Alterations of noradrenaline and serotonin uptake and metabolism in chronic cobalt-induced epilepsy in the rat

Degeneration of monoaminergic fibers in the aged micrencephalic rat

Age-related changes in the monoaminergic neuron systems in the brains of methylazoxymethanol acetate (MAM)-induced micrencephalic rats were studied. Neurochemical analysis revealed high levels of serotonin, norepinephrine and associated metabolites in several brain areas of MAM-treated rats. In particular, serotonin levels in the frontal cortex, cingulate cortex and hippocampus of 12-month-old (12 M) MAM-treated rats were significantly higher than in corresponding age-matched controls. Immunohistochemical analysis demonstrated numerous aberrant serotonin-immunoreactive fibers and small numbers of aberrant tyrosine hydroxylase-immunoreactive fibers in the septum, caudate putamen, thalamus, cerebral cortex, hippocampus and midbrain tegmentum of 12 M MAM-treated rats. Aberrant monoaminergic fibers characterized by swollen varicosities and thickening of intervaricose segments were common compared to 12 M control rats. In the cortex and hippocampus of 12 M MAM-treated rats, aberrant fibers were observed near cortical heterotopic tissue. These results indicate early onset of age-related degeneration of monoaminergic fibers in micrencephalic rats. Aged MAM-treated rats may thus offer a good model for studying age-related monoaminergic changes in the cortical heterotopic tissue of human cortical malformations.

Interictal and ictal activity in the rat cobalt/pilocarpine model of epilepsy decreased by local perfusion of diazepam

We investigated the efficacy of focal perfusion of diazepam (DZP) in reducing seizures produced by focal cobalt and systemic pilocarpine in the rat. Cobalt chloride crystals (3.5 mg/kg) were inserted stereotactically into the left hippocampus and recording electrodes affixed to the head of 23 rats. Focal spiking was evident within 5-7 days of implantation. Occasional ictal electrographic events were observed with cobalt alone, but consistent ictal events could be produced by intraperitoneal injection of pilocarpine hydrochloride (60 mg/kg) into the cobalt-treated animals. When rhythmical spiking was observed, the animals were treated either with DZP (0.25 mg in 50 microliters) or a vehicle (VEH) delivered into the left hippocampus. Blinded spike counts before and after injection showed spiking at 133.3 +/- 53.4% of baseline (mean +/- SD, n = 8) for the VEH-treated animals and 2.7 +/- 3.3% (n = 8) for the DZP-treated animals. Ictal events occurred in seven of the eight VEH-treated and two of the eight DZP-treated rats. Mean time to the first ictal event was 5.9 +/- 6.9 min for VEH-treated animals and 24 +/- 32.6 min for DZP-treated animals. DZP injected into the hippocampus contralateral to the cobalt did not reduce spiking. Systemic levels of DZP were unmeasurable in nine of ten tested animals. Focal perfusion of DZP therefore effectively reduced spiking in this cobalt chloride/pilocarpine model of focal and secondarily generalized epilepsy. This model, while involving GABAergic mechanisms, does not entirely depend upon GABAergic mechanisms. The findings therefore broaden the possibility of using focal DZP as a treatment for partial seizures.

Nuclear polyadenylate polymerase activity in the brain of seizure-prone EL mice

Nuclear polyadenylate polymerase from I activity in the brains of seizure-prone EL mice was significantly higher than in seizure-non-susceptible progenitor ddY mice. This finding may be essential in acquiring susceptibility to seizures, since there was no significant difference between EL(S) mice and those that did not receive stimulation, EL(NS) mice. Lower form II enzymatic activity was observed in both groups of EL mice but not in ddY mice. Moreover, significantly lower activities of form II 7 days after seizures were found in EL(S) mice compared with EL(NS) mice, suggesting that this is a consequence of repeated seizures. The activity of form I enzyme decreased immediately and at 30 and 60 min after seizures, then returned to control levels at 100 min. Form II enzymatic activity was significantly decreased only at 30 min after seizures, implying that seizures exerted a later effect on form II enzyme. These changes may cause a decrease in the rate of polyadenylation in the brain; thus, alteration of post-transcriptional events, including messenger RNA processing and transport, may occur during epileptic seizures.

