Neuronal network inactivity potentiates neuropeptide release from mouse cortical neurons.

Neurons adapt to chronic activity changes by modifying synaptic properties, including neurotransmitter release. However, whether neuropeptide release via dense core vesicles (DCVs)-a distinct regulated secretory pathway-undergoes similar adaptation remains unclear. Here, we demonstrate that 24-hour action potential blockade leads to significant DCV accumulation in primary mouse cortical neurons of both sexes. Reactivation with action potential trains induced enhanced Ca(2+)-influx and 700% more DCV exocytosis compared to control neurons. Notably, total DCV cargo protein levels were unchanged, while mRNA levels of corresponding genes were reduced. Blocking neurotransmitter release with Tetanus toxin induced DCV accumulation, similar to that induced by network silencing with TTX. Hence, chronic network silencing triggers increased DCV accumulation due to reduced exocytosis during silencing. These accumulated DCVs can be released upon reactivation resulting in a massive potentiation of DCV exocytosis, possibly contributing to homeostatic mechanisms.Significance Statement This study addresses an unexplored area - how dense core vesicles (DCVs) exocytosis adapts to chronic changes in activity - and demonstrates accumulation of DCVs and a massive upregulation of DCV exocytosis in response to 24h inactivity. The potentiation of neuropeptide release might contribute to homeostatic regulation of neuronal networks in the brain.