Suppression of amygdaloid kindled convulsion following unilateral injection of 2-amino-7-phosphonoheptanoic acid (2-APH) into the substantia innominata of rats

The NMDA receptor complex as a therapeutic target in epilepsy: a review

A substantial amount of research has shown that N-methyl-D-aspartate receptors (NMDARs) may play a key role in the pathophysiology of several neurological diseases, including epilepsy. Animal models of epilepsy and clinical studies demonstrate that NMDAR activity and expression can be altered in association with epilepsy and particularly in some specific seizure types. NMDAR antagonists have been shown to have antiepileptic effects in both clinical and preclinical studies. There is some evidence that conventional antiepileptic drugs may also affect NMDAR function. In this review, we describe the evidence for the involvement of NMDARs in the pathophysiology of epilepsy and provide an overview of NMDAR antagonists that have been investigated in clinical trials and animal models of epilepsy.

FK506 facilitates chemical kindling induced by pentylenetetrazole in rats

To clarify the possible role played by calcineurin in kindling development, we examined the effects of pretreatment with FK506, a selective calcineurin inhibitor, on pentylenetetrazole (PTZ) kindling in rats. FK506 facilitated the speed of kindling induced by repeated administration of 30-mg/kg PTZ, while FK506 did not ameliorate acute seizure manifestations after a single injection of PTZ. Our results suggested that calcineurin might exert an inhibitory effect on PTZ kindling.

Anticonvulsant action of metabotropic glutamate receptor agonists in kindled amygdala of rats

1S,3R-1-Aminocyclopentane-1,3-dicarboxylate (1S,3R-ACPD) and L-2-amino-4-phosphonobutyrate (L-AP4) are selective agonists of metabotropic glutamate receptors (mGluRs). 1S,3R-ACPD (200 nmol) injected into the amygdala (AM) of non-kindled rats produced immediate and transient seizures, characterized by immobility, searching, and wet-dog shakes. However, this ictal response was not observed in AM-kindled rats. Intra-AM injection of 1S,3R-ACPD (40 or 200 nmol) or L-AP4 (200 nmol) resulted in a delayed and marked suppression of kindled seizures, 3 days after 40 nmol of 1S,3R-ACPD, 1 day after 200 nmol of 1S,3R-ACPD, and from 1 to 3 days after 200 nmol of L-AP4. These and the previous findings suggest that: (1) the excitatory action of 1S,3R-ACPD in the AM, which may be mediated by the postsynaptic mGluRs, is reduced after completion of kindling; (2) 1S,3R-ACPD and L-AP4 exert anti-convulsant action in the AM, presumably by activating the presynaptic as well as postsynaptic mGluRs.

Ipsilateral hemiconvulsive seizure after unilateral injection of procaine into the substantia innominata of amygdaloid-kindled rats

The effects of procaine injected into the substantia innominata (SI) and the amygdala (AM) were compared in AM-kindled rats. Intra-SI injection of procaine (ipsilateral to the kindled AM) caused immediate contralateral hemiparesis lasting for about 30 min, associated with EEG amplitude reduction. When the kindled AM was stimulated at the previously established generalized seizure triggering threshold (GST), 8/15 animals had ipsilateral hemiconvulsive seizure 5 min after the injection. In all the animals, afterdischarge was readily produced with a significant reduction in its duration. When procaine was injected into the kindled AM, there was no paresis or EEG change. AM stimulation at the GST did not evoke afterdischarge 5 min after the injection, although the kindled seizure was reactivated by a more intense stimulus. After 24 hr, all the animals, regardless of the site of procaine injection, responded to GST stimulation with a kindled seizure. The data suggest that: (1) the effect of intra-SI procaine is not due to drug diffusion to the kindled AM, and (2) the kindled AM can gain access to the contralateral hemispheric motor mechanism without participation of the ipsilateral SI.

Epileptic seizure of El mouse initiates at the parietal cortex: depth EEG observation in freely moving condition using buffer amplifier

The initiation site of seizure discharges and the relationship between behavioral manifestations and electroencephalography were investigated in the El mouse, a hereditary epilepsy model. The chronic depth electrodes were implanted stereotaxically into the frontal cortex, parietal cortex, temporal cortex, hippocampus, striatum, amygdaloid complex, non-specific nuclei of thalamus and substantia nigra. Electrical activities were recorded in freely moving condition with use of the buffer amplifier devised in the laboratory and behaviors were monitored simultaneously. Seizure spike discharges started in the parietal cortex and spread out into other brain areas. When the hippocampus was involved, the tonic convulsion occurred behaviorally. The paper describes the first direct evidence of the initiation and propagation of seizure discharges in the brain of El mouse.

