Thapsigargin-induced mobilization of dendritic dense-cored vesicles in rat supraoptic neurons.
Dense-cored vesicles (DCVs) containing oxytocin or vasopressin are secreted from both the nerve terminals in the posterior pituitary and dendrites in the hypothalamus of magnocellular supraoptic neurons. Dendritic secretion can be enhanced (primed) by pretreatment with either thapsigargin or oxytocin for subsequent activity-dependent release. Here, we determined whether priming involves a translocation of DCV closer to the dendritic membrane. To reduce total vesicle content, rats were salt-loaded for 24 h before application of thapsigargin or vehicle onto the ventrally exposed surface of the supraoptic nucleus in vivo. Tissues were then prepared for quantitative electron microscopic analysis of the total incidence of DCVs within supraoptic dendritic cross-sections, and of the incidence and distance (within a 500-nm margin) of each DCV to the dendritic plasma membrane. Salt loading per se did not alter the frequency distribution or average proportion of DCVs found in the 500-nm margin but significantly decreased the average incidence of DCVs per dendrite by 30% (P < 0.05). However, thapsigargin treatment resulted in a significant increase in the total incidence of DCVs within the 500-nm margins and a higher incidence of DCVs within the first 200 nm of the plasma membrane (P < 0.05), indicating that the thapsigargin-induced priming involves a relocation of DCVs closer to sites of secretion.
Tobin
Vicky A
VA
Division of Biomedical Sciences, University of Edinburgh Medical School, George Square, Edinburgh EH8 9XD, UK.
Hurst
Gillian
G
Norrie
Linda
L
Dal Rio
Francesco P
FP
Bull
Philip M
PM
Ludwig
Mike
M
D000818:Animals; D001522:Behavior, Animal; D003712:Dendrites / Q000187:drug effects* / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D008854:Microscopy, Electron / Q000379:methods; D009474:Neurons / Q000166:cytology / Q000187:drug effects* / Q000648:ultrastructure; D051381:Rats; D017207:Rats, Sprague-Dawley; D022142:Secretory Vesicles / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D017673:Sodium Chloride, Dietary / Q000494:pharmacology; D013495:Supraoptic Nucleus / Q000166:cytology* / Q000187:drug effects; D019284:Thapsigargin / Q000494:pharmacology*
D004791:Enzyme Inhibitors; D017673:Sodium Chloride, Dietary; D019284:Thapsigargin