Monoaminergic correlates of kindling

Effect of saponin fraction from Ficus religiosa on memory deficit, and behavioral and biochemical impairments in pentylenetetrazol kindled mice

In our previous study, the saponin-rich fraction (SRF) of adventitious root extract of Ficus religiosa L. (Moraceae) was shown to have an anticonvulsant effect in acute animal models of convulsions. The present study was envisaged to study the effect of SRF in the pentylenetetrazol (PTZ) kindling mouse model and its associated depression and cognition deficit. Treatment with the SRF (1, 2 and 4 mg/kg; i.p.) for 15 days in kindled mice significantly decreased seizure severity on days 5, 10 and 15 when challenged with PTZ (35 mg/kg; i.p.). Marked protection against kindling-associated depression was also observed on days 10 and 15 in the SRF-treated groups when tested using the tail-suspension test. However, the SRF treatment failed to protect kindling-associated learning and memory impairments in the passive shock avoidance paradigm. The observed behavioral effects were corroborated with modulation in the levels of noradrenaline, dopamine, serotonin, GABA and glutamate in discrete brain regions.

The serotonergic and noradrenergic effects of antidepressant drugs are anticonvulsant, not proconvulsant

Contrary to existing evidence, convulsant liability of the antidepressants has been attributed to noradrenergic and serotonergic increments. This is a classic case of confusing treatment effects with the manifestations of illness. In fact, the remarkable anticonvulsant effectiveness of antidepressant-induced noradrenergic and serotonergic activation has been ignored. Some antidepressant drugs such as the specific serotonin reuptake inhibitor (SSRI) fluoxetine may be devoid of convulsant liability entirely, while having distinct anticonvulsant properties. Some authorities advance the notion that the seizure predisposition of patients with epilepsy increases risks for antidepressant-induced seizures. However, evidence does not support this contention. Instead, data increasingly support the concept that noradrenergic and serotonergic deficiencies contribute to seizure predisposition. Indeed, the antidepressants have the potential to overcome seizure predisposition in epilepsy. Whereas therapeutic doses of antidepressants elevate noradrenergic and serotonergic transmission, larger doses can activate other biological processes that may be convulsant.

Amygdala amino acid and monoamine levels in genetically Fast and Slow kindling rat strains during massed amygdala kindling: a microdialysis study

We investigated the neurochemistry of epileptic seizures in rats selectively bred to be seizure-prone (Fast) vs. seizure-resistant (Slow) to amygdala kindling. Microdialysis was used to measure levels of amino acids [glutamate, aspartate and gamma-aminobutyric acid (GABA)] and monoamines (noradrenaline, dopamine and serotonin) during 'massed' stimulation (MS) (every 6 min) of the ipsilateral amygdala for a total of 40 stimulation trials. Behavioral seizure profiles together with their afterdischarge thresholds (ADTs) and associated durations were assessed during the procedure, and subsequently were redetermined 1, 7 and 14 days later. Then normal 'daily' kindling commenced and continued until the animal reached the fully kindled state. During MS, several generalized seizures were triggered in Fast rats that were associated with long afterdischarge (AD) durations and intermittent periods of elevated thresholds, but in Slow rats, most stimulations were associated with stable ADTs and short ADs. Progressively increasing extracellular glutamate and decreasing GABA was observed in Fast rats during the MS, whereas Slow rats showed levels similar to baseline values. Levels of noradrenaline and dopamine, but not of serotonin, were also increased in both strains throughout the MS treatment. In Fast rats, a dramatic lengthening of AD durations occurred 7 and 14 days following MS, as well as subsequent strong positive transfer to daily kindling, all of which were not seen in Slow rats. Together, these results show that repeated, closely spaced stimulations of the amygdala can differentially alter excitatory and/or inhibitory transmitter levels in a seizure network, and that sensitivity to this manipulation is genetically determined.

