SEASONAL CHANGES IN HISTOLOGYOF THE THYROID GLAND CALOTIS VERSICOLOR

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1 SEASONAL CHANGES IN HISTOLOGYOF THE THYROID GLAND CALOTIS VERSICOLOR M. D. Kulkarni And A. H. Shinde Department of Zoology Yashwantrao Chavan Arts & Science College, Mangrulpir Dist. Washim. (Received : ; Revised : ; Accepted : ) ABSTRACT The study of the seasonal variation in Calotes versicoloris studied under laboratory conditions. In every month they are captured and brought in laboratory, dissect the thyroid fix in fixative and sections where cut and stained. Histology of thyroid was observed diameter of thyroid epithelium was measured. The percent activity was studied. The total number of epithelial cells per follicle was measured and observations were concluded as the thyroid gland was very active from April to July and minimum in the month of December which corresponds with the increased activity of spermatogenesis. There appears to be a correlation between the thyroidal and gonadal activity Key words:- Introduction:- Male Lizard, thyroid gland, histology, seasonal changes. Material and Methods:- Investigation on the seasonal changes of reptilian thyroid is being continued since the early study of Weigmann (1932) in the lizard, Lacerta vivipera. Eggart (1935) studied the seasonal changes in the thyroid of three species of Lacerta, namely L. agilis, L.muralis and L. vivipera. The non hibernating reptilian species studied are Anolis carolinensis Evans and Hergrey (193), Xantusia vigilis (Miller, 1955) and Sceloporous occidentalis (Wilhoft, 195). Thus, it is quite apparent that there are cyclic changes in thyroid morphology of tropical reptilian species. Therefore, study in the lizard under investigation may rewarding as it may throw some light on the functional activity of the gland. The animals were captured once in third week of every month. They are capture from Mangrulpir and Amravati Region.and brought to laboratory within hours of their capture in the fields The animals were sacrificed under ether anesthesia within next hours, after recording their body weights. Thyroid gland were carefully dissected, blotted on the filter paper and weighed on electronic balance to the nearest milligram. The tissue was fixed in Bouin s fluid, routinely processed through alcohol grades, embedded in paraffin at 56C. and serially cut at 5 µ. The sections were stained either with Heidenhain s Azan or with Haematoxylin and Eosin and examined under a microscope. The following measurements were made 6

2 either on 25 or the maximum number of follicles available in the broadest section of the gland with the help of an ocular micrometer (1mm x 1). These measurements included the diameter of the follicles and the cell height of the follicular epithelium. The ratio of epithelial cell height to follicular diameter was then expressed on percentage basis Observation Microscopic Morphology The thyroid gland of C. versicoloris bilobed and encapsulated. Each lobe is situated on the either side of the trachea anterior to the poin where the carotid arches bifurcate. The two lobes are joined in the middle by a very thin connective tissue band. During the period extending from September to March the thyroid gland is completely covered by adipose tissue and thereafter this covering of adipose tissue disappear completely. Thus from April to August the slightly pinkish colored thyroid gland is clearly visible. Histology: Microscopically, the thyroid gland of C. versicolor consists of number of closely associated follicles, enclosed in a common connective tissue sheath. Each follicle is lined by single layer of epithelial cells. Depending on the secretary state of the follicles, the height of follicular epithelial cells undergoes alteration. Each follicle contains a central lumen which is filled with colloid material. In the normal animals the follicular colloid is thin and stains blue with Azan method. Occasionally, a few follicles are observed which contain red stained colloid. With haematoxylin-eosin the colloid stains eosinophilic. The intrafollicular cells are also observed. However, it is not very clear whether they are involved in holocrine secretion as has been observed in the thyroid glands of some lower vertebrates. N o. o f A n i m a l s Average height of thyroid epithelial cell in µ* Average diameter of follicle in µ* No. of cells per follicle * Activit y in %

