Neurons of origin and fiber trajectory of amygdalofugal projections to the medial preoptic area in Syrian hamsters

The amygdaloid neurons of origin and the trajectory of amygdaloid fibers to the medial preoptic area of the adult male Syrian hamster were identified by using horseradish peroxidase (HRP) histochemistry. After iontophoresis of HRP into the medial preoptic area, retrogradely labeled amygdaloid neurons were located in the dorsal and caudal parts of the medial amygdaloid nucleus and throughout the amygdalohippocampal area. No amygdaloid neurons were labeled after HRP applications confined to the most rostral portion of the medial preoptic area (anterior to the body of the anterior commissure). Following more caudal medial preoptic area injections (body of the anterior commissure to the suprachiasmatic nucleus) the distribution of retrogradely labeled cells in the medial amygdaloid nucleus and the amygdalohippocampal area revealed no topographic organization of the amygdalopreoptic connections. When amygdaloid neurons were labeled, the amygdalohippocampal area contained two to five times as many HRP-filled cells as the medial amygdaloid nucleus. Retrogradely transported HRP could be followed from the medial preoptic area to the amygdala through fibers in the dorsomedial quadrant of the stria terminalis. In addition, electrolytic lesions of the stria terminalis prior to iontophoresis of HRP into the medial preoptic area prevented retrograde transport to neurons in both the dorsocaudal medial amygdaloid nucleus and the amygdalohippocampal area. These results confirm earlier observations describing the location of autoradiographically labeled efferents from the medial amygdaloid nucleus to the medial preoptic area and provide new information about the restricted region within the medial amygdaloid nucleus from which these projections arise. They also suggest that, unlike the projections from the medial amygdaloid nucleus to the bed nucleus of the stria terminalis, the efferents to the medial preoptic area travel entirely in the stria terminalis.     

Testosterone regulates substance P within neurons of the medial nucleus of the amygdala, the bed nucleus of the stria terminalis and the medial preoptic area of the male golden hamster

The medial nucleus of the amygdala, bed nucleus of the stria terminalis, and medial preoptic area appear to mediate steroidal regulation of mating behavior in male rodents. The mechanism of action has not been determined. One way testosterone could enhance neuronal function is by increasing neurotransmitter levels, thus altering neuronal transmission. To assess this hypothesis, we examined the effect of castration and testosterone treatment on substance P levels in the neurons of these three brain regions. Brains from male Syrian hamsters that were (1) gonadally intact, (2) castrated for 13 weeks, or (3) castrated for 9 weeks and treated with testosterone for 4 weeks, were processed for substance P, and the numbers of substance P immunoreactive neurons in the medial nucleus of the amygdala, bed nucleus of the stria terminalis, and medial preoptic area were determined. Castration reduced the number of substance P neurons in the bed nucleus of the stria terminalis and medial preoptic area relative to those in intact hamsters: the number of substance P neurons in these regions was restored by testosterone treatment. Castration did not reduce the number of substance P neurons in the medial nucleus of the amygdala; however, testosterone treatment increased the numbers of these neurons when compared to intacts. Thus, testosterone regulates substance P levels in areas that regulate mating behavior. As substance P enhances male copulatory behavior our results suggest that testosterone may regulate copulatory behavior by enhancing substance P levels in medial nucleus of the amygdala, bed nucleus of the stria terminalis and medial preoptic area.     

First and second order maternal behavior related afferents of the lateral habenula

We demonstrated previously that the lateral habenula (Lhb) mediates maternal behavior. Our present goal was to identify the first and second order afferent connections of the Lhb, particularly those relevant for maternal behavior. Using pseudorabies virus (PRV) as a retrograde transneuronal tracer and the retrograde tracer Fluoro-Gold, we identified first order Lhb afferent projections from the lateral preoptic area, bed nucleus of the stria terminalis, nucleus accumbens and ventral tegmental area, each important for the display of maternal behavior. Maternally relevant second order neurons originated from the medial preoptic area and amygdala. Additional regions with first and second order neurons afferent to the Lhb were also identified.     

Efferents from medial basal forebrain and hypothalamus in the rat. I. An autoradiographic study of the medial preoptic area.

