Alterations of 5-HT1A receptor-induced G-protein functional activation and relationship to memory deficits in patients with pharmacoresistant temporal lobe epilepsy

Epilepsy is more than a simple seizure disorder: Causal relationships between epilepsy and its comorbidities

This review draws connections between the pathogenesis of canine epilepsy and its most commonly recognised comorbidities: cognitive impairment (CI), attention deficit hyperactivity disorder (ADHD)-like behaviour, fear and anxiety. Uni/bidirectional causalities and the possibility of a common aetiology triggering both epilepsy and the associated diseases are considered. Research on this topic is sparse in dogs, so information has been gathered and assessed from human and laboratory animal studies. Anatomical structures, functional connections, disrupted neurotransmission and neuroinflammatory processes collectively serve as a common foundation for epilepsy and its comorbidities. Specific anatomical structures, especially parts of the limbic system, such as the amygdala and the hippocampus, are involved in generating seizures, as well as cognitive- and behavioural disorders. Furthermore, disturbances in inhibitory and excitatory neurotransmission influence neuronal excitability and networks, leading to underlying brain dysfunction. Functional magnetic resonance imaging (fMRI), interictal epileptiform discharges (IEDs), and electroencephalography (EEG) have demonstrated functional brain connections that are related to the emergence of both epilepsy and its various comorbidities. Neuroinflammatory processes can either cause or be a consequence of seizures, and inflammatory mediators, oxidative stress and mitochondrial dysfunction, can equally evoke mood disorders. The extensive relationships contributing to the development and progression of seizures and comorbid cognitive and behavioural conditions illustrate the complexity of the disease that is epilepsy.

The association between 5-HT1A binding and temporal lobe epilepsy: A meta-analysis of molecular imaging studies

BACKGROUND

Studies have shown conflicting results in the correlation between serotonin-1A (5-HT1A) receptor binding levels in the brain and temporal lobe epilepsy (TLE). There is a need to systematically evaluate the correlation between the 5-HT1A binding level and TLE from the perspective of the brain using molecular imaging.

METHODS

Chinese and English databases, such as the China National Knowledge Infrastructure (CNKI), the China Science and Technology Journal Database (VIP), WanFang, the Chinese Biomedical Literature Service System (SinoMed), PubMed and Web of Science, were searched.

RESULTS

Two evaluators independently screened the literature, extracted data, and evaluated the risk of bias in the included studies according to the inclusion and exclusion criteria. RevMan 5.4.1 was used to analyze the data. A total of 196 participants were included; of these, 95 had TLE and 131 were healthy controls who had never had a seizure before participating in the study. Meta-analysis results suggested that 1) decreased 5-HT1A binding was found on the affected side of patients with TLE (standard mean difference (SMD) = -1.45, 95% confidence interval (CI) [-2.27, -0.64], Z = 3.48, P = 0.0005); 2) decreased 5-HT1A binding was found in the ipsilateral hippocampus of patients with TLE (SMD = -1.76, 95% CI [-2.51, -1.00], Z = 4.57, P＜0.00001); 3) decreased 5-HT1A binding was found in the ipsilateral temporal lobe cortex of patients with TLE (SMD = -0.46, 95% CI [-0.80, -0.12], Z = 2.66, P = 0.008); 4) decreased 5-HT1A binding was found in the ipsilateral amygdala in patients with TLE (SMD = -1.36, 95% CI [-2.48, -0.23], Z = 2.37, P = 0.02); and 5) decreased 5-HT1A binding was found in the frontal lobe of patients with TLE(SMD = -0.75, 95% CI [-1.29, -0.20], Z = 2.67, P = 0.008).

CONCLUSION

A reduction in 5-HT1A binding in the hippocampus, temporal cortex, amygdala, and frontal lobe was observed on the affected side of patients with TLE. The decrease in 5-HT1A binding can be considered related to TLE. Potentially relevant factors should be considered in future molecular imaging studies.

