<i>Per3</i> rhythms in all isolated regional brain cultures from <i>per3-luc</i> zebrafish show entrainment to LD cycles and free-running in DD.

<p>Brains were dissected from adult <i>per3-luc</i> zebrafish and monitored for bioluminescence in either (A, C, E, G, J) 6 days of 12:12LD, 4 days of DD and 4 days back into LD, or (B, D, F, H, K) 7 days of 12:12LD followed by five cycles of 12:12DL. The mean bioluminescence in counts per second (CPS) is plotted (n = 3–4). All brain regions entrain to a 24-hour period in the LD cycle with a peak around ZT4–6 and free-run with a longer period in DD (p<0.0001, two-tailed paired t-test, n = 3–4 per tissue). All regions rapidly entrain to a new LD cycle or DL cycle with a peak at ZT3-5. Black and white boxes indicate the lighting regime and arrows indicate when this changes.