Are galaninergic RTN neurons involved in adaptation to long-term hypercapnia?
(2019) International Brain Research Organization (IBRO) — Location: Daegu, South Korea
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- Abstract
- Phox2b-expressing retrotrapezoid nucleus (RTN) neurons are CO2-responsive and critical in mediating the central respiratory chemoreflex. We know that 30% of RTN neurons are activated following acute hypercapnia. We wanted to determine if the RTN neurons responsiveness changes after acute hypercapnic chemoreflex (AH: 1 hr of 10% CO2, 40% O2, 50% N2) following LH (10 days of 8% CO2, balance room air (RA)) and if the inducible neuropeptide galanin is involved. Adult C57BL/6 mice (n=5/group) were exposed to LH or RA for 10 days followed by AH. To characterise neuronal activation, in situ hybridization was conducted for galanin followed by c-Fos and Phox-2b immunohistochemistry. In 10 days-RA, 32% (p<0.05) of Phox2b positive overall RTN neurons and 30% (p<0.001) of the population that is restricted to galaninergic neurons in the RTN were activated following AH which was higher than 8% in baseline conditions (RA, 10 days, no AH). After LH, the responsiveness to AH was not different to baseline conditions (LH, no AH) for both Phox2b or galaninergic RTN neurons. However, the baseline activation (LH, no AH) of galaninergic neurons was 36% compared to 19% in Phox2b neurons. The total number of galaninergic RTN neurons stayed the same in all conditions. Furthermore, while Phox2b neurons were 7% more responsive, galanin neurons were 9% less responsive at night compared to day. Finally, the distribution of GalR1 mRNA was determined in the adult mouse ventral respiratory column (VRC) using fluorescent ISH (RNAscope). There was an average of 219 (±13) GalR1+ neurons in the VRC, of which ~23% were inhibitory (glycinergic) (n=5). After compartmentalization of the VRC, the number of GalR1 and glycinergic GalR1 neurons in the Botzinger complex was two and three folds higher than in the preBötzinger complex respectively. In conclusion, LH blunts RTN responsiveness and mediates constitutive activity of the galaninergic RTN subpopulation.
- Affiliations
University of New South Wales
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Dereli, A., Yaseen, Z., & Kumar, N. N. (2019). Are galaninergic RTN neurons involved in adaptation to long-term hypercapnia? International Brain Research Organization (IBRO), Daegu, South Korea.