PRENATAL DEVELOPMENT OF THE CRANIAL MENINGES IN GOATS *

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1 Indian J. Anim. Res., 42 (1) : 23-28, 2008 PRENATAL DEVELOPMENT OF THE CRANIAL MENINGES IN GOATS * K. M. Lucy, K.R. Harshan 1, J.J. Chungath and N. Ashok 2 Department of Veterinary Anatomy and Histology, College of Veterinary and Animal Sciences, Mannuthy , Kerala, India ABSTRACT Prenatal development of the cranial meninges in goats was studied using 52 foetuses with a Crown Rump Length (CRL) ranging from 1.4cm (24 days of gestation) to 41.5cm (full term). The meninges arose as condensation of the neighbouring mesenchyme. The pia mater started differentiating by 24 days of gestational age and the dura at 40 days. Cartilaginous cranial vault also appeared by 40 days. The arachnoid developed at 48 days of age. The dura was generally thicker in the ventral aspect of brain when compared to the sides and top. Arachnoid, the thinnest of the three, followed the infoldings of the dura. It did not follow the sulci of cerebrum and cerebellum but bridged over them. From the arachnoid, strands of fibres formed a loose reticulum across the subarachnoid space. Pia was highly vascularised and extended deep into the sulci. Depending on the vascularity, thickness of the pia mater varied over different regions and at different ages. In the brainstem and cerebellum, thickness was maximum towards the end of second month. But on the cerebral surface it showed maximum development during fifth month. Pia-arachnoid gave a strong positive reaction for alkaline phosphatase. INTRODUCTION Meninges are fibrous membranes, which enclose, protect and nourish the brain and spinal cord. Studies on the meninges of mammals were made by several authors (Dellmann and Mc Clure, 1975; Jenkins, 1978; King, 1987; Dyce et al., 1996). However the literature on the prenatal development of the meninges of brain in ruminants is scanty; hence this study was carried out. It will form a basis for further physiological, pathological and diagnostic studies. MATERIAL AND METHODS Prenatal development of the cranial meninges was studied using 52 goat foetuses with a Crown Rump Length (CRL) ranging from 1.4cm (24 days of gestation) to 41.5cm (full term). The material available in the Department of Anatomy and those collected from the farms and clinics were used for the study. Body parameters of the subjects were recorded. Age of the foetuses was calculated from the formula, W 1/3 = (t-30) derived by Singh et al. (1979) for goat foetuses, where W is the body weight of the foetus in g and t is the age in days. Based on age, foetuses were divided into five groups, representing the five months of gestation. Embryos of the Group 1 were fixed in toto for histological and histochemical studies. From Group 2 onwards, the head was separated at occipito-atlantal junction and the brain along with the meninges was then carefully dissected out and fixed in 10 perc ent neutral buffered formalin. Standard procedures were adopted for histological and histochemical studies. The sections were stained using Haematoxylin and Eosin (H&E), Van Gieson s method for collagen, Holzer s method for glial fibres, Sevier-Munger silver impregnation method for neural tissues, Aldehyde-thionine-PAS method for central nervous system, Phosphotungstic acid haematoxylin (PTAH) method for CNS tissue and Periodic acid Schiff s reaction for carbohydrates (Luna, 1968). Histochemical studies employed were Gomori s alkaline phosphatase cobalt method for alkaline phosphatase and Gomori s method for acid phosphatase (Singh and Sulochana, 1996), Oil Red O in propylene glycol method for fat and Best s carmine method for glycogen (Luna, 1968). Measurements of the meninges were taken using an ocular micrometer. * Part of the Ph D thesis submitted by the first author to Kerala Agricultural University. 1,2 Present address: College of Veterinary and Animal Sciences, Pookot , India

