ELECTROPHYSIOLOGICAL PROPERTIES OF CA1 AND CA2 APICAL DENDRITES OF RABBIT HIPPOCAMPUS

Abstract

Using 3 molar KCl filled microelectrodes for recording and stimulation, the experiment was performed on the hippocampal pyramidal cells of curarized or Nembutalized rabbits. No essential difference was observed between the effects of these 2 kinds of drugs. During suprathreshold stimulation of the Schaffer collaterals or CA4, a spike of about 3 msec. in duration was generated in the apical dendrites. When a weak stimulus was applied to the same point, a slow negative wave of 15-35 msec. in duration was seen in the apical dendrites. This slow wave had an ability to summate, resulting in generation of the spike of the apical dendrites. Therefore, it was regarded as an excitatory postsynaptic potential (EPSP) of the apical dendrites. EPSP, which arose in the distal part of the apical dendrites, generated a spike initially in the shaft of the apical dendrites, and then conducted toward both the distal part and the cell body. The conduction velocity ranged from 0.15-0.5 m/sec. This result suggests that the threshold for the spike generation is the lowest at the shaft of the apical dendrites. The refractory period of the spike of the apical dendrites was usually less than 30 msec. and an increased excitability was observed at the end of the refractory period. But sometimes, the refractory period was far longer, even reaching 170 msec.