Abstract
Previous evidence suggests that medullary raphe nuclei may be involved in the regulation of breathing. This study was undertaken to examine the effects of change in low range end-tidal CO2 levels on the discharges of respiratory related neurons recorded in the medullary midline. The experiments were performed on pentobarbitone-anesthetized, paralysed, vagotomized and artifically ventilated rats. Extracellular recordings were made from neurons showing respiratory related activities in the midline medullary tegmentum. A total of 25 respiratory neurons were classified into Inspiratory (I) throughout (n=16), I-frequency modulated (n=3), Pre-I (n=2), Post-I (n=2), Expiratory (E) (n=1) and E-frequency modulated (n=1) neurons based on their firing patterns in relation to the phase of respiration. They were located in the raphe magnus, obscurus and pallidus. Changes in neuronal discharge of these respiratory neurons were assessed by recording ongoing activities of the neurons during times when the ventilator was stopped. When end-tidal CO2 concentration was raised (from 5±0.5% to 8±0.5%), 3 types of response of raphe respiratory neurons were shown to the change in end-tidal CO2 levels:firing rate 1) increased (n=18), 2) decreased (n=5) and 3) no response (n=2). These results suggest that the midline caudal raphe nuclei are involved in central chemoreception. [Jpn J Physiol 55 Suppl:S106 (2005)]
