Influence of melatonin upon the protective action of conventional anti-epileptic drugs against maximal electroshock in mice

Melatonin's Benefits and Risks as a Therapy for Sleep Disturbances in the Elderly: Current Insights

Aging is accompanied by circadian changes, including disruptive alterations in the sleep/wake cycle, as well as the beginning of low-degree inflammation ("inflammaging"), a scenario that leads to several chronic illnesses, including cancer, and metabolic, cardiovascular, and neurological dysfunctions. As a result, any effective approach to healthy aging must consider both the correction of circadian disturbance and the control of low-grade inflammation. One of the most important prerequisites for healthy aging is the preservation of robust circadian rhythmicity (particularly of the sleep/wake cycle). Sleep disturbance disrupts various activities in the central nervous system, including waste molecule elimination. Melatonin is a chemical with extraordinary phylogenetic conservation found in all known aerobic creatures whose alteration plays an important role in sleep changes with aging. Every day, the late afternoon/nocturnal surge in pineal melatonin helps to synchronize both the central circadian pacemaker found in the hypothalamic suprachiasmatic nuclei (SCN) and a plethora of peripheral cellular circadian clocks. Melatonin is an example of an endogenous chronobiotic substance that can influence the timing and amplitude of circadian rhythms. Moreover, melatonin is also an excellent anti-inflammatory agent, buffering free radicals, down-regulating proinflammatory cytokines, and reducing insulin resistance, among other things. We present both scientific and clinical evidence that melatonin is a safe drug for treating sleep disturbances in the elderly.

Insights into Potential Targets for Therapeutic Intervention in Epilepsy

Epilepsy is a chronic brain disease that affects approximately 65 million people worldwide. However, despite the continuous development of antiepileptic drugs, over 30% patients with epilepsy progress to drug-resistant epilepsy. For this reason, it is a high priority objective in preclinical research to find novel therapeutic targets and to develop effective drugs that prevent or reverse the molecular mechanisms underlying epilepsy progression. Among these potential therapeutic targets, we highlight currently available information involving signaling pathways (Wnt/β-catenin, Mammalian Target of Rapamycin (mTOR) signaling and zinc signaling), enzymes (carbonic anhydrase), proteins (erythropoietin, copine 6 and complement system), channels (Transient Receptor Potential Vanilloid Type 1 (TRPV1) channel) and receptors (galanin and melatonin receptors). All of them have demonstrated a certain degree of efficacy not only in controlling seizures but also in displaying neuroprotective activity and in modifying the progression of epilepsy. Although some research with these specific targets has been done in relation with epilepsy, they have not been fully explored as potential therapeutic targets that could help address the unsolved issue of drug-resistant epilepsy and develop new antiseizure therapies for the treatment of epilepsy.

Epilepsy Occurrence and Circadian Rhythm: A Bibliometrics Study and Visualization Analysis via CiteSpace

Objective: This study aimed to review the research status and to demonstrate the hot spots and frontiers of epilepsy and circadian rhythm via CiteSpace.

Method: We searched Web of Science (WoS) for studies related to epilepsy and circadian rhythm from inception to 2020. CiteSpace was used to generate network maps about the collaborations between authors, countries, and institutions and reveal hot spots and frontiers of epilepsy and circadian rhythm.

Results: A total of 704 studies related to epilepsy and circadian rhythm from the WoS were retrieved. Sanchez-Vazquez FJ was the most prolific author (17 articles). The USA and University of Murcia were the leading country and institution in this field with 219 and 22 publications, respectively. There were active collaborations among the authors, countries, and institutions. Hot topics focused on the interaction between epilepsy and circadian rhythm, as well as possible novel treatments.

Conclusions: Based on the results of CiteSpace, the current study suggested active cooperation between authors, countries, and institutions. Major ongoing research trends include the circadian rhythm of epilepsy based on different epileptic focus and the interaction between epilepsy and circadian rhythm, especially through melatonin, sleep–wake cycles, and clock genes, which may implicate possible treatments (such as chronotherapy, neural stem cells transplantation) for epilepsy in the future.

The role of melatonin and its analogues in epilepsy

Extensive research has gone into proposing a promising link between melatonin administration and attenuation of epileptic activity, the majority of which suggest its propensity as an antiseizure with antioxidant and neuroprotective properties. In the past few years, a number of studies highlighting the association of the melatonergic ligands with epilepsy have also emerged. In this context, our review is based on discussing the recent studies and various mechanisms of action that the said category of drugs exhibit in the context of being therapeutically viable antiseizure drugs. Our search revealed several articles on the four major drugs i.e. melatonin, agomelatine, ramelteon and piromelatine along with other melatonergic agonists like tasimelteon and TIK-301. Our review is suggestive of antiseizure effects of both melatonin and its analogues; however, extensive research work is still required to study their implications in the treatment of persons with epilepsy. Further evaluation of melatonergic signaling pathways and mechanisms may prove to be helpful in the near future and might prove to be a significant advance in the field of epileptology.

Role of oxidative stress in epileptogenesis and potential implications for therapy

In a state of balance between oxidants and antioxidants, free radicals play an advantageous role of “redox messengers”. In a state of oxidative stress, they trigger a cascade of events leading to epileptogenesis. During this latent, free of seizures period, a cascade of neurological changes takes place and finally leads to spontaneous recurrent seizures. The main processes involved in seizure generation are: neuroinflammation, neurodegeneration with anomalous neuroregeneration and lowering seizure threshold. Time of epileptogenesis offers a unique therapeutic window to prevent or at least attenuate seizure development. Animal data indicate that some antioxidants (for instance, resveratrol) may bear an anti-epileptogenic potential.

Adenosine receptor agonists differentially affect the anticonvulsant action of carbamazepine and valproate against maximal electroshock test-induced seizures in mice

Background.Adenosine is regarded as an endogenous anticonvulsant and its agonists have been proved to affect the anticonvulsant activity of a number of antiepileptic drugs (AEDs) in animal models of seizures.

Aim.To evaluate effects of adenosine agonists on carbamazepine (CBZ) and valproate (VPA) in mouse model of generalized tonic-clonic convulsions.

