Histological studies of the dorsal nasal,Angularis Oculi,and facial veins of sheep (Ovis aries)

Selective brain cooling (SBC) requires vasoactivity in the superficial veins of the face of the animal. This vasoactivity is possible because of an adequate amount of smooth muscle in the tunica media of each of these superficial vessels, enabling it to act as a “muscle sphincter.” In this study, the angularis oculi, dorsal nasal, distal, and proximal parts of the facial veins in sheep were examined histologically to describe an anatomical basis for SBC. Measurements of the tunica media thickness, the lumen diameter, and the ratio of these measurements showed that the relative tunica media thicknesses in the angularis oculi vein and the dorsal nasal vein are statistically smaller (P < 0.001) than in the distal or the proximal parts of the facial vein. In the angularis oculi, dorsal nasal, and distal part of the facial vein, the tunicae mediae were composed of five to seven circularly arranged smooth muscle layers, suggesting their ability to vasoconstrict. The proximal part of the facial vein possesses both circularly and longitudinally arranged smooth muscle layers. The circular smooth muscle layers suggest a vasoconstrictory function, whereas the longitudinal smooth muscle layers imply a vasodilatory function in this part of the facial vein. Both the dorsal nasal and the proximal part of the facial vein, but not the angularis oculi or the distal part of the facial vein, possess endothelial valves near their confluences with other veins. It was concluded from this study that the angularis oculi and the distal part of the facial vein vasoconstrict, whereas the proximal part of the facial vein vasodilates, enabling the necessary changes in blood flow in SBC. J. Morphol. 237:275–281, 1998. © 1998 Wiley-Liss, Inc.     

Humoral pathway for transfer of the boar pheromone, androstenol, from the nasal mucosa to the brain and hypophysis of gilts

Signaling and priming pheromones play an important role in intraspecies behavioral and sexual interactions and in the control of reproduction. It is generally accepted that pheromones act by stimulating the dendritic receptors in the mucus-imbedded cilia of olfactory neurons massed in the olfactory epithelium. The boar pheromone androstenol, known to induce sexual behavior in pigs, is 1 of 2 pheromones that have been chemically defined, tritiated and thus made available for use in studies. In Experiment 1, sexually mature cyclic gilts at Days 16 to 21 of the estrous cycle were humanely killed and the heads separated from the bodies. The heads were attached to a perfusion system using heated, oxygenated, heparinized, autologous blood. A total amount of 10(8) dpm (758 ng) of 3H-5 alpha-androstenol (3HA) was either infused into the angularis oculi veins that drain the nasal cavities (n = 7) over a 5-min period or applied through intranasal catheters onto the mucose surface (n = 16) for 2 min. In both groups frequent blood samples were collected from the carotid rete and from venous effluent. Concentration of 3HA in the arterial blood of the carotid rete after direct (into angularis oculi veins) or indirect (onto the nasal mucosa) administration of 3HA into veins draining the nasal cavities was significantly higher than background radioactivity before 3HA administration (P < 0.0001 and P < 0.05, respectively). The 3HA was selectively accumulated (compared with the respective control tissue) in the neurohypophysis (P < 0.001), adenohypophysis (P < 0.01), ventromedial hypothalamus (P < 0.05), corpus mammillare (P < 0.01), and perihypophyseal vascular complex (P < 0.001). In a second in vitro experiment, active uptake of 3HA into the nasal mucosa of the proximal, respiratory segment of the nasal cavity was observed. These results demonstrate a humoral pathway for the transfer of pheromones from the nasal cavity to the hypophysis and brain. Androstenol was taken up by the respiratory part of the nasal mucosa, resorbed into blood, transported to the cavernous sinus and transferred into the arterial blood of the carotid rete (supplying the hypophysis and brain), and then selectively accumulated in the hypophysis and certain brain structures.     

An angiographic study of the carotid arterial and jugular venous systems in the cat.