Efferent projections from the medial and periventricular preoptic area, bed nucleus of the stria terminalis and nuclei of the diagonal band were traced using tritiated amino acid autoradiography in albino rats. Medial and periventricular preoptic area efferents were not restricted to short-axon projections. Ascending projections from the medial preoptic area (mPOA) were traced through the diagonal band into the septum. Descending mPOA axons coursed in the medial parts of the medial forebrain bundle. Projections to most hypothalamic nuclei, including the arcuate nucleus and median eminence, were observed. In the midbrain, mPOA efferents were distributed in the central grey, raphe nuclei, ventral tegmental area and reticular formation. Projections from the mPOA were also observed to the amygdala through the stria terminalis, to the lateral habenula through the stria medullaris, and to the periventricular thalamus. Axons of the most medial and periventricular preoptic area (pvPOA) neurons had a distribution similar to more lateral mPOA neurons but their longest-axoned projections were weaker. The pvPOA did not send axons through the stria medullaris but did project more heavily than the more lateral mPOA to the arcuate nucleus and median eminence. Projections from the bed nucleus of the stria terminalis (nST) were in most respects similar to those from the medial preoptic area, with the major addition of a projection to the accessory olfactory bulb. The nuclei of the diagonal band of Broca (nDBB) gave a different pattern of projections than mPOA or nST, projecting, for instance, to the medial septum and hippocampus. Descending nDBB efferents ran in the ventral portion of the medial forebrain bundle. Among hypothalamic cell groups, only the medial mammillary nuclei received nDBB projections. nDBB efferents also distributed in the medial and lateral habenular nuclei and the mediodorsal thalamic nucleus.     

Photoperiodic regulation of substance P immunoreactivity in the mating behavior pathway of the male golden hamster

Mating behavior in the male golden hamster is regulated by both gonadal steroids and photoperiod. Gonadal steroids may regulate mating behavior by actions on the medial nucleus of the amygdala, bed nucleus of the stria terminalis, and medial preoptic area. Neurons in these areas actively accumulate gonadal steroids and lesions of these nuclei disrupt mating behavior in male hamsters. Photoperiodic regulation of mating behavior is regulated, at least in part, by decreased responsiveness to gonadal steroids. Therefore, we sought to determine if the changes induced by changes in gonadal steroids would mimic those induced by changes in photoperiod. The number of substance P-containing neurons in these areas decrease following castration and are restored with testosterone treatment suggesting that this peptide may mediate steroidal regulation of male mating behavior. To determine the effect of photoperiod on substance P, peptide containing neurons were counted in (1) enucleates (n = 6), (2) enucleated castrates treated with testosterone (n = 6), (3) castrates treated with testosterone (n = 4), and (4) intact controls (n = 6). Bilateral enucleation caused a decrease in the number of substance P neurons in the medial nucleus, bed nucleus of the stria terminalis, and medial preoptic area (P < 0.05). Testosterone treatment prevented this decrease (P < 0.05). Thus, a decrease in daylength causes a decrease in substance P in the medial nucleus of the amygdala, the medial bed nucleus of the stria terminalis and the medial preoptic area that is mediated by changes in testosterone levels.     

Substance P and neurokinin A are colocalized in the central chemosensory pathway of the male golden hamster

The medial nucleus of the amygdala, bed nucleus of the stria terminalis and medial preoptic area play critical roles in the regulation of mating behavior in the male hamster. Destruction of these nuclei or the pathways that connect them severely disrupt copulation. We have begun identifying the neuropeptides contained in these neurons as a prelude to determining the role of peptide neurotransmitters in the regulation of male copulatory behavior. We have found that substance P is localized within these neurons and is regulated by gonadal steroids. In this study we report 1) that a closely related peptide, NKA (substance K), is also present in the medial nucleus of the amygdala, the bed nucleus of the stria terminalis and the medial preoptic area; 2) that all those neurons which contain SP also contain NKA and 3) testosterone also regulates the production of NKA. Thus, NKA may also play a role in the regulation of male copulatory behavior.     

