Intra-accumbal orexin-1 receptor inhibition prevents the anxiolytic-like effect of ethanol and leads to increases in orexin-A content and receptor expression.

Alcohol use is frequently associated with mood disorders. Similarly, individuals suffering from these disorders have a higher risk of developing alcoholism. Several reports have implicated orexin signaling in different behaviors related to alcohol consumption, whereas antagonists block these actions. However, the involvement of orexin-1-receptor (Orx1R) in ethanol-induced anxiolysis remains relatively unexplored. The purpose of this study was to investigate whether intra-accumbal inhibition of Orx1R blocks the anxiolytic-like effect of ethanol and to determine if ethanol administration modifies orexin-A content and Orx1R expression in the nucleus accumbens (NAc). The elevated-plus-maze test (EPM-test) was used to measure anxiety; orexin-A content and Orx1R expression were determined by enzyme-immunoassay and western blot, respectively. The results showed that the pretreatment with a selective antagonist of Orx1R, SB-334867 (SB, 3 μg/side), prevents the anxiolytic-like behavior induced by acute ethanol (2.5 g/kg). SB-334867 per se had no effect on anxiety levels. Pretreatment with SB-334867 followed by ethanol (SB + Et) increased orexin-A content and Orx1R levels in the NAc in comparison to the groups that only received ethanol (V + Et) or SB-334867 (SB + S). Ethanol treatment significantly augmented Orx1R expression but not the peptide content. The increase in orexin-A observed in SB + Et animals could be due in part to the inhibition of Orx1R, since SB-334867 prevents the binding of orexin-A to the receptor. This increase in orexin-A may, in turn, induce an up-regulation of receptor. Other possible explanations were discussed. In general, these findings suggest that orexin-A contributes largely to expression of ethanol-induced anxiolytic-like effect through the signaling of Orx1R in the NAc.

Morales-Mulia M 《-》

Investigating the role of the amygdala orexin receptor 1 in memory acquisition and extinction in a rat model of PTSD.

Understanding the mechanisms underlying memory is essential for the treatment of post-traumatic stress disorder (PTSD). Orexin, as a lateral hypothalamic (LH) neuropeptide, interferes with the stages of memory, primarily through the orexin receptor1 (Orx1R). The aim of this study was to evaluate the effects of amygdala Orx1R in the acquisition and extinction processes of PTSD modeled in animals. In three experiments, rats were divided into three groups: control (Naïve), shock (receiving a foot shock), and PTSD (experiencing Single prolonged stress (SPS) method). The first experiment aimed to evaluate LH activity in PTSD modeled rats. The second and third experiments aimed to evaluate the effects of Orx1R in the acquisition and extinction of fear memory in PTSD modeled animals. SB334867 (SB) or its solvent was microinjected into the amygdala and the rats were subjected to conditioning thereafter. In the second group, we used a single injection after conditioning. In the third group, we used three consecutive injections (one after each memory test). Some behaviors and Orx1R expression were evaluated. The freezing response was significantly longer in the PTSD group than on the control. Similarly, anxiety and sensitized fear were also intensified. CFos expression levels in LH was higher in the PTSD group. Inhibition of Orx1R in the amygdala significantly decreased memory acquisition, diminished anxiety, and decreased the sensitized fear in the SB group. Applying SB to the amygdala after each fear memory test significantly decreased freezing. Expression of Orx1R was significantly higher following fear conditioning. These results indicate a likely involvement of the orexin and amygdalar Orx1R in memory acquisition and in extinction of PTSD.

Salehabadi S ，Abrari K ，Elahdadi Salmani M ，Nasiri M ，Lashkarbolouki T ... -  《-》

SB-334867, an orexin receptor 1 antagonist, decreased seizure and anxiety in pentylenetetrazol-kindled rats.

