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: There were statistically significant ( p < 0 . 05 ) decreases in MEK1 , Erk2p , GSK3alpha , 14 - 3 - 3e , and MEK7 in the striata of mice after multiple injections of METH .
### Output Text:
There were statistically significant ( p < 0 . 05 ) decreases in MEK1 , Erk2p , GSK3alpha , 14 - 3 - 3e , and MEK7 in the striata of mice after multiple injections of <span class="chemical">METH</span> . 