Decrementing expiratory neurons of the Bötzinger complex. I. Response to lung inflation and axonal projection.

In Nembutal-anesthetized, immobilized, and artificially ventilated cats with intact vagus nerves, extracellularly recorded activities of expiratory (E) neurons whose firing patterns were of decrementing, or the early expiration type (E-DEC neurons) were recorded in the vicinity of the Bötzinger complex (BOT). A total of 32 E-DEC neurons which were not vagal motoneurons was studied by determining 1) where they were distributed, 2) how their firing was modulated by lung inflation, and 3) if they projected their axons to the respiratory area of the brain stem. E-DEC neurons were located ventromedially to the retrofacial nucleus and were intermingled with E neurons of the augmenting type (E-AUG neurons), which were abundant and representative of neurons in the BOT. Firing of 25 E-DEC neurons was facilitated by lung inflation, indicating the existence of excitatory input from stretch receptors of the lungs, although the firing of 7 other neurons was not affected. On the other hand, firing of surrounding E-AUG neurons was suppressed by lung inflation. The E-DEC neurons fired in the E phase during a brief stop of the ventilator, indicating that they received central respiratory rhythm. However, they almost never fired during the inspiratory (I) phase even when the lungs were strongly inflated, indicating the existence of strong central inhibition during the I phase. Eight E-DEC neurons were tested for antidromic activation from the contralateral brain stem and the spinal cord by microstimulation.(ABSTRACT TRUNCATED AT 250 WORDS)