Research Paper. Accepted 15 th June, 2013 ABSTRACT

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1 Academia Journal of Scientific Research 1(6): , July 2013 DOI: ISSN: Academia Publishing Research Paper Investigation of histological characteristics of the human sensory neurons in ganglion trigeminale and nucleus tractus mesencephali Nervi trigemini with lightmicroscopic techniques Accepted 15 th June, 2013 ABSTRACT Krastev Dimo 1, Krastev Nikolay 2, Mileva Milka 3 * 1 Department of Anatomy and Histology, College of Medicine Yordanka Filaretova, Sofia, Bulgaria 2 Department of Anatomy and Histology, Medical University, Sofia, Bulgaria 3 Department of Virology, The Stephan Angeloff Institute of Microbiology, Bulgarian Academy of Sciences, Sofia, Bulgaria *Corresponding author: milkamileva@gmail.com Tel: Trigeminal ganglii (TG) and mesencephal trigeminal nucleus (MTN) are responsible for the development of trigeminal sensory system, which is represented by a cluster of neurons located both in the central midbrain as well as in the peripheral trigeminal ganglion. As long as the adaptive capacity of the body depends on the sensitivity of human neurons, although it also depends on different location, age, sex and the morphological characteristics, it is very important to compare their structures and localizations. The feature of macroscopic and lightmicroscopic characteristics of pseudounipolar neurons in the trigeminal ganglion and mesencephal trigeminal nucleus were analyzed. The differences between structure localization in the brain, age, and structure resembling the sensory ganglia were described. Sensory neurons in MTN are different from the TG neurons at the surface of perikaria and their appendages are localized synaptic contacts. In general, the variety of histological and morphological characteristics of TG and MTN probably result in their physiological function for adaptation of the body sensitivity. More information about these differences with respect to their morphology and function should be found in our future research. Key words: Sensory system, pseudounipolar neurons, trigeminal ganglion, mesencephal trigeminal nucleus. INTRODUCTION The structure of sensory ganglia in humans and animals has been subject of extensive studies over the time. Investigations of "sensitive" nervous system attend their functions, but even today morphofunctional data source of different opinions in the medical community. Trigeminal ganglion (TG) and mesencephal trigeminal nucleus (MTN) are participating in the development of trigeminal sensory system, which is represented by a cluster of neurons located both in the central midbrain as well as in the peripheral trigeminal ganglion (Karan and Oklu, 2012; Krastev et al., 2007; Lazarov, 2000). The neurons which are located in the brainstem of vertebrates form one unique building structure, differentiation the MTN (Krastev et al., 2008; Marani and Usunoff, 1998). The core is a cluster of large pseudounipolar neurons diffusely arranged rostrocaudal and they have drop-shaped design (Lazarov, 2002, Lazarov and Chouchkov, 1995; Lazarov, 1996). The narrow part is located in the cranial direction along the entire midbrain, lateral-from the gray matter of the brain near aquaeductus cerebri (mesencephal) and ends with the extended part the rostra part of the pons. Trigeminal ganglion is a structure located outside the brain on the rostra part of the pyramid of the temporal bone and is represented by pseudounipolar neurons. Histological characteristycs of MTN and TG is very important for elucidation of their function in human. The purpose of this study is to compare human pseudounipolar neurons of the trigeminal ganglia to mesencephal trigeminal nucleus via light-microscopic and histological methods.

