Suppression of the recurrent inhibitory pathway in lumbar cord segments during locus coeruleus stimulation in cats.

The present study revealed a consistent reduction of ventral root-induced recurrent inhibition of monosynaptic reflexes in both extensor (gastrocnemius-soleus) and flexor (common peroneal) motonuclei upon delivery of preconditioning stimuli to the locus coeruleus (LC) in decerebrate cats. The magnitudes of the LC-induced decrease in recurrent inhibition, functionally disinhibition, and of recurrent inhibition were significantly correlated. Direct recordings from Renshaw cells have indicated that LC conditioning stimuli cause a decrease in the number of spikes and the duration of firing in response to single antidromic (ventral root) volleys. These results suggest that the LC depression of the recurrent inhibitory pathway is attributed, in part at least, to inhibition of Renshaw cell activity.