The brain of the tree pangolin (Manis tricuspis). I. General appearance of the central nervous system

Abstract

Here, we describe the superficial appearance of the brain of the rarely studied tree pangolin. Phylogenetic analyses have placed the pangolins, order Pholidota, as a sister group to the order Carnivora. The majority of features visible on the surface of the tree pangolin brain, and its overall appearance can be described as typically mammalian. The pattern of sulci and gyri, while simple, appears very similar to that observed in carnivores. Two derived features of the Pholidota were observed, the first being the rostral decussation of the pyramidal tract, which instead of occurring at the spinomedullary junction, decussates at the level of the caudal pole of the facial nerve nucleus in the rostral medulla oblongata. This appears to be related to the need for voluntary control of the tongue, with a potentially enlarged corticobulbar tract ending in the hypoglossal nucleus. The second derived feature is the very short spinal cord, which terminates midway along the thoracic vertebrae before giving rise to a long and extensive cauda equina. This foreshortened spinal cord appears to be related to anisotropic growth of the somatic and neural elements following early development of the central nervous system. The olfactory system appears to be generally enlarged and is likely the predominant sense used in foraging. Vision and hearing do not appear specialized based on the relative size of the superior and inferior colliculi, but potential somatic specializations indicate that the somatosensory system is heavily relied upon for food consumption and prehensile tail usage.

The brain of the tree pangolin (Manis tricuspis). VI. The brainstem and cerebellum

“…Under this rubric we include the cephalic decussation of the pyramidal tract, the enlarged hypoglossal nucleus, the dorsal extension of the serotonergic raphe obscurus nucleus (RObd), the virtual absence of the inferior salivatory nucleus (pIX), and the expanded superior salivatory nucleus (pVII). The current observations regarding the general topography, course and cephalic decussation of the pangolin pyramidal tract, described first in the Chinese pangolin by Chang (), was confirmed in the current and an earlier study (Imam et al, ). Briefly, after forming a distinct bilaterally paired pyramidal tract in the rostral medulla, which is typical for Eutherian mammals, this tract decussates at the level of the facial nerve nuclear complex, which is unique to the pangolins.…”

“…A dorsoventrally oriented column of white matter located medial to the gigantocellular reticular nucleus and lateral to the raphe, housed several tracts, including the medial longitudinal fasciculus (mlf) dorsally, the tectospinal tract (ts) and in the rostral ventral portions of the medulla oblongata the pyramidal tract (py). The pyramidal tract of the tree pangolin is of specific interest due to the reported cephalic decussation of this tract in the Chinese and tree pangolins (Chang, ; Imam et al, ). In the rostral medulla oblongata, a bilateral pyramidal tract emerging from the longitudinal fasciculus of the pons is evident (Figures i,j, a,b).…”

The brain of the tree pangolin (Manis tricuspis). IV. The hippocampal formation

“…Here we continue our examination of the architecture and aspects of chemical neuroanatomy of the brain of the tree pangolin (Imam, Ajao, Bhagwandin, Ihunwo, & Manger, 2017;Imam, Bhagwandin, Ajao, Spocter, et al, 2018), the current study dealing specifically with the hippocampal formation. The only prior mention of the hippocampal formation in any species of pangolin was our estimate of the volume of the hippocampal formation in the tree pangolin, which, at 0.489 cm 3 , is very close to what would be predicted for a mammal with a brain mass of 10 g (Imam et al, 2017).…”

The brain of the tree pangolin (Manis tricuspis). V. The diencephalon and hypothalamus

“…2012/53/01), which parallel those of the NIH for the care and use of animals in scientific experimentation. In the current study, the brains of three of these tree pangolins (MT1 ♂, MT3 ♂, and MT5 ♀, all adults based on their body mass, but as they were caught in the wild we cannot provide a precise age, see Imam et al, 2017) were sectioned, stained, and analyzed.…”

“…Here, we continue our systematic analysis of the brain of the tree pangolin (Imam, Ajao, Bhagwandin, Ihunwo, & Manger, 2017;Imam, Bhagwandin, Ajao, Spocter, et al, 2018;Imam, Bhagwandin, Ajao, Ihunwo, Fuxe, et al, 2018; by providing a detailed account of the architecture of the tree pangolin diencephalon and hypothalamus using Nissl and myelin staining in conjunction with a range of immunohistochemical stains.…”