observations of the flow in the basilar artery. In both investigations it was arteries of the circle of Willis.

Transcription

1 236 J. Physiol. (I958) I40, THE DISTRIBUTION OF CAROTID AND VERTEBRAL BLOOD IN THE BRAIN OF THE CAT By R. L. HOLMES, P. P. NEWMAN AND J. H. WOLSTENCROFT From the Departments of Anatomy and Physiology, School of Medicine, University of Leeds (Received 30 August 1957) In animals commonly used in the laboratory the arteries supplying the blood to the brain may vary considerably from one species to another, especially in the contribution made to the circle of Willis by the vertebral and carotid arteries. In the cat the vertebral arteries unite near the anterior border of the foramen magnum to form the basilar artery. The basilar artery passes rostrally on the ventral surface of the brain stem to the upper border of the pons where it divides into the posterior cerebral arteries (Text-fig. 1). The carotid blood reaches the circle of Willis through anastomatic channels derived from the extracranial rete of the internal maxillary artery and via the ascending pharyngeal artery (Davis & Story, 1943; Chungcharoen, Daly, Neil & Schweitzer, 1952; Daniel, Dawes & Prichard, 1953). It has generally been assumed that vertebral blood passes along the basilar artery to contribute to the circle of Willis, the brain stem thus being supplied with vertebral blood. However, it is equally possible that carotid blood may flow from the circle of Willis into the basilar artery. This problem cannot be decided by the study of the anatomical data alone. Physiological studies have been made in dogs and monkeys by Kramer (1912) using a dye injection technique and in rabbits by McDonald & Potter (1951), who made direct observations of the flow in the basilar artery. In both investigations it was concluded that carotid and vertebral blood met in the posterior communicating arteries of the circle of Willis. The distribution of carotid and vertebral blood in the brain of the dog has been investigated in detail by Jewell & Verney (1957), who described a method based on the injection of dye suspensions into the blood stream. In the present investigation a similar method has been used to study the distribution of blood in the brain of the cat and also some direct observations have been made of flow in the basilar artery. It is often important to know what structures in the brain stem can be reached by blood from the carotid artery, and therefore

2 BLOOD DISTRIBUTION IN CAT BRAIN 237 special attention has been given to the determination of the caudal limit of tissue supplied by carotid blood. The effect on this distribution of heating the carotid blood has also been investigated, in view of the observation (Newman & Wolstencroft, 1956, 1957) that heating the carotid blood is followed by a fall of blood pressure in the intact and decerebrate cat, and that a similar fall of blood pressure can be obtained by direct heating of the medulla. Some preliminary results have already been reported (Holmes, Newman & Wolstencroft, 1957). v v Text-fig. 1. Diagram of the circle of Willis (CW) and its communications in the cat. Afferent vessels carrying carotid blood are shown on the right side only. AC, MC, PC, anterior, middle and posterior cerebral arteries; B, basilar; V, vertebrals; SC, IC, superior and inferior cerebellar arteries; AA, anastomotic branches from the carotid rete, CR; RA, ramus anastomoticus; AP, ascending pharyngeal; C, carotid artery.

