LENGTH OF CONTINUOUS COCAINE EXPOSURE DETERMINES THE PERSISTENCE OF MUSCARINIC AND BENZODIAZEPINE RECEPTOR ALTERATIONS

The effects of varied durations of cocaine (1, 3 or 5 days) on muscari nic (MSG) and benzodiazepine (BZD) binding sites in striatum and hippo campus were investigated using homogenate receptor binding. The progre ssive alterations in these receptor sites from a 5 day cocaine adminis tration were also examined 12 h, 2 days or 21 days after drug exposure . Neither a one nor a three day exposure to cocaine produced any long- term alteration in BZD binding in either structure whereas a 5 day adm inistration produced significant increases in binding. Decreases in MS C receptor binding were apparent in striatum from either a 3 or 5 day cocaine exposure and in hippocampus from a 5 day exposure. The 5 day c ocaine exposure produced immediate increases in striatal and hippocamp al BZD binding which persisted for 21 days. Conversely, 5 days of coca ine produced a short-term increase in MSC receptor binding in both str uctures which then became significantly decreased 21 days later. Based on the divergent pattern of changes in BZD and MSC receptor types ove r time in these structures, it appears that cocaine may induce such ch anges via separate mechanisms. In addition, it is apparent that change s in the numbers of these receptor sites after cocaine exposure can be quite dynamic, changing rapidly over time.