Enhancement of central dopaminergic activity in the kainate model of temporal lobe epilepsy: implication for the mechanism of epileptic psychosis

GL-II-73, a Positive Allosteric Modulator of α5GABAA Receptors, Reverses Dopamine System Dysfunction Associated with Pilocarpine-Induced Temporal Lobe Epilepsy

Although seizures are a hallmark feature of temporal lobe epilepsy (TLE), psychiatric comorbidities, including psychosis, are frequently associated with TLE and contribute to decreased quality of life. Currently, there are no defined therapeutic protocols to manage psychosis in TLE patients, as antipsychotic agents may induce epileptic seizures and are associated with severe side effects and pharmacokinetic and pharmacodynamic interactions with antiepileptic drugs. Thus, novel treatment strategies are necessary. Several lines of evidence suggest that hippocampal hyperactivity is central to the pathology of both TLE and psychosis; therefore, restoring hippocampal activity back to normal levels may be a novel therapeutic approach for treating psychosis in TLE. In rodent models, increased activity in the ventral hippocampus (vHipp) results in aberrant dopamine system function, which is thought to underlie symptoms of psychosis. Indeed, we have previously demonstrated that targeting α5-containing γ-aminobutyric acid receptors (α5GABA_ARs), an inhibitory receptor abundant in the hippocampus, with positive allosteric modulators (PAMs), can restore dopamine system function in rodent models displaying hippocampal hyperactivity. Thus, we posited that α5-PAMs may be beneficial in a model used to study TLE. Here, we demonstrate that pilocarpine-induced TLE is associated with increased VTA dopamine neuron activity, an effect that was completely reversed by intra-vHipp administration of GL-II-73, a selective α5-PAM. Further, pilocarpine did not alter the hippocampal α5GABA_AR expression or synaptic localization that may affect the efficacy of α5-PAMs. Taken together, these results suggest augmenting α5GABA_AR function as a novel therapeutic modality for the treatment of psychosis in TLE.

Differential diagnosis and comorbid physical illness of schizophrenia

Background: Schizophrenia is a neurodevelopmental disorder that generally develops during adolescence or early adulthood. However, differentiating it from psychosis caused by a physical illness is difficult due to the phenotypebased diagnostic system. In this review, differential diagnosis of schizophrenia and the comorbid physical illnesses of patients with schizophrenia will be discussed.Current Concepts: Psychotic symptoms can be caused by various physical illnesses, and patients with schizophrenia have many physical comorbidities. Symptoms of psychosis can also be expressed by physical illness including brain tumors, encephalitis, temporal lobe epilepsy, autoimmune disease, and genetic disease. For the differential diagnosis of other physical illnesses that can cause psychosis, biological tests are essential. Depending on the cause, antipsychotics and treatment of physical diseases are required. In addition, patients with schizophrenia have many comorbid medical conditions such as obesity, diabetes, cardiovascular disease, but the diagnosis rate is low, and the mortality is higher than that of the general population due to untreated medical diseases.Discussion and Conclusion: The differential diagnoses of schizophrenia and physical illness causing psychosis are important. To decrease the high mortality of patients with schizophrenia, periodic physical condition examinations and mental status examinations should be conducted.

Resting state functional network disruptions in a kainic acid model of temporal lobe epilepsy

We studied the graph topological properties of brain networks derived from resting-state functional magnetic resonance imaging in a kainic acid induced model of temporal lobe epilepsy (TLE) in rats. Functional connectivity was determined by temporal correlation of the resting-state Blood Oxygen Level Dependent (BOLD) signals between two brain regions during 1.5% and 2% isoflurane, and analyzed as networks in epileptic and control rats. Graph theoretical analysis revealed a significant increase in functional connectivity between brain areas in epileptic than control rats, and the connected brain areas could be categorized as a limbic network and a default mode network (DMN). The limbic network includes the hippocampus, amygdala, piriform cortex, nucleus accumbens, and mediodorsal thalamus, whereas DMN involves the medial prefrontal cortex, anterior and posterior cingulate cortex, auditory and temporal association cortex, and posterior parietal cortex. The TLE model manifested a higher clustering coefficient, increased global and local efficiency, and increased small-worldness as compared to controls, despite having a similar characteristic path length. These results suggest extensive disruptions in the functional brain networks, which may be the basis of altered cognitive, emotional and psychiatric symptoms in TLE.