Important roles of N-methyl-D-aspartate receptors in expression of amygdaloid-kindled seizure demonstrated by intraperitoneal administration of L-aspartate in dimethyl sulfoxide

Intraperitoneally (i.p.) administered L-aspartate (Asp) (20 mmol/kg) produced no behavioral or EEG change in nonkindled rats. Nonkindled rats that received 18, 19, or 20 mmol/kg Asp, dissolved in 10 or 15% dimethylsulfoxide (DMSO), i.p. developed masticatory movement, head nodding, and myoclonic jerks of the limbs, followed by wild running and subsequent tonic extension of the whole body. In contrast to the effects in nonkindled rats, i.p. injection of Asp 20 mmol/kg in 15% DMSO in amygdala-kindled rats precipitated electroclinical generalized seizures identical to kindled ones. When the kindled amygdala was pretreated with 2-amino-7-phosphonoheptanoic acid (2-APH), a potent and specific antagonist of N-methyl-D-aspartate (NMDA) receptors, the Asp/DMSO-induced generalized convulsion identical to kindled amygdala seizure was suppressed. 2-APH treatment of the contralateral amygdala was without such suppression. The results suggest that (a) Asp is ineffective when given alone (when given with DMSO, however, Asp evokes generalized seizures identical to kindled ones in amygdala-kindled rats, while it induces a qualitatively different generalized seizure in nonkindled rats; (b) NMDA receptors of the kindled amygdala play an important role in activation of the transsynaptic neurocircuit underlying the expression of kindled amygdala seizure; and (c) DMSO is useful in assessing potential central effects of compounds that do not readily penetrate the blood-brain barrier (BBB).

A review of evidence for GABergic predominance/glutamatergic deficit as a common etiological factor in both schizophrenia and affective psychoses: more support for a continuum hypothesis of "functional" psychosis

Virtually all antidepressant and antipsychotic drugs, including clozapine, rimcazole and lithium ion, are proconvulsants, and convulsive therapy, using metrazol, a known GABA-A antagonist, as well as electro-convulsive therapy, can be effective in treating both schizophrenia and affective psychoses. Many antidepressant and antipsychotic drugs, including clozapine, as well as some of their metabolites, reverse the inhibitory effect of GABA on 35S-TBPS binding, a reliable predictor of GABA-A receptor blockade. A review of relevant literature suggests that 1) "functional" psychoses constitute a continuum of disorders ranging from schizophrenia to affective psychoses with overlap of symptoms, heredity and treatments, 2) a weakening of GABergic inhibitory activity, or potentiation of counterbalancing glutamatergic neurotransmission, in the brain, may be involved in the therapeutic activities of both antidepressant and antipsychotic drugs, and 3) schizophrenia and the affective psychoses may be different expressions of the same underlying defect: GABergic preponderance/glutamatergic deficit. Schizophrenia and affective psychoses share the following: 1) several treatments are effective in both, 2) similar modes of inheritance, 3) congruent seasonal birth excesses, 4) enlarged cerebral ventricles and cerebellar vermian atrophy, 5) dexamethasone non-suppression. Both genetic and environmental factors are involved in both schizophrenia and affective psychoses, and several lines of evidence suggest that important environmental factors are neurotropic pathogens that selectively destroy glutamatergic neurons. One group of genes associated with psychoses may increase vulnerability to attack and destruction, by neurotropic pathogens, of excitatory glutamatergic neurons that counterbalance inhibitory GABergic neurons. A second group of genes may encode subunits of overactive GABA-A receptors, while a third group of genes may encode subunits of hypo-active glutamate receptors. Improved antipsychotic drugs may be found among selective blockers of GABA-A receptor subtypes and/or enhancers of glutamatergic neurotransmission. A mechanism similar to kindling, leading to long-lasting reduction of GABergic inhibition in the brain, may be involved in several treatments of psychoses.

An important role of non-NMDA receptors in the expression of kindled amygdaloid seizure in rats

gamma-D-glutamylaminomethylsulphonic acid (GAMS), a preferential antagonist of non-NMDA receptors (kainate and quisqualate receptors), was injected into the kindled amygdala (AM) of rats. When the kindled AM was stimulated at the previously established generalized seizure triggering threshold (GST) one hour after the GAMS (1 or 2 mumol) injection, afterdischarge (AD) generation was completely suppressed. However, a re-stimulation at the intensity of 40-200 microA above the GST generated AD associated with Stage 1 or 5 seizure. Our result suggests an important role played by non-NMDA receptors in the expression and generalization of AM-onset seizures.

Comparison between substantia innominata and amygdala kindling in rats

Kindling was induced in rats by electrical stimulation of the lateral portion of the substantia innominata (SI). The pattern of seizure development was similar to that of amygdala (AM) kindling. However, lateral SI kindling was associated with ipsilateral head turning as an initial manifestation. In addition, lateral SI kindling had a higher afterdischarge threshold than AM kindling, and the generalized seizure triggering threshold was more unstable in SI kindling than in AM kindling. These findings suggest that lateral SI participates in, but is not essential for, AM seizure development in rats.

Bidirectional transfer between kindling induced either by L-glutamate or L-aspartate and electrical stimulation in rats

Repeated spaced injections into the amygdala (AM) of rats of a subconvulsive dose of either L-glutamate (GLU) or L-aspartate (ASP) produced progressive seizure development culminating in generalized convulsion strikingly similar to electrically kindled seizure. Both GLU- and ASP-kindled AM sites responded to electrical stimulation with very rapid development of kindled seizure. When electrically kindled AM sites received identical injections of GLU or ASP, a similar positive transfer effect was obtained. These results suggest that (1) either GLU or ASP alone can kindle the AM and (2) GLU, ASP or GLU/ASP kindling share common neurobiological mechanisms with electrical kindling.