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 gamma - aminobutyric acid - transmitted thalamocortical circuitry accounts for a major part of the underlying neurophysiology of the absence epilepsy .
### Output Text:
The <span class="chemical">gamma - aminobutyric acid</span> - transmitted thalamocortical circuitry accounts for a major part of the underlying neurophysiology of the absence epilepsy . 