The serotonergic innervation of the cerebral cortex in man and its changes in focal cortical dysplasia

We present the morphology and the laminar distribution of the serotonin (5-hydroxytryptamine, 5-HT) innervation of the cerebral cortex of patients who underwent cortical resection for partial seizures. The limits of the resections were established by stereoelectroencephalography. The 5-HT innervation was mapped by using an antiserum anti-5-HT. Two patients had cryptogenic epilepsies and two others had seizures related to focal cortical dysplasia. 5-HT immunoreactive axons were morphologically heterogeneous and projected diffusely to the cerebral cortex with regional-specific densities. Two types of terminal axon were demonstrated. Type I had large and spherical (intensely immunoreactive) varicosities and was distributed sparsely with a characteristic predominance in the molecular layer. Type II had fine and pleiomorphic varicosities (granular or fusiform) and was distributed through all cortical layers. The distribution of the 5-HT innervation varied according to the different architectonic areas investigated. The granular cortical areas characterized by a highly developed layer IV (primary somatosensory, primary visual and prefrontal cortices) had the highest density of 5-HT-ir fibers distributed from layer I to layer V. The agranular primary motor cortex had the lowest density with fibers preferentially seen in layers I, IIIa and V-VI. The orbital cortex with a poorly defined layer IV had an intermediate density with a laminar repartition predominant in the supragranular layers. In patients with cryptogenic epilepsies, the brain epileptogenic tissue was histologically normal as well as the serotonergic innervation. In contrast, in patients with focal cortical dysplasia, the dysplastic epileptogenic tissue was characterized by a serotonergic hyperinnervation. In agreement with previous data in primates, we give morphological evidence for two morphologically distinct serotonergic subsystems and for regional specific densities in the human cerebral cortex. Moreover, we previously reported an altered pattern of the catecholaminergic innervation in the same dysplasia areas. All these results provide evidence that this development epileptogenic lesion involves several sets of neurons which may contribute to epileptogenic activity.

Locus coeruleus noradrenaline system and focal penicillin hippocampal epilepsy: neurophysiological study

Previous experimental investigations have shown that several neuronal systems modulate the spontaneous and paroxysmal electric activity of the hippocampus. The locus coeruleus-noradrenaline (LC-NA) system exerts an inhibitory influence on several brain areas including the ipsilateral hippocampus. Selective destruction of the LC increases the susceptibility to epileptiform phenomena in different models of experimental epilepsy. Our experiments were conducted on 34 rats in which a steady epileptiform interictal activity of the hippocampus was obtained by means of intrahippocampal administration of penicillin. Electrical stimulation of LC caused a significant decrease of penicillin spiking of hippocampus. Stimulation sessions given 10-15 min after i.p. propranolol administration (2 mg/kg) failed to induce any significant modification in the hippocampal spiking frequency. Intrahippocampal injection of L-noradrenaline mimicked the inhibitory effect of LC electrical stimulation on hippocampus. Finally, intrahippocampal administration of isoproterenol HCl, a beta-adrenoceptor agonist, caused a significant decrease of hippocampal penicillin spiking; this effect was antagonised by i.p. propranolol administration. The experimental data show a modulating influence of the LC-NA system on penicillin focal hippocampal epilepsy that probably involves beta-adrenoceptors.

High expression of noradrenaline, choline acetyltransferase and glial fibrillary acidic protein in the epileptic focus consecutive to GABA withdrawal. An immunocytochemical study

