[ROLE OF MAST CELLS IN BRONCHIAL CONTRACTION IN NONALLERGIC OBSTRUCTIVE LUNG PATHOLOGY]

In model of chronic obstructive pulmonary disease induced in rats by 60-day intermittent exposure to nitrogen dioxide mast cells participation in the mechanism of bronchial smooth muscle contractile activity patterns was evaluated. Since the 31st day, one group of rats was inhaled with sodium cromoglycate every day before the nitrogen dioxide exposure to stabilize the mast cell membrane. The other group (control) hasn’t been treated. Isometric contraction of the bronchial isolated preparations in response to nerve or smooth muscle stimulation were determined. Inhibition of mast cell degranulation and the release of endogenous histamine by stabilizing cell membranes prevented the development of bronchial smooth muscle hyperactivity caused by prolonged inhalation of nitrogen dioxide. It is believed that a mechanism to increase the contractile activity of the bronchial wall smooth muscles is mediated by activation of the transmembrane adenosine receptor in resident mast cells, leading to their partial degranulation with release of histamine, acting on the histamine Hl-receptors with the launch of reflex pathways through intramural ganglion neurons.

[THE INFLUENCE OF HISTAMINE ON THE EFFECTOR NEURONS OF INTRAMURAL GANGLIA OF THE TRACHEA AND BRONCHI]

We considered the influence of the neurons of intramural ganglia in the reaction of the smooth muscle trachea and bronchi caused by electric field stimulation, by the action of histamine. We studied the effect of neurons of intramural ganglia in the activity of the smooth muscle trachea and bronchi in the action of low doses of histamine (0,1 and 10 μg/ml), L-NAME and hexamethonium. It was shown the blockade of neuronal transmission decreased the contraction of the smooth muscles trachea and bronchi by stimulation of the afferent nerve structures. The smooth muscle relaxation under the influence of hexamethonium was also reduced. Histamine and hexamethonium increased contractile activity and increased the amplitude of the relaxation of the trachea and bronchi. The inhibition of NO- synthesis did not affect on the contraction, but reduced the relaxation of the trachea and bronchi. Histamine and L-NAME enhanced contractile activity, but not modified smooth muscle relaxation. Concluded that the neurons of intramural ganglia have an inhibitory effect on the smooth muscle of the trachea and bronchi and may have a modulating effect on contraction and dilatation of the smooth muscles of the airways.

[Role intramural ganglion airway on action of histamine]

Influence of low concentration histamine on reactivity isolated trachea and bronchus preparations of rat induced field stimulation were studied. Application of 0.01-10 mkg histamine decreased responses preparation of trachea to 83% and bronchus to 79% at smooth muscle stimulation dose-depended manner. At postganglionic nerves stimulation histamine potentiated contraction of trachea without ganglions to 123%, trachea with ganglions to 110% and decreased contraction of bronchus to 87%. At stimulation ofpreganglionic nerves histamine evoked insignificant changes of contraction. With novocaine treatment of preparations histamine decreased responses of trachea by 19-30% at preganglionic stimulation, while responses of bronchus reduced by 8.2% only. Capsaicin treatment potentiated responses of trachea and bronchus on the effect of histamine induced preganglionic stimulation by 12-14%. We conclude that the action of histamine depends on the presence of ganglions and kind of stimulation. Different structures airways have various availability histamine-receptors and it determines the reaction of smooth muscle for histamine.

[Effect of different therapy options on bronchial contraction in rats with modeled obstructive pulmonary disease]

In the model of chronic obstructive pulmonary disease, produced in rats by 60-day exposure to nitrogen dioxide, the effect of different options of combination therapy (corticosteroids, anticholinergics, adrenergic agonists) on the functional state of the bronchi was studied. The contractile activity of strips of the bronchi caused by nerve or smooth muscle stimulation was evaluated. Corticosteroid monotherapy resulted in deterioration of the functional state of the bronchial wall neuromuscular apparatus due to corticosteroid resistance, evolving under the influence of long-term exposure to nitrogen dioxide. Application of M-anticholinergic tiotropium had a beneficial effect on the functional state of the bronchi smooth muscles, leading to the full restoration of the bronchial wall contractile activity and removal the morphological manifestations of inflammatory lung tissue remodeling. Most effective in terms of impact on the functional state of the bronchial wall neuromuscular apparatus was corticosteroid therapy combined with M-cholinolytik or beta2-adrenoagonist.

