Dopamine in the Cerebrospinal Fluid of Prepubertal and Adult Horses

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Abstract
Catecholamine concentrations (pg/ml) in the cerebrospinal fluid (CSF) of prepubertal (n = 9) and adult (n = 18) horses were determined by radioenzymatic assay. Norepinephrine was low or non detectable in all CSF samples. In contrast, measurable CSF dopamine concentrations were effected by age, reproductive status and exogenous steroid treatments. The concentration of dopamine in the CSF of prepubertal females (733 .+-. 92) was greater (p < 0.05) than the concentration in the CSF of prepubertal males (117 .+-. 67). Prepubertal male horses which were treated with testosterone for 5 days (50 mg/day) had elevated (p < 0.05) dopamine concentrations (2,533 .+-. 1,160) in the CSF compared to control males. In adult mares, dopamine was lower (p < 0.05) in the ovulatory season (25 .+-. 10) than during the anovulatory season (200 .+-. 101). Daily intramuscular estradiol-17.beta. (5 mg/day) injections had no effect (p < 0.05) on dopamine concentrations in the CSF of seasonally anovulatory mares (250 .+-. 35). Further, concentrations of dopamine in the CSF of long-term ovariectomized mares (80 .+-. 21) were not influenced (p < .05) by season. These results suggest that age, sex and gonadal steroids may effect dopamine, but not norepinephrine, concentrations in the brain ventricular system of the equine species. Further, seasonal effects on CSF dopamine concentrations are dependent upon the presence of the ovaries.