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: The selective blockade of A2 adenosine receptors ( DMPX ) and non - selective blockade of adenosine receptors ( caffeine ) significantly increased the action of amphetamine in the locomotor activity test .
### Output Text:
The selective blockade of A2 <span class="chemical">adenosine</span> receptors ( <span class="chemical">DMPX</span> ) and non - selective blockade of <span class="chemical">adenosine</span> receptors ( <span class="chemical">caffeine</span> ) significantly increased the action of <span class="chemical">amphetamine</span> in the locomotor activity test . 