[Effect of endotelioprotectors on the tone of pulmonary arteries and bronchi in the model of obstructive lung pathology]

In the model of chronic obstructive pulmonary disease (COPD), produced in rats by 60-day exposure to nitrogen dioxide, the effect of drugs with endotelioprotector properties (sulodexide and rosuvastatin) on the functional state of small pulmonary arteries and bronchi was studied. We evaluated the contractile activity of smooth muscle strips of the bronchi caused by stimulation of the nerves or muscles, and changes in tone of isolated pulmonary artery rings at the application of reagents-vasodilators. The use of sulodexide promoted restoration NO-dependent mechanism of vasodilatation and improved β-adrenergic regulation of the pulmonary artery tone. The use of rosuvastatin had no effect on the dilator activity of pulmonary arteries. Both drugs improved the functional status of the bronchial smooth muscles and intrabronchial nervous system that controls the contractile activity of smooth muscle structures of the airways. The results of the study suggest that the one-way relaxing effect of sulodexide on pulmonary arterial and bronchial smooth muscles enables the recovery of coordinated regulation of the tone of these structures, which is essential for maintaining the optimal ratio of ventilation and pulmonary blood flow for efficient gas exchange.

Protective effect of fenspiride on the bronchi in rats with chronic obstructive pulmonary disease

We studied the effect of a non-steroidal anti-inflammatory drug fenspiride on contractive activity of bronchial smooth muscles on the model of chronic obstructive pulmonary disease of rats induced by 60-day exposure to nitrogen dioxide. The administration of fenspiride during the acute stage of the disease (day 15) abolished the constricting effect of the pollutant on the bronchial smooth muscles. Dilatation effect of fenspiride in a low dose (0.15 mg/kg) was mediated by its interaction with nerve endings of bronchial capsaicin-sensitive nerve C-fibers. The interaction of drug with receptors of C-fibers prevented neurogenic inflammation, which was confirmed by the absence of structural changes in the lungs typical of this pathology. The broncholytic effect of fenspiride in a high dose (15 mg/kg) was mediated by not only afferent pathways, but also its direct relaxing action on smooth muscle cells. The observed anti-inflammatory and bronchodilatation effect of fenspiride in very low doses can be used for prevention of chronic obstructive pulmonary disease in risk-group patients contacting with aggressive environmental factors.

[Changes in pulmonary arteries dilatation reserve during chronic obstructive pulmonary disease model formation]

Model of chronic obstructive pulmonary disease (COPD) was induced in rats by nitrogen dioxide inhalation for 60 days. The effect of reagents-vasodilators on the isolated pulmonary arteries with a diameter less than 0.5 mm was studied in 15, 30 and 60 days of COPD induction. All vasodilators (beta-adrenoreceptor agonist izopreterenol, nitric oxide donor nitrosorbid, acetylcholine, activator of C-fibers capsaicin, corticosteroid beclometasone) dose-dependently decreased vascular tone of pulmonary arteries isolated from intact rats. On extension nitrogen dioxide exposure pulmonary arteries responded to the impact of all vasodilators by smaller relaxation. Dose-dependence of dilatation reaction disappeared. In the process of COPD model formation functioning of almost all pulmonary arterial wall neurotransmitter systems were broken. This led to decrease in vasodilators influence on vascular tone and could facilitate the development of pulmonary hypertension which is typical of COPD.

[Determination of circulation disturbance in the rat lungs in modelling of chronic obstructive disease]

Development of chronic obstructive pulmonary disease (COPD) involves not only the bronchial and respiratory areas of the lungs, but also the system of pulmonary circulation, which begins with the defeat of capillary blood flow. One of radiological methods of studying lung microcirculatory functions is perfusion scintigraphy. We designed the technique of radiological examination and identified its abilities in determination of the role of vascular dysfunctions in experimental model of development of COPD. We assessed the results of pharmacological agents that affect the microcirculatory bed of the lungs and smooth muscles of pulmonary arteries in rats. Studies have shown the promise of the possibility of using the drug sulodexide for studying impaired endothelial function in clinical practice.

