Question going on for the brain?

Is there any molecule or substance unique to the brain that would not leave the brain? Sort of close to bile in the liver?
Answers:
Apart from neurons, not that I know of
neurotransmitter...we can possibly do anything without it
brain fluid, don't know term for it. but there's fluid in brain that absorb shock

Related Questions:
Would Prozac (fluoxetine) be my the best route?   Reglan take back for GERD?   How can classification and diagnosis of correct pesticide poisoning be achieve?   Blood transfusions and DNA?   What happen if you overdose medication?  
  • Doctors prescribing steroids?
  • This cross-examine is related to blood grouping & around blood group compatibility of the receiver & donor......?
  • Is nearby any meds for my friend?