Ions and amino acid analysis of Cyperus articulatus L. (Cyperaceae) extracts and the effects of the latter on oocytes expressing some receptors.

Extracts from rhizomes of Cyperus articulatus L. (Cyperaceae) used in Africa and Amazonia to treat many diseases has been shown to possess sedative and anticonvulsant properties. The aim of this study is to determine the mechanism of action of Cyperus articulatus extracts. In Xenopus oocytes expressing receptors, using electrophysiological measurement, extracts of rhizomes of Cyperus articulatus (300 microg/ml) inhibited 50% of the EC(50) and EC(80) of glutamate (1.3 and 2.9 microM, respectively) induced inward current through hNMDAR1A/2A receptors. Extracts induced very small current through rGluR3 receptors. The largest current induced by the extract (30 mg/ml) represents 128% of the EC(100) of glutamate induced inward current, through rGluR3 receptors. The excess 28% current could be induced by aspartate and/or glutamate in the extracts. The effect on Xenopus oocytes expressing heteromeric GABA(B)R1b/R2 receptors and rectifying potassium channels (Kir3) is clear. A decoction and water extract of Cyperus articulatus induced a large inward current that represented 71 and 57% (respectively) of the EC(100) of gaba (30 microM) induced inward current. The water extract induced also a large current through rectifying potassium channels (Kir3). Part of the current induced through GABA(B) receptors could be related to rectifying potassium channels and GABA(B) site receptors. Cyperus articulatus extracts possessed components that could decrease excitation (NMDA receptor antagonists) and increase inhibition (GABA(B) receptor agonists) in the central nervous system.

Anticonvulsant activity of Mimosa pudica decoction.

The decoction of Mimosa pudica leaves given intraperitoneally at dose of 1000-4000 mg/kg protected mice against pentylentetrazol and strychnine-induced seizures. M. pudica had no effect against picrotoxin-induced seizures It also antagonized N-methyl-D-aspartate- induced turning behavior. These properties could explain its use in African traditional medicine.

Electrophysiological studies on the hippocampus and prefrontal cortex assessing the effects of amyloidosis in amyloid precursor protein 23 transgenic mice.

In vitro and in vivo electrophysiological studies were done to investigate the neuronal function of the hippocampus and prefrontal cortex in the amyloid precursor protein (APP) 23 transgenic mouse model for amyloidosis developed by Sturchler-Pierrat et al. [Proc Natl Acad Sci USA 94 (1997) 13287]. Brain slices were taken from 3, 6, 9, 12, 18 and 24 month old wildtype and hemizygous type APP23 mice. Extracellular field potentials were recorded from the CA1 region of the hippocampus while stimulating the Schaffer collaterals. In addition, extracellular field potentials were elicited from areas within layer V/VI of the prefrontal cortex by stimulating the same layer V/VI. Basic synaptic function in the hippocampus was reduced in hemizygous APP23 mice compared with their wildtype littermates at 12 and 18 months of age, whereas, it was unaltered within the prefrontal cortex. Long-term potentiation in the hippocampus and the prefrontal cortex of hemizygous APP23 mice was similar compared with their wildtype littermates. In vivo electrophysiological experiments were done in 3, 9, 18 and 24 month old wildtype and hemizygous APP23 mice. No differences were observed in the number of single spontaneously active units recorded within the prefrontal cortex of hemizygous APP23 mice compared with their wildtype littermates. Field potentials elicited during stimulation of cortico-cortical pathways to assess synaptic transmission and short-term synaptic plasticity were also unchanged in hemizygous APP23 mice. Furthermore, presumable antidromic field potentials recorded in the prefrontal cortex during stimulation of the striatum were similar between the hemizygous APP23 and wildtype mice at each age. The present study shows that amyloidosis impairs basic synaptic function but not long-term potentiation in the hippocampus, however, does not alter any of the neurophysiological functions measured within the prefrontal cortex. These findings suggest that amyloidosis may be involved in altering some neurophysiological functions within only certain brain structures. Although APP23 mice have impaired cognitive performance, long-term plasticity, a cellular model for memory, is not affected, raising the question on the relationship between these processes.

Effects of clozapine, haloperidol and iloperidone on neurotransmission and synaptic plasticity in prefrontal cortex and their accumulation in brain tissue: an in vitro study.

