title: Modulation of motoneuron firing by recurrent inhibition in the adult rat in vivo.
abstract: Recent reports show that synaptic inhibition can modulate postsynaptic spike timing without having strong effects on firing rate. Thus synaptic inhibition can achieve multiplicity in neural circuit operation through variable modulation of postsynaptic firing rate vs. timing. We tested this possibility for recurrent inhibition (RI) of spinal motoneurons. In in vivo electrophysiological studies of adult Wistar rats anesthetized by isoflurane, we examined repetitive firing of individual lumbosacral motoneurons recorded in current clamp and modulated by synchronous antidromic electrical stimulation of multiple motor axons and their centrally projecting collateral branches. Antidromic stimulation produced recurrent inhibitory postsynaptic potentials (RIPSPs) having properties similar to those detailed in the cat. Although synchronous RI produced marked short-term modulation of motoneuron spike timing and instantaneous firing rate, there was little or no suppression of average firing rate. The bias in firing modulation of timing over average rate was observed even for high-frequency RI stimulation (100 Hz), perhaps because of the brevity of RIPSPs, which were more than twofold shorter during motoneuron firing compared with rest. These findings demonstrate that RI in the mammalian spinal cord has the capacity to support and not impede heightened motor pool activity, possibly during rapid, forceful movements.
authors.affiliation: Department of Neuroscience, Cell Biology, and Physiology, Wright State University, Dayton, Ohio; and.
authors.forename: Ahmed Z
authors.initials: AZ
authors.lastname: Obeidat
authors.affiliation: Department of Neuroscience, Cell Biology, and Physiology, Wright State University, Dayton, Ohio; and.
authors.forename: Paul
authors.initials: P
authors.lastname: Nardelli
authors.affiliation: Department of Physiology and Biophysics, University of Washington, Seattle, Washington.
authors.forename: Randall K
authors.initials: RK
authors.lastname: Powers
authors.affiliation: Department of Neuroscience, Cell Biology, and Physiology, Wright State University, Dayton, Ohio; and timothy.cope@wright.edu.
authors.forename: Timothy C
authors.initials: TC
authors.lastname: Cope
mesh_terms: D000200:Action Potentials; D000818:Animals; D005260:Female; D053444:Inhibitory Postsynaptic Potentials; D009046:Motor Neurons / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D013116:Spinal Cord / Q000166:cytology / Q000502:physiology
keywords: firing rate; phase lock; spike timing; spinal cord; synaptic inhibition