Neurotransmitter specificity of cells and fibers in the medial preoptic nucleus: an immunohistochemical study in the rat

Studies on the cellular architecture of the bed nuclei of the stria terminalis in the rat: II. Chemoarchitecture

In a companion paper (Ju and Swanson; J. Comp. Neurol. 280:587-602, '89) we described a parcellation scheme for the bed nuclei of the stria terminalis (BST) that was based on cytoarchitectonic criteria. In the work reported here, antisera to the neuropeptides corticotropin-releasing hormone, neurotensin, galanin, substance P, and cholecystokinin were used to determine the extent to which immunostained neuronal cell bodies and presumed terminal fields are correlated with this cytoarchitectonic scheme in the adult male rat. The results confirm the validity of the cytoarchitectonic parcellation and provide additional chemoarchitectonic criteria for determining the (as yet still somewhat arbitrarily defined) border between the BST and the ventrally adjacent preoptic region, for distinguishing between the anterior and posterior divisions of the BST, and for identifying and distinguishing between the particular cell groups or nuclei within each division. The projections of each neuropeptide-containing cell group in various parts of the BST remain to be determined, as do the precise origins of the localized immunoreactive terminal fields identified here.

Differential effects of beta-endorphin infused into the hypothalamic preoptic area at various phases of the male rat's sexual behaviour

Beta-Endorphin, infused into the pre-optic/anterior hypothalamus (40 pmoles bilaterally) of the male rat before he was placed in an arena containing an oestrous female, inhibited mounting, intromitting and ejaculation, but investigative behaviour continued at control levels. If the infusion was delayed until the male had made an intromission, then beta-endorphin no longer had any effect on sexual interaction, the male mounting and ejaculating as if he had received a control infusion of artificial cerebrospinal fluid. However, if the male was returned to a different female after the infusion had been completed, then the suppressive effects of beta-endorphin returned. Males infused during the refractory period following an ejaculation (and returned to the same female) showed unimpaired return of sexual activity. Imposing a delay of up to 2 h after an intromission and an infusion showed that the effect of beta-endorphin was still antagonized when the male was again paired with the same female; however, by 6 h, its inhibitory effects were beginning to return. Allowing the male to mount (but not intromit) a female whose vagina had been taped partially counteracted the behavioural effect of beta-endorphin. If the female was separated from the male by a small wire cage which allowed limited interaction with her, subsequently infusing the males with beta-endorphin suppressed their mounting behaviour. These results show that both investigative and mounting behaviour can occur after infusions of beta-endorphin into the pre-optic/anterior hypothalamus, but that the transition between them is prevented if infusions are made before a critical point in the behavioural sequence. This is the onset of following the female and mounting her. Analysis of the behavioural sequence after either artificial cerebrospinal fluid or beta-endorphin infusions confirmed this; beta-endorphin interrupted the sequence at the first transition between investigative and mounting behaviour. These results suggest that beta-endorphin acts on a neural mechanism in the medial preoptic area/anterior hypothalamus which allows matching of incentive stimulus to specific behavioural response, and this may be a general property of this part of the brain.

Long-lasting insomnia induced by preoptic neuron lesions and its transient reversal by muscimol injection into the posterior hypothalamus in the cat

In order to analyse the role of the anterior hypothalamus in the regulation of the sleep-waking cycle we made bilateral neuronal lesions at different levels of the anterior hypothalamus in cats, by means of microinjections of a cell-specific neurotoxin:ibotenic acid. These lesions resulted in severe insomnia in eight cats. This insomnia was characterized by a large decrease or even disappearance of paradoxical sleep and deep slow wave sleep and, to a lesser extent, by a decrease of light slow wave sleep, for 2-3 weeks. In the other five animals, we observed a large reduction of deep slow wave sleep (0-40% of control level), but a less intensive decrease of time spent in paradoxical sleep (50-75% of control level) and no marked effect on light slow wave sleep. During the first 3-6 postoperative days we also noticed hyperthermia in all cats; thereafter, the animals presented only a slight increase in brain temperature which did not appear to trigger the sleep impairment. Histological analysis of the different lesions revealed that the insomnia could be attributed to neuronal cell body destruction in the mediobasal part of the anterior hypothalamus covering; the medial preoptic area and a narrow portion of the lateral preoptic area as well as a restricted part of the anterior hypothalamic nucleus. In order to investigate the putative role of the posterior hypothalamic structures in the mechanism of insomnia after lesion of the mediobasal preoptic area neurons we injected an agonist of GABA into the ventrolateral part of the posterior hypothalamus to locally depress the neuronal activity. The bilateral intracerebral microinjection of muscimol (0.5-5 micrograms) induced a transient intensive hypersomnia (slow wave sleep and paradoxical sleep). These findings indicate that neuronal cell loss in the mediobasal preoptic area induced a long lasting insomnia. Thus, it may be hypothesized that the integrity of this structure is necessary for sleep appearance. Finally, our data are in keeping with an intrahypothalamic regulation of the sleep-waking cycle.

