Autoradiography of benzodiazepine receptor binding in the central nervous system of the normal C57BL6J mouse

The Neurotransmitter Receptor Architecture of the Mouse Olfactory System

The uptake, transmission and processing of sensory olfactory information is modulated by inhibitory and excitatory receptors in the olfactory system. Previous studies have focused on the function of individual receptors in distinct brain areas, but the receptor architecture of the whole system remains unclear. Here, we analyzed the receptor profiles of the whole olfactory system of adult male mice. We examined the distribution patterns of glutamatergic (AMPA, kainate, mGlu_2/3, and NMDA), GABAergic (GABA_A, GABA_A(BZ), and GABA_B), dopaminergic (D_1/5) and noradrenergic (α₁ and α₂) neurotransmitter receptors by quantitative in vitro receptor autoradiography combined with an analysis of the cyto- and myelo-architecture. We observed that each subarea of the olfactory system is characterized by individual densities of distinct neurotransmitter receptor types, leading to a region- and layer-specific receptor profile. Thereby, the investigated receptors in the respective areas and strata showed a heterogeneous expression. Generally, we detected high densities of mGlu_2/3Rs, GABA_A(BZ)Rs and GABA_BRs. Noradrenergic receptors revealed a highly heterogenic distribution, while the dopaminergic receptor D_1/5 displayed low concentrations, except in the olfactory tubercle and the dorsal endopiriform nucleus. The similarities and dissimilarities of the area-specific multireceptor profiles were analyzed by a hierarchical cluster analysis. A three-cluster solution was found that divided the areas into the (1) olfactory relay stations (main and accessory olfactory bulb), (2) the olfactory cortex (anterior olfactory cortex, dorsal peduncular cortex, taenia tecta, piriform cortex, endopiriform nucleus, entorhinal cortex, orbitofrontal cortex) and the (3) olfactory tubercle, constituting its own cluster. The multimodal receptor-architectonic analysis of each component of the olfactory system provides new insights into its neurochemical organization and future possibilities for pharmaceutic targeting.

In vitro proton and phosphorus NMR spectroscopic analysis of murine (C57Bl/6J) brain development

We report for the first time in vitro proton and phosphorus NMR spectroscopic analyses of murine brain development from fetal to adult stages. Chloroform-methanol extracts from C57B16/J mouse brain, at ages ranging from 15 days in utero (F15) to adult, permitted the simultaneous investigation of both cytosolic and membrane phospholipid compartments. The protein content of murine brain was determined and used for quantitation of individual metabolite levels. Proton NMR spectroscopy revealed that NAA, considered a neuronal marker, is undetectable at F15. Glutamate, GABA and creatine, however, are present at this time. All four compounds reach maximum levels at 21 days postnatal (P21). Choline and alanine levels are at their peak in fetal brain and progressively fall as the brain develops. Phosphorus NMR spectroscopy shows that phosphatidylcholine, phosphatidylinositol, sphingomyelin, and phosphatidylserine increase steadily from F15 to P21.

[Current hypotheses of the central mechanism of action of benzodiazepine tranquilizers]

Les benzodiazépines (BZD) produisent leurs effets cliniques en se liant à des récepteurs spécifiques du système nerveux central. Le récepteur BZD fait partie d'un complexe supramoléculaire qui possède également des sites allostériques pour les barbituriques et le GABA. En facilitant l'unité de couplage GABA-canal à CL-, les BZD potentialisent l'inhibition neuronale. Les recherches actuelles visent à préciser le fonctionnement moléculaire des récepteurs et à identifier leurs ligands endogènes.

Primary afferent terminal excitability in the normal and spastic mutant mouse spinal cord

A microcomputer-based system has been used to apply the technique of excitability testing to the study of the actions of a range of pharmacological agents on the excitability of single primary afferent terminals in the mouse spinal cord in vitro. GABAA analogues all evoked increases in excitability that were bicuculline sensitive. GABA itself also evoked biphasic changes in excitability, or occasionally only suppressed terminal excitability. This latter effect was often enhanced in the presence of bicuculline, and resembled the action of the GABAB agonist, baclofen. The GABAA action could be enhanced by concurrent application of either benzodiazepine, midazolam or flurazepam. Bicuculline alone frequently decreased excitability. This action could be abolished by blocking synaptic activity with a low Ca2+ high Mg2+ superfusate, and was therefore considered to be due to reduction of the tonic action of GABA released at synaptic connections. Comparison of the action of these agents on terminals in the spastic mutant mouse showed an increased sensitivity of the GABA response to the benzodiazepines in mutant animals.

