Types of NADPH-d+ neurons (Vincent et al., 1983) were identified in the striatum and basolateral nuclei of the amygdala; striocortical neurons were detected in the striatum using the DiI marker (Belichenko and Dahlström, 1995). NADPH-d+ cells were numerous. Staining of these cells and all their processes, along with our previous studies of the neurons in these formations in the human brain using the Golgi method, allowed us to identify their shapes and identify them as sparsely or extensively branched cells. The main efferent neurons of the striatum and basolateral amygdala (extensively branched medium spiny cells and bushy spiny cells respectively) and their extensively branched interneurons did not contain NADPH-d. Efferent NADPH-d+ neurons included reticular, sparsely branched cells with long dendrites, which were the most numerous cells in both formations, as well as occasional large multipolar branched neurons; the striatum also contained numerous sparsely branched short-dendrite cells (a neuron type most represented in the brainstem and especially the reticular formation). Projections of reticular cells from the striatum to the cortex were demonstrated. NADPH-d+ interneurons were sparsely branched: in the striatum, these were slender, long-dendrite, bipolar cells (numerous), ordinary bipolar cells, twisted and large dendrite-poor cells; the amygdala contained the same bipolar cells along with radial neurons. Thus, NADPH-d+ neurons in these formations were more ancient, i.e., structurally less complex, cell types.
The role of the substantia nigra in cognitive processes of different levels of complexity was studied using an original method. Neurosurgical or neurochemical exclusion of the substantia nigra in cats led to significant impairment of conditioned reflex activity, generalization and abstraction processes; these recovered with pharmacological treatment directed to the dopaminergic system, with partial recovery after treatment directed to the GABAergic and cholinergic systems. Treatment directed to the serotoninergic system was ineffective.
The functions of generalization and abstraction in an experimental model of Alzheimer's disease (the lesion of Meynert's nuclei in cats) were studied against the background of stimulation and inhibition of the cholinergic, GABAergic, and dopaminergic systems of the brain. It was demonstrated that the cholinergic system is a key system for the formation of the function of generalization, the dopaminergic system improves simple forms of learning, while the GABAergic system is actively involved in the establishment of complex types of associations.
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