The lateral reticular nucleus in the cat—II. Effects of lateral reticular lesions on posture and reflex movements

Abstract

Unilateral lesion of the lateral reticular nucleus produced a postural asymmetry characterized by ipsilateral hypertonia and contralateral hypotonia of the limb extensor muscles. Soon after the operation the cat was unable to stand or walk, and it laid on one side. Within 3 days, it began to walk, but it often deviated to its contralateral side, 'frequently falling in this direction. Some compensation for both postural and motor deficits occurred in chronic preparations maintained up to 154 days after the lesion. The postural asymmetry was reversed by the following operations: (1) section of the ipsilateral VIIIth nerve, (2) electrolytic lesion of the ipsilateral Deiters' nucleus, or (3) ablation of the contralateral vermal cortex of the cerebellar anterior lobe. The lateral reticular nucleus lesion also produced, in the ipsilateral limbs, a transient loss of the proprioceptive placing reaction and a persistent deficit of the tactile placing reflex. These effects on the ipsilateral side were not reversed by the procedures described above. All of these behaviors depended on selective destruction of the lateral reticular nucleus and were not due to damage to the nearby main reticular formation or ascending and descending pathways. Moreover, the postural changes did not involve mesencephalic or higher mechanisms, since they were still observed after decerebration. The forelimbs were affected primarily by lesions involving the dorsomedial, magnocellular part of the lateral reticular nucleus, whereas the hindlimbs also were affected by lesions including the ventrolateral, parvicellular part of the lateral reticular nucleus. The postural asymmetry is attributed to interruption of the crossed spinoreticulocerebellar pathway, acting on the vermal cortex of the anterior lobe and the fastigial nucleus, while the ipsilateral loss of the placing reaction is attributed to interruption of the uncrossed spinoreticulocerebellar pathway acting on the intermediate cortex of the anterior lobe and the interpositus nucleus. The lateral reticular nucleus appears, therefore, to be composed of two, more or less independent, parts, a crossed one being related to major changes in postural tone, equilibrium and locomotion of the entire body, and an uncrossed one restricted to discrete movements of the ipsilateral limbs.