NEUROTRANSMITTERS IN ATLANTOOCCIPITAL CEREBROSPINAL-FLUID OF NORMAL FOALS

Concentrations of the dopamine metabolite homovanillic acid (HVA) and the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) were meas ured in samples of atlanto-occipital cerebrospinal fluid (CSF) of 17 f oals at 1, 7, 28, 56, and 84 days of age. At all ages concentrations o f both metabolites were lower than in adult horse CSF. Low concentrati ons of neurotransmitter metabolites corresponded to the period when fo als have an immature type electroencephalogram. Concentrations of both metabolites were greater at 7 and 56 days than at 1, 28, or 84 days, but the differences were not significant. Change in the HVA/5-HIAA rat io to > 1 at 56 and 84 days indicated the dopaminergic system matured later than the serotonergic system. Changes in HVA and 5-HIAA concentr ations occurred at similar times, which indicated a coordinated matura tion of both dopaminergic and serotonergic systems in foal brain.