Fig. 9. Effects of microinjection of DAMGO into the middle medullary raphe region on the minute ventilation (VE; A ), respiratory frequency (f; B ), and tidal volume (VT; C ) responsiveness to progressive hypercapnia in the rats and the locations of the microinjections ( D ). “0” on the x-axis represents the onset of microinjection of DAMGO. Data are presented as mean ± SE; n = 6. Squares in D show the locations of the microinjections 10.5 mm caudal to the bregma and 9 mm ventral to the cerebellar surface. 7 = facial nucleus; IRt = intermediate reticular nucleus; PCRtA = parvicellular reticular nucleus, alpha; RMg = raphe magnus nucleus; RPa = raphe pallidus nucleus; Sp5O = spinal 5 nucleus, oral part.