Angularis Oculi Research Articles

A. facialis in ground squirrel (Citellus itellus)

A ground squirrel is a hibernator, which hibernation lasts, depending on the age and sex, since the end of the summer until the spring. During this period in the body of ground squirrel, as well as in other hibernators, starts lowering of all vital functions, what has been proven by numerous physiological, biochemical and histological examinations of some organ systems of this animal. The objective of our work was to investigate a part of cardiovascular system of ground squirrel so in that way to contribute to a better knowledge of this animal body structure and accordingly to comparative anatomy in general. The investigation included 6 ground squirrels, of both gender, body weight 200-300 grams. For obtaining head and neck arterial vascularization, after exsanguination of the animal, contrast mass of gelatin coloured with tempera was injected into thoracic aorta (Aorta thoracica). After injecting, the blood vessels were prepared and photographed. For obtaining the corrosive preparations of head and neck arterial blood vessels, after exsanguination of the animal, Biocryl (a mixture of liquid biocryl - methil - methacrylate monomer and biocryl in powder - methil - methacrylate polymer) was injected into thoracic aorta (Aorta thoracica). After injecting the preparations were placed into 5% NaOH, for 96 hours or into 10% NaOH for 48 hours. After that they were rinsed in hot water and photographed. A. facialis in ground squirrel is an extension of A. maxillaris. The branches of A. facialis are: A. labialis inferior, A. bursae buccalis dorsalis, A. labialis superior, A. dorsalis nasi and A. angularis oculi. The obtained results regarding A. facialis in ground squirrel (Citellus citellus) were compared to the same ones in rats. In rats, A. facialis is the biggest branch separating from A. carotis externa. The branches of A. facialis in rats are: Ramus glandularis, A. submentalis, A. masseterica ventralis, A. labialis inferior, A. angularis oris, A. labialis superior, Rami musculares, A. lateralis nasi and A. angularis oculi. Based on the above mentioned results, it can be concluded that both in ground squirrel and rat A. facialis branches into A. labialis inferior, A. labialis superior and A. angularis oculi. In ground squirrel the branches of A. facialis are also A. bursae buccalis dorsalis and A. dorsalis nasi, and in rat those are Ramus glandularis, A. submentalis, A. masseterica ventralis, A. angularis oris, Rami musculares and A. lateralis nasi.

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

Reindeer (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 to ×250 breaths min(-1), with a change to open-mouth panting (OMP) at T(brain) 39.0±0.1°C, and carotid and sublingual arterial flows increased by 160% and 500%, respectively. OMP caused jugular venous and carotid arterial temperatures to drop, presumably owing to a much increased respiratory evaporative heat loss. Angular oculi vein (AOV) flow was negligible until T(brain) reached 38.9±0.1°C, but it increased to 0.81 ml min(-1) 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.

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

To investigate the role of the angularis oculi vein (AOV) in selective brain cooling (SBC), we measured brain and carotid blood temperatures in six adult female Dorper sheep. 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) = 3.06, P = 0.03). Carotid blood temperature also was lower (by 0.28°C) at all times of day (t(5) = 3.68, P = 0.01), but the pattern of brain temperature was unchanged. The mean threshold temperature for SBC was not different before (38.85 ± 0.28°C) and after (38.85 ± 0.39°C) AOV surgery (t(5) =0.00, P = 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.

Distensible superficial venous orbital malformations involving the lower eyelid in two horses

2 horses were examined because of vascular masses involving the lower eyelid. Both horses had a unilateral, fluctuant mass involving the lower eyelid. For horse 1, the mass had been present since birth and had slowly increased in size over time. The mass also changed in size in response to various environmental stimuli, alterations in the position of the horse's head, and digital obstruction of superficial vessels adjacent to the mass. Horse 2 was brought to the hospital for euthanasia, and no historical or antemor-tem data were available. A combination of contrast angiography, Doppler ultrasonography, surgical exploration, and blood gas analysis (horse 1) and postmortem and histologic examination (horse 2) were used to determine that the masses consisted of non-neoplastic distended venous channels with anastomoses to the inferior lateral palpebral and angularis oculi veins (both horses) as well as the facial vein (horse 2). Histologic examination (horse 2) revealed large, endothelial cell-lined, blood-filled spaces within the deep dermis consistent with a distensible superficial venous orbital malformation. Horse 1 underwent surgical exploration and ligation of the vascular malformation. Six months after surgery, the mass was markedly reduced in size, and size of the mass was static regardless of head position or environmental stimuli. Thorough preoperative planning with Doppler ultrasonography, contrast angiography, and blood gas analysis is recommended when attempting surgical correction of these malformations in horses. Surgical ligation can result in a successful cosmetic and functional outcome.

