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The hydrolysis of p-nitrophenyl-2-acetamido-2-deoxy-fi-~-gluco-(I) and 8-Dgalacto-pyranoside (11) and of p-nitrophenyl-a-D-mannopyranoside (111) by neuronal cell bodies and glial cells isolated from the cerebral cortex of 18-day-old or adult rats was found to be equally efficient, with relative ratios of hydrolysis for I, I1 and I11 of approximately 10: 1 : 0 5 in both cell types and at both ages. Homogenatesoftheneuronal cell bodies obtained from cerebral cortices of 3-, 8-, 12-, 18-and 32-day-old rats were subjected to differential centrifugation and the subcellular localization of N-acetyl-fi-o-ghcosaminidase (EC 3.2.1.30) bydrolysing (I)] was compared to that of the mitochondrial marker, succinate-INToxidoreductase (EC 1.3.99.1). A fraction in which N-acetyl-B-D-ghcosaminidase exhibited maximal specific activity could be isolated at all ages, an observation indicating that the potential for active hydrolytic performance is incorporated into the neuronal lysosome very early post-natally. The specific activities of N-acetyl-fi-D-glucosaminidase and succinate-INT-oxidoreductase reached their respective maxima at widely different times postnatally: at 10-12 days for the mitochondrial enzyme and at about 18 days for the glycosidase, a difference suggesting that in the cortical neuron lysosomes and mitochondria develop out of step. The mitochondrial, lysosomal and microsomal fractions obtained by differential centrifugation were subjected to equilibrium density centrifugation and the presence of two populations of N-acetyl-fi-D-glucosaminidase-bearing particles was demonstrated. Although their presence was readily apparent in the neurons from 8-and 12-day old brains, it was difficult to discern their presence in the neurons from the 3-and the 18-day-old brains. In 8-day-old brains gradient fractions obtained from neurons containing N-acetyl-P-Dglucosaminidase of a specific activity up to %fold higher than that of the enzyme in the original neuronal homogenate were examined by electron microscopy and the concentration of numerous lysosomes and derivative bodies in these fractions was verified. Our present study demonstrates the capability of the immature and developing neuron to tightly couple the pace of its degradative processes to that of its highly efficient and highly selective synthetic activities. acetylaminodeoxyglucohydrolase) is localized in the lysosomes of the cerebral cortex of the rat (SELLINGER, RUCKER and DE BALBIAN VERSTER, 1964) and the guinea pig (BOSMANN and HEMSWORTH, 1970), as well as in the lysosomes of several other anatomical areas of the rat brain (SELLINGER and HIAIT, 1968; SELLINGER and NORDRUM, 1969; SELLINGER, NORDRUM and IDOYAGA-VAKGAS, 1971b). TALLMAN, BRADY and SUZUKI (1971) recently demonstrated the lysosomal localization of this hydrolase in

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Neuronal perikarya were isolated from rat cerebral cortex at different stages of postnatal development. Membranes sedimenting at 10000Og were obtained from these neurons to study several glycosyltransferases of the dolichol pathway. Enzyme activities from stages before and during synapse formation were compared (days 5 and 15 respectively). Dolichyl diphosphate (Dol-P-P) N-acetylglucosamine, dolichyl phosphate mannose and dolichyl phosphate glucose synthases and the enzymes catalysing Dol-P-P-GlcNAc2Man9Glc3 formation were higher at day 15 of postnatal development.The glycosyl transfer of the latter compound to endogenous protein(s) as well as to a dinitrophenyl-heptapeptide was also measured. The activity was higher at day 15. Furthermore, the activity of dolichyl phosphate mannose synthase was also measured during the time when the number of synapses ceased to increase (day 36) and in the adult stage. The activity of dolichyl phosphate mannose synthase was higher at day 36 than at day 15, and declined in the adult stage. From these results it may be concluded that there is an increase in the glycosylation of asparagine-type glycoproteins during synapse formation in the neurons of the cerebral cortex.

A soluble fraction from rat brain neuronal perikarya was shown to contain both the specific and nonspecific forms of the enzyme acetylcholinesterase (EC's 3.1.1.7. and 3.1.1.8., respectively). The ratio of the enzyme activities varied along the course of brain development: the nonspecific form being predominant from 1 to 15 days of age and the specific one showing the pattern of rising activity from day 15 onward. We suggest a possible relationship between this changing in cholinesterase activities and the establishment of synapses within the rat cerebral cortex.

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