Bicuculline-induced neocortical epileptiform foci and the effects of 6-hydroxydopamine in developing rats

Oscillotherapeutics - Time-targeted interventions in epilepsy and beyond

Oscillatory brain activities support many physiological functions from motor control to cognition. Disruptions of the normal oscillatory brain activities are commonly observed in neurological and psychiatric disorders including epilepsy, Parkinson's disease, Alzheimer's disease, schizophrenia, anxiety/trauma-related disorders, major depressive disorders, and drug addiction. Therefore, these disorders can be considered as common oscillation defects despite having distinct behavioral manifestations and genetic causes. Recent technical advances of neuronal activity recording and analysis have allowed us to study the pathological oscillations of each disorder as a possible biomarker of symptoms. Furthermore, recent advances in brain stimulation technologies enable time- and space-targeted interventions of the pathological oscillations of both neurological disorders and psychiatric disorders as possible targets for regulating their symptoms.

Models of epileptic seizures in immature rats

Models of basic types of epileptic seizures are elaborated not only in adult but also in immature rodents. It is important because at least half of human epilepsies starts during infancy and childhood. This paper presents a review of chemically and electrically induced models of generalized convulsive and nonconvulsive (absence) seizures as well as models of partial simple (neocortical) and complex (limbic) seizures in immature rats. These models can also serve as a tool for study the development of central nervous system and motor abilities because the level of maturation is reflected in seizure semiology. Age-dependent models of epileptic seizures (absences and flexion seizures) are discussed. Models of seizures in immature animals should be used for testing of potential antiepileptic drugs.

GABA-A receptors play a minor role in cortical epileptic afterdischarges in immature rats

The role of inhibitory γ-aminobutyric acid-A (GABA-A) system in the cortical epileptic afterdischarges (ADs) was studied at three different developmental stages of rats. Animals 12, 18 and 25days old with implanted epidural electrodes were pretreated with bicuculline (1 and 2mg/kgi.p.) and 15min later repeatedly stimulated with low frequency trains with stepwise increasing current intensity. Bicuculline only exceptionally decreased threshold current intensities necessary for elicitation of movements directly bound to stimulation, spike-and wave ADs, clonic seizures and transition into a limbic type of ADs. Duration of ADs was not systematically affected by either dose of bicuculline. In contrast, transcallosal evoked potentials exhibited under the influence of bicuculline steeper curve expressing relation between intensity of stimuli and amplitude of responses. In contrast to GABA-B receptors, GABA-A receptors do not play an important role in generation and arrest of cortical epileptic ADs in immature rats.

Convulsant action of systemically administered glutamate and bicuculline methiodide in immature rats

Developmental changes of transport of drugs into the brain play an important role in ontogenetic neuropharmacology. Two convulsant drugs with different mechanisms of action (glutamate and bicuculline methiodide) were chosen to demonstrate these changes in developing rats. High dose of glutamate (4 g/kg i.p.) induced both minimal (predominantly clonic) and generalized tonic-clonic seizures in rat pups 7, 12, and 18 days old. In contrast, seizures were only exceptionally observed in 25 and 90 days old animals. Bicuculline methiodide was administered in a dose of 2 or 20 mg/kg i.p. The first sign of bicuculline methiodide action in all age groups was represented by automatisms, a symptomatology never seen after bicuculline hydrochloride administration. Minimal seizures were induced in 12-day-old and in a few 18-day-old and adult rats. Generalized seizures were common after the higher dose of bicuculline methiodide in 7- and 12-day-old rat pups, seldom in 18-day-old ones and never seen in 25-day-old and adult animals. Both glutamate and bicuculline methiodide enter the brain in immature rats but the mechanisms are probably different - glutamate is transported actively through the blood-brain barrier whereas no similar system is known for bicuculline methiodide.

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).

