Antagonism of caffeine-induced seizures in mice by Ro15-1788

In Vivo Neuropharmacological Effects of Neophytadiene

Neophytadiene (NPT) is a diterpene found in the methanolic extracts of Crataeva nurvala and Blumea lacera, plants reported with anxiolytic-like activity, sedative properties, and antidepressant-like actions; however, the contribution of neophytadiene to these effects is unknown. This study determined the neuropharmacological (anxiolytic-like, antidepressant-like, anticonvulsant, and sedative) effects of neophytadiene (0.1-10 mg/kg p.o.) and determined the mechanisms of action involved in the neuropharmacological actions using inhibitors such as flumazenil and analyzing the possible interaction of neophytadiene with GABA receptors using a molecular docking study. The behavioral tests were evaluated using the light-dark box, elevated plus-maze, open field, hole-board, convulsion, tail suspension, pentobarbital-induced sleeping, and rotarod. The results showed that neophytadiene exhibited anxiolytic-like activity only to the high dose (10 mg/kg) in the elevated plus-maze and hole-board tests, and anticonvulsant actions in the 4-aminopyridine and pentylenetetrazole-induced seizures test. The anxiolytic-like and anticonvulsant effects of neophytadiene were abolished with the pre-treatment with 2 mg/kg flumazenil. In addition, neophytadiene showed low antidepressant effects (about 3-fold lower) compared to fluoxetine. On other hand, neophytadiene had no sedative or locomotor effects. In conclusion, neophytadiene exerts anxiolytic-like and anticonvulsant activities with the probable participation of the GABAergic system.

Preliminary Investigation into the Anticonvulsant, Sedative and Muscle Relaxant Effects of the Methanolic Extract of Capparis spinosa L. Leaves in Mice

Background Capparis spinosa L is a Mediterranean plant. In Libya, the plant grows in rocky areas and at high altitudes. It is commonly used by the inhabitants of the Mediterranean region in their kitchen and treatment of many diseases.

Aim This study was undertaken to investigate the central nervous system depressant, anticonvulsant, and the muscle relaxant activities of orally administered methanolic extract from the leaves of C. spinosa L. (MECS) in mice.

Methods The oral administration of three doses of the MECS in mice (500, 1000, and 2000 mg/kg) were evaluated in the picrotoxin (PC)-induced convulsion model, ketamine-induced sleep, and rota rod test. Diazepam was used as a reference drug for comparison. Results were analyzed using SPSS program version 16. Data are presented as mean ± SEM, and compared using one-way ANOVA followed by Duncan's test. The significance level was set at p < 0.05

Results Oral administration of MECS (1000 and 2000 mg/kg) significantly prolonged the onset of seizures (p < 0.01) and produced dose-dependent protection against PC-induced seizures compared with the control group (12.5% and 50% protection, respectively). MECS significantly (p < 0.05) and dose dependently reduced ketamine sleep latency (from 3.16 ± 0.16 to a minimum of 1.5 ± 0.22 minutes) and prolonged ketamine-induced sleeping time (from 11.33 ± 1.99 to a maximum of 33.33 ± 0.95 minutes). In the accelerated rotarod test, MECS significantly (p < 0.01) decreased the riding time on the rotarod (from 128.83 ± 14.6 to a minimum of 1.83 ± 0.47 seconds) as compared with the normal saline control group.

Conclusion The results showed that the MECS possesses anticonvulsant, sedative, and muscle relaxant properties in mice.

Estrous cycle modulates the anxiogenic effects of caffeine in the elevated plus maze and light/dark box in female rats

Caffeine is a commonly used stimulant of the central nervous system that reduces fatigue, increases alertness, and exerts positive effects on emotion through actions on various brain structures. High doses of caffeine can cause headaches, heart palpitations, hyperactivity, and anxiety symptoms. Consequently, reducing the consumption of stimulant substances, such as sugar and caffeine, is proposed to ameliorate symptoms of premenstrual syndrome in women. The administration of steroid hormones has been suggested to modulate the effects of caffeine, but unknown is whether endogenous hormone variations during the estrous cycle modulate the pharmacological effects of caffeine. The present study evaluated the effects of caffeine (10, 20, and 40 mg/kg) during metestrus-diestrus and proestrus-estrus of the ovarian cycle in rats on anxiety-like behavior using the elevated plus maze and light/dark box. During metestrus-diestrus, all doses of caffeine increased anxiety-like behavior, indicated by the main variables in both behavioral tests (i.e., higher Anxiety Index and lower percent time spent on the open arms in the elevated plus maze and less time spent in the light compartment in the light/dark box). During proestrus-estrus, only 20 and 40 mg/kg caffeine increased these parameters of anxiety-like behavior, albeit only slightly. In conclusion, caffeine increased anxiety-like behaviors in metestrus-diestrus, with an attenuation of these effects of lower doses of caffeine in proestrus-estrus. These effects that were observed in metestrus-diestrus and proestrus-estrus may be associated with low and high concentrations of steroid hormones, respectively, that naturally occur during these phases of the ovarian cycle.

Neuropharmacological Assessment of the Hydroethanolic Leaf Extract of Calotropis procera (Ait). R. Br. (Apocynaceae) in Mice

BACKGROUND

Calotropis procera has been widely used traditionally for its analgesic and anti-inflammatory effects. It is also reportedly used in ethnomedicine for mental health disorders including epilepsy even in the absence of supporting scientific data. Thus, the potential of the plant to affect neurological functions was evaluated.

METHODS

Irwin's test was performed to determine the effect of the oral administration of the extract (30-3000 mg kg^-1) on gross behaviour and physiological function. The activity meter, rotarod, pentylenetetrazol- (PTZ-) induced convulsion, pentobarbitone-induced sleep test, and the tail immersion tests were used to evaluate the spontaneous activity, neuromuscular function, convulsive threshold, sedation, and analgesic effects of the Calotropis procera extract (30-1000 mg/kg), respectively, in mice.

RESULTS

Calotropis procera extract (CPE) exhibited significant (p < 0.0001) anticonvulsant and analgesic effects. There was a significant increase in withdrawal latency of the CPE-treated animals in the tail immersion test for analgesia (p < 0.0001), while latency and duration of PTZ-induced convulsions were positively modulated. Calotropis procera extract showed significant (p < 0.0001) central nervous system depressant effects in pentobarbitone-induced hypnosis at 100-1000 mg/kg and spontaneous activity test (30-1000 mg/kg). The extract also depicted impaired motor coordination at 100-1000 mg/kg dose levels. LD₅₀ was estimated to be above 1000 mg kg^-1.

CONCLUSIONS

Calotropis procera extract has significant central nervous system depressant and analgesic effects in mice.

Neuropharmacological effects of d-pinitol and its possible mechanisms of action

The aim was to evaluate the diuretic and neuropharmacological actions of d-pinitol and describe a possible mechanism of action. The diuretic effects of d-pinitol were evaluated using mice placed in metabolic cages. The sedative, anxiolytic-like, antidepressant-like, and anticonvulsant effects of 1-100 mg/kg d-pinitol were assessed. The possible mechanisms of action of the anxiolytic-like, antidepressant-like, and anticonvulsant effects of d-pinitol were evaluated using inhibitors. d-pinitol lacked diuretic effects. However, d-pinitol showed the highest anxiolytic-like actions (ED₅₀  = 70 mg/kg p.o. in mice) in the cylinder exploratory test and the highest antidepressant-like activity in the forced swimming test (ED₅₀  = 26 mg/kg p.o. in mice). d-pinitol (100 mg/kg) exerted anticonvulsant actions in the pentylenetetrazole-induced seizures test. The pre-treatment with 2 mg/kg flumazenil reverted the anxiolytic-like actions and the anticonvulsant effects of d-pinitol, whereas the pre-treatment with 1 mg/kg yohimbine and 0.05 mg/kg prazosin abolished the antidepressant effects of d-pinitol. PRACTICAL APPLICATIONS: d-pinitol (3-O-methyl-d-chiro-inositol) is a polyol found in many fruits, as well as in many members of the Leguminosae and Fabaceae families. The results propose that this compound could contribute in the treatment of anxiety, depression, and convulsions. The findings suggest the possible participation of the GABAergic system in the anxiolytic-like and anticonvulsant actions of d-pinitol, whereas the noradrenergic system is probably involved in the antidepressant effects of d-pinitol. This study provides new information about other pharmacological uses for d-pinitol.

