A role for the ventral surface of the medulla in regulation of nasal resistance.

Nasal resistance is known to be affected by changes in nasal blood volume and hence to depend on sympathetic discharge to nasal blood vessels. Structures located superficially near the ventrolateral surface of the medulla significantly affect respiratory and sympathetic activity and the tone of the trachea. To assess the importance of these structures on nasal patency, we measured transnasal pressure at a constant flow and examined the change in pressure produced by topically applied N-methyl-D-aspartic acid (NMDA). Experiments were performed in chloralose-anesthetized, paralyzed, and artificially ventilated cats. NMDA administered on the intermediate area of the ventral surface of the medulla decreased transnasal pressure and increased phrenic nerve activity. The response to NMDA could be diminished or abolished by application to the ventral medullary surface of the NMDA antagonist 2-amino-5-phosphonovalerate (2-APV) or the local anesthetic lidocaine. Carotid sinus denervation and posthypothalamic decerebration did not alter the nasal and phrenic nerve responses to NMDA; however, cervical sympathetic denervation decreased these responses, both in intact and in bilaterally adrenalectomized animals. Therefore, activation of NMDA receptors on structures near the ventral surface of the medulla increases tone in the nasal vasculature and leads to a response pattern that includes changes in not only phrenic nerve activity and blood pressure but also nasal patency.