Comparison of the toxicokinetics of the convulsants picrotoxinin and tetramethylenedisulfotetramine (TETS) in mice.

Acute intoxication with picrotoxin or the rodenticide tetramethylenedisulfotetramine (TETS) can cause seizures that rapidly progress to status epilepticus and death. Both compounds inhibit γ-aminobutyric acid type-A (GABAA) receptors with similar potency. However, TETS is approximately 100 × more lethal than picrotoxin. Here, we directly compared the toxicokinetics of the two compounds following intraperitoneal administration in mice. Using LC/MS analysis we found that picrotoxinin, the active component of picrotoxin, hydrolyses quickly into picrotoxic acid, has a short in vivo half-life, and is moderately brain penetrant (brain/plasma ratio 0.3). TETS, in contrast, is not metabolized by liver microsomes and persists in the body following intoxication. Using both GC/MS and a TETS-selective immunoassay we found that mice administered TETS at the LD50 of 0.2 mg/kg in the presence of rescue medications exhibited serum levels that remained constant around 1.6 µM for 48 h before falling slowly over the next 10 days. TETS showed a similar persistence in tissues. Whole-cell patch-clamp demonstrated that brain and serum extracts prepared from mice at 2 and 14 days after TETS administration significantly blocked heterologously expressed α2ß3γ2 GABAA-receptors confirming that TETS remains pharmacodynamically active in vivo. This observed persistence may contribute to the long-lasting and recurrent seizures observed following human exposures. We suggest that countermeasures to neutralize TETS or accelerate its elimination should be explored for this highly dangerous threat agent.

[Determination of brucine and strychnine in rat after cutaneous administration of semen strychni niosome gel by LC-MS/MS].

OBJECTIVE: A sensitive liquid chromatography-tandem mass spectrometric (LC-MS/MS) method has been developed and validated for the determination of brucine and strychnine in rat plasma. METHOD: Samples were extracted by ethyl acetate-n-butanol (7: 3). Chromatographic separation was operated on ZORBAX XDB-C18 column with gradient elution of acetonitrile-methanol-water (0.05% acetic acid and 10 nmol x L(-1) ammonium formate contained), followed by LC-MS/MS in positive electrospray ionization. Quantification was carried out on multiple reaction monitoring (MRM) of the transition m/z 395.2/324.2, m/z 335.2/184.2 and m/z 199.1/171.1 for brucine, strychnine and tacrine (internal standard), respectively. RESULT: The method was linear in the range of 0.195-100 and 0.07840 microg x L(-1) for brucine and strychnine, with coefficient correlation 0.994 and 0.996 respectively. The recoveries of extraction were 78.9% - 102.4% for brucine and 95.2% - 106.1% for strychnine. Precision, accuracy, stability and matrix effect of the analytes met the requirement. The method was applied to a pharmacokinetic study of brucine and strychnine after cutaneous administration of Semen Strychni niosome gel. The C(max) were (26.20 +/- 5.81) and (12.50 +/- 3.00) microg x L(-1) while the AUC(0-infinity), were (193.75 +/- 39.43) and (98.25 +/- 28.54) microg x h x L(-1) of the two components. CONCLUSION: We conclude that the niosomes may reduce the systemic exposures and prolong the local release of brucine and strychnine.

Neurobehavioral effects of acute exposure to aromatic hydrocarbons.

This article reports the results of neurobehavioral tests on representative aromatic constituents, specifically C(9) to C(11) species. The testing evaluated effects in several domains including clinical effects, motor activity, functional observations, and visual discrimination performance. Exposures ranging from 600 to 5000 mg/m(3), depending on the molecular weights of the specific aromatic constituents, produced minor, reversible effects on the central nervous system (CNS), particularly in the domains of gait and visual discrimination. There was little evidence of effects at lower exposure levels. There was some evidence of respiratory effects at 5000 mg/m(3) in 1 study, and there were also minor changes in body weight and temperature. The CNS effects became less pronounced with repeated exposures, corresponding to lower concentrations in the brain of 1 representative substance, 1,2,4-trimethyl benzene (TMB). At high exposure levels, the alkyl benzenes apparently induced their own metabolism, increasing elimination rates.

