RESUMEN
Comparative analysis of the cholinergic system of the neocortex, consisting of the terminals of neurons from the magnocellular basal nuclei and intracortical neurons, in cats with strong and weak abilities to solve abstraction and generalization tasks was performed by isolating subfractions of synaptic membranes and synaptoplasm from "light" (C) and "heavy" (D) synaptosomes from associative field Ep and measuring choline acetyltransferase and acetylcholinesterase activities, protein content, and sulfhydryl group concentrations. These experiments showed that all measures were significantly lower in subfractions from C synaptosomes from cats with strong cognitive abilities. This leads to the conclusion that relatively small numbers of cholinergic synapses form in field Ep of the brains of cats with strong cognitive abilities, while their location in the C fraction demonstrates that they correspond to neurons of the magnocellular basal nuclei. The possible physiological significance of the "deficiency" of cholinergic inputs in field Ep from these nuclei as a correlate of the animal's cognitive ability is discussed. The D subfractions from able cats had significantly higher acetylcholinesterase activity, while choline acetyltransferase activity was not different; this identifies differences between groups of animals in the organization of non-cholinergic acetylcholinesterase-containing synapses in field Ep.