Depletion of calcium stores in injured sensory neurons: anatomic and functional correlates.
BACKGROUND
Painful nerve injury leads to disrupted Ca signaling in primary sensory neurons, including decreased endoplasmic reticulum (ER) Ca storage. This study examines potential causes and functional consequences of Ca store limitation after injury.


METHODS
Neurons were dissociated from axotomized fifth lumbar (L5) and the adjacent L4 dorsal root ganglia after L5 spinal nerve ligation that produced hyperalgesia, and they were compared to neurons from control animals. Intracellular Ca levels were measured with Fura-2 microfluorometry, and ER was labeled with probes or antibodies. Ultrastructural morphology was analyzed by electron microscopy of nondissociated dorsal root ganglia, and intracellular electrophysiological recordings were obtained from intact ganglia.


RESULTS
Live neuron staining with BODIPY FL-X thapsigargin (Invitrogen, Carlsbad, CA) revealed a 40% decrease in sarco-endoplasmic reticulum Ca-ATPase binding in axotomized L5 neurons and a 34% decrease in L4 neurons. Immunocytochemical labeling for the ER Ca-binding protein calreticulin was unaffected by injury. Total length of ER profiles in electron micrographs was reduced by 53% in small axotomized L5 neurons, but it was increased in L4 neurons. Cisternal stacks of ER and aggregation of ribosomes occurred less frequently in axotomized neurons. Ca-induced Ca release, examined by microfluorometry with dantrolene, was eliminated in axotomized neurons. Pharmacologic blockade of Ca-induced Ca release with dantrolene produced hyperexcitability in control neurons, confirming its functional importance.


CONCLUSIONS
After axotomy, ER Ca stores are reduced by anatomic loss and possibly diminished sarco-endoplasmic reticulum Ca-ATPase. The resulting disruption of Ca-induced Ca release and protein synthesis may contribute to the generation of neuropathic pain.
Gemes
Geza
G
Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA.
Rigaud
Marcel
M
Weyker
Paul D
PD
Abram
Stephen E
SE
Weihrauch
Dorothee
D
Poroli
Mark
M
Zoga
Vasiliki
V
Hogan
Quinn H
QH
D000818:Animals; D001896:Boron Compounds; D064032:Calbindin 2; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D003620:Dantrolene / Q000494:pharmacology; D004594:Electrophysiology; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D005456:Fluorescent Dyes; D006930:Hyperalgesia / Q000473:pathology; D007150:Immunohistochemistry; D008026:Ligation; D008297:Male; D008854:Microscopy, Electron; D010147:Pain Measurement / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D064030:S100 Calcium Binding Protein G / Q000378:metabolism; D011984:Sensory Receptor Cells / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D013127:Spinal Nerves / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure
C095489:4,4-difluoro-4-bora-3a,4a-diaza-s-indacene; D001896:Boron Compounds; D064032:Calbindin 2; D005456:Fluorescent Dyes; D064030:S100 Calcium Binding Protein G; D003620:Dantrolene; D002118:Calcium