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Hypoxic-ischemic brain damage and cerebral blood flow changes in young rabbits
Hypoxic-Ischemic Brain Damage and Cerebral Blood Flow Changes In Young Rabbits Sachio Takashima, MD, Yukinori Ando, MD and Kenzo Takeshita, MD Hypoxic-ischemic cerebral damage was demonstrated in the cerebral cortex of 2-week-old rabbits at 3 to 5 days after bilateral carotid artery ligation and reperfusion during hypoxemia. Carotid ligation and reperfusion had little effect on cortical blood flow during normoxemia, but the former suppressed a blood flow increase to hypoxemia and the latter suppressed a blood flow decrease to hyperoxemia. These results suggest a relative ischemia or vascular dysfunction which may playa part in the pathogenesis of the hypoxic-ischemic cortical necrosis. Takashima S, Ando Y, Takeshita K. Hypoxic-ischemic brain damage and cerebral blood flow changes in young rabbits. Brain Dev 1986;8:274-7
Hypoxia-ischemia is a common cause of brain damage in human infants and is responsible for neurological impairment of survivors. The permanent cell damage depends on the severity and duration of and recovery from hypoxia as well as ischemia. In small laboratory animals, it is difficult to produce perinatal hypoxicischemic brain damage, but the combination of hypoxemia and ischemia tends to cause brain damage [1-3]. In this study, we demonstrated cortical lesions in young rabbits with hypoxia and ischemia following reperfusion, and then examined the cerebral blood flow (CBF) dynamics in the rabbits.
From the Division of Child Neurology, Institute of Neurological Sciences, Tottori University School of Medicine, Y onago. Received for publication: November 16, 1985. Accepted for publication: January 24, 1986.
Key words: Brain damage, cerebral blood flow, hypoxia, ischemia. Correspondence address: Dr. S Takashima, Division of Child Neurology, Institute of Neurological Sciences, Tottori University School of Medicine, 86 Nishimachi, Yonago 683, Japan.
Materials and Methods Animals Thirty-nine young rabbits of both sexes aged 2 weeks after birth were used for acute asphyxia (AA group, 8 rabbits), partial asphyxia (PA group, 7 rabbits) and ischemia-asphyxia (IA group, 13 rabbits) groups. Eleven of the 24 rabbits died after convulsions during ischemia-asphyxia loading, and so are excluded from the data. Sixteen young rabbits were used for CBF measurements.
Methods of Hypoxemia and Ligation of Carotid Arteries The AA group was maintained in a chamber of nitrogen gas with a 0%-0 2 concentration for about 17 min until gasping, the PA group in a 6%-0 2 gas chamber for 3 or 4 hr, and the IA group in a 6%-0 2 gas chamber for 3 hr after transient ligation of the bilateral carotid arteries for 1 hr during the period of hypoxemia. Carotid artery ligation and reperfusion were prepared just before hypoxemia loading, and their procedures were done for 2 to 3 min inhalating low oxygen gas. The rabbits were sacrificed by injection with KCl solution 2 to 5 days after the experiment. The brains were fixed in 4% formalin solution and cut into coronal sections. The tissue sec-
tions were mounted in paraffin and stained with hematoxylin and eosin.
CBF Measurements Sixteen young rabbits were anesthetized with ether in air through a mask, and then tracheostomized, paralyzed by pancuronium bromide intravenous injection (0.01 mg/1 00 g), and mechanically ventilated (Harvard Small Animal Ventilator) with air or other gas mixtures. Arterial blood pressure and transcutaneous P0 2 and PC0 2 were also recorded. Hyper- and hypoxemia loadings were done to be 120 to 150 and 5 to 10 mmHg on transcutaneous P0 2 by oxygen and nitrogen gases, respectively. EEG was continuously recorded with a cerebral function monitor (Crotikon) and scalp electrodes. CBF was measured by the H2 clearance method (Unique Medical Co) [3,4]. The electrodes were inserted in to the parietal cortex through a small hole obtained by craniotomy.
