Increased synaptic input to gonadotropin releasing hormone cells in preoptic area grafts that support reproductive development in female hypogonadal mice

Ultrastructural studies have established that gonadotropin releasing hormone (GnRH) neuronal cell bodies receive sparse synaptic input compared to other neuronal cell types. In the present studies, immunocytochemistry for the presynaptic marker synaptophysin, coupled with confocal microscopy, was employed to evaluate whether there was a difference in synaptic input to GnRH cells within preoptic area grafts (hypogonadal, HPG; preoptic area, POA) in hypogonadal female mice that did or did not show ovarian development. GnRH cells in HPG/POA mice with ovarian development exhibited significantly higher numbers of synaptophysin immunoreactive (syn-IR) appositions as compared with HPG/POA mice without ovarian development. This suggests that synaptic input to the grafted GnRH cells is important for the correction of reproductive functions in HPG/POA mice. Following mating, Fos immunoreactivity was present in several GnRH cells in HPG mice with successful POA grafts, indicating the establishment of neuronal projections conveying somatosensory information to the GnRH cells in these mice. The presence of a higher number of syn-IR appositions to GnRH cells in the successful grafts supports this hypothesis.