Tolerance to the sedative and anxiolytic effects of diazepam is associated with different alterations of GABAA receptors in rat cerebral cortex

Application of nanofiber-based drug delivery systems in improving anxiolytic effect of new 1,2,3-triazolo-1,4-benzodiazepine derivatives

Anxiety disorders are highly prevalent worldwide and can affect people of all ages, genders and backgrounds. Much efforts and resources have been directed at finding new anxiolytic agents and drug delivery systems (DDSs) especially for cancer patients to enhance targeted drug delivery, reduce drug adverse effects, and provide an analgesic effect. The aim of this study was (1) to design and develop novel nanofiber-based DDSs intended for the oral administration of new 1,2,3-triazolo-1,4-benzodiazepines derivatives, (2) to investigate the physical solid-state properties of such drug-loaded nanofibers, and (3) to gain knowledge of the anxiolytic activity of the present new benzodiazepines in rodents in vivo. The nanofibers loaded with 1,2,3-triazolo-1,4-benzodiazepine derivatives were prepared by means of electrospinning (ES). Field-emission scanning electron microscopy and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy were used for the physicochemical characterization of nanofibers. The anxiolytic activity of new derivatives and drug-loaded nanofibers was studied with an elevated plus maze test and light-dark box test. New 1,2,3-triazolo-1,4-benzodiazepine derivatives showed a promising anxiolytic effect in mice with clear changes in behavioral reactions in both tests. The nanofiber-based DDS was found to be feasible in the oral delivery of the present benzodiazepine derivatives. The nanofibers generated by means of ES presented the diameter in a nanoscale, uniform fiber structure, capacity for drug loading, and the absence of defects. The present findings provide new insights in the drug treatment of anxiety disorders with new benzodiazepine derivatives.

Diazepam-Induced Down-Regulation of The Gabaa Receptor α1 Subunit, as Mediated by the Activation of L-Type Voltage-Gated Calcium Channel/Ca2+/Protein Kinase A Signaling Cascade

Benzodiazepines are among the most prescribed drug class worldwide to treat disorders such as anxiety, insomnia, muscle spasticity, and convulsive disorders, and to induce presurgical sedation. Although benzodiazepines exhibit a high therapeutic index and low toxicity in short-term treatments, prolonged administration induces tolerance to most of their therapeutic actions. The mechanism of this tolerance remains unclear. The central actions of benzodiazepines are mediated by binding to GABA_A receptors, which mediate most fast inhibitory transmission in the brain. The majority of GABA_A receptors are composed of two α-(1-6), two β-(1-3) and one γ-subunits (1-3). In a previous report, we demonstrated that the prolonged exposure of cerebrocortical neurons to diazepam produces a transcriptional repression of the GABA_A receptor α1 subunit gene via a mechanism dependent on the activation of L-type voltage-gated calcium channels (L-VGCCs). The results reported here confirm that the diazepam-induced downregulation of the α1 subunit is contingent upon calcium influx from extracellular space. In addition, this regulatory mechanism involves the activation of protein kinase A (PKA) and is accompanied by the activation of two transcription factors, the cAMP-response element-binding protein (CREB) and the inducible cAMP early repressor (ICER). Together, our results suggest that diazepam's activation of an L-VGCC/Ca²⁺/PKA/CREB-ICER signaling pathway is responsible for the regulation of GABA_A receptors. This elucidation of the intracellular signaling cascade activated by a prolonged benzodiazepine exposure, itself potentially involved in the development of tolerance, may contribute to locating molecular targets for future therapeutic interventions.

