Comparison between AMPA-evoked responses in SCN neurons of rats and mice. Optical imaging techniques were used to estimate Ca2+ responses to A MPA in ventral SCN neurons during the night (ZT 15–17). Application of PACAP increased AMPA-evoked currents and Ca2+ responses in ventral SCN region of mice and rats. The left two histograms compare PACAP (10 nM, 240 sec) enhancement of AMPA (25 μM, 120 sec) induced currents in mouse and rat. The right two histograms compare PACAP (10 nM, 240 sec) enhancement of AMPA (25 μM, 120 sec) induced Ca2+ transients in mouse and rat. Pretreatment with PACAP significantly increased AMPA evoked currents and Ca2+ transients in both mice and rats. In both cases, the effects of PACAP were significantly larger in the rat. Asterisks indicate values that are significantly greater in the rat then in the mouse (P < 0.05). Data is shown as means ± SE.