Modulating effect of cerulein on benzodiazepine receptors

Subcutaneous administration of caerulein (100-500 micrograms/kg) significantly reduced the development of picrotoxin (8 mg/kg) seizures in male mice. The same doses of caerulein inhibited 3H-flunitrazepam binding in in vivo experiments. Proglumide, an antagonist of cholecystokinin receptors, in low dose (5 mg/kg) potentiated the effects of caerulein (100 micrograms/kg), whereas the administration of proglumide in high dose (25 mg/kg) reduced the action of caerulein on 3H-flunitrazepam binding and picrotoxin seizures. Caerulein (5-1000 nM) decreased 3H-flunitrazepam binding in in vitro experiments only after supplementation of the binding medium with 120 mM NaCl and 5mM KCl. The results suggest the possible interaction of caerulein with chloride ionophor. It seems probable that the direct interaction of caerulein with chloride ionophor in involved in the inhibitory effect of caerulein on picrotoxin seizures and 3H-flunitrazepam binding.     

Effect of GABA-negative preparations on the anxiolytic and sedative effects of diazepam

Experiments on rats have shown that bicuculline (2 mg/kg) and picrotoxin (2 mg/kg) abolish the anxiolytic action of diazepam (2.5 mg/kg). Bicuculline (2 and 4 mg/kg) decreases while picrotoxin transforms the sedative effect of diazepam to the anxiolytic one. Picrotoxin (2 mg/kg) reduces the sedative action of gamma-acetylenic GABA (100 mg/kg) but does not favour the manifestation of its anxiolytic effect. It is suggested that the GABA-ergic mechanisms play an important role in the sedative effect of diazepam.     

Study of GABA<Subscript>A</Subscript> receptors on the sleep-like behavior in <Emphasis Type="Italic">Coturnix japonica</Emphasis> (Temminck Schlegel, 1849) (Galliformes: Aves)

The present study was carried out to investigate the influence of GABA_A signaling on sleep-like behaviors through systemic administration of bicuculline and picrotoxin (GABA_A antagonists) and thiopental (an allosterical modulator). A thiopental (20 mg/kg) injection increased the eye closure frequency compared to the control group. The birds quickly became sleepy with a low frequency of early behavioral stages, such as rapid oral movement (ROM), feather ruffling and blinking. A bicuculline administration (1 and 4 mg/kg) did not modify the frequency of feather ruffling, ROM, eye closure or blinking responses. A lower dose of picrotoxin (2 mg/kg) stimulated an active awakening status, while an intermediate dose (4 mg/kg) elicited a moderate awakening status, which was associated with an increase in the frequency of ROM, blinking and eye closure. At the higher dose (8 mg/kg), the birds exhibited thermoregulatory-like behaviors and convulsions immediately after the injection. Interestingly, picrotoxin (4 mg/kg) intensified the eye closures when given in combination with thiopental (20 mg/kg). Both barbiturate and picrotoxin-induced sleep-like responses have the same behavioral neuropharmacological properties, conceivably because they are correlated with action at an identical site on the GABA_A receptor.     

Reversal of the anti-conflict action of valproate by various GABA and benzodiazepine antagonists

The effects of RO 15-1788, RO 5-3663, picrotoxin and bicuculline on the anti-conflict properties of valproate were studied in rats using a modified Vogel 's conflict test procedure. A low dose of the benzodiazepine (BDZ) antagonist, RO 15-1788 (5 mg/kg), blocked the anti-punishment properties of valproate (400 mg/kg), whereas no antagonism was observed after a high dose (25 mg/kg) of the BDZ antagonist. High doses of RO 5-3663 or picrotoxin also reversed the anti-conflict action of valproate. Bicuculline did not change the effects of valproate in this test situation. The suppressive effect of valproate on locomotor activity was reversed by a low dose (5 mg/kg) of RO 15-1788, but not by the other antagonists. RO 5-3663 was the only antagonist which effectively reversed the muscle relaxant effects of valproate observed in a Rotarod performance test. These findings indicate that various pharmacological actions of valproate may be due to a complex interplay with several sites at the GABA-BDZ-receptor complex.     

Effects of clonazepam on picrotoxin-induced convulsions.

The convulsant effects of four doses of picrotoxin (PX)-2, 3, 4, and 6 mg/kg s.c.-were evaluated in the first part of the study. The 4-mg/kg dose, which elicited minimal seizures in all animals, generalized tonic-clonic (major) seizures in 75% of rats and fatal outcome in 69% of rats, was chosen for the second part, i.e. for testing the anticonvulsant action of clonazepam (Rivotril Roche, 0.1 or 1 mg/kg i.p.). Clonazepam exhibited a dose-dependent action against PX-induced seizures, being more efficient against major than against minimal seizures.     

