Comparison of the motor discharge to the crural and costal diaphragm in the rat

We compared the efferent innervation of the crural and costal regions of the mammalian diaphragm with regard to axonal motor discharge patterns and conduction speeds. Recordings were obtained from single crural (2 3 3) and costal (1 3 3) phrenic motoneurones. Median conduction speeds, calculated by spike triggered averaging (13.7 m s−1 crural and 11.8 m s−1 costal), and frequency histograms of conduction speed were not statistically significantly different between the two populations (p = 0.27: Mann–Whitney test and p = 0.9: Kolmogorov–Smirnov test, respectively). There was no difference in the proportions of inspiratory, post-inspiratory or non-respiratory units encountered in the crural and costal phrenic branches. Units that lacked respiratory rhythm did not express cardiac rhythm and were insensitive to ganglion blockade. In conclusion, there were few differences noted between the two motor pools and this may be related to the fact that the rat does not differentially regulate its diaphragm during swallowing and is not an emetic species.