Electrical stimulation of the midbrain central gray facilitates reticulospinal activation of axial muscle EMG

Abstract

EMG responses were recorded from axial muscles transversospinalis, medial longissimus, and lateral longissimus in urethane-anesthetized rats during combined electrical stimulation of the reticular formation and midbrain central gray. Central gray stimulation facilitated reticular formation-evoked EMG activity in the back muscles of the rat. Electrical stimulation of the central gray lowered the threshold for reticulo-spinal activation of axial muscles and could maintain firing in these muscles after the end of a reticular formation train. Units were recruited in order of size from small to large. In only one case, central gray stimulation activated axial muscles directly without reticular formation stimulation. The central gray may be important in relaying hypothalamic influences to the reticular formation, which has direct access to the axial muscles responsible for lordosis behavior.