The electrical stimulation of the central nucleus of the amygdala in combination with dopamine receptor antagonist reduces the acquisition phase of morphine-induced conditioned place preference in male rat.

Background and purpose: The central nucleus of the amygdala (CeA) is one of the nuclei involved in the reward system. The aim of the current study was to investigate the electrical stimulation (e-stim) effect of the CeA in combination with dopamine D1 receptor antagonist on morphine-induced conditioned place preference (CPP) in male rats. Experimental approach: A 5-day procedure of CPP was used in this study. Morphine was administered at an effective dose of 5 mg/kg, and SCH23390 as a selective D1 receptor antagonist was administrated into the CeA. In addition, the CeA was stimulated with an intensity of the current of 150 µA. Finally, the dependence on morphine was evaluated in all experimental groups. Findings/Results: Morphine significantly increased CPP. While the blockade of the D1 receptor of the CeA reduced the acquisition phase of morphine-induced CPP. Moreover, the combination of D1 receptor antagonist and e-stim suppressed morphine-induced CPP, even it induced an aversion. Conclusion and implication: The current study suggests that the administration of dopamine D1 receptor antagonist into the CeA in combination with e-stim could play a prominent role in morphine dependence.

Effect of electrical stimulation of central nucleus of the amygdala on morphine conditioned place preference in male rats.

Objectives: The central nucleus of the amygdala (CeA) is one of the most important areas for the morphine reward system. This study investigated the effect of electrical stimulation of CeA on morphine conditioned place preference (CPP) in male rats. Materials and Methods: After anesthetizing male Wistar rats, both electrode and cannula were implanted into CeA for stimulating (low intensity: 25 µA, and high intensity: 150 µA) and injecting (lidocaine and dopamine D2 receptor antagonist), respectively. Then, CPP induced by effective (5 mg/kg) and ineffective (0.5 mg/kg) doses of morphine was evaluated for five consecutive days (n = 6 / group). Results: The low electrical stimulation intensity of 25 µA suppressed both acquisition and expression phases, but the high intensity of 150 µA attenuated only the expression phase. On the other hand, intra-CeA administration of dopamine D2 receptor antagonist, eticlopride (2 µg/rat), with the effective dose of morphine, decreased CPP. In addition, infusion of lidocaine into the CeA inhibited morphine-induced CPP in both acquisition and expression phases with the effective dose of morphine. Conclusion: Electrical stimulation of the CeA may play an important role in attenuating morphine induced CPP via possible changes in neurotransmitters involved in the reward system such as dopamine (DA) and gamma-aminobutyric acid (GABA).

The role of trigeminal nucleus caudalis orexin 1 receptor in orofacial pain-induced anxiety in rat.

The relationship between anxiety and pain has received special attention. Orexins (A and B) are hypothalamic neuropeptides that have diverse functions in the regulation of different physiological and behavioral responses. This study was designed to evaluate the role of orexin 1 receptors (OX1R) within trigeminal nucleus caudalis (TNC) in anxiety following the induction of orofacial pain. The subcutaneous injection of capsaicin (CAP) into the rat upper lip region produced pain responses. OX1R agonist (orexin A) and antagonist (SB-334867) were microinjected into the TNC before the administration of CAP. Anxiety behaviors were investigated using elevated plus maze (EPM) and open-field tests. The results showed that CAP injection significantly decreases the percentage of time spent in the open arms of the EPM and the time spent in the center of the open field. Surprisingly, orexin (50, 100, and 150 pM/rat) significantly exaggerated the CAP effects, whereas SB-334867 (20, 40 nM/rat) significantly inhibited the CAP-induced anxiety. The CAP-injected group showed a significant decrease in the percentage of entries to open arms in the EPM and the number of visits in the center area of the open field compared with the control group. Orexin significantly potentiated the mentioned effects of CAP, whereas SB-334867 (40, 80 nM/rat) exerted a significant inhibitory effect on CAP-induced anxiety. The overall results indicated that the TNC OX1Rs play an important role in orofacial pain-induced anxiety.

Anti-inflammatory and Wound Healing Activities of Aloe vera, Honey and Milk Ointment on Second-Degree Burns in Rats.

The aim of the present study was morphological and morphometric investigation of burn healing impacts of an honey, milk, and Aloe vera (HMA) ointment on experimentally induced second-degree burns, to approve the medicinal basis of its use in Iranian traditional medicine. A total of 21 male Albino rats weighing 200 to 300 g were divided into 3 groups of 7, including (1) control group, (2) positive control group, and (3) the treatment group that were treated with eucerin, silver sulfadiazine 3% and HMA ointment 5% respectively.After anesthetizing, the second-degree burns (1 cm(2) areas) were made on the back of the animals using a digital controlled hot plaque, and each group was treated topically, based on the time scheduled. Then, skin punch biopsies were obtained on the 1st, 14th, and 28th days of post-burn induction; processed; and stained using hematoxylin and eosin and Masson's trichrome methods. The results showed that HMA ointment induces cell proliferation, increasing the wound closure rate, blood vessel counts, and collagen fiber density in treated animals. It also reduced the wound secretions, inflammation, and scar formation. According to the obtained morphological, morphometric results, we concluded that the traditional HMA ointment, which is rich in therapeutic biomaterials and minerals, has multiple healing effects on burn wounds in rats.

The effects of losartan on memory performance and leptin resistance induced by obesity and high-fat diet in adult male rats.

OBJECTIVE(S): Leptin is a hormone secreted by adipose tissue and is involved not only in the regulation of feeding and energy expenditure, but also its role in memory enhancement has been demonstrated as well. The partial transfer of leptin across the blood-brain barrier in obese individuals causes leptin resistance and prevents leptin reaching brain. On the other hand, studies have shown that angiotensin antagonists such as losartan can improve memory and learning abilities. The aim of this study was to evaluate the effects of losartan on improving memory and leptin resistance induced by high fat diet in obese rats. MATERIALS AND METHODS: 40 Wistar male rats were divided in 4 groups: control (C), losartan (LOS), high-fat diet (HFD) and high-fat diet and losartan (HFD and LOS). The spatial memory performances of the rats were assessed in the Morris water maze after 2 months of treatment. Then they were weighed and serum levels of leptin and triglyceride were measured. RESULTS: In spite of receiving high-fat diet, no significant differences in body weight were observed in the (HFD & LOS) group. In the Morris water maze trial, the (LOS) and (HFD & LOS) groups also showed a significant reduction (P <0.05) in latency and path length. In addition, a significant decrease (P <0.05) in serum levels of leptin and no significant difference in serum levels of triglyceride was observed in the (HFD & LOS) group. CONCLUSION: Losartan can improve leptin resistance induced by obesity and high fat diet. At the same time, it modulates body weight and enhances learning and memory.