Abstract
Considerable evidence has suggested that the midline region of the brainstem is involved in the control of respiration. Respiratory-modulated neuronal activities have been recorded in the raphe nuclei of rats, and some of these respiratory-related neurons were antidromically activated from the spinal cord. However, the role of the raphe neurons remains uncertain. Recently, it has been demonstrated that the medullary raphe nuclei form one of several brainstem regions of central chemoreception. Although there is abundant evidence for chemoreception within the ventrolateral medulla (VLM) in the intact animal, responsiveness of respiratory-related neurons in the medullary raphe nuclei to a ventilatory challenge has not been examined. The present study investigated whether the respiratory neurons in the medullary raphe nuclei are chemosensitive to the low range end-tidal CO2 levels that are relevant to normal physiological conditions. The experiments were conducted on decerebrated, vagotomized, paralyzed and artificially ventirated rats. Etracellular recordings were obtained from neurons showing firing patterns related to phrenic nerve discharge in the midline medullary tegmentum. The recorded respiratory-related neurons were tested for responsiveness to hypercarbic ventilatory challenge. The steady-state relationship between some inspiratory throughout neuronal activity was obtained by step-wise increases in the inspired CO2 level to various values (2.0-7.4%). These findings suggest that the midline caudal raphe nuclei are involved in central chemoreception. [J Physiol Sci. 2007;57 Suppl:S214]
