Ultrastructural evidence of long-lasting cerebellar degeneration after early exposure to phenobarbital in mice.

Previous studies in this laboratory demonstrated a 20 to 30% reduction in cerebellar Purkinje and granule cells after exposure to phenobarbital (PhB) early in life. Therefore, neurons in the cerebellar cortex were examined for signs of cytologic degeneration using transmission electron microscopy (TEM) after exposure to PhB pre- and postnatally. Pregnant mice were given the acid form of PhB in their milled food (3 g/kg, gestation days 9 to 18) and water, ad libitum. Neonates were injected s.c. with an aqueous solution of sodium PhB (50 mg/kg body weight), days 2 to 21 after delivery. Controls were fed regular food or injected with the vehicle. The offspring were anesthetized on day 14 or 50 by an acute overdose of PhB and immediately perfused with a formaldehyde-paraformaldehyde or glutaraldehyde solution. The pyramis vermis of the cerebellar cortex was excised and processed routinely for TEM. The three layers of the cortex were examined. A short-term effect (at day 14) was found. More significantly, the treatment appeared to establish or trigger a degenerative process, the results of which were still apparent at day 50, more than 30 days after the termination of PhB treatment. Using double-blind evaluation for the presence and frequency of abnormalities, the cerebellar neurons of treated animals had 155 to 300% more abnormalities compared with control animals. Abnormalities included (i) Mitochondrial degeneration, ranging from swelling, collapse of cristae, vacuolization, to total granularization; (ii) lamellar bodies distributed throughout the cytoplasm and in cell processes; and (iii) myelin sheath degeneration, including periodic swelling and collapse, twisting of the coat, and scattered, unevenly stained areas. Damage was usually focal. Affected cells were found adjacent to normal cells in all areas of the cortex. PhB may cause the neural damage through a possible hormonal role.