of LHRH immunoreactivity may be characteristic for microchiropteran (insectivorous) bats. The strong projections of LHRH-containing nuclei in the basal forebrain (including the arcuate nucleus) to the habenula, may indicate close functional contact between these brain areas via feedback loops, which could be important for the processing of thermal and other environmental stimuli correlated with hibernation.

An immunohistochemical study of the GnRH neuron morphology and topography in the adult female rabbit hypothalamus

The morphology and distribution of immunoreactive (GnRH) neural elements in the hypothalamus of the adult nulliparous female rabbit were examined. Approximately 1,000 GnRH cells (range 890-1136) were counted in the right half of the hypothalamus. Two distinct GnRH cell types were observed: GnRH cells with rough or spiny contours accounted for 64% of the total immunoreactive cells, and smooth-contoured cells represented 34% of the total. The majority of immunoreactive neural elements were found in the anterior hypothalamus. GnRH cells and processes were located primarily in the ventral and medial anterior hypothalamus forming an inverted V pattern. Processes were followed from the medial preoptic area and suprachiasmatic nucleus to the infundibular stem. Extrahypothalamic projections of GnRH cells were observed. Immunoreactive fibers were also found to contact the ependymal lining of the third ventricle. It is concluded that two morphologically distinct GnRH cell types exist and have a broad distribution in the rabbit hypothalamus. The functional significance of these cell types requires further study.

Neuroendocrine control of reproduction in lampreys

In most vertebrate classes, the hypothalamus and pituitary have well-defined roles in the control of reproduction. Until recently, there was little evidence for neuroendocrine control of reproduction in lampreys, one of the only two living representative groups of the oldest lineage of vertebrates, the Agnathans. The question whether there is hypothalamic control over reproduction has special significance since these fishes, with the hagfishes, are modern descendants of the most primitive vertebrates available for study. This paper summarizes the studies on the structure and function of lamprey GnRH which provide evidence for the regulatory influence of the hypothalamus on the pituitary-gonadal axis. These data imply that evolution of this mechanism most likely antedated the origin of all known vertebrates.

Anatomical distribution of LHRH-immunoreactive neurons in the human infant hypothalamus and extrahypothalamic regions

The morphological features and distribution of luteinizing hormone-releasing hormone (LHRH)-immunoreactive cell bodies and fibers of the hypothalamic and the neighboring mesencephalic regions were studied in the normal newborn infant by immunohistochemistry. Within the hypothalamus, numerous LHRH-immunoreactive like (IL) cell bodies were found mainly in the ventral portion of the infundibular nucleus close to the median eminence and at a lower extent in the medial preoptic area. In addition, sparse immunoreactive cell bodies were displayed in the paraventricular and medial mammillary nuclei. The mesencephalon also exhibited rare immunoreactive cell bodies in the periaqueductal gray. LHRH-IL fibers, predominantly varicose, formed a continuum from the septo-preoptico level to the mesencephalon. In the hypothalamus, the median eminence exhibited the highest LHRH innervation. LHRH-IL fibers are also observed in the lamina terminalis, the medial preoptic area, the suprachiasmatic, the supraoptic, the peri- and the paraventricular nuclei. In the last two nuclei, some fibers projected to the dorsomedial and ventromedial nuclei whereas others were in close relation with the ependyma. The mesencephalon displayed low LHRH-IL fibers, present essentially in the raphe and interpeduncular nuclei and around the ependyma. When compared with data obtained in other mammals, the present findings agree well with the general distribution and morphological features of LHRH-IL neuronal structures reported elsewhere.