The mode of action of the antipsychotic drugs clozapine, haloperidol and iloperidone was investigated in layer V of prefrontal cortex slices using extracellular field potential, intracellular sharp-electrode as well as whole-cell voltage clamp recording techniques. Intracellular investigations on a broad range of concentrations revealed that the typical neuroleptic haloperidol at higher concentrations significantly depressed the excitatory postsynaptic component induced by electrical stimulation of layer II. This was not seen with the atypical neuroleptics clozapine and iloperidone. None of the three compounds had any effect on the resting membrane potential, spike amplitude or input resistance at relevant concentrations. Synaptic plasticity was assessed by means of extracellular field potential recordings. Clozapine significantly facilitated the potentiation of synaptic transmission, whereas haloperidol and iloperidone showed no effects. In line with its facilitating effect on synaptic plasticity, it could be demonstrated by whole-cell voltage clamp recordings that clozapine increased N-methyl-D-aspartic acid receptor-mediated excitatory postsynaptic currents in the majority of prefrontal cortical neurones. These investigations were made with neuroleptic drugs applied to the bath in the micromolar concentration range in order to approach clinical brain concentrations that are reached after administration of therapeutic doses. The drug concentrations reached in the slices after the experiments were assessed by means of high-pressure liquid chromatography coupled with mass-spectrometric detection. Surprisingly, drug accumulation in the in vitro preparation was of similar degree as reported in vivo. In conclusion, the typical neuroleptic haloperidol significantly depressed excitatory synaptic transmission in layer V neurones of the prefrontal cortex. In contrast, the two atypical neuroleptics iloperidone and clozapine revealed no depressing effects. This feature of the atypical neuroleptics might be beneficial since a hypofunctionality of this brain area is thought to be linked with the pathophysiology of schizophrenia. Additionally, clozapine facilitated long-term potentiation, which might be linked with the clinically observed beneficial effects on certain cognitive parameters. The clozapine-induced increase of N-methyl-D-aspartic acid receptor-mediated currents suggests that clozapine facilitates the induction of long-term potentiation. Furthermore, the present study points to the importance of considering the significant accumulation of neuroleptic drugs in in vitro studies.

Anticonvulsant properties of the methanolic extract of Cyperus articulatus (Cyperaceae).

The methanolic extract of rhizomes of Cyperus articulatus, a plant used in traditional medicine in Africa and Latin America for many diseases, possesses anticonvulsant activity in mice. This extract protected mice against maximal electroshock (MES)- and pentylenetetrazol (PTZ)-induced seizures. It also delayed the onset of seizures induced by isonicotinic acid hydrazide and strongly antagonized N-methyl-D-aspartate-induced turning behavior. The ED(50) for protection against seizures was 306 (154-541) mg/kg intraperitoneally (i.p.) for the PTZ test and 1005 (797-1200) mg/kg i.p. for the MES test. The ED(50) of methanolic extract against N-methyl-D-aspartate-induced turning behavior was 875 (623-1123) mg/kg i.p. C. articulatus L. methanolic extract protected 54% of mice from seizures induced by strychnine at the dose of 1000 mg/kg i.p. but had no or a moderate effect only against picrotoxin- or bicuculline-induced seizures. With these effects, the rhizome of C. articulatus L. possesses anticonvulsant properties in animals that might explain its use as a traditional medicine for epilepsy in Africa.

The potency of the novel tachykinin receptor antagonist CGP49823 at rat and gerbil motoneurones in vitro.

