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Biomedical subjects

E Atanassova

Publications and source records attributed to E Atanassova.

At least 37 records · Page 2Linked to original sources
PubMed1982

On the character of the electrical activity of the stomach, pyloric sphincter and duodenum of cats.

In cats with chronically implanted electrodes in the muscle wall of the gastro-intestinal tract, the electrical activity of the stomach (S) pyloric sphincter (PS) and duodenum (D) is characterized by cycles consisting of two phases: active--whereby 2 to 3 slow potential changes (SPC) are accompanied by spike potentials (SP) and a pause during which for 60-90 s only SPC are recorded. After bilateral transthoracic vagotomy there is a disruption of the cyclic character of the electrical activity in the investigated regions of the gastro-intestinal tract--SP from S and PS are recorded with each SPC. The active phase of the cycle from D is strongly prolonged at the expense of the shorter pause. This lasts for 1-2 days, after which there is a tendency towards shaping the cycles characteristic of the electrical activity of S, PS and D of cats. The pauses, however remain relatively short and the number of SP in the group is much greater. Gradually during the second month the character of the electrical activity of S, PS, and D approaches that prior to the vagotomy, but even until the 6th month after vagotomy the number of SP in the group is greater and the active phase of the cycle is longer. On the background of antagonists of the adrenoreceptors (propranolol--2 mg/kg and dihydroergotamine--300 micrograms/kg), the cyclic character of the electrical activity of S, PS and D is disturbed. The relatively rapid restoration of the cyclic character of cat S, PS and D after vagotomy is assumed to be the result of the organizing role of the intrinsic nervous system. The disturbance of the cyclic character after adrenoblockers demonstrates the significance of the balance between the cholinergic and adrenergic parts of the intrinsic nervous system for the realization of the cyclic character of the electrical activity of S, PS and D of cats.

Animals↗
PubMed1982

Character of the nerve transmission in different stomach regions.

A microelectrode study is performed of the postsynaptic potentials of single smooth-muscle cells from various regions of cat stomach. The smooth-muscle cells from the region of the fundus, the corpus along the small curvature, as well as from the middle region of the anterior wall, produce more frequently inhibitory responses to transmural electrical stimulation, while the cells of the cardia, of the corpus along the big curvature and the antrum respond predominantly by depolarization and contraction of the muscle strip (excitatory responses). Administration of atropine in doses of 10(-6) M blocks the excitatory postsynaptic potentials, which suggests that the majority of them are cholinergic. By adding adrenergic antagonists in a dose of 10(-6) M it is demonstrated that a part of the inhibitory responses are produced by nonadrenergic inhibitory nerve fibres. The differences in the nerve transmission of different stomach regions may be associated with the possibilities of exercising the reservoir or evacuative function of these regions.

Animals↗
PubMed1982

Histochemical study of the myenteric plexus following gastric resection on dogs.

Enzyme histochemical methods were used to follow up to changes within the myenteric plexus from 1 week to 7 months following subtotal Billroth I gastric resection in dogs. Different regions of the resected stomach were examined. The changes affected the neurons and the neuropil of the myenteric ganglia, the connecting strands and the nerve bundles and fibers within the muscle layers. The changes in size, from and enzyme activity of some myenteric neurons correspond to those observed during axon regeneration. The 2nd week showed a significant reduction of the nerve cell number in most of the examined regions of the resected stomach. Along with, the amitotic forms of cell division and immature nerve cells became more numerous. The enzyme activity of the latter increased with the time elapsed after resection, 7 months afterwards, the size of the myenteric ganglia in the resected stomach did not differ from those in the control dogs. There were some hypertrophic nerve cells with higher enzyme activity. Some changes presume the formation of new intramural ganglia. The changes in the myenteric neurons were accompanied by reactive changes in the non-neuronal elements. Hyperinnervation was observed in the gastric muscles.

Animals↗
PubMed1982

Changes in the character of electrical and contractile activities of isolated fundus with functional loading (Billroth I).

A 2/3 resection of the stomach with restoration of the continuity by a Billroth I anastomosis was carried out on dogs and cats. At different times, following surgery, electrical activity of the fundus wall was recorded in vitro using pressure electrodes. Contractile activity of isolated fundus strips from these animals was also studied. Electrical activity of the isolated fundus of an intact (non resected) stomach was characterized by irregular low-amplitude slow waves of a sinusoidal type with a frequency of about 2 cpm, and in rare cases of about 4 cpm. Mechanical activity of the non-resected fundus was mainly tonic. In the isolated resected stomach (gastric remnant), a regular slow wave rhythm of about 4 cpm was established. Slow waves gradually increased in amplitude, achieving a plateau potential configuration. They were associated with low-amplitude contractions. The mechanical activity of the fundus after resection became mainly phasic. For the early establishment of this rhythm and configuration it was important to retain part of the pacemaker area of the stomach in the gastric remnant. In this case, electrical and contractile activities of the fundus became similar to those of the corpus and antrum, probably as a result of the functional loading of the fundus after resection.

