Differential depression of neuronal network activity by midazolam and its main metabolite 1-hydroxymidazolam in cultured neocortical slices

Uwe Rudolph,Harald Hentschke,Berthold Drexler,Monika Balk,Bernd Antkowiak

doi:10.1038/s41598-017-03154-5

Abstract

The benzodiazepine midazolam is widely used in critical care medicine. Midazolam has a clinically active metabolite, 1-hydroxymidazolam. The contribution of 1-hydroxymidazolam to the effects of midazolam is controversial. The aim of the current study was to compare the actions of midazolam and 1-hydroxymidazolam on network activity of cortical neurons. Midazolam depressed neuronal activity at a low concentration of 5 nM. When midazolam concentration was increased, it depressed neuronal discharge rates in a biphasic manner. In comparison, 1-hydroxymidazolam did not depress the cortical network activity at low nanomolar concentrations. Higher concentrations of 1-hydroxymidazolam consistently inhibited neuronal activity. Moreover, midazolam shortened cortical up states at low, but not at high concentrations, while the opposite effect was observed with 1-hydroxymidazolam. The network depressant action of midazolam at low concentrations was absent in slices from GABAA receptor α1(H101R)mutant mice. The α1(H101R)mutation renders α1-subunit containing GABAA receptors insensitive towards benzodiazepines. This GABAA receptor subtype is thought to mediate sedation. As midazolam is more potent than its metabolite 1-hydroxymidazolam, the major clinical effects are thus likely caused by midazolam itself. However, 1-hydroxymidazolam could add to the effects of midazolam, especially after the application of high doses of midazolam, and in case of impaired drug metabolism.

Highlights

Midazolam is a commonly used benzodiazepine in anaesthesia and intensive care medicine
In order to examine the contribution of α1-containing GABAA receptors to this phenomenon, in the current study clinically relevant concentrations of midazolam were tested in neocortical slice cultures from GABAA receptor α1(H101R) knock-in mice
Up states of neocortical slice cultures are characterized by high frequency action potential firing at the beginning of the up state, which is gradually decreasing over time[12]

Summary

Introduction

Midazolam is a commonly used benzodiazepine in anaesthesia and intensive care medicine. Midazolam has a clinical active metabolite: 1-hydroxymidazolam, which is, like the parent drug midazolam a neuronal depressant drug. The current study was designed to directly compare the effects of midazolam and 1-hydroxymidazolam on the activity of neocortical neurons in organotypic slice cultures, a model system in which, to the best of our knowledge, there is no relevant metabolism from midazolam to 1-hydroxymidazolam. Mice carrying a point mutation in the α1 subunit of the GABAA receptor at position 101 are resistant to the sedative action of diazepam, indicating that benzodiazepine-induced sedation is predominantly mediated via GABAA receptors containing the α1-subunit[8, 9]. In order to examine the contribution of α1-containing GABAA receptors to this phenomenon, in the current study clinically relevant concentrations of midazolam were tested in neocortical slice cultures from GABAA receptor α1(H101R) knock-in mice

Objectives

Methods

Results

Conclusion