TACTILE DISCRIMINATION PERFORMANCE DEFICITS FOLLOWING UNILATERAL MICRO-INJECTIONS OF CATECHOLAMINERGIC BLOCKERS IN THE RAT

Unilateral microinjections of aqueous solutions of acetylcholine, scopolamine, serotonin, methysergide, dopamine, haloperidol, or norepinephrine into the lateral hypothalamic region had no measurable effects on neurological tests or on an appetitive discrimination in which the rats were trained to turn toward the side opposite to a touch to the flank. Unilateral injections of the adrenergic blockers phentolamine or propranolol produced pronounced neurological asymmetries and selectively disrupted only those discrimination trials in which the touch was presented ipsilateral and the required response was a turn contralateral to the injection. The unimpaired performance seen on the remaining trials when the stimulus was contralateral to the injection suggested that the adrenergic blockers disrupted response output processes rather than sensory processes. In a second experiment using different rats and a slightly different task, the dopaminergic blocker haloperidol when injected into the caudate produced a deficit closely similar to that produced by phentolamine in the lateral hypothalamus. © 1979.