strychnine and pyridoxal-phosphate-6-azophenyl-2--4--disulfonic-acid

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

Adenosine trisphosphate (ATP) activates purinoceptors and acts as a neurotransmitter in the nervous system. In the retina, we previously reported that the immunohistochemical distribution of the subset of P2-purinoceptors differs between the ON and OFF pathways. Here, we investigated whether ATP activates P2-purinoceptors and modulates the physiological function of the mouse retina. We also examined if signal processing by P2-purinoceptors is pathway specific. Results showed that ATP activated both ON- and OFF-cholinergic amacrine cells. However, responses in OFF-cholinergic amacrine cells were greater than those in ON-cholinergic amacrine cells. Pharmacological studies in OFF-cholinergic amacrine cells showed that the response of OFF-cholinergic amacrine cells is mediated P2X(2)-purinoceptors. Further, ATP increased gamma-aminobutyric acid (GABA)ergic inhibitory postsynaptic currents (IPSCs) in OFF- but not ON-cholinergic amacrine cells. The increase in GABAergic IPSCs was mediated by P2-purinoceptors. P2-purinoceptor-mediated signals suppressed OFF ganglion cells but activated ON ganglion cells. Our findings indicate that ATP physiologically modulates signal processing of the ON and OFF pathways in a pathway-specific manner through P2-purinoceptors.

Topics: Action Potentials; Adenosine Triphosphate; Animals; GABA Antagonists; gamma-Aminobutyric Acid; Glycine Agents; Inhibitory Postsynaptic Potentials; Mice; Mice, Transgenic; Pyridazines; Pyridoxal Phosphate; Receptors, Purinergic P2; Retina; Signal Transduction; Strychnine

The effect of zinc on glycinergic spontaneous inhibitory postsynaptic currents (IPSCs) was investigated using the whole-cell patch-clamp technique in mechanically dissociated rat spinal dorsal horn neurons. Zinc at a concentration of 10 microM reversibly increased the spontaneous IPSC frequency without changing the current amplitudes, suggesting that zinc increases spontaneous glycine release from presynaptic nerve terminals. At a low concentration of 1 microM, on the other hand, zinc potentiated the amplitude of spontaneous IPSCs but had no effect on the frequency. At a high concentration of 100 microM, zinc increased the spontaneous IPSC frequency while it inhibited the IPSC amplitude. The current evoked by exogenously applied glycine was potentiated and inhibited by low and high concentrations of zinc, respectively. The increase in spontaneous IPSC frequency by 10 microM zinc was inhibited by blocking the voltage-dependent Ca(2+) channels in the presence of both omega-conotoxin-MVIIC and nifedipine. The facilitatory effect of zinc on spontaneous IPSC frequency was also inhibited in the presence of tetrodotoxin. In the slice preparation, 30 microM zinc potentiated the evoked IPSC amplitude and decreased the paired pulse ratio. These results suggest that, in addition to an action on the postsynaptic glycine receptors, zinc may depolarize the presynaptic nerve terminals, leading to an activation of voltage-dependent Na(+) and Ca(2+) channels that in turn increases glycine release. Since dorsal horn neurons receive nociceptive inputs, zinc may play an important role in the regulation of sensory transmission.

Topics: 4-Aminopyridine; Action Potentials; Adenosine Triphosphate; Animals; Animals, Newborn; Dose-Response Relationship, Drug; Drug Interactions; Glycine; Glycine Agents; In Vitro Techniques; Inhibitory Postsynaptic Potentials; Neural Inhibition; Platelet Aggregation Inhibitors; Posterior Horn Cells; Potassium Channel Blockers; Pyridoxal Phosphate; Rats; Rats, Wistar; Spinal Cord; Strychnine; Tetrodotoxin; Trace Elements; Zinc

The cellular mechanism(s) by which the brain senses changes in pH to regulate breathing (i.e., central chemoreception) have remained incompletely understood, in large part because the central respiratory chemoreceptors have themselves eluded detection. Here, we recorded from a newly identified population of central chemoreceptors located in the retrotrapezoid nucleus (RTN) on the ventral surface of the brainstem to test a recently proposed role for purinergic P2 receptor signaling in central respiratory chemoreception (Gourine et al., 2005). Using loose-patch current-clamp recordings in brainstem slices from rat pups (postnatal day 7-12), we indeed show purinergic modulation of pH-sensitive RTN neurons: activation of P2X receptors indirectly inhibited RTN firing by increasing inhibitory input, whereas P2Y receptor stimulation caused direct excitation of RTN chemoreceptors. However, after blocking P2 receptors with the broad-spectrum antagonists PPADS (pyridoxal-phosphate-6-azophenyl-2',4'-disulfonate) or RB2 (reactive blue 2), the pH sensitivity of RTN neurons remained intact. Therefore, we conclude that purinergic signaling can modulate RTN neuron activity but does not mediate the pH sensing intrinsic to these central respiratory chemoreceptors.

Topics: Adenosine Triphosphate; Animals; Bicuculline; Carbon Dioxide; Chemoreceptor Cells; Convulsants; Enzyme Inhibitors; Hydrogen-Ion Concentration; Organ Culture Techniques; Patch-Clamp Techniques; Platelet Aggregation Inhibitors; Potassium Channels; Protons; Purinergic P2 Receptor Agonists; Purinergic P2 Receptor Antagonists; Pyridoxal Phosphate; Rats; Receptors, Purinergic P2; Respiratory Center; Signal Transduction; Strychnine; Triazines; Uridine Triphosphate