Attenuation of the rate-altering effects of cocaine by magnesium chloride in squirrel monkeys.
Three adult male squirrel monkeys that were trained to respond on a 3-min fixed-interval schedule of food reinforcement were injected with various doses of magnesium chloride (MgCl(2), 30 and 100mg/kg), cocaine (0.03-3.0mg/kg), and their combination. The purpose of the study was to determine if MgCl(2) could alter the rate of responding and if it could alter the rate-increasing and rate-decreasing effects of cocaine. MgCl(2) had little effect on responding during the 2h sessions. Low doses of cocaine (0.03-0.1mg/kg) were ineffective, intermediate doses (0.1-1.0mg/kg) increased responding, and high doses (1.0-3.0mg/kg) decreased responding. When MgCl(2) was combined with intermediate doses of cocaine, the rate-increasing effects of cocaine were attenuated. Less reliably, increased rates of responding were sometimes observed when MgCl(2) was combined with low (ineffective) or high (rate-decreasing) doses of cocaine. These interactions depended both on the time following injection and the dose of MgCl(2) and showed marked individual differences. These effects observed in monkeys are similar to some of the interactions previously reported in rodents.
Harvard Medical School, New England Regional Primate Research Center, One Pine Hill Drive, Southborough, MA 01772, USA.
K.M.
KM
Kantak