Dopamine, serotonin and tachykinin in self-injurious behavior

The neurobiologic basis of self-injurious behavior (SIE) in Lesch-Nyhan syndrome and in other neuropsychiatric conditions remains unclear. The purpose of this review is to summarize recent data concerning SIE induced by the dopamine (DA) uptake inhibitor, GBR-12909 (GBR) and to compare the neurochemical data that have accumulated over the years on SIE in neonatal 6-hydroxydopamine (6OHDA) lesioned rats. The DA uptake inhibitor, GBR, upon repeated administration to adult rats elicits SIE that is temporally associated with a reduction of striatal DA (similar to 30%), increased turnover of serotonin and a robust induction of tachykinin transcription resulting in enhanced biosynthesis and presumably release of tachykinins (substance P and neurokinin A). GBR-induced SIE could be blocked by dopaminergic lesions or by D1 or D2 antagonists. Neonatal dopaminergic lesions result in a high degree of DA loss (>90%) and elevated levels of serotonin. In this model, SIE is precipitated by DA agonists via activation of D1 DA receptors which are in turn linked to an induction of tachykinin biosynthesis and release. The data taken together suggest that (a) a substantial reduction of DA accompanied by an increase in serotonin turnover may be essential conditions that are conducive to the occurrence of SIE, and (b) this phase is either superimposed with, or followed by a D1 and/or D2 DA receptor-linked activation of striatonigral tachykinin neurons resulting in enhanced tachykinin biosynthesis and release that may sustain the SIE. Thus, a dynamic interplay between DA, serotonin and tachykinin neuronal systems of the basal ganglia appear to influence the genesis and/or expression of SIE.