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IEM-2062 [1-(6-aminohexylamino)-1-phenylcyclohexyl dihydrochloride], causing a combined block NMDA and AMPA receptors, after chronic oral administration in doses, respectively, 0.3 and 3 mg/kg, induce maximal anticonvulsant effect in the pentylenetetrazol kindling rats because decrease the number of completely kindling rats by 100 %, and also decrease in 2.5-3.3 times the average severity of clonic-tonic kindling seizures. IEM-2062 causes significant anticon- 299 vulsant effects in the widest range of doses, 1-48 mg/kg, which is 24-22 times more than that of memantine (12-20 mg/kg) and sodium valproate (100-200 mg/kg). Sodium valproate and memantine cause significant disturbances of locomotor activity in the «open field» test in doses causing maximal anticonvulsant effect in the kindling rats. At the same time IEM-2062 cause disturbance of locomotor activity only in very high dose of 92 mg/kg, which exceeds in 30.7 times the dose causing the maximum anticonvulsive effect in the kindling rats. Thus, IEM-2062 reduces the severity of kindling seizures in 1.7-1.9 times stronger than sodium valproate and memantine and also by 30.7 times is safer than sodium valproate and memantine.

Sodium valproate after chronic intragastric administration in the high dose of 100-200 mg/kg eliminates generalized clonic-tonic pentylenetetrazol seizures in 100 % of rats, but only in 33-57 % of rats it prevents local clonic kindling seizures. Strong sedation is induced by the specified doses of sodium valproate. The combined oral chronic administration of phenylephrine in threshold, noneffective alone dose of 0.2 mg/kg and sodium valproate in high doses of 100 mg/kg and 200 mg/kg potentiates anticonvulsive action of sodium valproate, because prevents both clonic-tonic kindling. seizures in 100 % of rats and clonic kindling seizures in 86-100 % of rats, and also it increases in 1.7-1.9 times anticonvulsive activity of valproate. The specified combinations of sodium valproate with phenylephrine do not produce the sedative side effect. The basis of the mechanism of potentiation of anticonvulsive action and elimination of sedative action of sodium valproate in high doses is the stimulation of gastric mucosa afferents by phenylephrine.

Single i. m. injection of amitriptyline in rats in high doses of 10-30 mg/kg causes a weak an- tidepressive effect because only in 1.3-1.7 times decrease immobilization in Porsolt test. In the specified doses amitriptyline exhibits appreciable sedative effect because in 3-6 times decrease horizontal activity, and also in 2-2.5 times decrease vertical activity of rats in the open field test. Combined single i.m. injection of amitriptyline in a small dose of 3 mg/kg and high dose of 30 mg/kg with phenylephine in threshold, noneffective alone dose of 0.02 mg/kg, causes the ma- ximal antidepressive effect because decreases immobilization in Porsolt test, accordingly, in 3 and 4.6 times, but does not produce side sedative effect in the open field test. The basis of the mec- hanism of potentiation of antidepressive action and elimination of sedative action of amitriptyline is the stimulation of gastric mucosa afferents by phenylephine.

Intramuscular (i. m.) administration in the minimum effective dose (MED) of central analgesics of fentanyl and dipyrone, polyamine agonist spermine and also IEM-1460 (IEM-1460 is AMPA receptors antagonist and agonist of the NMDA polyamine receptor site) causes the maximal analgesic effect in the tail flick test in rats. The combined i.m. administration of dipyrone with IEM-1460 and spermine in threshold, noneffective alone doses according 1/5 part from their MED leads to decrease of MED dipyrone in the combination with IEM-1460 in 120 times, and MED dipyrone in combination with spermine--in 10 times. The combined i.m. administration of fentanyl with IEM-1460 and spermine in above mentioned threshold doses leads to decrease of MED fentanyl in the combination with IEM-1460 in 150 times, and MED fentanyl in the combination with spermine--in 15 times.

