The use of conditioned suppression to evaluate the nature of neuroleptic-induced avoidance deficits

Three groups (N = 8) of rats received five 10-trial sessions of one-way avoidance training in which each trial was initiated by a 10-sec tone stimulus and terminated either by a shuttle response during the tone (avoidance) or by a response during the electric shock (escape). Rats in groups treated with pimozide (0.5 or 1.0 mg/kg i.p.) failed to acquire to avoidance response although they escaped readily when shock was presented, whereas control rats consistently avoided the shock. The same rats then received several sessions of food-reinforced lever-pressing in a different apparatus; no drugs were given during these sessions. When responding had stabilized, the tone that had signalled shock in the avoidance sessions was presented for a 1-min period. A significant decrease in responding during the tone was observed in all groups when compared to unshocked controls, demonstrating that the pimozide-treated rats, although failing to acquire the avoidance response in the shuttle box, had learned the association between the tone and shock. The results suggested that the neuroleptic-treated animals failed to avoid because of a deficit in the ability to initiate responses rather than a deficit in associative learning.