Tachykinin
A family of neuropeptides, brain chemicals (short proteins), famously implicated in pain (Tachykinin-I/Substance P) and found to strongly promote aggression in flies and mediate effects of social isolation in mice.
Videos Mentioning Tachykinin

Science of Social Bonding in Family, Friendship & Romantic Love
Andrew Huberman
A peptide whose levels increase under social isolation, causing aggression and irritability.

Erasing Fears & Traumas Based on the Modern Neuroscience of Fear
Andrew Huberman
A molecule in the brain, activated in the central amygdala after traumatic events, that reinforces fearful experiences and is further increased by social isolation, contributing to anxiety and irritability. Its effectiveness is reduced by social connection.

The Biology of Aggression, Mating, & Arousal | Dr. David Anderson
Andrew Huberman
A family of neuropeptides, brain chemicals (short proteins), famously implicated in pain (Tachykinin-I/Substance P) and found to strongly promote aggression in flies and mediate effects of social isolation in mice.