Respiratory effects of stimulation of cell bodies of the A5 region in the anaesthetised rat

To assess the importance of the pontine A5 region in modulating respiratory activity, electric current or microinjections of glutamate (10-30 nl, 1-3 nmol) were used to stimulate discrete zones within this; region in the spon taneously breathing, anaesthetised rat. These stimuli evoked an expiratory facilitatory response, consisting of a decrease in respiratory rate (P<0.01 electrical, P<0.001 chemical) due to an increase of expiratory time (P<0.0 1 in both cases) as measured from recordings of phrenic nerve activity. No changes were observed in inspiratory time. To avoid changes in PCO2, which could modulate the respiratory response, stimulation was also made during a rtificial ventilation. Under these conditions the expiratory facilitatory r esponse elicited by glutamate was still present (P<0.05), although its dura tion was reduced (P<0.05), as was the magnitude of the phrenic burst (P<0.0 5). At all the sites at which electrical stimulation and glutamate injectio n had evoked a respiratory response, electrical stimulation evoked a concom itant increase in both blood pressure and heart rate. Glutamate injection e voked a presser response in 21 out of 30 animals. In eight animals the rise in blood pressure was followed by a fall in blood pressure and in one anim al, a depressor response was observed. In all cases glutamate evoked an inc rease in heart rate. The expiratory facilitatory response was clot evoked a s a consequence of the increase of blood pressure since it was still presen t after the administration of guanethidine, which abolished the blood press ure changes. As glutamate is believed to excite perikarya rather than axons of passage these data indicate that expiratory facilitatory responses and the accompanying cardiovascular changes are the consequence of activating n eurones located within the A5 region. The possible interactions between the A5 region and the medullary respiratory complex in eliciting these changes are discussed.