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 , a statistically significant reduction was also observed on the level of GABA and glycine but less than a drastic reduction of glutamate and aspartate level .
### Output Text:
In addition , a statistically significant reduction was also observed on the level of <span class="chemical">GABA</span> and <span class="chemical">glycine</span> but less than a drastic reduction of <span class="chemical">glutamate</span> and <span class="chemical">aspartate</span> level . 