Pulsatile release of GnRH is critical for the central regulation of fertility. Besides a brief perinatal elevation, GnRH release is thought to be minimal before puberty. Based on the pattern of gonadotropin release, this postulate is reasonable, but actual measurements of GnRH release during the neonatal and early prepubertal period are lacking. The electrochemical method fast-scan cyclic voltammetry (FSCV) can be used to identify changes in GnRH release. We used FSCV to examine changes in GnRH concentration in the median eminence (ME) in brain slices from gonad-intact male mice. In adults, the frequency of GnRH release in this preparation is similar to the LH pulse pattern in vivo. GnRH release in ME was observed well before outward measures of puberty, being very active at birth and less but still of greater frequency at 7-9d postnatal (~5 events/hr) than in adults. By 2wks postnatal, release essentially ceased, then slowly increased to adult levels. The regulation of GnRH release frequency at 1wk was examined. High frequency GnRH release persisted in kisspeptin knockout mice, demonstrating release is kisspeptin independent. Further, locally applied exogenous kisspeptin stimulated GnRH release in only 1/3 of slices from 1wk old mice; this percentage increased with age to 100% response by 3wks. Testosterone given in vivo 4hr before slice preparation reduced spontaneous GnRH release frequency at 1wk, as did GnIH applied via the bath during recording. Blocking the GnIH receptor (GPR147) reversed the inhibitory effect of testosterone. Exogenous GnRH failed to increase serum LH in 1wk old mice, but did in mice aged ≥2wk. These data indicate high frequency GnRH release in early prepubertal male mice appears to result from lack of endogenous inhibition of the GnRH network. Possible central roles of high-frequency GnRH release and of pituitary non-responsiveness at 1wk of age will be discussed. HD34860