The hippocampal formation plays an essential role in associative learning like passive avoidance (PA) learning. It has been shown; orexin-containing terminals and orexin receptors densely are distributed in the hippocampal formation. We have previously demonstrated that antagonization of orexin 1 receptor (OX1R) in CA1 region of hippocampus and dentate gyrus (DG) impaired spatial memory processing. Although, there are few studies concerning function of orexinergic system on memory processing in PA task, but there is no study about physiological function of OX1R on this process. To address this, the OX1R antagonist, SB-334867-A, was injected into DG or CA1 regions of hippocampus and evaluated the influence of OX1R antagonization on acquisition, consolidation and retrieval in PA task. Our results show that, SB-334867-A administration into CA1 region impaired memory retrieval but not PA acquisition and consolidation. However, SB-334867-A administration into DG region impaired acquisition and consolidation but not PA memory retrieval. Therefore, it seems that endogenous orexins play an important role in learning and memory in the rat through OX1Rs.
"Indeed, initially the pivotal role of orexins in short-term feeding was well documented (Sakurai et al., 1998; Dube et al., 1999; B€ ackeberg et al., 2002; Thorpe and Kotz, 2005; Xu et al., 2013). Other evidence linked orexins to metabolic regulation and thermogenesis (Kukkonen et al., 2002; Monda et al., 2004; Funato et al., 2009; Kukkonen, 2013), stress response (Huang et al., 2010; Gerashchenko et al., 2011; Kukkonen, 2013), circadian rhythms (Deboer et al., 2004; Pekala et al., 2011), the regulation of sleep/wakefulness (Gerashchenko et al., 2001; Inutsuka and Yamanaka, 2013; Mieda et al., 2013; de Lecea and Huertra, 2014), memory processing (Akbari et al., 2008; Selbach et al., 2010), pathogenesis of Alzheimer disease (Kang et al., 2009), and epilepsy (Doreulee et al., 2010). It was also demonstrated that orexins modulate arousal: specifically, rodents treated with orexins spend more time awake (Hagan et al., 1999; Piper et al., 2000), and manifest increased locomotor activity (Alexandre et al., 2013). "
"In our previous study, we have demonstrated that orexin A improves learning, consolidation and retrieval processes . Several other studies provided further evidence about the memory enhancing action of orexin A   and about the role of OX1R in memory   . In contrast, the effect of orexin B on memory processes has not been elucidated. "
[Show abstract][Hide abstract] ABSTRACT: The extensive projection of orexigenic neurons and the diffuse expression of orexin receptors suggest that endogenous orexins are involved in several physiological functions of the central nervous system, including learning and memory. Our previous study demonstrated that orexin A improves learning, consolidation and retrieval processes, which involves α- and β-adrenergic, cholinergic, dopaminergic, GABA-A-ergic, opiate and nitrergic neurotransmissions. However, we have little evidence about the action of orexin B on memory processes and the underlying neuromodulation. Therefore, the aim of the present study was to investigate the action of orexin B on passive avoidance learning and the involvement of neurotransmitters in this action in rats. Accordingly, rats were pretreated withthe selective orexin 2 receptor (OX2R) antagonist, EMPA; the γ-aminobutyric acid subunit A (GABA-A) receptor antagonist, the bicuculline; a D2, D3, D4 dopamine receptor antagonist, haloperidol; the nonselective opioid receptor antagonist, naloxone; the non-specific nitric oxide synthase (NOS) inhibitor, nitro-L-arginine; the nonselective α-adrenergic receptor antagonist, phenoxybenzamine and the β-adrenergic receptor antagonist, propranolol. Our results demonstrate that orexin B can improve learning, consolidation of memory and retrieval. EMPA reversed completely the action of orexin B on memory consolidation. Bicuculline blocked fully; naloxone, nitro-L-arginine, phenoxybenzamine and propranolol attenuated the orexin B-induced memory consolidation, whereas haloperidol was ineffective. These data suggest that orexin B improves memory functions through OX2R and GABA-ergic, opiate, nitrergic, α- and β-adrenergic neurotransmissions are also involved in this action.
Behavioural Brain Research 06/2014; DOI:10.1016/j.bbr.2014.06.016 · 3.03 Impact Factor
"β expresses the 'coupling' of responding to reinforcers, which is purported to be determined, in part, by the working memory limitations of the organism (Killeen, 1994). An effect of the OxSap lesion on this parameter might therefore have been expected, in view of evidence indicating that manipulation of orexinergic function in the medial septum, hippocampus and dentate gyrus, whose orexinergic afferents emanate from the LHA, can alter mnemonic functions, including working memory (Smith and Pang, 2005; Akbari et al., 2006, 2008). However, it has yet to be demonstrated experimentally that the empirical value of β derived from ratio schedule performance is sensitive to disruption of working memory. "
[Show abstract][Hide abstract] ABSTRACT: It has been suggested that a sub-population of orexinergic neurones whose somata lie in the lateral hypothalamic area (LHA) play an important role in regulating the reinforcing value of both food and drugs. This experiment examined the effect of disruption of orexinergic mechanisms in the LHA on performance on the progressive ratio schedule of reinforcement, in which the response requirement increases progressively for successive reinforcers. The data were analysed using a mathematical model which yields a quantitative index of reinforcer value and dissociates effects of interventions on motor and motivational processes. Rats were trained under a progressive ratio schedule using food-pellet reinforcement. They received bilateral injections of conjugated orexin-B-saporin (OxSap) into the LHA or sham lesions. Training continued for a further 40 sessions after surgery. Equations were fitted to the response rate data from each rat, and the parameters of the model were derived for successive blocks of 10 sessions. The OxSap lesion reduced the number of orexin-containing neurones in the LHA by approximately 50% compared with the sham-lesioned group. The parameter expressing the incentive value of the reinforcer was not significantly altered by the lesion. However, the parameter related to the maximum response rate was significantly affected, suggesting that motor capacity was diminished in the OxSap-lesioned group. The results indicate that OxSap lesions of the LHA disrupted food-reinforced responding on the progressive ratio schedule. It is suggested that this disruption was brought about by a change in non-motivational (motor) processes.
Journal of Psychopharmacology 09/2011; 26(6):871-86. DOI:10.1177/0269881111409607 · 3.59 Impact Factor
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.