[Heterogeneity of the rat respiratory way responses to serotonin]

In stimulation of preganglionic and postganglionic nervous fibres of the trachea and stimulation of preganglionic nervous fibres of the bronchi, serotonin strengthened reduction of a smooth muscle to 114 %. Methysergide (1.0 mkg) reduced responses to serotonin to 74-77 % on the trachea and practically didn't influence the bronchi. Against ketanserinum (1.0 mkg) serotonin is dose-dependent and reduced trachea's amplitude of the constriction to 60-63% and bronchi's amplitude of the constriction to 75-79%. Hexamethonium (100.0 mkg) reduced the serotonin amplitude of the constriction of the trachea at stimulation of postganglionic nerve to 64% and the bronchi at all kinds of irritation to 82-84%. Atropine (1.0 mkg) reduced effect of serotonin in stimulation of postganglionic nerve and tracheal smooth muscles to 75-77%. On preparations of bronchi, atropine reduced the serotonin effects in stimulation of preganglionic nervous fibres to 83% and strengthened to 117% in smooth muscles in stimulation of preganglionic nerve. Thus, there is heterogeneity of responses of smooth muscles of different sites of the tracheal-bronchial pathways of the rat to serotonin.

[Broncholytic effect of prednisolon in the rats inhaled with nitrogen dioxide]

In the rat model of chronic obstructive pulmonary disease, the dilatation effect of prednisolon was most obvious after 15 days of nitrogen dioxide inhalation. In a longer inhalation, the dilatation effect decreases, and on the 90th day of the inhalation prednisolon enhances contraction of the trachea and bronchi. Prednisolon seems to act upon the respiratory tract via interaction with endings of afferent C-fibres. In prolonged inhalation of nitrogen dioxide, resistance against corticosteroids develops as the result of the C-fibre ending inactivation.

[Alteration of trachea and bronchi smooth muscles constriction under long inhalation of dioxide nitrogen by rats]

On insulated preparation of trachea and bronchi, change of the smooth muscles constriction was studied in rats inhaling dioxide nitrogen during 15, 30 and 60 days. The inhalation enhanced 1.5-fold and bronchi 2.5-fold responses of tracheal smooth muscles to stimulation of preganglionic nerve. The delay of the response in both events increased 1.3-fold. Long repeated stimulation caused a further increase of the constriction of tracheas and bronchi (1.32-fold). Blocking receptor with Novocain (1.0 mcg/ml) reduced the amplitude of the constriction and enhanced the response delay. After 30 days of inhalation, repeated nerve stimulations enhanced the amplitude of the constriction up to 120%, but after 60 days it reduced the amplitude of the constriction to 71 and 77% in preparations of tracheas and bronchi, respectively. In our opinion, long inhalation of dioxide nitrogen broke functioning of local lung nervous system controlling activity of the smooth muscles. The research results indicate important role of neuron functional module in pathology of the respiratory ways caused inhalation of dioxide nitrogen.

[Functional disturbances in the nervous structures of the respiratory tract in rats following nitrogen dioxide inhalation]

The functional state of rat's airway smooth muscle was not changed after nitrogen dioxide inhalation for 30 days. The smooth muscle contraction increased only at second stimulation of preganglionic nervous fibers. Removal of mucosa or Novocain blockade of receptors decreased control smooth contraction at nerve and muscle fiber stimulation but the repeated stimulation of nerve increased the muscle contraction. The processing of trachea and bronchus preparations by prednisolon (1-10 microg/ml) decreased muscle reactions to 12% only at nerve stimulation. Prednisolon didn't change reactions of preparations with removed or blockaded receptors induced by nerve stimulation, but prednisolon (10 microg/ml) increased contraction at muscle stimulation. The relax effect of prednisolon on airway smooth muscle realizes via tracheobronchial receptors. High doses of prednisolon may direct effect on muscle increasing its contraction.

