Accelerated Electron Ionization-Induced Changes in the Myenteric Plexus of the Rat Stomach.

The influence of accelerated electrons on neuronal structures is scarcely explored compared to gamma and X-rays. This study aims to investigate the effects of accelerated electron radiation on some pivotal neurotransmitter circuits (cholinergic and serotonergic) of rats' myenteric plexus. Male Wistar rats were irradiated with an electron beam (9 MeV, 5 Gy) generated by a multimodality linear accelerator. The contractile activity of isolated smooth muscle samples from the gastric corpus was measured. Furthermore, an electrical stimulation (200 µs, 20 Hz, 50 s, 60 V) was performed on the samples and an assessment of the cholinergic and serotonergic circuits was made. Five days after irradiation, the recorded mechanical responses were biphasic-contraction/relaxation in controls and contraction/contraction in irradiated samples. The nature of the contractile phase of control samples was cholinergic with serotonin involvement. The relaxation phase involved ACh-induced nitric oxide release from gastric neurons. There was a significant increase in serotonergic involvement during the first and second contractile phases of the irradiated samples, along with a diminished role of acetylcholine in the first phase. This study demonstrates an increased involvement of serotonergic neurotransmitter circuits in the gastric myenteric plexus caused by radiation with accelerated electrons.

Effects of Electron Radiation on Serotonin Signaling and Reactivity of Rat Gastric Smooth Muscle.

Ionizing radiation in radiotherapy can disrupt cellular functions based on radiation type, energy, and dose. However, investigations on the effects of accelerated electrons, particularly on serotonin mediation, are limited. This study aimed to investigate changes in serotonin signal transduction (targeting 5-HT2A and 5-HT2B receptors) in gastric smooth muscle (SM) samples isolated from rats irradiated with accelerated electrons (linear accelerator Siemens Primus S/N 3561) and their effects on serotonin-induced reactions. The radiation effects were examined in samples prepared five days after the procedure. The contractile activity of smooth muscle samples was measured using an isometric method. The expression of 5-HT2A and 5-HT2B receptors was determined by immunohistochemical assay. Increased contractile reactivity to exogenous serotonin (1.10-8-1.10-4 mol/L) was observed in irradiated samples compared to controls. The expression of 5-HT2A and 5-HT2B receptors was significantly increased in the irradiated tissue. By selecting appropriate time intervals between equimolar (1.10-6 mol/L) sequential serotonin exposures, a process of desensitization associated with agonist-induced internalization was established in control samples, which was absent in irradiated samples. In conclusion, irradiation with accelerated electrons affects the agonist-induced receptor internalization of 5-HT2A and 5-HT2B receptors and increases their expression in rat gastric SM, which alters their contractile reactivity to exogenous serotonin.

Clostridium difficile toxins impact on rat colon smooth muscle reactivity.

AIM: The present study was conducted in an attempt to find possible direct mechanisms of action of Clostridium difficile toxins A and B (TCdA and TCdB) on contractility of isolated rat intestinal smooth muscles, as the contractive pathways affected by the toxins and responsible for motility disorders remain unclear. MATERIALS AND METHODS: Adult male Wistar rats were used in our experiments. Longitudinal smooth muscle (SM) preparations of proximal colon were isolated and their contractile activity was isometrically registered. The samples were mounted in tissue baths and exogenously treated with acetylcholine (ACh), serotonin (5-HT), dopamine, norepinephrine, TCdA and TCdB. The potential of TCdA and TCdB to affect the action of these mediators on SM activity was examined. RESULTS: The experiments have shown that exciting action of ACh and 5-HT on colonic contractility is enhanced by TCdA rather than TCdB. Conversely, relaxing effect of dopamine and norepinephrine on contractile activity of colonic SM is under impact of TCdB but not TcdA. TCdA has a stronger direct effect on in vitro SM sensitivity to ACh and 5-HT than TCdB. CONCLUSIONS: TCdA and TCdB affect directly the contractile reactivity of isolated rat colon smooth muscle. TCdA has a stronger direct effect on smooth muscle sensitivity to acetylcholine and 5-HT than TCdB. Such a trend has not been established for dopamine and norepinephrine.