3 238 R. L. HOLMES AND OTHERS METHODS Successful experiments were carried out on thirty-one cats of either sex, weighing between 4-0 and 6-0 kg, anaesthetized by intraperitoneal injection of sodium pentobarbitone (Nembutal, Abbott Laboratories Ltd., 45 mg/kg body wt.). The technique used for injection was similar to that described by Jewell & Verney (1957) and by Andersson & Jewell (1956). After a dye suspension had been injected into the artery whose field of distribution was to be investigated, the heart was stopped before recirculation had occurred, and sections of the brain were prepared and examined for the presence of injected material. Two dye suspensions recommended by Jewell & Verney (1957) were used. They were carbon black (11% solids) and Monastral Fast Blue (20% solids), the latter being diluted with an equal volume of sodium chloride solution (0.9%, w/v). Both these dye suspensions were supplied by the Imperial Chemical (Pharmaceuticals) Co. Ltd. The particle size was 1 u or less. In some animals decerebration was performed at the level of the superior colliculi, with the carotid arteries temporarily clamped. After about 10 min the clamps were removed. Carotid injections. After insertion of a tracheal cannula, the carotid arteries were exposed in the neck and one of the lingual arteries was cannulated close to its junction with the external carotid, for the recording of the blood pressure by a mercury manometer ml. of dye was injected on the same side as the cannulated lingual artery, using a 1 ml. tuberculin syringe and a no. 19 Record needle. The needle was inserted through the wall of the common carotid artery and the injection made manually at a rate of ml./sec. This rate of injection was chosen because it did not cause any change in lingual blood pressure. The injection. was continued for sec; then the heart was stopped by injecting sodium citrate solution (about 10%) through a polythene catheter which had previously been inserted through a femoral vein and pushed towards the heart. In some later experiments puncture of the carotid artery by a needle was avoided by cannulation of its ramus muscularis dorsalis branch. Dye was then introduced into the carotid by retrograde injection through this artery. Carotid heating. One of the common carotid arteries in the neck was dissected free from surrounding tissue and the muscular and thyroid branches tied and cut close to their origin from the carotid trunk. The common carotid artery was then enclosed in a Perspex chamber, 3-5 cm in length, through which was pumped warmed saline solution. The temperature of the saline was gradually raised until the blood pressure fell (Newman & Wolstencroft, 1956) and then an injection of dye was made into the carotid artery as described above. Vertebral injection8. After a tracheal cannula had been inserted and connected to a respiration pump part of the sternum and the anterior parts of the first three ribs were removed. The right subelavian artery was exposed and the dye injected at a point between the origin of the right carotid and vertebral arteries. The procedure following injection was the same as that described above. Histological techniques. Immediately after the injection of the dye and stopping of the heart a trephine hole was made in the skull; the neck was severed at about the 7th cervical vertebra and the atlanto-occipital membrane incised. The head and neck were then immersed in fixative (formalin 10 parts, acetic acid 5 parts, 50% (v/v) spirit 85 parts) for about 18 hr. The brain and spinal cord were then removed from the skull in one piece, and fixation continued for 2-3 days longer. The specimen was then stored until required in 96% (v/v) spirit. After surface examination, free-hand sections approximately 1 mm in thickness were cut. Initially these were taken at the following levels (Text-fig. 2): the plane of the optic chiasma; the plane of the superior colliculi; junction of rostral two-thirds and caudal third of the pons; caudal limit of trapezoid body; and caudal limit of the pyramids. These sections were dehydrated in alcohol, cleared and mounted in balsam for examination with a binocular microscope. In most cases, further sections were made at intermediate levels. Direct observation of the basilar artery in the anaesthetized animal. In these experiments the ventral surface of the brain stem was exposed. A length of trachea (including the larynx) and

4 BLOOD DISTRIBUTION IN CAT BRAIN 239 oesophagus was removed. The muscles attached to the occipital bone were removed and the bone itself cut away between the tympanic bullae, beginning at the junction with the atlanto-occipita membrane. It was considered inadvisable to extend the removal of bone as far as the rostra limit of the pons because of the bleeding that occurs when the bone in this region is cut. The meninges were cut and reflected and the basilar artery observed with the naked eye, or with a binocular dissecting microscope, during and after the injection of dye into the carotid or subclavian arteries. Instead of the dye suspensions mentioned above, a 1% solution of methylene blue was used in some experiments. I I b a I ch Text-fig. 2. Diagrams of the mid-sagittal and ventral surfaces of the cat brain, showing the levels of the main planes of section referred to in the text. (ch) plane of the optic chiasma; (a) plane of the superior colliculi; (b) pons; (c) caudal limit of trapezoid body; (d) caudal limit of pyramids. RESULTS Unilateral injection into a carotid artery Following the injection of dye into the carotid artery of one side in ten cats, a naked-eye examination of the brain always showed pigment in some of the surface vessels. Pigment in the circle of Willis and its branches was often greater in amount on the side of the injection. Pigment was often also observed

5 240 R. L. HOLMES AND OTHERS in the basilar artery and some of its main branches. On external examination the presence of dye in the minute vessels of the brain substance could be recognized by a greyish colour. This was always observed in the cerebral cortex and in parts of the cerebellar cortex, particularly dorsally on the side of the injection, but not in the medulla. Text-fig. 3. Sections of the brain stem, showing areas reached by injection of dye into the right carotid artery. The figures are drawings from sections, (a) at the level of the superior colliculi; (b) through the caudal pons; (c) at the level of the caudal limit of the trapezoid body; (d) at the level of the caudal limit of the pyramids. In this and in subsequent figures, all sections are viewed from their caudal aspect, and only brain stem and cerebellar tissue are shown. The presence of dye in any section is indicated by hatching; its presence in greater amount by cross-hatching. V, line of fourth ventricle. Examination of sections showed in all cases that the fine vessels of the cerebral hemispheres and thalamic region were well filled on the side of injection; on the opposite side some dye was present, but this was always less in amount. Passing caudally down the brain stem, the amount of pigment decreased. At the level of the superior colliculi the mid-brain was well injected, again more so on the side of the injection (Text-fig. 3a, Plate IA). At the level of the caudal third of the pons (Text-fig. 3b), all specimens showed a considerable amount of pigment in the dorso-lateral zone or in the cerebellar peduncles, while the more ventral parts of the pons showed no pigment, or

