Attenuation of the context effect and lack of unconditioned stimulus-preexposure effect in taste-aversion learning following treatment with DSP4, the selective noradrenaline neurotoxin

Abstract

The effect of varying the exteroceptive context and the unconditioned stimulus-preexposure effect were studied 2 weeks after N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride (DSP4) administration in three experiments. In Experiment 1, control and DSP4-treated rats were given paired presentations of saccharin in the presence of a noise-producing bottle and lithium chloride. During extinction trials, half the control and half the DSP4 rats received saccharin in “noisy” bottles while the other half received saccharin in “silent” bottles. Saccharin preference tests were given to all groups in the presence of the “noisy” bottles. Reinstatement of the conditioning context (“noisy” bottle) resulted in a stronger aversion in the case where a different context (“silent” bottle) was present during extinction, the “context effect.” This effect was attenuated in the DSP4 condition. Experiment 2 indicated that rats treated with desipramine, a selective noradrenaline (NA) uptake inhibitor, prior to DSP4, the selective NA neurotoxin, displayed, a greater “context effect” than DSP4 treated rats. In Experiment 3, lithium chloride was administered with or without “noisy” bottle presentation in a first conditioning trial, and the saccharin plus “noisy” bottle compound was paired with lithium chloride on two subsequent conditioning trials. The absence of the “noisy” bottle stimulus during the initial conditioning phase resulted in a much attenuated saccharin aversion following subsequent compound conditioning in the control condition; no such attenuation was obtained in the DSP4 condition. Postdecapitation reflex and dopamine-β-hydroxylase and noradrenaline uptake data confirm the NA depletions in DSP4, but not in control rats nor in rats treated with desipramine 30 min before DSP4 (DMI plus DSP4). A role for noradrenaline in attentional processes seems to be supported by these results.