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Developmental change in type VI collagen in human cerebral vessels
Developmental Change in Type VI Collagen in Human Cerebral Vessels A t s u s h i K a m e i , M D * t , S a d a t a k a H o u d o u , M D * , Takashi Mito, M D * , H i r o s h i K o n o m i , M D * , and Sachio Takashima, MD*
Vascular development in the human brain was studied by immunohistochemistry using an anti-type VI collagen antibody. Positive vessels were evident from an early gestational age in the meninges, from 21 weeks gestation in the basal ganglia and deep white matter, and from 38 weeks gestation in the cerebral cortex and superficial white matter; however, type VI collagen never appeared in the subependymal germinal layer. The absent or scarce type VI collagen in the subependymal germinal layer may be one of the important factors of subependymal/intraventricular/periventricular hemorrhage in premature neonates. The earlier appearance of positive vessels in the deep white matter than in the cortex and superficial white matter suggests that the medullary vein develops earlier than the cortical and subcortical veins and arteries. These characteristics of the developing vascular structure may be one cause of perinatal brain damage. Kamei A, Houdou S, Mito T, Konomi H, Takashima S. Developmental change in type VI collagen in human cerebral vessels. Pediatr Neurol 1992;8:183-6.
Introduction The anatomic immaturity of brain blood vessels is a major cause of perinatal hypoxic-ischemic brain damage and subependymal/intraventricular hemorrhage [1]. Leukomalacia in preterm and term neonates is closely related to the developing vasculature, which may act as a predisposing factor, as suggested by the characteristic location of damage in children as compared with that in adults [2,3]. In order to elucidate the mechanisms underlying perinatal brain damage, the structural and functional development of brain vasculature must be clarified. Type VI collagen has a very broad distribution throughout the connective tissues, including those of skin, muscle, blood vessel, cornea, sclera, perichondrium, dentine, elastic cartilage, ligament, tendon, amnion/chorion, liver, kidney, heart, pancreas, spleen, thyroid, and brain. It has been
From the *Divisionof Mental Retardation and Birth Defect Research; National Instituteof Neuroscience;National Center of Neurology and Psychiatry; Kodaira, Tokyo, Japan; tDepartmentof Pediatrics; Iwate Medical University;Morioka, lwate, Japan.
suggested that type VI collagen may function as an anchor for large interstitial structures, such as nerves, blood vessels, and collagen fibers in surrounding connective tissues [4-6]. Increases in type VI collagen synthesis and secretion were observed in cultures of fibroblasts from the skin of a patient with cutis laxa [7] which suggests that abnormal synthesis and deposition of type VI collagen may change the mechanical properties of affected tissue. Many anatomic, radiologic, and histochemical studies of vascular development in the human brain have been performed [2,3,8,9], but not on the vascular composition of type VI collagen. This report describes the developmental changes in type VI collagen in the human brain as observed with an immunohistochemical method.
Methods The materials were obtained from 19 autopsied brains, 14 fetuses (17-35 gestationalweeks), 3 term neonates,and 2 infants (ages 1 and 7 months). Nine fetuses were obtained after spontaneous abortion. The other 5 preterm and 3 term neonates died of intrapartum asphyxia or respiratory distress syndrome within 3 days of age. The 2 infants had congenital heart disease. The gestational age in each case was calculated from the date of the last menstrual period. All brains were both macroscopically and microscopicallynormal except for focal cerebral hemorrhage or mild brain edema. Fresh samples of the frontal cortex and basal ganglia were quickly frozen in acetone dry ice and stored in a freezer (-80°C). Frozen sections of 10 wn thickness were cut. For immunohistochemicalstaining, sections were exposed to a 0.3% solutionof hydrogen peroxide to inactivate endogenous peroxidases and stained with mouse monoclonal anti-type VI collagen antibody (Heyl Chemisch-Pharmazeutische Fabrik Gmb H & Co, KG) using the streptavidin-biotinprocedure [10] (Histofine SAB-PO kit; Nichirei Co., Tokyo, Japan). Control sections were incubated with normal mouse serum in place of the primary antibody. Immunoreactivitywas graded as follows: (-) negative staining; (+) a few vessels slightly stained;(+) all vessels positivelystained.
