The dopamine pathways
The dopamine hypothesis of schizophrenia proposed that schizophrenia is associated with an increase in dopamine transmission between the substantia nigra to the caudate nucleus-putamen (neostriatum) compared with normal, while in the other major dopaminergic pathways to the mesolimbic forebrain and the tubero-infundibular system ­ dopamine transmission is reduced.

[The nigrostriatal and mesolimbic dopamine tracts. In: Basic concepts in Neuroscience, international edition. Slaughter M. London, McGraw-Hill Medical Publishing Division 2002,187–208 ]

The glutamate pathways
Hypoactive glutamate pathways are believed to be associated with psychosis and confusion in schizophrenia. These pathways include: cortico-cortical pathways, thalamic-cortical, extrapyramidal pathways (cortical-striatum), and projections exist between the cortex, substantia nigra, subthalmic nucleus and pallidum.

[Brain structures and neuronal projections. Institute of Chemistry, Pharmacology and Biomedical Sciences. University of Sunderland. http://abdellab.sunderland.ac.uk/lectures/Brain/glu1.html. Accessed on 21 March 2003]


The serotonergic pathway
Up-regulation of the two serotonergic pathways: the dorsal raphe nuclei project into the substantia nigra and
the projections from the rostral raphe nuclei ascending into the cerebral cortex, limbic regions and basal ganglia
--> leads to hypofunction of the dopaminergic system, and this effect may be responsible for the negative symptoms of schizophrenia.

[The role or serotonin in schizophrenia. The American college of neuropsychopharmacology. www.acnp.org/g4/GN401000117/CH115.html. Accessed on 21 March 2003. ]