Autoradiographic mapping of 5-HT₁, 5-HT_1A, 5-HT_1B and 5-HT₂ receptors in the rat spinal cord

Abstract

The distribution of 5-HT₁, 5-HT_1A, 5-HT_1B and 5-HT₂ receptors in the rat spinal cord was investigated with quantitative autoradiography. Receptors were labeled respectively with [³H]serotonin (5-[³H]HT],8-hydroxy-2-[N-dipropylamino-³H]tetralin (8-OH-[³H]DPAT), [¹²⁵I]iodocyanopindolol and [³H]ketanserin. It is shown that 5-HT₁, 5-HT_1A and 5-HT_1B receptors are distributed within the spinal cord according to a rostro-caudal gradient. Both 5-HT₁ and 5-HT_1A receptors are mainly present in the dorsal horn and 5-HT_1B is present throughout the spinal cord, exhibiting high densities in the caudal-most part of the dorsal in lamina X and in the sacral parasympathetic area. On the other hand, 5-HT₂ receptors are shown mostly in the thoracic sympathetic area and in the thoracic ventral horn; the dorsal horn exhibits few 5-HT₂ receptors. The differential involvement of 5-Ht through different receptors in nociception, autonomous nervous system control and motility are discussed.