Electrical activity recorded from thin sections of the lateral geniculate body, and the effects of 5-hydroxytryptamine

Summary

Electrical activities were examined in vitro in thin sections taken from the lateral geniculate body (LGB) of the guinea-pig in the absence or presence of 5-hydroxytryptamine (5-HT). In the standard media, stimulation of the optic tract elicited in the LGB a field potential of mainly negative polarity on which single neuron discharges were superimposed. On the ascending slope of the single cell discharge, a synaptic potential (S-potential) was identified, which was suppressed by a decrease in Ca⁺⁺ and/or increase in Mg⁺⁺ concentrations. In addition, an increase in Mg⁺⁺ concentration lengthened the latency of the S-potential. The second S-potential evoked by paired stimuli to the optic tract was suppressed at intervals less than several hundred msec. The suppression was less marked in the media containing Ca⁺⁺ in low and/or Mg⁺⁺ in high concentrations. An EPSP followed by a long IPSP was recorded intracellularly. Application of 5-HT resulted in a suppression of the field potential and single cell discharges evoked synaptically. The chemically-induced discharges by homocysteate or glutamate were unaffected. The S-potential was also depressed by 5-HT without significant changes in latency. The long suppression of the test S-potential preceded by conditioning stimulus became less obvious in the presence of 5-HT. These findings were discussed in relation to the mechanism of action of 5-HT.