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 differential predictive value of levodopa responsiveness for the outcome of parkinsonian ' off ' signs and LID and the different correlations of ventral lesion volume with dyskinesias and parkinsonian ' off ' signs indicate that different anatomical or pathophysiological substrates may be responsible for the generation of parkinsonian ' off ' signs and dyskinesias .
### Output Text:
The differential predictive value of <span class="chemical">levodopa</span> responsiveness for the outcome of parkinsonian ' off ' signs and LID and the different correlations of ventral lesion volume with dyskinesias and parkinsonian ' off ' signs indicate that different anatomical or pathophysiological substrates may be responsible for the generation of parkinsonian ' off ' signs and dyskinesias . 