Distribution of opioid peptides in the preoptic region: immunohistochemical evidence for a steroid-sensitive enkephalin sexual dimorphism

The distribution of cells and fibers that contain opioid peptides within the preoptic region of the rat was examined immunohistochemically. Cells and/or fibers that contain peptides derived from each of the three major opioid peptide families were differentially stained by using antisera that recognize unique derivatives of each precursor molecule and do not cross-react with members of the other opioid peptide families. A beta-endorphin (beta E) antiserum was used to stain fibers that contain peptides derived from the proopiomelanocortin molecule, and dynorphin-containing cells were identified by using an antiserum directed toward dynorphin B (Dyn B) that does not show detectable cross-reactivity with enkephalin-related peptides. An antiserum raised against peptide E (PE), which does not appear to cross-react significantly with dynorphin peptides, was used to localize enkephalin cells and fibers. Each family of opioid peptides showed a unique distribution in the preoptic region. beta E-immunoreactive fibers were primarily localized to the preoptic part of the periventricular nucleus, with moderate densities of fibers contained in the anteroventral periventricular nucleus (AVPv) and medial preoptic nucleus (MPN). Dyn B-immunoreactive fibers showed a somewhat more uniform distribution throughout the region, and only a few Dyn B-stained cells bodies were found within the medial preoptic area. In contrast, the preoptic region contained hundreds of PE-immunoreactive cells, which were particularly numerous within the AVPv, MPN, and anterodorsal preoptic nucleus. The AVPv and MPN also contained discretely localized plexuses of PE-stained fibers. Although the overall distributions of opioid peptide-containing fibers within the preoptic region were quite similar in male and female rats, differential distributions of fibers were found in certain nuclei such as the AVPv and MPN, and they were correlated with previously identified cytoarchitectonic sexual dimorphisms. Such differential distributions were particularly distinct for enkephalin-containing fibers. Although the AVPv is larger in female rats, it contained more PE-immunoreactive cell bodies in male rats, and we have shown here that this sexual dimorphism appears to be at least partially dependent on perinatal levels of gonadal steroids. In contrast, no difference in the number of PE-stained cells was found within the anterodorsal preoptic nucleus of male and female animals, indicating that sexual differences are not a general characteristic of enkephalinergic cells in the preoptic region of the rat.(ABSTRACT TRUNCATED AT 400 WORDS)

Cytoarchitectonic analysis of the SDN-POA of the intact and gonadectomized rat

The densely staining group of cells referred to as the sexually dimorphic nucleus of the preoptic area (SDN-POA) is greater in volume in the male than in the female rat. Because we and others have reported absolute volumes that have been consistent within individual studies but that vary considerably, we characterized the SDN-POA by describing its morphology with respect to the cytoarchitectonic divisions of the medial preoptic nucleus (MPN) in intact and gonadectomized rats. We report three major findings: the SDN-POA is heterogeneous and is composed of cells belonging to three distinct cytoarchitectonic divisions; the cytoarchitecture of the MPN and its medial and lateral divisions (MPNm and MPNl, respectively) in male rats appear to be influenced by the hormonal status in adulthood; and a small anteroventral division of the MPN (MPNav) is present in males but virtually absent in females. Specifically, the SDN-POA is located within the MPNm, but consists of subcomponents located within the central division of the MPN (MPNc), the MPNav, and part of the MPNm-exclusive of the MPNc and MPNav. The percentage of the total SDN-POA located within the MPNc and MPNav. The percentage of the total SDN-POA located within the MPNc and MPNav was greater in males, and that in the MPNm-exclusive of the MPNc and MPNav was greater in females, indicating that the SDN-POA has a different cytoarchitectonic composition in the two sexes. Gonadectomy produced no significant differences in SDN-POA volume, but the MPN, MPNl, and MPNm were significantly reduced in gonadectomized versus intact males, suggesting an activational effect of testicular hormones on these structures.

