Expression of exocytosis proteins in rat supraoptic nucleus neurones

J Neuroendocrinol. 2012 Apr;24(4):629-41. doi: 10.1111/j.1365-2826.2011.02237.x.


In magnocellular neurones of the supraoptic nucleus (SON), the neuropeptides vasopressin and oxytocin are synthesised and packaged into large dense-cored vesicles (LDCVs). These vesicles undergo regulated exocytosis from nerve terminals in the posterior pituitary gland and from somata/dendrites in the SON. Regulated exocytosis of LDCVs is considered to involve the soluble N-ethylmaleimide sensitive fusion protein attachment protein receptor (SNARE) complex [comprising vesicle associated membrane protein 2 (VAMP-2), syntaxin-1 and soluble N-ethylmaleimide attachment protein-25 (SNAP-25)] and regulatory proteins [such as synaptotagmin-1, munc-18 and Ca(2+) -dependent activator protein for secretion (CAPS-1)]. Using fluorescent immunocytochemistry and confocal microscopy, in both oxytocin and vasopressin neurones, we observed VAMP-2, SNAP-25 and syntaxin-1-immunoreactivity in axon terminals. The somata and dendrites contained syntaxin-1 and other regulatory exocytosis proteins, including munc-18 and CAPS-1. However, the distribution of VAMP-2 and synaptotagmin-1 in the SON was limited to putative pre-synaptic contacts because they co-localised with synaptophysin (synaptic vesicle marker) and had no co-localisation with either oxytocin or vasopressin. SNAP-25 immunoreactivity in the SON was limited to glial cell processes and was not detected in oxytocin or vasopressin somata/dendrites. The present results indicate differences in the expression and localisation of exocytosis proteins between the axon terminals and somata/dendritic compartment. The absence of VAMP-2 and SNAP-25 immunoreactivity from the somata/dendrites suggests that there might be different SNARE protein isoforms expressed in these compartments. Alternatively, exocytosis of LDCVs from somata/dendrites may use a different mechanism from that described by the SNARE complex theory.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Exocytosis / physiology*
  • Female
  • Gene Expression / physiology
  • Immunohistochemistry / methods
  • In Vitro Techniques
  • Neuroglia / metabolism
  • Neurons / cytology
  • Neurons / metabolism
  • Oxytocin / physiology
  • Pituitary Gland, Posterior / cytology
  • Pituitary Gland, Posterior / metabolism*
  • Rats
  • Rats, Sprague-Dawley
  • SNARE Proteins / metabolism*
  • Secretory Vesicles / metabolism
  • Supraoptic Nucleus / cytology
  • Supraoptic Nucleus / metabolism*
  • Vasopressins / physiology


  • SNARE Proteins
  • Vasopressins
  • Oxytocin