Muscarinic regulation of neonatal rat bladder spontaneous contractions

In vitro preparations of whole urinary bladders of neonatal rats exhibit prominent myogenic spontaneous contractions, the amplitude and frequency of which can be increased by muscarinic agonists. The muscarinic receptor subtype responsible for this facilitation was examined in the present experiments. Basal spontaneous contractions in bladders from 1- to 2-wk-old Sprague-Dawley rats were not affected by M2 or M3 receptor antagonists. However, administration of 0.5 microM physostigmine, an anticholinesterase agent that increases the levels of endogenous acetylcholine, or 50-100 nM carbachol, a cholinergic agonist at low concentrations, which did not cause tonic contractions, significantly augmented the frequency and amplitude of spontaneous contractions. Blockade of M2 receptors with 0.1 microM AF-DX 116 or 1 microM methoctramine or blockade of M3 receptors with 50 nM 4-diphenylacetoxy-N-methylpiperidine methiodide or 0.1 microM 4-diphenylacetoxy-N-(2-chloroethyl)piperidine hydrochloride (4-DAMP mustard) reversed the physostigmine and carbachol responses. M2 and M3 receptor blockade did not alter the facilitation of spontaneous contractions induced by 10 nM BAY K 8644, an L-type Ca2+ channel opener, or 0.1 microM iberiotoxin, a large-conductance Ca2+-activated K+ channel blocker. NS-1619 (30 microM), a large-conductance Ca2+-activated K+ channel opener, decreased carbachol-augmented spontaneous contractions. These results suggest that spontaneous contractions in the neonatal rat bladder are enhanced by activation of M2 and M3 receptors by endogenous acetylcholine released in the presence of an anticholinesterase agent or a cholinergic receptor agonist.     

Effect of nifedipine on electrophysiological properties of rat ureter spontaneous activity

The work deals with effect of various concentrations of nifedipine on the slow and fast spontaneous activities evoked in the perivesical and perirenal areas of the rat ureter. Whereas in the proximal zone of the organ at the low dose of nifedipine (0.06 and 0.12 mg/kg), inhibition is revealed both of slow waves and of their corresponding spikes, in the perivesical part the opposite effect is observed. Besides, with further increase of the nifedipine dose to 0.15 and 0.2 mg/kg, in the ureter area adjacent to the urinary bladder, alongside with acceleration of slow pacemaker oscillations, the appearance of the antiperistaltically directed action potentials is also possible.     

Effect of histamine on spontaneous rhythmogenesis of the guinea pig ureter

Histamine changed characteristics of the perinephric spontaneous spike activity and of the spreading electrical wave. It was shown that histamine could activate latent pacemakers of the ureter's middle area. Morphological picture of the histamine effect was also shown.     

The functional role of the pedunculopontine nucleus in the regulation of the electrical activity of entopeduncular neurons in the rat

The purpose of this study was to investigate the influence of the pedunculopontine nucleus (PPN) on the electrical activity of entopeduncular nucleus (EP) in the rat and to analyze the influence of the subthalamic nucleus (STN) on the PPN-evoked responses of EP cells. Most of the EP neurons recorded (65.1%) were identified electrophysiologically as output cells projecting to the lateral habenula while only a minority (3.8%) were output cells to the PPN. Stimulation of the PPN in intact rats caused a short-latency (2.5 +/- 2.0, S.D. ms) activation in 22.6% and suppression of activity in 8.5% of EP neurons recorded. The mean impulse rate of EP neurons in intact rats was 27.0 +/- 5.5, S.D. imp./s and the overall mean interspike interval 36.8 +/- 7.1, S.D. ms. In rats where the PPN had been destroyed 10-12 days before recording by a local microinjection of kainic acid only a few EP neurons were still responsive to stimulation of the PPN showing suppression of activity. In these rats the kainate lesion slowed the impulse spontaneous activity to 14.3 +/- 6.3, S.D. imp./s and markedly altered the distribution of interspike intervals in 62.5% of the EP neurons recorded. The overall mean interspike interval in this group of deregulated neurons was 68.2 +/- 20.1, S.D. ms. A small kainate lesion of the STN placed 4-5 days before recording, on the other hand, did not affect the spontaneous activity of EP cells but increased the percentage of cells which were activated (43.6%) by stimulating the PPN. The present data demonstrate a predominant activatory influence of the PPN on EP cells and suggest that destruction of the STN may affect the responsiveness of entopeduncular cells to stimulation of the PPN possibly through the removal of a tonic inhibitory STN influence on the EP.     

