5-HT receptors on identified Lymnaea neurones in culture: pharmacological characterization of 5-HT3 receptors.

1. The selective agonist, 1-(m-chlorophenyl)-biguanide (m-CPBG) and antagonist, 3-tropanyl-3,5-dichlorobenzoate (MDL 72222) were used to characterize the 5-HT3 receptors in cultured identified neurones; the serotonin-containing cerebral giant cells (CGCs) and some follower neurones in the buccal ganglia of Lymnaea stagnalis. 2. 5-HT and its agonists were pressure ejected, while the 5-HT antagonists were bath applied. 3. Although m-CPBG evoked mostly depolarizing responses, hyperpolarizing responses were sometimes evoked. 4. At 10(-4) M, m-CPBG failed to mimic the responses of 5-HT, but at a concentration higher, 10(-3) M, pressure-ejected m-CPBG mimicked most 5-HT responses. 5. The 5-HT2 antagonist ketanserin failed to block the m-CPBG-evoked responses, whilst partially blocking the 5-HT responses. 6. These results suggest the presence of 5-HT3 receptors similar to those found in mammalian neurones, and that multiple subtypes of these receptors may be present in Lymnaea neurones.