Role of neurosteroids in the anticonvulsant activity of midazolam

Temporal development of seizure threshold and spontaneous seizures after neonatal asphyxia and the effect of prophylactic treatment with midazolam in rats

Birth asphyxia (BA) and subsequent hypoxic-ischemic encephalopathy (HIE) is one of the most serious birth complications affecting full-term infants and can result in severe disabilities including mental retardation, cerebral palsy, and epilepsy. Animal models of BA and HIE are important to characterize the functional and behavioral correlates of injury, explore cellular and molecular mechanisms, and assess the potential of novel therapeutic strategies. Here we used a non-invasive, physiologically validated rat model of BA and acute neonatal seizures that mimics many features of BA and HIE in human infants to study (i) the temporal development of epilepsy with spontaneous recurrent seizures (SRS) in the weeks and months after the initial brain injury, (ii) alterations in seizure threshold and hippocampal EEG that may precede the onset of SRS, and (iii) the effect of prophylactic treatment with midazolam. For this purpose, a total of 89 rat pups underwent asphyxia or sham asphyxia at postnatal day 11 and were examined over 8-10.5 months. In vehicle-treated animals, the incidence of electroclinical SRS progressively increased from 0 % at 2.5 months to 50 % at 6.5 months, 75 % at 8.5 months, and > 80 % at 10.5 months after asphyxia. Unexpectedly, post-asphyxial rats did not differ from sham-exposed rats in seizure threshold or interictal epileptiform discharges in the EEG. Treatment with midazolam (1 mg/kg i.p.) after asphyxia, which suppressed acute symptomatic neonatal seizures in about 60 % of the rat pups, significantly reduced the incidence of SRS regardless of its effect on neonatal seizures. This antiepileptogenic effect of midazolam adds to the recently reported prophylactic effects of this drug on BA-induced neuroinflammation, brain damage, behavioral alterations, and cognitive impairment in the rat asphyxia model of HIE.

Structure-based drug design for TSPO: Challenges and opportunities

The translocator protein 18 kDa (TSPO) is an evolutionarily conserved mitochondrial transmembrane protein implicated in various neuropathologies and inflammatory conditions, making it a longstanding diagnostic and therapeutic target of interest. Despite the development of various classes of TSPO ligand chemotypes, and the elucidation of bacterial and non-human mammalian experimental structures, many unknowns exist surrounding its differential structural and functional features in health and disease. There are several limitations associated with currently used computational methodologies for modelling the native structure and ligand-binding behaviour of this enigmatic protein. In this perspective, we provide a critical analysis of the developments in the uses of these methods, outlining their uses, inherent limitations, and continuing challenges. We offer suggestions of unexplored opportunities that exist in the use of computational methodologies which offer promise for enhancing our understanding of the TSPO.

Neurosteroid influence on affective tone

Affective disorders such as depression and anxiety are among the most prevalent psychiatric illnesses and causes of disability worldwide. The recent FDA-approval of a novel antidepressant treatment, ZULRESSO® (Brexanolone), a synthetic neurosteroid has fueled interest into the role of neurosteroids in the pathophysiology of depression as well as the mechanisms mediating the antidepressant effects of these compounds. The majority of studies examining the impact of neurosteroids on affective states have relied on the administration of exogenous neurosteroids; however, neurosteroids can also be synthesized endogenously from cholesterol or steroid hormone precursors. Despite the well-established influence of exogenous neurosteroids on affective states, we still lack an understanding of the role of endogenous neurosteroids in modulating affective tone. This review aims to summarize the current literature supporting the influence of neurosteroids on affective states in clinical and preclinical studies, as well as recent evidence suggesting that endogenous neurosteroids may set a baseline affective tone.

