Modulation of Quantal Synaptic Release by Serotonin and Forskolin in Crayfish Motor Nerve Terminals
In crustacea, serotonin is released into the haemolymph and acts as a neurohormone and modulator at central and peripheral neurons (see Kravitz et al. 1983, Harris-Warrick and Kravitz 1984). Serotonin applied to neuromuscular junctions increases excitatory postsynaptic potentials (Grundfest and Reuben 1961, Dudel 1965, Wheal and Kerkut 1976, Enyeart 1981, Glusman and Kravitz 1982, Fischer and Florey 1983, Dixon and Atwood 1985). The increased synaptic potentials are due to enhanced release of transmitter quanta from motor nerve terminals (Dudel 1965, Glusman and Kravitz 1982, Dixon and Atwood 1985). These presynaptic effects of serotonin were suggested to reflect improvement of the action potential in the terminal nerve branch (Dudel 1965), or increases of the Ca concentration in the terminal (Glusman and Kravitz 1982, Dixon and Atwood 1985). These investigations have elicited release by action potentials and employed bath application of serotonin. Effects on the action potential and its conduction could not be distinguished from changes in the coupling between depolarization and release. In the present study excitation of the nerve terminals could be blocked depolarizing them with graded pulses, and serotonin was applied only to the terminal under investigation.
KeywordsMagnesium Adenosine Serotonin Acetylcholine Forskolin
Unable to display preview. Download preview PDF.
- Dudel J (1965) Facilitatory effects of 5-hydroxy-tryptamine on the crayfish neuromuscular junction. Naunyn-Schmiedebergs Arch exp Path Pharm 249:515–528Google Scholar
- Dudel J (1988a) Calcium dependence of quantal release triggered by graded depolarization pulses to nerve terminals on crayfish muscle. Submitted for publicationGoogle Scholar
- Dudel J (1988b) Calcium and depolarization dependence of facilitation of synaptic release at nerve terminals on crayfish muscle. Submitted for publicationGoogle Scholar
- Glusman S, Kravitz E (1982) The action of serotonin on excitatory nerve terminals in lobster nerve-muscle preparations. J Physiol (Lond) 325:223–241Google Scholar
- Grundfest H, Reuben JP (1961) Neuromuscular synaptic activity in lobster. ‘Nervous inhibition’, Proceedings of an International Symposium, Ed. E. Florey, Oxford, Pergamon Press p 92–104Google Scholar
- Hatt H, Franke C, Dudel J (1987) Calcium dependent gating of the L-glutamate activated, excitatory synaptic channel in crayfish muscle. Pflügers Arch (in press)Google Scholar
- Katz B, Miledi R (1968) The role of calcium in neuromuscular facilitation. J Physiol (Lond) 195:481–492Google Scholar
- Seamon KB, Daly JW (1983) Forskolin, cyclic AMP and cellular physiology. TIPS 4:120–123Google Scholar
- Wheal HV, Kerkut GA (1976) The pre- and post-synaptic actions of 5-HT in crustacea. Comp Biochem Physiol 540:67–70Google Scholar