Developmental protein changes in normal and chromatolytic facial nerve nuclear regions

Abstract

Facial neurons were severed at the stylomastoid foramen in immature (15- and 20-day-old) and adult hamsters. Four days later animals were killed under Nembutal, in accordance with either of two approaches. In one series, after perfusion with physiological saline, the medullas were immediately removed, quickfrozen in liquid nitrogen, and sectioned in a cryostat. Facial nerve nuclear regions from the experimental and control sides were dissected free from the dehydrated sections and analyzed for protein differences by micro disc electrophoresis. In another series, 3H-leucine was injected intraperitoneally 24 hr before killing by perfusion-fixation. Isotope uptake in experimental and control facial neurons was determined by autoradiography. The pattern of protein changes and the uptake of the amino acid on the chromatolytic side became progressively more dissimilar from the normal, the more mature the neurons were at the time of operation. This involved an increase in both the number of separated proteins and the uptake of labeled leucine on the experimental side. We suggest that these reactive differences may reflect two different types of metabolism, present, respectively, in immature and mature nuclear regions. The first type, present in immature and chromatolytic regions, may be concerned with the synthesis of structural proteins. The second type, present in adult normal nuclear regions, may be concerned with the synthesis of proteins for cell maintenance and function.