Innervation of histaminergic neurons in the posterior hypothalamic region by medial preoptic neurons. Anterograde tracing with Phaseolus vulgaris leucoagglutinin combined with immunocytochemistry of histidine decarboxylase in the rat

By means of anterograde neuroanatomical tracing with Phaseolus vulgaris leucoagglutinin (PHA-L) combined with immunohistochemistry of histidine decarboxylase (HDC), we studied in the rat whether the histaminergic neurons in the posterior hypothalamic region are innervated by fibers arising from neurons in the medial preoptic region (MPO). We injected the tracer at various locations in the MPO. Following survival, frozen brain sections were dual-stained according to a protocol using PHA-L and HDC immunocytochemistry. From all parts of the MPO, PHA-L-labeled fibers course to ipsi- and contralateral clusters of histaminergic neurons located in the posterior hypothalamus. Varicosities on the PHA-L-labeled fibers can be observed in close association with HDC-immunoreactive cell bodies and dendrites in all the histaminergic cell clusters in the posterior hypothalamus. These associations suggest synaptic connectivity.

Projections of the medial preoptic nucleus: a Phaseolus vulgaris leucoagglutinin anterograde tract-tracing study in the rat

The projections of the medial preoptic nucleus (MPN) were examined by making injections of the anterogradely transported lectin Phaseolus vulgaris leucoagglutinin (PHA-L) into the MPN and charting the distribution of labeled fibers. The evidence indicates that the MPN projects extensively to widely distributed regions in both the forebrain and brainstem, most of which also supply inputs to the nucleus. An important neuroendocrine role for the MPN is underscored by its extensive projections to almost all parts of the periventricular zone of the hypothalamus, including the anteroventral periventricular, anterior part of the periventricular, paraventricular (PVH), and arcuate nuclei, and a role in autonomic mechanisms is indicated by projections to such regions as the dorsal and lateral parvicellular parts of the PVH, the lateral parabrachial nucleus, and the nucleus of the solitary tract. Other projections of the MPN suggest participation in the initiation of specific motivated behaviors. For example, inputs to two nuclei of the medial zone of the hypothalamus, the ventromedial and dorsomedial nuclei, may be related to the control of reproductive and ingestive behaviors, respectively, although the possible functional significance of a strong projection to the ventral premammillary nucleus is presently unclear. The execution of these behaviors may involve activation of somatomotor regions via projections to the substantia innominata, zona incerta, ventral tegmental area, and pedunculopontine nucleus. Similarly, inputs to other regions that project directly to the spinal cord, such as the periaqueductal gray, the laterodorsal tegmental nucleus, certain medullary raphe nuclei, and the magnocellular reticular nucleus may also be involved in modulating somatic and/or autonomic reflexes. Finally, the MPN may influence a wide variety of physiological mechanisms and behaviors through its massive projections to areas like the ventral part of the lateral septal nucleus, the bed nucleus of the stria terminalis, the lateral hypothalamic area, the supramammillary nucleus, and the ventral tegmental area, all of which have extensive connections with regions along the medial forebrain bundle. Although the PHA-L method does not allow a clear demonstration of possible differential projections from each subdivision of the MPN, our results suggest that each of them does give rise to a unique pattern of outputs.(ABSTRACT TRUNCATED AT 400 WORDS)

Distribution of cholecystokinin-immunoreactive cell bodies in the male and female rat: II. Bed nucleus of the stria terminalis and amygdala