Development of an experimental model of epilepsy in rats exposed to ozone

Paroxysmal activity has been reported in the olfactory bulb of rabbits chronically exposed to ozone (O3), postulating that this gas provokes alterations in the electrical activity of the central nervous system. The effects of 1 ppm of O3 inhaled daily for 1 or 3 h prior to each stimulation were studied using the kindling model of epilepsy. Results showed that O3 decreased the duration of the amygdaloid after-discharges during the development of kindling and shortened the latency to the onset of the first generalized seizure in rats exposed for 1 h to O3, while the group exposed for 3 h also decreased the after-discharge duration but delayed the appearance of seizures. Spread of seizure activity, defined as the latency to reach behavioral and electrographic signs of tonic clonic seizures was faster in the 1 h O3 exposed rats and slower in those exposed for 3 h. These findings demonstrate that O3 or its reaction products, such as free radicals, could affect the mechanisms involved in kindling course, such changes being dependent of the time of O3 exposure.

Monoamines and their metabolites in cerebrospinal fluid and temporal cortex of epileptic patients

The involvement of monoamines in the initiation or maintenance of epileptic phenomena has been extensively studied in cerebral tissues and in cerebrospinal fluid. The present work was undertaken to study monoamines and their metabolites in human spiking and non-spiking temporal cortex excised from patients with complex partial seizures unresponsive to available anticonvulsants. The same substances were also analyzed by HPLC-ED in cerebrospinal fluid obtained 24 h before the surgical procedure and compared with those from patients with chronic headache and normal neurological evaluation. The results show increased 5-HT, 5-HIAA and HVA levels in spiking compared with non-spiking cortex. Cerebrospinal fluid levels of 5-HIAA and HVA are concomitantly increased in epileptic compared with headache patients.

Brain region-specific and time-dependent decreases of G alpha i2 in amygdala-kindled rats

Immunoreactivity levels of G protein alpha-subunits, Galphas (45 and 52 kDa), Galphai1, and Galphai2, were determined in plasma membranes prepared from ipsilateral amygdala-pyriform cortex (AM/PC), contralateral AM/PC, dorsal hippocampus (DH), and ventral hippocampus (VH) in amygdala-kindled rats 24 h, 1 month, and 3 months after the last seizure. Relative to sham controls, immunoreactivity levels of Galphai2 were significantly reduced in ipsilateral AM/PC and DH, with maximal decreases observed, respectively, at 24 h (26% form control levels) and 1 month (18% from control levels) postseizure. No significant alterations in the levels of Galphai1 or either of the Galphas isoforms were observed. The reduction in Galphai2 levels was, however, not accompanied by measurable changes in Galphai-mediated inhibition of adenylyl cyclase, as estimated by GppNHp modulation of forskolin-activated adenylyl cyclase activity. The present findings add support to the hypothesis that long-term changes in brain functioning following kindling may involve altered expression and/or function of components of the transmembrane signalling cascade, including G proteins.

The role of dopamine in epilepsy

The clinical benefits of dopamine agonists in the management of epilepsy can be traced back over a century, whilst the introduction of neuroleptics into psychiatry practice 40 years ago witnessed the emergence of fits as a side effect of dopamine receptor blockade. Epidemiologists noticed a reciprocal relationship between the supposed dopaminergic overactivity syndrome of schizophrenia and epilepsy, which came to be regarded as a dopamine underactivity condition. Early pharmacological studies of epilepsy employed nonselective drugs, that often did not permit dopamine's antiepileptic action to be clearly dissociated from that of other monoamines. Likewise, the biochemical search for genetic abnormalities in brain dopamine function, as predeterminants of spontaneous epilepsy, proved largely inconclusive. The discovery of multiple dopamine receptor families (D1 and D2), mediating opposing influences on neuronal excitability, heralded a new era of dopamine-epilepsy research. The traditional anticonvulsant action of dopamine was attributed to D2 receptor stimulation in the forebrain, while the advent of selective D1 agonists with proconvulsant properties revealed for the first time that dopamine could also lower the seizure threshold from the midbrain. Whilst there is no immediate prospect of developing D2 agonists or D1 antagonists as clinically useful antiepileptics, there is a growing awareness that seizures might be precipitated as a consequence of treating other neurological disorders with D2 antagonists (schizophrenia) or D1 agonists (parkinsonism).

