Electrical transmission between nonsymmetrical neurons in the leech ganglion

Abstract

The extent of the electrical transmission (ET) between different nonsymmetrical neurons in the segmental ganglion of the abdominal nerve chain of the leechHirudo medicinalis L. was investigated. ET was demonstrated by simultaneous recording of the intracellular potentials in two neurons when bursts of a polarizing current were passed alternately into each of them. At least 16 different pairs of nonsymmetrical identifiable neurons with ET which, as a rule, was symmetrical with a coefficient of attenuation of the order of 10 in the direction of greater effectiveness, were found. In different pairs of nonsymmetrical identifiable neurons, the ET of hyperpolarizing currents as a rule is more effective from neurons with a higher frequency of background activity. The presence of ET was also shown between many nonsymmetrical unidentifiable neurons of the ganglion. The assymetrical ET in some of the combinations of neurons investigated did not have rectifying properties. The direction of the ET was retained in them for any polarity of the polarizing current. In some experiments hyperpolarization of one of the neurons of a pair evoked depolarization and an increase in the frequency of the impulse activity of the other, while depolarization had the opposite effect ("negative" ET). It was concluded that the broad extent of the ET between nonsymmetrical neurons indicates its important role in the integrating activity of the central nervous system of the leech.