Effect of naloxone infusion on the rate of epileptiform discharges in patients with complex partial seizures

Alternating and postictal psychoses: review and a unifying hypothesis

A comparison of the clinical and pathophysiological features of postictal psychosis and brief interictal or alternating psychosis was undertaken to examine if the underlying mechanisms are distinct in these 2 conditions. A selective review of the published literature in English on epilepsy and brief psychosis was carried out. The literature indicates that even though brief postictal and alternating psychoses are considered to be separate syndromes, they have a number of similarities. It can be argued that the underlying pathomechanisms are common, with the brain's inhibitory processes in response to seizures playing a key role in the development of the psychosis. These homeostatic mechanisms manifest as electrophysiological, cerebral blood flow, and neurotransmitter and receptor changes. Both syndromes are likely to be associated with prolonged inhibition in limbic circuits, with further seizures modifying the psychosis depending upon whether it is associated with disinhibition or hypersynchrony involving enhanced inhibition. The neurotransmitter with a key role is GABA, although ionic currents, catecholamines, opiates, adenosine, glutamate, and nitric oxide play a role. Brief postictal and alternating psychoses provide an opportunity to understand the complex relationships between epilepsy and schizophrenia-like brief psychotic episodes, and this understanding can assist in their management.

Ultra-low dose naltrexone potentiates the anticonvulsant effect of low dose morphine on clonic seizures

Significant potentiation of analgesic effects of opioids can be achieved through selective blockade of their stimulatory effects on intracellular signaling pathways by ultra-low doses of opioid receptor antagonists. However, the generality and specificity of this interaction is not well understood. The bimodal modulation of pentylenetetrazole-induced seizure threshold by opioids provide a model to assess the potential usefulness of this approach in seizure disorders and to examine the differential mechanisms involved in opioid anti- (morphine at 0.5-3 mg/kg) versus pro-convulsant (20-100 mg/kg) effects. Systemic administration of ultra-low doses of naltrexone (100 fg/kg-10 ng/kg) significantly potentiated the anticonvulsant effect of morphine at 0.5 mg/kg while higher degrees of opioid receptor antagonism blocked this effect. Moreover, inhibition of opioid-induced excitatory signaling by naltrexone (1 ng/kg) unmasked a strong anticonvulsant effect for very low doses of morphine (1 ng/kg-100 microg/kg), suggesting that a presumed inhibitory component of opioid receptor signaling can exert strong seizure-protective effects even at very low levels of opioid receptor activation. However, ultra-low dose naltrexone could not increase the maximal anticonvulsant effect of morphine (1-3 mg/kg), possibly due to a ceiling effect. The proconvulsant effects of morphine on seizure threshold were minimally altered by ultra-low doses of naltrexone while being completely blocked by a higher dose (1 mg/kg) of the antagonist. The present data suggest that ultra-low doses of opioid receptor antagonists may provide a potent strategy to modulate seizure susceptibility, especially in conjunction with very low doses of opioids.

Alfentanil-induced epileptiform activity: a simultaneous surface and depth electroencephalographic study in complex partial epilepsy

PURPOSE

Alfentanil is a high potency mu opiate receptor agonist commonly used during presurgical induction of anesthesia. This and other opiate receptor agonists have demonstrated proconvulsant effects in animals, but these properties have been less consistently demonstrated in humans. Most human scalp EEG studies have failed to demonstrate induction of epileptiform activity with these agents, which is inconsistent with findings using intracranial EEG. Simultaneous scalp and depth EEG recordings have yet to be performed in this setting. The relationship between opiate dose and proconvulsant activity is unclear.

METHODS

Simultaneous scalp and depth electrode recordings were performed on five patients with complex partial epilepsy (CPE) who underwent alfentanil anesthesia induction before depth electrode removal. Consecutive equal bolus doses of alfentanil were administered to each patient according to strict time intervals so as to assess their correlation with any induced epileptiform activity.

RESULTS

Epileptiform activity was induced by alfentanil in three of five patients. Two of these patients had electrographic seizures. Epileptiform activity was only detected from the depth electrodes, occurring within 2 min of the first bolus dose in all three cases. Further increase or spread of epileptiform activity did not occur despite cumulative bolus doses of alfentanil.

CONCLUSIONS

Alfentanil is proconvulsant in patients with CPE. Induced seizures may be subclinical and lack a scalp EEG correlate. There is a complex dose-response relationship. Alfentanil induction of anesthesia should be approached with caution in patients with CPE.

Nonconvulsive status epilepticus: the role of morphine and its antagonist

A 77-year-old woman with no history of epilepsy presented a probable nonconvulsive status epilepticus while receiving continuous intravenous morphine for back pain relating to vertebral metastasis of a malignant lymphoma. A generalized tonic-clonic seizure occurred a few minutes after injection of the morphine antagonist naloxone. No cerebral lesion was detected. This observation supports the notion of a possible pro-epileptogenic effect of opioid substances in association with metabolic and other toxic factors. Various hypotheses as to the complex actions of morphine and its antagonist in epileptogenesis are discussed.

