Ca2+ signalling in postsynaptic dendrites and spines of mammalian neurons in brain slice.
Postsynaptic Ca2+ changes are involved in control of cellular excitability and induction of synaptic long-term changes. We monitored Ca2+ changes in dendrites and spines during synaptic and direct stimulation using high resolution microfluorometry of fura-2 injected into CA3 pyramidal neurons in guinea pig hippocampal slice. When driven by current injection from an intracellular electrode or with synaptic stimulation, postsynaptic Ca2+ accumulations were highest in the proximal dendrites with a pronounced fall-off towards the soma and some fall-off towards more distal dendrites. Muscarinic activation by low concentrations of carbachol strongly increased intradendritic Ca2+ accumulation during directly-evoked repetitive firing. This enhancement occurred in large part because muscarinic activation suppressed the normal Ca(2+)-dependent activation of K-channels that mediates adaptation of firing. Repetitive firing of cholinergic fibers in the slice reproduced the effects of carbachol. Inhibition of acetylcholine-esterase activity by eserine enhanced the effects of repetitive stimulation of chlolinergic fibers. All effects were reversible and were blocked by the muscarinic antagonist atropine. Ca2+ accumulations in postsynaptic spines might be the basis of specificity of synaptic plasticity. With selective stimulation of few associative/comissural fibers, Ca2+ accumulated in single postsynaptic spines but not in the parent dendrite. With strong stimulation, dendrite levels also increased but spine levels were considerably higher. The NMDA-receptor antagonist AP-5 blocked Ca(2+)-peaks in spines, but left Ca2+ changes in dendrite shafts largely unaffected. Sustained steep Ca2+ gradients between single spines and the parent dendrite, often lasting several minutes, developed with repeated stimulation. Our results demonstrate a spine entity that can act independent from the dendrite with respect to Ca(2+)-dependent processes. Muscarinic augmentation of dendritic Ca2+ levels might reduce diffusional loss of Ca2+ from hot spines into the parent dendrite, thus supporting cooperativity and associativity of synaptic plasticity.
Müller
W
W
Roche Institute of Molecular Biology, Department of Neurosciences, Roche Research Center, Nutley, NJ 07110.
Connor
J A
JA
D000818:Animals; D001921:Brain / Q000166:cytology / Q000502:physiology*; D002118:Calcium / Q000502:physiology*; D003712:Dendrites / Q000502:physiology*; D005470:Fluorometry; D006168:Guinea Pigs; D066298:In Vitro Techniques; D009116:Muscarine / Q000378:metabolism; D009473:Neuronal Plasticity / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D015398:Signal Transduction; D013569:Synapses / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology
D009116:Muscarine; D002118:Calcium