Fig. 35. Proposed mechanism for the regulation of GnRH secretion by kisspeptin. Two populations of kisspeptin neurons, oppositely regulated by estrogen, impinge on GnRH neurons in the medial preoptic nucleus that project to the neural-hemal contact zone in the median eminence. Kisspeptin-containing axon terminals may also interact with GnRH axon terminals in the median eminence.