Activation of Neurons in the Rat Medulla Following a Gag Reflex Stimulus

Abstract

Despite the fact that a number of individuals present with a hypersensitive gag reflex, research in this area has been limited to clinical applications. An animal model that describes the neurologic underpinnings of the gag reflex has not been reported. Thus, the objective of the current study was to localize activated neurons in the rat medulla and to investigate their neurochemistry following mechanostimulation to the posterior pharyngeal wall eliciting a gag reflex response. Activated neurons, determined using c-fos immunohistochemistry, were observed in subnuclei of the nucleus tractus solitarius (NTS) and motor regions such as dorsal motor vagus, hypoglossal, and nucleus ambiguus. The lateral and dorsal paragigantocellular nuclei and the medial rostral ventrolateral nucleus involved in bitter taste processing, also showed robust activation. Tyrosine hydroxylase and/or choline acetyltransferase immunoreactivity was localized in many activated neurons. The results of the present study provide the first documentation of activated neurons and preliminary neurochemistry in brainstem nuclei that are unique to mechanostimulation to the posterior pharyngeal wall. Our results support postulated medullary structures involved with the gag reflex and propose new regions to be added to the circuitry model. Further, our results reveal an activation pattern within the NTS unique to the gag reflex.