Spatiotemporal alterations of central alpha 1-adrenergic receptor binding sites following amygdaloid kindling seizures in the rat: autoradiographic studies using [3H]prazosin

Noradrenergic neurons are thought to be involved in the process of seizure development and long-term central nervous system plasticity associated with kindling and epilepsy. These processes involve actions of noradrenaline at alpha 1-, alpha 2- and beta 1-adrenergic receptors. In this study, quantitative in vitro autoradiography was used to investigate possible changes in the density of brain alpha 1-adrenergic receptors in a kindling model of epilepsy in the rat. Kindling was produced by daily unilateral stimulation of the amygdala. The alpha 1A+alpha 1B subtypes of adrenergic receptors were labelled with the alpha 1-selective antagonist, [3H]prazosin and alpha 1B receptors, detected in the presence of 10 nM WB4101 to selectively occupy alpha 1A receptors, accounted for 50% of total alpha 1 receptors in cerebral cortex. Autoradiographic studies identified significant and long-lasting, ipsilateral increases in specific [3H]prazosin binding throughout layers I-III of the cortex in sham-operated, unstimulated rats, presumably caused by the surgical implantation of the stimulating electrode within the basolateral amygdaloid nucleus. Binding to alpha 1A + alpha 1B receptors and alpha 1B receptors was increased by an average of 35 and 60%, respectively under these conditions. Stimulation-evoked seizures produced dramatic bilateral increases in specific [3H]prazosin binding to alpha 1A + alpha 1B receptors and particularly to alpha 1B receptors in layers I-III of all cortical areas examined. These changes were rapidly induced and the largest increases (range alpha 1A + alpha 1B 80-340%; alpha 1B 165-380%) occurred at 0.5-2 h after the last stage 5 kindled seizure. At 1 and 3 days after the last seizure, increases were measured for both alpha 1A + alpha 1B and alpha 1B receptors in layers I-III of particular cortical regions, but not overall (e.g. 60-210% increase in perirhinal cortex at both times, with increases also in retrosplenial, hindlimb, occipital, parietal and temporal cortices). Between 2-8 wk post-stimulation specific receptor binding levels were equivalent to those in sham-operated, unstimulated rats. In contrast to the large and widespread increases in outer cortical [3H]prazosin binding, smaller increases were detected in the inner cortex (layer V-VI) at individual times (65-75% increase at 30 min), while no significant changes occurred in several other brain regions examined, including thalamus, which contained a high density of alpha 1A and alpha 1B receptors, or hippocampus which has a low density of both alpha 1 receptor subtypes.(ABSTRACT TRUNCATED AT 400 WORDS)

Elevated tyrosine hydroxylase mRNA levels in the adrenal medulla of spontaneously hypertensive rats

We investigated the expression of tyrosine hydroxylase (TH) mRNA and its activity in the adrenal medulla of spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY). The TH mRNA levels were determined by Northern blot and dot blot analyses. The TH activity and the expression of TH mRNA in the adrenal medulla of SHR were significantly higher than those of WKY (P < 0.01). These results suggested that the hypertension of SHR may be related to the high activity of TH due to the high level of TH mRNA, which increases epinephrine and norepinephrine levels in the adrenal medulla.

