Expression of 5-HT 1A receptor mRNA in rat lumbar spinal dorsal horn neurons after peripheral inflammation

Abstract

The present study observed the expression of the 5-hydroxytryptamine (5-HT) 1A receptor mRNA in the lumbar spinal dorsal horn neurons following carrageenan inflammation using in situ hybridization (ISH). We also studied the co-localization of 5-HT 1A receptor mRNA and γ-amino butyric acid (GABA) or enkephalin (ENK) immunoreactivities using a combined fluorescent ISH and immunofluorescent histochemical double-staining technique. The finding of this study demonstrated that 5-HT 1A receptor mRNA was widely distributed in the spinal dorsal horn with the highest density in laminae III–VI. Following carrageenan-induced inflammation, the 5-HT 1A receptor mRNA expression in all layers of ipsilateral dorsal horn was significantly enhanced, and the peak occurred after 8 h. Furthermore, the number of 5-HT 1A receptor mRNA and GABA or ENK immunoreactive double-labeled cells was also markedly increased 8 h after carrageenan injection. These findings suggested that following peripheral inflammation, the synthesis of 5-HT 1A receptor was increased in the lumbar spinal dorsal horn neurons, especially in spinal GABA and ENK neurons.