SYSTEMIC IDAZOXAN IMPAIRS PERFORMANCE IN A NON-REVERSAL SHIFT TEST - IMPLICATIONS FOR THE ROLE OF THE CENTRAL NORADRENERGIC SYSTEMS IN SELECTIVE ATTENTION

Two experiments examined the effect of pharmacological stimulation of the focus coeruleus in a non-reversal shift paradigm to test predictio ns concerning the role of the ceruleo-cortical noradrenergic system in processes of selective attention. Food-deprived rats were trained to make either visual (experiment 1) or spatial (experiment 2) discrimina tions in a parallel alley with both sets of cues being present at all times. Two groups of rats received treatments of either 2 mg/kg i.p, o f the selective alpha(2) adrenoceptor antagonist idazoxan or saline co ntrol injections before each daily block of trials. Following attainme nt of criterion, the reinforcement contingencies were altered accordin g to a non-reversal shift design, so that the alternative (i.e. either spatial or visual) set of cues now predicted reward. Rats treated wit h idazoxan were not impaired in the acquisition of either the spatial or visual discrimination task, but they were impaired in both forms of non-reversal shift. These deficits are interpreted as resulting from narrowed attention in idazoxan-treated rats, thus supporting a selecti ve attention hypothesis of locus coeruleus function.