The novel tachykinin receptor antagonist CGP49823 ((2R,4S)-2-benzyl-1-(3,5-dimethylbenzoyl)-4-(quinolin-4-y lmethylamino)piperidine) has been compared with three other selective non-peptide tachykinin NK1 receptor antagonists. The drugs were tested as antagonists of the depolarization of spinal motoneurones induced by bath application of the selective tachykinin NK1 receptor agonist septide-(6-11) (300 nM) for 120 s at 15 min intervals. The antagonists were bath applied and the depolarizations were recorded from lumbar ventral roots of 7 to 12 day old rat and gerbil hemisected spinal cords in vitro. The gerbil preparation is considered to model the human species variant of the tachykinin NK1 receptor. With the exception of SR140333 ((S)-1-[2-[3-(3,4-dichlorophenyl)-1-[[3-(1-methylethoxy)phenyl]ace tyl]-3-piperidinyl]ethyl]-4-phenyl-1-azoniabicyclo[2.2.2]octane chloride), the antagonists were approximately thirty-fold more potent on gerbil preparations. The respective mean IC50 values from gerbil preparations produced by CP96345 ((2S-cis)-2-(diphenylmethyl)-N-[(2-methoxyphenyl)methyl]-1-azabicy clo[2.2.2]octan-3-amine), CGP49823, SR140333 and CP99994 ((2S-cis)-N-[(2-methoxyphenyl)methyl]-2-phenyl-3-piperidinamine) were, in microM +/- S.E. (n) 0.10 +/- 0.02 (6), 0.22 +/- 0.03 (6), 0.30 +/- 0.10 (5) and 0.38 +/- 0.02 (5) and the corresponding values from the rat preparations were 3.7 +/- 0.4 (5), 7.8 + 1.3 (5), 1.06 +/- 0.16 (6) and 10.5 +/- 2.2 (7). Dominance of tachykinin NK1 receptor activity in the measured responses was confirmed by low potency of the tachykinin NK2-selective antagonist SR48968 ((S)-N-methyl-N[4-(4-acetylamino-4-phenyl piperidino)-2-(3,4-dichlorophenyl)butyl] benzamide) which yielded an IC50 value of 12.0 +/- 2.8 (5) on gerbil preparations and produced less than 50% depression of septide-induced depolarization of rat motoneurones at the highest concentration (100 microM) tested.

Comparative in vivo and in vitro studies with the potent GABAB receptor antagonist, CGP 56999A.

CGP 56999A ([3-[1-(R)-[(3-cyclohexylmethyl)hydroxyphosphinyl]-2-(S)- hydroxy-propyl] amino]ethyl]-benzoic acid) is a potent GABAB receptor antagonist showing much more pronounced convulsant features in mice than do other previously studied GABAB receptor antagonists. The goal of this study was to elucidate the physiological mechanisms underlying this effect. In mice a dose of 0.6 mg/kg intraperitoneal (i.p.) CGP 56999A elicited behavioral activation and stereotypy with periods of intensive scratching and grooming. At 1 mg/kg i.p. most mice displayed myoclonic seizure-like episodes lasting several min. Pretreatment with the lower dose of 0.6 mg/kg i.p. also induced seizures after treatment with a subthreshold dose of pentylenetetrazole (40 mg/kg i.p.). In rats a dose of 3 mg/kg CGP 56999A (i.p.) induced convulsions of tonic-clonic nature. Intracellular sharp microelectrode recordings from rat cortical neurons in slices revealed no paroxysmal actions of CGP 56999A (10 microM). Similar to other GABAB receptor antagonists, CGP 56999A suppressed the late inhibitory postsynaptic potential (i.p.s.p.), but had no effect on the excitatory postsynaptic potential (e.p.s.p.) in the cortex. In cortical slices exposed to picrotoxin (10 microM), the compound evoked pronounced, spontaneous and intense epileptiform discharges. In conclusion, these findings demonstrated that the convulsive feature of the potent GABAB receptor antagonist, CGP 56999A, may be due to suppression of the late i.p.s.p., which becomes apparent in the intact brain only, whereas this action remains undetected in untreated brain slices. This remarkable discrepancy between in vitro and in vivo may be a consequence either of disruption of neuronal circuits during slice preparation or of the pronounced hyperpolarization of pyramidal neurons, at least in the case of cortical slice preparations.

The effects of neurokinin-1 receptor agonists on spinal motoneurones of the neonatal rat.