Effects of (+)-bicuculline, a GABAa receptor antagonist, on auditory steady state response in free-moving rats.

Auditory steady-state responses (ASSRs) are states in which the electrical activity of the brain reacts steadily to repeated auditory stimuli. They are known to be useful for testing the functional integrity of neural circuits in the cortex, as well as for their capacity to generate synchronous activity in both human and animal models. Furthermore, abnormal gamma oscillations on ASSR are typically observed in patients with schizophrenia (SZ). Changes in neural synchrony may reflect aberrations in cortical gamma-aminobutyric acid (GABA) neurotransmission. However, GABA's impact and effects related to ASSR are still unclear. Here, we examined the effect of a GABAa receptor antagonist, (+)-bicuculline, on ASSR in free-moving rats. (+)-Bicuculline (1, 2 and 4 mg/kg, sc) markedly and dose-dependently reduced ASSR signals, consistent with current hypotheses. In particular, (+)-bicuculline significantly reduced event-related spectral perturbations (ERSPs) at 2 and 4 mg/kg between 10 and 30 minutes post-dose. Further, bicuculline (2 and 4 mg/kg) significantly and dose-dependently increased baseline gamma power. Furthermore, the occurrence of convulsions was consistent with the drug's pharmacokinetics. For example, high doses of (+)-bicuculline such as those greater than 880 ng/g in the brain induced convulsion. Additionally, time-dependent changes in ERSP with (+)-bicuculline were observed in accordance with drug concentration. This study partially unraveled the contribution of GABAa receptor signals to the generation of ASSR.

An investigation into the pharmacokinetics of 3-mercaptopropionic acid and development of a steady-state chemical seizure model using in vivo microdialysis and electrophysiological monitoring.

OBJECTIVES: The goal of the present study was to develop a chemical seizure model using the convulsant, 3-mercaptopropionic acid (3-MPA). A pharmacodynamics approach was taken, combining in vivo microdialysis sampling with electrophysiological methods to simultaneously monitor, in real-time, the 3-MPA concentration in the brain and the corresponding electrocorticographic (ECoG) activity. METHODS: The 3-MPA was administered in two doses (50 and 100 mg/kg) in order to study its pharmacokinetics. Microdialysis samples were collected from the striatum, hippocampus, and jugular vein every 5 min. The microdialysates were analyzed using high-performance liquid chromatography with electrochemical detection (HPLC-EC). The ECoG activity was monitored via screws placed onto the cortex. Noncompartmental pharmacokinetics analysis was performed to obtain the elimination constants (K(e)), the maximum concentration (C(max)), the time to achieve maximum concentration (T(max)), and the area under the concentration-time curves (AUC(inf)). RESULTS: The average brain K(e) for the 50 and the 100mg/kg doses were 0.060 and 0.018 min(-1), respectively. The brain AUC(inf) for the 50 and 100mg/kg doses were 353 and 2168 mg min(-1)mL(-1), respectively. This led to a 67-fold increase in the observed number of seizures in the higher dose with the average seizure intensity double that of the smaller dose. These data led to the dosing scheme for the chemical seizure model of administering a 3-MPA loading dose of 60 mg/kg followed by a constant infusion of 50 mg/(kg min(-1)). CONCLUSIONS: This study describes, to our knowledge, the first successful attempt to combine in vivo microdialysis with electrophysiology to monitor in real-time, the concentration and effects of 3-MPA in the brain. This led to the development of a steady-state chemical seizure model.

Pharmacological and behavioral characteristics of interactions between vigabatrin and conventional antiepileptic drugs in pentylenetetrazole-induced seizures in mice: an isobolographic analysis.

