High CO2/H+ dialysis in the caudal ventrolateral medulla (Loeschcke's area) increases ventilation in wakefulness

Central chemoreception, the detection of CO2/H+ within the brain and the resultant effect on ventilation, was initially localized at two areas on the ventrolateral medulla, one rostral (rVLM-Mitchell's) the other caudal (cVLM-Loeschcke's), by surface application of acidic solutions in anesthetized animals. Focal dialysis of a high CO2/H+ artificial cerebrospinal fluid (aCSF) that produced a milder local pH change in unanesthetized rats (like that with a ∼6.6 mm Hg increase in arterial PCO2PCO2) delineated putative chemoreceptor regions for the rVLM at the retrotrapezoid nucleus and the rostral medullary raphe that function predominantly in wakefulness and sleep, respectively. Here we ask if chemoreception in the cVLM can be detected by mild focal stimulation and if it functions in a state dependent manner. At responsive sites just beneath Loeschcke's area, ventilation was increased by, on average, 17% (P < 0.01) only in wakefulness. These data support our hypothesis that central chemoreception is a distributed property with some sites functioning in a state dependent manner.