title: Fatigue is mediated by cholinoceptors within the ventromedial hypothalamus independent of changes in core temperature.
abstract: We investigated brain mechanisms modulating fatigue during prolonged physical exercise in cold environments. In a first set of studies, each rat was subjected to three running trials in different ambient temperatures (T(a)). At 8 °C and 15 °C, core body temperature (T(core)) decreased and increased, respectively, whereas at 12 °C, the T(core) did not change throughout the exercise. In another set of experiments, rats were randomly assigned to receive bilateral 0.2 μL injections of 2.5 × 10(-2) M methylatropine or 0.15 M NaCl solution into the ventromedial hypothalamic nuclei (VMH). Immediately after the injections, treadmill exercise was started. Each animal was subjected to two experimental trials at one of the following T(a) : 5 °C, 12 °C or 15 °C. Muscarinic blockade of the VMH reduced the time to fatigue (TF) in cold environments by 35-37%. In all T(a) studied, methylatropine-treated rats did not present alterations in T(core) and tail skin temperature compared with controls. These results indicate that, below the zone of thermoneutrality, muscarinic blockade of the VMH decreases the TF, independent of changes in T(core). In conclusion, our data suggest that VMH muscarinic transmission modulates physical performance, even when the effects of thermoregulatory adjustments on fatigue are minimal.
authors.affiliation: Exercise Physiology Laboratory, Department of Physical Education, School of Physical Education, Physiotherapy and Occupational Therapy, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil.
authors.forename: J B
authors.initials: JB
authors.lastname: Guimarães
authors.forename: S P
authors.initials: SP
authors.lastname: Wanner
authors.forename: S C
authors.initials: SC
authors.lastname: Machado
authors.forename: M R M
authors.initials: MR
authors.lastname: Lima
authors.forename: L M S
authors.initials: LM
authors.lastname: Cordeiro
authors.forename: W
authors.initials: W
authors.lastname: Pires
authors.forename: R B
authors.initials: RB
authors.lastname: La Guardia
authors.forename: E
authors.initials: E
authors.lastname: Silami-Garcia
authors.forename: L O C
authors.initials: LO
authors.lastname: Rodrigues
authors.forename: N R V
authors.initials: NR
authors.lastname: Lima
mesh_terms: D000818:Animals; D001833:Body Temperature Regulation / Q000187:drug effects* / Q000502:physiology; D003080:Cold Temperature; D007033:Hypothalamus, Middle / Q000187:drug effects* / Q000502:physiology; D008297:Male; D018763:Muscle Fatigue / Q000187:drug effects; D005082:Physical Exertion / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D011976:Receptors, Muscarinic / Q000008:administration & dosage / Q000502:physiology*; D012420:Running / Q000502:physiology
chemical_list: D011976:Receptors, Muscarinic