Regional variability in changes in 5-HT2A receptor mRNA levels in rat brain following irreversible inactivation with EEDQ ☆

Abstract In this study, the relationship between the expression of 5-HT 2A receptors and level of 5-HT 2A receptor mRNA in discrete regions of rat brain was examined by inactivating 5-HT 2A receptors with the alkylating agent N -ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ; 10 mg/kg, i.p.) and measuring the time course of receptor recovery and changes in mRNA levels. In untreated controls, the distribution and levels of 5-HT 2A receptors labeled with [ 3 H]ketanserin and receptor mRNA labeled with a 230-base 33 P-labeled riboprobe were found to be highly correlated in most sub-regions of the cortex, the caudate-putamen and the claustrum but not in the piriform cortex or the hippocampus. Administration of EEDQ produced 90–99% inactivation of 5-HT 2A receptors and the rate of receptor recovery was uniform in most regions studied. 5-HT 2A receptors in most regions reached control levels by day 14, the lone exception being the caudate-putamen where receptors reached only 56% of control by day 14. Following inactivation of receptors with EEDQ there was a transient increase in levels of 5-HT 2A receptor mRNA in several regions. Although rates of receptor recovery were uniform, four distinct patterns of mRNA response were observed: (1) early elevation followed by late elevation, (2) early elevation only, (3) late elevation only, and (4) no detectable change. The absence of a direct relationship between changes in 5-HT 2A receptor mRNA and 5-HT 2A receptor recovery in this model system suggests that transcriptional regulation is not the mechanism controlling the recovery of these receptors after irreversible inactivation. This study also lends support to the idea that alternative mechanisms may play a role in 5-HT 2A receptor regulation after other pharmacological and physiological manipulations. The regional variability in 5-HT 2A mRNA regulation reported here highlights the importance of using techniques with a high level of anatomical resolution to study changes in 5-HT 2A receptor mRNA levels.