Methods.The following adenosine receptor agonists were used: A1– cyclohexyladenosine, A2A– CGS 21 680, A3– N6-benzyl-NECA and A1(preferentially) and A2– 2-chloroadenosine. Their possible anticonvulsant effects were studied in a threshold electroconvulsive test for maximal electroconvulsions. The protective activity of AEDs alone or in combinations with adenosine agonists was evaluated in the form of their respective ED50values necessary to protect 50% of mice against tonic extension of the hind limbs, following maximal electroshock, delivered through ear electrodes. The specificity of interactions between AEDs and adenosine agonists was challenged with an adenosine receptor A1and A2antagonist, aminophylline (5 mg/kg). The effects of AEDs alone or with adenosine agonists were tested for the occurrence of adverse effects (AE) (impairment of motor coordination) in a chimney test. All combinations with an enhancement the protective activity of CBZ or VPA were verified with the free plasma or brain concentration of these AED.

Results.Adenosine receptor agonists (cycloheksyladenosine up to 4 mg/kg; CGS 21 680 – 8 mg/kg; N6-benzyl-NECA – 1 mg/kg; 2-chloroadenosine – 2 mg/kg) did not significantly affect the threshold for maximal electroconvulsions. Cycloheksyladenosine (1 mg/kg), N6-benzyl-NECA (0.5 and 1 mg/kg) and 2-chloroadenosine (1 mg/kg) potentiated the anticonvulsant activity of CBZ. Valproate’s protective action was enhanced by one adenosine agonist – cycloheksyladenosine (1 mg/kg). Only the combination of CBZ + N6-benzyl-NECA (1 mg/kg) was resistant to aminophylline (5 mg/kg). Pharmacokinetic interactions were evident in case of the combination of CBZ + N6-benzyl-NECA (1 mg/kg) and resulted in an increased free plasma concentration of this CBZ. Interestingly, total brain concentration of CBZ confirmed the pharmacokinetic interaction as regards CBZ + N6-benzyl-NECA (1 mg/kg).

Conclusion.The best profile was shown by the combination of CBZ + 2-chloroadenosine which involved no AE or a pharmacokinetic interaction. The remaining positive combinations in terms of anticonvulsant activity were associated with general profound AE and pharmacokinetic interactions in some of them.

Agomelatine protects against neuronal damage without preventing epileptogenesis in the kainate model of temporal lobe epilepsy

Recent studies about the novel antidepressant agomelatine, which is a mixed MT₁ and MT₂ melatonin receptor agonist and 5HT_2C serotonin receptor antagonist possessing an anticonvulsant and neuroprotective action, suggest that it may have potential to contribute against epileptogenesis and epilepsy-induced memory impairment. In order to ascertain whether protection of some brain structures could suppress epileptogenesis, in the present study, we evaluated the effect of chronic post-status treatment with agomelatine on epileptogenesis, behavioral and neuronal damage induced by kainate acid (KA) status epilepticus (SE). Agomelatine/vehicle treatment (40mg/kg, i.p.) started one hour after SE and continued up to 10weeks in Wistar rats. Latency for onset of spontaneous motor seizures (SMS) and their frequency was detected by a 24-h video-recording. Locomotor activity, anxiety and hippocampus-dependent spatial memory in open field (OF), elevated plus maze (EPM), light-dark test (LDT) and radial arm maze (RAM) test, respectively, were evaluated during the last two weeks after SE. Agomelatine significantly decreased the latency for onset of SMS and increased the seizure frequency during the 2nd and the 3rd week of treatment. The MT₁ and MT₂ receptor agonist and serotonin 5HT_2C receptor antagonist exacerbated the KA-induced hyperlocomotion and impulsive behavior and it was unable to prevent spatial memory impairment of epileptic rats. However, agomelatine induced a neuroprotection in the dorsal hippocampus, specifically in the CA1, septal CA2 and partially in the CA3c region, the hilus of the dentate gyrus, piriform cortex and septo-temporal and temporal basolateral amygdala. Our findings suggest that the beneficial impact against SE-induced neuronal loss exerted by agomelatine is not crucial for the suppression of epileptogenesis and its deleterious consequences in KA model of temporal lobe epilepsy.

Therapeutic potential of agomelatine in epilepsy and epileptic complications

Epilepsy is a chronic neurologic disorder which often induces numerous adverse long-term neurologic effects, such as behavioral and cognitive deficits, increased predisposition to additional seizures, and cell injury or death. Cognitive dysfunction, depression, anxiety and sleep disorders are some of the highly prevalent and most disabling complications of epilepsy. The mechanisms that lead to the generation of epileptic comorbidities are poorly understood. Treatment for epileptic complications still remains a challenge because of the poor adherence and drug interactions associated with multi drug prescriptions and also for the fear of worsening seizures by the individual medications for complications. Melatonin, an endogenous hormone secreted by pineal gland has a prominent role in epilepsy. Agomelatine is a novel antidepressant which acts as melatonin MT1 and MT2 receptor agonist and serotonin 5Ht2C receptor antagonist. The combined action at MT1/2 and 5HT2C receptors, reduction in the depolarization-evoked release of glutamate, strong neuroprotective action and possible antioxidant properties of agomelatine could make it a potential agent in the treatment of epilepsy. The effect of agomelatine on hippocampal neuronal cell survival and neurogenesis, neuroprotective effect in hippocampus and frontal cortex and the antioxidant potential may contribute to the protective action of agomelatine against epilepsy induced memory decline. Agomelatine is proven to be an antidepressant and it has relieved anxiety symptoms and improved the quality of sleep in patients with depressive disorder. The action of agomelatine as a melatonin agonist and the consequent circadian resynchronizing property as well as its action as 5-HT2C receptor antagonist, could possibly suggest an antidepressant and anxiolytic action of agomelatine in epilepsy induced depressive behavior and anxiety. Since one of the many causes of sleep disruption in epilepsy is circadian rhythm disturbances and sleep promoting and circadian effects of melatonin is attributed to the MT1 and MT2 subtypes of human melatonin receptors, agomelatine may also have a promising effect on epilepsy induced sleep disruptions. Thus with all these potential pharmacological actions, agomelatine could be recommended as a potential drug to treat epilepsy and its complications.

Melatonin potentiates the anticonvulsant action of phenobarbital in neonatal rats

Phenobarbital is the most commonly utilized drug for neonatal seizures. However, questions regarding safety and efficacy of this drug make it particularly compelling to identify adjunct therapies that could boost therapeutic benefit. One potential adjunct therapy is melatonin. Melatonin is used clinically in neonatal and pediatric populations, and moreover, it exerts anticonvulsant actions in adult rats. However, it has not been previously evaluated for anticonvulsant effects in neonatal rats. Here, we tested the hypothesis that melatonin would exert anticonvulsant effects, either alone, or in combination with phenobarbital. Postnatal day (P)7 rats were treated with phenobarbital (0-40mg/kg) and/or melatonin (0-80mg/kg) prior to chemoconvulsant challenge with pentylenetetrazole (100mg/kg). We found that melatonin significantly potentiated the anticonvulsant efficacy of phenobarbital, but did not exert anticonvulsant effects on its own. These data provide additional evidence for the further examination of melatonin as an adjunct therapy in neonatal/pediatric epilepsy.

