5-HT1A receptor expression during memory formation

Rationale It has been reported that 5-HT_1A receptors modulate learning and memory and diverse pharmacological and genetic evidence supports this notion. Nevertheless, there are few works about expression of these receptors during memory formation. Objective We aimed to determine 5-HT_1A receptor expression in brain areas of untrained, passive, and autoshaping trained groups of rats. Methods Ex vivo receptor autoradiography using the ligand agonist [³H]8-hydroxy-2-[di-n-propylamino]tetralin] (8-OH-DPAT) was used. Results The trained group relative to untrained animals showed increases of 5-HT_1A receptor expression in 14 brain areas, decrements in 7, and no changes in 12. Thus, in contrast to untrained rats, 5-HT_1A receptor expression of autoshaping trained rats was augmented in the tubercule olfactory, septal nucleus, nucleus accumbens, caudate putamen, globus pallidus, striate, and parietal (1 and 2), temporal cortex (1 and 3), granular retrosplenial cortex (1), amygdala, and median and dorsal raphe nuclei. In contrast, in the latter group, receptors were decreased in the CA1 area, hypothalamus dorsal, frontal cortex (1 and 3), occipital cortex, cingulate cortex (1 and 2), and cuneiform nucleus. There were significant differences between passive vs trained groups, but not regarding untrained rats, in the lateral olfactory tract, dentate gyrus, CA3 area, ventromedial hypothalamic, lateral hypothalamus, preoptic medial, frontal cortex (2), granular retrosplenial cortex (2), entorhinal cortex (1 and 2), piriform cortex, and substantia nigra. Conclusions These data suggest that upregulated, downregulated, and “silence” of 5-HT_1A receptors in brain areas form part of neural circuits engaged in memory formation by demonstrating a high degree of specificity and memory mapping.