GABAA receptor subtypes and benzodiazepine use, misuse, and abuse

Benzodiazepines have been in use for over half a century. While they remain highly prescribed, their unfavorable side-effect profile and abuse liability motivated a search for alternatives. Most of these efforts focused on the development of benzodiazepine-like drugs that are selective for specific GABA_A receptor subtypes. While there is ample evidence that subtype-selective GABA_A receptor ligands have great potential for providing symptom relief without typical benzodiazepine side-effects, it is less clear whether subtype-selective targeting strategies can also reduce misuse and abuse potential. This review focuses on the three benzodiazepine properties that are relevant to the DSM-5-TR criteria for Sedative, Hypnotic, or Anxiolytic Use Disorder, namely, reinforcing properties of benzodiazepines, maladaptive behaviors related to benzodiazepine use, and benzodiazepine tolerance and dependence. We review existing evidence regarding the involvement of different GABA_A receptor subtypes in each of these areas. The reviewed studies suggest that α1-containing GABA_A receptors play an integral role in benzodiazepine-induced plasticity in reward-related brain areas and might be involved in the development of tolerance and dependence to benzodiazepines. However, a systematic comparison of the contributions of all benzodiazepine-sensitive GABA_A receptors to these processes, a mechanistic understanding of how the positive modulation of each receptor subtype might contribute to the brain mechanisms underlying each of these processes, and a definitive answer to the question of whether specific chronic modulation of any given subtype would result in some or all of the benzodiazepine effects are currently lacking from the literature. Moreover, how non-selective benzodiazepines might lead to the maladaptive behaviors listed in DSM and how different GABA_A receptor subtypes might be involved in the development of these behaviors remains unexplored. Considering the increasing burden of benzodiazepine abuse, the common practice of benzodiazepine misuse that leads to severe dependence, and the current efforts to generate side-effect free benzodiazepine alternatives, there is an urgent need for systematic, mechanistic research that provides a better understanding of the brain mechanisms of benzodiazepine misuse and abuse, including the involvement of specific GABA_A receptor subtypes in these processes, to establish an informed foundation for preclinical and clinical efforts.

Tolerance and dependence following chronic alprazolam treatment in rhesus monkeys: Role of GABAA receptor subtypes

BACKGROUND

To assess GABA_A receptor subtypes involved in benzodiazepine tolerance and dependence, we evaluated the ability of subtype-selective and non-selective ligands to substitute for (i.e., produce "cross-tolerance") or precipitate withdrawal during chronic alprazolam treatment.

METHODS

Four female rhesus monkeys (Macaca mulatta) were implanted with chronic intravenous catheters and administered alprazolam (1.0 mg/kg every 4 h). Following 14+ days of chronic alprazolam, acute administration of selected doses of non-selective and subtype-selective ligands were substituted for, or administered with, alprazolam, followed by quantitative behavioral observations. The ligands included alprazolam and midazolam (positive modulators, non-selective), zolpidem (positive modulator, preferential affinity for α1-containing GABA_A receptors), HZ-166 (positive modulator, preferential efficacy at α2- and α3-containing GABA_A receptors), and βCCT (antagonist, preferential affinity for α1-containing GABA_A receptors).

RESULTS

Acutely, alprazolam and midazolam both induced observable ataxia along with a mild form of sedation referred to as "rest/sleep posture" at a lower dose (0.1 mg/kg, i.v.), whereas at a higher dose (1.0 mg/kg, i.v.), induced deep sedation and observable ataxia. With chronic alprazolam treatment, observable ataxia and deep sedation were reduced significantly, whereas rest/sleep posture was unchanged or emerged. Zolpidem showed a similar pattern of effects, whereas no behaviors engendered by HZ-166 were changed by chronic alprazolam. Administration of βCCT, but not HZ-166, resulted in significant withdrawal signs.

CONCLUSIONS

These results are consistent with a role for α1-containing GABA_A receptor subtypes in tolerance and dependence observed with chronic alprazolam, although other receptors may be involved in the withdrawal syndrome.

Restoration of FMRP expression in adult V1 neurons rescues visual deficits in a mouse model of fragile X syndrome

