Distribution of dopamine -beta hydroxylase (DBH) immunoreactivity in male zebra finch brains: Effects of hormone and DSP-4 treatments

The goal of this research was to further examine the physiological mechanisms underlying the hormonal activation of singing behavior in male zebra finches. Research in zebra finches showed that hormone treatments, e.g. androstenedione (AE), which activated the highest levels of courtship behavior affected the levels and/or turnover of noradrenaline (NA) and dopamine, in nine of the ten brain areas examined. NA appears to be more hormone sensitive.;The first experiment of this study determined the distribution of noradrenergic cell bodies and projections in the male zebra finch brain. Immunocytochemical methods were used to stain cells containing the enzyme involved in the final step in the synthesis of NA, dopamine-beta hydroxylase (DBH). With the exception of the vocal control nuclei (VCN), the pattern of DBH labeling was similar to that observed in other birds and in rats. DBH-immunoreactive (DBH-ir) cells were restricted to hindbrain regions in the locus coeruleus (LoC) and ventral subcoeruleus (SCv).;Our previous research showed that CA levels and turnover were strongly modulated by gonadal hormones. The second experiment examined whether gonadal hormone treatment affected NA levels by changing the amount of DBH available for NA synthesis. Castrates treated with AE courted significantly more than sham-treated males. Hormone treatment significantly increased the area of DBH labeling only in the two hypothalamic nuclei examined.;The final experiment used DBH immunocytochemistry to investigate which brain regions were affected following treatment with the noradrenergic neurotoxin DSP-4. In mammals, DSP-4 affected NA function only in cortical areas leaving hypothalamic areas relatively unaffected. In prior experiments, NA levels in finch brains following DSP-4 treatment found that this neurotoxin depleted NA levels in hypothalamic as well as in cortical regions. Since studies in rats have typically used DBH immunocytochemistry (ICC) to assess the effects of DSP-4 on noradrenergic neurons, we used this technique as well. The pattern of destruction following DSP-4 treatment in finches was similar to that observed in rats. The areas of DBH-ir labeling in the telencephalic VCN of the DSP-4-treated males were significantly smaller than the saline-treated males, while labeling in hypothalamic areas was not significantly affected.