Anticonvulsant Effect of Antiaris toxicaria (Pers.) Lesch. (Moraceae) Aqueous Extract in Rodents

Antiaris toxicaria (Moraceae) was evaluated for anticonvulsant activity in rodents. Animal models used include maximal electroshock test (MEST); pentylenetetrazole-induced (PTZ) convulsions; picrotoxin-induced (PCT) convulsions; strychnine- (STR-) and 4-aminopyridine-induced convulsions. Increase in latency to seizures as well as reduction in duration and frequency of seizures indicated anticonvulsant activity. The extract was more effective in all models used except the maximal electroshock test and strychnine-induced convulsions. Antiaris toxicaria aqueous extract (200, 400, and 800 mg kg(-1)) significantly (P < 0.05 - 0.01) shortened the duration of convulsions in PTZ- and PCT-induced seizures. Delay in the onset of convulsions in the two tests was significant (P < 0.001). Reduction in the frequency of seizures was also significant (P < 0.05 - 0.001) in both tests. Antiaris further delayed the onset of seizures in 4-aminopyridine model while producing 75% protection against death in mice. Diazepam (0.1, 0.3, and 1 mg kg(-1)), carbamazepine (3, 10, and 30 mg kg(-1)), and sodium valproate (100-400 mg kg(-1)) were used as reference anticonvulsant drugs for various models. Flumazenil blocked the effect of the extract in the PTZ test significantly suggesting that Antiaris toxicaria may be acting by enhancing the effects of the GABAergic system. Antiaris toxicaria aqueous extract therefore possesses anticonvulsant activity.

Anticonvulsant and related neuropharmacological effects of the whole plant extract of Synedrella nodiflora (L.) Gaertn (Asteraceae)

Purpose:

The plant Synedrella nodiflora (L) Gaertn is traditionally used by some Ghanaian communities to treat epilepsy. To determine if this use has merit, we studied the anticonvulsant and other neuropharmacological effects of a hydro-ethanolic extract of the whole plant using murine models.

Materials and Methods:

The anticonvulsant effect of the extract (10–1000 mg/kg) was tested on the pentylenetetrazole-, picrotoxin-, and pilocarpine-induced seizure models and PTZ-kindling in mice/rats. The effect of the extract was also tested on motor coordination using the rota-rod.

Results:

The results obtained revealed that the extract possesses anticonvulsant effects in all the experimental models of seizures tested as it significantly reduced the latencies to myoclonic jerks and seizures as well as seizure duration and the percentage severity. The extract was also found to cause motor incoordination at the higher dose of 1000 mg/kg.

Conclusions:

In summary, the hydro-ethanolic extract of the whole plant of S. nodiflora possesses anticonvulsant effects, possibly through an interaction with GABAergic transmission and antioxidant mechanisms and muscle relaxant effects. These findings thus provide scientific evidence in support of the traditional use of the plant in the management of epilepsy.

Anticonvulsant activity of solasodine isolated from Solanum sisymbriifolium fruits in rodents

CONTEXT

Solanum sisymbriifolium Lam. (Solanaceae), commonly known as sticky nightshade, is traditionally used for central nervous system (CNS) disorders. Although solasodine has been isolated from this plant, little is known about its anticonvulsant and CNS depressant actions.

OBJECTIVE

We investigated anticonvulsant and CNS depressant effects of solasodine isolated from S. sisymbriifolium using several experimental models.

MATERIALS AND METHODS

Swiss albino mice (n=6) were employed for pentylenetetrazole (PTZ) and picrotoxin (PCT)-induced convulsions and thiopental-induced sleep time. Different groups of Wistar albino rats (n=6) were subjected to maximal electroshock (MES) test. Solasodine, a steroidal glycoalkaloid, was isolated from dried fruits of S. sisymbriifolium and identified by GC-MS.

RESULTS

The results showed that intraperitoneal (i.p.) injection of solasodine (25 mg/kg) significantly delayed (p < 0.01) latency of hind limb tonic extensor (HLTE) phase in the PCT-induced convulsions. In the MES model, solasodine significantly reduced (p < 0.001) duration of HLTE at 25, 50, and 100 mg/kg, i.p. in a dose-dependent manner. Interestingly, solasodine did not produce any significant reduction in PTZ-induced convulsions. Prior treatment of solasodine (25, 50, and 100 mg/kg, i.p.) significantly potentiated thiopental-provoked sleep in a dose-dependent manner (p < 0.001).

DISCUSSION AND CONCLUSION

Our study, for the first time, shows potent anticonvulsant and CNS depressant activities of solasodine. It is likely that solasodine, in part, is responsible for the anticonvulsant and sedative properties of S. sisymbriifolium. The future study should focus on the exact mechanism of action of solasodine.

Modeling seizure-related behavioral and endocrine phenotypes in adult zebrafish

Larval zebrafish (Danio rerio) have recently been suggested as a high-throughput experimental model of epilepsy-related pathogenetic states. Here we use adult zebrafish to study behavioral symptoms associated with drug-evoked seizures. Experimental epilepsy-like states were evoked in zebrafish by exposure for 20min to three chemoconvulsant drugs: caffeine (250mg/L; 1.3mM), pentylenetetrazole (1.5g/L; 11.0mM) and picrotoxin (100mg/L; 0.17mM). Fish behavior was analyzed using manual and video-tracking methods (Noldus Ethovision XT7). Compared to their respective controls, all three drug-treated groups showed robust seizure-like responses (hyperactivity bouts, spasms, circular and corkscrew swimming) accompanied by elevated whole-body cortisol levels (assessed by ELISA). In contrast, control fish did not display seizure-like behaviors and had significantly lower cortisol levels. Paralleling behavioral and endocrine phenotypes observed in clinical and rodent studies, our data implicates adult zebrafish as an emerging experimental model for epilepsy research.

Sanjoinine A isolated from Semen Zizyphi Spinosi protects against kainic acid-induced convulsions

These experiments were performed to know whether sanjoinine A, a component of the alkaloid fraction of Semen Zizyphi Spinosi, acts as an anti-convulsive agent in the kainic acid (KA)-induced experimental convulsion model and whether these effects are mediated by decreased intracellular calcium. Oral administration of sanjoinine A (4 and 8 mg/kg) increased the survival rate and latency of convulsion onset, and decreased the seizure scores and the weight loss induced by intraperitoneal (i.p.) injection of KA (50 mg/kg) in mice. In addition, sanjoinine A protected against neuronal damage and apoptosis in the hippocampus after KA administration, as analyzed by using immunohistochemistry and TUNEL assay. Sanjoinine A also significantly blocked seizure-form electroencephalogram alterations induced by KA. Moreover, in cultured rat neuronal cells, sanjoinine A inhibited KA-induced cell death, as measured by propidium iodide detection. Sanjoinine A also increased intracellular chloride and inhibited the elevation of intracellular calcium induced by KA. Sanjoinine A, therefore protects against KA-induced convulsions by increasing intracellular chloride and reducing intracellular calcium levels.