Persistent increases in dopamine D2 receptor mRNA expression in basal ganglia following kindling

Amygdala kindling resulted in significant increases in the expression of D2 receptor mRNA in the nucleus accumbens and striatum 30 days following the last kindling stimulation. Densitometric analyses of tissue sections incubated in the presence of an oligonucleotide probe directed against D2 receptor cDNA indicated a 20-35% increase in D2 receptor mRNA in these regions following kindling. Kindling from the amygdala followed by piriform cortical kindling in the transfer paradigm (overkindling) resulted in significant further increases in D2 receptor mRNA expression in both the accumbens (150% increase) and striatum (120% increase). There were no observed hemispheric asymmetries in D2 receptor mRNA in either kindled or overkindled animals. The data indicate an enduring upregulation of extrapyramidal D2 receptor mRNA following the kindling process. How this change may relate to kindling-induced alterations in seizure susceptibility or behaviors mediated by limbic dopaminergic pathways are questions for future studies.

Mechanisms of kindling: an evaluation of single trial seizure induction procedures for use as controls

Investigations into the neurochemical or molecular biological mechanisms underlying the kindled state require a seizure induction procedure for eliciting generalized tonic-clonic seizures in naive animals. Such seizure controls are necessary for dissociating the influence of ictal motor events on measures of interest from the influence of the kindling process on these same measures. In this study three procedures for inducing seizures in naive animals were evaluated against a set of criteria considered ideal.

Electrical kindling of rats treated discontinuously or continuously with haloperidol

Intermittent as opposed to continuous treatment of rats with haloperidol resulted in a long-lasting potentiation of oral activity. To examine if this behavioural sensitization to discontinuous neuroleptic treatment facilitates seizure development in electrical kindling, rats treated either intermittently or continuously with haloperidol for 15 weeks were kindled in the nucleus amygdala. Development of kindled seizures was significantly faster in the intermittently treated group (P < 0.01) than in controls or continuously treated rats. Furthermore, discontinuously treated animals displayed electroencephalographic afterdischarges in the substantia nigra from the beginning of treatment. The findings of cross-sensitivity between electrical amygdala kindling and pharmacological sensitization and of early appearance of epileptiform nigral activity have implications for the pathogenesis of both conditions. We suggest that depressed gamma-aminobutyric acid activity in substantia nigra could be a common mechanism.

Effect of amygdaloid kindling on [3H]dopamine and [14C]acetylcholine release from rat prefrontal cortex and striatal slices

The involvement of the dopaminergic (DA) systems in the control of limbic kindled seizures is ill defined. The effects of kindling on DA activity may have been overlooked in the past, because of its subtle unilateral occurrence and/or the variance of the endogenous imbalance of DA activity in normal animals. In the present study rats were screened for their endogenous DA imbalance using amphetamine-induced rotational behaviour. Electrical or sham kindling was applied in the hemisphere with the higher endogenous DA activity. Sections of the bilateral prefrontal cortex and dorsal and ventral striatum were dissected either 2 hours or 21 days after the final seizure and the electrically stimulated release of [3H]DA and [14C]acetylcholine (ACh) determined. Release was also measured in the presence of quinpirole or sulpiride to assess the activity of pre- and postsynaptic DA D2-receptors. Long-term effects of kindling consisted of facilitation of ACh release in the ventral striatum contralateral to the kindled amygdala and bilateral depression of DA release in the prefrontal cortex. Kindling therefore produced area specific changes in neurotransmitter systems giving rise to increased pro-convulsive cholinergic activity in the ventral striatum and decreased anti-convulsive dopaminergic activity in the prefrontal cortex.

Cerebrospinal fluid and serum levels of dopa, catechols, and monoamine metabolites in patients with epilepsy

We measured CSF and serum concentrations of monoamines and monoamine metabolites in normal control subjects and in patients with partial epilepsy between and less than 2 h after complex partial seizures (CPS) or secondarily generalized tonic-clonic seizures (SGTCs). After SGTCs, concentrations of norepinephrine in CSF were significantly higher (p less than 0.05) than interictal concentrations, concentrations after PSs, and concentrations in control subjects. Serum epinephrine levels also were significantly higher after SGTCs than interictal and control subjects' levels. CSF HVA levels were significantly higher after PSs than interictal or control subjects' levels. CSF concentrations of norepinephrine and its intraneuronal metabolite, dihydroxyphenylglycol, were highly correlated, both interictally and following SGTCs, whereas correlations between serum and CSF levels of these catechols generally were not statistically significant. The results indicate that seizures are associated with release of catecholamines in the central nervous system.

