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.

Pain-sensing sensory neurons of the dorsal root ganglion (DRG) can become sensitized or hyperexcitable in response to surgically induced peripheral tissue injury. We investigated the potential role and molecular mechanisms of nociceptive ion channel dysregulation in acute pain conditions such as those resulting from skin and soft tissue incision. We used selective pharmacology, electrophysiology, and mouse genetics to link increased current densities arising from the Ca3.2 isoform of T-type calcium channels (T-channels) to nociceptive sensitization using a clinically relevant rodent model of skin and deep tissue incision. Furthermore, knockdown of the Ca3.2-targeting deubiquitinating enzyme USP5 or disruption of USP5 binding to Ca3.2 channels in peripheral nociceptors resulted in a robust antihyperalgesic effect in vivo and substantial T-current reduction in vitro. Our study provides mechanistic insight into the role of plasticity in Ca3.2 channel activity after surgical incision and identifies potential targets for perioperative pain that may greatly decrease the need for narcotics and potential for drug abuse.

Over the last years, genetic studies have greatly improved our knowledge on the receptor subtypes mediating various pharmacological effects of positive allosteric modulators at GABA A receptors. This stimulated the development of new benzodiazepine (BZ)-like ligands, especially those inactive/low-active at GABA A receptors containing the α 1 subunit, with the aim of generating more selective drugs. Hereby, the affinity and efficacy of four recently-synthesized BZ site ligands: SH-053-2'N, SH-053-S-CH3-2'F, SH-053-R-CH3-2'F and JY-XHe-053 were assessed. They were also studied in behavioral tests of spontaneous locomotor activity, elevated plus maze, and water maze in rats, which are considered predictive of, respectively, the sedative, anxiolytic, and amnesic influence of BZs. The novel ligands had moderately low to low affinity and mild to partial agonistic efficacy at GABA A receptors containing the α 1 subunit, with variable, but more pronounced efficacy at other BZ-sensitive binding sites. While presumably α 1 receptor-mediated sedative effects of GABA A modulation were not fully eliminated with any of the ligands tested, only SH-053-2'N and SH-053-S-CH3-2'F, both dosed at 30 mg/kg, exerted anxiolytic effects. The lack of clear anxiolytic-like activity of JY-XHe-053, despite its efficacy at α 2 -and α 3 -GABA A receptors, may have been partly connected with its preferential affinity at α 5 -GABA A receptors © 2010 Elsevier Inc. All rights reserved. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. coupled with weak agonist activity at α 1 -containing subtypes. The memory impairment in watermaze experiments, generally reported with BZ site agonists, was completely circumvented with all four ligands. The results suggest that a substantial amount of activity at α 1 GABA A receptors is needed for effecting spatial learning and memory impairments, while much weaker activity at α 1 -and α 5 -GABA A receptors is sufficient for eliciting sedation. NIH Public Access

The clinical use of benzodiazepines (BZs) is hampered by sedation and cognitive deterioration. Although genetic and pharmacological studies suggest that α1- and α5-containing GABAA receptors mediate and/or modulate these effects, their molecular substrate is not fully elucidated. By the use of two selective ligands : the α1-subunit affinity-selective antagonist β-CCt, and the α5-subunit affinity- and efficacy-selective antagonist XLi093, we examined the mechanisms of behavioural effects of diazepam in the tests of spontaneous locomotor activity and water-maze acquisition and recall, the two paradigms indicative of sedative- and cognition-impairing effects of BZs, respectively. The locomotor-activity decreasing propensity of diazepam (significant at 1.5 and 5 mg/kg) was antagonized by β-CCt (5 and 15 mg/kg), while it tended to be potentiated by XLi093 in doses of 10 mg/kg, and especially 20 mg/kg. Diazepam decreased acquisition and recall in the water maze, with a minimum effective dose of 1.5 mg/kg. Both antagonists reversed the thigmotaxis induced by 2 mg/kg diazepam throughout the test, suggesting that both GABAA receptor subtypes participate in BZ effects on the procedural component of the task. Diazepam-induced impairment in the declarative component of the task, as assessed by path efficiency, the latency and distance before finding the platform across acquisition trials, and also by the spatial parameters in the probe trial, was partially prevented by both, 15 mg/kg β-CCt and 10 mg/kg XLi093. Combining a BZ with β-CCt results in the near to control level of performance of a cognitive task, without sedation, and may be worth testing on human subjects.

