Journal of neurophysiology
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Electrical stimulation of vagal afferents or cardiopulmonary sympathetic afferent fibers excites C(1)--C(2) spinal neurons. The purposes of this study were to compare the responses of superficial (depth <0.35 mm) and deeper C(1)--C(2) spinal neurons to noxious chemical stimulation of cardiac afferents and determine the relative contribution of vagal and sympathetic afferent pathways for transmission of noxious cardiac afferent input to C(1)--C(2) neurons. Extracellular potentials of single C(1)--C(2) neurons were recorded in pentobarbital anesthetized and paralyzed male rats. ⋯ Ipsilateral cervical vagotomy interrupted cardiac noxious input to 8/30 (6 E, 2 I) neurons; sequential transection of the contralateral cervical vagus nerve (bilateral vagotomy) eliminated the responses to intrapericardial chemicals in 4/22 (3 E, 1 I) neurons. Spinal transection at C(6)--C(7) segments to interrupt effects of sympathetic afferent input abolished responses to cardiac input in 10/10 (7 E, 3 I) neurons that still responded after bilateral vagotomy. Results of this study support the concept that C(1)-C(2) superficial and deeper spinal neurons play a role in integrating cardiac noxious inputs that travel in both the cervical vagal and/or thoracic sympathetic afferent nerves.
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Reaching to grasp is of fundamental importance to primate motor behavior and requires coordinating hand preshaping with limb transport and grasping. We aimed to clarify the role of cerebellar output via the magnocellular red nucleus (RNm) to the control of reaching to grasp. Rubrospinal fibers originating from RNm constitute one pathway by which cerebellar output influences spinal circuitry directly. ⋯ The results indicate that MCP extensions were consistently preceded by bursts of RNm discharge, and strong correlations were observed between parameters of discharge and the duration, velocity, and amplitude of corresponding MCP extensions. In contrast, relations between discharge and movements of proximal joints were poorly represented, and RNm discharge was not related to the speed of limb transport. Based on our data and those of others, we hypothesize that cerebellar output via RNm is specialized for controlling hand use and conclude that RNm may contribute to the control of hand preshaping during reaching to grasp by activating muscle synergies that produce the appropriate MCP extension at the appropriate phase of limb transport.
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The increasing use of transgenic mice for the study of pain mechanisms necessitates comprehensive understanding of the murine somatosensory system. Using an in vivo mouse preparation, we studied response properties of tibial nerve afferent fibers innervating glabrous skin. Recordings were obtained from 225 fibers identified by mechanical stimulation of the skin. ⋯ Only 11% of C fibers were insensitive to heat and/or cold. This in vivo study provides an analysis of mouse primary afferent fibers innervating glabrous skin including new information on encoding of noxious thermal stimuli within the peripheral somatosensory system of the mouse. These results will be useful for future comparative studies with transgenic mice.