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: Recent preclinical and clinical data from promising lines of research focus on the differential role of presynaptic versus postsynaptic mechanisms , dopamine receptor subtypes , ionotropic and metabotropic glutamate receptors , and non - dopaminergic neurotransmitter systems in the pathophysiology of levodopa - induced dyskinesias .
### Output Text:
Recent preclinical and clinical data from promising lines of research focus on the differential role of presynaptic versus postsynaptic mechanisms , <span class="chemical">dopamine</span> receptor subtypes , ionotropic and metabotropic <span class="chemical">glutamate</span> receptors , and non - dopaminergic neurotransmitter systems in the pathophysiology of <span class="chemical">levodopa</span> - induced dyskinesias . 