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Cold‐acclimation reduces CO 2 sensitivity of chemosensory locus coeruleus neurons of American bullfrogs, Lithobates catesbeianus
Author(s) -
Santin Joseph,
Hartzler Lynn
Publication year - 2015
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.29.1_supplement.686.7
Subject(s) - lithobates , hypercapnia , acclimatization , biology , locus coeruleus , ventilation (architecture) , respiratory system , amphibian , normocapnia , medicine , ecology , neuroscience , anatomy , nucleus , mechanical engineering , engineering
Breathing is essential for O 2 acquisition and CO 2 elimination in anuran amphibians at warm temperatures; however, at cold temperatures, frogs do not need to use lung ventilation because cutaneous gas exchange supports metabolic demands and acid‐base homeostasis. American bullfrogs, Lithobates catesbeianus , overwinter from ~November through March (depending on geographical location) leaving the respiratory motor system significantly less active during these months. The respiratory motor system with nominal activity during overwintering must, upon warming, sustain a metabolic rate that can no longer be met exclusively by gas exchange across the skin. Aspects of anuran amphibian ventilatory control affected by cold‐acclimation and the consequence of these changes on breathing upon returning to spring temperatures are unknown. We measured chemosensory responses of locus coeruleus (LC) neurons in bullfrogs acclimated to 5°C for three months. We found that putative respiratory chemosensors from the LC of cold‐acclimated (CA) bullfrogs are less sensitive to hypercapnia [CA: 0.30±0.1Hz vs . control: 0.83±0.12Hz increase from 1.3% CO 2 (normocapnia) to 5% CO 2 (hypercapnia); p=0.008]. Interestingly, normocapnic firing rates were not different between control and CA animals (p=0.70) implying that baseline excitability is sustained despite cold‐acclimation. These results suggest that processes controlling lung breathing ( e.g. chemosensitivity of LC neurons) may be preserved, albeit at reduced capacity, despite months of inactivity due to heavy dependence on cutaneous gas exchange. Maintenance of neuromuscular function in the absence of breathing may be critical for bullfrogs to resume breathing to meet metabolic demands upon warming.