Acute barbiturate administration increases benzodiazepine receptor binding in vivo

Real-time fingerprinting of structural isomers using laser induced breakdown spectroscopy

Laser induced breakdown spectroscopy (LIBS) has surfaced as an attractive alternative to mass spectrometry and wet chemistry methods for chemical identification, driven by its real-time, label-free nature. Rapid analysis needs, especially in high-energy materials and pharmaceutical compounds, have further fueled an increasing number of refinements in LIBS. Yet, isomers are seldom identifiable by LIBS as they generate nearly identical spectra. Here we employ a suite of chemometric approaches to exploit the subtle, but reproducible, differences in LIBS spectra acquired from structural isomers, a set of pyrazoles, to develop a sensitive and reliable segmentation method. We also investigate the possible mechanistic principles (causation) behind such spectral variations and confirm their statistically significant nature that empowers the excellent classification performance.

Toxin-related seizures

Toxin-related seizures result from an imbalance in the brain's equilibrium of excitation-inhibition. Fortunately, most toxin-related seizures respond to standard therapy using benzodiazepines. However, a few alterations in the standard approach are recommended to ensure optimal care and expedient termination of seizure activity. If 2 doses of a benzodiazepine do not terminate the seizure activity, a therapeutic dose of pyridoxine (5 g intravenously in an adult and 70 mg/kg intravenously in a child) should be considered. Phenytoin should be avoided because it is ineffective for many toxin-induced seizures and is potentially harmful when used to treat seizures induced by theophylline or cyclic antidepressants.

Acute treatment with pentobarbital alters the kinetics of in vivo receptor binding in the mouse brain

The effect of pentobarbital, a sedative-hypnotic barbiturate, on the in vivo binding of benzodiazepine receptors in the mouse brain was investigated. Dose-related changes in the apparent binding of [3H]Ro15-1788 ([3H]flumazenil) in the cerebral cortex, cerebellum and pons-medulla were observed by pretreatment with pentobarbital. For quantification of the kinetic properties of the in vivo binding of [3H]Ro15-1788, time courses of radioactivity following its injection were examined, and kinetic analysis was performed using the compartment model. The time courses of radioactivity following injection of [3H]Ro15-1788 with 3 mg/kg Ro15-1788 were used as input function. In all regions studied, rate constants between input compartment and specific binding compartment were significantly decreased by pentobarbital. However, no significant alterations in the binding potential (BP=K3/K4) of benzodiazepine receptors by pentobarbital were observed in any of the regions. A saturation experiment indicated that the decrease in the input rate constant (K3), which includes both the association rate constant (k(on)) and the number of binding sites available (B(max)), was mainly due to decrease in k(on). These results suggest that apparent increases in binding at 20 min after tracer injection were due to the decrease in the association and dissociation rates of binding in vivo.

Changes in mACh, NMDA and GABA(A) receptor binding after lateral fluid-percussion injury: in vitro autoradiography of rat brain frozen sections

Adult rats were subjected to a moderate lateral fluid percussion injury (FPI), followed by survival periods of 2 and 12 h. Regional NMDA subtype glutamate, muscarinic acetylcholine and GABA(A) receptor binding in various brain regions was analysed by quantitative in vitro autoradiography and short-lived positron emission tomography tracers [11C]cyano-dizocilpine, 4-N-[11C]methylpiperidylbenzilate (4-N-[11C]MPB), and [11C]flumazenil, respectively. The binding potential (BP, Bmax/KD) was calculated. The data with [11C]cyano-dizocilpine showed a significant decrease in BP bilaterally for the frontoparietal cortex and hippocampus at both time points, in comparison with that of the sham-operated controls. At 12 h the decrease was significantly more prominent for the ipsilateral cortex and hippocampus than for the contralateral side. The BP of 4-N-[11C]MPB was significantly decreased after 2 h for the trauma-side hippocampus, and after 12 h it had decreased for the trauma-site cortex and the bilateral hippocampus. The [11C]flumazenil exhibited a significant decrease in BP for the trauma-site cortex and the underlying hippocampus by 2 h after the traumatic brain injury. After 12 h a significantly decreased BP was observed only for the trauma-site cortex. The finding of a decreased BP demonstrates the involvement of these receptor systems in the development of cellular dysfunction, which is widespread and not limited to the site of lateral FPI.

