Short-latency interactions among dorsomedial medullary inspiratory neurons in the cat

Pairs of inspiratory neurons were recorded extracellularly with microelectrodes whose tips were close to one another (100 to 300 microns) in the ventrolateral region of the nucleus tractus solitarius. Each neuron was identified as an R beta or an R alpha type using lung volume manipulations. Those neuron pairs whose cross-correlation histograms indicated a positive interaction were tested for interneuronal connections by antidromic activation of one neuron of the pair combined with further cross-correlation. Three pairs of R alpha/R alpha, three pairs of R alpha/R beta, and three pairs of R beta/R alpha neurons were tested in this manner. One pair of R alpha/R alpha neurons and one pair of R beta/R beta neurons showed evidence of interneuronal interaction. We concluded that although the short-term synchronization in the firing patterns of these neurons was due mostly to common excitation of both neurons, interneuronal interactions were also responsible.