Sürekli karanlık ve ışığa maruz kalan sıçanların timusundaki histolojik değişiklikler

Sürekli karanlık ve ışığın, epifiz bezinden melatonin salgılanmasını inhibe ve s/tümü/e ettiği bilinir. Bu çalışmada, sıçan timus yapısını bir hayli etkileyen fotoperiyod ritmindeki değişikliklere deneysel kanıt sağladık. Erkek albino sıçanlar üç gruba ayrıldı. I. Grup kontrol sıçanlar, 12:12 saat, ışık: karanlık siklusuna; II. Grup sıçanlar, sürekli karanlık ortama; III. Gruptakiler ise parlak suni ışığa maruz bırakıldı. Tüm hayvanlar 8 hafta sonra öldürüldü. II. Grupta timus ağırlığı artmıştı. Timik epitelyal hücreler hipertrofikti. III. Grupta ise timus ağırlığı azalmıştı. Timik kortikal epitelyal hücreler ve lenfositler azalmıştı, piknotik çekirdekli lenfositler sıklıkla korteks ve medulladaydı. Sürekli karanlık hipertrofiye ve hücresel artışa neden olurken, sürekli aydınlık Umusun involüsyonuna, lenfositlerin ölümüne neden olmuştu. Timik lenfositler ve epitel hücrelerini, direkt veya indirekt olarak etkileyen bu durum melatoninin, immünositümülator etkisine atfedilebilir.

Histologic changes in thymus of the rats exposed continuous darkness and continous light

It is known that periods of constant darkness and constant light cause stimulation and inhibition of melatonin secretion from the pineal gland. In this study, we provide experimental evidence that changes in the rhythm of the photoperiod have considerable effects on thymic structure of the rats. Male albino rats were divided into 3 groups. Group I rats were exposed to a 12:12 h light: dark cycle, group II rats were kept in a dark vicinity, group III in a vicinity under a bright artificial light. All animals were killed after 8 wk. In group II, thymus weight increased. Thymic cortical epithelial cells hypertrophied. In group III thymus weight decreased. Thymic cortical epithelial cells and lymphocytes had decreased, pyknotic lymhocyte nuclei were frequently in the cortex and medulla. It is concluded that constant darkness causes hypertrophy and increased cellularity of the thymus, while constant light causes involution of the thymus and death of lymphocytes. These changes possibly may be atributed the immunostimulatory effects of melatonin acting directly or indirectly, on the lymphocytes and epithelial cells.

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