The data suggest that rostral ventromedial medulla orexin-A receptors are involved in pulpal nociceptive modulation and improvement of learning and memory deficits induced by intradental application of capsaicin.
Objective:
Due to the prevalence of stress in modern life and its impact on spatial memory, the role of inhibitory systems in brain areas such as the nucleus accumbens (NAc) in reducing stress is important. The current study aimed to examine the response of NAc shell GABA
B
receptors to stress and the role of intraperitoneally (i.p.) and intra-NAc injection of the GABA
B
receptor agonist baclofen on spatial memory impairments in stress-exposed rats.
Methods:
Eighty adult male Wistar rats were randomly divided into ten groups (n=8): two were control groups for intra-NAc and i.p baclofen; two groups were subjected to stress and injected with saline (baclofen vehicle); three groups were given baclofen (1, 5, and 10 µg/rat) intra-NAc 5 mins before stress was induced; and three groups received baclofen (1, 5, and 10 mg/kg/i.p.) 30 mins before being subjected to stress. Foot-shock stress was applied for 7 consecutive days. Behavioral assays using the Barnes maze were performed 24 hrs after the last baclofen injection.
Results:
Both the intra-NAc and the i.p administration of baclofen dose-dependently reduced escape latency and total distance and increased velocity in the treatment groups in the training trials. In the probe test, the rats that had received 5 mg/kg of baclofen had the highest target frequency, but there no significant differences were observed in velocity, duration, or distance to the target between the groups.
Conclusion:
According to the findings, baclofen can dose-dependently improve spatial memory, and GABA
B
receptor in the NAc plays an important role in spatial memory.
Background: The rostral ventromedial medulla (RVM) is a critical region for the management of nociception. The RVM is also involved in learning and memory processes due to its relationship with the hippocampus. The purpose of the present study was to investigate the molecular mechanisms behind orexin-A signaling in the RVM and hippocampus's effects on capsaicin-induced pulpal nociception and cognitive impairments in rats. Methods: Capsaicin (100 g) was applied intradentally to male Wistar rats to induce inflammatory pulpal nociception. Orexin-A and an orexin-1 receptor antagonist (SB-334867) were then microinjected into the RVM. Immunoblotting and immunofluorescence staining were used to check the levels of cyclooxygenase-2 (COX-2) and brain-derived neurotrophic factor (BDNF) in the RVM and hippocampus. Results: Interdental capsaicin treatment resulted in nociceptive responses as well as a reduction in spatial learning and memory. Additionally, it resulted in decreased BDNF and increased COX-2 expression levels. Orexin-A administration (50 pmol/1 μL/rat) could reverse such molecular changes. SB-334867 microinjection (80 nM/1 μL/rat) suppressed orexin's effects. Conclusions: Orexin-A signaling in the RVM and hippocampus modulates capsaicininduced pulpal nociception in male rats by increasing BDNF expression and decreasing COX-2 expression.
Ascorbic acid (AA) as a vitamin and neuromodulator is present in most parts of CNS such as nucleus accumbens shell (Acbsh). This study evaluates the effect of intra-nucleus accumbens shell injection of AA on spatial learning and memory. 35 adult male Wistar rats (220-270 g) were divided into 5 groups: control (intact), sham AA (injected normal saline as AA vehicle) as well as 3 groups of AA (12, 24 and 48 μg/rat/side). After one week of recovery injections were performed. Thirty minutes after each injection the rats were trained in the Morris Water Maze (MWM) and spatial learning and memory parameters were recorded and then analyzed. The results showed that AA at the dose of 48 μg/rat/side significantly increased the travelled distance and latency time to reach the hidden platform in comparison with either control or sham groups (p<0.001). Intra-Acbsh injection of AA led to deficiency of spatial learning.
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