Many people affected by fragile X syndrome (FXS) and autism spectrum disorders have sensory processing deficits, such as hypersensitivity to auditory, tactile, and visual stimuli. Like FXS in humans, loss of Fmr1 in rodents also cause sensory, behavioral, and cognitive deficits. However, the neural mechanisms underlying sensory impairment, especially vision impairment, remain unclear. It remains elusive whether the visual processing deficits originate from corrupted inputs, impaired perception in the primary sensory cortex, or altered integration in the higher cortex, and there is no effective treatment. In this study, we used a genetic knockout mouse model (Fmr1^KO), in vivo imaging, and behavioral measurements to show that the loss of Fmr1 impaired signal processing in the primary visual cortex (V1). Specifically, Fmr1^KO mice showed enhanced responses to low-intensity stimuli but normal responses to high-intensity stimuli. This abnormality was accompanied by enhancements in local network connectivity in V1 microcircuits and increased dendritic complexity of V1 neurons. These effects were ameliorated by the acute application of GABA_A receptor activators, which enhanced the activity of inhibitory neurons, or by reintroducing Fmr1 gene expression in knockout V1 neurons in both juvenile and young-adult mice. Overall, V1 plays an important role in the visual abnormalities of Fmr1^KO mice and it could be possible to rescue the sensory disturbances in developed FXS and autism patients.

Remimazolam Tolerance in Long-term Benzodiazepine Users: A Case Report of 2 Cases

A 60-year-old woman with a 5-year history of anxiolytic use, a diazepam-equivalent daily dose of 15 mg, was scheduled for esophageal stent removal. She was given remimazolam (0.5 mg/kg) but remained fully alert. She only lost consciousness with propofol (40 mg). A 61-year-old man with a 1-year history of anxiolytic use, diazepam-equivalent daily dose of 20 mg, was scheduled for hand tumor resection. He was given remimazolam (0.3 mg/kg) but remained fully alert. He only lost consciousness after desflurane inhalation. In a patient with a history of long-term benzodiazepine use, anesthetic or sedative agents aside from remimazolam should be considered.

Physiological role for GABAA receptor desensitization in the induction of long-term potentiation at inhibitory synapses

GABAA receptors (GABAARs) are pentameric ligand-gated ion channels distributed throughout the brain where they mediate synaptic and tonic inhibition. Following activation, these receptors undergo desensitization which involves entry into long-lived agonist-bound closed states. Although the kinetic effects of this state are recognised and its structural basis has been uncovered, the physiological impact of desensitization on inhibitory neurotransmission remains unknown. Here we describe an enduring form of long-term potentiation at inhibitory synapses that elevates synaptic current amplitude for 24 h following desensitization of GABAARs in response to agonist exposure or allosteric modulation. Using receptor mutants and allosteric modulators we demonstrate that desensitization of GABAARs facilitates their phosphorylation by PKC, which increases the number of receptors at inhibitory synapses. These observations provide a physiological relevance to the desensitized state of GABAARs, acting as a signal to regulate the efficacy of inhibitory synapses during prolonged periods of inhibitory neurotransmission.

Hypnotic Activity of Capparis spinosa Hydro-alcoholic Extract in Mice

BACKGROUND

Sleep disorders are among the most common psychiatric and medical conditions. Herbal medicine appears to be effective in the treatment of sleep disorders which have been valued by many of publications and patents.

OBJECTIVE

The present study aimed at investigating the hypnotic activity of the hydro-alcoholic extract of Capparis spinosa (HAE) in mice.

METHODS

Three doses of HAE (30, 60 and 120 mg/kg) and three fractions of it, namely n-hexane fraction (NHF), water fraction (WF), and ethyl acetate fraction (EAF), were given in comparison with diazepam (3 mg/kg body weight i.p.) as a positive control and saline as a negative control. After 30 min, pentobarbital (30 mg/kg body weight i.p.) was administered. In addition, LD50 of HAE was examined and the cytotoxicity of HAE was assessed in l929 cells using the MTT assay. Moreover, for motorcoordination ability, 30 mins after administration of HAE, the rotarod test was performed.

RESULTS

The results exhibited that the HAE and all the fractions significantly augmented pentobarbital induced sleeping time, which was comparable to that of induced by diazepam. The LD50 value was 2.4 g/kg. The extract did not induce any cytotoxic effects in L929 fibroblast cells. HAE did not affect the animals' performance on the rotarod test.

CONCLUSION

Our finding suggests that the hydro-alcoholic extract of C. spinosa possesses a hypnotic potential that may require further scientific investigations.

