Prodynorphin peptide distribution in the forebrain of the syrian hamster and rat: A comparative study with antisera against dynorphin A, dynorphin B, and the C-terminus of the prodynorphin precursor molecule

The neuroanatomical distribution of the prodynorphin precursor molecule in the forebrain of the male Syrian hamster ( Mesocricetus auratus ) has been studied with a novel antiserum directed against the C-terminus of the leumorphin [dynorphin B (1–29)] peptide product. C-peptide staining in sections from colchicine-treated hamsters is compared to staining in sections from untreated animals. In addition, the pattern of C-peptide immunostaining in hamster brain is compared to that in the rat brain. Finally, the C-peptide immunolabeling patterns in hamsters and rats are compared to those obtained with antisera to dynorphin A (1–17) and dynorphin B (1–13). Areas of heaviest prodynorphin immunoreactivity in the hamster include the hippocampal formation, lateral septum, bed nucleus of the stria terminalis, medial preoptic area, medial and central amygdaloid nuclei, ventral pallidum, substantia nigra, and numerous hypothalamic nuclei. Although this C-peptide staining pattern is similar to dynorphin staining reported previously in the rat, several species differences are apparent. Whereas moderate dentate gyrus granule cell staining and no CA4 cell staining have been reported in the rat hippocampal formation, intense immunostaining in the dentate gyrus and CA4 cell labeling are observed in the hamster. In addition, the medial preoptic area, bed nucleus of the stria terminalis, and medial nucleus of the amygdala stain lightly for prodynorphin-containing fibers and cells in the rat, compared to heavy cell and fiber staining in the hamster in all three of these regions. In the rat there is no differential staining between tissues processed with the C-peptide, dynorphin A, and dynorphin B antisera, but numerous areas of the hamster brain show striking differences. In most hamster brain areas containing prodynorphin peptides, the C-peptide antiserum immunolabels more cells and fibers than the dynorphin B antiserum, which in turn labels more cells and fibers than dynorphin A antiserum. However, exceptions to this hierarchy of staining intensity are found in the lateral hypothalamus, substantia nigra, arcuate nucleus, and habenula. The differences in staining patterns between rat and hamster are greatest when C-peptide antiserum is used; apparent species differences are present, though less pronounced, in dynorphin B– and dynorphin A–immunostained material.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50046/1/902880302_ftp.pd

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.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50056/1/903310402_ftp.pd

Mating-Induced c-fos Expression Patterns Complement and Supplement Observations after Lesions in the Male Syrian Hamster Brain a

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72544/1/j.1749-6632.1997.tb51924.x.pd

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.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29845/1/0000192.pd

Mating behavior induces selective expression of Fos protein within the chemosensory pathways of the male Syrian hamster brain

The effect of mating behavior on the expression of Fos protein was analyzed within the chemosensory pathways of the male Syrian hamster brain. Following a single mating test, the number of Fos-immunoreactive (Fos-ir) neurons increased within the amygdala, bed nucleus of the stria terminalis and medial preoptic area. The mating-induced pattern of Fos expression within these brain regions shows a strong correlation with the sites of lesions that eliminate or alter mating behavior. In addition, Fos expression was increased within the paraventricular nucleus of the hypothalamus. These results provide the first demonstration of a dynamic and selective pattern of neuronal activity within specific nuclei known to be essential for mating behavior in the male Syrian hamster.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29894/1/0000248.pd

Mating activates androgen receptor-containing neurons in chemosensory pathways of the male Syrian hamster brain

Fos-immunoreactivity is induced during mating in the male Syrian hamster in limbic areas that relay chemosensory information and contain receptors for gonadal steroid hormones. The induction of Fos is an index of neuronal activation. After mating, c-fos expression is greatest in subnuclei of the medial amygdaloid nucleus (Me), bed nucleus of the stria terminalis (BNST), and medial preoptic area (MPOA). The present study determined if individual neurons in these activated subnuclei contain androgen receptors. We aim to understand how essential chemosensory and hormonal signals are integrated to control copulation Adult male hamster (n = 6) were allowed to mate with a sexually receptive female for 30 min. They were perfused 1 h later with 4% paraformaldehyde and 40 [mu]m frozen sections were processed for immunocytochemistry using antisera against Fos (Cambridge Research Biochemicals) and the androgen receptor (G.S. Prins). The brains of three non-mated males were also processed for Fos immunocytochemistry. Mating significantly increased the number of Fos-immunoreactive neurons within subnuclei of Me, BNST, and MPOA relative to non-mated males (P < 0.05). These nuclei contained abundant androgen receptors. In the corticomedial amygdala, 20-40% of Fos-immunoreactive neurons in mated hamsters expressed androgen receptors. Although few androgen receptors are found in the anteromedial and postero-intermediate subdivisions of the BNST, these areas exhibited 26% and 47% co-localization, respectively. In posteromedial BNST, which contains large numbers of steroid receptor-containing neurons, androgen receptors were identified in 48% of Fos-immunoreactive neurons. In the MPOA, 54% of Fos-immunoreactive neurons expressed the androgen receptor throughout the rostrocaudal extent of the medial preoptic nucleus (MPN). The largest percentage of co-localized Fos neurons (70%) was found in the magnocellular subdivision of MPN. These results provide the first direct evidence that androgen receptor neurons are activated by mating behavior, suggesting that such neurons may be incorporated in the neural circuitry underlying copulation. Further, they show that mating selectively and differentially activates androgen receptor cells.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30740/1/0000389.pd

