Tamara Timić

The role of α1 and α5 subunit-containing GABAA receptors in motor impairment induced by benzodiazepines in rats.

Benzodiazepines negatively affect motor coordination and balance and produce myorelaxation. The aim of the present study was to examine the extent to which populations of &ggr;-aminobutyric acid A (GABAA) receptors containing &agr;1 and &agr;5 subunits contribute to these motor-impairing effects in rats. We used the nonselective agonist diazepam and the &agr;1-selective agonist zolpidem, as well as nonselective, &agr;1-subunit and &agr;5-subunit-selective antagonists flumazenil, &bgr;CCt, and XLi093, respectively. Ataxia and muscle relaxation were assessed by rotarod and grip strength tests performed 20 min after intraperitoneal treatment. Diazepam (2 mg/kg) induced significant ataxia and muscle relaxation, which were completely prevented by pretreatment with flumazenil (10 mg/kg) and &bgr;CCt (20 mg/kg). XLi093 antagonized the myorelaxant, but not the ataxic actions of diazepam. All three doses of zolpidem (1, 2, and 5 mg/kg) produced ataxia, but only the highest dose (5 mg/kg) significantly decreased the grip strength. These effects of zolpidem were reversed by &bgr;CCt at doses of 5 and 10 mg/kg, respectively. The present study demonstrates that &agr;1 GABAA receptors mediate ataxia and indirectly contribute to myorelaxation in rats, whereas &agr;5 GABAA receptors contribute significantly, although not dominantly, to muscle relaxation but not ataxia.

PWZ-029, AN INVERSE AGONIST SELECTIVE FOR α5 GABAA RECEPTORS, IMPROVES OBJECT RECOGNITION, BUT NOT WATER-MAZE MEMORY IN NORMAL AND SCOPOLAMINE-TREATED RATS

Inverse agonism at the benzodiazepine site of α(5) subunit-containing GABA(A) receptors is an attractive approach for the development of putative cognition-enhancing compounds, which are still far from clinical application. Several ligands with binding and/or functional selectivity for α(5) GABA(A) receptors have been synthesized and tested in a few animal models. PWZ-029 is an α(5) GABA(A) selective inverse agonist whose memory enhancing effects were demonstrated in the passive avoidance task in rats and in Pavlovian fear conditioning in mice. In the present study we investigated the effects of PWZ-029 administration in novel object recognition test and Morris water maze, in normal and scopolamine-treated rats. All the three doses of PWZ-029 (2, 5 and 10 mg/kg) improved object recognition after the 24-h delay period, as shown by significant differences between the exploration times of the novel and old object, and the respective discrimination indices. PWZ-029 (2 mg/kg) also successfully reversed the 0.3 mg/kg scopolamine-induced deficit in recognition memory after the 1-h delay. In the Morris water maze test, PWZ-029 (5, 10 and 15 mg/kg) did not significantly influence swim patterns, either during five acquisition days or during the treatment-free probe trial. PWZ-029 (2, 5 and 10 mg/kg) also proved to be ineffective in the reversal of the 1mg/kg scopolamine-induced memory impairment in the water maze. The present mixed results encourage use of a variety of tests and experimental conditions in order to increase the predictability of preclinical testing of selective α(5) GABA(A) inverse agonists.

Midazolam impairs acquisition and retrieval, but not consolidation of reference memory in the Morris water maze.

