The time course of minimal excitatory post-synaptic potentials evoked in spinal motoneurones by group la afferent fibres

摘要: 1. Group Ia EPSPs were recorded from lumbosacral motoneurones in anaesthetized cats after almost complete section of the relevant dorsal roots. The usually small amplitude (median value 230 muV) and an averaging device was used to improve definition their time course.2. From a total over 500 averaged smaller number (342) subjected analysis. other rejected either because they showed signs multiple origin rising phase course (see Methods) or resting membrane potential cell less than 50 mV. All selected had rise (from 10 90% level) half-width measured, semilogarithmic plot decay made.3. 252 exponential decline later slope this line give estimate constant. range constant for different 2.3-12.9 msec, with mean 5.8 msec.4. In ten cells EPSP which judged be generated exclusively by synaptic knobs located on soma. On assumption measurements normalized time, break point alpha, rho(infinity) L method suggested Jack & Redman (1971b). estimated alpha ranged 18 65. A positive correlation found between tau(m), indicating that these duration current injection independent peak wave form 0.1 0.25 msec. estimates not thought very accurate. lower limit 4 assumed highest measured 12, but three could fitted even high rho(infinity). Some possible explanations discrepancy are mentioned Discussion. electrotonic length dendrites (L) greater 1.0 lambda 0.75 1.5 lambda. Evidence open-circuit termination some cells.5. values make distance allocation 246 non-somatic. precise individual available motoneurones. Instead, maximum assumed: rho(infinity), 4-25; L, 0.75-1.5. also assumed, 12 100. With motoneurone model (Jack Redman, 1971b) set limits within all EPSPs, at single point, should lie. Twenty lay outside boundary lines hence did receive allocation. remaining 226 assigned 0.2 1.6 (in steps); majority allocations (183) proximal part (0.2, 0.4 0.6 lambda). relationship histological results Conradi (1969) is discussed.6. It concluded there no good evidence against view main minimal can explained generation brief pulse subsequent passive spread.