Central monoamines and convulsine thresholds in mice and rats

Effect of dopaminergic and GABA-ergic drugs given alone or in combination on the anticonvulsant action of phenobarbital and diphenylhydantoin in the electroshock test in mice

In the electroshock test--taking hind-limb tonic extension as the end point--apomorphine (10 mg/kg) exerted no effect on the anticonvulsant action of phenobarbital (PB; 20 mg/kg) or diphenylhydantoin (DPH; 8 mg/kg); amantadine (25 and 100 mg/kg) decreased that of DPH, while L-DOPA (500 mg/kg) and d,l-amphetamine (10 mg/kg) potentiated the action of both anticonvulsants. Fluphenazine (4 mg/kg) had no influence on the effects of the two anticonvulsants, but haloperidol lessened that of DPH. All GABA-ergic stimulants used, i.e., gamma-hydroxybutyric acid (GHBA/250 mg/kg), baclofen (2.5 and 10 mg/kg) and aminooxoacetic acid (AOAA; 15 and 20 mg/kg) potentiated the action of PB; the action of DHP was unaffected by these drugs except for AOAA (20 mg/kg). The combined treatment with dopaminergic and GABA-ergic stimulants, being ineffective in terms of anticonvulsant activity, resulted in a marked potentiation of the action of the anticonvulsants tested in this study. The most distinct potentiation was noted in the case of PB, baclofen (1 mg/kg), and amantadine (25 mg/kg).

Role of striatal acetylcholine and free ammmonia in the central stimulatory effects of pp'DDT in rats. Protective effects of barbiturates

pp'DDT (600 mg/kg, orally) produced an increase in the level of free ammonia and a decrease of acetylcholine in the corpus striatum of rats. These effects were maximal 5 h after the administration of pp'DDT. The animals showed tremors after 2 h, mild or moderate convulsions after 3.5 h and severe convulsions 5 h after treatment with pp'DDT. The neurochemical changes and convulsions induced by pp'DDT were modified to different degrees by barbiturates. Phenobarbitone sodium abolished the convulsions while prominal reduced the severity of convulsions in pp'DDT treated animals. The level of striatal acetylcholine in pp'DDT-phenobarbitone treated animals was not significantly different from the control values. In prominal-pp'DDT treated animals, it was slightly but significantly reduced. Primidone neither changed the severity of convulsions nor the level of striatal acetylcholine in pp'DDT treated animals. Further barbiturates had no significant effect on the level of free ammonia in pp'DDT treated rats. The results suggest that changes in the level of acetylcholine are not the cause but an effect of pp'DDT induced stimulatory effects or convulsions, mediated through an increase in the level of free ammonia or some other mechanism.

Effects of d-amphetamine and apomorphine in a new animal model of petit mal epilepsy

d-Amphetamine is effective in controlling seizures in petit mal epilepsy. The flash-evoked afterdis-charge (FEAD) in rats has been proposed as a model of the peit mal seizure. The experiments reported here investigated the dose response relationship for the suppression of FEAD by d-amphetamine, and compared its effects with those of the dopamine-mimetic, apomorphine. Significant suppression of FEAD was observed at doses of d-amphetamine greater than 0.2 mg/kg. A maximum decrease of 60% occurred at 1.2 mg/kg. Higher doses did not result in any further suppression. In contrast, apomorphine and no effect on the FEAD even at doses that induced intense stereotypic behavior. In other experiments, administration of either the dopamine antagonist pimozide or the alpha-adrenergic antagonist phenoxybenzamine exacerbated FEAD and also prevented the suppression of FEAD by d-amphetamine. The results of these experiments support the hypothesis that the FEAD is a valid model of the petit mal seizure. Furthermore, they provide evidence that norepinephrine is necessary for the seizure-suppressant action of d-amphetamine.

