General Paper
5-HT receptors on identified Lymnaea neurones in culture: Pharmacological characterization of 5-HT2 receptors

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Abstract

1. Pressure ejection techniques were used to investigate the identity of receptors mediating 5-HT (5-Hydroxytryptamine) effects on the serotonin-containing cerebral giant cells (CGCs) of the cerebral ganglia and some of their follower motorneurones from the buccal ganglia of Lymnaea stagnalis in culture.

2. The vertebrate 5-HT2 receptor agonist α-methylserotonin maleate (10−4 M), inhibited most of the neurones inhibited by 5-HT (10−3 M). Others were excited by both agonists. In cells where 5-HT failed to evoke any effects, the 5-HT2 agonist also lacked an effect.

3. Bath application of the 5-HT2 receptor antagonists ketanserin and methysergide (10−4 M), not only blocked spike generation, but also reduced both the excitatory and inhibitory responses to both 5-HT and α-methylserotonin maleate, while the 5-HT3 antagonist MDL 72222 (10−4 M) failed to block α-methylserotonin maleate effects.

4. At 10−3 M, α-methylserotonin maleate increased the amplitudes of the hyperpolarizing responses in a dose-dependent manner. These responses were blocked by ketanserin (10−4 M).

5. The above results suggest that 5-HT2 receptors are involved in the responses of the CGCs and the buccal motorneurones to 5-HT in Lymnaea stagnalis. The pharmacological characterization of these receptors indicates that the compounds that interact with the 5-HT2 receptors in mammals also interact with the 5-HT2 receptors in molluscs.

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