FIGURE 7.

DA (5 μM) activates a closed loop. DA (5 μM) acts at high affinity D1Rs to confer activity-dependence upon LP I_h (DAD regulation, coral). In addition, 5 μM DA acts at low affinity D1Rs to modulate LP I_A and circuit output (DA modulation, green). Note that the D1R high affinity (coral) and low affinity (green) effects each provide an arm of a closed loop. DA (5 μM) initially increases network cycle frequency, decreases LP burst duration and advances LP activity phase. The latter is due to a decrease in LP I_A. The phase advance not only prevents LP network function, which is to act as a brake on increasing cycle frequencies, but may even drive further increases in cycle frequency. DAD regulation permits these DA-induced changes in activity to subsequently produce a compensatory decrease in LP I_h G_max. This restores the LP I_A:I_h conductance ratio and the timing of LP activity phase at the increased cycle frequency and decreased burst duration. This will stabilize circuit output by limiting further increases in cycle frequency.