Biomedical subjects
Publications and source records attributed to L Turski.
Microinfusion of an excitatory amino acid, N-methyl-D-aspartate, into the ventral mid-striatum in the rat protects from amygdala kindled seizures. This result demonstrates that excitatory activity in the striatum modulates the threshold for seizures in the limbic forebrain.
The muscarinic cholinergic agonist bethanechol (0.25-1.0 micrograms) injected bilaterally into various parts of the rat neostriatum induced a tonic electromyogram (EMG) activity in the gastrocnemius muscle which is considered to be a measure of limb rigidity. This tonic EMG activity was found to be dose-dependent and muscarine-specific since it could be blocked by coadministration of the muscarinic antagonist N-methylscopolamine (1.0 micrograms). Tonic EMG activity of comparable amount was observed after injections of bethanechol (1.0 microgram) into all regions of the neostriatum but not into the globus pallidus, thalamus, zona incerta or cortex. The tonic EMG activity induced by intrastriatal injection of bethanechol (1.0 microgram) was abolished by a subsequent injection of the GABAmimetic drug muscimol (25 ng) into the posterior part of the substantia nigra pars reticulata suggesting that bethanechol-induced limb rigidity is mediated via impairment of GABAergic transmission within the substantia nigra pars reticulata.
Pilocarpine, given intraperitoneally to rats, reproduces the neuropathological sequelae of temporal lobe epilepsy and provides a relevant animal model for studying mechanisms of buildup of convulsive activity and pathways operative in the generalization and propagation of seizures within the forebrain. In the present study, the effects of manipulating the activity of the gamma-aminobutyric acid (GABA)-mediated synaptic inhibition within the substantia nigra on seizures produced by pilocarpine in rats, were investigated. In animals pretreated with microinjections of isoniazid, 150 micrograms, an inhibitor of activity of the GABA-synthesizing enzyme, L-glutamic acid decarboxylase, into the substantia nigra pars reticulata (SNR), bilaterally, non-convulsant doses of pilocarpine, 100 and 200 mg/kg, resulted in severe motor limbic seizures and status epilepticus. Electroencephalographic and behavioral monitoring revealed a profound reduction of the threshold for pilocarpine-induced convulsions. Morphological analysis of frontal forebrain sections with light microscopy revealed seizure-related damage to the hippocampal formation, thalamus, amygdala, olfactory cortex, substantia nigra and neocortex, which is typically observed with pilocarpine in doses exceeding 350 mg/kg. Bilateral intrastriatal injections of isoniazid did not augment seizures produced by pilocarpine, 200 mg/kg. Application of an irreversible inhibitor of GABA transaminase, gamma-vinyl-GABA (D,L-4-amino-hex-5-enoic acid), 5 micrograms, into the SNR, bilaterally, suppressed the appearance of electrographic and behavioral seizures produced by pilocarpine, 380 mg/kg. This treatment was also sufficient to protect animals from the occurrence of brain damage. Microinjections of gamma-vinyl-GABA, 5 micrograms, into the dorsal striatum, bilaterally, failed to prevent the development of convulsions produced by pilocarpine, 380 mg/kg. The results demonstrate that the threshold for pilocarpine-induced seizures in rats is subjected to the regulation of the GABA-mediated synaptic inhibition within the substantia nigra.
The anticonvulsant actions of memantine (1,3-dimethyl-5-aminoadamantane) have been evaluated in mice (seizures induced by maximal electroshock, pentylenetetrazol, bicuculline, picrotoxin, 3-mercaptopropionic acid and N-methyl-D,L-aspartic acid) and in photosensitive baboons, Papio Papio (clonic responses to intermittent photic stimulation). Memantine, 5-20 mg/kg, raised the threshold for electroconvulsions and protected mice against the tonic hind limb extension in pentylenetetrazol-, bicuculline-, picrotoxin- and 3-mercaptopropionic acid-induced seizures, but was ineffective against the clonic phase of chemically-induced seizures. In the baboons, no protection against photomyoclonic responses was observed within 5 h after the intravenous administration of memantine, 1-9 mg/kg. Amantadine, 100 mg/kg, reduced the protective effect of memantine against electroconvulsions. Apomorphine, haloperidol, pimozide, spiroperidol and bicuculline did not modify the anticonvulsant activity of memantine in electroconvulsions. These studies demonstrate an anticonvulsant action of memantine in rodents and suggest that dopaminergic mechanisms do not contribute to its mechanism of action.
