Differences in respiratory changes and Fos expression in the ventrolateral medulla of rats exposed to hypoxia, hypercapnia, and hypercapnic hypoxia

Jun Wakai, Daichi Takamura, Ryosuke Morinaga, Nobuaki Nakamuta, Yoshio Yamamoto
Respiratory Physiology & Neurobiology. Volume 215, 15 August 2015, Pages 64–72

The purpose of this paper was to try to reconcile the confusing and sometimes conflicting data that had previously been published on the differential effects of hypoxia and hypercapnia. In these experiments, they exposed rats to 2 hours of hypoxia, hypercapnia, or hypoxia plus hypercapnia. In this paper, they defined the rVLM as the region ventral to the facial nucleus, the mVLM as the region our lab generally considers the rVLM, and the cVLM was same thing we know it to be. They found that hypoxia increased respiratory frequency and Fos+ neurons in mVLM (our RVLM) and cVLM. Hypercapnia caused increased tidal volume, Fos+ neurons in the rVLM, RTN, and mVLM (our RVLM). Hypoxic hypercapnia caused a mixed result with increased tidal volume and Fos+ neurons in entire VLM. When they costained for FOS and DBH, they found that the Fos+ rVLM neurons were not DBH+, some of the cVLM and mVLM (our RVLM) neurons were double positive while some weren't.
They end the paper by speculating that based on their results and previous anatomical studies, hypoxia changes SNA activity through A1/C1 neurons in the cVLM (slightly different than our take) and hypercapnia changes activity through A1/C1 neurons in the RTN (which may partially include our RVLM). -DH