Afferent connections of the rat substantia nigra pars lateralis with special reference to peptide-containing neurons of the amygdalo-nigral pathway

The afferent connections of the rat substantia nigra pars lateralis have been studied using the retrograde axonal transport of fluorescent latex microspheres. The most numerous groups of retrogradely labelled nerve cell bodies were observed bilaterally in the parabrachial complex and several hypothalamic nuclei, whereas the parietal neocortex, the fundus striati, the central nucleus of the amygdala and the bed nucleus of the stria terminalis were labelled on the injected side only. The neuronal projections from the central amygdaloid nucleus to the substantia nigra pars lateralis and lateral part of the rostral pars compacta have additionally been confirmed by anterograde tracing using wheat-germ agglutinin coupled to horseradish peroxidase. The presence of some peptides in this pathway was studied by combining the use of the same retrograde tracer with immunofluorescence after intra-amygdaloid injections of colchicine. With this method, we have demonstrated that Met-enkephalin, dynorphin and neurotensin are probably utilized as neurotransmitters or co-transmitters in the neurons of the amygdalo-nigral pathway.

Anticonvulsant effects of ipsilateral but not contralateral microinjections of the dopamine D2 agonist LY 171555 into the nucleus accumbens of amygdala-kindled rats

Recent radioligand binding studies demonstrated an increase in the density of dopamine D2 receptors in the nucleus accumbens ipsilateral to the stimulating electrode in amygdala- or hippocampal-kindled rats. In the present study we examined the anticonvulsant effect of dopamine agonists by unilateral microinjections into the nucleus accumbens in rats kindled from the right basolateral amygdaloid nucleus. Microinjections of the D2 agonist LY 171555 into the ipsilateral nucleus accumbens 15 min prior to the kindling stimulation in fully kindled rats decreased significantly kindling parameters such as seizure severity, seizure duration and afterdischarge duration, whereas the D1 agonist SKF 38393 had no anticonvulsant effects. After ipsilateral microinjection of 40 pmol LY 171555 focal and generalized kindled seizures were totally blocked in almost 50% of the rats. The anticonvulsant effect of LY 171555 could be completely antagonised by systemic administration of the D2 antagonist sulpiride. Microinjection of the D1 or D2 agonist into the nucleus accumbens contralateral to the stimulating electrode had no anticonvulsant effects. In accordance with other reports our data indicate a possible topographic limitation of D2 receptor mediated anticonvulsant effects to specific regions of the basal ganglia.

Evidence for long-term reduction of noradrenaline release after kindling in the rat hippocampus

The in vivo microdialysis technique was used to monitor steady-state noradrenaline release in the rat hippocampus after hippocampal kindling. At 8 weeks after the last seizure, the noradrenaline release was reduced by 62% in the stimulated hippocampus in kindled animals as compared to non-kindled rats. The reduction was not due to the repeated handling of the animals as assessed in a separate experiment. The results suggest a decrease of inhibitory noradrenergic influence at the primary kindling site, which could play a role in kindling epileptogenesis.

Medial preoptic area kindling induces sexual behavior in sexually inactive male rats