Seizures produced by pilocarpine given i.p. to rats provide an animal model for studying the initiation, spread and generalisation of convulsive activity within the forebrain. Pilocarpine, 380 mg/kg, produces a sequence of behavioural and electroencephalographic alterations indicative of motor limbic seizures and status epilepticus, which is followed by widespread damage to the limbic forebrain resembling that occurring subsequent to prolonged intractable seizures. Microinjections of a selective antagonist at the N-methyl-D-aspartate receptor, (+/-)-2-amino-7-phosphonoheptanoate, into the substantia nigra pars reticulata, bilaterally, protects against the behavioural, electrographic and morphological features of seizures produced by pilocarpine, 380 mg/kg, with an ED50 of 0.0007 mumol (0.0004-0.0011). Microinjections of (+/-)-2-amino-7-phosphonoheptanoate, 0.005 or 0.01 mumol, into the substantia nigra pars compacta or into the dorsal part of mid-anterior striatum do not modify the electrographic and morphological sequelae of pilocarpine, 380 mg/kg. In rats pretreated with microinjections of N-methyl-D-aspartate into the substantia nigra pars reticulata, a non-convulsive dose of pilocarpine, 100 mg/kg, results in recurrent motor limbic seizures and status epilepticus. The ED50 of N-methyl-D-aspartate for the generation of seizures after pilocarpine, 100 mg/kg, is 0.0014 mumol (0.001-0.0019). Electrographic monitoring shows a pattern and sequence of evolution of convulsant activity within the hippocampus and cortex similar to that produced with pilocarpine, 380 mg/kg, alone. Morphological examination of brains from rats treated with N-methyl-D-aspartate in the substantia nigra pars reticulata and subsequently given pilocarpine, 100 mg/kg, which underwent status epilepticus, reveals widespread damage to the amygdala, thalamus, olfactory cortex, substantia nigra, neocortex, and hippocampus. Microinjections of N-methyl-D-aspartate, 0.002 mumol, into either the substantia nigra pars compacta or dorsal striatum, bilaterally, do not augment seizures produced by pilocarpine, 100 mg/kg. The results indicate that the threshold for pilocarpine-induced seizures in rats is modulated by excitatory amino acid neurotransmission within the substantia nigra pars reticulata.
In order to study the functional interaction between dopamine, acetylcholine and gamma-aminobutyrate within the rat neostriatum, we investigated the effect of intrastriatal injection of different drugs acting on these transmitter systems on muscle tone measured as tonic activity in the electromyogram of the gastrocnemius muscle. Bilateral injection of haloperidol (500 ng) into the rostral neostriatum (rostral injection: A8920-9650(46] induced tonic activity in the electromyogram, whereas injection into the intermediate part (intermediate injection; A7020-7890(46] was ineffective. Muscimol (25 ng) induced tonic activity in the electromyogram, when injected into the intermediate part and not into the rostral part, while bethanechol (1 microgram) was effective when injected into either site. Haloperidol-induced tonic activity in the electromyogram was prevented by coadministration of apomorphine (500 ng) or scopolamine (1 microgram), but not of bicuculline (300 ng). Haloperidol-induced tonic activity in the electromyogram was also reduced by subsequent intermediate injection of scopolamine or bicuculline, while apomorphine was ineffective. Tonic activity in the electromyogram induced by rostral injection of bethanechol was prevented by coadministration of scopolamine, but not of apomorphine. Intermediate injection of scopolamine or bicuculline reduced the tonic activity in the electromyogram after rostral or intermediate injection of bethanechol. Tonic activity in the electromyogram induced by intermediate injection of muscimol was prevented by coadministration of bicuculline, but not of scopolamine. Rostral injection of apomorphine or scopolamine failed to alter the tonic activity in the electromyogram induced by intermediate injection of bethanechol or muscimol. These results point to the existence of: a functional interaction between dopamine and acetylcholine in the rostral neostriatum; a functional interaction between acetylcholine and gamma-aminobutyrate in the intermediate neostriatum, and a functional flow of information from the rostral to the intermediate neostriatum.
