The Ferret as an Animal Model in Cerebrovascular Research
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1085
The Ferret as an Animal Model in
Cerebrovascular Research
C. Scott Atkinson, MD, Gary A. Press, MD, Patrick Lyden, MD, and Barrett Katz, MD
Clinical and pathologic observations have suggested analogies between the developing nervous
system of ferrets (Mustela putorius furo) and those of more traditional animal models employed
in stroke research. Experimental work has demonstrated advantages of the ferret as a model of
visual development. We performed in vivo cerebral angiography and postmortem neurovascu-
lar dissection of latex-injected specimens of adult ferrets. The great vessels include a cervical
arterial trunk that gives rise to both carotid arteries. The anatomy of the cranial arteries is
similar to that of rabbits. No carotid rete mirabile is present. There are no intracranial
anastomoses between the external and internal carotid systems. We present in vivo cerebral
angiograms with pathologic correlation that demonstrate that ferrets may provide the same
anatomic advantages as a rabbit model for the experimental study of cerebrovascular disease,
with the additional advantage of a long extracranial cervical segment of the carotid artery,
affording easier access to the intracranial vasculature. {Stroke 1989;20:1085-1088)
N onprimate animal research in regional cen-
tral nervous system ischemia and cerebro-
vascular disease has historically employed
rabbits1-4 and rats5-7 as animal models. These two
kee, Wisconsin). A common carotid artery was
exposed in the neck by direct cutdown. An 18-
gauge plastic catheter was inserted into the com-
mon carotid artery and sealed with an injection cap.
species are appropriate models because most of Conray 60 (Mallinckrodt, St. Louis, Missouri) was
their cerebral blood flow originates from the inter- hand-injected through the catheter, 1.5 ml (undi-
nal carotid arteries, without significant contribution luted) per standard angiographic or digital filming
from their external carotid system.8-9 In other lab- run. Ventrodorsal and lateral views of the cerebral
oratory animal models, including dogs and cats, the circulation were acquired in separate runs at a rate
circle of Willis is supplied mainly by branches of the of 3 films/sec for 6 seconds. To facilitate twofold
external carotid artery through distal intracranial linear magnification, we used a 0.15-mm focal spot,
anastomoses.10-11 This collateral circulation causes a target to film distance of 100 cm, and a target to
unpredictable variations in the size of infarcts fol- object distance of 50 cm. Films were acquired using
lowing occlusion of a single cerebral vessel.12 Rab- 60 kVp and 2 mAs for both the ventrodorsal and
bits and rats have been shown to have consistent lateral projections. Standard photographic subtrac-
patterns of infarction following controlled cerebral tion techniques were used on cut-film angiograms.
artery occlusion.2-4-5 We present in vivo cerebral In one ferret, the external carotid artery was tied off
angiograms with pathologic correlation that demon- at its origin to allow visualization of the internal
strate that ferrets {Mustela putorius furo) may pro- carotid artery in a ventrodorsal projection without
vide the same anatomic advantages as the rabbit superimposition of the large lingual artery.
model for cerebrovascular research.
The left heart (atrium or ventricle) was directly
Materials and Methods punctured through the unopened chest using a 2.5-
Following the intravenous administration of 35 in. 21-gauge needle attached to a 10-ml syringe
mg/kg ketamine hydrochloride with 5 mg/kg xyla- containing 6 ml Conray 60 to obtain aortograms. We
zine, ferrets were restrained in the supine position used a 20-30° RPO (right posterior oblique) projec-
on an angiographic table (General Electric, Milwau- tion to obtain 3 films/sec for 6 seconds with 20 kVp
and 1.6 mAs.
From the Departments of Ophthalmology (C.S.A., B.K.), The thorax was opened after a lethal dose of
Radiology (G.A.P), and Neurosciences (P.L., B.K.), The Uni- sodium thiamylal was administered, allowing cross-
versity of California, San Diego, La Jolla, California.
Address for correspondence: Barrett Katz, MD, Pacific Pres- clamping of the aorta and the inferior vena cava.
byterian Medical Center and The Smith-Kettlewell Eye Research The right atrium was opened for use as a vent. The
Institute, 2340 Clay Street, San Francisco, CA 94120. ferret was perfused with 300-400 ml normal saline
Received August 17, 1988; accepted January 20, 1989. until the atrial vent drained clear perfusate. A total
Downloaded from http://stroke.ahajournals.org/ by guest on August 29, 20151086 Stroke Vol 20, No 8, August 1989
of 24 ml silicone rubber compound was injected into
the cervical trunk at high pressure. After injection, the
cannulas were ligated and the atrial vent was sewn
closed. The ferret was refrigerated for 24 hours. The
brain was then removed and placed in 10% formalin.
The arterial system was dissected for analysis.
Results
The aorta gives rise proximally to a large arterial
trunk (diameter 1.5-2.0 mm), which ascends for
25-30 mm ventral to the trachea8 (Figure 1). At the
thoracic inlet, this arterial trunk divides into the
brachiocephalic artery and the left common carotid
artery. The brachiocephalic artery further divides
into the right common carotid artery and the right
subclavian artery. The common carotid arteries are
1.00-1.25 mm in diameter. An occipital artery leaves
the common carotid artery before the latter bifur-
cates into the internal and external carotid arteries.
The external carotid artery gives rise to superficial
and deep temporal branches as well as to the large
lingual artery.