Action Potentials↗
PubMed1981

Changes in the character of the postsynaptic potentials of the fundic smooth-muscle cells after functional loading.

The electrical activity of the smooth-muscle cells of the intact fundus led off intracellularly by glass microelectrodes with a resistance of 30 to 50 M omega was characterized by slow sinusoidal waves with a frequency of 1 to 2 cpm and an amplitude of 5 to 8 mV. They preceded low-amplitude contractile waves. The membrane potential was 29 +/- 9.83 mV. The resection of 2/3 of the stomach resulted in an increase of the frequency of slow waves--about 4 cpm and of their amplitude--from 12 to 25 mV. The membrane potential became 41.25 +/- 10.59 mV. The slow waves of the fundus after resection had the shape of action potentials type plateau. The contractile waves had a high amplitude and occurred in the same rhythm. The smooth-muscle cells of the intact fundus responded to transmural stimulation mainly with a hyperpolarization, while the smooth-muscle cells of the fundus after resection of the stomach--with depolarization and contraction of the muscle strip. It is concluded that the functional loading leads to deep changes in the pattern of the electrical and contractile activities of the gastric remnant.

Animals↗
PubMed1980

Changes in the myoelectric complex of the stomach and the small intestine under the influence of the intrinsic nervous system.

Chronic experiments have been carried out on dogs with implanted silver bipolar ball-shaped electrodes on the muscle wall of the stomach and of the duodenum after transthoracic truncus vagotomy. The appearance of incoordination in the rhythm of the slow potentials of the corpus and antrum is followed by an increase in the spike activity of the stomach and duodenum. The percentage of the spike activity increases, the active periods of the myoelectric complex become longer, with a decrease and even obliteration of the quiescent periods. These changes are most pronounced during the second post-vagotomy month, after which the spike activity gradually decreases and quiescent periods appear again. Nevertheless, at the end of the 6th month after the vagotomy, the spike activity has higher values than before the vagotomy. Chemical sympathectomy with 6-OHDA results in 100 per cent spike activity of the stomach and duodenum and complete absence of quiescent periods. It is concluded that the intrinsic nervous system is capable of organizing the phases of the myoelectric complex in the cases of absence of influence of the extrinsic nervous system.

Action Potentials↗
PubMed1979

Character of the gastric and duodenal electrical activity after blocking of the adrenoreactive structures.

Experiments are carried out on six dogs with chronically implanted electrodes in the gastric wall and in the duodenum. The electrical activity of the stomach (EGMG) and of the duodenum (EEG) is recorded. The myoelectrical complex of the stomach consists of four phases. The first phase records only slow potentials and lasts 40--60 min. The appearance of spike activity in the duodenum is always preceded by EGMG activation. Intravenous injection of the specific blocker of the alpha-adrenergic structures (phentolamine -- 1 mg/kg) leads to the appearance of spike activity in EGMG and EEG. 50--60 per cent of the slow waves being accompanied by spike potentials. At the same time the frequency of the slow potentials from EGMG is also decreased. Application of beta-adrenoblocker (propranolol -- 2 mg/kg) does not change subatantially EGMG and EEG. Simultaneous administration of alpha- and beta-adrenoblockers prolongs spiking time in the stomach and duodenum (spike potentials are recorded for 120--180 min, duration in the background 40--50 min). The influence of the interactions of cholinergic and adrenergic structures on the character of EGMG and EEG is discussed.

Animals↗
PubMed1978

Character of the spike activity on both sides of duodenal transection depending on the regeneration of the intrinsic nervous system.

Experiments are carried out on dogs with transection of the duodenum followed by end-to-end anastomosis and chronically implanted silver ball-shaped electrodes on the muscle wall of the stomach and on the segments of the duodenum proximal and distal to the transection. Dissociation of the spike activity of the two duodenal segments is established after the operation. As early as the second week after the transection, parallel with this single group of spike potentials propagating through the anastomosis are also observed. With increasing the time interval from the operation propagation of the spike activity along the length of the muscle occurs more and more frequently. The difference in the percentage of spike activity of the two duodenal segments is greatest during the first and second months after the operation. At the beginning of the third month it decreases gradually to reach 10 per cent approximately during the fifth month after the operation. In preliminary vagotomized dogs the difference in the percentage of the spike activity is maintained around 20-30 per cent. In dogs with definitely separated segment of the duodenum this difference becomes great and there are no tendencies towards reduction even in the sixth month post operation. Histological studies of the material taken from the area of the anastomosis of animals at different post-transection periods, subjected to silver impregnation after the method of Bielschowsky-Gross, show regeneration of the severed nerve bundles of plexus myentericus Auerbachi. The restoration of the spreading of the spike activity along the length of the duodenum is associated with restoration of the nerve structures in the muscle wall of the duodenum.

