Chemical stimulation of the area postrema induces cardiorespiratory changes in the cat

The purpose of our study was to determine the cardiorespiratory effects of exciting cell bodies of the area postrema of the cat. This was accomplished by local application of L-glutamic acid (bilateral application of 5 microliter of a 250-1000 mM solution) and kainic acid (bilateral application of 5 microliter of a 40 mM solution) to the area postrema of chloralose-anesthetized cats while monitoring arterial pressure, heart rate, tidal volume and respiratory rate. These excitatory amino acids activate neuronal cell bodies but not axons of passage. L-Glutamic acid produced a dose-dependent increase in arterial pressure, decreases in respiratory rate and minute volume and, occasionally, ventricular tachyarrhythmias. Kainic acid produced effects similar to those seen with L-glutamic acid except the changes in respiratory activity were more pronounced with each animal exhibiting respiratory arrest. In artificially respired animals, kainic acid produced similar cardiovascular changes as those occurring in spontaneously breathing animals (i.e. increases in arterial pressure of 61 +/- 5.7 mm Hg, and in heart rate of 32 +/- 8.3 beats/min). Finally, application of kainic acid to the area postrema abolished the pressor and tachycardic responses to bilateral occlusion of the carotid arteries. These results suggest that activation of cell bodies in the area postrema can result in pronounced cardiorespiratory changes.