Results Histology of Hypoxic-Ischemic Lesions Histological examination showed no neuronal necrosis in any parts of the brain in group AA, and little abnormality or only slight ischemic changes of individual cortical neurons in group PA. However, in group lA, there was selective necrosis of cortical neurons in the cerebral cortex of the frontal, parietal and temporal lobes. The neurons showed eosinophilic, swollen or pyknotic cytoplasm predominantly in pyramidal cells of the third to fifth layers 2 or 3 days after IA (Fig 1A). Five days after IA there was marked neuronal necrosis with neurono-
phagia and microglial activation in the cerebral cortex of the parietal to temporal lobes. These findings were very marked in the parasagittal areas which showed accompanying spongy changes with prominent capillaries (Fig 1B).
CBF Response to Hypoxemia or Hyperoxemia before, during and after Ligation of Carotid Arteries CBF measurements were performed on the parietal cortex during artificial ventilation, because no significant difference in cortical blood flow was seen between spontaneous respiration during ether anesthesia and artificial ventilation during pancuronium bromide paralysis. The blood flow showed no significant changes before, during or after ligation of bilateral carotid arteries for 1 hr. Arterial blood pressure increased in response to hypoxemia (P0 2, 5 to 10 mmHg) with nitrogen gas of a 10%-0 2 concentration, but remained unchanged on hyperoxemia (P0 2, 120 to 150 mmHg). Arterial pH and cerebral function monitor did not show any significant changes in hypoxemia and hyperoxemia loadings. The CBF response to hyperoxemia and hypoxemia was studied before, during and after ligation of the carotid arteries. CBF decreased on hyperoxemia and increased on hypoxemia before ligation. However, CBF decreased on hyperoxemia, but did not significantly increase on hypoxemia during ligation compared with that of normoxemia (Fig 2). In contrast, CBF increased on hypoxemia, but did not decrease on hyperoxemia during reperfusion after ligation was removed (Fig 3).
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Fig 1 There are an elective neuronal necrosis with eosinophilia (A), or neuronophagia and microglial activation (B) in the cerebral cortex of parietal to temporal lobes at 2 or 5 days after ischemia-asphyxia loadings. H&E stains, x 400.
Takashima et af: Brain damage and CBF of young rabbits 275
mm~ g
100
{
140
mmHg
100
CBF ml/lOOg/mln
100
{
140
120 :=
80
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Fig 2 CBF response to hyper- and hypoxemia during ligation of carotid arteries.
HYPOXEMIA
100 p
40
f
Hyper- Hyp oxerma oxerTlla
HYPEROXEMIA
120 80
20
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NormoxemIa
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80
(BF ml/lOOg/mtn
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Fig 3 CBF response to hyper- and hy poxemia in reperfusion after carotid artery ligation.
RECIRCULATION
-
The hemodynamic response to hyperoxemia and hypoxemia before , during and after carotid artery ligation is summarized in Fig 4. Discussion Following Levine's original adult model of hypoxic-ischemic neuronal damage due to a combination of hypoxia and carotid artery ligation [3], Rice et al [2] demonstrated that unilateral common carotid artery ligation with hypoxia resulted in ischemic neuronal changes in the ipsilateral cerebral cortex, striatum and hippocampus, and in necrosis of the white matter in the majority of 7-day-old rats. The evolution of ischemic cell damage and the associated gliomesodermal reaction was more rapid than in adults. In the present study, spontaneously breathing 2-week-old rabbits showed cortical damage
276 Brain & Development, Vo/8, No 3, 1986
-..
t
Fig 4 CBF changes before during and after ligation of carotid arteries.
