Responses of cortical neurons to local application of excitatory amino acids to their dendrites and soma

Abstract

The efficacy of excitation induced by iontophoretic application of excitatory amino acids to the soma or different parts of the dendritic tree has been compared in experiments performed on parietal cortex slices. Spike activity was recorded extracellularly from single nerve cells of layer V. In total, the responses of 125 neurons were analyzed. Upon application of glutamate and aspartate to the neuronal soma and the majority of dendrites, latencies of excitatory responses did not exceed 500 msec. In 18% of cases, neuronal responses to transmitter application to basal and apical dendrites had longer (2–3 sec) latencies. The maximum intensity of responses was observed when excitatory amino acids had been applied to the soma or proximal parts of dendrites. If applied at a distance of over 100 µm to basal and 300 µm to apical dendrites, glutamate and aspartate elicited cellular responses whose intensity was 2–3 times lower than that of the responses induced by application to the soma. The maximum distances at which somatic spike responses could be recorded were 350 µm and 800 µm for basal and apical dendrites, respectively. Different latencies of the responses to somatic and dendritic applications of excitatory amino acids in some neurons, as well as high efficacy of responses to stimulation of remote parts of dendritic tree, may indicate nonidentity of electrical properties of dendritic and somatic membranes.