Continuous cocaine induces persisting changes in behavioral responsivity to both scopolamine and diazepam

Forty-eight male rats were administered continuous cocaine, daily cocaine injections (intermittent), continuous amphetamine, or no drug for 5 days. Beginning 45 days after the administration all groups were tested for their responsivity, as measured by automated activity cages, to a low dose of the cholinergic agonist scopolamine. The continuous cocaine group showed decreased sensitivity to this challenge as compared to the other groups. When tested with a low dose of diazepam, the continuous cocaine group showed the greatest response. However, when observed following an injection of cocaine HCl, the intermittent cocaine group showed the greatest behavioral response. These findings support those of previous studies that indicated that the mode of initial cocaine administration is a key factor in the production of persisting changes in behavior and biochemistry.