Regional expression of 5-HT1B receptor mRNA in the human brain

The regional mRNA expression pattern of 5-HT1B receptors has been extensively characterized in the rodent and guinea pig brain, but a detailed mapping of the 5-HT1B receptor mRNA expression in the human brain has not previously been performed. In the present study, the mRNA expression of 5-HT1B receptors was analyzed using in situ hybridization histochemistry and whole hemisphere sections of the human postmortem brain. The mRNA expression was compared with the autoradio-graphic distribution of 5-HT1B receptors. High levels of mRNA expression were found in the striatum, cortex, lateral geniculate nucleus, and raphe nuclei. The expression was higher in ventral than in dorsal striatal regions and was absent from the substantia nigra and pallidum, where high levels of 5-HT1B receptors were found. A layer-specific expression pattern was observed in cortical regions. The results extend previous knowledge about the localization of the 5-HT1B receptor in the human brain. This study provides evidence of a mismatch of the regional expression of 5-HT1B receptor mRNA and the 5-HT1B receptor distribution in human brain, similar to what has been demonstrated in other species. This is in line with the localization of this receptor subtype in nerve terminals. The results give support to species differences in the cortical mRNA expression pattern of this receptor subtype.