Effect of serotonin on unit activity of the visual cortex evoked by direct cortical stimulation

Abstract

Acute experiments were carried out on 30 adult unanesthetized cats immobilized with diplacin, under local anesthesia. Unit activity was recorded in area 17 of the visual cortex and the substance was applied by microiontophoresis through double-barreled microelectrodes. One barrel of the microelectrode (recording) was filled with a 3 M solution of sodium chloride; its resistance was 5-10 Mfl. The second barrel was filled with a 0.05 M solution of serotonin (serotonin creatinine-sulfate, Reanal, pH 3.5). Bipolar nichrome electrodes with an interelectrode distance of 1.0-1.5 mm and with a diameter of 150 p were used for direct cortical stimulation. The first pair of stimulating electrodes was applied to area 18, the second pair to area 19 [12]. The cortex was stimulated intracortically with square pulses at a frequency of 0.i Hz with a duration of 0.2 msec; the strength of the current in each concrete case was chosen to be threshold and it varied from i0 to 1500 ~A. The experimental program, carried out on 82 neurons, included investigation of the spontaneous and evoked unit activity in area 17 of the cortex before and after application of serotonin. Each neuron was tested to exclude any direct action of the current.