piperidines and bicuculline-methochloride

Subunit composition of subsynaptic transmitter receptors is controlled presynaptically in the developing neuromuscular junction. To investigate presynaptic regulation of NMDA receptor subunit composition in the CNS, we co-cultured different types of hippocampal explants with dissociated target neurons. Postsynaptic NMDA receptors were studied using whole-cell patch-clamp recordings. After 1 week in culture with innervation by dentate gyrus (dg) explants, the kinetic and pharmacological properties of postsynaptic NMDA receptors indicated the expression of NMDA receptor subtypes containing NR2B subunits (NR1/NR2A/NR2B or NR1/NR2B or both). The properties of NMDA receptors in noninnervated neurons were similar to those of neurons innervated by dg explants. In contrast, after innervation by explants from the cornu ammonis (CA) region, we found an additional NMDA receptor subtype with properties consistent with the subunit composition NR1/NR2A. These findings indicate that presynaptic signals determine NMDA receptor subunit composition. After prolonged cultivation (11-12 d) the properties of synaptic NMDA receptors in the majority of dg-innervated neurons also indicated the expression of NR1/NR2A receptors. This suggests a delayed developmental maturation of NMDA receptors in dg-innervated neurons. Long-term plasticity of central glutamatergic synapses is critically influenced by the subunit composition of NMDA receptors, and thus presynaptic control of NMDA receptor subunit composition might regulate synaptic plasticity.

Topics: Animals; Bicuculline; Cells, Cultured; Coculture Techniques; Embryo, Mammalian; Evoked Potentials; Excitatory Amino Acid Antagonists; Hippocampus; Kinetics; Macromolecular Substances; Magnesium; N-Methylaspartate; Neuronal Plasticity; Neurons; Organ Culture Techniques; Patch-Clamp Techniques; Piperidines; Polymerase Chain Reaction; Presynaptic Terminals; Quinoxalines; Rats; Receptors, N-Methyl-D-Aspartate; Synapses

Divalent metal cations, including zinc, cadmium, cobalt, nickel, strontium, manganese, magnesium and calcium, reduced the depolarization by microelectrophoretic gamma-aminobutyric acid (GABA) and piperidine-4-sulphonic acid of the central terminations of muscle group Ia primary afferent fibres in the cat spinal cord without affecting the inhibition by GABA of the firing of spinal interneurones. There thus appears to be a difference in either the interaction of GABA with recognition sites, or in the mechanism by which such interaction activates chloride ionophores, at GABA-mediated bicuculline-sensitive synapses on the central terminals of peripheral primary afferent neurones and those on neurones located within the central nervous system.

Topics: Action Potentials; Animals; Bicuculline; Cations, Divalent; Cats; Electric Stimulation; gamma-Aminobutyric Acid; Interneurons; Membrane Potentials; Muscles; Neurons, Afferent; Piperidines; Spinal Cord

(RS)-5-(Aminomethyl)-2-isoxazolin-3-ol (dihydromuscimol, DHM) is a potent 4-aminobutyric acid (GABA) agonist, the inhibitory effects of which on neurons are sensitive to the antagonist bicuculline methochloride (BMC), and it also interacts with the GABA uptake system in vitro. (S)-(+)-DHM (4) and (R)-(-)-DHM (5) were obtained in optically pure forms via resolution of tert-butyloxycarbonyl-protected DHM (1) using cinchonidine as the only resolving agent. The optical purity and absolute stereochemistry of 4 and 5 were established by chemical correlation to the (S)-(+) enantiomer of 3-hydroxy-4-aminobutyric acid (GABOB). While 4 was a specific and potent BMC-sensitive GABA agonist in vivo and in vitro, possibly the most potent GABA agonist so far described, the inhibition of GABA uptake by DHM proved to reside exclusively in the (R)-(-) enantiomer (5). The affinity of 5 for BMC-sensitive GABA receptor sites in vitro was some 50 times lower than that of 4. Compounds 4 and 5 can be considered semirigid isosteres of the conformationally flexible GABA analogues (S)-(+)- and (R)-(-)-GABOB, respectively, which show a very low degree of enantioselectivity with respect to GABA synaptic mechanisms. This correlation between the degree of enantioselectivity and conformational mobility of chiral GABA analogues might be of importance for the design of new drugs with specific actions at synapses at which GABA is the transmitter.

Topics: Animals; Bicuculline; Brain; Cats; Chemical Phenomena; Chemistry; Diazepam; gamma-Aminobutyric Acid; Isoxazoles; Molecular Conformation; Muscimol; Neurons; Oxazolidinones; Piperidines; Rats; Receptors, GABA-A; Spinal Cord; Stereoisomerism; Structure-Activity Relationship; Synaptic Membranes