Differential expression levels of the hippocampal ghrelin and its receptor mRNA during memory consolidation.

Ghrelin is a peptide, secreted mainly from the stomach. But, it is also produced in the brain. Studies have confirmed the positive impact of ghrelin on memory formation. However, the expression levels of ghrelin or its receptors were not measured in the brain during the process of memory formation. The probable alteration in the expression levels of ghrelin or its receptors in the brain during memory formation can be a reason for the contribution of its signaling in this process. We quantified the gene expression levels of ghrelin and its receptors in the hippocampus during fear and spatial memory consolidation. Thirty- nine adult male Wistar rats weighing 180-220 g were utilized. Memory consolidation was evaluated using the inhibitory avoidance task and Morris water maze. Rats were euthanized at different times (1, 3, and 24 h) post-training and their hippocampi were removed and freezed directly in liquid nitrogen. Quantitative real-time polymerize chain reaction (PCR) was used to quantify the messenger ribonucleic acid (mRNA) expression levels of the hippocampal ghrelin and its receptors. The mRNA levels of ghrelin exhibited a significant increase, 24 h post-training in the inhibitory avoidance task, while its receptor levels were down-regulated. Also, the mRNA expression levels of the hippocampal ghrelin were not changed significantly during memory consolidation in the Morris water maze, while its receptor showed a significant increase, 24 h post-training. The results show a differential profile of the expression levels of the hippocampal ghrelin or its receptor mRNA during fear or spatial memory consolidation. This proposes that a local increase in the hippocampal ghrelin or its receptor levels might be crucial for fear, and spatial memory consolidation. However, due to the small sample sizes, it is worth noting the preliminary nature of the conclusions in the present study.

Frankincense upregulates the hippocampal calcium/calmodulin kinase II-α during development of the rat brain and improves memory performance.

BACKGROUND: Frankincense is an oleo gum resin derived from trees of genus Boswellia. It has favorable effects on memory formation. However, the probable underlying molecular mechanisms have not been assessed. Frankincense exerts some of its effects via activation of protein kinases. Calcium/calmodulin kinaseII (CaMKII) and CaMKIV are crucial mediators of learning and memory. We studied the effect of maternal injection of the aqueous extract of frankincense during gestation and lactation periods on spatial memory performance and the mRNA expression levels of the hippocampal CaMKIIand CaMKIV in the offspring rats. METHODS: Aqueous extract of Frankincense (50 and 100 mg/kg) or tap water was gavaged to distinct female rats during gestation and lactation periods. Memory performance was assessed in groups of male offspring using Morris water maze. In other groups of the offspring (with no memory test), the hippocampi of the juvenile rats were removed 30 days after labor. A real-time PCR method was used to measure the mRNA levels of CaMKII and CaMKIV. RESULTS: Frankincense improved spatial memory retrieval in the offspring rats in a dose-dependent manner. The mRNA expression of hippocampal CaMKIV was unchanged between groups. However, the mRNA expression of hippocampal CaMKII was dose-dependently upregulated in the rats, whose mothers had received frankincense. CONCLUSIONS: Due to the crucial role of the CaMKII in memory formation, the results provide a molecular basis for the effect of administration of frankincense to mother rats on improvement of the memory in the offspring.