Tryptophol-induced change in Brain 5-hydroxytryptamine Metabolism

The effects of tryptoiphol (TOL) on brain 5-hydroxytryptamine (5-HT) metabolism were studied. After TOL injection (200 mg/kg IP), brain 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) levels were increased, 5-HT synthesis rate was decreased, and monoamine oxidase (MAO) activity remained unchanged. Pretreatment of mice with p-chlorophenylalanine (PCPA), a potent inhibitor of 5-HT synthesis, did not affect the anticonvulsant action of TOL.. These results suggest that alteration of 5-HT metabolism after TOL injection is not directly related to the anticonvulsant action of TOL

Brain norepinephrine, dopamine, and 5-hydroxytryptamine in magnesium-deprivation encephalopathy in rats

The effect of Mg deficiency on the regional concentrations of norepinephrine, dopamine, and 5-hydroxytryptamine in the brain was studied in clinically symptomatic young rats fed a diet low in magnesium for 10 days. Decreases in magnesium concentration in the brain were not accompanied by any significant changes in these monoamines.

Effects of reserpine, propranolol, and aminophylline on seizure activity and CNS cyclic nucleotides

Convulsant doses of pentylenetetrazol (100 mg/kg) increase levels of both cyclic adenosine monophosphate (AMP) and cyclic guanosine monophosphate (GMP in mouse cerebral cortex and hippocampus. In animals pretreated with reserpine, propranolol, or aminophylline, pentylenetetrazol seizures were more severe, cyclic AMP elevations were attenuated or blocked, and cyclic GMP increases were unaffected or augmented. These data indicate that norepinephrine, adenosine, and perhaps other biogenic amines have a regulatory effect on cyclic AMP, but not cyclic GMP, levels in epileptic brain. An increased level of cyclic AMP in brain tissue may have an antiepileptic effect leading to seizure attenuation or termination. By contrast, elevated levels of cyclic GMP may have an epileptogenic effect in initiating or maintaining seizure activity.

The role of alpha-adrenoceptors in the regulation of pentylenetetrazol convulsions in mice

Typical ocular colobomas and associated orbital cysts are relatively common malformations that result from a defect in the fusion of the fetal optic fissure. Three cases studied with computed tomography (CT) are reported, and the spectrum of ocular colobomas, their associated findings, and CT differential diagnosis are reviewed. This experience indicates that the location and extent of colobomas can be determined with high-resolution CT.

Changes in brain dopamine, norepinephrine and serotonin associated with convulsions induced by pinealectomy in the gerbil

In three separate experiments, adult male gerbils 10 weeks of age were pinealectomized (PX), observed for convulsions, and sacrificed at various intervals after PX. Norepinephrine (NE), dopamine (DA) and serotonin (5-HT) in selected brain parts were determined by fluorometric procedures. No changes in DA were observed. Serotonin levels were shown to be elevated in sham-operated and PX animals, possibly due to stress phenomena associated with anesthesia or surgical procedures. Norepinephrine was significantly depressed over control and sham-operated animals by 1 hour after surgery with a post-operative duration of at least 12 hours. Results in this study did not indicate whether the decreased NE was the cause or an effect of the PX-induced convulsive activity.

Evidence against serotonin involvement in the tonic component of electrically induced convulsions and in carbamazepine anticonvulsant activity

Intraventricular injection of 5,7-dihydroxytryptamine, selective destruction of descending serotoninergic neurons by 5,6-dihydroxytryptamine or electrolytic and chemical lesions of the nucleus raphe dorsalis did not affect the electroconvulsive threshold in rats. No effect was observed after the systemic administration of drugs known to increase central serotonin transmission, such as quipazine, m-chlorophenylpiperazine, and moderate doses of d-fenfluramine, whereas p-chlorophenylalanine, an inhibitor of serotonin synthesis, decreased seizure susceptibility. The anticonvulsant activity of carbamazepine was not modified in animals with the same experimental lesions. The results, in relation to the high selectivity of the experimental procedures employed to deplete brain and spinal cord serotonin, do not bear out any involvement of serotonin in the tonic component of electrically induced convulsions or in the action of carbamazepine.

