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 other words , the present results suggest that the accumbal shell 5 - HT1B receptors play a permissive role in the behavioural response to the psychostimulant .
### Output Text:
In other words , the present results suggest that the accumbal shell 5 - HT1B receptors play a permissive role in the behavioural response to the psychostimulant . 