Early postnatal neuroactive steroid manipulation differentially affects recognition memory and passive avoidance performance in male rats

Early postnatal neuroactive steroids (NAS) play a significant role in the neurodevelopment. Their alteration can modify adult behavior, such as anxiety or learning. For this reason, we set out to observe if neonatal NAS levels alteration affects two types of learning implying low or high levels of emotional content, such as recognition memory and aversive learning respectively. Thus, we tested allopregnanolone or finasteride administered from postnatal days 5-9. In adulthood, recognition memory was assessed using the object recognition test, as well as aversive learning throughout the passive avoidance test (PA). Because of the important emotional component of PA, which can be influencing learning, we evaluated anxiety-like behavior by means of the open field test (OF). The results indicated that those animals administered with finasteride showed higher recognition levels of a familiar object. On the other hand, they showed an impairment in a stressful learning, such as PA. However, no effects of finasteride were observed on anxiety-like behavior in OF, despite it has been reported that neonatal finasteride treatment can promote an anxiety-like profile in the elevated plus-maze test in adulthood. Regarding neonatal allopregnanolone, animals showed higher levels in OF exploration only when they were already familiar with the apparatus. Furthermore, neonatal allopregnanolone did not affect recognition memory or aversive learning. In conclusion, the neonatal NAS manipulation by means of finasteride differently affected two types of learning implying distinct stress levels. Altogether, the results show the importance of the emotional content to explain the effects of neonatal NAS manipulation on learning.

The α2,3-selective potentiators of GABAA receptors, KRM-II-81 and MP-III-80, produce anxiolytic-like effects and block chemotherapy-induced hyperalgesia in mice without tolerance development

Opiate analgesics are one of the treatment options for severe chronic pain, including late-stage cancer, chronic back pain and other disorders. The recent resurgence in opioid overdose has highlighted the serious need for alternative medicines for pain management. While a role for potentiators of α2/3-containing GABA_A receptors in the modulation of pain has been known for several years, advancements in this area required data from selective compounds. KRM-II-81(5-(8-ethynyl-6-(pyridin-2-yl)-4H-benzo[f]imidazo[1,5-a][1,4]diazepin-3- yl)oxazole) and analogs selectively potentiate GABA_A receptors containing α2/3 subunits and have recently been shown to attenuate pain behaviors in several acute and chronic pain models in rodents. The present study was designed to ascertain whether KRM-II-81 and the structural analog MP-III-80 (3-ethyl-5-(8-ethynyl-6-(pyridin-2-yl)-4H-benzo[f]imidazo[1,5-a][1,4]diazepin-3-yl)-1,2,4-oxadiazole) would block chemotherapeutic agent paclitaxel-induced pain in male, C57BL/6 mice. Both compounds significantly inhibited pain behaviors evoked by cold and tactile stimulation in paclitaxel-treated mice as did the neuropathic pain drug gabapentin. Subchronic dosing for 22 days with KRM-II-81 and MP-III-80 demonstrated enduring analgesic efficacy without tolerance development, while the effects of gabapentin showed evidence of tolerance development. KRM-II-81 and MP-III-80 also decreased marble-burying behavior in this mouse strain as did the anxiolytic drug chlordiazepoxide. In contrast to KRM-II-81 and MP-III-80, chlordiazepoxide had motor-impairing effects at anxiolytic-like doses. The data add to the literature documenting that these selective potentiators of α2/3-containing GABA_A receptors are effective in a host of animal models used to detect novel analgesic drugs. The anxiolytic-like efficacy of these compounds fits well with the comorbidity of anxiety in patients with chronic pain and cancer.

