Figure 1

Medium-spiny neuron autaptic and synaptic responses. A. Autaptic response inhibited by bicuculline. Using a standard K-gluconate-based intracellular solution, an autaptic response (left, thick black trace) was evoked by a 1 msec depolarizing command, which triggered an inward action current (truncated off bottom of record, at start of trace). Local perfusion with the GABA_A antagonist bicuculline (gray trace; Bic, 50 μM) completely blocked the response (leaving a small inward tail of the action current). The autaptic response recovered fully (thin black trace), nearly superimposing on the initial, control trace. Perfusion with dopamine (DA, 1 μM) inhibited the autaptic response (right), and this recovered fully. The wash trace in the left panel is the same as control trace in the right panel. Cells were stimulated throughout the experiment at 0.1 Hz to avoid frequency-dependent effects. Control, drug-treatment, and wash traces were collected after responses had stabilized, typically 30 sec after drug application or wash. Averages of 10 traces are shown. The amplitude of the initial control response was 140 pA, which was representative of the amplitude of the autaptic responses measured. B.Synaptic current response inhibited by gabazine. In another experiment, a nearby neuron was stimulated with a loose-patch electrode, evoking a synaptic response in the recorded MSN (left, thick black trace). Local perfusion with the GABA_A antagonist gabazine (10 μM) completely (gray trace) blocked the response (leaving the small inward tail from the stimulus artifact). Following the wash (thin black trace), the synaptic response nearly recovered. Perfusion with DA (1 μM) inhibited the response (right), and this recovered with a second wash, although not completely. Traces shown are averages of 4 or 5 responses. Synaptic responses showed greater variation in amplitude than autaptic responses. The amplitude of the initial control synaptic response shown here was 220 pA, which was somewhat smaller than the typical synaptic response.