Previous studies by our laboratory established a rat model of neuropat
hic pain which displayed long-lasting heat hyperalgesia and mechanical
allodynia that are sympathetically maintained. The present study was
undertaken to extend our earlier findings by examining additional beha
vioral signs of ongoing pain and cold allodynia in our animal model an
d testing their sympathetic dependency. Neuropathic surgery was done b
y tightly ligating the L5 and L6 segmental spinal nerves of rats unila
terally. In addition to the behavioral signs of heat hyperalgesia and
mechanical allodynia observed before, these rats displayed signs of on
going pain (lasting at least 10 weeks) and cold allodynia (lasting at
least 16 weeks). These behaviors were reduced markedly after surgical
lumbar sympathectomy. The results of the present study, together with
the previous study, suggest that our animal model exhibits neuropathic
pain behaviors including ongoing pain, heat hyperalgesia, mechanical
allodynia and cold allodynia. Since all of these behavioral signs are
sympathetically maintained, our model represents a model for sympathet
ically maintained pain.