Anxiolytic Action Of Benzodiazepines Research Articles

Translocator protein (18kDa) TSPO: a new diagnostic or therapeutic target for stress-related disorders?

Efficient treatment of stress-related disorders, such as depression, is still a major challenge. The onset of antidepressant drug action is generally quite slow, while the anxiolytic action of benzodiazepines is considerably faster. However, their long-term use is impaired by tolerance development, abuse liability and cognitive impairment. Benzodiazepines act as positive allosteric modulators of ɣ-aminobutyric acid type A (GABAA) receptors. 3α-reduced neurosteroids such as allopregnanolone also are positive allosteric GABAA receptor modulators, however, through a site different from that targeted by benzodiazepines. Recently, the administration of neurosteroids such as brexanolone or zuranolone has been shown to rapidly ameliorate symptoms in post-partum depression or major depressive disorder. An attractive alternative to the administration of exogenous neurosteroids is promoting endogenous neurosteroidogenesis via the translocator protein 18k Da (TSPO). TSPO is a transmembrane protein located primarily in mitochondria, which mediates numerous biological functions, e.g., steroidogenesis and mitochondrial bioenergetics. TSPO ligands have been used in positron emission tomography (PET) studies as putative markers of microglia activation and neuroinflammation in stress-related disorders. Moreover, TSPO ligands have been shown to modulate neuroplasticity and to elicit antidepressant and anxiolytic therapeutic effects in animals and humans. As such, TSPO may open new avenues for understanding the pathophysiology of stress-related disorders and for the development of novel treatment options.

High-Dose Zolpidem Withdrawal Seizure in a Patient With Spinocerebellar Ataxia

To the Editor: Spinocerebellar ataxia (SCA) is an inherited disorder of brain function characterized by progressive incoordination of gait and is often associated with poor coordination of hands, speech, and eye movements. It is a slowly progressive disease that gradually worsens over a period of years. Zolpidem is a nonbenzodiazepine sedative in the imidazopyridine class and is chemically distinct from other sedatives. It is a short-acting hypnotic with a selective agonist effect for γ-aminobutyric acid (GABA) type A receptors in the brain. It was considered originally by physicians as almost devoid of abuse and dependence potential. Intriguingly, aside from its hypnotic effect, zolpidem has been shown to improve catatonia,1 aphasia,2 Parkinson's disease,3 and ataxia.4 However, reports of zolpidem abuse or dependence are increasing,5,6 and more attention should be paid in terms of zolpidem withdrawal. We report a patient with SCA who took zolpidem for movement difficulties initially, developed dependence on high-dose zolpidem treatment, and encountered serious withdrawal symptoms. We also review the literature on the possible mechanism for the effect of zolpidem on SCA. Case report. Ms A, a 40-year-old married woman, was referred in 2009 for psychiatric consultation due to high-dose zolpidem use. She was diagnosed with SCA type IV at age 35 years with initial symptoms of unsteady gait and mild slurred speech. Her father and brother were also afflicted with SCA. This time, she was admitted via emergency department to our neurology department because of loss of consciousness. Generalized seizure lasted for 1 minute at home, and initial management at the emergency department with phenytoin intravenous drip terminated further progression. Toxicology testing detected no plasma alcohol, whereas plasma benzodiazepine level was 64.80 ng/mL. She claimed she had abused triazolam and alcohol during early adulthood due to insomnia. Other illicit substance use was denied. She had started taking zolpidem 3 years earlier for insomnia, and, paradoxically, zolpidem relieved her ataxia and spasticity. She recalled being able to move her arms and turn her trunk more easily, although the improvement lasted only around 1 hour after taking zolpidem. The dose of zolpidem was gradually escalated by the patient to reach optimal effect. The dose usually amounted to 1,000 mg/d for the past year. Nausea, palpitation, jitters, hand tremor, and perspiration were noted if she did not take enough zolpidem. She was bedridden due to SCA and was cared for by her husband. Although she consumed high doses of zolpidem, her husband tried to cater to all her needs out of sympathy. Zolpidem had been prescribed from different physicians. Withdrawal seizures were noted several times if her supply of zolpidem fell short. Ms A was detoxified by taper of zolpidem gradually over 2 weeks. We prescribed trazodone 100 mg before sleep and diazepam 20 mg/d and propranolol 30 mg/d for anxiety. No seizure attack was noted during hospitalization. After this 2-week hospitalization, she was referred to the psychiatric clinic for further management. The imidazopyridine hypnotic zolpidem binds preferably to the α1 subtype of the benzodiazepine receptor, which is part of GABAA receptor complex. This highly accounts for its sedative effect, whereas the anxiolytic action of benzodiazepines appears to be mediated by receptors that contain the α2 subunit.7 Zolpidem at high doses might lose its selectivity on α1 subunits and bind to lower-affinity α2 units, leading to an anxiolytic effect. Thus, high-dose zolpidem may have a paradoxical effect for alleviating anxiety, and abrupt discontinuation would produce withdrawal symptoms such as palpitation, anxiety, tremor, or seizure similar to those seen with benzodiazepine withdrawal. There is no definite treatment that can prevent or slow the progression of SCA. Clauss et al4 reported transient improvement of SCA with zolpidem in 4 cases. Single photon emission computed tomography demonstrated that GABAergic function may be decreased in the cerebral cortex, thalamus, striatum, and cerebellum in patients with SCA.8 Zolpidem has been shown to mildly improve catatonia, aphasia, and Parkinson's disease.9 Such motor improvement may be due to selective inhibition by zolpidem of GABAergic inhibitory neurons in the internal globus pallidus and substantia nigra pars reticulata, resulting in activation of the thalamus and cerebral cortex.9 Positron emission tomography imaging also has shown normalized tracer uptake in the left thalamus and cerebellum after treatment with zolpidem.4 Our case further corroborates that zolpidem has a mode of action apart from hypnotic properties. To our knowledge, this is the first case report concerning high-dose zolpidem withdrawal seizure in a patient with SCA. We should be more cautious in prescribing zolpidem to patients with past drug abuse or dependence to prevent unwanted consequence. Further investigation of the pharmacologic efficacy of zolpidem in SCA might be needed.

