REGULATION OF CYCLIC ADENOSINE 3′, 5′‐MONOPHOSPHATE CONCENTRATION IN CHICK CEREBRAL HEMISPHERES DURING DEVELOPMENT

Abstract

Abstract— Investigations have been carried out into developmental aspects of cyclic AMP metabolism and responsiveness to neurohormones in chick cerebral hemispheres. The in vivo cyclic AMP concentration, measured after freeze‐blowing, was found to be highest in the embryonic brain, and changes in the cyclic nucleotide content produced by ischaemia increased with age. The magnitude of the in vivo increases in cyclic AMP produced by isoprenaline and by histamine decreased throughout the first postnatal month. The onset of isoprenaline‐ and histamine‐induced cyclic AMP accumulation in brain slices occurred around 17 days embryonic age, reached a maximum at about 3 days post‐hatch and fell to approx 50% of this response at 28 days of age. Adenosine stimulated cyclic AMP formation to a similar extent at all ages studied.The activities of adenylate cyclase and cyclic AMP phosphodiesterase of hemisphere homogenates were found to reach maximum near the time of hatching. Since the overall pattern of responsiveness of the cerebral cyclic AMP system to neurohormones does not correlate with these variations in enzyme activities, it is suggested that changes occurring at the synaptic receptor level may explain the developmental variations observed.