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 areas where calcitonin is most effective in decreasing locomotor activity are located in the hypothalamus and nucleus accumbens , suggesting that these areas are the major sites of action of calcitonin in inhibiting amphetamine - induced locomotor activity .
### Output Text:
The areas where <span class="chemical">calcitonin</span> is most effective in decreasing locomotor activity are located in the hypothalamus and nucleus accumbens , suggesting that these areas are the major sites of action of <span class="chemical">calcitonin</span> in inhibiting <span class="chemical">amphetamine</span> - induced locomotor activity . 