Pharmacological characterization of the response of the leech pharynx to acetylcholine

In this study we document the sensitivity of the leech pharynx to acetylcholine and begin to characterize the acetylcholine receptor mediating this response by examining the effects of selective cholinergic agonists and antagonists on the contractile behavior of the pharynx. The order of potency derived from the EC50 of each agonist was (+/-)epibatidine > acetylcholine (in the presence of physostigmine) > McN A-343 > carbachol > nicotine. However, when response amplitude was considered, the order of potency to the tested agonists was (+/-)epibatidine > nicotine > McN A-343 > carbachol > acetylcholine. Acetylcholine-induced contractions of the pharynx were antagonized by d-tubocurarine, but not by alpha-bungarotoxin, alpha-conotoxin M1, or mecamylamine. Application of high concentrations of hexamethonium (1 mM) augmented the acetylcholine-induced contractions. However, this augmentation was apparently due to inhibition of acetylcholinesterase by hexamethonium. The muscarinic antagonist atropine produced complex actions and apparently acted as a mixed agonist/antagonist. Atropine by itself produced an increase in basal tonus and increased the frequency and amplitude of phasic contractions. Atropine increased the peak tension of the acetylcholine-induced response; however, it reduced the amplitude of both the acetylcholine-induced increase in basal tonus and integrated area. Based on the pharmacological profile of the pharyngeal acetylcholine response, we conclude that the acetylcholine receptor mediating the response is a nicotinic receptor. However, the responsiveness of the pharynx to muscarinic agents diverges from that of a classical nicotinic receptor.     

Effects of cholinergic drugs on muscle contraction in Moniliformis moniliformis (Acanthocephala)

In whole Moniliformis moniliformis spontaneous muscle contractions were rhythmic; longitudinal contractions were measured with a force transducer. The cholinergic agonists levamisole and nicotine significantly increased muscle tension in whole worms; these contractions were tonic and were antagonised by the ganglionic blocker pentolinium and by piperazine. In addition, levamisole-induced contractions were inhibited by gallamine, hexamethonium, and norepinephrine. In worm segments, where drugs in solution were injected through the worms, acetylcholine (ACh) and nicotinic agonists were effective in causing contractions, whereas muscarinic agonists in concentrations up to 1 mM had no effect. Although muscle contraction in M. moniliformis was induced by nicotinic agonists, these contractions were effectively antagonised by a range of chemicals that block ganglionic, skeletal, and muscarinic sites in vertebrates. The presence of ACh in M. moniliformis and the effects of nicotinic agonists on muscle contraction suggest that ACh is a putative excitatory neurotransmitter.     

Nicotinic Stimulation of [3H]Acetylcholine Release from Mouse Cerebral Cortical Synaptosomes

The effects of nicotine and 1,1-dimethyl-4-phenylpiperazinium (DMPP) on the release of newly synthesized [3H]acetylcholine in mouse cerebral cortical synaptosomes were examined. Nicotine and DMPP produced increases in [3H]acetylcholine release, over the level of spontaneous release, of 24% and 30%, respectively, of a maximum depolarization-induced release produced by 50 mM potassium. The maximum effect was achieved at a concentration of 1 X 10(-4) M for both agents. The time course of release indicated a slow onset of action, reaching a maximum effect at 15 min of incubation. Both nicotine and DMPP also produced a slightly greater release of total tritium, measured in the absence of cholinesterase inhibition, than of [3H]acetylcholine. The release induced by nicotine was completely antagonized by hexamethonium and was largely (58%) calcium-dependent. Nicotine also produced an increase in [3H]choline accumulation into synaptosomes. These results indicate that the nicotinic agonists nicotine and DMPP can produce a moderate enhancement of acetylcholine release by a receptor-mediated action on cholinergic nerve terminals in the central nervous system.     

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.     

Cholinergic receptors in the Aplysia gill

Acetylcholine has been suggested as a neurotransmitter released in the Aplysia gill by peripheral afferents of central neurons and by peripheral neurons within the gill. The perfused gill, isolated from the abdominal ganglion, was examined. At concentrations greater than 1 microM, acetylcholine elicited a slowly developing tonic contraction of the afferent vein that reversed upon washout. This effect was observed on both quiescent and active preparations. At concentrations less than 1 microM, acetylcholine perfusion resulted in a reduction of gill tone. The excitatory effect of acetylcholine was reduced 80 and 60% by the cholinergic antagonists atropine and hexamethonium, respectively. The acetylcholine-evoked contraction was potentiated 2.5-fold when curare was coinfused. Carbachol did not mimic the excitatory effects of acetylcholine. At all concentrations examined (1-100 microM), carbachol infusion reduced baseline tension, the amplitude of spontaneous contractions and contractions evoked by FMRFamide and dopamine. Contractions evoked by perfusion of p-chlorophenylthiocyclic AMP were greatly reduced when carbachol was added to the perfusate. Further addition of curare reversibly blocked carbachol inhibition of the cyclic AMP-evoked contractions. These findings suggest that excitatory and inhibitory cholinergic receptors are involved in the regulation of gill contractile behavior by acetylcholine.     

