Figure 9.

SCI disrupts diurnal rhythms. A, Diurnal rhythm control under homeostatic conditions. Initial circadian input occurs via light activating specialized retinal ganglion cells that project directly to the SCN. The SCN is the master circadian oscillator; in turn, this regulates extra-SCN (“peripheral”) rhythms via direct and indirect routes. The SCN controls peripheral clocks directly via autonomic control (sympathetic and parasympathetic innervation), whereas the SCN controls peripheral clocks indirectly through the regulation of physiologic and humoral factors. Appropriately entrained clocks throughout the body (likely every cell) optimize organismal performance for time of day. B, Diurnal rhythm control is disrupted by SCI. Our data suggest that SCI disrupts rhythms of key zeitgeber times, including body temperature, activity, and CORT level (yellow bolts), which could disrupt peripheral clock entrainment. In addition, data from other groups suggest that SCI also disrupts additional entraining factors (e.g., feeding, melatonin, and autonomic input; gray bolts). Ultimately, prolonged SCI-elicited disruption of these entraining factors could contribute to the loss of homeostasis and suboptimal repair.