Neuroendocrine and behavioral response to amphetamine challenge after exposure to an organophosphorus pesticide

Objectives Exposure to various stressors is known to result in sensitization to psychostimulants, a state related to the psychostimulant dependence and addiction. It has been shown in some studies that the rise in corticosterone (CORT) concentration is indispensable for both the induction and the expression of behavioral sensitization. Therefore, it might be suspected that behavioral hyposensitivity to amphetamine (AMPH) is somehow related to a reduced CORT response to the psychostimulant subsequent to the chlorphenvinphos (CVP) intoxication. Materials and Methods The male adult Wistar rats received single i.p. injections of CVP at the doses 0.5, 1.0 or 3.0 mg/kg b.w., or pure corn oil. CORT concentration was determined in samples of blood drawn from the tail vein before and then 30, 60, 180 min and 24 h after injection. The other rats were divided into two groups and tested, three weeks after the CVP injection for the effect of AMPH (0.5 mg/kg b.w. i.p. ) on the serum CORT concentration. In addition, behavioral sensitivity to AMPH was assessed by measuring locomotor activity of the animals in an open-field. Results 1) The stressor property of CVP was confirmed. The injection resulted in up to tenfold increase in the serum CORT concentration. The magnitude and duration of this response were dose-related. 2) Three weeks after the CVP exposure, the CORT response to AMPH was significantly increased. 3) The behavioral response to the psychostimulant, i.e. augmented locomotion, was significantly reduced compared to the control. Conclusions The results confirm that CVP exposure causes behavioral hyposensitivity to AMPH. This effect, however, could not be ascribed to a diminished CORT response.