Activity of alpha and gamma extensor motor axons during metrazol-induced seizures in cat

Efferent discharges were recorded in nerves to extensor and flexor muscles simultaneously with EEG of contralateral motor area during Metrazol-induced seizures in anesthetized and curarized cats. Extensor motoneurons are much less active than flexors during typical EEG seizures. Unlike the flexor neurons α and γ extensor motoneurons are activated separately, without clear temporal relation between their discharges and electrocortical symptoms. Fusimotor activity of extensors increases only after the end of the cortical seizure. Convulsive activation of α and γ extensor motoneurons is often stronger in the absence of EEG paroxysmal waves than during a seizure. These observations suggest that convulsive activity of extensor motoneurons is not directly dependent on epileptic phenomena occurring in the motor cortex and extensor activation seems more likely connected to extrapyramidal projections of the epileptic process.     

Susceptibility to seizures produced by pilocarpine in rats after microinjection of isonnazid or γ-vinyl-GABA into the substantia nigra

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 γ-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 μg, an inhibitor of activity of the GABA-synthesizing enzyme, l-glutamic acid decar☐ylase, 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 transminase, γ-vinyl-GABA (d, l,-4-amino-hex-5-enoic acid), 5 μg, 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 γ-vinyl-GABA, 5 μg, 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.     

Distribution and density of contacts from noradrenergic and serotonergic boutons on the dendrites of neck flexor motoneurons in the adult cat

Serotonergic (5‐HT) and noradrenergic (NA) input to spinal motoneurons is essential for generating plateau potentials and self‐sustained discharges. Extensor motoneurons are densely innervated by 5‐HT and NA synapses and have robust plateau potentials and self‐sustained discharges. Conversely, plateau potentials and self‐sustained discharges are very rare in flexor motoneurons. The most likely reasons for this difference are that flexor motoneurons have few 5‐HT and NA synapses and/or they are distributed distant to the channels responsible for plateau potentials and self‐sustained discharges. However, the distribution of 5‐HT and NA synapses on flexor motoneurons is unknown. Here we describe the distribution and density of 5‐HT and NA synapses on motoneurons that innervate the flexor neck muscle, rectus capitis anterior (RCA), in the adult cat. Using a combination of intracellular staining, fluorescent immunohistochemistry, and 3D reconstruction techniques, we found that 5‐HT and NA synapses are widely distributed throughout the dendritic trees of RCA motoneurons, albeit with a strong bias to small‐diameter dendrites and to medial dendrites in the case of NA contacts. The number of 5‐HT and NA contacts per motoneuron ranged, respectively, from 381 to 1,430 and from 642 to 1,382, which is 2.3‐ and 1.4‐fold less than neck extensor motoneurons (Montague et al., J Comp Neurol 2013;521:638–656). These results suggest that 5‐HT and NA synapses on flexor motoneurons may provide a powerful means of amplifying synaptic currents without incurring plateau potentials or self‐sustained discharges. This feature is well suited to meet the biomechanical demands imposed on flexor muscles during different motor tasks. J. Comp. Neurol. 523:1701–1716, 2015. © 2015 Wiley Periodicals, Inc.     

Quasi-reversible Photo-axotomy Used to Investigate the Role of Extensor Muscle Tension in Controlling the Kick Motor Programme of Grasshoppers