Peroral chronic administration the standard antiepileptic drug sodium valproate in a dose of 200 mg/kg eliminates development of generalized clonic-tonic pentylenetetrazol kindling seizures in 100% of rats, but only in 57% of rats this treatment prevents clonic kindling seizures. In the specified dose sodium valproate decreases in 1.7 times average severity of pentylenetetrazol kindling seizures compare with control. IEM-2121, causing combined blockade of NMDA- and AMPA-glutamate receptors, as well as IEM-1676, which also blocks AMPA-, NMDA- and N-cholinoreceptors, both after peroral chronic administration in a doses 10 mg/kg and 20 mg/kg accordingly, possess higher, than sodium valproate, anticonvulsant activity because reduce average severity of pentylenetetrazol kindling seizures in 2.4-2.7 times in comparison with control and prevents clonic kindling seizures in 87% of rats. Combined blockade of AMPA- and NMDA-receptors and perhars N-cholinoreceptors has maximum effect to eliminate epileptogenesis both clonic, and clonic-tonic pentylenetetrazol kindling seizures.

The effects of non-competitive glutamate receptor antagonists on sleep-waking organization have been studied on Krushinskii-Molodkina rats having an inherited predisposition to audiogenic seizures and Wistar ones which are resistant to this action of sound. Two types of blockers of glutamate receptor open channels were used: selective blockers of NMDA receptors (memantine and IEM-1921) and blockers of mixed type, impacting both on the NMDA and Ca-permeable AMPA/ kainate receptors (IEM-1754 and IEM 1925). During the first 3 hours after administration of these glutamate antagonists the total or partial deprivation of fast-wave sleep was provoked. Additionally the selective NMDA receptor blocking drugs (memantine, IEM-1921) induced in the same period a significant increase of the representation of wakefulness at the cost of reducing of the total time of slow-wave sleep. These effects are most likely to be a consequence of the blockade of NMDA receptors responsible for the launch and maintenance of wakefulness, slow- and fast-wave sleep. In the same first 3 hours period after the administration of IEM-1754 and IEM-1925 the organization of sleep was not significantly affected. The evident reduction of wakefulness, total duration and increase of slow-wave sleep impact was observed, during the second three-hour period. It, apparently, can be caused by the blockade of AMPA/kainate receptors. The obtained results indicate the involvement of NMDA and AMPA/kainate receptors in the functioning of various parts of the sleep system of rats belonging to both lines.

Unlabelled: Intramuscular (i.m.) administration of the central analgesics fentanyl and dipyrone, and also mediators of pain such as L-glutamate, CCK, ATP, phenylephine and analgesic mediator adenosine, slightly penetrating in CNS, in the minimum effective dose (MED) cause the maximal analgesic effect in the tail flick test in rats. MED of dipyrone and fentanyl are decreased 50-220-fold after combined i.m. administration of each analgesic with L-glutamate, CCK, adenosine, ATP and phenylephrine in threshold, independently noneffective doses. The intragastric administration of lidocaine and also subdiaphragmatic vagotomy completely eliminate analgesic effects of the above mentioned combinations., Conclusion: the peripherically acting mediators of pain and analgesia after systemic administration potentiate central analgesic action of fentanyl and dipyrone as a result of the stimulation of vagal afferents of gastric mucosa.

Intramuscular (i.m.) administration ofdiazepam in a dose of 10 mg/kg and adrenaline in a dose of 0.2 mg/kg prevents generalized clonic-tonic pentylenetetrazol (PTZ) seizures in 75-80 % of rats, but only in 35-40 % of rats it prevents local clonic PTZ seizures. In the above mentioned dose, diazepam causes a strong sedation, but adrenaline does not cause a sedative effects. The combined administration of diazepam and adrenaline in threshold independently ineffective doses prevents both clonic-tonic and clonic PTZ seizures in 80 % of rats without a sedation development. The basis for mechanism of potentiation of anticonvulsant action of diazepam is the stimulation of gastric mucosa afferents by adrenaline.

In experiments on the nerve-muscle junction of the fly larva Calliphora vicina, regularities of the blocking action of organic cations on ion channels of glutamate postsynaptic receptors have been studied. In total, 26 compounds were studied. The following regularities of structural-functional relations have been revealed: 1) the channels are not blocked by monocation compounds; 2) bication derivatives block efficiently the channel with a certain distance between hydrophobic group and terminal amino group; 3) bication compounds with trimethylammonium terminal group are significantly more efficient than compounds with non-substituted amino group. All these regularities are characteristic of blockade of the AMPA channels, but not of the vertebrate type NMDA channels. Earlier it has been shown that differences in structural-functional relations during blockade of the AMPA and NMDA channels are determined by different location of the hydrophobic and hydrophilic components of the binding area as well as by different diameter of the channels. The fact that channels of the fly larva receptor demonstrate the same regularities of blockade as the vertebrate AMPA channels indicates their structural similarity that is a consequence of their high homology.

