Estrogen replacement attenuates effects of scopolamine and lorazepam on memory acquisition and retention.

A multiple-trial passive avoidance paradigm was used to examine and compare the ability for estrogen replacement to attenuate learning and memory deficits produced by the muscarinic antagonist scopolamine and the benzodiazepine lorazepam. The multiple-trial paradigm was used in order to distinguish effects on acquisition from effects on retention. Estrogen replacement significantly attenuated a scopolamine-induced deficit on passive avoidance acquisition, but not retention. The ability for estrogen to attenuate the effect of scopolamine on acquisition was observed only when the analysis was limited to animals with serum levels of estradiol <200 pg/ml, suggesting that higher levels of estradiol were ineffective. This observation is consistent with at least one recent study showing dose-related effects of estrogen on ChAT-like immunoreactivity in the basal forebrain and supports the hypothesis that effects of estrogen on basal forebrain cholinergic neurons can help to reduce cognitive deficits associated with cholinergic impairment. Estrogen replacement was also observed to protect against a lorazepam-induced impairment on passive avoidance retention. This effect was observed specifically in animals that received estrogen prior to and during training and was not due to any effect of estrogen on serum levels of lorazepam following acute lorazepam administration. Collectively, these data demonstrate the ability for estrogen replacement to attenuate specific pharmacologically induced impairments in learning and retention and provide additional clues as to potential mechanisms by which estrogen replacement may help to reduce cognitive deficits associated with aging and Alzheimer's disease in postmenopausal women.

Depression of thalamic metabolism by lorazepam is associated with sleepiness.

Though it is well recognized that the pharmacological actions of benzodiazepines are mediated by facilitation of GABAergic neurotransmission, the consequences of these changes in regional brain function are not well understood. This study measured regional brain glucose metabolism using Positron Emission Tomography and 2-deoxy-2[18F]fluoro-D-glucose in normal controls (n = 21) investigated with and without lorazepam (30 micrograms/kg IV) and with flumazenil given after lorazepam (n = 9). Lorazepam markedly decreased metabolism in thalamus (23 +/- 8%) and occipital cortex (19 +/- 8%), and flumazenil partially reversed these changes. Changes in metabolic activity in thalamus were significantly correlated with lorazepam-induced sleepiness (r = .69, df 20, p < .0005) and there was a trend of an association between the reversal by flumazenil of lorazepam-induced change in thalamus and in sleepiness (r = .63, df 8, p = .07). Benzodiazepine-induced changes in thalamic activity may account for their sedative properties.

Cleft palate and open eyelids inducing activity of lorazepam and the effect of flumazenil, the benzodiazepine antagonist.

Lorazepam (Ativan, Wyeth) at dosages of 20-36 mg/kg was used to test for developmental toxicity in the mouse embryo/foetus model. Two separate regions were considered: (1) the central nervous system and (2) the roof of the mouth and the eyelids. In the first case a single administration of lorazepam was applied at the very beginning of the 9th gestation day. In the second, it was administered in preliminary tests on two consecutive gestation days between the 11th and 14th days and in later experiments once only on the 13th or 14th gestation day. In the first part of investigations regarding the development of the central nervous system, lorazepam unlike many other neurotropic drugs, was found not to induce any aberrations in the process of the neural tube closure. In the second part, in which palate closure and the temporary closure of eyelids were monitored, it was found that lorazepam does interfere with these processes. In order to test whether lorazepam's neurocristopathic activity can be prevented, suggesting the presence of benzodiazepine receptors in the neural crest cells, we used the benzodiazepine antagonist, flumazenil (Anexate, Roche). The results of these experiments indicated the flumazenil was able to prevent cleft palate and open eyelids cases almost completely if it was administered 3 hr after administration of lorazepam. If the treatments were administered in the reverse order, the frequency of neurocristopathy cases was unaffected, i.e. flumazenil did not influence the teratogenic activity of lorazepam.

Chronic benzodiazepine administration. X. Concurrent administration of the peripheral-type benzodiazepine ligand PK11195 attenuates chronic effects of lorazepam.

