Epilepsy and schizophrenia: a neurochemical bridge

In Sickness and in Health: Perineuronal Nets and Synaptic Plasticity in Psychiatric Disorders

Rapidly emerging evidence implicates perineuronal nets (PNNs) and extracellular matrix (ECM) molecules that compose or interact with PNNs, in the pathophysiology of several psychiatric disorders. Studies on schizophrenia, autism spectrum disorders, mood disorders, Alzheimer's disease, and epilepsy point to the involvement of ECM molecules such as chondroitin sulfate proteoglycans, Reelin, and matrix metalloproteases, as well as their cell surface receptors. In many of these disorders, PNN abnormalities have also been reported. In the context of the “quadripartite” synapse concept, that is, the functional unit composed of the pre- and postsynaptic terminals, glial processes, and ECM, and of the role that PNNs and ECM molecules play in regulating synaptic functions and plasticity, these findings resonate with one of the most well-replicated aspects of the pathology of psychiatric disorders, that is, synaptic abnormalities. Here we review the evidence for PNN/ECM-related pathology in these disorders, with particular emphasis on schizophrenia, and discuss the hypothesis that such pathology may significantly contribute to synaptic dysfunction.

Treatment of interictal psychiatric disorder in epilepsy. II. Chronic psychosis

BACKGROUND

Interictal psychosis is a serious comorbid condition in epilepsy patients that would benefit from treatment with psychotropic medication.

OBJECTIVE

This paper gives an overview of the pathophysiology, symptomatology and treatment of the schizophrenia-like psychosis of epilepsy. Use of the term 'interictal chronic psychosis' is suggested, to conform to current DSM-IV classification of schizophrenia.

METHODS

Literature review supplemented by clinical experience. There is a lack of randomized control trials (RCTs) concerning effectiveness and side-effects of neuroleptics in epilepsy patients.

RESULTS

Hypotheses concerning the pathophysiology of the interictal chronic psychosis are discussed. The concept of forced normalization and alternative psychosis is based on case descriptions, and was not substantiated by systematic research. The kindling hypothesis seems promising, but was never confirmed in humans. A third theory, supported by some studies, suggests that inhibitory cerebral mechanisms enhance psychotic symptoms in epilepsy patients. Treatment strategies are based on case studies and open studies by lack of RCTs. Treatment should consider the optimalization of the dosage of antiepileptics in combination with one or two antidepressants, mood stabilizers and/or atypical neuroleptics. Surgery plays no significant role in the treatment of treatment-refractive epilepsy with interictal chronic psychotic symptoms.

CONCLUSION

There is a prominent role of antidepressant or double antidepressant treatment strategies in patients with epilepsy and interictal chronic psychosis compared with treatment guidelines of chronic psychotic patients in general psychiatry.

Enhancement of basal and pentylenetetrazol (PTZ)-stimulated dopamine release in the brain of freely moving rats by PTZ-induced kindling

The effects of pentylenetetrazol (PTZ)-induced kindling on the activity of mesocortical, mesoaccumbens, and nigrostriatal dopaminergic neurons was investigated with the transversal microdialysis technique in freely moving rats. Four days after the last chronic administration of PTZ, the basal extracellular concentrations of dopamine in the prefrontal cortex, nucleus accumbens, and striatum of kindled rats were significantly increased (+76, +36, +49%, respectively) relative to those of animals chronically treated with saline. Moreover, dopamine output was markedly more sensitive to the effect of a challenge injection of PTZ (20 mg/kg ip) in the prefrontal cortex (+93 vs. +50%, relative to basal values), the nucleus accumbens (+36 vs. +4%), and the striatum (+50 vs. + 35%) of kindled rats relative to that in the control animals. Because kindled rats and their controls are habituated to handling, the neurochemical mechanisms that underlie the effects of chemical kindling on the sensitivity of dopaminergic neurons to PTZ were investigated by comparing the effects of an acute administration of PTZ (20 mg/kg ip) between naive and handling-habituated animals. The sensitivity of dopamine output to PTZ in naive rats was markedly greater than that in handling-habituated animals for the prefrontal cortex (+83 vs. +50%) and nucleus accumbens (+35 vs. +4%), but not for the striatum (+35 vs. +32%). These results indicate that PTZ kindling enhances the basal activity and the sensitivity to PTZ of dopamine neurons in rat brain and suggest that mesocortical, mesoaccumbens, and nigrostriatal dopaminergic neurons contribute to the central alterations associated with experimental epilepsy.