Afferent connections to the amygdaloid complex of the rat and cat: II. Afferents from the hypothalamus and the basal telencephalon

The projections from the basal telencephalon and hypothalamus to each nucleus of the amygdaloid complex of the rat, and to the central amygdala of the cat, were investigated by the use of retrograde transport of horseradish peroxidase (HRP). The enzyme was injected stereotaxically by microiontophoresis, using three different approaches. The ventral pallidum (Heimer, '78) and ventral part of the globus pallidus were found to project to the lateral and basolateral nuclei of the amygdala. The substantia innominata projects diffusely to the entire amygdaloid complex, except to the lateral nucleus and the caudal part of the medial nucleus. The anterior amygdaloid area shows a similar projection field, the only difference being that this structure does not project to any parts of the medial nucleus. The dorsal subdivision of the nucleus of the lateral olfactory tract sends fibers to the ipsilateral as well as the contralateral basolateral nucleus, and possibly to the ipsilateral basomedial and cortical amygdala. The ventral subdivision of the nucleus of the lateral olfactory tract was massively labeled after an injection in the ipsilateral central nucleus, but this injection affected the commissural component of the stria terminalis. The nucleus of the horizontal limb of the diagonal band of Broca connects with the medial, central, and anterior cortical nuclei, whereas the bed nucleus of stria terminalis and medial preoptic area are related to the medial nucleus predominantly. The lateral preoptic area is only weakly labeled after intra-amygdaloid HRP injections. The hypothalamo-amygdaloid projections terminate preponderantly in the medial part of the amygdaloid complex. Thus, axons from neurons in the area dorsal and medial to the paraventricular nucleus of the hypothalamus distribute to the medial nucleus and intra-amygdaloid part of the bed nucleus of stria terminalis. Most of the amygdalopetal fibers from the ventromedial, ventral premammillary, and arcuate nuclei of the hypothalamus end in the medial nucleus, but some extend into the central nucleus. A few fibers from the ventromedial nucleus of the hypothalamus reach the basolateral nucleus. The lateral hypothalamic area projects heavily to the central nucleus, and more sparsely to the medial and basolateral nuclei. The dorsal hypothalamic area and supramammillary nucleus show restricted projections to the central and basolateral nuclei, respectively. There are only a modest number of crossed hypothalamo-amygdaloid fibers. Most of these originate in the ventromedial nucleus of the hypothalamus and terminate in the contralateral medial nucleus. The projections from the basal telencephalon and hypothalamus to the central nucleus of the amygdala of the cat are similar to the corresponding projections in the rat.     

Projections from Ventrolateral Hypothalamic Neurons Containing Progestin Receptor- and Substance P-Immunoreactivity to Specific Forebrain and Midbrain Areas in Female Guinea Pigs

Many neurons within the ventrolateral hypothalamus in guinea pigs contain estrogen-induced progestin receptors as well as substance P. Retrograde tracing combined with immunocytochemistry was used to determine the specific projections of this subset of steroid- sensitive cells. Unilateral Fluoro-Gold injections into the dorsal midbrain, including the central gray, labeled a large proportion of the ventrolateral hypothalamic neurons immunoreactive for both progestin receptors and substance P (approximately 30%); substantially fewer of these neurons were labeled by unilateral Fluoro-Gold injections into the preoptic area (approximately 6%), medial amygdala (approximately 10%), or the bed nucleus of the stria terminalis (approximately 11 %). The projections of progestin receptor-immunoreactive neurons in the ventrolateral hypothalamus were similar to those of progestin receptor/substance P double-labeled neurons, while a slightly lower percentage of the ventrolateral hypothalamic, substance P-immunoreactive neurons tended to project to each of these areas. These pathways may prove to be components of the neural circuitry underlying a variety of functions influenced by gonadal steroid hormones and substance P, such as female sexual behavior, salt intake, nociception and aggression.     

Distribution of cholecystokinin-like-immunoreactive neurons in the guinea pig forebrain