Chronic administration of benzodiazepine active at the tau-aminobutyric acidA receptor ("central" benzodiazepine sites) is associated with behavioral tolerance and receptor downregulation. Recent reports indicate possible interactions between central sites and benzodiazepines active at "peripheral-type" sites located primarily on non-neuronal cells. To evaluate these interactions during chronic administration, we treated mice with lorazepam for 1 to 14 days alone or in combination with the peripheral-type site ligand PK11195 [N-methyl-N-(methyl-1-propyl)chloro-2-phenyl-1-isoquinoline-3-carboxamid e]. Lorazepam was associated with tolerance at 7 days, but tolerance was not observed during concurrent administration of PK11195. Lorazepam was also associated with benzodiazepine receptor down-regulation in cortex and hippocampus at 7 days. With concurrent administration of PK11195, this effect remained in cortex but was absent in hippocampus. tau-Aminobutyric acid-dependent chloride uptake was reduced in both cortex and hippocampus with lorazepam, but not with concurrent lorazepam and PK11195. PK11195 administration alone did not affect behavior or neurochemical parameters, or did it alter brain lorazepam concentrations. These data indicate that concurrent PK11195 administration attenuates behavioral and neurochemical effects of chronic lorazepam administration.

Thyrotropin-releasing hormone selectively reverses lorazepam-induced sedation but not slowing of saccadic eye movements.

To investigate preliminary reports that benzodiazepine-induced sedation may be reversed by thyrotropin-releasing hormone (TRH), we examined the effect of TRH or saline placebo on two variables which are sensitive to benzodiazepine agonists: changes in sedation and saccadic eye movements. Lorazepam 10 micrograms/kg i.v. increased self-ratings of sedation and reduced self-ratings of alertness and these changes were almost completely reversed by TRH. In contrast the slowing of saccadic eye movements by lorazepam was not reversed by TRH. The effects of TRH do not appear to be due to a direct antagonism at the benzodiazepine receptor, since flumazenil reverses changes in both variables. Moreover ligand binding studies reveal that TRH has very low affinity at this receptor. These clinical data provide the first demonstration that it is possible to distinguish between the effects of benzodiazepines on saccadic eye movements and psychological self-ratings.

[Beta activation following the intravenous administration of benzodiazepines and the specific antagonist flumazenil (Ro 15-1788)]. / Beta-Aktivierung nach intravenöser Gabe von Benzodiazepinen und dem spezifischen Antagonisten Flumazenil (Ro 15-1788).

In a prospective randomized study involving 32 male subjects aged 18 to 38, the effects of flunitrazepam (0.25 to 2 mg/70 kg), lormetazepam (0.5 to 4 mg/70 kg), midazolam (1.5 to 12 mg/70 kg) and diazepam (4 to 32 mg/70 kg) on the beta-activity (13 to 20/s) were investigated. Each subject received four benzodiazepine injections of increasing dosage. The doses were selected so that the lowest had only a slight effect on the test person's condition, while the highest resulted in deep sedation. The increase in beta-activity started off with a latency of 30 to 60 s; it was proportional to the dosage and reached its maximum between the 2. and 3. minutes. The subsequent decrease in beta-activity could be represented by an exponential function. The effect could be cancelled temporarily by administering repeated doses of the specific antagonist, flumazenil (0.1, 0.3 and 0.9 mg/70 kg). The method is suited for describing pharmacodynamic processes, determining equipotential doses of benzodiazepines and detecting the interaction between benzodiazepines and specific antagonists.

Failure of Ro 15-4513 to antagonize ethanol in rat lines selected for differential sensitivity to ethanol and in Wistar rats.

An imidazobenzodiazepine, Ro 15-4513, acting as a partial inverse agonist at the central benzodiazepine receptors has been recently reported to reverse efficiently the intoxicating effects of ethanol. In studies designed to delineate the role of benzodiazepine receptors in the ethanol-induced motor impairment difference between two rat lines selectively bred for high and low sensitivity to ethanol, however, we could not antagonize the effects of ethanol by Ro 15-4513 in the tilting plane and horizontal wire tests. Neither could we observe any consistent antagonism of ethanol actions in Han:Wistar rats, although we used a wide range of Ro 15-4513 doses, injected the drug intraperitoneally or intragastrically and before or after ethanol administration, and carried out the tests for motor impairment (rotarod, horizontal wire test and intoxication rating) at various times after the drug administration. The ex vivo assay of flunitrazepam binding in brain homogenates revealed the presence of compound(s) inhibiting the binding after administration of Ro 15-4513. Ro 15-4513 antagonized the motor impairing effects of lorazepam. In conclusion, Ro 15-4513 failed to function as a specific antagonist of moderate doses of ethanol in several tests for motor impairment in different rat lines.

