Changes in the central respiratory rhythm following pharmacological blockade of the nucleus parabrachialis medialis in the rabbit

Experiments were performed in halothane-anesthetized, paralyzed, bilaterally vagotomized and artificially ventilated rabbits. Arterial blood pressure, expiratory carbon dioxide concentration, and electrical activity of the right phrenic nerve were recorded prior to and after xylocaine microinjection to the left nucleus parabrachialis medialis (NPBM). The location of the xylocaine blockade was verified histologically. It was found that blockade of the NPBM results in a decelerated respiratory rhythm due to lengthening of both phases of the respiratory cycle. These results do not corroborate the role of NPBM in the regulation of respiration as postulated by Bertrand and Hugelin (1971).