Spatial memory deficits following stimulation of hippocampal 5-HT1B receptors in the rat

In this study we examined a possible contribution of serotonin (5-hydroxytryptamine, 5-HT) to spatial memory performance in the rat. Rats were trained to run in a radial maze in a manner that involved two kinds of memory function, i.e. working memory and reference memory. They received intrahippocampal microinjections of a 5-HT1A [8-hydroxy-2-(di-n-propylamino)tetralin or 8-OH-DPAT], or a 5-HT1B [3-(1,2,5,6-tetrahydropyrid-4-yl)pyrrolo[3,2-b]pyrid-5-one or CP-93,129] receptor agonist, and a muscarinic receptor antagonist (scopolamine). 8-OH-DPAT (5 micrograms/microliters), like injections of saline, induced no change in performance levels. In contrast, rats suffered an impairment in both reference and working memory following injection of scopolamine (10 micrograms/microliters). CP-93,129 induced a higher frequency of reference memory errors than of working memory errors at the intermediate (10 micrograms/microliters) and higher doses (16 micrograms/microliters). Thus, the stimulation of 5-HT1B receptors in the CA1 field of the dorsal hippocampus impairs the performance of rats in a spatial learning task.