Mating-induced expression of c-fos in the male Syrian hamster brain: Role of experience, pheromones, and ejaculations

This study was designed to investigate the effects of pheromonal cues and specific behaviors within the male copulatory sequence on c-fos expression in the medial nucleus of the amygdala (Me), the bed nucleus of the stria terminalis (BNST), and the medial preoptic area (MPOA) of the Syrian hamster brain. Sexually experienced male hamsters were placed into clean testing arenas and were either: 1) left alone as handled controls; 2) exposed to female hamster vaginal secretion (FHVS) on cotton swabs; or mated to various end points of copulation with a sexually receptive female: 3) five intromissions, 4) one ejaculation, 5) five ejaculations, or 6) long intromissions. A seventh group of sexually naive control males 7) was left alone in the arena. The brains of these males were compared to those of the sexually experienced controls to determine whether exposure to cues associated with prior sexual experience could alter c-fos expression. In males exposed only to FHVS, Fos immunoreactivity (Fos-ir) increased within the posterodorsal Me, the anterodorsal part of the posteromedial BNST, and the magnocellular medial preoptic nucleus (MPNmag). Following one ejaculation, Fos-ir increased within the caudal posterodorsal Me, the dorsolateral MPOA, and the paraventricular nucleus of the hypothalamus. After multiple ejaculations, additional labeling was observed within the posteroventral part of the posteromedial BNST, the medial preoptic nucleus (MPN), the central tegmental field, and in cell clusters of the caudal posterodorsal Me and rostral posteromedial BNST. Fos-ir also increased within the posterodorsal Me, MPN, and MPNmag in sexually experienced control males exposed to the empty test chamber compared to sexually naive males exposed to an identical chamber. These results demonstrate that the mating-induced pattern of neuronal activation in sexually experienced males is dependent upon multiple factors, including prior sexual experience in the testing environment, investigation of FHVS, and the number of ejaculations achieved. © 1997 John Wiley & Sons, Inc. J Neurobiol 32: 481–501, 1997Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/34475/1/4_ftp.pd

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.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50043/1/902800106_ftp.pd

Role of the hypothalamic paraventricular nucleus in neuroendocrine responses to daylength in the golden hamster

Daylength regulates reproduction in golden hamsters through a mechanism which involves the pineal indoleamine, melatonin. Retinal input to the suprachiasmatic nucleus of the hypothalamus (SCN) and sympathetic innervation of the pineal are critical to the inhibition of reproduction by short photoperiods. Since the hypothalamic paraventricular nucleus (PVN) receives extensive input from the SCN in the rat, and may influence autonomic function via its brainstem and spinal cord projections, we studied the role of this nucleus in photoperiodically induced gonadal regression in the hamster. Bilateral electrolytic destruction of either the paraventricular nucleus (PVN) or suprachiasmatic nucleus (SCN) of the hypothalamus completely blocked testicular regression induced by either blinding or exposure to short days (10L:14D). Lesions in the retrochiasmatic hypothalamus (RCA) which may have interrupted the pathway of previously identified efferents from the SCN to the PVN were also effective in preventing short day-induced gonadal regression. Pineal melatonin content was measured in intact and lesioned hamsters sacrificed 3-5 h before lights on, at the time of the expected nocturnal peak. While SCN and RCA lesions significantly reduced pineal melatonin content, PVN lesions were still more effective in this regard. We conclude that the hamster's neuroendocrine response to photoperiod is mediated by neural pathways which include retinohypothalamic input to the SCN and efferents from this nucleus to the PVN which travel dorsocaudally through the retrochiasmatic area of the hypothalamus. Effectiveness of lesions restricted to the PVN suggests that direct projections from the PVN to spinal autonomic centers convey photoperiodic information which regulates pineal, and hence gonadal, function.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24726/1/0000148.pd

The colocalization of substance P and prodynorphin immunoreactivity in neurons of the medial preoptic area, bed nucleus of the stria terminalis and medial nucleus of the amygdala of the Syrian hamster

To determine the extent of colocalization of substance P (SP) and prodynorphin peptides within neurons of the medial nucleus of the amygdala (AMe), medial bed nucleus of the stria terminalis (BNSTm) and medial preoptic area (MPOA), we incubated colchicine-treated Syrian hamster brain tissue in an antiserum mixture containing rat anti-SP antibody combined with 1 of 3 rabbit antibodies against prodynorphin peptides: anti-dynorphin A(1-17), anti-dynorphin B(1-13) or anti-C-peptide. This was followed by incubation in a secondary antiserum mixture containing fluorescein-labelled anti-rabbit and rhodamine-labelled anti-rat antibodies. Sections were viewed with an epifluorescence microscope using blue light excitation for fluorescein and green light excitation for rhodamine. Colocalization of SP and prodynorphin labelling was observed in neurons of the caudal parts of AMe, BNSTm and MPOA, areas which are essential for male mating behavior. The colocalization was most extensive in the dorsolateral part of the caudal MPOA, the caudodorsal part of the BNSTm, and in the posterodorsal subdivision of AMe. Although all 3 dynorphin peptides coexisted with SP in these areas, dynorphin B did so less than C-peptide, and dynorphin A less than dynorphin B.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27761/1/0000154.pd