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Synaptic transmission between specific connection motifs undergoes plastic changes during the learning process; however, the exact mechanisms underlying synaptic plasticity are still under intense investigation. Long-term potentiation (LTP) of synaptic transmission is a widely used cellular model of synaptic plasticity occurring during learning. Here, we focused on studying LTP at excitatory synapses on layer (L) 2/3 vasoactive intestinal polypeptide-expressing interneurons (VIP-INs) in the mouse somatosensory (barrel) cortex. LTP was induced by a pairing protocol of postsynaptic depolarization with extracellular stimulation in acute brain slices of young mice (P21-P28). The pairing protocol evoked LTP in L2/3 VIP-INs under control conditions; however, pharmacological blockade of GABAaR inhibition enhanced LTP. Next, we found that LTP in L2/3 VIP-INs is dependent on metabotropic glutamate receptor type 1 (mGluR-1) and L-type voltage-gated calcium channels (L-type VGCCs) but not on NMDARs or mGluR-5. Here, mGluR-1 acts through a G-protein-coupled signaling pathway and Src-family kinases, independently of transient receptor potential channels (TRPCs). Analyses of the paired-pulse ratio (PPR) and coefficient of variation (CV) indicate a presynaptic locus of LTP expression. Presynaptic expression of LTP in VIP-INs relies on retrograde signaling through endocannabinoids (eCBs) but not on brain-derived neurotrophic factor (BDNF). In conclusion, we dissected the mechanisms of LTP induction and expression at excitatory inputs to L2/3 VIP-INs in the mouse barrel cortex. LTP at excitatory synapses on VIP-INs might serve as a positive feedback for enhanced VIP-IN-mediated inhibition of SST-INs, leading to disinhibition of excitatory neurons from SST-IN inhibition during the learning process. Show less

The serotonin receptor 7 (5-HT7R) has been indicated as a key modulator of neuronal structure and function, playing critical roles in synaptic plasticity, dendritic spine formation, and cytoskeletal remodeling. 5-HT7R activation promotes neurite outgrowth, enhances long-term potentiation (LTP), stimulates local protein synthesis at synapses, and regulates mitochondrial functions, and the mTOR pathway. These properties make the 5-HT7R a compelling candidate for therapeutic intervention in neurodevelopmental disorders characterized by synaptic dysfunctions. Angelman syndrome (AS) is a severe neurodevelopmental disorder caused by the loss of function of the maternal UBE3A gene, resulting in impairments of synaptic plasticity, dendritic spine density, protein synthesis, mitochondrial activity and mTOR signaling. Intriguingly, many of the processes altered in AS are the ones that are positively regulated by 5-HT7R activation. For instance, AS animal models exhibit reduced LTP and altered dendritic morphology and 5-HT7R stimulation enhances synaptic strength and spine formation in the brain of wild type rodents. Moreover, BDNF/TrkB function signaling is impaired and mitochondrial integrity is disrupted in AS and 5-HT7R agonists enhance the altered BDNF/TrkB signalling and restore mitochondrial dysfunctions in Rett syndrome (RTT) mice model. Interestingly, recent evidence demonstrates that pharmacological activation of 5-HT7Rs increases synaptic protein synthesis, restores LTP, enhances dendritic spine density, and improves cognitive function in an AS mouse model. These encouraging results open the way to future studies using neurons and brain organoids generated from iPSCs obtained from AS patients, which represent novel tools in preclinical research. Overall, 5-HT7R stimulation, by counteracting the molecular alterations associated with the loss of UBE3A, may represent a novel approach to restore neural function in the mature brain, leading to translational applications in AS patients, and possibly also in other synaptopathies. Clinical trial number: not applicable. Show less

Children who experience cardiac arrest often suffer lasting neurological deficits, including impairments to learning and memory, due to global cerebral ischemia (GCI). Using a juvenile mouse model of cardiac arrest and resuscitation, we investigated the long-term effects of GCI and potential therapeutic interventions. Following juvenile GCI, long-term potentiation (LTP) and memory were impaired for several weeks followed by endogenous recovery coinciding with changes in brain-derived neurotrophic factor (BDNF) levels, an essential regulator of synaptic plasticity specifically in juveniles but not adults. Given that BDNF is unstable in plasma and cannot cross the blood-brain barrier, we explored the use of type II ampakines, positive allosteric modulators of AMPA receptors, to increase BDNF protein levels in the brain. In vivo administration of type II ampakines 14 days after GCI increased hippocampal BDNF levels, restored LTP, and improved hippocampal-dependent memory and learning behavior. These findings highlight the potential of type II ampakines as an innovative therapeutic intervention to restore synaptic and cognitive function at delayed time points after juvenile GCI. Show less