Ultrastructural changes in the chick thymus following unilateral vagotomy

The ultrastructure of the thymus in the chick (Gallus domesticus) was studi ed after unilateral vagotomy at survival times of 3, 7 and 10 days. UItrast ructural changes in the ipsilateral thymus were observed in axon boutons as well as in myoid and cystic cells in the medulla, especially those situate d near the corticomedullary junction. Structural changes in axon boutons ra nged from granular degeneration of the axonal cytoskeleton to vacuolation o f the axoplasm. Myelin figures of different sizes and configurations and cl umping of small agranular vesicles were commonly observed in the axon termi nals. Degeneration of myoid cells appeared to peak at 7 days post-vagotomy. Changes ranged from oedematous appearance and intense vacuolation of the p eripheral cytoplasm to disorganisation and clumping of myofibrils. In some myoid cells the sarcomeres showed granular degeneration at the I-bands and in others, the myofibrils were completely degenerated such that amorphous m aterial and partially degenerated organelles filled the entire cell. The ma jority of cystic cells at 3 days post-vagotomy showed a uniform increase in electron density. Numerous electron dense bodies, some displaying concentr ic lamellation, were observed throughout the expanse of the cytoplasm. At 7 days post-vagotomy, the cytoplasm of some cells gave a "moth-eaten" appear ance. Dying cystic cells were encountered at 10 days after vagotomy. Degene ration in the myoid and cystic cells suggests that these cellular component s may be the putative targets of the vagal fibres in the chick thymus. The changes in these cells reflect a disturbance in the cell metabolism presuma bly brought about by the removal of vagal influence. Anat Rec 255:261-270, 1999. (C) 1999 Wiley-Liss, Inc.