Animals↗
PubMed1977

Modulation of the slow potentials frequency of the stomach under the effect of the intrinsic nervous system.

Chronic and in situ experiments on dogs have been carried out involving stomach transection at the level of incisura angularis. The electrical acivity of the muscle wall of the two stomach segments was recorded by silver bipolar ball-shaped electrodes. Two electrodes for myogenic stimulation were implanted in the distal segment. Transection caused dissociation of the slow potentials rhythm in both stomach segments: slow potentials frequency in the distal segment is considerably reduced. Infusion of cholino- and adreno-mimetics in the artery supplying the distal segment causes increase of the frequency of the slow potentials in the distal segment to reach the frequency of the proximal segment. Bocking of the intrinsic nervous system eliminates these responses. On the background myogenic stimulation induces increased frequency of the rhythm in the distal segment. It is concluded that the intrinsic nervous system plays a role in maintaining slow potentials frequency in the stomach at a higher level than the level characteristic of this stomach segment.

Action Potentials↗
PubMed1977

Increase in the intestinal slow-wave frequency below the transection through electrical stimulation.

Experiments are carried out on dogs with chronically implanted leading-off electrodes on both sides of the transection at the level of the proximal duodenum. A pair of stimulating electrodes are also implanted below the transection. Electrical stimulation with impulses synchronized with the slow waves generated by the segment proximal to the section (amplitude 3-7 V, delay 0.2 s and duration 0.5 s) as well as with periodic impulses (18-21 cpm, duration 0.2-0.5 s and amplitude 3-10 V) results in shortening of the period T of several slow waves from the distal segment. Subsequently the frequency of the slow waves from this segment approaches that of the proximal segment. The restoration of the slow-wave plateau at the beginning of the small intestine depends both on the amplitude and on the frequency of the stimulating impulses. On the background of antagonists of the cholinergic (atr. sulf. 200 microgram/kg) and of the adrenergic systems (propranolol 2 mg/kg and phentolamine 1 mg/kg), increasing the frequency of the slow waves of the segment which is distal to the section requires an increase in the amplitude of the stimulating impulses. The role of the intrinsic nervous system for the assimilation of the slow-wave rhythm from the distal segment by the proximal one is discussed.

Animals↗
PubMed1976

Disturbances in the electrical and contractile gastric activities after bilateral transthoracic vagotomy.

Experiments were made on four dogs with chronically implanted electrodes. Fistula according to Bassov was made in one of the animals, and in each of the remaining three - two semiconductor silicon tensotransducers were sewn to the gastric wall. Bilateral transthoracic vagotomy results in inco-ordination between the rhythm of slow potentials generation from the body and from the antrum of the stomach. Slow potentials and contractions with frequencies usual for the stomach are recorded from the body of the stomach, while in the antrum there appear from time to time bursts of slow potential groups with relatively high frequency. These groups are not followed by contractions of the stomach wall or by changes in the intragastric pressure. Bilateral transthoracic vagotomy leads to disturbances in the conduction of the slow potential generated in the proximal segments of the stomach, as well as to distrubances in the propagation of the peristaltic wave.

Action Potentials↗
PubMed1976

Dynamics of the partial restoration of slow-wave frequency of the duodenum below transection.

Transection of the proximal duodenum of dogs was followed by end-to-end anastomosis. The electrical activity of the duodenal wall of both segments was recorded. On the background of decreased slow-wave frequency below the section single slow waves were observed with duration similar to that of the slow waves above the section. In the days after surgery their number increased, small groups of such waves appearing during and after spike activity. In some of the experiments from the end of the first month of the sixth month after surgery the slow wave frequency below the section approached the slow wave rhythm above the section as evidenced by the histograms. This was a temporary phenomen, which was partly eliminated by cholinergic and alpha- and beta-adrenergic antagonists. Such a phenomenon was also observed in definitively spearated distal segments of the duodenum. Histological examination of intestinal wall taken from the area of anastomosis showed on the 3rd day the presence of single smooth-muscle cells among the granulation tissue, filling the gap between the wound edges; on the 6th day the number of these cells increased and on the 9th and 12th day they formed small groups. From the end of the first month to the sixth month small sheaves of smooth-muscle cells were observed in the cicatricial tissue. It is concluded that the intrinsic nervous system keeps the slow wave frequency below the duodenal transection at a higher level than the smooth muscle cell regeneration might ensure.

Animals↗