The rat ventromedial thalamic nucleus (VM) is a point of convergence of several pathways that are supposed to be involved in motor control. Cortical fibers terminating within this nucleus use an excitatory amino acid, possibly L-glutamate, as their transmitter. Excitatory amino acids are known to interact with N-methyl-D-aspartate (NMDA), kainate, and quisqualate receptors, the presence of which has been demonstrated within the thalamus, gamma-Amino-butyrate (GABA) has been identified as the transmitter of the basal ganglia afferents to the VM, whereas cerebellar afferents to the VM are supposed to release ACh acting on muscarinic receptors. The present study investigates the behavioral and motor consequences of local injections of drugs into the VM, which specifically interact with NMDA, GABA, and muscarine receptors. Both the NMDA antagonist (-)2-amino-7-phosphonoheptanoate [(-)AP7], and the GABA agonist muscimol, but not the muscarinic antagonist scopolamine, induced catalepsy and limb rigidity. Both the (-)AP7- and muscimol-induced catalepsy were antagonized by coadministration of NMDA and the GABA antagonist bicuculline. The (-)AP7-induced catalepsy was characterized as an akinetic-rigid syndrome, in which the ability to induce a phasic activation of a set of muscles is lost and replaced by exaggerated tonic muscular responses. NMDA, bicuculline, and the muscarinic agonist bethanechol induced an increase in locomotor activity. The present study provides evidence that an imbalance between NMDA-mediated excitation and GABAergic inhibition within the rat VM leads to disturbances of motility, whereas muscarinic transmission within this nucleus appears to be of minor importance.
Increasing doses of naloxone hydrochloride (100-1000 nmol) were micro-injected unilaterally into the rat amygdala and the behavioral, neuropathological and electrographic responses were studied. Microinjections of low doses of naloxone (100-250 nmol) produced staring, gustatory automatisms and wet shakes whereas higher doses additionally resulted in motor limbic seizures and status epilepticus. The electroencephalogram showed a sequence of alterations characterised by high voltage fast activity, spiking, bursts of polyspiking, electrographic seizures and postictal depression which first appeared in the amygdala and rapidly spread to hippocampal and cortical areas. The neuropathological analysis of frontal forebrain sections by means of light microscopy revealed seizure-related brain damage in amygdala, olfactory cortex, thalamus, hippocampal formation, substantia nigra and neocortex. Diazepam, 10 mg/kg i.p., when given prior to the microinjection of naloxone into the amygdala, abolished the epileptogenic and neurotoxic effects of the drug. The results suggest that naloxone, when microinjected into rat amygdala elicits electrographic and motor limbic seizures followed by seizure-related brain damage.
Microinjection of morphine hydrochloride into the substantia nigra pars reticulata, bilaterally, converts non-convulsant dose of pilocarpine hydrochloride, 100 mg/kg, into a convulsant one. The ED50 of morphine for the generation of seizures after pilocarpine, 100 mg/kg, is 3.8 nmol (2.5-5.8). Electrographic and behavioral monitoring both show a pattern of convulsant activity similar to those produced by pilocarpine in doses exceeding 350 mg/kg. Morphological analysis of frontal forebrain sections reveals epilepsy-related damage to the hippocampus, thalamus, olfactory cortex, substantia nigra, neocortex and amygdala. The proconvulsant action of morphine in the substantia nigra is reversed by co-administration of naloxone hydrochloride. The results show that the threshold for limbic seizures may be modulated by opiates in the substantia nigra.
The effects of 2-chloroadenosine, aminophylline, bicuculline, beta-carboline-3-carboxylic acid methylester and Ro 15-1788 on seizures produced by pilocarpine were examined in rats. In animals pretreated with aminophylline at doses of 25-100 mg/kg, non-convulsant dose of pilocarpine, 100 mg/kg, resulted in severe motor limbic seizures, which rapidly developed into the status epilepticus. Electroencephalographic monitoring showed progressive evolution of seizure activity with initial high-voltage fast activity followed by high-voltage spiking and electrographic seizures. Morphological analysis of frontal forebrain sections with light microscopy demonstrated widespread damage to the hippocampal formation, thalamus, amygdala, olfactory cortex, substantia nigra and neocortex. Bicuculline, 2 mg/kg, beta-carboline-3-carboxylic acid methylester, 5 mg/kg, and Ro 15-1788, 50 mg/kg, did not augment seizures produced by pilocarpine, 100 mg/kg. 2-Chloroadenosine, 5 and 10 mg/kg, blocked the appearance of behavioral and electrographic seizures produced by pilocarpine, 380 mg/kg, and prevented the occurrence of brain damage. The results indicate that purinergic mechanisms are involved in the buildup of pilocarpine-induced convulsions and seizure-related brain damage in rats.