Interaction of carbamazepine with herbs, dietary supplements, and food: a systematic review

Background. Carbamazepine (CBZ) is a first-line antiepileptic drug which may be prone to drug interactions. Systematic review of herb- and food-drug interactions on CBZ is warranted to provide guidance for medical professionals when prescribing CBZ. Method. A systematic review was conducted on six English databases and four Chinese databases. Results. 196 out of 3179 articles fulfilled inclusion criteria, of which 74 articles were reviewed and 33 herbal products/dietary supplement/food interacting with CBZ were identified. No fatal or severe interactions were documented. The majority of the interactions were pharmacokinetic-based (80%). Traditional Chinese medicine accounted for most of the interactions (n = 17), followed by food (n = 10), dietary supplements (n = 3), and other herbs/botanicals (n = 3). Coadministration of 11 and 12 of the studied herbal products/dietary supplement/food significantly decreased or increased the plasma concentrations of CBZ. Regarding pharmacodynamic interaction, Xiao-yao-san, melatonin, and alcohol increased the side effects of CBZ while caffeine lowered the antiepileptic efficacy of CBZ. Conclusion. This review provides a comprehensive summary of the documented interactions between CBZ and herbal products/food/dietary supplements which assists healthcare professionals to identify potential herb-drug and food-drug interactions, thereby preventing potential adverse events and improving patients' therapeutic outcomes when prescribing CBZ.

Prophylactic treatment with melatonin after status epilepticus: effects on epileptogenesis, neuronal damage, and behavioral changes in a kainate model of temporal lobe epilepsy

Melatonin is a potent antioxidant which showed anticonvulsant activities both in experimental and clinical studies. In the present study, we examined the effect of melatonin treatment (10mg/kg/day, diluted in drinking water, 8 weeks) during epileptogenesis on the consequences of a kainate (KA)-induced status epilepticus (SE) in rats. Melatonin increased the latency in the appearance of spontaneous recurrent seizures (SRSs) and decreased their frequency only during the treatment period. The behavioral alterations associated with hyperactivity, depression-like behavior during the light phase, and deficits in hippocampus-dependent working memory were positively affected by melatonin treatment in rats with epilepsy. Melatonin reduced the neuronal damage in the CA1 area of the hippocampus and piriform cortex and recovered the decrease of hippocampal serotonin (5-HT) level in rats with epilepsy. Taken together, long-term melatonin treatment after SE was unable to suppress the development of epileptogenesis. However, it showed a potential in reducing some of the deleterious alterations that develop during the chronic epileptic state in a diurnal phase-dependent mode.

Effect of melatonin on seizure frequency in intractable epilepsy: a pilot study

Melatonin is effective for treating sleep-wake cycle disturbances and has been reported occasionally to decrease epileptic seizure frequency, with no long-term side effects. In this pilot study, the investigators examined the effect of melatonin on seizures, sleep quality, and behavior in 10 patients aged 9 to 32 years with intractable epilepsy. Patients were randomized to receive melatonin (10 mg daily at bedtime) followed by placebo or placebo followed by melatonin for 3 weeks each, with a 1-week washout period in between. Seizure frequency was monitored by daily diaries and actigraphy recordings; behavioral and sleep parameters were rated by caregivers. Diurnal seizures decreased significantly with melatonin compared with placebo (P = .034, Wilcoxon test). Maximal number of seizures, seizure duration, sleep efficiency or latency, and behavioral parameters remained unchanged. No major side effects or seizure aggravation were documented. It is concluded that melatonin could be effective and safe for decreasing daytime seizure frequency in patients with intractable epilepsy.

Anticonvulsant effects of agomelatine in mice

Agomelatine is a potent MT1 and MT2 melatonin receptor agonist and a 5-HT2C serotonin receptor antagonist. We analyzed whether agomelatine has anticonvulsant properties. The anticonvulsant activity of agomelatine (25, 50 or 75 mg/kg, i.p.) was evaluated in mouse models of pentylenetetrazole (PTZ-85 mg/kg, i.p.), pilocarpine (400mg/kg, i.p.), picrotoxin (7 mg/kg, i.p.), strychnine (75 mg/kg, i.p.) or electroshock-induced convulsions. In the PTZ-induced seizure model, agomelatine (at 25 or 50mg/kg) showed a significant increase in latency to convulsion, and agomelatine (at 50 or 75 mg/kg) also increased significantly time until death. In the pilocarpine-induced seizure model, only agomelatine in high doses (75 mg/kg) showed a significant increase in latency to convulsions and in time until death. In the strychnine-, electroshock- and picrotoxin-induced seizure models, agomelatine caused no significant alterations in latency to convulsions and in time until death when compared to controls. Our results suggest that agomelatine has anticonvulsant activity shown in PTZ- or pilocarpine-induced seizure models.

An isolated epileptic seizure elicits learning impairment which could be prevented by melatonin

We tested the relation between a single short tonic-clonic seizure elicited by flurothyl vapors and changes of learning in Morris water maze (MWM) in Wistar rats. Oxidative stress usually accompanies seizures. Large melatonin doses were applied immediately before and after seizures to test consequences on learning impairment. One hour of hypobaric hypoxia (8000 m) three days prior to the seizure served as an activator of intrinsic antioxidant systems. Learning in MWM (7 days) started 24 h after seizures. Following seizures, latencies in MWM were longer than in controls and were shortened by hypoxia and preventive melatonin application. Melatonin was also applied before hypoxia to influence free radical (FR) production and intrinsic antioxidant activation. Some behavioral characteristics were changed and preconditioning effect of hypoxia was reduced. Melatonin after seizure (150 s and 6 h) had negligible effect. Results allow us to hypothesize about the role of FR and the beneficial effect of melatonin on the behavioral consequences of seizures.

