Neuroanatomical relationships of substance P and sex steroid hormone-sensitive neurons involved in sexual behavior

Co-localization of midbrain projections, progestin receptors, and mating-induced fos in the hypothalamic ventromedial nucleus of the female rat

In female rats, sexual behavior requires the convergence of ovarian hormone signals, namely estradiol and progesterone, and sensory cues from the male on a motor output pathway. Estrogen and progestin receptors (ER and PR) are found in neurons in the hypothalamic ventromedial nucleus (VMH), a brain region necessary for lordosis, the stereotypic female copulatory posture. A subset of VMH neurons sends axonal projections to the periaqueductal gray (PAG) to initiate a motor output relay, and some of these projection neurons express PR. Previous studies showed that VMH neurons are activated during mating, based on the expression of the immediate early gene Fos. Many of the activated neurons expressed ER; however, it is not known if such activated neurons co-express PR. Fluorogold, a retrograde tracer, was injected into the PAG of ovariectomized rats to label neurons projecting from the VMH. Hormone-treated animals then were mated, and their brains were immunohistochemically stained for PR and Fos. Of the Fos-positive neurons, 33% were double-labeled for PR, 19% were double-labeled with Fluorogold, and 5% were triple-labeled for Fos, PR, and the retrograde tracer. The majority of triple-labeled neurons were found in the rostral, rather than caudal, portion of the VMH. These results show that PR-containing neurons are engaged during sexual behavior, which suggests that these neurons are the loci of hormonal-sensory convergence and hormonal-motor integration.

Quantitative studies of progesterone receptor and nitric oxide synthase colocalization with somatostatin, or neurotensin, or substance P in neurons of the guinea pig ventrolateral hypothalamic nucleus: an immunocytochemical triple-label analysis

Previous double-label studies have demonstrated that progesterone receptors (PR) may coexist with nitric oxide synthase (NOS) and also with neuroactive peptides such as somatostatin (SOM), neurotensin (NT) and substance P (SP) in neurons of the ventrolateral hypothalamic nucleus (VL) of the guinea pig. In the present study, triple-label immunofluorescence histochemistry was used to determine whether neurons co-expressing both PR and NOS also contain one neuropeptide (SOM, NT or SP) and to quantify these colocalization relationships. Ovariectomized guinea pigs were primed with estradiol to induce PR immunoreactivity and treated with colchicine to visualize immunoreactive (IR) peptidergic neurons. Using three primary antibodies raised in different species and labeled with three different markers, it is possible to recognize which type(s) of immunoreactivity each cell contains on the same sections. We observed that PR, NOS and SOM co-occurred extensively, whereas PR, NOS and NT or PR, NOS and SP were colocalized infrequently in neurons of the VL. Combining our various quantitative observations, we found that SOM immunoreactivity appeared in 33% of the PR/NOS-IR neurons in the caudal aspect of the nucleus and that nearly all neurons containing SOM and NOS contained PR. The occasional localization between PR, NOS and SP seen in the rostral subdivision of the VL represented a very low proportion of the PR/NOS-IR neurons but 48% of NOS/SP-IR neurons. The relatively high proportion of PR/NOS-IR cells expressing SOM in the VL suggests that these neurons are part of a neural circuitry involved in a variety of steroid-dependent functions.

Testosterone increases the number of substance P-like immunoreactive neurons in a specific sub-division of the lateral hypothalamus of the weakly electric, brown ghost knifefish, Apteronotus leptorhynchus

