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 the frontal cortex , there was a statistically significant decrease in GSK3alpha after multiple ( but not single ) injections of METH .
### Output Text:
In the frontal cortex , there was a statistically significant decrease in GSK3alpha after multiple ( but not single ) injections of <span class="chemical">METH</span> . 