Endocrine aspects of postnatal mental disorders

Biological research in postnatal mental illness has only a short history and few encouraging data have yet emerged. The most promising positive findings are perhaps preliminary evidence for an increase of postnatal depression in women with postpartum thyroid dysfunction, some evidence for an enhanced sensitivity to changes in progesterone levels in postnatal depression, and the presence of an opioid peptide with unknown function in the cerebrospinal fluid of women with puerperal psychosis. Although steroid hormones are generally thought to be aetiologically relevant since they freely enter the brain and are known to interact with central monoamine neurotransmitter systems, attempts to demonstrate abnormal levels in postnatal disorders have been disappointing. An important reason for this outcome may be the usually employed approach of isolated hormone measurements. Ovarian steroid levels show marked interindividual variations. Thus significant between-group differences may only be obtained when large numbers of subjects are tested. Since only the unbound fraction can enter the brain, its measurement should be included in such studies. In the case of cortisol, single values are insufficient because of the pulsatile nature and the circadian pattern of its release. Thus serial sampling over 24 hours is more appropriate to detect secretory abnormalities. Measurements of circulating peptides are difficult to interpret since the amount reaching the brain is at best small. What is needed here are estimations of peptides in the cerebrospinal fluid which, however, pose ethical problems. Another explanation for the dearth of consistent positive data may be that women with postnatal mental disorders react to normal postnatal changes differently to women who remain well after childbirth. There is already evidence that patients at high risk of puerperal manic-depressive illness develop a hypersensitivity of central D2 receptors which may be related to the effects of oestrogen withdrawal on the function of DA systems. Further investigations of central neurotransmitter function are needed. In many ways postnatal mental disorders provide a unique opportunity for psychosomatic research since their onset can almost be predicted and follows an event which is associated with changes in many physiological systems. Results of recent neuropharmacological and behavioural investigations into the central effects of steroid and peptide hormones provide the basis for a multitude of pathogenetic hypotheses to be tested in postnatal mental disorders and research in this area may see exciting times ahead.

Differential effects of electrolytic and chemical hypothalamic lesions on LH pulses in rats

Electrolytic lesions of the arcuate nucleus were made in anesthetized adult castrated male rats. Luteinizing hormone (LH) pulse frequency averaged 2.4 pulses/h in controls but declined to a mean of 0.5 pulses/h in rats with bilateral damage to the arcuate nucleus. Because these lesions also damaged the median eminence, we tested the possibility that this disruption of LH secretion was due to coincidental damage to fibers of passage projecting to median eminence. Axon-sparing chemical lesions of the arcuate nucleus were made by intracranial injections of N-methyl-DL-aspartate (NMA) in anesthetized adult castrated rats. Mean LH pulse frequency was 2.3 and 2.5 pulses/h in control and NMA-injected rats, respectively. NMA injections destroyed arcuate neuronal cell bodies and produced a proliferation of glial cells within the nucleus. There was no apparent difference in the immunocytochemical staining intensity and distribution of luteinizing hormone-releasing hormone (LHRH) fibers in median eminence in rats receiving NMA or sham injections. These results suggest that the disruptive effects of electrolytic lesions of the arcuate nucleus on pulsatile LH secretion are a result of coincidental damage to LHRH neuronal projections to the median eminence and that neuronal cell bodies within the arcuate nucleus are not necessary for normal pulsatile LH secretion in male rats.

The nervus terminalis in the mouse: light and electron microscopic immunocytochemical studies

The distribution of gonadotropin-releasing hormone (GnRH)-containing neurons and fibers in the olfactory bulb was studied with light and electron microscopic immunohistochemistry in combination with retrograde transport of "True Blue" and horseradish peroxidase and lesion experiments. GnRH-positive neurons are found in the septal roots of the nervus terminalis, in the ganglion terminale, intrafascicularly throughout the nervus terminalis, in a dorso-ventral band in the caudal olfactory bulb, in various layers of the main and accessory olfactory bulb, and in the basal aspects of the nasal epithelium. Electron microscopic studies show that the nerve fibers in the nervus terminalis are not myelinated and are not surrounded by Schwann cell sheaths. In the ganglion terminale, "smooth" GnRH neurons are seen in juxtaposition to immunonegative neurons. Occasionally, axosomatic specializations are found in the ganglion terminale, but such synaptic contacts are not seen intrafascicularly in the nervus terminalis. Retrograde transport studies indicate that certain GnRH neurons in the septal roots of the nervus terminalis were linked to the amygdala. In addition, a subpopulation of nervus terminalis-related GnRH neurons has access to fenestrated capillaries whereas other GnRH neurons terminate at the nasal epithelium. Lesions of the nervus terminalis caudal to the ganglion terminale result in sprouting of GnRH fibers at both sites of the knife cut. The results suggest that GnRH in the olfactory system of the mouse can influence a variety of target sites either via the blood stream, via the external cerebrospinal fluid or via synaptic/asynaptic contacts with, for example, the receptor cells in the nasal mucosa.