The distribution of cholecystokinin-immunoreactive (CCK-I) cell bodies was studied in the bed nucleus of the stria terminalis (BST) and amygdaloid complex of colchicine-treated male and female rats. Immunoreactive cells were visualized in the BST medial amygdaloid (MeA), central lateral, basolateral, basolateral ventral, medial, intercalated, anterior cortical, and posterior cortical nuclei and the amygdalohippocampal zone. Several significant sex differences were observed. In the male, a dense aggregation of CCK-I cell bodies was visualized in the MeA, especially in the dorsocaudal part and in the encapsulated part of the BST. In comparison, female rats had relatively fewer immunoreactive cells in both of these regions. In the lateral and basolateral amygdaloid nuclei, however, more CCK-I cells were visualized in the female than in the male, but the difference was not statistically significant. These data provide characterization of a sexually differentiated CCK system. In addition, we observed that the number of CCK-I cells in the BST and posterodorsal part of the MeA was substantially reduced after castration. The number of CCK-I cells in female rats, however, was not significantly reduced after ovariectomy in any of the regions studied. These findings imply that the steroid regulation of CCK is sexually differentiated. The sexually dimorphic distribution of CCK-I cells in areas that are targets of steroid hormones and regulate reproductive processes is consistent with the possibility that CCK participates in central integration of sensory and steroidal input that modulates reproductive behavior.

Evidence for an absence of estrogen-concentration by CCK-immunoreactive neurons in the hypothalamus of the female rat

It is becoming increasingly clear that the neuropeptide cholecystokinin (CCK), widely distributed in the rat hypothalamus and limbic system, is subject to both organizational and activational influences of steroid hormones. Sex differences in numbers of CCK-immunoreactive elements have been demonstrated in sexually dimorphic structures such as the bed nucleus of the stria terminalis, medial preoptic nucleus, and ventromedial nucleus of the hypothalamus. Steroid activation of CCK has been indicated by findings that hypothalamic CCK levels and binding capacity vary over the estrous cycle. These studies, in combination with evidence of CCK mediation of sexually differentiated functions, prompted us to test for estrogen concentration among CCK-containing cells of the female rat hypothalamus by combining the techniques of immunohistochemistry and autoradiography. A method employing 2-week ovariectomies and perfusion fixation with 4% paraformaldehyde was compatible with the localization of both estrogen-accumulating and CCK-immunoreactive cell bodies. The maintenance of numbers of CCK-positive cells after gonadectomy suggested that expression of this peptide may not be directly regulated by ovarian steroids in female rats. This suggestion was substantiated by the finding that, with rare exceptions, CCK-immunoreactive cells did not concentrate estrogen in tissues collected from the anterior-posterior extent of the bed nucleus of the stria terminalis, medial preoptic nucleus, anterior hypothalamic area, and paraventricular nucleus.

Selective effects of beta-endorphin infused into the hypothalamus, preoptic area and bed nucleus of the stria terminalis on the sexual and ingestive behaviour of male rats

beta-Endorphin was infused bilaterally into the medial preoptic area-anterior hypothalamic continuum at doses of 5, 10 and 40 pmol each side. The highest dose selectively abolished mounting, intromitting and ejaculating in sexually experienced male rats paired with an oestrous female. Males infused with 40 pmol beta-endorphin still followed the female, investigated her anogenital region and other parts of her body, but made abortive attempts to mount. A dose of 5 pmol beta-endorphin had no effect, but 10 pmol proved partially effective. The same males, in other tests, were allowed to ingest a highly preferred, sweet, non-calorific solution (acesulfame-K) in the absence of a female. beta-Endorphin infusions (up to 40 pmol) into the same area of the hypothalamus had no effect on this behaviour. Control males allowed simultaneous access both to an oestrous female and to the sweet solution copulated normally but reduced their ingestive behaviour, despite there being sufficient time during tests for both to occur. beta-Endorphin (40 pmol) infused into the preoptic area-anterior hypothalamic continuum under these conditions suppressed sexual interaction, but ingestion of acesulfame-K increased to values observed when the female was absent. beta-Endorphin infused into neighbouring areas of the brain had different behavioural effects. Sexual behaviour was not inhibited, and ingestion of acesulfame-K was unaltered, when beta-endorphin was infused either into the bed nucleus of the stria terminalis or the rostral ventromedial hypothalamus. However, infusions of cholecystokinin-8 into the ventromedial hypothalamus suppressed acesulfame-K ingestion in most animals, showing that the cannulae were placed in an area regulating ingestive behaviour. The inhibition of sexual behaviour after preoptic area-anterior hypothalamic continuum infusions of beta-endorphin was prevented by either pretreating rats with 1 mg/kg naloxone intraperitoneally, or by infusing a putative delta opiate receptor blocker (0.5 pmols ICI 174864) into the preoptic area-anterior hypothalamic continuum 5 min prior to beta-endorphin treatment. ICI 174864 administered alone significantly increased mount rate and reduced the post-ejaculatory refractory period in copulating males. These experiments suggest that there is both neurochemical and neuroanatomical specificity relating beta-endorphin to sexual behaviour in the male rat.

