snx-482 and nickel-chloride

R-type calcium channels in postsynaptic spines signal through functional calcium microdomains to regulate a calcium/calmodulin-sensitive potassium channel that in turn regulates postsynaptic hippocampal long-term potentiation (LTP). Here, we ask whether R-type calcium channels in presynaptic terminals also signal through calcium microdomains to control presynaptic LTP. We focus on presynaptic LTP at parallel fiber to Purkinje cell synapses in the cerebellum (PF-LTP), which is mediated by calcium/calmodulin-stimulated adenylyl cyclases. Although most presynaptic calcium influx is through N-type and P/Q-type calcium channels, blocking these channels does not disrupt PF-LTP, but blocking R-type calcium channels does. Moreover, global calcium signaling cannot account for the calcium dependence of PF-LTP because R-type channels contribute modestly to overall calcium entry. These findings indicate that, within presynaptic terminals, R-type calcium channels produce calcium microdomains that evoke presynaptic LTP at moderate frequencies that do not greatly increase global calcium levels.

Topics: Adenosine A1 Receptor Antagonists; Analysis of Variance; Animals; Animals, Newborn; Calcium; Calcium Channel Blockers; Calcium Channels, R-Type; Calcium Signaling; Cerebellum; Dose-Response Relationship, Drug; Electric Stimulation; Excitatory Amino Acid Antagonists; GABA Antagonists; In Vitro Techniques; Long-Term Potentiation; Membrane Microdomains; Neural Pathways; Nickel; omega-Agatoxin IVA; omega-Conotoxin GVIA; Patch-Clamp Techniques; Phosphinic Acids; Piperidines; Presynaptic Terminals; Propanolamines; Purkinje Cells; Pyrazoles; Quinoxalines; Rats; Rats, Sprague-Dawley; Sodium Channel Blockers; Spider Venoms; Tetrodotoxin; Xanthines

Striatal spiny neurons (SPNs) associate a diverse array of cortically processed information to regulate action selection. But how this is done by SPNs is poorly understood. A key step in this process is the transition of SPNs from a hyperpolarized 'down state' to a sustained, depolarized 'up state'. These transitions are thought to reflect a sustained synaptic barrage, involving the coordination of hundreds of pyramidal neurons. Indeed, in mice, simulation of cortical input by glutamate uncaging on proximal dendritic spines produced potential changes in SPNs that tracked input time course. However, brief glutamate uncaging at spines on distal dendrites evoked somatic up states lasting hundreds of milliseconds. These regenerative events depended upon both NMDA receptors and voltage-dependent Ca(2+) channels. Moreover, they were bidirectionally regulated by dopamine receptor signaling. This capacity not only changes our model of how up states are generated in SPNs, it also has fundamental implications for the associative process underlying action selection.

Topics: 2-Amino-5-phosphonovalerate; Adenosine; Adenosine A2 Receptor Agonists; Anesthetics, Local; Animals; Animals, Newborn; Biophysics; Calcium; Calcium Channel Blockers; Corpus Striatum; Dendrites; Dopamine Agents; Electric Stimulation; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Green Fluorescent Proteins; In Vitro Techniques; Membrane Potentials; Mibefradil; Mice; Mice, Transgenic; Microscopy, Confocal; Models, Neurological; N-Methylaspartate; Nerve Net; Neurons; Nickel; Patch-Clamp Techniques; Phenethylamines; Spider Venoms; Synapses; Tetrodotoxin; Time Factors

R-type Ca(2+) channels are expressed by myenteric neurons in the guinea pig ileum but the specific function of these channels is unknown.. In the present study, we used intracellular electrophysiological techniques to determine the function of R-type Ca(2+) channels in myenteric neurons in the acutely isolated longitudinal musclemyenteric plexus. We used immunohistochemical methods to localize the Ca(V)2.3 subunit of the R-type Ca(2+) channel in myenteric neurons. We also studied the effects of the non-selective Ca(2+) channel antagonist, CdCl₂ (100 μmol L⁻¹), the R-type Ca(2+) channel blockers NiCl₂ (50 μmol L⁻¹) and SNX-482 (0.1 μmol L⁻¹), and the N-type Ca(2+) channel blocker x-conotoxin GVIA (CTX 0.1 μmol L⁻¹) on action potentials and fast and slow excitatory postsynaptic potentials (fEPSPs and sEPSPs) in S and AH neurons in vitro.. Ca(V)2.3 co-localized with calretinin and calbindin in myenteric neurons. NiCl₂ and SNX-482 reduced the duration and amplitude of action potentials in AH but not S neurons. NiCl₂ inhibited the afterhyperpolarization in AH neurons. x-conotoxin GVIA, but not NiCl₂, blocked sEPSPs in AH neurons. NiCl₂ and SNX-482 inhibited cholinergic, but not cholinergic/purinergic, fEPSPs in S neurons.. These data show that R-type Ca(2+) channels contribute to action potentials, but not slow synaptic transmission, in AH neurons. R-type Ca(2+) channels contribute to release of acetylcholine as the mediator of fEPSPs in some S neurons. These data indicate that R-type Ca(2+) channels may be a target for drugs that selectively modulate activity of AH neurons or could alter fast synaptic excitation in specific pathways in the myenteric plexus.