The effects of substance P (SP) and the selective NK1 receptor agonist [Sar9Met(O2)11] substance P on neonate rat spinal motoneurones were examined using intracellular recordings. Bath-administration of SP (0.1-3 microM) or [Sar9Met(O2)11] substance P (0.01-3 microM) induced a tetrodotoxin (TTX)-insensitive (10 microM) depolarization and a tetraethylammoniumchloride (TEA)-sensitive (3 mM) decrease in membrane conductance. The duration of the slow afterhyperpolarizations (AHPs) following the action potentials were significantly reduced (p = 0.003) by both NK1 receptor agonists. The mean duration of the sAHPs (+/- SEM) in control was 67.8 +/- 6.3 ms whereas in the presence of SP and [Sar9Met(O2)11] substance P their duration was reduced to 41.7 +/- 4.6 ms. Low Ca2+ (0.2 mM)-containing artificial cerebrospinal fluid (ACSF) or addition of BaCl2 or CdCl2 (2 mM) reduced the durations of the slow AHPs by 55%. In the presence of these agents SP and [Sar9Met(O2)11] substance P practically abolished the remaining slow AHPs, suggesting that the agonists also reduce a calcium-independent current. None of the effects induced by the NK1 receptor agonists were antagonized by the NK1 receptor antagonists (+/-)-CP-96,345 (10 microM), RP 67580 (1 microM) or GR 82334 (3-5 microM). In conclusion this study demonstrates that SP and [Sar9Met(O2)11] substance P elicit their effects on NK1 receptors by modulating at least two potassium currents, namely IK and ICa(K).

Phosphinic acid analogues of GABA. 1. New potent and selective GABAB agonists.

The antispastic agent and muscle relaxant baclofen 1 is a potent and selective agonist for bicuculline-insensitive GABAB receptors. For many years efforts to obtain superior GABAB agonists were unsuccessful. We describe the syntheses and biological properties of two new series of GABAB agonists, the best compounds of which are more potent than baclofen in vitro and in vivo. They were obtained by replacing the carboxylic acid group of GABA or baclofen derivatives with either the phosphinic acid or the methylphosphinic acid residue. Surprisingly, ethyl- and higher alkylphosphinic acid derivatives of GABA yielded novel GABAB antagonists, which are described in part 2 of this series. Structure-activity relationships of the novel GABAB agonists are discussed with respect to their affinities to GABAB receptors as well as to their effects in many functional tests in vitro and in vivo providing new muscle relaxant drugs with significantly improved side effect profiles.

Physiological and pharmacological characterization of the spinal tachykinin NK2 receptor.

The goal of these investigations was to study the role of tachykinin NK2 receptors in neonatal spinal cords using the selective NK2 receptor agonist [beta-Ala8]neurokinin A-(4-10) and the new NK2 receptor antagonist GR 94800. Experiments were performed with superfused hemisected rat and gerbil spinal cords. Dorsal roots were electrically stimulated and the synaptically elicited responses and the DC-potentials were recorded extracellularly from the corresponding ventral roots. [beta-Ala8]neurokinin A-(4-10) depolarized ventral roots (0.01-10 microM) and increased their spontaneous activity in a concentration-dependent manner. These effects of [beta-Ala8]neurokinin A-(4-10) were reduced by GR 94800. The action of GR 94800 was selective because the depolarizing effects of similar magnitude evoked by the NK1 receptor agonist [Sar9,Met(O2)11]substance P were not affected by GR 94800. The pA2 values of GR 94800 amounted to 6.0 +/- 0.4 in the rat and 5.4 +/- 0.3 in the gerbil. The NK2 receptor agonist was more potent in the rat than in the gerbil. The estimated EC50 (mean +/- S.E.M.) was found to be 3.9 + 6.0/-1.3 microM in the rat and 2.4 + 2.9/-1.3 microM in the gerbil spinal cord. The NK2 receptor agonist [beta-Ala8]neurokinin A-(4-10) potentiated the monosynaptic reflex evoked by dorsal root stimulation. The potentiation manifested itself as an increase in the amplitude of the early component of the response. The receptor type mediating this effect could not be elucidated. The potentiation ranged between 30 +/- 27 and 110 +/- 36% (0.3 and 10 microM), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Contribution of presynaptic GABA-B receptors to paired-pulse depression of GABA-responses in the hippocampus.

