Morphofunctional state of microglia and hippocampal neurons in aged rats after anesthesia with chloral hydrate

Introduction. Successful translating of the fundamental research results into clinical practice is determined by a sufficiently large number of components, including the age of experimental animals and the anesthesia used. Chloral hydrate is often used as an anesthetic in preclinical studies, while its effect on the morphofunctional characteristics of the hippocampus in aged animals remains unexplored, which can lead to significant distortion and incorrect interpretation of the obtain results. Objective – morphofunctional assessment of the neurons and microglia in the layers of CA1, CA2, CA3 and CA4 fields of the hippocampus in aged rats anesthetized with chloral hydrate. Materials and methods. Male Wistar rats at the age of 24 months were anesthetized with chloral hydrate (400 mg/kg). In the early (2 days) period after chloral hydrate anesthesia, the morphofunctional state of neurons and the reaction of microglia were qualitatively and quantitatively assessed by histological, immunohistochemical, and morphometric analysis in the marginal, pyramidal, and molecular layers of fields CA1, CA2, CA3, and CA4 of the hippocampus. Results. 48 hours after 24-month-old Wistar rats were anesthetized with chloral hydrate, changes in the morphofunctional state of the pyramidal layer of the hippocampus were shown to be characterized by a significant decrease in the number of neurons in fields CA1 and CA3 with two nucleoli by 42 and 54 %, respectively, and a decrease in the width of the layer of fields CA1 and CA3 and CA4 by 27, 29 and 21 %, respectively, compared with similar indicators in the control group (P<0.05). In all layers of fields CA1, CA2, CA3 and CA4 of hippocampus, microglia reacted by the transformation of Iba-1-positive microgliocytes body and processes and a significant increase of the Iba-1 protein expression compared to the animals without administration of chloral hydrate (P<0.05). Conclusions. A single chloral hydrate dose administration necessary to anesthetized the aged Wistar rats without model surgery leads to morphofunctional changes in neurons in the most vulnerable fields of the hippocampus with simultaneous activation of microglia in all fields. This circumstance must be taken into account when conducting basic research and preclinical studies.