Modification of motor activity, passive avoidance conditioning and evoked potentials by microinjections of strychnine...

Passive avoidance conditioning (PAC) seems to depend on inhibitory actions within the caudate nucleus (CN). Thus topical application of strychnine could block these influences. In cats, with permanently implanted cannulae in the head of the CN, bilateral microinjections of 100 micrograms of strychnine produced a stereotyped behavior of grooming and running with the extremities flexed to dark places. When placed into a two compartment chamber for a PAC acquisition they would not move from the dark compartment to the illuminated one. After decreasing the illumination some cats crossed and the acquisition test was performed. Twenty four hours later they showed the learned response. A second retention test was not modified by another strychnine application. These results contrast with those obtained by picrotoxin microinjections which disrupt the retention of a PAC. However, strychnine affects the evoked potentials (EP) recorded in CN by n. centralis medialis (NCM) stimulation by decreasing a positive peak, which probably represents post-synaptic inhibition and increasing the late positive component. In the lateral geniculate body strychnine affected a late positive wave and in the occipital cortex it increased the initial negative peaks and decreased the late positive ones of the potentials evoked by flash stimulation. These findings suggest a more suitable role of the CN in the regulation of visual information, which is probably related with the attention processes.