Fos expression in A1/C1 neurons of rats exposed to hypoxia, hypercapnia, or hypercapnic hypoxia.

The distribution of Fos expression in catecholaminergic neurons with immunoreactivity for dopamine β-hydroxylase (DBH) of the ventrolateral medulla was compared between rats exposed to hypoxia (10 % O), hypercapnia (8 % CO), and hypercapnic hypoxia (8 % CO and 10 % O) for 2 h. Among the experimental groups, hypoxia-exposed rats had more Fos/DBH double-immunoreactive neurons than the control group (20 % O) in the rostral area of the ventrolateral medulla, specifically in the range of + 150 μm to + 2,400 μm from the caudal end of the facial nerve nucleus. On the other hand, Fos/DBH double-immunoreactive neurons were scarcely observed in the ventrolateral medullary region of hypercapnia-exposed rats. The number of double-immunoreactive neurons in hypercapnic hypoxia-exposed rats was comparable to that in the control group. The present results suggest that adrenergic C1 neurons are specifically activated by hypoxia and are involved in the regulation of respiratory and circulatory functions.