Amnesia is one of the most discussed properties of the benzodiazepine class of drugs. The effects of benzodiazepines on human memory are usually anterograde, while changes in retrograde memory functions were seldom reported. Such inconsistent findings have prompted numerous animal studies investigating the influences of these positive modulators of inhibitory neurotransmission on different stages of memory. Among the benzodiazepines, memory effects of midazolam are of special interest due to its many and varied clinical applications. The present Morris water maze study in adult male Wistar rats was performed in three experiments in which midazolam was administered at doses of 0.5, 1 and 2 mg/kg intraperitoneally, before or immediately after each of five daily learning sessions, with two trials in a session, as well as before the probe test. Midazolam impaired acquisition and subsequent retention of spatial learning of the position of the hidden platform even at a pre-training dose of 0.5 mg/kg. This low dose was not associated with impairment of the procedural component of learning, manifested by increased time spent in the periphery of the pool. The lack of midazolam effect on consolidation has not been confounded by the observed below-chance performance of the control group since our additional experiment using diazepam also administered immediately after each of five learning sessions has revealed a similar pattern of results. Finally, midazolam administered before the probe test impaired retrieval of reference memory at all tested doses. Hence, induction of retrograde, besides anterograde amnesia should be kept in mind as a possibility when midazolam is used in clinical settings.

Sex-Dependent Anti-Stress Effect of an α5 Subunit Containing GABAA Receptor Positive Allosteric Modulator

Rationale: Current first-line treatments for stress-related disorders such as major depressive disorder (MDD) act on monoaminergic systems and take weeks to achieve a therapeutic effect with poor response and low remission rates. Recent research has implicated the GABAergic system in the pathophysiology of depression, including deficits in interneurons targeting the dendritic compartment of cortical pyramidal cells. Objectives: The present study evaluates whether SH-053-2’F-R-CH3 (denoted “α5-PAM”), a positive allosteric modulator selective for α5-subunit containing GABAA receptors found predominantly on cortical pyramidal cell dendrites, has anti-stress effects. Methods: Female and male C57BL6/J mice were exposed to unpredictable chronic mild stress (UCMS) and treated with α5-PAM acutely (30 min prior to assessing behavior) or chronically before being assessed behaviorally. Results: Acute and chronic α5-PAM treatments produce a pattern of decreased stress-induced behaviors (denoted as “behavioral emotionality”) across various tests in female, but not in male mice. Behavioral Z-scores calculated across a panel of tests designed to best model the range and heterogeneity of human symptomatology confirmed that acute and chronic α5-PAM treatments consistently produce significant decreases in behavioral emotionality in several independent cohorts of females. The behavioral responses to α5-PAM could not be completely accounted for by differences in drug brain disposition between female and male mice. In mice exposed to UCMS, expression of the Gabra5 gene was increased in the frontal cortex after acute treatment and in the hippocampus after chronic treatment with α5-PAM in females only, and these expression changes correlated with behavioral emotionality. Conclusion: We showed that acute and chronic positive modulation of α5 subunit-containing GABAA receptors elicit anti-stress effects in a sex-dependent manner, suggesting novel therapeutic modalities.

Tolerance liability of diazepam is dependent on the dose used for protracted treatment.

BACKGROUND Behavioral effects of benzodiazepines following repeated exposure vary according to the intrinsic efficacy of the benzodiazepine studied, treatment schedule and the behavioral parameters evaluated. METHODS We applied the behavioral paradigms of spontaneous locomotor activity, elevated plus maze and grip strength to investigate the sedative, anxiolytic and myorelaxant effect of acute challenge with 2 mg/kg diazepam administered after 14 days of protracted treatment with 0.5, 2 or 10 mg/kg of diazepam. In addition, we studied the effects of everyday handling and intraperitoneal (ip) administration on animal behavior. RESULTS Tolerance to the sedative effect of 2 mg/kg diazepam ensued after 14 days of protracted treatment with 2 and 10 mg/kg of diazepam. In contrast, treatment with the lowest dose (0.5 mg/kg) of diazepam resulted in potentiation of the sedative effect of acute challenge with 2 mg/kg diazepam thus confounding the detection of the anxiolytic effect of diazepam. Asensitization-like response to the anxiolytic action of 2 mg/kg diazepam was seen after protracted treatment with the intermediate dose (2 mg/kg); however, anxiolytic effect was absent after protracted administration of the highest dose. Partial tolerance to the muscle relaxant effect of 2 mg/kg diazepam ensued after protracted treatment with diazepam regardless of the dose. Daily handling or ip administration did not alter the behavioral response to acute challenge with 2 mg/kg diazepam in all the three behavioral paradigms studied. CONCLUSION The presented results showed that behavioral effects of acute challenge with diazepam were differently affected by the dose administered during protracted treatment.