Pharmacological analysis of anti-inflammatory effects of low-intensity extremely high-frequency electromagnetic radiation

The anti-inflammatory effect of low-intensity extremely high-frequency electromagnetic radiation (EHF EMR, 42.0 GHz, 0.1 mW/cm2) was compared with the action of the known anti-inflammatory drug sodium diclofenac and the antihistamine clemastine on acute inflammatory reaction in NMRI mice. The local inflammatory reaction was induced by intraplantar injection of zymosan into the left hind paw. Sodium diclofenac in doses of 2, 3, 5, 10, and 20 mg/kg or clemastine in doses of 0.02, 0.1, 0.2, 0.4, and 0.6 mg/kg were injected intraperitoneally 30 min after the initiation of inflammation. The animals were whole-body exposed to EHF EMR for 20 min at 1 h after the initiation of inflammation. The inflammatory reaction was assessed over 3 - 8 h after the initiation by measuring the footpad edema and hyperthermia of the inflamed paw. Sodium diclofenac in doses of 5 - 20 mg/kg reduced the exudative edema on the average by 26% as compared to the control. Hyperthermia of the inflamed paw decreased to 60% as the dose of was increased diclofenac up to 20 mg/kg. EHF EMR reduced both the footpad edema and hyperthermia by about 20%, which was comparable with the effect of a single therapeutic dose of diclofenac (3 - 5 mg/kg). The combined action of diclofenac and the exposure to the EHF EMR caused a partial additive effect. Clemastine in doses of 0.02-0.4 mg/kg it did not cause any significant effects on the exudative edema, but in a dose of 0.6 mg/kg it reduced edema by 14 - 22% by 5 - 8 h after zymosan injection. Clemastine caused a dose-dependent increase in hyperthermia of inflamed paw at doses of 0.02-0.2 mg/kg and did not affect the hyperthermia at doses of 0.4 and 0.6 mg/kg. The combined action of clemastine and EHF EMR exposure caused a dose-dependent abolishment of the anti-inflammatory effect of EHF EMR. The results obtained suggest that both arachidonic acid metabolites and histamine are involved in the realization of anti-inflammatory effects of low-intensity     

Analgesic and anti-inflammatory activity of the proanthocyanidin shellegueain A from Polypodium feei METT.

Analgesic and antiinflammatory activity of proanthocyanidin isolated from Polypodium feei roots has been tested using acetic acid-induced writhing and carrageenan-induced paw edema methods, respectively. The compound at doses of 50 and 100 mg/kg significantly decreased writhing responses of mice induced by 0.7 % acetic acid along the 60 min test in a dose-dependent manner. The compound at a dose of 100 mg/kg gave the percent protection of 76.23 higher than that of acetylsalicylic acid (59.84 %) at a dose of 50 mg/kg. In the antiinflammatory test, this compound caused significant inhibition of the rats' plantar edema induced by 1 % of carrageenan, but this activity was observed only at a higher dose (200 mg/kg). These findings suggest that proanthocyanidin of P. feei roots might have analgesic and antiinflammatory activity, and its mechanism of action might be due to the inhibition of prostaglandin biosynthesis, because the proanthocyanidin fraction had an inhibitory effect on cyclooxygenase, but not on 5-lypoxygenase enzymes.     

Sex related differences in the response of mice, rats and cats to administration of picrotoxin

Picrotoxin, 2.5 mg/kg, which was subconvulsive in male rats was 92% convulsive in female rats. Four mg/kg of picrotoxin, a dose which did not produce death in the male rats, was 75% lethal in the female rats. Picrotoxin also produced a significantly greater increase in the frequency of the spinal motoneurons discharge in the female than in male rats (444% of control compared to 222% of control). A similar significant difference to the analogous treatment was obtained in the female and male cats (439% of control compared to 368% of control). To counteract the picrotoxin-induced increased frequency of the spinal motoneurons discharge a double dose of diazepam had to be given to females of both species. A sex related difference in the occurrence of convulsions, latency and death following picrotoxin administration was also present in mice. However, mice responded in an opposite direction to rats and cats. Three mg/kg of picrotoxin was 100% convulsive and 27% lethal in male mice, while only 40% convulsive and 0% lethal in female mice. In male mice treated with a 100% lethal dose of picrotoxin, diazepam, 3.0 mg/kg, did not diminish the occurrence of convulsions but reduced the incidence of death to 70%. In equally treated female mice the same dose of diazepam reduced the occurrence of convulsions from 100 to 70% and the incidence of death to 10%. The existence of sex related differences in the response of mice, rats and cats to administration of picrotoxin might have its origin in the dimorphisms of the GABA system in these animal species.     

