Abstract
Background Ocimum basilicum (O. basilicum) was described to have antidepressant and anxiolytic activities. Although the relationship between the main olfactory bulb (MOB) and depression was recently reported, the chronic stress-induced dysfunction of the MOB is not clearly described.ObjectivesThis study aimed to assess the efficacy of inhalation of O. basilicum essential oils in improving chronic unpredictable mild stress (CUMS)-induced changes in MOB of mice and understand the mechanism underlying such effect.Materials and MethodsAdult male mice (n=40) were assigned into four groups included the control, CUMS-exposed, CUMS + fluoxetine (FLU), CUMS + O. basilicum. Behavioral changes, serum corticosterone level, and gene expression of GFAP, Ki 67, and caspase-3 were assessed using real-time PCR (RT-PCR). Histopathological and immunochemical examination of the MOB was performed.ResultsFLU and O. basilicum significantly down-regulated (p = 0.002, p<0.001) caspase-3 gene expression indicating reduced apoptosis and up-regulated (p = 0.002, p < 0.001) Ki67 gene expression indicating enhanced neurogenesis in MOB, respectively. FLU and O. basilicum-treated mice markedly improved MOB mitral cell layer distortion and shrinkage induced by CUMS.Conclusion O. basilicum relieved both biochemically and histopathological chronic stress-induced changes in the main olfactory bulb possibly through up-regulation of gene expression of GFAP and Ki67 and down-regulation of caspase-3 in the MOB.
Highlights
Chronic stress results in deterioration in mood, cognition, memory and may be a leading cause in the occurrence of many systemic diseases as Parkinson’s disease, type 2 diabetes, gastric ulceration, and Alzheimer’s disease [1].Olfactory system is distinctive as it is considered the most proliferative CNS system entertaining differentiating progenitor cells, migrating from the subventricular zone to the olfactory bulb (OB), where they differentiate into tyrosine hydroxylase (THC) or GABA (C) interneurons [2]
Administration of FLU or O. basilicum for 2 weeks after induction of depression significantly decreased immobility time compared to untreated mice (p = 0.02, p < 0.001) respectively (Figure 1)
Both FLU and O. basilicum could significantly increase (p=0.001, p < 0.001) the duration the mice spent in the open arm during the elevated plus maze test (EPM) and significantly reduce (p < 0.001) entries to closed arms compared to untreated animals, respectively
Summary
Chronic stress results in deterioration in mood, cognition, memory and may be a leading cause in the occurrence of many systemic diseases as Parkinson’s disease, type 2 diabetes, gastric ulceration, and Alzheimer’s disease [1].Olfactory system is distinctive as it is considered the most proliferative CNS system entertaining differentiating progenitor cells, migrating from the subventricular zone to the olfactory bulb (OB), where they differentiate into tyrosine hydroxylase (THC) or GABA (C) interneurons [2]. The main olfactory bulb (MOB) is an important part of the olfactory system that results in post developmental neurogenesis [3]. It was reported that olfactory deficits often accompany neurodegenerative diseases This was noticed in idiopathic Parkinson’s disease where advanced olfactory deficits were initial signs of the disease that occurs before the first motor dysfunctions [4]. The model of (CUMS) is one of the common and verified models used to study depression This model is characterized by the occurrence of long-lasting neurodegenerative changes including behavioral, neurochemical, and neuroendocrinal changes that mimic those observed in depressed patients [5]. The relationship between the main olfactory bulb (MOB) and depression was recently reported, the chronic stress-induced dysfunction of the MOB is not clearly described
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