Does the behavioural activation detected after a single dose of a benzodiazepine reflect a withdrawal response?

The effects, in mice, of a single dose of lorazepam or oxazepam were determined, in the holeboard, 24, 48 and 72 hours after treatment. Lorazepam produced significant increases in both spontaneous locomotor activity and in rearing 48 hours after treatment and oxazepam produced a significant overall increase in rearing over the three time points. There was no detectable in vivo receptor occupancy for either drug at the 48 hour time point, so that these effects were not due to residual concentrations of drug in the brain. We therefore suggest that we were detecting a spontaneous withdrawal response to a single dose of benzodiazepine. The increases in both locomotor activity and rearing, detected 48 hours after lorazepam, could be reversed by treating simultaneously with Ro 15-1788 (a benzodiazepine antagonist). When Ro 15-1788 was injected 20 minutes prior to testing, the mice that had been treated 48 hours previously with lorazepam still showed increased locomotor activity and rearing. We conclude that the hyperactivity was not caused by any change in the levels of endogenous substances acting at the benzodiazepine receptor.

Human studies on the benzodiazepine receptor antagonist beta-carboline ZK 93 426: antagonism of lormetazepam's psychotropic effects.

The effects of lormetazepam (0.03 mg/kg IV) a benzodiazepine (BZ) derivative in combination with ZK 93 426 (0.04 mg/kg IV) a beta-carboline, benzodiazepine receptor antagonist were evaluated in humans. Independently, the effects of ZK 93 426 on its own were investigated. A psychometric test battery to evaluate sedation (visual analog scales (VAS), anxiolysis (state-trait-anxiety inventory scale (STAIG X1) and cognitive functions [logical reasoning test (LR), letter detection test (LD)] was applied before and several hours after initiation of treatment. Multiple sleep latency test (MSLT), which measures day time sleepiness, was also applied. Vigilosomnograms analysed from standard EEG recordings were evaluated shortly before and for 1 h after treatment. Treatment started with an intravenous injection of either lormetazepam (LMZ) or placebo (PLA), which was followed 30 min later by administration of either ZK 93 426 or placebo; thus four treatment groups were created (PLA + PLA, LMZ + PLA, LMZ + ZK 93 426 and PLA + ZK 93 426). ZK 93 426 antagonized the sedative and hypnotic effect of LMZ as estimated by MSLT and vigilosomnograms, respectively. Impairment of cognitive functions (LR and LD) induced by LMZ was also antagonized by ZK 93 426. ZK 93 426 had no effect on the changes in the time estimation seen in the LMZ group. Furthermore, ZK 93 426 on its own increased vigilance (alertness) as measured by the vigilosomnogram. A competitive antagonism at the benzodiazepine binding site between ZK 93 426 and LMZ is suggested by their combination effects; the intrinsic activity of ZK 93 426 seems to be due to its weak partial inverse agonist component.

Amnestic effects of lormetazepam and their reversal by the benzodiazepine antagonist Ro 15-1788.

A combined visual (pictures) and auditory (word lists) memory test developed to trace the course of information processing under pharmacological or other influences was validated in a group of 20 subjects (control group) and then applied to determine the amnesic effects of lormetazepam and the reversal of these effects by the benzodiazepine antagonist Ro 15-1788. Three groups of n = 10 subjects received either 0.02 mg/kg IV lormetazepam (groups B and C) or placebo (group A) followed 14 min later by 0.03 mg/kg IV Ro 15-1788 (groups A and C) or placebo (group B). The time course of memory performance in the three groups was investigated and compared across three consecutive 14-min phases: before (phase 1) and after (phase 2) the first intravenous administration, and after the second treatment (phase 3). Results were also compared with those of 20 subjects from a drug-free control group in order to verify the memory test. Lormetazepam clearly impaired immediate and delayed free recall as well as recognition in both visual and auditory tasks. These effects were completely reversed by Ro 15-1788, which alone had no clear effect on memory performance in this study. Psychometric scales indicated concomitant sedation and impaired concentration after lormetazepam alone. Interestingly, lormetazepam retrogradely enhanced performance in the visual test of delayed free recall. The impaired acquisition of new information after the administration of lormetazepam may be associated with an improvement of the consolidation process of information acquired before drug treatment.