Effect of neuroactive steroids on [3H]flumazenil binding to the GABAA receptor complex in vitro

Modulation of benzodiazepine receptor ligand binding to the GABAA receptor complex by the neuroactive steroids 3 alpha-hydroxy-dihydroprogesterone (3 alpha-OH-DHP) and 3 alpha-hydroxycorticosterone (3 alpha- THDOC) was assessed in an in vitro binding assay with the benzodiazepine antagonist [3H]flumazenil using rat cortical membranes. Neuroactive steroids, pentobarbital, GABA and bicuculline did not significantly affect flumazenil binding. However, the addition of neuroactive steroids significantly decreased the Ki of benzodiazepine agonists, including alprazolam, diazepam and clonazepam, indicating an increase in agonist affinity. Only the addition of 3 beta-OH-DHP, an inactive stereoisomer had no effect on the Ki of these agonists. The binding of the benzodiazepine inverse agonist FG 7142 was not significantly affected by these steroids, but the addition of GABA significantly increased the Ki of FG 7142 indicating a decrease in inverse agonist affinity. High concentrations of GABA or bicuculline were able to occlude the 3 alpha-THDOC mediated decrease in alprasolam Ki, indicating a GABA dependent mechanism of binding enhancement. An advantage of using [3H]flumazenil is that neither the Ki nor the Bmax change in the presence of allosteric site modulators, permitting the simple and direct assessment of alterations in benzodiazepine ligand affinity for the GABAA receptor complex by neuroactive steroids.

L-lysine is a barbiturate-like anticonvulsant and modulator of the benzodiazepine receptor

Our earlier observations showed that L-lysine enhanced the activity of diazepam against seizures induced by pentylenetetrazol (PTZ), and increased the affinity of benzodiazepine receptor binding in a manner additive to that caused by gamma-aminobutyric acid (GABA). The present paper provides additional evidence to show that L-lysine has central nervous system depressant-like characteristics. L-lysine enhanced [3H]flunitrazepam (FTZ) binding in brain membranes was dose-dependent and stimulated by chloride, bromide and iodide, but not fluoride. Enhancement of [3H]FTZ binding by L-lysine at a fixed concentration was increased by GABA but inhibited by pentobarbital between 10(-7) to 10(-3)M. While GABA enhancement of [3H]FTZ binding was inhibited by the GABA mimetics imidazole acetic acid and tetrahydroisoxazol pyridinol, the enhancement by pentobarbital and L-lysine of [3H]FTZ binding was dose-dependently increased by these two GABA mimetics. The above results suggest that L-lysine and pentobarbital acted at the same site of the GABA/benzodiazepine receptor complex which was different from the GABA binding site. The benzodiazepine receptor antagonist imidazodiazepine Ro15-1788 blocked the antiseizure activity of diazepam against PTZ. Similar to pentobarbital, the anti-PTZ effect of L-lysine was not blocked by Ro15-1788. Picrotoxinin and the GABA, receptor antagonist bicuculline partially inhibited L-lysine's enhancement of [3H]FTZ binding with the IC50s of 2 microM and 0.1 microM, respectively. The convulsant benzodiazepine Ro5-3663 dose-dependently inhibited the enhancement of [3H]FTZ binding by L-lysine. This article shows the basic amino acid L-lysine to have a central nervous system depressant characteristics with an anti-PTZ seizure activity and an enhancement of [3H]FTZ binding similar to that of barbiturates but different from GABA.

Attenuation of anticonvulsant effects of diazepam after chronic treatment with bicuculline

Changes in the GABAergic system after chronic treatment with bicuculline were examined in two strains of inbred rats, Fischer 344 (F344) and Lewis (LEW). Rats received an IP injection of either bicuculline (2 mg/kg) or vehicle once a day for 12 days. After this chronic treatment, the effects of diazepam (1 mg/kg, IP) and pentobarbital (20 mg/kg, IP) on bicuculline-induced convulsions were measured. Bicuculline was acutely infused into a tail vein at 0.0415 mg/min, and the infusion was terminated when rats showed seizure. Following the chronic bicuculline treatment, the anticonvulsant effect of diazepam, but not of pentobarbital, was significantly reduced as compared to its effect following chronic vehicle treatment in both strains. Both diazepam and pentobarbital showed a significant difference in anticonvulsant effects between strains (F344 > LEW). The hypnotic effects of muscimol, barbital, pentobarbital, and ethanol following chronic bicuculline treatment were examined. There was no significant difference in sleep time induced by these drugs between bicuculline- and vehicle-treated rats. These results suggest that the attenuation of diazepam's anticonvulsant effect after chronic bicuculline treatment may result from functional changes in benzodiazepine receptors and that the anticonvulsant effects of diazepam and pentobarbital may be influenced by genetic factors. Moreover, the hypnotic effects of several drugs tested are apparently not affected by chronic bicuculline treatment.

