Background: Cigarette smoking is a public health problem worldwide. Nicotine content in cigarettes causes dependence and many diseases. Olfactory bulb neurons are damaged early in neurodegenerative diseases. 

Aim of the work: to demonstrate effects of nicotine administration on the structure of mitral cells of olfactory bulbs in growing rats, and the outcome of nicotine withdrawal. 

Materials and Methods: 24 pregnant rats were randomly equally divided into two groups; a control group received no treatment, and a treated group received nicotine 6 mg/kg body weight/day subcutaneously daily from gestational day 8 until postnatal day 21. Six male offspring rats in each group at ages of newborn, 10 days, 21 days, and 2 months were included in this study. On the postnatal day 21, six male offspring rats were sacrificed, and another six rats were allowed to survive without any treatment until the age of 2 months and considered as the recovery group. Olfactory bulbs were dissected, fixed, and processed for light and transmission electron microscopy. 

Results: olfactory bulbs in all ages of the treated group had neuropil vacuolations in several layers. Mitral cells were degenerating with shrunken nuclei, nuclear membrane indentations, cytoplasmic and mitochondrial vacuolization, and lipofuscin granules as compared to the control. Neurodegenerative changes increased with increasing the age of rats and showed widened perinuclear spaces and swollen irregular axons with splitting of myelin sheaths at postnatal day 21 as compared to the control. Upon nicotine withdrawal, the structure of olfactory bulbs returned to normal features. 

Conclusion: Nicotine induced neurodegenerative changes in mitral cells. Recovery of mitral cells to normal occurred upon nicotine withdrawal.