on hypoxia following bilateral carotid artery ligation, although only small ischemic neuronal changes occur on hypoxia only or carotid artery ligation with hypoxia. The morphological changes are found predominantly in the parasagittal areas of the cerebral cortex, in which blood supply is at the border zones of the anterior and middle cerebral arteries. These young rabbits often have convulsions just before or after the end of hypoxia loading, but show no paralytic movement. The effects of carotid artery ligation on the cerebral hemispheres differ among different kinds of animals. Adult gerbils subjected to unilateral carotid artery ligation without hypoxia show severe neurological disturbances and cerebral infarction since this animal lacks efficient connecting arteries between the carotid and vertebrobasilar arterial circulations [6, 7]. However, in rats and other animals, uni-
lateral carotid artery occlusion produces no CBF changes on normoxemia , but relative ischemia on hypoxemia [8 , 9] . EklOf and Siesj6 [8] have shown that in normotensive animals with an arterial oxygen tension of 20 mmHg, contralateral cerebral cortical flow increases fourfold, while cortical flow to the ipsilateral side only doubles. A similar situation with respect to blood flow probably exists between the carotid and vertebrobasilar arteries of the present model. CBF is unchanged by pancuronium paralysis in newborn animals, and shows an intact responsiveness to hypoxemia [10] . In our study the cortical blood flow showed no significant changes on bilateral carotid artery ligation, and no significant increase even on hypoxia during bilateral ligation, which suggests relative ischemia. On the other hand, CBF decreases in responsiveness to hyperoxemia . In this study, the cortical blood flow decreased on hyperoxemia before and during bilateral carotid artery ligation , but not in reperfusion after ligation. The latter phenomenon suggests the absence of vascular contraction responsiveness to hyperoxemia. Experimental ischemia and reperfusion in the adult gerbil showed that during reperfusion, there are marked changes in the arachidonic acid metabolites, prostaglandins, water content and vascular premeability [11]. The increases in PGF2(X and water contents during the initial phase of reperfusion , reaching peak values around 1 hr, are followed by increases in PGE 2 and vascular permeability. CBF unresponsiveness to hyperoxemia during reperfusion may be related to these metab olic changes of cerebral vessels and surrounding tissue, which may disturb the vascular function . The capacity of neural and vascular tissue to recover from hypoxia-ischemia not only depends upon the degree of damage that occurs during this initial insult, but also may be influenced by cellular events that occur as a result of subsequent recirculation [12] . The hypoxicischemic neuronal changes in the IA group in our study seem to be closely related to the vascular pathology per reperfusion, although relative ischemia during carotid artery ligation with hypoxia is also an important pathogenetic factor. This relative ischemia and vascular dysfunction seen in this study may occur in focal cerebral infarction or hypoperfusion areas
which are often found at parasagittal cerebral arterial border zones in asphyxiated infants
[13 , 14] .
Acknowledgment This study was supported by Grant No 85-15 from NCNMMD of the Ministry of Health and Welfare, Japan.
References 1. Heiss WD , Rosner G. Functional recovery of cortical neurons as related to degree and duration of ischemia. Ann Neurol 1983 ;14:294-301. 2. Rice JE, Vannucci RC, Brierley lB . The influence of immaturity on hypoxic-ischemic brain damage in the rat. Ann Neurol 1981 ;9:131-41. 3. Levine S. Anoxic-ischemic encephalopathy in the rats. Am J PathoI1960;36:1-17. 4. Haining 1L, Turner D, Pantall RM . Measurement of local cerebral blood flow in the unanesthetized rat using a hydrogen clearance method. Circulation Res 1968;23:313-24 . 5. Nakamura T, Suzuki T, Tsuiki K, Tominaga S. Nonnutritional blood flow in skeletal muscle determined with hydrogen gas. Tohoku J Exp Med 1972;106 :135-45. 6. Matsuyama T, Matsumoto M, Fujisawa A, et al. Why are infant gerbils more resistant than adults to cerebral infarction after carotid ligation? J cereb Blood Flow Metabol 1983;3:381-5. 7. Mies G, Kloiber 0, Drewes LR, Hossmann KA. Cerebral blood flow and regional potassium distribution during focal ischemia of gerbil brain. Ann Neural 1984 ;16:232-7. 8. EklOf B, Siesjo BK. Cerebral blood flow in ischemia caused by carotid artery ligation in the rat. Acta Physiol Scand 1973 ;87 :69-77. 9. Laptook AR, Stonestreet BS , Oh W. The effect of carotid artery ligation on brain blood flow in newborn piglets. Brain Res 1983;276:51-4. 10. Belik 1, Wagerle C, Delivoria-Papadopoulos M. Cerebral blood flow and metabolism following pancuronium bromide in newborn lambs. Pediatr Res 1984 ;18: 1305-8. 11. Bhakoo KK, Crockard A, Lascelles PT. Regional studies of changes in brain fatty acids following experimental ischemia and reperfusion in the gerbil. J Neurochem 1984;43:1025-31. 12. Pulsinelli WA, Brierley JB, Plum F. Temporal profile of neuronal damage in a model of transient forebrain ischemia. Ann Neurol 1982;11 : 491-8 . 13. Myers RE. Four patterns of perinatal brain damage and their conditions of occurrence in primates. Adv NeuroI1975;10:223-34. 14. Volpe JJ, Herscovitch P, Perlman 1M, et al. Positron emission tomography in the asphyxiated term newborn: parasagittal impairment of cerebral blood flow. Ann Neurol 1985;17 :287-96.
