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Abstract

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.

Chronic Cerebral Ischaemia Forms New Cholinergic Mechanisms of Learning and Memory

“…Our data confirmed that synaptic populations of cholinergic projective neurons and of the interneurons of the cortex and the hippocampus can have positive and negative connections with cognitive functions. A negative dependence of cognitive functions on cholinergic cortical efficiency was also revealed earlier in cats using a similar methodology for researching the cholinergic synaptic organization of cognitive functions [29]. Therefore, our data demonstrate that the cholinergic mechanisms of learning and memory are more complex than currently perceived.…”

“…We previously showed that for both the cortex and the hippocampus the cholinergic presynapses from different sources are isolated in different synaptosomal fractions during preparation in the sucrose density gradient. The presynapses of cholinergic projections from the forebrain nuclei are accumulated mainly in the light synaptosomal fractions whereas the presynapses of cholinergic interneurons are accumulated mainly in the heavy synaptosomal fractions [29–31]. It is probable that the heavy synaptosomal fraction of the hippocampus may also accumulate a small part of the cholinergic projective presynapses (lateral projection pathway into the hippocampus [32]) [31].…”

“…It is probable that the heavy synaptosomal fraction of the hippocampus may also accumulate a small part of the cholinergic projective presynapses (lateral projection pathway into the hippocampus [32]) [31]. Our studies on the cortical synaptosomal fractions of cats allowed suggest the involvement of the cholinergic interneurons in cognitive functions [29]. In the studies on the cortical and hippocampal synaptosomal fractions of rat we revealed that during the first three hours of chronic brain ischaemia the cholinergic projective neurons were reactive, as were the interneurons of the cortex and the hippocampus as well [33].…”

Evaluation of the Activity of Choline Acetyltransferase From Different Synaptosomal Fractions at the Distinct Stages of Spatial Learning in the Morris Water Maze

“…After 5 days of learning, there was only an association between behavioural measures and sChAT activity from heavy synaptosomal cortical fraction, which seems to include synaptosomes from cortical interneurons (Mukhin et al, 2002). The existence of cholinergic cortical interneurons is well established, and many populations of these cells were shown to excrete GABA and other transmitters or modulators together with ACh (Dudai et al, 2020).…”

“…In the hippocampus, the bulk of ACh is found in projections from the diagonal band of Broca and the medial septum, but there are also intrinsic hippocampal cholinergic neurons ( Frotscher et al, 2000 ; Yi et al, 2015 ). Based on previous studies ( Mukhin et al, 2002 ; Zakharova et al, 2010b ), the synaptic activity of cholinergic interneurons and cholinergic projection fibres can be estimated by the activity of choline acetyltransferase (ChAT) from two distinct fractions of synaptosomes: light (obtained mainly from projection fibres) and heavy (obtained mainly from interneurons). Other authors have emphasised that light and heavy synaptosomes display markedly different functional proteomics and metabolic machinery; these differences suggest their functional specificity ( Gorini et al, 1999 ).…”