Plasma corticosterone and brain catecholamines in stress: effect of psychotropic drugs

In nonstressed rats, subcutaneous administration of haloperidol (HAL) and large doses of diazepam (DZ) increased plasma corticosterone (CS). Hypothalamic norepinephrine (NE) was lowered significantly by desmethylimipramine (DMI), HAL and, to a lesser extent, by DZ and phenobarbital (PHB). In rats pretreated with either DZ, DMI, HAL or PHB the restraint-induced rise of CS was diminished, DZ being most potent. CPZ had a variable effect, slightly increasing or decreasing the CS response. Pretreatment (16 hr) with pargyline (PA) did not affect the CS rise to stress. The reduction of hypothalamic NE evoked by restraint was attenuated by DZ, and to a lesser extent, by PHB and HAL. Restraint of PA-treated rats did not lower the PA-elevated hypothalamic NE. The stress-induced increase in hypothalamic dopamine was prevented by CPZ and, partially, by PHB. It is emphasized that the net plasma CS and brain catecholamine changes in response to stress are dependent on the drug-induced neuroendocrine feedback state prevalent immediately before commencement of the stress procedure.