NEUROCHEMICAL MEDIATORS OF ANXIETY HAVE INCONSISTENT EFFECTS ON HYPOTHALAMIC SELF-STIMULATION IN RATS

We studied effects of anxiogenic and anxiolytic compounds on the elect ric self-stimulation of the medial forebrain bundle in male rats to fi nd out if there is a link between reward and anxiety-related behaviour s. The cholecystokinin agonist, caerulein (25-100 mu g/kg) and the 5-H T agonist 1-(3-chlorophenyl)piperazine (0.2-1 mg/kg) dose-dependently inhibited the electric self-stimulation. The 5-HT2A antagonist, ketans erin, at 2.5 mg/kg, increased the self-stimulation at high currents bu t not at threshold current. The 5-HT3 antagonist ondansetron (10 and 1 00 mu g/kg). The alpha(1)-adrenergic antagonist, prazosin (0.125 and 0 .5 mg/kg), the beta-adrenergic antagonist, propranolol (5 and 10 mg/kg ) and the alpha(2)-adrenoreceptor antagonist, atipamezole (4 mg/kg), d id not affect the self-stimulation Nor did the benzodiazepine agonist, diazepam (5-15 mg/kg), a benzodiazepine receptor antagonist flumazeni l (at 10 and 25 mg/kg) or the inverse agonist of benzodiazepine recept ors, N-methyl-beta-carboline-3-carboxamide (10 and 20 mg/kg), cause an y substantial changes of the self-stimulation. We conclude that only t wo anxiolytic drugs (caerulein and 1-(3-chlorophenyl)piperazine) suppr ess the electric self-stimulation. These findings indicate that anxiog enicity as such is not able to weaken the hypothalamic electric self-s timulation. Anxiety and reward are apparently mediated through separat e neural pathways.