Results The immunologic reaction against anti-type VI collagen antibody was observed in the outer part of the media and the adventitia of the meningeal artery, and in those of the meningeal vein; however, it was difficult to differentiate
Communicationsshould be addressed to: Dr. Kamei; Divisionof Mental Retardationand Birth Defect Research; National Instituteof Neuroscience;NCNP; 4-1-1 Ogawahigashimachi; Kodaira, Tokyo 187, Japan. Received December 31, 1991; accepted February28, 1992.
Kamei et al: Type VI Collagen 183
Table 1. Developmental changes in immunohistochemical type VI collagen in human brain Cerebral Cortex (frontal) L S
Cerebral White Matter Superficial Deep L S L S
Gestational Ages (wks)
N
Meninges
17-20
3
+
21-24
4
+
26-28
4
+
.
30-35
3
+
+
-
38-41
3
+
+
+
+
2
+
+
+
+
-
.
L
S
Germinal Layer
-
.
Basal Ganglia
.
+
-
_+
+
-
+
-
_
+
+
+
-
_
-
+
+
+
+
-
+
+
+
+
+
*
Age
1-7 mos
* No existence of germinal layer. Abbreviations: + = Positive +_ = Slightly positive - = Negative
L : Large vessel N = Number of materials S = Small vessel
the artery and vein in the parenchyma. D e v e l o p m e n t a l changes in type V I c o l l a g e n - p o s i t i v e vessels are sum-
Figure 1. Although they are found in the cortex (arrows), vessels are immunostained with anti-type VI collagen antibody at 26 weeks gestation: original magnification, x250. not
184 PEDIATRIC NEUROLOGY
Vol. 8 No. 3
marized in Table 1. In the l e p t o m e n i n g e s of fetuses of 17-20 w e e k s gestation, vessels and perivascular tissue were already positive. In the cerebral cortex, a positive reaction was found in a few vessels o f the superficial cortical layer from 30-35 w e e k s gestation. In the superficial white matter, large vessels w e r e positive from 38 w e e k s gestation and small vessels f r o m 1 m o n t h of postnatal age (Fig 1 ). In the deep white matter, large vessels w e r e slightly p o s i t i v e from 21-29 w e e k s (Fig 2) and m o r e strongly positive from 30 weeks gestation. Small vessels disclosed positive staining from 30 weeks and all small vessels were stained after 37 weeks gestation. In the basal ganglia, reactive products were o b s e r v e d in large vessels f r o m 21 w e e k s gestation and in small vessels f r o m 30 weeks gestation (Fig 3). In the subependymal germinal layer the terminal vein was only positive for type VI collagen, being n e g a t i v e in all other vessels o f infants of any age.
Figure 2. A vessel is strongly positive in the deep white matter at 26 weeks gestation: original magnification, x250.
Figure 3. In the putamen, there are many small and large positive vessels at 41 weeks gestation: original magnification, xlO0.
Discussion Collagen is a major component of human connective tissue. Our previous immunohistochemical studies of the vessels in the developing human brain involving anti-type IV collagen, antilaminin, and antifibronectin antibodies revealed that there were developmental changes in the basement membrane matrix [8]. During cortical angiogenesis, the density and diameter of vessels increase rapidly from about 26 weeks gestation and peak at 35 weeks; after
Cortex
Superficial white matter
Deep white matter ventricle ==,,°
Type ~ collagen positive vein. (medullary vein) ¢'"-'J Type ~ collagen negative vein. (cortical vein) , ~ Type ~I collagen negative artery. (cortical, medullary artery) ~" Type ~ collagen positive tissue. (leptomeninges) Type ~ collagen negative tissue. (subependymal germinal layer) Figure 4. This figure discloses the developmental discrepancy of type VI collagen between the medullary vein and the medullary artery in the deep white matter in the immature brain.