The synaptic release of gamma-aminobutyric acid (GABA) is thought to be regulated by presynaptic GABA receptors of the B-type. It was the goal of this study to validate this concept electrophysiologically using four selective antagonists of GABA-B receptors. Experiments were performed in hippocampal slices exposed to 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX 30 microM) and D-2-amino-5-phosphonopentanoate (AP5 40 microM) in order to block excitatory transmission. Consequently, electrical stimulation of the Schaffer collateral/commissural fibers evoked monosynaptic inhibitory potentials (IPSP) recorded intracellularly from CA 1 pyramidal neurons. In a test called paired-pulse paradigm two identical stimuli were applied at intervals ranging from 350 to 4000 ms. The IPSP evoked by the second stimulation was smaller in its amplitude over the entire interval range. This reduction of the second GABA-response is thought to result from the activation of presynaptic GABA receptors. The GABA-uptake inhibitor SKF 89976 (100 microM) increased the amplitude of the IPSP's and increased the ratio of the first to the second IPSP amplitude. These findings indicate that the drug increases the GABA content in the synaptic cleft leading to a facilitation of paired-pulse depression. The actions of four bath-applied GABA-B receptor antagonists were examined in the paired-pulse paradigm. None of these compounds abolished paired-pulse inhibition completely even at concentrations higher than those required to block postsynaptic GABA-B responses. The potent GABA-B antagonists CGP 55845 and CGP 52432 reduced paired-pulse depression by 80% at 10 microM (maximal effect).(ABSTRACT TRUNCATED AT 250 WORDS)

Oxcarbazepine: preclinical anticonvulsant profile and putative mechanisms of action.

Oxcarbazepine (OCBZ, Trileptal) and its main human monohydroxy metabolite (MHD) protected mice and rats against generalized tonic-clonic seizures induced by electroshock with ED50 values between 13.5 and 20.5 mg/kg p.o. No tolerance toward this anticonvulsant effect was observed when rats were treated with OCBZ or MHD daily for 4 weeks. The therapeutic indices were 4 (OCBZ) and > 6 (MHD) for sedation (observation test, mice and rats) and 8 (MHD) or 10 (OCBZ) for motor impairment (rotorod test, mice). Both compounds were less potent in suppressing chemically induced seizures and did not significantly influence rat kindling development. At doses of 50 mg/kg p.o. and 20 mg/kg i.m. and higher, OCBZ and, to a lesser extent, MHD protected Rhesus monkeys from aluminum-induced chronically recurring partial seizures. In vitro, OCBZ and MHD suppressed sustained high-frequency repetitive firing of sodium-dependent action potentials in mouse neurons in cell culture with equal potency (medium effective concentration 5 x 10(-8) M/L). This effect is probably due in part to a direct effect on sodium channels. Patch-clamp studies on rat dorsal root ganglia cells revealed that up to a concentration of 3 x 10(-4) M, MHD did not significantly interact with L-type calcium currents, whereas OCBZ diminished them by about 30% at the concentration of 3 x 10(-4) M. In biochemical investigations, no brain neurotransmitter or modulator receptor site responsible for the anticonvulsant mechanism of action of OCBZ and MHD was identified.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxcarbazepine: mechanisms of action.

The antiepileptic drug (AED) oxcarbazepine (OCBZ) and its rapidly formed 10-monohydroxy metabolite (MHD) protect against electroshock-induced tonic hindlimb extension in rodents (ED50 14-21 mg/kg p.o.). Both stereoisomers of MHD also protect. As with carbamazepine (CBZ), these findings suggest clinical efficacy against generalized tonic-clonic and, to some extent, partial seizures. OCBZ (IC50 5 x 10(-8) M), MHD (IC50 2 x 10 (-8) M), and CBZ (IC50 6 x 10(-7) M) limit the frequency of firing of sodium-dependent action potentials by cultured mouse central neurons and reduce Vmax progressively in a use-dependent manner at concentrations below therapeutic plasma concentrations in OCBZ-treated patients. This suggests that blockade of voltage-sensitive sodium channels could contribute to the antiepileptic efficacy of OCBZ. Blockade of penicillin-induced epileptiform discharges in hippocampal slices by MHD and its stereoisomers was diminished when the potassium channel blocker 4-aminopyridine was added to the bath fluid. This indicates that additional mechanisms of action, e.g., an effect on potassium channels, might be clinically important. In addition, both stereoisomers are equally responsible for the antiepileptic activity of the racemate, i.e., MHD, and are therefore likely to play a therapeutic role. Such actions could confer broad clinical utility on OCBZ.

Multiphasic responses of cerebellar Purkinje cells to 1S,3R-ACPD: an in vivo study.