Standard techniques for performing carotid angiography in dogs and in man were adapted to the cat in order to study the vascularization of both intracranial and extracranial structures. Venous drainage was examined by venography of selected vessels. The carotid-cerebral and the vertebral-basilar arterial systems of the cat were studied, although no attempt was made to define the territory supplied by each system. In serial angiograms, vascularization of the rete mirabile conjugatum was visualized and distinct arterial and venous retia were delineated. Large facial veins were seen approximately one second after the intra-arterial injection of radio-contrast material. The early filling of the large facial veins appeared to be the result of an artery-to-venous shunt. Contrast material flowed posteriorly in these veins and drained into the venous rete. When contrast material was injected either into the sagittal sinus or retrograde in the external jugular vein, the internal jugular vein was visible in four of ten cats. This vessel drained blood directly from intracranial contents before anastomosis with the vertebral and external jugular veins.     

Anatomy of the veins of the head in the domestic fowl

The anatomy of the cephalic venous system in the fowl was studied in 19 specimens by means of latex-injected preparations and by dissection. The brain sinuses converge dorsally upon the large cervical sinus and vertebral veins. Dorso-ventral communication is provided by the occipital veins posteriorly, while the ophthalmic system unites both dorsal and ventral sinuses and the temporal rete with the extracranial veins anteriorly. The jugular veins are formed from the superficial branches of the facial veins and serve mainly as outlets for extracranial blood. They are united at the base of the head by a prominent transverse anastomosis which slopes caudally towards the larger, right jugular. As in mammals, the carotid veins envelop the internal carotid arteries and anteriorly form a bulbous sinus cavernosus around the inter-carotid anastomosis.     

The influence of steroids on vascular tension of isolated superficial veins of the nose and face during the estrous cycle of gilts

The arrangement of the superficial facial veins enables blood flow from the nasal cavity into the peripheral circulation by two pathways: through the frontal vein into the cavernous sinus and through the facial vein into the external jugular vein. The current study was designed to determine whether estradiol and progesterone affect the vascular tone of the superficial veins of the nose and face in cycling gilts (Sus scrofa f. domestica) and to analyze the immunolocalization of progesterone receptors and estradiol receptors in these veins. The influence of hormones on vascular tension differed depending on the type of vessel and the phase of the estrous cycle. Estradiol decreased vascular tension in the nasal vein during the follicular phase (P < 0.05) and increased tension in the frontal vein during the luteal phase (P < 0.05). Progesterone increased the vascular tension of the frontal vein (P < 0.05) and decreased the tension of the other veins (P < 0.05) in both phases of the cycle. Expression of estradiol receptor β but not of progesterone receptor was observed in the superficial veins of the nose and face. In conclusion, the effect of ovarian steroid hormones on the vascular tension of the superficial veins of the nose and face in female pigs as well as the reactivity of these veins to steroid boar pheromones can affect the blood supply from the nasal cavity to the venous cavernous sinus. We propose that the ovarian steroid hormones that modulate the vascular tension of the nasal and facial veins may also influence the action of boar pheromones absorbed into the nasal mucosa in gilts and may reach the brain via local destination transfer.     

Limitations on arteriovenous cooling of the blood supply to the human brain

Arteriovenous heat transfer (AVHT) is a thermoregulatory phenomenon which enhances tolerance to thermal stress in a variety of animals. Several authors have speculated that human responses to thermal stress reflect AVHT in the head and neck, even though primates lack the specialized vascular arrangements which characterize AVHT in other animals. We modeled heat transfer based on the anatonmical relationships and blood flows for the carotid artery and associated venous channels in the human neck and cavernous sinus. Heat transfer rate was predicted using the effectiveness-number of transfer units method for heat exchanger analysis. Modeling showed that AVHT is critically dependent upon (1) heat exchanger effectiveness and (2) arteriovenous inlet temperature difference. Predicted heat exchanger effectiveness is less than 5.5% for the neck and 0.3% for the cavernous sinus. These very low values reflect both the small arteriovenous interface for heat exchange and the high flow rate in the carotid artery. In addition, humans lack the strong venous temperature depression required to drive heat exchange; both the cavernous sinus and the internal jugular vein carry a large proportion of venous blood warmed by its passage through the brain as well as a small contribution from the face and scalp, whose temperature varies with environmental conditions. Under the most optimistic set of assumptions, carotid artery temperature would be lowered by less than 0.1° C during its passage from the aorta to the base of the brain. Physiologically significant cooling of the blood supply to the brain cannot occur in the absence of a suitably scaled site specialized for heat exchange.     

