SPINAL CORD INFLUENCES ON FORELIMB MOVEMENTS INDUCED FROM THE RETICULAR FORMATION IN THE CAT

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Abstract
Ten adult cats were stimulated with monophasic square waves through bipolar electrodes chronically implanted within the reticular formation of the midbrain, at 500 and 50 c.p.s. In six of these, the stimulations were repeated after postbrachial section of the spinal cord. Forelimb movements obtained in the intact animals consisted mainly of flexion of the shoulder and elbow with extension of the wrist and toes in the ipsilateral forelimb, and extension of the elbow, wrist, and toes with abduction and a flexed or extended shoulder in the contralateral forelimb. Movements obtained at the two frequencies were occasionally different: 500 c.p.s. seem to favor flexion; 50 c.p.s., extension. Postbrachial sections of the spinal cord favored flexion of the extended elbows in both forelimbs, most often the contralateral, and extension of the flexed shoulder in the contralateral forelimb. These results show that the forelimb movements obtained by stimulation of the reticular formation of the midbrain are, at least in part, dependent upon the intersegmental spinal cord organization. Extension of the contralateral elbow seems to be particularly dependent upon pathways arising from cord levels below T4.