Interruption of a chronic GABA infusion into the rat somatosensory cortex induces the appearance of focal epileptic manifestations, known as the 'GABA withdrawal syndrome' (GWS). The aim of the present study was to determine, by immunocytochemistry, if neurotransmitters other than GABA are involved in GWS, namely: noradrenaline (NA), serotonin, choline acetyltransferase (CAT), cholecystokinin, neuropeptide Y, somatostatin and glial fibrillary acid protein (GFAP). Immunocytochemical data were compared in three animal groups: GABA-, saline- and L-aspartate (L-Asp)-infused rats. Only GABA-infused rats presented epileptic manifestations after interruption of the infusion. Saline- and L-Asp-infused rats served as controls. Observations were limited to the region surrounding the cortical infusion site. GABA-infused rats showed in the zone of the epileptic focus a number of cell bodies strongly immunoreactive to NA antibodies much larger than control rats. In addition, NA-immunoreactive fibers formed a dense plexus and some of them were observed around perikarya. In saline- and L-Asp-infused rats, the NA-immunolabelled fibers were sparse and NA immunolabelling was rarely observed in cell bodies. These results contrast to those obtained for the serotonergic system, where no significant difference was observed among the three groups of rats. CAT immunolabelling was observed in cell bodies, but not in nerve terminals in rats of the three groups. The number of CAT-immunoreactive cell bodies was much greater in GABA-infused rats than in the control animals. GFAP immunolabelling showed an important number of astrocytes throughout the cortex of the GABA-infused hemisphere, whereas, astrocytic reaction was limited to the infusion site in controls. Immunocytochemical data concerning peptides revealed cortical neuronal elements labelled similarly in the three groups of rats. Noradrenergic, cholinergic and glial modifications observed mainly in GABA-infused rats can result from lesion and from a specific action of GABA in chronic infusion. These modifications may contribute to the epileptogenesis of GWS, as recently demonstrated by electrophysiological recordings that show a modulating action of NA on firing activity of neurons involved in the epileptic focus.

Anticonvulsant activity of the noradrenergic locus coeruleus system: role of beta mediation

Many experimental observations have demonstrated the modulatory role exerted by several neural structures and neurotransmitters on spontaneous and paroxysmal bioelectric activity of the hippocampus. Recently, the control exerted by locus coeruleus (LC) and its noradrenergic (NA) efferent pathway on different experimental models of epilepsy (e.g. cortical cobalt chronic epilepsy, amygdaloid and hippocampal kindling) was emphasised. On this basis, a series of experiments was performed to elucidate the functional role of LC-NA system on the hippocampal penicillin (PCN) focus and the type of adrenergic receptor involved. The experiments were carried out on 25 rats in which an epileptiform hippocampal focus was obtained through intrahippocampal PCN administration (100-200 I.U.). In these conditions, LC, ipsilateral to PCN hippocampal focus, was stimulated before and after intraperitoneal (i.p.) administration of a beta-adrenergic receptor antagonist propranolol (2 mg/kg). Results showed a significant reduction of hippocampal spiking frequency during LC stimulation; after i.p. propranolol injection, LC stimulation, at the same parameters, failed to induce any sort of modification of PCN hippocampal spiking frequency. Furthermore, intrahippocampal application of a beta-selective agonist 2-fluoro-noradrenaline (2-FNA) mimics the inhibitory effects of LC stimulation. All data suggest that the LC-NA system is able to induce a net reduction of hippocampal epileptiform focus and the inhibitory NA control involves the activation of adrenergic beta receptors.

Genetic and phenotypic heterogeneity of inherited spike-wave epilepsy: two mutant gene loci with independent cerebral excitability defects

Two recessive gene loci controlling cerebral excitability in the mouse (tg, chr 8 and stg, chr 15) share generalized neocortical spike-wave seizures as a common mutant phenotype. Although the primary molecular defects are unknown, homozygous tg mutants display a gene-linked hyperplasia of central noradrenergic axons originating in the locus ceruleus, and early selective lesions of these fibers correct the epileptic phenotype in the adult. In contrast, we find that stg homozygotes, despite a more severe seizure disorder, show no alterations in regional noradrenergic fiber innervation, and seizure frequency is unaffected by neonatal noradrenergic depletion. These mutations demonstrate that excessive synchronous neuronal discharges alone are insufficient to trigger abnormal growth of locus ceruleus fibers, and reveal the existence of two distinct intervening brain neuromodulatory mechanisms, norepinephrine (NE)-dependent and NE-independent, underlying the inheritance of this common pattern of epilepsy.

