The Testosterone-Derived Neurosteroid Androstanediol Is a Positive Allosteric Modulator of GABA_A Receptors

Abstract

Testosterone modulates seizure susceptibility, but the underlying mechanisms are obscure. Recently, we demonstrated that testosterone affects seizure activity via its conversion to neurosteroids in the brain. Androstanediol (5␣-androstan-3␣,17␤-diol) is an endogenous neurosteroid synthesized from testosterone. However, the molecular mechanism underlying the seizure protection activity of androstanediol remains unclear. Here, we show that androstanediol has positive allosteric activity as a GABA A receptor modulator. In whole-cell recordings from acutely dissociated hippocampus CA1 pyramidal cells, androstanediol (but not its 3␤-epimer) produced a concentration-dependent enhancement of GABA-activated currents (EC 50 of 5 M). At 1 M, androstanediol produced a 50% potentiation of GABA responses. In the absence of GABA, androstanediol has moderate direct effects on GABA A receptor-mediated currents at high concentrations. Systemic doses of androstanediol (5-100 mg/kg), but not its 3␤-epimer, caused dose-dependent suppression of behavioral and electrographic seizures in mouse hippocampus kindling, which is a model of temporal lobe epilepsy. The ED 50 value for antiseizure effects of androstanediol was 50 mg/kg, which did not produce sedation/motor toxicity. At high (2ϫ ED 50 ) doses, androstanediol produced complete seizure protection that lasted for up to 3 h after injection. The estimated plasma concentrations of androstanediol producing 50% seizure protection in the kindling model (10.6 M) are within the range of concentrations that modulate GABA A receptors. These studies suggest that androstanediol could be a neurosteroid mediator of testosterone actions on neuronal excitability and seizure susceptibility via its activity as a GABA A receptor modulator and that androstanediol may play a key role in men with epilepsy, especially during the age-related decline in androgen levels.

Development and Persistence of Limbic Epileptogenesis Are Impaired in Mice Lacking Progesterone Receptors

“…The development of kindling epileptogenesis and its preservation were assessed by hippocampus or amygdala kindling (He et al, 2004;Reddy and Jian, 2010). Mice were anesthetized by an intraperitoneal injection of ketamine (100 mg/kg) and xylazine (20 mg/kg), and a stimulation-recording bipolar electrode (Plastics One) was stereotaxically implanted in the right basolateral nucleus of the amygdala (1.3 mm posterior, 3 mm lateral to bregma, and 4.6 mm below dura) or in the right ventral hippocampus (2.9 mm posterior, 3.0 mm lateral, and 3.0 mm below dura) using the Franklin and Paxinos (1997) atlas.…”

The Brain, Seizures and Epilepsy Throughout Life: Understanding a Moving Target

“…The cyclical nature of hormonal release during the menstrual cycle in women promotes cyclical or catamenial seizures and epilepsy, often complicating the management of seizures in women (47,51). In analogy to the female sex hormones, the effects of testosterone-directly and indirectly-on neuronal excitability are complex (55,56).…”

3β-Methyl-Neurosteroid Analogs Are Preferential Positive Allosteric Modulators and Direct Activators of Extrasynapticδ-Subunitγ-Aminobutyric Acid Type A Receptors in the Hippocampus Dentate Gyrus Subfield

“…For whole-cell GABA current recordings, fractional potentiation generated by allosteric modulator was expressed as IA/IGABA, where IGABA is the GABA peak current amplitude and IA is the peak current response of the co-application of GABA and the allosteric drug (0.05 to 1 M). GABA at 3 M produced 10% of the maximal current (EC10), as described previously in dissociated murine CA1PCs (Reddy and Jian, 2010) and DGGCs (Wu et al, 2013;Carver and Reddy, 2016). The concentration-response relationship was fitted by the nonlinear Hill function to This article has not been copyedited and formatted.…”

“…Electrophysiological recordings in dissociated cells were conducted in the wholecell mode as described previously (Reddy and Jian, 2010). Recordings were acquired with an Axopatch 200B amplifier (Molecular Devices, Sunnyvale, CA) with a holding potential of -70 mV.…”

“…GABA-A receptor currents were recorded from acutely dissociated, voltage-clamped DGGCs or CA1PCs from adult male mice in wholecell mode. We utilized 3 M GABA, which was within the range of EC10 response for both DGGCs (Wu et al, 2013;Carver and Reddy, 2016) and CA1PCs (Reddy and Jian, 2010), to determine a baseline response and allosteric activation by tested compounds. We confirmed the EC10 value of GABA in DGGCs (Fig.…”