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: Our findings indicate that cocaine induced hyperlocomotion is modified by 5 - HT1B receptor ligands microinjected into the accumbens shell , but not core , this modification consisting in inhibitory and facilitatory effects of the 5 - HT1B receptor antagonist ( GR 55562 ) and agonist ( CP 93129 ) , respectively .
### Output Text:
Our findings indicate that <span class="chemical">cocaine</span> induced hyperlocomotion is modified by 5 - HT1B receptor ligands microinjected into the accumbens shell , but not core , this modification consisting in inhibitory and facilitatory effects of the 5 - HT1B receptor antagonist ( <span class="chemical">GR 55562</span> ) and agonist ( <span class="chemical">CP 93129</span> ) , respectively . 