INCREASE OF 5-HT7 (SEROTONIN-7) AND 5-HT1A (SEROTONIN-1A) RECEPTOR MESSENGER-RNA EXPRESSION IN RAT HIPPOCAMPUS AFTER ADRENALECTOMY

The brain 5-HT (serotonin) system and circulating corticosteroids are in close interaction and both are implicated in the pathogenesis of af fective disorders. The 5-HT1A receptor is thought to play a major role in this relationship. However, the recently cloned 5-HT7 receptor may also be involved, given its pharmacological similarities to the 5-HT1 A receptor and its high expression in corticolimbic structures, Using in situ hybridization histochemistry, we have investigated 5-HT7 and 5 -HT1A receptor mRNA expression in selected areas of the rat brain 7 da ys post-adrenalectomy, 5-HT7 receptor mRNA was increased in CAI and CA 3b after adrenalectomy, with no alterations in other hippocampal subfi elds or in retrosplenial cortex. Adrenalectomy was associated with a m arked increase of 5-HT1A receptor mRNA in dentate gyrus, CA3 and CA2, but not in CA1, nor in the raphe. These data indicate that circulating adrenal steroids have a inhibitory role on the expression of hippocam pal 5-HT7 receptors as well as 5-HT1A receptors, but the effect upon t he two transcripts occurs in different subfields. The 5-HT7 receptor i s an additional candidate for mediating the interactions between 5-HT and corticosteroids within the hippocampus.