Figure 4. Interneuron population size is not a primary determinant of the level of functional cortical inhibition.

(a) Representative traces of spontaneous inhibitory postsynaptic currents (sIPSCs) recorded from endogenous neocortical pyramidal neurons in vitro (media vehicle (Con), top; interneuron transplant recipient (Int), bottom). Vertical scale bar, 40 pA; horizontal scale bar, 200 ms. (b) Transplanted interneurons increase the frequency (top), but not the amplitude (bottom) of sIPSCs recorded at 30 to 40 DAT (Wilcoxon rank-sum test, * P < 0.05 and P = 0.22, respectively; n = 23 recorded cells from control animals, n = 37 recorded cells from interneuron transplant recipients). Mean transplanted cell density for transplant recipient group = 23.3 ± 3.8 cells/mm². Error bars represent the standard error of the mean. (c) The frequency of sIPSCs onto host pyramidal neurons does not increase with the density of transplanted interneurons (linear regression analysis, slope = 0.0003, r² = 0.0003).