N-(5-Hydroxynicotinoil)-L-Glutamic Acid Calcium Salt Modifies Responses of Rat Hippocampal CA1 Pyramidal Neurons during Orthodromic Stimulation.

The study examined the effect of calcium salt of N-(5-hydroxynicotinoil)-L-glutamic acid (Ampasse preparation) on neuronal activity in hippocampal CA1 area evoked by stimulation of Schaffer collaterals at a rate of 1 Hz (30 impulses during 30 sec) in the surviving hippocampal slices of Wistar rats. The records of 1st and 30th orthodromic population spikes showed that Ampasse in concentrations of 500 µM, 1, 2, and 10 mM facilitated the synaptic transmission in Schaffer collaterals - hippocampal CA1 pyramidal neurons axis; the maximum effect was observed at 2 mM Ampasse. When used in a concentration of 10 mM, Ampasse provoked epileptiform activity, which could be prevented by MK-801, a specific noncompetitive antagonist of the NMDA-receptor complex.

ACTION OF NEW 3-HYDROXYPYRIDINE DERIVATIVES WITH ANTI-NAUPATHIA PROPERTIES ON CENTRAL NEURONS.

Experiments with cats showed that microinjections into the lung of new 3-hydroxypyridine derivatives SK-119 and IBKhF-27 had a direct action on 50 and 84 % of medial vestibular nucleus (MVN) neurons respectively. The inhibitory response to the compounds was observed 6 and 25 times more frequently than exciting; inhibition by IBKhF-27 was observed 1.9 times more frequently than by SK-119. Also, microinjections of SK-1 19 and IBKhF-27 acted directly on 44 % and 81 % of cat's Purkinje cells, respectively. In case of Purkinje cells, the inhibitory reaction was seen 5.5 and 25 times oftener than exciting, respectively, and inhibition by IBKhF-27 occurred 2.1 times more frequently than by SK-119. Investigations of rat's cerebellum sections evidenced that 5 mM of IBKhF-27 inhibited population responses of Purkinje cells 95 1 3 %. In the presence of specific noncompetitive NMDA-receptor antagonist (MK-801, 100 pM) the depressive effect was annulled almost fully by 96 * 2 %. It follows that IBKhF-27 nearly entirely inhibits synaptic transmission from cerebellar parallel fibers to Purkinje cells, while MK-801 has a similarly strong anti-depression effect that testifies the involvement of the NMDA-receptor complex predominantly.

Effect of NMDA, a Specific Agonist to NMDA Receptor Complex, on Rat Hippocampus.

Removal of Mg2+ ions from perfusion medium provoked epileptiform activity in CA1 field of surviving rat hippocampal slices manifested in generation of extra population spikes. MK-801 (100 µM), a specific non-competitive antagonist to NMDA-receptor complex, prevented this effect. NMDA (20 µM), the specific agonist to this complex, produced no significant effect on the orthodromic population spikes, but when applied at concentrations of 30 or 40 µM, it inhibited them partially (by 21-28%) or almost completely (by 98-99%), correspondingly. Thus, depending on concentration, NMDA can inhibit the synaptic transmission in Schaffer collaterals-hippocampal CA1 pyramidal neurons axis without triggering the epileptiform activity. D-AP5 (50 µM), a competitive antagonist to NMDA-receptor complex, completely prevented the inhibitory effect of NMDA (40 µM). While MK-801 (100 µM) almost completely prevented the inhibitory effect of NMDA, it did not eliminate it when applied after the agonist. Thus, MK-801 can prevent the inhibitory action of NMDA on synaptic transmission in Schaffer collaterals-hippocampal CA1 pyramidal neurons axis via blocking the channel of NMDA-receptor complex, while NMDA exerts its effect only via activation of NMDA receptors.

[Study of neuroprotective, antihypoxic and antiamnesic effects of new mixture of tripeptides].

