EFFECTS OF 2 DIKETOPIPERAZINES, CYCLO (HIS-PRO) AND CYCLO (ASP-PHE), ON STRIATAL DOPAMINE - A MICRODIALYSIS STUDY

The effects of two diketopiperazines, Cyclo (His-Pro) (CHP) and Cyclo (Asp-Phe) (CAP), on striatal extracellular levels of dopamine (DA), di hydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydro xyindoleacetic acid (5-HIAA) were examined using in vivo microdialysis in anaesthetized rats. Treatment with neither CHP (0.1-10 mg/kg IP an d 0.3 mg/kg IV) nor CAP (0. 1-10 mg/kg IP and 10 mg/kg PO) significant ly changed the efflux of DA, DOPAC, HVA, or 5-HIAA when compared to th e effects of treatment with saline. Our results suggest that systemic administration of CHP or CAP alone does not modify striatal dopaminerg ic neurotransmission. The previous findings of enhanced DA release by systemic administration of thyrotropin releasing hormone (TRH) are pro bably not explained by formation of CHP from TRH.