A cross-correlation study of interactions among respiratory neurons of dorsal, ventral and retrofacial groups in cat medulla.

In anesthetized or decerebrated cats, extracellular activities of pairs of respiratory neurons located in the regions of the dorsal (DRN), ventral (VRN) and retrofacial (RFN) medullary respiratory nuclei were recorded using two separate microelectrodes. Neurons were classified as bulbospinal or laryngeal if stimulation of the spinal cord or vagus nerve elicited antidromic action potentials, or as propriobulbar if they were not antidromically activated. Of 163 pairs of single unit activities, either inspiratory (143 pairs) or expiratory (20 pairs), cross-correlation analyses indicated that 23% had short latency peaks, either broad (12%) or sharp (1%) in their cross-correlograms, 3% had short latency troughs and 74% had flat cross-correlograms. When the two neurons were located in the DRN (68 pairs) the probability of obtaining a positive cross-correlogram was high for inspiratory bulbospinal neurons, indicating shared inputs and excitatory relationships. When one neuron of the pair was located in the RFN and the other in either the DRN or VRN (95 pairs), cross-correlation analysis revealed shared inputs, excitatory and inhibitory relationships. Among expiratory neurons interactions were only inhibitory with a more frequent incidence (3/20) than between inspiratory neurons (2/143). Our results indicate that: short time scale synchrony due to shared inputs (broad peaks) are largely distributed in the respiratory neuronal network and operate over long distance (i.e. RFN, caudal medulla); excitatory coupling may exist between remote neurons but is more frequent between inspiratory bulbospinal neurons located in the DRN.