A new mixture of tripeptides (NMT: H-Lys-Asp-Glu-OH, H-Asp-Glu-Pro-OH, H-Asp-Glu-Arg-OH) in doses of 150 and 300 mg/kg per day produces clearly pronounced neuroprotective effect in rats with brain ischemia and decreases neurologic deficiency 1.1 times more effectively than reference drug semax. NMT (10, 50 and 150 mg/kg) had marked antihypoxic effect on mice in hermetic and altitude chamber. NMT in doses of 10 and 50 mg/kg was more effective than semax in hermetic chamber (1.3 and 1.5 times, respectively) and in a dose of 150 mg/kg in altitude chamber (1.9 times). NMT (50 and 150 mg/kg) had also marked antiamnesic effect on model amnesia caused by scopolamine in rats and was more effective (1.5 and 1.4 times, respectively) than semax in equal doses. NMT (50 and 150 mg/kg) also had marked antiamnesic effect on model amnesia caused by maximal electroshock and complex extreme factors in mice and in both doses was 4 times more effective than semax on the first model and in a dose of 150 mg/kg was 2.9 times more effective on the second model. NMT (50 mg/kg) increased the amplitude of transcallosal evoked potential in rat brain by 69% and was more effective than semax in equal dose. Thus, NMT is a promising neurotropic drug with neuroprotective, antihypoxic and antiamnesic activity.

[STUDIES OF THE ANTIHYPOXIC AND ANTIAMNESTIC EFFECTS OF MELATONIN IN ANIMALS].

Experiments with mice showed that in a multitude of acute hypoxia models (normobaric hypoxic hypoxia with hypercapnia, hypobaric, hemic and histotaxic) the antihypoxic action of a single intra-abdominal dose of melatonin surpasses greatly amtisol, the standard antihypoxic agent. Single melatonin injection produced a strong antiamnestic action on various amnestic models (scopolamine-induced, acute normobaric hypoxia with hypercapnia, and a combination of extreme factors) which was much better than of pyracetame, a well-known nootropic (mind-stimulating) drug. Increase of the melatonin dose from 1 mg/kg to 20 mg/kg amplified both the antihypoxic and antiamnestic effects. Melatonin inhibited orthodromal population responses in surviving sections of rat's hippocampus (by 24 ± 3% at 2 mM; by 72 ± 6% at 5 mM). Besides, the inhibiting action of lusindol, a blocker of melatonin receptors MT1 and MT2--was virtually fully neutralized. Therefore, melatonin inhibits transmission within the Schaffer collateral--CA1 pyramidal neurons synapse by stimulation of melatonin receptors MT1 and MT2; higher melatonin concentrations (0.5 to 5 mM) enhance its effectiveness.

[Study of some pharmacological properties of a new adenine derivative].

It is established that the new compound, 9-[2-(4-isopropylphenoxy)ethyl]adenine (9-IPE-adenine) in a dose of 10 mg/kg per day produces neuroprotective effect in rats with brain ischemia model. 9-IPE-adenine decreased the neurologic deficiency 1.2 times more effectively (p < 0.05) than the reference drug mexidol in analogous dose, and had equal effect with this drug at 25 mg/kg per day on the neurologic deficiency and survival of animals. Electrophysiological studies in hippocampal slices in rats showed that 9-IPE-adenine depressed orthodromic population spikes in CA1 area by 42 ± 4%. Non-competitive antagonist of NMDA receptor complex MK-801, in contrast to D-AP5 (competitive NMDA receptor antagonist) and CNQX (competitive AMPA receptor antagonist), enhanced the depressive effect of the new drug more than two times. These ese results are indicative of the ability of 9-IPE-adenine to modulate the ion channel of NMDA receptor complex.

[Investigation into the vestibular protective properties of melatoninergic agents].

Experiments with rats showed that melatonin (2.5 mg/kg) produces a distinct vestibular protective effect excelling promethazine (50 mg/kg) as a reference agent, and also antidepressant agomelatine (5 mg/kg) as another melatoninergic agent. Lusindol, a blocker of MT1/MT2-receptors (2.5 mg/kg), and bicuculline (1.5 mg/kg), a specific GABA-receptors antagonist, weakened the melatonin effect significantly. The results testify mediation of the melatonin action by these receptors. Whole-cell patch clamp in an experiment with convoluted oblongata sections from white nonlinear infant male rats (14-d old) disclosed that melatonin (2 mM) inhibited drastically (29 +/- 3%) the excitatory postsynaptic current caused by depolarization step in neurons of the medial vestibular nucleus. Lusindol (0.1 mM) inhibited the effect of melatonin (2 mM) significantly (71 +/- 6%) which suggests involvement of melatonin MT1/MT2-receptors.

