CORTICOTROPIN-RELEASING FACTOR ENHANCES LOCOMOTION AND MEDULLARY NEURONAL FIRING IN AN AMPHIBIAN

Corticotropin-releasing factor (CRF) administration has been shown to act centrally to enhance locomotion in rats and amphibians. In the pre sent study we used an amphibian, the roughskin newt (Taricha granulosa ), to characterize changes in medullary neuronal activity associated w ith CRF-induced walking and swimming in animals chronically implanted with fine-wire microelectrodes. Neuronal activity was recorded from th e raphe and adjacent reticular region of the rostral medulla. Under ba seline conditions most of the recorded neurons showed low to moderate amounts of neuronal activity during periods of immobility and pronounc ed increases in firing that were time-locked with episodes of walking. These neurons sometimes showed further increases in discharge during swimming. Injections of CRF but not saline into the lateral ventricle produced a rapidly appearing increase in walking and pronounced change s (mostly increases) in firing rates of the medullary neurons. CRF pro duced diverse changes in patterns of firing in different neurons, but for these neurons as a group, the effects of CRF showed a close tempor al association with the onset and expression of the peptide's effect o n locomotion. In neurons that were active exclusively during movement prior to CRF treatment, the post-CRF increase in firing was evident du ring episodes of walking; in other neurons that also were spontaneousl y active during immobility prior to CRF infusion, post-CRF activity ch anges were evident during immobility as well as during episodes of loc omotion. Thus, a principal effect of CRF was to potentiate the level o f neuronal firing in a population of medullary neurons with locomotor- related properties. Due to the route of administration CRF may have ac ted on multiple central nervous system sites to enhance locomotion, bu t the results are consistent with neurophysiological effects involving medullary locomotion-regulating neurons. (C) 1996 Academic Press, Inc .