Acute and multiple injection effects of magnesium of responding maintained by cocaine, extinction from cocaine, glucose + saccharin, and food

In a variety of behavioral experiments, magnesium has effects that are similar to cocaine and other psychomotor stimulants. Of particular relevance to the present experiments is the recent finding that magnesium maintains responding in cocaine-trained rats. It would be expected, therefore, that injections of magnesium would alter the rate of responding maintained by self-administered cocaine in rats. Five experiments examined the specificity and selectivity of this interaction. Acute and multiple injections of MgCl 2 (15–250 mg/kg) produced dose-dependent reductions in responding maintained by cocaine (0.1–2 mg/kg/infusion). Testing for acute injection effects occured following injections, while testing for multiple injection effects occured prior to daily injections. Doses of 30 and 125 mg/kg MgCl 2 reduced responding maintained by doses of cocaine that were below the training dose of 0.75 mg/kg/infusion. MgCl 2 in a dose of 250 mg/kg markedly suppressed responding maintained by each dose of cocaine. A magnesium-deficient diet produced a dose-dependent increase in responding maintained by 0.1 mg/kg/infusion cocaine. In order to determine the specificity and selectively of these effects, acute and multiple injections of MgCl 2 were examined on glucose + saccharin- and food-maintained responding. The acute effects of MgCl 2 injections were specific because food-maintained responding was not affected, except by the highest dose of 250 mg/kg. This demonstrates that lever pressing was not nonspecifically reduced by 30 and 125 mg/kg MgCl 2 during cocaine availability. However, the effects on cocaine-maintained responding were not selective for cocaine because glucose + saccharing-maintained responding and responding during extinction from cocaine were affected by MgCl 2 in a manner similar to cocaine-maintained responding. effects of MgCl 2 were both specific and selective for cocaine-maintained responding because multiple injections did not influence glucose + saccharin- or food-maintained responding.