Regional difference in responsiveness of norepinephrine-sensitive cyclic AMP-generating systems of rat cerebral cortex with iron-induced epileptic activity

Responsiveness of norepinephrine (NE)-sensitive cyclic AMP (cAMP)-generating systems was determined in slices from different areas of the rat cerebral cortex in which FeCl2 solution was injected unilaterally into the sensorimotor cortex to induce epileptic activity. In anterior cortical areas of rats in which the appearance of electrographic isolated spikes was dominant either ipsilaterally or contralaterally to the injection site 8-10 days after the injection, the cAMP accumulations elicited by NE and an NE-phentolamine combination were greater on the side of dominant spike activity than on the other. In anterior cortical areas of rats showing dominant spike activity on either side of the cortex 31-60 days after the injection, the cAMP accumulation elicited by NE was smaller on the dominant side than on the other. In anterior cortical areas of rats showing nearly equal spike activity on the two sides 31-60 days after the injection, the cAMP accumulations elicited by NE and an NE-phentolamine combination were greater on the side ipsilateral to the injection site than on the other. In anterior and posterior cortical areas of rats in which the appearance of spike and wave complexes, as well as isolated spikes, was detected 31-60 days after the injection, the cAMP accumulations elicited by NE and combinations of NE and phentolamine or propranolol were greater on the side ipsilateral to the injection site than on the other. The elicitation by an NE-propranolol combination, but not by an NE-phentolamine combination, of cAMP accumulation was almost completely inhibited by 8-phenyltheophylline.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipid peroxidation and glutathione peroxidase, glutathione reductase, superoxide dismutase, catalase, and glucose-6-phosphate dehydrogenase activities in FeCl3-induced epileptogenic foci in the rat brain

This study investigated the relationship between lipid peroxidation, subsequent activation of antioxidative enzymes, and development of iron-induced epilepsy in the rat. Epileptic foci were produced in rat cerebral cortex by intracortical injection of ferric chloride (FeCl3). The epileptic foci were identified by electrocorticography (ECoG). Epileptiform ECoG activity was shown to occur in the contralateral homotopic cerebral cortex as well. We measured levels of lipid peroxides and changes in the activities of the enzymes: superoxide dismutase (SOD), glutathione peroxidase (GP), glutathione reductase (GR), catalase (CA), and glucose-6-phosphate dehydrogenase (G6P) in the epileptogenic focus (both ipsilateral and contralateral) at days 3, 8, 15, and 23 after FeCl3 injection. Biochemical estimations were made in subcellular fractions, and changes in the ipsilateral site were compared with those in the contralateral site. The results of this study showed that large increases in lipid peroxidation were associated with development and buildup of the ECoG epileptiform discharges. Lipid peroxides increased in the ipsilateral focus by approximately 100% as compared with control. In the contralateral site, however, the increase in lipid peroxides was marginal only. The increase in lipid peroxidation was concomitant with development of the high level of epileptiform activity. The time course of changes in lipid peroxidation paralleled the time course of development and persistence of the epileptiform activity. Regarding changes in the enzyme activities accompanying development of iron epilepsy, the data showed that although SOD and G6P increased by approximately 60% and GR increased by approximately 40%, the increases in the enzyme GP and CA were much lower, less than 20%. Thus, comparatively less increase in CA and GP activities produces a deficiency of these two enzymes in the iron (ipsilateral) focus. Among the various biochemical disturbances that have been identified as involved in epileptogenesis, peroxidative injury resulting from lipid peroxidation in neural plasma membrane may be causally related to development of paroxysmal epileptiform activity in the iron focus. Since GP is an enzyme of major importance in detoxification of lipid peroxides in the brain, based on the results presented in this article, it appears reasonable to suggest that GP deficiency causes lipid peroxidation to increase tremendously during iron epileptogenesis.

Facilitation of focal cobalt-induced epilepsy after lesions of the noradrenergic locus coeruleus system

In this study we analyzed the electrophysiological and clinical effects of selective removal of the forebrain noradrenergic projection from the locus coeruleus, induced by bilateral injections of 6-hydroxydopamine into the dorsal tegmental bundle on focal cobalt-induced epilepsy. Noradrenaline depletion caused a marked potentiation of the epilepsy by increasing the duration and intensity of both the clinical and electrophysiological epileptic parameters: epileptic discharges and myoclonic jerks started earlier; spiking and clinical activity were facilitated; duration of the epileptic syndrome was prolonged. On the basis of the present and previous results it is proposed that the ascending noradrenergic system plays a modulatory role on the spread of paroxysmal activities and on the severity of cobalt-induced epilepsy.