Fasciola hepatica: the effects of neuropharmacological agents upon in vitro motility

The effects of a wide range of neuropharmacological agents on the motility in vitro of Fasciola hepatica have been determined using an isometric transducer system. The neuromuscular blocking agents tubocurarine and decamethonium cause a long-term stimulation of the basal activity of the fluke. Acetylcholine causes an inhibition of activity. This effect is mimicked by the cholinergic agonists carbachol and nicotine, antagonised by the cholinergic blocking agents atropine and mecamylamine, and potentiated by eserine, a cholinesterase inhibitor. With nicotine and atropine the effects are accompanied by an increase in muscle tone at a concentration of 1 X 10(-2) M. Noradrenaline and adrenaline also cause some inhibition of activity, an effect antagonised by guanethidine, which blocks the release of noradrenaline. In contrast, dopamine stimulates fluke motility, whilst its antagonist dihydroergotamine causes an inhibition of activity. The monoamine oxidase inhibitors iproniazid and p-chloromercuribenzoic acid induce a stimulation of activity; with the latter there is an increase in muscle tone at a concentration of 1 X 10(-3) M. The amine depleting agents chloroamphetamine and reserpine, and the monoamine uptake inhibitors desipramine and nortriptyline produce an inhibition of fluke activity, as does the serotonin uptake inhibitor fluoxetine. High concentrations of chloroamphetamine (1 X 10(-2) M) and the uptake inhibitors (1 X 10(-3) M and above) also induce an increase in muscle tone. Serotonin causes a marked stimulation of motility. The pharmacological evidence is consistent with a neurotransmitter role of acetylcholine (inhibitory), dopamine (excitatory), and noradrenaline (inhibitory). The status of serotonin is discussed.     

Effects of the methanolic extract of Chrysanthemum trifurcatum (Desf.) Batt. and Trab. on rat duodenal motility

The effect of the methanolic extract of flowers of Chrysanthemum trifurcatum (Desf.) Batt. and Trab. Var. macrocephalum (viv.) Beg. on the rat duodenum smooth muscle motility was examined in vitro. The extract has shown dose-dependent stimulator effects on the amplitude of the spontaneous contractions. With 0.1 g/ml of extract, maximal stimulation was obtained. With that dose, the variation (%) was significantly 1050 +/- 13 (P<0.001) compared with control and represented 80 +/- 5.83% (P<0.001) of the maximum effect of acetylcholine. Atropine (2 microg/ml) reduced by 81 +/- 4% (P<0.05) the spasmogenic effects of C. trifurcatum and by 92 +/- 3% (P<0.05) the acetylcholine effects, while papaverine (2 microg/ml) completely inhibited the spasmogenic effects of extract. With a fixed dose of acetylcholine added (20 microg/ml), the extract increases its effect, but acetylcholine decreases its action. These results suggested that the methanolic extract of C. trifurcatum could stimulate duodenal smooth muscle contractions through muscarinic receptors. Thy explain the respective traditional use of plant in gastrointestinal problems, especially constipation.     

Effects of cholinergic drugs on longitudinal contraction in levamisole-susceptible and -resistant Haemonchus contortus.

A novel force transducer was used to measure the effects of cholinergic agonists on longitudinal contraction in Haemonchus contortus. Drugs were applied to whole worms or injected via a cannula in the pseudocoelomic cavity. A number of agonists, including nicotine and the anthelmintics m-aminolevamisole, levamisole and morantel, caused contractions in whole worms. Four- to 25-fold increases in concentration of the active compounds were required to cause contractions in each of two levamisole-resistant strains of H. contortus. Of the other compounds tested, bephenium had equivalent activity against susceptible and resistant strains. Anticholinesterase compounds caused contractions after a slight delay in susceptible, but not resistant worms. Numerous cholinergic agonists and other compounds did not cause contraction when applied to whole worms. One of these, acetylcholine, caused contractions in cannulated worms. Compared with the susceptible strain, five- to six-fold higher concentrations of acetylcholine were required to cause equivalent contractions in the resistant strains. Levamisole resistance in adult H. contortus is likely to be due to a change in the characteristics of the cholinergic receptor(s).     