Alterations in GABAA Receptor Subunit Expression in the Amygdala and Entorhinal Cortex in Human Temporal Lobe Epilepsy

The amygdala has long been implicated in the pathophysiology of human temporal lobe epilepsy (TLE). The different nuclei of this complex structure are interconnected and share reciprocal connections with the hippocampus and other brain structures, partly via the entorhinal cortex. Expression of GABAA receptor subunits α1, α2, α3, α5, β2, β2/3, and γ2 was evaluated by immunohistochemistry in amygdala specimens and the entorhinal cortex of 12 TLE patients and 12 autopsy controls. A substantial decrease in the expression of α1, α2, α3, and β2/3 subunits was found in TLE cases, accompanied by an increase of γ2 subunit expression in many nuclei. In the entorhinal cortex, the expression of all GABAA receptor subunits was decreased except for the α1 subunit, which was increased on cellular somata. The overall reduction in α subunit expression may lead to decreased sensitivity to GABA and its ligands and compromise phasic inhibition, whereas upregulation of the γ2 subunit might influence clustering and kinetics of receptors and impair tonic inhibition. The description of these alterations in the human amygdala is important for the understanding of network changes in TLE as well as the development of subunit-specific therapeutic agents for the treatment of this disease.

Tolerance and dependence following chronic alprazolam treatment: quantitative observation studies in female rhesus monkeys

RATIONALE

In order to understand mechanisms underlying tolerance and dependence following chronic benzodiazepine treatments, quantitative and reproducible behavioral models of these phenomena are required.

OBJECTIVES

This research evaluated the ability of chronic treatment with a commonly prescribed benzodiazepine, alprazolam, to induce tolerance to sedative effects and physical dependence using a novel set of behavioral measurements in rhesus monkeys.

METHODS

Four female rhesus monkeys (Macaca mulatta) were implanted with chronic intravenous catheters and administered i.v. alprazolam (1.0 mg/kg every 4 h, 38 days total). Quantitative observation measures were obtained during the 38 days of treatment. Acute administration of the benzodiazepine receptor antagonist flumazenil (0.1, 0.3 mg/kg, i.v.) was given to assess precipitated withdrawal. On day 39, saline was substituted for alprazolam and withdrawal signs were assessed for 7 days.

RESULTS

Maximal sedation ("deep sedation") was evident on day 1 but was not significantly different from baseline levels by day 4 and was absent for the remainder of the 38 days of treatment. A milder form of sedation, "rest/sleep posture," emerged by day 3 and did not decline over 38 days. Cessation of alprazolam treatment resulted in significant withdrawal signs (nose rub, vomit, procumbent posture, tremor/jerk, rigid posture) that dissipated by day 3. These signs also were observed with flumazenil (0.3 mg/kg).

CONCLUSIONS

Chronic alprazolam treatment resulted in rapid tolerance to some behaviors (e.g., deep sedation) but no tolerance to others (e.g., rest/sleep posture). Physical dependence was observed via both spontaneous and precipitated withdrawal. Based on previous research, these phenomena may reflect differential plasticity at GABA_A receptor subtypes.

Benzodiazepine exposure induces transcriptional down-regulation of GABAA receptor α1 subunit gene via L-type voltage-gated calcium channel activation in rat cerebrocortical neurons

GABA_A receptors are targets of different pharmacologically relevant drugs, such as barbiturates, benzodiazepines, and anesthetics. In particular, benzodiazepines are prescribed for the treatment of anxiety, sleep disorders, and seizure disorders. Benzodiazepines potentiate GABA responses by binding to GABA_A receptors, which are mainly composed of α (1-3, 5), β2, and γ2 subunits. Prolonged activation of GABA_A receptors by endogenous and exogenous modulators induces adaptive changes that lead to tolerance. For example, chronic administration of benzodiazepines produces tolerance to most of their pharmacological actions, limiting their usefulness. The mechanism of benzodiazepine tolerance is still unknown. To investigate the molecular basis of tolerance, we studied the effect of sustained exposure of rat cerebral cortical neurons to diazepam on the GABA_A receptor. Flunitrazepam binding experiments showed that diazepam treatment induced uncoupling between GABA and benzodiazepine sites, which was blocked by co-incubation with flumazenil, picrotoxin, or nifedipine. Diazepam also produced selective transcriptional down-regulation of GABA_A receptor α1 subunit gene through a mechanism dependent on the activation of L-type voltage-gated calcium channels. These findings suggest benzodiazepine-induced stimulation of calcium influx through L-type voltage-gated calcium channels triggers the activation of a signaling pathway that leads to uncoupling and an alteration of receptor subunit expression. Insights into the mechanism of benzodiazepine tolerance will contribute to the design of new drugs that can maintain their efficacies after long-term treatments.

