The development of POMC gene expression in the medial basal hypothalamus of prepubertal rats

Alterations in brain opioid gene expression may underlie the dramatic change in the latency to display parental behavior in juvenile rats. Male and female juvenile rats (18-25 days of age) exhibit parental behavior either immediately or within 1-2 days after coming in contact with foster pups. By 30 days of age, however, their response latencies increase to adult levels of 5-10 days. Given the established involvement of the endogenous opioid system in adult maternal and juvenile parental behaviors, the objective of the present report was to determine possible changes in proopiomelanocortin (POMC) gene expression in the medial basal hypothalamus (MBH) during this early developmental window. We compared POMC gene expression in the MBH of male and female juvenile rats from 21 to 33 days of age by in situ hybridization histochemistry. A significant increase in the number of POMC cells in males and females was detected at 30 days of age in the central portion of the arcuate nucleus. This increase in POMC mRNA may contribute to the shift in parental behavior that occurs in male and female juvenile rats. (C) 1999 Elsevier Science B.V. All rights reserved.