Levels of catechols in epileptogenic and nonepileptogenic regions of the human brain

Recent reports about tyrosine hydroxylase and alpha 1-adrenoceptors in epileptic foci have suggested increased regional catecholaminergic activity, which may serve a compensatory, inhibitory role. We measured levels of catechols, including the precursor 3,4-dihydroxyphenylalanine (DOPA) and the catecholamines dopamine (DA) and norepinephrine (NE), in surgically removed foci identified by electrocorticography and in nonepileptogenic sites from 23 patients with intractable temporal lobe epilepsy. The following values (mean +/- 1 SD) were obtained: DOPA = 142 +/- 60 ng/g of protein in the focus vs. 115 +/- 39 ng/g in the nonfocus (p less than 0.01); DA = 168 +/- 85 vs. 106 +/- 54 ng/g (p less than 0.001); and NE = 267 +/- 117 vs. 181 +/- 80 ng/g (p less than 0.001). The results are consistent with increased catecholaminergic activity in epileptic foci.

Impairment of the cortical and thalamic electrical activity in scrapie-infected rats

Cortical and thalamic EEG and somatosensory evoked potential (SEP) induced by stimulation of the somesthetic radiations were studied in scrapie-infected rats. Animals were inoculated intracerebrally with a rat-adapted strain (originating in the C506 M3 mouse scrapie strain). EEG and SEP were recorded from 9 to 17 months after inoculation (ti). Abnormalities (paroxysmal bursts, isolated spikes) first occurred in the cortex (parietal areas) and later in the thalamus, where they were usually less marked. Latencies of the postsynaptic components of the SEP increased at ti + 9 months. This effect became progressively more pronounced and at ti + 15 months, latencies of presynaptic components were also delayed. Nevertheless, marked alteration of the SEP occurred only at the terminal stage of the disease. These findings show that the scrapie-induced disturbances affect more especially the cortex. Decrease of inhibitory processes as well as electronic coupling between cells, resulting from the virus-induced membrane fusion, could produce paroxysmal activity of EEG and SEP impairments.

Decreased GABA, benzodiazepine, and picrotoxinin receptor binding in brains of rats after cobalt-induced epilepsy

In previous studies of experimental and human epilepsy, defects have been shown in the gamma-aminobutyric acid (GABA) receptors. We further investigated the role of the GABA/benzodiazepine/picrotoxinin receptor complex in the epileptic focus and also in other regions of the rat brain. The focus was induced by cobalt implantation to the right motor cortex, and the brains were dissected 16-19 days after the operation. Benzodiazepine (using [3H]flunitrazepam as a ligand; FLU), GABA [3H]muscimol; MUS), and picrotoxinin [( 35S]t-butylbicyclophosphorothionate; TBPS) receptor bindings were measured in different brain areas and the values were compared with glass-implanted controls. In the focal area, the specific receptor binding decreased in the order TBPS greater than FLU greater than MUS. In the perifocal area only TBPS binding decreased, and Scatchard analysis showed a decrease in the number of binding sites (p less than 0.05) without any effect on binding affinity. No change was seen in the binding characteristics of the other areas studied. According to our results, in cobalt-induced epilepsy the GABA/benzodiazepine/picrotoxinin receptor complex is modulated in the focal area; this may lead to a defect in chloride conductance, which in turn induces disturbed control of neuronal activity in the epileptic focus.

Convulsive activity of alpha-guanidinoglutaric acid and the possible involvement of 5-hydroxytryptamine in the alpha-guanidinoglutaric acid-induced seizure mechanism

alpha-Guanidinoglutaric acid (alpha-GGA) was first found in cobalt-induced epileptogenic focus tissue in the cerebral cortex of cats. We examined the effect of alpha-GGA on the electroencephalogram and on the brain 5-hydroxytryptamine (5-HT) level after intraventricular administration into rats. Sporadic low-voltage spikes appeared 4 min after the administration of alpha-GGA. Spikes increased in voltage 6 min after the administration. Multiple spikes appeared 10 min after the administration, and they reached maximal frequency 30 min after the administration. The epileptic discharges disappeared 100 min after the administration. The 5-HT level increased in the right and left cortices 3 min after the administration. The 5-HT level decreased in the mid-brain 5 min after the administration and subsequently in all regions of the brain 10 min after the administration. No change in the 5-HT level was found 30 min and 100 min after the administration. These results show that alpha-GGA induces epileptic seizures in rats after intraventricular administration. The results also suggest that alpha-GGA-induced seizures are associated with abnormal serotonergic function and that they are initiated by a decrease in the 5-HT level.