Effects of diazepam on BOLD activation during the processing of aversive faces

This study aimed to measure, using fMRI, the effect of diazepam on the haemodynamic response to emotional faces. Twelve healthy male volunteers (mean age = 24.83 ± 3.16 years), were evaluated in a randomized, balanced-order, double-blind, placebo-controlled crossover design. Diazepam (10 mg) or placebo was given 1 h before the neuroimaging acquisition. In a blocked design covert face emotional task, subjects were presented with neutral (A) and aversive (B) (angry or fearful) faces. Participants were also submitted to an explicit emotional face recognition task, and subjective anxiety was evaluated throughout the procedures. Diazepam attenuated the activation of right amygdala and right orbitofrontal cortex and enhanced the activation of right anterior cingulate cortex (ACC) to fearful faces. In contrast, diazepam enhanced the activation of posterior left insula and attenuated the activation of bilateral ACC to angry faces. In the behavioural task, diazepam impaired the recognition of fear in female faces. Under the action of diazepam, volunteers were less anxious at the end of the experimental session. These results suggest that benzodiazepines can differentially modulate brain activation to aversive stimuli, depending on the stimulus features and indicate a role of amygdala and insula in the anxiolytic action of benzodiazepines.

5-HT1A receptor blockade reverses GABAA receptor α3 subunit-mediated anxiolytic effects on stress-induced hyperthermia

RationaleStress-related disorders are associated with dysfunction of both serotonergic and GABAergic pathways, and clinically effective anxiolytics act via both neurotransmitter systems. As there is evidence that the GABAA and the serotonin receptor system interact, a serotonergic component in the anxiolytic actions of benzodiazepines could be present.ObjectivesThe main aim of the present study was to investigate whether the anxiolytic effects of (non-)selective α subunit GABAA receptor agonists could be reversed with 5-HT1A receptor blockade using the stress-induced hyperthermia (SIH) paradigm.ResultsThe 5-HT1A receptor antagonist WAY-100635 (0.1–1 mg/kg) reversed the SIH-reducing effects of the non-α-subunit selective GABAA receptor agonist diazepam (1–4 mg/kg) and the GABAA receptor α3-subunit selective agonist TP003 (1 mg/kg), whereas WAY-100635 alone was without effect on the SIH response or basal body temperature. At the same time, co-administration of WAY-100635 with diazepam or TP003 reduced basal body temperature. WAY-100635 did not affect the SIH response when combined with the preferential α1-subunit GABAA receptor agonist zolpidem (10 mg/kg), although zolpidem markedly reduced basal body temperature.ConclusionsThe present study suggests an interaction between GABAA receptor α-subunits and 5-HT1A receptor activation in the SIH response. Specifically, our data indicate that benzodiazepines affect serotonergic signaling via GABAA receptor α3-subunits. Further understanding of the interactions between the GABAA and serotonin system in reaction to stress may be valuable in the search for novel anxiolytic drugs.

