Summary: | The interplay of neural discharge patterns involved in “respiration”, “circulation”, “opening movements in the
mandible”, and “locomotion” was investigated electrophysiologically in a decerebrate and arterially perfused
in situ rat preparation. Sympathetic tone increased with increases in perfusion flow rate. All nerve discharges
became clearly organized into discharge episodes of increasing frequency and duration punctuated by quiescent
periods as the perfusion flow rate increased at 26ºC. The modulated sympathetic tone at 10× total blood volume/
min activated the forelimb pattern generator and spontaneously generated fictive forelimb movement during
discharge episodes. The coupling rhythm of respiration and locomotion during motion occurred at frequency
ratios ranges of 1:2 and 1:3. Small increases in systemic pressure were always generated after the initiation of
motion. Opening movements in the mandible, occurring during the inspiratory phase at all tested flow rates,
were generated in both the inspiratory and expiratory phases during motion. Although the central mechanism
for the entrainment of respiratory and locomotor rhythms has not been identified, a spinal-feedback mechanism
generating fictive locomotion in the upper spinal cord contributed to generating the opening movement in
the mandible in the expiratory phase during motion. The existence of this mechanism implies that there is a
reciprocal functional interaction between the brainstem and the spinal cord, whereby the intake and output
of air by the lungs is efficiently improved during movement by both nasal and mouth breathing. These results
suggest that this reciprocal functional interaction plays an important role in increasing oxygenated blood flow
during locomotion.
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