To be fair, as Seth Redmore mentions in his comment, some signalling proteins do get actively moved across the Blood Brain Barrier (BBB). I don’t expect you to have much luck with significantly affecting brain BDNF levels via peripheral injection but… it’s not a completely black and white case, because few things in biology are. Of course, if you could isolate just the BDNF fraction and inject a large quantity, then a low BBB-crossing rate would still amount to a meaningful effect.
The Blood Brain Barrier (BBB) isn’t perfect, stuff leaks from time to time. You can deliberately (and very unwisely!) temporarily degrade the BBB with certain chemicals. I’ve assisted in studies taking advantage of this fact to get things into rat brains that otherwise would be restricted by the BBB. But, you can kill or permanently cripple yourself doing that, so I really don’t recommend it.
To be fair, as Seth Redmore mentions in his comment, some signalling proteins do get actively moved across the Blood Brain Barrier (BBB). I don’t expect you to have much luck with significantly affecting brain BDNF levels via peripheral injection but… it’s not a completely black and white case, because few things in biology are. Of course, if you could isolate just the BDNF fraction and inject a large quantity, then a low BBB-crossing rate would still amount to a meaningful effect.
The Blood Brain Barrier (BBB) isn’t perfect, stuff leaks from time to time. You can deliberately (and very unwisely!) temporarily degrade the BBB with certain chemicals. I’ve assisted in studies taking advantage of this fact to get things into rat brains that otherwise would be restricted by the BBB. But, you can kill or permanently cripple yourself doing that, so I really don’t recommend it.