1.       Introduction 

The bulbar part of the parasympathetic nervous system, according to the opinion of some anatomists, does not innervate the pelvic organs, uterus and its tubes, bladder, and distal part of colon including [1]. “Bulbar (n.salivatorius superor et inferior, n. dorsalis nervi Vagi) within VII, IX, X CN’s innervate parotid, sublingual, submandibular glands and internal organs (except the pelvic organs)” [2]. However, the results of recent physiological studies indicate presence of the cholinergic innervation in the uterine fundus and its tubes [3]. Cholinergic neurons form moderately dense plexuses in myometrium, the microarterial system of the fallopian tubes. [4] found that in humans the pelvic plexus is formed by dead-end parasympathetic branches (anterior sacral roots S2-S4) and sympathetic fibers of the hypogastric nerve. The pelvic plexus is located on the anterolateral wall of the rectum, retroperitoneal, near the apex of the seminal vesicles and the posterolateral surface of the prostate [4]. Showed that the fibers innervating the sphincter of the bladder and cavernous bodies are located mainly in the back of the human pelvic plexus [5]. It is known that acetylcholine stimulates uterine contractions [6]. In studies of innervation of the uterus of mice, it has been shown that acetylcholine, histamine, serotonin, phenylepinephrine and oxytocin cause uterine contractions, that are inhibited by the ATPase blocker [7]. Acetylcholine, norepinephrine and serotonin regulate the motor function of the uterus and hormonal status in a dose-dependent manner. Blockade of α-adrenoreceptors of longitudinal muscles prevents a decrease contractile activity of myometrium, while blockade of β-adrenergic receptors of circular muscle fibers prevents a decrease of muscle tone caused by the action of noradrenaline [8]. Immunohistochemistry has shown that the myometrium of young mice contains P2x1 purinoreceptors [9], which play the role in the mechanisms of the smooth muscles contraction of the uterus and its tubes. In particular, the activation of P2-receptors leads to a reduction in the non-pregnant uterus of guinea-pig [10]. Contractions of smooth muscles are also caused by the serotonin. Preincubation of the rat uterus with an extract of dichloromethane causes a dose-dependent inhibition of the serotonin contractile effect [11]. Acetylcholine, neurotensin and oxytocin stimulate the mobility of the fallopian tubes. Catecholamines exert both relaxing and contracting effect in isolated fallopian tubes. In particular, the vasoconstrictive effect of catecholamines is realized through activation of α₂-adrenoreceptors [12]. During the ovulation period, the spontaneous contractile activity of the uteral tubes multiplies many times under the influence of acetylcholine, serotonin, prostaglandin PGF2α. 

Peristalsis of the fallopian tube due to active contractions of its smooth muscles, along with the activity of cells of the ciliated epithelium, plays an important role in ensuring the movement of the egg through the tube into the uterus. The peristalsis of the tube is most pronounced during the period of ovulation. Since one of the main functions of the fallopian tube is the movement of the oocyte after ovulation, the funnel of the tube touches at the time of ovulation with the ovary, which is ensured by contractions of the muscles of the tube. The nature of the response of the uterus and tubes depends by the hormonal background, from the phase of estrus, in which the animal is. Cajal cells of human myometrium express the receptors of estrogen and progesterone. The rabbit myometrial strips treated with estrogen or progesterone in response to a series of electrical stimuli exhibit multidirectional contractile responses: strips treated with estrogen give rise to the phenomenon of a positive reduction staircase, and the strips treated with progesterone in response to each successive electrical impulse show a negative ladder phenomenon [13]. In view of the need to conduct studies on the cholinergic regulation of the uterine fundus contractile activity and its right tube on the tested hormonal background, the task of selecting the experimental animal was very important. Rabbit, as is known, is unique not only because the vagus nerve and sympathetic trunk pass separately on the neck and do not form anastomoses, but also because when the animals are kept separately, ovulation does not occur in females, and they have a natural stable background I phase of estrus. In connection with the special role of the tube funnel and the adjacent proximal part of the funnel of the muscular layer contraction, cholinergic regulation of the right tube proximal part and the uterine fundus was investigated. 

2.       The Aim 

Is to identify the role of bulbar parts of the cholinergic system in regulation of the uterine fundus and its right tube contractile function. 

3.       Materials and Methods 

Experiments were carried out on 10 rabbits, chinchillas, females weighing 3.5-4 kg. In sparing conditions, the animals of the first group (n = 5) were stimulated the peripheral segment of the right vagus nerve at the C5-C6 level, recorded an electromyogram (EMG) of the smooth muscles of the uterine fundus and the proximal part of the right fallopian tube using bipolar silver electrodes with a contact surface area of ​​1, 5-2 mm2, placed on the surface of the organs. The EMG was recorded by Nichon-Cohden polygraph under pre-amplification conditions. The second group of rabbits (n = 5) injected toluidine blue into the peripheral trunk of both vagus nerves of the neck level. The dye is transferred by axoplasmic current to the organs and tissues innervated by the vagus nerve for 9-10 h. The tissues of the uterine fundus and right tube were then taken. Biopsies were fixed in 9% neutral formalin, dehydrated in alcohols of increasing concentration 70-96^o, inclosed in paraffin and histological sections were prepared. The resulting sections were stained with hematoxylin and eosin and visualized at a light-optical level with magnification of 240-600. Control was the uterus and the its right tube of 5 intact rabbits. Statistical processing of data was carried out on a personal computer using the computer program "SPSS-Statistics 17". In analyzing the distributions of quantitative data, measures of the central trend-the median (Me) – were determined, and the variance measures are the interquartile range in the form of 25 and 75% of percentiles. To calculate the reliability of differences in small samples, a nonparametric Mann-Whitney test was used. The criterion of statistical significance was the level p ≤ 0.05. 

