Focal acidification of the caudal ventrolateral medulla (Loeschcke's area) increases ventilation during wakefulness but not in sleep

Abstract

The classic central chemoreceptors were originally described as the regions bilaterally located on the surface of the rostral and caudal ventrolateral medulla (rVLM and cVLM). The cVLM, just lateral to the pyramidal tract between the roots of the hypoglossal nerve, also known as Loeschcke's area, was excited by focal application of H+ and subsequently has not received much of attention in the past decade. Salgueiro et al. recently showed that some of the neurons in the cVLM increased firing rate in response to focal acidification in anaesthetized rats (2003). Here we hypothesize that in conscious rat, focal acidification of the cVLM region would increase ventilation in a sleep‐awake state dependent manner. In unanesthetized rats, normal (5%) or high (25%) CO2 equilibrated aCSF was unilaterally dialyzed into the cVLM region and ventilation was recorded using a whole body plethysmograph. In the responsive group (n=8), focal acidification with high CO2 significantly increased ventilation by 17% in wakefulness due to both VT and frequency but not in sleep comparing with the baseline. In the non‐responsive group (n=7), focal acidification did not affect VE, f and VT either in wakefulness or sleep. The focal acidification data suggest that the cVLM, the area that is partially overlapping Loeschcke's area, participates in the central chemoreception in an arousal state dependent manner. (HL‐28066)