Anticonvulsant activity of Nylandtia spinosa L. Dumont (Polygalaceae) aqueous and methanol leaf extracts in mice

Aqueous and methanol leaf extracts of Nylandtia spinosa L. Dumont (Polygalaceae) were evaluated for anticonvulsant activity against tonic seizures produced in mice by pentylenetetrazole (PTZ), bicuculline, picrotoxin, and N-methyl-DL-aspartic acid (NMDLA). Aqueous leaf extract of N. spinosa (50–400 mg/kg, i.p.) and methanol extract (50–400 mg/kg, i.p.) significantly attenuated PTZ (95 mg/kg, i.p.)-induced tonic seizures. Doses of 400 mg/kg (i.p.) and 100–400 mg/kg (i.p.) of aqueous extract of N. spinosa significantly delayed the onset of tonic seizures elicited by bicuculline (35 mg/kg, i.p.) and picrotoxin (12 mg/kg, i.p.), respectively. Methanol extract (200–400 mg/kg, i.p.) and (50–400 mg/kg, i.p.) significantly delayed the onset of tonic seizures induced by bicuculline (35 mg/kg, i.p.) and picrotoxin (12 mg/kg, i.p.), respectively, whereas 400 mg/kg (i.p.) significantly reduced the incidence of picrotoxin (12 mg/kg, i.p.)-induced seizures. Both aqueous and methanol leaf extracts of N. spinosa did not affect NMDLA (400 mg/kg, i.p.)-induced tonic seizures. Phenobarbitone (12.5 mg/kg, i.p.) and diazepam (0.5 mg/kg, i.p.) antagonized tonic seizures induced by PTZ (95 mg/kg, i.p.), bicuculline (35 mg/kg, i.p.), and picrotoxin (12 mg/kg, i.p.) but did not affect NMDLA (400 mg/kg, i.p.)-induced seizures. Phenytoin (30 mg/kg, i.p.) did not alter the tonic seizures produced by either PTZ (95 mg/kg, i.p.), bicuculline –2-(35 mg/kg, i.p.), or picrotoxin (12 mg/kg, i.p.). The results obtained indicate that both aqueous and methanol leaf extracts of N. spinosa possess anticonvulsant property, thus justifying the use of the plant by traditional medicine practitioners in the treatment of epilepsy. The relatively high LD50 of greater than 3600 mg/kg (p.o.) and 1780 mg/kg (i.p.) obtained with the aqueous extract suggest that the plant is relatively safe in mice. The phytochemical analysis carried out showed the presence of tannins, saponins, reducing sugars, alkaloids, flavonoids, triterpene steroids, and cardiac glycosides in the plant material.

Protective effects of sanjoinine A against N-methyl-D-aspartate-induced seizure

Sanjoinine A is a component of the alkaloid fraction of Zizyphi Spinosi Semen. This experiment was performed to investigate whether sanjoinine A acts as an anticonvulsive in the N-methyl-D-aspartate (NMDA)-induced experimental seizure model. We also examined whether it protects against seizure-form electroencephalogram (EEG) alterations induced by NMDA in vivo and/or cell killing due to NMDA in cultured cerebellar granule cells. Administration of sanjoinine A increased the survival rate and the latency of seizure onset, and decreased the seizure scores and the weight-loss induced by NMDA in mice, in a dose-dependent manner. In addition, sanjoinine A blocked seizure-form EEG alterations induced by NMDA and inhibited NMDA-induced cell killing in cultured rat cerebellar granule cells, measured by both the trypan blue exclusion test and the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay. Moreover, sanjoinine A inhibited the elevation of intracellular calcium influx induced by NMDA, which was measured using a fluorescent dye, Furo 3-AM. It is suggested that sanjoinine A protects against NMDA-induced seizures by inhibiting intracellular calcium influx.

Phythochemical screening and anticonvulsant activity of Cymbopogon winterianus Jowitt (Poaceae) leaf essential oil in rodents

Cymbopogon winterianus (Poaceae) is used for its analgesic, anxiolytic and anticonvulsant properties in Brazilian folk medicine. This report aimed to perform phythochemical screening and to investigate the possible anticonvulsant effects of the essential oil (EO) from fresh leaves of C. winterianus in different models of epilepsy. The phytochemical analysis of EO showed presence of geraniol (40.06%), citronellal (27.44%) and citronellol (10.45%) as the main compounds. A behavioral screening demonstrated that EO (100, 200 and 400mg/kg; ip) caused depressant activity on CNS. When administered concurrently, EO (200 and 400mg/kg, ip) significantly reduced the number of animals that exhibited PTZ- and PIC-induced seizures in 50% of the experimental animals (p<0.05). Additionally, EO (100, 200 and 400mg/kg, ip) significantly increased (p<0.05) the latencies of clonic seizures induced by STR. Our results demonstrated a possible activity anticonvulsant of the EO.

Anticonvulsant effect of Rhus chirindensis (Baker F.) (Anacardiaceae) stem-bark aqueous extract in mice

Extracts of Rhus chirindensis stem-bark are used extensively in South African traditional medicines for the treatment, management and/or control of an array of human ailments, including childhood convulsions and epilepsy. In this study, we investigated the anticonvulsant activity of the plant's stem-bark aqueous extract (RCE, 50-800 mg/kg i.p.) against pentylenetetrazole (PTZ)-, picrotoxin (PCT)- and bicuculline (BCL)-induced seizures in mice. Phenobarbitone and diazepam were used as reference anticonvulsant drugs for comparison. Single intraperitoneal injections of PTZ (90 mg/kg), PCT(10 mg/kg) or BCL (30 mg/kg) produced tonic-clonic seizures. Like the standard antiseizure drugs used, Rhus chirindensis stem-bark aqueous extract (RCE, 100-800 mg/kg i.p.) significantly delayed (p<0.05-0.001) the onset of, and antagonized pentylenetetrazole-induced seizures. The plant's stem-bark aqueous extract (RCE, 100-800 mg/kg i.p.) also profoundly antagonized picrotoxin-induced seizures, but only weakly antagonized bicuculline-induced seizures. Although the data obtained in the present study do not provide conclusive evidence, it would appear that RCE produces its antiseizure effect by enhancing GABAergic neurotransmission and/or action in the brain. The results of this laboratory animal study indicate that RCE possesses anticonvulsant activity in the mammalian experimental model used, and thus suggest that the plant may be used as a natural supplementary remedy in the management, control and/or treatment of childhood convulsions and epilepsy. In conclusion, the findings of this study lend pharmacological credence to the suggested folkloric, ethnomedical uses of Rhus chirindensis in the management of childhood convulsions and epilepsy in some rural communities of South Africa.

Anticonvulsant activity of Hypoxis hemerocallidea Fisch. & C. A. Mey. (Hypoxidaceae) corm (‘African potato’) aqueous extract in mice

Extracts of Hypoxis hemerocallidea Fisch. & C. A. Mey. (Hypoxidaceae) corm (popularly known as 'African potato') are extensively used in South African traditional medicines for the treatment, management and/or control of an array of human ailments, including childhood convulsions and epilepsy. This study examined the anticonvulsant activity of the plant's corm aqueous extract (APE, 50-800 mg/kg i.p.) against pentylenetetrazole (PTZ)-, picrotoxin (PCT)- and bicuculline (BCL)-induced seizures in mice. Phenobarbitone and diazepam were used as reference anticonvulsant drugs for comparison. Like the reference antiseizure drugs used, Hypoxis hemerocallidea corm aqueous extract (APE, 100-800 mg/kg i.p.) significantly delayed (p < 0.05-0.001) the onset of, and antagonized, pentylenetetrazole (PTZ)-induced seizures. The plant's corm aqueous extract (APE, 100-800 mg/kg i.p.) also profoundly antagonized picrotoxin (PCT)-induced seizures, but only weakly antagonized bicuculline (BCL)-induced seizures. Although the data obtained in the present study do not provide conclusive evidence, it would appear that 'African potato' aqueous extract (APE) produces its antiseizure effect by enhancing GABAergic neurotransmission and/or action in the brain. The results of this laboratory animal study indicate that APE possesses anticonvulsant activity in the mammalian experimental model used and, therefore, tend to suggest that the herb may be used as a natural supplementary remedy in the management, control and/or treatment of childhood convulsions and epilepsy. In conclusion, the findings of this study indicate that Hypoxis hemerocallidea corm aqueous extract possesses anticonvulsant activity, and thus lend pharmacological credence to the suggested folkloric, anecdotal ethnomedical uses of the herb in the management of childhood convulsions and epilepsy in some rural communities of South Africa.

