Anatomy of the spinal cord of Alouatta belzebul

Article history The genus Alouatta hosts species popularly known as red-handed howler, presenting wide geographic distribution and being found in several biomes. The objective is to describe the anatomy of the spinal cord of Alouatta belzebul specimens, focusing on the topography of the medullary cone, stressing the cervical and lumbar intumescences and cauda equina, to provide anatomical data and compare it with other species to assist in anesthetic and surgical procedures. Four animals were received for scientific research, post mortem, from the fauna rescue program of the Hydroelectric Plant of Belo Monte Pará, and they were fixed in 10% formaldehyde solution. Structures such as the medullary cone, cervical and lumbar intumescence, and cauda equina were photographed (Sony α200-10.2 mpx). After thawing, we measured the specimens and observed a size of 80 to 82 cm from head to toe. After the skin and musculature were removed, it was observed that the spine of all specimens presented 7 cervical, 13 thoracic, 5 lumbar and 3 fused sacral vertebrae. The spinal cord was exposed after the removal of vertebral arches, it has 22 cm length in all animals, presenting the cervical intumescence between C3 and C6 vertebrae, with average of 2.2 cm and lumbar intumescence between T11 and T12 vertebrae, with average of 1.65 cm. The medullary cone is located between T12 and L1 vertebrae, with average of 1.5 cm, and the cauda equina between L1 and S3, with an average of 15 cm. This study has an important role as the basis for epidural anesthesia in the species. Received 03 October 2017 Received in revised form 23 March 2018 Accepted 28 March 2018


INTRODUCTION
Advances in comparative animal anatomy possess fundamental importance due to the scarcity of information available in the literature.The anatomical descriptions subsidize comparative and evolutionary studies, since through these descriptions one can succeed in anesthetic procedures essential to diagnostic and surgical processes (SLULLITELL, 2008).
Regional anesthetic techniques are used with a suitable safety margin, aiming to anesthetize spinal nerves of the lumbar and sacral regions, thus the location of anesthetic application in the epidural space varies according to the species and the ending site of the spinal cord.The use of sites caudal to the medullary cone makes the application technique safer, consequently avoiding spinal cord injuries and helping professionals who need to perform surgical procedures (GREGORES et al., 2010;SOUZA et al., 2014).
Primates of the genus Alouatta are medium-sized mammals, yet they are considered robust animals and well-known for long-range vocalization.Their jaw accommodates a rather large hyoid bone, mainly in males, which forms an oval resonance chamber, responsible for the characteristic vocalizations related to group location and territory defense (HIRSCH et al., 1991).Research about these primates involves diet, vocalization, life style and ecology of the species (AGUIAR et al., 2003;BICCA-MARQUES et al., 2009;BICCA-MARQUES, 2003;CAMARGO, 2005;GRECORIN, 2006;MARTINS, 2002;NEVILLE et al., 1988).However, information regarding the comparative and/or evolutionary anatomy of these animals is scarce, as well as clinical correlations with the described structures.The red-handed howler Alouatta belzebul is endemic to Brazil, occurring in the states of Amazonas, Pará, Maranhão, Piauí, Ceará, Rio Grande do Norte, Paraíba, Pernambuco and Alagoas (BONVICINO, 1989;RUSSELL et al., 2013).It is a neotropical primate, pertaining to the family Atelidae.Due to the fundamentally folivorous feeding habit (NEVILLE et al., 1988), howlers present slow and discrete behavior and spend more than 70% of their time resting (SOUZA, 2005).

Habitat destruction and fragmentation has placed all
Alouatta species and subspecies in the endangered species category (BICCA-MARQUES, 2003;CHIARELLO et al., 2008;RUSSELL et al., 2013).Due to the huge threat, howler management tools as translocation and reintroduction are being increasingly observed and successfully applied in Alouatta conservation programs (JERUSALINSKY et al., 2010;SOUZA, 2005).The management techniques require ecological, behavioral and morphological data of the target species (STERLING; BYNUM; BLAIR, 2013).
The collection and analysis of cerebrospinal fluid (CSF) present a safe, viable and effective means of access and evaluation of the nervous system, for diagnosis and prognosis of its diseases, such as encephalopathies and myelopathies that affect the Alouatta (GAMA et al., 2005;TRANQUILIM et al., 2013).According to Bailey and Vernau (1997), this test can detect diseases in the central nervous system with reasonable sensitivity and low specificity and thus provide a general index of health of the system.
The use of anesthesia in wildlife management is a common practice in veterinary medicine, in which safe and effective drugs are used to contain the animal during the procedures (WOLFE-COOTE, 2005).Epidural anesthesia is a frequently used technique because of its good margin of safety and ease, showing itself as an effective and practical alternative in cases that the animals present risk factors to inhaled or intravenous anesthetics.This technique is used to anesthetize the spinal nerves of the lumbar and sacral regions and data about the application procedure and anatomy of the manipulated species are necessary (CARVALHO, 2004;GREGORES et al., 2010).
The place of application of the anesthetic in the epidural space varies according to the species, being related to the ending site of the spinal cord.However, the use of sites caudal to the medullary cone makes the application safer, thus avoiding spinal cord injuries (GREGORES et al., 2010).The objective of the present study was to describe the anatomy of the spinal cord of A. belzebul, emphasizing in its structure the vertebrae and intumescences location, as well as the morphology of the medullary cone, in order to contribute with anatomical bases to the practice of epidural anesthesia in this species.