Effect of dimedrol on the regulation by histamine of the pacemaker activity of the cat ureter

A certain concentration of Dimedrol (0.5 x 10(-6) mol/l) turned out to be capable of neutralising the histamine regulation of the slow-wave activity. The histamine H1-receptors were shown to modulate the cat general pace-maker's activity as well as the Na+ mechanism of the slow wave genesis.     

The role of GABA-ergic regulation in organizing spontaneous and evoked activity of the septal neurons

Effects of GABA, pentobarbital and picrotoxin upon spontaneous and evoked activity of neurones of the medial septal nucleus and the nucleus of the diagonal band (MS-DB) were investigated in the guinea pig septal slices. GABA and pentobarbital have similar effect upon all neurones, but the cells with a regular single spike and rhythmic burst activity of pacemaker type were less sensitive to their inhibitory influence. Picrotoxin affects neither frequency, nor pattern of activity. Electrical stimulation of the medial forebrain bundle evoked initial suppression of activity in majority of the neurones (74%); the remaining cells reacted mainly with an initial burst. GABA and pentobarbital increased the duration of the initial inhibition and revealed it in all cells with initial excitation in the control state. Picrotoxin did not influence this type of response, but revealed initial short-latency bursts in the cells with inhibitory effect in control state. The experiments show double nature of the effect of afferent stimulation controlling the activity of the MS-DB neurones. The mechanism of synchronization of the rhythmic activity in MS-DB, resulting in generation of the hippocampal theta-rhythm, is discussed.     

Developmental changes in spontaneous smooth muscle activity in the neonatal rat urinary bladder

Changes in spontaneous activity of the urinary bladder during postnatal development were examined in muscle strips from the base and dome of bladders from 1- to 5-wk-old rats. Activity was analyzed using fast Fourier transformation (FFT), nonlinear cross prediction, and the Shannon entropy test. Spontaneous activity was not detected in strips from 1- to 5-day-old rats but was observed in 50% of strips from 6- to 7-day-old rats and was prominent in strips from 2-wk-old animals. FFT analysis revealed one peak in activity, which was significantly faster in the bladder base (0.21 +/- 0.03 Hz) than in the dome (0.08 +/- 0.01 Hz). A second peak at approximately 0.5 Hz was detected at 3-5 wk of age. Atropine but not tetrodotoxin decreased the amplitude of spontaneous contractions, whereas carbachol, a muscarinic agonist, unmasked or stimulated spontaneous activity. These data suggest that slow rhythmic activity observed previously in neonatal whole bladders is generated by pacemaker cells in the bladder base or dome. The emergence of faster activity in bladders from older animals may reflect the development of multiple pacemaker sites, which would reduce coordination within the bladder wall and improve storage function in the mature bladder.     

The role of parvalbumin-containing interneurons in the regulation of spontaneous synchronous activity of brain neurons in culture

Subtypes of inhibitory GABAergic neurons containing Ca²⁺-binding proteins play a pivotal role in the regulation of spontaneous synchronous [Ca²⁺]_i transients in a neuronal network. In this study it is shown that: (1) the interneurons that containing Ca²⁺-binding proteins at buffer concentration can be identified by the shape of Ca²⁺-signa1 in response to depolarization or activation of ionotropic glutamate receptors; (2) Ca²⁺-binding proteins are involved in desynchronization of spontaneous Ca²⁺ transients. At low frequencies of spontaneous synchronous [Ca²⁺]_i transients (less than 0.2 Hz) neurons show quasi-synchronous pulsations. At higher frequencies, synchronization of spontaneous synchronous [Ca²⁺]_i transients occurs in all neurons; (3) it is established that several synchronous oscillations with different frequencies coexist in the network and the amplitude of their depolarizing pulse also varies. This phenomenon is apparently the mechanism that selectively directs information in separate neurons using the same network; and (4) in one population of interneurons at high frequencies of spontaneous synchronous [Ca²⁺]_i transients the inversion of Cl^– concentration gradient is observed. In this case, the inhibition of GABA(A) receptors suppresses the activity of neurons in this population and excites other neurons in the network. Thus, the GABAergic neurons that contain Ca-binding proteins show different mechanisms to regulate the synchronous neuronal activities in cultured rat hippocampal cells.     