Effects of various experimental manipulations on neostriatal acetylcholine and dopamine release

The release of endogenous acetylcholine and dopamine and the appearance of their metabolites, choline and dihydroxyphenylacetic acid (DOPAC), from neostriatal slices prepared from Fischer 344 rats was examined under various experimental conditions. There was a dose-dependent increase in the amount of neurotransmitter or metabolite as the medium potassium concentration was increased from 5 to 50 mM. Over an eight minute period in Krebs Ringer bicarbonate buffer containing 25 mM potassium, the rate of release of acetylcholine was 6 to 13 times greater than that of dopamine. The dopamine endogenous to the slice preparation appeared to have little effect on the release of endogenous acetylcholine since manipulations that significantly altered dopamine release (depletion with 6-hydroxydopamine or uptake inhibition with nomifensine) had minimal effects on the cholinergic neurons. In contrast, increasing the endogenous acetylcholine in the preparation by inhibiting acetylcholinesterase resulted in a 1.2 to 12 fold increase in dopamine release depending upon the incubation time and the potassium concentration. These studies indicate that within the neostriatal slices there is minimal influence of the endogenous dopamine on the cholinergic neurons, whereas the extracellular acetylcholine can influence dopamine release when its concentration is increased by inhibition of acetylcholinesterase.     

Antifilarial activity of Centratherum anthelminticum seed extracts on Setaria cervi.

Effect of aqueous and alcoholic extract of C. anthelminticum was studied on the spontaneous movements of the whole worm and nerve-muscle preparation of S. cervi. Ethylacetate, acetone and methanol extract showed similar effect, of causing inhibition of spontaneous motility of the nerve-muscle preparation of S. cervi characterized by decreased amplitude and frequency of contractions. The inhibitory effect on the motility was reversible. Further, the extracts did not involve the blockade of cholinergic receptors as evidenced by the presence of unaltered stimulant response of acetylcholine in the presence of drug in bathing fluid.     

Prejunctional alpha 2-adrenoceptor mediated inhibitory action of clonidine and B-HT 920, but not urapidil in guinea pig ileum

Isolated guinea pig ileal longitudinal muscle was stimulated transmurally with a frequency of 0.1 Hz, duration of 0.5 msec, and supramaximal voltage (80-100 V). Transmural stimulation induces ileal contractions via activation of cholinergic neurons. alpha 2-Adrenergic agonists block the response to transmural stimulation via activation of prejunctional alpha 2 receptors which inhibit release of acetylcholine from cholinergic nerve terminals. Urapidil has been reported to have alpha 2-agonistic actions, and therefore was compared to the prototypic alpha 2 agonists, clonidine and B-HT 920. Clonidine and B-HT 920 depressed responses to transmural stimulation in the guinea pig ileum. Clonidine was the most potent inhibitor of the contractions, followed closely by B-HT 920. Very high concentrations of urapidil were necessary to suppress nerve-induced contractions of the ileum. The effects of clonidine and B-HT 920, but not urapidil, were antagonized by the selective alpha 2 antagonist, yohimbine. In unstimulated preparations, in which exogenous acetylcholine was used to elicit contractions of the ileum, urapidil depressed the response while clonidine and B-HT 920 had no effect. When PGF1 alpha was used to contract the ileum, no inhibitory effects were noted for urapidil, clonidine, or B-HT 920. Therefore urapidil, only in high concentrations, inhibits the contraction to transmural stimulation by depressing the response at a postjunctional cholinergic site. No evidence was found that urapidil can act as an agonist at a prejunctional alpha 2-receptor site.     

Mechanism of inhibitory action of peptide YY on cholecystokinin-induced contractions of isolated dog ileum

In isolated canine ileal longitudinal muscle preparations, cholecystokinin-octapeptide (CCK-8) produced a concentration-dependent contraction, which was suppressed by peptide YY (PYY) and was abolished by tetrodotoxin and atropine. PYY was approximately 2200-times as potent as CR1505, a CCK-receptor antagonist. PYY opposed the action of CCK-8 to a greater extent than that of nicotine and transmural electrical stimulation. Acetylcholine-induced contractions were not influenced by PYY. It seems likely that the CCK-8-induced ileal muscle contraction is associated with an activation of CCK receptors in cholinergic nerves, which generates nerve action potentials and releases acetylcholine, whereas CCK-8 acts on CCK receptors in gallbladder smooth muscle, producing contractions. It may be concluded that PYY inhibits the action of CCK-8 on ileal muscle strips, by inhibiting the release of acetylcholine from cholinergic nerve terminals. On the other hand, in the gallbladder, PYY does not appear to block cholinergic nerve function.     