Thermoregulatory anatomy of pronghorn (Antilocapra americana)

We have found that pronghorn (Antilocapra americana) use external heat exchange with the environment and internal heat exchange between the carotid artery rete and cavernous venous sinus blood to regulate body temperature. Now we have investigated the relationship between the histological structure of the skin, cephalic veins, and carotid rete–cavernous sinus system and the physiological mechanisms pronghorn use, and whether their thermoregulatory anatomy has adaptive advantages. We harvested tissue samples of skin, three veins (i.e., angularis oculi vein, dorsal nasal vein, and facial vein), and the carotid rete–cavernous sinus system from four pronghorn, two culled in summer and two in winter, and examined each histologically. The three veins had the typical structure of veins with large lumina and thin walls. The carotid rete consisted of small (0.1–0.5 mm) arterioles with a density of ~10/mm2, intertwined with veins (~2/mm2), enclosed within the cavernous sinus; a structure ideal for heat exchange. We concluded that the main function of the dorsal nasal and facial veins is to return cold blood to the body to effect whole body cooling. The cavernous sinus is supplied with warm blood by the palatine veins in winter and cold blood by the deep facial veins in summer, an arrangement different to that in other ungulates, such as sheep, in which the angularis oculi vein supplies the cavernous sinus. Pronghorn skin is richly supplied with blood vessels that facilitate convective heat loss in summer. In winter, the number of coarse and fine hairs per square millimeter increases more than in European deer to form a thick pelage that minimizes heat loss. In summer, the pelage is shed because hair follicles involute. Unlike in other ungulates, pronghorn skin has little adipose tissue. The number of apocrine glands increases in winter rather than in summer. We concluded that the glands have a reproductive/social function rather than a thermoregulatory one. In summary, our study shows that the thermoregulatory anatomy is consistent with our physiological data and has adaptive advantages that help explain the survival of pronghorn in an arid habitat characterized by extreme temperature variation and sparse vegetation.

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-5α-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.

The inhibitory effect of hCG on counter current transfer of GnRH and the presence of LH/hCG receptors in the perihypophyseal cavernous sinus - carotid rete vascular complex of ewes

The existence of the hormone passage from venous blood into arterial blood in the area of the perihypophyseal vascular complex has been demonstrated in some mammals, but its mechanism has not been defined. To study the regulatory mechanism we infused hCG into perihypophyseal cavernous sinus of ovariectomized, conscious ewes to test if the hCG would affect putative LH/hCG receptors and inhibit counter-current transfer of GnRH from the venous cavernous sinus to the arterial carotid rete. The latter study was done on an isolated head model. Ewes were ovariectomized in mid-anestrus and, after 4 to 5 wk were used in the experiments. On the day of experiment ewes were treated intramuscularly with estradiol benzoate or oil vehicle, and 18 to 20 h later were infused either with a multielectrolyte solution or hCG for 2 h via the venae angularis oculi. Immediately thereafter the ewes were anesthetized and exanguinated, and subsequently decapitated. The isolated head was perfused with Dextran in multielectrolyte. The 125I-GnRH was infused into the cavernous sinus via the venae angularis oculi for 5 min; contemporaneous samples were taken from the carotid rete and both jugular veins at 1-min intervals. Transfer of 125I-GnRH from the cavernous sinus to the carotid rete was inhibited by hCG in ewes pretreated with estradiol benzoate but not with oil (P<0.005). We collected tissue samples from the vascular complex of the cavernous sinus and carotid rete of cyclic ewes to determine the presence of LH/hCG receptors. In situ hybridization showed the presence of LH/hCG receptor mRNA transcripts in the walls of both arterial and venous compartments of the cavrnous sinus-carotid rete complex, and immunohistochemistry revealed the presence of receptor proteins. These novel findings confirm previously obtained data suggesting that LH is a modulatory factor for the counter-current transfer of neuropeptides from the venous blood of the cavernous sinus to the arterial blood supplying the brain and hypophysis. The LH could modulate 1251-GnRH transfer acting directly on the vascular smooth muscle.

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 suggest a vasoconstrictory 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.