Nervus terminalis, olfactory nerve, and optic nerve representation of luteinizing hormone-releasing hormone in primates

The luteinizing hormone-releasing hormone (LHRH) system was examined immunocytochemically in olfactory bulbs of adult monkeys, including two New World species (squirrel monkey, Saimiri sciureus and owl monkey, Aotus trivirgatus) and one Old World species (cynomolgus macaque, Macaca fasciculata), and in the brain and nasal region of a fetal rhesus macaque Macaca mulatta. LHRH neurons and fibers were found sparsely distributed in the olfactory bulbs in all adult monkeys. There was more LHRH in the accessory olfactory bulb (which is absent in Old World monkeys). In the fetal macaque there was a rich distribution of LHRH neurons and fibers along the pathway of the nervus terminalis, anterior and ventral to the olfactory bulb, and in the nasal septum, with fibers branching into the olfactory epithelium. In addition, there were LHRH neurons and fibers in the optic nerve.

Functional-anatomical studies on the terminal nerve projection to the retina of bony fishes

We have explored the structure and actions of terminal nerve (TN) fibers in the teleostean retina, the most accessible of TN projections. Using immunocytochemistry we have shown that the goldfish TN contains neuropeptides related to the molluscan cardioexcitatory peptide (FMRFamide) as well as luteinizing hormone-releasing hormone (LHRH). Retinal TN terminals were found upon major dendrites in the distal inner plexiform layer and neuronal cell bodies in the amacrine cell layer. Electron-microscopic double-labeling revealed TN terminals applied to the surface of [3H]-dopamine-, glycine-, and gamma-aminobutyric acid (GABA)-accumulating cells. Synthetic LHRH and FMRFamide at less than 1 microM modified spontaneous and light-evoked activity of ganglion cells in isolated superfused goldfish retina, especially during the active breeding season. Salmon(I)-LHRH was 10-30 times as potent as mammalian LHRH and caused rapid, prolonged desensitization. We conclude that LHRH- and FMRFamide-like peptides may be released by retinal TN endings, probably in concert with reproductive activity, and that they act independently through horizontal and/or amacrine cell pathways to modify visual information processing in the retina.

Characterization of LH-RH immunoreactivity in mammalian pituitary neural lobe by HPLC

High performance liquid chromatography was used to characterize luteinizing hormone-releasing hormone (LH-RH) immunoreactivity that was previously identified immunocytochemically in the pituitary neural lobes of bats, ferrets and humans. Extracts of bat posterior lobe and hypothalamus, ferret posterior lobe and hypothalamus and human neurohypophysis were partially purified with C-18 Bond-Elut cartridges. Samples were chromatographed using a C-18 reverse phase HPLC column, and LH-RH-immunoreactive moieties were separated by gradient elution (TFA/acetonitrile solvent system). For bats and ferrets, the major peak of neural lobe LH-RH immunoreactivity eluted with a retention time identical to that of hypothalamic LH-RH. Synthetic mammalian standard added to bat and ferret hypothalamic extracts coeluted as a single peak with the predominant form of LH-RH immunoreactivity present in those tissues. In humans, the peak of LH-RH immunoreactivity in neural lobe extracts coeluted with synthetic standard. These results provide strong evidence that the LH-RH-immunoreactive fibers which terminate within the neural lobe contain authentic LH-RH. Additional minor peaks of LH-RH immunoreactivity were observed in posterior lobe and hypothalamic extracts of both bats and ferrets. Comparisons of posterior lobe content of LH-RH immunoreactivity across species verify that the neural lobe projection is a major component of the LH-RH system in bats, whereas it is represented only minimally in the laboratory rat.

Aging changes in synaptology of luteinizing hormone-releasing hormone neurons in male rat preoptic area

This study was undertaken to examine some aspects of the anatomical substrate for reproductive senescence. Immunocytochemically identified luteinizing hormone-releasing hormone neurons and their processes in the male rat brain preoptic area were compared in young adult (2-4 months), middle-aged (12-14 months) and old (20-23 months) animals. At the light microscopic level there were no age-dependent differences in total numbers or sizes of LHRH neurons nor in their distribution in the brain. Examination of these neurons at the electron microscopic level did reveal significant differences in certain organelles and in the degree and kind of synaptic input. Random sections of middle-aged luteinizing hormone-releasing hormone neurons more frequently passed through the nucleolus and the incidence of nematosomes was higher than in luteinizing hormone-releasing hormone neurons from the young and old animals. Quantitative measures of synaptic input to luteinizing hormone-releasing hormone soma and dendrites as well as to unidentified neurons in the same thin section were made. These are reported as percent of membrane that showed synaptic structure. Dendrites of both luteinizing hormone-releasing hormone and nonidentified neurons were more densely innervated than perikarya. The density of synaptic input to luteinizing hormone-releasing hormone neurons was significantly greater than that to nonidentified neurons in young and middle-aged animals, but was equal to that of nonidentified neurons by old age. Age-related changes were noted in synaptic organization with the most significant change being an increased input to luteinizing hormone-releasing hormone perikarya. Indeed, synaptic input to luteinizing hormone-releasing hormone perikaryal membrane was increased three-fold by middle age and ten-fold by old age. Density of synaptic input to luteinizing hormone-releasing hormone dendritic membrane did not change with age. There were no aging changes in percentage of membrane with synaptic structure in nonidentified elements. Synapses were also classified on the basis of their synaptic vesicle content. There were proportionately more synaptic boutons containing round clear than pleomorphic vesicles in the young sample. The proportion of synapses with pleomorphic vesicles increased with age onto both luteinizing hormone-releasing hormone perikarya and their dendrites. The proportion of boutons containing some electron dense-core vesicles along with clear vesicles decreased with age onto both luteinizing hormone-releasing hormone and nonidentified neurons and their processes.