Pharmacological and computational analysis of alpha-subunit preferential GABA A positive allosteric modulators on the rat septo-hippocampal activity

Clinically most active anxiolytic drugs are positive allosteric modulators (PAMs) of GABA A receptors, represented by benzodiazepine compounds. Due to their non-selective profile, however, they potently modulate several sup-type specific GABA A receptors, contributing to their broad-range side effects. Based on observations in genetically altered mice, however, it has been proposed that anxiolytic action of benzodiazepines is predominantly mediated by GABA A α2/3 subunit-containing receptors. In the present study we analyzed the actions of the preferential GABA A α1 and α2/3 PAMs, zolpidem and L-838417, respectively on hippocampal EEG and medial septum neuronal activity in anesthetized rats. In parallel, a computational model was constructed to model pharmacological actions of these compounds on the septo-hippocampal circuitry. The present results demonstrated that zolpidem inhibited theta oscillation both in the hippocampus and septum, and profoundly inhibited firing activity of septal neurons. L-838417 also inhibited hippocampal and septal theta oscillation, however, it did not significantly alter firing rate activity of septal neurons. Our computational model showed that cessation of periodic firing of hippocampo-septal neurons, representing absence of hippocampal theta activity, disrupted oscillation of septal units, without altering their overall firing activity, similar to changes observed in our in vivo experiments following administration of L-838417. Understanding the correlation between changes in septo-hippocampal activity and actions of selective modulators of GABA A subtype receptor modulators would further advance design of anxiolytic drugs.

Effects of chlordiazepoxide on single-unit activity in the septal region of the freely moving rat: aversive vs. non-aversive contexts

Evidence suggests that stimuli that have the property of inhibiting fear in a Pavlovian fear conditioning paradigm increase cellular activity in the lateral septum, a result consistent with the idea that the lateral septum is actively involved in the inhibition of fear. The experiments reported here were designed to determine if an anxiolytic drug with fear-inhibiting properties would also increase neuronal activity in the lateral septum in a manner that might relate to its mechanism of action as an anxiolytic. An experiment was performed to compare the effects of the benzodiazepine anxiolytic chlordiazepoxide (CDP) upon single-unit activity in the septal region of the rat brain during Pavlovian aversive conditioning with the effects of CDP in a non-aversive context. During Pavlovian conditioning there was a decrease in unit activity in the more lateral regions of the septum, the dorsolateral and ventrolateral nuclei, when a stimulus signaling footshock (CS+) was presented. This conditioned suppression of unit activity was blocked by an intraperitoneal injection of CDP. Additionally, CDP increased baseline unit activity in these regions in the absence of conditioned stimuli. In the more medial regions of the septum, the intermediate lateral septum, we observed few consistent changes either to the conditioned stimuli or to the drug. In a non-aversive context CDP had either no effect at low to moderate doses, or a suppressant effect at a higher dose. The results support a fear-relief hypothesis of lateral septal functioning and suggest the lateral septum as a possible site for the anxiolytic action of benzodiazepines.

Neurosteroids, GABA A receptors, and escalated aggressive behavior

Aggressive behavior can serve important adaptive functions in social species. However, if it exceeds the species-typical pattern, it may become maladaptive. Very high or escalated levels of aggressive behavior can be induced in laboratory rodents by pharmacological (alcohol-heightened aggression), environmental (social instigation), or behavioral (frustration-induced aggression) means. These various forms of escalated aggressive behavior may be useful in further elucidating the neurochemical control over aggression and violence. One neurochemical system most consistently linked with escalated aggression is the GABAergic system, in conjunction with other amines and peptides. Although direct stimulation of GABA receptors generally suppresses aggression, a number of studies have found that positive allosteric modulators of GABA A receptors can cause increases in aggressive behavior. For example, alcohol, benzodiazepines, and many neurosteroids are all positive modulators of the GABA A receptor and all can cause increased levels of aggressive behavior. These effects are dose-dependent and higher doses of these compounds generally shift from heightening aggressive behavior to being sedative and anti-aggressive. In addition, these modulators interact with each other and can have additive effects on the GABA A receptor and on behavior, including aggression. The GABA A receptor is a heteropentameric protein that can be constituted from various subunits. It has been shown that subunit composition can affect sensitivity of the receptor to some modulators and that subunit composition differentially affects the sedative vs anxiolytic actions of benzodiazepines. Initial studies targeting α subunits of the GABA A receptor point to their significant role in the aggression-heightening effects of alcohol, benzodiazepines, and neurosteroids.