In the present experiments, sexually experienced and non-copulating male rats were kindled in the medial preoptic area (MPOA) or the amygdala (AMG) with the purpose to investigate if the widespread modification of brain function produced by kindling induces sexual behavior in non-copulating rats and if kindling facilitates sexual behavior in copulating rats. Since kindling in the MPOA has been little studied, a description of this phenomenon is also presented. The animals were stimulated 4 times daily on odd days and sexual behavior monitored on even days. The results showed that the MPOA required higher stimulus intensity to elicit an afterdischarge (AD) than the AMG. The AD duration was significantly longer in animals kindled in the MPOA than in animals kindled in the AMG. No difference was found in the development of kindling between these brain structures. Kindling had no effect upon sexual behavior in copulating rats. In contrast, MPOA kindling induced copulation in non-copulating male rats. Seven out of 9 animals displayed sexual behavior. No significant facilitation was observed after AMG kindling in non-copulating male rats. Furthermore, the sexual behavior displayed by the previously non-copulating MPOA kindled rats was similar to the sexual behavior displayed by sexually experienced animals. It is proposed that sexual behavior is facilitated in these male rats by local neural changes produced by kindling.

Antikindling effects of locus coeruleus stimulation: mediation by ascending noradrenergic projections

Electrical stimulation of the noradrenergic locus coeruleus (LC) delays the generalization of partial seizures during amygdaloid kindling by increasing the time spent in the earliest stages of seizure development. To determine whether noradrenergic axons projecting to the midbrain and forebrain are involved in this antikindling effect, we examined the effects of lesions of the dorsal noradrenergic bundle, induced by intracerebral infusions of 6-hydroxydopamine (6-OHDA), on kindling and the antikindling action of stimulation of the LC. Stimulation of the LC during amygdaloid kindling increased the number of afterdischarges (ADs) spent in the early stages of partial seizure and decreased the number of ADs spent in later stages of generalized seizure, as has been described previously. LC-stimulated rats also displayed longer durations of AD during early stages of kindling. The antikindling effect of LC stimulation was blocked by lesions of the dorsal bundle, whereas the facilitatory effects of LC stimulation on generalization and on the duration of AD were unaffected by the lesions. These results suggest that the antikindling action of LC stimulation is mediated by the ascending projections of noradrenergic neurons, presumably through enhanced release of noradrenaline. On the other hand, the facilitatory effects of LC stimulation on the development of later stages of seizure and on the duration of AD appear to be independent of the ascending dorsal bundle.

The effect of regional differences in noradrenergic neuron growth patterns on juvenile kindling

Kindling can be altered by a variety of lesions designed to deplete norepinephrine (NE). However, the effect of the regional alteration in NE concentration on seizure susceptibility has not been studied. Two different concentrations of 6-hydroxydopamine (6-OHDA) were administered to one-day-old rat pups. At age 18 days, rat with significant rostral brain NE loss, due to high dose 6-OHDA, had a faster rate of electrical kindling in the entorhinal cortex than controls. In contrast rats receiving low dose 6-OHDA which resulted in comparable forebrain NE depletion but with a dramatic hindbrain noradrenergic overgrowth showed no enhancement of kindling. These results suggest that in the immature rat the proconvulsant effect of forebrain NE depletion can be overridden by an augmentation of hindbrain NE growth patterns.

Catecholaminergic systems and amygdala kindling development. Effects of bilateral lesions of substantia nigra dopaminergic or locus coeruleus noradrenergic neurones

The effects of the bilateral and selective destruction of substantia nigra (SN) dopaminergic or locus coeruleus (LC) noradrenergic neurones, consecutive to a local injection of 6-hydroxydopamine, were studied on the development of amygdala kindling. Immunohistochemical controls of lesions were performed using selective dopamine (DA) or norepinephrine (NE) antibodies. The results demonstrated that a massive destruction of SN pars compacta neurones did not modify the rate of kindling development. Conversely, the lesions of LC neurones (sparing lateral tegmental nuclei) markedly facilitated the development of amygdala kindling. This effect was related to the extent of NE denervation. Together, these results suggest that DA is not strongly involved in the development of kindling, and that the nigrostriatal output does not play a major role in the generalization of kindled seizures. In contrast, they confirm an inhibitory influence exerted by LC noradrenergic ascending pathways on the development of kindling.

