Activation of the cholinergic system of the striatum improves attention to conditioned reflex stimuli.

Chronic experiments were performed on 16 dogs using a model of an operant defensive reflex associated with maintenance of a flexion pose to study the effects of uni- and bilateral microinjections of the acetylcholine agonist carbacholine (0.05-0.4 microg) and the choline receptor blocker scopolamine (0.5 microg) into the dorsolateral part of the head of the caudate nucleus and CM-Pf intralaminar thalamic nuclei. These experiments produced data showing that the cholinergic system of the striatum has an important role in realizing the sensory and motor components of the learned movement. Activation of the cholinergic system of the dorsal striatum led to general calming of behavior and inhibition of intersignal limb elevation and the phasic components of the movement, along with ordering and stabilizing of the pose and an increase in the tonic component of the operant response. This suggests that the cholinergic system of the striatum receives an indirect efferent output via motor structures and takes part in preparing the motor apparatus needed for transferring attention to significant stimuli. Microinjections of scopolamine had the opposite effects. Use of differential signals in the same behavioral model, along with special tests for attention, showed that the cholinergic system of the striatum plays an important role in the sensory control of attention. Activation of the striatal cholinergic system led to a significant improvement in responses to differential signals and defensive signals of intensity 2-3 times slower than normal signals, and these changes were accompanied by clearer responses in special tests for attention. Scopolamine microinjections had the opposite effects. Carbacholine microinjections into the intralaminar thalamic nuclei potentiated the effects of cholinergic activation of the striatum. These data indicate that the dorsal striatum can be regarded not only as a parallel level of information processing, but also as a control system for passing this information to various levels of both sensory and motor structures. One important result of this type of control may be that of improving attention to significant stimuli.

Afferent and efferent mechanisms of the intensification of neostriatal cholinergic activity.

Data have been obtained in chronic experiments on 34 dogs, based on an instrumental defense reflex model associated with the maintenance of a specific posture, which suggest that activation of the cholinergic system of the neostriatum leads to a large number of changes in both the sensory and the motor spheres. The influences on motor behavior, observed mainly through effects on the cholinergic system of the contralateral caudate nucleus, reside in the intensification of the tonic constituent of movement, in inhibition of the phasic component of movement, and restriction of locomotor activity, all the way up to complete shutdown. The influences on sensory mechanisms, observed both through ipsi- and contralateral effects on the cholinergic system of the neostriatum, reside in an improvement of the differentiation of significant signals and are evidently through inhibition of the nonspecific afferent stream. Data are presented on the important role of the cholinoreactive systems of the CM-Pf complex of the thalamus in the intensification of the cholinergic activity of the neostriatum.

[Role of intralaminar thalamic nuclei in strengthening inhibition induced by stimulation of the caudate nucleus]. / Rol' intralaminarnykh iader talamusa v usilenii tormozheniia, vyzvannogo stimuliatsiei khvostatogo iadra.

The influence of preliminary subthreshold activation of thalamic intralaminary nuclei on achievement of instrumental reflex and on inhibitory effects, caused by stimulation of the caudate nucleus head, were studied in chronic experiments on 5 dogs with a model of instrumental defensive conditioned reflexes, providing for maintainance of a given posture. It was shown that the preceding high-frequency electrostimulation of intralaminary nuclei activates motor components of the instrumental response (shortened latency, EMG and mechanogram of the response, increased amplitude of instrumental response) and significantly lowers threshold strength of the current, necessary for obtaining "caudate pause". The greatest increase in inhibitory influences, caused by stimulation of the caudate nucleus head, was observed when thalamic stimulation preceded stimulations, localized in the dorsolateral segment of the caudate nucleus head. The obtained data are discussed in aspect of Buchwald et al. hypothesis on the existence of "caudate loop".

[The effect of electrostimulation of the caudate nucleus and somatosensory cortex on defensive instrumental reactions in dogs]. / Vliianie élektrostimuliatsii khvostatogo iadra i somatosensornoi kory na oboronitel'nuiu instrumental'nuiu reaktsiiu u sobak

It has been shown that the effect of stimulation of the caudate nucleus head in the contralateral hemisphere differs at different stages of achievement of a defensive instrumental habit in dogs. Stimulation preceding the action of the conditioned signal or delivered simultaneously with the beginning of the latter did not change the criteria for the achievement of successive programs of the instrumental defensive reaction. Stimulation of the same areas in the last phase of the instrumental response, as a rule, lead to the cessation of instrumental movement. A conclusion has been drawn that in a defensive situation the inhibitory influence of the caudate nucleus on instrumental behaviour of intact dogs is not so sharply expressed as in experiments with alimentary reinforcement. In dogs with a preliminary ablation of the CI and CII cortical zones of the contralateral hemisphere, stimulation of the caudate nucleus head was attended with a sharp drop in every criterion of the instrumental defensive reactions.