The jump and kick of the grasshopper are behaviours which are potentially critical for the survival of the animal, and whose maximal Performance depends upon optimizing the rate and level of tension development in the extensor tibiae muscle of the hind legs. In experimental conditions extensor tension control can be reduced to a single motoneuron, the fast extensor tibiae (FETi). The axon of FETi can be cut using dye-mediated laser photo- axotomy without damaging the central or peripheral portions of that neuron or any other neuron innervating the leg. The axotomy can be functionally reversed (i.e. the cut axon repaired) by an electronic axonal bypass which detects FETi spikes on the proximal side of the cut and stimulates the axon on the distal side of the cut. In this way motor spikes can either be allowed to reach the muscle or prevented from doing so (by switching the bypass on or off), and the motor programmes produced with and without extensor tension can be compared. The jump and kick are normally produced by a three-stage motor programme: (i) initial flexion brings the tibia into the fully flexed position; (ii) coactivation of extensor and flexor muscles allows the extensor muscle to develop maximal tension almost isometrically, while the simultaneous contraction of the flexor muscle holds the tibia flexed; (iii) sudden trigger inhibition of the flexor system (motoneurons and muscle) releases the tibia and allows the behaviour to be expressed. The grasshopper can produce fictive kicks with motor programmes which show each of these three major structural features of a normal kick, but without any extensor tension whatsoever. There is no significant difference in the frequency of FETi spikes, the duration of coactivation or the maximum depolarization of the flexor motoneurons between fictive and quasi-normal (i.e. reversed axotomy) kicks. The trigger inhibition of flexor motoneurons is shallower in fictive than in quasi-normal kicks. The significance of this is discussed in relation to the activity of the interneuron M, which is known to mediate trigger inhibition onto FlTi motoneurons. There are two main conclusions from this study. First, the CNS does not need feedback from ETi muscle tension in order to produce the three-stage motor programme of the kick (and, by implication, the jump). Second, the CNS does not adjust the frequency or duration of FETi activity in response to unexpected changes in ETi tension. ETi tension appears to be under open-loop control in the kick motor programme.     

Epileptiform EEG activities of the centromedian thalamic nuclei in patients with intractable partial motor, complex partial, and generalized seizures

Centromedian thalamic nuclei (CM) epileptiform EEG activities were recorded in patients with intractable partial motor, complex partial, and generalized seizures through implanted recording-stimulating electrodes, used for seizure control. CM epileptiform activities showed either little or no correlation to focal surface cortical and amygdaloid activities in patients with partial motor and complex partial seizures: CM paroxysmal discharges were correlated to focal epileptiform ictal activities only during the contraversive movements of partial motor and complex partial seizures. In contrast, CM epileptiform activities were consistently correlated to widespread surface cortical activities and clinical symptoms of fully developed nonconvulsive and convulsive tonic-clonic generalized seizures; i.e., unilateral CM double spike-wave complex discharges significantly preceded (p less than 0.001) the contralateral CM and bilateral surface cortical discharges and symptoms of nonconvulsive generalized seizures. Unilateral CM fast-slow-fast paroxysmal discharges significantly preceded (p less than 0.005) those of the contralateral CM and bilateral surface cortical regions and symptoms of the convulsive tonic-clonic generalized seizures. Individual spike-wave complexes from the frontal region preceded (p less than 0.001 and p less than 0.005) those at CM and other cortical regions during the nonconvulsive and clonic generalized attacks. No correlations between CM and cortical epileptiform activities were found, however, in the case of abortive, subclinical thalamocortical EEG discharges.     

Generalized Convulsive Status Epilepticus in the Adult

Summary: Status epilepticus (SE) is denned as recurrent epileptic seizures without full recovery of consciousness before the next seizure begins, or more-or-less continuous clinical and/or electrical seizure activity lasting for more than 30 min whether or not consciousness is impaired. Three presentations of SE are now recognized: recurrent generalized tonic and/or clonic seizures without full recovery of consciousness between attacks, nonconvulsive status where the patient appears to be in a prolonged "epileptic twilight state," and continuous/repetitive focal seizure activity without alteration of consciousness. Generalized convulsive status epilepticus (GCSE) encompasses a broad spectrum of clinical presentations from repeated overt generalized tonic-clonic seizures to subtle convulsive movements in a profoundly comatose patient. Thus, GCSE is a dynamic state that is characterized by paroxysmal or continuous tonic and/or clonic motor activity, which may be symmetrical or asymmetrical and overt or subtle but which is associated with a marked impairment of consciousness and with bilateral (although frequently asymmetrical) ictal discharges on the EEG. Just as there is a progression from overt to increasingly subtle clinical manifestations of GCSE, there is also a predictable sequence of progressive EEG changes during untreated GCSE. A sequence of five patterns of ictal discharges has been observed: discrete electrographic seizures, waxing and waning, continuous, continuous with flat periods, and periodic epileptiform discharges on a relatively flat background. A patient actively having seizures or comatose who exhibits any of these patterns on EEG should be considered to be in GCSE and should be treated aggressively to stop all clinical and electrical seizure activity to prevent further neurological morbidity and mortality.     

