Structure-function relationships in rat brainstem subnucleus interpolaris: XII. neonatal deafferentation effects on cell morphology.

In the developing whisker-barrel neuraxis, it is known that pattern formation, receptive fields, axon projections, and even cell survival are under the control of peripheral signals transmitted through the infraorbital nerve. However, afferent influences upon the development of single-cell morphologies have not received thorough study. Intracellular recording, antidromic activation, receptive field mapping, dye injection, and computer-assisted cell reconstruction methods were used to assess the morphology of trigeminal (V) brainstem neurons in adult rats whose infraorbital nerves were transected at birth. Projection and local-circuit neurons in the spinal V subnucleus interpolaris (SpVi; n = 43) and local-circuit neurons in the adjacent subnucleus caudalis (SpVc; n = 11) were compared with similar cell types in normal control rats, as well as with spinal V neurons located outside of the deafferented region in experimental rats. SpVi cells displayed abnormally convergent and discontinuous receptive fields that included greater-than-normal numbers of vibrissae and other receptor organs. However, their morphologies did not differ significantly from normal on any quantitative measure, including soma size, number of proximal dendrites, or dendritic tree area, perimeter, or shape. Moreover, SpVi cells near deafferented brainstem territories did not display dendritic tree polarity toward or away from the deafferented region. In SpVc, laminae I-V cells had responses and morphologies that were indistinguishable from those of controls. Thus, (1) altered receptive fields of neonatally deafferented SpVi neurons are not attributable to changes in their morphology; (2) SpVc cells are resilient following deafferentation; and (3) the development of SpV dendrites and local axon collaterals is controlled by factors other than those directly conveyed by primary afferents.