[Effects of vestibuloprotectors mexidol and melatonin on animal cerebellum].

In experiments with cats, air-assisted microinjections of mexidol and melatonin had a direct effect on 71-81% Purkinje cells inducing the inhibitory response 4.2-6.3 times more often than exiting. In case of concurrent action of MK-801 (a specific noncompetitive NMDA-receptor antagonist) the mexidol effect on the spontaneous activity was suppressed fully or abated significantly in 88% Purkinje cells. Lusindol (a specific melatonin MT2- and MT2-receptor antagonist) and GABA-negative bicuculline prevented the inhibiting effect of melatonin fully or abated significantly the spontaneous activity of 86% and 71% Purkinje cells, respectively. This means that melatonin-produced inhibition recruits both melatonin MT1- and MT2-receptors, and also the GABA-ergic component (stimulation of GABAA-receptors). Investigation of rat's cerebellum slices with prolonged survival showed that 5 mM of mexidol inhibited reliably Purkinje cells population responses by 93 +/- 4%; the presence of MK-801 (100 microMM) weakened this effect by 82 +/- 3%. Consequently, mexidol is capable to inhibit strongly the parallel fibers--Purkinje cells synaptic transmission in the rat's cerebellum, whereas MK- 801 abates this effect appreciably.

[On the mechanism of ikaron-1 anti-naupathia action].

Pneumomicroinjection of vestibuloprotector ikaron-1 (Russia) in specific neurons of the medial vestibular nucleus (MVN) was studied in cats immobilized by muscle relaxants using microelectrode devices. The original preparation had a direct effect on the majority of MVN neurons (95 %). Thirty four neurons of 37 cells (92 %) developed an inhibitory response, only one cell (3 %) was activated and 2 neurons (5 %) were areactive. Therefore, the inhibitory reaction to the preparation was 34 times more often than excitatory. An investigation of the MVN neurons activity evoked by adequate stimulation of the vestibular apparatus showed that ikaron-1 attenuates the evoked response in 92 % cells. This phenomenon could be behind the ikaron-lantinaupathia action.

[Analgesic effect of succinate-containing preparations].

It was established that mexidol (100 mg/kg, i.v.) in contrast to cytoflavin (1 ml/kg, i.v.) and reamberin (100 mg/kg, i.v.) produced analgesic effect in rabbits by raising pain threshold under electric stimulation of dental pulp. Mexidol (200 mg/kg, i.p.) also raised the nociceptive threshold of the same tail stimulation by in rats (vocalization test). Non-competitive antagonist of NMDA receptor complex, MK-801 (0.1 mg/kg, i.p.), and selective GABAA receptor antagonist bicuculline (1.5 mg/kg, i.p.) decrease the effect of mexidol. Therefore, the antinociceptive effect of mexidol in rats is mediated by the NMDA receptor complex and GABAA receptors. It was also found that mexidol (microiontophoretic application) produced inhibiting effect on spontaneous and evoked (caused by nociceptive electric stimulation of hind paw) activity of neurons (major part) of sensorimotor cortex and ventral posterior thalamic nucleus in rabbits. On the background of MK-801 and GABA blockers (bicuculline and picrotoxin), this action of mexidol was completely prevented or considerably decreased (by almost 80 and 60% of cells, respectively). Therefore, the effect of mexidol on these neurons is realized by inhibiting ion currents through NMDA receptor complex and via GABAA/benzodiazepine receptor complex.

[Electrophysiological study of the mechanism of mexidol action].