Efferent Pattern of Fictive Locomotion in the Cat Forelimb: with Special Reference to Radial Motor Nuclei

In immobilized decerebrate cats fictive locomotion was evoked by midbrain stimulation to analyse the efferent pattern to elbow and to distal forelimb muscles innervated by the deep radial nerve. The locomotor activity was assessed by recording nerve discharges and motoneuronal membrane potential changes. The elbow flexor and extensor motoneurons showed a reciprocal activity; the membranes were correspondingly depolarized and hyperpolarized. In the motor nuclei to the wrist and digit extensors the active phases changed systematically according to the radio-ulnar order of the muscles: the extensor carpi radialis (ECR) was flexor-coupled, the ulnaris (ECU) extensor-coupled, the digitorum communis (EDC), the lateralis (EDL) and the indicis proprius (EIP) displayed intermediate patterns. Intracellular recordings from these motoneurons revealed in all motor nuclei, except ECR, a double depolarization. The first occurred early and the second later in the flexor phase; a hyperpolarization was interposed. The second depolarization mainly determined the active phase. According to the radio-ulnar order of the muscles the onset and termination of the second depolarization were delayed. This was presumably due to the interposed hyperpolarization, which progressively increased in amplitude. The ECR exhibited a single depolarization, into which the double depolarization apparently merged. The other radial motor nuclei, supinator (Sup) and Abductor pollicis longus (APL) displayed complex patterns. Sup showed tonic discharges, flexor-type discharges or discharges extending both into the flexor and extensor phase, APL showed discharges similar to either EIP or Sup. Membrane potential changes were small in APL and Sup. Thus, the central locomotor network generates differentiated efferent activities in the distal forelimb muscles, the radio-ulnar order of the muscles being important for the generated pattern.     

Cingulate Kindling in Senegalese Baboons,Papio papio

Summary: Kindling of the cingulate cortex in the Senegalese baboon Papio papio led to a protracted nonconvulsive seizure state characterized by immobile staring with (anterior cingulate, AC) or without (posterior cingulate, PC) widening of eyelids and neck flexion, followed by postictal visual searching behavior. Despite early bilateral spread of EEG discharges, ictal and interictal patterns remained persistently asymmetric. Secondary generalization was rapid and predictable once contralateral lower facial twitching associated with sustained adversion developed. After the primary site had been kindled, stimulation of the contralateral homotopic posterior cingulate cortex readily produced afterdischarge. However, it remained localized and kindling growth did not occur. The findings suggest that (a) the cingulate cortex can support nonconvulsive seizures; (b) cingulate seizures are accompanied by asymmetric convexity EEG discharges indicating its lateralized onset; (c) further evolution to convulsive seizures after kindling of cingulate cortex requires access to the ipsilateral frontocentral cortex responsible for facial twitching; and (d) the development of focal epileptogenesis at one cingulate site interferes with clinical seizure development at the homotopic contralateral site.     

