Do you have a citation? A search for "cocaine rat study" mostly turned up references to the Rat Park experiment, which used morphine. A later study comparing heroin and cocaine found that social isolation increased overall usage of heroin (apparently because the isolated rats picked up the habit faster) but not cocaine, and that by the fifth week of the study usage rates were similar between isolated and non-isolated groups for both drugs [1].

[1] https://pubmed.ncbi.nlm.nih.gov/2616610/