35 weeks, the density and diameter of vessels are the same as those in adult brain; however, the white matter discloses no major changes in vessel density, although the pattem of changes in vessel diameter resembles that in the cortex. In this study, the positive vessels already appeared at 17 weeks gestation in the leptomeninges, from 21 weeks gestation in the basal ganglia, from 21-29 weeks in the deep white matter, and from 38 weeks in the cerebral cortex and superficial white matter. The positivity of vessel staining persists once it appears in the leptomeninges, cortex, and superficial white matter at an early developmental age, and increases with maturation especially in the deep white matter. Type VI collagen was never found in the subependymal germinal layer, except for the terminal vein. This characteristic vascular structure contrasts sharply with the well developed structure of veins in the deep white matter. In the cerebral hemispheres, the perforating arteries branching from the leptomeningeal artery (i.e., cortical, subcortical, and medullary arteries) supply the cortex to the deep white matter. The ventriculofugal arteries are short in the premature infant [2]. Conversely, venous drainage is divided into 2 sides, in the meningeal direction from the cortex and subcortical white matter (cortical and subcortical veins) and in the ventricular direction from the deep white matter (medullary veins) [2]. The earlier appearance of type VI collagen-positive vessels in the deep white matter suggests that the medullary veins, a terminal branch of the internal cerebral vein, develop earlier than the cortical and subeortical veins, and all perforating arteries because they were not stained in early gestation (Fig 4); therefore, a developmental discrepancy exists between the arteries and veins in the deep white matter, although we could not microscopically differentiate artery (arteriole) and vein (venule). The pathogenesis of intraventricular hemorrhage is related to intravascular, vascular, and extravascular factors [1,11-15]. Our study demonstrates a coexistence of more mature venous and less mature arterial systems in the periventricular white matter of the premature infant, which may be a predisposing factor for local circulatory disturbance. Lack of interstitial type VI collagen in the subependymal germinal layer may be related to a change of mechanical or functional property in immature brain vessels, and poses a greater risk for hemorrhage; however, these characteristics of vascular development may result in ischemic or stagnant injury of the vessels (i.e., periventricular leukomalacia or hemorrhagic infarction). This study demonstrated two characteristics of vascular development: earlier maturation of the medullary vein than perforating arteries in the periventricular white matter and the lack of type VI collagen in vessels of the subependymal germinal layer, in contrast to the early development of the medullary vein of the deep white matter. These developmental discrepancies may be important predisposing factors for periventricular leukomalacia and subependymal/intraventricular/periventricular hemorrhage.
Kameiet al: Type VI Collagen 185
References
[1] Volpe JJ. Intraventricular hemorrhage in the premature i n f a n t Current concepts, part I. Ann Neurol 1989;25:3-11. [2] Takashima S, Tanaka K. Development of cerebrovascular architecture and its relationship to periventricular leukomalacia. Arch Neurol 1978;35:11-6. [3] Takashima S, Armstrong DL, Becker LE. Subcortical leukomalacia. Relationship to development of the cerebral sulcus and its vascular supply. Arch Neurol 1978;35:470-2. [4] Burgeson RE. New collagens, new concepts. Ann Rev Cell Biol 1988;4:551-77. [5] Keene DR, Engvall E, Glanville RW. Ultrastmcture of type VI collagen in human skin and cartilage suggests an anchoring function for this filamentous network. J Cell Biol 1988; 107:1995-2006. [6] C h u M, Pan T, Conway D, et al. The structure of type VI collage. Ann NY Acad Sci 1990;580:55-63. [7] Crawfold SW, Featherstone JA, Holbrook K, Young SL, Bomstein P, Sage H. Characterization of a type VI collagen-related Mr-140000 protein from cutis-laxa fibroblasts in culture. Biochem J 1985;227:491-502. [8] Mito T, Konomi H, Houdou S, Takashima S. lmmunohistochemical study of the vasculature in the developing brain. Pediatr Neurol 1991 ;7:18-22.
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[9] Povlishoek JT, Martinez AJ, Mossy J. The fine structure of blood vessels of the telencephalic germinal matrix in the human fetus. Am J Anat 1977; 149:439-52. [10] Kitamntu T, Ogomori K, Tateishi J, Prusiner SB. Methods in laboratory investigation. Formic acid pretreatment enhances immunostaining of cerebral and systemic amyloid. Lab Invest 1987;57:230-6. [11] Hambletnn G, Wigglesworth JS. Origin of intraventricular haemorrhage in the preterm infant. Arch Dis Child 1976;51:651-9. [12] Goldstein GW. Pathogenesis of brain edema and hemorrhage: Role of the brain capillary. Pediatrics 1979;64:357-60. [13] K u b a n KCK, Gilles FH. Human telencephalic angiogenesis. Ann Neurol 1985;17:539-48. [14] H a r u d a F, Blanc WA. The structure of intracerebral arteries in premature infants and the autoregulation of cerebral blood flow. Ann Neurol 1981;10:303. [15] Pinar MH, Edwards WH, Fratkin J, Marin-Padilla M. A transmission electron microscopy study of human cerebral cortical and germinal matrix (GM) blood vessels in premature neonates. Pediatr Res 1985;19:394A.
