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 present study aimed to investigate the effects of pallidal neurotensin on haloperidol - induced parkinsonian symptoms .
### Output Text:
The present study aimed to investigate the effects of pallidal <span class="chemical">neurotensin</span> on <span class="chemical">haloperidol</span> - induced parkinsonian symptoms . 