Abstracts

ANIMAL MORPHOPHYSIOLOGY

Macroscopic aspects of Saimiri sciureus dura mater

Aspectos macroscópicos da dura mater de Saimiri sciureus

José Fernando Marques Barcellos^I; Érika Branco^II,* * Corresponding author: erika.bran co@ufra.edu.br ; Emerson T. Fioretto^III; Aline A. Imbeloni^IV; José A.P.C. Muniz^IV; Ana R. Lima^II

^IDepartamento de Morfologia, Instituto de Ciências Biológicas (ICB), Universidade Federal do Amazonas (UFAM), Av. General Rodrigo Octávio Jordão Ramos 3000, Campus Universitário, Coroado I, Manaus, AM 69299-999, Brazil

^IIInstituto de Saúde e Produção Animal (ISPA), Faculdade de Medicina Veterinária, Universidade Federal Rural da Amazônia (UFRA), Av. Presidente Tancredo Neves 2501, Bairro Montese, Belém, PA 66077-530, Brazil

^IIILaboratório de Biologia Celular e Estrutural, Departamento de Morfologia, Centro de Ciências Biológicas e da Saúde, Universidade Federal do Sergipe (UFS), Av. Marechal Rondon s/n, Bairro Rosa Elze, São Cristóvão, SE 49100-

^IVCentro Nacional de Primatas (CENP), Instituto Evandro Chagas (IEC), Secretaria de Vigilância em Saúde (SVS), Ministério a Saúde (MS), BR 316 Km 7, Cx. Postal 44, Ananindeua, PA 67030-000, Brazil

ABSTRACT

Saimiri sciureus is a small New World primate (NHP) commonly called macaco-de-cheiro that inhabits the tropical forests of the Amazon basin. Anatomical features are not well studied in most primates, and the encephalic morphology and related structures are still quite unknown. Comparative anatomy of the meninges in South American primates is still scarce. Dura mater, arachnoid and pia mater are a group of stratified layers that surrounds and promotes protection to the medulla spinalis. This study aimed to shed light on the anatomy of dura mater in Samiri sciureus in order to contribute to the neuroscience in primates. We investigated three young females and two males of S. sciureus. Specimens were fixed through perfusion with a 10% formaldehyde aqueous solution. In S. sciureus encephalus few gyrus and circunvolutions, and a very delicate system consisting of eight sinus venosus was found between the dura mater layers. Based on our findings, we can conclude that the Saimiri sciureus dura mater is quite similar to other mammals, however we detected a new sinus venosus formation at the level of parietal bone, named sinus parietalis, what appears to be its first description.

Index terms:Saimiri sciureus, brain, dura mater, sinus venosus, sinus parietalis.

RESUMO

Saimiri sciureus, com nome comum de macaco-de-cheiro, é um pequeno primata do Novo Mundo (PNM) que habita as florestas tropicais da Bacia Amazônica. Os detalhes anatômicos de primatas são pouco conhecidos e a anatomia comparada de animais selvagens da América do Sul é escassa, mais especificamente, sobre as meninges de PNM. Meninges pertencem a um sistema de membrana responsável por envolver e proteger o Sistema Nervoso Central; consiste em três membranas: dura mater, aracnoide e pia mater. Este estudo objetivou a elucidação do comportamento anatômico da dura mater de S. sciureus com o intuito de contribuir para a área de neurociências em primatas. Foram investigados três fêmeas e dois machos jovnes de S. sciureus. Os espécimes de meninges foram fixados por perfusão usando solução aquosa 10% de formaldeído. O encéfalo de S. sciureus demonstrou um número baixo de giros e circunvoluções, e um sistema delicado de oito seios venosos foi verificado entre as camadas da dura mater. Baseados em nossos achados podemos concluir que a dura mater de S. sciureus é similar aos de outros mamíferos, no entanto, apresenta a formação de um novo seio venoso em nível ao osso parietal, sendo denominado de seio parietal. Isto parece ser a primeira descrição deste seio.

Termos de indexação:Saimiri sciureu, encéfalo, dura mater, seio venoso, seio parietal.

INTRODUCTION

Saimiri sciureus is a common small New World primate (NHP) that inhabits the tropical forests in Amazon basin.

Its common name is Macaco-de-cheiro, the weight of which varies from 554g to 1150g for males and 651g to 1250g for females. S. sciureus is considered the smallest primate in the Cebidae family; usually males are a little larger than females, 318mm and 316mm respectively. Its fur is short, thick, soft, blitheness and colored. A light-warm colored hair is present around the eyes and in the ears (white tuft); head and neck are usually dark gray or dark-cool, while hands, feet, forearm are yellow-orange; shoulder demonstrates a thin grayish fur; tail is bicolored. Hands have nails instead of claws, and teeth are sexually dimorphic; males have large canine teeth (Hill 1957, 1958, Auricchio 1995, Castelo et al. 1997, Emmons & Feer 1997).

Meninges are a system of membranes which surrounds and protects the nervous system. It consists of three layers: Dura mater (pachymeninge), arachnoid membrane and pia mater, both known as leptomeninge (Pereira et al. 2010). In the skull, dura mater demonstrates two layers, endosteal and meningeal. Endosteal dura mater is the most external, thick layer, closest to the calvaria; additionally, it is tough and inflexible. Meningeal dura mater demonstrates two major folds and two minor folds. Major folds are the tentorium cerebelli (separates cerebellum and brainstem) and the falx cerebri (separates hemispheres). Minor folds are the cerebellar flax (partially separates the cerebellar hemispheres) and sellar diaphragm (roof over the hypophysial fossa) (Crippen 2009, Vinas & Pilitsis 2009). These structures limit oscillatory brain movements and have been considered a major obstacle to remove the intact brain during necropsy of domestic animals (Dyce et al. 2004).

