A practicable variant of the ion exchange method for the radiometric estimation of ornithine decarboxylase activity.

A known ornithine decarboxylase assay working with ion exchang separation of [3H]ornithine and [3H]putrescine has been revised. The assay can be performed in disposable 1.5 ml vessels with a total of four pipetting steps. The separation of enzyme substrate and product, respectively, requires 3 h per 50 samples. The detection limit is about 50 pmoles [3H]putrescine formed

Sexual dimorphism of newborn mouse epithalamus after fractionated X-irradiation at late stage of organogenesis.

Fractionated X-irradiation with 3 x 0.95, 3 x 1.05, 3 x 1.15 or 3 x1.35 Gy on gestational days 11-13 in the mouse results in two discrete, clearly distinguishable forms of an epithalamic malformation observable on gestational day 18. Type A is characterized by a rhombic shape of the dorsal diencephalic sulcus which first narrows at the occipital edge. The habenular diameters in the plane of the habenular commissure are in the range between 81 and 88% of the control measurements. The anterior colliculi are quite well developed. The type B lesion is characterized by a rather narrow epithalamus with a sandglass-shaped dorsal diencephalic sulcus and habenular diameters that are only about 56 to 64% of the control values. With the exception of the group with the lowest radiation dose (3 x 0.95 Gy), the type B lesion predominates. The B:A ratios are 1.5 and 1.6 in the highest dosage groups, and show the most drastic increase to a ratio of 4.0 after application of 3 x 1.05 Gy. Type B lesions occur in female fetuses at a higher frequency than in males and thus shows a clear-cut correlation with the frequency and severity of neocortical lesions in the same individuals. This is again most marked in the 3 x 1.05 Gy dosage group, where the type B lesion occurs five times more frequently in females than in males. This sexual dimorphism in the reaction pattern of the epithalamus after X-irradiation in utero, can best be explained by postulating a causal link with the forebrain lesions which were recently shown to exhibit similar sexual dimorphism. We therefore postulate a retrograde transsynaptic degeneration of the thalamo-cortical fibres that develop pre-term, which is significantly expressed only after low X-irradiation dose, but is partly abolished in the higher dosage groups. This leads to hypoplastic alterations of the epithalami, a secondary phenomenon to the neocortical lesions in the animals most affected. The resulting dysfunction of the epithalamus in the immediate neonatal period is then responsible for the preferential death of the animals with B-type lesions and also explains why female mortality is significantly higher than male mortality which occurs only in the 3 x 1.05 Gy dosage group

The postnatal pattern of ornithine decarboxylase activity reveals a disparity of rat brain regeneration capacity after prenatal X-ray or 5-azacytidine treatment.

Pregnant Wistar rats were treated on the 15th day of gestation either with 1.4 Gy X-radiation, or with 2 x 2.5 mg 5-azacytidine per kg body weight. X-irradiation caused negligible mortality among the offspring, despite of a 35% reduction of brain weights. The course of brain ornithine decarboxylase activity exhibited two breaches within 5 days after birth, each followed by recovery to control levels. After 5-azacytidine treatment brain weights were reduced by 16% only, but two thirds of the young died within a short time after birth. During three days following birth, the activity of ornithine decarboxylase in the brains of the young animals split into two ranges, a high one at control level and a low one at about fifth of control level. As the ratio of brains with low to those with high enzyme activities correlated with the rate of postnatal mortality, the splitting of early postnatal enzyme activities was interpreted in terms of a nothing-or-all-law: beyond a certain amount of 5-azacytidine incorporated into brain DNA, gene expression was impaired to an extent not compatible with the survival of the animals

Developmental patterns of three X chromosomal enzyme activities in the brains of female and male mice. Lack of sex-dependent reaction to a fractionated prenatal X-ray dose.

The developmental profiles of the activities of the X chromosome-linked enzymes α-galactosidase, hypoxanthine guanine phosphoribosyltransferase, and glucose-6-phosphate dehydrogenase were studied in the brains of mice. X chromosome inactivation, which takes place at an early stage of development, led to identical enzyme activities in females and males between the 15th day of gestation and the 64th day after birth. The enzyme activities were also studied after an X-ray dose of 3 times 1.05 Gy, delivered on gestational days 11, 12, and 1. Treatment with this dose, but not with 3 times 0.95 Gy or 1.15 Gy, respectively, was followed by the death of predominantly female offspring within 2 days after birth. The assumption that the reason for this might be a reactivation of inactive female X chromosomal genes in brain cells was tested in the present experiment. There were marked radiation-induced alterations of the activities of the above-mentioned enzymes. However, sex differences of these enzyme activities were not found after the irradiation treatment. A participation of X chromosome reactivation in the elevated mortality of female offspring is therefore unlikely