To characterize the anticonvulsant effects and types of interactions exerted by mixtures of vigabatrin (VGB) and conventional antiepileptic drugs (valproate (VPA), ethosuximide (ESM), phenobarbital (PB), and clonazepam (CZP)) in pentylenetetrazole (PTZ)-induced seizures in mice, the isobolographic analysis for three fixed-ratio combinations of 1 : 3, 1 : 1, and 3 : 1 was used. The adverse-effect profile of the combinations tested, at the doses corresponding to their median effective doses (ED(50)) at the fixed-ratio of 1 : 1 against PTZ-induced seizures, was determined by the chimney (motor performance), step-through passive avoidance (long-term memory), pain threshold (pain sensitivity), and Y-maze (general explorative locomotor activity) tests in mice. Additionally, the observed isobolographic interactions were verified in terms of a pharmacokinetic interaction existence. VGB combined with PB or ESM exerted supra-additive (synergistic) interactions against the clonic phase of PTZ-induced seizures, which was associated with the increment of PB or ESM concentrations in the brains of examined animals. The remaining combinations tested (ie VGB+VPA and VGB+CZP) occurred additive in the PTZ test, which was associated with no significant changes in the brain concentrations of VPA and CZP. None of the examined combinations exerted motor impairment in the chimney test in mice. In the standard variant of passive avoidance task (current of 0.6 mA; 2 s of stimulus duration), the combinations of VGB+CZP and VGB+VPA significantly affected long-term memory in mice. Moreover, VGB in a dose-dependent manner lengthened the latency to the first pain reaction in the pain threshold test in mice. The modified variant of step-through passive avoidance task (current of 0.6 mA; stimulus duration based on the latency from the pain threshold test) revealed no significant changes in the long-term memory of animals for the combinations of VGB+VPA and VGB+CZP; so the observed effects in the standard variant of passive avoidance task were a result of the antinociceptive effects produced by VGB. In the Y-maze test, VGB also, in a dose-dependent manner, increased the general explorative locomotor activity of the animals tested. Similarly, the total number of arm entries in the Y-maze was significantly increased for the combinations of VGB+CZP and VGB+ESM, but not for VGB+PB and VGB+VPA. The application of VGB in combination with PB, ESM, CZP, and VPA suppressed the clonic phase of PTZ-induced seizures, having no harmful or deleterious effects on behavioral functioning of the animals tested, which might be advantageous in further clinical practice.

3-Heteroaryl-2-pyridones: benzodiazepine site ligands with functional delectivity for alpha 2/alpha 3-subtypes of human GABA(A) receptor-ion channels.

A novel series of 3-heteroaryl-5,6-bis(aryl)-1-methyl-2-pyridones were developed with high affinity for the benzodiazepine (BZ) binding site of human gamma-aminobutyric acid (GABA(A)) receptor ion channels, low binding selectivity for alpha 2- and/or alpha 3- over alpha 1-containing GABA(A) receptor subtypes and high binding selectivity over alpha 5 subtypes. High affinity appeared to be associated with a coplanar conformation of the pyridone and sulfur-containing 3-heteroaryl rings resulting from an attractive S.O intramolecular interaction. Functional selectivity (i.e., selective efficacy) for alpha 2 and/or alpha 3 GABA(A) receptor subtypes over alpha1 was observed in several of these compounds in electrophysiological assays. Furthermore, an alpha 3 subtype selective inverse agonist was proconvulsant and anxiogenic in rodents while an alpha 2/alpha 3 subtype selective partial agonist was anticonvulsant and anxiolytic, supporting the hypothesis that subtype selective BZ site agonists may provide new anxiolytic therapies.

Simultaneous central nervous system distribution and pharmacokinetic-pharmacodynamic modelling of the electroencephalogram effect of norfloxacin administered at a convulsant dose in rats.

The objective of this study was to investigate the contribution of norfloxacin blood-brain barrier (BBB) transport to its delayed electroencephalogram (EEG) effect in rats. Norfloxacin was injected as a bolus dose of 150 mg kg(-1). Blood samples were collected for total norfloxacin plasma concentration measurements. The corresponding unbound levels were determined in brain extracellular fluid (ECF) using microdialysis. Quantitative EEG recording was conducted during 9 h post-dose. Brain ECF norfloxacin concentrations were much lower than plasma levels (AUC ratio=9.7+/-2.8%) but peaked very early, and concentration versus time profiles were parallel in both biological fluids. The best pharmacokinetic (PK) modelling was obtained by considering that ECF concentrations were part of the central compartment, with a proportionality factor. The peak of EEG effect was delayed and the effect versus plasma concentration curves exhibited a dramatic hysteresis. A PK-pharmacodynamic (PD) effect compartment model with a spline function to describe the relationship between effect and concentration at the effect site successfully described the data. Comparisons of PK-PD parameters estimated from plasma and ECF concentrations show that most of the delayed norfloxacin EEG effect is not due to BBB transport, but also that PD parameters derived from plasma data must be carefully interpreted when drug distribution at the effect site is restricted, as may often be the case for centrally acting drugs.