The effects of iontophoretically applied (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD), an agonist of metabotropic glutamate receptors, were examined in rat cerebellar Purkinje cells in vivo. Multibarrel electrodes were used for extracellular recordings of spontaneous single unit discharges and iontophoretic ejection of 1S,3R-ACPD. The effect of 1S,3R-ACPD depended on both the strength and the duration of the iontophoretic current. Application of the agonist with ejection currents at or slightly above the response threshold for up to 60 s resulted in an increased rate of action potential firing. With larger ejection currents of the same duration the initial increase in activity was followed by a depression and eventually a cessation of activity. In the transition phase between low frequency firing and firing arrest, Purkinje cells generated almost exclusively complex spikes. When the drug application was continued for longer durations (1-10 min) the initial response was followed by a characteristic cyclic firing pattern. These cycles consisted of alternating phases of mainly simple spike activity, predominantly complex spike activity and silent intervals. At the end of drug applications using large ejection currents, a prolonged period (on average 66 s) with almost no spiking activity was observed. This period ended with an abrupt onset of simple spike firing. These findings point to an important function of cerebellar metabotropic glutamate receptors in the regulation of Purkinje cell activity.

Phenylglycine derivatives antagonize the excitatory response to Purkinje cells to 1S,3R-ACPD: an in vivo and in vitro study.

The interactions of the phenylglycine derivatives (S)-4-carboxyphenylglycine (S-4CPG) and (R,S)-alpha-methyl-4-carboxyphenylglycine (MCPG) with responses of rat cerebellar Purkinje cells to (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD) were examined by intracellular recordings in acute cerebellar slices and extracellular recordings in vivo, using multibarrel electrodes. In vitro, both S-4CPG (100 microM to 1 mM) and MCPG (250 microM to 1 mM) reversibly and dose-dependently reduced an inward current induced by bath-applied 1S,3R-ACPD, an agonist at metabotropic glutamate receptors (mGluRs), in Purkinje cells voltage-clamped at -60 to -65 mV. S-4CPG applied at a concentration of 1 mM reduced the 1S,3R-ACPD induced current to 17% of control values but when applied alone also produced an inward current amounting to 26.8% of that induced by 1S,3R-ACPD. MCPG bath-applied at 250 microM, 500 microM, or 1 mM reduced the 1S,3R-ACPD-induced current to 85%, 56% or 3% of control values, respectively, and did not cause any current when applied alone even at a concentration of 1 mM. In vivo, iontophoretic application of 1S,3R-ACPD induced a transient increase followed by a decrease in the firing rate of Purkinje cells. The excitatory response of Purkinje cells to 1S,3R-ACPD was suppressed during ejection of either one of the phenylglycine derivatives, while the mechanism resulting in the decreased firing rate was not affected. Our observations demonstrate that both S-4CPG and MCPG antagonized the excitatory response of cerebellar Purkinje cells to 1S,3R-ACPD.(ABSTRACT TRUNCATED AT 250 WORDS)

The modulation of the monosynaptic reflex by substance P in the hemisected spinal cord preparation of the rat and gerbil.

The effects of substance P and the selective neurokinin-1 receptor antagonist (+/-)-CP-96,345 have been compared on in vitro spinal cord preparations from the rat and the gerbil. Substance P produced a concentration-dependent depolarization of motoneurons recorded from ventral roots of both species. The EC50 values (microM mean +/- S.E.M.) obtained in rat (0.95 + 1.0/-0.49) and gerbil (0.47 + 0.26/-0.17) preparations were comparable. The mean maximal depolarization (mV mean +/- S.E.M.) evoked in rat (2.07 + 0.26/-0.25) was approximately two-fold greater than that evoked in gerbil (1.21 + 0.15/-0.14) preparations. In the rat substance P had a biphasic effect (depression followed by potentiation) on the short latency probably monosynaptic reflex evoked by electrical stimulation of a dorsal root. In gerbil preparations substance P produced only potentiation of the monosynaptic reflex. The EC50 values (microM) mean +/- S.E.M.) for this potentiating action in rat (0.97 + 0.75/-0.43) and gerbil (0.46 + 3.6/-0.4) preparations were similar. This potentiation demonstrates a positive modulation of an endogenous excitatory probably glutamatergic transmission by substance P in the ventral horn of the spinal cord. The depressant phase observed in rat preparations may be related to the relative immaturity of myelination in rat ventral root fibres compared to the gerbil. The selective neurokinin-1 antagonist (+/-)-CP-96,345 was one hundred-fold less potent as an antagonist of substance P-induced depolarizations in the rat (pA2 4.69 +/- 0.18, n = 7) than in the gerbil (pA2 6.79 +/- 0.16, n = 5) spinal cord. This finding suggests that (+/-)-CP-96,345 may not act solely at the neurokinin-1 recognition site. In conclusion this study demonstrates that substance P modulates the monosynaptic reflex in the spinal cord presumably via activation of neurokinin-1 receptors.

