6-cyano-7-nitroquinoxaline-2-3-dione and 1-naphthylacetylspermine

Cerebellar Purkinje cells have the most elaborate dendritic trees among neurons in the brain. To date, the contributions of calcium-permeable AMPA receptors (CP-AMPARs) in calcium signaling and dendrite formation of Purkinje cells remain to be elucidated. In the present study, therefore, we examined the effects of 1-naphthyl acetyl spermine (NAS), a blocker of CP-AMPARs, on dendrite formation by cultured Purkinje cells. NAS markedly inhibited elongation and branching of Purkinje cell dendrites. Calcium imaging experiments using caged glutamate demonstrated that NAS inhibits the increase of intracellular calcium concentration in Purkinje cells after glutamate release. These results suggest that calcium signaling mediated through CP-AMPARs plays an important role in Purkinje cell dendrite formation.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Calcium; Cells, Cultured; Dendrites; Excitatory Amino Acid Antagonists; Fluorescence; Glutamic Acid; Immunohistochemistry; Mice; Mice, Inbred C57BL; Microscopy, Confocal; Purkinje Cells; Receptors, AMPA; Spermine

Axon guidance molecules trigger a cascade of local signal in growth cones and evoke various morphologic responses, including axon attraction, repulsion, elongation, and retraction. However, little is known about whether subcellular compartments, other than axonal growth cones, control axon outgrowth. We found that in isolated dentate granule cells, local application of glutamate to the somatodendritic areas, but not the axon itself, induced rapid axon retraction, during which a calcium wave propagated from the somata to the axon terminals. The calcium wave and axon retraction were both inhibited by blockade of voltage-sensitive calcium channels and intracellular calcium dynamics. A combination of perisomatic application of calcium ionophore and depolarizing current injection induced axonal calcium sweep and axon retraction. Thus, perisomatic environments can modulate axon behavior through long-range intracellular communication.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Animals, Newborn; Axons; Calcium; Calcium Signaling; Cell Communication; Cells, Cultured; Dendrites; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Glutamic Acid; Growth Cones; Hippocampus; Ionophores; Membrane Potentials; Neurons; Patch-Clamp Techniques; Rats; Rats, Wistar; Spermine

Synaptic potentials were recorded intracellularly from Purkinje cells in guinea pig cerebellar slices. EPSPs evoked by stimulation of parallel fibers were effectively blocked by perfusion of a slice with the synthetic analog of Joro spider toxin, 1-naphthylacetyl-spermine (NAS) at 250 microM. However, it did not influence those responses evoked by stimulation of climbing fibers. This action of NAS is in contrast to other commonly used glutamate antagonists, CNQX or APV: CNQX (5 microM) blocked both parallel fiber- and climbing fiber-induced responses, while APV (up to 1 mM) did not influence either except for a weak reduction observed in climbing fiber responses. NAS thus provides a useful tool for pharmacologically distinguishing parallel fiber and climbing fiber synapses.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Cerebellum; Dendrites; Electric Stimulation; Evoked Potentials; Guinea Pigs; In Vitro Techniques; Nerve Fibers; Quinoxalines; Spermine; Spider Venoms; Synapses