Takashima et al: Brain damage and CBF of young rabbits 277
Hypoxia-ischemia is a common cause of brain damage in human infants and is responsible for neurological impairment of survivors. The permanent cell damage depends on the severity and duration of and recovery from hypoxia as well as ischemia. In small laboratory animals, it is difficult to produce perinatal hypoxicischemic brain damage, but the combination of hypoxemia and ischemia tends to cause brain damage [1-3]. In this study, we demonstrated cortical lesions in young rabbits with hypoxia and ischemia following reperfusion, and then examined the cerebral blood flow (CBF) dynamics in the rabbits.
From the Division of Child Neurology, Institute of Neurological Sciences, Tottori University School of Medicine, Y onago. Received for publication: November 16, 1985. Accepted for publication: January 24, 1986.
Key words: Brain damage, cerebral blood flow, hypoxia, ischemia. Correspondence address: Dr. S Takashima, Division of Child Neurology, Institute of Neurological Sciences, Tottori University School of Medicine, 86 Nishimachi, Yonago 683, Japan.
Materials and Methods Animals Thirty-nine young rabbits of both sexes aged 2 weeks after birth were used for acute asphyxia (AA group, 8 rabbits), partial asphyxia (PA group, 7 rabbits) and ischemia-asphyxia (IA group, 13 rabbits) groups. Eleven of the 24 rabbits died after convulsions during ischemia-asphyxia loading, and so are excluded from the data. Sixteen young rabbits were used for CBF measurements.
Methods of Hypoxemia and Ligation of Carotid Arteries The AA group was maintained in a chamber of nitrogen gas with a 0%-0 2 concentration for about 17 min until gasping, the PA group in a 6%-0 2 gas chamber for 3 or 4 hr, and the IA group in a 6%-0 2 gas chamber for 3 hr after transient ligation of the bilateral carotid arteries for 1 hr during the period of hypoxemia. Carotid artery ligation and reperfusion were prepared just before hypoxemia loading, and their procedures were done for 2 to 3 min inhalating low oxygen gas. The rabbits were sacrificed by injection with KCl solution 2 to 5 days after the experiment. The brains were fixed in 4% formalin solution and cut into coronal sections. The tissue sec-
tions were mounted in paraffin and stained with hematoxylin and eosin.
CBF Measurements Sixteen young rabbits were anesthetized with ether in air through a mask, and then tracheostomized, paralyzed by pancuronium bromide intravenous injection (0.01 mg/1 00 g), and mechanically ventilated (Harvard Small Animal Ventilator) with air or other gas mixtures. Arterial blood pressure and transcutaneous P0 2 and PC0 2 were also recorded. Hyper- and hypoxemia loadings were done to be 120 to 150 and 5 to 10 mmHg on transcutaneous P0 2 by oxygen and nitrogen gases, respectively. EEG was continuously recorded with a cerebral function monitor (Crotikon) and scalp electrodes. CBF was measured by the H2 clearance method (Unique Medical Co) [3,4]. The electrodes were inserted in to the parietal cortex through a small hole obtained by craniotomy.
Results Histology of Hypoxic-Ischemic Lesions Histological examination showed no neuronal necrosis in any parts of the brain in group AA, and little abnormality or only slight ischemic changes of individual cortical neurons in group PA. However, in group lA, there was selective necrosis of cortical neurons in the cerebral cortex of the frontal, parietal and temporal lobes. The neurons showed eosinophilic, swollen or pyknotic cytoplasm predominantly in pyramidal cells of the third to fifth layers 2 or 3 days after IA (Fig 1A). Five days after IA there was marked neuronal necrosis with neurono-
phagia and microglial activation in the cerebral cortex of the parietal to temporal lobes. These findings were very marked in the parasagittal areas which showed accompanying spongy changes with prominent capillaries (Fig 1B).
