Sarah Winans Newman

Mating and agonistic behavior produce different patterns of fos immunolabeling in the male Syrian hamster brain

Previous work has shown that mating induces the expression of Fos protein within the chemosensory pathways of the male Syrian hamster brain. However, it is not known if this pattern of labeling is specific to mating or the result of social interactions in general. To determine the behavioral specificity of activation within these pathways, Fos immunostaining following mating was compared to that following agonistic behavior. Both mating and agonistic behavior are dependent upon chemosensory cues and gonadal steroids (reviewed in Refs 64, 65) and areas belonging to the olfactory and vomeronasal pathways process chemosensory and hormonal information (reviewed in Ref. 48). The results of this study demonstrate both similarities and differences in brain activation patterns following these two social behaviors. Agonistic behavior increased the number of Fos-immunoreactive neurons within most subdivisions of the medial amygdala, the anteromedial and posterointermediate bed nucleus of the stria terminalis, the ventrolateral septum and the ventral premammillary nucleus of the hypothalamus in a pattern comparable to that observed after mating. This pattern of activation common to mating and agonistic behavior may reflect an increase in an animals general state of arousal during social interactions. In contrast, although mating and agonistic behavior both activated neurons within the caudal subdivision of the medial nucleus of the amygdala, the anterodorsal level of posteromedial bed nucleus of the stria terminalis and the paraventricular and ventromedial nuclei of the hypothalamus, in these areas either the distribution and/or number of Fos-immunoreactive neurons differed. In addition, agonistic behavior selectively activated neurons within the anterolateral bed nucleus of the stria terminalis, the anterior nucleus of the hypothalamus and the dorsal periaqueductal gray, whereas mating alone activated neurons within the posteroventral level of posteromedial bed nucleus of the stria terminalis and the medial preoptic area. No differences were found between dominant and subordinate males following agonistic behavior. These observations along with results from other laboratories suggest that mating and agonistic behavior activate distinct neural circuits.

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.

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 hamsters (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 microns 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).(ABSTRACT TRUNCATED AT 250 WORDS)

Androgen and estrogen receptors coexist within individual neurons in the brain of the Syrian hamster.

Many aspects of reproductive neuroendocrine function and sexual behavior are responsive to both androgens and estrogens, suggesting that receptors for these steroid hormones may reside within single cells in brain regions that control reproductive function. We determined the distribution of estrogen receptor-containing neurons in 40-microns coronal brain sections in gonadectomized, DHT-treated male Syrian hamsters using immunocytochemistry with the H222 antibody (10 micrograms/ml; Abbott Laboratories). Subsequently, we colocalized estrogen receptors with androgen receptors using the PG-21 antibody (0.5 microgram/ml; G.S. Prins). In males, the distribution of estrogen receptor-containing neurons was similar to that reported previously for the female hamster. Colocalization of androgen and estrogen receptor immunoreactivity was observed in brain regions that contain numerous androgen and estrogen receptor-positive neurons, including subdivisions of the medial preoptic area, bed nucleus of the stria terminals, ventromedial nucleus of the hypothalamus, and the amygdalohippocampal area. Single-labelled estrogen receptor-containing neurons were most numerous in the amygdalohippocampal area and the rostral medial preoptic nucleus; androgen receptor-immunoreactive cells were most abundant in the ventral premammillary nucleus and the lateral septum. These data suggest the potential of androgens and estrogens to influence neuronal function within individual steroid receptor-containing neurons of the hamster limbic system.

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.

Androgen and estrogen concentrating neurons in chemosensory pathways of the male Syrian hamster brain

The medial preoptic area (MPOA), bed nucleus of the stria terminalis (BNST), and medial amygdaloid nucleus (Me) are essential for male sexual behavior in the Syrian hamster. These nuclei received chemosensory stimuli and gonadal steroid signals, both of which are required for mating behavior. The objective of this study was to compare the distribution of androgen- and estrogen-concentrating neurons in MPOA, BNST, and Me in the adult male hamster using steroid autoradiography for estradiol (E2), testosterone (T) and dihydrotestosterone (DHT). Adult males (n = 4 per group) received two i.p. injections of tritiated steroid 4-7 days after castration. Six-microns frozen sections through the brain were mounted onto emulsion-coated slides, and exposed for 11-16 months. In MPOA, BNST, and Me, neurons were more abundant and heavily labelled after [3H]E2 treatment than after either [3H]T or [3H]DHT. Tritiated estradiol- and DHT-labeled cells were found throughout the rostrocaudal extent of Me, with a high concentration in posterodorsal Me. Tritiated testosterone treatment labelled cells largely within posterodorsal Me. In MPOA, the majority of E2-, T-, and DHT-labelled neurons were in the medial preoptic nucleus (MPN) and the preoptic continuation of the posteromedial bed nucleus of the stria terminalis (BNSTpm). Few T-labelled cells were present outside these subdivisions. In the BNST, E2- and DHT-labelled neurons were present in all subdivisions, whereas T labelling was confined to the antero- and posteromedial subdivisions of BNST. These results suggest that the distribution of androgen- and estrogen receptor-containing neurons overlap considerably in nuclei which transmit chemosensory signals in the control of mating behavior.

