The study was performed on 26 sexually mature female Wistar rats weighing 180– 250 g, that were divided into two groups – control (n = 12) and experimental (n = 14). In order to reproduce menopause, we provided ovariohisterectomia. Medial laparotomy without ovariohisterectomia was performed to the animals of the control group for exception the impact of stress on the postoperative course of the experiment. Both groups of animals were kept in standard vivarium conditions (22 ± 2 °C, light / dark cycle was 12/12 hrs.) at a standard diet during 120 days, whereupon acute animal experiments were carried out. Sodium thiopental at a dose of 50 mg / kg was used for total anesthesia. Isolated sciatic nerve was placed on bipolar stimulating electrodes, and were submerged in vaseline oil to prevent drying. The nerve was stimulated by single square pulse with duration of 0.3 ms and an amplitude of 1 to 5 thresholds. The registration of the induced action potential of the proximal portion of dorsal roots with using bipolar electrodes.

We investigated such parameters as the amplitude, latenty period and duration of the induced action potential, threshold and hronaxy. The stimulation threshold was determined by amperage. The phenomenon of refractoriness was analyzed by studying the electrical activity of the nerve fibers in response to stimulation with paired stimuli at intervals of 1 to 20 ms. Irritating stimulus amplitude was equal to 5 thresholds, duration of 0.3 ms. The study was carried out by using the standard electrophysiological equipment (electronic stimulator with independent power supply, amplifier, analog-to-digital converter with registration and processing of information with personal computer). The reliability of the data was assessed using parametric methods (Student test) and nonparametric statistics (Mann-Whitney test). Changes recognized statistically significant at p < 0.05. All experimental procedures were performed according to the European Communities Council Directive of 24 November 1986 (86/609 / EEC), euthanasia was performed by administering a lethal dose of thiopental sodium.

Threshold of total action potential neurons of the spinal ganglia was 45.76 ± 7.41 %, chronaxy 114.69 ± 3.48 %, the latent period of 113.12 ± 2.32 % compared with the control group. The duration of the action potential has not changed. The amplitude of the action potential is increased by 31.46 ± 4.29 %. In analyzing the dynamics of the recovery of the amplitude of the second of the action potential during application of paired stimulation showed a significant delay in the recovery of the amplitude response testing stimulus animals with ovariohysterectomy. Thus, in condition of surgical menopause occurs the increase of excitability and response of dorsal root ganglion neurons despite deteriorating the temporal characteristics and reduce lability. Probably, this mode of functioning afferent input causes the amplification of pain intensity and occurrence acroparesthezia against lowering surface sensitivity in patients with early surgical menopause.

Keywords: menopause, action potential of dorsal root, spinal cord, dorsal root ganglion, rat