A mutant strain of Wistar rats which carries an autosomal gene defect is characterized by a progressively developing hyperexcitability, tremor, olfactory and gustatory movements, bradykinesia, ataxia and a pathologically increased muscle tone of hindlimbs which can be measured by recording tonic activity in the electromyogram (EMG) of the gastrocnemius-soleus muscle. The activity of the GABA synthesizing enzyme glutamic acid decarboxylase (GAD) and the receptor binding of GABA as estimated by [3H]GABA binding to synaptic membranes were examined in olfactory bulbs, frontal cerebral cortex, corpus striatum, hippocampus, thalamus, hypothalamus, tectum, substantia nigra, medulla oblongata, cerebellum, and pons of mutant rats. Mutant rats exhibit a lower activity of GAD in synaptosomal fractions of olfactory bulbs and substantia nigra whereas GAD activity within the pons was increased. The changes in the activity of GAD were accompanied by alterations in [3H]GABA binding to synaptic membranes: GABA binding was significantly elevated in the olfactory bulbs and the substantia nigra, but it was markedly reduced in the pons. The functional importance of impaired nigral GABAergic transmission in mutant rats was demonstrated by the fact that intranigral injection of the GABA agonist muscimol reduced the tonic extension of the hindlimbs as indicated by reduced tonic EMG activity of the gastrocnemius-soleus muscle, while intranigral injection of the GABA antagonist bicuculline increased the disturbance.
Genetically spastic rats were used for studying the effect on muscle tone of beta-carboline-3-carboxylic acid methylester (beta-CCM), an inverse benzodiazepine (BDZ) agonist, and that of Ro 15-1788 and CGS 8216, both putative antagonists of pharmacological actions of BDZs. These animals exhibit pathologically increased muscle tone, which can be recorded and quantified in the electromyogram (EMG) of the gastrocnemius (GS) muscle. beta-CCM, 2.5 and 3.0 mg/kg i.p., augmented the tonic activity in the EMG of GS muscle in spastic rats while it did not modify muscle tone at doses of 1.0 and 2.0 mg/kg. Diazepam, 0.4 mg/kg i.p., and Ro 15-1788, 5 mg/kg i.p., but not CGS 8216, 5 mg/kg i.p., antagonised the effect of the beta-carboline on muscle tone. Ro 15-1788, at doses of 0.1-5 mg/kg i.p., did not affect muscle tone in the genetically spastic rats, whilst at doses of 25-200 mg/kg the imidazodiazepine dose dependently increased the tonic activity in the EMG. The action of Ro 15-1788, 50 mg/kg i.p., was reversed by diazepam, 0.4 mg/kg i.p., and beta-CCM, 2 mg/kg i.p., while CGS 8216, 5 mg/kg i.p., facilitated the effect of Ro 15-1788 on muscle tone. CGS 8216 at doses of 5 and 25 mg/kg i.p. was devoid of any effect on muscle tone, whilst at doses of 50 and 200 mg/kg the pyrazoloquinoline increased the tonic activity recorded in the EMG from the GS muscle of the spastic rats.(ABSTRACT TRUNCATED AT 250 WORDS)
An effect of the beta-stereoisomer of kainic acid on seizures produced by intracerebroventricular injections of excitatory amino acids was tested in mice. beta-Kainic acid preferentially antagonizes myoclonic seizures induced by N-methyl-D-aspartate and quinolinate, has less pronounced anticonvulsant action against alpha-kainate, D-homocysteinesulphinate and quisqualate, and no effect on convulsions induced by L-glutamate. The anticonvulsant activity of beta-kainic acid matches that of 2-amino-7-phosphonoheptanoic and kynurenic acids, both preferential N-methyl-D-aspartate receptor antagonists, and differs considerably from the profile of anticonvulsant action of gamma-D-glutamylaminomethylsulphonic acid, a preferential kainate/quisqualate antagonist.
The effects of stereoisomers of gamma-glutamylaminomethylsulphonic acid (GAMS) on convulsions produced by intracerebroventricular injections of excitatory amino acids were studied in mice. gamma-D-GAMS preferentially blocked myoclonic seizures induced by kainate and had less pronounced anticonvulsant effect against quisqualate, N-methyl-D-aspartate, quinolinate, D-homocysteine sulphinate and L-glutamate. gamma-L-GAMS displayed only a relatively weak protective effect against kainate- and, to some extent, quisqualate-induced seizures, with little or no effect on the convulsant properties of the other excitatory amino acids. These results indicate that the D configuration of the gamma-carbon atom of excitatory amino acid antagonists is preferred not only for NMDA receptor antagonism but for antagonism at non-NMDA receptors as well.