In-vitro heat exchange at the rete of the Boer goat under specified laboratory conditions

1. Each half rete from five Boer goats was perfused with water at 38 °C and flow rate of 2 ml min⁻¹ while simultaneously perfusing the cavernous sinus with water at different temperatures and flow combinations and recording temperatures across the rete.

2. The minimum temperature difference across the rete was recorded at a cavernous sinus perfusion temperature of 37.8 °C and flow rate of 2 ml min⁻¹.

3. Slopes of heat exchange increased threefold when the flow was increased four times.

4. These results support the idea that the rete is an obligate heat exchanger.

Clinical anatomy of the blood spaces and blood vessels surrounding the siphon of the internal carotid artery

The anterior blood space of the cavernous sinus is situated anterolateral to the carotid siphon in 70%, anterior to it in 15%, and lateral to it in 15%. Its height, depth, and mediolateral breadth were measured. The mean distance between the carotid siphon and the skin at the supraorbital foramen was measured with 63 (52.4-71.4) mm. The drainage of the orbital veins was studied and described as well as the area of origin and first course of the ophthalmic artery and its clinical importance.     

Adaptive heterothermy and selective brain cooling in arid-zone mammals

Adaptive heterothermy and selective brain cooling are regarded as important thermal adaptations of large arid-zone mammals. Adaptive heterothermy, a process which reduces evaporation by storing body heat, ought to be enhanced by ambient heat load and by water deficit, but most mammals studied fail to show at least one of those attributes. Selective brain cooling, the reduction of brain temperature below arterial blood temperature, is most evident in artiodactyls, which possess a carotid rete, and traditionally has been considered to protect the brain during hyperthermia. The development of miniature ambulatory data loggers for recording body temperature allows the temperatures of free-living wild mammals to be measured in their natural habitats. All the African ungulates studied so far, in their natural habitats, do not exhibit adaptive heterothermy. They have low-amplitude nychthemeral rhythms of temperature, with mean body temperature over the night exceeding that over the day. Those with carotid retes (black wildebeest, springbok, eland) employ selective brain cooling but zebra, without a rete, do not. None of the rete ungulates, however, seems to employ selective brain cooling to prevent the brain overheating during exertional hyperthermia. Rather, they use it at rest, under moderate heat load, we believe in order to switch body heat loss from evaporative to non-evaporative routes.     

Corrosion anatomical studies of the rete mirabile and the brain basal vessels of pygmy goats

The rete mirabile and cerebral arteries represent a multifunctional system. Age-associated morphological changes at the rete mirabile and major cerebral arteries were observed in pygmy goats. The most important arteries for cerebral circulation are the ramus rostralis and ramus caudalis of the maxillary artery. The persistence of the internal carotid artery ( = 80%) in newborn and adult goats is a quite new result. The thermoregulatory function of head fighting-mammals with a large frontal sinus and the mechanical function of the rete mirabile were discussed.     

Dominance,Age and Aggression among Female Pronghorn,Antilocapra americana (Family: Antilocapridae)

The relationships among dominance, age and aggressive behaviour of marked, female pronghorn (Antilocapra americana; Family Antilocapridae) were studied in north central Colorado. Females formed dominance hierarchies with few circular relationships. Unlike other female ungulates, dominance rank was not correlated with age. Dominance rank was negatively correlated with rate of aggression initiated in summer and winter; however, aggressiveness as an individual trait was not related to dominance. Older females received higher rates of aggression than younger females in summer and winter. During the rut, dominance rank was correlated with rate of aggression received but not with rate of aggression initiated. Patterns of aggression that differ by season within a given hierarchy of dominance relationships suggest a different cause or function of aggressive behaviour in different seasons.     

