title: Muscarinic cholinoceptors in the ventromedial hypothalamic nucleus facilitate tail heat loss during physical exercise.
abstract: The aim of this study was to evaluate the participation of ventromedial hypothalamic nucleus (VMH) muscarinic cholinoceptors in heat balance and central fatigue during treadmill exercise (24 m min(-1), 5% inclination). The animals were anesthetized with pentobarbital sodium (50 mg/kg body weight i.p.) and fitted with bilateral cannulae into the VMH 1 week prior to the experiments. Tail skin (T(tail)) and core body temperatures (T(b)) were measured after the injection of 0.2 microL of 5 x 10(-9) mol methylatropine (Matr) or 0.15 M NaCl solution (Sal) into the hypothalamus. Methylatropine injection into the VMH greatly increased heat storage rate (HSR) measured until fatigue (19.7+/-4.6 cal min(-1) Matr versus 9.7+/-3.3 cal min(-1) Sal; P<0.05) and attenuated the exercise-induced tail vasodilation as seen by T(tail) (23.98+/-0.43 degrees C Matr versus 25.52+/-0.85 degrees C Sal; at 6.5 min; P<0.05), indicating inhibition of the heat loss process. The 2 min delay and the increased DeltaT(b), which triggered the heat loss mechanisms observed in Matr-treated rats, are associated with increased HSR and may be responsible for the decreased running performance of these animals (21.0+/-2.9 min Matr versus 33.5+/-3.4 min Sal; P<0.001). In fact, a close negative correlation was observed between HSR and time to fatigue (r=-0.61; P<0.01). In conclusion, VMH muscarinic cholinoceptors facilitate tail heat loss mechanisms, and a delay in this adjustment would lead to a decrease in physical exercise performance due to excess heat storage.
authors.affiliation: Exercise Physiology Laboratory, Department of Physical Education, School of Physical Education, Federal University of Minas Gerais, Av. Antônio Carlos, 6627, 31270-901 Belo Horizonte, Minas Gerais, Brazil.
authors.forename: Samuel P
authors.initials: SP
authors.lastname: Wanner
authors.forename: Juliana B
authors.initials: JB
authors.lastname: Guimarães
authors.forename: Luiz Oswaldo C
authors.initials: LO
authors.lastname: Rodrigues
authors.forename: Umeko
authors.initials: U
authors.lastname: Marubayashi
authors.forename: Cândido C
authors.initials: CC
authors.lastname: Coimbra
authors.forename: Nilo R V
authors.initials: NR
authors.lastname: Lima
mesh_terms: D000818:Animals; D001286:Atropine Derivatives / Q000494:pharmacology; D015374:Biosensing Techniques; D001833:Body Temperature Regulation / Q000187:drug effects / Q000502:physiology*; D004567:Electrodes, Implanted; D008297:Male; D018727:Muscarinic Antagonists / Q000494:pharmacology; D018763:Muscle Fatigue / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D011976:Receptors, Muscarinic / Q000502:physiology*; D012039:Regional Blood Flow / Q000235:genetics / Q000502:physiology; D012420:Running / Q000502:physiology; D012867:Skin / Q000098:blood supply; D013623:Tail / Q000098:blood supply / Q000502:physiology*; D014697:Ventromedial Hypothalamic Nucleus / Q000502:physiology*
chemical_list: D001286:Atropine Derivatives; D018727:Muscarinic Antagonists; D011976:Receptors, Muscarinic; C006649:methylatropine