Pharmacokinetic-pharmacodynamic modelling of the convulsant interaction between norfloxacin and biphenyl acetic acid in rats.

Fluoroquinolones (FQs) are associated with a low incidence of central nervous system (CNS) side effects, possibly leading to convulsions, especially when co-administered with nonsteroidal anti-inflammatory drugs (NSAIDS). Although the in vivo pro-convulsant activity of NSAIDS is essentially unknown, the convulsant potential of FQs is traditionally evaluated by in vitro gamma-aminobutyric acid (GABA) binding experiments in the presence of 4-biphenyl acetic acid (BPAA), the active metabolite of fenbufen. The aim of this study was therefore to investigate the BPAA-norfloxacin convulsant interaction in vivo. Male Sprague-Dawley rats (n = 27) were given BPAA orally, at various doses 1 h before norfloxacin infusion, which was maintained until the onset of maximal seizures, when cerebrospinal fluid (CSF) and plasma samples were collected for analysis. An inhibitory E(max) effect model with a baseline effect parameter was fitted to the norfloxacin versus BPAA concentrations in the CSF, previously shown to be part of the biophase. This model includes three parameters: the concentrations of norfloxacin in the absence of BPAA (C(CSF0, Nor)), and when BPAA concentration tends toward infinity (C(CSFbase, Nor)), and the BPAA concentration for which half of the maximal effect is observed (C(CSF50, BPAA)). The maximal proconvulsant effect of BPAA is given by the C(CSF0, Nor) / C(CSFbase, Nor) ratio, estimated to approximately 6 in this study. Derived models were developed in plasma to account for the non-linear CSF diffusion of norfloxacin and protein binding of BPAA. In conclusion this study has shown that the convulsant interaction between norfloxacin and BPAA in rats, can be adequately characterized by modelling of the CSF concentrations of the two drugs at the onset of activity, following their administration in various proportions.

Proconvulsive effects of histamine H1-antagonists on electrically-induced seizure in developing mice.

The purpose of this study was to investigate the developmental differences in seizure susceptibility in mice and the roles of the histaminergic neuron system in inhibition of convulsions in development. First, we studied developmental differences in electrically-induced seizures. Since the 14-day-old mice showed a different seizure pattern from that of older mice, we evaluated the seizure susceptibility of mice older than 21 days. The durations of all the convulsive phases were significantly increased in 21- and 30-day-old mice, compared with older mice. Second, pyrilamine (or mepyramine), ketotifen, and d-chlorpheniramine, centrally-acting H1-antagonists, increased the durations of all the convulsive phases in the 21- and 30-day-old mice, but did not increase duration in 42-day-old mice. Terfenadine and astemizole, H1-antagonists that hardly enter the brain, did not affect the durations of all the convulsive phases in 21-, 30- and 42-day-old mice. The proconvulsant effect of centrally-acting H1-antagonists in 21- and 30-day-old mice were considered to be mediated via the central H1-receptors. Thus, the histaminergic neuron system may have an important physiological role in inhibition of seizures in 21- and 30-day-old mice which have higher seizure susceptibility. This would compensate for the immaturity of the other protective neuron systems such as NMDA receptor complexes and GABA receptors. In conclusion, the present findings support the view that the central histaminergic system plays a role in inhibition of convulsions.

Critical volume of rat cortex and extracellular threshold concentration for a pentylenetetrazol-induced epileptic focus.