[Effect of prednisolon on trachea smooth muscle of normal rats and rats with fibrosing alveolitis]

Effect of prednisolone on isolated preparations of trachea of normal rats and rats with fibrosing alveolitis was studied. Prednisolone at a concentration of 0.4 microg/l decreased responses of smooth muscle on stimulation of preganglionar nerve fibers at trachea areas with intramural ganglia in rats with acute alveolitis by 48%, while in normal rats--by 19% of control. In trachea preparations without ganglia, prednisolone at a dose of 10 microg/l decreased responses of muscle to the nerve fiber stimulation by 21.3%. The higher prednisolone doses were less efficient: 0.1-10 microg/l glucocorticoid practically did not affect the smooth muscle responses produced by stimulation of muscle cells. In rats with fibrosing alveolitis, 10 microg/l prednisolone restored the smooth muscle responses to control values in preparations of trachea with intramural ganglia. After the prednisolone treatment, amplitude of the rat trachea muscle contraction in response to the nerve fiber electric stimulation did not differ statistically significantly from control and 0.1-10 microg/l prednisolone did not change the response value. The conclusion is made that prednisolone affected the diseased rats more efficiently than the healthy animals. The character of the glucocorticoid effect depends on the presence of intramural ganglia in the trachea wall.

[Involvement of adenylyn cyclase signaling mechanisms in relaxing effect of relaxin and insulin on the rat uterus, trachea and human myometrium]

Participation of adenylyl cyclase signaling mechanisms of relaxin and insulin action in their regulating influence on the process of relaxation of the rat uterine and tracheal smooth muscles and human myometrium was shown. The study was based on the discovery of novel adenylyl cyclase signaling mechanisms of relaxin and insulin action in the muscle of vertebrates which involve: receptor --> Gi protein (betagamma dimer) --> phosphatidylinositol-3-kinase --> protein kinase Csigma (zeta) --> Gs protein --> adenylyl cyclase --> cAMP. In the rat uterus, trachea and human myometrium, relaxin, insulin and isoproterenol induced relaxation of KCl-contraction. The order of efficiency of the agents based upon their ability to induce the inhibiting effect on the KCl-contraction was as follows: relaxin = insulin > isoproterenol. The hormones induce activating effect on adenylyl cyclase leading to production of cAMP in the rat uterine and tracheal smooth muscles and human myometrium. It is shown that cAMP reproduces relaxing effect of the hormones under study. Thus, the involvement of novel adenylyl cyclase signaling mechanisms of relaxin and insulin action in realization of their relaxation effect on rat uterus, trachea and human myometrium was revealed for the first time.

Interaction of histamine and glucocorticoids with neural structures of the respiratory tract

The effects of dexamethasone on the actions of histamine on isolated tissue and large bronchus preparations and the interactions of these substances with intramural neural structures were studied. Low histamine concentrations (10(-12)-10(-8) g/ml) decreased muscle responses induced by stimulation of preganglionic nerve fibers, while high concentrations (10(-7)-10(-4) g/ml) increased these responses. Dexamethasone at concentrations of 10(-7)-10(-6) g/ml decreased muscle responses, while concentrations of 10(-5)-10(-6) g/ml produced biphasic changes in responses. Dexamethasone decreased the effects of histamine at high concentrations. Atropine eliminated the effects of simultaneous application of histamine and dexamethasone on respiratory tract preparations; hexamethonium blocked the effects of substances associated with decreased responses and had virtually no effect on those potentiating responses. Novocaine eliminated the actions of histamine at low and high concentrations and the dilatory effect of dexamethasone. These experimental results led to the conclusion that changes in the responses of muscles from the rat respiratory tract induced by stimulation of preganglionic nerve fibers were modified by low concentrations of histamine and dexamethasone and that these modifications were associated with interactions of these substances with tracheobronchial receptors.

[Interactions of histamine and glucocorticoids with nerve structures of respiration passages]

Histamine was shown to exert various effects upon respiratory pathway wall's structures in rats. Glucocorticoids were shown to inhibit an increase in intracellular calcium induced by histamine. This investigation involved study of the interaction mechanisms between histamine and dexamethasone, on one hand, and intramural neural structures, on the other hand.

[Effect of histamine on duration of phases of the respiration cycle]

Histamine produced either a bronchodilation or a bronchoconstriction in rats. In a 0.01-1.0 mcg/ml concentration histamine augmented the contractions amplitude in electrical stimulation of the trachea, in a 10-100 mcg/ml concentration histamine enhances the muscle tone thus decreasing the induced contractions. The histamine effects seems to be connected with its prevailing influence on different structures of the airways depending on the concentration. Its high concentrations act directly on the smooth muscle whereas its lower concentration affects receptors signaling the functional modules of the metasympathetic nervous system within the intramural ganglia of the trachea.

