Histologic and physiologic comparisons of the thyroid glands of the wild and domesticated norway rat

Abstract

A comparison of the histological pattern of the thyroid glands of 138 wild and 157 domesticated Norway rats showed that the domesticated rat has smaller epithelial cells, greater uniformity in the size of follicles, larger follicular lamina, and fewer vacuoles in the iiitrafollicular colloid. These differences are not present at birth but develop gradually with age. Hypophysectomy causes a loss of these differences and results in an identical histologic pattern of atrophy in the two strains of rats. There is greater uniformity of thyroid uptake and labelling of the components of thyroglobulin in the domesticated rat, but the average percent uptake of IL3' in the thyroid glands of hoth strains is the same.These differences may bc accountable partly on the basis of different reactions to the environment conditioned by diffcrent temperaments in the two strains, by actual differences in the environrncnt, and by genetic differences.Striking physiological and temperamental differences between the wild and domesticated Norway rat have been described by Richter ('49). The present paper is concerned with comparisons of the thyroid glands of wild and domesticated Norway rats. Although previous workers found no difference in the weight of the gland (Hatai, '14; Donaldson, '24; King and Donaldson, '29), we have observed a tendency for heavier gland weight in the wild Norway rat and other differences in the gross appearance of the glands of many hundreds of adult live and dead rats. The thyroid glands of wild rats are long, slender, and a brownish hue; those of domesticated rats are short, round, and pink or red in color (Richter and Dieke, unpublished), A further study now has been made to determine whether there are any differences in thyroid histology or function between the two strains. METHODSOne hundred thirty-eight wild Norway rats and 157 domesticated rats were used for the study. The wild rats were trapped or shot on farms in Maryland or in the municipal dump, alleys and backyards in Baltimore. Captive wild rats were fed Purina Fox-chow. The domesticated rats were all from the Richter colony which has been in continuous existence since 1923, having been started with albino rats from ANAT. REC., 158: 263-274. The Wistar Institute. A few non-albinos from the stock of Dr. E. V. McCollum were added about 35 years ago. During a fouryear period (12th-16th year) of the colony's existence some rats, especially females, were selected for running activity. There has been no other planned selection. From the time of weaning the domesticated rats were fed a standard diet and tap water ad lib., with a weekly supplement of lettuce. They were kept in a wellventilated room at an average temperature of 25°C and all were handled at least once a week. The wild rats used for thyroid weight measurement were killed and dissected as soon as they were brought into the laboratory. No control of the quality or quantity of food eaten by the rats in the wild environment was possible. This is thus a n uncertain factor except in the ca...

Genetics and animal domestication: new windows on an elusive process

“…Studies on variations in thyroid hormones in lab rats show that not only do domesticated rats have smaller thyroid glands than wild rats but also this smaller gland reduces escape readiness and escape distance within domestic laboratory rats (Mosier & Richter, 1967). Additionally, domestic rats reach fertility earlier, end it later and have more offspring per pregnancy.…”

Topographic anatomy and vascularization of the glandula thyroidea in rats

“…The glandula thyroidea has an oval cranial end and presents as a butterfly‐shaped organ in the lower part of the larynx cartilages and does not join dorsal part of the trachea (La Perle et al, 2018; Tadjalli & Faramarzi, 2016; Yavru & Yavru, 1996). In rats, the glandula thyroidea is generally an oval‐shaped long reddish body with smooth surfaces (Enemali et al, 2016) but in wild rats, it is long, thin and brownish, while in domesticated rats it is short, rounded and pink‐red (Mosier & Richter, 1967). In the adult mongoose, the glandula thyroidea is dark brown (Tadjalli & Faramarzi, 2016).…”