Effect of cocaine on afterdischarge threshold in previously kindled rats

Previous experiments have yielded conflicting reports on the effect of cocaine on the after discharge (AD) threshold for electrical stimulation. The present study was designed to determine if differences in the type of stimulation used could account for these discrepancies. Male Long-Evans rats which had been previously kindled by stimulation of the olfactory bulb were used to determine the AD threshold of the olfactory bulb following the intraperitoneal injection of saline or 20 mg/kg cocaine hydrochloride. AD's were elicited by trains of square-wave pulses which varied in frequency and train duration. Cocaine significantly increase the amount of current required to produce AD's using stimulus trains with frequencies of 30-100 pulses/sec, while evidence of a decrease in AD threshold by cocaine was found at a frequency of 20 pulses/sec. The results suggest that cocaine has opposite effects on AD threshold at high and low frequencies of stimulation.