Convulsive seizures are due to abnormal synchronous and repetitive neuronal discharges in the central nervous system (CNS). Finding new therapeutics to overcome the side effects of the current drug therapies and to increase their effectiveness is ongoing. Orexin-A and orexin-B are brain neuropeptides originating from postero-lateral hypothalamic neurons. Studies show that orexins, through activation of OX1 and OX2 receptors, have excitatory effects in the CNS. Accordingly, this study was designed to evaluate the effect of OX1 receptor antagonist (SB-334867) on seizure- and anxiety-related behaviors of pentylenetetrazol (PTZ)-kindled rats. Kindling was induced by repeated intraperitoneal (IP) injections of PTZ (32 mg/kg) with two-day intervals for 24 days in male Wistar rats. Three groups received intracerebroventricular (ICV) injections of SB-334867 (2.5, 5, and 10 μg/rat) before PTZ injections. Two control groups received vehicle (2 μL/rat, ICV) and valproate (26 μg/rat, ICV) before PTZ injections. An extra group of control animals received saline both ICV and IP. Seizure-related behaviors were monitored for 30 min following PTZ administration. The anxiety-like behaviors were also assessed using elevated plus-maze in the first and last days of the study. The results revealed that ICV injection of SB-334867, mainly at the dose of 10 μg/rat, decreased the median of seizure stages, prolonged the latency and reduced the duration of different seizure stages, and reversed the PTZ-induced anxiety-like behaviors. Based on the presented results, it is suggested that pharmacological blockade of the OX1 receptor is a potential target in the treatment of seizure and concomitant anxiety disorders.

Kordi Jaz E ，Moghimi A ，Fereidoni M ，Asadi S ，Shamsizadeh A ，Roohbakhsh A ... -  《-》

Role of orexin-1 and -2 receptors within the nucleus accumbens in the acquisition of sensitization to morphine in rats.

It has been reported that orexins A and B are involved in the mediation of drug reward. In addition, the nucleus accumbens (NAc) has an important role in the development of morphine-conditioned place preference (CPP) and morphine sensitization. In the present study, we aimed to evaluate the role of orexin receptors within the NAc in morphine sensitization using CPP paradigm. Adult male Wistar rats were used and were bilaterally implanted by two cannulae in the NAc. The animals received intra-accumbal administration of OX1 or OX2 receptor antagonists, SB-334867 (0.1, 1, and 10 nM/side) or TCS OX2 29 (2, 10, and 20 nM/side), 10 min before morphine injection during the sensitization period, during which the animals received repeated administration of morphine (5 mg/kg; s.c.) once daily for three days followed by 5 morphine injection-free days. Then the CPP paradigm was conducted for the evaluation of morphine rewarding properties by injecting a sub-threshold dose of morphine (0.5 mg/kg; s.c.). The results showed that bilateral administration of OX1 receptor antagonist into the NAc reduced acquisition of morphine sensitization in a dose-dependent manner, but OX2 receptor antagonist produced similar effect only at its highest dose, indicating that OX1 and OX2 receptors within the NAc are involved in the acquisition of morphine sensitization.

Assar N ，Mahmoudi D ，Mousavi Z ，Zarrabian S ，Haghparast A ... -  《-》

Involvement of orexin-A in the regulation of neuronal activity and emotional behaviors in central amygdala in rats.

The amygdala is a complex structure involved in the regulation of emotional behaviors including fear and anxiety. The central amygdala is the main output of the amygdala and plays an important role in emotional processing. Recent studies indicate that orexin, a kind of neuropeptides responsible for maintaining wakefulness, is also associated with emotion-related behaviors, such as depression- and anxiety-like behaviors. Central amygdala receives orexinergic fibers originating from the lateral hypothalamus and expresses OX1 receptors in rats. To test the electrophysiological and behavioral effects of orexins in the central amygdala, single unit in vivo extracellular recordings, open field and elevated plus maze tests were performed in rats. Micro-pressure administration of orexin-A (0.01 mmol/L) increased the firing rate in 18 out of the 31 central amygdala neurons, while the other 13 neurons were not excited by orexin-A. The excitatory effects of orexin-A on central amygdala neurons were mainly mediated by OX1 receptors rather than OX2 receptors. Orexin-B (0.01 mmol/L) did not change the firing activity in all recorded central amygdala neurons. Selectively blocking OX1 receptors by SB-334867 (0.01 mmol/L) significantly decreased the spontaneous firing rate in 14 out of the 33 central amygdala neurons, leaving the remaining 19 neurons were not affected. However, blocking OX2 receptors by TCS-OX2-29 (0.01 mmol/L) did not change the firing activity. Finally, both open field test and elevated plus maze test showed that bilateral microinjection of orexin-A into the central amygdala induced significantly anxiolytic-like behaviors. The specific OX1 receptor antagonist tended to produce opposite effects although there was no statistical difference. The present electrophysiological and behavioral studies suggested that orexin-A participates in anxiety-like behaviors by modulating the spontaneous firing activity of central amygdala neurons.

Pan YP ，Liu C ，Liu MF ，Wang Y ，Bian K ，Xue Y ，Chen L ... -  《-》