Physiology and Pharmacology
Physiol Pharmacol
Medical Sciences
http://ppj.phypha.ir
32
journal32
24765236
24765244
10.61186/phypha
(previous ISSN: 17350581)
en
jalali
1387
8
1
gregorian
2008
11
1
12
3
online
1
fulltext
en
Comparing the analgesic effects of periaqueductal gray matter injection of orexin A and morphine on formalin- induced nociceptive behaviors.
Pain and addiction
Neurophysiology/Pharmacology
Experimental research article
Experimental research article
Introduction: Orexin-A and B (Hypocretin 1 and 2) are neuropeptides that are mostly expressed in the posterior
and lateral hypothalamus (LH). Intracisternal (ICV) and intratechal (IT) injections of orexin-A (hypocretin-1) have been
shown to elicit analgesic responses in formalin test. However, the locations of central sites that may mediate these
effects have not been clearly elucidated. Orexin-containing fibers are projected to periaqueductal gray matter (PAG),
which is involved in pain modulation.
Methods: Behavioral study was done on male Sprague Dawley rats (200-300 g) in formalin induced nociceptive
behaviour.
Results: Intra-PAG microinjection of orexin-A produced a dose-dependent inhibition of formalin-evoked behaviour
in interphase and phase 2, but not in phase 1, indicating an antinociceptive role of exogenous orexin-A in the PAG.
Analgesic effect of orexin-A was less than and specific to inter- and late phase of formalin test, when compared with
that of morphine (5 μg/0.5μl) after intra-PAG administration.
Conclusion: The obtained results suggest that orexin-A plays an anti-nociceptive role in PAG, on the interphase and
late phase of formalin test in rats. So it is possible that orexin-A might be involved in the mechanisms of inter- and last
phases of formalin induced behaviours.
orexin-A, analgesic, periaqueductal gray matter, formalin test, morphine
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193
http://ppj.phypha.ir/browse.php?a_code=A-10-192-7&slc_lang=en&sid=1
Hassan
azhdari Zarmehri
azhdariz@yahoo.com
320031947532846004623
320031947532846004623
No
Saead
Semnanian
ssmnan@modares.ac.ir
320031947532846004624
320031947532846004624
Yes
Yaghoub
Fathollahi
320031947532846004625
320031947532846004625
No