EFFECTS OF DORSAL RHIZOTOMY AND SELECTIVE LESION OF SEROTONERGIC AND NORADRENERGIC SYSTEMS ON 5-HT1A, 5-HT1B AND 5-HT3 RECEPTORS IN THE RATSPINAL-CORD

Autoradiographic studies were performed in combination with dorsal rhi zotomy or selective lesion of descending serotonergic or noradrenergic systems in an attempt to identify the neuronal cell types endowed wit h the serotonin 5-HT1A, 5-HT1b and 5-HT3 receptors in the rat spinal c ord. Unilateral. sectioning of seven dorsal roots (C4-T2) at the cervi cal level produced a marked decrease (similar to-75%, 10 days after th e surgery) in the binding of [I-125]iodozacopride to 5-HT3 receptors i n the superficial layers of the ipsilateral dorsal horn, further confi rming the preferential location of these receptors on primary afferent fibres. In addition, a significant decrease (similar to 20%) in the b inding of [H-3]8-OH-DPAT to 5-HT1A receptors and of [I-125]GTI to 5-HT 1B receptors was also observed in the same spinal area in rhizotomized rats, suggesting that a small proportion of these receptors are also located on primary afferent fibres. The labelling of 5-HT1B receptors was significantly decreased (-12%) in the dorsal horn at the cervical (but not the lumbar) level, and that of 5-HT3 receptors was unchanged in the whole spinal cord in rats whose descending serotonergic project ions had been destroyed by 5,7-dihydroxytryptamine. Conversely, the la belling of 5-HT1A receptors was significantly increased in the cervica l (+13%) and lumbar (+42%) dorsal horn in 5,7-dihydroxytryptamine-lesi oned rats. Similarly, [H-3]8-OH-DPAT binding to 5-HT1A receptors signi ficantly increased (+26%) in the lumbar (but not the cervical) dorsal horn in rats whose noradrenergic systems had been lesioned by DSP-4. T he labelling of 5-HT1B receptors was also increased (+ 31% at the cerv ical level; +17% at the lumbar level), whereas that of 5-HT3 receptors remained unchanged in these animals. These data indicate that complex adaptive changes in the expression of 5-HT1A and 5-HT1B receptors occ urred in the rat spinal cord following the lesion of descending monoam inergic systems.