Homeostatic plasticity is a type of neuroplasticity that involves changes in the number of receptors in the postsynaptic neuron in response to changes in neural activity. This can lead to overall circuits becoming more or less excitable.
The pleasure/pain balance hinges on the amount of dopamine that is readily available for release in the system. Pursuing drugs or an activity that leads to huge increases in dopamine can deplete the readily releasable pool, resulting in addiction.
Animals feel agitation in stressful environments which causes the release of cortisol, leading to foraging and searching for food and mates. Dopamine is released when they catch the scent of something they need, while depression and disappointment signal the suppression of dopamine to avoid repeating mistakes.
Our neurochemical systems, including adrenaline, cortisol, dopamine, and epinephrine, were not designed to help us build Fortune 500 companies, but rather to be generic and adaptable depending on our circumstances, such as foraging for food or searching for a mate.
The vagus nerve plays a significant role in transmitting information from the gut to the brain, affecting serotonin levels and thereby influencing mood and overall well-being.