Thomas R. Akesson

Estrogen-concentrating cells within cell groups of the medial preoptic area: sex differences and co-localization with galanin-immunoreactive cells

Male and female rats have approximately equal numbers of estrogen(E)-concentrating cells within the medial preoptic area (MPOA). Several cell groups within this brain region are sexually dimorphic, however, and these groups may have sexually different numbers of E-containing cells; this, in turn, may reflect sex differences in neural-regulated functions. In order to study this possibility, the distribution of E-concentrating cells was determined using estrogen autoradiography. Except for the lateral portion of the medial preoptic nucleus (MPNl), the density of E-concentrating cells was 3-5-times higher within the most medially situated cell groups of the female than the male, i.e., within the anteroventral periventricular nucleus (AVPv), periventricular preoptic area (PVPO), medial portion of the medial preoptic nucleus (MPNm), and its central portion (MPNc). In addition, we determined whether E-concentrating cells also express the neuropeptide, galanin. An average of 13% of the E-concentrating cells were galanin positive, which represented 15% of the galanin-immunoreactive population. These results demonstrate a frank and dramatic sex difference in the distribution of E-concentrating cells within sexually dimorphic regions of the MPOA, and also suggest that an interaction between galanin and gonadal steroids may be an important means by which cells within the MPOA regulate reproductive function.

Estrous cyclicity of 125I-cholecystokinin octapeptide binding in the ventromedial hypothalamic nucleus. Evidence for downmodulation by estrogen.

Although there is a good correlation between the levels of gonadal steroids and sex differences in reproductive behavior and food intake, the neurochemical mechanisms by which a gonadal steroid may regulate these behaviors remain unknown. An important central nervous site for steroid modulation of food intake and reproduction is the ventromedial nucleus of the hypothalamus (VMH). Recently it has been suggested that some of the activities of the VMH are dependent on the neuroactive peptide cholecystokinin octapeptide (CCK). High levels of CCK in the VMH have been measured by radioimmunoassay, and immunohistochemical analysis has revealed a dense plexus of CCK fibers and terminals which appose and make synaptic contact with VMH neurons. There is, however, a paucity of information concerning the presence of CCK-binding sites in the VMH. This study demonstrates high levels of 125I-CCK8 binding in the VMH of male and female rats. Tissue sampled on the morning of estrus revealed depressed levels of CCK binding, and, while ovariectomy itself did not affect binding, ovariectomy followed by estrogen replacement depressed CCK binding. These results provide evidence for an estrogenic effect on CCK-binding sites that may help elucidate a role of CCK in the VMH.

Estrogen-concentrating hypothalamic and limbic neurons project to the medial preoptic nucleus.

Estrogen-concentrating neurons that project to the medial preoptic nucleus of the male rat were found to be numerous in limbic and hypothalamic cell groups including the ventral part of the lateral septum, bed nucleus of the stria terminalis, medial amygdaloid nucleus, the ventromedial nucleus, and the amygdalohippocampal zone. This steroid-sensitive circuitry is implicated in the activation of reproductive processes in the male.

Continuous estrogen decreases neurokinin B expression in the rat arcuate nucleus.

Immunohistochemical and in situ hybridization histochemical techniques were used to identify neurokinin B (NKB, also known as neuromedin K or neurokinin beta) as the predominant tachykinin present in cells of the arcuate nucleus of the rat. Little is known about the function of NKB; however, its localization in the arcuate nucleus and the observation that Silastic implants of estrogen for 2 weeks decreases the numbers of labeled cells sutgest a role in gonadal steroid-dependent mechanisms that regulate the anterior pituitary.

Retrograde HRP demonstration of afferent projections to the midbrain and nest calls in the ring dove

Midbrain control of vocalization was evaluated in the ring dove by determining the major afferent inputs with retrograde tract tracing technique. Horseradish peroxidase was infused into various portions of the nucleus intercollicularis, an estrogen concentrating area, which disrupts nest calls when lesioned and induces the vocalization when stimulated by estrogen. Most labelled cell bodies were found in the archistriatum, including a region homologous to the mammalian amygdala.

Binding of125I-cholecystokinin-octapeptide in the paraventricular but not the supraoptic nucleus is increased by ovariectomy

Specific, high affinity binding of 125I-cholecystokinin-octapeptide (CCK) in the paraventricular nucleus was found to be confined to the anterior pole of the posterior magnocellular subdivision (PVHpm). Tissue sampled from intact male and female rats revealed only low CCK binding in the PVHpm; however, binding was greatly increased by ovariectomy. By contrast, binding was uniformly high throughout the supraoptic nucleus of intact males and females and was unaffected by ovariectomy. These results are interpreted in terms of the potential influence of CCK and estrogen on neurosecretion of oxytocin and CCK.