5-HT1A receptor expression during memory formation

Rationale: It has been reported that 5-HT1A 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-HT1A receptor expression in brain areas of untrained, passive, and autoshaping trained groups of rats. Methods: Ex vivo receptor autoradiography using the ligand agonist [H-3]8-hydroxy-2-[di-n-propylamino]tetralin] (8-OH-DPAT) was used. Results: The trained group relative to untrained animals showed increases of 5-HT1A receptor expression in 14 brain areas, decrements in 7, and no changes in 12. Thus, in contrast to untrained rats, 5-HT1A 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 CAI 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-HT1A receptors in brain areas form part of neural circuits engaged in memory formation by demonstrating a high degree of specificity and memory mapping.