The acute effects of juvenile isolation on sucrose intake and its long-term
consequences on adult social behavior were investigated. Additionally, the
role of the endogenous opioid systems was studied. Juvenile rats were hous
ed in one of three conditions: in groups or in isolation with (partial isol
ation, PI) or without 30 min of daily social contact from 22 to 35 days-of-
age. During this period the rats were treated daily with saline or morphine
.
Juvenile isolated rats showed an increased sucrose intake as compared to no
n-isolated controls, with PI-rats somewhere in-between, suggesting a negati
ve correlation between the amount of social contact and sucrose consumption
. Morphine treatment during the isolation period enhanced the sucrose intak
e in non-isolated rats, whereas it decreased sucrose consumption in (partia
l) isolated rats. With regard to the long-term effects, (partial) isolated
rats decreased social activity as compared to non-isolated controls which w
as reversed by morphine treatment during the isolation period. In non-isola
ted rats, morphine treatment caused an opposite effect: it decreased social
activity as compared to the saline treated controls.
The data suggest that stimulation of endogenous opioid systems in the juven
ile phase may have an important modulatory role in the expression of adult
social behavior. The results are discussed in relation to a possible functi
on of morphine as a substitute for the release of endogenous opioid peptide
s during social play. (C) 2000 Elsevier Science Ltd. All rights reserved.