ERK1/2 Phosphorylation in the Rat Supraoptic Nucleus, Dorsal Raphe Nucleus, and Locus Coeruleus Neurons Following Noxious Stimulation to the Hind Paw

Phospho-ERK1/2 (pERK1/2) fluorescence-immunohistochemistry is specifically well suited to mirror neuronal activity in the pain pathway at the cellular level. This study employed this method to visualize neuronal activity in 3 rat CNS nuclei following an acute noxious stimulation. The rat hind paw was stimulated either by heat or by a sequence of mustard oil and heat. Two min after the thermal stimulation or after the combined mustard oil and thermal stimulation, there was a significant increase in cells showing pERK1/2 immunoreactivity in the supraoptic nucleus (SON), in the dorsal raphe nucleus (DRN), and in the locus coeruleus (LC). Pretreatment with the opioid analgesic morphine or the N-methyl-D-aspartate antagonist MK-801 markedly attenuated ERK1/2 phosphorylation. These findings support the concept that the SON, the DRN, and the LC are integrated into pain processing at the hypothalamic and brain stem level. (C) 2015 S. Karger AG, Basel