A STUDY OF RETICULAR FORMATION ACTION ON SPINAL INTERNEURONS AND MOTONEURONS

Abstract

Recording of transmembrane resting and action potentials of interneurons and motoneurons by microelectrodes was used to study reticular formation facilitatory and inhibitory action. Both facilitation and inhibition of motoneurons occurred without detectable change in resting membrane potential. During facilitation the action potential rose earlier from the postsynaptic potential as though a change in threshold potential had occurred. Miniaturepotentials associated with reflex activation of motoneurons were seen and these were increased in number and fused as activation occurred during facilitatory action of the reticular formation. Reticular formation stimulation caused some motoneurons which normally were not excited by any of the orthodromic volleys to participate in one of the reflexes but in only one. Interneurons were found to be activated by more than one reflex and reticular formation facilitatory action increased the number of afferent nerve to which they would respond. Interneurons apparently participated in both inhibitory and facilitatory actions of the reticular formation. The various forms of interneuron participation in reticular formation actions were discussed. Activity of interneurons aroused by brief single pulse stimulation of the reticular formation lasted for over 500 milliseconds and could be considered to be a major factor in the prolonged effect of reticular formation stimulation on the reflex pathway. Recordings were made from anterior horn neurons which resembled Renshaw cells in activity. They were found to be inhibited by stimulations of the reticular formation which facilitated reflex action. Activity of other anterior horn neurons were described and discussed.