Duration of treatment and activation of α1-containing GABAA receptors variably affect the level of anxiety and seizure susceptibility after diazepam withdrawal in rats

Long-term use of benzodiazepine-type drugs may lead to physical dependence, manifested by withdrawal syndrome after abrupt cessation of treatment. The aim of the present study was to investigate the influence of duration of treatment, as well as the role of α1-containing GABAA receptors, in development of physical dependence to diazepam, assessed through the level of anxiety and susceptibility to pentylenetetrazole (PTZ)-induced seizures, 24h after withdrawal from protracted treatment in rats. Withdrawal of 2mg/kg diazepam after 28, but not after 14 or 21 days of administration led to an anxiety-like behavior in the elevated plus maze. Antagonism of the diazepam effects at α1-containing GABAA receptors, achieved by daily administration of the neutral modulator βCCt (5mg/kg), did not affect the anxiety level during withdrawal. An increased susceptibility to PTZ-induced seizures was observed during diazepam withdrawal after 21 and 28 days of treatment. Daily co-administration of βCCt further decreased the PTZ-seizure threshold after 21 days of treatment, whilst it prevented the diazepam withdrawal-elicited decrease of the PTZ threshold after 28 days of treatment. In conclusion, the current study suggests that the role of α1-containing GABAA receptors in mediating the development of physical dependence may vary based on the effect being studied and duration of protracted treatment. Moreover, the present data supports previous findings that the lack of activity at α1-containing GABAA receptors is not sufficient to eliminate physical dependence liability of ligands of the benzodiazepine type.

βCCT, an antagonist selective for α1GABAA receptors, reverses diazepam withdrawal-induced anxiety in rats

The abrupt discontinuation of prolonged benzodiazepine treatment elicits a withdrawal syndrome with increased anxiety as a major symptom. The neural mechanisms underlying benzodiazepine physical dependence are still insufficiently understood. Flumazenil, the non-selective antagonist of the benzodiazepine binding site of GABA(A) receptors was capable of preventing and reversing the increased anxiety during benzodiazepine withdrawal in animals and humans in some, but not all studies. On the other hand, a number of data suggest that GABA(A) receptors containing α(1) subunits are critically involved in processes developing during prolonged use of benzodiazepines, such are tolerance to sedative effects, liability to physical dependence and addiction. Hence, we investigated in the elevated plus maze the level of anxiety 24 h following 21 days of diazepam treatment and the influence of flumazenil or a preferential α(1)-subunit selective antagonist βCCt on diazepam withdrawal syndrome in rats. Abrupt cessation of protracted once-daily intraperitoneal administration of 2 mg/kg diazepam induced a withdrawal syndrome, measured by increased anxiety-like behavior in the elevated plus maze 24 h after treatment cessation. Acute challenge with either flumazenil (10mg/kg) or βCCt (1.25, 5 and 20 mg/kg) alleviated the diazepam withdrawal-induced anxiety. Moreover, both antagonists induced an anxiolytic-like response close, though not identical, to that seen with acute administration of diazepam. These findings imply that the mechanism by which antagonism at GABA(A) receptors may reverse the withdrawal-induced anxiety involves the α(1) subunit and prompt further studies aimed at linking the changes in behavior with possible adaptive changes in subunit expression and function of GABA(A) receptors.

Lipopolysaccharide exposure during late embryogenesis results in diminished locomotor activity and amphetamine response in females and spatial cognition impairment in males in adult, but not adolescent rat offspring.