It has been found that mexidol (5 mM) significantly (96 +/- 2%) depressed excitatory postsynaptic current caused by step depolarization in neurons of medial vestibular nucleus of medulla oblongata slices in young (aged 13 - 17 days) male albino rats. In addition, mexidol (2,5 - 5 mM) depressed by 94 +/- 3% excitatory postsynaptic current caused by Shaffer collaterals stimulation of CA1 pyramidal neurons of hippocampal slices in young rats. Complex MK-801 (non-competitive antagonist of NMDA receptors), in contrast to CNQX (competitive AMPA receptor antagonist), considerably decreased the depressant effect of the drug in both brain structures. Therefore, the central favorable effect of mexidol can be mediated by ion mechanisms with glutamate- and GABA-ergic components, primarily by the inhibition of ion currents through NMDA receptor complex.

[Comparative studies of antihypoxic, neuroprotective and analgesic action of succinate-containing drugs].

Experiments with mice showed that, unlike reamberin (100 mg/kg), mexidol (100 mg/kg) and cytoflavin (1 ml/kg) act as antihypoxants in pressure and hermetic chambers but not in case of acute hemic and histotoxic hypoxia. Amtisol succinate (100 mg/kg), a reference antihypoxant, excels the other tried succinate-containing drugs in all models of acute hypoxia except the hermetic chamber. In addition, the neuroprotective action of mexidol (100 mg/kg/d) and cytoflavin (100 ml/kg/d) in rats with induced ischemic stroke which was stronger than that of reamberin and amtisol succinate (100 mg/kg/d). Besides, mexidol (100 mg/kg) but not cytoflavin (1 ml/kg), reamberin or amtisol succinate (100 mg/kg) had a distinct analgesic effect in rabbits. On the neuronal level, mexidol interacts with the GABAA- benzodiazepine-receptor complex in nearly 60% cells and inhibits ion currents through the NMDA-receptor ion channels in nearly 80% neurons.

[Effects of different neuromediators and regulatory peptides on the impulse activity of neurons in the superior vestibular nucleus].

The microelectrode technique and microiontophoresis of physiologically active substances in experiments with cats immobilized with the muscle relaxants made it clear that different classical neuromediators (acetylcholine, norepinephrine, gamma-aminobutyric acid (GABA) and others), as well as regulatory peptides (enkephalins, thyrotropin-releasing hormone (TRH), vasoactive interstitial peptide (VIP), somatostatin (SS) and others) can exert a direct effect on the majority (61 to 100%) of neurons in the superior vestibular nucleus (SVN). The inhibiting effect of enkephalins, VIP and SS on the neurons impulse activity remained essentially unchanged by L-glutamate. Also, enkephalins, VIP and SS were found to amplify the inhibiting action of GABA and glycine. Consequently, these substances can fulfill the role of SVN neuromediators and/or neuromodulators.

Acetylcholine precursor choline evokes NMDA-dependent epileptoid activity in rat hippocampal CA1 area.

Application of choline (5 and 10 mM) to electrically stimulated (1 Hz) rat hippocampal slices evoked epileptoid activity manifested by generation of extra population spikes. Application of methyllycaconitine (10 nM), a specific agonist for α7-subunit of nicotinic acetylcholine receptors, did not prevent generation of extra population spikes. In contrast, pretreatment of slices with Mg(2+) (5 mM) or blockade of NMDA-type glutamate receptors with MK-801 (100 µM) prevented generation of the extra population spikes. It was hypothesized that elevation of choline concentration during cerebral pathology can promote activation of NMDA-receptors and provoke epileptoid activity not related to activation of α7-subunit of nicotinic acetylcholine receptor.

[On the mechanism of antimotion sickness effects of mexidol].

The path-clamp method used within the whole-cell configuration in experiments with convoluted medullar oblongata sections obtained from white mongrel male rats aged 13 to 17 days evidenced that 5 mV of mexidol caused 96 +/- 2% inhibition of the excitation postsynaptic current in neurons of the medial vestibular nucleus generated by the depolarization step of 10 mV (holding potential = -70 my). This means that the antimotion sickness effect of mexidol has its origin in the ion mechanisms with involvement of the glutamate- and GABAergic components, primarily inhibition of ion currents through channels of the NMDA-receptor complex.

