Effects of NGF-antiserum in sympathetic neurons during early postnatal development

Mice at birth and on days 4, 7, and 14 were injected with nerve growth factor antiserum (A-NGF) to determine any changes in the nature of lesions during the early postnatal development of the superior cervical sympathetic ganglion. Correlative light and electron microscopic studies revealed both numerical and morphological changes between the first and second weeks of life. The alterations present in the two younger groups resembled those previously described in the newborn. The three zones were seen in many of the nuclei of affected neurons, resulting from nucleolar segregation. Zones A and B contained RNA and probably represent the pars granulosa and pars fibrosa, respectively, of the nucleolus, while zone C contained DNA, initially forming from the nucleolus-associated chromatin. Lesions were fewer in number and less severe in 7- and 14-day-old mice, but still included similar nucleolar alterations. Zone C differed significantly in structure, however, in that large numbers of vacuoles, many of which contained inclusions of varying form and density, were present throughout its substance. Evidence from ³H-uridine experiments, the similarity of nucleolar alterations to those produced by agents known to block DNA-dependent nucleolar RNA synthesis, and the absence of comparable lesions in the adult strongly suggest that A-NGF produces a block in rRNA synthesis in early neuronal development.