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: Plasma CGRP concentration increased significantly ( P < 0 . 01 ) during the migraine attack and returned to baseline after the cessation of the migraine .
### Output Text:
Plasma <span class="chemical">CGRP</span> concentration increased significantly ( P < 0 . 01 ) during the migraine attack and returned to baseline after the cessation of the migraine . 