The initiation of focal interictal epileptiform activity (FIEA) has been shown to depend on the activation of a sufficiently large volume of brain tissue. We estimated the size of this 'critical volume' for the convulsant pentylenetetrazol (PTZ) by analyzing the diffusion following its microinjection into rat motor cortex. PTZ concentration was monitored 100-200 microm away from the injection site with a PTZ-sensitive microelectrode. Diffusion analysis in 0.3% agar yielded the free diffusion coefficient D (8.50 +/- 0.15 X 10(-6) cm2 x s(-1) at 37 degrees C, median +/- S.E.M.). In brain tissue, diffusion was modified by extracellular volume fraction (alpha), tortuosity (lambda = (D/ADC)1/2; ADC = apparent diffusion coefficient) and non-specific uptake (k'). Using a value of 0.2 for alpha from previous studies, we found values of lambda = 1.61 +/- 0.01, k' = 3.37 +/- 0.15 X 10(-3) s(-1) and an injected volume U of 5.16 +/- 0.45 X 10(-10) l for pulses without FIEA, and lambda = 1.95 +/- 0.06, k' = 6.24 +/- 1.73 X 10(-3) s(-1) and U = 7.40 +/- 0.66 X 10(-10) l for pulses with FIEA. From the calculated concentration distribution of PTZ during FIEA we estimated a threshold concentration of about 1.77 mM PTZ and a volume with a radius of about 219 microm in which this concentration had to be exceeded. Since this critical volume was comparable in size to foci elicited by penicillin or electric stimuli in previous studies, it is concluded that it is determined by intrinsic tissue properties rather than by the convulsive agent being used.

Effect of hypoosmotic stress on peripheral-type benzodiazepine receptors in cultured astrocytes.

Astrocytes appear to be the primary source of peripheral benzodiazepine (PBZD) receptors in brain. The function of this receptor is not well understood. Since there is evidence that this receptor may be involved in cell volume control, we examined the effect of hypoosmotic stress on the regulation of the PBZD receptors in homogenates of cultured astrocytes derived from neonatal rat cerebral cortex. Exposure of astrocytes that were maintained in the presence of dibutyryl cAMP (dBcAMP) to hypoosmotic medium (200 mOsm) for 24 h resulted in 27 and 57% increased in the number of [3H]PK 11195 and [3H]Ro5-4864-binding sites, respectively, as compared with isoosmotic media (320 mOsm). This receptor upregulation is osmolarity- and time-dependent. However, hypoosmotic stress had no effect on PBZD receptor-binding in astrocytes that were maintained in the absence of dBcAMP. Under isoosmotic conditions, dBcAMP appears to regulate [3H]Ro5-4864 but not [3H]PK 11195-binding sites, a finding which further supports a partial distinction between the binding sites labeled with these ligands. The modulation of PBZD receptors by hypoosmotic stress suggests a possible role for these receptor sites in astrocyte volume control.

Interaction of allosteric ligands with GABAA receptors containing one, two, or three different subunits.

The presence of allosteric binding sites on recombinant GABAA receptors formed after transfection of human embryonic kidney (HEK) 293 cells with alpha 1-, beta 3-, or gamma 2-subunits, or with various combinations of these subunits, was systematically investigated. From all possible subunit combinations, high affinity [3H]muscimol binding sites were induced in cells transfected with alpha 1 beta 3- or alpha 1 beta 3 gamma 2-subunits only. GABAA receptor associated [3H]flunitrazepam binding sites were induced in cells after transfection with alpha 1 gamma 2- or alpha 1 beta 3, gamma 2-subunits, and [35S]r-butylbicyclophosphorothionate (TBPS) binding sites were found in cells transfected with beta 3-, beta 3 gamma 2-, alpha 1 beta 3-, or alpha 1 beta 3 gamma 2-subunits. Binding of [35S]TBPS could be inhibited by pentobarbital, etazolate, (+)-etomidate, alphaxalone, propofol, chlormethiazole, and 4'-chlorodiazepam (Ro 5-4864) with a potency which differed in cells transfected with beta 3-, beta 3 gamma 2-, alpha 1 beta 3-, or alpha 1 beta 3 gamma 2-subunits. Results obtained indicate that receptors with different subunit composition actually can be formed in HEK cells and exhibit distinct pharmacological properties.

Allosteric modulation of [35S]TBPS-binding in the cerebral cortex of the rat during postnatal development.