Anticonvulsant activity of Cotyledon orbiculata L. (Crassulaceae) leaf extract in mice

The anticonvulsant activity of Cotyledon orbiculata L. (Crassulaceae) was investigated by studying the effects of both aqueous and methanol extracts of the plant species on seizures induced by pentylenetetrazole, bicuculline, picrotoxin and N-methyl-dl-aspartic in mice. Aqueous extract of Cotyledon orbiculata (50-400mg/kg, i.p.) and methanol extract (100-400mg/kg, i.p.) significantly prolonged the onset of tonic seizures induced by pentylenetetrazole (95mg/kg, i.p.). Methanol extract (400mg/kg, i.p.) also significantly reduced the incidence of the seizures. One hundred to two hundred milligrams/kilogram (i.p.) of aqueous extract of Cotyledon orbiculata significantly delayed the onset of the tonic seizures induced by bicuculline (40mg/kg, i.p.), picrotoxin (12mg/kg, i.p.) and N-methyl-dl-aspartic acid (NMDLA, 400mg/kg, i.p.). Similarly, methanol extract (100-400mg/kg, i.p.) significantly delayed the onset of the tonic seizures induced by bicuculline (40mg/kg, i.p.) and picrotoxin (12mg/kg, i.p.) while 100mg/kg (i.p.) significantly delayed the onset of N-methyl-dl-aspartic acid (NMDLA, 400mg/kg, i.p.)-induced seizures. Methanol extract (200mg/kg, i.p.) significantly reduced the incidence of the seizures induced by bicuculline (40mg/kg, i.p.). Phenobarbitone (12mg/kg, i.p.) and diazepam (0.5mg/kg, i.p.) effectively antagonized only seizures induced by PTZ (95mg/kg, i.p.), bicuculline (40mg/kg, i.p.) and picrotoxin (12mg/kg, i.p.). Phenytoin (30mg/kg, i.p.) did not affect any of the seizures to any significant extent. The data obtained suggest that both aqueous and methanol extracts of Cotyledon orbiculata have anticonvulsant property and may probably be affecting both gabaergic and glutaminergic mechanisms to exert its effect. The phytochemical analysis carried out revealed the presence of cardiac glycosides, saponins, tannins, reducing sugar and triterpene steroids in the plant extract.

Modelling anxiety in humans for drug development

Animal behavioural profiles are commonly employed to investigate new therapeutic agents to treat anxiety disorders as well as to investigate the mechanism of action of anxiolytic drugs. However, many clinically important symptoms of anxiety can not be modelled directly in animals. Human models of anxiety should bridge between animal models and anxiety disorders. Experimental anxiety states in humans can be induced by either pharmacological means such as CO(2) inhalation or psychological means such as aversive conditioning of skin conductance responses to tones. Investigation of these models may contribute to a better understanding of anxiety disorders, both from a biological and behavioural point of view. In a comprehensive review existing models of human experimental anxiety states are summarized and validity is discussed.

Anticonvulsant effect of Persea americana Mill (Lauraceae) (Avocado) leaf aqueous extract in mice

Various morphological parts of Persea americana Mill (Lauraceae) (avocado) are widely used in African traditional medicines for the treatment, management and/or control of a variety of human ailments, including childhood convulsions and epilepsy. This study examined the anticonvulsant effect of the plant's leaf aqueous extract (PAE, 50-800 mg/kg i.p.) against pentylenetetrazole (PTZ)-, picrotoxin (PCT)- and bicuculline (BCL)-induced seizures in mice. Phenobarbitone and diazepam were used as reference anticonvulsant drugs for comparison. Like the reference anticonvulsant agents used, Persea americana leaf aqueous extract (PAE, 100-800 mg/kg i.p.) significantly (p < 0.05-0.001) delayed the onset of, and antagonized, pentylenetetrazole (PTZ)-induced seizures. The plant's leaf extract (PAE, 100-800 mg/kg i.p.) also profoundly antagonized picrotoxin (PCT)-induced seizures, but only weakly antagonized bicuculline (BCL)-induced seizures. Although the data obtained in the present study do not provide conclusive evidence, it would appear that 'avocado' leaf aqueous extract (PAE) produces its anticonvulsant effect by enhancing GABAergic neurotransmission and/or action in the brain. The findings of this study indicate that Persea americana leaf aqueous extract possesses an anticonvulsant property, and thus lends pharmacological credence to the suggested ethnomedical uses of the plant in the management of childhood convulsions and epilepsy.

Analgesic and anticonvulsant properties of Tetrapleura tetraptera (Taub) (Fabaceae) fruit aqueous extract in mice

Previous studies in our laboratories and elsewhere have shown that the fruit of Tetrapleura tetraptera (Taub) (family: Fabaceae) is widely used in African traditional medicine for the management and/or control of an array of human ailments, including schistosomiasis, asthma, epilepsy, hypertension and so on. The present study was designed to investigate the analgesic and anticonvulsant effects of Tetrapleura tetraptera (Taub) fruit aqueous extract (TTE) in mice. Morphine (MPN, 10 mg/kg i.p.), diclofenac (DIC, 100 mg/kg i.p.), phenobarbitone (20 mg/kg i.p.) and diazepam (0.5 mg/kg i.p.) were used, respectively, as reference analgesic and anticonvulsant agents for comparison. T. tetraptera fruit aqueous extract (TTE, 50-800 mg/kg i.p.) produced dose-dependent, significant (p < 0.05-0.001) analgesic effects against thermally and chemically induced pain in mice. Like the standard anticonvulsant agents (phenobarbitone and diazepam) used, T. tetraptera fruit aqueous extract (TTE, 50-800 mg/kg i.p.) significantly (p < 0.05-0.001) delayed the onset of, and antagonized, pentylenetetrazole (PTZ)-induced seizures. Aqueous extract of the fruit (TTE, 50-800 mg/kg i.p.) also profoundly antagonized picrotoxin (PCT)-induced seizures, but only partially and weakly antagonized bicuculline (BCL)-induced seizures. However, the results of this experimental animal study indicate that Tetrapleura tetraptera (Taub) fruit aqueous extract (TTE) possesses analgesic and anticonvulsant properties. These findings lend pharmacological support to the suggested folkloric uses of the plant's fruit in the management and/or control of painful, arthritic inflammatory conditions, as well as for the management and/or control of epilepsy and childhood convulsions in some tropical African countries.

Anticonvulsant activity of Harpagophytum procumbens DC [Pedaliaceae] secondary root aqueous extract in mice

Harpagophytum procumbens DC [family: Pedaliaceae] is widely used in South African traditional medicine for the treatment, management and/or control of a variety of human ailments. In the present study, we have examined the anticonvulsant activity of Harpagophytum procumbens secondary root aqueous extract (HPE, 50-800 mg/kg i.p.) against pentylenetetrazole (PTZ)-, picrotoxin (PCT)- and bicuculline (BCL)-induced seizures in mice. Phenobarbitone and diazepam were used as reference anticonvulsant drugs for comparison. Like the reference anticonvulsant agents used, H. procumbens secondary root aqueous extract (HPE, 100-800 mg/kg i.p.) significantly (P<0.05-0.001) delayed the onset of, and antagonized, pentylenetetrazole (PTZ)-induced seizures. The plant's extract (HPE, 100-800 mg/kg i.p.) also profoundly antagonized picrotoxin (PCT)-induced seizures, but only partially and weakly antagonized bicuculline (BCL)-induced seizures. Although the data obtained in the present study do not provide conclusive evidence, it would appear that H. procumbens secondary root aqueous extract (HPE) produces its anticonvulsant activity by enhancing GABAergic neurotransmission and/or facilitating GABAergic action in the brain. In general, the average onset of convulsion was delayed, while the average duration of convulsion was markedly reduced. The plant's extract also depressed the central nervous system (CNS). It is, therefore, thought that the anticonvulsant property of the herb may be linked, at least in part, to its ability to depress the central nervous system. However, the results of this experimental animal study indicate that H. procumbens secondary root aqueous extract possesses anticonvulsant activity, and thus lend pharmacological support to the suggested folkloric, ethnomedical uses of the plant's extract in the treatment, management and/or control of epilepsy and childhood convulsions in some rural communities of South Africa.

