I need a little medical information for a story I'm writing.

When you're exerting yourself physically, are there changes to your brain
chemistry that don't also occur during times of stress (so adrenaline is
out) and that don't last for more than five or ten minutes after you're done?

Barring that, how about changes to {*filter*} chemistry that could reach the
brain?  A friend suggested that there might be higher levels of metabolic
waste products, but he thought they'd be filtered out of the {*filter*} before
reaching the brain.

Please reply by E-mail (in as much detail as you like).  I'll summarize
any responses in a few days.

Thanks!

-Steve