Conditioned taste aversion induced in rats by intracerebral or systemic administration of monoamine oxidase inhibitors

Conditioned taste aversion (CTA) elicited by systemic or intracerebral application of the monoamine oxidase inhibitors clorgyline (C), pargyline (P) or deprenyl (D) was studied in 402 rats. Water-deprived animals were allowed 15 min access to 0.1% sodium saccharin (CS) followed 10 min later by IP or by intracerebral injection of the drug. In the latter case, the animals were anesthetized 5 min after saccharin drinking with pentobarbital and the drug was stereotaxically injected (1 l/min, 1–2 l) into the target structure. CTA was assessed in a two-choice retention test performed 2 days later. A geometric progression of three to six dosages applied to groups of rats (n=10) was employed to establish the effective doses of the drugs which were 4, 20 and 32 mg/kg with IP and 2.5, 10 and 80 g per rat with intracerebral (n. raphé magnus) injections of C, P, and D, respectively. The ratios of intracerebral to systemic dosages eliciting comparable CTA were 1:300 for C, 1:800 for P and 1:100 for D. Injections of 2.5 g C and 10 g P into the mesencephalic reticular formation, medial hypothalamus and cerebral cortex were ineffective, as were injections of 10 g P into the nucleus of the solitary tract and cerebellum. The results indicate that CTA is elicited more efficiently by inhibition of monoamine oxidase A (selectively inhibited by C) than of monoamine oxidase B (selectively inhibited by D).