Petrosal ganglion responses to acetylcholine and ATP are enhanced by chronic normobaric hypoxia in the rabbit

- Rabbits exposed to chronic (14 d) normobaric (PB ≈ 719 mm Hg) hypoxia (FIO2≈9.1%).
- Chronic normobaric hypoxia (CNH) increased hematocrit but stagnated body weight.
- Carotid nerve responses to ACh and ATP applied to the petrosal ganglion after CNH.
- ATP and ACh increased carotid nerve discharge frequency in a dose-dependent manner.
- ACh- and ATP-induced responses significantly increased their duration after CNH.

In mammals, adaptation to chronic hypoxia requires the integrity of the arterial chemoreceptors, specially the carotid body (CB). Chronic hypoxia increases the sensibility of the CB by acting on the receptor cells, but there is limited information on the effects of chronic hypoxia on the sensory neurons that innervate the CB. Therefore, we studied the responses evoked by ACh and ATP, the main transmitters that generate the chemoafferent activity, on the petrosal ganglion (PG) of rabbits exposed to chronic normobaric hypoxia (CNH) during fourteen days. ATP and ACh increased the activity of PG neurons in a dose-dependent manner, in a similar way than in rabbits not exposed to hypoxia (naïve). However, the duration of the responses were significantly increased by CNH, with the mean maximal responses to ACh and ATP increased by a factor of two and four, respectively. Our results suggest that CNH increases duration of the responses by modifying the expression and/or content of ACh and ATP receptors.