Morphometric characteristics of the structural components of the intervertebral disc in rats at different times of the experimental opioid exposure and after its withdrawal

Abstract

Background. The world and domestic literature from time to time report about the problems of uncontrolled drug abuse. This problem is associated not only with the negative impact on the morphological structure, but also is a serious factor which, if it has been exposing for a long time, leads to disability and death. Despite a significant number of studies in this area, the problem of changes in the morphometric parameters of the intervertebral disc’s structural components under chronic exposure of opioid agents still remains unresolved. That is why the study of morphometric characteristics of the intervertebral disc’s structural components under experimental opioid exposure will be interesting for both - morphologists and practical traumatologists. Objective. To study the morphometric parameters of the structural components of the intervertebral disc in rats at different times of the experimental opioid exposure and after its withdrawal. Methods. The objects of the study were 61 mature outbred male rats, weight - 80-135g, age - 4.5-7.5 months. Animals were injected with nalbuphine intramuscularly once daily (at 10-11 am) for 42 days. Histological specimens were stained with alcyan blue (for the study of the collagen fibers thickness of the anterior and posterior longitudinal ligaments) and PAS-reaction (for the study of the gelatinous nucleus and its capsule thickness). For measurements of collagen fiber thickness, were taken images at x100 magnification, for measurements of the gelatinous nucleus and its capsule thickness - at x40 magnification. Measurements were performed with ImageJver software. 1.51 using the tool "straight" for linear measurements. Results. Thus, changes in the collagen fibers thickness of the anterior and posterior longitudinal ligaments during the experiment were uneven and had different tendencies. The thickness of the posterior longitudinal fibers changed mostly within the central trend of the control group with a significant decrease only at the 2^nd, 3^rd, and 4^th weeks. However, more significant, as for pathogenetic changes, was a sharp decrease in the number of fibers thicker than 25 μm in animals of the experimental group after 2 weeks of the study, and the maximum thickness at 5^th and 6^th week was only 31.41 μm and 35.24 μm whereas the maximum thickness of the control group was 81.48 μm. In the withdrawal group, only a decrease in sites with nuclear edema can be considered positive, which is displayed by morphometrical decrease in the maximum value, but the central trend remains much lower than in the control group, which also indicates the predominance of decompensatory changes. Conclusion. During the whole experiment, we observed similar changes in the nucleus capsule thickness: non-systemic fluctuations of the central parameters ​​up to the 5^th week and a sharp decompensation at the 6^th week, which was manifested by a sharp decrease in thickness. Simultaneously, we observed numerous sites of edema and thickening by more than 100 μm on the 2^nd week. Despite a general decrease in median and quartile at this time, such sites were also noted at the 6^th week. Thickness of the nucleus capsule in the withdrawal group did not demonstrate significant dynamics and remained similar to those at the 6^th week. Although, this can be interpreted as the stabilization at a certain level without further negative dynamics.