[Functional characteristics of ganglion neurons of the lower respiratory system]

In article it was shown our and literature date, in which examine of structural and electrophysiological properties of trachea and bronchi intramural neurons plexus. The interaction between different neurons are studied. It was shown that on the basis functional properties a neurons of intramural ganglion are divided on oscillatory, sensory, tonic and effectoric exciteties and inhibitory activation of muscle cells. The neurons are united to functional models controlling work of airway wall smooth muscle.

[The evaluation of the action of microbial enzyme preparations on the motility of the rat and canine small intestine]

The effect of combined microbial enzyme agents trizyme and triaze containing alkaline and neutral proteases, lipase, and amilase on the evacuation capacity of the small intestine of conscious rats and of the dog small intestine operated on by the Thiry-Vella method. Therapeutic doses of the enzymatic agents had no noticeable effect on the evacuation function of the intestine. The contraction of bands of the rat intestine induced by electrical stimulation depended on the concentration of the perfusate of the solution of the enzymatic agents. Low concentration of the agents caused no effect or weakly activated the contractions of the smooth intestinal muscles. Doses of the agents higher than the mean therapeutic doses caused decrease of the contraction amplitude of the intestinal bands by 30-40%.

[Mediators of the local reflex arc in airways of the rat and guinea pig]

Transmission of neural pulses from afferents to functional module's neurons in rats and guinea pigs can be carried out with the aid of the P substance. Further transmission to a smooth muscle of the trachea occurs through a neuro-muscular junction with acetylcholine as a transmitter. Transmission of inhibitory influences from the tracheo-bronchial receptors to the smooth muscle is carried out via nicotinic cholinoreceptors. Adrenergic mechanisms can modulate neural transmission at the level of intramural ganglia.

[The mechanisms of serotonin participation in the smooth-muscle reactions of the trachea]

Serotonin was shown to induce a dose-dependent enhancement of the tonus of the rat and guinea pig trachea smooth muscle: low concentrations facilitated the contractile activity, whereas high doses relaxed the muscle via transmural stimulation of nervous fibres. The serotonin receptors were found to be located at the postganglionic cholinergic fibres and metasympathetic neurons of the trachea intramural ganglia. Presence of the receptors at the trachea smooth muscle cells seems to be highly improbable.

[The local reflex responses of rat tracheal smooth muscle]

In isolated thoracic segments of the trachea, the effect of novocain involved an increase in the muscle tone and an initial augmentation of the muscle responses to transmural stimulation with subsequent reversal of the reaction. The effect seems to be based on blockade of a sensory link of local reflex arches implemented by the metasympathetic nervous system.

[The smooth-muscle adrenoreceptors of rat and guinea pig tracheas]

Effects of adrenaline and noradrenaline upon the smooth muscle contractile activity were shown to have a biphasic character. In low concentrations the effects coincide with that of phenylephrine, in high concentrations--with that of isadrine. The alpha-adrenoreceptors seem to be located at the metasympathetic neurons of the intramural ganglia and at postganglionic cholinergic nervous fibers, whereas the beta-adrenoreceptors at the smooth muscle cells.

[The metasympathetic mechanisms supporting the constancy and stability of the internal environment in vertebrates]

The data were obtained with the aid of extracellular recording of unit activity in the cardial, enteral and respiratory parts of the metasympathetic nervous system, staining of the neural tissue preparations of atrial walls, intestine and lower part of the guinea pig trachea. The neurons were shown to be very sensitive to the main homeostatic contants: pH of the perfusion solution, its temperature and the grade of oxygenation. These structures were shown to take a direct part in maintenance of the constancy and stability of the organism inner milieu. Sympathetic nervous system differs from the above system in that the former is the system of transmission, defence, mobilisation of resources which is necessary for active interaction of the organism with ambient milieu.

[The mechanisms of the rhythmic movements of the tracheal smooth-muscle wall during breathing]

Change of the lumen of respiratory pathways in breathing was shown to be determined by the electric and mechanical activity of the smooth muscle wall. The rhythmic activity of the smooth muscle is formed by the neuronal apparatus of intramural ganglia. The correlation of this apparatus work with the respiratory centre is performed via the efferents of the n. vagus.

[The action of adrenergic substances on the smooth muscle of the rat trachea]

Adrenalin and noradrenaline first induced an increase in the trachea smooth muscle response with its subsequent decline in rats. Phentolamine decreases the muscle responses in its thoracic part and practically does not affect it in the cervical segments. The adrenergic neural fibres seem to terminate at the smooth muscle cells and the neurons of intramural ganglia.

