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Dose-dependent antinociceptive response of morphine microinjected into the nucleus cuneiformis andeffect of inactivation of this area on pain modulation in rat
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A. حق پرست   , G. R. سپهری , M. N. شافعی |
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Abstract: (16395 Views) |
| Introduction: The cuneifo rmis nu cle us (CnF) is o ne of th e re t icu lar fo rmation e nti ties
which rests in midbrain region. Th is nucle us co nt ro ls pain indi rec tly thro ugh its binding with
rostr al ve ntromedi al medulla (RVM). From previous res ea rches, it's been pr oved th at th is
nucleus has ult rastructural similarities and bidir ec tio nal connections with pe riaq ueductal gray
(PAG) matt er. In present study, in according to these similarities and connections, we tried to
know the antinociceptive response of morphine microinjected into the nucleus cuneiformis and
effect of inactivation of this area on pain modulation.
Materials and Methods: Rats were pl aced in ste reotaxic instrument, with a hole being
drilled over cerebellum on skull and a guide cannula was forced down just 1 mm above the CnF.
Followin g surgery and re cove ry period, vario us doses of morphine ( 10, 20 and 40 }Lg/0.5}Ll
saline) and lidocaine 5% (0.5 }Ll) were microinjected into the CnF. Tail Flick Latency (TFL) and
Maximal Possible Effect (%MPE) were measu red 30 min in 5-min interva ls, before and afte r any
injection as an index for nociceptive responses. Naloxone was injec ted intravenously to exactly
pinpoint morphine action as a non -selective antago nist.
Results: Morphine increased TFL in a dose dependent manner. Also inactivation of CnF by
lidocaine inc reased TFL. Simultaneously micro injection of morphine and lidoc ai ne inc reased
TFL which was le ss th an morph ine effect (%MPE) alone. While inje ct in g mo rphine
intravenouslywith lidocain e microinjection increased significa ntly TFL bu t th ese effects were
reversed by naloxone administration.
Conclusion: It is clear that CnF has opioid receptors, specially }L receptor, that follow in a
dose dep endent manner. On th e ot her han d, we suggest th at CnF inactivation with lidocaine
inhib its a n inhibitory o utput tha t pr oject s to RVM specially off-cells in t his area and th is
disinhibition causes pain modulation. |
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| Keywords: Nucleus Cuneiformis, Morphine, Lidocaine, Tail flick test, Pain modulation, Rat |
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Full-Text [PDF 1958 kb]
(2113 Downloads)
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Type of Study: Research |
Subject:
medical education
Received: 2008/11/29 | Published: 2003/02/15
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