J. Quillfeldt - Academia.edu (original) (raw)
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The five muscarinic acetylcholine receptors (M 1 -M 5 ) are differentially expressed in the brain... more The five muscarinic acetylcholine receptors (M 1 -M 5 ) are differentially expressed in the brain. M 2 and M 4 are coupled to inhibition of stimulated adenylyl cyclase, while M 1 , M 3 and M 5 are mainly coupled to the phosphoinositide pathway. We studied the muscarinic receptor regulation of adenylyl cyclase activity in the rat hippocampus, compared to the striatum and amygdala. Basal and forskolin-stimulated adenylyl cyclase activity was higher in the striatum but the muscarinic inhibition was much lower. Highly selective muscarinic toxins MT1 and MT2-affinity order M 1 C M 4 [ [ others-and MT3-highly selective M 4 antagonist-did not show significant effects on basal or forskolin-stimulated cyclic AMP production but, like scopolamine, counteracted oxotremorine inhibition. Since MTs have negligible affinity for M 2 , M 4 would be the main subtype responsible for muscarinic inhibition of forskolin-stimulated enzyme. Dopamine stimulated a small fraction of the enzyme (3.1% in striatum, 1.3% in the hippocampus). Since MT3 fully blocked muscarinic inhibition of dopamine-stimulated enzyme, M 4 receptor would be responsible for this regulation.
The five muscarinic acetylcholine receptors (M 1 -M 5 ) are differentially expressed in the brain... more The five muscarinic acetylcholine receptors (M 1 -M 5 ) are differentially expressed in the brain. M 2 and M 4 are coupled to inhibition of stimulated adenylyl cyclase, while M 1 , M 3 and M 5 are mainly coupled to the phosphoinositide pathway. We studied the muscarinic receptor regulation of adenylyl cyclase activity in the rat hippocampus, compared to the striatum and amygdala. Basal and forskolin-stimulated adenylyl cyclase activity was higher in the striatum but the muscarinic inhibition was much lower. Highly selective muscarinic toxins MT1 and MT2-affinity order M 1 C M 4 [ [ others-and MT3-highly selective M 4 antagonist-did not show significant effects on basal or forskolin-stimulated cyclic AMP production but, like scopolamine, counteracted oxotremorine inhibition. Since MTs have negligible affinity for M 2 , M 4 would be the main subtype responsible for muscarinic inhibition of forskolin-stimulated enzyme. Dopamine stimulated a small fraction of the enzyme (3.1% in striatum, 1.3% in the hippocampus). Since MT3 fully blocked muscarinic inhibition of dopamine-stimulated enzyme, M 4 receptor would be responsible for this regulation.