Effects of the cholinergic system of the rat neostriatum on learning active escape in normal animals and in animals with lesions to the intralaminar thalamic nuclei.

Studies were carried out into the role of the parafascicular (Pf) nuclei of the rat thalamus in learning a conditioned active escape reflex (CAER) in a T-maze, a reflex associated with discrimination of visual stimuli, and into the regulatory effect on this learning process of activation of the neostriatal cholinergic system. The following results were obtained using 57 Sprague-Dawley rats divided into a number of experimental groups: 1) bilateral microinjection of carbacholine (0.03 microgram) into the neostriatum on days 4, 5, and 6 of training produced significant (p < 0.01) increases in the proportion of correct discriminant CAER performances; 2) bilateral lesioning of the Pf nuclei led to irreversible disruption of the previously learned CAER. Rats with initially bilaterally lesioned Pf nuclei did not learn the discriminant CAER at all after 10 days of training (16 combinations), and microinjection of carbacholine into the neostriatum of these animals was ineffective. It is concluded that the integrity of the afferent input into the Pf nuclei of the thalamus is an important factor for activation of the neuronal background of the neostriatum, and is required for cholinergic activation of the neostriatum to be effective.