A neurosteroid analogue with T-type calcium channel blocking properties is an effective hypnotic, but is not harmful to neonatal rat brain

Abstract

Background: More than 4 million children are exposed annually to sedatives and general anaesthetics (GAs) in the USA alone. Recent data suggest that common GAs can be detrimental to brain development causing neurodegeneration and long-term cognitive impairments. Challenged by a recent US Food and Drug Administration (FDA) warning about potentially neurotoxic effects of GAs in children, there is an urgent need to develop safer GAs. Methods: Postnatal Day 7 (P7) rat pups of both sexes were exposed to six (repeated every 2 h) injections of equipotent hypnotic doses of ketamine or the neuroactive steroid (3b,5b,17b)-3-hydroxyandrostane-17-carbonitrile (3b-OH) for 12 h. Loss of righting reflex was used to assess hypnotic properties and therapeutic index; quantitative caspase-3 immunohistochemistry was used to assess developmental neuroapoptosis; patch-clamp recordings in acute brain slices were used to assess the effects of 3b-OH on neuronal excitability and synaptic transmission. Cognitive abilities of rats exposed to ketamine, 3b-OH, or vehicle at P7 were assessed in young adulthood using the radial arm maze. Results: The neuroactive steroid 3b-OH has a therapeutic index similar to ketamine, a commonly used clinical GA. We report that 3b-OH is safe and, unlike ketamine, does not cause neuroapoptosis or impair cognitive development when administered to P7 rat pups. Interestingly, 3b-OH blocks T-type calcium channels and presynaptically dampens synaptic transmission at hypnotically-relevant brain concentrations, but it lacks a direct effect on g-aminobutyric acid A or glutamate-gated ion channels.

Novel neuroactive steroid with hypnotic and T‐type calcium channel blocking properties exerts effective analgesia in a rodent model of post‐surgical pain

“…3β-OH (3β,5β,17β)-3-hydroxyandrostane-17-carbonitrile and ent-3β-OH ent-[(3β,5β,17β)-3-hydroxyandrostane-17-carbonitrile] are a synthetic neurosteroid analogues synthetized using procedures that have been described in our previous publications (Atluri et al, 2018;Han, Zorumski, & Covey, 1996;Todorovic et al, 2004). ent-3β-OH was also produced from ent-testosterone (Hu et al, 1997) using the procedure reported for the preparation of 3β-OH from testosterone (Atluri et al, 2018). Morphine was purchased through University of Colorado Hospital Pharmacy (Morphine sulfate inj.…”

The T-type calcium channel isoform Cav3.1 is a target for the hypnotic effect of the anaesthetic neurosteroid (3β,5β,17β)-3-hydroxyandrostane-17-carbonitrile

“…We first examined the effects of 3 mM 3b-OH on well-isolated Tcurrents in CeM neurones from adolescent WT mice using acute brain slices as we have previously determined that this is a relevant brain concentration during hypnosis. 1 Representative current traces from a steady-state inactivation protocol are presented in Fig 1a. The left panel shows traces of inward Tcurrent of a CeM neurone under control conditions, and the right panel shows traces from the same neurone in the presence of 3b-OH, both recorded using a tetramethylammonium with adenosine triphosphate (TMA with ATP) internal solution. 3b-OH stabilised inactive states of the channel and shifted inactivation V 50 values of about e5 mV (Fig 1b).…”

Does pediatric anesthesia cause brain damage? – Addressing parental and provider concerns in light of compelling animal studies and seemingly ambivalent human data

“…Moreover, no clearly superior injectable anesthetic has been identified. Most recently, the experimental neuroactive steroid 3β-OH has demonstrated anesthetic properties without neurotoxicity [ 63 ]. In summary, animal studies into comparable neurotoxicity have demonstrated widely conflicting results; therefore, no general anesthetic was consistently identified to be safer than others.…”