Possible involvement of brainstem norepinephrine in pentylenetetrazol convulsions in rats

The thresholds of twitch and clonic convulsion induced by intravenous infusion of pentylenetetrazol (PTZ) were measured in rats treated with 6-hydroxydopamine (6-OHDA). In adult rats, intraventricularly applied 6-OHDA increased susceptibility to PTZ convulsions and decreased norepinephrine (NE) contents of the cortex, hypothalamus and brainstem. When 6-OHDA was applied intraventricularly at 8 days after birth, PTZ convulsion susceptibility was slightly decreased and brainstem NE content was significantly increased. However, the effects of 6-OHDA given at 20 days after birth were similar to those observed in adults. Significant decrease of cortical and hypothalamic NE contents, but no change in PTZ convulsion susceptibility, occurred following 6-OHDA injections into the dorsal and ventral NE bundles. These results suggest that the brainstem NE neurons play an inhibitory role on the development of PTZ convulsions.

Anticonvulsant action of cannabis in the rat: role of brain monoamines

The role of brain monoamines in the anticonvulsant action of Cannabis indica resin (CI), against maximal electroshock-induced seizures in albino rats, was investigated by using pharmacologic agents that influence brain monoamine activity. Delta-9-tetrahydrocannabinol content of cannabis resin was estimated to be 17%. The anticonvulsant action of CI (200 mg/kg, i.p.) was significantly inhibited after pretreatment with drugs that reduce brain serotonin activity but not by drugs that reduce brain catecholamine activity. Similarly, the anticonvulsant action of a subanticonvulsant dose (50 mg/kg, i.p.) of CI was potentiated by serotonin precursors but not by catecholamine precursors. Potentiation of the anticonvulsant action of CI by nialamide or by imipramine was inhibited after pretreatment with 5,6-dihydroxytryptamine. The results suggest that the anticonvulsant action of CI in the rat is serotonin- and not catecholamine-mediated.

Effect of a new benzodiazepine bromazepam on locomotor performance and brain monoamine metabolism

Administration of a single dose (10 mg/kg) of a relatively new benzodiazepine, bromazepam to rats markedly suppressed their spontaneous locomotor activity. Hypomobility became apparent 15 min after the injection and remained significantly lower during the period of observation for 6 hours when locomotor activity was 27% of controls. Following 2 hours after bromazepam treatment, no change was noted in tyrosine levels and tyrosine hydroxylase activity in striatum or rate of catecholamine synthesis in synaptosomal preparation (P2 pellet). However, the endogenous levels of norepinephrine, dopamine and 5-hydroxytryptamine were significantly increased not only in several brain areas examined, but also in P2 pellet. Bromazepam failed to change 3H-norepinephrine and 3H-5-hydroxytryptamine uptake in synaptosomes suggesting that the increased levels of monoamines are not related to laterations in uptake mechanisms, but probably to a diminished release. This is supported by the data on striatal homovanillic acid and whole brain 4-hydroxy-3-methoxyphenyl glycol whose concentrations were significantly lowered following a single injection of this benzodiazepine. However, bromazepam increased 5-hydroxyindole-acetic acid levels in hypothalamus, mid-brain and pons-medulla. The present study demonstrates that bromazepam elicits its tranquilizing action by lowering the release of catecholamines in brain; however, its anti-anxiety action might be associated with a reduction in 5-hydroxytryptamine turn over. Our data also suggest that bromazepam is almost as potent as diazepam in altering the metabolism of certain putative neurotransmitters in brain.

Enhancement of alcohol withdrawal seizures with 6-hydroxydopamine

The relationship between central catecholamine neurons and alcohol withdrawal seizures was studied in rats pretreated with 6-hydroxydopamine to selectively destroy the central catecholamine nerve terminals. The alteration of alcohol withdrawal seizures was manifested by (1) a higher percentage of the rats developing the seizures, (2) an earlier onset of seizures, and (3) a greater severity of seizure activity. Seizure status was exhibited in 25% of the 6-hydroxydopamine-treated rats.

Differential blockade of bicuculline convulsions by neuroleptics

Haloperidol, pimozide, sulpiride and metoclopramide blocked bicuculline-induced convulsions in mice. Chlorpromazine and thioridazine exhibited this effect at low doses whereas at higher doses (e.g. 1 mg/kg i.p. chlorpromazine) this activity was no longer apparent. A dose of phenoxybenzamine which was inactive alone (7.5 mg/kg i.p.) completely blocked the anti-bicuculline effect of sulpiride and antagonized that of haloperidol. These data are interpreted as indicating that intact noradrenergic systems are necessary for the anti-bicuculline effect of the neuroleptics.