CBF Response to Hypoxemia or Hyperoxemia before, during and after Ligation of Carotid Arteries CBF measurements were performed on the parietal cortex during artificial ventilation, because no significant difference in cortical blood flow was seen between spontaneous respiration during ether anesthesia and artificial ventilation during pancuronium bromide paralysis. The blood flow showed no significant changes before, during or after ligation of bilateral carotid arteries for 1 hr. Arterial blood pressure increased in response to hypoxemia (P0 2, 5 to 10 mmHg) with nitrogen gas of a 10%-0 2 concentration, but remained unchanged on hyperoxemia (P0 2, 120 to 150 mmHg). Arterial pH and cerebral function monitor did not show any significant changes in hypoxemia and hyperoxemia loadings. The CBF response to hyperoxemia and hypoxemia was studied before, during and after ligation of the carotid arteries. CBF decreased on hyperoxemia and increased on hypoxemia before ligation. However, CBF decreased on hyperoxemia, but did not significantly increase on hypoxemia during ligation compared with that of normoxemia (Fig 2). In contrast, CBF increased on hypoxemia, but did not decrease on hyperoxemia during reperfusion after ligation was removed (Fig 3).
"'' ,
: ~-.:: ~f A"'~' .. l.....?'I; ~"'itIfJ*', _l'
!
~
/
•
<''''~
.t.
V .• .. ~~ QI>.
~
-"
• -
.h
,
4IIh ""I>-
Fig 1 There are an elective neuronal necrosis with eosinophilia (A), or neuronophagia and microglial activation (B) in the cerebral cortex of parietal to temporal lobes at 2 or 5 days after ischemia-asphyxia loadings. H&E stains, x 400.
Takashima et af: Brain damage and CBF of young rabbits 275
mm~ g
100
{
140
mmHg
100
CBF ml/lOOg/mln
100
{
140
120 :=
80
NS
60 P
+
40
20
Q
te
,
0
te pe02
=
:=
80
f
60 60
40
9
60
20
40
9
to
po,
20
+ pco~ tc
Normox.eml8
Hyperoxemla
Hyp . o:wemla
No rm 0 xe ma
Fig 2 CBF response to hyper- and hypoxemia during ligation of carotid arteries.
HYPOXEMIA
100 p
40
f
Hyper- Hyp oxerma oxerTlla
HYPEROXEMIA
120 80
20
PO~
NormoxemIa
t
80
(BF ml/lOOg/mtn
BEFORE
LIGATION
~
~
t
Hyper-
oxemla
Hyp -
oxem.a
No rm -
Hyper-
oxem ia oxemla
Hyp _
oxemla
Fig 3 CBF response to hyper- and hy poxemia in reperfusion after carotid artery ligation.
RECIRCULATION
-
The hemodynamic response to hyperoxemia and hypoxemia before , during and after carotid artery ligation is summarized in Fig 4. Discussion Following Levine's original adult model of hypoxic-ischemic neuronal damage due to a combination of hypoxia and carotid artery ligation [3], Rice et al [2] demonstrated that unilateral common carotid artery ligation with hypoxia resulted in ischemic neuronal changes in the ipsilateral cerebral cortex, striatum and hippocampus, and in necrosis of the white matter in the majority of 7-day-old rats. The evolution of ischemic cell damage and the associated gliomesodermal reaction was more rapid than in adults. In the present study, spontaneously breathing 2-week-old rabbits showed cortical damage
276 Brain & Development, Vo/8, No 3, 1986
-..
t
Fig 4 CBF changes before during and after ligation of carotid arteries.