Secondary psychoses: an update

Psychotic disorders due to a known medical illness or substance use are collectively termed secondary psychoses. In this paper, we first review the historic evolution of the concept of secondary versus primary psychosis and how this distinction supplanted the earlier misleading classification of psychoses into organic and functional. We then outline the clinical features and approach to the diagnosis of secondary psychotic disorders. Features such as atypical presentation, temporal relation to detectable medical cause, evidence of direct physiological causal relationship to the etiological agent, and the absence of evidence of a primary psychotic illness that may better explain the presentation suggest consideration of a secondary psychosis. Finally, we discuss how careful studies of secondary psychotic disorders can help elucidate the pathophysiology of primary, or idiopathic, psychotic disorders such as schizophrenia. We illustrate this issue through a discussion of three secondary psychotic disorders - psychoses associated with temporal lobe epilepsy, velocardiofacial syndrome, and N-methyl D-aspartate (NMDA) receptor encephalitis - that can, respectively, provide neuroanatomical, genetic, and neurochemical models of schizophrenia pathogenesis.

Changes on D2-like receptor induced Gi protein activation and hippocampal dopamine release in kindled rats

The present study aimed to characterize dopamine release in the hippocampus and D2-like receptor-induced Gi protein activation in several brain areas of fully kindled rats. During the interictal period, kindled rats showed lower extracellular levels of dopamine when compared with those obtained in the control group under basal conditions, a situation that was not modified when an afterdischarge was evoked. Hippocampal perfusion of sulpiride, a D2 receptor antagonist, enhanced dopamine release, which was more evident when an afterdischarge was induced in kindled rats. In addition, sulpiride perfusion was associated with longer seizure duration. Functional autoradiography experiments revealed increased [(35)S]GTPγS incorporation as a consequence of D2-like receptor activation in different brain areas of fully kindled animals, including the ventral hippocampus. The present study reveals that hippocampal kindling is associated with alterations in dopamine release and D2-like receptor-induced neurotransmission.

Pilocarpine-induced temporal lobe epilepsy in the rat is associated with increased dopamine neuron activity

Temporal lobe epilepsy (TLE) is defined as the occurrence of spontaneous seizures that involve the limbic system, with the hippocampal formation and associated structures being central to the most prevalent refractory form of adult focal epilepsy. TLE is often associated with psychotic features resembling the hallucinations and delusions that occur with schizophrenia. Given evidence that the ventral hippocampus plays an important role in the maintenance of temporal lobe seizures, we investigated whether an animal model of TLE using intrahippocampal injection of pilocarpine induces alterations in mesolimbic dopamine neuron activity. We found that in 60% of rats in which pilocarpine induced seizure activity, there was a significant increase in the number of dopamine neurons firing per electrode track. Furthermore, this occurred in concert with an increase in amphetamine-stimulated locomotor activity. Both observations are similar to those observed in a rodent developmental model of psychosis. Therefore, as in animal models of schizophrenia, TLE-associated psychosis is probably due to abnormal hippocampal overdrive of dopamine neuron activity.

Increased PLA2 activity in the hippocampus of patients with temporal lobe epilepsy and psychosis

OBJECTIVE

The aim of this work was to investigate whether increased activity of the enzyme phospholipase A(2) (PLA(2)) in the brain, as frequently reported in schizophrenia, is also related to psychosis in epilepsy. Our working hypothesis was based on the increased prevalence of schizophrenia-like psychosis in patients with temporal lobe epilepsy (TLE) secondary to mesial temporal sclerosis (MTS), as compared to patients with other forms of epilepsy.

METHODS

We determined PLA(2) activity in hippocampal tissue from 7 patients with TLE-MTS and psychosis, as compared to 9 TLE-MTS patients without psychosis. Hippocampal tissue was obtained from patients who underwent an anterior temporal lobectomy due to therapy-resistant epilepsy.

RESULTS

We found that patients with TLE-MTS and psychosis had a significantly increased calcium-independent PLA(2) activity as compared to patients without psychosis (p = 0.016).

