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The Journal of Neuroscience, May 1, 2001, 21(9):3184-3195
Disruption of Layers 3 and 4 during Development Results in
Altered Thalamocortical Projections in Ferret Somatosensory Cortex
Stephen C.
Noctor1,
Sidney L.
Palmer2,
Debra F.
McLaughlin1, 2, and
Sharon L.
Juliano1, 2
1 Program in Neuroscience and 2 Department
of Anatomy and Cell Biology, Uniformed Services University of the
Health Services, Bethesda, Maryland 20814
The precision of projections from dorsal thalamus to neocortex are
key toward understanding overall cortical organization and function. To
identify the significance of layer 4 cells in receiving the bulk of
thalamic projections in somatosensory cortex, we disrupted layer 4 genesis and studied the effect on thalamic terminations in ferrets.
Second, we ascertained the result of layer 4 disruption on functional
responses and topographic organization. Methylazoxy methanol (MAM) was
injected into pregnant ferrets on embryonic day 33 (E33), when most
layer 4 neurons of somatosensory cortex are generated. This treatment
resulted in dramatic reduction in the thickness of targeted layer 4. E38 MAM treatment was used as a control, when layer 2-3 neurons are
generated. The projections of ventrobasal thalamus into
somatosensory cortex were studied using DiI injections. We found only
subtle differences between groups (normal, E33, or E38 MAM-treated) in
the thalamic afferent pattern on postnatal day 1 (P1) and P7. On
P14, thalamic terminations distribute almost equally throughout the
remaining cortical layers in the E33 MAM-treated group compared with
normal and E38 MAM-treated animals, in which the ventrobasal thalamus
projects primarily to central layers. Electrophysiological recordings
conducted on mature ferrets treated with MAM on E33 demonstrated that
somatotopic organization and receptive field size are normal. These
findings emphasize the importance of layer 4 in determining the normal laminar pattern of thalamic termination and suggest that, although its
absence is likely to impact on complex neocortical functional responses, topographic organization does not arise from the influence of layer 4.
Key words:
cerebral cortex; development; MAM; migration disorder; ventrobasal thalamus; BrdU
Copyright © 2001 Society for Neuroscience 0270-6474/01/2193184-12$05.00/0
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