Molting in the Djungarian hamster (Phodopus sungorus Pallas): seasonal or continuous process?

After transfer into a short daylight regimen, the brownish summer pelage of the Djungarian hamster (Phodopus sungorus) changes into the whitish winter phenotype. Although changes in serum prolactin levels are identified as the initiating hormonal signal, morphological data about molting in that species are sparse. The aim of this study was to characterize in detail the summer and winter pelage of the Djungarian hamster and to analyze the alterations in the skin and pelage induced by photoperiodic changes. The main difference between summer and winter hair types is the pattern of pigmentation. In contrast to other mammalian species showing seasonal changes, the winter coat of the Djungarian hamster is not characterized by an increase in hair density. Molting patches were observed at all times, even in the winter coat, showing that the light regimen does not control the process of molting itself but the pattern of pigmentation and eventually the loss of hair during the single molting wave.     

Seasonal variations in the behavioural thermoregulation of roosting Humboldt penguins ( Spheniscus humboldti) in north-central Chile

We examined the thermoregulatory behaviour (TRB) of roosting Humboldt penguins (Spheniscus humboldti) in north central Chile during summer and winter, when ambient temperatures (T_a) are most extreme. Each body posture was considered to represent a particular TRB, which was ranked in a sequence that reflected different degrees of thermal load and was assigned an arbitrary thermoregulatory score. During summer, birds exhibited eight different TRBs, mainly oriented to heat dissipation, and experienced a wide range of T_a (from 14 to 31°C), occasionally above their thermoneutral zone (TNZ, from 2 to 30°C), this being evident by observations of extreme thermoregulatory responses such as panting. In winter, birds exhibited only three TRBs, mainly oriented to heat retention, and experienced a smaller range of T_a (from 11 to 18°C), always within the TNZ, even at night. The components of behavioural responses increased directly with the heat load which explains the broader behavioural repertoire observed in summer. Since penguins are primarily adapted in morphology and physiology to cope with low water temperatures, our results suggest that behavioural thermoregulation may be important in the maintenance of the thermal balance in Humboldt penguins while on land.     

Arterio-venous heat exchange systems in the Jackass penguin Spheniscus demersus

Extensive arterio-venous associations occur in the head, axillae and legs of the Jackass penguin Spheniscus demersus. These vascular arrangements appear to facilitate counter-current heat exchange. The major heat exchange system in the head is the post orbital rete mirabile formed by the superior orbital artery. Blood from this rete supplies the eye, nasal passages and superficial jaw muscles. Other blood vessels supplying the superficial areas of the head and mouth associate closely with their corresponding veins.
In the axilla the brachial artery divides to form a humeral plexus of parallel running arteries each associating with up to three interlinking veins. Only the marginal vein does not associate with an artery. It appears that a shunt mechanism, which bypasses the veins in the humeral plexus, functions to permit heat loss when required; for instance in a heat-stressed bird breeding or moulting on land.
In both the upper and lower leg all the major arteries and their branches associate closely with corresponding veins.
The development of these arterio-venous associations indicates that Spheniscus demersus is adapted to a cool aquatic environment in which heat retention is of prime importance.     

Orbital rete and red muscle vein anatomy indicate a high degree of endothermy in the brain and eye of the salmon shark

The salmon shark has been ranked as the most endothermic lamnid shark based upon geographical range, extent of slow twitch muscle, supra-hepatic rete size, and limited temperature measurements, yet its anatomy has remained largely undescribed, and measurements of brain or eye temperatures have not been reported. In this study, four specimens are examined to determine if the morphological requirements for warming the brain and eyes are present. A well-developed arterial orbital rete lies within a venous sinus on both sides of the cranium. Cool, oxygenated blood from the gills can pass through the vessels of this exchanger before reaching the brain or eyes. Since venous blood in the sinus flows opposite the arterial blood, counter-current heat exchange can occur. A vein originating in the red swimming muscle likely contributes to the warmth of the venous sinus by supplying blood directly from the warmest region of the shark. Before collecting in the orbital sinus, this red muscle vein bathes the brain in warm blood. These morphological data suggest the salmon shark has a significant capacity to warm the brain and eyes.     