Two dicarboxylic piperazine derivatives, 1-(p-chlorobenzoyl)-piperazine-2,3-dicarboxylic acid (pCB-PzDA) and 1-(p-bromobenzoyl)-piperazine-2,3-dicarboxylic acid (pBB-PzDA), that block excitation at glutamate receptors have been evaluated as anticonvulsants in rodent models of epilepsy by i.c.v. or i.p. injection. In DBA/2 mice, pBB-PzDA (0.01 mumol i.c.v.) or pCB-PzDA (0.03 mumol i.c.v.) protects against the clonic and tonic seizures induced by loud sound. Protection is also seen following i.p. injection of pBB-PzDA (0.33-1.0 mmol/kg) or pCB-PzDA (0.66-1.0 mmol/kg). In Swiss S mice suppression of seizure activity induced by i.c.v. injection of excitatory amino acid agonists shows that both compounds are preferentially active against alpha-kainate, with the following rank orders (for pBB-PzDA); alpha-kainate greater than quisqualate greater than N-methyl-D-aspartate greater than quinolinate greater than L-glutamate; and (for pCB-PzDA): alpha-kainate greater than quinolinate greater than N-methyl-D-aspartate greater than quisqualate greater than L-glutamate. These compounds are the most potent preferential alpha-kainate antagonists so far tested. The relationship between antagonism at the various receptor subtypes and anticonvulsant action is not adequately defined.
ZK 91296, a newly synthesised beta-carboline with partial agonistic activity at the benzodiazepine receptor raised the threshold current necessary to elicit electroconvulsions in mice. This effect was dose-dependent and could be reversed by Ro 15-1788. ZK 91296 antagonised the anticonvulsant action of diazepam, but potentiated that of phenobarbitone. ZK 91296 protected mice from DMCM-induced seizures with high potency, this effect being benzodiazepine specific. In mutant rats exhibiting an increased muscle tone of the hindlimbs, ZK 91296 was devoid of muscle relaxant effect and antagonised the muscle relaxant action of both diazepam and phenobarbitone. The latter effect could be blocked by Ro 15-1788. The results suggest that the actions of ZK 91296 are only partly due to its partial agonistic properties at the benzodiazepine receptor.
The role played by benzodiazepine (BDZ) receptors and GABAergic mechanisms in the muscle relaxant effect of the adenosine receptor agonist, 2-chloroadenosine (2-CLA) was evaluated in genetically spastic rats. 2-CLA reduced in a dose-related manner the spontaneous tonic activity in the electromyogram (EMG) of the gastrocnemius-soleus muscle. While the muscle relaxant effect produced by the adenosine analogue was abolished by aminophylline, a methylxanthine with potent antagonistic activity of adenosine-mediated inhibition, the two gamma-aminobutyric acid (GABA) antagonists bicuculline and picrotoxin did not reverse it. Neither Ro 15-1788 nor CGS 8216, specific BDZ receptor antagonists, nor beta-carboline-3-carboxylic acid methyl ester, an inverse agonist at BDZ receptors, affected the depressant effect of 2-CLA in the EMG. These results suggest that 2-CLA does not interact with GABA or BDZ receptor-mediated events in vivo to produce the muscle relaxant action. It is proposed that purinergic mechanisms may be involved in the muscle relaxant effects of a variety of drugs.
Antagonists of neuronal excitation induced by dicarboxylic amino acids were tested in genetically spastic rats of the Han-Wistar strain. These animals exhibit an increased muscle tone which can be measured as a spontaneous tonic activity in the electromyogram of the gastrocnemius-soleus muscle. Compounds that block excitation due to N-methyl-D-aspartic acid reduced the spontaneous activity measured in the electromyogram in a dose-related manner. The most potent compounds, 2-amino-7-phosphonoheptanoic and kynurenic acids were effective muscle relaxants when given either intraperitoneally or intracerebroventricularly. 2-Amino-5-phosphonopentanoic acid possessed much weaker muscle relaxant activity, while L-glutamic acid diethylester was inactive by either route. The results suggest that blockade of N-methyl-D-aspartic acid receptors results in a myorelaxant effect. Specific antagonists of excitation at N-methyl-D-aspartic acid receptors may provide a new class of muscle relaxants.