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Somatotopic organization related to nuclear morphology in the cuneate-gracile complex of opossumsDidelphis marsupialis virginiana

Brain Research
Publication Date
DOI: 10.1016/0006-8993(73)90368-5


Summary This study was performed to determine whether the mechanosensory projections to the cuneate-gracile nuclear complex are somatotopically organized, with nuclear subdivisions corresponding to regions of special projections, in marsupial opossums as they are in placental mammals. Neuronal spike discharges in response to mechanical stimulation of peripheral receptors were mapped, using tungsten microelectrodes, throughout the cuneate-gracile complex of opossums Didelphis marsupialis virginiana. The somatotopic organization of sensory projections is similar to that reported in placental mammals. However the detailed somatotopy seen in, for example, placental raccoons was not evident in opossums: in opossums individual neurons responded to larger receptive fields with greater overlap of receptive fields than in raccoons. No rostrocaudal differences in intra-nuclear distributions of receptive field sizes or modality representations were evident. A pronounced subdivision of the nuclear complex, related to projections from separate body regions, occurs in the caudal half of the nuclear complex. A midline nuclear column receives projections in its dorsal part from the tail; ventral to these are projections from the trunk. Distinct gracile nuclei on either side of the midline column receive projections from the hind feet. Lateral and ventral to these are the largest nuclear groups, the cuneate nuclei; most projections here are from the hand along with some from the forearm and fewer from the upper arm and shoulder region. Most lateral in the cuneate nuclei are projections from the neck and pinna. These results indicate that the organization of this nuclear complex in this marsupial is essentially similar to that of placentals, and support the use of opossums, where the complex differentiates and develops postnatally, as valid experimental models from which findings can be generalized to placentals.

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