Selective brain cooling: a multiple regulatory mechanism

The mechanism of selective brain cooling (SBC) allows the brain to remain cooler than the rest of the body. This paper aims to provide new ideas to better understand SBC, emphasizing how it works, how it is controlled and what its role is. There are two distinct types of SBC in homeotherms: (1) using precooling of arterial blood destined for the brain, with cool venous blood returning from the nose and head skin, (2) using venous blood to cool the brain directly. There is a common mechanism of control of SBC intensity. Reduced sympathetic activity leads to simultaneous dilation of the angular oculi veins, supplying the intracranial heat exchangers, and constriction of the facial veins, supplying the heart. Therefore, SBC is enhanced during heat exposure, endurance exercise, relaxed wakefulness and NREM sleep, and vanishes in the cold and during emotional distress. SBC is a multifunctional effector mechanism: it protects the brain from heat damage; it intensifies in dehydrated mammals, thereby saving water; it helps exercising animals delay exhaustion; it might thermally modulate alertness; it is used in diving animals to drop cerebral temperature much below its normal level, expanding diving capacity and protecting the brain from asphyxic damage. Altogether, SBC integrates both thermal and non-thermal regulatory functions.     

Seasonal Foraging Ecology of Non-Migratory Cougars in a System with Migrating Prey

We tested for seasonal differences in cougar (Puma concolor) foraging behaviors in the Southern Yellowstone Ecosystem, a multi-prey system in which ungulate prey migrate, and cougars do not. We recorded 411 winter prey and 239 summer prey killed by 28 female and 10 male cougars, and an additional 37 prey items by unmarked cougars. Deer composed 42.4% of summer cougar diets but only 7.2% of winter diets. Males and females, however, selected different proportions of different prey; male cougars selected more elk (Cervus elaphus) and moose (Alces alces) than females, while females killed greater proportions of bighorn sheep (Ovis canadensis), pronghorn (Antilocapra americana), mule deer (Odocoileus hemionus) and small prey than males. Kill rates did not vary by season or between males and females. In winter, cougars were more likely to kill prey on the landscape as: 1) elevation decreased, 2) distance to edge habitat decreased, 3) distance to large bodies of water decreased, and 4) steepness increased, whereas in summer, cougars were more likely to kill in areas as: 1) elevation decreased, 2) distance to edge habitat decreased, and 3) distance from large bodies of water increased. Our work highlighted that seasonal prey selection exhibited by stationary carnivores in systems with migratory prey is not only driven by changing prey vulnerability, but also by changing prey abundances. Elk and deer migrations may also be sustaining stationary cougar populations and creating apparent competition scenarios that result in higher predation rates on migratory bighorn sheep in winter and pronghorn in summer. Nevertheless, cougar predation on rare ungulates also appeared to be influenced by individual prey selection.     

The contribution of carotid rete variability to brain temperature variability in sheep in a thermoneutral environment

The degree of variability in the temperature difference between the brain and carotid arterial blood is greater than expected from the presumed tight coupling between brain heat production and brain blood flow. In animals with a carotid rete, some of that variability arises in the rete. Using thermometric data loggers in five sheep, we have measured the temperature of arterial blood before it enters the carotid rete and after it has perfused the carotid rete, as well as hypothalamic temperature, every 2 min for between 6 and 12 days. The sheep were conscious, unrestrained, and maintained at an ambient temperature of 20-22 degrees C. On average, carotid arterial blood and brain temperatures were the same, with a decrease in blood temperature of 0.35 degrees C across the rete and then an increase in temperature of the same magnitude between blood leaving the rete and the brain. Rete cooling of arterial blood took place at temperatures below the threshold for selective brain cooling. All of the variability in the temperature difference between carotid artery and brain was attributable statistically to variability in the temperature difference across the rete. The temperature difference between arterial blood leaving the rete and the brain varied from -0.1 to 0.9 degrees C. Some of this variability was related to a thermal inertia of the brain, but the majority we attribute to instability in the relationship between brain blood flow and brain heat production.