Vascular development in the human brain was studied by immunohistochemistry using an anti-type VI collagen antibody. Positive vessels were evident from an early gestational age in the meninges, from 21 weeks gestation in the basal ganglia and deep white matter, and from 38 weeks gestation in the cerebral cortex and superficial white matter; however, type VI collagen never appeared in the subependymal germinal layer. The absent or scarce type VI collagen in the subependymal germinal layer may be one of the important factors of subependymal/intraventricular/periventricular hemorrhage in premature neonates. The earlier appearance of positive vessels in the deep white matter than in the cortex and superficial white matter suggests that the medullary vein develops earlier than the cortical and subcortical veins and arteries. These characteristics of the developing vascular structure may be one cause of perinatal brain damage. Kamei A, Houdou S, Mito T, Konomi H, Takashima S. Developmental change in type VI collagen in human cerebral vessels. Pediatr Neurol 1992;8:183-6.
Introduction The anatomic immaturity of brain blood vessels is a major cause of perinatal hypoxic-ischemic brain damage and subependymal/intraventricular hemorrhage [1]. Leukomalacia in preterm and term neonates is closely related to the developing vasculature, which may act as a predisposing factor, as suggested by the characteristic location of damage in children as compared with that in adults [2,3]. In order to elucidate the mechanisms underlying perinatal brain damage, the structural and functional development of brain vasculature must be clarified. Type VI collagen has a very broad distribution throughout the connective tissues, including those of skin, muscle, blood vessel, cornea, sclera, perichondrium, dentine, elastic cartilage, ligament, tendon, amnion/chorion, liver, kidney, heart, pancreas, spleen, thyroid, and brain. It has been
From the *Divisionof Mental Retardation and Birth Defect Research; National Instituteof Neuroscience;National Center of Neurology and Psychiatry; Kodaira, Tokyo, Japan; tDepartmentof Pediatrics; Iwate Medical University;Morioka, lwate, Japan.
suggested that type VI collagen may function as an anchor for large interstitial structures, such as nerves, blood vessels, and collagen fibers in surrounding connective tissues [4-6]. Increases in type VI collagen synthesis and secretion were observed in cultures of fibroblasts from the skin of a patient with cutis laxa [7] which suggests that abnormal synthesis and deposition of type VI collagen may change the mechanical properties of affected tissue. Many anatomic, radiologic, and histochemical studies of vascular development in the human brain have been performed [2,3,8,9], but not on the vascular composition of type VI collagen. This report describes the developmental changes in type VI collagen in the human brain as observed with an immunohistochemical method.
Methods The materials were obtained from 19 autopsied brains, 14 fetuses (17-35 gestationalweeks), 3 term neonates,and 2 infants (ages 1 and 7 months). Nine fetuses were obtained after spontaneous abortion. The other 5 preterm and 3 term neonates died of intrapartum asphyxia or respiratory distress syndrome within 3 days of age. The 2 infants had congenital heart disease. The gestational age in each case was calculated from the date of the last menstrual period. All brains were both macroscopically and microscopicallynormal except for focal cerebral hemorrhage or mild brain edema. Fresh samples of the frontal cortex and basal ganglia were quickly frozen in acetone dry ice and stored in a freezer (-80°C). Frozen sections of 10 wn thickness were cut. For immunohistochemicalstaining, sections were exposed to a 0.3% solutionof hydrogen peroxide to inactivate endogenous peroxidases and stained with mouse monoclonal anti-type VI collagen antibody (Heyl Chemisch-Pharmazeutische Fabrik Gmb H & Co, KG) using the streptavidin-biotinprocedure [10] (Histofine SAB-PO kit; Nichirei Co., Tokyo, Japan). Control sections were incubated with normal mouse serum in place of the primary antibody. Immunoreactivitywas graded as follows: (-) negative staining; (+) a few vessels slightly stained;(+) all vessels positivelystained.
Results The immunologic reaction against anti-type VI collagen antibody was observed in the outer part of the media and the adventitia of the meningeal artery, and in those of the meningeal vein; however, it was difficult to differentiate
Communicationsshould be addressed to: Dr. Kamei; Divisionof Mental Retardationand Birth Defect Research; National Instituteof Neuroscience;NCNP; 4-1-1 Ogawahigashimachi; Kodaira, Tokyo 187, Japan. Received December 31, 1991; accepted February28, 1992.