Gamma-aminobutyric acid and mefloquine-induced seizures in mice

The role of GABAergic mechanism in the convulsant effect of mefloquine was investigated in mice. Mefloquine dose dependently induced tonic seizures in mice. Aminooxyacetic acid, diaminobutyric acid and muscimol significantly protected mice against mefloquine-induced seizures by significantly delaying the onset and decreasing the incidence of the seizures. Bicuculline and picrotoxin significantly enhanced the seizure producing effect of mefloquine and also significantly antagonised the protective effect of muscimol against the seizures. Phenobarbitone and diazepam effectively protected mice against mefloquine-induced seizures. Phenytoin did not alter mefloquine-induced seizures. These data indicate that GABA mechanisms might be involved in seizures produced by mefloquine in mice.

Anticonvulsant activity of aqueous extract of Leonotis leonurus

Water extract of Leonotis leonurus was tested for anticonvulsant activity against seizures produced in mice by pentylenetetrazole, picrotoxin, bicuculline and N-methyl-DL-aspartic acid (intraperitoneal injections). L. leonurus extract in the doses of 200 and 400 mg/kg respectively protected 37.5% and 50% of animals used and significantly (p < 0.05; Student's t-test) delayed pentylenetetrazole (90 mg/kg)-induced tonic seizures. Similarly, the same doses of L. leonurus extract significantly (p < 0.05; Student's t-test) delayed the onset of tonic seizures produced by picrotoxin (8 mg/kg) and N-methyl-DL-aspartic acid (400 mg/kg). However, all the doses of aqueous extract of L leonurus used did not alter the seizures induced by bicuculline (20 mg/kg) to any significant extent. The data suggest that the extract of L. leonurus has anticonvulsant activity and may probably be acting through non-specific mechanisms, since it affects both gabaergic and glutaminergic systems. High performance liquid chromatography (HPLC) and phytochemical tests carried out respectively show a spectrum profile, characteristic of L. leonurus and the presence of alkaloids, saponins and tannins in the extract.

Gamma-aminobutyric acid and glutamic acid receptors may mediate theophylline-induced seizures in mice

The effects of drugs affecting GABA and glutamic acid receptors on theophylline-induced seizures were investigated in mice. Theophylline elicited tonic seizures in mice in a dose dependent manner. Muscimol, DABA and AOAA significantly prolonged the onset and significantly decreased the incidence of theophylline-induced seizures. Baclofen significantly delayed the onset of the tonic seizures induced by theophylline. Bicuculline and picrotoxin significantly shortened the onset and significantly increased the incidence of seizures induced by a low dose of theophylline and also significantly antagonized muscimol-attenuating effect against theophylline seizures. N-methyl-DL-aspartic acid significantly shortened the onset and significantly increased the incidence of seizures elicited by a low dose of theophylline. D-(-)-2-amino-phosphonopentanoic acid effectively delayed the onset and significantly decreased the incidence of seizures elicited by theophylline and also significantly antagonized the potentiating effect of N-methyl-DL-aspartic acid on seizures induced by a low dose of theophylline. Dextromethorphan and ketamine profoundly shortened the onset of theophylline-induced seizures. Clonidine effectively prolonged the onset and significantly decreased the incidence of theophylline-induced seizures. These data indicate that GABA(A) and N-methyl-D-aspartic acid receptors may mediate theophylline-elicited tonic seizures in mice.

Antimicrobial and anticonvulsant activities of Viscum capense

Dichloromethane, methanol and water extracts of Viscum sapense L.f., of the Loranthaceae family, were tested for antimicrobial activities against Staphylococcus aureus, Pseudomonas aeruginosa and Candida albicans. Methanol extract was also tested for activity against seizures in albino mice induced by pentylenetetrazole (PTZ), bicuculline and N-methyl-DL-aspartic acid (NMDLA). Methanol extract of V. capense inhibited the growth of S. aureus. Methanol extract also protected the mice against PTZ- and bicuculline-induced tonic seizures but did not significantly alter NMDLA-induced tonic seizures. The data indicate that the extract of V. capense has antibacterial activity against S. aureus and also anticonvulsant activity.

Diazepam alters caffeine-induced effects on beta-endorphin levels in specific rat brain regions

The present study was conducted to evaluate the effects of caffeine and the benzodiazepine agonist diazepam, and a combination of both on beta-endorphin (beta-EN) levels in specific rat brain regions. Male Sprague-Dawley rats (150-200 g) adapted to a 12-hour light: 12-hour dark illumination cycle were used in this study. Caffeine (10 mg/kg), diazepam (2 mg/kg) or a combination of caffeine (10 mg/kg) and diazepam (2 mg/kg) were administered intraperitoneally to rats at 11:00 hr. Control animals were injected with saline. Animals were sacrificed by decapitation 1 h after injection, the brains were immediately removed; the cortex, hippocampus, hypothalamus and midbrain were dissected and their B-EN levels measured by radioimmunoassay. Caffeine administration significantly increased B-EN levels in the cortex. Similarly, administration of diazepam alone resulted in a significant increase of B-EN levels in cortex. However, concurrent administration of diazepam and caffeine resulted in higher increase of B-EN levels in cortex. No significant changes in B-EN levels were detected in hippocampus and midbrain after administration of either caffeine or diazepam alone. On the other hand, when diazepam and caffeine were concurrently administered a significant increase of B-EN levels were observed in the midbrain. Moreover, administration of diazepam alone resulted in a significant increase of B-EN levels in hypothalamus. This increase was still observed following concurrent administration of diazepam and caffeine. These results clearly indicate that diazepam alters caffeine-induced effects on B-EN in specific rat brain regions.

Anxiogenic action of caffeine: an experimental study in rats

The anxiogenic action of caffeine (10, 25 and 50 mg/kg, i.p.) was investigated in rats and compared with that of yohimbine (2 mg/kg, i.p.). The experimental methods used were the open-field, elevated plus-maze, social interaction and novelty-suppressed feeding latency tests. Caffeine produced a dose-related profile of behavioural changes, which were qualitatively similar to those induced by yohimbine and which indicate an anxiogenic activity in rodents. Thus, both the drugs reduced ambulation and rears, and increased immobility and defaecation in the open-field test. They decreased the number of entries and time spent on the open arms of the elevated-plus maze, reduced social interaction in paired rats and increased the feeding latency in an unfamiliar environment in 48-h food-deprived rats. Lorazepam, a well known benzodiazepine anxiolytic agent, attenuated the anxiogenic effects of caffeine and yohimbine. Subchronic administration of caffeine (50 mg/kg, i.p.) for 21 days, in different groups of animals, induced a significant degree of tolerance in the elevated plus-maze test, which was statistically significant after 14 and 21 days' treatment. Yohimbine, however, did not induce similar tolerance. When caffeine (50 mg/kg, i.p.) was withdrawn after 21 days' administration, to a separate group of rats, significant withdrawal anxiety was observed 48 h later as noted in the elevated plus-maze test. The investigations support clinical evidence of caffeine-induced anxiety, tolerance to anxiety on continued use, and withdrawal anxiety in chronic caffeine-containing beverage users.

Influence of chronic aminophylline on antielectroshock activity of diazepam and aminophylline-induced convulsions in mice

The effects of chronic administration of aminophylline (AMPH; 50 mg/kg, twice daily for 14 consecutive days) were studied on both antielectroshock efficacy of diazepam (DZP) and convulsive activity of AMPH in mice. AMPH injected acutely at a dose of 50 mg/kg significantly reduced anticonvulsant action of DZP elevating ED50 from 10.9 (control) to 15.9 mg/kg (p < 0.01). After the administration of AMPH for 3 days, ED50 value was still higher compared with control. Chronic treatment with AMPH resulted in further increase of ED50 of DZP, which was 20.2 mg/kg, and this elevation was significant not only when compared with saline-treated animals, but also with acute and 3-day administration of the xanthine (p < 0.01, 0.05, and 0.001, respectively). Therefore, no tolerance to this AMPH-mediated effect was found, and even an enhancing influence was observed. On the other hand, chronic treatment with AMPH decreased convulsive activity of AMPH elevating ED50 for induction of clonic seizures from 218 to 252 mg/kg (p < 0.01). The remaining seizure parameters were unaffected. Furthermore, in both cases pharmacokinetic interactions were excluded, at least in terms of total plasma levels of the drugs. The results suggest that the mechanisms governing AMPH-induced reversal of the anticonvulsant efficacy of DZP qualitatively differ from those underlying AMPH-induced convulsions. Moreover, these data support the claim that AMPH should be avoided in patients suffering from different types of epilepsy.

