Inhibition of somatostatinergic interneurons of the lateral parafacial region reduces the ventilatory response to hypercapnia of mice
Authors: Salim Nathalia , Magalhães Karolyne , Martins Renato , Moraes Davi 
Published: May 2024

The lateral parafacial region (pFL), which contains excitatory and inhibitory neurons and interneurons, generates active expiration in response to hypercapnia. Inhibition of inhibitory somatostatinergic (Sst)-positive neurons in parafacial region increases pulmonary ventilation, while hypercapnia inhibits some of them intrinsically. However, the role of pFL Sst-positive interneurons (with local projections) in regulating pulmonary ventilation during hypercapnia is unclear. We hypothesized that the pFL Sst-positive interneurons control the pulmonary ventilation of mice under normocapnia and hypercapnia, as part of a local neural network. Herein, we evaluated the impact of pFL Sst-positive interneurons inhibition on pulmonary ventilation of non-anesthetized mice during normocapnia and hypercapnia. We used genetically modified mice, expressing the cre recombinase in Sst-positive neurons, and injected unilaterally a cre-dependent adeno-associated (AAV) retrograde virus in the pFL region to express the FLP recombinase, followed by a cre- and FLP-dependent AAV to express the inhibitory Designer Receptors Exclusively Activated by Designer Drugs (hM4D-Gi) in the pFL Sst-positive interneurons. We used whole-body plethysmography to measure the respiratory frequency (fR), tidal volume (VT), pulmonary ventilation (VE), as well as the duration of the respiratory cycle, inspiration (DI) and expiration (DE) at normocapnia and hypercapnia (7% CO2) after activation of hM4D-Gi in the pFL Sst-positive interneurons using JHU 37160 (JHU; 0.1 mg/kg; i.p.). Data are expressed as mean ± standard deviation. By analyzing the expression of mCherry fluorescent protein, we found a significant number of Sst-positive interneurons (73.43 ± 10.52) in the pFL region (n=14). JHU administration did not affect the ventilatory parameters of Sst(cre/cre) (n= 9) and Sst(cre/cre + hM4D-Gi) (n= 14) groups at normocapnia [(Δ fR: 6.5 ± 33.56 vs. -14.86 ± 49.03 cpm; p= 0.42) (Δ VT: 0.87 ± 1.15 vs. -0.97 ± 2.58 μL·g−1; p= 0.19) (Δ VE: 235.8 ± 388.8 vs. -315.9 ± 725.1 μL·g−1·min−1; p= 0.16) (Δ duration of the respiratory cycle: -13 ± 45.11 vs. 12.34 ± 53.07 ms; p= 0.39) (Δ DI: 10.36 ± 11.23 vs. 14.7 ± 16.38 ms; p= 0.62) (Δ DE: -23.36 ± 42.42 vs. -2.41± 53.58 ms; p= 0.48)]. On the other hand, JHU administration attenuated the hypercapnia-induced responses of all ventilatory parameters, such as fR (Δ: 44.57 ± 56.66 vs. 126± 21.28 cpm; p= 0.0002), VT (Δ: 1.32 ± 3.35 vs. 4.16 ± 2.56 μL·g−1; p= 0.04), VE (Δ: 948.7 ± 1407.1 vs. 2183 ± 909.4 μL·g−1·min−1; p= 0.03), duration of the respiratory cycle (Δ: -44.57 ± 46.31 vs. -122.1 ± 30.7 ms; p= 0.0002), DI (Δ: 6.79 ± 16.36 vs. -13.03 ± 10.19 ms; p= 0.003) and DE (Δ: -51.37 ± 37.50 vs. -109.1 ± 32.78 ms; p= 0.001) in the Sst(cre/cre + hM4D-Gi) compared with the Sst(cre/cre) group. Thus, we conclude that the pFL Sst-positive interneurons control the ventilatory parameters of mice during hypercapnia, but not during normocapnia. FAPESP, CNPq and CAPES. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.