Sex differences in the response of rats to drugs affecting GABAergic transmission

The administration of diazepam 1.0 mg/kg decreased the level of plasma corticosterone in female but not in male Wistar rats. Picrotoxin, another drug affecting GABAergic transmission, also brought about an increase of plasma corticosterone in both sexes. However, in order to achieve a plasma corticosterone increase of similar magnitude (more than 500%) a threefold higher dose of picrotoxin had to be given to males. When the convulsive properties of picrotoxin were tested, it became evident that the dose of picrotoxin (2.5 mg/kg) which was subconvulsive in male was almost 100% convulsive in female rats. The existing sex differences in the response of rats to drugs affecting GABAergic transmission might have possible implications in the treatment of GABA system dysfunction.     

Gabamimetic properties of anxiolytic drugs

Diazepam (5 mg/kg, ip) and tracazolate (40 mg/kg, ip), a nonbenzodiazepine anxiolytic, blocked electrically-induced head-turning without producing sedation. Bicuculline and picrotoxin, GABA antagonists, at doses not affecting head-turning (2 mg/kg, ip) antagonized the effects of diazepam and tracazolate on head-turning. However, at the same dose, bicuculline was more effective as an antagonist of diazepam whereas picrotoxin was more effective as an antagonist of tracazolate. These results suggest that benzodiazepine as well as nonbenzodiazepine anxiolytics possess GABAmimetic activity. The difference in potency between bicuculline and picrotoxin as antagonists of diazepam and tracazolate may be related to their reported differences as GABA antagonists (e.g., site of receptor interaction).     

Peculiarities of the development of chloramine induced pulmonary edema in rabbits in various age periods]

Rabbits under three weeks of age were found to be less tolerant to chloramine (CA) than adult rabbits. For them the lethal dose of CA was 40--50 mg/kg. They perished from intoxication with the symptoms of protracted collapse without any manifestations of edema. For older rabbits the lethal dose of CA was 60--70 mg/kg. Death occurred with phenomena of acute and sharp edema of the lungs. In young rabbits atypical edema of the lungs occurred only with the administration of very high doses of CA--200--250 mg/kg. Edematous fluid is present in small amount only; there is a prevalence of hemorrhage, this being possibly caused by a direct alterating action of the CA excreted through the lungs on the walls of the arterioles and capillaries of the vascular system of the lungs.     

In vivo studies with ICI 154,129, a putative delta receptor antagonist

We studied the in vivo pharmacology of ICI 154,129, a new antagonist that is claimed to show selectivity for delta opiate receptors. At s.c. doses of 30 and 100 mg/kg, ICI 154,129 had no marked effect on the gastrointestinal transit of a charcoal meal in mice. In this test, ICI 154,129 reversed the inhibitory action of metkephamid (a proposed delta receptor agonist) but not that of levorphanol. ICI 154,129 was proconvulsant in the mouse picrotoxin potentiation test; the dose-response curve had a low ceiling and was biphasic. Naloxone (1 mg/kg, s.c.) enhanced the proconvulsant action of ICI 154,129 (40 mg/kg, s.c.) by an unknown mechanism.     

The anaesthetic agent propofol interacts with GABA(B)-receptors: an electrophysiological study in rat

The mode of action by which propofol induces anaesthesia is not fully understood, although several studies suggest that the compound acts via potentiation of brain GABA(A)-receptors. The aim of the present study is to investigate a putative GABA(B)-receptor agonistic action of propofol. For this purpose the action of propofol on a GABA-receptor mediated regulation of dopamine neurons was analyzed with extracellular single unit recordings of dopaminergic neurons of the substantia nigra in chloral hydrate anaesthetized rats.Intravenous administration of propofol (1-16 mg/kg) was found to dose-dependently decrease the firing rate and burst firing activity of nigral DA neurons. These effects by propofol were effectively antagonized by pretreatment with the selective GABA(B)-receptor antagonist CGP 35348 (200 mg/kg, i.v.) but not by pretreatment with the GABA(A)-receptor antagonist picrotoxin (4.5 mg/kg, i.v.).It is proposed that an activation of central GABA(B)-receptors may, at least partially, contribute to the anesthetic properties of propofol.     

