Neural circuits involved in the control of LHRH secretion: a model for estrous cycle regulation.

These studies have identified a core of hypothalamic neuronal systems in the regulation of episodic basal and preovulatory LH release during the estrous cycle. Steroid concentrating neurons under the direction of ovarian steroid milieu promote LHRH accumulation and either independently or in association with the opioid peptide neurons modulate the episodic LHRH discharge. The sequence of neural events that occur preceding the preovulatory LH surge on the afternoon of proestrus are described. Evidence is presented to support the hypothesis that a transient curtailment in the inhibitory influence of hypothalamic opioid peptides in the morning of proestrus, sets in motion a chain of temporally-related events starting with augmentation of adrenergic tone, leading to accumulation of neuropeptide Y and LHRH in the median eminence and culminating in episodic LHRH and LH hypersecretion in the afternoon of proestrus.