Repeated electroconvulsive shock or chronic morphine treatment increases the number of ³HDALA², DLEU⁵enkephalin binding sites in rat brain membranes

Experiments were performed in rats to evaluate the possible mechanisms responsible for the pharmacological cross-sensitization observed between repeated electroconvulsive shock (ECS) and chronic morphine administration. Repeated daily ECS for 9 days as well as chronic morphine pellet implantation resulted in a significant increase in the number of ³H-DADLE binding sites (B_max values of 231 and 196 fmoles/mg protein, respectively). By contrast, single ECS, repeated sham ECS, and placebo pellet-treated rats all had significantly lower B_max values (approx. 170 fmoles/mg protein). Affinities were not significantly altered by these treatments (Kd values between 3.1 and 4.0 nM). These data may link pharmacological cross-sensitization (repeated ECS and chronic morphine treatment) with a functional increase in the number of available opioid receptors.