Final answer:
Dr. Seelig's drug may be acting on the neurotransmitter dopamine, as schizophrenia is associated with overactive dopamine neurotransmission.
Step-by-step explanation:
Based on the information provided, the drug discovered by Dr. Seelig that produces schizophrenic-like side effects may be acting on the neurotransmitter dopamine. Schizophrenia is associated with overactive dopamine neurotransmission, and antipsychotic medications used to treat the symptoms of schizophrenia work by blocking dopamine receptors and decreasing dopamine neurotransmission in the brain.