Immunocytochemical identification of proteins involved in dopamine release from the somatodendritic compartment of nigral dopaminergic neurons

Abstract

We examined the somatodendritic compartment of nigral dopaminergic neurons by immunocytochemistry and confocal microscopy, with the aim of identifying proteins that participate in dopamine packaging and release. Nigral dopaminergic neurons were identified by location, cellular features and tyrosine hydroxylase immunoreactivity. Immunoreactive puncta of vesicular monoamine transporter type 2 and proton ATPase, both involved in the packaging of dopamine for release, were located primarily in dopaminergic cell bodies, but were absent in distal dopaminergic dendrites. Many presynaptic proteins associated with transmitter release at fast synapses were absent in nigral dopaminergic neurons, including synaptotagmin 1, syntaxin1, synaptic vesicle proteins 2a and 2b, synaptophysin and synaptobrevin 1 (VAMP 1). On the other hand, syntaxin 3, synaptobrevin 2 (VAMP 2) and SNAP-25-immunoreactivities were found in dopaminergic somata and dendrites Our data imply that the storage and exocytosis of dopamine from the somatodendritic compartment of nigral dopaminergic neurons is mechanistically distinct from transmitter release at axon terminals utilizing amino acid neurotransmitters. Keywords dopamine; substantia nigra; somatodendritic; exocytosis; dopamine release proteins Parkinson's disease, a movement disorder involving the basal ganglia, results primarily from degeneration of the dopaminergic (DAergic) projection from substantia nigra (SN) to striatum (Birkmayer and Hornykiewicz, 1976). The underlying nigrostriatal pathway arises from large midbrain DAergic neurons situated in the SN pars compacta (SNc). Laterally extending dendrites emitted by the DAergic perikarya intermingle in the SNc and vertical dendrites extend ventrally into the adjacent pars reticulata (SNr) (Dahlström and Fuxe, 1964;Juraska et al., 1977;Wassef et al., 1981, Tepper et al., 1987. USA, pw20@nyu.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access Author ManuscriptNeuroscience. Author manuscript; available in PMC 2010 December 1. Previous studies have shown that dopamine (DA) is released both by the nigrostriatal axonal terminals within striatum and by DAergic somata and dendrites in the midbrain (Björkland and Lindvall, 1975;Groves et al., 1975;Geffen et al., 1976;Nieoullon et al., 1977;Rice et al., 1994, Jaffe et al., 1998Chen and Rice, 2001 (Patel et al., 2009). Another important distinction is that DAergic terminals in striatum show typical presynaptic aggregates of agranular vesicles Nirenberg et al., 1997), whereas DAergic somata in SNc lack these aggregates , as do DAergic den...

Dendritic SNAREs add a new twist to the old neuron theory

“…Importantly, potent inhibition of dopamine secretion from somato-dendritic compartments of these neurons by CNTs in vitro and in vivo confirmed the involvement of SNAREs (50,51). These functional data received support from more recent immunocytochemical studies, which highlighted the presence of the main CNTs-sensitive SNARE variants, including syntaxin3, VAMP2, and SNAP-25, in dendrites of nigral dopaminergic neurons (52).…”

Somatodendritic dopamine release: recent mechanistic insights

“…Vesicles involved in exocytosis at fast glutamate synapses express a large number of intrinsic proteins [130,132]. However, consistent with the relative absence of conventional synaptic vesicles in DA neurons, immunohistochemical studies show that TH-positive somata and dendrites in the substantia nigra lack proteins typically associated with vesicles, including sv2a and sv2b (isoforms of synaptic vesicle protein 2), synaptophysin and the Ca 2þ sensors synaptotagmin 1 and 2 [27]. Moreover, several common SNARE proteins involved in vesicle docking, including the plasma membrane protein syntaxin 1a and the vesicle protein synaptobrevin 1 (Vamp 1), are also absent ( figure 5).…”

“…Moreover, several common SNARE proteins involved in vesicle docking, including the plasma membrane protein syntaxin 1a and the vesicle protein synaptobrevin 1 (Vamp 1), are also absent ( figure 5). However, other plasma membrane SNARE protein isoforms are present throughout DA perikarya, including SNAP-25 and syntaxin 3b [27,63], which is also used at 'slow' photoreceptor ribbon synapses [133]. DA somata express synaptobrevin 2 (Vamp 2), an intrinsic vesicle protein ( figure 5).…”

“…Overall, the molecular organization of DA release in the SNc appears to differ substantially from conventional vesicular release, with an unconventional triad of Vamp 2/SNAP-25/ syntaxin 3 ( figure 5). Importantly, although SNc DA somata and dendrites lack synaptotagmin 1 and 2 [27,63], which are low-affinity isoforms of the vesicular Ca 2þ sensors found at fast synapses [134], they have the higher affinity isoforms, synaptotagmin 4 and 7 [63]. This could contribute to the high rstb.royalsocietypublishing.org Phil.…”

Multiple signalling modalities mediated by dendritic exocytosis of oxytocin and vasopressin

“…There is evidence for the involvement of SNARE proteins in the release of LDCVs from dendrites, with the majority of the data arising from studies of substantia nigra dopamine cells [46][47][48]. Data from several other brain regions, including hippocampus [49,50], olfactory bulb [51], cerebellum [52] and neocortex [53], indicate the requirement for SNARE variants in dendritic transmitter release.…”