GABAergic and dopaminergic systems may be involved in seizures induced by pyrimethamine in mice

1. The effects of some GABAergic and dopaminergic agents on pyrimethamine-induced tonic seizures were investigated in mice. 2. Pyrimethamine dose dependently induced seizures in mice. 3. Muscimol, AOAA and DABA significantly protected mice against pyrimethamine-induced seizures. 4. Bicuculline and picrotoxin effectively potentiated seizures elicited by pyrimethamine and significantly antagonized the protective effect of muscimol against the seizures. 5. Diazepam and phenobarbitone effectively protected mice against seizures elicited by pyrimethamine. 6. L-Dopa significantly potentiated pyrimethamine-induced seizures. 7. Apomorphine and pargyline significantly reduced the latency of seizures induced by pyrimethamine. 8. Haloperidol and pimozide effectively protected mice against pyrimethamine-elicited seizures and also significantly antagonized the potentiating effects of apomorphine and L-dopa on the seizures. 9. Disulfiram significantly potentiated seizures induced by pyrimethamine and also significantly enhanced the seizure-potentiating effect of L-dopa. 10. alpha-Methyl-p-tyrosine effectively protected against seizures induced by pyrimethamine. However, L-dopa significantly potentiated the seizures in alpha-methyl-p-tyrosine-pretreated animals. 11. Muscimol significantly attenuated the potentiating effect of L-dopa on pyrimethamine-induced seizures while bicuculline significantly enhanced the effect of L-dopa. Furthermore, haloperidol significantly potentiated the protective effect of muscimol against pyrimethamine-induced seizures. 12. These results suggest that both GABA and dopamine might be involved in the mechanism(s) of pyrimethamine seizures in mice.

Strychnine-induced seizures in mice: the role of noradrenaline

1. The effects of some noradrenergic agents on seizures induced by strychnine were investigated in mice. 2. Strychnine (0.5-4 mg/kg, i.p.) dose-dependently produced tonic seizures. 3. DOPS (4-8 mg/kg, i.p.) significantly shortened the latency of seizures elicited by strychnine (2 mg/kg, i.p.). Similarly, DOPS (4 mg/kg, i.p.) effectively increased the incidence and significantly shortened the latency of seizures induced by strychnine (1 mg/kg, i.p.). 4. Imipramine (20-40 mg/kg, i.p.) and pargyline (200 mg/kg, i.p.) significantly shortened the latency of strychnine (2 mg/kg, i.p.)-induced seizures. 5. Phentolamine (5-20 mg/kg, i.p.) effectively antagonised the seizures elicited by strychnine (2 mg/kg, i.p.). Furthermore, phentolamine (10 mg/kg, i.p.) attenuated the seizure-potentiating effect of DOPS (4 mg/kg, i.p.). 6. Propranolol (0.5-2 mg/kg, i.p.) and prazosin (1-2 mg/kg, i.p.) reduced the incidence and significantly delayed the latency of seizures induced by strychnine (2 mg/kg, i.p.). 7. Reserpine (5-10 mg/kg, i.p.) significantly prolonged the latency of strychnine (2 mg/kg, i.p.)-induced seizures. 8. Clonidine (0.25-1 mg/kg, i.p.) dose-dependently and significantly antagonised strychnine (2 mg/kg, i.p.)-induced seizures. 9. Idazoxan (1-4 mg/kg, i.p.) in a dose related manner significantly shortened the latency of seizures induced by strychnine (2 mg/kg, i.p.). Similarly, idazoxan (2 mg/kg, i.p.) profoundly potentiated seizures elicited by strychnine (1 mg/kg, i.p.). Idazoxan (4 mg/kg, i.p.) significantly antagonised the protective effect of clonidine (1 mg/kg, i.p.) against strychnine (2 mg/kg, i.p.)-induced seizures. 10. Disulfiram (3 x 25 - 3 x 100 mg/kg, i.p.) significantly attenuated strychnine (2 mg/kg, i.p.)-induced seizures. DOPS (4 mg/kg, i.p.) significantly potentiated strychnine seizures in disulfiram (3 x 100 mg/kg, i.p.)-pretreated animals. 11. These results indicate that enhancement of noradrenergic neurotransmission potentiates strychnine seizures in mice.

gamma Aminobutyric acid mediation of the anticonvulsant effect of clonidine on pentylenetetrazol-induced seizures in mice

The effects of muscimol, amino-oxyacetic acid (AOAA), diamino-N-butyric acid (DABA), bicuculline, picrotoxin, diazepam and phenobarbitone on the protective effect of clonidine against pentylenetetrazol-induced seizures were studied in mice. Muscimol, AOAA, DABA, phenobarbitone and diazepam significantly protected mice against pentylenetetrazol-induced seizures and also significantly potentiated the protective effect of clonidine against the seizures. Bicuculline and picrotoxin significantly potentiated seizures induced by pentylenetetrazol and significantly attenuated both the protective effects of muscimol and clonidine against the seizures. These data suggest that activation of gamma-aminobutyric acid systems may underlie the protective effect of clonidine against seizures induced by pentylenetetrazol in mice.

Perceptual masking of the chlordiazepoxide discriminative cue by both caffeine and buspirone

Twelve male Sprague-Dawley rats were trained to discriminate between the interoceptive stimulus attributes of 5 mg/kg chlordiazepoxide (CDP) and saline in a two-lever operant task under a fixed-ratio 10 (FR-10) schedule of food reinforcement. Caffeine, buspirone, and Ro 15-1788 failed to engender complete generalization when tested in combination with saline. In drug interaction test sessions caffeine (56 mg/kg) blocked the discriminative stimulus properties of the training dose of CDP and shifted the CDP discriminative dose-response function to the right. This rightward shift in CDP discriminative function was paralleled by a concomitant downward shift in the rate-of-responding dose-response function. Drug interaction test sessions conducted with 3.2 mg/kg of buspirone in combination with various doses of CDP engendered a downward shift in both the discriminative and rate-of-responding dose-response functions. Because 3.2 mg/kg buspirone in combination with the training dose of CDP resulted in complete response rate suppression, additional combination tests were conducted with 3 mg/kg CDP, a dose which reliably engendered > 90% CDP-appropriate responding, and various doses of buspirone. Similar to the CDP-caffeine interactions, buspirone blocked the cueing properties of 3 mg/kg CDP with a parallel reduction in response rates. Interaction test sessions conducted with Ro 15-1788 and CDP resulted in rightward shifts in both the discriminative and rate functions of CDP. We suggest that the interactions between CDP and both caffeine and buspirone resulted from the perceptual masking of the interoceptive (subjective) effects of CDP, whereas the interaction between Ro 15-1788 and CDP reflect pharmacological antagonism.

Cimetidine-induced seizures in mice. Antagonism by some GABAergic agents

The effects of muscimol, aminooxyacetic acid (AOAA), diamino-n-butyric acid (DABA), baclofen, bicuculline, picrotoxin, strychnine, diazepam, phenobarbitone and phenytoin on cimetidine-induced seizures were studied in mice. Cimetidine (400-1000 mg/kg, i.p.) induced dose-dependent tonic convulsion. Muscimol, AOAA and DABA effectively protected mice against cimetidine-induced seizures. Bicuculline and picrotoxin significantly potentiated the seizures induced by cimetidine and effectively antagonized the protective effects of muscimol, AOAA and DABA against the seizures. Diazepam and phenobarbitone significantly protected the mice against cimetidine-induced seizures while phenytoin and strychnine did not significantly alter the seizures. These results indicate that the attenuation of central gamma-aminobutyric acid neurotransmission may underlie cimetidine-induced seizures in mice.

