Differential effects of clonidine on alpha 1- and alpha 2-adrenoceptors in footshock-induced jumping behavior.

The effects of clonidine (0.01-100 micrograms/kg i.p.) on jumping behavior in rats were investigated using different shock conditions (low shock: 40 V or high shock: 60 V). Under the low shock condition, 0.01-0.05 micrograms/kg doses of clonidine reduced jumping frequency and the effect was antagonized by yohimbine (1 micrograms/kg i.p.) or tolazoline (1 mg/kg i.p.) indicating alpha 2-adrenoceptor involvement. Under the high shock condition, 10-100 micrograms/kg doses of clonidine increased jumping frequency and the effect was antagonized by phenoxybenzamine (20 mg/kg i.p.), indicating alpha 1-adrenoceptor involvement.