Monoammonium N-alkyl derivative of decylamine (IEM-1678), which blocks alpha3beta4 N-cholinoreceptors (but does not block GluR1 AMPA receptors), in doses of 1.0 - 3.0 mg/kg produces a 4-fold decrease in the frequency and lethality of nicotinic clonic-tonic seizures. However, even in the maximum dose of 3 mg/kg, IEM-1678 only slightly decreases kainate clonic-tonic seizures. Bis-ammonium compound IEM-1460 (containing adamantyl radical), which blocks both GluR1 AMPA receptors and alpha3beta4 N-cholinoreceptors, in a range of doses 0.1 - 3 mg/kg produces a 5- to 8-fold decrease in the frequency and virtually completely eliminates lethality of both clonic-tonic nicotinic and kainate seizures. Hence, the complete elimination of generalized kainate and nicotinic seizures requires combined blockade GluR1 AMPA and alpha3beta4 N-cholinoreceptors.

The experimental allergic encephalomyelitis (EAE) developed on the 11 - 12th day after inoculation of encephalitogenic mixture in 96% of female Wistar rats in the control group. In the majority of control rats, severe EAE with a long duration of action prevailed (average cumulative index, 25.6; average duration of illness, 15.8 days). A course of NMDA-antagonist memantine administration in a doze of 10 and 20 mg/kg prevented the development of EAE in 10% of rats. In rats with EAE (on the average, 12-13 days after the administration of encephalitogenic mixture) the drug slightly reduced the severity and duration of neurological disorder: the average cumulative index and duration of illness decreased by a factor of 1.4-1.5 in comparison to the control. The antagonist of NMDA and GluR1 AMPA receptors, IEM-1913, upon a course of administration in a doze of 0.1-1 mg/kg prevented the EAE development in 23-25% of rats. In the rats with EAE treated with IEM-1913 in the maximum doze (1 mg/kg), the EAE developed only after completion of the course of drug administration (on the 19-20th day), proceeded quickly (no more than 5 days), and in the easy form (average cumulative index. 8.3). High efficacy of IEM-1913 administration in rats with EAE is apparently connected with its neuroprotective and antiinflammatory action, which is related, on the one hand, to a combined block of NMDA and GluR1 AMPA of receptors in brain and, on the other hand, to a reduction of the permeability of BBB for encephalitogenic T-lymphocytes owing to the blockade of NMDA receptors in BBB.

The muscarinic agonist arecoline (6 mg/kg, subcutaneously in mice) induced a long-lasting tremor. The inhibitory potency of non-competitive antagonists of ionotropic glutamate receptors has been studied. These antagonists are the derivatives of adamantane and phenylcyclohexyl. A part of them: monocationic compounds, selectively block the NMDA-receptor channels, their dicationic analogues affecting both channels of the NMDA- and the AMPA-glutamate receptors. Monocationic blockers effectively reduced the arecoline-evoked tremor and their potency correlated with ability to block the NMDA-receptor channels. Dicationic blockers revealed protective effect only in low range doses (0.0001-0.01 microM/kg). Further increase of the dose reduced or completely abolished this effect. This suggests that the NMDA-receptors are involved in the genesis of arecoline-evoked tremor. The only moderate blockade of the AMPA-receptors potentiates the drug blocking action but the prevalent blockade of these receptors impedes the effect on arecoline-evoked tremor.

Effects of mono- and dicationic derivatives of adamantane and phenylcyclohexyl on the petyleneterazole-induced (35 mg/kg i. p.) kindling were studied in the experiments on mice. Monocationic derivative of phenylcyclohexyl IEM-1921, effectively retarded the development of kindling beginning the dose 0.0001 microM/kg. Memantine: derivative of adamantane (derivative of adamatane) produced the same effect with 100-fold increased dose. Dicationic derivative ofphenylcyclohexyl: IEM-1925, is able to block equally the open channels of both NMDA and subtype of Ca-permeable AMPA receptors. Its effect on kindling differed markedly from selective NMDA antagonists (IEM-1921 and memantine) in more complicated dose-dependence. The retardation of kindling IEM-1925 was induced at 0.001 microM/kg. On the contrary, a 10-time lower dose: 0.0001 microM/kg, facilitated the development of kindling. The observed difference in the activity of selective NMDA antagonists and the drugs combining anti-NMDA and anti-AMPA potency indicates that both types of ionotropic glutamate receptors are involved in the mechanism of petyleneterazole-induced kindling. The integral effect of channel blockade evoked by drugs seems to be dependent not only upon the ratio of the receptor types but on the kinetics of drug action, too.

