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Journal of Experimental Biology 149,161-176 (1990)
Published by Company of Biologists 1990

MODULATION OF TENSION PRODUCTION BY OCTOPAMINE IN THE METATHORACIC DORSAL LONGITUDINAL MUSCLE OF THE CRICKET TELEOGRYLLUS OCEANICUS

BRUCE A. O'GARA 1 and CHARLES D. DREWES 2

1 Present address: Department of Biology, Gilmer Hall, University of Virginia, Charlottesville.VA 22901, USA
2 Department of Zoology, Iowa State University, Ames, IA 50011, USA; Present address: Department of Biology, Gilmer Hall, University of Virginia, Charlottesville.VA 22901, USA

1. Application of octopamine to the metathoracic dorsal longitudinal muscle (DLM) of the cricket Teleogryllus oceanicus produced dose-dependent increases twitch amplitude, contraction rate and relaxation rate. The threshold for octopamine effects was between 10-8 and 10-7moll-1, while maximal effects were seen at approximately 10-5moll-1

2. The octopamine receptors were classified as octopamine2 receptors on the basis of the differential responsiveness of the muscle to the octopamine agonists naphazoline, tolazoline, clonidine and the octopamine antagonists metoclopramide and chlorpromazine. It was not possible to distinguish between octopamine2A or octopamine2B receptors in this preparation.

3. Octopamine had both presynaptic and postsynaptic effects, since it increased both miniature end-plate potential (mEPP) frequency and muscle relaxation rate

4. At a calcium concentration of 11 mmoll-1, octopamine did not affect muscle membrane potential, input resistance or EJP amplitude, but the EJP duration at half amplitude (T1/2) was slightly increased. In low-calcium saline (1.8 mmol-1), octopamine did not affect membrane potential or T1/2, but EJP amplitude was increased

5. Stimulation of the octopaminergic dorsal unpaired median neuron (DUMDL), which innervates the metathoracic DLM, increased twitch amplitude about 25% of the preparations. Failure in the other preparations wasapparently due to spike conduction failure within the metathoracic ganglion.6. These results show that octopamine can be an important modulator of metathoracic DLM tension production

Key words: octopamine, receptor, insect muscle, modulation

Accepted on November 16, 1989






© The Company of Biologists Ltd 1990