Testosterone implants into the lateral septum of male rats, a positive effect on LH and FSH secretion

After two days, testosterone implanted into the lateral septum increased serum levels of LH and FSH in male Wistar rats. As measured by RIA, LH in animals with testosterone implanted in them in comparison to those with an empty cannula was 0.220 +/- 0.015 vs. 0.111 +/- 0.019 ng/ml; p less than 0.001 and FSH was 3.20 + 0.21 vs. 1.50 + 0.21 ng/ml; p less than 0.001. Serum testosterone was not increased to a statistically significant extent by the implants (4.12 +/- 0.54 vs. 2.87 +/- 0.42 ng/ml; ns). It was concluded that testosterone or possibly one of its metabolites acting in the lateral septum facilitates the release of LH and FSH.

Implantation of fetal preoptic area into the lateral ventricle of adult hypogonadal mutant mice: the pattern of gonadotropin-releasing hormone axonal outgrowth into the host brain

Transplantation of fetal preoptic area tissue containing gonadotropin-releasing hormone neurons into the third ventricle of male hypogonadal mice resulted in an elevation of pituitary gonadotropin levels and correction of hypogonadism. This reversal of the neuroendocrine deficit was correlated with innervation of the median eminence by gonadotropin-releasing hormone axons. The specificity of fiber outgrowth suggested that local neuromodulatory factors might guide these axons to the nearby median eminence. To test this hypothesis, 14 adult hypogonadal males received unilateral fetal preoptic area grafts into the lateral ventricle, a site distant from the median eminence. After four months, healthy grafts containing numerous gonadotropin-releasing hormone neurons were seen in 9 hosts. However, none of these grafts corrected the hypogonadism of the host and there was no gonadotropin-releasing hormone innervation of the median eminence in any of these animals, thus demonstrating that the presence of gonadotropin-releasing hormone neurons in the ventricular space is itself not sufficient to stimulate the pituitary-gonadal axis. Instead, gonadotropin-releasing hormone axons coursed in the host fimbria, fornix, corpus callosum, and stria terminalis. These fibers could be traced into the anterior hippocampal area, medial and lateral septum, and the anterior hypothalamus. The distribution of these fibers included a number of regions which receive gonadotropin-releasing hormone fiber input in the normal mouse. These findings show that gonadotropin-releasing hormone neurons transplanted into the lateral ventricle can survive and extend processes into the host brain, often projecting to sites of normal gonadotropin-releasing hormone innervation. Their success in contacting these sites suggests that gonadotropin-releasing hormone fiber outgrowth may be influenced by regionally specified trophic and/or guidance factors.

The development of differential mabQ113-immunoreactivity in the rat habenular complex

Monoclonal antibody mabQ113 selectively labels a subset of Purkinje cells which are arranged in parasagittal bands throughout the vermis and hemispheres of the rat cerebellar cortex. No other cerebellar cell types are immunoreactive. By contrast, in the remainder of the brain the mabQ113 epitope is located primarily in glial cells. In general, the glial immunoreactivity is not differentially distributed. An exception is that mabQ113 densely and uniformly stains the lateral habenula (LHb) but gives no labelling of the medial habenula (MHb). During cerebellar development, the mabQ113 epitope is expressed in three stages. Before postnatal day 7 (P7) all Purkinje cells are negative. Secondly, all Purkinje cells become mabQ113+ between P7 and P12. The parasagittal bands are created between P12 and P30 by selective suppression of epitope expression. To explore whether epitope suppression is also responsible for differential staining patterns in other brain regions the ontogenic development of mabQ113 immunoreactivity has been mapped in the habenular complex. Neither the MHb nor the LHb express the mabQ113 epitope prenatally. P1 is the first age at which the LHb is stained. During the next few days the intensity of staining within the LHb steadily increases until the adult pattern is attained at P6. At no time is there expression of the mabQ113 antigen in the MHb. This also confirms that the two classes of habenular astrocytes, mabQ113-/GFAP+ and mabQ113+/GFAP+, are intrinsically different throughout postnatal life.