Alpha-1 adrenoceptors are decreased in human epileptic foci

Cortical alpha-1 adrenoceptors were measured in tissues obtained from 10 patients immediately following temporal lobectomy for intractable partial epilepsy. At operation each patient exhibited spontaneous spiking restricted to either the anterior (n = 5) or posterior (n = 5) portion of the first two temporal gyri. Control samples were obtained from the nonspiking half of the same gyrus. Receptor-binding assays were performed on isolated cortical membranes using [3H]prazosin. There was a reduction (p less than 0.01) in the receptor density (beta max) of the sites in the epileptic foci without any change in affinity (mean +/- SEM): spiking--beta max, 160.5 +/- 11.3 fmol/mg protein; affinity, 0.17 +/- 0.04 nM; nonspiking--beta max, 218.8 +/- 15.6 fmol/mg protein; affinity 0.17 +/- 0.04 nM. This relative decrease in alpha-1 adrenoceptor density may be the substratum of a noradrenergic hyposensitivity that could contribute to a localized diminution in inhibitory mechanisms in epileptic foci.

Neurochemical studies on the existence, origin and characteristics of the serotonergic innervation of small pial vessels

Substantial concentrations of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA), comparable to those found in brain tissue, were measured in the small pial vessels of the rat, rabbit and cat. Both rat and rabbit pial vessels exhibited a high affinity uptake process with kinetic parameters similar to those identified for the cerebral cortex. Labelled 5-HT, taken up by isolated rabbit pial vessels was released, in a calcium-dependent manner, by potassium-induced depolarization. Various pharmacological manipulations were carried out in the rat. Systemic administration of the 5-HT precursor, 5-hydroxytryptophan and the monoamine oxidase inhibitor, pargyline, significantly increased the concentration of 5-HT in the pial vessels; in contrast, two depleting agents (p-chloroamphetamine and reserpine) and the tryptophan hydroxylase inhibitor, p-chlorophenylalanine, all decreased the perivascular 5-HT levels. A serotonergic antagonist (methysergide) and a 5-HT receptor agonist (MK 212) respectively increased and decreased the concentrations of 5-HIAA in the pial vessels. These pharmacologically induced changes observed in pial vessels were not dissimilar from those noted for cortical tissue. Electrolytic lesions of the nuclei raphes medianus and/or dorsalis markedly decreased the levels of 5-HT and 5-HIAA in these small cerebral arterioles. Electrical stimulation of these nuclei decreased 5-HT although 5-HIAA concentrations tended to increase. A number of conclusions may be drawn from these studies. Thus, there is a serotonergic innervation of the cerebral circulation in several laboratory species which unequivocally originates in the raphé nuclei. Furthermore, these perivascular fibres possess synthetic, storage, release, inactivation and autoregulatory processes for 5-HT which, when further elucidated, may offer some rationale for the treatment of those cerebrovascular diseases in which this neurotransmitter and vasoactive agent is believed to be of pathological importance.

Monoamine abnormalities in the brain of scrapie-infected rats

The effects of the scrapie agent on the levels of monoamines and their metabolites, and on choline acetyltransferase (CAT) activity have been investigated in discrete brain areas in the rat. Two strains of scrapie (8745 from sheep brain and C506 M3 from mice brain) were inoculated. Scrapie-infected rats showed a reduction in the levels of serotonin (prefrontal cortex, hippocampus, striatum) and dopamine (striatum) and an elevation of 5-HIAA levels (cerebral cortex, striatum, thalamus). Noradrenaline levels were decreased only in the cerebral cortex and cerebellum of rats infected with the scrapie strain C506 M3. CAT activity remained unchanged. These data suggest that the scrapie agent causes a derangement of noradrenergic, serotonergic and dopaminergic systems in the rat brain.