[The effect of Triethylenmelamin (TEM) on the retinal development of the newt (Triturus alpestris): An electron microscopic study].

Larvae ofTriturus alpestris (stages according to Glaesner: 27, 34, 39 and 43) were kept for 24 hours in a solution containing 10 gr Triethylenmelamin (TEM) per ml tap water. Thereafter, they were further grown in pure tap water. Light microscopically, a fading of mitotic figures and an enlargement of cells prepared to divide were observed within the retina. Pyknotic nuclei and cell death occured in the zones of cell differentiation. The various developmental stages were differently affected by TEM.Electron microscopically, alterations of retinal cell nuclei were found to occur as early as 12 h after the onset of TEM- incubation. Fragments of nuclei which otherwise appeared morphologically normal were observed to develop by an invagination of the nuclear membrane and a subsequent fusion of the small vesicles which originated from the nuclear envelope. These fragments became completely digested. The fragmentation process eventually involved the entire nucleus and resulted in cell death.In peripheral zones of the retina, cells became enlarged, their nuclei being lobulated and their chromatin becoming transposed towards the periphery. Autolytic processes were observed to start in particular areas of the cytoplasm and to extend all over entire cells. In TEM-treated eyes, the pigment epithelium became grossly hypertrophied. This epithelium impressed by elongated and round melanosomes and a surprisingly large number of premelanosomes.The mechanism of TEM-effect was compared to that of other alkylating cytostatic drugs and discussed in connection with the observed cytological alterations.