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: Analysis of neurotransmitter concentration in some brain regions on the test day showed that dopamine concentration of the vehicle / scopolamine group was significantly lower than that of the vehicle / vehicle group , but this phenomenon was reversed when s - limonene or s - perillyl alcohol were administered before the injection of scopolamine .
### Output Text:
Analysis of neurotransmitter concentration in some brain regions on the test day showed that <span class="chemical">dopamine</span> concentration of the vehicle / <span class="chemical">scopolamine</span> group was significantly lower than that of the vehicle / vehicle group , but this phenomenon was reversed when <span class="chemical">s - limonene</span> or <span class="chemical">s - perillyl alcohol</span> were administered before the injection of <span class="chemical">scopolamine</span> . 