ACTIVITY OF 2′,3′‐CYCLIC‐NUCLEOTIDE 3′‐PHOSPHODIESTERASE IN REGIONS OF RAT BRAIN DURING DEVELOPMENT: QUANTITATIVE RELATIONSHIP TO MYELIN BASIC PROTEIN

2′,3′‐Cyclic‐nucleotide‐3′‐phosphodiesterase activity was examined in several regions of rat brain during development, namely optic nerve, olfactory bulb, cerebrum, cerebellum, midbrain, brain stem, and spinal cord. From 4 to 120 days the total activity increased in all regions, although the specific activity approached a constant value in adults. The developmental profile of the enzyme appeared to correlate with the onset of myelination and with the levels of myelin basic protein as well as the appearance of galactocerebroside sulfotransferase. A correlation coefficient of 0.91 was found between total basic protein, expressed as the per cent of the adult (120 day) value, and total enzyme activity over 12–42 days of age (P < 0.001) from six different brain regions as well as for whole brain. By increasing the sensitivity of the assay with the use of [³H‐8]adenosine 2′,3′‐cyclic monophosphate, we were able to detect activity at birth in both whole brain and spinal cord.