Effects of ambient temperature on the relative reinforcing strength of MDMA using a choice procedure in monkeys

Abstract

Rationale: 3,4-Methylenedioxymethamphetamine (MDMA, ecstasy) is frequently used in hot environments, such as rave parties. Studies in laboratory animals have shown that ambient temperature can alter the behavioral and neurochemical effects of MDMA.

Objective: To examine the influence of ambient temperature on the relative reinforcing strength of MDMA and reinstatement of behavior previously maintained by MDMA is the objective of the study.

Methods: The effects of cool (18 degrees C), room (24 degrees C), and warm (31 degrees C) temperatures were examined when MDMA was available under a concurrent fixed-ratio 30 schedule of MDMA (saline, 0.03-0.3 mg/kg/injection) and food choice in rhesus monkeys (n = 5). During saline substitutions, the effect of noncontingent MDMA (0.03-0.3 mg/kg) on response allocation was examined at each ambient temperature.

Results: At room temperature, MDMA choice increased as a function of dose, such that food was preferred over a low MDMA dose (0.03 mg/kg/injection), whereas higher doses were preferred over food. Elevating the ambient temperature significantly increased the relative reinforcing strength of 0.03 mg/kg/injection MDMA, and lowering the ambient temperature significantly attenuated the choice of 0.1 mg/kg/injection MDMA. Noncontingent injections of MDMA administered before a session in which saline was the alternative to food dose-dependently increased injection-lever responding; this effect was not influenced by ambient temperature.

Conclusions: These results suggest that ambient temperature can affect the relative reinforcing strength of MDMA, but not MDMA-induced reinstatement. Furthermore, these results suggest environmental strategies for decreasing the reinforcing strength of MDMA.

Figure 1

Effects of ambient temperature on MDMA choice under a concurrent schedule of MDMA and food availability. Data are represented as mean ± SEM (n=5). Abscissa represents the MDMA dose (0.03 – 0.3 mg/kg/inj). Values above S represent when saline was the alternative to food. Ordinates represent (A) MDMA choice, (B) MDMA injections earned and (C) food pellets earned. * indicates significantly different from other ambient temperatures at that dose (p<0.001) and filled symbols indicates significantly different from vehicle (saline) at an ambient temperature (p<0.05).

Figure 2

Effects of ambient temperature on MDMA-induced reinstatement during concurrent saline and food availability. Data are represented as mean ± SEM (n=4). Abscissa represents S (saline) and the pretreatment dose of MDMA (0.03 – 0.3 mg/kg). Ordinates represent (A) % injection-lever responding, (B) saline injections earned and (C) food pellets earned. Filled symbols indicate significantly different from vehicle (saline) for that ambient temperature (p<0.05).