The olfactory gonadotropin-releasing hormone immunoreactive system in mouse

The olfactory gonadotropin-releasing hormone (GnRH) system in mice was studied with immunofluorescence in combination with lesions of the olfactory bulb and retrograde transport of horseradish peroxidase (HRP) which was administered intravascularly, intranasally or into the subarachnoid space. GnRH-positive neurons were located in the two major branches forming the septal roots of the nervus terminalis, in the ganglion terminale, within the fascicles of the nervus terminalis throughout its extent, in a conspicuous band which connects the ventral neck of the caudal olfactory bulb with the accessory olfactory bulb and in the nasal mucosa. GnRH-positive fibers were seen in all areas in which neurons were found, i.e. in the rostral septum, the ganglion and nervus terminalis and in the nasal subepithelium. In addition, a broad bundle of fibers was observed to surround the entire caudal olfactory bulb, connecting the rostral sulcus rhinalis with the ventrocaudal olfactory bulb. Fibers were seen in close association with the main and accessory olfactory bulb, with the fila olfactoria and with the nasal mucosa. Throughout the olfactory bulb and the nasal epithelium, an association of GnRH fibers with blood vessels was apparent. Intravascular and intranasal injection of HRP resulted in labeling of certain GnRH neurons in the septal roots of the nervus terminalis, the ganglion terminale, the nervus terminalis, the caudal ventrodorsal connection and in the accessory olfactory bulb. After placement of HRP into the subarachnoid space dorsal to the accessory olfactory bulb, about 50% of the GnRH neurons in the accessory olfactory bulb and in the ventrodorsal connection were labeled with HRP. Also, a few GnRH neurons in the rostral septum, the ganglion terminale and in the fascicles of the nervus terminalis had taken up the enzyme. Lesions of the nervus terminalis caudal to the ganglion terminale resulted in sprouting of GnRH fibers at both sites of the knife cut. Lesions rostral to the ganglion terminale induced sprouting mostly at the distal site of the knife cut while most but not all GnRH fibers proximal to the lesion had disappeared. The results of the present study indicate that the olfactory GnRH system is mostly associated with the nervus terminalis. This cranial nerve apparently projects to the central nervous system as well as the periphery. The results of the HRP uptake studies suggest that the GnRH neurons in the nervus terminalis have access to fenestrated capillaries in the subepithelial connective tissue of the nasal mucosa, to the nasal epithelium proper, and to the subarachnoid space.(ABSTRACT TRUNCATED AT 400 WORDS)

The amygdala and male reproductive functions: I. Anatomical and endocrine bases

The present review is mainly concerned with the role of the amygdala (AMY) in male sexual behaviour and presents the characteristics of neuroanatomical and neuroendocrine organization of the cortico-medial amygdala as compared to the medial preoptic area (MPOA), in relation to sexual behaviour and gonadotropin secretion. It stresses the part played by AMY in processing sensory information which afterwards reaches the hypothalamus (HYP). Some data on the different function of steroids and luteinizing hormone releasing hormone (LHRH) systems within AMY and MPOA are provided. The role of AMY in the positive feedback effect on luteinizing hormone (LH) secretion and the involvement of steroid and opiate interaction as its mechanism are suggested. AMY is proposed to integrate external and internal sensory information granting the optimal conditions for sexual performance and possibly for regulation of LH release according to the behavioural context. The steroid content of AMY may influence these processes.

