behavioralmousewild-type and prepro-orexin knockout mice
Objective: Measurement of morphine-induced hyperlocomotion in wild-type and prepro-orexin knockout mice to investigate the role of orexinergic systems in dopamine-related behaviors
Materials & Equipment Checklist
7 items
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Equipment3
Not specified • Not specified • Not specified • Not specified
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Protocol Steps
View Abstract
In this study, we investigated the role of orexinergic systems in dopamine-related behaviors induced by the μ-opioid receptor agonist morphine in rodents. Extensive coexpression of tyrosine hydroxylase with orexin receptors was observed in the mouse ventral tegmental area (VTA). The levels of dopamine and its major metabolites in the nucleus accumbens were markedly increased by the microinjection of orexin A and orexin B into the VTA. The subcutaneous morphine-induced place preference and hyperlocomotion observed in wild-type mice were abolished in mice that lacked the prepro-orexin gene. An intra-VTA injection of a selective orexin receptor antagonist SB334867A [1-(2-methylbenzoxazol-6-yl)-3-[1.5]naphthyridin-4-yl urea] significantly suppressed the morphine-induced place preference in rats. Furthermore, the increased level of dialysate dopamine produced by morphine in the mouse brain was significantly decreased by deletion of the prepro-orexin gene. These findings provide new evidence that orexin-containing neurons in the VTA are directly implicated in the rewarding effect and hyperlocomotion induced by morphine through activation of the mesolimbic dopamine pathway in rodents.
1
Morphine administration
Subcutaneous injection of morphine to induce hyperlocomotion in wild-type and prepro-orexin knockout mice
Not specifiedNot specified
Note: Administered subcutaneously; hyperlocomotion was observed in wild-type mice but abolished in knockout mice
View evidence from paper
“subcutaneous morphine-induced place preference and hyperlocomotion observed in wild-type mice were abolished in mice that lacked the prepro-orexin gene”
2
Measurement of hyperlocomotion
Measurement of locomotor activity following morphine administration in both wild-type and prepro-orexin knockout mice
Not specifiedNot specified
Note: Hyperlocomotion was the primary behavioral outcome measured
View evidence from paper
“subcutaneous morphine-induced place preference and hyperlocomotion observed in wild-type mice were abolished in mice that lacked the prepro-orexin gene”
3
Microinjection of orexin peptides into VTA
Microinjection of orexin A and orexin B into the ventral tegmental area to measure effects on dopamine levels
Not specifiedNot specified
Note: Orexin A and B were microinjected to assess their effects on dopamine and metabolite levels
View evidence from paper
“levels of dopamine and its major metabolites in the nucleus accumbens were markedly increased by the microinjection of orexin A and orexin B into the VTA”
4
Measurement of dopamine and metabolites
Measurement of dopamine and its major metabolites in the nucleus accumbens following orexin microinjection
Not specifiedNot specified
Note: Dopamine levels were markedly increased following orexin A and B microinjection
View evidence from paper
“levels of dopamine and its major metabolites in the nucleus accumbens were markedly increased by the microinjection of orexin A and orexin B into the VTA”
5
Intra-VTA injection of orexin receptor antagonist
Intra-VTA injection of selective orexin receptor antagonist SB334867A to suppress morphine-induced place preference in rats
Not specifiedNot specified
Note: SB334867A significantly suppressed morphine-induced place preference
View evidence from paper
“intra-VTA injection of a selective orexin receptor antagonist SB334867A [1-(2-methylbenzoxazol-6-yl)-3-[1.5]naphthyridin-4-yl urea] significantly suppressed the morphine-induced place preference in rats”
6
Measurement of dialysate dopamine in morphine-treated mice
Measurement of increased dialysate dopamine levels produced by morphine in wild-type versus prepro-orexin knockout mice
Not specifiedNot specified
Note: Dopamine increase was significantly decreased in prepro-orexin knockout mice compared to wild-type
View evidence from paper
“increased level of dialysate dopamine produced by morphine in the mouse brain was significantly decreased by deletion of the prepro-orexin gene”
Subjects / Specimens
Species
mouse
Strain
wild-type and prepro-orexin knockout mice
Age
Not specified
Sex
unknown
Weight
Not specified
Comparison between wild-type mice and mice that lacked the prepro-orexin gene