Inhibition of medullary reticulospinal neurons by excitation of the dorsolateral parts of the pons which block movement and muscle tone in rats.

Analysis of the response of 128 reticulospinal neurons in the magnocellular and ventral reticular nuclei showed that 36.7% of these cells responded with short-latency (2-4 msec) action potentials and increased their tonic activity in response to electrical stimulation of the central parts of the hypothalamus, which evoked increases in hindlimb muscle tone in rats. These cells completely stopped producing action potentials during electrical stimulation and during chemical stimulation of the dorsolateral parts of the pons, which inhibited movement and muscle tone. A total of 23.4% of the cells produced only short-latency (1-4 msec) action potentials in response to stimulation of the inhibitory parts of the pons. A total of 3.9% of reticulospinal neurons increased their activity during stimulation of the hypothalamic zones and pontine areas of the brain. No responses were obtained from 35.9% of neurons. It is suggested that excitation of pontine structures inhibiting movement and muscle tone may prevent conduction in descending activatory systems from the rostral parts of the brain (which increase muscle tone) to the reticulospinal neurons of the medulla oblongata.