a) Average period length (± SEM) in vitro of SCN slices collected from three anteroposterior positions. b) Average change in cellular period (± SEM) relative to control conditions (line at 0) across anteroposterior positions. c) Period maps (color-coded in online version) illustrating regional effects of V1 antagonism. d) Average period length (± SEM) of cellular rhythms in different SCN regions. e) Magnitude of the period lengthening across neurochemically-distinct regions. Left: Representative images illustrating AVP- and VIP-immunoreactivity in cultured SCN slices (color-coded in online version). Note VIP+ neurons are located in the ventral region of the anterior and middle SCN slice, which can be distinguished from VIP+ fibers in other regions by the brighter, circular staining pattern. Right: Average change in cellular period (± SEM) relative to control conditions (dashed line at 0) across neuropeptide regions. Regions used for grouping are AVP: 1, 4, 7, 8; VIP: 3, 6; Other: 2, 5. For A–E) * p < 0.01, + p < 0.05, n = 7–8 slices per group for each plane. Note that small error bars may be obscured by symbols.