To study
GnRH neuron projections to the systemic circulation during sexual maturation and in photoperiod-induced
delayed puberty, we injected
fluorogold (i.p.) into long- or short-day-reared male Djungarian hamsters. Five days after
fluorogold treatment, at 15, 25, or 40 days of age, most
GnRH neurons were found to access the systemic vasculature from terminal fields in the median eminence and organum vasculosum of the lamina terminalis. More than 80% of
GnRH cell bodies in the medial preoptic area and diagonal band of Broca contained
fluorogold, the locus for the majority of the
GnRH neuron system in this species.
GnRH cell numbers (approximately 180) and percentages with
fluorogold were the same in 15- and 25-day-old males in long days, respectively pre-and peripubertal, and were not different from that in short-day hamsters with
delayed puberty. Neither the number of
fluorogold-labeled
GnRH somata nor intensity of the
fluorogold per cell was altered in hamsters during the critical period for initiation of reproductive maturation. Only later, at age 40 days, was the percentage of
GnRH somata with
fluorogold increased in long-day hamsters or reduced in 40-day-old males in short days relative to that in males at 15 days of age (same day length). The findings indicate that
GnRH neuron projections to regions outside the blood-brain barrier are established before puberty and are independent of photoperiod control of reproductive development.