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

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Abstract
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 spontaneously breathing, anaesthetised rat. These stimuli evoked an expiratory facilitatory response, consisting of a decrease in respiratory rate (P PP PCO2, which could modulate the respiratory response, stimulation was also made during artificial ventilation. Under these conditions the expiratory facilitatory response elicited by glutamate was still present (PPP<0.05). At all the sites at which electrical stimulation and glutamate injection had evoked a respiratory response, electrical stimulation evoked a concomitant increase in both blood pressure and heart rate. Glutamate injection evoked a pressor 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 animal, a depressor response was observed. In all cases glutamate evoked an increase in heart rate. The expiratory facilitatory response was not evoked as a consequence of the increase of blood pressure since it was still present after the administration of guanethidine, which abolished the blood pressure 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 neurones located within the A5 region. The possible interactions between the A5 region and the medullary respiratory complex in eliciting these changes are discussed.

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