Topics: Acetylcholine; Action Potentials; Adenosine Triphosphate; Animals; Cadmium Chloride; Calbindin 2; Calbindins; Calcium Channel Blockers; Calcium Channels, R-Type; Cells, Cultured; Electrophysiology; Excitatory Postsynaptic Potentials; Ganglionic Blockers; Guinea Pigs; Ileum; Male; Mecamylamine; Myenteric Plexus; Neurons; Nickel; omega-Conotoxin GVIA; Protein Subunits; S100 Calcium Binding Protein G; Spider Venoms; Synaptic Transmission

Postsynaptic induction of long-term potentiation (LTP) at cortical and thalamic afferent synapses onto lateral amygdala (LA) projection neurons not only involves NMDA receptor activation, but also depends on L-type voltage-dependent calcium channels (L-VDCCs). Here we show, using whole cell recordings and two-photon Ca2+ imaging, that L-VDCCs contribute to the induction of dendritic Ca2+ spikes in LA projection neurons. Dendritic Ca2+ spikes can be induced in the absence of sodium spikes by supra-threshold somatic depolarization or by pairing sub-threshold depolarization with synaptic stimulation. Moreover, synaptic induction of Ca2+ spikes is facilitated by R-VDCCs in a pathway-specific manner. Once induced, dendritic Ca2+ spikes propagate into large parts of the dendritic tree. We show that pairing synaptic stimulation with single dendritic Ca2+ spikes can induce bi-directional plasticity, the sign of which might be determined by the anatomical location of active synaptic inputs relative to the spike initiation zone. These data suggest an important role for dendritic Ca2+ spikes in dendritic integration and provide a mechanism by which local synaptic activity may influence global dendritic integration in LA projection neurons.

Topics: Action Potentials; Amygdala; Anesthetics, Local; Animals; Calcium; Calcium Channel Blockers; Dendrites; Electric Stimulation; Excitatory Postsynaptic Potentials; In Vitro Techniques; Lidocaine; Male; Mice; Mice, Inbred C57BL; Neural Pathways; Neuronal Plasticity; Neurons; Nickel; Patch-Clamp Techniques; Reaction Time; Spider Venoms; Synapses; Verapamil

The possibility that R-type calcium channels contribute to fast glutamatergic transmission in the hippocampus has been assessed using low concentrations of NiCl(2) and the peptide toxin SNX 482, a selective antagonist of the pore-forming alpha(1E) subunit of R-type calcium channel. EPSPs or EPSCs were recorded in the whole-cell configuration of the patch-clamp technique mainly from CA3 hippocampal neurons. Effects of both NiCl(2) and SNX 482 were tested on large (composite) EPSCs evoked by mossy and associative-commissural fiber stimulation. NiCl(2) effects were also tested on minimal EPSPs-EPSCs. Both substances reduced the amplitude of EPSPs-EPSCs. This effect was associated with an increase in the number of response failures of minimal EPSPs-EPSCs, an enhancement of the paired-pulse facilitation ratios of both minimal and composite EPSCs, and a reduction of the inverse squared coefficient of variation (CV(-2)). The reduction of CV(-2) was positively correlated with the decrease in EPSC amplitude. The inhibitory effect of NiCl(2) was occluded by SNX 482 but not by omega-conotoxin-MVIIC, a broad-spectrum antagonist thought to interact with N- and P/Q-type calcium channels, supporting a specific action of low concentrations of NiCl(2) on R-type calcium channels. Together, these observations indicate that both NiCl(2) and SNX 482 act at presynaptic sites and block R-type calcium channels with pharmacological properties similar to those encoded by the alpha(1E) gene. These channels are involved in fast glutamatergic transmission at hippocampal synapses.

Topics: Animals; Calcium Channel Blockers; Calcium Channels, R-Type; Excitatory Postsynaptic Potentials; Hippocampus; In Vitro Techniques; Mossy Fibers, Hippocampal; Neurons; Nickel; Presynaptic Terminals; Rats; Rats, Wistar; Spider Venoms; Synaptic Transmission