The distribution of cholecystokinin (CCK)-immunoreactive nerve fibers and cell bodies was studied in the forebrain of control and colchicine-treated guinea pigs by using an antiserum directed against the carboxyterminus of CCK octapeptide (CCK-8) in the indirect immunoperoxidase technique. Virtually all forebrain areas examined contained immunoreactive nerve fibers. A dense innervation was visualized in; neocortical layers II-III, piriform cortex, the medial amygdala, the medial preoptic area, a circumventricular organ-like structure located at the top of the third ventricle in the preoptic area, the subfornical organ, the posterior bed nucleus of the stria terminalis, the posterior globus pallidus (containing labeled woolly fiber-like profiles), the ventromedial hypothalamus, the median eminence, and the premammillary nucleus. A moderately dense innervation was visualized elsewhere excepted in the septum and thalamus where labeled axons were comparatively few. Immunoreactive perikarya were abundant in: neocortex (especially layers II-III), piriform cortex, amygdala, the median preoptic nucleus, the bed nucleus of the stria terminalis, the hypothalamic paraventricular (parvicellular part), arcuate, and dorsomedial (pars compacta) nuclei, the dorsal and perifornical hypothalamic areas, and throughout the thalamus. Areas also containing a moderate number of labeled cell bodies were the medial preoptic area, the globus pallidus, the caudate-putamen, and the periventromedial area in the hypothalamus. Immunostained perikarya were absent or only occasionally observed in the septum, the suprachiasmatic nucleus, the magnocellular hypothalamoneurohypophyseal nuclei, and the ventral mesencephalon. In the adenohypophysis, corticomelanotrophs were labeled in both males and females, and thyrotrophs were labeled in females only. This distribution pattern of CCK-8 immunoreactivity is compared to those previously recorded in other mammals. This shows that very few features are peculiar to the the guinea pig. It is discussed whether some interspecific differences in immunostaining are real rather than methodological.     

Afferent and efferent connections of the olfactory bulbs in the lizard Podarcis hispanica.

The connections of the olfactory bulbs of Podarcis hispanica were studied by tract-tracing of injected horseradish peroxidase. Restricted injections into the main olfactory bulb (MOB) resulted in bilateral terminallike labeling in the medial part of the anterior olfactory nucleus (AON) and in the rostral septum, lateral cortex, nucleus of the lateral olfactory tract, and ventrolateral amygdaloid nucleus. Bilateral retrograde labeling was found in the rostral lateral cortex and in the medial and dorsolateral AON. Ipsilaterally the dorsal cortex, nucleus of the diagonal band, lateral preoptic area, and dorsolateral amygdala showed labeled cell bodies. Retrogradely labeled cells were also found in the midbrain raphe nucleus. Results from injections into the rostral lateral cortex and lateral olfactory tract indicate that the mitral cells are the origin of the centripetal projections of the MOB. Injections in the accessory olfactory bulb (AOB) produced ipsilateral terminallike labeling of the ventral AON, bed nucleus of the accessory olfactory tract, central and ventromedial amygdaloid nuclei, medial part of the bed nucleus of the stria terminalis, and nucleus sphericus. Retrograde labeling of neurons was observed ipsilaterally in the bed nucleus of the accessory olfactory tract and stria terminalis, in the central amygdaloid nucleus, dorsal cortex, and nucleus of the diagonal band. Bilateral labeling of somata was found in the ventral AON, the nucleus sphericus (hilus), and in the mesencephalic raphe nucleus and locus coeruleus. Injections into the dorsal amygdala showed that the mitral neurons are the cells of origin of the AOB centripetal projections. Reciprocal connections are present between AOB and MOB. To our knowledge, this is the first study to address the afferent connections of the olfactory bulbs in a reptile. On the basis of the available data, a discussion is provided of the similarities and differences between the reptilian and mammalian olfactory systems, as well as of the possible functional role of the main olfactory connections in reptiles.     

Paced mating behavior in the female rat following lesions of three regions responsive to vaginocervical stimulation

The present study examines the effects of ibotenic acid lesions of the medial amygdala, the bed nucleus of the stria terminalis and the medial preoptic area on the display of paced mating behavior in female rats. Lesions of either the medial amygdala or the bed nucleus of the stria terminalis have no effect on the display of paced mating behaviors in ovariectomized, hormone-primed rats. In contrast, lesions of the medial preoptic area significantly lengthen contact-return latencies following intromissions and ejaculations and increase withdrawal from the male following intromissions. The present study demonstrates that the medial amygdala and the bed nucleus of the stria terminalis are not involved in the behavioral responses accompanying paced mating behavior, whereas the medial preoptic area is a critical component of the neural circuit mediating paced mating behavior as well as other appetitive aspects of mating.     

Colocalization of androgen receptors and mating-induced FOS immunoreactivity in neurons that project to the central tegmental field in male rats.