Alzheimer's disease: pathological mechanisms and the beneficial role of melatonin

Alzheimer's disease (AD) is a highly complex neurodegenerative disorder of the aged that has multiple factors which contribute to its etiology in terms of initiation and progression. This review summarizes these diverse aspects of this form of dementia. Several hypotheses, often with overlapping features, have been formulated to explain this debilitating condition. Perhaps the best-known hypothesis to explain AD is that which involves the role of the accumulation of amyloid-β peptide in the brain. Other theories that have been invoked to explain AD and summarized in this review include the cholinergic hypothesis, the role of neuroinflammation, the calcium hypothesis, the insulin resistance hypothesis, and the association of AD with peroxidation of brain lipids. In addition to summarizing each of the theories that have been used to explain the structural neural changes and the pathophysiology of AD, the potential role of melatonin in influencing each of the theoretical processes involved is discussed. Melatonin is an endogenously produced and multifunctioning molecule that could theoretically intervene at any of a number of sites to abate the changes associated with the development of AD. Production of this indoleamine diminishes with increasing age, coincident with the onset of AD. In addition to its potent antioxidant and anti-inflammatory activities, melatonin has a multitude of other functions that could assist in explaining each of the hypotheses summarized above. The intent of this review is to stimulate interest in melatonin as a potentially useful agent in attenuating and/or delaying AD.

Melatonin utility in neonates and children

Melatonin (N-acetyl-5-methoxytryptamine) is an endogenously produced indoleamine secreted by the pineal gland and the secretion is suppressed by light. Melatonin is a highly effective antioxidant, free radical scavenger, and has anti-inflammatory effect. Plenty of evidence supports the utility of melatonin in adults for cancer, neurodegenerative disorders, and aging. In children and neonates, melatonin has been used widely, including for respiratory distress syndrome, bronchopulmonary dysplasia, periventricular leukomalacia (PVL), hypoxia-ischemia encephalopathy and sepsis. In addition, melatonin can be used in childhood sleep and seizure disorders, and in neonates and children receiving surgery. This review article discusses the utility of melatonin in neonates and children.

The interaction of melatonin and agmatine on pentylenetetrazole-induced seizure threshold in mice

Melatonin, the major hormone produced by the pineal gland, has a number of functions in mammals, for example, its function as an anticonvulsant. Agmatine, a biogenic amine formed by decarboxylation of L-arginine by arginine decarboxylase, also has anticonvulsant effects. This study investigated the effect of the interaction of melatonin and agmatine on seizure susceptibility in the mouse model of pentylenetetrazole (PTZ)-induced clonic seizures. Further, the researchers investigated the involvement of melatonin receptors in this interaction using luzindole, a ML(1/2) receptor antagonist and prazosin, a ML(3) receptor antagonist. Melatonin, at 40 and 80 mg/kg, and agmatine, at 10 and 20mg/kg, exerted anticonvulsant effects. Luzindole, at 1.25 and 2.5mg/kg, or prazosin, at 0.5mg/kg, did not change the seizure threshold as compared with that of vehicle-treated mice. The anticonvulsant effect of melatonin (40 and 80 mg/kg) was prevented by luzindole (2.5mg/kg) (P<0.001) but not prazosin (0.5mg/kg), indicating the possible involvement of ML(1/2) receptors in the anticonvulsant effect of melatonin. Agmatine (5mg/kg) significantly increased the anticonvulsant effect of both the noneffective dose (20mg/kg) (P<0.05) and the effective dose (80 mg/kg) (P<0.001) of melatonin. Luzindole (2.5mg/kg), but not prazosin (0.5mg/kg), decreased the anticonvulsant effect of agmatine (20mg/kg) (P<0.05). Luzindole (2.5mg/kg), but not prazosin (0.5mg/kg), also decreased the seizure threshold when agmatine (5mg/kg) was administered before melatonin (20mg/kg); the decrease was significant compared with that of the group that received only agmatine and melatonin (P<0.001). In conclusion, melatonin and agmatine exhibit an additive effect in decreasing pentylenetetrazole-induced seizure threshold in mice, probably through ML(1/2) receptors.

Melatonin in experimental seizures and epilepsy

Although melatonin is approved only for the treatment of jet-lag syndrome and some types of insomnia, clinical data suggest that it is effective in the adjunctive therapy of osteoporosis, cataract, sepsis, neurodegenerative diseases, hypertension, and even cancer. Melatonin also modulates the electrical activity of neurons by reducing glutamatergic and enhancing GABA-ergic neurotransmission. The indoleamine may also be metabolized to kynurenic acid, an endogenous anticonvulsant. Finally, the hormone and its metabolites act as free radical scavengers and antioxidants. The vast majority of experimental data indicates anticonvulsant properties of the hormone. Melatonin inhibited audiogenic and electrical seizures, as well as reduced convulsions induced by pentetrazole, pilocarpine, L-cysteine and kainate. Only a few studies have shown direct or indirect proconvulsant effects of melatonin. For instance, melatonin enhanced low Mg2+-induced epileptiform activity in the hippocampus, whereas melatonin antagonists delayed the onset of pilocarpine-induced seizures. However, the relatively high doses of melatonin required to inhibit experimental seizures can induce some undesired effects (e.g., cognitive and motor impairment and decreased body temperature). In humans, melatonin may attenuate seizures, and it is most effective in the treatment of juvenile intractable epilepsy. Its additional benefits include improved physical, emotional, cognitive, and social functions. On the other hand, melatonin has been shown to induce electroencephalographic abnormalities in patients with temporal lobe epilepsy and increase seizure activity in neurologically disabled children. The hormone showed very low toxicity in clinical practice. The reported adverse effects (nightmares, hypotension, and sleep disorders) were rare and mild. However, more placebo-controlled, double-blind randomized clinical trials are needed to establish the usefulness of melatonin in the adjunctive treatment of epilepsy.

Parkinson's disease as a neuroendocrine disorder of circadian function: dopamine-melatonin imbalance and the visual system in the genesis and progression of the degenerative process

