The effect of repeated electroconvulsive shock on corticosterone responses to centrally acting pharmacological stimuli in the male rat

The effect of repeated and single electroconvulsive shocks (ECS) on the corticosterone response to pharmacological stimuli has been studied in male rats. Plasma corticosterone concentrations are elevated by oxotremorine, a muscarinic agonist, and by 5-hydroxy-l-tryptophan, a precursor of serotonin. Both these agonists probably stimulate corticotrophinreleasing-factor release from the hypothalamus. The log dose-response curves of the corticosterone response to oxotremorine and to 5-hydroxy-l-tryptophan are shifted to the left after a single ECS given daily for 10 days compared with sham-shocked controls. Plasma corticosterone concentrations are elevated by treatment with -methyl-p-tyrosine methyl ester (400 mg/kg IP). This rise is suppressed by clonidine. The log dose-response curve for the corticosterone response to clonidine after -methyl-p-tyrosine methyl ester is also shifted to the left by repeated ECS, compared with controls. There is no difference in the corticosterone response of ECS and sham-treated groups given vasopressin, which is thought to act directly on the pituitary to release ACTH.A single ECS produces a slight enhancement of the response to 5-hydroxy-l-tryptophan, a slight decrease in the response to oxotremorine and no change in the response to clonidine after -methyl-p-tyrosine.The disappearance of the difference in response between ECS and sham-treated animals was also studied 1,3, and 6 days after a series of ten ECS or sham procedures. Significant differences in the corticosterone responses to oxotremorine, 5-hydroxy-l-tryptophan and clonidine after -methyl-p-tyrosine between ECS and sham-treated animas were found 24 h after the last ECS or sham shock. These differences were in decline 3 days after the last procedure and had completely disappeared by day 6. The decline was largely due to an increase in plasma corticosterone responsiveness to pharmacological stimuli of the shamshocked controls. Responses in the ECS-treated groups remained constant.It is apparent that the anaesthetic procedure suppresses the effect of oxotremorine, 5-hydroxy-l-tryptophan and clonidine after -methyl-p-tyrosine on corticosterone concentrations in plasma. This effect is spontaneously reversible. Repeated ECS reverses the effect of the anaesthetic procedure but produces no reversible enhancement of its own.