During spawning, male and female brown ghost knife fish modulate their electric organ discharge to produce discrete courtship signals known as chirps. However, non-spawning fish show clear sex differences in chirp responsiveness to electrosensory stimuli; males consistently chirp, whereas females do not. This behavioral dimorphism is paralleled by sex differences in substance P-like immunoreactivity (SPl-ir) in the prepacemaker nucleus (PPn) which regulates chirping. The PPn is densely innervated by SPl-ir fibers in males, but not in females. However, we have shown that both female chirping behavior and the expression of SPl-ir in the PPn are enhanced following adult testosterone treatment [J.G. Dulka, L. Maler, W. Ellis, Androgen-induced changes in electrocommunicatory behavior are correlated with changes in substance P-like immunoreactivity in the brain of the electric fish, Apteronotus leptorhynchus, J. Neurosci. 15 (1995) 1879-1890]. Thus, testosterone-induced changes in SPl-ir input to the PPn may modulate female chirping during spawning. Recent evidence suggests that SPl-ir projections to the PPn may originate from SPl-ir neurons in the lateral hypothalamus (Hl). If so, one might expect to see a greater number of SPl-ir neurons in the Hl of testosterone-implanted females compared to Blank-implanted controls. In making this comparison, we found that both groups of females had similar numbers of SPl-ir neurons in the anterior Hl, but that testosterone-implanted females had significantly (p<0.01) more SPl-ir neurons in a distinct part of the posterior Hl. This sub-population of testosterone-sensitive, SPl-ir neurons may contribute to the regulation of chirping, since an increase in their number is positively correlated with the appearance of SPl-ir fibers in the PPn [J.G. Dulka, L. Maler, W. Ellis, Androgen-induced changes in electrocommunicatory behavior are correlated with changes in substance P-like immunoreactivity in the brain of the electric fish, Apteronotus leptorhynchus, J. Neurosci. 15 (1995) 1879-1890].

Opiate receptors modulate estrogen-induced cholecystokinin and tachykinin but not enkephalin messenger RNA levels in the limbic system and hypothalamus

Cholecystokinin, substance P and methionine enkephalin all regulate the display of reproductive behaviour. Their expression is exquisitely regulated by estrogen in the limbic-hypothalamic circuit, a circuit that regulates the display of estrogen-sensitive female reproductive behavior. Relatively little is known, however, about the interaction of endogenous opioid peptides with cholecystokinin and substance P in the limbic-hypothalamic circuit. Opiates antagonize the release of cholecystokinin and substance P in the hypothalamus and periaqueductal gray and stimulate cholecystokinin messenger RNA levels in the amygdala. To determine the effect of endogenous opioid input on estrogen-induced cholecystokinin, enkephalin and substance P expression, in situ hybridization histochemistry was used to examine estrogen-induced messenger RNA levels of these neuropeptides in specific nuclei of the limbic system and hypothalamus in the presence of opiate receptor antagonists. Estrogen treatment of ovariectomized rats significantly elevated cholecystokinin messenger RNA levels in the central portion of the medial preoptic nucleus, the encapsulated portion of the bed nucleus of the stria terminalis and the posterodorsal medial amygdala, as well as increased preproenkephalin and preprotachykinin messenger RNA levels in the ventromedial hypothalamic nucleus and the posterodorsal medial amygdala. The universal opiate receptor antagonist naltrexone and the delta-opiate receptor antagonist naltrindole each potentiated the estrogen-induced increase and elevated cholecystokinin messenger RNA levels an additional 1.9- to 2.8-fold depending on the nucleus examined, but had no effect on the estrogen-induced expression of either preproenkephalin or preprotachykinin messenger RNA. beta-Funaltrexamine, a mu-opiate receptor antagonist, had no effect on the medial preoptic or medial amygdaloid cholecystokinin messenger RNA levels or on the estrogen-induced expression of preproenkephalin messenger RNA but did cause a decrease in estrogen-induced cholecystokinin messenger RNA levels in the bed nucleus of the stria terminalis and a decrease in the preprotachykinin messenger RNA levels in the ventromedial hypothalamic nucleus. These results indicate that endogenous opioids, acting on the delta-opiate receptor within nuclei of the limbic-hypothalamic circuit, restrain the estrogen-induced increase of cholecystokinin messenger RNA expression. Activation of the mu-opiate receptor, however, may facilitate cholecystokinin messenger RNA expression in the bed nucleus of the stria terminalis and preprotachykinin messenger RNA expression in the ventromedial hypothalamic nucleus. Thus, endogenous opioid peptides may act in a site- and receptor-specific manner to modulate estrogen-induced neuropeptide levels in the limbic system and hypothalamus.