Distribution of cocaine recognition sites in monkey brain: II. Ex vivo autoradiography with [3H]CFT and [125I]RTI-55

CFT [WIN 35,428, 2 beta-carbomethoxy-3 beta-(4-fluorophenyl)tropane] and its 4-iodinated analog RTI-55 have been proposed as imaging probes for cocaine recognition sites and for dopamine transporters. The central and peripheral distribution of radiolabeled forms of these compounds was studied 30 minutes after intravenous administration in squirrel monkey (Saimiri sciureus). Quantitative ex vivo autoradiography of brain tissue sections from animals receiving [3H]CFT (2.5 nmol/kg) revealed radioligand distribution primarily in dopamine-rich brain regions, and treatment with cocaine or mazindol substantially reduced [3H]CFT accumulation. The caudate nucleus, putamen, and nucleus accumbens/olfactory tubercle accumulated the highest levels of [3H]CFT, and within the caudate nucleus, medial-to-lateral and anterior-to-posterior gradients were observed. Low levels of [3H]CFT were found in the cortex, thalamus, hypothalamus, and background levels in white matter and in the cerebellum (striatal:cerebellar ratio > 3). The in vivo distribution of [3H]CFT closely paralleled its in vitro distribution (Synapse, 9:177-187). Although [125I]RTI-55 (0.2 nmol/kg) also distributed to dopamine-rich brain regions (striatal: cerebellar ratio of 3.6), high levels also were detected in cortex, thalamus, and in midbrain/brainstem structures. In the periphery, [125I]RTI-55 accumulation, measured as percent of administered dose, was higher than [3H]CFT in liver and lung, respectively. Of the radioactivity detected in soluble extracts of striatum, liver, and lung, greater than 90% comigrated with [3H]CFT or [125I]RTI-55 standards. The results support the hypothesis that dopamine-rich brain regions may be relevant to the effects of cocaine, and that both CFT and RTI-55 may be suitable imaging probes for these sites.

Effects of acute pentobarbital administration on GABAA receptor-regulated chloride uptake in rat brain synaptoneurosomes

Effects of acute pentobarbital administration on GABAA receptor-regulated muscimol-stimulated, pentobarbital-stimulated, or flunitrazepam-enhanced, muscimol-stimulated chloride uptake were studied in the brains of Sprague-Dawley rats. Animals received sodium pentobarbital, 60 mg/kg IP, and cerebral cortical and cerebellar synaptoneurosomes were isolated at 10 min, 1 h, and when animals had awakened. The basal uptake of chloride was not changed in either cerebral cortex or cerebellum at different time periods after pentobarbital administration. Ten minutes after sodium pentobarbital administration, muscimol-stimulated chloride uptake was significantly reduced in cerebellum when the muscimol concentration was 2.5, 5, or 20 microM and in cerebral cortex when the concentration of muscimol was 5 or 10 microM (p less than 0.05, Duncan multiple-range test). One hour after pentobarbital administration or after animals had awakened, chloride uptake in brains from pentobarbital-treated animals was less at low concentration of muscimol (2.5 microM). No significant difference was found in either cerebral cortex or cerebellum in pentobarbital-(125-1,000 microM) stimulated or flunitrazepam-(2.5-20 microM) enhanced, muscimol-(3 microM) stimulated chloride uptake at different time periods after pentobarbital administration. Saline treatment had no effects on the basal or muscimol-stimulated chloride uptake in cerebellar synaptoneurosomes when compared with naive animals. The results demonstrate that GABAA receptor-regulated chloride uptake is decreased after acute pentobarbital administration, an effect that is reversible.

