Veronica Nguyen

Background: Insomnia is a sleep disorder with 33% of adults in the general population reporting symptoms.¹ Characterized by difficulties with initiating and maintaining sleep, both acute and chronic insomnia can precipitate cognitive challenges, fatigue, irritability, and increased risk of accidents.^1,2 Pharmacological approaches usually target GABA-A ion channels (GABA-ARs), which are thought to balance the excitatory and inhibitory activities that regulate circadian rhythm and sleep.¹

Objective: In this review, we explored the interactions between common hypnotic agents and specific subunits of the GABA-A ion channels and how this knowledge can improve future insomnia treatment.

Search Methods: I used the PubMed database and filtered through high impact journals that published relevant work between 2017-2023. I narrowed my search using the following keywords: “GABA-A ion channel”, “insomnia”, and “sleep regulation.”

Methods. Mice were injected with 3-carene from Korean pine trees and affinity 3-carene for the GABA-ARs BZ receptor was measured using radioligand binding assays.³ Molecular docking analysis of traditional Chinese hypnotic agent, Ziziphi Spinsaw Semen extract (ZSSE), was carried out to evaluate the binding affinity and conformation of the receptors to the ligands.⁴ Using fibroblast cells LtK-11 expressing human GABA-AR subunits from mice, manual whole cell patch-clamp experiments were administered to evaluate the potential of subunit targeting and pharmacodynamic fingerprinting.⁵ CRISPR-Cas9 and an adeno-associated viral (AAV) vector were used to mediate ablation in the α3 subunit in the TRN of mice and assess GABA-ARs α3 subunits’ effects on suppressing NREM sleep delta oscillation.⁶ Finally, extracellular tetrode recording electrodes in the prelimbic cortex and hippocampus of mice injected with Zolpidem were used to understand how common sleep agents affect NREM oscillations and neuronal activity.⁷

Results. 3-Carene not only showed an affinity for the GABA-ARs at the α1 and γ2 subunit, but it also increased the delay time of spontaneous inhibitory postsynaptic currents (sIPSCs) at those subunits.³ The molecular docking results showed that ZSSE increased α1 and γ2 expression in GABA-ARs in the hypothalamus and hippocampus. Thus, one of ZSSE’s mechanism to improve sleep is by increasing these subunits’ expression and inhibiting neuronal excitation.⁴ Seeing that CND does not feature the same sedative effects as ALZ and BRO does, which both increased current amplitudes of GABA-ARs with α1 subunit, further supports the hypothesis that α1 is highly involved in sedation and sleep.⁵ Recordings of the spontaneous inhibitory postsynaptic currents (sIPSCs) from TRN parvalbumin (PV) showed that α3 knockout (α3KD) led to increased delta oscillations.⁶ Zolpidem increased slow-wave activity (SWA), ripple activity in the hippocampus, and coupling between slow-waves and spindles. Interestingly, Zolpidem was able to increase SWA’s modulation of coordinated firing rates between the hippocampus and prefrontal cortex.⁷

 Conclusion. GABA-A ion channel α1, α3, and γ2 subunits play an important role in sleep regulation.^2,3,4,6 Stimulation of α1 and γ2 and inhibition of α3 can help avoid unwanted anxiolytic effects.^5,6 Pharmacodynamic fingerprinting via subunit selectivity used to individualize insomnia therapies.⁶ Synchronous inhibitory activity between CA1 cells of hippocampus and prefrontal cortex are vital to improving quality and length of sleep.⁷

Works Cited

1. Avidan AY, Neubauer DN. Chronic Insomnia Disorder. Continuum (Minneap Minn). 2017;23(4, Sleep Neurology):1064-1092. doi:10.1212/01.CON.0000522244.13784.bf
2. Bollu PC, Kaur H. Sleep Medicine: Insomnia and Sleep. Mo Med. 2019 Jan-Feb;116(1):68-75. PMID: 30862990; PMCID: PMC6390785.
3. Woo J, Yang H, Yoon M, et al. 3-carene, a phytoncide from Pine Tree has a sleep-enhancing effect by targeting the GABA-A-benzodiazepine receptors. Experimental Neurobiology. 2019;28(5):593-601. doi:10.5607/en.2019.28.5.593
4. Xiao F, Shao S, Zhang H, et al. Neuroprotective effect of Ziziphi spinosae semen on rats with P-chlorophenylalanine-induced insomnia via activation of Gabaa receptor. Frontiers in Pharmacology. 2022;13. doi:10.3389/fphar.2022.965308
5. Fernandes H, Batalha V, Braksator E, et al. Voltage-clamp evidence of Gabaa receptor subunit-specific effects: Pharmacodynamic fingerprint of chlornordiazepam, the major active metabolite of mexazolam, as compared to alprazolam, bromazepam, and Zolpidem. Pharmacological Reports. 2022;74(5):956-968. doi:10.1007/s43440-022-00411-x
6. Uygun DS, Yang C, Tilli ER, et al. Knockdown of Gabaa alpha3 subunits on thalamic reticular neurons enhances deep sleep in mice. Nature Communications. 2022;13(1). doi:10.1038/s41467-022-29852-x
7. Kersanté F, Purple RJ, Jones MW. The GABAA receptor modulator zolpidem augments hippocampal-prefrontal coupling during non-REM sleep. Neuropsychopharmacology. 2022;48(4):594-604. doi:10.1038/s41386-022-01355-9