Ultrastructural characterization of the central component of the medial preoptic nucleus

The fine structure of the sexually dimorphic central part of the medial preoptic nucleus was studied in male and female rats. Neurons of this subnucleus are characterized by having convoluted nuclear membranes and fibrillar nuclear inclusions. Within the perinuclear domain there is a well developed neurosecretory apparatus, i.e., Golgi complexes, assorted types of secretory granules, and lysosome-like bodies, whereas the marginal cytosol contains stacked cisterns of rough endoplasmic reticulum, nucleolus-like inclusions, and few mitochondria. The neuropil is made up of thick dendrites, fascicles of thin unmyelinated axons, and few small myelinated axons. Additionally four types of synaptic boutons were found according to the morphology of their vesicular contents. No apparent qualitative sex differences were noted. These cytologic features which suggest secretory activity, coupled with reports that have shown the presence of several neurohormones and peptides within the central part of the medial preoptic nucleus lend further support to the neuroendocrine nature of these neurons.

Development of the preoptic area: time and site of origin, migratory routes, and settling patterns of its neurons

Neurogenesis and morphogenesis in the rat preoptic area were examined with [3H]thymidine autoradiography. For neurogenesis, the experimental animals were the offspring of pregnant females given an injection of [3H]thymidine on two consecutive gestational days. Nine groups were exposed to [3H]thymidine on embryonic days E13-E14, E14-E15, E21-E22, respectively. On postnatal day P5, the percentage of labeled cells and the proportion of cells originating during 24-hr periods were quantified at four anteroposterior levels in the preoptic area. Throughout most of the preoptic area there is a lateral to medial neurogenetic gradient. Neurons originate between E12-E15 in the lateral preoptic area, between E13-E16 in the medial preoptic area, between E14-E17 in the medial preoptic nucleus, and between E15-E18 in the periventricular nucleus. These structures also have intrinsic dorsal to ventral neurogenetic gradients. There are two atypical structures: (1) the sexually dimorphic nucleus originates exceptionally late (E15-E19) and is located more lateral to the ventricle than older neurons; (2) in the median preoptic nucleus, where older neurons (E13-E14) are located closer to the third ventricle than younger neurons (E14-E17). For an autoradiographic study of morphogenesis, pregnant females were given a single injection of [3H]thymidine during gestation, and their embryos were removed either two hrs later (short survival) or in successive 24-hr periods (sequential survival). Short-survival autoradiography was used to locate the putative neuroepithelial sources of preoptic nuclei, and sequential survival autoradiography was used to trace the migratory waves of young neurons and their final settling locations. The preoptic neuroepithelium is located anterior to and in the front wall of the optic recess. The neuroepithelium lining the third ventricle is postulated to contain a mosaic of spatiotemporally defined neuroepithelial zones, each containing precursor cells for a specific structure. The neuroepithelial zones and the migratory waves originating from them are illustrated. Throughout most of the preoptic area, neurons migrate predominantly laterally. The older neurons in the lateral preoptic area migrate earlier and settle adjacent to the telencephalon. Younger neurons migrate in successively later waves and accumulate medially. The sexually dimorphic neurons are exceptional since they migrate past older cells to settle in the core of the medial preoptic nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Preoptic area opioids and opiate receptors increase during pregnancy and decrease during lactation

