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Objective: The removal of bilateral olfactory bulbs (OBs) can lead to serious behavioral alterations in rats. Olfactory bulbectomy (OBX) might lead to deficits on psychomotor and psychosocial behaviors by effecting raphe nucleus. Therefore, we investigated whether OB lesions led to dorsal raphe degeneration.
Methods: 48 rats were used (24 female and 24 male) for this study. Four male and four female rats were taken as the control group. Forty rats (20 male and 20 female rats) were taken as the study group, and frontal burr holes were performed at the OB level on these rats. OB cauterization was applied to 10 male and 10 female rats (n=10, 10; study group 1), mechanical OBX by compression was applied to 5 male and 5 female rats (n=5, 5; study group 2), and no procedure was performed on the remaining 10 rats (n=5, 5). Psychomotor condition, feeding, nutrition, pregnancy ratios, maternity and lactation behaviors, number of delivered offspring, and stillbirths, abortus prevalence were examined. Their OBs, olfactory cortices, raphe nucleus were extracted, fixed with 0.9% formalin solution, and examined by using histopathological methods. All tissue specimens were embedded in paraffin blocks and cut into 5- micrometer thick sections using a microtome. Hematoxylin-eosin staining was used to assess histological structures, S-100 staining for morphological changes and Tunnel staining for apoptosis. The morphologically deformed neuronal density of the dorsal raphe nuclei was estimated using stereological methods. Neurons stained with NSE were counted with a stereological method by means of detecting neuronal density. The Cavalieri volume estimation method was applied to evaluate the total number of neurons in each specimen by multiplying the volume (mm3) and the numerical density of the neurons in dorsal raphe nuclei. The numbers of normal, morphologically deformed and degenerated neurons in the dorsal raphe nuclei of each animal were counted. The differences between OB volumes and neuronal densities in the dorsal raphe nuclei were compared statistically and taken as the criteria for neuronal degeneration.
Results: All of the animals in the study groups, especially in the cauterization group demonstrated psychomotor retardation, sexual aversion, and nutritional deficiency, similar to depression symptoms in human beings. In the study groups the pregnancy rates, number of offspring per mother rat, and birth weights in the study groups were lower, whereas the number of stillbirths was higher than the control group. Histopathological examinations showed prominent neuronal loss due to apoptosis and morphological changes in the dorsal raphe nuclei in all study groups.
Conclusion: We detected a decreased neuronal density of the dorsal raphe nuclei and in olfactory bulbectomized rats. We emphasize that olfaction disorders might cause neuropsychiatric disorders by leading neuronal degeneration in dorsal raphe nuclei.