Stimulated formation of cyclic AMP in different areas of chick brain.

Marked accumulation of cerebral cyclic AMP was induced in the chick by the i.v. administration of isoprenaline or histamine of by decapitation. These responses were examined in various cerebral regions and compared to the responses produced in vitro when maximal concentrations of isoprenaline, histamine or adenosine were added to appropriate brain slices. Histamine only markedly stimulated cyclic AMP formation in the cerebral hemispheres. Isoprenaline was equally potent in the cerebellum and the cerebral hemispheres though the medulla-diencephalon and optic lobes were less responsive. There was a lack of correlation between the effects of decapitation in vivo and the responses to adenosine in vitro. Similar accumulations of cyclic AMP were produced by decapitation in the cerebral hemispheres and cerebellum though adenosine was much more effective on cerebellar slices in vitro. The topographical distribution of catecholamine and histamine sensitive cyclic AMP forming sites do not correlate with endogenous levels of noradrenaline or histamine in chick brain and possible interpretations are discussed.