Trigeminal mediation of the diving response in the muskrat

Stimulation of the nasal cavity elicits powerful cardiorespiratory responses similar to the diving response. In the present study, bradycardia and apnea were elicited in muskrats by stimulation of the nasal cavity with ammonia vapors. These responses could be blocked by injections of 2% lidocaine made bilaterally into the medullary dorsal horns of the trigeminal sensory complex. However, the bradycardia due to activation of the baroreceptor reflex with intravenous phenylephrine was retained. These data implicate trigeminal neurons in the medullary dorsal horn as modulators of autonomic activity, especially in the cardiorespiratory adjustments after nasal stimulation.