6 BLOOD DISTRIBUTION IN CAT BRAIN 241 only a small amount, often confined to the larger vessels. In this plane the whole of the cerebellar tissue on the side of the injection usually showed some pigment; less was present on the opposite side. Sections at the level of the caudal limit of the trapezoid body showed little or no pigment in the medulla (Text-fig. 3c), and when present, this was usually confined to the larger vessels. The cerebellum showed some injection, especially in its dorsal and medial part. In no specimen of this series was pigment observed in fine medullary vessels at the level of the caudal end of the pyramids (Text-fig. 3d), although some was occasionally present in the larger superficial vessels. Text-fig. 4. Sections showing the distribution following injection into the right carotid artery while blood in that vessel was being heated. Section levels as in Text-fig. 3. Unilateral injection into a carotid artery while the carotid blood was heated on that side In five preparations the distribution of pigment in the superficial vessels appeared to be more extensive than in the previous series. In the vessels of the rostral part of the brain bilateral distribution of pigment was now more marked, and the amount was often found to be equal in both thalami, irrespective of the side of injection. Cortical. tissue, however, still usually showed some inequality. The other notable difference was the extension of d

7 242 R. L. HOLMES AND OTHERS pigment to a more caudal level. An appreciable amount was now found bilaterally at the level of the mid-brain (Text-fig. 4a, Plate IB) and of the caudal end of the pons (Text-fig. 4b) and was not only confined to the dorsal region, although this was still often the most heavily injected part. Some pigment was observed in the medulla at the level of the trapezoid body (Text-fig. 4c), while in all cases except one pigment was present at the level of the most caudal extent of the pyramids (Text-fig. 4d). The cerebellum showed bilateral distribution of dye. /~~~~ ab Text-fig. 5. Sections showing the distribution of dye injected into the right vertebral artery via the subclavian. Section levels as in Text-fig. 3. Unilateral injection into a vertebral artery Sections showed in one cat that vessels of the dorso-lateral regions of the cervical cord and lowest medulla were well filled on the injected side only (Text-fig. 5d). In the higher medulla and pons vessels were injected on both sides, and in the cerebellum widespread bilateral filling of fine vessels was observed, particularly in the more caudal and ventral zones (Text-fig. 5c). Above this level the amount of dye progressively diminished (Text-fig. 5b, a). The distribution in the cerebral cortex was limited to a sharply demarcated zone in the posterior part of the hemisphere and along the edges of the intercerebral fissure, i.e. in the probable field of supply of the posterior cerebral

8 243 BLOOD DISTRIBUTION IN CAT BRAIN arteries; this zone was also filled in the carotid injections. Very little dye was present in other parts of the forebrain. The results of the one experiment of this type were confirmed by the four experiments of the next series, except that in one of these dye injected into the vertebral artery did not reach any area above the level of the pons. Simultaneous injections into carotid and vertebral arteries on the same side A different coloured pigment was injected simultaneously into each vessel and the heart stopped as described under 'Methods'. In four cats the field of distribution of carotid and vertebral blood was as described above, but this group of experiments demonstrated a variable overlap of the carotid and vertebral fields of supply between the level of the trapezoid body below, and that of the optic chiasma above. The proportions of vertebral (blue) pigment decreased from below upwards in accordance with the descriptions already given. In the upper medulla, cerebellum and mid-brain, vessels which contained both the blue (vertebral) and black (carotid) pigment were found, as well as others which held pigment of one colour. Direct observation of blood flow in the basilar artery The main basilar trunk runs somewhat tortuously about the mid line. Under the binocular microscope pulsations could be clearly seen. Eight cats were used in this series. Dye was injected into one common carotid artery whilst the basilar artery was kept under observation. In three of the cats, dye appeared in the rostral part of the basilar artery, and was observed either to form a fluctuating boundary there, or to stream caudally to the origin of one of its lower branches, usually one of the inferior cerebellar vessels. No dye was seen to reach the vertebral arteries. These observations could be repeated a number of times in the same animal. In the remaining five animals, however, dye injected into the carotid artery was not observed to reach the basilar, although it must be noted that the extreme rostral part of the latter had not been exposed. When dye was injected into a vertebral artery, pigmented blood could be observed passing rostrally up the basilar artery and filling the inferior cerebellar and medullary vessels. The rostral limit of this flow varied, and in three out of four animals passed beyond the field of vision, presumably into the circle of Willis. Streamline flow (confined to the side of injection) has been observed following both carotid and vertebral injections, but was more usual in the latter.

