[Spread of excitation in the upper layers of the auditory cortex with the participation of intracortical interneuronal connections].

In the chronically isolated slab of the cat auditory cortex when lower layers were additionally undercut and one, two or three cortical layers under the pial surface remained structurally intact, impulse reactions of slab neurons to the intracortical stimulation applied on the other side of this additional undercut were investigated. High effectiveness of axo-dendritic and axo-spinal excitatory contacts formed by nerve elements of intracortical origin in the upper cortical layers was shown. Participation of geniculo-cortical fibres in the spread of excitation in the cortex through synaptic contacts in layer I with dendrites of pyramidal neurons of the lower layers is discussed.

[Intrinsic cholinergic components in the cholinergic innervation of the auditory cortex in the cat (zone AI)].

Neuronally isolated auditory cortical slabs (zone Al) of cat were studied using histochemical AChE reaction 3 days and 1, 2, 3 weeks after isolation. Following structures were observed: cholinergic long-axon associative neurons responding to the cortex isolation by retrograde degeneration and AChE hyperreaction (Cajal-Retzius cells of layer I and neurons of layer VI whose axons travel to the subcortical layer of the associative fibres); cholinergic short-axon associative cells of layers II-VI, which retain normal structure and moderate AChE activity after isolation; their axon collaterals terminate on neighbouring neurons; short-axon neurons are more numerous in deeper layers of the cortex; on the whole they predominate over the long-axon associative neurons; cholinoceptive cells (pyramidal and stellate) were found with cholinergic terminals on the soma and proximal parts of the dendrites; these terminals were formed by associative cell axons. Cholinoceptive neurons occurred more frequently in deeper layers of the cortex.

[Cholinergic structures in the auditory area of the cerebral cortex in the cat (zone AI)].

Histochemical reaction to AChE was used to reveal the network of cholinergic varicose fibres in the neuropile of different cortical layers. Its density was maximal in layer I and deeper, and minimal in layers II and III. Among neurons of zone AI few stellate neurons located in layers II-VI are cholinergic.

[Primary inhibitory responses of neurons of a chronically isolated band of auditory cortex to intracortical stimulation].

The reactions of 579 neurons to intracortical stimulation of an auditory cortex slab (three weeks after its isolation) were studied intracellularly in three series of experiments on cats. The distances between stimulating and recording electrodes were 0.5, 1.