Effects of caudate nuclei or frontal cortex ablations in cats: III. Recovery of limb placing reactions, including observations in hemispherectomized animals

A substantial recovery of the contact placing reactions was observed in frontal cats and the recovery started very late (third or fourth month) and was considered as complete within 6 to 9 months in four cats, while a variable degree of impairment occurred in caudatectomized cats.

Abstract

This is a long-term study of the time course of impairments of the limb placing reactions in cats following bilateral removal of the frontal cortical areas (n = 9), bilateral (n = 11), or unilateral (n = 10), ablation of the caudate nuclei or removal of one cerebral hemisphere (n = 5). In addition the effects of d-amphetamine and of removal of the remaining frontal cortex on the placing reactions of the limbs contralateral to the hemispherectomy were assessed. The main results were: (i) a substantial recovery of the contact placing reactions was observed in frontal cats; the recovery started very late (third or fourth month) and was considered as complete within 6 to 9 months in four cats. (ii) A variable degree of impairment of the contact placing reactions occurred in caudatectomized cats; both the magnitude of the impairments and the length of the recovery period (up to 4 months) were proportional to the extent of the ablation. (iii) No recovery of the contact placing reactions was observed in limbs contralateral to the hemispherectomy either spontaneously, under the action of d-amphetamine (producing a transient enhancement of proprioceptive components and a pseudocontact placing reaction), or following removal of the remaining frontal cortex. The meaning of the above findings in the context of pertinent literature, the mechanisms of compensation following frontal ablation, and the possible participation of the caudate in the physiological control of the contact placing reactions are discussed.