Zinc released from olfactory bulb glomeruli by patterned electrical stimulation of the olfactory nerve

Abstract

Zinc is a trace element with a multitude of roles in biological systems including structural and cofactor functions for proteins. Although most zinc in the central nervous system (CNS) is protein bound, the CNS contains a pool of mobile zinc housed in synaptic vesicles within a subset of neurons. Such mobile zinc occurs in many brain regions, such as the hippocampus, hypothalamus, and cortex, but the olfactory bulb (OB) contains one of the highest such concentrations in the CNS. Zinc is distributed throughout the OB, with the glomerular and granule cell layers containing the highest levels. Here, we visualize vesicular zinc in the OB using zinc-responsive fluorescent probes developed by one of us. Moreover, we provide the first demonstration that vesicular pools of zinc can be released from olfactory nerve terminals within individual glomeruli by patterned electrical stimulation of the olfactory nerve designed to mimic the breathing cycle in rats. We also provide electrophysiological evidence that elevated extracellular zinc potentiates α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated synaptic events. AMPA receptors are required for the synchronous activation of neurons within individual OB glomeruli, and zinc-mediated potentiation leads to enhanced synaptic summation.

Two-photon imaging of Zn 2+ dynamics in mossy fiber boutons of adult hippocampal slices

“…We evaluated the ability of 6-CO 2 H-ZAP4 to image Zn 2+ in living brain tissues and compared it with the membrane-permeant ZP1, which was used previously to study olfactory bulb tissues (21). We first examined the excitation profiles using two-photon microscopy, which allows for fluorescent imaging of thicker living tissues (33).…”

“…4B). This property effectively reduces its sensitivity in detecting Zn 2+ dynamics and limits its use solely to the detection of the massive Zn 2+ release expected during strong electric stimulation in tissue-level assays (21). However, for synapse-level Zn 2+ imaging, local electric stimulation (42,44) and highly magnified observation optics are needed to measure Zn 2+ .…”

“…The molecular structure of ZAP4 was modeled after earlier ZAP probes (17), with pentafluorobenzyl groups chosen as the alkyl groups to reduce the basicity of the probe and minimize protoninduced enhancement of the emission. The 6-CO 2 H-ZAP4 probe was constructed as a membrane-impermeant Zn 2+ probe, analogous to the previously reported 6-CO 2 H-ZP1 (20).Previous attempts to monitor presynaptic Zn 2+ dynamics in living brain tissues used membrane-permeant probes to detect intracellular Zn 2+ from populations of presynaptic terminals at relatively low spatial resolution at the tissue level (21,22). In addition, activity-dependent extracellular Zn 2+ release has been monitored with membrane-impermeant probes (16,(23)(24)(25)(26)(27)(28)(29)(30).…”

Metalloneurochemistry and the Pierian Spring: ‘Shallow Draughts Intoxicate the Brain’

“…Synaptic zinc is released in regions of the olfactory bulb in tissue slices stimulated with electrophysiological pulses. [31] Does vesicular zinc modulate postsynaptic receptors in the olfactory bulb during olfaction the same way it does in the DCN during audition? In addition to acting on receptors directly, synaptic zinc can also alter endocannabinoid synthesis and thus modulate neurotransmission through a completely separate pathway.…”

Zn(ii)-coordination modulated ligand photophysical processes – the development of fluorescent indicators for imaging biological Zn(ii) ions

“…Trombley and coworkers stained live OB slices with ZP1 , which illuminated the high free Zn(II) content in the two outer layers of an OB slice – glomerular layer and granule cell layer. 358 The intervening external plexiform layer contains a much lower level of stainable Zn(II). Patterned electrical stimulation causes the fluorescence intensity of ZP1 from the individual glomeruli adjacent to the microelectrode to decrease, suggesting Zn(II) release from the glomeruli upon stimulation.…”