Respiratory motor output of the sectioned medulla of the neonatal rat.

The respiratory motor output of the isolated medulla-spinal cord of the neonatal rat was recorded after three types of sections: (1) Complete midsagittal section of the medulla abolished all rhythmic neural activity recorded from the hypoglossal C4 ventral rootlets. (2) Complete transection at the level of the root of cranial nerve X decreased the burst frequency of the respiratory related motor output; transection of the medulla caudal to the obex had no effect on burst frequency recorded from the hypoglossal roots. Combining these rostral and caudal transections resulted in a transverse slice preparation 1.6-2.0 mm thick, which displayed spontaneous burst activity in the hypoglossal roots. (3) After rostral unilateral transection, a mid-coronal section produced a ventral medullary slice connected to the intact spinal cord. This 1.5 mm thick ventral medulla preparation displayed a spontaneous bursting rhythm. Both the transverse and coronal slices exhibited changes in burst frequency with changes in superfusate PCO2. These results demonstrate that respiratory rhythmogenesis and chemoreception are preserved in transverse and coronal medullary slices of the neonatal rat having substantially reduced diffusion distances.