Bumetanide potentiates the anti-seizure and disease-modifying effects of midazolam in a noninvasive rat model of term birth asphyxia

Birth asphyxia and the resulting hypoxic-ischemic encephalopathy (HIE) are highly associated with perinatal and neonatal death, neonatal seizures, and an adverse later-life outcome. Currently used drugs, including phenobarbital and midazolam, have limited efficacy to suppress neonatal seizures. There is a medical need to develop new therapies that not only suppress neonatal seizures but also prevent later-life consequences. We have previously shown that the loop diuretic bumetanide does not potentiate the effects of phenobarbital in a rat model of birth asphyxia. Here we compared the effects of bumetanide (0.3 or 10 mg/kg i.p.), midazolam (1 mg/kg i.p.), and a combination of bumetanide and midazolam on neonatal seizures and later-life outcomes in this model. While bumetanide at either dose was ineffective when administered alone, the higher dose of bumetanide markedly potentiated midazolam's effect on neonatal seizures. Median bumetanide brain levels (0.47-0.53 µM) obtained with the higher dose were in the range known to inhibit the Na-K-Cl-cotransporter NKCC1 but it remains to be determined whether brain NKCC1 inhibition was underlying the potentiation of midazolam. When behavioral and cognitive alterations were examined over three months after asphyxia, treatment with the bumetanide/midazolam combination, but not with bumetanide or midazolam alone, prevented impairment of learning and memory. Furthermore, the combination prevented the loss of neurons in the dentate hilus and aberrant mossy fiber sprouting in the CA3a area of the hippocampus. The molecular mechanisms that explain that bumetanide potentiates midazolam but not phenobarbital in the rat model of birth asphyxia remain to be determined.

The loop diuretic torasemide but not azosemide potentiates the anti-seizure and disease-modifying effects of midazolam in a rat model of birth asphyxia

Loop diuretics such as furosemide and bumetanide, which act by inhibiting the Na-K-2Cl cotransporter NKCC2 at the thick ascending limb of the loop of Henle, have been shown to exert anti-seizure effects. However, the exact mechanism of this effect is not known. For bumetanide, it has been suggested that inhibition of the NKCC isoform NKCC1 in the membrane of brain neurons may be involved; however, NKCC1 is expressed by virtually all cell types in the brain, which makes any specific targeting of neuronal NKCC1 by bumetanide impossible. In addition, bumetanide only poorly penetrates the brain. We have previously shown that loop diuretics azosemide and torasemide also potently inhibit NKCC1. In contrast to bumetanide and furosemide, azosemide and torasemide lack a carboxylic group, which should allow them to better penetrate through biomembranes by passive diffusion. Because of the urgent medical need to develop new treatments for neonatal seizures and their adverse outcome, we evaluated the effects of azosemide and torasemide, administered alone or in combination with phenobarbital or midazolam, in a rat model of birth asphyxia and neonatal seizures. Neither diuretic suppressed the seizures when administered alone but torasemide potentiated the anti-seizure effect of midazolam. Brain levels of torasemide were below those needed to inhibit NKCC1. In addition to suppressing seizures, the combination of torasemide and midazolam, but not midazolam alone, prevented the cognitive impairment of the post-asphyxial rats at 3 months after asphyxia. Furthermore, aberrant mossy fiber sprouting in the hippocampus was more effectively prevented by the combination. We assume that either an effect on NKCC1 at the blood-brain barrier and/or cells in the periphery or the NKCC2-mediated diuretic effect of torasemide are involved in the present findings. Our data suggest that torasemide may be a useful option for improving the treatment of neonatal seizures and their adverse outcome.

Midazolam Prevents the Adverse Outcome of Neonatal Asphyxia

OBJECTIVE

Birth asphyxia (BA) is the most frequent cause of neonatal death as well as central nervous system (CNS) injury. BA is often associated with neonatal seizures, which only poorly respond to anti-seizure medications and may contribute to the adverse neurodevelopmental outcome. Using a non-invasive rat model of BA, we have recently reported that the potent benzodiazepine, midazolam, prevents neonatal seizures in ~50% of rat pups. In addition to its anti-seizure effect, midazolam exerts anti-inflammatory actions, which is highly relevant for therapeutic intervention following BA. The 2 major aims of the present study were to examine (1) whether midazolam reduces the adverse outcome of BA, and (2) whether this effect is different in rats that did or did not exhibit neonatal seizures after drug treatment.

METHODS

Behavioral and cognitive tests were performed over 14 months after asphyxia, followed by immunohistochemical analyses.

