Good point. But I'm not implying chronic degeneration. Dopamine is Excitatory. The more it touches nerves, the nerves will hide their receptors to stop being overly tickled. Then they eventually die if Dopamine isn't stopped. But Dopamine down-regulates Serotonin. Dopamine is pleasure, Serotonin is happiness. The more pleasure you have, the more you want, and the less happy you get. While Serotonin is inhibitory, meaning it "untickles" nerves, encouraging them to reveal their receptors again. Serotonin is the feeling of "enough", "grateful", and "satisfied". Dopamine is "more, more...". SO, in answer to your point about degeneration! Serotonin regens damaged neurons. But it requires a Dopamine detox. We don't start falling apart chronically forever, unless the excitatory neurotransmitters keep spamming the neurons. It's in our control.