The different changes of phrenic nerve activity and frequency elicited by microinjection of L-glutamic acid into ventrolateral nucleus of the tractus solitarius in cats.

There is only limited information of the neurotransmitters in central respiratory control. L-glutamic acid has been proposed as the primary neurotransmitter in the nucleus of the tractus solitarius (NTS) in cats. To test whether there is a respiratory effect of glutamic acid in the respiratory center or not, we microinjected L-glutamic acid (1 M, 0.1 microliter) via 1 microliter Hamilton microsyringe into the ventrolateral nucleus of NTS, namely dorsal respiratory group (DRG) over two-second intervals with continuous monitoring of phrenic nerve activity (PNA), frequency (f), end tidal CO2, blood pressure and heart rate. Glutamate induced various respiratory changes including: increase in PNA and f decrease in PNA and f [corrected] increase in PNA but decrease in f and decrease in PNA but increase in f. In addition to regular changes of PNA or f elicited by glutamate microinjection were found. Other patterns of irregular rhythmic changes such as absence of PNA, continuous phrenic nerve discharge and irregular phrenic nerve discharge with reflex apnea, apneusis and irregular respiration respectively were also observed. Glutamic acid appears to significantly modulate respiratory drive in DRG. We suggested that L-glutamic acid may be a neurotransmitter in the respiratory center and be involved in central respiratory control.