Regulation of brain temperature in winter-acclimatized reindeer under heat stress

Abstract

SUMMARYReindeer (Rangifer tarandus) are protected against the Arctic winter cold by thick fur of prime insulating capacity and hence have few avenues of heat loss during work. We have investigated how these animals regulate brain temperature under heavy heat loads. Animals were instrumented for measurements of blood flow, tissue temperatures and respiratory frequency (f) under full anaesthesia, whereas measurements were also made in fully conscious animals while in a climatic chamber or running on a treadmill. At rest, brain temperature (T brain ) rose from 38.5±0.1°C at 10°C to 39.5±0.2°C at 50°C, while f increased from ~7 tõ 250breathsmin kg -1 at T brain 39.2±0.2°C. Bilateral occlusion of both AOVs induced OMP and a rise in T brain and f at T brain >38.8°C. We propose that reindeer regulate body and, particularly, brain temperature under heavy heat loads by a combination of panting, at first through the nose, but later, when the heat load and the minute volume requirements increase due to exercise, primarily through the mouth and that they eventually resort to selective brain cooling.

Investigating the case of human nose shape and climate adaptation

“…Arterial blood leaving the rete eventually perfuses the brain through the Circle of Willis. Venous blood traveling back from the nasal mucosa interacts with the carotid rete in the cavernous sinus and is thought to cool the blood entering the brain in arid-zone mammals, such as Oryx [49], as well as in winter-acclimatized animals, such as reindeer [50]. Although, humans do not possess such a rete and instead have a single artery going through the cavernous sinus, which has led some to question the role of SBC in humans [51], proponents argue that the carotid rete is not a pre-requisite as SBC is present in some animals who don’t possess a rete, such as horses [52].…”

Adaptations to polar life in mammals and birds

“…Heat is then exchanged between the cold blood in the sinus and warm blood in a rete of the carotid artery (6) on its way to the brain. Adapted from Johnsen et al (1985a), Johnsen and Folkow (1988) and Blix et al (2011). seals.…”

“…The result of this is that the brain is cooled selectively while heat is stored (as increased temperature) in the rest of the body to be dissipated when the stress has passed (Fig. 2C) (see Johnsen et al, 1987;Johnsen and Folkow, 1988;Blix et al, 2011).…”

Vocal anatomy, tongue protrusion behaviour and the acoustics of rutting roars in free‐ranging Iberian red deer stags (Cervus elaphus hispanicus)

“…In Norwegian reindeer (Rangifer tarandus tarandus), the air flow is bidirectional during both high-frequent but shallow close-mouthed and openmouthed panting. Interestingly, nasal airflow is drastically reduced during open-mouthed panting so that most of the evaporative cooling occurs via the surfaces of the oral cavity and the richly vascularized tongue (Schmidt-Nielsen et al 1970;Biewener et al 1985;Aas-Hansen et al 2000;Blix et al 2011). In Iberian red deer stags, the airflow during the common roars is unidirectional and the roars are produced during strong expiration along the extended tongue through the wide-open mouth.…”