Inhibition of pentylenetetrazol-induced convulsions in rats by prostaglandin E1: role of brain monoamines

Prostaglandin E1-(PGE1-) induced inhibition of pentylenetetrazol (PTZ) convulsions in rats were significantly antagonized after pretreatment with drugs known to reduce brain serotonin activity, but not by pharmacological agents that decrease brain catecholamine activity. PGF2alpha also significantly inhibited PGE1 action. The results suggest that PGE1-induced inhibition of PTZ convulsions is not a direct effect, but an indirect one mediated through increase in brain serotonin activity.

Brain monoamines in seizure mechanism (review)

A majority of experimental studies have strongly suggested that catecholamine and/or 5-HT play an important role for regulating the seizure susceptibility. As mentioned previously, however, the relative significance of individual monoamine has not yet been fully clarified. Since it is well known that the interaction between catecholaminergic and serotonergic neuronal activity is quite complex, a causal relationship between each monoamine and seizure susceptibility cannot be easily established if results are obtained from the whole brain study on pharmacologic manipulation of experimental seizures. The extensive study, including the monoamine turnover rates and concentrations in specific brain regions, may help to delineate such a correlation in the future. Further, when an object of study is concerned in excitability of the central nervous system, it should be necessary to elucidate the mutual relationship of monoamines to the other putative neurotransmitters (e.g., acetylcholine, amino acid). Does there exist an abnormal metabolism of monoamines in the brain of epileptic patients? If so, how is it related to the elaboration or maintenance of epileptic seizures? Unfortunately, we have no sufficeint information on the monoamine metabolism of epileptic patients.

Effect of benzodiazepines on central serotonergic neuron systems

Intracerebral (i.c.) injection of serotonin (5-HT) into mice induced head twitches in a dose-dependent manner at 10 min after injection. The head twitches induced by 5-HT (i.c.) were potentiated by the pretreatment of isocarboxazid (3 mg/kg i.p.), and inhibited by cyproheptadine (0.3 mg/kg i.p.), a 5-HT antagonist. Benzodiazepines such as fludiazepam and diazepam potentiated the head twitches induced by 5-HT (i.c.) in a dose-dependent manner. Mescaline (50 mg/kg i.p.) also induced head twitches in mice at 15 and 30 min after injection. Benzodiazepines potentiated the head twitches induced by mescaline in a dose-dependent manner. Cyproheptadine blocked the potentiating effect of benzodiazepines on the head twitches induced by both 5-HT (i.c.) and mescaline. By repeated administration of fludiazepam or diazepam for 5 days, the potentiating effect of both drugs on the head twitches induced by mescaline was unchanged and their anticonvulsant effects were not modified. In contrast, the potency of both drugs on muscle relaxation was significantly decreased by repeated administration. Benzodiazepines failed to change the uptake of 5-HT into the synaptosomal fractions from the rat brain. These results suggest that the pharmacological action of benzodiazepines is derived at least in part from their activating effect on 5-HT receptors.

Quipazine-induced head-twitch in mice

Quipazine has been reported to be a direct serotonin receptor agonist. In this laboratory, quipazine produced head-twitch in mice similar to that produced by the serotonin precursor, 5-hydroxytryptophan (5-HTP). Three antiserotonergic drugs (methiothepin, methysergide, and cinanserin) antagonized both the 5-HTP and quipazine-induced head-twitch responses. In addition, the quipazine response was significantly potentiated by a monoamine oxidase (MAO) inhibitor, pargyline. Since it is not likely that quipazine itself is metabolized by MAO, these results suggested that quipazine might cause release of endogenous serotonin. Parachlorophenylalanine, a serotonin depletor, significantly antagonized the potentiation of quipazine by the MAO inhibitor but failed to antagonize the head-twitch produced by quipazine itself. The present studies suggest that quipazine influences serotonin receptors in the brain to produce head-twitch by two mechanisms of action: (1) by direct serotonin receptor activation, and (2) indirectly by causing a release of endogenous serotonin.