Involvement of Proprioceptive Feedback in Brainstem-Triggered Convulsions

Summary: Purpose : In rodents, specific motor components of generalized convulsive seizures depend on two distinct anatomic substrates: (a) forebrain networks are responsible for facial and forelimb clonus with or without rearing and falling; and (b) brainstem networks are responsible for running-bouncing fits and tonic convulsions. To investigate the requirement of proprioceptive inputs in the generation of these two different types of seizures, we compared the effects of neuromuscular blockade by D-tubocurarine on the EEG expression of brainstem and forebrain-triggered seizures.
Methods : Unilateral electrical stimulations were applied for 50 consecutive days in freely moving male adult rats through a bipolar electrode aimed at the dorsal hippocampus (n = S), the occipital cortex (n = 4), the inferior colliculus (n = 6), or the midbrain reticular formation (n = 6). Two days after the last stimulation, rats were paralyzed with d-tubocurarine and stimulated in the same way.
Results : In brainstem structures, the first electrical stimulation induced tonic seizures concomitant with low-voltage cortical activity; repetition of daily stimulations progressively induced tonic-clonic seizures associated with high-amplitude cortical spike-wave discharges. After immobilization by d-tubocurarine, brainstem stimulations failed to induce any EEG paroxysm. In forebrain structures, repeated electrical stimulations produced a classic kindling with progressive occurrence of clonic seizures associated with large cortical discharges; d-tubocurarine left unchanged the EEG pattern of these latter seizures.
Conclusions : These data suggest that proprioceptive reafferentation resulting from movement is necessary for the generation of self-sustained brainstem seizures but is not implicated in the elaboration of forebrain seizures.     

Fast epileptic discharges associated with ictal negative motor phenomena

ObjectiveFocal motor negative phenomena have been described in seizures primarily involving “negative” motor areas (opercular pre-motor and medial pre-motor regions) and the rolandic region (post-central or pre-central). The localizing value of such signs and the mechanisms by which an epileptic discharge may generate negative phenomena remain debated.MethodsIctal positive and negative motor phenomena occurring during seizures affecting the rolandic area were studied in a patient having intracerebral recordings (stereo-electro-encephalography, SEEG) for drug resistant epilepsy.ResultsDuring the video-SEEG and EMG recording, nine positive and 27 negative motor seizures were recorded. All were generated within the same area (right opercular central area, Brodmann Area 4). The 2 different types of clinical seizure were differentiable by their power/frequency spectrum: positive motor seizures were associated with a prominent alpha–beta band discharge while negative motor seizures were associated with a gamma band discharge (>45 Hz).ConclusionsWe propose that within the primary motor cortex, high frequency sustained discharges may disrupt the ongoing excitatory drive to the peripheral motoneurons and produce negative motor signs, while sustained lower frequency discharges (alpha and beta bands) may activate the cortico-nuclear or cortico-spinal pathway and produce positive motor signs.SignificanceBoth positive and negative ictal motor phenomena can be observed in the primary motor cortex depending on the properties of the epileptic discharge.     

Selective susceptibility to inhibitors of GABA synthesis and antagonists of GABA(A) receptor in rats with genetic absence epilepsy

Thalamocortical spike-and-wave discharges characterize the nonconvulsive absence seizures that occur spontaneously in genetic absence epilepsy rats from Strasbourg (GAERS), a selected strain of Wistar rats. GABA is crucial in the generation of absence seizures. The susceptibility to convulsions induced by threshold doses of various GABA receptor antagonists and inhibitors of GABA synthesis, kainic acid and strychnine, was compared in GAERS and in nonepileptic rats from a selected control strain (NE). The brain structures involved in the drug-elicited convulsive seizures were mapped by c-Fos immunohistochemistry. Injection of various antagonists of the GABA(A) receptor, bicuculline and picrotoxin, and inverse agonists of the benzodiazepine site (FG 7142 and DMCM) induced myoclonic spike-and-wave discharges followed by clonic or tonic-clonic seizures with high paroxysmal activity on the cortical EEG. The incidence of the convulsions was dose-dependent and was higher in GAERS than in NE rats. Mapping of c-Fos expression showed that the frontoparietal cortex was constantly involved in the convulsive seizures elicited by a threshold convulsant dose, whereas limbic participation was variable. In contrast, GAERS were less susceptible than NE rats to the tonic-clonic convulsions induced by the inhibitors of glutamate decarboxylase, isoniazide and 3-mercaptopropionic acid. The GABA(B) receptor antagonist CGP 56999 and kainic acid induced a similar incidence of seizures in GAERS and NE rats and predominantly activated the hippocampus. No difference in the tonic seizures elicited by strychnine could be evidenced between the strains. These results suggest that an abnormal cortical GABAergic activity may underlie absence seizures in GAERS.     

