Heterogeneous expression of SNAP-25 in rat and human brain.
Synaptosomal associated protein of 25 kDa (SNAP-25) is a SNARE component of the exocytotic apparatus involved in the release of neurotransmitter. We used multiple-labeling immunofluorescence, confocal microscopy, and ultrastructural immunocytochemistry to examine the expression of SNAP-25 in excitatory and inhibitory terminals from different rat and human brain areas. Glutamatergic and GABAergic terminals were identified by staining for the vesicular glutamate transporter (vGLUT1), glutamic acid decarboxylase (GAD67), or the vesicular GABA transporter (vGAT). In all examined areas GABAergic terminals did not display detectable levels of SNAP-25, whereas glutamatergic terminals expressed the protein to a variable extent. Codistribution analysis revealed a high colocalization between pixels detecting SNAP-25 labeling and pixels detecting vGLUT1 immunoreactivity. On the contrary, a low degree of pixel colocalization, comparable to that between two unrelated antigens, was detected between SNAP-25 and vGAT, thus suggesting a random overlap of immunofluorescence signals. Our immunofluorescence evidence was supported by ultrastructural data, which clearly confirmed that SNAP-25 was undetectable in GABAergic terminals identified by both their typical morphology and specific staining for GABA. Interestingly, our ultrastructural results confirmed that a subset of glutamatergic synapses do not contain detectable levels of SNAP-25. The present study extends our previous findings obtained in rodent hippocampus and provides evidence that SNAP-25 expression is highly variable between different axon terminals both in rat and human brain. The heterogeneous distribution of SNAP-25 may have important implications not only in relation to the function of the protein as a SNARE but also in the control of network excitability.
Clinical Epileptology and Experimental Neurophysiology Unit, Fondazione IRCCS, Istituto Neurologico C Besta, via Celoria 11, Milano, Italy.
Rita
R
Garbelli
Francesca
F
Inverardi
Valentina
V
Medici
Alida
A
Amadeo
Claudia
C
Verderio
Michela
M
Matteoli
Carolina
C
Frassoni
D000818:Animals; D000906:Antibodies / Q000737:chemistry; D015153:Blotting, Western; D001923:Brain Chemistry / Q000235:genetics*; D002118:Calcium / Q000502:physiology; D019084:Fluorescent Antibody Technique, Indirect; D018698:Glutamic Acid / Q000502:physiology; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007150:Immunohistochemistry; D051379:Mice; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D017729:Presynaptic Terminals / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D050825:Synaptosomal-Associated Protein 25 / Q000096:biosynthesis* / Q000235:genetics; D016610:Tissue Embedding
D000906:Antibodies; C494208:SNAP25 protein, human; C494209:Snap25 protein, mouse; D050825:Synaptosomal-Associated Protein 25; D018698:Glutamic Acid; D002118:Calcium