The phenomenon of one-trial tolerance to the anxiolytic effect of chlordiazepoxide in the elevated plus-maze test is abolished by previous administration of chlordiazepoxide or buspirone

It has been repeatedly reported that the anxiolytic action of benzodiazepines in the elevated plus-maze test is abolished in rats that have received a single prior experience of the test apparatus (one-trial tolerance effect). To analyze whether the one-trial tolerance effect of chlordiazepoxide can be influenced by administration of chlordiazepoxide or buspirone on trial 1, male Wistar rats received an IP injection of vehicle, chlordiazepoxide (8 mg/kg) or buspirone (2.5 mg/kg) 30 min. before testing for 5 min. in the plus-maze (trial 1). Seventy-two hours later, the rats received vehicle or chlordiazepoxide 30 min. before the re-exposure to the plus-maze for 5 min. (trial 2). Groups injected with chlordiazepoxide or buspirone on trial 1 and with chlordiazepoxide on trial 2 showed an anxiolytic effect of chlordiazepoxide on trial 2, as opposed to rats injected with vehicle on trial 1 and with chlordiazepoxide on trial 2. As opposed to previous studies, the present results suggest that the influence of prior experience with the plus-maze on the anxiolytic action of chlordiazepoxide during re-exposure seems to depend critically on the drug state in which trial 1 is experienced. These results are discussed with respect to the hypothesis proposed to explain the phenomenon of one-trial tolerance.

Smart Benzos in the Age of Anxiety

Benzodiazepines are widely used drugs that enhance inhibitory GABAergic neurotransmission in the central nervous system. This pharmacological profile causes both anxiolytic and sedative effects. In an attempt to better understand the enormous heterogeneity of GABA A receptors, Löw et al . selectively tried to silence specific receptor subunits. They discovered that the α2 subunit of the GABA A receptor mediates the anxiolytic action of benzodiazepines. This finding could lead to the development of new drugs for the treatment of anxiety without the side effects of sedation or motor impairment. Löw, K., Crestani, F., Keist, R., Benke, D., Brünig, I., Benson, J.A., Fritschy, J.-M., Rülicke, T., Bluethmann, H., Möhler, H., and Rudolph, U. (2000) Molecular and neuronal substrate for the selective attenuation of anxiety. Science 290 : 131-134. [Abstract] [Full Text]

Changes in nociceptive and anxiolytic responses following herpes virus-mediated preproenkephalin overexpression in rat amygdala are naloxone-reversible and transient.

These results using herpes virus-mediated gene transfer to overexpress enkephalin in the amygdala support the role of amygdalar opioids in the anxiolytic actions of benzodiazepines and supraspinal nociception (see ref. 1). These studies also demonstrate the usefulness of recombinant herpes virus in evaluating the role of single gene products within specific brain sites in pharmacological responses and complex behaviors.

Maternal care during infancy regulates the development of neural systems mediating the expression of fearfulness in the rat.

The mothers of infant rats show individual differences in the frequency of licking/grooming and arched-back nursing (LG-ABN) of pups that contribute to the development of individual differences in behavioral responses to stress. As adults, the offspring of mothers that exhibited high levels of LG-ABN showed substantially reduced behavioral fearfulness in response to novelty compared with the offspring of low LG-ABN mothers. In addition, the adult offspring of the high LG-ABN mothers showed significantly (i) increased central benzodiazepine receptor density in the central, lateral, and basolateral nuclei of the amygdala as well as in the locus ceruleus, (ii) increased alpha2 adrenoreceptor density in the locus ceruleus, and (iii) decreased corticotropin-releasing hormone (CRH) receptor density in the locus ceruleus. The expression of fear and anxiety is regulated by a neural circuitry that includes the activation of ascending noradrenergic projections from the locus ceruleus to the forebrain structures. Considering the importance of the amygdala, notably the anxiogenic influence of CRH projections from the amygdala to the locus ceruleus, as well as the anxiolytic actions of benzodiazepines, for the expression of behavioral responses to stress, these findings suggest that maternal care during infancy serves to "program" behavioral responses to stress in the offspring by altering the development of the neural systems that mediate fearfulness.

