Distribution of norepinephrine, epinephrine, dopamine, serotonin, 3,4-dihydroxyphenylacetic acid, homovanillic acid and 5-hydroxyindole-3-acetic acid in dog brain

Abstract

The distribution of endogenous concentration of norepinephrine, epinephrine, dopamine, serotonin, 3,4-dihydroxyphenylacetic acid, homovanillic acid and 5-hydroxyindole-3-acetic acid were determined in the brains of adult dogs. Norepinephrine and epinephrine were localized primarily in ‘central core’ areas in brain stem and hypothalamus. Dopamine (DA) and its major metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acids (HVA), were localized primarily in basal ganglia with relatively high concentrations also found in amygdala, septum and substantia nigra. HVA was also found in relatively high concentrations in areas where DA concentration was very low. Serotonin and 5-hydroxyindole-3-acetic acid levels were highest in brain stem, hypothalamus, globus pallidus and nucleus accumbens. Epinephrine levels were higher than in previously studied species, at times as much as 25–30% of norepinephrine and frequently greater than dopamine in brain stem and hypothalamus.Using the ratios 5-hydroxyindole-3-acetic acid/serotonin and homovanillic acid/dopamine as indicators of serotonin and dopamine turnover and utilization, both putative transmitters were found to be generally more highly utilized in areas of lower concentration, especially in brain stem and cortex. Catecholamines were found to be unconjugated in dog brain. DOPAC and HVA were found to exist primarily in the unconjugated form. DOPAC was found to be slightly conjugated in most areas while 10–20% of HVA was present in the conjugated form in most cases.