2 24 INDIAN JOURNAL OF ANIMAL RESEARCH RESULTS AND DISCUSSION The meninges arose as condensation of the neighbouring mesenchyme. The pia mater started differentiating at 24 days (1.4cm CRL) of age (Fig. 1). Externally, the dura mater started developing at 40 days (2.5cm CRL). The cartilagenous cranial vault also appeared during this stage. The arachnoid developed in between these two at 48 days (4.0cm CRL). Studies on the morphogenesis of the hypophyseal meninges in the goat by Singh and Dhingra (1978) revealed that the hypophyseal dura mater started differentiating in embryos of 2.48cm CRL at caudodorsal surface of the primordium of neurohypophysis. The formation of arachnoid was evident in embryos of 5.55cm CRL. It assumed a typical fibrous structure at 13.50cm CRL. Pia mater encapsulated the whole primordium in 1.20cm CRL embryos. 1. Dura Mater: Dura mater started differentiating at 40 days and was a distinct entity by 48 days of gestation. It was made up of two layers, which were closely adherent (Fig. 2) except in regions of cranial venous sinuses (Fig. 3). The outer layer constituted internal periosteum of the cranial bones while the inner layer formed the dura mater proper. At the age of 48 days, the outer layer measured 15.0μm and the inner, 3.8μm. It was the thickest among the three meninges as reported by Jenkins (1978) in domestic animals. Thickness of dura varied greatly at different locations. It was generally thicker in the ventral aspect of brain, especially in the hypothalamic region (52.5μm at 48 days). On the sides and top of the brain it was thin. Dura was made up of collagen fibres predominantly. Elastic fibres were also present. The outer layer was rich in blood vessels. The inner layer folded itself to form several partitions that projected into the cranial cavity, viz., falx cerebri, tentorium cerebelli and diaphragma sellae. Similar observations were made in Fig.1 C.S. of the telencephalon showing double layer of pia mater (27 days). H&E x Telencephalic wall 2. Primitive pia mater 3. Lateral ventricle

3 domestic animals by Dellmann and Mc Clure (1975), Jenkins (1978) and Dyce et al. (1996). The surface facing the arachnoid was covered by simple squamous epithelium. A thin subdural space separated the dura and arachnoid (Fig. 2). 2. Arachnoid: Arachnoid was very thin (3.8μm) and appeared by 48 days of gestational age. Connective tissue fibres of the arachnoid formed an outer surface parallel to the inner surface of the dura mater and was covered on either side by simple squamous epithelium (Fig. 4) as noticed by King (1987) in domestic animals. This epithelial covering was PAS-positive as reported by Prasad and Sinha (1983) in buffaloes. From the arachnoid, strands of fibres formed a loose reticulum across the subarachnoid space, which lay between the arachnoid and pia mater (Figs. 2 and 3). These arachnoid trabeculae were attached to the pia mater. Thus the subarachnoid space contained Vol. 42, No. 1, a loose sponge-like tissue with spaces filled with cerebrospinal fluid (CSF). King (1987) reported that the arachnoid was a very thin membrane in domestic animals, which pressed against the dura mater by the pressure of CSF. This space was also traversed by numerous blood vessels to and from the pia mater and the nerves (Figs. 2 and 4). Arachnoid followed the infoldings of the dura mater but it did not follow the sulci of cerebrum and cerebellum and bridged over them (Fig. 5). The network of trabeculae and spongy reticulum occupied the sulci. Similar observations were made in domestic animals by Dellmann and Mc Clure (1975). In some regions, the subarachnoid spaces were of considerable depth constituting subarachnoid cisterns, viz., cisterna magna, cisterna fossa lateralis and cisterna pontis. 3. Pia Mater: The pia mater started differentiating at the age of 24 days. Fine collagen and elastic fibres, mesenchymal cells and erythrocytes constituted the pia. At 27 days, Fig. 2 Section through the meninges (58 days). H&E x Dura mater 2. Subdural space 3. Subarachnoid space 4. Blood vessel 5. Pia mater 6. Cerebrum

