Localization of the VIP2 receptor protein on GnRH neurons in the female rat

In mammals, the timing and occurrence of the preovulatory LH surge critical ly depends on the proper functioning of the suprachiasmatic nucleus (SCN). Recent evidence suggests that vasoactive intestinal polypeptide (VIP) conve ys time of day information from the SCN to GnRH neurons. However, it is not completely clear whether this action is exerted directly at the level of t he GnRH neuron. To determine if GnRH neurons are direct targets for VIP, tr iple-label immunofluorescence was utilized to simultaneously localize GnRH, VIP and VIP2 receptor protein. The present results demonstrate that about 40% of all GnRH neurons analyzed contain VIP2 receptor immunoreactivity and that VIP-containing processes were seen in close apposition to a significa nt number of VIP2 receptor-positive GnRH neurons. GnRH neurons that exhibit immunoreactivity for the VIP2 receptor are located predominantly in the OV LT region and the rostral preoptic area. In the median eminence, where the majority of GnRH neurons terminate, VIP2 receptor immunoreactivity was abse nt. In summary, these findings indicate that VIP can communicate directly w ith GnRH neurons.