[The comparative action of cholinergic substances on the cervical and thoracic trachea of the rat]

Different reactions were found in the cervical and thoracal parts of the trachea to application of acetylcholine, cholinomimetics and cholinolytics. The effect of acetylcholine on the cervical part is associated with muscarinic receptors in muscles. In the thoracal trachea, the effect of acetylcholine at a low concentration is associated mainly with muscle cholinoreceptors, whereas at high concentrations its effect is determined by both myogenic and neurogenic factors. Cholinergic systems of the intramural ganglia are involved in contraction and relaxation of tracheal smooth muscle in rats.

[Relaxant effects of oligopeptides isolated from the tracheal mucosa and pulmonary parenchyma on the smooth muscle of isolated rat trachea]

Relaxant effect of oligopeptides extracted from tracheal mucosa (PTM), lung parenchyma (PLP), aortal wall (PAW) and thymic gland (PTG) was investigated using acetylcholine-induced constriction of tracheal strips. Time of 50 percent relaxation of constricted strips treated with saline, atropine or peptides was measured. Both PTM and PLP in concentrations 10(-6)-10(-3) g/ml accelerated relaxation in dose-dependent manner, however this effect was less prominent compared with atropine. Relaxant effect of PTM was found using different parts of trachea (cervical of thoracal), indicating independence of PTM action of intramural ganglia which are present only in the thoracal part. PAW and PTG did not show any significant effect on relaxation time. These results suggest the presence of oligopeptides, capable to relax airways smooth muscle, in tracheal mucosa and lung parenchyma.

[The electrical activity of the dorsal wall of the rat trachea]

It was demonstrated that changes in the diameter of respiratory pathways during respiration process are associated with the activity of the plain muscles of the walls. Formation of this activity in a form of potential groups during inspiration phase is realized by the peripheral nervous apparatus. Co-ordination of the activity of this apparatus with the work of the respiratory center is realized via efferent vagal fibres.

[The effect of sensitization to the electrical activity of the muscles of the lower respiratory tract in the rat]

The electrical activity of the smooth muscle of the trachea was studied on sensibilized ovalbumine rats. The role of intramural ganglions of the airway was shown.

[Effect of cholinergic substances on the spontaneous activity of lower respiratory tract neurons]

Acetylcholine and low concentrations of nicotine were shown to increase firing rate, to induce grouping of spikes of spontaneously active cells and to activate "silent" neurons. High concentrations of nicotine exert a biphasic (excitatory-inhibitory) effect. Atropine just alters and benzohexonium suppresses the spontaneous unit activity. Changes in the unit activity seem to stem from an interaction of cholinergic substances with the nicotine and muscarine cholinoreceptors. Neurons with a mixed type activity were found to receive inhibitory cholinergic projections.

[Analysis of the spike activity of neurons of the ganglia of the muscular wall of the respiratory tract]

Neuronal impulse activity of the dorsal muscular wall's micro-ganglia was studied in isolated preparations of the rat trachea. Neurons with single and mixed types of spike generation were revealed. A separate group included neurons responding to mechanical stimulation. Activating, inhibiting and regulating connections were revealed among active neurons. General and specific features of the respiratory and other parts of the metasympathetic nervous system are discussed.

[Background activity of neurons of the tracheal plexus in the rat]

Morphological structure of the nerve plexus of the rat tracheal dorsal muscle wall is described and electrophysiological data on neuronal activity of this plexus are presented. Extracellular recording revealed two types of spontaneous activity including a single-spike type and a serial-spike type. The presence of excitatory and inhibitory interaction between neurons of a single ganglion is shown. Characteristic features of the tracheal part are discussed in comparison with other parts of the metasympathetic system.

[Certain functional connections of neurons control the walking of the cockroach Periplaneta americana]

On isolated abdominal nervous chain of the cockroach studies have been made of the responses of motoneurones of the thoracic ganglion to electrical stimulation of afferent axons of the leg nerve under normal conditions and during application of an anticholinesterase drug, GD-7. Depending on the type of stimulated axons, monosynaptic response, as well as polysynaptic phasic and tonic responses of motoneurones were recorded. A scheme of activation of motoneurones is suggested which evokes slow contractions of muscles in cockroach extremities.