Homogeneous distribution of excitatory and inhibitory synapses on the dendrites of the cat surea triceps alpha-motoneurons increases synaptic efficacy: Computer model

The effects of input distribution in dendrites on postsynaptic inhibition o f spinal monosynaptic reflex were studied in morphologically and physiologi cally characterized alpha-motoneurons. In homogeneous (HOM) and heterogeneo us (HEM) models, the location of the excitatory and inhibitory synapses was randomly selected for each bin of dendritic length. In the HOM, each compa rtment was forced to contain only one synapse as long as other compartments did not have at least one synapse. In the HEM, no restriction was made for synaptic distribution within a bin. EPSP amplitude in the HOM was enhanced by 28% and inhibition of EPSP peak (upon activation of inhibition) was inc reased by 66%, compared to the HEM. These results indicate that synaptic ef ficacy is greater in the HOM, both for excitatory and inhibitory synapses. Thus, it is suggested that homogeneously distributed postsynaptic inhibitio n may serve as the powerful inhibition of the monosynaptic reflex in realis tic alpha-motoneurons. (C) 1999 Elsevier Science B.V. All rights reserved.