RESULTS

All vehicle-treated rats had seizures after asphyxia and developed behavioral and cognitive abnormalities, neuroinflammation in gray and white matter, neurodegeneration in the hippocampus and thalamus, and hippocampal mossy fiber sprouting in subsequent months. Administration of midazolam (1 mg/kg i.p.) directly after asphyxia prevented post-asphyctic seizures in ~50% of the rats and resulted in the prevention or decrease of neuroinflammation and the behavioral, cognitive, and neurodegenerative consequences of asphyxia. Except for neurodegeneration in the thalamus, seizures did not seem to contribute to the adverse outcome of asphyxia.

INTERPRETATION

The disease-modifying effect of midazolam identified here strongly suggests that this drug provides a valuable option for improving the treatment and outcome of BA. ANN NEUROL 2023;93:226-243.

The novel dual-mechanism Kv7 potassium channel/TSPO receptor activator GRT-X is more effective than the Kv7 channel opener retigabine in the 6-Hz refractory seizure mouse model

Epilepsy, one of the most common and most disabling neurological disorders, is characterized by spontaneous recurrent seizures, often associated with structural brain alterations and cognitive and psychiatric comorbidities. In about 30% of patients, the seizures are resistant to current treatments; so more effective treatments are urgently needed. Among the ∼30 clinically approved antiseizure drugs, retigabine (ezogabine) is the only drug that acts as a positive allosteric modulator (or opener) of voltage-gated Kv7 potassium channels, which is particularly interesting for some genetic forms of epilepsy. Here we describe a novel dual-mode-of-action compound, GRT-X (N-[(3-fluorophenyl)-methyl]-1-(2-methoxyethyl)-4-methyl-2-oxo-(7-trifluoromethyl)-1H-quinoline-3-carboxylic acid amide) that activates both Kv7 potassium channels and the mitochondrial translocator protein 18 kDa (TSPO), leading to increased synthesis of brain neurosteroids. TSPO activators are known to exert anti-inflammatory, neuroprotective, anxiolytic, and antidepressive effects, which, together with an antiseizure effect (mediated by Kv7 channels), would be highly relevant for the treatment of epilepsy. This prompted us to compare the antiseizure efficacy of retigabine and GRT-X in six mouse and rat models of epileptic seizures, including the 6-Hz model of difficult-to-treat focal seizures. Furthermore, the tolerability of the two compounds was compared in mice and rats. Potency comparisons were based on both doses and peak plasma concentrations. Overall, GRT-X was more effective than retigabine in three of the six seizure models used here, the most important difference being the high efficacy in the 6-Hz (32 mA) seizure model in mice. Based on drug plasma levels, GRT-X was at least 30 times more potent than retigabine in the latter model. These data indicate that GRT-X is a highly interesting novel anti-seizure drug with a unique (first-in-class) dual-mode mechanism of action.

Determination of minimal steady-state plasma level of diazepam causing seizure threshold elevation in rats

OBJECTIVE

Diazepam, administered by the intravenous, oral, or rectal routes, is widely used for the management of acute seizures. Dosage forms for delivery of diazepam by other routes of administration, including intranasal, intramuscular, and transbuccal, are under investigation. In predicting what dosages are necessary to terminate seizures, the minimal exposure required to confer seizure protection must be known. Here we administered diazepam by continuous intravenous infusion to obtain near-steady-state levels, which allowed an assessment of the minimal levels that elevate seizure threshold.

METHODS

The thresholds for various behavioral seizure signs (myoclonic jerk, clonus, and tonus) were determined with the timed intravenous pentylenetetrazol seizure threshold test in rats. Diazepam was administered to freely moving animals by continuous intravenous infusion via an indwelling jugular vein cannula. Blood samples for assay of plasma levels of diazepam and metabolites were recovered via an indwelling cannula in the contralateral jugular vein.

RESULTS

The pharmacokinetic parameters of diazepam following a single 80-μg/kg intravenous bolus injection were determined using a noncompartmental pharmacokinetic approach. The derived parameters Vd , CL, t1/2α (distribution half-life) and t1/2β (terminal half-life) for diazepam were, respectively, 608 mL, 22.1 mL/min, 13.7 minutes, and 76.8 minutes, respectively. Various doses of diazepam were continuously infused without or with an initial loading dose. At the end of the infusions, the thresholds for various behavioral seizure signs were determined. The minimal plasma diazepam concentration associated with threshold elevations was estimated at approximately 70 ng/mL. The active metabolites nordiazepam, oxazepam, and temazepam achieved levels that are expected to make only minor contributions to the threshold elevations.