The monoaminergic innervation of the amygdala in the squirrel monkey: an immunohistochemical study

The monoaminergic innervation of the amygdala of the squirrel monkey (Saimiri sciureus) was studied by using immunohistochemical methods with primary antisera raised against serotonin, and the catecholamine synthesizing enzymes tyrosine hydroxylase, dopamine-beta-hydroxylase and phenylethanolamine-N-methyltransferase. Serotonin was widely distributed within the amygdala including profuse terminal labeling in central, basolateral and cortical nuclear groups. The accessory basal and medial nuclei were the only two areas receiving relatively poor serotoninergic innervation. Tyrosine hydroxylase was more discretely distributed, with very dense to moderate terminal labeling in central, basal and lateral nuclei, but only scant labeling within accessory basal and corticomedial nuclei, except at the cortical transitional area where dense terminal labeling was noted. Dopamine-beta-hydroxylase immunoreactivity was moderate in central and corticomedial nuclei, but comparatively light in other nuclear groups. Phenylethanolamine-N-methyltransferase was only sparsely distributed in the amygdala. The findings of the present study reveal that the monoaminergic innervation of the primate amygdala is similar to that reported in rodents, although some conspicuous exceptions do exist. Whereas the noradrenergic and serotoninergic neuronal systems ramify profusely within the amygdala, the dopaminergic system appears to be more discretely and topographically organized.

Noradrenaline and 5-hydroxytryptamine release in the hippocampus during seizures induced by hippocampal kindling stimulation: an in vivo microdialysis study

The intracerebral microdialysis technique has been used to monitor extracellular levels of noradrenaline, 5-hydroxytryptamine and 5-hydroxyindoleacetic acid in the rat hippocampus in vivo in response to focal and generalized seizures induced by hippocampal kindling stimulation. In fully kindled animals a stimulus-induced generalized seizure gave rise to a three-fold increase of noradrenaline levels in the stimulated hippocampus as compared to baseline levels (15-min samples). The maximal increase of noradrenaline levels occurred within the first minutes after onset of seizure activity, as assessed in 2-min sample fractions with the noradrenaline uptake blocker desipramine added to the perfusion medium. After the peak increase, the noradrenaline levels tapered off, reaching baseline after 8-10 min. In 6-hydroxydopamine-treated animals, baseline noradrenaline levels were markedly reduced and there was no significant increase in noradrenaline release in response to a generalized seizure. These data support the hypothesis that the high extracellular levels of noradrenaline measured in seizures are of neuronal origin. There were no significant changes in extracellular 5-hydroxytryptamine or 5-hydroxyindoleacetic acid levels after a generalized seizure. In non-kindled animals the steady state noradrenaline levels during uptake blockade were two-three times higher than in the kindled rats. However, the peak noradrenaline levels measured in both hippocampi after the first two electrical kindling stimulations giving rise to focal epileptiform activity (afterdischarge) were similar to those observed in the kindled animals in response to generalized seizures. The increase of noradrenaline release in the non-kindled animals was significantly correlated to the duration of afterdischarge. In conclusion, the present study demonstrates the usefulness of the intracerebral dialysis technique for monitoring noradrenaline, 5-hydroxytryptamine and 5-hydroxyindoleacetic acid release during seizures. The results indicate that both focal and generalized hippocampal seizures evoked by electrical kindling stimulation lead to a marked increase of transmitter release from noradrenergic but not from serotonergic neurons in the hippocampus. The ability of the noradrenergic system to respond by increased transmitter release to epileptic seizures is thus retained also in the kindled state.

Mesolimbic dopamine receptor increases two weeks following hippocampal kindling

Kindled seizures developed in rats following repeated electrical stimulation of the left CA1 region of the hippocampus. Two weeks after the final kindled seizure, the densities of dopamine (DA) D2 receptors were assayed in the left and right amygdaloid area, nucleus accumbens, and nucleus caudatus. A significant increase (107%) in the density of DA D2-receptors in the ipsilateral nucleus accumbens occurred. This finding may help to define the long-term neurochemical consequences of kindling.