Low dosages of vitamin A may cause a decrease in the total neuron number of fetal hippocampal rat cells

We investigated the effect of low, medium and high doses of oral vitamin A, on the number of fetal hippocampal neurons.

High doses of vitamin A during pregnancy may cause embryonic malformations. There are reports about dosages that don't cause macroscopic malformations, but may cause mental and behavioral disorders. Still, quantitative morphological studies explaining this topic are lacking.

We administered oral vitamin A to pregnant rats on the 10th-12th days of pregnancy at doses of 10000, 20000, 30000, 40000, 50000, 100000 and 200000 IU/kg. We collected the fetuses on the 19th day and removed their brains. After staining with cresyl violet and immunolabeling with Tunel and Ki67 antibody, we examined the hippocampi with stereological methods.

Vitamin A decreased hippocampal neuron numbers beginning from 20000 IU/kg. While the number of Ki67 positive cells increased with the dosage, the increase of apoptotic cells begun at the dose of 50000 IU/kg.

Our study demonstrates that vitamin A, beginning from the dosage of 20000 IU/kg, is decreasing the total hippocampal neuron numbers during the critical period of embryonic brain development and that apoptosis may not be the only factor in this outcome (Tab. 1, Fig. 3, Ref. 27).