Breathing pattern during pharmacological activation and blockade of the intermediate area of the ventrolateral surface of the cat medulla.

The present study analyzes the respiratory pattern of chloralose-(50-60 mg/kg, iv) anesthetized cats treated with Nembutal (NE) (30 mg/ml), glycine (GL) (200 mg/ml) or leptazol (LE) (200 mg/ml) topically applied to the intermediate area of the ventrolateral surface of the medulla oblongata in a volume of 20 microliters. Application of NE and GL produced a decrease in ventilation (approximately 24%) and tidal volume (approximately 25%) suggesting that the intermediate area facilitates respiratory drive and inhibits the inspiratory off-switch mechanism. These results are consistent with the view that intermediate area is necessary for the central chemosensitivity to CO2. The topical application of LE produced an increase in inspiration time (12.5%), expiration time (20.8%) and tidal volume (7%). The increased tidal volume caused by LE is compatible with its action as a GL antagonist.