Lorazepam and pentobarbital drug discrimination in baboons: cross-drug generalization and interaction with Ro 15-1788.

Four baboons were trained to discriminate lorazepam (1.0 mg/kg i.m.) and two baboons were trained to discriminate pentobarbital (5.6 mg/kg i.m.) in a two-lever drug discrimination procedure. Food delivery depended on 20 consecutive responses on one lever in sessions preceded by an injection of the training drug and on 20 consecutive responses on the other lever after no drug. All baboons reliably completed 100% of the response runs on the appropriate lever in training sessions. Test sessions were conducted in which a drug dose different from the training dose was injected and 20 consecutive responses on either lever produced food. Drug lever responding occurred after a range of lorazepam and diazepam doses in both lorazepam- and pentobarbital-trained baboons. Drug lever responding also occurred after a range of doses of pentobarbital in the pentobarbital-trained baboons but in only one of the four lorazepam-trained baboons. Ro 15-1788 (0.1-1.0 mg/kg p.o.) antagonized the effect of lorazepam but had no effect on the pentobarbital discriminative stimulus. The asymmetrical generalization with lorazepam and pentobarbital suggests a specificity of discriminative stimulus effects that heretofore have not been documented in drug discrimination experiments with benzodiazepines and barbiturates. The selective antagonism of lorazepam by the benzodiazepine-receptor antagonist Ro 15-1788 suggests that the lorazepam but not the pentobarbital discriminative stimulus is mediated at the benzodiazepine receptor.

Physostigmine fails to reverse clinical, psychomotor, or EEG effects of lorazepam.

Physostigmine salicylate (2.0 mg) or 0.9% NaCl (2.0 ml) was administered intravenously in a double-blind fashion to adult volunteers in an attempt to reverse the effects of a 0.05-mg/kg dose of lorazepam given intravenously 30 min earlier. No other medication affecting the central nervous system was given. No differences were observed between the two groups with regard to the frequency of amnesia, psychomotor impairment, or EEG changes during a period of 4 h. The only significant difference in the level of sedation between the two groups was observed 60 min into the study. This difference is attributed to the high incidence of nausea and vomiting that occurred at that time exclusively in one group. Time to complete recovery was the same in both groups. However, physostigmine, not saline, was associated with a high incidence of muscarinic and sympathetic stimulating effects. The results obtained indicate that at the dose used, physostigmine is of no clinical value in treating sedation induced by lorazepam.

Differential effects of the benzodiazepine antagonist Ro 15-1788 on two types of myoclonus in baboon Papio papio.

Certain benzodiazepines (BZs) like lorazepam, diazepam or clonazepam induce myoclonus jerks in photosensitive and non-photosensitive baboons. Papio papio, which are not accompanied by EEG paroxysmal discharges (type B). The effect of the selective BZ antagonist R0 15-1788 was evaluated in this myoclonus. Ro 15-1788 completely blocked type B myoclonus without decreasing the level of vigilance in the two types of baboons, and reversed the antiepileptic action of the BZs in the photosensitive ones, permitting the reappearance of myoclonus following EEG paroxysmal discharges (type A). L-5-hydroxytryptophan and progabide also blocked type B myoclonus, but the blockade was only transiently effective and was always accompanied by slight drowsiness.

[The antagonistic effect of physostigmine on sedation by lormetazepam (author's transl)]. / Die antagonistische Wirkung von Physostigmin auf die Sedierung durch Lormetazepam.

The purpose of this study was to determine the arousal effect of physostigmine after lormetazepam sedation on the human EEG. 12 male volunteers received 2 mg/kg bm lormetazepam and 30 minutes later physostigmine 2 mg preceded by atropine 1 mg. Generally an arousal effect of physostigmine could be clinically observed and more objectively demonstrated by reduced sleep stages in the vigilosomnogram (p less than 0.05). 2 volunteers did not fall asleep. 9 volunteers were awake 5-12 minutes after termination of physostigmine injection. 1 volunteer did not show any effect. Resedation and parasympathetic side effects did not occur. In earlier studies deep sleep stages after lormetazepam 1 or 2 mg/70 kg bm lasted 70 to 120 minutes. Physostigmine is recommended to counteract undesirable benzodiazepine induced sedation.