Regulation of mating behaviour in the female rat by gonadotropin-releasing hormone in the ventral tegmental area: effects of selective destruction of the A10 dopamine neurones

Microinfusions of gonadotropin-releasing hormone (GnRH) into the ventral tegmental area (VTA) potentiated lordosis behaviour in oestrogen-primed ovariectomised female rats. Facilitation was observed within 5 min after the infusion and lasted for about 90 min. When GnRH was infused into the VTA of oestrogen-primed animals which were previously subjected to 6-hydroxydopamine treatment (to destroy the A10 dopamine cells), it produced a marked facilitation of lordosis lasting for about 24 h. These results suggest that the A10 dopamine neurones in the VTA may be critically involved in the mechanisms by which GnRH may modulate midbrain circuits involved in the regulation of lordosis behaviour in the female rat. The lesion studies also imply that the A10 dopamine neurones function as inhibitory neurones regulating lordosis behaviour by suppressing the activity of those cells in the VTA which are sensitive to GnRH. Removal of this inhibitory input leads to an exaggerated response.

Evidence for, and nature of, the tonic inhibitory influence of habenulointerpeduncular pathways upon cerebral dopaminergic transmission in the rat

The potential role of the habenula in the transsynaptic regulation of the activity of ascending dopaminergic systems has been investigated in the rat by studying the effect of an acute interruption of impulse traffic in the diencephalic conduction system (stria medullaris-habenula-fasciculus retroflexus) and of pharmacological manipulation of various neurotransmitter systems in the interpeduncular nucleus on dopamine metabolism in several dopaminergic projection fields. The bilateral infusion of tetrodotoxin into the fasciculus retroflexus (which conveys the habenulointerpeduncular tract) of conscious rats markedly increased homovanillic acid levels and dopamine synthesis and utilization in the medial prefrontal cortex, nucleus accumbens, olfactory tubercle and striatum. Similar changes in dopamine metabolism were observed in these areas after bilateral infusion of tetrodotoxin into the stria medullaris (which conveys most of the afferents to the habenula). Infusion of atropine (0.4-1 micrograms) into the interpeduncular nucleus increased homovanillic acid concentrations and dopamine utilization in the medial prefrontal cortex and nucleus accumbens but not in the olfactory tubercle and striatum. Moreover, intra-interpeduncular injection of oxotremorine (17 micrograms) antagonized the increase in dopamine utilization in the nucleus accumbens (but not in the olfactory tubercle) induced by an intrafasciculus retroflexus infusion of tetrodotoxin. Local infusion of naloxone (20 micrograms) into the interpeduncular nucleus increased homovanillic acid concentrations in the nucleus accumbens and olfactory tubercle but not in the medial prefrontal cortex and striatum. In contrast, intra-interpeduncular nucleus infusion of the substance P antagonist D-Arg1, D-Pro2, D-Trp7,9, Leu11-substance P or of substance P antiserum failed to alter homovanillic acid levels in the 4 dopamine-rich areas investigated. Finally, intraraphé medianus (but not intraraphé dorsalis) infusion of muscimol (25 ng) moderately increased dopamine synthesis in the nucleus accumbens and striatum. The present findings suggest that the habenulointerpeduncular pathways exert a tonic inhibitory influence on mesocortical, mesolimbic and mesostriatal dopaminergic neurons. Cholinergic and/or opioid peptidergic neurons coursing through the fasciculus retroflexus as well as ascending serotonergic neurons originating in the raphé medianus could take part in this inhibitory control of ascending dopaminergic neurons.

Extrahypothalamic projection of luteinizing hormone-releasing hormone fibers in the brain of the toad, Bufo japonicus

Extrahypothalamic projection of luteinizing hormone-releasing hormone (LHRH) fibers in the brain of the toad (Bufo japonicus) was examined immunohistochemically by the avidin-biotin-peroxidase complex (ABC) method. Immunoreactive LHRH perikarya are localized in the nuclei medialis septi and of the diagonal band of Broca. A part of the LHRH fibers are sent anteriad to the medial and dorsal pallia. Some fibers reach the olfactory bulb. Dorsocaudally, LHRH neurons in the medial septum project their fibers to the deep layers of the optic tectum and the posterior mesencephalon including the nucleus pretrigeminalis, which is considered to be a generator of mate calling behavior, via the habenular and posterior thalamic regions. In addition, LHRH fibers which run caudad through the dorsal infundibular region and then the mesencephalic reticular formation were widely distributed in both the gray and the white matter of the medulla oblongata. These findings suggest that LHRH acts as a neurotransmitter or a neuromodulator in the various neuronal circuitries for reproductive behavior in the central nervous system, because LHRH has been considered to be related to amphibian seasonal breeding, and many regions where the immunoreactive LHRH fibers were observed are the loci concerned with mating behavior.

