Catecholaminergic depressant effects on bulbar respiratory mechanisms

On the basis of histochemical and pharmacological studies, catecholamines have been implicated in central mechanisms controlling respiration. This hypothesis was tested in iontophoretic studies on neurones located in bulbar respiratory centres. Adrenaline and noradrenaline had a predominantly depressant effect on respiratory as well as on closely situated non-respiratory units. These depressions were mimicked by the application of isoproterenol and clonidine; acetylcholine and serotonin had inconsistent effects on these neurones. In control experiments, microinjections, using a Hamilton syringe, were made in the area of bulbar respiratory centres: noradrenaline, but not serotonin, depressed the central respiratory activity reflected in the phrenic nerve discharge. These results suggest that specific adrenergic and noradrenergic depressant mechanisms could affect both respiratory and other physiological centres at the bulbar level.