Effects of Nucleus Basalis Lesions on the Muscarinic and Nicotinic Modulation of [3H] Acetylcholine Release in the Rat Cerebral Cortex

Presynaptic muscarinic and nicotinic receptors in the cerebral cortex reportedly inhibit and increase acetylcholine (ACh) release, respectively. In this study, we investigated whether these receptors reside on cholinergic nerve terminals projecting to the cerebral cortex from the nucleus basalis magnocellularis (nbm). Adult male rats received unilateral infusions of ibotenic acid (5 micrograms/1 microliter) in the nbm. Two weeks later, cerebral cortical cholinergic markers (choline acetyltransferase activity, high-affinity choline uptake, and coupled ACh synthesis) were significantly reduced in synaptosomes prepared from the lesioned hemispheres compared to contralateral controls. The depolarization-induced release of [3H]ACh from these synaptosomes was also reduced in the lesioned hemispheres, reflecting the reduced synthesis of transmitter. However, the nbm lesions had no effect on the inhibition of release induced by 100 microM oxotremorine. Synaptosomal [3H]ACh release was not altered by nicotine or the nicotinic agonists anabaseine and 2-(3-pyridyl)-1,4,5,6-tetrahydropyrimidine. Nicotine (10-100 microM) did increase [3H]ACh release in control and lesioned hemispheres in cortical minces, but to a similar extent. These results suggest that neither muscarinic nor nicotinic receptors modulating ACh release reside on nbm-cholinergic terminals.     

Cholinergic neurons of the pelvic autonomic ganglia and uterus of the female rat: distribution of axons and presence of muscarinic receptors

Acetylcholine (ACh) stimulates contraction of the uterus and dilates the uterine arterial supply. Uterine cholinergic nerves arise from the paracervical ganglia and were, in the past, characterized based on acetylcholinesterase (AChE) histochemistry. However, the histochemical reaction for acetylcholinesterase provides only indirect evidence of acetylcholine location and is a nonspecific marker for cholinergic nerves. The present study: (1) reevaluated cholinergic neurons of the paracervical ganglia, (2) examined the cholinergic innervation of the uterus by using retrograde axonal tracing and antibodies against molecules specific to cholinergic neurons, choline acetyltransferase and the vesicular acetylcholine transporter, and (3) examined muscarinic receptors in the paracervical ganglia using autoradiography and a radiolabeled agonist. Most ganglionic neurons were choline acetyltransferase- and vesicular acetylcholine transporter-immunoreactive and were apposed by choline acetyltransferase/vesicular acetylcholine transporter-immunoreactive terminals. Retrograde tracing showed that some cholinergic neurons projected axons to the uterus. These nerves formed moderately dense plexuses in the myometrium, cervical smooth muscle and microarterial system of the uterine horns and cervix. Finally, the paracervical ganglia contain muscarinic receptors. These results clearly reveal the cholinergic innervation of the uterus and cervix, a source of these nerves, and demonstrate the muscarinic receptor content of the paracervical ganglia. Cholinergic nerves could play significant roles in the control of uterine myometrium and vasculature.     

Pharmacological responses by different portions of guinea pig vas deferens circular muscle preparation

