title: Diphtheria toxin treatment of Pet-1-Cre floxed diphtheria toxin receptor mice disrupts thermoregulation without affecting respiratory chemoreception.
abstract: In genetically-modified Lmx1b(f/f/p) mice, selective deletion of LMX1B in Pet-1 expressing cells leads to failure of embryonic development of serotonin (5-HT) neurons. As adults, these mice have a decreased hypercapnic ventilatory response and abnormal thermoregulation. This mouse model has been valuable in defining the normal role of 5-HT neurons, but it is possible that developmental compensation reduces the severity of observed deficits. Here we studied mice genetically modified to express diphtheria toxin receptors (DTR) on Pet-1 expressing neurons (Pet-1-Cre/floxed DTR or Pet1/DTR mice). These mice developed with a normal complement of 5-HT neurons. As adults, systemic treatment with 2-35μg of diphtheria toxin (DT) reduced the number of tryptophan hydroxylase-immunoreactive (TpOH-ir) neurons in the raphe nuclei and ventrolateral medulla by 80%. There were no effects of DT on minute ventilation (VE) or the ventilatory response to hypercapnia or hypoxia. At an ambient temperature (TA) of 24°C, all Pet1/DTR mice dropped their body temperature (TB) below 35°C after DT treatment, but the latency was shorter in males than females (3.0±0.37 vs. 4.57±0.29days, respectively; p<0.001). One week after DT treatment, mice were challenged by dropping TA from 37°C to 24°C, which caused TB to decrease more in males than in females (29.7±0.31°C vs. 33.0±1.3°C, p<0.01). We conclude that the 20% of 5-HT neurons that remain after DT treatment in Pet1/DTR mice are sufficient to maintain normal baseline breathing and a normal response to CO2, while those affected include some essential for thermoregulation, in males more than females. In comparison to models with deficient embryonic development of 5-HT neurons, acute deletion of 5-HT neurons in adults leads to a greater defect in thermoregulation, suggesting that significant developmental compensation can occur.
authors.affiliation: Department of Neurology, Yale University, New Haven, CT 06520, United States; Department of Cellular & Molecular Physiology, Yale University, New Haven, CT 06520, United States; Department of Neurology, University of Iowa, Iowa City, IA 52242, United States; Department of Molecular Physiology & Biophysics, University of Iowa, Iowa City, IA 52242, United States; Departamento de Fisiología, Facultad de Medicina, Universidad del Desarrollo, Santiago 8320000, Chile.
authors.forename: V
authors.initials: V
authors.lastname: Cerpa
authors.affiliation: Department of Neurology, Yale University, New Haven, CT 06520, United States; Department of Cellular & Molecular Physiology, Yale University, New Haven, CT 06520, United States.
authors.forename: A
authors.initials: A
authors.lastname: Gonzalez
authors.affiliation: Department of Neurology, Yale University, New Haven, CT 06520, United States; Department of Cellular & Molecular Physiology, Yale University, New Haven, CT 06520, United States; Department of Neurology, University of Iowa, Iowa City, IA 52242, United States; Department of Molecular Physiology & Biophysics, University of Iowa, Iowa City, IA 52242, United States; Veterans Affairs Medical Center, Iowa City, IA 52242, United States. Electronic address: george-richerson@uiowa.edu.
authors.forename: G B
authors.initials: GB
authors.lastname: Richerson
mesh_terms: D000818:Animals; D001833:Body Temperature Regulation / Q000502:physiology*; D004167:Diphtheria Toxin / Q000494:pharmacology*; D005260:Female; D066257:Heparin-binding EGF-like Growth Factor / Q000235:genetics / Q000378:metabolism*; D006935:Hypercapnia / Q000503:physiopathology; D000860:Hypoxia / Q000503:physiopathology; D008297:Male; D008526:Medulla Oblongata / Q000502:physiology; D008822:Mice, Transgenic; D009474:Neurons / Q000502:physiology*; D011903:Raphe Nuclei / Q000502:physiology; D012119:Respiration; D012701:Serotonin / Q000378:metabolism*; D012727:Sex Characteristics; D014365:Tryptophan Hydroxylase / Q000378:metabolism
chemical_list: D004167:Diphtheria Toxin; D066257:Heparin-binding EGF-like Growth Factor; D012701:Serotonin; D014365:Tryptophan Hydroxylase
keywords: chemoreception; gender differences; serotonin; thermoregulation