CONCLUSION

Our finding suggest that an increment in brain PLA(2) activity is not specific for schizophrenia, but rather may be associated to the manifestation of schizophrenia-like psychotic symptoms in general.

Psychotic disorders in Argentine patients with refractory temporal lobe epilepsy: a case-control study

The issue of psychotic disorders in epilepsy has given rise to great controversy among professionals; however, there are not many studies in this area and the physiopathological mechanisms remain unknown. The aim of this study was to describe the spectrum of psychotic disorders in an Argentine population with refractory temporal lobe epilepsy (RTLE) and to determine the risk factors associated with psychotic disorders. Clinical variables of the epileptic syndrome were compared among a selected population with RTLE with and without psychotic disorders (DSM-IV/Ictal Classification of psychoses). Logistic regression was performed. Sixty-three patients with psychotic disorders (Psychotic Group, PG) and 60 controls (Control Group, CG) were included. The most frequent psychotic disorders were brief psychotic episodes (35%) (DSM-IV) and interictal psychosis (50%) (Ictal Classification). Risk factors for psychotic disorders were bilateral hippocampal sclerosis, history of status epilepticus, and duration of epilepsy greater than 20 years.

Dysfunctional GABAergic inhibition in the prefrontal cortex leading to "psychotic" hyperactivation

Background

The GABAergic system in the brain seems to be dysfunctional in various psychiatric disorders. Many studies have suggested so far that, in schizophrenia patients, GABAergic inhibition is selectively but consistently reduced in the prefrontal cortex (PFC).

Results

This study used a computational model of the PFC to investigate the dynamics of the PFC circuit with and without chandelier cells and other GABAergic interneurons. The inhibition by GABAergic interneurons other than chandelier cells effectively regulated the PFC activity with rather low or modest levels of dopaminergic neurotransmission. This activity of the PFC is associated with normal cognitive functions and has an inverted-U shaped profile of dopaminergic modulation. In contrast, the chandelier cell-type inhibition affected only the PFC circuit dynamics in hyperdopaminergic conditions. Reduction of chandelier cell-type inhibition resulted in bistable dynamics of the PFC circuit, in which the upper stable state is associated with a hyperactive mode. When both types of inhibition were reduced, this hyperactive mode and the conventional inverted-U mode merged.

Conclusion

The results of our simulation suggest that, in schizophrenia, a reduction of GABAergic inhibition increases vulnerability to psychosis by (i) producing the hyperactive mode of the PFC with hyperdopaminergic neurotransmission by dysfunctional chandelier cells and (ii) increasing the probability of the transition to the hyperactive mode from the conventional inverted-U mode by dysfunctional GABAergic interneurons.

Effects of neurotransmitter agonists on electrocortical activity in the rat kainate model of temporal lobe epilepsy and the modulatory action of basic fibroblast growth factor

We used systemic kainic acid (KA) injection to investigate how the development of temporal lobe epilepsy and the associated network reorganization affect the electrocorticogram (ECoG) responses to various neurotransmitter agonists. Unrestrained rats chronically implanted with electrodes over somatosensory cortex and dorsal hippocampus and a cannula into the right lateral ventricle were used to investigate the ECoG frequency responses of intracerebroventricularly applied agonists (NMDA, clonidine, muscimol, and baclofen) at several types of receptors [NMDA, alpha2-adrenergic (NE), GABAA, and GABAB, respectively] in KA-treated versus naïve animals. The ECoG was analyzed 2, 5, and 9 weeks after intraperitoneal injection of KA alone or in combination with basic fibroblast growth factor (bFGF, intracerebroventricularly). Within the first 5 weeks of KA injection, the ECoG power shifted towards the lower-frequency range. Concurrently, the electrographic responses to NMDA and clonidine were potentiated, whereas the ECoG effects mediated by GABAA and GABAB receptors remained largely unaffected. In control rats, bFGF strongly enhanced the electrographic NMDA responses. In sharp contrast, bFGF potently mitigated the abnormally increased NMDA sensitivity of epileptic rats, if applied 4 weeks post KA injection. These data suggest that upregulation and downregulation of the NMDA receptor-mediated effects on cortical activity might be a prominent feature of bFGF signaling in the intact and the damaged brain, respectively.