The long range goal of this research is to clarify the cellular mechanisms by which neurons in the limbic system and hypothalamus integrate and process endocrine and sensory information relevant to reproductive function. Central to this goal is the definition of pathways for convergence of neural and endocrine information. Previous work supported by this grant indicates that the anteroventral periventricular nucleus of the preoptic region (AVPV) represents a model point for integration of neural and endocrine influences on gonadotropin secretion. The AVPV plays an essential role in the generation of the preovulatory surge in luteinizing hormone (LH). Moreover it contains sexually dimorphic populations of peptidergic neurons that display sex specific patterns of hormonal regulation which correlate with changes in expression on hormone receptors, and in the activation of transcription factor CREB. Our overall hypothesis is that the AVPV exerts both stimulatory and inhibitory influences on preovulatory surges of LH and prolactin secretion through distinct populations of peptidergic neurons. The activity of these neurons is hormonally regulated by the direct actions of estrogen (E2) and progesterone (P4), as well as by the combined influence of changes in afferent neurotransmitter and postsynaptic regulation of their receptors. Anterograde axonal transport, histochemical and biochemical methods, as well as both in vivo and in vitro model systems, will be used to address the following specific aims.:
Specific aim 1. We will determine if gonadal steroid hormones regulate the expression of cholecystokinin (CCK) or enkephalin (ENK) in sexually dimorphic afferents to the AVPV in a sex specific pattern.
Specific aim 2. In situ hybridization and RT PCR will be used to determine whether E2 and P4 regulate the expression of receptors for glutamate, CCK, and ENK in the AVPV.
Specific aim 3. Histochemical methods will be used to study the influence of E1 and P4 treatment on MRNAS encoding neurotensin (NT) and dynorphin (DYN) in the AVPV of juvenile female rats, since these peptides appear to have opposing actions on phasic LH secretion.
Specific aim 4. In addition, we will examine whether the ability of E2 and P4 to regulate levels of phosphorylated CREB, NT, and DYN in cultured explants of the AVPV is influenced by transsynaptic mechanisms involving receptors for glutamate or ENK.
Specific aim 5. Finally, we will use a combined anterograde transport/immunohistochemical triple labeling method and confocal microscopy to determine if NT and DYN containing neurons in the AVPV project directly to GnRH or tuberoinfundibular dopaminergic neurons which are thought to control the release of LH and prolactin from the pituitary. The results of these experiments will demonstrate cellular mechanisms underlying neurohumoral integration, and may provide new clues about the etiology of hormone-dependent abnormalities in the neural control of ovulation and puberty.
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