Selective inhibition of olfactory guanylyl cyclase D neurons does not affect the ventilatory response to CO₂in mice

Recent findings suggest that within the olfactory system, there is a specialized group of neurons called the necklace glomeruli (GC-D+), known for their molecular machinery necessary for detecting CO 2 . This raises the intriguing possibility that this subsystem influences respiratory control. The regulation of breathing involves a network that maintains basal respiratory rhythms and specialized chemosensors that detect changes in blood gases (CO 2 and O 2 ). These chemosensors activate pathways that adjust respiratory output, ensuring proper gas exchange and homeostasis. This study investigates the olfactory system's role in the hypercapnic ventilatory response (HCVR). Olfactory neuron silencing was achieved pharmacologically with the injection of GABA-A agonist muscimol (10 mM) in the olfactory bulb (OB) or olfactory epithelium (OE - intranasal) or pharmacogenetically by the injection of the AAV8 vector encoding the inhibitory chemogenetic actuator hM4D(Gi) in a cre-recombinase dependent manner (GC-D cre mice). Breathing parameters were measured by whole-body plethysmography in conscious unrestrained C57BL/6, GC-D knockout (GC-D KO), and GC-D cre mice. Pharmacological inhibition of olfactory neurons using intranasal muscimol (10 mM) resulted in a significant HCVR increase compared to saline-treated mice (491 ± 0.72 vs. saline: 381 ± 0.49%, p<0.05). Similarly, bilateral muscimol injections into the OB augmented HCVR amplitude (153 ± 0.20 vs. saline: 110 ± 0.10%, p<0.05). No significant differences in the HCVR were noticed between GC-D KO and wild-type (WT) mice (480.5 ± 181.1, vs. WT: 384.3 ± 93.8%, p = 0.3262). Similarly, chemogenetic inhibition of GC-D + neurons failed to alter HCVR (377.7% ± 229.6, vs. saline: 277.3 ± 156.5%, p = 0.4897). These findings suggest that the olfactory system contributes to HCVR modulation through mechanisms independent of GC-D + neurons. Broader populations of olfactory neurons may underlie this effect, positioning the olfactory system as an unconventional regulator of respiratory chemoreception. Further studies are needed to elucidate the neuronal circuits and molecular pathways involved in this process. FAPESP, CAPESP-PROEX. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.