OSCILLATORY-SENSITIZATION MODEL OF REPEATED DRUG EXPOSURE - COCAINE EFFECTS ON SHOCK-INDUCED HYPOALGESIA

1. The authors have recently proposed that the sensitization produced by repeated exposure to drugs or stress may give way to an alternating pattern of increases and decreases in the response to each subsequent exposure (i.e., oscillate), as the limits of the physiological system are approached. 2. Evidence for oscillation has been obtained for 6 d rug/non-drug stressors and 9 neurochemical or endocrine endpoints. Thi s paper extends the model to a behavioral outcome. 3. In the first exp eriment, rats were given 0,1,2 or 3 pretreatments with cocaine hydroch loride (COC; 12 mg/kg IF), separated by 1-week intervals, and then wer e tested for footshock-induced hypoalgesia (5-sec, 2-mA), as measured by withdrawal latencies from a hot-plate. 4. The second experiment rep licated the first and extended the pretreatment sequence to 5 COC inje ctions. 5. In both experiments, shock significantly increased latencie s over the no-shock controls. COC enhanced shock-induced hypoalgesia a nd this sensitization reached its maximum after 2 COC pretreatments. T hereafter, oscillation developed such that the sensitization was atten uated by 3 as compared to 2 COC injections, enhanced by 4 injections, and reattenuated after 5 COC pretreatments. 6. These data complement o ther findings by demonstrating that the oscillation model extends to a stress-induced behavioral outcome.