Ghrelin improves cognition in depressed mice by activating the cAMP-CREB signaling pathway
Background
Depression is frequently associated with a significant cognitive decline, a symptom linked to reduced levels of Brain-derived neurotrophic factor (BDNF). Lower ghrelin levels are also observed in depression, and ghrelin is known to influence BDNF production through the cAMP-CREB signaling pathway. This suggests a potential causal chain: in depression, diminished ghrelin may suppress the cAMP-CREB pathway, leading to lower BDNF levels in the hippocampus and, consequently, impaired cognition. This study investigates whether supplementing ghrelin can interrupt this pathological cascade and restore cognitive function in a depression model.
Study Design
Researchers used 120 male C57BL/6J mice, dividing them into six groups of 20. A depression model was established in three groups. Interventions involved injecting either normal saline (control), ghrelin, or ghrelin + (D-lys3)-GHRP-6 (a ghrelin receptor antagonist) into the lateral ventricle. The study assessed cognition, hippocampal long-term potentiation (LTP), and measured hippocampal levels of ghrelin mRNA and protein, BDNF, and CREB to evaluate the effects of the treatments in both depressed and non-depressed mice.
Results
The depression mouse model exhibited significant negative changes across all measured indexes, including cognition, hippocampal LTP, ghrelin mRNA and protein levels, and levels of BDNF and CREB. In depressed mice treated with ghrelin, all these indicators showed significant positive changes, suggesting a restorative effect. The combination of ghrelin with its antagonist, (D-lys3)-GHRP-6, produced even more significant positive changes than ghrelin alone.
The study concludes that in the depression model, lower endogenous ghrelin levels cause a decrease in hippocampal
BDNF, leading to cognitive decline, and that this process is mediated by thecAMP-CREBsignaling pathway. Exogenous ghrelin administration appears to reverse these deficits.
Key Findings
- In a mouse model of depression, cognition, hippocampal LTP, ghrelin mRNA, BDNF, and CREB levels were all significantly decreased.
- Administration of ghrelin to depressed mice resulted in significant positive changes in all measured cognitive and biochemical markers.
- Co-administration of ghrelin and the antagonist (D-lys3)-GHRP-6 produced even more significant positive changes than ghrelin alone.
- Lower ghrelin in the depression model causes hippocampal BDNF to decrease, resulting in cognitive decline.
- The mechanism of ghrelin's cognitive-enhancing effect in this model is mediated via the cAMP-CREB signalling pathway.
Why It Matters
This research reinforces the link between ghrelin, mood, and cognitive function, suggesting a specific biological pathway (cAMP-CREB -> BDNF) through which this occurs. For individuals exploring peptides, this highlights a potential mechanism by which ghrelin or GHSR agonists might offer nootropic benefits, particularly in states of stress or depression characterized by low ghrelin. Targeting the ghrelin system could be a viable strategy for mitigating the cognitive symptoms of depression. However, this is a preclinical mouse study using intraventricular injections, a route not used in humans. Significant further research is needed to determine if systemic administration of ghrelin or its mimetics can produce similar cognitive benefits in human depression and to establish safe and effective protocols.
