Complex sentence: Historically, pharmacological, or drug-induced models were the most widely used, these involved the manipulation of various neurotransmitter systems, including dopamine, glutamate, serotonin, and GABA.
Split into simpler sentences: Historically, pharmacological, or drug-induced models were the most widely used. These involved the manipulation of various neurotransmitter systems, including dopamine, glutamate, serotonin, and GABA.