Characterization of the coupling strength and its determinants. (A and B) The injection of a series of hyperpolarizing current pulses of increasing intensity into one cell produces corresponding voltage responses in the same cell (Vm Cell 1) and in the coupled cell (Vm Cell 2) in rat (A, left) and mouse (B, left). From these recordings, the CC was estimated by plotting the amplitude of membrane voltage changes (measured at the peak of hyperpolarizing responses, vertical dashed lines) in the postsynaptic cell (Vm Cell 2, ordinates) as a function of membrane voltage changes in the presynaptic cell (Vm Cell 1, abscissas). Each data set was fitted with a straight-line function and the slope values representing the CC are indicated (A and B, right). (C) Histogram showing the distribution of CC calculated for the population of recorded directions in rats (purple) and mice (green). Vertical bars above histograms indicate the population average for each data set (rat: 0.44 ± 0.18 [SD], n = 70 directions, N = 31 animals; mouse: 0.44 ± 0.11 [SD], n = 128, N = 53 animals; P = 0.981, unpaired, two-tailed t test). (D) Rin measured in the population of recorded neurons in rats and mice (rat: 92.3 ± 25.3 MΩ [SD], n = 70 cells, N = 31 animals; mouse: 89.9 ± 27.1 MΩ [SD], n = 128 cells, N = 53 animals; P = 0.538, unpaired, two-tailed t test). (E) Gj values estimated in each assessed direction in rats and mice (rat: 7.54 ± 5.64 nS [SD], n = 70 directions, N = 31 animals; mouse: 6.64 ± 2.56 nS [SD], n = 128 directions, N = 53 animals; P = 0.210, unpaired, two-tailed t test). Horizontal bars in D and E represent population averages. (F) Resting membrane potential (RMP) measured in the population of recorded neurons in rats and mice (rat: −55.6 ± 4.6 mV [SD], n = 70, N = 31 animals; mouse: −55.3 ± 4.0 mV [SD], n = 128, N = 50 animals; P = 0.696, unpaired, two-tailed t test). Horizontal bars in D, E, and F represent population averages.