Characterization of spontaneous electrical activity of the urinary tract: Ureter,bladder, urethra

The study aimed to characterize spontaneous electrical activity of the ureter, urinary bladder and urethra as well as their interrelationship. The basic parameters of pacemaker activity (amplitude, frequency, peak rise rate, peak rise time, peak half-width) were comparatively analyzed in each of the active areas. Out of the three areas compared, the ureteral rhythmogenic zone displayed the maximum amplitude and apex formation rate. Under conditions of urine influx from the ureter into the bladder and isolation of these organs from the urethra, the amplitude and peak rise rate in the latter decreased by almost 20%. At the same time, all the parameters of the ureter and bladder remained intact. Complete block of urine influx into the bladder by transecting the ureter at the appropriate area led to a slight decrease in the amplitude of action potentials, peak rise rate and rhythmogenicity frequency in the bladder, respectively, by 14.2, 12.5 and 16% at the constancy of other parameters of its activity. Subsequent isolation of the bladder from the urethra had no appreciable effect on the altered parameters of the former. The similar tendency towards a reduction of the parameters was observed under the same conditions in the urethra. Thus, a relationship was revealed between autonomous activities of the ureter, bladder and urethra. The regulatory role in this process is provided by the urine flow through these organs.     

The role of the ovarian horn locus in regulation of spontaneous electric activity of myometrial rhythmogenic areas

The role of the ovarian area of the uterine horn in coordination of spontaneous activity of myometrial rhythmogenic areas was studied in nonpregnant rats both under normal conditions and following transection of the uterine horn in its middle part to isolate the ovarian locus from the distally located uterine active areas. The effect of oxytocin as a factor that reveals a leading role of the ovarian locus in synchronization of myometrial spontaneous activity was studied under the above conditions. Intravenous oxytocin administration (10^–1 μg/kg) under normal conditions promotes a considerable increase in the peak amplitude and mean rise rate in all the three rhythmogenic areas (%; ovarian horn area—by 148.63 ± 6.1, p ≤ 0.001 and 141.04 ± 7.6, p ≤ 0.01; cervical horn area—by 143.85 ± 3.5, p ≤ 0.001 and 146.89 ± 8.5, p ≤ 0.001; uterine corpus—by 146.20 ± 7.2, p ≤ 0.001 and 139.73 ± 8.2, p ≤ 0.05, respectively). Under the same conditions, also there is a similar increase in the active state duration in all the three areas (%; 132.70 ± 4.5, p ≤ 0.05; 124.90 ± 9.6, p ≤ 0.05; 128.03 ± 7.2, p ≤ 0.05, respectively). Following transection of the uterine horn, oxytocin administration causes an increase in all the three activity indicators only in the ovarian horn area (%; 134.86 ± 2.5, p ≤ 0.05; 139.49 ± 4.5, p ≤ 0.001; 123.8 ± 7.3, p ≤ 0.05, respectively). In the cervical horn area and uterine corpus, no appreciable changes in these indicators were detected under both conditions. We believe that the ovarian locus is involved in coordination of activities of all the three myometrial rhythmogenic areas as revealed by oxytocin.     

Modulation of spontaneous activity in the overactive bladder: the role of P2Y agonists

Spinal cord transection (SCT) leads to an increase in spontaneous contractile activity in the isolated bladder that is reminiscent of an overactive bladder syndrome in patients with similar damage to the central nervous system. An increase in interstitial cell number in the suburothelial space between the urothelium and detrusor smooth muscle layer occurs in SCT bladders, and these cells elicit excitatory responses to purines and pyrimidines such as ATP, ADP, and UTP. We have investigated the hypothesis that these agents underlie the increase in spontaneous activity. Rats underwent lower thoracic spinal cord transection, and their bladder sheets or strips, with intact mucosa except where specified, were used for experiments. Isometric tension was recorded and propagating Ca(2+) and membrane potential (E(m)) waves were recorded by fluorescence imaging using photodiode arrays. SCT bladders were associated with regular spontaneous contractions (2.9 ± 0.4/min); ADP, UTP, and UDP augmented the amplitude but not their frequency. With strips from such bladders, a P2Y(6)-selective agonist (PSB0474) exerted similar effects. Fluorescence imaging of bladder sheets showed that ADP or UTP increased the conduction velocity of Ca(2+)/E(m) waves that were confined to regions of the bladder wall with an intact mucosa. When transverse bladder sections were used, Ca(2+)/E(m) waves originated in the suburothelial space and propagated to the detrusor and urothelium. Analysis of wave propagation showed that the suburothelial space exhibited properties of an electrical syncitium. These experiments are consistent with the hypothesis that P2Y-receptor agonists increase spontaneous contractile activity by augmenting functional activity of the cellular syncitium in the suburothelial space.     

