Developmental profiles of SMI-32 immunoreactivity in monkey striate cortex

A monoclonal antibody that recognizes a nonphosphorylated epitope on the me dium and high molecular weight subunits of neurofilament (NF) proteins was used to investigate laminar and cell morphology changes in monkey striate c ortex during post-natal development. Six cortices were obtained from monkey s of a variety of ages: five from developing animals with ages spanning the critical period and one adult. At post-natal day (PD) 0, immunohistochemis try with the SMI-32 antibody revealed immunoreactive (IR) cells in layer IV B and in infragranular layer VI. Early in the critical period (PD 7), these layers become more defined with an increase in the density of immunopositi ve cells. At the height of the critical period (PD 30 and 42), a drastic in crease in the density of SMI-32 labelled pyramidal neurons in layers V and VI was observed. Similarly, layer IVC showed an abundance of dendritic frag ments and dendrites that appeared to originate from the infragranular layer s. At the end of the critical period (PD 103), a trend toward morphological maturation for individual neurons found within each layer was observed. Du ring any developmental time point, neurons at first appearance tended to sh ow an immature morphology with staining largely restricted to the cell bodi es. As such, the characteristic arborizations common to mature pyramidal an d multipolar cells was not evident. We propose that the staining pattern se en in this study is consistent with the idea that layers anatomically assoc iated with the magnocellular (M) pathway develop earlier than their parvoce llular (P) counterparts. (C) 2000 Elsevier Science B.V. All rights reserved .