Morphological and Immunohistochemical Study on the Cranial Cervical Ganglion of Dromedary Camel (Camelus dromedarius)

Abstract

Anatomical, histological, ultrastructural, and immunohistochemical studies were carried out on the cranial cervical ganglion(CCG)of the one-humped dromedary camel (Camelus dromedarius). Twenty-eight CCGwere collected from adult animals of both sexes and different agesduring the period of November 2015 to June 2016, from Al-Salam slaughterhouse, Sudan, and processed for histological, ultrastructural, and immunohistochemical techniques. Sixheads of dromedary camels were used to investigate the position and topography of the CCG.The average weight, length, width and thickness (Mean ± SD) of the right CCG were 0.6±0.08 g, 16.33±1.41 mm, 7.0±1.03 mm and 3.03±0.54 mm, respectively, whereas average weight, length, width and thickness of the left CCG were 0.53±0.09 g, 16.65±1.21 mm, 7.21±0.82 mm and 3.21±0.37 respectively. The CCG of the camel was located ventral to the atlas and dorsal to the pharynx on the rostrolateral surface of the longus capitis muscle.The CCG waswhite in colour and triangular or fusiform in shape. The main branches of the CCG were the internal and external carotid nerves in addition to the jugular nerve. Histological samples collected from ten adult camels were fixed in10% neutral buffered formalin and conventionally processed for hematoxylin and eosin (H&E) and some special stains. The CCG was surrounded by dense connective tissue capsule measuring about 155.92±19.43 μm. The capsule was composed of three layers. The CCG was divided into several ganglionic lobules by connective tissue septa. Each lobule was further subdivided into several ganglionic units which were formed of different types of cells that included the principal ganglionic neurons (PGNs), satellite glial cells (SGCs), Schwann’s cells, small intensely-fluorescent (SIF)cells, mast cells, microglial cell, fibroblasts and pericytes. The principal ganglionic neurons (PGNs) showedsignificant differences between the diameters (p<0.05) and as a result it had been divided into three types: small, medium and large-sized neurons. All the PGNs showed large cytoplasm with Nissl’s substances and peripheral lipofuscin granules. Satellite glial cells (SGCs) surrounding the PGNs, together with the collagen fibres formed the glial capsule. The small intensely-fluorescent (SIF)cells showed dark centrally located nuclei and pale cytoplasm. The ultrastructure of thePGNsin the CCG showed an eccentric nucleus with one or two nucleoli, chromatin and heterochromatin granules, and nuclear envelope with pores.The cytoplasm was pale and contained numerous mitochondria, Golgi apparatus, smooth and rough endoplasmic reticulum, free ribosomes, lysosomes, neurofilaments and microtubules. The ultrastructure of theSGCs showedan irregular, eccentric nucleus, faint cytoplasm with numerous mitochondria, rough endoplasmic reticulum, Golgi complex, lysosomes as well as neurofilaments and microfilaments. The ultrastructure of theSchwann cells showed pale cytoplasm with numerous mitochondria, rough endoplasmic reticulum in addition to the presence of 1-5 homogeneous, dense bodies. The Schwann cell measured about 46.47±1.46 µmin width and about 67.20±2.01 µm in length. The ultrastructure of the mast cell showed the small irregular nucleus which contained heterochromatin. The cell membrane hadmany cytoplasmic processes. The cytoplasm was packed densely staining granules and showed few organelles. The mast cellmeasured88.04±3.09µm in width and about 94.07±2.67µm in length. The ultrastructure of the microglial cell showed irregular nucleus with clumps of chromatin.The cytoplasm was dark and contained fine granules and numerous mitochondria. The measurements ofthe microglial cellmeasured 53.15±2.09µmin width and about 68.75±1.88 µm in length. The stromal components of the CCG consisted of the neuropil and the blood vessels. The ultrastructure of the neuropilin the CCG showed both myelinated and nonmyelinated axons in addition to dendrites showing dilatations containing densely packed dark mitochondria. The axoplasm of the myelinated axons was formed of neurofilaments, microtubules, smooth endoplasmic reticulum, small mitochondria and covered with basal membrane, whereas that of the nonmyelinated axons wascovered by plasmalemmal folds of Schwann cells and their axoplasms contained mitochondria, neurofilament and microtubules. Numerous axodendritic synapses and few axosomatic synapses of the neuropils were observed throughout the ganglionic units. Two types of of vasculature were observed in the stroma; the first type was numerous with different sizes and composed of a single layer of endothelium with many basally accumulated micropinocytotic vesicles. The second type was few in number and larger in size and composed of an inner endothelial lining and an outer layer of smooth muscles. The immunopositive reactions for S-100 protein were observed in the cytoplasm of large and intermediate sizedPGNs, SGCs and Schwann’s cells in addition to myelinated and non-myelinated nerve fibres. The PGNs and myelinated and unmyelinated axonspositively reacted with anti-neurofilaments monoclonal antibodies (ANMA).