Role of acetylcholine in coordination of spontaneous electrical activity of various areas of the rat uterus

Spontaneous electrical activity of myometrium was studied in areas of the uterus body, zone of its connection with uterine tube, and cervix at intravenous administration of various acetylcholine concentrations. Under these conditions, changes of the frequency and amplitude characteristics of rhythmogenesis were studied both separately and in their combined active state. The presence of 10^?3 M acetylcholine in the animal blood creates the most optimal conditions for synchronization and coordination of activities of all studied uterus areas.     

Factors controlling the intracellular concentration of calcium and the spontaneous activity of the ureter

The role of the electrogenic Na(+)-Ca(2+)-exchange mechanism in regulating the spike activity of the ureter was studied. The ureter cells were shown to be capable of generating action potentials (AP) in sodium-free Krebs solution. The time during which the spikes are generated is in exponential dependence on the concentration of calcium ions in the medium, [Ca2+]o within 2.5 to 15 mmol/l. Simultaneously with the generation of the spikes, accumulation of calcium in the muscles is observed, proportional to the increase of [Ca2+]o. The addition of as little as 20 mmol/l Na+ or Li+ ions into the solution restores the prolonged electrical activity of the ureter. Under these conditions, the decrease of intracellular Ca2+ within 5 min was more than two times larger as compared with that in sodium-free medium. Upon substituting Ba2+ ions for Ca2+ ions in Krebs solution AP are generated within an interval which was the longer the higher the Ba2+ concentration in the medium. Li+ ions can replace Na+ ions in maintaining AP and in extruding calcium from the cell. It is supposed that the generation of the stable spike activity of the ureter depends on the functioning of Na(+)-Ca(2+)-exchange mechanism.     

Analysis of electrical activities of the junction region of the ureter with bladder and surrounding zones in rats

Spontaneous electrical activity of the rat ureters per bladder zone was studied. In area of ureter connection with bladder, slow-wave activity was revealed. In bladder bordering ureter zone, rapid spike activity was found that was fully correlated with the genesis of upper located fluctuation processes.     

Na+,K+,2Cl(-)-cotransport and chloride permeability of the cell membrane in mezaton and histamine regulation of electrical and contractile activity in smooth muscle cells from the guinea pig ureter

Influence of Na+,K+,2Cl(-)-cotransport and chloride permeability of the cell membrane on electrically-induced action potential and contraction of smooth muscle cells from guinea pig ureter was examined with the methods of the double sucrose gap junction. Mesatone (10 microM) and histamine (10 microM) induced prolongation of the action potential and elevation of smooth muscle cell contraction, whereas hyperosmic medium (+150 mM sucrose), and recovery of solution osmolality in hyposmic condition (70 mM NaCl) after a single contraction. Inhibitor Na+,K+,2Cl(-)-cotransport bumetanide (10 microM) and chloride permeability blockers niflumic acid (10-100 microM) and SITS (10-500 microM) attenuated stimulating effects of mesatone, histamine and hyperosmic medium. In opposite to adenylate cyclase activation with forskolin (1 microM), guanylate cyclase activation with sodium nitroprusside (SN, 100 microM) decreased both inhibitory action of bumetanide, niflumic acid and activating effects of mesatone, histamine on action potential and elevation contraction of smooth muscle cells. Influence of forskolin rather and not SN on AP and SMC C was inhibited with tetraethylammonium (5 mM). These results suggest that influence of Na+,K+,2Cl(-)-cotransport on electrical and contractil properties of ureter smooth muscle cells is mediated by stimulation of Ca(2+)-activated chloride permeability of the cell membrane and modulated by intracellular cGMP, but not triggered by Ca2+ release from sarcoplasmic reticulum.     

The role of thymus gland in the regulation of the activity of peripheral T-lymphocytes in the process of spontaneous blastogenesis in mice

The total count, spontaneous proliferation and proliferative response of thymic and spleen T-cells in mixed lymphocyte culture and Con A-induced suppressor activity do not reveal significant disorders in 10-14-month A/Sn and C3H/He mice with spontaneous mammary tumors (weight under 2-3 g). However, these indices are quite different in varying age (2, 6, 12 month) A/Sn mice and C57Bl/6 mice with low rates of spontaneous tumors. The analysis of thymus-dependent immunity changes observed with age shows that relatively intensive migration of nonmature thymocytes, T-suppressor precursors is noted in mice with high cancer incidence. This phenomenon is considered to be one of major mechanisms regulating immune response in spontaneous-carcinogenesis.