Potentiation of dopaminergic transmission by phosphodiesterase inhibitors and cyclic nucleotides.

Experiments were made to determine whether cyclic AMP plays a role in transmission at identified dopaminergic synapses in the water snail Planorbis corneus. Intracellular stimulation of a specific dopamine neuron produces direct inhibitory postsynaptic potentials (ipsps) in a number of other neurons. These ipsps, which are mediated by dopamine, were potentiated by as much as 120% by caffeine, theophylline or dibutyryl cyclic AMP, although they were unaffected by cyclic AMP and prostaglandin E1. Caffeine and theophylline also potentiated the inhibitory response to dopamine, applied to the postsynaptic neurons by perfusion or iontophoresis, but the effects were generally much smaller (maximum potentiation 30%). The results provide evidence that postsynaptic cyclic AMP is involved in transmission at these synapses, but that the phosphodiesterase inhibitors may also have a presynaptic effect.