The involvement of noradrenaline, 5-hydroxytryptamine and acetylcholine in imipramine-induced seizures in mice

The influence of some noradrenergic, 5-hydroxytryptaminergic and cholinergic agents on imipramine-induced seizures were investigated in mice. DL-threo-3,4-dihydroxyphenylserine (DOPS) and pargyline significantly potentiated imipramine-induced seizures. Phentolamine and prazosin significantly attenuated seizures elicited by imipramine and significantly attenuated the seizure-enhancing effect of DOPs. alpha-Methyl-p-tyrosine and reserpine significantly attenuated seizures induced by imipramine. Disulfiram significantly protected mice against imipramine-induced seizures. However, DOPS significantly potentiated seizures induced by imipramine in disulfiram-pretreated animals. Clonidine effectively protected mice against imipramine-induced seizures. Idazoxan, on the other hand, significantly potentiated seizures induced by imipramine and significantly antagonised the protective effect of clonidine against the seizures. 5-HTP, PCPA, cyproheptadine, mianserin, ketanserin and trazodone did not affect imipramine-induced seizures to any significant extent. Physostigmine antagonised seizures induced by imipramine while atropine significantly potentiated the seizures, and significantly attenuated the protective effect of physostigmine against the seizures. These data suggest that enhancement and attenuation of central noradrenergic and cholinergic neurotransmissions respectively, and not 5-HT mechanisms, may underlie imipramine-induced seizures in mice.

Chloroquine-induced seizures in mice: the role of monoaminergic mechanisms

The influence of some dopaminergic and noradrenergic agents on seizures induced by chloroquine (45-100 mg/kg, i.p.) was investigated in mice. Apomorphine (0.2-0.8 mg/kg, s.c.). L-dopa (25-50 mg/kg, s.c.) benserazide (5 mg/kg, i.p.) plus L-dopa (50 mg/kg, s.c.), pargyline (100 mg/kg, i.p.), FLA-63 (10-20 mg/kg, s.c.) and FLA-63 (10 mg/kg, s.c.) plus L-dopa (50 mg/kg, s.c.) profoundly shortened the latency of seizures induced by chloroquine (65 mg/kg, i.p.). L-Dopa (50 mg/kg, s.c.) weakly reduced the latency and weakly increased the incidence of chloroquine (50 mg/kg, i.p.)-induced seizures. alpha-Methyl-p-tyrosine (25-100 mg/kg, i.p.) dose-dependently and significantly reduced the incidence and significantly prolonged the latency of chloroquine (65 mg/kg, i.p.)-induced seizures. However, L-dopa (50 mg/kg, s.c.) effectively increased the proportion of animals convulsing and effectively reduced the latency of seizures induced by chloroquine (65 mg/kg, i.p.) in alpha-methyl-p-tyrosine-pretreated mice. Haloperidol (0.25-1.0 mg/kg, i.p.) and pimozide (2-4 mg/kg, i.p.) markedly reduced the incidence and markedly prolonged the latency of seizures induced by chloroquine (65 mg/kg, i.p.) in a dose-related manner. However, apomorphine (0.4-0.8 mg/kg, s.c.) and L-dopa (25-50 mg/kg, s.c.) profoundly attenuated the protective effects of haloperidol (0.5 mg/kg, i.p.) and pimozide (4 mg/kg, i.p.) against chloroquine (65 mg/kg, i.p.)-induced seizures.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of some GABAergic agents on quinine-induced seizures in mice

The effects of some GABAergic agents on seizures induced by quinine were studied in mice. Muscimol, AOAA, DABA and baclofen significantly protected mice against quinine-induced convulsions. Bicuculline effectively enhanced quinine-induced convulsions, and significantly attenuated the protective effects of muscimol, AOAA and DABA against convulsions induced by quinine. Diazepam and phenobarbitone significantly protected mice against convulsions induced by quinine. However, phenytoin did not affect quinine-induced seizures to any significant degree. These results indicate that the convulsant effect of quinine may be due to a disturbance in the status of the GABAergic system.

Potentiation of cocaine and d-amphetamine toxicity with caffeine

The effect of caffeine when combined with cocaine or amphetamine was studied in rats. Animals were pretreated with intraperitoneal vehicle (normal saline [NS]) or caffeine 100 mg/kg, then challenged with intraperitoneal cocaine (0, 35, 50, 70, or 90 mg/kg) or intraperitoneal d-amphetamine (0, 15, 25, 35, or 42 mg/kg). Animal behavior, time to, and incidences of seizures and death were recorded. This dose of caffeine alone did not cause seizures or death. Caffeine pretreatment significantly increased the incidence of overt seizures induced by either cocaine or amphetamine. Caffeine increased the incidence of cocaine-induced death from 10% to 90% at the 70 mg/kg cocaine dose (P less than .01). Caffeine increased amphetamine-induced death from 0% to 80% at 15 mg/kg (P less than or equal to .01), 10% to 70% at 25 mg/kg (P less than or equal to .01), and 30% to 80% at 35 mg/kg (P less than or equal to .01). To investigate mechanisms, additional animals were pretreated with the adenosine agonist, 2-chloroadenosine (2.5 and 10 mg/kg), before being challenged with NS, 90 mg/kg cocaine, or 42 mg/kg amphetamine. Pretreatment with 2-chloroadenosine had no affect in reducing cocaine or amphetamine toxicity. Combination pretreatment with caffeine and 2-chloroadenosine potentiated cocaine toxicity. The phosphodiesterase inhibitor, pentoxifylline, did not potentiate cocaine toxicity. The authors conclude that caffeine potentiates the acute toxicity of both cocaine and amphetamine, and that the failure of 2-chloroadenosine to alter this suggests that the toxicity of the stimulants cocaine and amphetamine may be modulated by nonspecific rather than specific adenosine- or phosphodiesterase-induced mechanisms.

Involvement of GABAergic mechanisms in chloroquine-induced seizures in mice

1. The influence of some GABAergic agents on tonic seizures elicited by chloroquine was investigated in mice. 2. Chloroquine (45-100 mg/kg) elicited seizures in mice in a dose related manner. 3. Muscimol (1-2 mg/kg), DABA (8-16 mg/kg) and baclofen (4-16 mg/kg) profoundly delayed the onset of chloroquine (65 mg/kg)-induced seizures. The incidence of the seizures was also significantly reduced by muscimol (1-2 mg/kg), DABA (8 mg/kg) and baclofen (4-8 mg/kg). 4. AOAA (10 mg/kg) profoundly reduced the proportion of mice that convulsed while AOAA (20 mg/kg) completely protected mice against chloroquine (65 mg/kg)-induced seizures. 5. Bicuculline (5 mg/kg) and picrotoxin (0.5-1 mg/kg) significantly potentiated chloroquine (50 mg/kg)-induced seizures. The onset of seizures and the number of mice that convulsed were shortened and increased respectively. The onset of chloroquine (65 mg/kg)-elicited seizures was also profoundly shortened. Bicuculline (5 mg/kg) and picrotoxin (0.5 mg/kg) effectively antagonised the protective effects of muscimol (2 mg/kg), AOAA (10 mg/kg) and DABA (8 mg/kg) against chloroquine (65 mg/kg)-elicited seizures. 6. Diazepam (1 mg/kg) and phenobarbitone (20 mg/kg) significantly antagonised chloroquine (65 mg/kg) seizures. The onset of seizures was significantly delayed by both diazepam (0.25-1 mg/kg) and phenobarbitone (10-20 mg/kg). 7. These data suggest that enhancement and inhibition of GABAergic neurotransmission respectively attenuate and potentiate chloroquine seizures in mice.

