title: Chronic stress enhances calcium mobilization and glutamate exocytosis in cerebrocortical synaptosomes from mice.
abstract: OBJECTIVE
  Our previous study showed that acute restraint stress enhances depolarization-induced increases in intrasynaptosomal free calcium (Ca(2+)) concentration ([Ca(2+)](i)) and Ca(2+)-dependent glutamate release in  mouse cerebrocortical nerve terminals (synaptosomes). In the present study, we investigated the effects of chronic stress on [Ca(2+)](i) and glutamate release in cerebrocortical synaptosomes from mice.
  
  
  METHODS
  Male ddY strain mice were randomly assigned  to one of two experimental groups: control group and chronic stressed group. Mice in the chronic stressed group were subjected to immobilization stress for 2 hours daily for a period of 21 days. [Ca(2+)](i) and glutamate release in cerebrocortical synaptosomes isolated from  the mice were determined by fura-2 fluorescence assay and enzyme-linked fluorometric assay, respectively.
  
  
  RESULTS
  Chronic stress caused a significant increase in resting [Ca(2+)](i) and significantly enhanced the ability of the depolarizing agents K(+)  and 4-aminopyridine (4-AP) to increase [Ca(2+)](i). It also brought about a significant increase in spontaneous (unstimulated) glutamate release and significantly enhanced K(+)- and 4-AP-evoked Ca(2+)-dependent glutamate release. Synaptosomes were more sensitive  to the depolarizing agents at lower concentrations following chronic stress than after acute stress. The pretreatment of synaptosomes with a combination of omega-agatoxin IVA (a P-type Ca(2+) channel blocker) and omega-conotoxin GVIA (an N-type Ca(2+) channel blocker) completely  suppressed the enhancements of [Ca(2+)](i) and Ca(2+)-dependent glutamate release in chronic stressed mice.
  
  
  CONCLUSIONS
  These results indicate that chronic stress enhances depolarization-evoked glutamate release by increasing [Ca(2+)](i)  via stimulation of Ca(2+) entry through P- and N-type Ca(2+) channels, and that chronic stress increases the sensitivity to depolarizing agents.
authors.affiliation: Research Center for Animal Hygiene and Food Safety, Obihiro University of Agriculture and Veterinary Medicine, Japan. es@obihiro.ac.jp
authors.forename: Eiki
authors.initials: E
authors.lastname: Satoh
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Tada
authors.forename: Fumikazu
authors.initials: F
authors.lastname: Matsuhisa
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002540:Cerebral Cortex / Q000378:metabolism*; D005089:Exocytosis / Q000502:physiology; D018698:Glutamic Acid / Q000378:metabolism*; D007103:Immobilization; D008297:Male; D051379:Mice; D013315:Stress, Psychological / Q000378:metabolism*; D013574:Synaptosomes / Q000378:metabolism*
chemical_list: D018698:Glutamic Acid; D002118:Calcium