Noradrenaline and the context-dependent extinction effect.

Three experiments were performed to examine the effects of noradrenaline (NA) depletion upon the context-dependent extinction effects in conditioned taste-aversion learning. Three different methods were used to deplete NA: lesions of the dorsal noradrenergic bundle (DNAB) with 6-hydroxydopamine (6-OHDA), lesions induced by neonatal treatment with 6-OHDA and lesions induced by systemic administration with the NA neurotoxin, N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4). In each experiment, novel saccharin was presented in novel noisy bottle followed by lithium chloride. Later, during the extinction phase, half the control and half the NA depleted rats received saccharin in noisy bottles while the other half received saccharin in silent bottles. In the control condition, the rats that received saccharin in the noisy bottles (same context as conditioning) showed considerably more aversion than those that received saccharin in the silent bottles (different context to conditioning); NA depletion attenuated this effect. Reinstatement of the conditioning context (noisy bottle) resulted in a stronger aversion in the case where the different context (silent bottle) was present during extinction; this effect was attenuated in the NA depletion condition. These findings maintain a role for noradrenaline in compound conditioning tasks.