Bilateral lesions of the central tegmental field (CTF) in male rats virtually eliminate mating behavior. This study examined if mating-induced Fos expression (a measure of neuronal activation) and androgen receptors (AR) are colocalized in brain and spinal cord neurons which project to the CTF. Animals received unilateral injections of the retrograde tracer Fluorogold (FG) in the lateral part of the CTF (CTFl), and 10 days later were killed after ejaculating with females. Brains and spinal cords were examined for FG transport, AR-immunoreactivity (AR-ir), and Fos-immunoreactivity (Fos-ir). AR-ir and Fos-ir were visualized with fluorescence microscopy using cyanine-conjugated and fluorescein-conjugated secondary antibodies. The CTFl received projections from AR-containing neurons in forebrain structures (bed nucleus of stria terminalis, medial preoptic area, lateral and ventromedial hypothalamus), in the central amygdala and various mid- and hindbrain structures (dorsolateral tegmentum, superior and inferior colliculi, pedunculopontine nucleus), and in the lumbosacral spinal cord (lamina X). Some of the AR-containing neurons in bed nucleus of stria terminalis and in the dorsal part of the medial preoptic area with projections to the CTFl were activated by mating. Most AR-containing neurons in spinal lamina X with projections to the CTFl were also activated by mating. Information from spinal cord and pontine nuclei and from outputs descending from the forebrain may be relayed in the CTFl. Thus, as part of a network of hormone-sensitive neurons linking brain and spinal cord mechanisms for mating, the CTFl could participate in the integration of visceral and somatic information relevant for sexual behavior.     

Supracapsular bed nucleus of the stria terminalis contains central and medial extended amygdala elements: evidence from anterograde and retrograde tracing experiments in the rat

Neurons that accompany the stria terminalis as it loops over the internal capsule have been termed collectively the supracapsular bed nucleus of the stria terminalis (BSTS). They form two cell columns, a lateral column and a considerably smaller medial column. The lateral column merges rostrally with the lateral bed nucleus of the stria terminalis and caudally with the central amygdaloid nucleus (central extended amygdala components). The medial column is continuous with the medial bed nucleus of the stria terminalis and the medial amygdaloid nucleus (medial extended amygdala districts). The connections of the BSTS were investigated in the rat by placing injections of Phaseolus vulgaris-leucoagglutinin (PHA-L) or retrograde tracers in different parts of the extended amygdala or in structures related to the extended amygdala. BSTS inputs and outputs were identified, respectively, by the presence of varicose fibers and retrogradely labeled neurons within the stria terminalis. The results suggest that the medial-to-lateral compartmentalization of BSTS neurons reflects their close alliance with the medial and central divisions of the extended amygdala. The medial BSTS contains primarily elements that correspond to the posterodorsal part of the medial amygdaloid nucleus and the medial column of the posterior division of the medial bed nucleus of the stria terminalis, and the lateral BSTS contains elements that correspond to the medial and lateral parts of the central amygdaloid nucleus and lateral bed nucleus of the stria terminalis. These results add strong support to the concept of the extended amygdala as a ring-like macrostructure around the internal capsule, and they are of theoretical interest for the understanding of the organization of the basal forebrain.     

Tyrosine hydroxylase neurons in the male hamster chemosensory pathway contain androgen receptors and are influenced by gonadal hormones

Chemosensory and hormonal signals, both of which are essential for mating in the male Syrian hamster, are relayed through a distinct forebrain circuit. Immunocytochemistry for tyrosine hydroxylase, a catecholamine biosynthetic enzyme, previously revealed immunoreactive neurons in the anterior and posterior medial amygdaloid nucleus, one of the nuclei within this pathway. In addition, dopamine-immunoreactive neurons were located in the posterior, but not hte anterior, medial amygdala. In the present study, tyrosine hydroxylase-immunostained neurons were also observed in other areas of the chemosensory pathway, including the posteromedial bed nucleus of the stria terminalis and the posterior, lateral part of the medial preoptic area, while dopamine immunostaining was only seen in the posteromedial bed nucleus of the stria terminalis. The colocalization of tyrosine hydroxylase and androgen receptors was examined in these four tyrosine hydroxylase cell groups by a double immunoperoxidase technique. The percentage of tyrosine hydroxylase-immunolabeled neurons that were also androgen receptor-immunoreactive was highest in the posterior medial amygdaloid nucleus (74%) and the bed nucleus of the stria terminalis (79%). Fewer tyrosine hydroxylase-immunostained neurons in the anterior medial amygdala (33%) and the medial preoptic area (4%) contained androgen receptors. Surprisingly, castration resulted in a significant decrease in the number of tyrosine hydroxylase-immunoreactive neurons only in the anterior medial amygdaloid nucleus, and this effect was transient. Six weeks after castratio, the anterior medial amygdala contained 61% fewer tyrosine hydroxylase-immunolabeled neurons, but 12 weeks after gonadectomy, immunostaining returned to intact values. The number of immunostained neurons in testosterone-replaced, castrated hamsters was not significantly different from that of intact or castrated animals at any time. The results of this study indicate that a substantial number of tyrosine hydroxylase-immunostained neurons in the chemosensory pathway are influenced by androgens; the majority of these neurons in the posterior medial amygdala and the posteromedial bed nucleus of the stria terminalis produce androgen receptors, and tyrosine hydroxylase immunoreactivity is altered by castration in the anterior medial amygdala. © 1993 Wiley-Liss, Inc.     