Tetanus toxin-induced seizures in infant rats and their effects on hippocampal excitability in adulthood

A new experimental model of developmental epilepsy is reported. Behavioral and EEG features of seizures produced by unilateral intrahippocampal injection of tetanus toxin in postnatal day 9-11 rats, are described. Within 24-72 h of tetanus toxin injection, rat pups developed frequent and often prolonged seizures which included combinations of repetitive wet dog shakes, and wild running-jumping seizures. Intrahippocampal and cortical surface EEG recordings showed that coincident with these behaviors, electrographic seizures occurred not only in the injected hippocampus, but also in the contralateral hippocampus and bilaterally in the neocortex. Analysis of the interictal EEG revealed multiple independent spike foci. One week following tetanus toxin injection, the number of seizures markedly decreased; however, interictal spiking persisted. After injection rats were allowed to mature some were observed to have unprovoked behavioral seizures and/or epileptiform EEG activity. Mature animals were also studied using in vitro slice techniques. Recordings from hippocampal slices demonstrated spontaneous epileptiform burst discharges in the majority of rats which had tetanus toxin induced seizures as infants. These events occurred in area CA3 and consisted of interictal spikes and intracellularly recorded paroxysmal depolarization shifts (PDSs). On rarer occasions, electrographic seizures were recorded. The use of the tetanus toxin model in developing rats may facilitate a better understanding of the unique features of epileptogenesis in the developing brain and the consequences early-life seizures have on brain maturation and the genesis of epileptic conditions in later life.

Effect of hypoxia/ischemia on bicuculline-induced seizures in immature rats: behavioral and electrocortical phenomena

The relation between hypoxia/ischemia and subsequent alterations in seizure susceptibility in developing brain remains unclear. We assessed the behavioral and electrocorticographic (ECoG) effects of hypoxic/ischemic brain damage on bicuculline (BIC)-induced seizures in 7-day postnatal rats, and determined maturational changes in seizure susceptibility, behavior and ECoG activity. Rat pups were subjected to unilateral common carotid artery ligation, followed by exposure to 8% O2 at 37 degrees C for 2 h, an insult that produces brain damage in the cerebral hemisphere ipsilateral to carotid artery occlusion. The experimental group consisted of rat pups previously subjected to hypoxia/ischemia; control littermates received neither arterial ligation nor systemic hypoxia. Experimental animals received 4, 5, or 6 mg/kg BIC subcutaneously (s.c.) at 2 and 24 h, and at 3, 7, and 21 days of recovery from hypoxia/ischemia. Two animals at each interval of recovery, 1 each from the experimental and control groups, were used for ECoG monitoring. After BIC injection, animal behavior was observed for 2 h. Behaviors and seizures were classified in five categories based on severity, duration, and character: 1, mild irritability; 2, few clonic seizures and agitation; 3, few tonic-clonic seizures with swimming movements; 4, frequent tonic-clonic seizures with apneic episodes; 5, continuous tonic-clonic seizures and death. Rat pups previously subjected to hypoxia/ischemia had lesser seizure susceptibility than controls at 2-h recovery (p < 0.05) and greater susceptibility than controls at 24 h (p < 0.05). Tonic seizures were prominent at 2 and 24 h in both the experimental and control groups, whereas lesion-sided circling was prominent only in the hypoxic/ischemic rat pups.(ABSTRACT TRUNCATED AT 250 WORDS)

New model of cortical epileptic foci in freely moving developing rats

Electrocorticographic and motor phenomena produced by epileptogenic foci were studied in freely moving rats with implanted electrodes in five age groups (7, 12, 18, 25 days and adults). Foci were induced by local application of a 1 or 2 mM solution of bicuculline methiodide to the sensorimotor cortical area by means of an implanted cannula in 106 rats. Interictal focal discharges formed by mono- to triphasic spikes (in rats aged 18 days and more) or sharp waves (in 7-day-old rats) were recorded in all animals. Spontaneous transition into an ictal phase was common in all age groups, there was no clear dependence on the age. Ictal EEG was formed by spike-and-wave rhythm in rats 18 days old and older, by huge delta waves in the youngest rats. Electroclinical correlation was poor in the youngest rats and ameliorated with age. The most frequent motor counterpart of focal discharges was represented by a jerk of the contralateral limbs or of the whole body. EEG seizures were mostly accompanied by clonus of facial and forelimb muscles, but EEG ictal phases without any motor correlate were also common.