Functional importance of benzodiazepine binding in brain

QuEChERS extraction of benzodiazepines in biological matrices

Two common analytical chemical problems often encountered when using chromatographic techniques in drug analysis are matrix interferences and ion suppression. Common sample preparation often involves the dilution of the sample prior to injection onto an instrument, especially for liquid chromatography–mass spectrometry (LC–MS) analyses. This practice frequently does not minimize or eliminate conditions that may cause ion-suppression and therefore, suffer more from reduced method robustness. In order to achieve higher quality results and minimize possible interferences, various sample preparation techniques may be considered. Through the use of QuEChERS (“catchers”), a novel sample preparation technique used for high aqueous content samples, benzodiazepines can be extracted from biological fluids, such as blood and urine. This approach has shown increased recoveries of target compounds when using quantification by both external and internal standard. This increase in the recoveries has been attributed to a matrix enhancement and was determined through the use of the method of standard addition. While improving the overall analytical method for gas chromatography–mass spectrometry (GC–MS) analysis, it is not clear if this approach represents an overall benefit for laboratories that have both GC–MS and high performance liquid chromatography tandem mass spectrometry (HPLC–MS/MS) capability. Demonstrating evidence of variable ionization (enhancement, ion source inertness, etc.), the method of quantification should be focused on in future studies.

Modulation of release of acetylcholine from the striatum by a proposed excitatory amino acid antagonist U-54494A: Comparison with known antagonists, diazepam and phenytoin

The effect of (U-54494A) cis-3,4-dichloro-N-methyl-N-[2-(1-Pyrrolidinyl)- cyclohexyl] benzamide monohydrochloride, an excitatory amino acid antagonist, on N-methyl-D-aspartic acid (NMDA)- and K(+)-evoked release of [3H]acetylcholine [( 3H]ACh) from slices of striatum was investigated. For the purpose of comparison, MK 801, PCP, CGP 37849, CPP, phenytoin and diazepam were investigated under identical conditions. Both U-54494A and the excitatory amino acid antagonists blocked NMDA-evoked release of [3H]ACh but these compounds failed to inhibit K(+)-evoked release of this neurotransmitter. Phenytoin blocked both NMDA and K(+)-evoked release of [3H]ACh, whereas diazepam was ineffective under similar conditions. These observations indicate that excitatory amino acid antagonists, including U-54494A, may mediate their anticonvulsant effect by blocking the activity of NMDA receptors, diazepam by activating the benzodiazepine receptors and phenytoin by inhibiting the activity of various depolarizing agents.

The GABA/benzodiazepine receptor-chloride ionophore complex: nature and modulation

1. A high affinity, saturable, stereospecific binding site for Benzodiazepines has been found to be functionally and possibly structurally related to a GABA receptor-chloride ionophore complex. 2. There are both central (CNS) as well as "peripheral" binding sites, involving multiple organs. 3. Evidence strongly suggests that mutually exclusive Benzodiazepine agonists and antagonists bind to the same receptor, possibly in an agonist-antagonist-inverse agonist continuum. 4. The search for an endogenous ligand has been inconclusive and the question of such a substance remains open. 5. Although the relationship between this receptor and the Limbic System remains unclear, it seems certain that the Benzodiazepine receptor plays an important role in the modulation of Limbic System excitability.

[Intramuscular premedication with midazolam in infants and children]

The useful intramuscular premedication dose of midazolam was determined in 100 children divided up in three age groups: one month to three years, 3 to 10 years, 10 to 15 years. All biometric parameters were normal for the age, and comparable between similar age groups. Haemodynamic and respiratory parameters were not altered by the premedication. The reduction in anxiety, as assessed by the child's behaviour, was good or excellent in more than 85% of cases from all age groups; it was proportional to the dose used. The doses that had, for equivalent reductions in anxiety as assessed by the chi-square test, the least hypnotic effect, were: 0.5 mg X kg-1 before three years of age, 0.4 mg X kg-1 for the 3 to 10 yr olds, and 0.25 mg X kg-1 for the 10 to 15 yr olds. This fall in dose with age, quite usual in paediatrics, was not unexpected. The level of consciousness, one hour after surgery, was always normal. No undesirable side-effect was observed. These results, together with its physical, chemical and pharmacodynamic characteristics, make midazolam a choice drug for intramuscular premedication in children, with a foreseeable use in day-care anaesthesia. The unexpected finding of an age-dependent dissociation between the reduction in anxiety and the hypnotic effect is discussed in the light of a study carried out in the adult and recent data from the literature.

Prenatal exposure to electroconvulsive seizures and phenytoin: development of benzodiazepine binding sites, reflex behaviors and seizure thresholds in exposed offspring

Electroconvulsive seizures administered during the period of fetal benzodiazepine (BZ) binding site proliferation (days 16, 18 and 20 in gestation) significantly decreased the density of cerebral cortical benzodiazepine binding sites in exposed pups up to 21 days postnatal age. Significant decreases in seizure threshold were also found in exposed offspring. However, decreases in BZ sites were not accompanied by significant alterations in RO5-4864-displaceable benzodiazepine binding as seen after in utero exposure to phenytoin (DPH). Neither prenatal treatment affected the ability of GABA to enhance BZ binding in vitro. Prenatal exposure to electroshock delayed the onset of acoustic startle and eye-opening during postnatal development; similar effects were not seen following in utero exposure to DPH. These data suggest that prenatal exposure to seizures and DPH decrease postnatal BZ site proliferation by different mechanisms.

Effects of phenytoin on [3H]diazepam binding in dissociated primary cortical cell culture

The effects of chronic exposure of primary dissociated cerebral cortical cells in culture to the anticonvulsant drug phenytoin have been investigated using benzodiazepine binding techniques. By separating benzodiazepine binding into pharmacologically distinct subtypes, the data indicate that clonazepam-displaceable benzodiazepine binding (associated primarily with neuronal membranes) is significantly decreased by exposure to therapeutic and toxic doses of phenytoin while R05-4864-displaceable benzodiazepine binding (associated principally with non-neuronal elements) is enhanced. The ratio of clonazepam-displaceable to R05-4864-displaceable benzodiazepine binding appears to be the most sensitive indicator for these changes.