Lesions in the cat spinal cord following local injections of 6-aminonicotinamide

Lesions were made in the spinal cord of cats by means of local injections of 6-aminonicotinamide. The concentration needed to induce primary demyelination also caused extensive axonal death. In the early stages following injection there was evidence of astrocyte and oligodendrocyte destruction and with longer survival times most of the surviving demyelinated axons were remyelinated by Schwann cells. This experimental system indicates that Schwann cell remyelination of central axons follows astrocyte destruction, but it was not considered a suitable model system for the study of cellular relationships in remyelination because of the extensive concomitant axonal damage.

Differences in the size of the palatal processes in mouse embryos with cleft palate induced in two critical periods

Using planimetric measurements of projections of the space between the palatal processes of ICR-Velaz mouse embryos, we indirectly demonstrated that the pre-horizontalization size of the palatal processes after the i.m. administration of 7.5 mg cortsone acetate on the 12th day of gestation was smaller than in the controls. After horizontalization, the inadequate palatal processes were unable to meet in the midline as they do in the majority of normal embryos. The administration of 0.5 mg 6-amino-nicotinamide on the 14th day of gestation did not significantly affect the size of the palatal processes.

6-Aminonicotinamide-induced cleft palate in the mouse: the nature of the difference between the A/J and C57Bl/6J strains in frequency of response and its genetic basis

Cleft palate induction by 6-aminonicotinamide (6-AN) was examined in the A/J and C57BL/6J strains of mice to determine the nature of the strain difference in frequency of cleft-palate response. Probit analysis of the cleft-palate response to dose of different genotypes revealed a family of linear and parallel dose-response curves. The genotypes differ only in dosage tolerance (log ED50) to 6-AN that is required for the cleft-palate response. No evidence for a maternal cytoplasmic effect on 6-AN-induced cleft palate was found under the conditions of the present study. When the difference is dosage tolerance to 6-AN between A/J and C57BL/6J was examined with a single dose and measured by differences in frequency of induced cleft palate on a probit scale, there was some departure from genetic additivity. There was an indication off dominance deviation of the F1 embryos in the direction of C57BL/6J.A3-locus, epistatic model is proposed to account for the difference in embryonic tolerance ot 6-AN-induced cleft palate. There was a suggestion of association with the brown (b) locus.

Remyelination by Schwann cells of axons demyelinated by intraspinal injection of 6-aminonicotinamide in the rat

Focal areas of primary demyelination were produced in the spinal cords of rats by means of local injections of 6-aminonicotinamide. Both astrocytes and oligodendrocytes underwent degeneration in the demyelinated area. Nearly all the demyelinated axons were remyelinated by Schwann cells; only a very small number of axons located adjacent to normally myelinated axons were remyelinated by oligodendrocytes. The glial limiting membrane was reconstituted around the ecge of the area remyelinated by Schwann cells. This experiment offers further evidence for an important role of astrocytes in controlling Schwann cell invasion of the central nervous system, and in addition suggests that astrocytes are also needed for oligodendrocyte remyelination to take place.

Inhibition of ATP synthesis associated with 6-aminonicotinamide (6-AN) teratogenesis in rat embryos

Pregnant rats were injected ip with 6 mg/kg 6-aminonicotinamide (6-AN) at day 12 of gestation. Embryos removed between 1 and 48 h later had reduced adenosine triphosphate (ATP) concentrations, of about 50% of control values. All fetuses examined near term were malformed. Nicotinamide (NAM, 100 mg/kg) given ip 1 h after 6-AN afforded protection: malformations occurred in only 15% of the survivors; and there was minimal ATP reduction, 15% below control values. NAM given 2 and 4 h after 6-AN produced intermediate ATP concentrations and malformation frequencies. Thus, there was a relation between the embryotoxic and ATP-depressant actions of 6-AN in day 12 rat embryos.