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Corticofugal actions on lemniscal neurons of the cuneate gracile and lateral cervical nuclei of the cat



Corticofugal actions on lemniscal neurons of the cuneate gracile and lateral cervical nuclei of the cat



Experimental Brain Research 90(2): 384-392



Extracellular records were made from single identified lemniscal neurons of the cell-cluster regions of the cuneate and gracile nuclei, and of the lateral cervical nucleus, in pentobarbitone-anaesthetized cats. Forepaw, hind paw or face regions of the contralateral Sm I cortex were identified by recording through an inserted microelectrode which was then used for stimulation. The effect of a double cortical shock or train of shocks was usually inhibition: occasionally facilitation was observed, or mixed effects with facilitation preceding inhibition. Effects were seen in about half the cells studied in all three nuclei. Some cells of the lateral cervical nucleus were strongly excited, an effect not seen in the other nuclei. No component of these responses depended on suprathreshold stimulus intensities. Some lateral cervical cells were studied after deafferentiation by section of the dorsolateral spinal white matter; the same pattern of effects was seen. With an upper stimulus limit of 200 .mu.A, cuneate but not gracile cells were affected from the cortical forepaw region, and gracile but not cuneate cells from the hind paw region. With threshold stimuli in an identified part of the forepaw cortical representation it was clear that cuneate cells with cutaneous receptive fields in corresponding parts of the forepaw had the lowest threshold (minimum 6 .mu.A). Threshold rose steeply with distance across the paw, suggesting quite sharp focusing of corticofugal effects in this system. When using similar procedures with the lateral cervical nucleus, with an upper limit of 200 .mu.A, stimulation of forelimb cortex, or of facial cortex, affected both neurons with forelimb and those with hind limb fields. With near-threshold stimuli (minimum 11 .mu.A) a broad but inconsistent somatotopic relationship emerged between cortical site and cutaneous receptive field. We conclude that under these circumstances corticofugal actions are much more sharply focused spatially on lemniscal neurons of the dorsal column nuclei than on those of the lateral cervical nucleus.

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Accession: 007165057

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PMID: 1397152

DOI: 10.1007/bf00227252


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