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Adam C. Hall
Bachelor of Arts
Cyclohexanol, GABA, Electrophysiology, Anesthetic antagonist, Anesthetic
GABA receptors are the primary mediators of inhibitory neurotransmission in the mammalian nervous system, and the main target for anesthetics (Franks and Lieb, 1994; Krasowski et al., 1998). Propofol (2,6-diisopropylphenol) is commonly used as an intravenous anesthetic agent during outpatient procedures to induce sedation via positive modulation of the GABAA receptor (Frank and Lieb, 1994). Occasionally there is a requirement to reverse propofol anesthesia in cases of anesthetic neurotoxicity or during surgical complications. Hence, an “anesthetic antagonist” would allow for a more rapid restoration of physiology and consciousness. Currently, the main antagonist used for propofol is aminophylline, a xanthine derivative, that has been found to reverse sedation at high concentrations (5 mg/kg-1 ) (Sakurai et al., 2008). Unfortunately, prolonged intravenous delivery of aminophylline has been found to be toxic, sometimes resulting in life-threatening cardiovascular conditions(Sakurai et al., 2008). Therefore, there is a medical need for efficacious clinical anesthetic antagonists for propofol. In the Hall laboratory, cyclohexanol analogues have been shown to positively modulate GABAA currents, and have been the focus of ongoing research. Recently, we have characterized four novel compounds 2,6 dimethylcyclohexanol (2,6 DMCH), 2,6 diisopropylcyclohexanol (2,6 DICH), 2,6 diethylcyclohexanol (2,6 DECH), and 2,6 dibenzylcyclohexanol (2,6 DBCH) that may act as propofol antagonists at the GABAA receptor at high concentrations. The current whole-cell patch clamp electrophysiological study sought to characterize the positive modulatory and inhibitory effects of these cyclohexanol compounds. Using human embryonic kidney cells stably expressing a1b3g2s GABAA receptors, increasing concentrations of the cyclohexanols (30- 300µM) were co-applied with 10µM GABA. Positive modulation of GABAA receptor currents by 2,6 diethylcyclohexanol demonstrated the highest potency compared to 2,6 dimethylcyclohexanol, 2,6 diisopropylcyclohexanol, or 2,6 dibenzylcyclohexanol. For the characterization of inhibition, a novel single-sweep “notch” protocol established by Ziemba and Forman, 2016, was used. Results revealed significant inhibition of current by 2,6 dimethylcyclohexanol, 2,6 diethylcyclohexanol, and 2,6 diisopropylcyclohexanol at high concentrations (500-4000µM). In conclusion, we have demonstrated that the cyclohexanols are weak positive modulators but effective inhibitors of GABA currents. Thus, these compounds may be further developed into viable anesthetic antagonists for propofol.
Subramaniam, Varsha, "Differential potency of cyclohexanol isomers for positive modulation and inhibition of GABAa receptor currents" (2017). Honors Project, Smith College, Northampton, MA.
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