STRUCTURE-FUNCTION-RELATIONSHIPS IN RAT BRAIN-STEM SUBNUCLEUS INTERPOLARIS .12. NEONATAL DEAFFERENTATION EFFECTS ON CELL MORPHOLOGY

In the developing whisker-barrel neuraxis, it is known that pattern fo rmation, receptive fields, axon projections, and even cell survival ar e under the control of peripheral signals transmitted through the infr aorbital nerve. However, afferent influences upon the development of s ingle-cell morphologies have not received thorough study. Intracellula r recording, antidromic activation, receptive field mapping, dye injec tion, and computer-assisted cell reconstruction methods were used to a ssess the morphology of trigeminal (V) brainstem neurons in adult rats whose infraorbital nerves were transected at birth. Projection and lo cal-circuit neurons in the spinal V subnucleus interpolaris (SpVi; n = 43) and local-circuit neurons in the adjacent subnucleus caudalis (Sp Vc; n = 11) were compared with similar cell types in normal control ra ts, as well as with spinal V neurons located outside of the deafferent ed region in experimental rats. SpVi cells displayed abnormally conver gent and discontinuous receptive fields that included greater-than-nor mal numbers of vibrissae and other receptor organs. However, their mor phologies did not differ significantly from normal on any quantitative measure, including soma size, number of proximal dendrites, or dendri tic tree area, perimeter, or shape. Moreover, SpVi cells near deaffere nted brainstem territories did not display dendritic tree polarity tow ard or away from the deafferented region. In SpVc, laminae I-V cells h ad responses and morphologies that were indistinguishable from those o f controls. Thus, (1) altered receptive fields of neonatally deafferen ted SpVi neurons are not attributable to changes in their morphology; (2) SpVc cells are resilient following deafferentation; and (3) the de velopment of SpV dendrites and local axon collaterals is controlled by factors other than those directly conveyed by primary afferents.