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

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

Selective brain cooling: role of angularis oculi vein and nasal thermoreception.

We have measured blood flows in the angularis oculi (AOV), facial, and jugular veins and temperatures in the carotid artery and near the hypothalamus in three lightly anesthetized sheep while body and nasal mucosal (Tnm) temperatures were varied independently. Above a threshold hypothalamic temperature (Thyp) of 39 degrees C both selective brain cooling (SBC) and AOV blood flow increased. For a given Thyp, the increase in AOV flow and SBC was inversely proportional to Tnm: low Tnm resulted in high AOV flow and SBC, whereas increasing Tnm attenuated both AOV flow and SBC. This decrease in AOV flow results in submaximal SBC, which does not concur with the hypothesis that SBC functions to protect a thermally vulnerable brain. The trigger for these changes in AOV blood flow was Tnm. Occlusion of the AOV during SBC showed that AOV flow accounted for over 80% of SBC. We conclude that SBC is not only a mechanism for reducing brain temperature but may also be a means of adjusting Thyp to facilitate the appropriate thermoregulatory responses.

Anatomical and physiological evidence for efficacious selective brain cooling in rats

1. 1. To describe a mechanism of selective brain cooling (SBC), vascular structures constituting main parts of the SBC system were studied in 40 control and 13 warm-reared adult Wistar rats. Deleterious effects of invasive techniques of cerebral temperature measurement on cranial vascularization and SBC were also investigated in another group of 20 warm-reared rats. 2. 2. There were two main venous pathways from thermolytic surfaces of the head to the intracranial cooling system, consisting of dural sinuses via the dorsal nasal and frontal veins and via the diploic network of the nasal bones conveying venous blood through the frontoparietal diploic network. 3. 3. The diploic network covered 9.0±1.1% of the frontoparietal surface area in control rats and 12.4±1.3% in warm-reared rats. 4. 4. Dural sinuses covered nearly 30% of dorsal cerebral surface area, a pattern unaffected by warm rearing. 5. 5. Histological studies showed the existence of muscular sphincters in the angularis oculi and facial veins. Their contraction in hyperthermia is likely to divert cool blood, returning from the head skin to the brain. 6. 6. Replacing an invasive measurement of cerebral temperature by a non-invasive technique increased the magnitude of SBC from 0.15±0.09°C to 0.90±0.27°C. 7. 7. It is concluded that venous mechanisms of SBC in rats are well developed and efficacious.

Cavernous sinus and carotid rete of sheep and sows as a possible place for countercurrent exchange of some neuropeptides and steroid hormones

This study was conducted in order to scrutinise the countercurrent exchange of luteinising hormone releasing hormone (LH-RH), β-endorphin and progesterone in the carotid rete and cavernous sinus of sheep and gilts. The ewes ( n=30) and gilts ( n=20) were anaesthetised and had catheters inserted into their jugular veins and carotid common arteries from which heparinised blood was then collected. After exsanguination, the head with the neck was immediately removed and about 30 min later supplied with oxygenated and heated autologous blood mixed with saline (1:1), through one of the carotid arteries at a stable flow rate. Blood samples were collected every minute from the carotid artery contralateral to the arterial blood supply (blood from the carotid rete) and from both jugular veins. Arterial blood pressure was continuously measured and regulated. Radiolabelled hormones 3H-progesterone ( 3H-P 4), 125I-luteinising hormone releasing hormone ( 125I-LH-RH), 125I-β-endorphin ( 125I-En), or 51Cr-labelled red blood cells (control) were infused for 5 min into the cavernous sinuses through catheterised angularis oculi veins. Infusions were carried out on gilts and sheep which were in different phases of the oestrous cycle and on sheep during anoestrus and after oestrogen treatment. As a control, 3H-P 4 was infused into the facial vein instead of into the cavernous sinus. In all experiments with 3H-P 4 and 125I-En infusions, labelled hormones were found in arterial blood collected from the carotid rete. No radioactivity was present in arterial blood in the experiment with seasonally anoestrous sheep. However, 125I-LH-RH was found in the arterial blood of anoestrous oestrogen-treated sheep and of sheep in the early luteal phase. No radioactivity was ascertained in arterial blood after 3H-P 4 infusion into the facial vein (control) or 51Cr-labelled red blood cells into the cavernous sinus (control). These results demonstrate that two neuropeptides (LH-RH and β-endorphin) and a steroid hormone (progesterone) can be transferred from venous to arterial blood at the cavernous sinus and carotid rete in the base of the brain in sheep and pigs. This indicates that there is a powerful exchange system for resupplying hormones to the brain and that this system is dependent on the phase of the oestrous cycle.