Anxiolytic effects of benzodiazepines in amygdala-lesioned rats

The role of the amygdala in the anxiolytic action of benzodiazepines was examined. Performance on a water-licking conflict paradigm was tested in rats with localized damage to the central nucleus of the amygdala (ACE) or with general damage to the entire amygdaloid complex. The effects of the benzodiazepine chlordiazepoxide (2.5-20.0 mg/kg) on conflict behavior in these animals was also examined. Electrolytic lesions of either ACE or of the entire amygdaloid complex resulted in a pronounced increase of punished responding, an effect that persisted for at least 12 sessions postoperatively. After shock levels were adjusted in the lesioned groups to match their baseline punished behavior to that of the controls, various doses of chlordiazepoxide were administered. Not only did the lesioned animals show an increase in punished behavior in response to the drug, they were more sensitive than controls to the lower drug doses. A complete model of anxiolytic action may have to include both mechanisms that block anxiogenic regions and those that activate anxiolytic regions.

The anxiolytic action of benzodiazepines is not present in handling-habituated rats

The acquisition of two-way shuttle avoidance (40 first trials) was used to test the anxiolytic activity of diazepam (2 and 4 mg/kg) and alprazolam (1.25 mg/kg) vs. vehicle, IP, in rats. These rats had received three different previous treatments: acute, acute with previous handling habituation for 15 days, and handling habituation combined with chronic treatment for 15 days. Results of the acute treatment showed a comparable anxiolytic action of diazepam and alprazolam, reflected by an improvement in avoidance acquisition. After handling habituation, no effect on shuttle box acquisition was obtained in rats acutely treated with diazepam, whereas the alprazolam-treated group showed a significantly impaired avoidance performance. When handling habituation was combined with chronic benzodiazepine treatment, the drugs' anxiolytic action persisted although there was a complete disappearance of their sedative effects. These behavioral results are discussed in relation to the emotional changes induced by the procedures of handling. They are tentatively linked with possible changes in the functionality of GABA neurotransmission, possibly at the level of the GABA-benzodiazepine receptor which some studies have found associated to handling habituation.

Behavioral effects of GABA agonists in relation to anxiety and benzodiazepine action

A considerable body of biochemical and neurophysiological evidence implicates GABA in anxiety and in benzodiazepine action. The present article surveys the behavioral effects of GABA agonists and their interactions with drugs acting at the benzodiazepine receptor in animal anxiety paradigms. Certain GABA agonists, notably valproate, simulate many behavioral actions of benzodiazepines. Moreover, several behavioral studies of the interaction of GABA agonists with benzodiazepines support the hypothesis of a benzodiazepine receptor complex with one or more GABA, benzodiazepine and probably other binding sites. However, there are also a number of anomalous findings of GABA agonist action alone and in combination with benzodiazepines. It is argued that these paradoxical results can better be accounted for in terms of the receptor complex and the distribution of the drugs, rather than by suggesting that the anxiolytic actions of benzodiazepines are not mediated by GABA systems. The potential clinical usefulness of GABA agonists in anxiety is commented upon.

5-HT and anxiety: Promises and pitfalls

This review examines the evidence implicating serotonergic systems in the control of anxiety. The effects of manipulations of 5-HT, including 5-HT lesions, pharmacological reduction and enhancement of serotonergic function in animal tests of anxiety are reviewed. Biochemical and behavioral evidence implicating serotonergic pathways in the anxiolytic action of benzodiazepines is presented. In each section the promises of a sertonergic involvement, as indicated by positive findings, and the pitfalls, evidenced by inconsistent and conflicting results, are discussed. Finally the dangers of a superficial interpretation of the behavioral and biochemical findings is stressed.

Low doses of muscimol produce anticonflict actions in the lateral septum of the rat

Muscimol microinjected into the lateral septum of the rat produced a dose dependent increase in punished responding over the dose range of 100 pg-5 ng. The higher doses used (10 ng and 1 μg) produced sedation and ataxia, markedly reducing the number of approaches to the water spout. This steep, biphasic dose response curve for the anticonflict actions of muscimol may explain contradictory findings in the literature concerning GABAergic involvement in the anxiolytic actions of benzodiazepines. The low dose of muscimol needed to produce a significant anticonflict effect in the lateral septum suggests that this nucleus may be a critical site in anxiety-related behaviors.