Cannabidiol Acts at 5-HT1A Receptors in the Human Brain: Relevance for Treating Temporal Lobe Epilepsy

Experimental evidence indicates that cannabidiol (CBD) induces anxiolytic and antiepileptic effects through the activation of 5-HT_1A receptors. These receptors are coupled to G_i/o proteins and induce inhibitory effects. At present, the interaction of CBD with 5-HT_1A receptors in the human brain is unknown. The aim of this study focused on evaluating the interaction between CBD and 5-HT_1A receptors in cell membranes obtained from the hippocampus and temporal neocortex of autopsies and patients with drug-resistant mesial temporal lobe epilepsy (DR-MTLE). Cell membranes were isolated from the hippocampus and temporal neocortex of a group of patients with DR-MTLE who were submitted to epilepsy surgery (n = 11) and from a group of autopsies (n = 11). The [³H]-8-OH-DPAT binding assay was used to determine the pharmacological interaction of CBD with 5-HT_1A receptors. The [³⁵S]-GTPγS assay was used to investigate the CBD-induced activation of G_i/o proteins through its action on 5-HT_1A receptors.The CBD affinity (pK _i) for 5-HT_1A receptors was similar for autopsies and patients with DR-MTLE (hippocampus: 4.29 and 4.47, respectively; temporal neocortex: 4.67 and 4.74, respectively). Concerning the [³⁵S]-GTPγS assay, no statistically significant changes were observed for both hippocampal and neocortical tissue (p > 0.05) at low CBD concentrations (1 pM to 10 μM). In contrast, at high concentrations (100 μM), CBD reduced the constitutive activity of G_i/o proteins of autopsies and DR-MTLE patients (hippocampus: 39.2% and 39.6%, respectively; temporal neocortex: 35.2% and 24.4%, respectively). These changes were partially reversed in the presence of WAY-100635, an antagonist of 5-HT_1A receptors, in the autopsy group (hippocampus, 59.8%, p < 0.0001; temporal neocortex, 71.5%, p < 0.0001) and the group of patients with DR-MTLE (hippocampus, 53.7%, p < 0.0001; temporal neocortex, 68.5%, p < 0.001). Our results show that CBD interacts with human 5-HT_1A receptors of the hippocampus and temporal neocortex. At low concentrations, the effect of CBD upon G_i/o protein activation is limited. However, at high concentrations, CBD acts as an inverse agonist of 5-HT_1A receptors. This effect could modify neuronal excitation and epileptic seizures in patients with DR-MTLE.

Characterization and functional analyses of the human HTR1A gene: 5' regulatory region modulates gene expression in vitro

BACKGROUND

The serotonin neurotransmitter (5-HT) and its receptors have important roles in neuropsychiatric disorders such as schizophrenia. The aim of this study was to investigate the functional sequences of the 5' regulation region of the human HTR1A gene to explore the effects on the expression of the 5-HT1A receptor.

METHODS

Fourteen recombinant pGL3-basic vectors containing deletion fragments of the HTR1A gene regulatory region were transfected with HEK-293 and SK-N-SH cells. The relative chemiluminescence intensities of different length fragments were analyzed. The JASPAR software was used for the prediction of transcription factors.

RESULTS

In the HEK-293 cells, the relative chemiluminescence intensity of the - 1649 bp to - 1550 bp (ATG + 1) fragment was significantly different. Two inhibitory activity regions were found in the - 1409 bp to - 1381 bp and - 1196 bp to - 1124 bp fragments, which might be bound to the GATA or SOX10 transcription factors as predicted by the JASPAR software. In addition, the fragments located from - 1124 bp to - 1064 bp and from - 908 bp to - 722 bp up-regulated protein expression. Only the sequence from - 1550 bp to - 1409 bp demonstrated a difference in luciferase expression in the both cell lines. According to the results of the 5'-UTR truncated vectors, there was a repression region at the distal end of the 5'-UTR, an enhancer region might be present at the proximal end of the transcription start site.

CONCLUSIONS

Although the functional sequences of the HTR1A gene regulatory region were confirmed, the regulatory factors and functional components require further investigation.