Aihua Li

Ventilatory effects of muscimol microdialysis into the rostral medullary raphé region of conscious rats.

We hypothesized that inhibition of the rostral medullary raphe region (MRR), a putative central chemoreceptor location, with the GABA(A) receptor agonist muscimol would decrease ventilatory responses to hypercapnia and hypoxia in conscious rats, and that its known effect at this site on body temperature might alter its effect upon these ventilatory responses. At ambient temperatures of 24.5-26.5 degrees C (Cool), microdialysis of 1mM muscimol into the MRR significantly decreased body temperature by approximately 0.5 degrees C, increased the ventilatory response to 7% CO(2) and decreased the response to 10% O(2). At ambient temperatures of 29.5-30.5 degrees C (Warm), 1 mM muscimol microdialysis no longer decreased body temperature and increased the ventilatory response to hypercapnia and to hypoxia. Muscimol did not significantly affect the VE/VO2 ratio at either temperature. Muscimol significantly increased the hypercapnic ventilatory responses in Cool and Warm conditions and the hypoxic response in Warm conditions, which indicates the presence of an inhibitory effect of rostral MRR neurons sensitive to muscimol. In the Cool condition the ventilatory response to hypoxia is inhibited but appropriately so for the lower VO2 .

Modulation of hypoxic depressions of ventilatory activity in the newborn piglet by mesencephalic mechanisms

In neonates, ventilatory responses to hypoxia are biphasic, with an augmentation followed by a decline. The hypoxia-induced augmentations in ventilation are attenuated and the depressions are accentuated following denervation of the peripheral chemoreceptors. Piglets that were decerebrated at a rostral mesencephalic level exhibited these hypoxia-induced depressions. These depressions were lessened following transection through the caudal mesencephalon. Mesencephalic mechanisms play a fundamental role in the brainstem regulation of ventilatory responses to hypoxia.