Receptor-mediated biological effects of extracts obtained from three Asplenium species.

This study reports the effects of aqueous extracts obtained from three fern species of Bulgarian origin: Asplenium ceterach L., Asplenium scolopendrium L., and Asplenium trichomanes L. on the contractility and bioelectrogenesis of rat gastric smooth muscle tissues. In the concentration range 0.015-0.150 mg/mL the three extracts contracted smooth muscle tissues in a concentration-dependent manner. The contractions caused by A. ceterach L. and A. scolopendrium L. extracts (0.150 mg/mL) were reduced by ketanserin (5 × 10-7 and 5 × 10-6 mol/L), an antagonist of serotonin 5-HT2 receptor. The contraction evoked by A. trichomanes L. (0.150 mg/mL) was significantly reduced by 1 × 10-6 mol/L atropine, an antagonist of muscarinic receptors, and turned into relaxation against the background of 3 × 10-7 mol/L galantamine. After combined pretreatment with galantamine and l-arginine (5 × 10-4 mol/L), this relaxation become more pronounced. The study demonstrates that constituents of A. ceterach L. and A. scolopendrium L. extracts act as agonists of 5-HT2 receptors and cause contraction by activating serotonergic signaling system. A. trichomanes L.-induced reaction is an additive result of two opposite-in-character effects. The dominant contraction is initiated by inhibition of acetylcholinesterase activity. The relaxation develops with pre-inhibited acetylcholinesterase, it is significantly potentiated by l-arginine, and therefore associated with nitrergic signaling pathway.

Study on in Vivo Pial Vessels Alterations and Activity of Isolated Vascular Smooth Muscles in Abdominal Hypertension Rats.

BACKGROUND: Intra-abdominal hypertension is known as a factor affecting cerebral haemodynamics. Sustainably elevated abdominal pressure may disturb the balance of intracranial/blood pressure ratio, eventually developing perfusion pressure to drop. AIM: The aim of this study is to investigate the influence of artificially elevated intra-abdominal pressure upon brain pial vessels condition and contractile reactivity of isolated rat arteria carotis communis and vena jugularis to norepinephrine and serotonin. MATERIALS AND METHODS: The abdominal pressure of rats anaesthetized with xylazine 10 mg/kg and ketamine 100 mg/kg was increased up to 25 mm Hg by insufflation of air through venflon cannula and maintained for period of 1 to 3 hours. Craniotomy of left parietal area was carried out by micro drill. Open scull and cranial window techniques were applied. Outer diameters of superficial pial vessels were measured by USB digital microcamera (magnification up to 400x). Contractile reactivity of smooth muscle preparations from arteria carotis communis and vena jugularis of euthanized abdominal-hypertensive (AH) rats was registered isometrically. RESULTS: Increased smooth muscle reactivity of a. carotis communis from AH rats to serotonin (10-8-10-4 mol/l) but not to norepinephrine compared to controls was registered. The changes tended to be higher in long lasting (3 hours) exposure of AH rats. Increase in outer diameter of pial vessels during maintenance of abdominal hypertension in both open scull and cranial window techniques was found. CONCLUSIONS: The increased intra-abdominal pressure causes dilatation of small superficial cerebral blood vessels and increases the smooth muscle reactivity of isolated arteria carotis communis to 5-HT.

Changes in the Contractile Activity and Reactivity to 5-HT of Smooth Muscles of Rats Following Total Body Irradiation with Accelerated Electrons.

