STIMULUS EFFECTS OF THE MEDIAL PONTINE RETICULAR-FORMATION AND THE MESENCEPHALIC LOCOMOTOR REGION UPON MEDULLARY RETICULOSPINAL NEURONS IN ACUTE DECEREBRATE CATS

In acute decerebrate cats, medial pontine reticular formation (MLR) an d the mesencephalic locomotor region (MLR) were stimulated and their s timulus effects upon 250 medullary reticulospinal neurons (RSNs) were studied. One hundred and twenty-six RSNs were mono- and disynaptically activated. From the response patterns of the RSNs, they were divided into the mPRF-activated RSNs (n = 67) and the MLR-activated RSNs (n = 59). The former group of RSNs was located in the nucleus reticularis g igantocellularis (NRGc), while the latter group of RSNs was distribute d in both the NRGc and the nucleus reticularis magnocellularis (NRMc). The activity of MLR-excited 12 RSNs was suppressed with the preceding mPRF stimulation. These RSNs were mainly located in the NRMc. Most mP RF-excited RSNs increased their discharge rates during mPRF-evoked sup pression of postural muscle tone, and most MLR-excited RSNs increased their discharge rates during MLR-evoked locomotion. With mPRF stimulat ion, MLR-evoked locomotion was suppressed with cessation of MLR-excite d RSNs activity. These results suggest that mPRF stimulation suppresse s the activity of the locomotor rhythm generating system at the levels of not only the spinal cord but also the medullary output cells.