The different segments of the guinea pig vas deferens circular muscle exhibit differential response patterns upon pharmacological stimulation. Namely, apart from barium chloride, the affinity and intrinsic activity of certain agonists and the strength of maximum contractions they induce appear to decrease along the path from the epididymis toward the prostate. If one subdivides the vas deferens into 3 parts of equal length such as epididymal, medial and prostatic portions, then adrenaline, acetylcholine, acetyl-beta-methylcholine, dopamine, histamine and bradykinin induce contractions on each of the 3 parts; whereas tyramine, ephedrine elicit responses in the epididymal and medial portions; amphetamine, DMPP, serotonin and PGF2 alpha in turn provoking contractions exclusively on the epididymal portion. The effects of adrenaline and noradrenaline are blocked by phentolamine and tolazoline; the responses to acetylcholine, acetyl-beta-methylcholine and carbamyl-beta-methylcholine are antagonized by atropine over a specific concentration range. The effects of tyramine, ephedrine and amphetamine are inhibited by phentolamine in an remarkably low dose range (pA2 = 13.51 +/- 0.09; 14.54 +/- 0.31; 14.35 +/- 0.12). The situation was the same when tyramine-dibenamine and tyramine-phenoxybenzamine combinations were tested (pD'2 = 14.03 +/- 0.37; 13.26 +/- 0.03). Based on these findings the presence of a peculiar alpha adrenergic receptor is suggested on the sympathetic postganglionic fibres. In addition to the already identified alpha adrenergic, muscarinic cholinergic and histamine H1 receptors, we could show the presence of dopaminergic receptors too in the vas deferens circular muscle.     

Altered Cholinergic Metabolism in Rat CNS Following Aluminum Exposure: Implications on Learning Performance

Abstract: The effects of Al on the central cholinergic system have been studied. Al, at a dose of 10 mg/kg of body weight/day for 4 weeks, had a deleterious effect on the activities of biosynthetic (choline acetyltransferase) and hydrolytic (acetylcholinesterase) enzymes of the neurotransmitter acetylcholine. The levels of acetylcholine were also significantly lowered in different brain regions at the end of the dose regimen. There was a significant decrease in high-affinity choline uptake following Al exposure. Muscarinic acetylcholine receptor binding studies revealed a decreased number of binding sites ( B _max), with the maximum effects being manifested in the hippocampus. Exogenous addition of 10 µ M desferrioxamine restored the muscarinic receptor binding completely. The impaired cholinergic functioning had severe effects on cognitive functions. Neurobehavioral deficits were manifested in terms of decreased active (52%) and passive (73.30%) avoidance tests. The results suggest that Al exerts its toxic effects by altering cholinergic transmission, which is ultimately reflected in neurobehavioral deficits.     

Neurotensin and cholecystokinin depress motility in isolated Lumbricus terrestris crop-gizzard preparations

The effects of neurotensin (NT) and cholecystokinin (CCK) were studied on isolated crop-gizzard preparations of Lumbricus terrestris suspended in a smooth muscle organ bath. Changes in the amplitude and frequency of contractions associated with spontaneous motility were observed in response to neurotransmitters known to have an excitatory effect (acetylcholine) and an inhibitory effect (serotonin); and to the hormones NT and CCK, which in vertebrate models have both been shown to inhibit gastric motility. The overall contractile amplitude and frequency of crop-gizzard contractions were decreased in response to increasing concentrations of NT and CCK. In general, both hormone-induced responses were similar when compared at equal molar concentrations. Cholecystokinin, however, did exhibit a greater reduction in contractile frequency than NT. It is speculated that possible desensitization of earthworm NT-receptors to higher hormone concentrations resulted in a depressed maximal response in the concentration–response curve. Despite that possibility, the overall hormonal inhibition was statistically significant. These results infer that NT- and CCK-induced inhibition of crop-gizzard motility may have a modulatory role in the transport of nutrients and overall efficiency of worm metabolism.     

The non-neuronal cholinergic system in peripheral blood cells: effects of nicotinic and muscarinic receptor antagonists on phagocytosis, respiratory burst and migration

Peripheral blood cells express the complete non-neuronal cholinergic system. For example synthesis of acetylcholine and nicotinic as well muscarinic receptors have been demonstrated in leucocytes isolated from human peripheral blood. In the present experiments mononuclear cells and granulocytes were isolated from the peripheral blood to investigate content and synthesis of acetylcholine as well as phenotypic functions like respiratory burst, phagocytosis and migration. Mononuclear cells (T-cells and monocytes) contained 0.36 pmol/10(6) cells acetylcholine, whereas acetylcholine content in granulocytes was 100-fold lower. Acetylcholine synthesis amounted to 23.2+/-4.7 nmol/mg protein/h and 2.90+/-0.84 in CD15+ (granulocytes) and CD3+ cells (T-lymphocytes), respectively. Neither atropine (blockade of muscarinic receptors) nor tubocurarine (blockade of nicotinic receptors) exerted an effect on the respiratory burst. Tubocurarine (30 muM), alone or in combination with atropine (1 microM), reduced phagocytosis in granulocytes by 13% and 19%, respectively (p<0.05). Spontaneous transwell migration of granulocytes was doubled by tubocurarine combined with atropine (p>0.05). Also alpha-bungarotoxin (10 microg/ml) enhanced spontaneous granulocyte migration, but hexamethonium (300 microM) was without effect. The present experiments demonstrate a cholinergic modulation of immune functions in peripheral leucocytes under in vitro conditions, i.e. in the absence of a neuronal innervation. Blockade of nicotine receptors (alpha1 muscular subtype) facilitates spontaneous migration of granulocytes.     