Effect of sedative drugs upon receptor binding in vivo

Acute treatment with pentobarbital (PB), ethanol and flunitrazepam significantly decreased 3H-SCH 23390 binding in mouse striatum in a dose dependent manner. In contrast, no significant alterations in 3H-SCH 23390 binding in the cerebral cortex have been observed in mice treated with these sedative and hypnotic drugs. Flumazenil Ro15-1788) reversed the effect of flunitrazepam suggesting the reduction in dopamine D1 receptor binding in the striatum was mediated via GABA-Bz-Cl channel complex. Using kinetic analysis, it was found that such changes in dopamine D1 receptor binding in vivo were mainly due to changes in rates of ligand-receptor binding in vivo. Other non-site-specific drugs such as propanol and butanol also decreased 3H-SCH 23390 binding in vivo, depending on their lipophilicities. These results indicated that micro-environmental factors surrounding receptors, including cell membranes seem to have important roles in receptor binding in vivo. Both PB and flunitrazepam decreased muscarinic acetylcholine receptor binding in mouse cortex, striatum, hippocampus and other regions. Together with the fact that PB also altered 3H-Ro15-1788 binding in vivo, this suggested global changes in microenvironmental factors may occur due to these sedative drugs. In vivo quantitative analysis of neuroreceptors with positron emission tomography (PET) seems to have some potencies to reveal the neurochemical base of benzodiazepine dependence.

Midazolam potentiates thiopental sodium anesthetic induction in patients

STUDY OBJECTIVE

To test the hypothesis that midazolam potentiates thiopental sodium-induced unconsciousness.

DESIGN

Randomized, double-blind study.

SETTING

A university medical center.

PATIENTS

Fifty nonpremedicated ASA physical status I and II adult patients scheduled for eye surgery.

INTERVENTIONS

Intravenous (IV) injections of thiopental sodium in doses ranging from 1.0 mg/kg to 4 mg/kg with or without the addition of midazolam 0.02 mg/kg.

MEASUREMENTS AND MAIN RESULTS

Inability to open eyes on command was used as an end point of anesthesia and the dose-response curves were determined using a probit procedure. A dose of 0.02 mg/kg, which constitutes less than one-tenth of the hypnotic ED50 value for midazolam, potentiated thiopental sodium anesthesia. The thiopental sodium ED50 value was decreased from 2.4 mg/kg to 1.6 mg/kg (p less than 0.001). Midazolam also reduced individual variability in the response to thiopental sodium. As a result, the thiopental sodium dose that reliably induced any nonpremedicated patient decreased from 6 mg/kg (ED99 of 5.57 mg/kg) to 2.5 mg/kg (ED99 of 2.37 mg/kg).

CONCLUSIONS

A subhypnotic dose of midazolam potentiates thiopental sodium-induced unconsciousness. This effect suggests the possibility that midazolam enhances barbiturate binding.

Quantitative in vivo analysis of benzodiazepine binding sites in the human brain using positron emission tomography

Central-type benzodiazepine binding sites were characterized in a single normal human subject, using positron emission tomography (PET) and the radiolabelled benzodiazepine antagonist, carbon-11 labelled flumazenil ([11C] Ro 15-1788). The subject was scanned using tracer alone and tracer plus 4 different concentrations of unlabelled Ro 15-1788, including one concentration of unlabelled Ro 15-1788, chosen to produce maximum displacement of [11C] Ro 15-1788 from specific binding sites. Concentrations of free, unmetabolized [11C] Ro 15-1788 in plasma were estimated using a simple extraction and ultrafiltration method. Radioactivity in the regional exchangeable pool in brain was estimated under non-saturation conditions from the ratio of radioactivity in brain to plasma, under saturation conditions and the kinetics of free ligand in plasma. The specific binding was, then, estimated by the difference between the total radioactivity in brain and exchangeable pool radioactivity. Scatchard analyses were performed to yield Bmax and Kd values under pseudo-equilibrium conditions, which was observed as an increase of specific binding/free with reduction in specific binding. In cerebral cortex and cerebellum, the Bmax values were about 62-73 nmol/l and the Kd values were 3.6-6 nM in the estimation of free ligand in plasma and 12-15 nM in the estimation of exchangeable pool in brain, as free in brain.

