NDLI: Calcium influx-independent depression of transmitter release by 5-HT at lamprey spinal cord synapses

Content Provider	PubMed Central
Author	Takahashi, Michiko Freed, Rachel Blackmer, Trillium Alford, Simon
Copyright Year	2001
Abstract	The mechanisms by which 5-hydroxytryptamine (5-HT) depresses transmitter release from lamprey reticulospinal axons were investigated. These axons make glutamatergic synapses onto spinal ventral horn neurons. 5-HT reduces release at these synapses, yet the mechanisms remain unclear. Excitatory postsynaptic currents (EPSCs) evoked by stimulation of reticulospinal axons were recorded in ventral horn neurons. 5-HT depressed the EPSCs in a dose-dependent manner with an apparent K m of 2.3 μm. To examine the presynaptic effect of 5-HT, electrophysiological and optical recordings were made from presynaptic axons. Action potentials evoked Ca2+ transients in the axons loaded with a Ca2+-sensitive dye. 5-HT slightly reduced the Ca2+ transient. A third-power relationship between Ca2+ entry and transmitter release was determined. However, presynaptic Ca2+ currents were unaffected by 5-HT. Further, in the presence of a K+ channel blocker, 4-aminopyridine (4-AP), 5-HT left unaltered the presynaptic Ca2+ transient, ruling out the possibility of its direct action on presynaptic Ca2+ current. 5-HT activated a 4-AP-sensitive current with a reversal potential of -95 mV in these axons. The basal Ca2+ concentration did not affect 5-HT-mediated inhibition of release. Although 5-HT caused a subtle reduction in resting axonal [Ca2+]i, synaptic responses recorded during enhanced resting [Ca2+]i, by giving stimulus trains, were equally depressed by 5-HT. 5-HT reduced the frequency of TTX-insensitive spontaneous EPSCs at these synapses, but had no effect on their amplitude. We propose a mechanism of inhibition for transmitter release by 5-HT that is independent of presynaptic Ca2+ entry.
Related Links	http://dx.doi.org/10.1111/j.1469-7793.2001.0323f.x
Ending Page	336
Page Count	14
Starting Page	323
File Format	PDF
ISSN	00223751
e-ISSN	14697793
Journal	The Journal of Physiology
Issue Number	Pt 2
Volume Number	532
Language	English
Publisher	Blackwell Science Inc
Publisher Date	2001-04-01
Access Restriction	Open
Rights Holder	Blackwell Science Inc
Subject Keyword	Physiology Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Physiology Sports Science

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