SIGNIFICANCE

Diazepam elevates seizure threshold at steady-state plasma concentrations lower than previously recognized. The minimally effective plasma concentration provides a reference that may be considered when estimating the diazepam exposure required for acute seizure treatment.

Overexpression of the 18 kDa translocator protein (TSPO) in the hippocampal dentate gyrus produced anxiolytic and antidepressant-like behavioural effects

The 18 kDa translocator protein (TSPO) is a five transmembrane domain protein that plays a crucial role in neurosteroid (e.g., allopregnanolone) synthesis by promoting the transport of cholesterol to the inner mitochondrial membrane. This protein is predominantly expressed in steroid-synthesizing tissues, including the central and peripheral nervous system, affecting stress-related disorders such as anxiety and depression. Recent studies have focused on the hippocampal dentate gyrus, which is very important for involvement of anxiety and depression. However, the exact role that TSPO plays in the pathophysiology of anxiety and depression and the involvement of the hippocampal dentate gyrus in regulating these behavioural effects remain elusive. This study used the lentiviral vectors mediating TPSO overexpression to assess the effects of TPSO overexpression in the hippocampal dentate gyrus on anxiolytic and antidepressant-like behavioural effects in mice. The expression of TSPO and the concentration of allopregnanolone in hippocampus tissues (3 mm in diameter around the injection site on both sides) were measured by Western blot and ELISA, respectively. The results indicated that microinjection of the LV-TSPO resulted in a significant increase in TSPO expression and allopregnanolone concentration in the hippocampus. Moreover, TSPO overexpression of the mouse hippocampal dentate gyrus generated significant anxiolytic and antidepressant-like behavioural effects in a series of behavioural models. These effects were completely blocked by the TSPO antagonist PK11195 (3 mg/kg, intraperitoneally) and the 5α-reductase inhibitor finasteride (5 mg/kg,intraperitoneally). Meanwhile, the increased allopregnanolone was also reversed by PK11195 and finasteride. In addition, neither PK11195 nor finasteride had an effect on the expression of TSPO. Overall, our results are the first to suggest that the overexpression of TSPO in the hippocampal dentate gyrus produced anxiolytic and antidepressant-like behavioural effects that are partially mediated by downstream allopregnanolone biosynthesis. Our results suggest that TSPO would be a potential anxiolytic and antidepressant therapeutic target.

Contrasting actions of a convulsant barbiturate and its anticonvulsant enantiomer on the α1 β3 γ2L GABAA receptor account for their in vivo effects

KEY POINTS

Most barbiturates are anaesthetics but unexpectedly a few are convulsants whose mechanism of action is poorly understood. We synthesized and characterized a novel pair of chiral barbiturates that are capable of photolabelling their binding sites on GABAA receptors. In mice the S-enantiomer is a convulsant, but the R-enantiomer is an anticonvulsant. The convulsant S-enantiomer binds solely at an inhibitory site. It is both an open state inhibitor and a resting state inhibitor. Its action is pH independent, suggesting the pyrimidine ring plays little part in binding. The inhibitory site is not enantioselective because the R-enantiomer inhibits with equal affinity. In contrast, only the anticonvulsant R-enantiomer binds to the enhancing site on open channels, causing them to stay open longer. The enhancing site is enantioselective. The in vivo actions of the convulsant S-enantiomer are accounted for by its interactions with GABAA receptors.

