Facilitatory effect of ritanserin is mediated by dopamine D-1 receptors onolfactory learning in young rats

The olfactory bulb is critically involved in early olfactory learning. In t his study, we examined the effect of intrabulbar intrusion of ritanserin, a 5-hydroxytryptamine(2) (5-HT2) receptor antagonist on a one-trial aversive olfactory learning in young rats. Ritanserin, a 5-HT2 receptor antagonist, was continuously infused into the olfactory bulb of postnatal day-11 (PND 11) rat pups during a 30-min training session of pairing citral odor and fo ot shock. On the following day, the time spent in the part of the apparatus where the odor was present was measured as an index of odor aversion. Cons istent with a previous study on olfactory preference learning, 1 nM ritanse rin, but not 10 nM, blocked the olfactory aversive learning. We further exa mined the ability of 10 nM ritanserin to induce olfactory learning in the a bsence of the unconditioned stimulus foot shock. Pups that received intrabu lbar infusion of 10 nM ritanserin in the presence of citral odor developed art aversion to the odor without foot shock. Since ritanserin has been show n to have an affinity far dopamine receptors, we examined the effect of dop amine antagonists on the ritanserin-induced aversive olfactory learning. Co -infusion of the dopamine D-1 receptor antagonist (+/-)-SKF-83566 with rita nserin dose-dependently prevented induced learning. In contrast, the D-2 re ceptor antagonist spiperone was without effect. These results extend the pr evious finding on the role of bulbar 5-HT2 receptors in early olfactory lea rning and suggest that high concentration of ritanserin facilitatesaversive olfactory learning through D-1 receptors in the olfactory bulb. (C) 2000 J ohn Wiley & Sons, Inc. Dev Psychobiol 37: 246-252, 2000.