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Specificity of the newly formed cortico rubral synapses in the kitten red nucleus


Experimental Brain Research 51(1): 45-56
Specificity of the newly formed cortico rubral synapses in the kitten red nucleus
The formation of new synapses that occurs in the kitten red nucleus (RN) following lesions of the cerebral cortex or cerebellum were examined. In normal 2-3 mo. old kittens, stimulation of the cerebral cortex or cerebral peduncle (CP) produces slow-rising monosynaptic EPSP [excitatory postsynaptic potential] in ipsilateral RN cells; while fast-rising EPSP are produced by stimulating the contralateral nucleus interpositus (IP) of the cerebellum. In these normal animals stimulation of the contralateral cerebral cortex, or CP, or the ipsilateral IP never produces detectable postsynaptic potentials. In kittens with chronic lesions of the ipsilateral sensorimotor cortex performed < 2 mo. after birth, stimulation of the contralateral sensorimotor cortex or CP produced slow-rising EPSP. Upon stimulation of the contralateral IP a slow-rising component appeared superimposed on the fast-rising IP-EPSP. In some cells, stimulation of the ipsilateral IP produced slow-rising EPSP. New synapses were formed on the dendrites of RN cells by neurons from the contralateral CP, contralateral IP and ipsilateral IP. The majority of denervated RN neurons received new synapses from only 1 of these 3 inputs, those from the contralateral cerebral cortex being most prominent. The conduction velocities of corticorubral fibers responsible for the EPSP recorded in these lesioned animals are similar to those of slow conducting pyramidal trace fibers. Sometimes IPSP [inhibitory postsynaptic potential] were also produced by a train of CP stimuli. The IPSP are probably mediated by fast conducting pyramidal tract fibers because their threshold is lower than that of the EPSP. Newly formed crossed corticorubral projections have organizational specificity with respect to excitatory vs. inhibitory connections which is similar to that of normal ipsilateral corticorubral projections. Somatotopical organization was found in the newly formed corticorubral excitatory projections. The forelimb cortical area projected to contralateral RN neurons innervating the forelimb spinal segments, while the hindlimb cortical area was found to project to RN neurons innervating the lumbar segments. After chronic ablation of the forelimb area of the contralateral sensorimotor cortex, in addition to the ipsilateral cerebral cortex, a new connection was formed from the hindlimb area of the contralateral cerebral cortex to the RN neurons innervating the spinal forelimb segments. The specificity of the topographical organization is subject to reorganization. In chronically hemicerebellectomized kittens, ipsilateral IP stimulation produced fast-rising monosynaptic EPSP in some cases. New synapses were formed on the somatic or proximal dendritic portion of RN cells from the ipsilateral IP after ablation of the contralateral IP.


Accession: 006459103

PMID: 6309548



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