Descending Inhibition of Slow Spinal Reflex in an in Vitro Preparation of the Newborn Rat and Its Possible Involvement in Pain Control

An isolated brainstem-spinal cord preparation of the newborn rat is described in which brainstem stimulation inhibits a spinal reflex of slow time course possibly associated with nociception. The inhibition-producing area is localized in the rostral medulla and caudal pons. Perfusion of the preparation with phentolamine or strychnine antagonizes the inhibition, suggesting the involvement of alpha-adrenergic and glycine-mediated inhibitory mechanisms. Results are discussed in relation to descending inhibition of nociception.