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1. 1. Makii E, Nerush P, Rodinskii A, Myakoushko V. Evoked activity of afferent and efferent fibers of the sciatic nerve in rats under conditions of experimental hyperthyroidism. Neurophysiology. 2002;34(1):51-59.doi.org/10.1023/A:1020218008768
2. 2. Malichenko S, Volkova V, Khalidova K. System changes in menopause. Role of deficiency of calcium and vitamin D in the formation of post-menopausal symptom. Sovpemennaya rheumatologiya. 2008;(1):20-31.
3. 3. Rodinsky O, Tkachenko S, Mozgunov O. Electrophysiological analysis of the excitability of the neuromuscular complex in experimental menopause. Experimental and Clinical Physiology and Biochemistry. 2014;(3):7-13.
4. 4. Rodins'kiy O, Tkachenko S. Bioelectric activity of interneurons pools of spinal cord in the experimental menopause in femal rats. Fiziologichnyj Zhurnal. 2015;61(5):50-55.
5. 5. Fedotov Y, Sapronov N. Effects of estrogen in the central nervous system. Uspekhi fiziologicheskikh nauk. 2007;38(2):46-52.
6. 6. Aloisi A, Bonifazi M. Sex hormones, central nervous system and pain. Hormones and Behavior. 2006;50:1-7.doi.org/10.1016/j.yhbeh.2005.12.002
7. 7. Baulieu E, Schumacher M. Progesterone as a neuroactive neurosteroid, with special reference to the effect of progesterone on myelination. Human Reproduction. 2000;15(1):1-13.doi.org/10.1093/humrep/15.suppl_1.1
8. 8. Bruce-Keller A, Keeling J, Keller J, Huang F, Camondola S, Mattson M. Antiinflammatory effects of estrogen on microglia activation. Journal of Endocrinology. 2000;141:3646-3456.doi.org/10.1210/endo.141.10.7693
9. 9. Cairns B, Sessle B, Hu J. Characteristics of glutamate-evoked temporomandibular joint afferent activity in the rat. Journal of Neurophysiology. 2001;85(1):2446-2454.
10. 10. Chaban V, Micevych P. Estrogen receptor-α mediates estradiol attenuation of ATP-induced Ca2+ signaling in mouse dorsal root ganglion neurons. Journal of Neuroscience Research. 2005;81(1):31-37.doi.org/10.1002/jnr.20524
11. 11. Dawson-Basoa M, Gintzler A. Gestational and ovarian sex steroid antinociception: synergy between spinal and opioid system. Brain Research. 1998;757:37-42.doi.org/10.1016/S0006-8993(98)00192-9
12. 12. Frankenhaeuser B, Hodgkin A. The action of calcium on the electrical properties of squid axons. Journal of Physiology. 1957;137(2):218-244.doi.org/10.1113/jphysiol.1957.sp005808
13. 13. Hille B. Ionic channels of excitable membranes. Sunderland: Mass., Sinauer Assoc.; 1984. 814.
14. 14. Holdcroft A, Sapsed-Byrne S, Ma D, Hammal D, Forsling M. Sex and oestrous cycle differences in visceromotor responses and vasopressin release in response to colonic distension in male and female rats anaesthetized with halothane. British Journal of Anaesthesia. 2000;85(6):907-910.doi.org/10.1093/bja/85.6.907
15. 15. Li Y, Yang J, Li S, Zhang J, Zheng J, Hou W. N-myc downstream-regulated gene 2, a novel estrogen-targeted gene, is involved in the regulation of Na+/K+-ATPase. Journal of Biological Chemistry. 2011;286:32289-32299.doi.org/10.1074/jbc.M111.247825
16. 16. Ma B, He P, Cong B-H, Han H, Gao L, Wang L-G, Ni X. Modulatory effect of estradiol on P2X3 receptors expression in dorsal root ganglion of female rats. J FASEB. 2007;21:911.7
17. 17. Ogunshola O, Antic A, Donoghue M, Fan S, Kim H, Stewart W, Madri J, Ment L. Paracrine and autocrine functions of neuronal vascular endothelial growth factor (VEGF) in the central nervous system. Journal of Biological Chemistry. 2002;277(13):11410-11415.doi.org/10.1074/jbc.M111085200
18. 18. Papka R, Mowa C. Estrogen receptors in the spinal cord, sensory ganglia, and pelvic autonomic ganglia. International Review of Cytology. 2003;231:91-127.doi.org/10.1016/S0074-7696(03)31003-4
19. 19. Paul M, Andrew J, Benjamin K, Thant S, Hedward C, Michael G. Steroid hormone signaling between schwann cells and neurons regulates the rate of myelin synthesis. Annal of the New York Academy Sciences. 2003;1007:340-348.doi.org/10.1196/annals.1286.033
20. 20. Robbins A, Berkley K, Sato Y. Estrous cycle variation of afferent fibers supplying reproductive organs in the female rat. Brain Research. 1992;596(1-2):353-356.doi.org/10.1016/0006-8993(92)91572-V
21. 21. Sreekantha Satisha T, Avinash S, Manjunatha Goud B, Remya Sudhakar G, Rangaswamy R, Raghavendra Vikram Tey. Magnesium and Calcium levels in early surgical menopause. Journal of Clinical and Diagnostic Research. 2011;5(1):55-57.
22. 22. Stephanova D. Conduction along myelinated and demyelinated nerve fibres during the recovery cycle: model investigations. Biological Cybernetics. 1989;62(1):83-87.doi.org/10.1007/BF00217663
23. 23. Unal D, Halici Z, Altunkaynak Z, Keles O, Oral E, Unal B. A new hypothesis about neuronal degeneration appeared after a rat model of menopause. Neurodegener Diseases. 2012;9(1):25-30.doi.org/10.1159/000329721
24. 24. Verthelyi D. Female's heightened immune status: estrogen, T cells, and inducible nitric oxide synthase in the balance. Journal of Endocrinology. 2006;147(2):659-661.doi.org/10.1210/en.2005-1469