Effects of neonatal naltrexone on neurological and somatic development in rats of both genders.

The effects of a daily injection of the opioid antagonist naltrexone (NALTX, 1 mg/kg, s.c.) from birth to weaning on various parameters were investigated in male and female rats during postnatal development until adulthood. NALTX increased cerebellar DNA and protein content as well as cerebellar weight at 7 days. Eye opening was not affected by NALTX but it appeared advanced by 1 day in all groups compared to other studies, possibly due to a handling effect caused by the daily injection. Water and food consumption were augmented by NALTX during days 23-32 and days 55-70. Treated preweaning animals showed lower body growth rates than controls. However, NALTX caused a moderate increase in body weight measured during postweaning until adulthood. The effects of NALTX on the parameters evaluated (excepting the cerebellar measurements on day 7), although clearly statistically significant, were small in absolute terms. The preweaning opioid blockade caused by our NALTX treatment seems to affect more markedly the neural and behavioural development than the somatic growth. This work also provides potentially useful baseline data for the study of male and female rats during postnatal development.