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Synaptic connections of PDF‐immunoreactive lateral neurons projecting to the dorsal protocerebrum of Drosophila melanogaster
Author(s) -
Yasuyama Kouji,
Meinertzhagen Ian A.
Publication year - 2009
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.22210
Subject(s) - biology , neuroscience , neurite , drosophila melanogaster , neuropil , synaptic vesicle , anatomy , microbiology and biotechnology , central nervous system , vesicle , genetics , membrane , in vitro , gene , biochemistry
Abstract Recent studies in Drosophila melanogaster indicate that the neuropeptide pigment‐dispersing factor (PDF) is an important output signal from a set of major clock neurons, s‐LN v s (small ventral lateral neurons), which transmit the circadian phase to subsets of other clock neurons, DNs (dorsal neurons). Both s‐LN v s and DNs have fiber projections to the dorsal protocerebrum of the brain, so that this area is a conspicuous locus for coupling between different subsets of clock neurons. To unravel the neural circuits underlying the fly's circadian rhythms, we examined the detailed subcellular morphology of the PDF‐positive fibers of the s‐LN v s in the dorsal protocerebrum, focusing on their synaptic connections, using preembedding immunoelectron microscopy. To examine the distribution of synapses, we also reconstructed the three‐dimensional morphology of PDF‐positive varicosities from fiber profiles in the dorsal protocerebrum. The varicosities contained large dense‐core vesicles (DCVs), and also numerous small clear vesicles, forming divergent output synapses onto unlabeled neurites. The DCVs apparently dock at nonsynaptic sites, suggesting their nonsynaptic release. In addition, a 3D reconstruction revealed the presence of input synapses onto the PDF‐positive fibers. These were detected less frequently than output sites. These observations suggest that the PDF‐positive clock neurons receive neural inputs directly through synaptic connections in the dorsal protocerebrum, in addition to supplying dual outputs, either synaptic or via paracrine release of the DCV contents, to unidentified target neurons. J. Comp. Neurol. 518:292–304, 2010. © 2009 Wiley‐Liss, Inc.