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: Such attenuation was not found in animals which had been injected with GR 55562 into the accumbens core .
### Output Text:
Such attenuation was not found in animals which had been injected with <span class="chemical">GR 55562</span> into the accumbens core . 