Microsc. Microanal. 23, 1173–1188, 2017 doi:10.1017/S1431927617012727
© MICROSCOPY SOCIETY OF AMERICA 2017
Melatonin Elicits Stimulatory Action on the Adrenal Gland of Soay Ram: Morphometrical, Immunohistochemical, and Ultrastructural Study
Doaa M. Mokhtar,* Manal T. Hussein, and Ahmed H. S. Hassan Department of Anatomy and Histology, Faculty of Veterinary Medicine, Assiut University, Assiut, Egypt
Abstract: Endogenous melatonin is a hormone secreted by pineal gland; it has several roles in metabolism, reproduction, and remarkable antioxidant properties. Studies on the melatonin effect on the adrenal glands which are important endocrine organs, controlling essential physiological functions, are still deficient. In this study, we attempted to investigate the effect of exogenous melatonin treatment on the adrenal cortex and medulla using several approaches. Adrenal glands of 15 Soay ram were examined to detect the effect of melatonin treatment. Our results revealed that the cells of adrenal cortex of the treated animals were separated by wide and numerous blood sinusoids and showed signs of increase steroidogenic activity, which are evidenced by functional hypertrophy with increase profiles of mitochondria, smooth endoplasmic reticulum, and lipid droplets. The most striking ultrastructural features in the medulla of the treated group were the engorgement of chromaffin cells with enlarged secretory granules enclosed within a significantly increased diameter of these cells. The cytoplasm of these cells showed numerous mitochondria, rough endoplasmic reticulum (rER), Golgi apparatus, lysosomes, and glycogen granules. Exocytosis of secretory granules to the lumen of blood vessels was evident in the treated group. Piecemeal degranulation mode of secretion was recorded after melatonin treatment. Chromaffin cells in the control group expressed moderate immunoreactivity to Synaptophysin and tyrosine hydroxylase, compared with intensified expression after melatonin treatment. The ganglion cells of the melatonin-treated group showed a significant increase in diameter with numerous rER. The most interesting feature in this study is the presence of small granule chromaffin cells (SGC) and telocytes (TCs) for the first time in the adrenal glands of sheep. Moreover, these SGC cells, Schwann cells, fibroblasts, and progenitor stem cells showed a stimulatory response.
The TCs were small branched cells scattered in the adrenal glands around cortical cells, chromaffin cells, nerve fibers, and blood vessels. These cells increased significantly in number, length of their telopodes, and secretory activity after melatonin treatment. In addition, multiple profiles of unmyelinated nerve fibers were demonstrated in all treated specimens. These results indicated that melatonin treatment caused a stimulatory action on all cellular and neuronal elements of the adrenal gland. This study may act as a new direction for treatment of adrenal insufficiency.
Key words: adrenal cortex, chromaffin cells, telocytes, nerve fibers, Synaptophysin INTRODUCTION
The adrenal gland has crucial roles in the maintenance of metabolism, body activities, and protecting the body against the acute and chronic stresses. The mammalian adrenal gland consists of two anatomically distinct parts derived from different embryological origins; the outer cortex (mesodermal origin), which synthesizes steroid hormones, and the central medulla (neuroectodermal origin), which contains catecholamine-producing chromaffin cells. The adrenal cortex and medulla are functionally and structurally closely connected (Shepherd & Holzwarth, 2001). The adult adrenal cortex is subdivided into three principal
concentric biochemically and morphologically different zones of steroid synthesizing cells (Junqueira & Carneiro, 2003). The outer zona glomerulosa synthesizes the mineralocorticoid
*Corresponding author.
doaamokhtar33@yahoo.com Received August 23, 2017; revised October 15, 2017; accepted October 28, 2017
aldosterone; the middle zona fasciculate produces the gluco- corticoid cortisol; and the inner zona reticularis produces the sex hormone, androgen (Greco & Stabenfeld, 2007). Adrenal cortical hormones play vital roles in a number of physiologic processes, including electrolyte and fluid balance, cardio- vascular homeostasis, carbohydrate, protein and lipid metabolism, immune and inflammatory responses, sexual development and reproductive function (Hart & Barton, 2011). The adrenal medulla consists mainly of chromaffin cells
that synthesize catecholamines (Coupland, 1989). Chro- maffin cells of adrenal medulla are viewed as the endocrine counter part of postganglionic sympathetic neurons, which derived from neural crest precursors (Maxwell et al., 1988; Langley & Grant, 1999). These cells secrete the circulating catecholamines, comprising dopamine (DA), adrenaline (A) and noradrenaline (NA), in addition to a number of other substances, such as chromogranins and neuroactive peptides (Burgoyne, 1991; Goldstein et al., 2003). Under physiological (nonstress) conditions, the adrenal medulla secretes ~80% of
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156 |
Page 157 |
Page 158 |
Page 159 |
Page 160 |
Page 161 |
Page 162 |
Page 163 |
Page 164 |
Page 165 |
Page 166 |
Page 167 |
Page 168 |
Page 169 |
Page 170 |
Page 171 |
Page 172 |
Page 173 |
Page 174 |
Page 175 |
Page 176 |
Page 177 |
Page 178 |
Page 179 |
Page 180
