title: Glutamate-like immunoreactivity in ascending spinofugal afferents to the rat periaqueductal grey.
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.
authors.affiliation: Department of Neurosciences, School of Medicine and Dentistry, University of the Basque Country, PO Box 699, E-48080 Bilbao, Spain. onbazbaj@lg.ehu.es
authors.forename: J J
authors.initials: JJ
authors.lastname: Azkue
authors.forename: J M
authors.initials: JM
authors.lastname: Mateos
authors.forename: I
authors.initials: I
authors.lastname: Elezgarai
authors.forename: R
authors.initials: R
authors.lastname: Benítez
authors.forename: E
authors.initials: E
authors.lastname: Lázaro
authors.forename: P
authors.initials: P
authors.lastname: Streit
authors.forename: P
authors.initials: P
authors.lastname: Grandes
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal; D003712:Dendrites / Q000737:chemistry / Q000648:ultrastructure; D018698:Glutamic Acid / Q000032:analysis* / Q000276:immunology; D008297:Male; D051379:Mice; D016253:Microscopy, Immunoelectron / Q000379:methods; D009475:Neurons, Afferent / Q000737:chemistry* / Q000648:ultrastructure; D010487:Periaqueductal Gray / Q000166:cytology*; D017729:Presynaptic Terminals / Q000737:chemistry / Q000648:ultrastructure; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000737:chemistry / Q000166:cytology*; D016610:Tissue Embedding / Q000379:methods
chemical_list: D000911:Antibodies, Monoclonal; D018698:Glutamic Acid