For more than 50 years, Parkinson's disease (PD) has been conceptualized as a product of nigro-striatal dopamine (NSD) system degeneration. In spite of a growing body of evidence depicting the mammalian brain as an interrelated complexity of circuitous systems, dopamine (DA) deficiency of the NSD is still regarded as the main problem, with DA replacement being the purpose of therapeutic intervention. For at least 191 years circadian involvement in various aspects of PD, including depression and insomnia, has been recognized as an integral part of the symptom matrix of PD and yet attempts to elucidate the involvement of this system is uncharted territory. The present review attempts a major reorganization of mammalian brain into a coordinated complex involving the NSD and the retinal hypothalamic tract (RHT) as the primary systems involved in the retino-diencephalic/mesencephalic-pineal (RDMP) axis. Secondary systems including the lateral hypothalamus (LH), the area postraema (AP) and the subthalamic nucleus (STN) also form an integral part of this system as they have been shown to be either intimately related to the primary systems of the RDMP axis or have been shown to be significantly involved in the expression and treatment of PD. A large volume of evidence suggests that the RDMP axis is activated during the course of PD and during therapeutic intervention. Four types of neurotoxicity associated with melatonin are identified and the susceptibility of various parts of the RDMP axis to undergo neuropathological change, the tendency for melatonin to induce PD-like behavioural toxicity, and the relationship of this to PD symptomotology are described. This includes adverse effects of melatonin on motor function, hypotension, the adjuvant use of benzodiazepines, depression, insomnia, body weight regulation and various biochemical effects of melatonin administration: all problems currently facing the proposal to introduce melatonin as an adjuvant. It is suggested further that traditional DA replacement may well work by exerting its effect upon the circadian system, rather than simply replacing deficient DA. Activation of the circadian function by antagonizing melatonin with bright light not only has therapeutic value in treating the primary symptoms of PD but it shares a common mechanism with L-dopa in reducing the occurrence of seborrheic dermatitis. Concepts at the centre of understanding pineal function in PD, including pineal calcification, melatonin deficiency, symptomatic versus protective features of melatonin and antioxidative effects, are explained in a counterintuitive context. Intriguing propositions including the role of the retina in the aetiology of PD and that the nigra functions as a retina in this disorder are presented with the intention to provide a new understanding of the underlying compromised function in PD and to provide new treatment strategies. For the first time, abundant evidence is presented describing PD as an endocrine disorder of melatonin hyperplasia. The role of circadian interventive therapies and internal desynchrony in the aetiology and progression of PD provides a new direction for understanding the underlying physiology of a disease which is currently in a state of impasse and provides new hope for those who suffer from its debilitating effects.

Melatonin enhances the anticonvulsant and proconvulsant effects of morphine in mice: Role for nitric oxide signaling pathway

Melatonin has different interactions with opioids including enhancing their analgesic effect and reversal of opioid tolerance and dependence. Opioids are known to exert dose-dependent anti- and proconvulsant effects in different experimental seizure paradigms. This study investigated the effect of melatonin on biphasic modulation of seizure susceptibility by morphine, in mouse model of pentylenetetrazole (PTZ)-induced clonic seizures. We further investigated the involvement of the nitric oxidergic pathway in this interaction, using a nitric oxide synthase inhibitor, NG-nitro-L-arginine-methyl-ester (L-NAME). Melatonin exerted anticonvulsant effect with doses as high as 40-80 mg/kg, but with a dose far bellow that amount (10 mg/kg), it potentiated both the anticonvulsant and proconvulsant effects of morphine on the PTZ-induced clonic seizures. Possible pharmacokinetic interaction of melatonin and morphine cannot be ruled out in the enhancement of two opposing effects of morphine on seizure threshold. L-NAME (1 mg/kg) reversed the anticonvulsant property of the combination of melatonin (10 mg/kg) plus morphine (0.5 mg/kg). Moreover, L-NAME (5 mg/kg) blocked the enhancing effect of melatonin (10 mg/kg) on proconvulsant activity of morphine (60 mg/kg). Our results indicate that co-administration of melatonin enhances both anti- and proconvulsant effects of morphine via a mechanism that may involve the nitric oxidergic pathway.

Effect of chronic consumption of sodium valproate and melatonin on seizure activity in Krushinskii-Molodkina rats

Experiments on Krushinskii-Molodkina rats with hereditary predisposition to audiogenic seizures showed that chronic consumption of aqueous solution of melatonin (50 mg/liter) had no effect on the pattern of seizures induced by 20-fold acoustic stimulation. Sodium valproate (50 mg/liter) insignificantly decreased the seizure response. Combined treatment with sodium valproate and melatonin produced a potent anticonvulsant effect, i.e. increased the latency and decreased the severity of audiogenic seizures. However, myoclonus in animals receiving combined treatment with these drugs developed much more rapidly compared to rats receiving melatonin or sodium valproate monotherapy.

Anticonvulsant effects of melatonin on penicillin-induced epileptiform activity in rats

In the present study, we investigated the effects of melatonin on penicillin-induced epileptiform activity in female Wistar rats. The left cerebral cortex was exposed by craniotomy under urethane anesthesia for the induction of epilepsy by intracortical microinjection of penicillin (200 IU) into the left sensorimotor cortex. The epileptiform activity was analyzed by electrocorticogram (ECoG). Ten minutes before the penicillin injection, 20, 40 or 80 microg of melatonin was administered intracerebroventricularly and ECoG was monitored for 1 h. Forty or 80 microg of melatonin significantly increased the latency to epileptiform activity. Furthermore, melatonin significantly decreased the frequency of spike and spike-wave activity, whereas the amplitude of spikes remained unchanged. In conclusion, data obtained from the present study suggest that melatonin suppresses penicillin-induced epileptiform activity, and it may be an endogenous anticonvulsant.

Involvement of nitric oxide pathway in the acute anticonvulsant effect of melatonin in mice

Melatonin, the major hormone produced by the pineal gland, is shown to have anticonvulsant effects. Nitric oxide (NO) is a known mediator in seizure susceptibility modulation. In the present study, the involvement of NO pathway in the anticonvulsant effect of melatonin in pentylenetetrazole (PTZ)-induced clonic seizures was investigated in mice. Acute intraperitoneal administration of melatonin (40 and 80 mg/kg) significantly increased the clonic seizure threshold induced by intravenous administration of PTZ. This effect was observed as soon as 1 min after injection and lasted for 30 min with a peak effect at 3 min after melatonin administration. Combination of per se non-effective doses of melatonin (10 and 20 mg/kg) and nitric oxide synthase (NOS) substrate L-arginine (30, 60 mg/kg) showed a significant anticonvulsant activity. This effect was reversed by NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME, 30 mg/kg), implying an NO-dependent mechanism for melatonin effect. Pretreatment with L-NAME (30 mg/kg) and N(G)-nitro-L-arginine (L-NNA, 10 mg/kg) inhibited the anticonvulsant property of melatonin (40 and 80 mg/kg) and melatonin 40 mg/kg, respectively. Specific inducible NOS (iNOS) inhibitor aminoguanidine (100 and 300 mg/kg) did not affect the anticonvulsant effect of melatonin, excluding the role of iNOS in this phenomenon, while pretreatment of with 7-NI (50 mg/kg), a preferential neuronal NOS inhibitor, reversed this effect. The present data show an anticonvulsant effect for melatonin in i.v. PTZ seizure paradigm, which may be mediated via NO/L-arginine pathway by constitutively expressed NOS.

