The specific response of neurons and glial cells of the ventromedial reticular formation in the rat brainstem to acute pain

We studied the time course of changes in neurochemical modifications in neurons and glial cells of the ventromedial reticular formation of the rat brainstem during the development of acute inflammatory pain. The development of the pain response was associated with a twofold increase in the number of neurons that expressed NADPH diaphorase in the ventromedial reticular formation as compared to the norm. At 2 hours after the development of the pain response, we observed an increase in the number of tyrosine hydroxylase-positive elements, which was 1.5 times higher as compared to the norm. The development of acute pain was also associated with a glial response in the nucleus: the activity of mature astrocytes increased by a factor of 1.9 whereas the area of immunohistochemically stained microglia decreased by a factor of 7.6 compared to the norm. The results of our study demonstrate that development of the acute-pain response is related to the activation of both neurons and glial cells of the ventromedial nucleus of the reticular formation.