Fig. 7.
A change in μss, but not in τ, can account for the effect of ZD-7288 on nIB frequency and regularity. A, CIHs of experimental nIBs from a P6 slice in control ACSF (× symbols) was fitted by a curve (solid line) computed with the parameter values μss = 184 and τ = 4 sec. The effect of 20 μm ZD-7288 (squares) was well fitted (solid line) by reducing μss to 167.5, with only a minor increase in τ (to 4.6 sec). With μssunchanged, a 2.5-fold increase in τ (to 10.5 sec) was required to achieve the same rightward shift in the median IBI, but the resulting curve (dotted line) did not reproduce the pronounced decrease in the slope of the experimental CIH. Experimental CIHs were calculated in 1 sec bins. B, The value of the model parameter μ (lefty-axis) in control ACSF (heavy solid line) and in ZD-7288 (heavy dashed-dotted line), as a function of the time elapsed because the previous burst, for the same parameter values used inA. The relatively small reduction in μssrequired to simulate the effect of the drug caused a dramatic drop in the probability of burst occurrence per 100 msec (righty-axis) in ZD-7288 (light dashed-dotted line) compared with control ACSF (light solid line), because now fluctuations around μ only rarely crossed threshold (compare with Fig.6C,D).