EFFECTS OF DOXAPRAM ON CAROTID CHEMORECEPTOR ACTIVITY IN NEWBORN KITTENS

Doxapram is a respiratory stimulant which acts on peripheral chemorece ptors and central respiratory neurons in a dose-dependent fashion in t he adult cat. In the newborn, the mechanisms of action of doxapram are still unclear. To evaluate the effects of doxapram on the carotid che mosensory discharge and its relationship with dopaminergic mechanisms in the carotid body, two groups of kittens less than 13 days old, anes thetized, artificially ventilated and paralyzed, were prepared for the recording of a single or a few chemosensory afferents of the carotid sinus nerve. The chemosensory activity was recorded under five conditi ons of inspired gas mixtures (21 and 8% O2 in N2, 100% O2, 5 and 10% C O2 in O2). Group 1 (n = 9) received only doxapram and group 2 (n = 8) was pretreated with haloperidol (1 mg/kg), a dopamine D2-receptor bloc ker, before receiving doxapram. Doxapram significantly stimulated the discharge rate of the carotid chemoafferents under all conditions of i nspired gas. The chemosensory discharge was increased by haloperidol, and was raised further after doxapram by an amount similar to group 1. For instance, in normoxia, the activity increased from 2.9 +/- 0.4 to 7.5 +/- 0.9 impulse/s (mean +/- SEM, p < 0.01) in group 1 and from 3. 8 +/- 0.6 to 9.1 +/- 1.0 impulse/s (p < 0.01) in group 2. These result s indicate that the mechanisms of response of carotid chemoreceptor to doxapram are developed in the newborn kitten and doxapram acts indepe ndent of the dopaminergic mechanisms in the carotid body.