THE EFFECT OF CONVULSANT DRUGS ON TRANSMISSION THROUGH THE CUNEATE NUCLEUS

¹ Department of Pharmacology, The University of Rochester, Rochester, New York

The recovery cycle of the cuneate nucleus, isolated from structures above the mesencephalon and below C₃ was studied, in unanesthetized animals, with the aid of a computer which was used both for averaging and, by a subtraction process, for separating overlapping responses. Picrotoxin and pentylenetetrazol increased recoveries (decreased the reduction of the second response, as compared to control values) at interstimulus intervals of 1 to at least 40 msec with the maximum effect occurring at intervals of 4 to 6 msec. Strychnine widened responses to conditioning stimuli. Strychnine plus mephenesin increased recoveries at intervals of 1 to 15 msec with the maximum effect occurring at 2 msec, and decreased recoveries at longer intervals. The latter effect was blocked by picrotoxin. The results are consistent with results reported from microelectrode studies of the cuneate nucleus and with the hypothesis that picrotoxin and strychnine selectively block pre- and postsynaptic inhibitions, respectively. Using this hypothesis, it is concluded that picrotoxin and pentylenetetrazol block presynaptic inhibition of cuneothalamic relay cells, that strychnine blocks a postaynaptic inhibition of the relay cells, that strychnine potentiated by mephenesin blocks a second postsynaptic inhibition of the relay cells as well as a postsynaptic inhibition of the interneurons responsible for presynaptic inhibition and that both the absolute and relative magnitudes of pre- and postsynaptic inhibition can result in selective discrimination between inputs of different frequencies.