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 striatum as a target for anti - rigor effects of an antagonist of mGluR1 , but not an agonist of group II metabotropic glutamate receptors .
### Output Text:
The striatum as a target for anti - rigor effects of an antagonist of mGluR1 , but not an agonist of group II metabotropic <span class="chemical">glutamate</span> receptors . 