ABSTRACT

Most barbiturates are anaesthetics but a few unexpectedly are convulsants. We recently located the anaesthetic sites on GABAA receptors (GABAA Rs) by photolabelling with an anaesthetic barbiturate. To apply the same strategy to locate the convulsant sites requires the creation and mechanistic characterization of a suitable agent. We synthesized enantiomers of a novel, photoactivable barbiturate, 1-methyl-5-propyly-5-(m-trifluoromethyldiazirinyl) phenyl barbituric acid (mTFD-MPPB). In mice, S-mTFD-MPPB acted as a convulsant, whereas R-mTFD-MPPB acted as an anticonvulsant. Using patch clamp electrophysiology and fast solution exchange on recombinant human α1 β3 γ2L GABAA Rs expressed in HEK cells, we found that S-mTFD-MPPB inhibited GABA-induced currents, whereas R-mTFD-MPPB enhanced them. S-mTFD-MPPB caused inhibition by binding to either of two inhibitory sites on open channels with bimolecular kinetics. It also inhibited closed, resting state receptors at similar concentrations, decreasing the channel opening rate and shifting the GABA concentration-response curve to the right. R-mTFD-MPPB, like most anaesthetics, enhanced receptor gating by rapidly binding to allosteric sites on open channels, initiating a rate-limiting conformation change to stabilized open channel states. These states had slower closing rates, thus shifting the GABA concentration-response curve to the left. Under conditions when most GABAA Rs were open, an inhibitory action of R-mTFD-MPPB was revealed that had a similar IC50 to that of S-mTFD-MPPB. Thus, the inhibitory sites are not enantioselective, and the convulsant action of S-mTFD-MPPB results from its negligible affinity for the enhancing, anaesthetic sites. Interactions with these two classes of barbiturate binding sites on GABAA Rs underlie the enantiomers' different pharmacological activities in mice.

Translocator protein mediates the anxiolytic and antidepressant effects of midazolam

The translocator protein (18 kDa) (TSPO) plays an important role in stress-related disorders, such as anxiety, depression and post-traumatic stress disorder (PTSD), caused by neurosteroids (e.g. allopregnanolone). The present study sought to evaluate the significance of TSPO in anxiolytic and antidepressant effects induced by midazolam. The animals were administrated midazolam (0.25, 0.5 and 1 mg/kg, i.p.) and subjected to behavioral tests, including Vogel-type conflict test, elevated plus-maze test, forced swimming test. Midazolam produced anxiolytic- and antidepressant-like effects Vogel-type conflict test (1 mg/kg, i.p.), elevated plus-maze test (0.5 and 1 mg/kg, i.p.), and forced swimming test (0.5 and 1 mg/kg, i.p.). These effects of Midazolam were totally blocked by the TSPO antagonist PK11195 (3 mg/kg, i.p.). To evaluate the role of allopregnanolone in the anxiolytic- and antidepressant-like effects of midazolam, the animals were decapitated at the end of the behavioral tests. The allopregnanolone levels of the prefrontal cortex and hippocampus were measured by enzyme-linked immunosorbent assay (ELISA). The allopregnanolone level of the prefrontal cortex and hippocampus was increased by midazolam (0.5, 1 mg/kg, i.p.) and the increase was reversed by PK11195 (3 mg/kg, i.p.). Overall, the results indicated that the anxiolytic- and antidepressant-like effects of midazolam were mediated by TSPO, via stimulation of allopregnanolone biosynthesis.

Antiseizure Activity of Midazolam in Mice Lacking δ-Subunit Extrasynaptic GABA(A) Receptors

Midazolam is a benzodiazepine anticonvulsant with rapid onset and short duration of action. Midazolam is the current drug of choice for acute seizures and status epilepticus, including those caused by organophosphate nerve agents. The antiseizure activity of midazolam is thought to result from its allosteric potentiation of synaptic GABA(A) receptors in the brain. However, there are indications that benzodiazepines promote neurosteroid synthesis via the 18-kDa cholesterol transporter protein (TSPO). Therefore, we investigated the role of neurosteroids and their extrasynaptic GABA(A) receptor targets in the antiseizure activity of midazolam. Here, we used δ-subunit knockout (DKO) mice bearing a targeted deletion of the extrasynaptic receptors to investigate the contribution of the extrasynaptic receptors to the antiseizure activity of midazolam using the 6-Hz and hippocampus kindling seizure models. In both models, midazolam produced rapid and dose-dependent protection against seizures (ED50, 0.4 mg/kg). Moreover, the antiseizure potency of midazolam was undiminished in DKO mice compared with control mice. Pretreatment with PK11195 [1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxamide], a TSPO blocker, or finasteride, a 5α-reductase neurosteroid inhibitor, did not affect the antiseizure effect of midazolam. The antiseizure activity of midazolam was significantly reversed by pretreatment with flumazenil, a benzodiazepine antagonist. Plasma and brain levels of the neurosteroid allopregnanolone were not significantly greater in midazolam-treated animals. These studies therefore provide strong evidence that neurosteroids and extrasynaptic GABA(A) receptors are not involved in the antiseizure activity of midazolam, which mainly occurs through synaptic GABA(A) receptors via direct binding to benzodiazepine sites. This study reaffirms midazolam's use for controlling acute seizures and status epilepticus.

