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CO2 dialysis in one chemoreceptor site, the RTN: stimulus intensity and sensitivity in the awake rat

2002; Elsevier BV; Volume: 133; Issue: 1-2 Linguagem: Inglês

10.1016/s1569-9048(02)00134-9

1878-1519

Aihua Li, Eugene Nattie,

Neuroendocrine regulation and behavior

We stimulate single central chemoreceptor sites in the unanesthetized rat by focal microdialysis of artificial cerebrospinal fluid (aCSF) equilibrated with 25% CO2. Here, in the retrotrapezoid nucleus (RTN) we measured the focal stimulus intensity with a pH electrode adjacent to the dialysis probe. During 25% CO2 dialysis, RTN pH decreased by 0.069 (0.013, SEM) pH units (N=5), 44% of the change observed during 7% CO2 breathing, −0.157 (0.019) pH units (N=4). During 7% CO2 breathing, PaCO2 increased by 15 Torr (N=5). We calculate the ΔPaCO2 that would produce a ΔpH at the RTN approximately like that observed during 25% CO2 dialysis as 44% of 15 Torr, or 6.6 Torr ΔPaCO2. Using ventilatory response data from our lab, we estimate overall chemoreceptor sensitivity as 13% ΔV̇e/Torr ΔPaCO2 and RTN sensitivity as 3% ΔV̇e/Torr ΔPaCO2. The RTN provides 23% of the overall response. This may be an underestimate. During RTN stimulation PaCO2 decreases by 4.9 (0.7) Torr (N=5), which may inhibit other chemoreceptor sites. Multiple chemoreceptor sites may interact to provide high sensitivity in systemic hypercapnia and stability during heterogeneous stimulation and inhibition.