Fos expression in tyrosine hydroxylase-containing neurons in rat brainstem after visceral noxious stimulation: an immunohistochemical study.

Abstract

To prove that neurons in the different structures of the brainstem that express tyrosine hydroxylase (TH) are involved in the transmission and modulation of visceral or somatic nociceptive information in rat. Immunohistochemical double-staining method was used to co-localize TH and Fos expression in neurons of the rat brainstem in visceral or subcutaneous noxious stimulation models. Neurons co-expressing TH/Fos were observed in lateral reticular nucleus (LRT), rostroventrolateral reticular nucleus (RVL), solitary tract nucleus (SOL), locus coeruleus (LC), A5, A7 neuronal groups and ventrolateral subdivision of the periaqueductal gray (vlPAG) in both models. But the proportion and number of the double-labeled neurons responding to the two noxious stimuli were significantly different in the LRT, RVL and LC nuclei. The proportion and number of the TH/Fos double-labeled neurons in the visceral pain model were smaller than that in the subcutaneous pain model. However, in the case of SOL, they were similar in the two models. Differences of Fos expression in TH immunoreactive neurons in animals after visceral and somatic noxious stimulation indicate that the mechanisms of the transmission and modulation of visceral nociceptive information in the brainstem may be different from that of somatic nociceptive information.