Interactions of delta9-tetrahydrocannabinol with d-amphetamine, cocaine, and nicotine in rats

The acute, reciprocal dose-response interactions between delta9-tetrahydrocannabinol (delta9-THC; 2.5, 5.0 and 10.0 mg/kg; IG) and each of three stimulants - d-amphetamine (dA; 1, 2 and 4 mg/kg; IP), cocaine (COC; 10, 20 and 30 mg/kg; IP), and nicotine (NIC; 0.25, 0.5 and 1.0 mg/kg; IP) were studied for their effects on performance of a conditioned avoidance response (CAR), photocell activity, heart rate, body temperature, and rotarod performance. delta9-THC impaired CAR and rotarod performance, depressed photocell activity, and decreased heart rate and body temperature. None of the three stimulants influenced CAR performance, but dA and COC increased the number of intertrial responses, and this latter effect was partially antagonized by delta9-THC. dA and COC, but not NIC, stimulated photocell activity. delta9-THC completely blocked this effect of dA, whereas there was mutual antagonism between delta9-THC and COC on this measure and NIC markedly potentiated the depression caused by delta9-THC. dA and COC tended to offset the impairment of rotarod performance caused by delta9-THC, whereas NIC augmented it. The bradycardia and hypothermia caused by delta9-THC tended to be augmented by these stimulants, especially NIC. The interactions were also studied after subacute treatment for six days with delta9-THC and/or each of the three stimulants. There was evidence for tolerance to the effects of delta9-THC on all measures and this tolerance generally resulted in less interactive effects between delta9-THC and the stimulants. Little or no tolerance was seen for the effects of the three stimulants or their interaction with delta9-THC. The time course of radioactivity derived from 14C-delta9-THC and each of the radiolabelled stimulants was determined in plasma and brain. Only minor interactive effects were found and, in general, they could not account for the functional interactions.