2 Academia Journal of Scientific Research; Dimo et al. 105 Figure 1. A tightly grouped perikaryon of pseudounipolar neurons of different sizes, surrounded by connective tissue fibers (arrows). Each cluster is associated to the branch of the trigeminal nerve. Material from human HE 100. MATERIALS AND METHODS For the present morphological study, tissues from a human corpse material are used (5 women, 5 men mean age 27 to 50 years from the Department of Forensic Medicine and Deontology) in accordance with the ethical principles applied by the Sofia s Medical University. All legislative requirements to protect human rights have been respected as well. The procedure for preparing samples went by the standard protocol approved by the Department of Anatomy and Histology. Macroscopic and microscopic evaluation and histological analyses for the classification of neurons were performed. The tissue samples were embedded into paraffin and were cut into slices of 20 µm. The colorations are H&E and Nissl. RESULTS Macroscopic and light-microscopic characteristics of pseudounipolar neurons in the trigeminal ganglion and mesencephal trigeminal nucleus were investigated. The results are described separately for both structures: Research of ganglia trigeminale. The investigation of TG as a structure located outside the brain, tissue encased in meanings is described by Karan (2012) and Krastev et al. (2007). As can be seen in Figure 1, TG formed separate nests divided by connective tissue and fibers responsible for the three peripheral branches of the trigeminal nerve. In every one of the nests, neurons are densely located close to each other. All of the formed cell groups comprised of neurons with pseudounipolar form (Figures 1 and 3). Each of the three separate wells are divided into two parts - dorsomedial and ventrolateral. It is obvious that trigeminal neurons differ in their density of cell contents. Figures 2 and 3 present rings of satellite cells around each neuron. Data show that the size of the neurons varies widely (from 10 to more than 100 μm). As shown in Figure 3, they are differences between the internal and external morphological characteristics of the neurons. In the material of the elderly patients appear pigments, probably lipofuscin in perikaryon of nerve cells (Figures 1, 2 and 3). From the neurons growths a fiber, divided itself dichotomycaly to axon and dendrite. The profiles of the fibers are with different thickness and they are located along the ganglia trigeminale without specific arrangement (Krastev et al., 2008; Lazarov, 2002). Research on the mesencephal trigeminal nucleus. Mesencephal trigeminal nucleus is a structure located in the brain tissue along midbrain and the rostral part of the ponse, as illustrated in Figures 4 and 5. In principal, morphological core is a longitudinal column of neurons with pseudounipolar shape of perikaria near the central gray tissue near the aqueduct (Lazarov, 2002; Lazarov and Chouchkov, 1995). As can be seen in Figure 5, around every neuron are located single satellite cells. The results show that the size of the neurons varies within narrow limits. Internal and external morphological characteristics of neurons are similar. The structure of mesencephal trigeminal nucleus is the only nucleus composed of primary afferent neurons with pseudounipolar form located in the brain, and structure resembling the sensory ganglia. The central growth of cells in MTN are divided into two axon, central and peripherial, that is dendrites are missing. The same observations are found irrespective of the technique of staining of tissues.

3 Academia Journal of Scientific Research; Dimo et al. 106 Figure 2. Form and intensity of neurons (arrows) and nucleus (arrow head) depending of varying of tissues density. Position and localisation of the nucleolus - visible in all neurons, centrally and closely located. Material from the human. HE 150. Figure 3. Neurons of medium size and polygonal (fusiform) shape, located between a group of oval neurons and fibers (arrow). Human material. HE 150. DISCUSSION In this work we present the main characteristics of the two morphological structures - Trigeminal ganglia (TG) and Mesencephal trigeminal nucleus (MTN). Sensitivity in humans and other mammals is at the basis of their adaptation to changing conditions of internal and external environment (Naushad, 2010; Eftekhari, 2010). Its characteristics largely determine the behavior of individuals through relevant reactions adequate to annoyance (Karan and Oklu, 2012). By the observation of human TG from different ages by light microscopy, it is obvious that the individual wells are delicately separated from one another by collagen fibers passing between them separating groups of neurons responsible for the three branches of the trigeminal nerve. Each one of the so formed groups is composed of neurons with pseudounipolar form diffuse scattered in the ganglia

4 Academia Journal of Scientific Research; Dimo et al. 107 Figure 4. Preparation of human MTN - without accumulation of pigment and roughly dispersed cytoplasm (arrows). Nissl 150. Figure 5. Immunoprecepitates in a small PV (parvalbumin), containing neuron (short arrow), elongated form (long arrow) and its growth (head of arrow). Human material (Figures 1 and 3). Through various histological techniques, it is clearly visible that each of three separate wells are divided into two parts - dorsomedial and ventrolateral. The bodies of neurons in the dorsomedial subdivision are tightly grouped by ventrolateral and have smaller size of the perikaria. Ventrolateral located neurons are larger in their bodies, and from that part of the ganglia come the three peripheral branches (nn. ophthalmic, maxillar and mandibular). In the light microscopic picture in Figures 1, 2 and 3, it was shown that at small increase in early release of the first and second branch, the presence of single neurons surrounded by loose ring of satellite cells is often observed (Figure 2). In the tested preparations of both genders, nveroni was absent as in the initial modulus and in the length of the mandibular nerve. Cytological picture in Figure 1 is presented by pseudounipolar neurons. A closer view shows that some of them have bodies with a distinctive of pseudounipolar neurons typically form, as presented on Figures 1 and 3. Dimensions of their bodies also vary widely (from 10 to 110 μm). Morphological characteristics of neurons are different. The studies by staining of Golgi TG method (Karan and Oklu, 2012; Krastev et al., 2008, Marani and Usunoff, 1998) found that qualify impregnated neurons based on some morphological criteria - characteristics of knots: the number,