Effect of Ocimum basilicum, Ocimum selloi, and Rosmarinic Acid on Cerebral Vascular Damage in a Chronic Hypertension Model

The main objective of treatment against hypertension is not only to reduce blood pressure levels, but also to reduce vascular risk in general. In the present work, administering angiotensin II (AGII; 0.2 µg/kg intraperitoneally (i.p.) for 12 weeks) activates the hypothalamic-pituitary-adrenal (HPA) axis, which caused an increase in corticosterone levels, as well as in proinflammatory cytokines (interleukin 1β (IL-1β), interleukin 6 (IL-6), and tumor necrosis factor alpha (TNF-α)) and macrophage chemotactic protein 1 (MCP-1), and decreased anti-inflammatory cytokines (interleukin 10 (IL-10) and interleukin 4 (IL-4)). On observing the behavior in the different models, an anxiogenic effect (elevated plus maze (EPM)) and cognitive impairment (water Morris maze (WMM)) was observed in animals with AGII. By administering organic extracts from Ocimum basilicum (Oba-EtOAc) and Ocimum selloi (Ose-EtOAc), and some doses of rosmarinic acid (RA) (6 weeks per os (p.o.)), the damage caused by AGII was stopped by re-establishing corticosterone serum levels and by decreasing the proinflammatory cytokines and MCP-1.

Daily maternal separations during stress hyporesponsive period decrease the thresholds of panic-like behaviors to electrical stimulation of the dorsal periaqueductal gray of the adult rat

The present study examined whether early life maternal separation (MS), a model of childhood separation anxiety, predisposes to panic at adulthood. For this purpose, male pups were submitted to 3-h daily maternal separations along postnatal (PN) days of either the 'stress hyporesponsive period' (SHRP) from PN4 to PN14 (MS11) or throughout lactation from PN2 to PN21 (MS20). Pups were further reunited to conscious (CM) or anesthetized (AM) mothers to assess the effect of mother-pup interaction upon reunion. Controls were subjected to brief handling (15 s) once a day throughout lactation (BH20). As adults (PN60), rats were tested for the thresholds to evoke panic-like behaviors upon electrical stimulation of dorsal periaqueductal gray matter and exposed to an elevated plus-maze, an open-field, a forced swim and a sucrose preference test. A factor analysis was also performed to gain insight into the meaning of behavioral tests. MS11-CM rather than MS20-CM rats showed enhanced panic responses and reductions in both swimming and sucrose preference. Panic facilitations were less intense in mother-neglected rats. Although MS did not affect anxiety, MS11-AM showed robust reductions of defecation in an open-field. Factor analysis singled out anxiety, hedonia, exploration, coping and gut activity. Although sucrose preference and coping loaded on separate factors, appetite (adult weight) correlated with active coping in both forced swim and open-field (central area exploration). Concluding, whereas 3h-daily maternal separations during SHRP increased rat's susceptibility to experimental panic attacks, separations throughout lactation had no effects on panic and enhanced active coping.

Agarwood Essential Oil Displays Sedative-Hypnotic Effects through the GABAergic System

Although agarwood has been used as a tranquilizer in Asian countries for hundreds of years, the underlying pharmacological basis is still unclear. This study investigated the sedative-hypnotic effect of agarwood essential oil (AEO) using locomotor activity and pentobarbital-induced sleeping assays in mice. Single (1-day) and multiple (7- and 14-days) administrations of 60 mg/kg AEO generated significant sedative effect on inhibiting locomotor activity and hypnotic effect on pentobarbital-induced sleeping in mice. Interestingly, prolonged AEO treatment did not result in obvious desensitization. Concoitant measurement of the levels of brain neurotransmitters using ultrafast liquid chromatography-tandem mass spectrometry (UFLC-MS/MS) indicated that AEO had no significant effect on the levels of glutamic acid (Glu) and γ-aminobutyric acid (GABA) in the brain. However, the sedative-hypnotic effects were blocked by the type A GABA (GABA_A) receptor antagonists bicuculline and flumazenil. In addition, AEO significantly elevated the expression of GABA_A receptor subunits and subtypes in the cerebral cortex. Furthermore, AEO increased chlorine ion (Cl⁻) influx through GABA_A receptors in human neuroblastoma cells. These results together demonstrate that AEO exerts its sedative-hypnotic effects through regulating gene expression of GABA_A receptors and potentiating GABA_A receptor function.

