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 was designed to examine the effect of 5 - HT1B receptor ligands microinjected into the subregions of the nucleus accumbens ( the shell and the core ) on the locomotor hyperactivity induced by cocaine in rats .
### Output Text:
The present study was designed to examine the effect of 5 - HT1B receptor ligands microinjected into the subregions of the nucleus accumbens ( the shell and the core ) on the locomotor hyperactivity induced by <span class="chemical">cocaine</span> in rats . 