Stimulation parameters determine role of GABAB receptors in long-term potentiation.

Blockade of GABAB receptors was reported to improve cognitive performance in mammals. The physiological basis of this effect is poorly understood. We investigated the effect of the GABAB receptor antagonist CGP 35348 on long-term potentiation (LTP) in the CA1 area of the hippocampus in vitro and in vivo. In vitro the effect of CGP 35348 on LTP, induced either by two non-primed tetanic stimulations or by two primed bursts of stimuli, was investigated. In the presence of 1 mM CGP 35348 LTP was significantly facilitated following two non-primed tetanic trains, but was impaired following two primed burst stimulations. In vivo LTP was induced by applying non-primed trains of stimuli of increasing duration to the Schaffer collateral/commissural fibers. The potentiation of the population spike recorded in CA1 was significantly facilitated by CGP 35348 (100 mg/kg i.v.). In conclusion these findings demonstrate that the GABAB antagonist CGP 35348 facilitates LTP in vitro and in vivo if induced by non-primed tetanic stimulation. In vitro, the mode of stimulation determines the effect of the GABAB antagonist on LTP.

The action of new potent GABAB receptor antagonists in the hemisected spinal cord preparation of the rat.

CGP 52432 (3-N-(3,4-dichlorobenzyl)aminopropyl-P-diethoxymethylphosphinic acid), CGP 54062 (3-N[1-(R,S)-(3,4-dichlorophenyl)ethyl]amino-2-(S)-hydroxypropyl-P-benzy l- phosphinic acid), CGP 54626 (3-N[[1-(S)-(3,4-dichlorophenyl)ethyl]amino-2-(S)- hydroxypropyl-P-cyclohexylmethylphosphinic acid) and CGP 55845 (3-N[1-(S)-(3,4-dichlorophenyl)ethyl]amino-2-(S)- hydroxypropyl-P-benzyl-phosphinic acid) are novel selective GABAB receptor antagonist. The apparent Kd values for the complex formed between the GABAB receptor and these compounds were determined using the monosynaptic reflex in the hemisected rat spinal cord preparation in vitro. CGP 55845 was found to be the most potent GABAB receptor antagonist tested (apparent Kd = 30 nM). On the same preparation 0.3 microM CGP 55845 was equipotent with 100 microM of CGP 35348 (P-(3-aminopropyl)-P-diethoxymethyl-phosphinic acid) for reversal of the depressant action of (R)-(-)-baclofen.

The actions of orally active GABAB receptor antagonists on GABAergic transmission in vivo and in vitro.

The goal of this report is to present the results obtained with three new GABAB receptor antagonists. CGP 54062 has an IC50 in a GABAB binding test of 0.013 microM which is roughly 2500-fold lower than one of the most potent blockers known so far, CGP 35348 (IC50 = 34 microM). CGP 46381 and CGP 36742 have IC50s of 4.9 and 36 microM respectively. The latter two compounds are the first orally active GABAB receptor antagonists. All three compounds bind to the GABAB receptor selectively, and are inactive in a number of binding tests assessing the compounds' affinity to various other receptor sites. The effect of these blockers on GABAergic transmission was investigated in the CA1 area of hippocampal slices. The Schaffer collateral/commissural fibers were stimulated and the evoked postsynaptic potentials were recorded intracellularly in pyramidal neurons. The three antagonists blocked the late inhibitory postsynaptic potential with the following rank order of potency CGP 54062 > 46381 > 36742 approximately 35348. These findings support the hypothesis that these potentials are mediated by GABAB receptors. Orally administered CGP 36742 and CGP 46381 block the neuronal depression induced by iontophoretically applied baclofen in anaesthetised rats. Up to a dose of 10 mg/kg i.v. CGP 54062 was inactive and thus does not appear to cross the blood-brain barrier at this dose. In anaesthetised rats the effects of the three new GABAB antagonists and of CGP 35348 were investigated on the paired-pulse inhibition of the population spikes evoked in the CA1 area of the hippocampus.(ABSTRACT TRUNCATED AT 250 WORDS)