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: A dystonia - like syndrome after neuropeptide ( MSH / ACTH ) stimulation of the rat locus ceruleus .
### Output Text:
A dystonia - like syndrome after neuropeptide ( <span class="chemical">MSH</span> / <span class="chemical">ACTH</span> ) stimulation of the rat locus ceruleus . 