Further identification of multiple responses mediated by dopamine in the CNS of Planorbis corneus

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Abstract
Intracellular recordings from neurons, receiving monosynaptic contacts from a dopamine-containing (DA-containing) neuron in the central ganglia of the gastropod mollusk P. corneus, revealed that there are at least 3 DA-mediated responses. These are fast excitatory postsynaptic potentials (EfPSP) (200 ms), slow excitatory postsynaptic potentials (EsPSP) (900 ms) and inhibitory postsynaptic potentials (IPSP) (200-900 ms). Various combinations of these synaptic potentials were recorded from postsynaptic neurons: EsPSP, EfPEP, EsEfPSP, or EfIPSP. Neurons receiving such connections responded appropriately to iontophoresized DA with a fast depolarization (EfPSP), a slow depolarization (EsPSP) or a hyperpolarization (IPSP). These responses could be distinguished on the basis of function (excitation or inhibition), duration, rate of desensitization and sensitivity to apomorphine, D-LSD and tubocurarine. The neuroleptic drugs (DA antagonists) haloperidol, fluphenazine and metoclopramide reduced excitatory and inhibitory DA transmission. DA is probably the transmitter mediating multiple synaptic responses in Planorbis.