Extrinsic and intrinsic substance P innervation of the rat lateral septal area calbindin cells

The electrophysiological observations that substance P administration to the lateral septal area elicits both excitatory and inhibitory responses, together with earlier reports on the multiple sources of substance P innervation of the septum, implies that these axons with distinct origins have different functions. This prompted us to examine the origin and neurochemical character of substance P afferents to the lateral septal area. Chronic surgical isolation of the septum from its ventral afferents and retrograde tracer experiments using wheat germ agglutinin-conjugated horseradish peroxidase, both followed by an immunostaining for substance P, were employed to elucidate the origin of these axon terminals. In order to assess the possible co-existence of substance P with other neurotransmitter substances in the parent cells of the septopetal projections, co-localization studies for substance P and choline acetyltransferase, as well as substance P and GABA, were performed. The comparative distribution of substance P fibers and septal calbindin-containing neurons was also investigated using correlated light and electron microscopic double immunostaining. The results are summarized as follows: (i) the substance P innervation of the lateral septal area derives from several hypothalamic nuclei (including the lateral and lateroanterior hypothalamic area, tuber cinereum and ventromedial hypothalamic nucleus) and tegmental nuclei (the majority of fibers from the laterodorsal and a few from the pedunculopontine tegmental nucleus), as well as intrinsic septal cells; (ii) the septopetal substance P fibers of tegmental origin are cholinergic; intraseptal substance P neurons located in the dorsolateral part of the lateral septum also contain GABA, while substance P neurons seen on the border between the medial and lateral septal area and septopetal hypothalamic substance P cells do not contain GABA or acetylcholine; (iii) substance P fibers from pericellular baskets around calbindin-containing lateral septal neurons with a high degree of selectivity; (iv) approximately 90% of the entire calbindin cell population are postsynaptic targets of substance P axons; (v) their terminals contact the soma and the dendrites of these cells, among them the somatospiny neurons; and (vi) the extrinsic substance P boutons establish asymmetric, while the intrinsic substance P axon terminals form symmetric membrane specializations. Because neurons in the lateral septal area receive hippocampal input and project massively to hypothalamic areas, the different types of substance P input on these neurons can modify the information flow arriving from the hippocampus to diencephalic brain structures at the level of the lateral septal area.

Hypothalamic estrogen receptor-immunoreactivity in prepubertal vs adult female guinea pigs

Juvenile guinea pigs (18-20 days old) rarely display lordosis in response to estradiol and progesterone treatments that elicit sexual behavior in adult females. Nor do immature animals release a preovulatory-like surge of luteinizing hormone in response to estradiol. In vitro radioligand binding assays have revealed similar concentrations of estrogen receptors in the hypothalamus and preoptic area of prepubertal and adult guinea pigs. The aim of the present study was to compare estrogen receptor-immunoreactivity in a variety of forebrain regions of immature and adult guinea pigs, to determine whether age differences in estrogen receptor levels in more discrete portions of the hypothalamus and preoptic area exist. Forebrain tissue from juvenile (17 days) and adult females (> 6 weeks), ovariectomized 6 days previously, was processed for estrogen receptor-immunoreactivity, using Abbott Laboratories' H222 anti-human estrogen receptor antibody. Juveniles had estrogen receptor-immunoreactive cells in all of the same regions as adults: medial preoptic area, medial preoptic nucleus, bed nucleus of the stria terminalis, periventricular, paraventricular, dorsomedial and arcuate nuclei, ventrolateral and anterior hypothalamic regions, and amygdala. Among the areas in which estrogen receptor-immunoreactivity was quantified (medial preoptic area, medial preoptic nucleus, anterior periventricular nucleus, arcuate nucleus and ventrolateral hypothalamus), the only region in which an age difference in estrogen receptor-immunostaining was observed was the rostral portion of the ventrolateral hypothalamus. Juvenile females had, on average, 30% fewer estrogen receptor-immunoreactive cells in a sample of this region than adults (440 +/- 25 vs. 626 +/- 25, P = 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)