ABSTRACT
A new AMPA receptor antagonist, Ro 48-8587, was characterized pharmacologically in vitro. It is highly potent and selective for AMPA receptors as shown by its effects on [3H]AMPA, [3H] kainate, and [3H] MK-801 binding to rat brain membranes and on AMPA- or NMDA-induced depolarization in rat cortical wedges. [3H]Ro 48-8587 bound with a high affinity (KD = 3 nM) to a single population of binding sites with a Bmax of 1 pmol/mg of protein in rat whole brain membranes. [3H]Ro 48-8587 binding to rat whole brain membranes was inhibited by several compounds with the following rank order of potency: Ro 48-8587 > 6-nitro-7-sulphamoylbenzo[f] quinoxaline-2,3-dione (NBQX) > YM 90K > 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) > quisqualate > AMPA > glutamate > kainate > NMDA. The distribution and abundance of specific binding sites (approximately 95% of total) in sections of rat CNS, revealed by quantitative receptor radioautography and image analysis, indicated a very discrete localization. Highest binding values were observed in cortical layers (binding in layers 1 and 2 > binding in layers 3-6), hippocampal formation, striatum, dorsal septum, reticular thalamic nucleus, cerebellar molecular layer, and spinal cord dorsal horn. At 1 nM, the values for specific binding were highest in the cortical layers 1 and 2 and lowest in the brainstem (approximately 2.6 and 0.4 pmol/mg of protein, respectively). Ro 48-8587 is a potent and selective AMPA receptor antagonist with improved binding characteristics (higher affinity, selectivity, and specific binding) compared with those previously reported.
Subject(s)
Anti-Anxiety Agents , Brain Chemistry , Excitatory Amino Acid Antagonists/pharmacology , Imidazoles/pharmacology , Quinazolines/pharmacology , Receptors, AMPA/antagonists & inhibitors , Receptors, AMPA/genetics , Animals , Benzodiazepines/pharmacology , Dizocilpine Maleate/metabolism , Dizocilpine Maleate/pharmacology , Electrophysiology , Excitatory Amino Acid Agonists/metabolism , Excitatory Amino Acid Agonists/pharmacology , Excitatory Amino Acid Antagonists/metabolism , Imidazoles/metabolism , In Situ Hybridization , Kainic Acid/metabolism , Kainic Acid/pharmacology , Kinetics , Male , N-Methylaspartate/metabolism , N-Methylaspartate/pharmacology , Quinazolines/metabolism , Quinoxalines/pharmacology , RNA, Messenger/analysis , Radioligand Assay , Rats , Rats, Inbred Strains , Receptors, AMPA/agonists , Tritium , alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid/metabolism , alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid/pharmacologyABSTRACT
The minor branch of the tritocerebral commissure of the locust, Locusta migratoria, contains only two axons which are from interneurons in the brain descending to the ventral cord ganglia. The smaller of these two neurons, the tritocerebral commissure dwarf (TCD), is immunoreactive to GABA, suggesting that it may be an inhibitory interneuron. We have exploited the accessibility of its axon in the commissure, first, to fill it with cobalt to define its morphology, and second, to record its input characteristics. It has a cell body and arborization of fine branches in the deutocerebrum of the brain, its axon passes contralateral through the tritocerebral commissure and it forms bilateral arborizations in the suboesophageal and three thoracic ganglia. It receives mechanosensory input from many regions of the ipsilateral body and head, and it is sensitive to illumination levels, generally showing greater spontaneous activity in the dark. It is one of the largest GABA-immunoreactive descending interneurons in the locust, suggesting it plays a prominent role in behaviour. Since it is easily accessible for physiological recording, its roles in circuits for particular components of behaviour should be amenable to investigation.
Subject(s)
Brain/cytology , Grasshoppers/anatomy & histology , Interneurons/cytology , Neurons, Afferent/cytology , gamma-Aminobutyric Acid/metabolism , Action Potentials , Animals , Brain/metabolism , Brain/physiology , Brain Mapping , Cobalt , Efferent Pathways/anatomy & histology , Ganglia/cytology , Grasshoppers/physiology , Immunohistochemistry , Interneurons/metabolism , Interneurons/physiology , Neurons, Afferent/metabolism , Neurons, Afferent/physiology , Photic Stimulation , Physical StimulationABSTRACT
Multiunit activity was recorded simultaneously in the substantia nigra pars compacta, the pyramidal layer of the hippocampus dorsalis CA 1 area, the nucleus locus coeruleus and the nucleus raphé dorsalis of encéphale isolé rats; drugs were injected intravenously in increasing doses. Chlordiazepoxide decreased multiunit activity dose-dependently to a similar extent in substantia nigra, hippocampus and dorsal raphé, but was less effective in the locus coeruleus. Midazolam reduced multiunit activity in all 4 nuclei to a similar degree and was more potent than chlordiazepoxide. Specific benzodiazepine antagonists completely reversed the effects of the two benzodiazepines. Pentobarbitone was a less potent depressant than chlordiazepoxide, and its effect was not reversed by the benzodiazepine antagonist Ro 15-1788.
