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: In recent years , evidence from animal models of Parkinson ' s disease has provided important information to understand the effect of specific receptor and post - receptor molecular mechanisms underlying the development of dyskinetic movements .
### Output Text:
In recent years , evidence from animal models of Parkinson ' s disease has provided important information to understand the effect of specific receptor and post - receptor molecular mechanisms underlying the development of dyskinetic movements . 