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: Our results have shown that all adenosine receptor agonists ( A1 and A2 ) reduce cocaine - and amphetamine - induced locomotor activity and indicate that cocaine - induced hyperactivity is more influenced by adenosine receptor agonists ( particularly A1 receptors ) than amphetamine - induced hyperactivity .
### Output Text:
Our results have shown that all <span class="chemical">adenosine</span> receptor agonists ( A1 and A2 ) reduce <span class="chemical">cocaine</span> - and <span class="chemical">amphetamine</span> - induced locomotor activity and indicate that <span class="chemical">cocaine</span> - induced hyperactivity is more influenced by <span class="chemical">adenosine</span> receptor agonists ( particularly A1 receptors ) than <span class="chemical">amphetamine</span> - induced hyperactivity . 