MATERIALS AND METHODS
In the present study, four male A. belzebul specimens were collected from the Wild Animals Triage Center linked to the fauna rescue program of the Hydroelectric Plant of Belo Monte under license nº 473, frozen and subsequently donated to the Federal University of Goiás -Regional Jataí.
Prior to fixation, the specimens were thawed for partial dissection, starting an incision at the dorsal midline to remove the skin, from the cranial region to the base of the tail, separating it from the tissue underneath.After the skin was removed, the animals were fixed in 10% formaldehyde solution and kept in tanks with the same solution for preservation.Once fixed, the dorsal musculature and the vertebral arches were removed to expose the spinal cord.Then the cervical and lumbar intumescences, the medullary cone and cauda equina were exposed and measured with a pachymeter and photo documented with a Sony α200-10.2 mpx digital camera.The project was approved by the Ethics Committee in Animal Experimentation (CEUA) with protocol nº 083/17.The data described for cervical intumescence, lumbar intumescence, medullary cone (base and apex) and cauda equina, in their length and location, were compared with the literature available of other wild primates and mammals, according to the NAV (2017).

RESULTS AND DISCUSSION
After the dissection of the dorsal region, from the cranial region to the base of the tail, the spine of A. belzebul was evidenced and showed for all the specimens: 7 cervical vertebrae, 13 thoracic vertebrae, 5 lumbar vertebrae and 3 fused sacral vertebrae (Figure 1).A similar result was found by Silva et al. (2013)   The cervical intumescence (IC) of A. belzebul is located between C3 and C6 vertebrae, measuring on average 2.2 cm in length (Figure 2B and Table 1).In A. belzebul, the lumbar intumescence (IL) is located between T11 and T12 vertebrae, with an average size of 1.65 cm in length (Figure 3).Compared with tayra, crabeating raccoon and other primate species, the IL of A.
belzebul presents its location more cranially.However, among the primates studied, a certain similarity is observed regarding the position and length of lumbar intumescence (Table 2).The medullary cone (CM) of A. belzebul is located between T12 and L1 vertebrae, measuring 1.5 cm in length (Figure 3A and 3B).The cauda equina is located between L1 and S3 vertebrae, presenting 15 cm in length (Figure 2A and 3C).The morphological differences of both the measurement and the topography of the IC, IL, CM and CE among the species described in the literature, show the importance of knowing the location of these structures to apply anesthetics in surgical procedures, which is specific for each species.Silva et al. (2013) states that epidural anesthetics should be applied in the lumbosacral region for Callithrix jacchus corroborating the findings of LA Salles et al. ( 2017) for this species, in Saguinus midas it should be applied in the spaces between the vertebral arches of the lumbosacral region (MARTINS et al., 2013), in Sapajus libidinosus, in the epidural space of the lumbosacral region (CORDEIRO et al., 2014) and in Saimiri sciureus in the girdle and pelvic limbs (LIMA et al., 2011a).For A. belzebul, epidural anesthesias should be applied in the lumbosacral region, specifically between L2 and S3 vertebrae.

CONCLUSIONS
To perform epidural anesthesia, it is necessary to take into account the information about the topography and measurement of IC, IL, CM and possible anatomical variations of the spinal cord.It was concluded that the cervical intumescence of A. belzebul (IC) is located between C3 and C6 vertebrae, the lumbar intumescence is located between T11 and T12 vertebrae, the cauda equina is located between L1 and S3 vertebrae.The anatomy of the medullary cone of A. belzebul shows that its base is located in the T12 vertebra and apex in the L1 vertebra, suggesting that the epidural anesthesia in this species should be performed in the lumbosacral region between the L2 and S3 vertebrae, differing from other species of primates described in the literature.

Figure 3 -
Figure 3 -A, B and C: Macro-photography of the dorsal view of the thoracolumbar region of A. belzebul, highlighting the Lumbar Intumescence region (IL); Medullary Cone region (CM); Cauda Equina region (CE).In red, the position of the vertebrae (T11, T12, L1, L5, S1 and S3) is observed.In B, the pachymeter to assist CM measurement.Bar: 1 cm.

Table 1
describes the results of IC measurement of A. Belzebul and other primate and mammal wild species.The comparative results of the IC of A. Belzebul are not similar to the topography of the IC of other primates and wild mammals observed in the literature.

Table 1 -
Measurement of the Cervical Intumescence of A. belzebul and other species of wild primates and mammals.

Table 2 -
Measurement of the Lumbar Intumescence of A. belzebul and other species of wild primates and mammals.

Table 3
describes the results of CM measurement of A. belzebul and other primates.The comparative results of CM of A. Belzebul do not present similarity to the topography of CM of other primates described in the literature.Table4describes the results of the CM measurement of A. belzebul in relation to other wild mammal species described in the literature.

Table 3 -
Measurement of the medullary cone of A. belzebul and other species of Primates.

Table 4 -
Measurement of the medullary cone of A. belzebul and other wild mammals.