The carotid and orbital retia of the pronghorn, deer and elk

Journal of Experimental Biology

et al. 2008

SUMMARYConservation of energy is a prerequisite thermoregulatory strategy for survival in northern hemisphere winters. We have used thermistor/data logger assemblies to measure temperatures in the brain, carotid artery, jugular vein and abdominal cavity, in pronghorn antelope to determine their winter body temperature and to investigate whether the carotid rete has a survival role. Over the study period mean black globe and air temperature were -0.5±3.2°C and -2.0±3.4°C, respectively, and mean daytime solar radiation was ~186·W·m -2 . Brain temperature (T brain , 39.3±0.3°C) was higher than carotid blood temperature (T carotid , 38.5±0.4°C), and higher than jugular temperature (T jugular , 37.9±0.7°C). Minimum T brain (38.5±0.4°C) and T carotid (37.8±0.2°C) in winter were higher than the minimum T brain (37.7±0.5°C) and T carotid (36.4±0.8°C) in summer that we have reported previously. Compared with summer, winter body temperature patterns were characterized by an absence of selective brain cooling (SBC), a higher range of T brain , a range of T carotid that was significantly narrower (1.8°C) than in summer (3.1°C), and changes in T carotid and T brain that were more highly correlated (r=0.99 in winter vs r=0.83 in summer). These findings suggest that in winter the effects of the carotid rete are reduced, which eliminates SBC and prevents independent regulation of T brain , thus coupling T brain to T carotid . The net effect is that T carotid varies little. A possible consequence is depression of metabolism, with the survival advantage of conservation of energy. These findings also suggest that the carotid rete has wider thermoregulatory effects than its traditional SBC function.

Section: Discussionmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Thermoregulation in pronghorn antelope (Antilocapra americana,Ord) in winter

Hébert

Lust

Journal of Experimental Biology

et al. 2008

“…CBF is controlled to some extent by nerves but mostly by metabolic rate and the demands for glucose and oxygen and, we think, for heat removal. The temperature of cerebral blood can be altered by the carotid rete-cavernous sinus system which exists in all artiodactyls including pronghorns (Carlton and McKean, 1977).…”

Section: Discussionmentioning

confidence: 99%

“…Carotid blood temperature had a circadian/nycthemeral rhythm weakly but significantly (r=0.634) linked to the time of sunrise, of amplitude Pronghorn thermoregulation animals on which McKean and Walker based their report (McKean and Walker, 1974), however, it is also clear that pronghorns have very different blood indices compared to those calculated from average data for nine different species of southern African antelope (Rhodes, 1975 for 10·min (McKean and Walker, 1974). The anatomy of their cranial vasculature has been described (Carlton and McKean, 1977) and it is similar to that in other artiodactyls, specifically in that it has a well developed carotid rete-cavernous sinus system, one of the functions of which is to cool arterial blood destined for the brain (Maloney and Mitchell, 1997 (Thorne, 1975). Both animals were semi-tame.…”

Section: --In My Walk I Killed a Buck Goat Of This Countrey About Thmentioning

confidence: 97%

Thermoregulation in pronghorn antelope (Antilocapra americanaOrd) in the summer

Lust

Journal of Experimental Biology

Maloney

et al. 2007

0.8±0.1°C. There were daily variations of up to 2.3°C in carotid body temperature in individual animals. An average range of carotid blood temperature of 3.1±0.4°C over the study period was recorded for the group, which was significantly wider than the average variation in brain temperature (2.3±0.6°C). Minimum carotid temperature (36.4±0.8°C) was significantly lower than minimum brain temperature (37.7±0.5°C), but maximum brain and carotid temperatures were similar. Brain temperature was kept relatively constant by a combination of warming at low carotid temperatures and cooling at high carotid temperatures and so varied less than carotid temperature. This regulation of brain temperature may be the origin of the amplitude of the average variation in carotid temperature found, and may confer a survival advantage.

“…However, these experiments, in which blood flow was occluded briefly by investigators compressing the veins manually, do not exclude the possibility that high levels of sympathetic activity, associated with stress, attenuated SBC through another mechanism. It also is likely, at least in some species, that the AOV is not the only major conduit for venous return to the cavernous sinus; in sheep and pronghorn antelope, blood from deeper veins in the nose and posterior turbinates passes via the sphenopalatine vein to the deep facial vein and then to the cavernous sinus (4,17). The AOV is not present in pigs, yet SBC can be rapidly abolished in these animals (8).…”

mentioning

confidence: 99%

Angularis oculi vein blood flow modulates the magnitude but not the control of selective brain cooling in sheep

American Journal of Physiology-Regulatory, Integrative and Comp

Hetem

Meyer

et al. 2011

Halfway through the study, a section of the AOV, just caudal to its junction with the dorsal nasal vein, was extirpated on both sides. Before and after AOV surgery, the sheep were housed outdoors at 21-22°C and were exposed in a climatic chamber to daytime heat (40°C) and water deprivation for 5 days. In sheep outdoors, SBC was significantly lower after the AOV had been cut, with its 24-h mean reduced from 0.25 to 0.01°C (t 5 ϭ 3.06, P ϭ 0.03). Carotid blood temperature also was lower (by 0.28°C) at all times of day (t 5 ϭ 3.68, P ϭ 0.01), but the pattern of brain temperature was unchanged. The mean threshold temperature for SBC was not different before (38.85 Ϯ 0.28°C) and after (38.85 Ϯ 0.39°C) AOV surgery (t 5 ϭ0.00, P ϭ 1.00), but above the threshold, SBC magnitude was about twofold less after surgery. SBC after AOV surgery also was less during heat exposure and water deprivation. However, SBC increased progressively by the same magnitude (0.4°C) over the period of water deprivation, and return of drinking water led to rapid cessation of SBC in sheep before and after AOV surgery. We conclude that the AOV is not the only conduit for venous drainage contributing to SBC in sheep and that, contrary to widely held opinion, control of SBC does not involve changes in the vasomotor state of the AOV. brain temperature; evaporative heat loss; thermoregulation ARTIODACTYLS AND FELIDS HAVE the capacity to lower brain temperature below arterial blood temperature through a process termed selective brain cooling (SBC) (for reviews see Refs. 11 and 26). In artiodactyls, blood destined for the brain enters the carotid rete, a bilateral network of small arteries at the base of the brain embedded in the cavernous sinus, a venous lake containing relatively cool blood from the nasal mucosa and other areas of the head. Heat exchange between the warm arterial blood in the rete and the cool venous blood in the sinus cools cerebral arterial blood, so that brain temperature (measured near the hypothalamus) is lower than carotid arterial blood temperature (23). Historically, SBC has been investigated mainly in the laboratory, where it is conspicuous in hyperthermic animals (25). However, recent studies, particularly in free-living animals, have revealed that SBC is not exclusively under thermal control. Nonthermal inputs, particularly sympathetic nervous system activity, also influence its magnitude. While a resting, moderately hyperthermic antelope may exhibit SBC, intense exercise, for example, to escape predation, rapidly leads to a cessation of SBC and an increase in brain temperature (11,26).Largely as a result of an elegant series of experiments in reindeer (14 -16), it is widely held that the mechanism that allows SBC to be facilitated or inhibited involves relative blood flow in two routes of venous return from the nose (11,26). Cool blood drains from the nasal mucosa on each side of the head into the dorsal nasal vein, which in turn bifurcates into the angularis oculi vein (AOV) and facial vein. Blood that passes into the AOV...