Cholinergic transmission at mechanosensory afferents in the crayfish terminal abdominal ganglion

Electrical stimulation of mechanosensory afferents innervating hairs on the surface of the exopodite in crayfish Procambarus clarkii (Girard) elicited reciprocal activation of the antagonistic set of uropod motor neurones. The closer motor neurones were excited while the opener motor neurones were inhibited. This reciprocal pattern of activity in the uropod motor neurones was also produced by bath application of acetylcholine (ACh) and the cholinergic agonist, carbamylcholine (carbachol). The closing pattern of activity in the uropod motor neurones produced by sensory stimulation was completely eliminated by bath application of the ACh blocker, d-tubocurarine, though the spontaneous activity of the motor neurones was not affected significantly. Bath application of the acetylcholinesterase inhibitor, neostigmine, increased the amplitude and extended the time course of excitatory postsynaptic potentials (EPSPs) of ascending interneurones elicited by sensory stimulation. These results strongly suggest that synaptic transmission from mechanosensory afferents innervating hairs on the surface of the tailfan is cholinergic.Bath application of the cholinergic antagonists, dtubocurarine (vertebrate nicotinic antagonist) and atropine (muscarinic antagonist) reversibly reduced the amplitude of EPSPs in many identified ascending and spiking local interneurones during sensory stimulation. Bath application of the cholinergic agonists, nicotine (nicotinic agonist) and oxotremorine (muscarinic agonist) also reduced EPSP amplitude. Nicotine caused a rapid depolarization of membrane potential with, in some cases, spikes in the interneurones. In the presence of nicotine, interneurones showed almost no response to the sensory stimulation, probably owing to desensitization of postsynaptic receptors. On the other hand, no remarkable changes in membrane potential of interneurones were observed after oxotremorine application. These results suggest that ACh released from the mechanosensory afferents depolarizes interneurones by acting on receptors similar to vertebrate nicotinic receptors.Abbreviations ACh cetylcholine - mns motor neurones - asc int ascending interneurone     

Effect of KATP channel openers on myogenic and neurogenic responses in goat urinary bladder

Isolated goat detrusor muscle exhibited spontaneous contractility with an irregular amplitude and frequency. The spontaneity of detrusor muscle exhibited a mean amplitude as 11.99 +/- 0.83 mm and frequency as 1.37 +/- 0.16/min. KATP-channel openers namely, cromakalim or pinacidil (10(-7) - 10(-4) M) added cumulatively, elicited a concentration-related inhibition of both amplitude and rate of spontaneous contractions. The mean IC50 values for both amplitude and frequency for cromakalim were 3.3 x 10(-6) M and 2.9 x 10(-6) M, respectively; and for pinacidil were 2.0 x 10(-5) M and 1.5 x 10(-5) M, respectively. Glibenclamide, a KATP-channel blocker inhibited the cromakalim-induced concentration-related relaxation of spontaneous contractions with a significant increase in its mean IC50. ACh-induced concentration-related contractile response was inhibited in the presence of either cromakalim (10(-4) M) or pinacidil (10(-4) M). The mean EC50 value of ACh, in the presence of cromakalim (2.5 x 10(-3) M) was significantly increased as compared to the control (1.2 x 10(-6) M). In the presence of glibenclamide (10(-5) M) the inhibitory effect of cromakalim was significantly reduced with consequent decrease in the EC50 value (1.9 x 10(-5) M). Application of EFS (30 V and 5 ms) on goat urinary bladder strips at 1, 2, 5, 10, 20 and 30 Hz elicited frequency-related contractile responses. Both cromakalim and pinacidil caused a rightward shift in the frequency-related contractile response curve with significant increase in the mean EF25 and EF50 values, respectively. In the presence of glibenclamide (10(-4) M), the frequency-related inhibitory response curve was shifted to left with significant (P < 0.001) increase in the mean EF25, EF50 and EF75. The present results suggest that in the goat detrusor muscle, agonist and EFS-induced contractile responses were more potently inhibited by cromakalim than pinacidil with activation of glibenclamide sensitive KATP channels.