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 rats which were pretreated with nicotine for 5 days , there was a significant increase in the nicotine - stimulated locomotor response which was associated with an increase in the number of L - [ 3H ] nicotine binding sites and also with an elevated dopamine ( DA ) level in the striatum .
### Output Text:
In rats which were pretreated with <span class="chemical">nicotine</span> for 5 days , there was a significant increase in the <span class="chemical">nicotine</span> - stimulated locomotor response which was associated with an increase in the number of L - [ 3H ] <span class="chemical">nicotine</span> binding sites and also with an elevated <span class="chemical">dopamine</span> ( <span class="chemical">DA</span> ) level in the striatum . 