9 244 R. L. HOLMES AND OTHERS Carotid injection in the decerebrate animal Examination of three specimens showed that the greater part of the circle of Willis was unaffected by the decerebration, and that anastomoses between it and the basilar artery remained intact. Sections of the brain stem after the injection of dye revealed a pattern of distribution similar to that of the normal animal. DISCUSSION The anatomy of the carotid vessels of the cat has been the subject of detailed examination in recent years (Davis & Story, 1943; Uhungeharoen et al. 1952; Daniel et al. 1953). On most points the accounts of these workers are in agreement. The vessels supplying the rostral parts of the brain arise from the circle of Willis, which connects the basilar, superior cerebellar, posterior, middle and anterior cerebral arteries (Text-fig. 1). In the cat the internal carotid artery is not patent; the blood reaches the circle mainly by way of the anastomotic arteries which pass from the carotid rete via the orbital fissure into the cranial cavity (Text-fig. 1). In addition, a small ramus anastomoticus from the internal maxillary artery enters the skull via the foramen ovale, and a branch of this joins the anastomotic arteries. Another minor contribution is carried by the ascending pharyngeal, which enters the skull via the foramen lacerum medium, and joins the anastomotic artery where this passes through the dura. Daniel et at. (1953) state that there is an occipito-vertebral anastomosis, presumably of minor importance. Our observations show that the middle and anterior cerebral vessels receive blood from the carotid arteries and not from the vertebrals, since dye injected into the carotids always reached the rostral parts of the cerebral cortex and dye injected into the vertebral arteries never did except in insignificant amounts. On the other hand, some dye injected into the vertebral arteries did reach the areas supplied by the superior cerebellar or posterior cerebral vessels, although the carotid seemed to be the main source of the blood flowing into these vessels. The distribution of carotid and vertebral blood to the brain stem via branches of the basilar artery has been studied in several species. Both Kramer (1912), using dogs, and McDonald & Potter (1951), using rabbits, found that the carotid and vertebral blood streams met in the posterior communicating arteries of the circle of Willis so that the brain stem was supplied by vertebral blood. Jewell & Verney (1957), however, found that in some dogs carotid blood also reached the brain stem. They explained this in terms of the mixing of vertebral with carotid blood that had passed through the occipitovertebral anastomosis, which is well developed in the dog (Jewell, 1952). Their evidence for this was that in one animal in which the occipital arteries had been tied no dye appeared in the brain stem after carotid injection.

10 BLOOD DISTRIBUTION IN CAT BRAIN 245 Using a radiographic technique, Daniel et al. (1953) observed in the sheep that a considerable quantity of carotid blood entered the basilar artery under normal conditions. They also predicted, on anatomical grounds, a similar condition in the goat, and this was confirmed by Andersson & Jewell (1956), who showed that almost the entire brain of the goat is supplied by carotid blood. The basilar artery of the goat narrows as it is followed caudally, and its anastomoses with the vertebral vessels are small. Examination of the basilar artery of the cat, both in plastic-injected specimens (Holmes, unpublished) and also by direct observation, shows a different condition. The two vertebral arteries unite to form the basilar which is considerably larger than either vertebral. When followed cranially, this gives off an inferior cerebellar branch on each side (which may be duplicated), either at the same or at different levels (Text-fig. 1). Rostral to this point the basilar artery narrows, and maintains approximately the same external dimensions for the rest of its course. We have found that in the cat carotid blood reaches the dorsal part of the pons and cerebellum via the circle of Willis and superior cerebellar arteries, and may also reach medullary levels, apparently via branches of the basilar artery. The pattern of distribution rules out the possibility of the results being due to flow via an occipito-vertebral anastomosis. Vertebral blood supplies the greater part of the medulla, and may also pass rostrally as far as the superior cerebellar and posterior cerebral vessels. Thus in the cat the junction of the carotid and vertebral blood apparently occurs in the upper end of the basilar artery or posterior part of the circle of Willis, and in some instances we were able to see the junction in the portion of the basilar artery that it was possible to expose. The position of the junction presumably varies with relative pressures and flows in the various vessels. It moves caudally if the vertebral artery is obstructed and in some animals after clamping the costo-cervical arteries near their origins. In those animals the costo-cervical arteries appear to make a significant contribution to the vertebral flow. Heating the carotid blood resulted in an enlargement of the field of supply of that vessel, apparently with the movement of the junction of carotid and vertebral blood flows towards the lower end of the basilar artery. One objection to the dye method is the possibility of interference with the normal flow of blood. We consider it unlikely that this occurnred in the present series of experiments; the distribution appeared to be the same whether the injection was made into the common carotid artery itself, or by a retrograde injection into one of its fine branches. Precautions were taken to prevent a rise in pressure during injection, although, surprisingly, direct observations of the basilar artery during intentionally high injection pressures showed no obvious difference in the point reached by the dye.