Forebrain afferents to the cat posterior hypothalamus: a double labeling study

Using a double immunostaining technique with cholera toxin (CT) as a retrograde tracer, we examined the cells of origin and the histochemical nature of afferents to the cat posterior hypothalamus. After injection in the tuberomamillary nucleus, a number of CT-labeled cells were observed in: medial preoptic area, nuclei of the septum and the stria terminalis, amygdaloid complex, anterior hypothalamic, ventromedial hypothalamic and premamillary nuclei. CT injections in the lateral hypothalamic area gave an additional heavy labeling of neurons in: lateral preoptic area, nuclei of the diagonal band of Broca, substantia innominata, and nucleus accumbens. The posterior hypothalamus receives: 1) cholinergic inputs from the septum, the lateral preoptic area and the nuclei of the diagonal band of Broca; 2) dopaminergic afferents from A11, A13, and A14 groups; 3) histaminergic afferents from the posterior hypothalamus; and 4) peptidergic afferents such as methionin-enkephalin, galanin and neurotensin, substance P and corticotropin-releasing factor from the medial preoptic area, the nucleus of the stria terminalis and/or the posterior hypothalamic structures.     

Alteration in [11C]vorozole binding to aromatase in neuronal cells of rat brain induced by anabolic androgenic steroids and flutamide

In a previous study, we demonstrated that androgenic-anabolic steroids increased aromatase expression in the bed nucleus of stria terminalis and preoptic area in rat brain, as evaluated using autoradiography with [11C]vorozole, a potential positron emission tomography tracer for aromatase. In this study, we explored whether the increase in aromatase binding is mediated via androgen receptors and whether this increase occurs in neurons or glial cells. Rats were given nandrolone decanoate (15 mg/kg body weight once every 3 days) and flutamide (20 mg/kg/day) alone or in combination for 20 days. Results indicated a significant increase of [11C]vorozole binding by nandrolone decanoate in the bed nucleus of the stria terminalis and preoptic area, as in our previous study. Flutamide treatment, on the other hand, decreased [11C]vorozole binding in the bed nucleus of the stria terminalis, preoptic area, and medial amygdala. Immunohistochemical examination demonstrated that upregulation of aromatase expression occurred in neurons. Our findings suggest that aromatase is regulated through an androgen receptor-mediated system. This aromatase-specific tracer and the positron emission tomography technique could be useful for exploring the role of aromatase in anabolic androgenic steroids abusers.     

Collateral input to the paraventricular and supraoptic nuclei in rat. I. Afferents from the subfornical organ and the anteroventral third ventricle region

Injections of two fluorescent retrograde tracers were used to investigate the existence of collateral branching of input to the hypothalamic magnocellular neuroendocrine neurons. Injection of one tracer (either Fluoro-Gold or rhodamine-labeled microspheres) into the supraoptic nucleus and the other tracer into the ipsilateral paraventricular nucleus produced labeled neurons within the subfornical organ and the anteroventral third ventricle area. Some labeled cells were found to contain both fluorescent tracers (double-labeled cells), suggesting that they project to both the paraventricular and supraoptic nuclei via branching axons. Most double-labeled cells were found within the subfornical organ. Fewer of these cells were located within the nucleus medianus preopticus, and still fewer were distributed in the organum vasculosum lamina terminalis, the bed nucleus of the stria terminalis, and the medial and the lateral preoptic areas. These data present the first direct evidence that single cells may provide input to more than one magnocellular neuroendocrine nucleus. Hypothetically, hormonal release would require coordinated firing of many magnocellular cells. Thus, the branched input to these neurons may assist in the organization and the timely activation of this system in response to physiological stimuli.     