Background Early postnatal exposure to general anesthesia (GA) may be detrimental to brain development, resulting in long-term cognitive impairments. Older literature suggests that in utero exposure of rodents to GA causes cognitive impairments in the first-generation as well as in the second-generation offspring never exposed to GA. Thus, the authors hypothesize that transient exposure to GA during critical stages of synaptogenesis causes epigenetic changes in chromatin with deleterious effects on transcription of target genes crucial for proper synapse formation and cognitive development. They focus on the effects of GA on histone acetyltransferase activity of cAMP-responsive element-binding protein and the histone-3 acetylation status in the promoters of the target genes brain-derived neurotrophic factor and cellular Finkel-Biskis-Jinkins murine sarcoma virus osteosarcoma oncogene (c-Fos) known to regulate the development of neuronal morphology and function. Methods Seven-day-old rat pups were exposed to a sedative dose of midazolam followed by combined nitrous oxide and isoflurane anesthesia for 6 h. Hippocampal neurons and organotypic hippocampal slices were cultured in vitro and exposed to GA for 24 h. Results GA caused epigenetic modulations manifested as histone-3 hypoacetylation (decrease of 25 to 30%, n = 7 to 9) and fragmentation of cAMP-responsive element-binding protein (two-fold increase, n = 6) with 25% decrease in its histone acetyltransferase activity, which resulted in down-regulated transcription of brain-derived neurotrophic factor (0.2- to 0.4-fold, n = 7 to 8) and cellular Finkel-Biskis-Jinkins murine sarcoma virus osteosarcoma oncogene (about 0.2-fold, n = 10 to 12). Reversal of histone hypoacetylation with sodium butyrate blocked GA-induced morphological and functional impairments of neuronal development and synaptic communication. Conclusion Long-term impairments of neuronal development and synaptic communication could be caused by GA-induced epigenetic phenomena.

Several studies suggest that voltage-gated calcium currents are involved in generating high frequency burst firing in the subiculum, but the exact nature of these currents remains unknown. Here, we used selective pharmacology, molecular and genetic approaches to implicate Cav3.1-containing T-channels in subicular burst firing, in contrast to several previous reports discounting T-channels as major contributors to subicular neuron physiology. Furthermore, pharmacological antagonism of T-channels, as well as global deletion of CaV3.1 isoform, completely suppressed development of long-term potentiation (LTP) in the CA1-subiculum, but not in the CA3-CA1 pathway. Our results indicate that excitability and synaptic plasticity of subicular neurons relies heavily on T-channels. Hence, T-channels may be a promising new drug target for different cognitive deficits.

Prevailing literature supports the idea that common general anesthetics (GAs) cause long-term cognitive changes and neurodegeneration in the developing mammalian brain, especially in the thalamus. However, the possible role of GAs in modifying ion channels that control neuronal excitability has not been taken into consideration. Here we show that rats exposed to GAs at postnatal day 7 display a lasting reduction in inhibitory synaptic transmission, an increase in excitatory synaptic transmission, and concomitant increase in the amplitude of T-type calcium currents (T-currents) in neurons of the nucleus reticularis thalami (nRT). Collectively, this plasticity of ionic currents leads to increased action potential firing in vitro and increased strength of pharmacologically induced spike and wave discharges in vivo. Selective blockade of T-currents reversed neuronal hyperexcitability in vitro and in vivo. We conclude that drugs that regulate thalamic excitability may improve the safety of GAs used during early brain development.

Background and Purpose Neuroactive steroid (3β,5β,17β)‐3‐hydroxyandrostane‐17‐carbonitrile (3β‐OH) is a novel hypnotic and voltage‐dependent blocker of T‐type calcium channels. Here, we examine its potential analgesic effects and adjuvant anaesthetic properties using a post‐surgical pain model in rodents. Experimental Approach Analgesic properties of 3β‐OH were investigated in thermal and mechanical nociceptive tests in sham or surgically incised rats and mice, with drug injected either systemically (intraperitoneal) or locally via intrathecal or intraplantar routes. Hypnotic properties of 3β‐OH and its use as an adjuvant anaesthetic in combination with isoflurane were investigated using behavioural experiments and in vivo EEG recordings in adolescent rats. Key Results A combination of 1% isoflurane with 3β‐OH (60 mg·kg−1, i.p.) induced suppression of cortical EEG and stronger thermal and mechanical anti‐hyperalgesia during 3 days post‐surgery, when compared to isoflurane alone and isoflurane with morphine. 3β‐OH exerted prominent enantioselective thermal and mechanical antinociception in healthy rats and reduced T‐channel‐dependent excitability of primary sensory neurons. Intrathecal injection of 3β‐OH alleviated mechanical hyperalgesia, while repeated intraplantar application alleviated both thermal and mechanical hyperalgesia in the rats after incision. Using mouse genetics, we found that CaV3.2 T‐calcium channels are important for anti‐hyperalgesic effect of 3β‐OH and are contributing to its hypnotic effect. Conclusion and Implications Our study identifies 3β‐OH as a novel analgesic for surgical procedures. 3β‐OH can be used to reduce T‐channel‐dependent excitability of peripheral sensory neurons as an adjuvant for induction and maintenance of general anaesthesia while improving analgesia and lowering the amount of volatile anaesthetic needed for surgery.