fg-9041 and fluorocitrate

Subplate (SP) neurons exhibit spontaneous plateau depolarizations mediated by connexin hemichannels. Postnatal (P1-P6) mice show identical voltage pattern and drug-sensitivity as observed in slices from human fetal cortex; indicating that the mouse is a useful model for studying the cellular physiology of the developing neocortex. In mouse SP neurons, spontaneous plateau depolarizations were insensitive to blockers of: synaptic transmission (glutamatergic, GABAergic, or glycinergic), pannexins (probenecid), or calcium channels (mibefradil, verapamil, diltiazem); while highly sensitive to blockers of gap junctions (octanol), hemichannels (La3+, lindane, Gd3+), or glial metabolism (DLFC). Application of La3+ (100 μM) does not exert its effect on electrical activity by blocking calcium channels. Intracellular application of Gd3+ determined that Gd3+-sensitive pores (putative connexin hemichannels) reside on the membrane of SP neurons. Immunostaining of cortical sections (P1-P6) detected connexins 26, and 45 in neurons, but not connexins 32 and 36. Vimentin-positive glial cells were detected in the SP zone suggesting a potential physiological interaction between SP neurons and radial glia. SP spontaneous activity was reduced by blocking glial metabolism with DFLC or by blocking purinergic receptors by PPADS. Connexin hemichannels and ATP release from vimentin-positive glial cells may underlie spontaneous plateau depolarizations in the developing mammalian cortex.

Topics: Action Potentials; Animals; Bicuculline; Calcium Channel Blockers; Calcium Signaling; Cerebral Cortex; Citrates; Connexin 26; Connexins; Ependymoglial Cells; Excitatory Amino Acid Antagonists; GABA-A Receptor Antagonists; Gadolinium; Gap Junction beta-1 Protein; Gap Junction delta-2 Protein; Gap Junctions; Glycine Agents; Hexachlorocyclohexane; Lanthanum; Mice; Neuroglia; Neurons; Octanols; Patch-Clamp Techniques; Probenecid; Pyridoxal Phosphate; Quinoxalines; Receptors, N-Methyl-D-Aspartate; Strychnine; Valine; Vimentin

The role of glial cells in nitric oxide production in the cerebellum of conscious rats was investigated with a glial selective metabolic inhibitor, fluorocitrate. The levels of nitric oxide metabolites (nitrite plus nitrate) in the dialysate following in vivo microdialysis progressively increased to more than 2-fold the basal levels during a 2-h infusion of fluorocitrate (1 mM), and the increase persisted for more than 2 h after the treatment. Pretreatment with N(G)-nitro-L-arginine methyl ester attenuated the fluorocitrate-induced increase in nitric oxide metabolite levels. None of the glutamate receptor antagonists, including D(-)-2-amino-5-phosphonopentanoic acid, 6,7-dinitroquinoxaline-2,3-dione, and (+/-)-alpha-methyl-4-carboxyphenylglycine, inhibited the fluorocitrate-induced increase. The L-arginine-induced increase was significantly reduced by fluorocitrate treatment, while N-methyl-D-aspartate, (+)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid, and trans-(+/-)-1-amino-(1S,3R)-cyclopentane-dicarboxylic acid increased nitric oxide metabolites levels in the fluorocitrate-treated rats, as much as in control animals. These results suggest that glial cells play an important role in modulating nitric oxide production in the cerebellum by regulating L-arginine availability.

Topics: Aconitate Hydratase; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Behavior, Animal; Benzoates; Cerebellum; Citrates; Citric Acid Cycle; Cycloleucine; Enzyme Inhibitors; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Extracellular Space; Glycine; Male; N-Methylaspartate; Neuroglia; Neuroprotective Agents; NG-Nitroarginine Methyl Ester; Nitrates; Nitric Oxide; Nitrites; Nitroarginine; Quinoxalines; Rats; Rats, Wistar; Substrate Specificity