Muscarinic actions in hippocampus are probably not mediated by cyclic GMP.
It has been proposed that, in a variety of tissues, guanosine 3':5'-monophosphate (cyclic GMP) is the intracellular mediator of muscarinic effects. This hypothesis was tested in the CA1 region of the hippocampus, in urethane-anaesthetized rats, by studying extracellularly muscarinic disinhibition of disfacilitation and the effect of dibutyryl cyclic GMP, muscarinic agents and an inhibitor of cyclic nucleotide-dependent kinase (H-8), all applied by microiontophoresis. The main findings were: (a) cyclic GMP analogues do not mimic disfacilitation or disinhibition produced by muscarinic agents; (b) N-(2-(methylamino)ethyl)-5-isoquinoline sulfonamide (H-8) does not prevent the excitatory actions of muscarinic agents; and (c) H-8 alone does not change the field responses. In conclusion, cyclic nucleotide-dependent kinases do not seem to play a major role in the on-going modulation of excitability in the hippocampus and cyclic GMP is unlikely to be a major intracellular messenger mediating directly or indirectly the excitatory actions of acetylcholine.
Agopyan
N
N
Department of Physiology, McGill University, Montréal, Qué., Canada.
Krnjević
K
K
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000494:pharmacology / Q000502:physiology*; D003995:Dibutyryl Cyclic GMP / Q000494:pharmacology; D005071:Evoked Potentials / Q000187:drug effects; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D007546:Isoquinolines / Q000494:pharmacology; D010277:Parasympathomimetics / Q000494:pharmacology*; D047428:Protein Kinase Inhibitors; D051381:Rats; D011919:Rats, Inbred Strains
D007546:Isoquinolines; D010277:Parasympathomimetics; D047428:Protein Kinase Inhibitors; D015124:8-Bromo Cyclic Adenosine Monophosphate; C016276:8-bromocyclic GMP; D003995:Dibutyryl Cyclic GMP; C053177:N-(2-(methylamino)ethyl)-5-isoquinolinesulfonamide; D006152:Cyclic GMP; D000109:Acetylcholine