Neuromorphological changes in mouse olfactory bulb after neonatal exposure to phenobarbital

Heterogeneous Sabra mice pups were injected daily with 50 mg/kg phenobarbital (B₅₀) or 40 mg/kg (B₄₀) from postnatal day 2 (P₂) to P₂₁. Control litter mates (C) received vehicle injections. All animals were killed on P₅₀ and their brains removed for histological analysis. The volumetric growth of the main olfactory bulb (MOB) was assessed in hematoxylin and eosin-stained serial sections cut in the sagittal plane. The volume of MOB was reduced 20 to 25% in barbiturate-treated mice. The greatest reductions in volume were seen in the external layers of the bulb (20 to 28%). There were moderate reductions in the internal granular layer (IGL, 6 to 20%) and no reductions in the subependymal layer that contains the migrating and immature cells. The number of prenatally-formed mitral cell neurons was unaffected by the treatment while the number of the pre- and postnatally generated granule cells was significantly reduced in the B₄₀ group. There were no treatment effects on the sizes or packing densities of the mitral or granule cells. Like the hippocampus and the cerebellum, the developing MOB is vulnerable to barbiturate-exposure.