ANATOMICAL AND IMMUNOHISTOCHEMICAL STUDIES OF THE SPINAL CORD OF THE GRASSCUTTER

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Department of Medicine

ABSTRACT
Grasscutters are currently being explored as laboratory models for scientific, medical and behavioural researches. In the present study, the anatomical, histological, histochemical and immunohistochemical studies of the spinal cord of the grasscutter was evaluated. Twelve adult Grasscutters comprising six males and six females were utilized for the study. The studies on the spinal cord of Grasscutter were done by gross observations and light microscopical methods. The animals were weighed and sacrificed by dissected. The spinal cords were removed by splitting open the vertebrae to expose the spinal cords which were then cleaned by removing the meninges surrounding them. The gross morphology of the spinal cord was studied while the segments were fixed, processed, sectioned and were taken for histological, histochemical and immunohistochemical studies using H and E, Cresyl fast violet, Golgi-Cox and Alpha-1 antityrosine hydroxylase methods respectively for detailed studies of the spinal cord segments of the Grasscutter. Histometrical evaluation wasdone for detailed studies on the areas and perimeters of the various neurons in the spinal cord segments of Grasscutter. The results showed that the mean weight of the males was significantly higher than the females (P<0.05) while the mean weight of the spinal cord did not show sexual dimorphism. The mean weight of the Grasscutter was 4700.27±0.05 g and 3633.40±0.80 g for males and females respectively. The spinal cord of the Grasscutter was observed to be made up of 28 segments which are regionally divided into 7 cervical, 13 thoracic, 6 lumbar and 2 sacral spinal segments. Two enlarged regions were observed in the spinal cord of Grasscutters namely, the cervical enlargement which was observed between C2 and C7 and lumbosacral enlargement observed between L1 and S2 spinal cord segments. The result showed that the histological features of the spinal cord of the Grasscutter with H & E method, has inner gray matter core surrounded by an outer white matter. No histological difference was observed between male and female Grasscutter. The basic structural pattern was the same throughout the length of the spinal cord of the Grasscutter. The present study using Cresyl fast violet method showed that the gray matter was stained dark purple due to the abundant presence of Nissl bodies in the neuronal cell bodies while the outer zone of white matter stained relatively lighter due to the presence of nerve fibers in the region. The neurons in the anterior gray horns of cervical, thoracic, lumbar and sacral segments of the spinal cord are multipolar motor neurons with prominent vesicular nucleus while cells in the posterior gray horns of cervical, thoracic, lumbar and sacral segments are sensory neurons. The spinal cord of the Grasscutter when stained with Golgi-Cox method revealed neurons which are of various shapes in the gray matter of the spinal cord of the Grasscutter. The gray matters of the spinal cord which had posterior and anterior horns were seen to contain neurons which were composed of several dendrites and one axon. Neurons found mainly in the posterior horns of the spinal cord of Grasscutter especially in the cervical and lumbar spinal segments were unipolar neurons while neurons of the anterior horns of the spinal cord of cervical, thoracic, lumbar and sacral spinal segments of Grasscutter were multipolar neurons. The result of immunohistochemical studies of the spinal cord of the Grasscutter treated with alpha-1 antityrosine hydroxylase, showed that dopaminergic neurons are present in the spinal cord of Grasscutters. The dopaminergic neurons were deeply stained in the lumbosacral segments than in other spinal cord segments of Grasscutters. The result of the histometrical studies of cell areas and cell sizes of the spinal cord of Grasscutters showed that the greatest value for mean for cell perimeter and cell area was observed in the lumbar spinal cord segment to be 9.30± 0.67 and 3.28± 0.59 respectively while the least values cell perimeters and cell areas were calculated to be 3.86± 0.24 and 0.83± 0.09 respectively were observed in the cervical spinal cord segment. Using t- test analysis the cell area in cervical ventral horn wassignificantly higher than cell area in the sacral ventral horn (P<0.05) and cell area in the dorsal horn of cervical spinal cord was significantly higher than the cell area in the dorsal horn of the thoracic spinal cord segment of Grasscutter. The cell perimeter of the cells of the ventral horn of lumbar spinal cord segment was significant larger than cell perimeter of the cells of the ventral horn of the cervical spinal cord segment (P<0.05) and the cell sizes of the dorsal horns of lumbar spinal cord segment was significantly higher of the dorsal horn cell of the cervical spinal cord segment (P<0.05). The anatomical, histological, Histochemical, immunohistochemical and histometrical studies on the spinal cord of Grasscutter (thryonomysswinderianus) showed unique features which include cervical and lumbosacal enlargements, presence of Nissl bodies in the cell bodies of neurons and abundance of dopamergic neurons in the cervical and lumbosacral regions. These features could be helpful in understanding the biology and behaviour of this rodent.