5 Academia Journal of Scientific Research; Dimo et al. 108 thickness, manner of branching, the presence or absence of studs and sockets, axonal course, length and presence of collateral. It is noteworthy that this staining pattern is specific to all other neurons in the CNS perikaryons and growths of pseudounipolar neurons in TG are more difficult to be seen. In light microscopic monitoring of human TG, abundant accumulations of pigment in nerve cells were observed in Figure 3. In young adults it is more discreet, located mainly in the periphery of neurons. Mesencephal trigeminal nucleus is one of the sensory nuclei of the trigeminal nerve directly responsible for the transfer of deep (proprioceptive) information from orofacial complex (Lazarov, 2000; Usunoff, 1997). Sensory neurons in MTN differ from TG neurons in that, the surface of perikaria and their appendages are synaptic contacts (Lazarov, 2002; Lazarov and Chouchkov, 1995). Looking at MTN, we can deduce that it is one of the sensory nuclei of the trigeminal nerve directly responsible for the transport of deep (proprioceptive) information from orophacial complex. Morphological nucleus is longitudinal column of pseudounipolar neurons. It is located along the whole rostro-caudal lenght of the midbrain and the rostral part of the bridge, near the central gray matter. By structure, MTN is the only nucleus composed of primary afferent neurons with pseudounipolar form located in the brain, with a structure resembling the sensory ganglia. Difference in the two types of neurons was observed in their growths. Upon leaving the central perikarion outgrowth of cells in MTN are divided into two axon (central and peripheral), that is no dendrites. It was found that peripheral growth is also divided into ascending and descending bundle. The ascending is directed upward in the rostral direction, forming the mesencephal route of trigeminal nerve and the caudal and downward directed beam forms cluster of Probst (Marani and Usunoff, 1998; Usunoff, 1997). Sensitivity in human is the basis of his adaptation capability. It takes the information from both the outer and the inner environment. Through it the homeostasis of the organism is achieved. Based on studies conducted using different techniques, the following conclusions were made: (i) Primary sensory neurons of the two structures are involved in sensory innervation of orofacial complex; (ii) Although the general principles in the construction of pseudounipolar neurons, there are significant differences between them. These differences related to their morphology and function should be discovered for future interest to our research. REFERENCES Karan M, Oklu K (2012). (Hystrix cristata) Trigeminal Ganglyon unda Calbindin-D28k nin immunohistokimyasal Lokalizasyonu. Firat üniversitesi, sağlik bilimleri veteriner dergisi; 26(1): Krastev D, Paloff A, Hinova-Palova D, Apostolov A, Ovtscharoff W (2007). Light- microscopic structure of trigeminal ganglion in humans. Ann. Proc. J. IMAB 1: Krastev D, Paloff A, Krastev N, Apostolov A. Ovtscharoff W (2008). Ultrastructure of trigeminal ganglion in human. Ann. Proc. J. IMAB; 1: Lazarov NE (2002). Comparative analysis of the chemical neuroanatomy of the mammalian trigeminal ganglion and mesencephal trigeminal nucleus. Prog. Neurobiol. 66: Lazarov NE, Chouchkov CN (1995). Serotonin-containing projection to the mesencephal trigeminal nucleus of the cat. Anat. Rec. 241: Lazarov NE (1996). Fine structure and synaptic organization of the mesencephal trigeminal nucleus of the cat: a quantitative electron microscopic stady. Eur. J. Morphol. 34: Lazarov NE (2000). The Mesenephalic Trigeminal Nucley in the cat. Adv. Anat. Embryol. Cell Biol. 153: Marani E, Usunoff KG (1998). The trigeminal motonucleus in man. Arch. Hysiol. Biochem. 106: Naushad M, Dilkash A, Ahmed SS, Khan AA (2010). Comparative Light Microscopic Study of Trigeminal Ganglion Neurons in Mammals. Curr. Neurobiol. 1: Eftekhari S, Salvatore CA, Calamari A, Kane SA, Tajti J, Edvinsson L (2010). Differential distribution of calcitonin gene-related peptide (CGRP) and CGRP receptor components (CLR and RAMP1) in the human trigeminal ganglion. Neuroscience. 169: Usunoff KG, Marani E, Schoen JR (1997). The trigeminal system in man. Adv. Anat. Embryol. Cell. Biol. 136: Cite this article as: Krastev Dimo, Krastev Nikolay and Mileva Milka (2013). Investigation of histological characteristics of the human sensory neurons in ganglion trigeminale and nucleus tractus mesencephali Nervi trigemini with lightmicroscopic techniques. Acad. J. Sci. Res. 1(6): Submit your manuscript at