Serotonin in the basal ganglia: functions and interactions with other neuronal pathways

The serotoninergic innervation of the striatum and substantia nigra has been confirmed by a number of techniques. Inputs to both these regions appear to be inhibitory, but the possibility of non-serotoninergic pathways also originating from the raphe should be explored. No conclusions can yet be reached regarding the serotoninergic innervation of the globus pallidus or subthalamic nucleus. Behavioral studies show that serotonin, like dopamine, produces asymmetries when administered into the striatum or substantia nigra. These might be mediated though altered dopaminergic, cholinergic or GABA neuronal activity. Manipulation of the DRN or MRN serotoninergic projections suggest these nuclei serve different functional roles, though their exact nature is not understood. Defective serotonin neurotransmission is implicated in a number of neurological disorders, though a rational regimen of replacement therapy has been difficult to establish. Possibly, closer monitoring of relative transmitter deficiencies might select patients who would benefit from serotonin replacement therapy. Different types of serotonin receptors in basal ganglia suggest that altered serotonin neurotransmission might be involved in the catalepsy or dyskinesias produced by neuroleptic therapy.