Effects of pre- and postnatal exposure to 5-methoxytryptamine and early handling on an object-place association learning task in adolescent rat offspring

A reduction in 5-HT1A receptor response enhances learning and memory performance in rats. Pre- and postnatal treatment with 5-methoxytryptamine (5MT), a non-selective serotonergic agonist, and early handling, reduce the number of 5-HT1A receptors in neonatal and pre-pubertal rat progeny. The aim of this study was to investigate in adolescent male rats the consequences of pre- and postnatal treatment with 5MT and its interaction with early handling on an object-place association learning task, the "Can test", a motivated, non-aversive, spatial/object discrimination task. Results show that a single daily injection of 5MT from gestational days 12 to 21 (1 mg/kg s.c.) and from postnatal days 2 to 18 to pups (0.5 mg/kg s.c.), increases the level of activity and the number of correct responses, and decreases the number of reference memory errors in the progeny as adolescent, compared to vehicle-treated rats. Similar effects are observed following a daily, brief, maternal separation of the pups from postnatal days 2 until 21. Furthermore, when 5MT-treated rats underwent to early handling procedure, the effects induced by 5MT increased handling-induced facilitation of the object-place association. These results suggest that pre- and postnatal treatment with 5MT enhances learning in the "Can test", probably due to a reduction in 5-HT1A receptors in the hippocampus. Whether the potentiation exerted by pre- and postnatal 5MT on early handling effects may be related to a further damping of 5-HT1A receptor response is not yet assessed; however, our data demonstrate that this association is able to induce long-term facilitative effects on spatial learning performance in a non-aversive spatial/object discrimination task in the adolescent rat offspring. (C) 2007 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.