The postictal state: a neglected entity in the management of epilepsy

Some of the disability deriving from epilepsy derives from the postictal state (PS). The PS may be complicated by impaired cognition, headache, injuries, or secondary medical conditions. Postictal depression is common, postictal psychosis relatively rare, but both add to the morbidity of seizures. The mechanisms of the PS are poorly understood. Alteration of cerebral blood flow both results from and contributes to the PS. Many neurotransmitters or neuromodulators are involved in the physiology of the PS. Response to glutamate may partially desensitize after a seizure. Endogenous opiates and adenosine serve as natural antiepileptic medications in some circumstances. Nitric oxide has numerous effects on brain excitability, and may be particularly important in regulating postictal cerebral blood flow. Just as the pathophysiology of seizures is complicated, so is that of the PS multifactorial. As a practical issue, it would be very useful to have medications that reduce the morbidity of the PS.

Imaging of delta- and mu-opioid receptors in temporal lobe epilepsy by positron emission tomography

The involvement of opioid neurotransmitter systems in seizure mechanisms is well documented. In previous positron emission tomography (PET) studies in patients with unilateral temporal lobe epilepsy, we have found evidence for differential regulation of the opioid-receptor subtypes. The present study extends our previous observations to delta-opioid receptors by using the delta-receptor-selective antagonist [11C]methylnaltrindole ([11C]MeNTI). Paired measurements of delta- and mu-opioid receptor binding and metabolic activity were performed with PET using [11C]MeNTI and [11C]carfentanil ([11C]CFN) and [18F]fluorodeoxyglucose ([18F]FDG), respectively. Binding of [11C]MeNTI and [11C]CFN increased and [18F]FDG uptake decreased in the temporal cortex (TC) ipsilateral to the focus. Decreases in [18F]FDG uptake were more widespread regionally than were increases in opioid receptors. Increases in the delta- and mu-receptor binding showed different regional patterns. Increases in mu-receptor binding were confined to the middle aspect of the inferior TC, whereas binding of delta receptors increased in the mid-inferior TC and anterior aspect of the middle and superior TC. The increase in delta receptors suggests their anticonvulsant action, as previously shown for the delta-receptor subtype, whereas the different regional pattern of receptor alterations suggest the distinct roles of different opioid-receptor subtypes in seizure phenomena.

Dynorphin and epilepsy

Studies on dynorphin involvement in epilepsy are summarised in this review. Electrophysiological, biochemical and pharmacological data support the hypothesis that dynorphin is implicated in specific types of seizures. There is clear evidence that this is true for complex partial (limbic) seizures, i.e. those characteristic of temporal lobe epilepsy, because; (1) dynorphin is highly expressed in various parts of the limbic system, and particularly in the granule cells of the hippocampus; (2) dynorphin appears to be released in the hippocampus (and in other brain areas) during complex partial seizures; (3) released dynorphin inhibits excitatory neurotransmission at multiple synapses in the hippocampus via activation of kappa opioid receptors; (4) kappa opioid receptor agonists are highly effective against limbic seizures. Data on generalised tonic-clonic seizures are less straightforward. Dynorphin release appears to occur after ECS seizures and kappa agonists exert a clear anticonvulsant effect in this model. However, more uncertain biochemical data and lack of efficacy of kappa agonists in other generalised tonic-clonic seizure models argue that the involvement of dynorphin in this seizure type may not be paramount. Finally, an involvement of dynorphin in generalised absence seizures appears unlikely on the basis of available data. This may not be surprising, given the presumed origin of absence seizures in alterations of the thalamo-cortical circuit and the low representation of dynorphin in the thalamus. In conclusion, it may be suggested that dynorphin plays a role as an endogenous anticonvulsant in complex partial seizures and in some cases of tonic-clonic seizures, but most likely not in generalised absence. This pattern of effects may coincide with the antiseizure spectrum of selective kappa agonists.

Failure of naloxone to modify electroencephalogram interictal epileptiform discharges in patients with primary generalized epilepsy after slation

Sleep deprivation (SD) is a method widely used to activate EEG epilept oform activity, but the basis of this effect remains unknown. One possibilty is that SD shares a common mechanism with physical and psychological stresses that also precipitate seizures. Because endogenous opioids are released during stress, opioids may play a role in enhancing epileptiform EEG patterns after SD. We report the effects of SD on EEG epileptiform activity in a small but highly homogeneous population of 13 epileptic patients with idiopathic (primary) generalized epilepsy (IGE). SD increased EEG interictal epileptiform discharges (IEDs); this activation was not modified by naloxone (NAL). Our results, in contrast to those of previous investigations of localization-related epilepsy, which showed an increase in IEDs after NAL administration, suggest a possible difference in the mechanism whereby SD enhances IEDs in IGE and localization-related epilepsy.