Acute effects of gamma-vinyl-GABA on low-magnesium evoked epileptiform activity in vitro

Vigabatrin (γ-vinyl-GABA, VGB) is a γ-aminobutyric acid (GABA) derivative designed to boost synaptic inhibition by inhibiting the degradation of GABA in brain tissue. Indeed, VGB shows potent anti-convulsant activity in animal models of epilepsy and in humans with complex partial seizures. However, details of the mechanism of action of VGB are not well understood and the systemic effects include possible pro-convulsant actions. We therefore analysed the effects of VGB in rat brain slices in the low-Mg²⁺ model in vitro. VGB at 100 μM–5 mM showed a concentration- and time-dependent reduction of interictal-like events in the hippocampal CA1 region. Likewise, VGB suppressed epileptiform discharges in the medial entorhinal cortex (mEC), which are known to resist conventional anti-convulsants. In contrast, evoked population spikes in CA1 (which became repetitive after washout Mg²⁺) were not altered by VGB. Our data show that VGB is efficient against epileptiform discharges in temporal structures including pharmacoresistant patterns of activity. The waveform of evoked population spikes in this in vitro model is no indicator for the anti-convulsant properties of drugs.     

Reciprocal effect of single corticomotoneuronal cells on wrist extensor and flexor muscle activity in the primate

Action potentials of single motor cortex cells were recorded extracellularly in awake monkeys trained to make alternating wrist movements between flexion and extension position zones. Spike-triggered averaging of rectified EMG activity was used to test each cell's output effect on both the coactivated (agonist) forearm muscles and their antagonists. Five of 18 adequately tested motor cortex cells, whose activity covaried strongly with alternating wrist movement, not only produced postspike facilitation of agonist muscles but also postspike suppression of antagonist muscles. Five additional cells only facilitated the agonist muscles and had no effect on the recorded antagonists; 8 cells had no effect on either agonist or antagonist muscles. We conclude that the synaptic terminations of some motor cortex cells with flexor and extensor spinal motoneurons are reciprocally organized.     

Synaptic drive contributing to rhythmic activation of motoneurons in the deafferented stick insect walking system

A general feature of motor patterns for locomotion is their cyclic and alternating organization. In walking, for example, rhythmic activity in leg motoneurons innervating antagonistic muscles of a joint is primarily antiphasic within each cycle. We investigate which role central pattern generating networks play in the generation of leg motoneuron activity in the absence of sensory feedback. We elicited activity in antagonistic flexor and extensor tibiae motoneurons in the deafferented mesothoracic ganglion of the stick insect by mechanically stimulating the head or abdomen, while recording intracellularly from their neuropilar processes. In most cases, tactile stimulation induced coactivation of tibial motoneurons. However, in approximately 25% of the trials, tibial motoneurons generated alternating cycles consisting of bursts of action potentials that were terminated by strong inhibitory synaptic inputs. Injection of depolarizing current increased the amplitude of the inhibitory phase of the oscillation, while hyperpolarizing current decreased it and revealed a tonic depolarization of the motor neurons during the bout of rhythmic motor activity. The same results were gathered from recording tibial leg motoneurons during 'twitching' motor activity in decerebrated animals. Our results indicate that alternating rhythmic motoneuron activity in the deafferented stick insect walking system results from phasic inhibitory drive provided by central pattern generating networks. This inhibitory input patterns the firing of the motoneurons that results from a tonic depolarizing drive. This tonic depolarizing drive was also observed in tibial motoneurons of the deafferented mesothoracic ganglion during walking movements of the intact ipsilateral front leg.     

