Effect of adrenalectomy on the circadian rhythm of LTP.

Long-term potentiation (LTP) of hippocampal granule cells was studied in vivo at various times during the light-dark cycle in both intact control and adrenalectomized (ADX) rats. Both groups of rats demonstrated a circadian rhythm of LTP, however the rhythmicity of the ADX animals was the opposite to that found in intact controls. Thus, in experiments performed during the dark phase, intact control animals demonstrated more LTP than did the ADX animals. During the light period ADX animals demonstrated more LTP than intact controls. These data suggest that adrenal hormones play a role in regulating the circadian rhythm of LTP.