DOPAMINE REVERSES THE DEPRESSION OF RAT CORTICOSTRIATAL SYNAPSES WHICH NORMALLY FOLLOWS HIGH-FREQUENCY STIMULATION OF CORTEX IN-VITRO

Learning deficits resulting from dopamine depletion suggest that stria tal dopamine release is crucial for reinforcement.(13) Recently descri bed firing patterns of dopamine neurons in behaving monkeys(7) show th at transient increases in dopamine release are brought about by reinfo rcement. We describe an enduring change in the strength of synaptic tr ansmission following pulsatile application of dopamine intended to mim ic the transient increases associated with reinforcement. Intracellula r records were made from neurons in slices of the rat corticostriatal system. Neurons having the properties of the medium-sized spiny neuron s responded to cortical stimulation with depolarizing potentials (peak amplitude 12.0 +/- 1.3 mV; latency 9.2 +/- 0.1 ms; mean +/- S.D., n = 19), which had the properties of monosynaptic excitatory postsynaptic potentials. After trains of stimuli to the cortex had been applied in conjunction with intracellular depolarizing current, the size of thes e excitatory postsynaptic potentials was reduced (-27% at 20 min). App lication of dopamine (similar to 30 mu M) in a solution containing KCl concomitant with depolarization and presynaptic activation increased the subsequent excitatory postsynaptic potentials (+21% at 20 min) wit hout significant lasting change in the membrane properties of the post synaptic cell. This suggests that dopamine has an enduring, activity-d ependent action on the efficacy of corticostriatal transmission, which may be a cellular basis for the learning-related effects of the nigro striatal system.