Participation of the cholinergic system of the dorsal and ventral striatum in the regulation of various forms of defense behavior.

Abstract

It is known that the level of acetylcholine, of the enzymes that synthesize it, and metabolism in the neostriatum is very high [1]; further, that the interneurons are regarded as one of the principal sources. The striatum is subdivided into the dorsal and ventral striatum on the basis of the features of its internal structure and the organization of its connections. It has been demonstrated that there are both common and specific features in the Organization and functioning of the dorsal and ventral striatum [2, 4]; however, there have been no investigations comparing the role of the cholinergic systems of the dorsal and ventral striatum in the regulation of motor behavior. The present study is devoted to the investigation of the participation of the cholinergic systems of the dorsal and ventral striatum in the regulation of two forms of motor behavior: the instrumental defense reflex and active avoidance. The investigations, using the method of an instrumental defense reflex associated with the maintenance of a specific posture, were carried out in eight mongrel dogs [2, 3]. The second portion of the investigations was carried out in 73 Sprague-Dawley male rats, using two methods: 1) open-field testing, in which the level of locomotor activity was evaluated; and 2) the development of a one-sided active avoidance conditioned reflex in a T-maze in response to the light of an electric lamp. The microinjections were carried out unilaterally into the dorsal (the head of the caudate nucleus in dogs and the dorsal portion of the neostriamm in rats) or ventral (nucleus accumbens) striatum. The microinjections of carbacholine (0.05-0.2 ~zg) into the dorsal and ventral striatum were accompanied by an increase in the correctness of the realizations of the instrumental movement, for example, in dog No. 10, from 60-70 in he baseline to 100% after the microinjection. Carbacholine, injected into the dorsal striatum, altered first and foremost the principal component of postural reorganization, the time of relief of the working limb, from which alterations in the latent periods of the initiation of the movement and the accomplishment of the task result. For example, the latent period of the initiation of the movement in dog No. 12 increased from 1.2 to 2.3 sec (p < 0.001) after the contralateral microinjecliot~. The injection of carbacholine into the dorsal striatum induced an intensification of the tonic component of the movement arK1 an increase in the time the limb was held in the flexed posture. Thus, this indicator increased in dog No. 11 from 3.8 to 6.9 sec (p < 0.05). At the same time, the phasic component of the movement was inhibited; the mechanogram of the movement took on a ramp-like character; the number of intersignal elevations decreased by a factor of 1.5-2.0. Contralateral micro_ injections were more effective. By contrast with the dorsal striatum, other components of the instrumental movement cl~anged after the injection of carbacholine into the ventral striatum: the instrumental response corresponded precisely to the beginning and end of the action of the conditional signal, and was maintained at one and the same amplitude. This is evidently ~ssociat. ed with the more precise tracking of the signal after activation of the chotinergic system of the ventral striatum. Tiae latent periods of the postural reorganization, the initiation of the movement, and the accomplishment of the task changed insigrlifi_ cantly. The phasicity of the response did not decrease, while the number of intersignal elevations increased by a factor of 1.5 as compared with the baseline. If improvements were observed in the realization of the instrumental movement during the activation of the cholinergic system of the dorsal striatum only on the day of the injection, in the case of the influeoce on the cholinergic system of the ventral striatum, the effects were also manifested on the following days. Both ipsi- and contralater~ microinjections were effective after the injection of carbacholine into the ventral striatum.