Midazolam as an anticonvulsant antidote for organophosphate intoxication--A pharmacotherapeutic appraisal

OBJECTIVE

This review summarizes the therapeutic potential of midazolam as an anticonvulsant antidote for organophosphate (OP) intoxication.

METHODS

Benzodiazepines are widely used to treat acute seizures and status epilepticus (SE), a neurologic emergency of persistent seizures that can lead to severe neuronal damage or death. Midazolam is a benzodiazepine hypnotic with a rapid onset and short duration of action.

RESULTS

Midazolam is considered the new drug of choice for persistent acute seizures and SE, including those caused by neurotoxic OPs and nerve agents. Midazolam is a positive allosteric modulator of synaptic γ-aminobutyric acid (GABA)A receptors in the brain. It potentiates GABAergic inhibition and thereby controls hyperexcitability and seizures. Midazolam is administered intravenously or intramuscularly to control acute seizures and SE. Due to its favorable pharmacokinetic features, midazolam is being considered as a replacement anticonvulsant for diazepam in the antidote kit for nerve agents. Clinical studies such as the recent Rapid Anticonvulsant Medication Prior to Arrival Trial (RAMPART) trial have confirmed the anticonvulsant efficacy of midazolam in SE in prehospital settings.

SIGNIFICANCE

In experimental models, midazolam is effective when given at the onset of seizures caused by nerve agents. However, benzodiazepines are less effective at terminating seizures when given 30 min or later after OP exposure or seizure onset, likely because of internalization or downregulation of synaptic, but not extrasynaptic, GABAA receptors, which can lead to diminished potency and seizure recurrence.

GABAA receptor-acting neurosteroids: a role in the development and regulation of the stress response

Regulation of hypothalamic-pituitary-adrenocortical (HPA) axis activity by stress is a fundamental survival mechanism and HPA-dysfunction is implicated in psychiatric disorders. Adverse early life experiences, e.g. poor maternal care, negatively influence brain development and programs an abnormal stress response by encoding long-lasting molecular changes, which may extend to the next generation. How HPA-dysfunction leads to the development of affective disorders is complex, but may involve GABAA receptors (GABAARs), as they curtail stress-induced HPA axis activation. Of particular interest are endogenous neurosteroids that potently modulate the function of GABAARs and exhibit stress-protective properties. Importantly, neurosteroid levels rise rapidly during acute stress, are perturbed in chronic stress and are implicated in the behavioural changes associated with early-life adversity. We will appraise how GABAAR-active neurosteroids may impact on HPA axis development and the orchestration of the stress-evoked response. The significance of these actions will be discussed in the context of stress-associated mood disorders.

Role of GABA-active neurosteroids in the efficacy of metyrapone against cocaine addiction

Previous research has demonstrated a complicated role for stress and HPA axis activation in potentiating various cocaine-related behaviors in preclinical models of drug dependence. However, the investigation of several antiglucocorticoid therapies has yielded equivocal results in reducing cocaine-related behaviors, possibly because of varying mechanisms of actions. Specifically, research suggests that metyrapone (a corticosterone synthesis inhibitor) may reduce cocaine self-administration in rats via a nongenomic, extra-adrenal mechanism without altering plasma corticosterone. In the current experiments, male rats were trained to self-administer cocaine infusions and food pellets in a multiple, alternating schedule of reinforcement. Metyrapone pretreatment dose-dependently decreased cocaine self-administration as demonstrated previously. Pharmacological inhibition of neurosteroid production by finasteride had significant effects on cocaine self-administration, regardless of metyrapone pretreatment. However, metyrapone's effects on cocaine self-administration were significantly attenuated with bicuculline pretreatment, suggesting a role for GABA-active neurosteroids in cocaine-reinforced behaviors. In vitro binding data also confirmed that metyrapone does not selectively bind to GABA-related proteins. The results of these experiments support the hypothesis that metyrapone may increase neurosteroidogenesis to produce effects on cocaine-related behaviors.

