Effects of lung inflation on the excitability of dorsal respiratory group neurons.

The effect of lung inflation on the excitability of inspiratory neurons of the dorsal respiratory group was studied in decerebrate, paralyzed, artificially ventilated cats. Variations in the antidromic latency (AL) were used as a measure of the changes in excitability. The antidromic responses of single cells were recorded extracellularly during electrical stimulation (20 Hz) of their spinal axons. Single-breath test inflations were delivered at the onset of inspiration (I) or expiration (E), and then maintained for the duration of that respiratory phase. In the absence of inflation during E, most of the inspiratory cells underwent progressive lengthening of the AL, indicating inhibition or disfacilitation. This effect was stronger in I beta than in I alpha cells but there was considerable overlap. In every cell (21 I alpha, 17 I beta), inflation during E caused a prompt AL shortening (excitation or disinhibition) that was evident in single tests. On average, I beta neurons were more strongly excited by the test inflation during E, but again there was considerable overlap. The excitation was maintained for the duration of the inflation, indicating that pulmonary stretch receptor afferents (PSR) were involved. The response to slow inflations (that preferentially excite PSR) was a progressive shortening of the AL that mirrored the increase in lung volume. The results emphasize the qualitative similarity in the responses of I alpha and I beta neurons to lung inflation and in their excitability changes during normal respiratory cycles.