Neurotoxicity of Lindane and Picrotoxin: Neurochemical and Electrophysiological Correlates in the Rat Hippocampus In Vivo

In the present study, we compared in vivo changes of extracellular amino acid levels and nucleotide derivatives to a single ip dose of lindane (10-60 mg/kg) and picrotoxin (5 mg/kg) in the hippocampus of halothane anaesthetized rat by microdialysis-coupled HPLC analysis. Brain activity was monitored by EEG. The effects of lindane and picrotoxin on EEG pattern of rats as well as on hippocampal amino acid and nucleotide status were studied in 0-50 min, 50-100 min and 100-150 min periods post-dosing. Significant decreases in Glu and Asp were found after picrotoxin treatment. After 50-100 min post-dosing, hippocampal hypoxanthine and inosine levels increased to both lindane (10 mg/kg) and picrotoxin whereas xanthine and uridine levels increased to picrotoxin, only. Lindane elicited a dose-dependent occurrence of negative spikes accompanied with rhythmic activity at 4-5 Hz. The picrotoxin-induced 4-5 Hz activity did not display negative sharp waves and was accompanied by 10 Hz oscillations.     

Antiinflammatory effect of a protein kinase C inhibitor (K-252a) on the development of the dextran-induced paw edema in the rat (preliminary results).

The effect of a metabolite of Nocardiopsis sp. as a protein kinase C inhibitor from microbial origin was investigated on the onset and development of dextran-induced paw edema in the rat. It was published that this compound (K-252a) interferes with histamine release from mast cells, while dextran-induced paw and nose edema are induced by vasoactive agents, like histamine etc., released from the disrupted mast cells. The antiinflammatory effect of the K-252a is effectuated by the inhibition of protein kinase C. Groups of male Wistar rats with 180-200 g b.w. were used; each group consisted of 10-10 rats. The following groups were consisted: rats given orally DMSO (control), rats given 1 mg/kg, or 3 mg/kg b.w. of K-252a dissolved in DMSO and given p.o. one hour before dextran injection. Dextran (BDH Chem. LTD, molW: 200.000, England) was injected intraperitoneally in 10% solution, in a dose of one ml/100 g b.w. Volume of the hind leg was measured by a mercury plethysmometer. Time-sequence of the edema was followed. Increase in volume of hind leg paw was related to its 0-min volume in %. Results were analyzed by the Kruskal-Wallis-test. Edema of the legs and noses appeared in each of the control rats in one hour. The 1 mg/kg dose of K-252a retarded the appearance of the edema by 1 hour, the 3 mg/kg dose, however, prevented its onset for 4 hours.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pharmacological evidence for a role of gamma-aminobutyric acid A receptor mechanism in modulating nitric oxide synthase activity in rat brain

The role of gamma-aminobutyric acid (GABA) mechanism on the synthesis of nitric oxide (NO) has been investigated by measuring the activity of nitric oxide synthase (NOS) and the concentration of NO in rat brain 15 min after administration of anticonvulsant doses of diazepam (0.25 and 0.5 mg/kg) which is known to activate GABA A receptor for its anticonvulsant action. Diazepam enhanced both NOS activity and the concentration of NO in a dose-dependent manner. A reversal has been observed in animals treated with a convulsant dose of picrotoxin (5 mg/kg) which is known to produce convulsions by blocking GABA A receptor mechanism. These results suggest that a functional interaction occurs between GABA A receptor activity and NO synthesis in the brain.     

Effects of Picrotoxin Treatment on GABAA Receptor Supramolecular Complexes in Rat Brain

The effects of acute and chronic administration of a subconvulsive dose of picrotoxin on t-[35S]butylbicyclophosphorothionate ([3S]TBPS), [3H]muscimol, and [3H]flunitrazepam binding characteristics in various regions and on the convulsant potency of picrotoxin in Sprague-Dawley rats were examined. Acute administration of a subconvulsive dose of picrotoxin (3 mg/kg, i.p.) significantly increased [35S]TBPS and [3H]muscimol binding in cerebellum (CB) with no change in frontal cortex (FC). In rats treated chronically with picrotoxin (3 mg/kg, i.p., daily for 10 days), the Bmax of [35S]TBPS binding site was significantly decreased in the FC, striatum (ST), and CB with no change in KD values. Neither [3H]muscimol binding in the FC and CB nor [3H]flunitrazepam binding in the FC was affected in these rats. In addition, the potency of pentobarbital to inhibit [35S]TBPS binding in vitro was not altered following acute or chronic treatment of picrotoxin. Chronic administration of picrotoxin did not affect convulsive ED50 or LD50 of picrotoxin; however, it delayed the onset of convulsions and increased the time to death. These results suggest that treatment with picrotoxin at a subconvulsive dose for 10 days causes down-regulation of [35S]TBPS binding sites and that this down-regulation might be related, at least in part, to the decreased extent of convulsant potency of picrotoxin. In addition, the results indicate possible interaction between convulsant binding sites and GABAA receptor sites in the CB following picrotoxin treatment.     

