Fig. 1

A schematic diagram for the overall timeline for the experimental protocol used to investigate PGE₂-induced sensitization of the cough reflex. Intracerebroventricular (i.c.v.) cannulae were implanted and guinea pigs were then injected with tramadol (i.m.) and enrofloxacin (s.c.) for three consecutive days. After a one-week recovery period, drugs were infused through i.c.v. route for 30 minutes followed by a 15-minute absorption phase. In case of two drug treatments, the antagonist was infused first for 30 minutes followed by a 15-minute absorption phase, then the agonist was infused for 30 minutes followed by a 15 minute absorption phase. Animals were then challenged with 0.2 M citric acid for 10 minutes followed by a 10-minute post-nebulization recording period. Cough number was assessed over the entire 20-minute nebulization/recording period