on hypoxia following bilateral carotid artery ligation, although only small ischemic neuronal changes occur on hypoxia only or carotid artery ligation with hypoxia. The morphological changes are found predominantly in the parasagittal areas of the cerebral cortex, in which blood supply is at the border zones of the anterior and middle cerebral arteries. These young rabbits often have convulsions just before or after the end of hypoxia loading, but show no paralytic movement. The effects of carotid artery ligation on the cerebral hemispheres differ among different kinds of animals. Adult gerbils subjected to unilateral carotid artery ligation without hypoxia show severe neurological disturbances and cerebral infarction since this animal lacks efficient connecting arteries between the carotid and vertebrobasilar arterial circulations [6, 7]. However, in rats and other animals, uni-
lateral carotid artery occlusion produces no CBF changes on normoxemia , but relative ischemia on hypoxemia [8 , 9] . EklOf and Siesj6 [8] have shown that in normotensive animals with an arterial oxygen tension of 20 mmHg, contralateral cerebral cortical flow increases fourfold, while cortical flow to the ipsilateral side only doubles. A similar situation with respect to blood flow probably exists between the carotid and vertebrobasilar arteries of the present model. CBF is unchanged by pancuronium paralysis in newborn animals, and shows an intact responsiveness to hypoxemia [10] . In our study the cortical blood flow showed no significant changes on bilateral carotid artery ligation, and no significant increase even on hypoxia during bilateral ligation, which suggests relative ischemia. On the other hand, CBF decreases in responsiveness to hyperoxemia . In this study, the cortical blood flow decreased on hyperoxemia before and during bilateral carotid artery ligation , but not in reperfusion after ligation. The latter phenomenon suggests the absence of vascular contraction responsiveness to hyperoxemia. Experimental ischemia and reperfusion in the adult gerbil showed that during reperfusion, there are marked changes in the arachidonic acid metabolites, prostaglandins, water content and vascular premeability [11]. The increases in PGF2(X and water contents during the initial phase of reperfusion , reaching peak values around 1 hr, are followed by increases in PGE 2 and vascular permeability. CBF unresponsiveness to hyperoxemia during reperfusion may be related to these metab olic changes of cerebral vessels and surrounding tissue, which may disturb the vascular function . The capacity of neural and vascular tissue to recover from hypoxia-ischemia not only depends upon the degree of damage that occurs during this initial insult, but also may be influenced by cellular events that occur as a result of subsequent recirculation [12] . The hypoxicischemic neuronal changes in the IA group in our study seem to be closely related to the vascular pathology per reperfusion, although relative ischemia during carotid artery ligation with hypoxia is also an important pathogenetic factor. This relative ischemia and vascular dysfunction seen in this study may occur in focal cerebral infarction or hypoperfusion areas
which are often found at parasagittal cerebral arterial border zones in asphyxiated infants
[13 , 14] .
Acknowledgment This study was supported by Grant No 85-15 from NCNMMD of the Ministry of Health and Welfare, Japan.
References 1. Heiss WD , Rosner G. Functional recovery of cortical neurons as related to degree and duration of ischemia. Ann Neurol 1983 ;14:294-301. 2. Rice JE, Vannucci RC, Brierley lB . The influence of immaturity on hypoxic-ischemic brain damage in the rat. Ann Neurol 1981 ;9:131-41. 3. Levine S. Anoxic-ischemic encephalopathy in the rats. Am J PathoI1960;36:1-17. 4. Haining 1L, Turner D, Pantall RM . Measurement of local cerebral blood flow in the unanesthetized rat using a hydrogen clearance method. Circulation Res 1968;23:313-24 . 5. Nakamura T, Suzuki T, Tsuiki K, Tominaga S. Nonnutritional blood flow in skeletal muscle determined with hydrogen gas. Tohoku J Exp Med 1972;106 :135-45. 6. Matsuyama T, Matsumoto M, Fujisawa A, et al. Why are infant gerbils more resistant than adults to cerebral infarction after carotid ligation? J cereb Blood Flow Metabol 1983;3:381-5. 7. Mies G, Kloiber 0, Drewes LR, Hossmann KA. Cerebral blood flow and regional potassium distribution during focal ischemia of gerbil brain. Ann Neural 1984 ;16:232-7. 8. EklOf B, Siesjo BK. Cerebral blood flow in ischemia caused by carotid artery ligation in the rat. Acta Physiol Scand 1973 ;87 :69-77. 9. Laptook AR, Stonestreet BS , Oh W. The effect of carotid artery ligation on brain blood flow in newborn piglets. Brain Res 1983;276:51-4. 10. Belik 1, Wagerle C, Delivoria-Papadopoulos M. Cerebral blood flow and metabolism following pancuronium bromide in newborn lambs. Pediatr Res 1984 ;18: 1305-8. 11. Bhakoo KK, Crockard A, Lascelles PT. Regional studies of changes in brain fatty acids following experimental ischemia and reperfusion in the gerbil. J Neurochem 1984;43:1025-31. 12. Pulsinelli WA, Brierley JB, Plum F. Temporal profile of neuronal damage in a model of transient forebrain ischemia. Ann Neurol 1982;11 : 491-8 . 13. Myers RE. Four patterns of perinatal brain damage and their conditions of occurrence in primates. Adv NeuroI1975;10:223-34. 14. Volpe JJ, Herscovitch P, Perlman 1M, et al. Positron emission tomography in the asphyxiated term newborn: parasagittal impairment of cerebral blood flow. Ann Neurol 1985;17 :287-96.
Takashima et al: Brain damage and CBF of young rabbits 277