Figure 4. Effect of microinjecting capsaicin and substance P into the cnTS on respiratory rate in anaesthetized guinea-pigs.

Capsaicin (0.5 nmol), substance P (0.5–5 nmol) or vehicle (20% ethanol in saline) was microinjected (0.5 μl) into the cnTS. A, representative injection site, indicated by arrow (∼0.5 mm caudal to obex). CC, central canal. B, representative traces showing respiration before and 10 min after microinjection of capsaicin. C, mean ± s.e.m. effects of cnTS microinjection of capsaicin, substance P and vehicle (0.5 μl over 3 min beginning at time 0) on respiratory rate. Microinjecting 0.5 nmol capsaicin into brainstem subnuclei rostral and lateral to cnTS, including the interpolar trigeminal nucleus (n = 4) and the intermediate and ventrolateral nTS (n = 3) was without effect on respiration (not shown).