COMPARISON OF THE EFFECTS OF DEPOLARIZING AGENTS AND NEUROTRANSMITTERS ON REGIONAL CNS CYCLIC GMP LEVELS IN VARIOUS'ANIMALS

Abstract— The effects of 121 mm‐K⁺, 10 mm‐glutamate, 5 mm‐GABA, 1 mm‐glycine, 0.1 mm‐NE, and 1–10 μmACh on cyclic GMP levels in tissue slices prepared from cerebral cortex and cerebellum of mouse, rabbit, guinea‐pig, cat, and rat were studied. Basal levels of cyclic GMP in the cerebella of mice, guinea‐pigs and cats were 4–15 and 70 pmol/mg prot in rat, whereas in the cerebral cortex of the same animals, levels were only 0.6–2 pmol/mg prot. In contrast, basal levels of the cyclic nucleotide were 1–2 pmol/mg prot in both of these regions in rabbit brain. Only 121 mm‐K⁺ was capable of increasing cyclic GMP levels in all the tissues studied. Elevations ranged from 30% in rat cerebral cortex to 2800% in mouse cerebellum. Glutamate produced a 30–1000% rise of cyclic GMP levels in all tissues except rabbit cerebellum. NE elevated levels of cyclic nucleotide 2‐ to 3‐fold in slices of cerebellum from all species studied but had no effect in cerebral cortex. GABA and glycine had no effect in any tissue except mouse cerebellum. ACh had no consistent effect on levels of cyclic GMP in any brain region investigated. These results suggest that mechanisms regulating cyclic GMP levels in mammalian CNS vary among brain regions and among animal species.