Isolation stress during adolescence increases conditioned place preference to cocaine in female rats

Abstract

Adolescence is a developmental period characterized by neuronal growth. Environmental factors such as maternal neglect, social stress and drugs of abuse have a direct impact on future behavioral patterns. Because rats are highly social animals, we decided to investigate if isolation stress during adolescence increases conditioned place preference (CPP) to drugs of abuse. Since lower D2 receptor expression in the mesocorticolimbic system is known to increase cocaine conditioning in adult animals, and because adolescents and adults differ in dopaminergic connectivity and D2 receptor populations, we investigated if D2 receptors are altered during these conditions. Female rats were weaned at postnatal day 23 and housed singly or in pairs. At day 34 rats were tested in an open field, at day 35 in an elevated plus maze and at day 36 they were tested for CPP to cocaine (15mg/kg). At post‐natal day 48, rats were euthanized, brains collected and stored at −80°C. Single‐housed rats showed greater conditioning to cocaine when compared to group‐housed rats. This suggest that housing rats singly increases the rewarding properties of cocaine. Single‐housed rats also show lower D2 receptor immunoreactivity in the Nucleus accumbens (NAc) and the Prefrontal cortex (PFC) when compared to group‐housed rats. This correlates with the greater conditioning observed in single housed rats. Isolation stress had the effect of lowering D2 receptor populations in the NAc and PFC thus augmenting the rewarding properties of cocaine in adolescent female rats. Chronic stress during adolescence thus can lower D2 receptors and could be a determining factor in substance abuse and relapse. Support or Funding Information Financial assistance was provided by the Office of International Science and Engineering (OISE) of NSF through the Partnerships for Research and Education (PIRE) Program (OISE‐#1545803).