Opiate receptor and endogenous opioid content were determined in pregnant, lactating, ovariectomized, and ovariectomized and subsequently estradiol- and progesterone-treated adult female rats. Levels of estradiol and progesterone produced by Silastic capsules implanted in animals of the ovariectomized, hormone-treated group were similar to natural levels of those hormones induced during pregnancy. Quantitative receptor autoradiography and radioimmunoassay were used to determine [3H]naloxone binding density and immunoreactive beta-endorphin content, respectively, in the preoptic area of the hypothalamus. Both opiate receptor binding density and beta-endorphin content in the preoptic area varied in the same direction in all experimental groups. The highest levels of both were observed during pregnancy and the lowest levels during lactation. Ovariectomy without subsequent hormone treatment produced intermediate levels of both opiate receptor and beta-endorphin. Ovariectomy with experimentally-induced estradiol and progesterone levels similar to those of pregnancy produced opiate receptor density and beta-endorphin content similar to those observed in pregnant animals. These data suggest that gonadal steroids are capable of altering function of the endogenous opiate system in the preoptic area. Moreover, preoptic area levels of opioids and opiate receptors are normally elevated during pregnancy and reduced during lactation. Since opiates are known to disrupt ongoing maternal behavior, a reduction of preoptic opiate function during lactation may be required to promote normal maternal behavior. The specific preoptic region involved in opiate regulation of maternal behavior may be illustrated by the zone of opiate receptor alteration observed herein.

Efferent projections of the suprachiasmatic nucleus: II. Studies using retrograde transport of fluorescent dyes and simultaneous peptide immunohistochemistry in the rat

In a previous study (Watts et al., '87) we reexamined the projections of the suprachiasmatic nucleus (SCh) with the PHA-L method and found that they could be divided conveniently into six groups of fibers. By far the densest projection ends just dorsal to the SCh in a comma-shaped region designated the "subparaventricular zone," although some fibers continue on through the paraventricular nucleus of the hypothalamus to end in the overlying midline thalamus, and others continue on to end in the dorsomedial nucleus, the region around the ventromedial nucleus, and the posterior hypothalamic area. Other relatively sparse projections from the SCh were also described to the preoptic region, lateral septal nucleus, parataenial and paraventricular nuclei of the thalamus, and ventral lateral geniculate nucleus. In addition, the same method was used to show that the subparaventricular zone projects in turn massively to these same regions, as well as back to the SCh itself and to the periaqueductal gray. The present series of experiments was designed to confirm these observations with retrograde tracer injections and to investigate the cellular and possible neurotransmitter organization of the major projections from the SCh and subparaventricular zone with a combined retrograde tracer-immunohistochemical method. For this, the distribution of neuronal cell bodies within the SCh that stain with antisera to vasopressin, vasoactive intestinal polypeptide (VIP), corticotropin-releasing factor, bombesin, substance P, neurotensin, somatostatin, thyrotropin-releasing hormone, and angiotensin II was described in detail first. Then the distribution of retrogradely labeled neurons that were also stained for one or another of these peptides was described after injections of true blue, or in some cases SITS, into the regions of the subparaventricular zone, the paraventricular and parataenial nuclei of the thalamus, the ventromedial nucleus, the dorsomedial nucleus, and the periaqueductal gray. The results confirm previous immunohistochemical and anterograde tracing studies and in addition indicate that cells in dorsal as well as ventral parts of the SCh project to each of the terminal fields examined, as do many cells in surrounding areas, including the subparaventricular zone. Our results also suggest that, at the very least, vasopressin-, VIP-, and neurotensin-stained cells in the SCh project to the subparaventricular zone, midline thalamus, and dorsomedial nucleus, and that the vasopressin and VIP-stained fiber systems are partially segregated at the level of the subparaventricular zone.(ABSTRACT TRUNCATED AT 400 WORDS)

Castration reversibly alters levels of cholecystokinin immunoreactivity within cells of three interconnected sexually dimorphic forebrain nuclei in the rat