Reduced fertility and neuroendocrine dysfunction in women with epilepsy

A reduction of fertility in women with epilepsy has been reported since 1950 and is confirmed in recent epidemiological studies. This phenomenon has usually been attributed to the increase of medical and socioeconomic problems in these patients or to hyposexuality, which has been consistently observed in epileptic subjects. Recently, a higher occurrence of reproductive endocrine diseases has been reported in epileptic women and proposed as an important cause of reduced fertility. In particular, polycystic ovary syndrome and hypothalamic ovarian failure have been reported in epileptic women with increased frequency compared to the general population. Moreover, an abnormal pattern of luteinizing hormone (LH) pulsatility has been observed in normally cycling, drug-free epileptic women. We suggest that epilepsy may interfere with the functional activity of the gonadotropin releasing hormone (GnRH) pulse generator. It is possible that paroxysmal discharges spreading within the hypothalamus might affect the regularity of the GnRH pulse generator; alternatively, a neurotransmitter dysfunction might at the same time be responsible both for the lowering of the seizure threshold and for the dysfunction of GnRH secretion. The consequent alteration of LH pulsatility might in the long run, under the effect of additional factors, give rise to a clinical reproductive endocrine disorder.

The effect of naloxone on cerebral blood flow and glucose metabolism in patients with complex partial seizures

We used positron emission tomography with [15O]water and [18F]fluoro-2-deoxyglucose (FDG) to study the effect of naloxone on cerebral blood flow (CBF) and glucose metabolism (LCMRglc) in patients with complex partial seizures. There was no effect on glucose metabolism, but blood flow was reduced 7-12% 45-60 min after infusion of 1 mg/kg naloxone, as was the degree of lateral temporal CBF asymmetry in patients with > 10% baseline hypoperfusion. Endogenous opiates are involved in regulation of human CBF, and possibly in hypoperfusion in epileptic foci. Since [18F]FDG PET measures mean LCMRglc over the tracer uptake and scanning periods, it is inferior to [15O]H2O PET for detecting drug effects which may be time dependent.

Derangement of the hypothalamic GnRH pulse generator in women with epilepsy

An increased frequency of reproductive endocrine diseases has been described in women with epilepsy and a subclinical reproductive dysfunction has been suggested in normally menstruating epileptic women. We assessed the reproductive endocrine function in 11 normally menstruating, drug-free epileptic women, evaluating the basal hormonal profile and LH pulsatile secretion during continuous EEG monitoring. A significant LH hyperpulsatility was observed in epileptic women compared with controls; moreover, a significant increase of gonadotropin basal secretions was observed when inter-ictal paroxysmal activity increased. The derangement of the hypothalamic GnRH pulse generator may represent a subclinical condition associated with epilepsy, not necessarily affecting the regularity of menstrual function. However, it is possible that the alteration of LH pulsatile pattern might eventually cause reproductive endocrine diseases. Paroxysmal activity seems to be an important additional factor in the derangement of gonadotropin secretion.

PET imaging of opiate receptor binding in human epilepsy using [18F]cyclofoxy

We used [18F]cyclofoxy (CF), a potent opiate antagonist with affinity for mu and kappa receptors, and the Scanditronix PC1024-7B PET scanner to study 14 patients with complex partial seizures (CPS), and 14 normal controls. Epileptic foci were localized by prolonged EEG-video monitoring. EEG was recorded continuously during each scan. Immediately before CF administration, [15O]labeled water was used to measure cerebral blood flow, and showed hypoperfusion ipsilateral to the EEG focus. Blood samples (corrected for radiolabeled metabolites) and tissue time-activity data were acquired over 90 min following bolus CF injection. Anatomic regions were outlined directly on the PET images. A kinetic model was used to derive the total volume of distribution (Vt) in each brain region. Specific binding (Vs) was determined by substracting non-specific binding (Vt) measured in a receptor-poor brain region (occipital cortex). Regions with high Vs included mesial temporal lobes, thalamus, basal ganglia, and frontal cortex. Individual patients appeared to have higher binding in temporal lobe ipsilateral to the EEG focus, but there was no asymmetry for the patients as a group in mean Vt or Vs in anterior mesial, posterior mesial, anterior lateral, posterior lateral temporal cortex, thalamus, basal ganglia, or, for Vt, in regions of low specific binding: occipital lobe, parietal lobe, cerebellum.

Abnormal pattern of luteinizing hormone pulsatility in women with epilepsy

Dysfunction of the hypothalamic-pituitary-ovarian axis in epileptic females has been suggested in the latest years. To further elucidate this issue, we assessed reproductive endocrine function in 10 normally cycling, drug-free epileptic women and in 5 normal controls, evaluating the basal hormonal profile and luteinizing hormone (LH) pulsatility in the midfollicular phase. Luteinizing hormone pulse frequency was significantly higher in epileptic women with a consequent reduction of the LH interpulse interval. We suggest that epilepsy may interfere with the functional activity of the gonadotropin-releasing hormone pulse generator. The pathogenetic mechanisms for this phenomenon may be the spreading of paroxysmal activity within the hypothalamic areas or, alternatively, a neurotransmitter dysfunction giving rise both to the seizure disorder and to the abnormal LH pulsatile pattern.

Endogenous opiates: 1989

This paper is the twelfth installment of our annual review of the research published during 1989 involving the behavioral, nonanalgesic, effects of the endogenous opiate peptides. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal and renal functions; mental illness; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; locomotor activity; sex, development, pregnancy, and aging; immunological responses; and other behavior.