Anatomical features are usually little known about most primates; nonetheless, encephalic morphology and related structure are still not well known. Comparative anatomy involving South American wild animals, more specifically NHPs, regarding about meninges are very scarce. This study aims to shed light on the anatomical features of dura mater in Samiri sciureus in order to contribute to the neuroscience in primates.

MATERIALS AND METHODS

We investigated young Saimiri sciureus, three females and two males. Animals came to death by natural cause, and were obtained at Centro Nacional de Primatas (CENP) in Ananindeua, PA, Brazil. All procedures were in accordance to the Ethical Committee for Animal Research of Evandro Chagas Institute (CEPAN/ IEC), Process nº 0007/2004.

Specimens were fixed by perfusion using a 10% formaldehyde aqueous solution. Perfusion was made through right common carotid artery. In order to optimize brain fixation, we injected the fixative solution in the brain cavity through a small aperture on the frontal bone. Specimens were kept immersed in fixative solution for seven days, after bone removal: frontal, parietal, occipital and part of the temporal, exposing the entire brain covered by three meninges, which were carefully removed sectioning the spinal cord. The first meninge to be accessed was the Dura mater, following a longitudinal fissure along the brain. When opened was possible to identify the arachnoid and pia mater. All meninges were gently removed with the aid of an anatomical clamp to expose the cerebral cortex and cerebellum.

Nomenclature followed the International Committee on Veterinary Gross Anatomical Nomenclature (2005) and Illustrated Nomina Anatomica (Schaller 1999).

RESULTS

Saimiri sciureus encephalus showed a small number of gyrus and circunvolutions (Fig.1A). Dura mater was firmly attached to the bones, and projected two laminar folds at the level of internal parietal crest, the falx cerebri and the tentorium cerebelli (Fig.1D). Encephalus longitudinal fissure was deep (Fig.1A).

A very delicate system of venous sinus was observed between the dura mater layers. Eight venous sinus were identified: 1) transverse sinus - bilateral laying along the insertion of tentorium cerebrelli (Fig.1C, ^2A, ^B ); 2) Dorsal sagittal sinus - single, median, laying along the insertion of falx cerebri (Fig.1B, D); 3) Ventral sagittal sinus - single, median, laying along the free border of falx cerebri (Fig.1D, ^2A, ^B ); 4) recto sinus - single, median, laying along the common border of tentorium cerebrelli and falx cerebri (Fig.1D, ^2A, ^B ); 5) temporal sinus - bilateral, laying along the meningeal rostral border of temporal lobe and ventral to the parietal sinus (Fig.1B, ^2C ); 6) sigmoid sinus - bilateral, laying rostral-caudally along the meningeal basal layer (Fig.1C, ^2A, ^B ); 7) basilar sinus - bilateral, laying along the hypophysial region at the meningeal basal layer (Fig.1C, ^2A); 8) parietal sinus - bilateral, laying dorsally to the temporal sinus, linking to the dorsal sagittal sinus (Fig.1B, ^2C ).

DISCUSSION

Not differently to other animals (Hildebrand 2006), Saimiri sciureus presented covering membranes over brain, oblongata medulla, pons, cerebral peduncles and cerebellum, however, not clearly delimitation was observed between the membranes.

Besides, S. sciureus encephalon demonstrates few gyrus, circunvolutions, its general appearance is considered quite similar to most human primates (Van de Graaff 2003, Drake et al. 2005, Dangelo & Fattini 2007), nevertheless, S. sciureus' should be classified as lisencephalic. It is worthwhile to appoint that lisencephaly in human is a rare brain disorder, the symptoms of which include psychomotor retardation, failure to thrive, seizures, muscle spasticity or hypotonia (Jones 2006); Despite demonstrating a lisencephalic brain morphology, S. sciureus develops normally.

Falx cerebri and tentorium cerebrelli are proportionally well developed in S. sciureus, in agreement to human descriptions, however, S. sciureus falx cerebri differs from domestic mammals which demonstrate a narrow Falx cerebri and a shallow longitudinal fissure (Habel 1951, Schwarze & Schröder 1972, Getty 1975, Bruni & Zimmerl 1977, Evans & De Lahunta 1994). This feature was similar to Bradypus torquatus and Bradypus variegatus (Ferreira et al. 2005).

S. sciureus sinus venosus are connected to regional veins similarly to human (Machado 2004), meanwhile, due to the presence of transverse sinus, S. sciureus differs from Nemestrina macaca (Hill 1990); S. sciureus sinus venosus have some similarity to Bradypus torquatus and Bradypus variegatus (Ferreira et al. 2005), which, additionally, have the orbicular-olfactory sinus, cerebellar parasagittal sinus and intertransverse sinus. It is worthy to detach that the parietal sinus is, by now, the first time described in literature.

Dorsal sagittal sinus in S. sciureus were slightly different from B. torquatus and B. variegatus (Ferreira et al. 2005) in the angle of its relation to the transverse sinus. This particular arrangement is related to the position of the brain in relation to the cerebellum, which in primates are ventral to the brain, whereas it is caudal in quadrupeds (Hill 1960, Lockhart et al. 1983, Dangelo & Fattini 1988, Gosling et al. 1992, Machado 2004, Abrahams et al. 2005, Rohen et al. 2006).

CONCLUSION

Based on our findings, we can conclude that the Saimiri sciureus dura mater has some similarity to the one of other mammals; however, we found a new venous sinus formation at the level of parietal bone, which was named sinus parietalis.

Ackowledgements.- National Primates Center (Cenp), Ananideua, PA, Brazil , for the support and donation of the specimens.

Received on March 23, 2011.

Accepted for publication on September 14, 2011.

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