Direct suppression by odorants of ionotropic glutamate receptors in newt retinal neurons

Monoterpenes as a perspective for the treatment of seizures: A Systematic Review

BACKGROUND

Epilepsy affects more than 65 million people worldwide. Treatment for epileptic seizures is ineffective and has many adverse effects. For this reason, the search for new therapeutic options capable of filling these limitations is necessary.

HYPOTHESIS/PURPOSE

In this sense, natural products, such as monoterpenes, have been indicated as a new option to control neurological disorders such as epilepsy.

STUDY DESIGN

Therefore, the objective of this study was to review the monoterpenes that have anticonvulsive activity in animal models.

METHODS

The searches were performed in the PubMed, Web of Science and Scopus databases in September, 2020 and compiled studies using monoterpenes as an alternative to seizure. Two independent reviewers performed the study selection, data extraction and methodological quality assessment using the Syrcle tool.

RESULTS

51 articles that described the anticonvulsant activity of 35 monoterpenes were selected with action on the main pharmacological target, including GABAA receptors, glutamate, calcium channels, sodium and potassium. In addition, these compounds are capable of reducing neuronal inflammation and oxidative stress caused by seizure.

CONCLUSION

These compounds stand out as a promising alternative for acting through different pharmacological mechanisms, which may not only reduce seizure, but also promote neuroprotective effect by reducing toxicity in brain regions. However, further studies are needed to determine the mechanism of action and safety assessment of these compounds.

Metabolic Products of Linalool and Modulation of GABAA Receptors

Terpenoids are major subcomponents in aroma substances which harbor sedative physiological potential. We have demonstrated that various monoterpenoids such as the acyclic linalool enhance GABAergic currents in an allosteric manner in vitro upon overexpression of inhibitory α1β2 GABA_A receptors in various expression systems. However, in plants or humans, i.e., following intake via inhalation or ingestion, linalool undergoes metabolic modifications including oxygenation and acetylation, which may affect the modulatory efficacy of the generated linalool derivatives. Here, we analyzed the modulatory potential of linalool derivatives at α1β2γ2 GABA_A receptors upon transient overexpression. Following receptor expression control, electrophysiological recordings in a whole cell configuration were used to determine the chloride influx upon co-application of GABA EC₁₀₋₃₀ together with the modulatory substance. Our results show that only oxygenated linalool metabolites at carbon 8 positively affect GABAergic currents whereas derivatives hydroxylated or carboxylated at carbon 8 were rather ineffective. Acetylated linalool derivatives resulted in non-significant changes of GABAergic currents. We can conclude that metabolism of linalool reduces its positive allosteric potential at GABA_A receptors compared to the significant potentiation effects of the parent molecule linalool itself.

Requirement of the tumour suppressor APC for the clustering of PSD-95 and AMPA receptors in hippocampal neurons

Mutations in the adenomatous polyposis coli (APC) gene are associated with familial adenomatous polyposis and sporadic colorectal tumours. The APC gene is expressed ubiquitously in various tissues, especially throughout the large intestine and central nervous system (CNS). In the CNS, the expression of the APC protein is highest during embryonic and early postnatal development. APC associates through its C-terminal region with postsynaptic density (PSD)-95, a neuronal protein that participates in synapse development. Here, we examined the involvement of APC in synaptogenesis. In cultured hippocampal neurons, both overexpression of a dominant-negative construct that disrupts the APC-PSD-95 interaction and knockdown of APC expression using small interfering RNA (siRNA) inhibited the clustering of PSD-95 and a glutamate receptor subunit, and reduced alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA)-induced activity of AMPA receptors; however, the clustering of an N-methyl-D-aspartate (NMDA) receptor subunit was unaffected. These results are suggestive of APC involvement in the development of glutamatergic synapses.

N-methyl-D-aspartate receptors influence the intracellular calcium concentration of keratinocytes

In the present study, the distribution of ionotropic glutamate receptors of the N-methyl-D-aspartate (NMDA)-receptor type was immunohistochemically demonstrated in healthy human skin (n = 22) and healthy buccal mucosa (n = 20). Moreover, the intracellular calcium concentration of HaCaT-cells and native human keratinocytes were studied under the influence of the selective agonist NMDA and the selective NMDA-antagonist MK-801. Immunohistochemical imaging of NMDA receptors in healthy epidermis showed a positive reaction in the stratum basale, spinosum and granulosum, whereby the greatest expression was observed in the granular layer. In the mucosal preparations, the distribution of NMDA receptors was observed to be equal in all cell layers. In the cell culture (HaCaT-cells), NMDA concentrations between 25 microM and 1 mM resulted in a significant increase in the number of cells showing elevated intracellular calcium concentration. This effect could be significantly reduced by prior application of MK-801 (100 micro M). In supplementary tests on HaCaT-keratinocytes, blockade of the keratinocytic NMDA receptors with MK-801 suppressed the differentiation of the cells (expression of cytokeratin 10). The proliferation of cells was not influenced by NMDA. The investigations showed that glutamate receptors of the NMDA type have an influence on keratinocytic calcium concentration. This appears especially important for the differentiation of keratinocytes.