Summary
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1.
The effects of different neurotransmitters on cAMP levels in segmental ganglia ofHirudo were studied. Serotonin and dopamine caused a significant increase in cAMP levels. Norepinephrine, octopamine, glutamate, and carbachol were ineffective.
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2.
The stimulation of cAMP levels by dopamine was blocked by increasing the concentration of Mg2+ ions in the incubation bath. Serotonin was still effective in stimulating cAMP synthesis in the presence of high Mg2+ concentrations. Imidazole, a cAMP-phosphodiesterase activator, markedly inhibited the increase in cAMP induced by serotonin. Serotonin, but not dopamine, significantly stimulated adenylate cyclase activity in homogenates of segmental ganglia. The serotonin effect was blocked by RMI 12330A.
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3.
Electrical stimulation of peripheral roots induced excitation of the fast conducting system. Repetitive stimulation (0.1/sec) resulted in a waning of firing discharge (habituation). A strong noxious stimulus applied to another pathway gave rise to a potentiation of the depressed response (dishabituation). The dishabituation was abolished by methysergide.
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4.
These results indicate that serotonin may mediate short-term plastic changes such as dishabituation through a mechanism involving cAMP in the leechHirudo.
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Biondi, C., Belardetti, F., Brunelli, M. et al. Increased synthesis of cyclic AMP and short-term plastic changes in the segmental ganglia of the LeechHirudo medicinalis . Cell Mol Neurobiol 2, 81–92 (1982). https://doi.org/10.1007/BF00711074
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DOI: https://doi.org/10.1007/BF00711074