Kamei et al: Type VI Collagen 183
Table 1. Developmental changes in immunohistochemical type VI collagen in human brain Cerebral Cortex (frontal) L S
Cerebral White Matter Superficial Deep L S L S
Gestational Ages (wks)
N
Meninges
17-20
3
+
21-24
4
+
26-28
4
+
.
30-35
3
+
+
-
38-41
3
+
+
+
+
2
+
+
+
+
-
.
L
S
Germinal Layer
-
.
Basal Ganglia
.
+
-
_+
+
-
+
-
_
+
+
+
-
_
-
+
+
+
+
-
+
+
+
+
+
*
Age
1-7 mos
* No existence of germinal layer. Abbreviations: + = Positive +_ = Slightly positive - = Negative
L : Large vessel N = Number of materials S = Small vessel
the artery and vein in the parenchyma. D e v e l o p m e n t a l changes in type V I c o l l a g e n - p o s i t i v e vessels are sum-
Figure 1. Although they are found in the cortex (arrows), vessels are immunostained with anti-type VI collagen antibody at 26 weeks gestation: original magnification, x250. not
184 PEDIATRIC NEUROLOGY
Vol. 8 No. 3
marized in Table 1. In the l e p t o m e n i n g e s of fetuses of 17-20 w e e k s gestation, vessels and perivascular tissue were already positive. In the cerebral cortex, a positive reaction was found in a few vessels o f the superficial cortical layer from 30-35 w e e k s gestation. In the superficial white matter, large vessels w e r e positive from 38 w e e k s gestation and small vessels f r o m 1 m o n t h of postnatal age (Fig 1 ). In the deep white matter, large vessels w e r e slightly p o s i t i v e from 21-29 w e e k s (Fig 2) and m o r e strongly positive from 30 weeks gestation. Small vessels disclosed positive staining from 30 weeks and all small vessels were stained after 37 weeks gestation. In the basal ganglia, reactive products were o b s e r v e d in large vessels f r o m 21 w e e k s gestation and in small vessels f r o m 30 weeks gestation (Fig 3). In the subependymal germinal layer the terminal vein was only positive for type VI collagen, being n e g a t i v e in all other vessels o f infants of any age.
Figure 2. A vessel is strongly positive in the deep white matter at 26 weeks gestation: original magnification, x250.
Figure 3. In the putamen, there are many small and large positive vessels at 41 weeks gestation: original magnification, xlO0.
Discussion Collagen is a major component of human connective tissue. Our previous immunohistochemical studies of the vessels in the developing human brain involving anti-type IV collagen, antilaminin, and antifibronectin antibodies revealed that there were developmental changes in the basement membrane matrix [8]. During cortical angiogenesis, the density and diameter of vessels increase rapidly from about 26 weeks gestation and peak at 35 weeks; after
Cortex
Superficial white matter
Deep white matter ventricle ==,,°
Type ~ collagen positive vein. (medullary vein) ¢'"-'J Type ~ collagen negative vein. (cortical vein) , ~ Type ~I collagen negative artery. (cortical, medullary artery) ~" Type ~ collagen positive tissue. (leptomeninges) Type ~ collagen negative tissue. (subependymal germinal layer) Figure 4. This figure discloses the developmental discrepancy of type VI collagen between the medullary vein and the medullary artery in the deep white matter in the immature brain.
