Novel neurosteroid hypnotic blocks T-type calcium channel-dependent rebound burst firing and suppresses long-term potentiation in the rat subiculum

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Background: The mechanisms underlying the role of T-type calcium channels (T-channels) in thalamocortical excitability and oscillations in vivo during neurosteroid-induced hypnosis are largely unknown. Methods: We used patch-clamp electrophysiological recordings from acute brain slices ex vivo, recordings of local field potentials (LFPs) from the central medial thalamic nucleus in vivo, and wild-type (WT) and Ca v 3.1 knockout mice to investigate the molecular mechanisms of hypnosis induced by the neurosteroid analogue (3b,5b,17b)-3hydroxyandrostane-17-carbonitrile (3b-OH). Results: Patch-clamp recordings showed that 3b-OH inhibited isolated T-currents but had no effect on phasic or tonic gaminobutyric acid A currents. Also in acute brain slices, 3b-OH inhibited the spike firing mode more profoundly in WT than in Ca v 3.1 knockout mice. Furthermore, 3b-OH significantly hyperpolarised neurones, reduced the amplitudes of low threshold spikes, and diminished rebound burst firing only in WT mice. We found that 80 mg kg À1 i.p. injections of 3b-OH induced hypnosis in >60% of WT mice but failed to induce hypnosis in the majority of mutant mice. A subhypnotic dose of 3b-OH (20 mg kg À1 i.p.) accelerated induction of hypnosis by isoflurane only in WT mice, but had similar effects on the maintenance of isoflurane-induced hypnosis in both WT and Ca v 3.1 knockout mice. In vivo recordings of LFPs showed that a hypnotic dose of 3b-OH increased d, q, a, and b oscillations in WT mice in comparison with Ca v 3.1 knockout mice. Conclusions: The Ca v 3.1 T-channel isoform is critical for diminished thalamocortical excitability and oscillations that underlie neurosteroid-induced hypnosis.

Section: Resultssupporting

confidence: 85%

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

Stamenić

Feseha

Manzella

et al. 2021

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“… 32 , 33 Although 3β-OH is devoid of direct GABAergic activity in both thalamic 34 and hippocampal brain slices, 4 it produces an apparently similar EEG signature in rats. We have shown previously that 3β-OH may suppress neuronal excitability by inhibiting T-channel-dependent rebound bursting 5 and by decreasing presynaptic glutamatergic transmission. 4 Furthermore, 3β-OH may hyperpolarise thalamocortical neurones by inhibiting the baseline influx of Ca 2+ via T-type ‘window’ currents.…”

Section: Discussionmentioning

confidence: 91%

“…Based on loss of righting reflex data in juvenile rats, 5 we first examined the effects of a relatively low dose of 3β-OH (30 mg kg −1 , i.p.) on behaviour and cortical EEG activity in male and female rats.…”

Section: Resultsmentioning

confidence: 99%

Differential effects of the novel neurosteroid hypnotic (3β,5β,17β)-3-hydroxyandrostane-17-carbonitrile on electroencephalogram activity in male and female rats

Joksimović

Sampath

Krishnan

et al. 2021

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Background We recently showed that a neurosteroid analogue, (3β,5β,17β)-3-hydroxyandrostane-17-carbonitrile (3β-OH), induced hypnosis in rats. The aim of the present study was to evaluate the hypnotic and anaesthetic potential of 3β-OH further using electroencephalography. Methods We used behavioural assessment and cortical electroencephalogram (EEG) spectral power analysis to examine hypnotic and anaesthetic effects of 3β-OH (30 and 60 mg kg −1 ) administered intraperitoneally or intravenously to young adult male and female rats. Results We found dose-dependent sex differences in 3β-OH-induced hypnosis and EEG changes. Both male and female rats responded similarly to i.p. 3β-OH 30 mg kg −1 . However, at the higher dose (60 mg kg −1 , i.p.), female rats had two-fold longer duration of spontaneous immobility than male rats (203.4 [61.6] min vs 101.3 [32.1] min), and their EEG was suppressed in the low-frequency range (2–6 Hz), in contrast to male rats. Although a sex-dependent hypnotic effect was not confirmed after 30 mg kg −1 i.v., female rats appeared more sensitive to 3β-OH with relatively small changes within delta (1–4 Hz) and alpha (8–13 Hz) bands. Finally, 3β-OH had a rapid onset of action and potent hypnotic/anaesthetic effect after 60 mg kg −1 i.v. in rats of both sexes; however, all female rats and only half of the male rats reached burst suppression, an EEG pattern usually associated with profound inhibition of thalamocortical networks. Conclusions Based on its behavioural effects and EEG signature, 3β-OH is a potent hypnotic in rats, with female rats being more sensitive than male rats.

“…Our investigations of novel general anaesthetics have focused on a class of agents referred to as the neuroactive steroids (neurosteroids). We recently published that the neurosteroid analogue (3b,5b,17b)-3-hydroxyandrostane-17-carbonitrile (3b-OH) blocks T-type calcium currents (T-currents) in the subiculum, 6 and is an effective hypnotic with a good safety profile when administered to rat pups. 7 The most currently used general anaesthetics are potent positive modulators of postsynaptic g-aminobutyric acid A (GABA A ) receptors and are invariably neurotoxic during the early stages of brain development in preclinical animal models.…”

mentioning

confidence: 99%

Neuroactive steroids alphaxalone and CDNC24 are effective hypnotics and potentiators of GABAA currents, but are not neurotoxic to the developing rat brain

Tešić

Joksimović

Quillinan

et al. 2020

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Background: The most currently used general anaesthetics are potent potentiators of g-aminobutyric acid A (GABA A ) receptors and are invariably neurotoxic during the early stages of brain development in preclinical animal models. As causality between GABA A potentiation and anaesthetic-induced developmental neurotoxicity has not been established, the question remains whether GABAergic activity is crucial for promoting/enhancing neurotoxicity. Using the neurosteroid analogue, (3a,5a)-3-hydroxy-13,24-cyclo-18,21-dinorchol-22-en-24-ol (CDNC24), which potentiates recombinant GABA A receptors, we examined whether this potentiation is the driving force in inducing neurotoxicity during development. Methods: The neurotoxic potential of CDNC24 was examined vis-a-vis propofol (2,6-diisopropylphenol) and alphaxalone (5a-pregnan-3a-ol-11,20-dione) at the peak of rat synaptogenesis. In addition to the morphological neurotoxicity studies of the subiculum and medial prefrontal cortex (mPFC), we assessed the extra-, pre-, and postsynaptic effects of these agents on GABAergic neurotransmission in acute subicular slices from rat pups. Results: CDNC24, like alphaxalone and propofol, caused dose-dependent hypnosis in vivo, with a higher therapeutic index. CDNC24 and alphaxalone, unlike propofol, did not cause developmental neuroapoptosis in the subiculum and mPFC. Propofol potentiated post-and extrasynaptic GABA A currents as evidenced by increased spontaneous inhibitory postsynaptic current (sIPSC) decay time and prominent tonic currents, respectively. CDNC24 and alphaxalone had a similar postsynaptic effect, but also displayed a strong presynaptic effect as evidenced by decreased frequency of sIPSCs and induced moderate tonic currents. Conclusions: The lack of neurotoxicity of CDNC24 and alphaxalone may be at least partly related to suppression of presynaptic GABA release in the developing brain.