Vesicular glutamate transporter‐1 colocalizes with endogenous opioid peptides in axon terminals of the rat locus coeruleus

Abstract

We have previously shown that a subset of axon terminals in the locus coeruleus (LC) containing methionine 5 -enkephalin (ENK) forms type I (asymmetric-type) synaptic specializations that are characteristic of excitatory-type transmitters. In addition, we previously provided ultrastructural evidence showing that ENK is colocalized with glutamate using a combination of preand postembedding immunohistochemistry. To examine cellular substrates for interactions between glutamate and other endogenous opioid peptides in the LC, we examined the localization of the vesicular glutamate transporter 1 (VGLUT1), a transporter protein involved in the accumulation of the transmitter glutamate into synaptic vesicles, with either ENK or preprodynorphin (ppDYN). Dual-immunofluorescence and electron microscopy showed prominent coexistence of VGLUT1 and ENK in varicose processes of the LC, confirming our previous report using postembedding immunolabeling for glutamate. Likewise, VGLUT1 and ppDYN were identified in common varicose processes in the LC using confocal fluorescence microscopy. Immunoelectron microscopy using gold-silver labeling for VGLUT1 and peroxidase labeling for ppDYN established that this endogenous opioid peptide also colocalizes with glutamate transporters. The majority of these formed asymmetric-type synapses. Taken together, these results demonstrate that excitatory LC afferents are enriched with endogenous opioid peptides and are positioned to modulate LC neuronal activity dually. © 2005 Wiley-Liss, Inc. Key words: norepinephrine; excitatory amino acid; dynorphin; encephalin; glutamateThe nucleus locus coeruleus (LC), located on the floor of the fourth ventricle in the rostral pons, provides extensive noradrenergic projections throughout the neuraxis. The collection and processing of salient sensory information having effects on memory, attention and arousal, cardiovascular regulation, antinociception, regulation of anxiety states and stress response have been associated with these neurons (Berridge and Waterhouse, 2003). The LC receives a major glutamatergic input from the medullary nucleus paragigantocellularis (PGi) (Ennis and AstonJones, 1988; Aston-Jones et al., 1991). These afferents also express endogenous opioid peptides, including methionine 5 -enkephalin (ENK) (Drolet et al., 1992).Modulation of postsynaptic glutamate receptors activates LC neurons (Oleskevich et al., 1993;Van Bockstaele et al., 2000), while the activity of LC neurons is inhibited by opioid peptides via activation of an inward rectifying

Molecular and Cellular Diversity of Neuronal G-Protein-Gated Potassium Channels

“…tamatergic neurons (Li et al, 2003;Todd et al, 2003;Alvarez et al, 2004;Barr and Van Bockstaele, 2005). The subcellular distribution and expression level of GIRK2 seen in sections from GIRK1 KO and GIRK3 KO mice were indistinguishable from those seen in WT sections (data not shown).…”

Notch-Rbpj signaling is required for the development of noradrenergic neurons in mouse locus coeruleus

“…S2). These findings were further confirmed by examining the expression of L-amino acid decarboxylase (L-AADC) (Eaton et al, 1993), monoamine oxidase type A (MaoA) (Arai et al, 1997), calcitonin gene related protein (CGRP) (Holm et al, 2003;Ma et al, 2003), vesicular glutamate transporter 1 (vGluT1) (Barr and Van Bockstaele, 2005), brainderived neurotrophic factor (BDNF) (Holm et al, 2003) and c-Ret (Holm et al, 2002) at E17.5 or P0 (supplementary material Fig. S2).…”

Dynorphin-containing axons directly innervate noradrenergic neurons in the rat nucleus locus coeruleus

“…Interestingly, our laboratory described the presence of vesicular glutamate transporters (V-Glut) in DYN afferents to the LC (Barr and Van Bockstaele, 2005). However, this study did not examine synaptic contacts formed by DYN afferents with noradrenergic somatodendritic processes.…”

“…Asymmetric synapses have been correlated with excitatory transmission whereas symmetric synapses have been correlated with inhibitory transmission (Gray, 1959,Peters et al, 1991,Peters and Palay, 1996. We have recently shown that V-Glut-1-labeled terminals also contain DYN in LC and the majority of these terminals form asymmetric synapses with unidentified dendrites (Barr and Van Bockstaele, 2005). Hence, DYN is likely a co-transmitter in glutamatergic axons that to some extent directly synapses on catecholaminergic neurons in the LC.…”