35 weeks, the density and diameter of vessels are the same as those in adult brain; however, the white matter discloses no major changes in vessel density, although the pattem of changes in vessel diameter resembles that in the cortex. In this study, the positive vessels already appeared at 17 weeks gestation in the leptomeninges, from 21 weeks gestation in the basal ganglia, from 21-29 weeks in the deep white matter, and from 38 weeks in the cerebral cortex and superficial white matter. The positivity of vessel staining persists once it appears in the leptomeninges, cortex, and superficial white matter at an early developmental age, and increases with maturation especially in the deep white matter. Type VI collagen was never found in the subependymal germinal layer, except for the terminal vein. This characteristic vascular structure contrasts sharply with the well developed structure of veins in the deep white matter. In the cerebral hemispheres, the perforating arteries branching from the leptomeningeal artery (i.e., cortical, subcortical, and medullary arteries) supply the cortex to the deep white matter. The ventriculofugal arteries are short in the premature infant [2]. Conversely, venous drainage is divided into 2 sides, in the meningeal direction from the cortex and subcortical white matter (cortical and subcortical veins) and in the ventricular direction from the deep white matter (medullary veins) [2]. The earlier appearance of type VI collagen-positive vessels in the deep white matter suggests that the medullary veins, a terminal branch of the internal cerebral vein, develop earlier than the cortical and subeortical veins, and all perforating arteries because they were not stained in early gestation (Fig 4); therefore, a developmental discrepancy exists between the arteries and veins in the deep white matter, although we could not microscopically differentiate artery (arteriole) and vein (venule). The pathogenesis of intraventricular hemorrhage is related to intravascular, vascular, and extravascular factors [1,11-15]. Our study demonstrates a coexistence of more mature venous and less mature arterial systems in the periventricular white matter of the premature infant, which may be a predisposing factor for local circulatory disturbance. Lack of interstitial type VI collagen in the subependymal germinal layer may be related to a change of mechanical or functional property in immature brain vessels, and poses a greater risk for hemorrhage; however, these characteristics of vascular development may result in ischemic or stagnant injury of the vessels (i.e., periventricular leukomalacia or hemorrhagic infarction). This study demonstrated two characteristics of vascular development: earlier maturation of the medullary vein than perforating arteries in the periventricular white matter and the lack of type VI collagen in vessels of the subependymal germinal layer, in contrast to the early development of the medullary vein of the deep white matter. These developmental discrepancies may be important predisposing factors for periventricular leukomalacia and subependymal/intraventricular/periventricular hemorrhage.
Kameiet al: Type VI Collagen 185
References
[1] Volpe JJ. Intraventricular hemorrhage in the premature i n f a n t Current concepts, part I. Ann Neurol 1989;25:3-11. [2] Takashima S, Tanaka K. Development of cerebrovascular architecture and its relationship to periventricular leukomalacia. Arch Neurol 1978;35:11-6. [3] Takashima S, Armstrong DL, Becker LE. Subcortical leukomalacia. Relationship to development of the cerebral sulcus and its vascular supply. Arch Neurol 1978;35:470-2. [4] Burgeson RE. New collagens, new concepts. Ann Rev Cell Biol 1988;4:551-77. [5] Keene DR, Engvall E, Glanville RW. Ultrastmcture of type VI collagen in human skin and cartilage suggests an anchoring function for this filamentous network. J Cell Biol 1988; 107:1995-2006. [6] C h u M, Pan T, Conway D, et al. The structure of type VI collage. Ann NY Acad Sci 1990;580:55-63. [7] Crawfold SW, Featherstone JA, Holbrook K, Young SL, Bomstein P, Sage H. Characterization of a type VI collagen-related Mr-140000 protein from cutis-laxa fibroblasts in culture. Biochem J 1985;227:491-502. [8] Mito T, Konomi H, Houdou S, Takashima S. lmmunohistochemical study of the vasculature in the developing brain. Pediatr Neurol 1991 ;7:18-22.
186
PEDIATRIC NEUROLOGY
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[9] Povlishoek JT, Martinez AJ, Mossy J. The fine structure of blood vessels of the telencephalic germinal matrix in the human fetus. Am J Anat 1977; 149:439-52. [10] Kitamntu T, Ogomori K, Tateishi J, Prusiner SB. Methods in laboratory investigation. Formic acid pretreatment enhances immunostaining of cerebral and systemic amyloid. Lab Invest 1987;57:230-6. [11] Hambletnn G, Wigglesworth JS. Origin of intraventricular haemorrhage in the preterm infant. Arch Dis Child 1976;51:651-9. [12] Goldstein GW. Pathogenesis of brain edema and hemorrhage: Role of the brain capillary. Pediatrics 1979;64:357-60. [13] K u b a n KCK, Gilles FH. Human telencephalic angiogenesis. Ann Neurol 1985;17:539-48. [14] H a r u d a F, Blanc WA. The structure of intracerebral arteries in premature infants and the autoregulation of cerebral blood flow. Ann Neurol 1981;10:303. [15] Pinar MH, Edwards WH, Fratkin J, Marin-Padilla M. A transmission electron microscopy study of human cerebral cortical and germinal matrix (GM) blood vessels in premature neonates. Pediatr Res 1985;19:394A.