FIG 5. Network properties convey temperature resistance to the SCN.
(a) Bioluminescence trace from an SCN explant obtained from PER2∷LUC mice (bioluminescence represents PER2∷LUC expression). The SCN is resistant to perturbation by temperature signals. Blocking communication among SCN neurons with TTX allows a 6h temperature pulse (temperature increased to 38.5°C, indicated by yellow bar) to reset the phase of the SCN. (b) Phase transition curves (PTCs) plotting phase prior to temperature pulse (“old phase”) against phase following temperature pulse (“new phase”). PTCs are from SCN cultures from PER2∷LUC mice without drug (gray), with 1μM TTX (red), and with 5μM TTX (blue). Following TTX treatment, the SCNs display type 0 phase-resetting. Type 0 resetting is strong resetting, with oscillators resetting to a common phase, regardless of the phase at which the resetting signal is administered. (c) Heat maps demonstrating the effects of TTX on temperature resetting in individual neurons within an SCN culture. In whole SCN explants, phase and period length are stable and robust, although some variability in phase can be observed (left). Following TTX treatment, SCN neurons are uncoupled (right). Individual neurons in the TTX-treated condition free-run, resulting in a wide range of phases. TTX also renders individual SCN neurons sensitive to temperature-induced phase resetting. A 6h temperature pulse (temperature increased to 38.5°C, indicated by yellow bar) synchronizes the phases of individual neurons in the TTX-treated SCN. No effect on phase was observed when a temperature pulse was administered in the absence of TTX. Heat maps were generated by imaging single cell-sized regions of interest using a cooled charge-coupled device (CCD) camera. Maps display voxels measured from dorsal to ventral through the SCN. Red corresponds to the peak of bioluminescence and green to the trough. Reproduced, with permission, from AAAS [72].