Does Fibromyalgia Affect the Structure of the Dentate Gyrus?

Abstract

Abstract Background The hippocampus is considered an important component of the limbic system of the brain. It is involved in memory and functional diversities. The term hippocampus typically refers to the dentate gyrus and the hippocampus proper, the cornu ammonis (CA). Fibromyalgia is known to cause memory and cognitive function impairment and is characterized by causing chronic widespread muscular pain. Aim of the Work The aim of this work was to study the possible structural and morphometric changes in rats’ hippocampal dentate gyrus induced by repeated intramuscular injections of acidic saline in the left gastrocnemius and to compare it with the control. Material and Methods Fifty-four adult female albino Swiss rats were divided into three equal groups (18 rats each): control group (I), natural saline group (II) and acidic saline group (III). Group I received no medication, group II received two i.m. injections of 100 μl saline (pH 7.4) into the left gastrocnemius muscle at day 0 and 5 respectively under sedation with halothane (2-4%), while group III received two i.m. injections of 100 μl saline (pH 4) into the left gastrocnemius muscle at day 0 and 5 respectively under sedation with halothane (2-4%). Rats of each group were further subdivided into 3 subgroups (a, b, c) 6 rats each. Rats were sacrificed by decapitation at day 7, 14, 21 from the start of experiment and their brains were excised. Results Histological examination of H&E-stained sections of groups I and II showed no difference and were both considered control groups. The dentate region was formed of three laminae: the molecular, granular and polymorphic. The granular cell layer is the principal layer separating the molecular and polymorphic layers and was formed of aggregation of granular cells. They were rounded to oval with large vesicular nuclei and .prominent nucleoli The examination of the H&E-stained sections of rats’ dentate gyrus granular cells (DG) appeared darkly stained with pyknotic nuclei I group III as compared to the control. Glial cells slightly increased especially among molecular and polymorphic layers. Neurofibrillary tangles and vacuolations started to appear in silver-stained sections. The neurodegenerative findings started to be more notable in subgroup (b) then became more prevalent in subgroup(c) together with the appearance of clear areas among the sub granular zone. Morphometric studies detected non-significant difference in mean area percentage of astrocytes between group I and group II subgroups. The statistical analysis demonstrated high significant difference in mean area percentage of astrocytes between control groups and acidic saline groups. Evident gliosis was confirmed in group IIIc when the astrocytes percentage areas become very highly significantly increased compared to groups I and II. Conclusion In conclusion, repeated acidic saline injection induced dentate gyrus alterations obvious but minimal at week 1 and become intense at week 3 after the first injection. This effect ended with neuronal death and gliosis.