Octopamine is released by the intrinsic OC interneurons in the paired buccal ganglia and serves both as a. neurotransmitter and a. neuromodulator in the central feeding network of the pond snail Lymnaea stag-nalis .
The identified Bl buccal motoneuron receives excitatory inputs from the OC interneurons and is more excitable in the presence of 10 |lM octopamine in the bath. This modulatory effect of octopamine on the B1 motoneuron was studied using the two electrode voltage clamp method.
In normal physiological saline depolarising voltage steps from the holding potential of-80 mV evoke a. transient inward current, presumably carried by Na+ ions. The peak values of this inward current are increased in the presence of 10 |lM octopamine in the bath. In contrast, both the transient (IA) and delayed (IK) outward currents are unaffected by octopamine application.
Replacing the normal saline with aNa+-free bathing solution containing K+ channel blockers (50 mM TEAC1, 4 mM 4AP) revealed the presence of an additional inward current of the Bl neurons, carried by Ca2+. Octopamine (10 |lM) in the bath decreased the amplitudes of this current.
These results suggest that the membrane mechanisms which underlie the modulatory effect of octopamine on the Bl motoneuron include selective changes of the Na+- and Ca2+-channels.
Lymnaeaoctopamine modulation membrane current voltage clamp
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