Influence of pinealectomy on the amygdala kindling development in rats

A considerable number of studies have demonstrated the anticonvulsant effect of melatonin. The present study examines the influence of pinealectomy on the amygdala kindling development in rats. Animals were divided into three groups: Pinealectomized rats (PNT) Sham rats (SHAM) and Control rats (CTL). The mean number of stimulations and the afterdischarge (AD) duration for each stage of kindling were similar among CTL and SHAM animals. Conversely, PNT animals showed particular characteristics during kindling development. They did not present stage 1 and spent a shorter time in stage 2 in relation to the CTL and SHAM animals. Consequently, the number of stimulations required to reach stage 5 was lower for the PNT group when compared to the CTL and SHAM groups. Besides, a longer AD duration during stage 5 in the PNT group was also observed. The present findings indicate that the pineal gland removal exert a significant influence on amygdala kindling development suggesting that melatonin holds potential interest in experimental therapy for epilepsy.

Possible role of free radicals in theophylline-induced seizures in mice

Theophylline is a methylxanthine bronchodilator with a narrow therapeutic index and is prone to induce seizures, the mechanisms for which are not clearly defined. Free radicals have considerable neurotoxic potential and the present study evaluated the possible involvement of these bioactive moieties in aminophylline-induced seizures in mice. Aminophylline (50-250 mg/kg) induced convulsions and mortality in mice in a dose-dependent manner. The anti-oxidants, melatonin (25-100 mg/kg) and N-actylcysteine (100 and 200 mg/kg) attenuated aminophylline seizures and mortality. Similar antagonism of aminophylline seizures was also observed after pretreatments with nitric oxide (NO) synthase inhibitors, L-NAME (3 and 10 mg/kg) and 7-nitroindazole (10 and 30 mg/kg). Further, combined treatment with otherwise sub-effective doses of melatonin and L-NAME or 7-nitroindazole produced marked protective effects against these seizures. Aminophylline-induced seizures enhanced malondialdehyde (MDA) concentrations and NO metabolite (NOx) levels in the brain homogenates of mice, and these were attenuated by melatonin and L-NAME pretreatments. The results are suggestive of the possible involvement of free radicals (reactive oxygen and reactive nitrogen species) in the convulsiogenic effects of aminophylline.

Hippocampal melatonin receptors modulate seizure threshold

PURPOSE

The pineal hormone melatonin has been shown to enhance hippocampal excitability. We therefore investigated whether inactivation of hippocampal melatonin receptors affects behavioral seizures.

METHODS

Intrahippocampal infusions were performed in rats to study the effect of different melatonin receptor antagonists on behavioral activity, EEG, and seizure susceptibility. Experiments were conducted at 2 times of the day that coincided with the peak and trough of the daily melatonin rhythm.

RESULTS

Local infusion of the Mel(1b) receptor antagonist 4-phenyl-2-propionamidotetralin (4-P-PDOT) into the hippocampus, but not the overlying neocortex, significantly increased seizure latency and in some cases provided complete protection against seizure development. In addition, 4-P-PDOT suppressed open field activity and hippocampal EEG amplitude. The mixed Mel(1a)/Mel(1b) receptor antagonist luzindole also increased seizure latency but to a lesser degree than 4-P-PDOT. The behavioral effects of Mel(1b) receptor inhibition were comparable to those of the gamma-aminobutyric acid (GABA)(A) receptor agonist muscimol and were observed during the dark phase (2400-0200 h) but not the light phase (1200-1400 h) of the daily photocycle. The anticonvulsant effect of intrahippocampal infusion of 4P-P-DOT was blocked by coadministration of the GABA(A) antagonist bicuculline.

CONCLUSIONS

Our results suggest that nocturnal activation of hippocampal Mel(1b) receptors depresses GABA(A) receptor function in the hippocampus and enhances seizure susceptibility.

Isobolographic and subthreshold methods in the detection of interactions between oxcarbazepine and conventional antiepileptics--a comparative study

Until now, a character of interactions among the antiepileptic drugs (AEDs), in some experimental models of epilepsy, has been determined alternatively with subthreshold and isobolographic methods. In order to elicit the precise and adequate method for evaluating two drug interactions, the comparative study was performed in the maximal electroshock-induced seizure test in mice. In this experimental model, the exact types of interactions among oxcarbazepine (OXC) and conventional AEDs (diphenylhydantoin, phenobarbital, valproate, carbamazepine, and clonazepam) were determined with both methods. Results from the subthreshold method showed a considerable reduction of ED(50) values of clonazepam, diphenylhydantoin and valproate (after administration of OXC at the highest subthreshold dose of 2.5 mg/kg), whilst ED(50)s of carbamazepine or phenobarbital were almost unchanged when OXC (2.5 mg/kg) was co-administered with these AEDs. Results from the 2-dimensional (2-D) isobolographic analysis of interactions for a 50% anticonvulsant effect, for three fixed drug dose ratio combinations of 1:2, 1:1, and 2:1, indicate antagonism between OXC and diphenylhydantoin as regards their anticonvulsant (protective) activity. Furthermore, the interactions between OXC and clonazepam occurred either antagonistic (for the fixed-ratios of 1:4 and 1:3) or synergistic (for the fixed-ratio combinations of 1:1 and 2:1) depending on the proportions of used drugs. Remaining interactions between OXC and carbamazepine, OXC and valproate, or OXC and phenobarbital (for the fixed-ratios of 1:3, 1:1, and 3:1) were isobolographically additive for a 50% anticonvulsant effect tested. The 3-dimensional (3-D) isobolographic analysis of interactions between OXC and CZP revealed that the dual character of interactions (antagonistic and synergistic) observed for a 50% anticonvulsant effect (ED(50)) was also present for additional drug-dose effects tested, i.e. ED(16) and ED(84). The 3-D isobologram for the combination of OXC with CZP clearly visualized either synergy or antagonism between the drugs in combinations.Distinct differences resulting from two experimental methods prove evidently the superiority of isobolographic analysis over the subthreshold method. The former clearly and adequately detects the exact types of interactions between two AEDs, becoming a potent and powerful paradigm for further studies evaluating the character of interactions among AEDs.