Distribution and vasomotor effects of neuropeptides in angular oculi and facial veins of reindeer

1. 1. The vasomotor responses to neuropeptides of the angular oculi and facial veins of reindeer were examined in vitro and correlated with the neuropeptide distribution in the perivascular nerves, as demonstrated by immunohistochemistry. 2. 2. Nerves displaying calcitonin gene related peptide (CGRP)- or neuropeptide Y (NPY)-like immuno-reactivity (-LI) were observed in the media of both veins, while very few fibers were immunoreactive to vasoactive intestinal polypeptide (VIP) or substance P (SP) in either vein. 3. 3. The staining pattern for NPY-LI was largely identical to that ofdopamine-β-hydroxylase, a marker for noradrenaline (NA) producing fibers, indicating coexistence of NPY and NA. 4. 4. Administrations of NPY in vitro elicited contractions in both veins in the presence of propranolol, though more conspicuously in the angular oculi vein. 5. 5. The peptide was without any modulating effect on NA-stimulated contractions in the angular oculi vein, whereas a small enhancement of the NA-induced tone was seen in the facial vein. 6. 6. CGRP caused partial relaxation of both veins, whereas atrial natriuretic polypeptide caused relaxation only in the facial vein. VIP and SP had no effect on either vein. 7. 7. The results suggest that in reindeer the sympathetic nerve fibres to both facial and angular oculi veins contain the vasoconstrictor neuropeptide NPY besides NA, even though these fibres exert a vasodilator action on the myogenically active facial vein. 8. 8. The vasodilator neuropeptide CGRP, which is present in other more sparse perivascular nerve fibres mainly in angular oculi vein, is perhaps of afferent nature in which case CGRP might subserve axon reflex functions. 9. 9. If, however, also the CGRP fibres are truly efferent in nature, chances for a central reciprocal control of flow through angular oculi vein might be at hand.

Selective brain cooling in desert animals: The camel ( Camelus dromedarius)

1. 1. Animals living in the Arabian desert are subjected to extremely high temperatures during the day in summer and very cold nights in winter. They have developed various adaptive mechanisms in order to cope with these severe heat conditions. 2. 2. The camel ( Camelus dromedarius), like many other land animals, resorts to selective brain cooling when it is subjected to heat stress. 3. 3. This mechanism protects the heat-sensitive brain tissue from heat stress and at the same time increases the animals' tolerance to high temperatures. 4. 4. The blood cooled in the nasal cavity by evaporative heat loss is diverted to the brain sinuses via the nasal and angular veins. 5. 5. In the cavernous sinus, the arterial blood in the carotid rete is cooled by the cold venous blood before entering the brain. This will lead to significant cooling of the brain tissue. 6. 6. Active myogenic tone was mainly observed in the facial, nasal and angular oculi veins of the camels head. This tone was found to be sensitive to small changes in temperature in the range 33–45°C. 7. 7. The facial veins constricted, while the nasal and angular oculi veins relaxed to increasing temperatures. This leads to a coursing of cold venous return to the brain's sinuses for selective brain cooling. 8. 8. It is concluded that this myogenic vasoactive mechanism is a major factor in the control of blood flow in the facial area of the camel during heat stress.

Dural Sinuses in the Camel and Their Extracranial Venous Connections

The dural sinuses of one-humped camel (Camelus dromedarius) and their connections with veins of the head and neck were described and, whenever possible, were compared with other domestic animals emphasizing species differences. Information obtained from gross dissection of embalmed camel heads was correlated with latex injected vascular casts, as well as venographs. Although the disposition of the dural sinuses, in general, was similar to those of other domestic animals, they were somewhat complex in the camel. An important venous flow mechanism which functions in the thermoregulation of the brain in the camel was described. The venous drainage of the nasal cavity and its surrounding areas had five connections with the ophthalmic plexus and the cavernous sinus: (1) the infraorbital vein----ophthalmic plexus; (2) the medial superior palpebral vein----ophthalmic plexus; (3) the medial inferior palpebral vein----ophthalmic plexus; (4) the angularis oculi----frontal----supraorbital----dorsal external ophthalmic----emissary vein of the foramen orbitorotundum----cavernous sinus; and (5) the deep facial vein----ventral external ophthalmic----emissary vein of the foramen orbitorotundum----cavernous sinus.

