Cardiorespiratory effects of intravenous N-methyl-D-aspartate challenge in anaesthetized rats.

1. Experiments were performed to determine the effects of systemic application of N-methyl-d-aspartate (NMDA) on respiratory variables and blood pressure in 22 urethane/chloralose-anaesthetized, spontaneously breathing rats. 2. Bolus injection of NMDA at a dose of 27 micro mol/kg, i.v., in neurally intact rats evoked a depression of breathing, most apparent at 30 s, comprising a decrease in tidal volume (P < 0.001) and respiratory rate (P < 0.001). The expiratory apnoea appeared in three intact rats only. 3. The respiratory effects of NMDA were independent of the vagal integrity between lungs and the nodose ganglia. Elimination of supranodose connection to the medulla reduced the prolongation of the expiratory time (P < 0.01). 4. N-Methyl-d-aspartate induced an initial rise in blood pressure followed by hypotension in rats treated by infra- and supranodose vagotomy. 5. It is concluded that the respiratory response to systemic NMDA challenge occurs beyond lung vagi and indicates that neurons of the nodose ganglia contribute to NMDA inhibition of the expiratory time.