Three sexually dimorphic cell groups in the forebrain of the rat--the central part of the medial preoptic nucleus, the encapsulated part of the bed nucleus of the stria terminalis, and the posterodorsal part of the medial nucleus of the amygdala--are larger in males, contain a high density of gonadal-steroid-concentrating cells, and are thought to play important roles in the control of reproductive behavior and physiology. Since each of these regions contains a large number of cholecystokinin-immunoreactive cells, we used an indirect immunohistochemical method to examine the possibility that levels of this peptide are modulated by circulating gonadal steroids in adult male rats. Rats were castrated at 60 days of age, and one group each was pretreated with colchicine and then killed 3, 7, and 14 days after gonadectomy. Castration clearly decreased CCK immunoreactivity within cells of each region, with the most dramatic effects occurring 7 and 14 days after gonadectomy, and these effects were reversed by treatment with testosterone over a 14-day period. The results suggest that CCK levels within individual cells in each of the interconnected sexually dimorphic nuclei examined here are regulated by circulating gonadal steroids and may be related to the hormonal modulation of reproductive functions thought to be mediated by these cell groups.

Anatomical and electrophysiological evidence for a projection from the medial preoptic area to the 'mesencephalic and subthalamic locomotor regions' in the rat

There is considerable physiological evidence indicating that the medial preoptic area plays an important role in neural circuits mediating ingestive, thermoregulatory, and reproductive behaviors, all of which involve foraging. The current series of anatomical and electrophysiological experiments was therefore designed to characterize a direct projection from the medial preoptic area to a region in the zona incerta just dorsal to the subthalamic nucleus, which appears to lie within the 'subthalamic locomotor region', and to the pedunculopontine nucleus, which lies within the 'mesencephalic locomotor region'. First, implants of the fluorescent tracer True blue were placed in the pedunculopontine nucleus, and retrogradely labeled neurons were consistently found in dorsal regions of the medial preoptic nucleus, anteroventral preoptic nucleus, rostral tip of the medial preoptic area, lateral parts of the medial preoptic area, and median preoptic nucleus. Second, combined retrograde-immunostaining experiments indicated that a small number of galanin-stained neurons in the rostral tip of the medial preoptic area project to the pedunculopontine nucleus, whereas in nearby regions some galanin- or neurotensin-stained neurons in the lateral preoptic area, and some neurotensin-stained neurons in the substriatal gray appear to project to the pedunculopontine nucleus, as do some neurotensin- or corticotropin releasing factor (CRF)-stained cells in the bed nucleus of the stria terminalis. Third, injections of the anterograde tracer Phaseolus vulgaris leukoagglutinin (PHA-L) into various parts of the medial preoptic area all labeled axons with terminal boutons in the caudal zona incerta and pedunculopontine nucleus. Fourth, single-pulse stimuli were delivered to the zona incerta and pedunculopontine nucleus and the location of antidromically activated neurons in the medial preoptic area was mapped using extracellular recordings. Somewhat less than one-third of the cells recorded from in the medial preoptic area were antidromically activated from either site and some 14% were influenced from both sites. The application of a reciprocal collision test to a small number of neurons suggested that at least some neurons in the medial preoptic area may send collaterals to both sites. And fifth, injections of procaine into the zona incerta were shown to block the antidromic activation of medial preoptic neurons by single-pulse stimulation of the pedunculopontine nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

MPOA and BNST lesions in male Syrian hamsters: differential effects on copulatory and chemoinvestigatory behaviors

Electrolytic lesions were made in the medial preoptic area (MPOA) and bed nucleus of the stria terminalis (BNST) to evaluate their participation in the neural regulation of copulatory and chemoinvestigatory behaviors in male hamsters. Damage to either the MPOA or the BNST caused severe deficits in copulatory performance in a subset of the animals in each group. In the MPOA group all males displaying severe deficits had lesions which included a small central region of the caudal MPOA. In the BNST group, animals with severe copulatory deficits all had large lesions which covered most of both the medial and lateral parts of the nucleus. In contrast, MPOA and BNST lesions differentially affected chemoinvestigatory behaviors. MPOA lesions did not affect any of the males' anogenital investigation rates or attraction to female odors, even though some of these hamsters had stopped mating completely. Males with BNST lesions, on the other hand, all displayed significant reductions in their chemoinvestigatory responding even though the majority of them continued to mate normally. We suggest that the MPOA and BNST may in part regulate male sexual behavior by differentially responding to 'attractant' and 'mounting' substances within female hamster vaginal secretion.