Selective brain cooling after bilateral superior cervical sympathectomy in sheep (Ovis aries)

We have investigated the role of the sympathetic innervation of the vasculature of the head in the control of selective brain cooling of sheep, during exposure to high and low ambient temperatures and during endotoxin-induced fever. Bilateral removal of the superior cervical ganglia resulted in a significant reduction of hypothalamic temperature during all procedures. Respiratory rate was also depressed by the sympathectomy, apparently mainly as a result of a decrease in nasal airway patency. Rectal temperature changes after sympathectomy were dependent on the experimental conditions, and the rectal - hypothalamic temperature difference was enhanced during heat exposure and fever. Our results support the contention that sympathetically mediated changes in nasal blood flow and in venous return from the nasal cavity, via the angularis oculi and facial veins, may be involved in the control of selective brain cooling in sheep.

Sympathetic control of brain cooling in reindeer

Abstract: T h e cold venous blood returning from the nose o f the heat stressed reindeer (Rangifer tarandus tarandus) may be distributed both through the angular oculi veins for selective cooling o f the brain, and through the facial veins for general body cooling. In vitro experiments indicate that the adrenergic receptors o f the angular oculi veins are exclusively o f the fiadrenergic type, while the facial veins contain mainly B adrenergic receptors. W e suggest that the antagonistic neuroeffector organization o f these veins play a major role in the control o f brain cooling. Thus , simultaneous sympathetic stimulation wil l result in constriction o f the angular oculi veins and release o f a pre-existing stretch-induced tone in the facial veins. In this situation the cold venous blood is directed via the facial veins and used for general body cooling. Reduction o f sympathetic activity, on the other hand, will result in dilatation o f the angular oculi veins and constriction or the facial veins, due to development o f myogenic tone in the latter vessels. In this situation the cold venous blood is distributed via the angular oculi veins and used for selective cooling o f the brain.

Vascular control of brain cooling in reindeer

The cold venous effluent returning from the nose of the heat-stressed reindeer may be distributed through angular oculi veins for selective cooling of the brain and through facial veins for general body cooling. In vitro experiments indicate that adrenergic receptors of the angular oculi vein are exclusively of the alpha-adrenergic type, whereas facial veins contain mainly beta-adrenergic receptors. We suggest that the antagonistic adrenergic neuroeffector organization of these veins plays a major role in control of brain cooling. Thus simultaneous sympathetic stimulation results in constriction of angular oculi veins and release of a preexisting stretch-induced tone in facial veins. In this situation cold venous blood is directed via facial veins and used for general body cooling. Reduction of sympathetic activity, on the other hand, results in dilatation of angular oculi veins and constriction of facial veins, due to development of myogenic tone in the latter vessels. In this situation cold venous blood is distributed via angular oculi veins and used for selective cooling of the brain.

Selective cooling of the brain in reindeer.

Cineangiographic examination of reindeer exposed to local (hypothalamic) or general heating and cooling revealed that the angular oculi veins are constricted during cold stress but dilated during heat stress. Moreover, during heat stress a segment of the facial vein appeared to be occluded, causing the cold venous return from the nasal mucosa to be routed directly to the cavernous sinus for selective cooling of the brain. Histological examination of the vasoactive segment of the facial vein showed unusually thick longitudinal and circular layers of smooth muscle cells. Obstruction of angular oculi blood flow by clamping of the veins in the heat-stressed animal resulted in an immediate rise in brain temperature. When reindeer under heat stress shift from closed- to open-mouth panting, only the expiratory phase of the respiratory cycle takes place through the mouth, whereas inspiration through the nose is continued. In this way, cooling of the nasal mucosa and, hence, cooling of the brain, is maintained.

VENOGRAPHY OF THE ORBITAL VENOUS SYSTEM AND CAVERNOUS SINUSES IN THE GOAT

The technique of venography is described for visualizing the orbital veins and the cavernous sinuses following cannulation of the angularis oculi vein and the subsequent injection of 10 ml sodium iothalamate. The venograms clearly demonstrated the veins of the orbit and cavernous sinuses in most of the animals. Two intercavernous sinuses, rostral and caudal, were visualized. In a few goats, transverse and dorsal longitudinal sinuses of the dorsal system of the dural sinuses were also visualized.