Antinociceptive action of GABA-mimetic agent--N-phthaloyl GABA

N-phthaloyl GABA (P-GABA), a nonselective GABA-ergic drug, showed positive analgesic response in four different models in mice, viz-tail immersion, tail clip, hot plate and writhing-induced by acetic acid. Antinociceptive ED50 (ip in mice) of P-GABA was lowest in tail immersion method (ED50 = 24.27, mg/kg). Though pethidine (10 mg/kg, ip) significantly potentiated the antinociceptive action of P-GABA (20 mg/kg, ip), pretreatment of naloxone (5 mg/kg, im) did not influence the same. Pretreatment with atropine (10 mg/kg, im), picrotoxin (0.08 mg/kg) and 3-mercaptopropionic acid (2 mg/kg) reduced the antinociceptive action of P-GABA significantly. But pretreatment with bicuculline (0.4 mg/kg), a specific GABA antagonist, did not reduce the antinociceptive action of P-GABA.     

Possible involvement of GABA mechanisms in central cardiovascular and respiratory control. Studies on the interaction between diazepam, picrotoxin and clonidine

Various doses (0.1-1 mg/kg) of diazepam were given to chloralose anesthetized rats, with both systemic (i.p.) and central injections being tested. Arterial pressure, heart rate, respiration depth and frequency were recorded. Diazepam caused a dose-dependent decrease in the arterial pressure after systemic administration and also decreased it after central administration. However, only intraventricular but not intracisternal injections of diazepam were effective. The hypotensive effect of systemic diazepam was competitively counteracted by pretreatment with picrotoxin, a putative gamma-aminobutyric acid receptor blocking agent. The hypotensive effect of the centrally acting alpha-adrenoreceptor agonist clonidine was not influenced by picrotoxin pretreatment. The effect of diazepam on heart rate was inconsistent. Diazepam caused a reduction of respiratory frequency, which was not counteracted by picrotoxin pretreatment. It is concluded that central gabergic mechanisms are to some extent involved in the hypotensive effect of diazepam, probably at a supramedullary level. The hypotensive effect of a threshold dose of diazepam was blocked by a small dose of clonidine. Likewise, diazepam pretreatment could counteract the hypotension, bradycardia and respiratory frequency reduction caused by a threshold dose of clonidine. These results suggest that gabergic and/or other benzodiazepine-sensitive receptors may interact with alpha-adrenoreceptors in the control of central cardiovascular and respiratory mechanisms.     

Role of benzodiazepine-GABAA receptor complex in attenuation of U-50,488H-induced analgesia and inhibition of tolerance to its analgesia by ginseng total saponin in mice

In the present study, the role of benzodiazepine-GABAA receptor complex in the attenuation of U-50,488H (U50), a selective kappa opioid agonist-induced analgesia and inhibition of tolerance to its analgesia by ginseng total saponin (GTS) was investigated using the mice tail-flick test. The intraperitoneal (i.p.) treatment of GTS (100 and 200 mg/kg) and diazepam (0.1-1 mg/kg) dose-dependently attenuated the U50 (40 mg/kg, i.p.)-induced analgesia. GTS (0.001-10 microg/ml) did not alter binding of [3H]naloxone to mice whole brain membrane. The attenuation effect of GTS (100 mg/ kg) and diazepam (0.5 mg/kg) on U50-induced analgesia was blocked by flumazenil (0.1 mg/kg, i.p.), a benzodiazepine receptor antagonist, and picrotoxin (1 mg/kg, i.p.), a GABAA-gated chloride channel blocker. However, bicuculline (1 mg/kg, i.p.), a GABAA receptor antagonist blocked the attenuation effect of diazepam (0.5 mg/kg) but not GTS (100 mg/kg) on U50-induced analgesia. Chronic treatment (day 4-day 6) of GTS (50-200 mg/kg) and diazepam (0.1-1 mg/kg) dose-dependently inhibited the tolerance to U50-induced analgesia. Flumazenil (0.1 mg/kg) and picrotoxin (1 mg/kg) on chronic treatment blocked the inhibitory effect of GTS (100 mg/kg) and diazepam (0.5 mg/kg) on tolerance to U50-induced analgesia. On the other hand, chronic treatment of bicuculline (1 mg/kg) blocked the inhibitory effect of diazepam (0.5 mg/kg) but not GTS (100 mg/kg) on tolerance to U50-induced analgesia. In conclusion, the findings suggest that GTS attenuates U50-induced analgesia and inhibits tolerance to its analgesia and this action involves benzodiazepine receptors and GABAA-gated chloride channels.