4.       Results of the Study and Discussion 

Irritation of the right vagus nerve increases the amplitude and frequency of slow waves of electromotive activity of the smooth muscles of the uterine fundus (Table 1).

The magnitude of the stimulant effect studied is 30.2% in frequency and 62.5% in amplitude (Table 1), 110,9% - in power of contractions. It should be noted that the vagal stimulatory effect on the EMA of the uterus is detected with intact α- and β-adrenergic receptors. Isolated stimulation of the sympathetic trunk in none of the experiments on rabbits did not result in an increase in the motility of the smooth muscle cells of the uterine fundus. Thus, with the help of the physiological method, the presence of a vagal stimulatory effect on the EMA of smooth muscles of the uterine fundus has been established. The irritation of the right vagus nerve leads to an increase in the motor function of the proximal part of the right tube of the uterus. Thus, the wave frequency of the slow waves of the right tube is 17.0 ± 1.1 / min, the amplitude is 0.17 ± 0.03 mV. The contraction power was increased on 111.6%. Irritation of the vagus nerve leads to an increase in the frequency of slow waves of the right tube to 19.5 ± 2.4 / min (by 14.7% p <0.05), amplitude to 0.27 ± 0.05 mV (by 58.8% p <0.05) and the of the power of contractions to 4.265 (addition by 47.8% p <0.05). That is, it is physiologically shown that the right vagus nerve can regulate the proximal part of the right uterus tube.

The anatomical evidence of the presence of vagal innervation of the uterine fundus were the experiments with intravital endoneural injection of toluidine blue under the myelin sheath of the right and left vagus nerves, followed by staining of the neural structures of the uterine fundus, and its right tube. Vessels of the uterus are expanded, full-blooded, in the subserous muscle layer are determined by nerve trunks. There is a transition of smooth muscle bundles from the tube into the uterine tissue with a slight defibration of the muscle fibers. Bunches of smooth muscle cells go in different directions. In the thickness of the muscular tissue, blue neuronal ganglia, colored by toluidine, are surrounded by perineurium and containing a different number of neurons - from 3-4 to 15-20 cells. The muscular layer of the uterine fundus of the control group of animals contains only smooth muscle cells going in different directions. Intramural ganglia were not identified. Between the bundles of smooth muscle cells there are connective tissue interlayers. Thus, intramural ganglions that have synaptic contacts with the preganglionic cholinergic fibers of the vagus nerve are visualized by staining the vagal trunks. Staining of intramural ganglia confirms their presynaptic regulation by the cholinergic fibers of the vagus nerve - bulbar regulation of the uterine fundus and its tubes. The functional role of the vagus nerve in the regulation of electromotor activity of the uterine fundus and its right tubr has been confirmed in our studies. 

5.       Conclusion 

The irritation of the vagus nerve leads to an increase in contraction of the smooth muscles of both the uterus and the proximal end of the right fallopian tube. Consequently, the cholinergic fibers of the vagus nerve are involved in the neural regulation of the female reproductive system. When analyzing chrono-inotropic relationships in systems of the right tube, the vagus nerve exerts predominantly inotropic influence, whereas in the uterus it is chronotropic. With regard to the effect of stimulation of the right vagus nerve on the contraction power, it should be noted that the effect predominates on the smooth muscles of the uterine fundus, which is probably due to a more powerful muscle layer in this section of the reproductive system. Bunches of smooth muscle cells go in different directions. In the thickness of the muscular tissue, blue neuronal ganglia, colored by toluidine, are surrounded by perineurium and containing different number of neurons - from 3-4 to 15-20 cells. 

The muscular layer of the uterine fundus of the control group of animals contains only smooth muscle cells going in different directions. Intramural ganglia were not identified. Between the bundles of smooth muscle cells there are connective tissue interlayers. Thus, intramural ganglions that have synaptic contacts with the preganglionic cholinergic fibers of the vagus nerve are visualized by staining the vagal trunks of experimental animals. Staining of intramural ganglia confirms their presynaptic regulation by the cholinergic fibers of the vagus nerve - bulbar regulation of the uterine fundus and its right tube. The functional role of the vagus nerve in the regulation of electromotor activity of the uterine fundus has been confirmed in studies. 

Table 1: Electromotor activity of the uterine fundus with stimulation of the vagus nerve.

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