Puberty and adolescence are associated with a gain of function in brain circuits that regulate sex-specific physiology and behavior.  One of the most striking sex differences to arise during puberty in rats is the capacity for females, but not males, to generate a surge of luteinizing hormone (LH).  The preovulatory LH surge is governed by the anteroventral periventricular nucleus of the hypothalamus (AVPV), a sexually dimorphic structure that is larger and contains more neurons in females compared to males.  Previous studies from our laboratory have established that there are sex differences in the addition of pubertally born cells to the rat AVPV (females > males), and that ovarian hormones drive this sex difference.  Whether these pubertally born cells in the AVPV mediate the pubertal gain of function remains unknown.  A key step is to determine whether pubertally born AVPV cells survive into adulthood and differentiate into cell types known to be involved in reproduction.  Using the cell birthdate marker bromodeoxyuridine (BrdU) to identify cells born during puberty, female rats (n=6) received daily injections of BrdU (200 mg/kg, ip) from P28-P56.  In adulthood, on P77, when BrdU-labeled cells ranged from 21-49 days of age, rats were perfused and tissue was processed to colocalize BrdU with the mature neuron marker, NeuN, or the glial marker, GFAP.  The proportion of BrdU cells that colocalized with either marker was determined throughout the extent of the AVPV using confocal microscopy.  Approximately 2/3 of pubertally born AVPV cells were not phenotypically identified as either mature neurons or astrocytes.  However, about 1/3 of the cells were colocalized with either NeuN (15%) or GFAP (19%).  Because multiple cell types are involved in the generation of the LH surge, these pubertally born neurons and astrocytes, and the as yet unidentified cells may mediate this pubertal gain of function.