Variance-mean analysis of the dm-cNTS (NTS) and DMX neurons revealed distinct synaptic properties. A, variance-mean analysis of three representative neurons. Stable successive EPSC responses were recorded in the presence of 5.0 (shown for only DMX neurons), 2.0, 1.0, 0.5 and 0.25 mM [Ca2+]o solutions. Aa, the EPSC amplitude in response to each stimulation under different [Ca2+]o (shown above). Ab-c, the relationship between the mean EPSC amplitude (abscissa) and its variance (ordinates) over 70-94 consecutive trials. The quadratic functions of each graph show the best-fit estimation obtained by fitting the formula onto the actual values obtained in each neuron. B, the relationships between PPR and release probability (Pr; a), number of release sites (b) and quantal EPSC size (c). Note the strong and significant correlation between PPR and Pr (ρ = -0.88, n = 17, p < 0.01). C, summary of estimated Pr (a), number of release sites (b) and quantal size (c). **, p < 0.01; *, p < 0.05; Mann-Whitney U-test. The same comparison was made for all other combinations in Ca-c but the values were not significantly different.