Vesicular glutamate transporters type 1 and 2 expression in axon terminals of the rat nucleus of the solitary tract

doi:10.1016/j.neuroscience.2005.08.048

Neuroscience

Volume 137, Issue 1, 2006, Pages 73-81

https://doi.org/10.1016/j.neuroscience.2005.08.048 Get rights and content

Abstract

The nucleus of the solitary tract is the site of termination of primary afferent fibers running in the facial, glossopharyngeal and vagus nerves. The present study was performed to map the distribution of glutamatergic axons terminals in the rat nucleus of the solitary tract using immunodetection of vesicular glutamate transporter 1 and vesicular glutamate transporter 2. The two vesicular glutamate transporters were differentially distributed among nucleus of the solitary tract subdivisions. Vesicular glutamate transporter 1 immunoreactivity was mostly found in the lateral part of the nucleus (ventrolateral, interstitial and intermediate subdivisions) whereas vesicular glutamate transporter 2 labeling was distributed throughout the nucleus of the solitary tract. Electron microscope examination indicated that vesicular glutamate transporter immunoreactivity was localized in axon terminals filled with round synaptic vesicles. After injection of cholera toxin B subunit in sensory ganglia, anterograde labeling was found in vesicular glutamate transporter 1, as well as vesicular glutamate transporter 2-immunoreactive boutons. Double immunolabeling experiments allowed distinctions between terminals expressing either vesicular glutamate transporter 1 or vesicular glutamate transporter 2 or both vesicular glutamate transporter 1 and vesicular glutamate transporter 2 immunoreactivities. The latter population, expressing both transporters immunolabeling, completely disappeared after deafferentation induced by removal of sensory ganglia.

This study indicates that vesicular glutamate transporter content identifies three different subpopulations of glutamatergic boutons in the nucleus of the solitary tract and provides definitive evidence that primary afferent neurons contribute glutamatergic terminals to the nucleus of the solitary tract.

Section snippets

Animals and tissue preparation

Experiments were performed on 10 adult Wistar rats weighing 180–200g. All procedures were in accordance with the European Communities Council directive (86/609/EEC) for the care and use of laboratory animals. All efforts were made to minimize the number of animals used and their suffering.

Animals were anesthetized with a mixture of ketamine (50mg/kg) and xylazine (15mg/kg) and perfused through the ascending aorta with 300ml of cold 4% paraformaldehyde in phosphate buffer (PB, 0.1 M, pH 7.4).

Regional distribution of VGLUT1 and VGLUT2 in the NTS and adjacent nuclei

The regional distributions of VGLUT1 and VGLUT2 immunolabeling found in the present study (Fig. 1A, C) were in agreement with the detailed description by Lin et al. (2004). Briefly, VGLUT1 immunoreactivity was mostly found at caudal and subpostremal levels in the lateral half of the NTS, i.e. in the intermediate, interstitial, dorsolateral and ventrolateral subnuclei (Fig. 1A). VGLUT2 immunolabeling was present throughout the NTS (Fig. 1C). Fiber bundles of the solitary tract were devoid of

Discussion

In this paper, we demonstrate that VGLUTs are present in primary afferent terminals anterogradely labeled by CTB injection into sensory ganglia. In addition, we show that VGLUTs immunolabeling identifies at least three subpopulations of glutamatergic terminals in the NTS.

Note added in proof

While this paper was in press, a study addressing similar issues was published by Corbett et al. (Differential expression of vesicular glutamate transporters by vagal afferent terminals in rat nucleus of the solitary tract: Projections from the heart preferentially express vesicular glutamate transporter 1. Neuroscience 135:133–145).

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Nodosectomy, which removes the vagal afferent cell bodies, results in a 40% reduction in the high-affinity uptake of glutamate in the medial NTS of rats [14]. Furthermore, immunohistochemical data suggests that both types of vesicular glutamate transporter, VGLUT1 and VGLUT2, required for packaging cytoplasmic glutamate into vesicles, are present in vagal fibers and terminals in the NTS since they are significantly reduced following nodose ganglionectomy [15]. Interestingly, vagal afferents fibers retrogradely labeled from the stomach are predominantly VGLUT2 positive, while fibers retrogradely labeled from the heart are VGLUT1 positive [16].
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¹: Present address: Biology Department, Pennsylvania State University, 419 Mueller Laboratory, University Park, PA 16802, USA.

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Cellular neuroscienceVesicular glutamate transporters type 1 and 2 expression in axon terminals of the rat nucleus of the solitary tract

Abstract

Section snippets

Animals and tissue preparation

Regional distribution of VGLUT1 and VGLUT2 in the NTS and adjacent nuclei

Discussion

Note added in proof

Neuroscience

Brain Res

J Auton Nerv Syst

Neuron

Trends Neurosci

Neuroscience

Brain Res Mol Brain Res

Prog Neurobiol

Neuroscience

Brain Res

J Biol Chem

Brain Res

Brain Res

Neuroscience

Viscerotopic representation of the upper alimentary tract in the ratsensory ganglia and nuclei of the solitary and spinal trigeminal tracts

J Comp Neurol

Vesicular glutamate transporters in the spinal cord, with special reference to sensory primary afferent synapses

J Comp Neurol

Sensory afferent neurotransmission in caudal nucleus tractus solitarius common denominators

Chem Senses

Uptake of glutamate into synaptic vesicles by an inorganic phosphate transporter

Science

The lower brainstem and bodily homeostasis

Ultrastructural organization of the interstitial subnucleus of the nucleus of the tractus solitarius in the catidentification of vagal afferents

J Neurocytol

Cellular neuroscience
Vesicular glutamate transporters type 1 and 2 expression in axon terminals of the rat nucleus of the solitary tract