RESUMEN
A variety of definitions involving body temperature (Tb), metabolic rate and behavior have been used to define torpor in mammals and birds. This problem is confounded in some studies of free-ranging animals that employ only skin temperature (Tsk), a measure that approximates but may not precisely reflect Tb. We assess the accuracy of Tsk in the context of a recent definition for torpor called active temperature. We compared the active temperatures of individual big brown bats (Eptesicus fuscus), which aggregate in cavities, with solitary, foliage-roosting hoary bats (Lasiurus cinereus). In captive big brown bats, we compared Tsk and core Tb at a range of ambient temperatures for clustered and solitary roosting animals, compared Tsk and Tb during arousal from torpor, and quantified the effect of flight on warming from torpor. Hoary bats had significantly lower active temperatures than big brown bats despite having the same normothermic Tsk. Tsk was significantly lower than Tb during normothermia but often greater than Tb during torpor. Flight increased the rate of warming from torpor. This effect was more pronounced for Tsk than Tb. This suggests that bats could rely on heat generated by flight muscles to complete the final stages of arousal. Using active temperature to define torpor may underestimate torpor due to ambient cooling of external transmitters or animals leaving roosts while still torpid. Conversely, active temperature may also overestimate shallow torpor use if it is recorded during active arousal when shivering and non-shivering thermogenesis warm external transmitters. Our findings illuminate the need for laboratory studies that quantify the relationship between metabolic rate and Tsk over a range of ambient temperatures.
Asunto(s)
Aclimatación/fisiología , Regulación de la Temperatura Corporal/fisiología , Quirópteros/fisiología , Temperatura Cutánea/fisiología , Animales , Nivel de Alerta/fisiología , Metabolismo Energético/fisiología , Vuelo Animal , Saskatchewan , TemperaturaRESUMEN
The neuroanatomy of the mammalian visual system has received considerable attention through electrophysiological study of cats and non-human primates, and through neuroimaging of humans. Canine neuroanatomy, however, has received much less attention, limiting our understanding of canine vision and visual pathways. As an early step in applying blood oxygenation level dependant (BOLD) functional magnetic resonance imaging (fMRI) for veterinary use, we compared visual activity in the thalamus and occipital cortex of anesthetized dogs presented with binocular and monocular visual stimuli. Activity in the left and right thalamus and occipital cortex during monocular stimulation was also compared. Six beagles were presented with a vertical grating visual stimulus and scanned at 4 Tesla. Each dog was scanned twice under each of 3 anesthetic protocols (isoflurane, propofol, and fentanyl/midazolam). We found: 1) significant BOLD activation in the lateral geniculate nucleus (LGN) of the thalamus and the occipital cortex; 2) a significantly larger area of activation in the LGN during monocular stimulation than during binocular stimulation; and 3) that activity in the hemisphere contralateral to the stimulus was not significantly greater than that ipsilateral to it.
Asunto(s)
Anestésicos/administración & dosificación , Perros/fisiología , Imagen por Resonancia Magnética/veterinaria , Tálamo/fisiología , Corteza Visual/fisiología , Animales , Femenino , Cuerpos Geniculados , Imagen por Resonancia Magnética/métodos , Masculino , Estimulación Luminosa , Visión Binocular/fisiología , Visión Monocular/fisiologíaRESUMEN
Functional magnetic resonance imaging (fMRI) is a recent advance in neuroimaging that provides a picture of brain activity with excellent spatial resolution. Current methods used to evaluate canine vision are poorly standardized and vulnerable to bias. Functional MRI may represent a valuable method of testing vision in dogs if the impacts of anesthesia on fMRI are understood. Six dogs were scanned during visual stimulation, each under three different anesthetic protocols (isoflurane, propofol, fentanyl/midazolam) to address the questions: (1) Can visually evoked fMR signals be reliably recorded in anesthetized dogs? and (2) Which anesthetic agent permits the least suppression of visually induced fMR signal in dogs? This study confirms that visual stimuli reliably elicit neural activity and fMR signal change in anesthetized dogs. No significant differences in images acquired under the three anesthetics were found, and there was no significant relationship between anesthetic dose and brain activity, within the range of doses used in this study. Images obtained during isoflurane anesthesia were more consistent between dogs than those obtained with the other two agents. This reduced variation may reflect the fact that inhalant anesthesia is more easily controlled than intravenous anesthesia under conditions associated with high field fMRI.