Immunocytochemical localization of luteinizing hormone-releasing hormone (LHRH) pathways in the sheep brain during anestrus and the mid-luteal phase of the estrous cycle

The luteinizing hormone-releasing hormone (LHRH) system of the sheep brain was examined by light microscopic immunocytochemistry with thick, unembedded sections. We compared the distribution and morphology of LHRH cells and their fibers in intact and ovariectomized anestrous ewes, and in breeding season ewes during the mid-luteal phase of their estrous cycle. In all animals, a majority of LHRH neurons were found in the medial preoptic area adjacent to the organum vasculosum of the lamina terminalis. These cells formed a continuum rostrally with immunoreactive neurons in the diagonal band of Broca and medial septum and caudally with cells in the ventrolateral anterior hypothalamus and lateral hypothalamus. Relatively few cells (1-2%) were seen in the arcuate nucleus or its vicinity. Preoptic LHRH neurons project to the tubero-infundibular sulcus of the median eminence by at least two routes: a major ventrolateral projection above the optic tract in the anterior and lateral hypothalamus, and a less prominent periventricular pathway along the third ventricle. LHRH fibers were also observed in a number of extrahypothalamic regions, including the medial amygdala and the accessory olfactory bulb. Immunoreactive LHRH neurons in the sheep exhibited a complex light microscopic morphology unlike that seen in LHRH cells of any other species to date. LHRH cells with extensive, branching processes were frequently found in clusters with close somatic appositions between neighboring cells. Multiple thin protuberances emanated from the soma of many immunoreactive neurons. Immunoreactive fibers with beaded varicosities often were intimately associated with both cell bodies and their dendritic processes. Morphometric analyses revealed that preoptic LHRH neurons in three of four mid-luteal phase ewes had a shorter total dendritic length than those neurons in either intact or ovariectomized anestrous ewes, but this difference between breeding season and anestrous ewes was not statistically significant. Evidence for possible seasonal and/or steroid-induced alterations in the morphology of LHRH neurons must be documented by further studies, including immunocytochemical observations at an ultrastructural level.

Physiological interactions of the basic rest--activity cycle of the brain: pulsatile luteinizing hormone secretion as a model

The hypothesis of the "basic rest--activity cycle" (BRAC) as an ultradian rhythm of CNS activity which integrates many somatic, visceral, and behavioral functions is supported by a variety of studies which demonstrate similar periodicities in the expression of a remarkable number of critical physiological systems. However, the existence of this BRAC has been supported primarily only by this similarity in cyclicity, and the argument in support of this potentially meaningful CNS oscillator is thus largely inferential. Since resolving consistent temporal relationships between a variety of these apparently otherwise unrelated rhythmic functions would strongly support the hypothesized existence of the BRAC, this article first presents methodology for reliable evaluation of these difficult to analyze interactions. Then, a relationship between rhythmic physical activity and pulsatile luteinizing hormone (LH) secretion is employed as a model interaction which allows analysis of the rhythmicity of the BRAC itself. This BRAC entrainment of pulsatile LH secretion is also utilized as a model to demonstrate how the BRAC may modulate the activity of various physiological functions via relatively direct mechanisms, secondary interactions, or entrainment of tissue with its own intrinsic pacemaker activity. The physiological function of the BRAC is discussed relative to this entrainment of pulsatile LH release.

An autoradiographic study of projections ascending from the midbrain central gray, and from the region lateral to it, in the rat

Ascending projections from the midbrain central gray (CG) and from the region lateral to it were traced in the rat using tritiated amino acid autoradiography. Leucine or a cocktail of amino acids (leucine, proline, lysine, histidine, and tyrosine) were used as tracers. In addition to projections within the midbrain, ascending fibers follow three trajectories. The ventral projection passes through the ventral tegmental region of Tsai and the medial forebrain bundle to reach the hypothalamus, preoptic area, caudoputamen, substantia innominata, stria terminalis, and amygdala. There are labeled fibers in the diagonal bands of Broca and medial septum, and terminal labeling in the lateral septum, nucleus accumbens, olfactory tubercle, and frontal cortex. The dorsal periventricular projection terminates in the midline and intralaminar thalamic nuclei. The ventral periventricular projection follows the ventral component of the third ventricle into the hypothalamus, passing primarily through the dorsal hypothalamic area and labeling the rostral hypothalamus and preoptic area. Projections from the region lateral to the CG are similar, but exhibit stronger proximal, and weaker distal, projections. Rostral levels of the CG send heavier projections to the fields of Forel and the zona incerta, but fewer fibers through the supraoptic decussation, than do caudal levels. Ascending projections from the CG are both strong and widespread. Strong projections to the limbic system and the intralaminar thalamic nuclei provide an anatomical substrate for CG involvement in nociception and affective responses.