Difference in in vivo receptor binding between [3H]N-methylspiperone and [3H]raclopride in reserpine-treated mouse brain

The in vivo binding of [3H]N-methylspiperone (NMSP) and [3H]raclopride was compared in mice treated with reserpine (5 mg/kg, 24 hr prior to the tracer injection). With both radioligands, selective accumulation of radioactivity in the striatum following intravenous injection was observed, whereas a relatively low accumulation and a rapid decline in radioactivity in the cerebellum was seen. Reserpine significantly decreased [3H]NMSP binding in vivo, however it increased [3H]raclopride binding. By compartment model analysis, it was found that the decrease in [3H]NMSP binding was primarily due to the decrease in the association rate (K3) and the increase in [3H]raclopride was due to the decrease in the dissociation rate (K4) in vivo. As both Kd and Bmax of dopamine D2 receptors have been reported to be unaltered by reserpine, these results suggested that some unknown factors except Kd and Bmax which influence on in vivo binding of receptors might be changed by reserpine. These results revealed that it is of importance to measure kinetics of ligand-receptor binding in vivo rather than static analysis. These two different types of radioligands can be combined to reveal functional roles of dopamine receptor in vivo, especially in the study of the human brain with positron emission tomography (PET).

Modulation of benzodiazepine receptor binding in mouse brain by adrenalectomy and steroid replacement

Adrenal steroids alter neuronal excitability in the central nervous system (CNS), and evidence from in vitro studies indicates that at least some of these effects are mediated by the GABAergic system. Benzodiazepine receptor binding, among other sites on the GABA complex, has been implicated in steroid-induced alterations in the CNS. To investigate the modulation of benzodiazepine receptor binding by adrenal steroids, we examined receptor binding determined by an in vivo technique in mice after adrenalectomy, hypophysectomy and after replacement with several naturally occurring and synthetic steroids. Benzodiazepine receptor binding was substantially augmented in cortex, hypothalamus, and hippocampus in mice 1 week after adrenalectomy, and these increases appeared to be due to increased receptor number rather than changes in apparent affinity. Similar results in cortex were found after hypophysectomy. Replacement with physiologic, but not lower doses, of corticosterone reversed the changes induced by adrenalectomy. Chronic treatment with deoxycorticosterone also returned binding to control values, but chronic administration with dexamethasone, aldosterone and dihydroprogesterone did not alter binding after adrenalectomy. Adrenalectomy did not alter non-specific binding or GABA concentrations in cortex, and delivery of radioligand did not appear to be affected. These results indicate that adrenal steroids modulate benzodiazepine receptor binding in vivo, perhaps via the CR subtype of corticosteroid receptors. The steroid-benzodiazepine interaction may be especially important in the stress response.

Benzodiazepine receptor binding of triazolobenzodiazepines in vivo: increased receptor number with low-dose alprazolam

Triazolobenzodiazepines are in clinical use as hypnotics and anxiolytics. We analyzed in vivo receptor binding and brain concentrations of alprazolam, triazolam, and estazolam. Drug concentrations measured in the cerebral cortex 1 h after administration were directly proportional to dose for all three compounds. In vivo receptor binding, as defined by the specific uptake of [3H]Ro15-1788, decreased with increasing doses of estazolam and triazolam, a finding indicating dose-related increases in receptor occupancy due to these compounds. Triazolam was substantially more potent, with an IC50 value of 16 ng/g, compared with 117 ng/g for estazolam. At higher doses of alprazolam (greater than 0.2 mg/kg), receptor binding by [3H]Ro15-1788, likewise decreased with increasing dose of the former drug. However, at lower doses of alprazolam (0.02-0.05 mg/kg), which resulted in cortex concentrations of 2-7 ng/g, receptor binding was increased above control values in cortex, hypothalamus, and hippocampus but not in several other brain regions. Binding returned to control values at doses of greater than or equal to 0.01 mg/kg. Similar results were obtained in time course studies. At 8 and 10 h after a dose of 1 mg/kg i.p., corresponding to cortex concentrations of 2.7-7 ng/g, receptor binding was increased compared with controls. Similarly, at 1, 2, and 3 h after a single dose of 0.05 mg/kg, corresponding to cortex concentrations of 3.7-5.8 ng/g, receptor binding was also increased. The apparent affinity of benzodiazepine receptors for clonazepam in mice receiving alprazolam (0.05 mg/kg) was unchanged from that in untreated control mice, an observation suggesting that low doses of alprazolam increased receptor number.(ABSTRACT TRUNCATED AT 250 WORDS)