The ontogenesis of the GABA-gated Cl- channel was investigated in the cerebral cortex of the rat by monitoring the binding parameters of [35S]t-butylbicyclophosphorothionate ([35S]TBPS) at intervals after birth (1-90 days). To investigate the influence of the developmental changes in the content of GABA on [35S]TBPS-binding, the assays were carried out in unwashed membranes, in which the concentration of GABA was dependent on its content in vivo, and in repeatedly washed membranes in the presence of defined concentrations of exogenous GABA. At birth, the density (Bmax) of [35S]TBPS-binding sites in unwashed membranes was similar to that found in well-washed membranes. However, in unwashed membranes, the number of [35S]TBPS-binding sites increased by two-fold within 10 days after birth whereas in washed membranes it increased by four-fold during the same period. The higher density of [35S]TBPS-binding sites in washed membranes as compared with the unwashed counterparts persisted throughout development. In unwashed membranes, the apparent Kd for [35S]TBPS-binding increased with age whereas in washed membranes the affinity of [35S]TBPS for its binding sites remained constant throughout development. The binding of [35S]TBPS to the GABA-gated Cl- channel is allosterically modulated by drugs acting on different sites of the GABAA receptor complex. Thus, GABA and diazepam decrease [35S]TBPS-binding whereas the GABAA receptor antagonist, bicuculline, and the inverse agonist for benzodiazepine receptors, 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylic acid methyl ester, increase it.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of the pharmacokinetics of 2-amino-7-phosphonoheptanoate in rat plasma and cerebrospinal fluid.

The pharmacokinetics of 2-amino-7-phosphonoheptanoate (AP7) in rat plasma and appearance in cerebrospinal fluid (CSF) are reported. Using high-performance liquid chromatography (HPLC) with fluorescence detection, concentrations of AP7 can be detected as low as 1.0 microM. Peak CSF concentrations (12-15 microM) for both the D-AP7 and D,L-AP7 are observed 10-15 min after i.v. administration and amount to approximately 0.1% of a 1 mmol/kg dose. Significant quantities (3 microM) are present in CSF at 2 h and no AP7 is detectable at 4 h. Following i.v. administration, a monoexponential clearance was observed for D-AP7 clearance from plasma, 15.4 +/- 0.8 S.E.M. ml/min/kg with a t1/2 of 38.9 +/- 0.8 S.E.M. min. However, a biexponential clearance from plasma was observed for D,L-AP7.

Convulsive action and toxicity of uremic guanidino compounds: behavioral assessment and relation to brain concentration in adult mice.

Four guanidino compounds that are known to accumulate in uremia, namely creatinine, guanidine, guanidinosuccinic acid and methylguanidine, were administered intraperitoneally and intracerebroventricularly to adult albino mice and the compounds epileptogenic and toxic properties were behaviorally assessed. After intraperitoneal injection, brain concentration of the compounds as a function of injected dose was monitored additionally. Guanidino compound brain concentration was determined by cation exchange chromatography with fluorescence ninhydrin detection. After systemic administration, especially guanidinosuccinic acid and methylguanidine induced long-lasting generalized convulsions which gradually increased in severity. Increasing the dose injected intraperitoneally resulted in linear increase in brain concentration of the injected compounds, in parallel with increase in proportion of animals presenting with convulsions and/or severity of convulsions. Guanidinosuccinic acid brain concentration increased more slowly than that of the other 3 compounds and guanidinosuccinic acid also exerted its effect later than the others. Since none of the other metabolically related guanidino compounds determined was significantly increased in the brains of the injected animals, the observed behavior was most certainly induced by the compounds injected and not by some secondary metabolite. Epileptogenic properties of the four compounds were markedly and qualitatively different in systemic administration, but rather similar in intracerebral administration. A tentative epileptogenic potency order was inferred from the combined behavioral and biochemical results. All 4 of the compounds tested displayed the ability to induce full-blown clonic-tonic convulsions and they did so in a dose-related manner. Guanidinosuccinic acid appeared to be slightly more potent than methylguanidine, but both guanidinosuccinic acid and methylguanidine were considerably more potent than guanidine. Creatinine was many times less potent than the other 3 guanidino compounds. Revised epileptogenic potency order on the basis of guanidino compound brain concentration after systemic administration as well as potency order after intracerebral administration paralleled the potency order of these compounds in their GABA antagonism reported earlier. It was therefore postulated that the GABA antagonism of uremic guanidino compounds could underlie their epileptogenic character. Moreover, these compounds could very likely be at the basis of the neurological complications including epilepsy of uremic patients in whom they accumulate in physiological fluids and brain.