Influence of antazoline and ketotifen on the anticonvulsant activity of conventional antiepileptics against maximal electroshock in mice

Experimental studies have indicated that the central histaminergic system plays an important role in the inhibition of seizures through the stimulation of histamine H1 receptors. H1 receptor antagonists, including classical antiallergic drugs, occasionally may induce convulsions in healthy children and patients with epilepsy. The purpose of this study was to investigate the effects of antazoline and ketotifen (two H1 receptor antagonists) on the anticonvulsant activity of antiepileptic drugs against maximal electroshock (MES)-induced convulsions in mice. The following antiepileptic drugs were used: valproate, carbamazepine, diphenylhydantoin and phenobarbital. In addition, the effects of antiepileptic drugs alone or in combination with antazoline or ketotifen were studied on long-term memory (tested in the passive avoidance task) and motor performance (evaluated in the chimney test), acutely and after 7-day treatment with these H1 receptor antagonists. The influence of antazoline and ketotifen on the free plasma and brain levels of the antiepileptics was also evaluated. Antazoline (at 0.5 mg/kg), given acutely and after 7-day treatment, significantly diminished the electroconvulsive threshold. Similarly, ketotifen, after acute and chronic doses of 8 mg/kg markedly reduced the threshold for electroconvulsions. In both cases, antazoline and ketotifen were without effect upon this parameter at lower doses. Antazoline (0.25 mg/kg) significantly raised the ED50 value of carbamazepine against MES (both, acutely and after 7-day treatment). Furthermore antazoline (0.25 mg/kg) also reduced the anticonvulsant activity of diphenylhydantoin, but only after repeated administration, without modifying the brain and free plasma level of this drug. Moreover, valproate and phenobarbital did not change their protective activity when combined with antazoline. Ketotifen (4 mg/kg) possessed a biphasic action, acutely it enhanced the anticonvulsant action of carbamazepine and phenobarbital while, following 7-day treatment, reduced the antiseizure activity of carbamazepine. Ketotifen did not affect the free plasma or brain levels of antiepileptics tested. Only acute antazoline (0.25 mg/kg) applied with valproate impaired the performance of mice evaluated in the chimney test. Ketotifen (4 mg/kg) co-administered with conventional antiepileptic drugs impaired motor coordination in mice treated with valproate, phenobarbital or diphenylhydantoin. Acute and chronic antazoline (0.25 mg/kg) alone or in combination with antiepileptic drugs did not disturb long-term memory, tested in the passive avoidance task. Similarly, ketotifen (4 mg/kg) did not impair long-term memory, acutely and after 7-day treatment. However, valproate alone or in combination with chronic ketotifen (4 mg/kg) worsened long-term memory. The results of this study indicate that H1 receptor antagonists, crossing the blood brain barrier, should be used with caution in epileptic patients. This is because antazoline reduced the protective potential of diphenylhydantoin and carbamazepine. Also, ketotifen reduced the protection offered by carbamazepine and elevated the adverse activity of diphenylhydantoin, phenobarbital and valproate.

Changes in brain amino acids and nitric oxide after melatonin administration in rats with pentylenetetrazole-induced seizures

We examined the effect of melatonin on brain levels of amino acids and nitric oxide (NO) after pentylenetetrazole (PTZ)-induced seizures in rats. Animals were treated with melatonin (10-160 mg/kg, i.p.) 30 min before PTZ administration (100 mg/kg, s.c.), and were killed 3 hr later. At the dose of 80 mg/kg, melatonin significantly increased the latency (5.7-12.7 min) and decreased the duration (31.2-18.4 s) of the first seizure, reducing PTZ induced mortality from 87.5 to 25%. After kill, brains were removed and neurotransmitters and nitrite levels measured in prefrontal cortex (PF), parieto-temporal cortex (PF), striatum (ST), hippocampus (HP) and brain stem (BS) by high performance liquid chromatography. PTZ treatment increased glutamine levels in all brain areas studied, without changes in glutamate, gamma-amino butyric acid (GABA) and glycine. Aspartate and taurine increased in PF and PT and in HS and PT, respectively. Melatonin administration displayed a dose-dependent effect. At doses of 10-40 mg/kg, melatonin counteracted the PTZ-induced glutamine increase and reduced both glutamate and aspartate levels in the studied areas, with minor changes in GABA and glycine content. At doses of 80 and 160 mg/kg, the levels of glutamine, and glutamate, and to a lesser extent aspartate increased, whereas serine levels did not change. These two doses of melatonin also increased taurine, GABA and glycine in most brain areas studied. Treatment with melatonin (40-160 mg/kg) significantly decreased nitrite content in PT cortex, ST and BS areas of epileptic rats, without changes in the other brain regions. The results suggest that the anticonvulsant property of melatonin involves a modulation of both brain amino acids and NO production.

[Video screen exposure and 6-sulfatoxymelatonin urinary excretion in women]

A study in blind conditions was conducted on 13 women (mean age < 30 years). Six women worked at least four hours per day, five days a week, since more than one month, in front of a video screen constituted the exposed group. Radioimmunoassay of 6-sulfatoxymelatonin was done on urine collected during night. Results were analysed by a non parametric rank-test (Mann-Withney). It was observed an important (- 54%) and significant lower level (p < 0.01) of 6-sulfatoxymelatonin in urine of women exposed to video screen.

Melatonin: reducing the toxicity and increasing the efficacy of drugs

Melatonin (N-acetyl-5-methoxytryptamine) is a molecule with a very wide phylogenetic distribution from plants to man. In vertebrates, melatonin was initially thought to be exclusively of pineal origin recent studies have shown, however, that melatonin synthesis may occur in a variety of cells and organs. The concentration of melatonin within body fluids and subcellular compartments varies widely, with blood levels of the indole being lower than those at many other sites. Thus, when defining what constitutes a physiological level of melatonin, it must be defined relative to a specific compartment. Melatonin has been shown to have a variety of functions, and research in the last decade has proven the indole to be both a direct free radical scavenger and indirect antioxidant. Because of these actions, and possibly others that remain to be defined, melatonin has been shown to reduce the toxicity and increase the efficacy of a large number of drugs whose side effects are well documented. Herein, we summarize the beneficial effects of melatonin when combined with the following drugs: doxorubicin, cisplatin, epirubicin, cytarabine, bleomycin, gentamicin, ciclosporin, indometacin, acetylsalicylic acid, ranitidine, omeprazole, isoniazid, iron and erythropoietin, phenobarbital, carbamazepine, haloperidol, caposide-50, morphine, cyclophosphamide and L-cysteine. While the majority of these studies were conducted using animals, a number of the investigations also used man. Considering the low toxicity of melatonin and its ability to reduce the side effects and increase the efficacy of these drugs, its use as a combination therapy with these agents seems important and worthy of pursuit.

