Objective: Sedative and anticonvulsant drugs, which inhibit N-methyl-D-aspartate receptor-mediated excitation or enhance GABA-mediated action, may cause apoptotic neurodegeneration in the developing mammalian brain. Here we explored whether such agents influence early postnatal neurogenesis.
Methods: The N-methyl-D-aspartate antagonist MK801 and the GABA subtype A agonists phenobarbital and diazepam were administered to infant rats, and cell proliferation and neurogenesis were studied in the brain using 5-bromo-2'-deoxyuridine and doublecortin immunohistochemistry and stereology. Using confocal microscopy, we quantified neurogenesis in the dentate gyrus on postnatal day 15 (P15) after treatment with MK801 or phenobarbital on P6 to P10. Learning and memory were assessed at the age of 6 months after early postnatal treatment with phenobarbital.
Results: MK801, phenobarbital, and diazepam reduced numbers of newly born cells in the brain. We found no evidence that these agents caused apoptosis of 5-bromo-2'-deoxyuridine-positive cells. In the dentate gyrus, many of the newly formed cells differentiated toward a neuronal phenotype. Phenobarbital and MK801 reduced numbers of newly formed neurons in the dentate gyrus. At the age of 6 months, phenobarbital-treated rats had fewer neurons in the dentate gyrus and performed worse than saline-treated littermates in water maze learning and memory task.
Interpretation: These findings show that blockade of N-methyl-D-aspartate receptor-mediated excitation and enhancement of GABA subtype A receptor activation impair cell proliferation and inhibit neurogenesis in the immature rat brain. Because many sedative and antiepileptic drugs used in pediatric medicine act via these mechanisms, our findings raise concerns about their potential impact on human brain development.