The potency of mono- and dikationic derivatives of adamantane and phenylcyclohexyl to prevent seizures induced in mice by intraperitoneal administration of 80 mg/kg pentylenetetrazol (corazol), was studied. Monocationic derivatives of phenylcyclohexyl, being the selective channel blockers of NMDA glutamate receptors, as well memantine and MK-801 in micromolar concentrations, prevented both clonic and tonic components of corazol-induced convulsions. Their dicatonic derivatives which are channel blockers of NMDA and AMPA types of glutamate receptors, failed to prevent clonic seizures but at submicromolar concentrations prevented the tonic extensions provoked by corazol. Evidently, convulsive action of corazol originating from suppression of GABA-ergic inhibition is realized through activation of glutamergic synaptic transmission, and NMDA receptors are mainly involved in genesis of clonic seizures whereas activation of AMPA receptors is important for the tonic component of the corazol-induced syndrome.

Effects of mono- and dicationic derivatives of adamantine and phenylcyclohexyl were studied on: (i) open channels of NMDA and AMPA glutamate receptors in the experiments on the isolated rat brain neurones, and (ii) convulsions induced by intraventricular injections of NMDA or kainate in mice. Monocations inhibited the NMDA receptors in vitro and prevented convulsions induced by NMDA in vivo, but failed to affect both the AMPA receptors and kainite-induced convulsions. Dications (IEM-1754 and IEM-1925) revealed both anti-NMDA and anti-AMPA potency in vitro, were highly effective against kainite-induced convulsions and excelled monocations in preventing the NMDA-induced ones. Evidently some steps connected with the AMPA receptor activity are involved in the genesis of the NMDA-induced convulsions. Anticonvulsant potency of IEM-1754 and IEM-1925 is comparable with those of known NMDA receptor inhibitors: memantine and MK-801. The IEM-1754 and IEM-1925 show no side effects. An incomplete correspondence between the activity in vitro and in vivo found studying some derivatives, may be due to peculiarities of their pharmacokinetics.

Forty-three bisammonium ganglionic blockers were synthesized to study the structure of the ion channel of nicotinic acetylcholine receptor. The conformational parameters of these blockers were studied, and their effects toward the ganglionic transmission in situ on the sympathetic feline upper cervical ganglions and in vitro on the parasympathetic guinea-pig small intestine ganglions were determined. A model of the binding site for the bisammonium ganglionic blockers in the neuronal ion channel was proposed.

The experiments on rats showed that IEM-1460, IEM-1490, and IEM-1755 (bisammonium adamantyl-containing compounds possessing fast NMDA channel blocking activity) and polyamines (spermine and arcain) do not alter acquiring of the passive avoidance reaction. All these compounds improve, albeit with different efficacy, the memory traces impaired by scopolamine and/or electroshock: IEM-1755 eliminated amnesia induced by the electroshock, but enhanced the amnesia evoked by scopolamine. Arcain inhibited (for a short time and in a narrow dose range) the antiamnesic effect of IEM-1460. It is suggested that the antiamnesic effect of compounds from both groups is related to the ability of slowing down the NMDA receptor desensitization.

Action of mono- and dication derivatives of phenylcyclohexyl was compared with effects of known NMDA-antagonists memantine and dizocilpine. Seizures induced with the NMDA were effectively prevented both by mono- and dications, whereas against the kainate seizures dication alone was effective. Anticataleptic activity was much stronger in monocations, and the side effect of the substances under study on motor co-ordination was obviously weaker than in dizocilpine. Thereupon, the phenylcyclohexyl derivatives might be regarded as potential means for treatment of parkinsonism and other motor disorders.