Numerous basic and epidemiological studies have connected prenatal maternal immune activation with the occurrence of schizophrenia and/or autism. Depending on subtle differences in protocols of the used animal model, a variety of behavioral abnormalities has been reported. This study investigated behavioral differences in Wistar rat offspring of both genders, exposed to the 100 μg/kg per day dose of lipopolysaccharide (LPS) in late embryogenesis (embryonic days 15 and 16), while tested at their adolescent and young adult age (postnatal days 40 and 60, respectively). Immune activation was confirmed by detecting high levels of TNF-α and IL-6 in dam blood withdrawn 2h after the first dose of LPS. The animals were assessed in three consecutive trials of locomotor activity (novelty exploration, response to i.p. saline injection and challenge with 0.5mg/kg amphetamine), Morris water maze and social interaction tests. Overt behavioral dysfunction was perceived in adult rats only, and these changes were gender-distinctive. When compared with control rats, LPS females displayed baseline hypolocomotion and a decreased reactivity to amphetamine, while LPS males exhibited spatial learning (acquisition trials) and memory (probe trial) impairments. Prenatal treatment did not affect the time spent in social interaction. As maternal exposure to LPS in late gestation resulted in behavioral changes in offspring in early adulthood, it may model schizophrenia-like, but not autism-like endophenotypes. However, lack of a potentiated response to amphetamine testified that this model could not mimic positive symptoms, but rather certain traits of cognitive dysfunction and deficit symptoms, in males and females, respectively.

Synthesis, structural and biological characterization of 5-phenylhydantoin derivatives as potential anticonvulsant agents

Considering the importance of hydantoin derivatives in treatment of status epilepticus, four 5-phenylhydantoins, whose lipophilicities were estimated to be similar to that of phenytoin, were synthesized. Evaluation of their anticonvulsant activities was performed on rats by subcutaneous pentylenetetrazol seizure test and intravenous pentylenetetrazol threshold test, and spontaneous locomotor activity test was used to assess possible sedative effects. X-ray analysis of three compounds suggested that certain analogies might be drawn between interactions in crystal packing and biological interactions responsible for their anticonvulsant activity. It was found that 5-ethyl-5-phenyl-3-propylhydantoin exhibits the most favorable pharmacological properties among the synthesized compounds, i.e., anticonvulsant activity comparable to phenytoin with lower liability for induction of sedation in rats.Graphical Abstract

Benzodiazepine-induced spatial learning deficits in rats are regulated by the degree of modulation of α1 GABAA receptors

Despite significant advances in understanding the role of benzodiazepine (BZ)-sensitive populations of GABAA receptors, containing the α1, α2, α3 or α5 subunit, factual substrates of BZ-induced learning and memory deficits are not yet fully elucidated. It was shown that α1-subunit affinity-selective antagonist β-CCt almost completely abolished spatial learning deficits induced by diazepam (DZP) in the Morris water maze. We examined a novel, highly (105 fold) α1-subunit selective ligand-WYS8 (0.2, 1 and 10 mg/kg), on its own and in combination with the non-selective agonist DZP (2 mg/kg) or β-CCt (5 mg/kg) in the water maze in rats. The in vitro efficacy study revealed that WYS8 acts as α1-subtype selective weak partial positive modulator (40% potentiation at 100nM). Measurement of concentrations of WYS8 and DZP in rat serum and brain tissues suggested that they did not substantially cross-influence the respective disposition. In the water maze, DZP impaired spatial learning (acquisition trials) and memory (probe trial). WYS8 caused no effect per se, did not affect the overall influence of DZP on the water-maze performance and was devoid of any activity in this task when combined with β-CCt. Nonetheless, an additional analysis of the latency to reach the platform and the total distance swam suggested that WYS8 addition attenuated the run-down of the spatial impairment induced by DZP at the end of acquisition trials. These results demonstrate a clear difference in the influence of an α1 subtype-selective antagonist and a partial agonist on the effects of DZP on the water-maze acquisition.