Synaptic physiology of spinal motoneurones of normal and spastic mice: an in vitro study

Spinal cord reflexes have been examined in a preparation of the mouse spinal cord maintained in vitro. Responses of the motoneurone population of normal and spastic mutant mice to stimulation of a segmental dorsal root were compared. In the normal spinal cord, a monosynaptic response with very little polysynaptic excitation was typical. In the mutant, the monosynaptic response was typically followed by a depolarizing wave on which asynchronous compound action potentials were superimposed. In some spastic cords, an oscillating depolarizing wave was seen, lasting up to 500 ms. The stimulus range from threshold to maximal response was the same for the normal and mutant. The dorsal root reflex (d.r.r.) and dorsal root potential (d.r.p.) were prominent in both normal and mutant, and no consistent difference could be identified. Intracellular recordings were made from motoneurones using electrodes filled with potassium acetate. Mean resting potentials and input resistances were not significantly different in mutant and normal mice. The voltage-dependent conductances, seen as the after-depolarization and after-hyperpolarizations following antidromic action potentials and the responses of motoneurones to depolarizing current injection were similar in both populations. The synaptic responses of motoneurones following stimulation of the segmental dorsal root were clearly abnormal in the mutant. In the normal mice, a monosynaptic excitatory post-synaptic potential (e.p.s.p.), seen at low stimulus intensities, was followed at higher stimulus intensities by polysynaptic activity lasting up to 100 ms, which rarely reached threshold for action potential discharge. In the mutant mice, the monosynaptic response was typically followed by depolarizing synaptic responses which often evoked action potentials before the monosynaptic response reached threshold. At higher stimulus intensities, the monosynaptic response was followed by at least one and often multiple action potentials generated on prolonged depolarizing synaptic activity. When cells were impaled with potassium-acetate-filled electrodes, very little spontaneous synaptic activity was seen in either normal or mutant mice. Spontaneous depolarizing post-synaptic potentials (p.s.p.s) were prominent in normal motoneurones when potassium chloride was used to fill electrodes and were increased in amplitude by ionophoresis of chloride into the cells. Under these conditions stimulation of a ventral root evoked a depolarizing p.s.p. and the Renshaw i.p.s.p. reversed. The spontaneous p.s.p.s were blocked by ionophoresis or bath application of the glycine antagonist strychnine.(ABSTRACT TRUNCATED AT 400 WORDS)

Autoradiographic localization of benzodiazepine receptor binding in dissociated cultures of fetal mouse cerebral cortex

Autoradiography utilizing photoaffinity labelling with [3H]flunitrazepam was used in living cultures of fetal mouse cerebral cortex in situ to localize benzodiazepine receptor binding sites. There was a predominant localization of silver grains over neurons; however, substantial labelling also occurred over nonneuronal background cells. Clonazepam (0.1 microM) and Ro 5-4864 (0.1 microM) displaced substantial numbers of silver grains over neurons and background cells, respectively. In addition, clonazepam displaced 58-68% of specific grains over background cells and Ro 5-4864 displaced 30% of grains over neurons, suggesting that multiple cell types in the CNS may participate in the neuropharmacologic actions of the benzodiazepines.

Changes in benzodiazepine receptor binding as seen autoradiographically in the central nervous system of the spastic mouse

Quantitative light-microscope autoradiography has been used to compare the specific, clonazepam-displaceable binding of [3H]flunitrazepam, a photoaffinity label for the 1,4-benzodiazepine receptor, in different regions of the brain and spinal cord of spastic mice and their unaffected littermates. Specific binding of [3H]flunitrazepam in the central nervous system of the spastic mouse showed significant increases in the anterior colliculus and pretectal area and in all laminae of the grey matter in the lumbar spinal cord. These results confirm homogenate binding assays suggesting an increased number of benzodiazepine receptors in the spinal cord of the spastic mouse. Possible sites are therefore provided at which disorders of function could arise, associated with changes seen at the gamma-aminobutyric acid (GABA)-benzodiazepine receptor complex in spinal cord homogenates from the mutant mouse spastic.