Cardiorespiratory response to bicuculline during resistive loaded breathing in anesthetized rabbits.

We hypothesized that hypoventilation induced by resistive loaded breathing may result in part from an increase in gamma-aminobutyric acid (GABA) concentration in the central nervous system. Accordingly, ventilatory depression should be minimized by GABA receptor blockade. The effects of subseizure doses of the GABAA receptor antagonist bicuculline on the cardiorespiratory variables and cortical activities were evaluated in two groups of urethane anesthetized rabbits, breathing either through an inspiratory resistive load (IRL) or not. Bicuculline induced cardiorespiratory changes which consisted mainly of an augmented respiratory rate, through shortening of expiratory duration, and of bradycardia. Bicuculline effects did not significantly differ between both groups and were accompanied by high amplitude delta rhythmic cortical activities. These data show that GABAA receptors may exert a tonic depressive effect on the respiratory circuit and suggest that endogenous GABA release is not augmented by an acute increase in the work of breathing.