THE DISTRIBUTION OF CYCLIC NUCLEOTIDE PHOSPHODIESTERASE IN THE HYPOTHALAMUS

— Quantitative measurements of capacities of microgram‐sized samples of tissue to hydrolyze adenosine 3′,5′‐phosphate (cyclic AMP) and guanosine 3′,5′‐phosphate (cyclic GMP) have been made in 32 discrete regions of the rabbit hypothalamus. The capacities to hydrolyze the two cyclic nucleotides were found to be distributed over a 3‐fold range and to vary in parallel from region to region. Notable exceptions, however, were observed. A positive association was found between the capacity to hydrolyze cyclic AMP and the reported density of catecholaminergic innervation. No clear relationship was observed between the distributions of the cyclic nucleotide phosphodiesterase activities and that of other enzymes and neurotransmitters.