Glycine seems to build up in a part of the brain called the pineal body, according to this study

Source Excerpt

“Seki S, Ono-Takesue K, Yoshida S, Inagawa K, Murakami N, Takahashi M. Accumulation of peripheral glycine in the pineal body. Bull. Jpn Soc. Neurochem. 2004; 43: 558.”