Changes in GABA-benzodiazepine receptor complex and in peripheral benzodiazepine receptors in male mice after copulation.

We studied the effect of copulation on GABA and benzodiazepine (BZD) receptors in the male mouse. After copulation, there was an 18% increase in the in vitro number of [3H]muscimol binding sites in frontal cortex. No changes were observed in central BZD binding sites labelled either in vivo by [3H]flunitrazepam or in vitro (in olfactory bulbs and in frontal cortex) by [3H]flumazenil, but further in vitro studies demonstrated that the GABA-stimulated [3H]flunitrazepam binding was reduced in both frontal cortex and olfactory bulbs. Copulation increased the number of peripheral BZD binding sites labelled by 3H-Ro 5-4864 in olfactory bulbs by 22% and in heart by 36%, but not in frontal cortex or in testes. The changes of GABA/BZD and peripheral BZD receptors in mouse suggest that the GABAergic system may be affected by copulation.

Toxicokinetics of Ro 5-4864, lindane and picrotoxin compared.

The effects produced by IP administration of these three agents in the rat were compared because of in vitro evidence that each modulates the picrotoxinin site of the GABAA receptor. For each, hypothermia had the lowest threshold and convulsions the next, with hypophagia produced only by the highest dose of either Ro 5-4864 or lindane. Convulsant effects had a shorter latency and a shorter duration than did hypothermia. Hypophagia, when present, lasted the longest. Myoclonus was the seizure type with the lowest threshold for all three agents. At the highest dose, lindane produced a high incidence of maximal clonic (hopping) seizures, whereas Ro 5-4864 and picrotoxin produced a high incidence of maximal tonic seizures instead. On a mole/kg basis, picrotoxin was 40 times more effective than the other two agents and produced seizures which started later, peaked later, and persisted longest. Ro 5-4864 and lindane were effective at equimolar concentrations and, in combination, produced effects which suggested either dose-addition or synergism. The data are consistent with the hypothesis that the toxic effects of both Ro 5-4864 and lindane may be attributable, at least in part, to an action at a subpopulation of GABAA receptors.

Interaction between pefloxacin and aminophylline in genetically epilepsy-prone rats.

The effects of a chronic treatment with pefloxacin on aminophylline-induced seizures in genetically epilepsy-prone rat have been investigated. Two series of experiments were performed. In the first, animals received pefloxacin orally twice a day for five days, then were administered aminophylline intraperitoneally and the occurrence of seizures was evaluated. In the second series of experiments, theophylline serum concentration was evaluated in rats subject to the same experimental protocol. Pefloxacin significantly, and in a dose-dependent manner, increased the occurrence of seizure phases induced by aminophylline, but did not influence theophylline serum levels measured at different times after the injection of aminophylline. We suggest that additive neurotoxic effects of both pefloxacin and aminophylline might contribute to the increased severity of seizure score. The possible role of GABA-benzodiazepine, excitatory amino acid and purinergic mechanism, and the role of pharmacokinetic factors are discussed.

The pharmacodynamics of anticonvulsant and subconvulsant effects of ethanol in CBA and C57BL/6 mice.

A method of determination of minimal effective doses (MEDs) of bicuculline causing clonic-tonic convulsions (CTC) and tonic extension (TE) was used to investigate ethanol pharmacodynamics in C57BL/6 and CBA mice, differing in levels of alcohol predisposition. It is observed that ethanol produces a powerful anticonvulsant action antagonizing convulsant effects of bicuculline. On a long-term scale, the pharmacological action of alcohol had two phases in both strains of mice: anticonvulsant (in the interval 5 min to 4 h after ethanol administration) and subconvulsant (4-24 h after ethanol administration). C57BL/6 mice were characterized by a more rapid development of the anticonvulsant effect and its faster decay in comparison to CBA strain. A possibility of correct quantitative evaluation of data allows using the method of MED determination as an express model of an acute alcohol abstinence syndrome, as well as for screening of new antialcohol drugs.