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).

Dopaminergic modulation of pilocarpine-induced motor seizures in the rat: the role of hippocampal D2 receptors

This study examined the role of hippocampal dopamine D2 receptors in the genesis of limbic seizures induced by muscarinic agonists in the rat. Pilocarpine, 600 mg/kg, elicited rapid and usually fatal convulsions. These were not affected by focal injections of saline (1 microliter) into both hippocampi. Pretreatment of the dorsal, but not the lateral hippocampus, with the D2 agonist trans-(+)-4,4a,5,6,7,8,8a,9-octahydro-5-propyl-2H-pyrazolo-(3,4-g)quinol ine hydrochloride (LY 171555, 2 micrograms per side), did not alter the frequency of pilocarpine-induced convulsions, but significantly delayed their appearance and reduced their intensity. LY 171555 similarly increased the latency of seizures induced by focal hippocampal injection of carbachol (100 micrograms), without changing the frequency or the severity. The selective D2 antagonist raclopride, injected dorsally into both hippocampi dose-dependently facilitated motor seizures evoked by pilocarpine (100 mg/kg), the cholinomimetic at this dose being ineffective as a convulsant in saline-treated animals. Intrahippocampal administration of the D1 agonist 2,3,4,5-tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine hydrochloride (SKF 38393, 2 micrograms per side) did not facilitate pilocarpine seizures and did not potentiate the proconvulsant action of raclopride. These data demonstrate that activation of the dopaminergic system, via D2 receptors in the dorsal hippocampus, is capable of protecting the animal against limbic motor seizures arising from excessive muscarinic stimulation of the hippocampus. Since the blockade of D2 receptors in the hippocampus markedly lowered the seizure threshold to pilocarpine, this would suggest that the dopaminergic input to the hippocampus is normally tonically active and functions physiologically to prevent epileptogenesis.

Clinical features, pathogenesis and management of drug-induced seizures

Many classes of pharmacological agents have been implicated in cases of drug-induced seizures. The list includes antidepressant drugs, lithium salts, neuroleptics, antihistamines (H1-receptor antagonists), anticonvulsants, central nervous system stimulants, general and local anaesthetics, antiarrhythmic drugs, narcotic and non-narcotic analgesics, non-steroidal anti-inflammatory drugs, antimicrobial agents, antifungal agents, antimalarial drugs, antineoplastic drugs, immunosuppressive drugs, radiological contrast agents and vaccines. For each of these classes of drugs, this article offers a revision of the literature and emphasises in particular the frequency of the adverse reaction, its clinical presentation, its presumed epileptogenic mechanism and the therapeutic strategy for the management of drug-induced seizures. An attempt is also made to distinguish seizures induced by standard dosages from those provoked by accidental or self-induced intoxication. For some classes of drugs such as antidepressants, neuroleptics, central nervous system stimulants (e.g. theophylline, cocaine, amphetamines) and beta-lactam antibiotics, seizures are a well recognised adverse reaction, and a large body of literature has been published discussing exhaustively the major aspects of the issue; sufficient data are available also for the other classes of pharmacological agents mentioned above. In contrast, several other drugs [e.g. allopurinol, digoxin, cimetidine, protirelin (thyrotrophin releasing hormone), bromocriptine, domperidone, insulin, fenformin, penicillamine, probenecid, verapamil, methyldopa] have not been studied thoroughly under this aspect, and the only source of information is the occasional case report. This review does not address the issue of seizures induced by drug withdrawal.

Psychopathology in epilepsy: prevalence, phenomenology and management

Epilepsy is associated with interictal behavioral disturbances. The pattern of specific psychopathology differs from that of other chronic diseases because of the higher incidence of psychosis and characterological disorders. Approximately 7 percent of epileptics develop a chronic atypical psychosis with paranoid and affective features, and this may be more common in patients with a definite temporal lobe focus. Brief psychotic episodes occur and are more directly related to cerebral dysrhythmia. A subgroup of epileptics develop specific personality traits, aggressive behaviors under certain circumstances, and hyposexuality. Affective illness and suicide are also prevalent. There are special issues in the management of psychopathology in the setting of epilepsy such as the relative seizure threshold lowering effects of psychotropic drugs and the behavioral effects of altering the seizure control. This article discusses both diagnostic and management aspects of the interictal psychopathology of epilepsy.