Figure 1.

Neuroinfectious diseases and cytokine modulation of brain functions. (a) Neurotropic pathogens gain access to the CNS parenchyma (bacteria, viruses and parasites) or CSF compartments (bacteria, viruses and fungi), the latter of which includes the subarachnoid space and the ventricular system. (b, c) Increased expression of cytokines and chemokines modulate brain function via effects on dopaminergic pathways (b) and glutamatergic pathways (c). Dopamine is manufactured in the substantia nigra (SN), which affects motor function, and in the ventral tegmental area (VTA), which is involved in memory, motivation and reward. Dopaminergic neurons of the SN project to the dorsal striatum, and those of the VTA project to the nucleus accumbens (NA) and the prefrontal cortex. Glutamatergic pathways are involved in learning and memory formation, which also require long-term potentiation, characterized by a persistent increase in synaptic strength following high-frequency stimulation, and genesis of new neurons within the dentate gyrus (adult neurogenesis). Molecules labeled in red have inhibitory effects; those labeled in blue have stimulatory effects.