Implantation of normal fetal preoptic area into hypogonadal mutant mice: temporal relationships of the growth of gonadotropin-releasing hormone neurons and the development of the pituitary/testicular axis

Central nervous system tissue which included the preoptic area (an area rich in gonadotropin-releasing hormone neurons) was taken from normal 17-day fetal mice and transplanted into the infundibular recess of the third ventricle of the hypothalamus of 90-day male mutant hypogonadal mouse hosts that are unable to synthesize the neurohormone, gonadotropin-releasing hormone. The growth and development of gonadotropin-releasing hormone neurons and fibers in the donor and host tissue as well as recovery of the pituitary-testicular axis were followed from 10 to 120 days post-implantation. Testicular growth was evident in 94% of the hypogonadal animals within 30 days post-implantation, continued for 90 days but showed no further increase during the remainder of the experiment. Increases in seminal vesicle weight, an index of testosterone secretion, were measurable at 30 days and continued through to the end of the experiment. Pituitary concentrations of gonadotropins were doubled at 30 days over that seen in the control mutant mouse and were maintained thereafter at normal or supranormal concentrations. In contrast plasma levels of gonadotropins, although above baseline at 30 days, never reached normal circulating levels. Nevertheless, it appeared that the concentration of luteinizing hormone achieved was sufficient to initiate and maintain testicular growth and testosterone secretion for the entire duration of the experiment. Immunocytochemical analysis of brain tissue was used to determine the presence and numbers of gonadotropin-releasing hormone neurons in the transplant and the distribution of their fibers in the donor and host tissue. The numbers of immunoreactive gonadotropin-releasing hormone neurons present at the time of sacrifice ranged from 3 to 140. Fiber outgrowth from the donor cells into the host was noted as early as 10 days post-implantation and the density of outgrowth continued to increase over the course of the experiment. Positive fibers tended to accumulate over the tuberoinfundibular sulci as they do in normal animals. In those instances where the transplant was placed a long distance from the median eminence, the gonadotropin-releasing hormone axons grew on the internal surface of the third ventricle until they reached these specific exit zones. These studies indicate that in the mutant hypogonadal mouse, central nervous system transplants from normal fetal mice can maintain the function of the pituitary-gonadal axis for periods of up to 120 days post-implantation. Outgrowth of the neurosecretory fibers begins very soon after implantation and the axons tend to follow pathways seen in normal tissue.(ABSTRACT TRUNCATED AT 400 WORDS)

Organization of LHRH cells: differential apposition of neurotensin, substance P and catecholamine axons

A wealth of evidence suggests that catecholamines (particularly norepinephrine) influence gonadotropin secretion via a direct interaction with the LHRH neurons. Neuropeptides such as neurotensin (NT) and substance P (SP) are likewise implicated in the control of LHRH secretion, based on pharmacological and preliminary anatomical studies. Since sub-populations of LHRH neurons project to areas of the brain other than the median eminence, a detailed analysis of the topography of axonal interactions of catecholamines (CA), substance P and neurotensin with LHRH cells was conducted in adult male mice using dual immunocytochemical techniques. An analysis of the patterns of apparent contact of NT or SP axons on LHRH cells as determined by close apposition of immunoreactive axons to LHRH cells when viewed under a light microscope at high magnification revealed that the density of NT or SP axons was not a reliable index of the degree of contact; in many locations, NT and SP had similar densities yet a greater portion of the LHRH cells appeared contacted by SP than NT. NT axons were in close contact with up to one-third of the LHRH cells. Analysis of the location of these "contacted" cells did not reveal a discrete subnucleus controlled by NT. Rather, the NT-contacted cells were scattered throughout the LHRH cell field. Interactions of LHRH cells with SP axons were likewise uniform throughout most of the LHRH cell field, with the exception of the most anterior portion of the field. In the anterior septum, few SP axons appeared to contact LHRH cells. Elsewhere, most of the LHRH cells were in contact with SP axons. For the CAs, the fiber density in the regions of the LHRH cells was uniformly moderate, yet the pattern of cells contacted showed variation across the LHRH cell field, with most of the "contacted" cells located near the OVLT and medial preoptic area. These data suggest that LHRH cells may be differentially regulated by NT, SP and the CAs.