The distribution of neurotransmitter-specific cells and fibers in the anteroventral periventricular nucleus: implications for the control of gonadotropin secretion in the rat

The anteroventral periventricular nucleus (AVPv), which lies in the periventricular zone of the preoptic region, is critical for normal phasic gonadotropin secretion since lesions of this nucleus abolish the progesterone-induced surge of luteinizing hormone secretion from the anterior pituitary, block ovulation, and induce persistent vaginal estrus in female rats. However, very little is known about the neurotransmitter-specific pathways associated with this nucleus. In the present study we evaluated the distribution of biochemically specific cells and fibers within the AVPv and adjacent regions by using an indirect immunohistochemical method with antisera to serotonin (5-HT), dopamine beta-hydroxylase (DBH), tyrosine hydroxylase (TH), neuropeptide Y (NPY), cholecystokinin-8 (CCK), vasoactive intestinal polypeptide (VIP), substance P (SP), neurotensin (NT), corticotropin-releasing factor (CRF), luteotropin-releasing hormone (LRH), somatostatin (SS), thyrotropin-releasing hormone (TRH), oxytocin (OXY), vasopressin (VAS), adrenocorticotropic hormone (ACTH1-24), alpha-melanocyte-stimulating hormone (alpha-MSH), leucine-enkephalin (L-ENK), and calcitonin gene-related peptide (CGRP). Our findings indicate that both cells and fibers containing these putative neurotransmitters are differentially distributed in and around the AVPv in accordance with the cytoarchitectonic organization of this part of the preoptic region. The AVPv itself appears to receive strong inputs from SP-, VAS-, CCK-, and SS-containing pathways, whereas the highest densities of L-ENK-, NT-, 5-HT-, NPY-, and DBH-immunoreactive fibers were found in the cell-sparse zone just lateral to the AVPv. The suprachiasmatic preoptic nucleus (PSCh), a small group of cells located ventral to the AVPv just dorsal to the optic chiasm, contained high densities of alpha-MSH- and ACTH-immunoreactive fibers, as well as substantial numbers of fibers containing catecholamines or NPY. In contrast, a dense plexus of VAS-stained fibers was distributed fairly evenly throughout the AVPv and PSCh. Numerous L-ENK-immunoreactive cell bodies, and moderate numbers of CCK-, NT-, and CRF-stained cell bodies were found in the AVPv. The PSCh contained many TH-stained cells (presumably dopaminergic), in addition to a moderate number of CCK-containing cell bodies, while a high density of NT- and CRF-stained cells were found in the cell-sparse zone lateral to the AVPv, in addition to several CCK-, SP-, VIP-, and TH-containing cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Cholecystokinin synapses in the sexually dimorphic central part of the medial preoptic nucleus

The distribution of immunoreactive cholecystokinin synapses in the medial preoptic nucleus was studied. At the light microscopic level, the relative density of cholecystokinin in the nucleus corresponds to its three subdivisions. The sexually dimorphic central part of the nucleus was filled with a very dense plexus of cholecystokinin fibers/terminals. At the ultrastructural level, cholecystokinin-positive boutons contained labeled, dense core vesicles and clear vesicles as well as a population of unlabeled vesicles. The cholecystokinin boutons formed axodendritic, axosomatic, and axoaxonic interactions. Very few of the boutons were found in apposition with unlabeled elements but without any evidence of contact, i.e., synaptoid-type. Interestingly, cholecystokinin-positive, dendrite-like structures occasionally extended thin processes that were observed to end in a bouton containing both light and dense core vesicles. These varicosities were observed to have synaptoid endings. The dense innervation and synaptoid interaction of cholecystokinin elements in the central part of the medial preoptic nucleus may help to clarify the peptide's function in the medial preoptic area.