Prolactin levels in juvenile and adult rats following acute restraint and the open field

Acute restraint and exposure to a novel environment alter behavior and incr ease prolactin levels in rats quickly and reliably. However, little researc h is available that examines behavior and levels of prolactin as a result o f acute exposure to one stressor immediately followed by a second stressor. Similarly, a relationship between prolactin and behavior has not been esta blished. In the present study, juvenile (35-day-old) and adult (5-month-old ) rats were either placed in a novel open field for 10 min or restrained fo r 10 min prior to exposure to the open field. Restrained juveniles groomed more than control juveniles and restrained adults. Conversely, restraint open Field reduced ambulation and rearing among juvenile males and females, and adult females ambulated less than control females and restrained males across both behaviors. In addition, results from the present study demonst rated the first reported relationship between prolactin and open-field beha viors. Prolactin was positively correlated with rearing and number of fecal boli, and levels were negatively correlated with Freezing. Among adult fem ales, prolactin levels were lower following restraint + open field than aft er exposure only to the open field. This may be explained by the psychologi cal response to the open field when it directly followed the physical stres sor of acute restraint. (C) 2000 Elsevier Science Inc. All rights reserved.