Comparison between the effect of propofol and midazolam on picrotoxin-induced convulsions in rat

Propofol is a short acting intravenous anesthetic that has been used in the treatment of status epileptics. However, the occurrence of seizures in epileptic and non-epileptic patients during recovery from propofol induced anesthesia suggests that propofol may have proconvulsant effects. We have previously shown that propofol displays anticonvulsant effects against picrotoxin (PTX) induced seizures during its peak sedative effects. The purpose of the present study was to compare the time course of the effect of intravenous administration of various doses (2.5, 5, and 10 mg/kg) of propofol and midazolam on PTX-induced seizures in adult female Sprague-Dawley rats. The latency to onset of clonic seizures induced by intraperitoneal injection of PTX was significantly increased by the highest dose of propofol and all doses of midazolam, suggesting that both agents display anticonvulsant effects. The anticonvulsant effects of propofol (10 mg/kg) lasted about 20 min and PTX-induced clonic seizures were observed thereafter and peaked within 30 min post drug administration. Clonic seizures progressed rapidly to tonic seizures leading to high rate of PTX-induced mortality. In midazolam (10 mg/kg) treated rats, clonic seizures were observed 25 min after drug administration and the number of rats exhibiting clonic seizures was highest within 40 min. However, clonic seizures did not progress into tonic seizures and thus, PTX-induced seizure related mortality was significantly reduced. In conclusion, this study provides further evidence for the anticonvulsant effects of propofol and midazolam against PTX-induced seizures. Furthermore, the data of the current study showed that midazolam was more effective than propofol against PTX-induced tonic seizures.

Early life maternal separation stress augmentation of limbic epileptogenesis: the role of corticosterone and HPA axis programming

Early life stress causes long-lasting effects on the limbic system that may be relevant to the development of mesial temporal lobe epilepsy (MTLE) and its associated psychopathology. Recent studies in rats suggest that maternal separation (MS), a model of early life stress, confers enduring vulnerability to amygdala kindling limbic epileptogenesis. However, the mechanisms underlying this remain unknown. Here, we tested whether hypothalamic-pituitary-adrenal (HPA) axis hyper-reactivity induced by MS - specifically the excessive secretion of corticosterone following a seizure - was involved in this vulnerability. In adult female rats subjected to MS from postnatal days 2-14, seizure-induced corticosterone responses were significantly augmented and prolonged for at least two hours post-seizure, compared to control early-handled (EH) rats. This was accompanied by reduced seizure threshold (p<0.05) and increased vulnerability to the kindling-induced progression of seizure duration (p<0.05) in MS rats. Pre-seizure treatment with the corticosterone synthesis inhibitor, metyrapone (MET) (50mg/kgsc) effectively blocked seizure-induced corticosterone responses. When delivered throughout kindling, MET treatment also reversed the MS-induced reduction in seizure threshold and the lengthened seizure duration back to levels of EH rats. These observations suggest that adverse early life environments induce a vulnerability to kindling epileptogenesis mediated by HPA axis hyper-reactivity, which could have relevance for the pathogenesis of MTLE.

Common medical illnesses that affect anesthesia and their anesthetic management

Patients undergoing an office-based anesthetic require a thorough preoperative evaluation to identify medical illnesses and undertake appropriate investigations or studies. This article addresses common medical illnesses seen in oral surgery offices and provides insight into their anesthetic management, concentrating on open-airway office-based anesthesia.

The combination of metyrapone and oxazepam for the treatment of cocaine and other drug addictions

