Fig. 2.

Daily expression profiles of genes involved in phrenic long-term facilitation elicited by acute intermittent hypoxia (Htr2a, Htr2b, Bdnf, and Ntrk2) in caudal medulla and ventral C3–C5 cervical spinal cord homogenates (n = 8 samples/time point). Real-time reverse transcription-polymerase chain reaction (RT-PCR) was performed to determine mRNA levels of Htr2a, Htr2b, Bdnf, and Ntrk2. Caudal medulla and ventral C3–C5 spinal cord mRNA levels were normalized to the β-actin. The black line shows the corresponding fitted cosine function. The photoperiod is represented by the white and black bars, representing the light/rest phase and dark/active phase, respectively. Time in hours is denoted by ZT because light is a zeitgeber. ZT0 = lights on (rest onset) in the entrained cycle and ZT12 = lights off (active onset). *Significance of daily rhythmicity (P < 0.05) determined from the zero-amplitude test.