Effect of hypothermia on respiratory rhythm generation in hamster brainstem-spinal cord preparations.

This study examined the effect of hypothermia on respiratory neural output from brainstem-spinal cord preparations of a cold tolerant rodent, the Syrian hamster. Brainstem-spinal cords from neonatal hamsters (0-6 days) were placed in a recording dish and respiratory-like neural activity was recorded from roots of the first cervical nerve. The preparations were cooled and warmed in a continuous or stepwise fashion. Inputs from the pons completely inhibited neural activity under steady state conditions. With the pons removed, fictive breathing was robust. Cooling caused respiratory arrest, followed by spontaneous resumption of activity on re-warming. Preparations from older hamsters (4-6 days old) were more cold tolerant than younger preparations (0-3 days old). Motor discharge was episodic during continuous cooling, and seizure-like discharge was observed during continuous warming. These phenomena were not observed with stepwise temperature changes suggesting that transient temperature effects on membrane properties may be involved. These preparations were not as cold tolerant as hamster pups in vivo but they retained the ability to autoresuscitate at all ages studied.