Although scientists have been investigating the neurobiology of psychomotor stimulant reward for many decades, there is still no FDA-approved treatment for cocaine or methamphetamine abuse. Research in our laboratory has focused on the relationship between stress, the subsequent activation of the hypothalamic-pituitary-adrenal (HPA) axis, and psychomotor stimulant reinforcement for almost 30 years. This research has led to the development of a combination of low doses of the cortisol synthesis inhibitor, metyrapone, and the benzodiazepine, oxazepam, as a potential pharmacological treatment for cocaine and other substance use disorders. In fact, we have conducted a pilot clinical trial that demonstrated that this combination can reduce cocaine craving and cocaine use. Our initial hypothesis underlying this effect was that the combination of metyrapone and oxazepam reduced cocaine seeking and taking by decreasing activity within the HPA axis. Even so, doses of the metyrapone and oxazepam combination that consistently reduced cocaine taking and seeking did not reliably alter plasma corticosterone (or cortisol in the pilot clinical trial). Furthermore, subsequent research has demonstrated that this drug combination is effective in adrenalectomized rats, suggesting that these effects must be mediated above the level of the adrenal gland. Our evolving hypothesis is that the combination of metyrapone and oxazepam produces its effects by increasing the levels of neuroactive steroids, most notably tetrahydrodeoxycorticosterone, in the medial prefrontal cortex and amygdala. Additional research will be necessary to confirm this hypothesis and may lead to the development of improved and specific pharmacotherapies for the treatment of psychomotor stimulant use.

Drug repositioning for orphan genetic diseases through Conserved Anticoexpressed Gene Clusters (CAGCs)

Background

The development of new therapies for orphan genetic diseases represents an extremely important medical and social challenge. Drug repositioning, i.e. finding new indications for approved drugs, could be one of the most cost- and time-effective strategies to cope with this problem, at least in a subset of cases. Therefore, many computational approaches based on the analysis of high throughput gene expression data have so far been proposed to reposition available drugs. However, most of these methods require gene expression profiles directly relevant to the pathologic conditions under study, such as those obtained from patient cells and/or from suitable experimental models. In this work we have developed a new approach for drug repositioning, based on identifying known drug targets showing conserved anti-correlated expression profiles with human disease genes, which is completely independent from the availability of ‘ad hoc’ gene expression data-sets.

Results

By analyzing available data, we provide evidence that the genes displaying conserved anti-correlation with drug targets are antagonistically modulated in their expression by treatment with the relevant drugs. We then identified clusters of genes associated to similar phenotypes and showing conserved anticorrelation with drug targets. On this basis, we generated a list of potential candidate drug-disease associations. Importantly, we show that some of the proposed associations are already supported by independent experimental evidence.

Conclusions

Our results support the hypothesis that the identification of gene clusters showing conserved anticorrelation with drug targets can be an effective method for drug repositioning and provide a wide list of new potential drug-disease associations for experimental validation.

Novel modulatory effects of neurosteroids and benzodiazepines on excitatory and inhibitory neurons excitability: a multi-electrode array recording study

The balance between glutamate- and GABA-mediated neurotransmission in the brain is fundamental in the nervous system, but it is regulated by the “tonic” release of a variety of endogenous factors. One such important group of molecules are the neurosteroids (NSs) which, similarly to benzodiazepines (BDZs), enhance GABAergic neurotransmission. The purpose of our work was to investigate, at in vivo physiologically relevant concentrations, the effects of NSs and BDZs as GABA modulators on dissociated neocortical neuron networks grown in long-term culture. We used a multi-electrode array (MEA) recording technique and a novel analysis that was able to both identify the action potentials of engaged excitatory and inhibitory neurons and to detect drug-induced network up-states (burst). We found that the NSs tetrahydrodeoxycorticosterone (THDOC) and allopregnanolone (ALLO) applied at low nanomolar concentrations, produced different modulatory effects on the two neuronal clusters. Conversely, at high concentrations (1 μM), both NSs, decreased excitatory and inhibitory neuron cluster excitability; however, even several hours after wash-out, the excitability of inhibitory neurons continued to be depressed, leading to a network long-term depression (LTD). The BDZs clonazepam (CLZ) and midazolam (MDZ) also decreased the network excitability, but only MDZ caused LTD of inhibitory neuron cluster. To investigate the origin of the LTD after MDZ application, we tested finasteride (FIN), an inhibitor of endogenous NSs synthesis. FIN did not prevent the LTD induced by MDZ, but surprisingly induced it after application of CLZ. The significance and possible mechanisms underlying these LTD effects of NSs and BDZs are discussed. Taken together, our results not only demonstrate that ex vivo networks show a sensitivity to NSs and BDZs comparable to that expressed in vivo, but also provide a new global in vitro description that can help in understanding their activity in more complex systems.