Structural determinants of blocking the glutamate receptors of AMPA and NMDA subtypes, were studied. Close location of hydrophobic and ammonium groups is necessary for affective blocking of the NMDA receptor channels, whereas blockers of the AMPA receptor channels have a distance of about 10 angstroms between these two groups. Models of the channels meeting these topographic data have been devised using a molecular mechanics approach. The accomplished studies revealed molecular basis of channel blockade of the NMDA and AMPA receptors. This may allow designing predictable new blocking compounds with a desired selectivity.

Experiments on intact mice and rats showed that the monoammonium adamantyl-containing compounds memantine, amantadine, and IEM-1958 (an N-propyl amantadine analog) are capable of blocking the NMDA receptors and producing the anticonvulsant and antihypoxant effects in the case of a systemic administration in doses close to toxic. The acute toxicity of these compounds upon intraperitoneal injections to mice is manifested in doses only 2-8 times the minimum effective dose level. The bis-cationic compounds (arcaine, IEM-1464, and IEM 1490) containing two identical cation groups, exhibit a more pronounced activity and higher safety as compared to those of their monocationic counterparts. This is explained by the ability of the bis-cationic compounds to block a polyamine site of the NMDA receptor. Arcaine (the polyamine site blocker) and IEM-1464 produce the NMDA-receptor-blocking effect and exhibit the anticonvulsant and antihypoxant activity in doses 5-10 times smaller as compared to the effective dose of memantine. At the same time, arcaine is 5 times less toxic than memantine. The bis-adamantyl derivative IEM-13490 is 100-150 times more active and has a 139 times greater therapeutic ratio than memantine.

The topography of the channel binding site in glutamate receptors (AMPA and NMDA types of rat brain neurons, receptors of molluscan neurons and insect muscle), and in two subtypes of nicotinic cholinoreceptors (in frog muscle and cat sympathetic ganglion), has been investigated by comparison of the blocking effects of mono- and dicationic derivatives of adamantane and phenylcyclohexyl. The channels studied can be divided into two groups. The first one includes AMPA receptor and glutamate receptors of mollusc and insect, and is characterised by the absence of activity of monocationic drugs and the strong dependence of dicationic once on the internitrogen distance in the drug molecule. The second group includes NMDA receptor and both nicotinic cholinoreceptors. Contrary, here the blocking potency of monocations and dications are practically equal irrespective of molecule length. The data obtained suggest that hydrophobic and nucleophilic components of the binding site are located close to each other in the channels of the NMDA receptor type but are separated by approximately 10 A in the AMPA receptor channel.

A long-term akinesia induced by haloperidol used as an experimental model of catalepsy helped to reveal that a dicationic derivatives adamantane (IEM-1754) and phenylcyclohexyl (IEM-1925) exerted different degrees of inhibition of the haloperidol effect: the IEM-1754 proved to be not inferior to the most effective NMDA antagonist MK-801. A relatively low potency of the IEM-1925 may be due to its obvious equal effects both on the NMDA and the AMPA receptor channels. A good correlation between the anticataleptic effects of the glutamate antagonists and the NMDA receptor blocking activity, were found. The AMPA receptor blockade might negatively affect the anticataleptic potency of the drugs under study.

Experiments on intact rats and mice showed that the polyamine agonist spermine and the bis-ammonium adamantyl-containing compounds IEM-1460 and IEM-1754 potentiate the NMDA induced analgesia and convulsions and eliminate the analgesic effects of nicotine and kainate. Arcain, a competitive polyamine antagonist, eliminated (at the same dose) the activating and blocking effects of spermine, IEM-1460 and IEM-1754. In small doses, IEM-1754 (similarly to arcain) removed the analgesic effect of NMDA. It is suggested that IEM-1460 (similarly to spermine) is a polyamine agonist, while IEM-1754 is an antagonist/agonist of the polyamine site of NMDA, AMPA/kainate, and nicotinic receptors. The potentiating activity of IEM-1460 is two orders higher as compared to that of spermine.