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 hamsters 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.

Androgen receptor immunoreactivity in the male and female Syrian hamster brain

To investigate potential mechanisms for sex differences in the physiologic response to androgens, the present study compared the hormonal regulation of intracellular androgen receptor partitioning and the distribution of androgen receptor immunoreactivity in select brain regions from male and female hamsters. Androgen receptors were visualized on coronal brain sections. Two weeks after castration, androgen receptor immunoreactivity filled the neuronal nuclei and cytoplasm in males and females. In gonad-intact males and females, androgen receptor immunoreactivity was limited to the cell nucleus. Whereas exogenous dihydrotestosterone prevented cytoplasmic immunoreactivity, estrogen at physiologic levels did not. These results suggest that nuclear androgen receptor immunoreactivity in gonad-intact females is maintained by endogenous androgens, and that androgens have the potential to influence neuronal activity in either sex. However, sex differences in the number and staining intensity of androgen-responsive neurons were apparent in select brain regions. In the ventral premammillary nucleus, ventromedial nucleus of the hypothalamus, and medial amygdaloid nucleus, androgen receptor staining was similar in gonadectomized males and females. In the lateral septum, posteromedial bed nucleus of the stria terminalis (BNSTpm), and medial preoptic nucleus, the number of androgen receptor-immunoreactive neurons was significantly lower in females (p < .05). Moreover, the integrated optical density/cell in BNSTpm was significantly less in females (1.28+/-0.3 units) than in males (2.21+/-0.2 units; p < .05). These sex differences in the number and staining intensity of androgen-responsive neurons may contribute to sex differences in the behavioral and neuroendocrine responses to androgens.

Evidence for a projection from the globus pallidus to the entopeduncular nucleus in the rat

Iontophoretic injections of the fluorescent retrograde tract tracer, Fluoro-gold, into the entopeduncular nucleus of the rat (homologous to the internal segment of the primate globus pallidus) resulted in a substantial number of retrogradely labeled neurons in the ipsilateral globus pallidus (homologous to the external segment of the primate globus pallidus). In experiments confirming this projection, iontophoretic injections of the anterograde tract tracer, Phaseolus vulgaris-leucoagglutinin, in the globus pallidus resulted in dense fiber and terminal labeling in the ipsilateral entopeduncular nucleus. This projection is topographically organized in rostral-caudal, medial-lateral and dorsal-ventral orientations.

6-Hydroxydopamine lesions of the nigrostriatal pathway alter the expression of glutamate decarboxylase messenger RNA in rat globus pallidus projection neurons

In situ hybridization was used to study the effect of 6-hydroxydopamine-induced damage to the midbrain dopaminergic neurons on the level of glutamate decarboxylase mRNA in globus pallidus neurons in the rat. Some animals received an injection of Fluoro-gold in the entopeduncular nucleus or the substantia nigra prior to the 6-hydroxydopamine lesion in order to identify glutamic acid decarboxylase mRNA levels in pallidal neurons that project to one of these targets. Analysis was carried out on a sample of all pallidal neurons as well as neurons that were identified as projection neurons in control and lesioned groups. The loss of the dopamine-containing neurons in the substantia nigra resulted in significant increases in the percentage of globus pallidus neurons that expressed glutamate decarboxylase mRNA and in the amount of glutamate decarboxylase mRNA per globus pallidus neuron. These increases were noted in a sample of all pallidal neurons, as well as pallidal neurons that were identified as projecting to either the entopeduncular nucleus or the substantia nigra. In control animals, glutamate decarboxylase mRNA was clearly identified in globus pallidus neurons projecting to the entopeduncular nucleus, indicating that this recently reported projection is at least partially GABAergic. The results of this study indicate that substantia nigra dopaminergic neurons regulate globus pallidus neurons in the rat, and that removal of the dopaminergic input to the corpus striatum results in a significant increase in the amount of glutamate decarboxylase mRNA in pallidal neurons. The decreased firing rate of pallidal neurons that is seen following the loss of dopamine input appears to be accompanied by an increase in the level of glutamate decarboxylase mRNA in these neurons.