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: As the most potent dose ( 1 mg / kg ) of lipopolysaccharide was administered two weeks , one day before or after the methamphetamine dosing regimen , methamphetamine - induced striatal dopamine and 3 , 4 - dihydroxyphenylacetic acid depletions remained unaltered .
### Output Text:
As the most potent dose ( 1 mg / kg ) of <span class="chemical">lipopolysaccharide</span> was administered two weeks , one day before or after the <span class="chemical">methamphetamine</span> dosing regimen , <span class="chemical">methamphetamine</span> - induced striatal <span class="chemical">dopamine</span> and <span class="chemical">3 , 4 - dihydroxyphenylacetic acid</span> depletions remained unaltered . 