Effects of repeated injections of cocaine on catecholamine receptor binding sites, dopamine transporter binding sites and behavior in rhesus monkey

Abstract

In order to determine if repeated injections of cocaine produced long-lasting alterations in catecholaminergic binding sites, rhesus monkeys were treated with saline (1.0 ml/15 kg) or cocaine (3.0-4.0 mg/kg) four times daily for 14 consecutive days and sacrificed two weeks after the last injection. The densities of dopamine D1 receptor binding sites, dopamine transporter binding sites and beta adrenergic receptor binding sites were significantly decreased in caudate nucleus to 51%, 17% and 61% of control, respectively, two weeks after repeated cocaine injections. There were no differences in D2 receptor binding site densities in the caudate, nor were there differences in binding sites between groups in the other brain regions examined: prefrontal cortex (D1, D2, dopamine transporter, beta), nucleus accumbens (D1, D2, dopamine transporter) and substantia nigra (D2). Behavioral observation showed that the cocaine-treated monkeys became sensitized to the repeated injections. Early in the regimen, these animals displayed stereotypic grooming, buccal movements and visual checking after each injection that differed significantly from the saline-treated animals. As the regimen progressed, the frequency of grooming decreased while the frequencies of visual tracking and splayed legs increased in a manner consistent with the development of behavioral sensitization. Together, these findings suggest that the caudate nucleus may be more sensitive than other dopamine-containing brain regions to long-lasting pre- and post-synaptic effects of repeated cocaine administration, and that the changes seen in dopaminergic neurons may be related to behavioral sensitization.