Participation of the dorsal periaqueductal grey matter in the hypoxic ventilatory response in unanaesthetized rats

Abstract

Aim Although periaqueductal grey matter activation is known to elicit respiratory and cardiovascular responses, the role of this midbrain area in the compensatory responses to hypoxia is still unknown. To test the participation of the periaqueductal grey matter in cardiorespiratory and thermal responses to hypoxia in adult male Wistar rats, we performed a chemical lesion of the dorsolateral/dorsomedial or the ventrolateral/lateral periaqueductal grey matter using ibotenic acid. Methods Pulmonary ventilation, mean arterial pressure, heart rate and body temperature were measured in unanaesthetized rats during normoxic and hypoxic exposure (5, 15, 30min, 7% O2). Results An ibotenic acid lesion of the dorsolateral/dorsomedial periaqueductal grey matter caused a higher increase in pulmonary ventilation (67.1%, 1730 +/- 282.5mLkg-1min-1) compared to the Sham group (991.4 +/- 194mLkg-1min-1) after 15min in hypoxia, whereas for the ventrolateral/Lateral periaqueductal grey matter lesion, no differences were observed between groups. Mean arterial pressure, heart rate and body temperature were not affected by a dorsolateral/dorsomedial or ventrolateral/lateral periaqueductal grey matter lesion. Conclusion Middle to caudal portions of the dorsolateral/dorsomedial periaqueductal grey matter neurones modulate the hypoxic ventilatory response, exerting an inhibitory modulation during low O2 situations. In addition, the middle to caudal portions of the dorsolateral/dorsomedial or ventrolateral/lateral periaqueductal grey matter do not appear to exert a tonic role on cardiovascular or thermal parameters during normoxic and hypoxic conditions.