892
Restoring the balance between excitatory and inhibitory circuits in the basal ganglia , following the loss of dopaminergic ( DA ) neurons of the substantia nigra pars compacta , represents a major challenge to treat patients affected by Parkinson ' s disease ( PD ) .
 None
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
 Entities:  
Answer:
 None