CO2 dialysis in one chemoreceptor site, the RTN: stimulus intensity and sensitivity in the awake rat.
We stimulate single central chemoreceptor sites in the unanesthetized rat by focal microdialysis of artificial cerebrospinal fluid (aCSF) equilibrated with 25% CO(2). Here, in the retrotrapezoid nucleus (RTN) we measured the focal stimulus intensity with a pH electrode adjacent to the dialysis probe. During 25% CO(2) dialysis, RTN pH decreased by 0.069 (0.013, SEM) pH units (N=5), 44% of the change observed during 7% CO(2) breathing, -0.157 (0.019) pH units (N=4). During 7% CO(2) breathing, Pa(CO(2)) increased by 15 Torr (N=5). We calculate the deltaPa(CO(2)) that would produce a deltapH at the RTN approximately like that observed during 25% CO(2) dialysis as 44% of 15 Torr, or 6.6 Torr deltaPa(CO(2)). Using ventilatory response data from our lab, we estimate overall chemoreceptor sensitivity as 13% deltaVE/Torr deltaPa(CO(2)) and RTN sensitivity as 3% deltaVE/Torr deltaPa(CO(2)). The RTN provides 23% of the overall response. This may be an underestimate. During RTN stimulation Pa(CO(2)) 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.
Li
Aihua
A
Department of Physiology, Dartmouth Medical School, 706E Borwell Building, Lebanon, NH 03756-0001, USA.
Nattie
Eugene
E
D000818:Animals; D002245:Carbon Dioxide / Q000097:blood / Q000494:pharmacology*; D002628:Chemoreceptor Cells / Q000187:drug effects* / Q000502:physiology; D016857:Hypocapnia / Q000097:blood; D008526:Medulla Oblongata / Q000187:drug effects* / Q000502:physiology; D017551:Microdialysis / Q000379:methods*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014851:Wakefulness / Q000187:drug effects / Q000502:physiology
D002245:Carbon Dioxide