BACKGROUND: Besides its "classical" neurotransmitter function in the central and peripheral nervous systems, serotonin, or 5-hydroxytryptamine (5-HT) is also a local hormone in a number of tissues, including those of the GI tract. Radiation is known to be able to disrupt certain functions of the tract, modulated by 5-HT-signaling pathways, or the serotonin receptors themselves. AIM: The present investigation focused on clarifying the nature and extent of influence of an accelerated electron beam with energy of 9 MeV on the serotonergic mediation of healthy smooth muscle gastric tissue of rats following total body irradiation of the animals. MATERIALS AND METHODS: The study involved a control group and two experimental groups of animals exposed to 1 and 5 Gy, respectively, using Siemens Primus S/N 3561. Circular smooth muscle tissues were isolated from rats 1 hour and 18 hours after they were exposed to 1 and 5 Gy and also 5 days after irradiation from the rats that received a dose of 5 Gy in order to investigate the action of exogenous serotonin at increasing concentrations from 10-8 to 10-4 mol/l. The contractile reactivity of each group SM preparations was registered isometrically. RESULTS: Electron beams with energy of 9 MeV did not damage the contractile apparatus of gastric SM of rats and had a stimulating effect on contractility resulting from rapidly developing processes (1 hour) or later occurring once (5 days). CONCLUSIONS: Difference was observed in the importance of the factors of received dose, lapse of time from irradiation to investigation of SM tissues, and exogenous 5-HT concentration for the changes in SM reactivity in serotonin-induced tonic and phasic responses.

Biochemical Changes in Experimental Rat Model of Abdominal Compartment Syndrome.

BACKGROUND: Increased intra-abdominal pressure (IAP) causes tissue ischemia, subsequent hypoxia, and impairment of normal tissue metabolism. Elevation of IAP above 20 mmHg leads to progression of abdominal compartment syndrome (ACS) that is associated with organ dysfunction or failure not previously manifested. AIM: To evaluate the eff ects of diff erent grades and time of exposure to IAP on biochemical parameters and oxidative stress in organs aff ected by ischemia using previously developed rat model. RESULTS: Three experimental groups exposed to diff erent IAP and time frames were tested for liver, kidney, and pancreas injury by measuring the activities of tissue specifi c enzymes in blood serum. Elevated activities of aspartate aminotransferase, pancreatic amylase, lipase, and higher concentrations of D-lactate, urea, and creatinine were found in some of the experimental groups compared to a control group of animals not subjected to increased IAP. Increased levels of biomarkers of oxidative stress as well as decrease in concentration of the major cellular antioxidant glutathione indicated the presence of oxidative injury as a result of elevated IAP. CONCLUSIONS: The developed rat model is appropriate to study the mechanism and manifestation of tissue injury during diff erent grades of elevated IAP but also to test approaches aimed to attenuate the detrimental eff ects of ACS. This study also underlines the necessity of using not a single but a set of biochemical parameters in order to assess the severity of tissue injury during elevated IAP and progression to ACS.

Sensitizing effect of tacrine on M-cholinergic receptors in gastric smooth muscle of rats.

AIM: To find if tacrine exerts a sensitizing effect on the cholinergic receptors of gastric smooth muscles, and study some of the mechanisms inducing it and measure the relative intensity of tacrine's effects on contractile activity. MATERIAL AND METHODS: Isometric recording of the mechanical activity of gastric smooth muscle preparations; determination of acetyl-cholinesterase activity in smooth-muscle tissue homogenates using Ellman's method. RESULTS: We found that the threshold concentration for tacrine not reducing the acetylcholinesterase activity and not having an effect on the smooth muscle preparations was 1 x 10(-8) mol/l. This concentration, however, significantly increased the acetylcholine-induced contraction compared with the controls, after the smooth-muscle tissue was incubated for 60 or 100 min. Treating smooth-muscle preparations with tacrine in a concentration of 5 x 10(-6) mol/l triggered a contraction induced by the drug's anti-cholinesterase activity. A secondary contraction was induced after 38.6 +/- 5.6 min. There was no secondary contraction after the control acetylcholine-induced effect. Atropine (1 x 10(-6) mol/l) inhibits this effect. Preliminary treatment of smooth muscle preparations with hexamethonium (1 x 10(-6) mol/l) did not change significantly the intensity of the first phase of tacrine-induced contraction and shifted in time the appearance of the second contractile phase. CONCLUSION: Tacrine has a sensitizing effect on M-cholinergic receptors; it occurs after a long incubation of the gastric smooth muscles with the drug and is manifested as a secondary contraction which is shifted in time and is significantly inhibited by atropine.