Gestational exposure to diazepam increases sensitivity to convulsants that act at the GABA/benzodiazepine receptor complex

Experiments examining seizure sensitivity were conducted on adult male offspring exposed to diazepam at 1.0 or 2.5 mg/kg per day in utero over gestational days 14-20. Threshold dosages to facial clonus, myoclonic jerk, clonic seizure, and extensor tonus were determined via i.v. infusion of bicuculline, methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM), picrotoxin, pentylenetetrazol, caffeine and strychnine. Relative to uninjected and vehicle-exposed adult male offspring, prenatal diazepam administration reduced the threshold for bicuculline- and DMCM-induced facial clonus and myoclonic jerk by 40-50%. The threshold dosages to facial clonus, myoclonic jerk and clonic seizure from picrotoxin infusion were similarly reduced in animals exposed to diazepam in utero. In contrast, seizure thresholds to pentylenetetrazol, caffeine and strychnine were not affected by early developmental exposure to diazepam. In parallel biochemical studies, an increased sensitivity to the antagonistic effects of bicuculline methiodide on gamma-aminobutyrate (GABA)-stimulated chloride influx was observed in cortical synaptoneurosomes from adult male progeny of diazepam-treated dams. The results are interpreted to reflect a long-lasting alteration in the function of the GABA/benzodiazepine receptor complex by prenatal diazepam exposure that is manifest at the behavioral and neurochemical level in a pharmacologic specific manner.

Isobolographic assessment of the convulsant interaction between theophylline and caffeine or pentylenetetrazol in rats

To characterize the convulsant interaction between theophylline and caffeine, male Sprague-Dawley rats received an iv infusion of one of seven different combinations of these drugs and of each drug individually until the onset of maximal seizures (which occurred within 30 to 40 min after the start of the infusion). The total infused doses of the two drugs and their respective concentrations in the serum, brain, and cerebrospinal fluid (CSF) were used for isobolographic analysis. The results are consistent with classical dose- and concentration-addition and do not suggest either antagonism or synergism. The potency ratio based on the doses or serum concentrations was appreciably different from that based on brain or CSF concentrations. The brain:serum and CSF:serum concentration ratios of caffeine were appreciably higher than those of theophylline. Similar experiments were performed with seven combinations of theophylline and pentylenetetrazol (PTZ) and with each of these drugs individually. This second set of experiments also yielded essentially linear isobolographs indicative of dose- and concentration-addition. The potency ratio based on CSF concentrations was appreciably different from ratio values based on doses, and from those based on brain or serum concentrations. These results illustrate a useful strategy for the characterization of pharmacodynamic drug interactions and highlight the importance of the choice of sampling site for determinations of the potency of drug.

Separate and combined effects of caffeine and alprazolam on motor activity and benzodiazepine receptor binding in vivo

CD-1 mice received single intraperitoneal (IP) doses of caffeine-sodium benzoate (caffeine doses: 0, 20 and 40 mg/kg) followed by injections of alprazolampropylene glycol (0, 0.05, and 2 mg/kg, IP) to determine brain concentrations, effects on in vivo receptor binding of a specific high-affinity benzodiazepine receptor ligand [3H]Ro15-1788, and effects on motor activity over a 1-h period. A behavioral monitoring device, using infrared sensors, measured horizontal and ambulatory activity. Caffeine produced significant increases in all motor activity measures as compared to vehicle treatment, with low dose caffeine (with brain concentrations of 13 micrograms/g) stimulating activity to a greater degree than the high dose (with brain concentrations of 30 micrograms/g). The overall effect of caffeine on benzodiazepine receptor binding was not significant. Alprazolam significantly diminished motor activity and altered benzodiazepine receptor binding. Low dose alprazolam increased binding, while the high dose diminished it. Caffeine and alprazolam antagonized each other's behavioral effects in this study, but did not alter each other's uptake into brain. Alprazolam's antagonism of caffeine-induced motor stimulation was associated with decreases in receptor binding, whereas caffeine's reversal of alprazolam-induced motor depression was not associated with any changes in binding. The lack of a clear association between drug effects on benzodiazepine binding and on motor activity suggests that behavioral effects of caffeine and alprazolam may be mediated by other sites in addition to the benzodiazepine receptor.

The pharmacology of human anxiety

The human pharmacology of anxiety disorders, including panic disorder, is detailed. The major theories center around the role of benzodiazepine receptor, noradrenergic and serotonergic dysfunction. The contribution that challenge tests with lactate, hyper- and hypocapnia, beta- and alpha-2-adrenoceptor agonists, peptides, pentylenetetrazol, and caffeine make to our understanding of the biological basis of anxiety and these major theories are described and discussed.

Interaction of caffeine with the GABAA receptor complex: alterations in receptor function but not ligand binding

Behavioral and neurochemical evidence indicates interactions between caffeine and other adenosine receptor ligands and the gamma-aminobutyric acid (GABA)-benzodiazepine system. To assess the effects of caffeine on binding and function at the GABAA receptor, we studied the effects of behaviorally-active doses of caffeine on benzodiazepine and Cl- channel binding and on overall function of the GABAA receptor as measured by Cl- uptake. There was no effect of caffeine on benzodiazepine receptor binding in cortical synaptosomal membranes at concentrations of 1-100 microM. No effects on benzodiazepine binding were found ex vivo in mice treated with caffeine, 20 and 40 mg/kg. At the putative Cl- channel site labeled by t-butylbicyclophosphorothionate (TBPS), binding was unchanged in vitro after caffeine treatment (1 and 10 microM) in washed and unwashed membranes. However, in ex vivo studies caffeine (20 and 40 mg/kg) increased numbers of TBPS sites in unwashed but not washed membranes. Muscimol-stimulated Cl- uptake into cortical synaptoneurosomes was decreased in mice treated with caffeine, 20 and 40 mg/kg. Similar results were observed in in vitro preparations treated with 50 microM but not 100 microM caffeine. These results indicate that caffeine administration significantly alters the Cl- transport function of the GABAA receptor complex.

Potent convulsant actions of the adenosine receptor antagonist, xanthine amine congener (XAC)

The convulsant properties of xanthine amine congener (XAC, 8-(4-(2-aminoethyl)-aminocarboxylmethyloxy)phenyl-1,3-dipropylxant hine) are compared to those of caffeine. Male Swiss albino mice were infused with convulsants through a lateral tail vein. Convulsion thresholds (i.e. the amount of convulsants required to elicit convulsions) of 39.8 +/- 2.0 mg/kg (n = 10) and 109.8 +/- 2.3 mg/kg (n = 10) were calculated for XAC and caffeine respectively. Pretreatment of animals with the adenosine receptor agonists 2-chloroadenosine, N6-cyclohexyladenosine or 5'-N-ethylcarboxamido-adenosine (1 mg/kg, i.p., 20 minutes prior to infusion) significantly decreased the seizure threshold of both XAC and caffeine. The adenosine uptake blockers, 6-nitrobenzylthioinosine or dipyridamole (0.25 mg/kg, i.p., 20 minutes prior to infusion) did not significantly affect the seizure threshold to either XAC or caffeine. The benzodiazepine agonist diazepam (5 mg/kg, i.p., 20 minutes prior to infusion) significantly increased the seizure threshold to both XAC (p less than 0.05) and caffeine (p less than 0.01), whereas the benzodiazepine antagonist Ro 15-1788 (10 mg/kg, i.p., 20 minutes prior to infusion) significantly increased the seizure threshold to caffeine (p less than 0.01), but not XAC. The results suggest that actions at benzodiazepine receptors may be a tenable hypothesis to explain the convulsant actions of caffeine, but not those of XAC.

Effects of caffeine on social behavior, exploration and locomotor activity: interactions with ethanol

The effects of caffeine and its interaction with ethanol were examined in a test of social behavior and a holeboard test of exploration and locomotion. Male mice were injected i.p. with 15, 30 or 60 mg/kg caffeine alone or in combination with 2 g/kg ethanol. The animals were then put in pairs into a familiar arena, or examined individually in the holeboard. Only the highest dose of caffeine (60 mg/kg) had a significant effect on the time spent in social interaction and motor activity in the social behavior test: both measures were reduced. The duration and frequency of avoidance-irritability behavior was dose-dependently increased by caffeine. In the holeboard, caffeine caused a dose-dependent increase in locomotor activity. 30 mg/kg caffeine reversed the ethanol-induced reduction of time spent in social interaction, and 60 mg/kg caffeine antagonized the ethanol-induced increase in locomotor activity in both the social behavior and holeboard tests. Caffeine's effects on ethanol-induced behavioral changes are compared with those of other drugs.