EFFECTS OF THIOPENTONE ON EXCITATION AND INHIBITION IN THE CENTRAL NERVOUS-SYSTEM OF HELIX

1. 1. The effects of perfusing thiopentone (0.1-1.0 mM) on the membrane properties and postsynaptic responses to nerve stimulation and putative transmitters in two identified neurones (F1 and E4) in Helix were studied using intracellular recording techniques. 2. 2. The ionic mechanisms of the postsynaptic responses to nerve stimulation and iontophoretic application of putative transmitters in F1 and E4 were determined by reversal potential measurements and by changing the ionic gradients across the cell membrane. 3. 3. Thiopentone reversibly potentiated and prolonged the slow potassium-dependent synaptically produced inhibitory potential in F1 in a dose dependent manner. A similar effect was obtained on the potassium-dependent inhibitory responses to iontophoretically applied dopamine in F1 and E4. Dopamine is believed to be the transmitter for the synaptic event. 4. 4. Thiopentone reversibly depressed the depolarizing sodium-dependent response to acethylecholine in F1 without an effect on the input resistance of the cell. 5. 5. Thiopentone reversibly depressed in a dose dependent manner the fast chloride-dependent inhibitory responses and associated conductance increases to acetylcholine and glutamate in E4 and to glutamate in F1 with no effect on the input resistance. In some cells the duration of these inhibitory events was prolonged after their depression by thiopentone. 6. 6. These results show that thiopentone potentiated slow potassium-dependent inhibitory events but depressed fast sodium-dependent excitatory events and fast chloride-dependent inhibitory events in Helix neurones. 7. 7. The possible mechanism of action of the effects of thiopentone on the excitatory and inhibitory events is discussed in relation to a receptor or receptor-coupled ionophore interaction. © 1979.