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 present results suggest a selective involvement of central noradrenergic neurones in the locomotor stimulant effect of amphetamine in the rat .
### Output Text:
The present results suggest a selective involvement of central noradrenergic neurones in the locomotor stimulant effect of <span class="chemical">amphetamine</span> in the rat . 