Pyrilene acts as a central H-cholinoblocker upon intramuscular injection at a dose of 0.02-0.08 mg/kg, and as an NMDA-blocker, when the dose is increased to 0.2-0.8 mg/kg. Similarly, amantadine exhibits the properties of H-cholinoblocker and NMDA-blocker in the dose intervals 10-15 mg/kg and 120-180 mg/kg, respectively. The activity of MK-801 markedly exceeds that of memantine, although close doses of both NMDA-blockers inhibit the NMDA and corazole effects, as well as the central effects (analgesia and seizure) of nicotine, thus showing no significant selectivity with respect to NMDA. IEM-1754 tested on intact animals exhibited a selective action upon the NMDA receptors, preventing the NMDA-induced analgesia and lethality and the corazole-induced convulsions at doses 10-100 times lower as compared to those preventing nicotine-induced seizure and analgesia.

Two groups of substances capable of selectively blocking the NMDA and AMPA/kainate receptors in experiments on intact animals were found in a series of bis-ammonium compounds with adamantyl radicals. The selective NMDA receptor blockers (IEM-1754, IEM-1755, IEM-1752), as well as the reference agents MK-801 and memantine, produced anticonvulsant, anti-ischemic, and antihypoxant effects and prevented the loss of experimental animals from toxic doses of NMDA. The selective AMPA/kainate receptor blockers (IEM-1553, IEM-1751, IEM-1592, and DNQX)) also produced the anticonvulsant, anti-ischemic, and antihypoxant effects, but did not prevent from the loss of animals caused by the toxic doses of NMDA. The maximum activity was observed for IEM-1754, the activity of which exceeded that of MK-801 (by a factor of 5-10) and memantine (by a factor of 300-800) in all the test objects.

Administration of MK-801 or IEM-1754 prevented akinesia in mice induced by reversing rotation, not less effectively than scopolamine. Quaternary adamantane derivative IEM-1857 was ineffective. IEM-1925 enhanced the locomotor disturbance induced by reversing rotation due, probably, to different spectrum of its antiglutamate action. The data obtained suggest involvement of glutamate synaptic transmission in development of locomotor disturbances of a vestibular origin.

Adrenaline-induced stress as well as exogenous cholecystokinin exerted analgetic, antidepressant, and antistress effect upon depressive rats with high nociceptive sensitivity. The effect seems to be due to stimulation of chemoreceptors of the stomach vagal afferents by means of cholecystokinin secretion into the gastric lumen.

Effects of open channel blockers of AMPA/kainate receptors have been examined using whole cell recordings and kainate application in the neurons freshly isolated by vibrodissociation from the rat hippocampal slice preparation. Although the hippocampal neurons differed little in the voltage-current relations and sensitivity to kainate, a prominent difference was found in their susceptibility to the blocking action of adamantane derivatives studied. The pyramidal neurons had low sensitivity to the open channel blockers but the neurons which might be assigned most probably to the group of inhibitory interneurons proved to be highly sensitive. A group of neurons of intermediate sensitivity have also been found. The ability of the same blocking drugs to depress the excitatory inputs in the inhibitory interneurons has been demonstrated in the experiments on the hippocampal slice preparation. Enhancement of the field spike and excitatory postsynaptic potential amplitude was observed in the presence of adamantane derivatives. An additional treatment of the preparation with a GABA receptor antagonist, bicuculline, did not potentiate this effect. In conclusion, the observed difference in the pharmacological properties of inhibitory interneurons may be effectively used for detailed analysis of the brain synaptic transmission.

Stress and subsequent release of biologically active compounds exerted an antihypoxic and antishock reaction, simultaneously enhancing physical efficiency. The data obtained suggest endogenous adenosine and cholinergic interneurons of the gastric intramural ganglia to take part in reflex activation of vagal gastric afferents. Activation of gastric afferents by stress releasing compounds is a significant factor for rapid adaptation of the organism to stress exposure.

It has been shown that a homologous series of adamantane derivatives of general structure Ad-CH2-N+H2-(CH2)5-N+R3, where Ad, adamantane, R varied from H (hydrogen) to t-Bu (tertiary butyl), blocks the open state of postsynaptic activated channels. In the presence of the drugs studied the decay of evoked cholinergic postsynaptic currents in frog neuromuscular junction could be fitted by two exponentials. However, the rate constants of interaction of blocker with channel did not depend on the R structure and membrane potential. The rate of blockade of glutamatergic postsynaptic currents in insect neuromuscular junction increased as the radicals at nitrogen atom became heavier, but was independent on membrane potential. The drugs studied affected in voltage dependent manner the kinetic properties of single channels (recorded in outside-out patches excised from cultured neurones of embryonic rat brain cortex) induced by NMDA application. Each of these compounds evoked fast flickering of single channels between an open and blocked state. Drugs effectively prevented the convulsions evoked by intraventricular injection of NMDA into mouse brain. The compound IEM-1754 that was the most potent blocker in the experiments on NMDA-activated single channels possessed six times higher anticonvulsant activity than dizocilpine (MK-801).

