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.