[Effects of different neuromediators and regulatory peptides on the impulse activity of neurons in vestibular zone-I of the cerebral cortex].

Microelectrodes and micro-iontophoresis of physiologically active substances in experiments with cats immobilized by muscle relaxants made it apparent that different classical neuromediators (acetylcholine, norepinephrine, GABA and others) and regulatory peptides (enkephalins, thyrotropin-releasing hormone, vasoactive intestinal peptide (VIP), somatostatin (SS) and others) are capable to influence directly 68 to 100% of neurons in vestibular zone-I of the cerebral cortex. In the presence of L-glutamate, the inhibiting effect of enkephalins, VIP and SS on the neurons impulse activity was essentially unaltered. Also it was shown that enkephalins, VIP and SS are potent to augment the inhibiting effect of GABA and glycine. Therefore, these substances may have the neuromediator and/or neuromodulator role in this cortical zone.

[Effects of various neuromediators and regulatory peptides on the impulse activity of neurons in the lateral vestibular nucleus].

The myoelectrode technique and microiontophoresis of physiologically active substances were applied to cats immobilized with neuromuscular relaxant to show that the classic neuromediators (acetylcholine, norepinephrine, GABA etc.) and regulatory peptides (enkephalins, TRHs, vasoactive intestinal peptide (VIP), somatostatin (SS) and others) can influence directly most neurons (58 to 100%) in the lateral vestibular nucleus (LVN). Enkephalins, VIP and SS retained largely their inhibitory effect on the neuron impulse activity in the presence of L-glutamate. Also, enkephalins, VIP and SS are able to stimulate or suppress the inhibitory effect of GABA and glycine. Consequently, the substances under study may act as LVN neuromediators and/or neuromodulators.

[Modification by various neuromediators and regulatory peptides of the impulsation activity of neurons in the medial vestibular nucleus].

Cats were immobilized with myorelaxation agents to apply the microelectrode technique and microlonophoresis of physiologically active substances. As a result it was shown that various classic neuromediators (GABA, taurine and others) and regulatory peptides (vasoactive intestinal peptide (VIP), somatostatine (SS) and others) have effect on the majority (62 to 100%) of neurons in the medial vestibular nucleus. In the presence of L-glutamate VIP and SS CC retained essentially their inhibitory effect on the neurons impulse activity. Both VIP and SS were found to amplify the inhibitory action of GABA and glycine. To sum up, the substances under study can function as neuromediators and/or neuromodulators in the medial vestibular nucleus.

[On the glycinergic component of the mechanisms of medial vestibular nucleus neurons functioning].

Tests with surviving medulla sections of white non-strain male rats showed 100 microM of strychnine (glycine antagonist) but not 20-100 microM GABA-negative biku-kullin and picrotoxin reduced almost double the postsynaptic N1-amplitude of the population response to afferent vestibular stimulation in the ventral region of the medial vestibular nucleus (MVN). This suggests a glycinergic component in the mechanisms of MVN neurons functioning and absence of a GAMA-ergic analog in healthy adult rats.

Effects of antibodies against protein S100b on synaptic transmission and long-term potentiation in CA-1 hippocampal neurons in rats.

Effects of idiotypic and antiidiotypic antibodies against protein S100b on synaptic transmission and long-term potentiation of CA1 pyramidal neurons in rat hippocampus were studied. Idiotypic antibodies against protein S100b inhibited synaptic transmission from Schaffer collateral axons to pyramidal neurons, but had no effect on neuronal responses to antidromic stimulation. Antiidiotypic antibodies against protein S100b facilitated neuronal responses to orthodromic stimulation. Idiotypic antibodies against protein S100b suppressed changes in neuronal responses to orthodromic stimulation during long-term potentiation, while antiidiotypic antibodies facilitated these effects. Our findings suggest that the effects of idiotypic and antiidiotypic antibodies to protein S100b are associated with their regulatory influences on synaptic transmission. These mechanisms differ from mechanisms of synaptic plasticity involved in long-term potentiation.