Effects of Immobilised Stress on Neuronal Plasticity of Pyramidal Neurons in Prefrontal Cortex of Female Wistar RatsAn Experimental Study

Abstract

Introduction: Stress is a normal response of an organism to any threat which can be physical, emotional or psychological. Positive stress is called eustress whereas negative stress is distress. Neuronal plasticity is a term which indicates the changes in brain. There can be structural and functional neuroplasticity. Aim: To study the neuronal plasticity (dendritic branching pattern and their lengths) of pyramidal neurons in Prefrontal Cortex (PFC) of female wistar rats after immobilised stress. Materials and Methods: It was an experimental study conducted in Nepalese Army Institute of Health Sciences, Kathmandu, Nepal from May 2021 to July 2022. Based on the age, 24 female rats were divided into three groups, group A>12 weeks, group B 8 to 12 weeks and group C 3 to 7 weeks. Each group contained eight rats, of which four were control and four were experimental. Experimental rats underwent immobilised stress. After stress protocol, rats were sacrificed and PFC was taken out and stained. The images of neurons were taken by confocal microscope. The neuronal reconstruction was done using IMARIS software for dendritic lengths. The parameters in apical dendrite category-length of principal dendrite, branch points and lengths of different branches were compared between control and stressed groups. In basal dendrite category-number of basal dendrites, lengths of different basal dendrites and branch points were compared between control and stressed groups using unpaired t-test. The data was analysed with Statistical Package for Social Sciences (SPSS) version 20.0. Results: It was observed that there was a statistically significant increase in all basal dendrite parameters in experimental category as compared with controls in group A with p-value<0.001, and in group B, significant increase in branch points with a p-value<0.001 in experimental category, and significant increase in branch length of basal dendrites in group C of experimental rats with p-value<0.001. The parameters related to apical dendrites of pyramidal neurons also showed significant shrinkage in experimental rats as compared to control groups. Especially in group C all the apical dendrite parameters were significantly decreased compared with control group (p-values 0.013, 0.001 and 0.006 for principal dendrite’s length, branch points and branch lengths, respectively). Conclusion: Stress induces neuronal plasticity in pyramidal neurons of PFC of rats. Findings of this study suggest stress induces significant increase in the basal dendrite parameters of pyramidal neurons of PFC of all age group of rats, especially in the rats of more than 12 weeks age and significant shrinkage of apical dendrites was seen in all age group of rats and more so in the rats between 3 to 7 weeks of age.

Keywords

• brain plasticity
• dendrites
• projection neurons