The internal carotid and basilar artery systems
combine within the cranium to form the circle of
Willis (Figure 2). The basilar artery is larger in
diameter than the internal carotid artery. After
giving rise to the cerebellar arteries, the basilar
artery divides to form the posterior communicating
arteries. These in turn supply the posterior cerebral
arteries. The small internal carotid artery joins the
posterior communicating artery to form the middle
cerebral artery. The two anterior cerebral arteries
complete the circle of Willis and unite to form an
azygos anterior cerebral artery. No branches of the
external carotid artery directly communicate with
the internal carotid artery, nor is a rete mirabile
present. Latex injection dissection confirmed the
origin and course of the internal carotid artery and
the structure of the circle of Willis demonstrated
angiographically.
Discussion
Ferrets are carnivores belonging to the family
Mustelidae, which also includes weasels and minks. FlGURE 1. Standard subtraction film from aortogram of
Young ferrets (kits) are born deaf and blind after a ferret performed after percutaneous cardiac puncture
gestation of 42 days. Ferrets reach adult weight by using 21-gauge needle. Cervicothoracic great vessels are
4 months of age and achieve sexual maturity in the demonstrated in 25° RPO (right posterior oblique) projec-
spring following their birth. Two litters (average tion. Injected contrast fills left atrium (A) and refluxes
size eight kits) per year can be obtained if females into pulmonary veins. Left ventricle (V)fillsand gives rise
are bred early in their breeding season. Ferrets to ascending aorta (a). First branch of aorta is large
typically have genial dispositions and adapt well to arterial trunk (t), which then divides into right brachio-
the laboratory. Maintenance of colonies is simple, cephalic (b) and left common carotid (large solid arrow)
with nutritional requirements met by standard wet- arteries. Right brachiocephalic artery subsequently gives
feed mink diet (30% fat, 35% protein, 5% ash) or rise to right subclavian (curved arrow) and right common
commercially available cat food. Ferrets are easily carotid (large open arrow) arteries. Left subclavian artery
available and can be time-bred. They are less expen- (s) arises directly from arch of aorta just distal to origin of
sive to purchase and maintain than cats. major trunk artery. Vertebral arteries (double small
Although their suitability for the study of the arrows) are proximal branches of subclavian arteries
cerebrovascular system has not been described, (best seen on right side in this projection).
ferrets have been useful as models in the study of
the visual system and the cerebral anatomy. Inves-
Downloaded from http://stroke.ahajournals.org/ by guest on August 29, 2015Atkinson et al Ferret as Animal Model 1087
6—
14
FIGURE 2. Standard subtraction films from right common carotid artery injection demonstrate cranial arteries of ferret
in ventrodorsal (left) and lateral (right) projections. 0, common carotid; 1, proximal external carotid; 2, internal
maxillary; 3, lingual; 4, internal carotid; 5, anterior cerebral; 6, middle cerebral; 7, basilar; 8, first cervical ventral
radicular; 9, anterior spinal; 10, vertebral; 11, occipital; 12, common trunk of auricular and superficial temporal; 13,
auricular; 14, superficial temporal; 15, deep temporal; 16, external ophthalmic; 17, internal ophthalmic arteries. Arteries
11-17 are best seen in lateral projection.
tigations of the histogenesis of the retina,13'14 retinal artery anastomotic channels analogous to the angio-
neurotransmitter systems,15-16 the influence of reti- graphically demonstrable arterius anastomoticus of
nal afferent connections on the development of the dogs or the rete mirabile of cats. The existence of
lateral geniculate nucleus,17 and the development of some collateral circulation not apparent radiograph-
gyral patterns18 have successfully employed a ferret ically or at postmortem examination cannot be
model. Relative neurologic immaturity at birth has completely excluded. It is therefore likely that
afforded significant advantages in such inves- predictable regional cerebral ischemic lesions can
tigations.19 Anatomic studies have shown that the be experimentally produced without extensive intra-
cerebral cortex of ferrets is similar to that of cats,20 cranial surgical preparation. Angiograms and injected
while the retina is similar to that of dogs.21 In all specimens in our study indicate that the basilar
these investigations, ferrets proved to be easy to artery is the largest-caliber vessel supplying the
handle and breed.19-20 circle of Willis. It may be that the vertebrobasilar
We believe ferrets are an appropriate animal system contributes most of the hemispheric blood
model for the study of the cerebrovascular system. supply in ferrets.
Our results confirm that a long cervical arterial We believe that ferrets offer significant advan-
trunk provides an easily accessible site for blood tages in the experimental study of cerebrovascular
bound for both sides of the brain, as previously disease: 1) ferrets are docile laboratory animals that
described.22 We find no internal-to-external carotid are inexpensive to acquire and maintain, 2) the
Downloaded from http://stroke.ahajournals.org/ by guest on August 29, 20151088 Stroke Vol 20, No 8, August 1989
central nervous and visual systems of ferrets have 9. McDonald DA, Potter JM: The distribution of blood to the
been shown to be analogous in structure to those of brain. J Physiol 1951;114:356-371
10. Luginbuhl H: Vascular disease in animals: Comparative
more intensively studied animals, 3) postnatal neu- aspects of cerebrovascular anatomy and physiology in dif-
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nity to study development and teratology, 4) in vivo (eds): Cerebral Vascular Diseases. New York, Grune &
cerebral angiography can be easily and reproduc- Stratton, 1966, p 5
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Blood supply to brains of carnivores, in Crosby EL, Schnit-
internal and external carotid artery systems are zlein HN (eds): Comparative Correlative Neuroanatomy of
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13. Greiner JV, Weidman TA, Bodley HD, Greiner CAM:
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Downloaded from http://stroke.ahajournals.org/ by guest on August 29, 2015The ferret as an animal model in cerebrovascular research.
C S Atkinson, G A Press, P Lyden and B Katz
Stroke. 1989;20:1085-1088
doi: 10.1161/01.STR.20.8.1085
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