STRAIN AND HOUSING AFFECT COCAINE SELF-SELECTION AND OPEN-FIELD LOCOMOTOR-ACTIVITY IN MICE

We recently conducted an experiment to investigate the possible cooper ation between genetic makeup and differential housing on cocaine self- administration in male and female C57BL/6J and DBA/2J mice. Cocaine se lf-selection was measured in a two-choice test with one choice being c ocaine-HCl solution of 40 mg% in tap water and the other choice being plain tap water. Housing conditions began at weaning (21-23 days of ag e) and consisted Of group housed (GH) with 2-3 mice per cage, and isol ated housed (IH) with 1 mouse per cage. The results of this study reve aled overall strain, sex and housing differences, with C57BL/6Js consu ming more cocaine solution than DBA/2J subjects, females consuming mor e cocaine solution than males, and group housed consuming more than is olate housed subjects. In a second study, the effect of differential h ousing on open-field locomotor activity was investigated. Testing was conducted on two consecutive days, with subjects receiving an IP injec tion of saline on day 1, and 15 mg/kg cocaine HCI on day 2. Four behav iors were recorded, including: total distance, nosepokes, stereotypy, and margin time. Overall, the results revealed significant strain diff erences for stereotypy and nosepokes, and males were found to be more activated by cocaine than females. Additionally, DBA males tended to b e differentially affected by housing condition, with IH showing suppre ssed locomotor activity as compared to GH subjects. Last, significant strain by housing interactions occurred in nosepokes and stereotypy ti me.