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 beta2 - adrenoceptor overstimulation during an early critical period results in microglial activation associated with innate neuroinflammatory pathways and behavioral abnormalities , similar to those described in autism .
### Output Text:
Our findings indicate that beta2 - adrenoceptor overstimulation during an early critical period results in microglial activation associated with innate neuroinflammatory pathways and behavioral abnormalities , similar to those described in autism . 