The double bath method has been used to study reflex inhibition of cholinergic transmission in the guinea-pig ileum segment. It is shown that adenosine, noradrenaline, 5-methylfurmethide as well as acute hypoxia, which affect the oral part of the intestine are able to evoke two kinds of effects in its anal part firstly, the depression of cholinergic transmission, and secondly, the stimulation of non-adrenergic, non-cholinergic contractions. A preliminary treatment with capsaicin and with hexamethonium on the oral part of the gut prevents these effects, and the chymotrypsin abolishes these effects. A mechanism of this reflex descending inhibition of cholinergic transmission is realised apparently through the stimulation of the chemoreceptors in afferent capsaicin-sensitive nerves with participation of cholinergic interneurons and activation of the inhibitory, most probably vasoactive intestinal peptidergic (VIP) neurons in the enteric plexuses.

Pharmacological tests in vitro on the cat isolated superior cervical and ciliary ganglia identified the IEM-1194 as a selective parasympathetic ganglion-blocking agent. The ganglion-blocking activity of this drug was three times as high in parasympathetic ganglion (EC50 = 1.15 +/- 0.34 M/1 x 10(-5)) as in sympathetic one (EC50 = 3.2 +/- 0.2 M/1 x 10(-5)). I. v. administration of the IEM-1194 in a dose effectively (50%) blocking responses of the heart (bradycardia) and duodenum (peristaltics) to vagal stimulation, did not lower arterial blood pressure.

In experiments on the isolated ileum of guinea pigs and rats it was shown that 1,3-dipropyl-8-phenylxanthine (DPPX) is a highly potent adenosine antagonist blocking A1-adenosine receptors of the myenteric plexus (pA2 = 7.29 +/- 0.06) and allosterically modulating affinity of A2-receptors of the intestinal smooth muscles to adenosine (pA2 = 6.64 +/- 0.05). DPPX exerted no influence on purinergic (PR2), adrenergic and opiate receptors of the nervous and muscular cells of the intestine. Exceeding the activity of theophylline by 339-87 times, DPPX failed to exert the selective effect on A1- and A2-subtypes of adenosine receptors.

The effect of IEM-1742, a pentaethonium derivative, on the currents induced by iontophoretic applications of acetylcholine was studied in rat superior cervical ganglion neurons using patch-clamp method in the whole-cell modification. Blocking action increased with membrane hyperpolarization and was removed by strong membrane depolarization. Apparent dissociation constant for the receptor-blocker reaction was found to be (2.9 +/- 0.6) 10(-6) M (n = 6) at -50 mV and 20-23 degrees C. IEM-1742 blocks the nicotinic acetylcholine receptor in its activated form. The dissociation of IEM-1742 from the receptor was drastically accelerated during its activation by agonist (trap-block). Trapped receptor was not released from the blocker only by membrane depolarization to the level at which any blocking effect is absent. The data obtained show that IEM-1742 in rat sympathetic ganglion neurons acts in the potential-dependent manner and displays a trap-effect.

The actions of bis-ammonium compounds on acetylcholine-activated channels were studied in voltage-clamped neurons of isolated superior cervical ganglion in a rabbit. The kinetics of the compound binding to open channels was estimated from shortening of the decay of fast excitatory postsynaptic current (which is determined by the rate of channels closure). The kinetics of dissociation of the compound from open channels was estimated from the kinetics of the restoration of the second response to double-pulse application of acetylcholine in presence of the blocking compound. The rate constant of bindings of the bis-ammonium compounds to open channels increased while the rate constant of dissociation decreased with membrane hyperpolarization. This voltage-dependence increased with the lengthening of the polymethylene chain in the compound and remained unchanged with the lengthening of nitrogen group radicals. The ganglion-blocking activities of the compounds as determined in the cat ganglion in situ correlated with their rate constants of binding to open channels. It was concluded that ganglion-blocking actions of bis-ammonium compounds is determined by their channel-blocking activities.