The Importance of L-Arginine:NO:cGMP Pathway in Tolerance to Flunitrazepam in Mice

The goal of the study was to investigate the effects of drugs modifying l-arginine:NO:cGMP pathway on the development of tolerance to flunitrazepam (FNZ)-induced motor impairment in mice. FNZ-induced motor incoordination was assessed on the 1st and 8th days of experiment, using the rotarod and chimney tests. It was found that (a) both a non-selective nitric oxide synthase (NOS) inhibitor: N^G-nitro-l-arginine methyl ester (l-NAME) and an unselective neuronal NOS inhibitor: 7-nitroindazole (7-NI) inhibited the development of tolerance to the motor-impairing effects of FNZ in the rotarod and the chimney tests and (b) both a NO precursor: l-arginine and a selective inhibitor of phosphodiesterase 5 (PDE5): sildenafil did not affect the development of tolerance to FNZ-induced motor impairment in mice. Those findings provided behavioural evidence that NO could contribute an important role in the development of tolerance to FNZ in mice.

Low dose X-irradiation mitigates diazepam induced depression in rat brain

Depression is considered as one of the most prevalent health ailments. Various anti-depressant drugs have been used to provide succour to this ailment, but with little success and rather have resulted in many side effects. On the other hand, low dose of ionizing radiations are reported to exhibit many beneficial effects on human body by stimulating various biological processes. The present study was conducted to investigate the beneficial effects of low doses of X-rays, if any, during diazepam induced depression in rats. Female Sprague Dawley rats were segregated into four different groups viz: Normal control, Diazepam treated, X-irradiated and Diazepam + X-irradiated. Depression model was created in rats by subjecting them to diazepam treatment at a dosage of 2 mg/kg b.wt./day for 3 weeks. The skulls of animals belonging to X-irradiated and Diazepam + X-irradiated rats were X-irradiated with a single fraction of 0.5 Gy, given twice a day for 3 days, thereby delivered dose of 3 Gy. Diazepam treated animals showed significant alterations in the neurobehavior and neuro-histoarchitecture, which were improved after X-irradiation. Further, diazepam exposure significantly decreased the levels of neurotransmitters and acetylcholinesterase activity, but increased the monoamine oxidase activity in brain. Interestingly, X-rays exposure to diazepam treated rats increased the levels of neurotransmitters, acetylcholinesterase activity and decreased the monoamine oxidase activity. Further, depressed rats also showed increased oxidative stress with altered antioxidant parameters, which were normalized on X-rays exposure. The present study, suggests that low dose of ionizing radiations, shall prove to be an effective intervention and a novel therapy in controlling depression and possibly other brain related disorders.

Activation-induced regulation of GABAA receptors: Is there a link with the molecular basis of benzodiazepine tolerance?

Benzodiazepines have been used clinically for more than 50 years to treat disorders such as insomnia, anxiety, and epilepsy, as well as to aid muscle relaxation and anesthesia. The therapeutic index for benzodiazepines if very high and the toxicity is low. However, their usefulness is limited by the development of either or both tolerance to most of their pharmacological actions and dependence. Tolerance develops at different rates depending on the pharmacological action, suggesting the existence of distinct mechanisms for each behavioral parameter. Alternatively, multiple mechanisms could coexist depending on the subtype of GABAA receptor expressed and the brain region involved. Because most of the pharmacological actions of benzodiazepines are mediated through GABAA receptor binding, adaptive alterations in the number, structure, and/or functions of these receptors may play an important role in the development of tolerance. This review is focused on the regulation of GABAA receptors induced by long-term benzodiazepine exposure and its relationship with the development of tolerance. Understanding the mechanisms behind benzodiazepine tolerance is critical for designing drugs that could maintain their efficacy during long-term treatments.