Decreased anticonvulsant activity of carbamazepine in 6-hydroxydopamine-treated rats

An intraventricular injection of 6-hydroxydopamine, which produced a marked decrease of catecholamines in the forebrain, significantly lowered the electroconvulsive threshold in rats. The anticonvulsant effect of carbamazepine was also significantly reduced in the animals treated with 6-hydroxydopamine. The results are consistent with the hypothesis that brain catecholamines may play an important role in seizure susceptibility as well as in the anticonvulsant activity of carbamazepine in rats.

Changes in receptor sensitivity of the cerebral cortex and liver during chronic ethanol ingestion and withdrawal

The evidence was reviewed supporting the noradrenergic sub- and supersensitivity hypothesis of ethanol withdrawal pathogenesis. New data indicates that the cAMP generating system linked to noradrenergic receptor sensitivity is in a steady state in the brain during ethanol withdrawal since the cAMP levels were not different from controls in vivo. Propranolol blocking experiments indicated the beta-adrenergic receptor is a necessary link in the increased cAMP response induced by ethanol withdrawal. The changes in sensitivity observed in the ethanol withdrawn rats were reproduced by acute and chronic reserpinization.

Brain areas involved in the catecholamine mediated regulation of electroshock seizure intensity

Selective treatments which alter the catecholamine content of discrete areas of the brain were tested for their effect on electroshock seizure intensity in the rat. The data indicate that depletion of noradrenaline and dopamine in near ventricular areas by the intracerebroventricular administration of the benzoquinolizine, Ro 4-1284, enhances electroshock seizure intensity. The enhancement of seizure produced by systemic Ro 4-1284 was antagonized by the intracerebroventricular injection of noradrenaline or dopamine which do not appear to penetrate more than 1 mm into the brain. Further, pretreatment with systemic iproniazid and L-dopa completely antagonized the increased seizure intensity produced by intracerebroventricular Ro 4-1284 and repleted brain catecholamines in both near and far ventricular areas. Thus, the effects of both noradrenaline and dopamine in attenuating electroshock seizure intensity appear to be exerted principally through periventricular structures.

The role of serotonergic pathways in isolation-induced aggression in mice

Male mice that became aggressive following four weeks of social isolation were treated with seven known serotonin receptor antagonists. All of the antiserotonergic drugs selectively antagonized the fighting behavior of the isolated mice; the antiaggressive activity was selective since, at antifighting doses, none of the drugs either significantly altered spontaneous motor activity or impaired inclined-screen performance. Antagonism of 5-HTP-induced head-twitch was used as an in vivo measure of antiserotonergic activity and a statistically significant correlation existed between potency as an antiserotonergic and potency as an antiaggressive. PCPA, a serotonin depletor, also significantly antagonized isolation-induced aggression for at least 24 hr postdrug administration. The interrelationship between cholinergic and serotonergic mechanisms in the mediation of isolation aggression was investigated. The involvement of serotonergic systems in isolation-induced aggression is discussed.

Catecholamine levels in penicillin-induced epileptic focus of the cat cerebral cortex

In 25 cats an unilateral epileptic focus was produced by intracortical injection of potassium benzyl penicillin and on the other hemisphere, sham-operation was done by injection of the same volume of saline solution without penicillin. Catecholamine analysis was performed for each hemisphere separately. In a second series of 15 cats, the effect of catecholamines and of 1-DOPA on penicillin-induced spike activity was examined. In the first and second stage of propagation of penicillin-induced spikes, dopamine and norepinephrine significantly decreased in the focus. In the third stage no differences existed. The penicillin-induced spike activity was reduced as well by the topical application of dopamine as of 1-DOPA, whilst no inhibitory effect was observed in the topical application of norepinephrine.

Increased susceptibility to seizures and decreased catecholamine turnover in spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) were compared with normotensive Wistar rats for their sensitivity to tonic extensor seizures. SHR were more sensitive to seizures and did not respond to the anticonvulsant effects of L-DOPA. SHR had a slower turnover rate of norepinephrine in brain stem and cortex and of dopamine in striatum. Steady-state levels of catecholamines were similar in both groups. These findings are consistent with earlier ones that reported an inverse relationship between central catecholamine activity and sensitivity to electroconvulsive seizures.