105 research outputs found
Involvement of orexin-1 receptors in the ventral tegmental area and the nucleus accumbens in antinociception induced by lateral hypothalamus stimulation in rats
Previous studies have demonstrated that chemical stimulation of the lateral hypothalamus (LH) with
carbachol has an important role in the induction of antinociception in tail-flick test as a model of acute
pain. In this study, we tried to evaluate the involvement of orexin-1 receptors in the ventral tegmental
area (VTA) and the nucleus accumbens (NAc) on antinociceptive responses induced by LH stimulation in
rats. One hundred twenty adult male albino Wistar rats weighing 200–250 g were unilaterally implanted
with two separate cannulae into the LH, and VTA or NAc. Antinociceptive effects for two doses of intra-LH
carbachol (125 and 250 nmol/0.5 μl saline), as a cholinergic agonist, were evaluated in this study. In another
set of experiments, animals received intra-VTA or -NAc infusions of SB334867 as a selective orexin-A receptor
antagonist (0.3, 1, 3 and 10 nmol/rat), just 5 min before microinjection of an effective dose of carbachol into
the LH. In the tail-flick test, antinociceptive responses of drugs were obtained by tail-flick analgesiometer and
represented as maximal possible effects (%MPE) at 5, 15, 30, 45 and 60 min after their administrations.
The results showed that unilateral intra-LH administration of carbachol (125 and 250 nmol/rat) induced
antinociception in rats (P b 0.01). There were no significant differences between the antinociceptive effects of
these two doses. In the second part of our study, intra-VTA and intra-accumbal administrations of different
doses of SB334867, 5 min before microinjection of carbachol, could dose-dependently prevent the development
of LH stimulation-induced antinociception in rats. However, this effectwas less in the NAc. It is supposed that the
orexinergic projections from the LH to the VTA and NAc are direct/indirectly involved in the antinociception
induced by LH chemical stimulation, and orexin-1 receptors in the ventral tegmental area have amore substantial
role in this phenomenon
The Effect of Food Deprivation on Nociception in Formalin Test and Plasma Levels of Noradrenaline and Corticosterone in Rats
Introduction: The concentration of noradrenalin and corticosterone as the two nociception
modulators change after fasting or stress situation. The aim of present study was to investigate
the effect of food deprivation on formalin-induced nociceptive behaviours and plasma levels
of noradrenalin and corticosterone in rats.
Methods: Food was withdrawn 12, 24 and 48 h prior to performing the formalin test, but
water continued to be available ad libitum. The formalin solution (50 μL, 2%) was injected
into plantar surface of hind paw. The nociception responses of the animals during the first
phase (1-7 minutes), the inter-phase (8-14), the phase 2A (15-60) and the phase 2B (61-90)
was separately evaluated. The plasma concentrations of noradrenalin and corticosterone were
measured using specific ELISA and IRA kits, according to manufacturer's instructions.
Results: In contrast to the increasing of 48 h food deprived animals during phase 2, the
nociceptive behaviours of 12 and 24 h groups decreased through the interphase, phase 2A
and phase 2B. The injection of formalin in the normal male rats significantly decreased the
plasma level of noradrenalin and corticosterone. Food deprivation for 12 and 24 h increased
noradrenalin level significantly in comparison with control group which has caused by fasting
induced antinociceptive behaviours. There was no significant change in food deprivation for 48
h group. Food deprivation for 12, 24 and 48 h had no effect on corticosterone level in male rats.
Discussion: The present study emphasizes that the acute food deprivation diminished the
nociceptive behaviours in the formalin test and show a correlation with increase in plasma
noradrenalin level
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