3 (* This figure represents standard errors of themean) Seasonal changes in the histology of thyroid:. The lizard C. versicolor exhibits a wide range of variation in thyroidal histology in particular sample. The thyroid epithelial cell height shows a progressive increase from month of March and reaches a peak in the month of June thereafter; a sudden reduction in the cell height is noted µ in the month of July and this trend continues till December when the lowest value µ is recorded. In the following month viz. from January till March there is a slight recovery in the height of the thyroidal secretary epithelium. When the figures for average diameter of thyroid follicles are taken into consideration over a period of one year it is seen that from January onward there is gradual decrease in the follicular diameter. The minimum value is recorded in the month of April (.19+3.). An increase in the follicular diameter is noted in the

4 month of May with a maximal value in the month of June ( ). In the following two months there is slight decline in this and thereafter again an increase is noted which continues till November. This value for follicular diameter remains almost constant till January. The percentage values of the ratios of epithelial cell height to follicular diameter presents a trend which is comparable to some extent to that of epithelial cell height. The lowest percentage value is recorded in December (5.9%). From January and onwards there is gradual increase in the value till March. In the month of April there is sudden increase in the value. The values in April and June are almost the same. However in the month of May there appears to be a slight decline in this value the reason behind this is not very clear. There is significant drop in the percentage value, in July and August. From September onwards this decrease is gradual till a minimum is reached in the month of December. The total number of epithelial cells lining a single follicle also shows great variation. The maximum number of cells per follicle are noticed in June (1.96+.). The cells during this period are tall and columnar. The number of cells per follicle starts decreasing from July and onwards and minimum is reached in January ( ). This reduction in the total number of cells per follicle is accompanied by a change in the morphology of the cells lining the follicle, which become flat and cubical. Discussion In the adult lizard, Lacerta agili, L. murali, L.vivipera (Eggart,1935), Xantusia vigilis ( Miller,1955) and Sceloporous occidentalis (Wilhoft, 195) belonging to the temperate zone, the increased thyroidal activity has been directly correlated with the reproductive activity, the males of S. occidentalis exhibit an increase in the thyroid epithelial height during May and June (Wilhoft, 195), the period when spermatozoa are abundant in seminiferous tubules. Similarly, the thyroid gland of male Xantusia vigilis (Miller,1955) shows two peaks in its activity which correspond with the increased spermatogenesis and spermiogenesis respectively. Our observations, on the thyroid ofc. versicoloragree to certain extent with those of the above mentioned workers. There appears to be a correlation between the thyroidal and testicular activities. The minimum thyroid activity as judged by the histological appearance is recorded in December (epithelial cell height µ) and percent activity 5.9%. This period correspond with the minimum gonadal activity. From January till March, there is gradual increase in thyroidal epithelial cell height which becomes quite striking in April accompanied by sudden spurt of spermatogenic activity. The functional activity of thyroid gland attain its peak in June and percent activity 1.22% which coincides with the period of maximal spermatogenic activities of thyroid and gonads is persuasive evidence though perhaps still not convincing to support the presumption that a direct interrelationship exists 1

5 between the activity of thyroid gland and the process of spermatogenesis. However, this become questionable when our observations on the thyroid histology of the animal under investigation during the period ranging from July to December are taken into consideration. It is observed that the testicular activity after reaching the peak level is maintained in that steady state till August but there is a decrease in the thyroidal activity from July onwards. Thus the process of active spermatogenesis continues inspite of the fact there is a decrease in the thyroidal activity. This can be explained, if we presume that the testicular activity is dependent on the thyroid activity only initially and once the testes are primed by the increased level of thyroid hormone, there is no further necessity of their continued stimulation. However, this hypothesis, cannot explained the sudden decline in the spermatogenic activity during the month of September. During this and following months the gonads are completely inactive, but no histological signs of the thyroid gland being non-functional are evident. Therefore, it appears that the increased thyroid activity during the period ranging from April to June might have some other explanations. References Eggart (1935): Zoo morphology and physiology Lacerta vivipera thyroid changes. Z.wiss.Zool Evans and Hergrey (193) : The effect of ovarian hormones and seasonal changes on the thyroid of both sexes Anolis carolinensis. Anat. Rec. ; Supple1.62. (Miller, 1955) Weigmann (1932) (Wilhoft, 195) : Wilhoft, D C (1963b): Gonadal histology and seasonal changes in the tropical Australian Snake L. rhomboidalis J. Morph