Ultrastructural Characteristics of Axodendritic and Axosomatic Synapses in the Orbitofrontal Cortex of White Laboratory Rats Associated with Low-Protein Food after Acute Sound Exposure

Abstract

This paper investigates the state of axodendritic (ADS) and axosomatic (ASS) synapses in orbitofrontal cortex (OFC) layers I-IV of adult white laboratory rats associated with balanced and low-protein food after acute sound exposure. Experiments were performed on 64 white non-linear sexually mature laboratory male rats weighing 180–230 g (eight intact, 56 experimental). After a continuous call with an intensity of 120 db for 120 seconds, 56 rats were divided into two groups: those receiving balanced (control – 28) and low-protein food (basic – 28). Each of these two groups was divided into two subgroups: stress-resistant (12 animals in each) and stress-unstable animals (16 animals in each). Water intake was unlimited. The animals were removed from the experiment on the 10th, 20th, 30th, and 40th day after sound exposure. Along with histological and immunohistochemical analysis, the samples of OFC layers I–IV were studied by transmission electron microscopy. Electron microscopic changes in the structure of ADS and ASS were found in all OFC layers. Violations of the fine structure of both the presynaptic and postsynaptic poles were noted. The maximum severity of ultrastructural changes was observed in the ADS of the surface (I, molecular), outer granular (II), pyramidal (III), and inner granular (IV) OFC layers. ASS disorganization was noted mainly in contacts, the postsynaptic pole of which was formed by the bodies of small pyramidal neurons of layer III, as well as pyramidal and stellate neurons of layer IV of the OFC. During all periods of observation, violations of fine organization were most pronounced in stress-unstable animals of the main experimental group, especially on the 10th and 20th day after exposure. Acute sound exposure initiates disturbances in the fine organization of axodendritic and axosomatic synapses in OFC layers I–IV of white laboratory rats. Focal destruction of a part of the noted synapses in rats with a low-protein diet after acute auditory stress is irreversible.