Forebrain projections from cholecystokininlike-immunoreactive neurons in the rat midbrain

The purpose of the present study was to analyze the distribution of cholecystokininlike-immunoreactive (CCK-I) neurons within the rat ventral mesencephalon which project to several forebrain areas. The peroxidase-antiperoxidase immunocytochemical technique was used to examine the anatomical localization of CCK-I within the ventral midbrain and in the following forebrain regions: caudate-putamen, nucleus accumbens, olfactory tubercle, bed nucleus of the stria terminalis, septum, amygdala, and prefrontal, anterior cingulate, and piriform cortices. CCK-I perikarya were distributed throughout the substantia nigra, ventral tegmental area, and several midline raphe nuclei to a greater extent than previously reported, particularly in the substantia nigra pars compacta. Terminallike immunoreactivity for CCK was observed in all of the above forebrain sites. In addition, infrequent CCK-I cell bodies were localized in the caudate-putamen, nucleus accumbens, olfactory tubercle, septum, and bed nucleus of the stria terminalis. To analyze forebrain projections of the ventral midbrain CCK-I neurons, indirect immunofluorescence was combined with fluorescence retrograde tracing. CCK-I neurons of the substantia nigra and/or ventral tegmental area were found to project, to varying extents, to all of the above CCK-I forebrain terminal fields. The nucleus accumbens, olfactory tubercle, and septal and prefrontal cortical projections arose primarily from CCK-I perikarya in the ventral tegmental area whereas the projections to the caudate-putamen and anterior cingulate cortex arose predominantly from immunoreactive neurons in the substantia nigra pars compacta. The amygdala received innervation mainly from CCK-I cell bodies located in the substantia nigra pars lateralis. CCK-I afferents to the bed nucleus of the stria terminalis and piriform cortex originated from perikarya distributed approximately equally across the ventral tegmental area and substantia nigra pars compacta. The general topography of CCK-I forebrain innervation observed in this study is similar to that previously reported for the ascending dopaminergic projections from ventral mesencephalic neurons. CCK-I neurons of the midline raphe nuclei were found to provide relatively minor afferents to the caudate-putamen, bed nucleus of the stria terminalis, septum, and prefrontal cortex and more substantial projections to the amygdala. The results of this study demonstrate that CCK-I neurons of the ventral midbrain supply a much broader innervation of forebrain regions than previously appreciated.(ABSTRACT TRUNCATED AT 400 WORDS)     

Efferent Projections from the Ovarian Steroid Receptor-Containing Area of the Ventrolateral Hypothalamus in Female Guinea Pigs

The ventrolateral hypothalamus (VLH) in female guinea pigs includes a subset of neurons which contain estrogen and progestin receptors, and which are implicated in the regulation of female sexual behavior by steroid hormones. However, little is known about where these neurons project, and consequently which other brain areas are involved in sexual behavior in female guinea pigs. The anterograde tracer Phaseolus vulgaris -Leucoagglutinin was used to label efferents from the ovarian steroid receptor-containing part of the VLH. To identify the correct placement of the tracer specifically within the group of neurons containing estrogen receptors, medial hypothalamic sections were also immunostained for estrogen receptors. Forebrain areas receiving dense projections from the ventrolateral hypothalamus included the bed nucleus of the stria terminalis, medial preoptic area, anterior hypothalamic area, anterior ventromedial hypothalamus, and caudal ventrolateral hypothalamus. The midbrain central gray was also heavily labeled. Moderate innervation was observed in the forebrain in the basolateral amygdala, medial preoptic nucleus, lateroanterior hypothalamic nucleus, dorsal hypothalamic areas, posterior hypothalamus, zona incerta, and in the midbrain interspersed among the central and lateral tegmental tracts. The major efferent pathways from the VLH appeared to travel rostrally through the mediobasal hypothalamus and preoptic area, and caudally via the medial thalamic nuclei and periventricular fiber system. These findings are similar to those of previous studies tracing the efferents from the ventromedial nucleus in rats and from the lateral hypothalamus in guinea pigs. Many of these areas that receive input from the steroid receptor rich area within the VLH are likely to be involved in the regulation of female sexual behavior.