Answer: D. glutamate
Explanation:
The GLUTAMATE HYPOTHESIS OF SCHIZOPHRENIA is based around the belief that schizophrenia may be due to a low level of activity of glutamate in the glutamate synapse, especially in the prefrontal cortex.
This is because, increased levels of dopamine have been known to lead to schizophrenia according to the DOPAMINE THEORY of schizophrenia and dopamine inhibits the release of glutamate as well as inhibiting neurons that glutamate excites.
In short, INCREASED levels of dopamine show symptoms similar to DECREASED levels of glutamate meaning that schizophrenia may be due to a deficiency of activity of the glutamate synapse .