Do Interictal Discharges Promote or Control Seizures? Experimental Evidence from an In Vitro Model of Epileptiform Discharge

Summary: Interictal and ictal discharges are recorded from limbic structures in temporal lobe epilepsy patients. In clinical practice, interictal spikes are used to localize the epileptogenic area, but they also are assumed to promote ictal events. Here I review data obtained from combined slices of mouse hippocampus–entorhinal cortex that indicate an inverse relation between interictal and ictal events. In this preparation, application of 4-aminopyridine or Mg²⁺-free medium induce (a) interictal discharges that originated from CA3 and propagate (via the Schaffer collaterals) to CA1 and entorhinal cortex, to return to the hippocampus through the dentate area; and (b) ictal discharges that initiate in the entorhinal cortex and propagate to the hippocampus via the dentate gyrus. Interictal activity occurs throughout the experiment (up to 6 h), whereas ictal discharges disappear after 1–2 h. Schaffer collateral cut abolishes interictal discharges in CA1, entorhinal cortex, and dentate and reestablishes entorhinal ictal discharges. Moreover, ictal discharge generation in the entorhinal cortex after Schaffer collateral cut is prevented by mimicking CA3 activity with rhythmic electrical stimulation of CA1 outputs. Thus hippocampal interictal activity controls the ability of the entorhinal cortex to generate seizures. It also may be proposed that Schaffer collateral cut may model the epileptic condition in which CA3 damage results in loss of hippocampal control over the entorhinal cortex. In conclusion, these experiments demonstrate that interictal activity controls rather than promotes ictal events, and functional integrity of CA3 constitutes a critical control mechanism in temporal lobe epilepsy.     

Cingulate cell discharge patterns related to hippocampal EEG and their modulation by muscarinic and nicotinic agents

Surface to depth recordings of slow wave θ activity were made through the posterior cingulate cortex (area 29). In other experiments the discharge patterns of neurons located throughout this region were recorded during the occurrence of large amplitude irregular activity (LIA) and slow wave θ activity (type 2) in the hippocampal formation of the urethane-anesthetized rat. The response of these neurons to the systemic administration of the cholinergic agonists, eserine and nicotine, was also tested. The majority of cells (80%) related to hippocampal EEG states were classified as tonic θ-on cells (non-rhythmic). These cells increased their discharge rates significantly, when the slow wave activity in the hippocampus changed from LIA to θ. The administration of eserine and nicotine induced slow wave θ in the hippocampus accompanied by the increased discharge rate of tonic θ-on cingulate cells. The excitatory action of nicotine on the discharges of tonic θ-on cingulate cortical cells is in direct contrast to its inhibitory action on phasic and tonic hippocampal θ-on cell discharges. The observation that phase reversals did not occur in area 29, together with the low incidence of phasic (rhythmic) θ-on cells, suggests that the posterior cingulate cortex does not independently generate type 2 θ. Possible significance of these findings for the interactive functioning of the hippocampal formation and posterior cingulate cortex is discussed.     

A progressive sequence of electroencephalographic changes during generalized convulsive status epilepticus

Review of 60 electroencephalograms recorded during episodes of generalized convulsive status epilepticus suggested that there are 5 identifiable EEG patterns which occur in a predictable sequence during the course of generalized convulsive status epilepticus in man: (1) discrete seizures; (2) merging seizures with waxing and waning amplitude and frequency of EEG rhythms; (3) continuous ictal activity; (4) continuous ictal activity punctuated by low voltage 'flat periods'; and (5) periodic epileptiform discharges on a 'flat' background. We confirmed our hypothesis that this sequence represents the natural history of electroencephalographic changes in untreated generalized convulsive status epilepticus by observing the same sequence in the EEGs of rats in which status epilepticus had been induced by 3 different methods: (1) systemic administration of kainic acid, (2) injection of homocysteine thiolactone to cobalt-lesioned rats; and (3) injection of lithium chloride followed 24 h later by injection of pilocarpine.     

