Distribution of VGLUT3 in highly collateralized axons from the rat dorsal raphe nucleus as revealed by single-neuron reconstructions

PLoS One. 2014 Feb 4;9(2):e87709. doi: 10.1371/journal.pone.0087709. eCollection 2014.

Abstract

This study aimed at providing the first detailed morphological description, at the single-cell level, of the rat dorsal raphe nucleus neurons, including the distribution of the VGLUT3 protein within their axons. Electrophysiological guidance procedures were used to label dorsal raphe nucleus neurons with biotinylated dextran amine. The somatodendritic and axonal arborization domains of labeled neurons were reconstructed entirely from serial sagittal sections using a computerized image analysis system. Under anaesthesia, dorsal raphe nucleus neurons display highly regular (1.72 ± 0.50 Hz) spontaneous firing patterns. They have a medium size cell body (9.8 ± 1.7 µm) with 2-4 primary dendrites mainly oriented anteroposteriorly. The ascending axons of dorsal raphe nucleus are all highly collateralized and widely distributed (total axonal length up to 18.7 cm), so that they can contact, in various combinations, forebrain structures as diverse as the striatum, the prefrontal cortex and the amygdala. Their morphological features and VGLUT3 content vary significantly according to their target sites. For example, high-resolution confocal analysis of the distribution of VGLUT3 within individually labeled-axons reveals that serotonin axon varicosities displaying VGLUT3 are larger (0.74 ± 0.03 µm) than those devoid of this protein (0.55 ± 0.03 µm). Furthermore, the percentage of axon varicosities that contain VGLUT3 is higher in the striatum (93%) than in the motor cortex (75%), suggesting that a complex trafficking mechanism of the VGLUT3 protein is at play within highly collateralized axons of the dorsal raphe nucleus neurons. Our results provide the first direct evidence that the dorsal raphe nucleus ascending projections are composed of widely distributed neuronal systems, whose capacity to co-release serotonin and glutamate varies from one forebrain locus to the other.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amygdala / metabolism
  • Animals
  • Axons / metabolism*
  • Corpus Striatum / metabolism
  • Diencephalon / metabolism
  • Dorsal Raphe Nucleus / metabolism*
  • Male
  • Neurites / metabolism
  • Neurons / cytology
  • Neurons / metabolism*
  • Prefrontal Cortex / metabolism
  • Protein Transport
  • RNA-Binding Proteins / metabolism
  • Rats
  • Serotonin / metabolism
  • Vesicular Glutamate Transport Proteins / metabolism*
  • Vesicular Monoamine Transport Proteins / metabolism

Substances

  • RNA-Binding Proteins
  • Sert1 protein, rat
  • Slc17a8 protein, rat
  • Slc18a2 protein, rat
  • Vesicular Glutamate Transport Proteins
  • Vesicular Monoamine Transport Proteins
  • Serotonin

Grant support

This research was supported by grant from the Natural Sciences and Engineering Research Council of Canada (#386396-2010, www.nserc-crsng.gc.ca). DG was the recipient of a PhD fellowship from the “Centre Thématique de Recherche en Neurosciences.” The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.