Attenuating effects of melatonin on pilocarpine-induced seizures in rats

Daily melatonin (10-50 mg/kg, i.p.) treatment at 08.30 h or 17.00 h for 1 week of female rats (2-months-old) increased the latency to the appearance of the first convulsion in the pilocarpine-induced seizure model. Other behavior parameters remained unaltered. The anticonvulsant effect of melatonin seemed to be more intense at the light-dark transition. Moreover, the effect of repeated melatonin treatment was also age-related, since it showed a lower threshold in 2-month-old than in 21-day-old rats, and the acute treatment was not efficient. [3H]N-methylscopolamine binding was unaltered in the hippocampus and striatum of adult rats after the association of melatonin and pilocarpine. While muscarinic binding was unaltered in adult rats, it increased in the hippocampus of young rats in the presence of melatonin (50 mg/kg) and pilocarpine, and did not change in the striatum. Melatonin partially recovered [3H]GABA binding in the hippocampus in the presence of pilocarpine-induced seizures, and intensified pilocarpine effects in the striatum of adult rats.

Propranolol and metoprolol enhance the anticonvulsant action of valproate and diazepam against maximal electroshock

The anticonvulsive potential of classical antiepileptics co-administered with beta-adrenergic receptor antagonists against generalized tonic-clonic seizures was evaluated in the model of maximal electroshock (MES)-induced convulsions. Propranolol, acebutolol, metoprolol and atenolol were tested in the doses not affecting the electroconvulsive threshold. Propranolol and metoprolol lowered the ED(50) of valproate and diazepam. Acebutolol reduced valproate's but not diazepam's ED(50) value. In contrast, hydrophilic atenolol, not penetrating via blood-brain barrier, affected neither the action of valproate nor diazepam. None of the studied drugs changed the protective activity of carbamazepine and phenytoin against MES. beta-blockers per se did not alter the motor performance of mice. Moreover, propranolol and metoprolol did not influence diazepam-evoked impairment of locomotor activity. The free plasma and brain levels of antiepileptic drugs were not affected by beta-blockers. In conclusion, the use of certain beta-adrenoceptor antagonists, such as propranolol and metoprolol, might improve the antiepileptic potential of valproate and diazepam.

Melatonin effect on seizures in children with severe neurologic deficit disorders

PURPOSE

Recently, melatonin has been associated with antiepileptic activity, most probably because of its antioxidant activity as a free radical scavenger. This study aimed to expand the clinical experience with melatonin as an antiepileptic drug (AED) in humans.

METHODS

Six children (aged 2-15 years), with severe intractable seizures, were treated with 3 mg of oral melatonin 30 min before bedtime, in addition to their previous AED treatment for 3 months. A diary of clinical seizure activity (time of day, duration, and type) was kept by parents for a month before and during treatment. Five patients underwent a baseline polysomnography, and three also were monitored during melatonin treatment.

RESULTS

With the exception of the parents of one child, all reported a significant clinical improvement in seizure activity during treatment, particularly during the night. Sleep studies showed a decrease in epileptic activity in two of the three patients who were monitored during treatment, and a change of sleep efficiency from 84.2% to 89.7% (NS). Improvement in daytime behavior and in communication abilities was reported by parents, although it was not objectively measured.

CONCLUSIONS

This clinical observation adds to the growing data showing the antiepileptic effect of melatonin. However, owing to the paucity of well-controlled studies, using melatonin as an AED should be limited to this specific group of patients with intractable seizures.

Changes in the antioxidant system in epileptic children receiving antiepileptic drugs: two-year prospective studies

The aim of this study was to measure changes in the antioxidant systems of epileptic children who had been receiving either valproate or carbamazepine monotherapy for 2 years. For this purpose, levels of erythrocyte glutathione, glutathione peroxidase, superoxide dismutase, and serum lipid peroxidation in 25 healthy children and 27 children who had previously been diagnosed as having epilepsy but who had not, prior to the study, received antiepileptic drugs were tested. Of the 27 epileptic children, 14 were given valproate, and the remaining 13 were given carbamazepine; these tests were repeated in the 13th and 24th months of treatment. The results showed that, during valproate therapy, the lipid peroxidation levels of the epileptic children increased and the glutathione peroxidase levels decreased in comparison with those levels recorded in the control and pretreatment groups. In addition, the superoxide dismutase levels were found to be increased during the first year of valproate therapy when compared with those of the pretreatment group. However, during carbamazepine therapy, lipid peroxidation levels increased when compared with the control group only, not the pretreatment group. Furthermore, the results showed that during the second year of treatment, the superoxide dismutase levels of the children receiving carbamazapine monotherapy were found to be higher than those of both the control and pretreatment groups. From these results, it can be concluded that the antioxidant systems of the children who had been receiving valproate therapy during the 2 years were more significantly affected than those of the children who had been receiving carbamazepine.

Endogenous melatonin and epileptogenesis: facts and hypothesis

In human epilepsy, diurnal variation in seizure phenomena suggests the involvement of a time-dependent biological signal. Clinical evidence indicates that in some cases, temporal clustering of epileptic seizures is in phase with the nocturnal rise in circulating melatonin. Although this hormone has been reported to stabilize the brain against seizure-producing stimuli, these pharmacological doses are not representative of physiological conditions but would nonetheless facilitate widespread inhibitory neurotransmission characteristic of traditional anticonvulsants. Instead, it is proposed that endogenous melatonin contributes to epileptiform activity through inhibitory actions on dopaminergic activity. Dopamine is considered a natural downregulator of seizure activity in a number of species, including humans, and numerous lines of evidence suggest that melatonin is capable of stimulating a decrease in dopamine output within areas of the brain thought to participate in the control of epileptic seizures. Pharmacological manipulation of the endogenous melatonin rhythm may provide a useful therapeutic strategy against the occurrence of seizures during increased hormone production.

Strong olfactory stimulation reduces seizure susceptibility in amygdala-kindled rats

Seizures in human temporal lobe epilepsy are characterized by paroxysmal activity in the limbic system. The primary olfactory or piriform cortex is a central part of the limbic system. Since a relationship between olfactory sensation and limbic seizures has been described, we were interested in the effect of strong olfactory stimulation on the seizure susceptibility of amygdala-kindled rats, a model of human temporal lobe epilepsy. Olfactory stimulation with toluene was able to suppress seizures in most kindled rats after stimulation at 20% above the threshold for eliciting epileptic afterdischarges. Olfactory stimulation with toluene or ammonia increased the threshold by 27 and 25% compared to control conditions. Our data substantiate that olfactory brain regions, such as the piriform cortex, are involved in amygdala-kindled seizures and suggest that strong physiological stimulation of this nucleus interferes with on-going seizure activity in the limbic system. Thus, olfactory stimulation could contribute to anticonvulsant therapy.