Distribution of rubrospinal synaptic input to cat triceps surae motoneurons. J. Neurophysiol., 70:1460-1468

Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle 98195.
Journal of Neurophysiology (Impact Factor: 2.89). 11/1993; 70(4):1460-8.
Source: PubMed


1. We evoked steady-state synaptic potentials in triceps surae motoneurons of the cat by stimulating the hindlimb projection area of the contralateral magnocellular red nucleus at 200 Hz. We measured the effective synaptic currents (IN) underlying the synaptic potentials using a modified voltage-clamp technique. We also determined the effect of the rubrospinal input on the discharge rate of some of the motoneurons by inducing repetitive discharge with long injected current pulses during which the red nucleus stimulation was repeated. 2. At motoneuron resting potential, the distribution of IN from the red nucleus within the triceps surae pools was qualitatively similar to the distribution of synaptic potentials: 86% of the putative type F motoneurons received a net depolarizing IN from the red nucleus stimulation, whereas only 38% of the putative type S units did so. The mean values of IN were significantly different in the two groups [+4.1 +/- 5.0 nA (SD) for putative type F and -1.6 +/- 3.1 nA for putative type S]. 3. However, when the values of IN at threshold for repetitive firing were estimated, the distribution of IN from the red nucleus was quite different. At threshold, all of the putative type S units received hyperpolarizing IN but so did nearly half of the putative type F units. 4. As would be expected from the wide range of IN at threshold (-20 to +12 nA), the red nucleus input produced dramatically different effects on the discharge of different motoneurons.(ABSTRACT TRUNCATED AT 250 WORDS)

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    • "The appropriate recruitment of these motor units relies on descending inputs, whose activity generates motor responses matched to behavioral demands (Alstermark and Isa, 2012; Drew et al., 2004; Dubuc et al., 2008; Le Ray et al., 2011; Lemon, 2008). Studies of a variety of descending inputs have revealed that less excitable hindlimb motoneurons receive greater effective excitatory synaptic input than more excitable ones (Binder et al., 1998; Burke and Rymer, 1976; Grillner et al., 1970, 1971; Powers et al., 1993; Westcott et al., 1995). One unresolved issue that has been technically difficult to address in vivo is how weighted descending inputs optimized for synchronous activation of motor pools could generate differential activation of spinal motoneurons, as required for gradations in movement intensity. "
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