4 26 INDIAN JOURNAL OF ANIMAL RESEARCH Fig. 3 C.S. of the cranial vault showing venous sinus of the cranial dura (58 days). H&E x Cartilagenous cranial vault 2. Endosteal layer of dura 3. Meningeal layer of dura 4. Great petrosal sinus 5. Subarachnoid space Fig. 4 Section through the meninges and cerebral cortex (144 days). H&E x Arachnoid 2. Subarachnoid space 3. Blood vessel 4. Pia mater 5. Cerebral cortex

5 Vol. 42, No. 1, Fig. 5 Section through the meninges and cerebral cortex (124 days). H&E x Arachnoid 2. Subarachnoid space 3. Pia mater 4. Sulcus 5. Cerebral cortex the pia appeared as a continuous layer (Fig. 1). In most regions it was double-layered. Pia mater was highly vascularised and extended deep into the sulci of cerebrum and cerebellum (Fig. 5) and measured 5.5μm at 40 days. It was thicker than the arachnoid but thinner than the dura mater as reported by King (1987) in domestic animals. Its inner surface was fused to the brain. Depending on vascularity, thickness of the pia varied over the surface of different regions of brain and in different age groups. In the diencephalon region, it was comparatively thicker and formed roof of the third ventricle. In the regions of brainstem and cerebellum, thickness was maximum towards the end of second month as noticed by Morse and Low (1972) in rats and Shrivastava et al. (1989) in foetal goats. But on the cerebral surface, it showed maximum development during fifth month. Differentiation of cerebral cortical cells also occurred during the same period. It is suggested that the variation in the regional thickness of pia mater might be based on the regional vascularity since pia mater served as a pathway for the blood vessels supplying different parts of the brain. Blood vessels of pia-arachnoid and choroid plexus showed a PAS-positive reaction. Choroid plexus of lateral and third ventricles, which merged within the interventricular foramen, developed within an invagination of pia that became entrapped between the expanding telencephalic vesicles and the roof of the diencephalon. The plexus of the fourth ventricle developed separately within the pia over the caudal medullary velum as reported by Dyce et al. (1996) in domestic animals. Choroid plexus of the ventricles and pia-arachnoid gave a strong positive reaction for alkaline phosphatase. From this study it was concluded that the pia mater was the early differentiating layer followed by the dura and arachnoid. The dura was the thickest coat and was generally thicker in the ventral aspect of brain when compared to

6 28 INDIAN JOURNAL OF ANIMAL RESEARCH the sides and top. Arachnoid was the thinnest of the three. Depending on vascularity, thickness of the pia varied over the surface of different regions of brain and in different age groups. The cranial meninges were well developed towards term. REFERENCES Dellmann, H.D. and Mc Clure, R.G. (1975) In: Sisson and Grossman s the Anatomy of the Domestic Animals. 5 th Ed. (Ed. Getty, R.). W.B. Saunders Company, Philadelphia. pp Dyce, K.M. et al. (1996). Textbook of Veterinary Anatomy. 2 nd Ed. W.B. Saunders Company, Philadelphia. Jenkins, T.W. (1978). Functional Mammalian Neuroanatomy. 2 nd Ed. Lea and Febiger, Philadelphia. King, A.S. (1987). Physiological and Clinical Anatomy of the Domestic Mammals. Oxford University Press, New York. Luna, L.G. (1968). Manual of Histological Staining Methods of the Armed Forces Institute of Pathology. 3 rd ed. Mc Graw-Hill Book Company, New York. Morse, D.E. and Low, F.N. (1972). Am. J. Anat., 133 : Prasad, J. and Sinha, R.D. (1983). Indian J. Anim. Sci., 53 : Shrivastava, A.M. et al. (1989). Indian J. Anim. Sci., 59 : Singh, Y. and Dhingra, L.D. (1978). Indian J. Anim. Sci., 48 : Singh, Y. et al (1979). Indian J. Anim. Sci., 49 : Singh, U.B. and Sulochana, S. (1996). Handbook of Histological and Histochemical Techniques. Premier Publishing House, Hyderabad.