Glutamate-like immunoreactivity in ascending spinofugal afferents to the rat periaqueductal grey

Brain Res. 1998 Apr 20;790(1-2):74-81. doi: 10.1016/s0006-8993(98)00050-x.

Abstract

The midbrain periaqueductal gray is a key structure for the mediation of an integrated defence behaviour. Although a prominent role for glutamate in PAG mechanisms is supported by both behavioural and morphological studies, whether PAG afferents conveying somatosensory information constitute a source of glutamatergic input to the PAG remains unknown. Here, we have compared the projection pattern of orthogradely-labelled spinoannular fibres with the distribution of glutamate-like immunoreactivity in the PAG at the light microscopic level. Transaxonal labelling was observed throughout the whole rostrocaudal axis of the PAG except for the dorsolateral regions. Cell-processes and terminal-reminiscent puncta were strongly immunoreactive in all PAG regions, including the dorsolateral areas. To ascertain whether glutamate-immunoreactive puncta observed at light microscopy indeed constituted axon terminals of the spinoannular system, glutamate-like immunoreactivity was assessed in orthogradely-labelled synaptic terminals using a post-embedding immunogold procedure for electron microscopy. Quantitative analysis of gold particle densities revealed over twice as strong an immunoreactivity in anatomically-identified spinoannular axon terminals as in dendrites postsynaptic to them, perikarya and inhibitory Gray II synapses, as well as an over 5-fold heavier immunolabelling than in glial profiles. These findings reveal that glutamate is accumulated in synaptic terminals of the spinoannular system, supporting a neurotransmitter role for this acidic amino acid in spinofugal afferents to the PAG.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibodies, Monoclonal
  • Dendrites / chemistry
  • Dendrites / ultrastructure
  • Glutamic Acid / analysis*
  • Glutamic Acid / immunology
  • Male
  • Mice
  • Microscopy, Immunoelectron / methods
  • Neurons, Afferent / chemistry*
  • Neurons, Afferent / ultrastructure
  • Periaqueductal Gray / cytology*
  • Presynaptic Terminals / chemistry
  • Presynaptic Terminals / ultrastructure
  • Rats
  • Rats, Sprague-Dawley
  • Spinal Cord / chemistry
  • Spinal Cord / cytology*
  • Tissue Embedding / methods

Substances

  • Antibodies, Monoclonal
  • Glutamic Acid