Dopamine inhibits transmission between the interneuron initiating pacemaker activity in a bursting neuron and the bursting neuron on the snail Helix pomatia.

1. The effect of external application of dopamine on connection between a peptidergic interneuron initiating bursting pacemaker activity in non-active burster RPa1 and the bursting neuron itself of the snail Helix pomatia has been investigated under clamp conditions. 2. External application of dopamine in a dose-dependent manner (Kd 15 microM) produces a reversible inhibition of slow inward current (SIC) in the RPa1 neuron evoked by stimulation of peptidergic interneuron. At the same time, an increase of duration and amplitude of interneuronal action potential was observed. 3. Stimulation of the anal nerve evokes in RPa1 neuron postsynaptic current consisting of at least three components: two fast ones with reversal potentials -50 and -70 mV and a long-lasting one with no reversal potential between -50 and -95 mV. 4. It is concluded that inhibition of SIC by dopamine is due to the processes occurring in the postsynaptic RPa1 neuron. 5. Based on the hypothesis that bursting activity of RPa1 neuron results from the activation of presynaptic unidentified peptidergic interneuron(s) with persistent activity and on data presented it is suggested that inhibition of bursting activity evoked by application of dopamine or anal nerve stimulation is a consequence of decreased efficiency of synaptic transmission between the interneuron initiating bursting activity and the burster.