A role for endocannabinoids in viral-induced dyskinetic and convulsive phenomena

Dyskinesias and seizures are both medically refractory disorders for which cannabinoid-based treatments have shown early promise as primary or adjunctive therapy. Using the Borna disease (BD) virus rat, an animal model of viral encephalopathy with spontaneous hyperkinetic movements and seizure susceptibility, we identified a key role for endocannabinoids in the maintenance of a balanced tone of activity in extrapyramidal and limbic circuits. BD rats showed significant elevations of the endocannabinoid anandamide in subthalamic nucleus, a relay nucleus compromised in hyperkinetic disorders. While direct and indirect cannabinoid agonists had limited motor effects in BD rats, abrupt reductions of endocannabinoid tone by the CB₁ antagonist SR141716A (0.3 mg/kg, i.p.) caused seizures characterized by myoclonic jerks time-locked to periodic spike/sharp wave discharges on hippocampal electroencephalography. The general opiate antagonist naloxone (NLX) (1 mg/kg, s.c.), another pharmacologic treatment with potential efficacy in dyskinesias or L-DOPA motor complications, produced similar seizures. No changes in anandamide levels in hippocampus and amygdala were found in convulsing NLX-treated BD rats. In contrast, NLX significantly increased anandamide levels in the same areas of normal uninfected animals, possibly protecting against seizures. Pretreatment with the anandamide transport blocker AM404 (20 mg/kg, i.p.) prevented NLX-induced seizures. These findings are consistent with an anticonvulsant role for endocannabinoids, counteracting aberrant firing produced by convulsive agents, and with a functional or reciprocal relation between opioid and cannabinoid tone with respect to limbic convulsive phenomena.     

Electrical activity and Na, K-ATPase levels in an epileptic focus caused by application of penicillin to rat cerebral cortex and the effect of diazepam on them

Penicillin application to the rat brain motor cortex resulted in appearance of interictal discharges and seizures. After diazepam injection (2 mg/kg) a 100% increase in Na, K-ATPase activity of neuronal membranes in the epileptogenic focus was shown as compared to enzyme activity before diazepam injection. Interictal discharges and seizures changed in different ways after intramuscular injection of diazepam. The frequency and amplitude variation of interictal discharges increased but the seizures were suppressed. These effects increased with the dose of diazepam. It is suggested that the different influence of diazepam upon seizures and interictal discharges may reflect different mechanisms of these phenomena.     

Fluorocitrate-mediated astroglial dysfunction causes seizures

A role for astroglia in epileptogenesis has been hypothesised but is not established. Low doses of fluorocitrate specifically and reversibly disrupt astroglial metabolism by blocking aconitase, an enzyme integral to the tricarboxylic acid cycle. We used cerebral cortex injections of fluorocitrate, at a dose that we demonstrated to inhibit astroglial metabolism selectively, to determine whether astroglial disturbances lead to seizures. Rats were halothane-anesthetized, and 0.8 nmol of sodium fluorocitrate was injected into the cerebral cortex. Extradural electroencephalogram (EEG) electrodes were implanted, after which the anesthesia was ceased and the animals were observed. In all experiments, 14 of 15 fluorocitrate-treated animals exhibited epileptiform EEG discharges, with some animals exhibiting convulsive seizures. Discharges commenced as early as 30 min postfluorocitrate injection. Intraperitoneal octanol, but not halothane by inhalation, given to test the possible participation of gap junctions in EEG discharge generation, blocked or delayed the occurrence of discharges after fluorocitrate. These results indicate that focal cerebrocortical astroglial dysfunction leads to focal epileptiform discharges and sometimes to convulsive seizures and that the process possibly depends on effects mediated by gap junctions.