The role of the thyroid in the development of Mauthner's neuron. A karyometric study in thyroidectomized anuran larvae

Forebrain development in control and hypothyroid larvae of Triturus cristatus carnifex

Some cytological and developmental aspects of the forebrain gray matter were studied in the control and the hypothyroid larvae of Triturus cristatus carnifex. The mitotic cell percentages in the periventricular germinal layer, the fusiform shape of the recently divided neuronal cells and the transitory gray matter cleavage, are characteristic of the immature status of the central nervous system (CNS) in this species. The hypothyroidism obtained during two months of thiourea treatment slows down the development in all the forebrain areas of the experimental larvae. Nevertheless, the nucleus olfactorius anterior and the corpus striatum, which have a longer mitotic activity with respect to the other neuronal structures, are more deeply affected by thyroid atrophy. Thyroid activity and forebrain maturation are discussed on the basis of the literature and our data with regard to their influence on behavior and evolution.

Effects of thyroid hormones on the hippocampal glial cells of fasting rats

The effects of the oral administration of thyroid hormones on the hippocampal glial cells in fasting or fed adult rats were studied. The hormone treatment and/or fasting were done during two periods of five days interpolated by ten days without any hormone treatment or fasting. Prominent histological changes and increased number of glial cells were observed in the hippocampus of rats when the thyroid hormone administration was associated with fasting.