Figure 2.

A: example of a recording of baseline spontaneous breathing in one control mouse. The mouse was exposed to dim light and placed in a plethysmographic box for 2 h. Spontaneous instantaneous respiratory flow (V̇), minute ventilation (V̇e), and V̇co₂ are shown. Note the spontaneous change in breathing associated with proportional changes in metabolic rate, reflecting fluctuations in the level of vigilance, in behavior and motor activity. B: frequency distribution of ventilation during a 1 h-period of recording in all control (top) and β-arr2-deficient (bottom) mice. Note the first peak corresponds to the lowest levels of ventilation measured when animals were immobile. Arrb2^tm1Rjl, Arrb2 knockout mice; β-arr2, β arrestin 2.