11 246 2R. L. HOLMES AND OTHERS SUMMARY 1. The distribution of carotid and vertebral blood in the brain of the cat has been studied by the injection of dye suspensions in anaesthetized animals followed by histological examination. 2. Carotid blood supplies the cerebral hemispheres and thalamic regions. It also contributes to the blood supply of the cerebellum, pons and medulla, perhaps as low as the caudal limit of the trapezoid body. In nearly all specimens the vessels were better filled with dye on the side of injection. 3. Vertebral blood supplies medullary, pontine and cerebellar tissue. The vertebral and carotid fields overlap in the upper brain stem and cerebellum. 4. In some of the animals direct observation has shown that blood may flow caudally in the upper part of the basilar artery, so that carotid blood may reach lower branches. In other instances carotid blood did not extend below the upper end of the basilar artery into the available field of vision. 5. The point of junction of carotid and vertebral blood is variable, but is usually in the upper end of the basilar artery or in the posterior communicating arteries of the circle of Willis close to the basilar artery. 6. Decerebration, by the method employed, does not change the pattern of distribution of carotid blood in the brain stem and cerebellum. 7. Caudal extension of the carotid stream is favoured by heating the carotid blood or by any factor which diminishes the vertebral flow. We thank Messrs Imperial Chemical (Pharmaceuticals) Ltd., for the gift of dye suspension. REFERENCES ANDERSSON, B. & JEWELL, P. A. (1956). The distribution of carotid and vertebral blood in the brain and spinal cord of the goat. Quart. J. exp. Physiol. 41, CHUNGCEAROEN, D., DALY, M. DE B., NEIL, E. & SCHWEITZER, A. (1952). The effect of carotid occlusion upon the intrasinusal pressure with special reference to vascular communications between the carotid and vertebral circulations in the dog, cat and rabbit. J. Physiol. 117, DANIEL, P. M., DAWES, J. D. K. & PRICHARD, M. M. L. (1953). Studies of the carotid rete and its associated arteries. Phil. Trans. B, 237, DAVIS, D. D. & STORY, H. E. (1943). The carotid circulation in the domestic cat. Publ. Field. Mus. (Zool. Ser.), 28, HOLMES, R. L., NEWMAN, P. P. & WOLSTENCROFT, J. H. (1957). The distribution of carotid blood in the brain of the anaesthetized cat. J. Physiol. 137, 60P. JEWELL, P. A. (1952). The anastomoses between internal and external carotid circulations in the dog. J. Anat., Lond., 86, JEWELL, P. A. & VERNEY, E. B. (1957). An experimental attempt to determine the site of the neurohypophyseal osmoreceptors in the dog. Phil. Trans. B, 240, KRAMER, S. P. (1912). On the function of the Circle of Willis. J. exp. Med. 15, MCDONALD, D. A. & POTTER, J. M. (1951). The distribution of blood to the brain. J. Phy8iol. 114, NEWMAN, P. P. & WOLSTENCROFT, J. H. (1956). Influence of the orbital cortex on the changes in blood pressure produced by heating the carotid blood. J. Physiol. 132, 48P. NEwMAN, P. P. & WOLSTENCROFT, J. H. (1957). Changes in blood pressure produced by local heating of the brain stem. J. Physiol. 135, 56P.

12 THE JOURNAL OF PHYSIOLOGY, VOL. 140, No. 2 PLATE 1 :.:.: MO...1 ;z:1.. B Photographs of sections at the level of the superior colliculi viewed from their caudal aspect A shows the distribution following injection of dye into the right carotid artery. B shows the distribution when the dye is injected during heating of the blood in the right carotid artery. (Facing p. 246)