Background A naturally occurring mutant mouse strain, hairless (Hr), develops seemingly normal hair follicles during their first 10 postnatal days, but by the end of the third week the animals lose all their fur in a rostral-caudal wave of molting. The epidermis and whiskers in the mystacial pad are subsequently hyperinnervated. In light of the extensive remodeling in the periphery, we asked whether there are also changes in central projections of these peripheral nerves to the spinal trigeminal nucleus pars caudalis of the brainstem, in concordance with rearrangements in the periphery.
Methods Sections from the brainstem trigeminal nucleus caudalis from adult (≥60 days old) mice of Swiss-Webster (SW) (N=6) and Hr (N=6) strains were examined using immunohistochemistry with antibodies against CGRP, substance P, and galanin, the predominate sensory neuropeptides in A-delta and C-fibers axons, and lectin-histochemistry using fluorescent conjugated Griffonia simplicifolia (GSA) which labels a separate, non-peptidergic population of neuron and their thin-fiber projections. Areas of central termination identified by immuno-/lectin fluorescence were measured.
Results Data were analyzed using a two-sample equal variance t-test and considered statistically significant at p ≤ 0.05. For CGRP, labeled projections in Hr covered 100150 ± 24047 μm2 compared to 72660 ± 16017 μm2 in SW (p≤0.001), and for GSA, Hr projections covered 46381 ± 5763 μm2 compared to 40286 ± 6914 μm2 in SW (p=0.035). Galanin labeling in Hr extended over 103235 ± 15272 μm2 and over 113528 ± 10213 μm2 in SW (p=0.147), and substance P projections in Hr covered 108200± 17916 μm2 and over 100228 ± 17563 μm2 in SW (p=0.279). Only for CGRP and GSA were the differences between labeling patterns in the brainstem between Hr and SW statistically significant.
Conclusion In the spinal trigeminal nucleus pars caudalis of the brainstem, CGRP and GSA projections covered a significantly larger area in Hr mice compared with SW mice. Galanin and substance P projections were not significantly altered in Hr compared with SW. Substantial plastic and biochemical alterations in Hr CGRP-, and GSA-positive central projections from the infraorbital nerve may suggest modifications in processing of some cutaneous inputs in response to massive peripheral reorganization.
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