In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: In addition , GABA content of mice hippocampus treated with GFC75 plus P400 showed an increase of 46 . 90 % when compared with seized mice .
### Output Text:
In addition , <span class="chemical">GABA</span> content of mice hippocampus treated with GFC75 plus P400 showed an increase of 46 . 90 % when compared with seized mice . 