Changes in catecholamine levels and turnover rates in hypothalamic, vocal control, and auditory nuclei in male zebra finches during development.

The catecholamines norepinephrine (NE) and dopamine (DA) have been implicated in the sexual differentiation of brain and behavior and in species-specific learning in several species. To determine if these neurotransmitters might be involved in sexual differentiation of the vocal control system and song learning in male zebra finches, NE and DA levels and turnover rates were quantified in 10 behaviorally relevant brain nuclei [6 vocal control (VCN), 2 auditory (AN), and 2 hypothalamic (HN)] at four critical points during sexual differentiation of the VCN and the period of song learning, 25, 35, 55, and 90 days of age. Some birds were pretreated with alpha-methyl-para-tyrosine (alphaMPT) to allow estimation of NE and DA turnover rates. NE and DA levels in microdissected nuclei were quantified using high-performance liquid chromatography with electrochemical detection. AlphaMPT treatment suppressed catecholamine synthesis just as effectively in juveniles as it does in adults and proved an effective method for estimating NE and DA turnover rates. Patterns of NE and DA function in most VCN and AN over development were quite different from those in HN in which NE and DA function changed gradually and showed no striking peaks. NE turnover rates changed significantly over development in all six VCN [nucleus interfacialis (Nlf), high vocal center (HVC), nucleus robustus of the archistriatum (RA), dorsomedial portion of the intercollicular nucleus (DM), Area X of the parolfactory lobe, and lateral portion of the magnocellular nucleus of the anterior neostriatum (IMAN)]; one AN [nucleus mesencephalicus lateralis pars dorsalis (MLd)], and one HN [preopticus anterior (POA)]. NE levels changed significantly in two VCN (Nlf and Area X). In Nlf, RA, Area X, IMAN, and MLd, NE levels and/or turnover rates showed a striking peak at day 25, which was not seen in HN. Both DA levels and turnover rates changed profoundly over development in 5 of 6 VCN (Nlf, RA, DM, Area X, and IMAN) and both AN (MLd and Field L). These nuclei showed striking peaks in DA levels and turnover rates, primarily on day 35 and/or 55, which then declined profoundly by day 90. This contrasted with the minimal change in DA turnover rates seen in one HN (POA) and the sixth VCN, HVC. In several VCN and AN, NE and DA levels and turnover rates during development reached levels never seen in adult males. Previous research has shown that catecholamine function is heightened in VCN during development compared to surrounding tissues. Our data demonstrate that NE and DA function during development shows pronounced peaks in most VCN not seen in HN. This is interesting because both VCN and HN are hormone sensitive, and both show hormone-modulated NE and DA function in adult males. The timing of these peaks suggests that increased catecholaminergic function may be involved in sexual differentiation of the VCN and song learning in finches.

Central DSP-4 treatment decreases norepinephrine levels and courtship behavior in male zebra finches.

In zebra finches, gonadal steroids activate male courtship, including singing, and also strongly modulate norepinephrine (NE) levels and turnover in brain areas regulating courtship behavior. In a previous study, systemic administration of DSP-4 caused significant decreases in courtship singing. These behavioral decrements were correlated with the degree of NE depletion in several vocal control nuclei. In the present study, we attempted to further decrease brain NE levels while minimizing systemic effects by infusing DSP-4 directly into the third ventricle. DSP-4 treatment significantly reduced NE levels in three of six vocal control nuclei and both hypothalamic nuclei sampled without significantly altering dopamine or serotonin levels in any areas. DSP-4-treated males took longer to begin singing and performed fewer song bouts and courtship displays. Interestingly, behavioral deficits were limited to courtship song displays, other behavior patterns, including female-directed behaviors like approach and follow, were unaffected by DSP-4 treatment. DSP-4 treatment appeared to affect singing behavior by causing deficits in initial attentiveness to females and initiation of singing rather than by affecting song structure.

Role of catecholamines in the courtship behavior of male ring doves.

The role of catecholamines in the expression of male courtship behavior in ring doves was examined using central administration of pharmacological agents. Males treated with 6-hydroxydopamine or U-14,624, which depleted norepinephrine (NE) levels in the preoptic-hypothalamic area, showed increased levels of bow-coo and nest-coo displays. Conversely, males treated with tyramine or desipramine, which elevated NE levels in the preoptic-hypothalamic area, showed decreased levels of bow-coo and nest-coo displays. Drug-induced changes in dopamine levels were not consistent with any changes in behavior. This suggests that in the male ring dove NE in the preoptic-hypothalamic area is important in the expression of courtship displays.

Correlations between catecholamine levels and sexual behavior in male zebra finches.

In zebra finches, the combined actions of estrogens and androgens activate male courtship, including singing, and also strongly modulate norepinephrine (NE) levels and turnover in brain areas known to be involved in controlling courtship behavior. To determine whether changes in NE levels mediate changes in courtship, we administered DSP-4 to males and measured its effects on monoamine levels and reproductive behavior. DSP-4 treatment did not affect serotonin (5-HT), had small, variable effects on dopamine (DA), and caused moderate, nonsignificant reductions in NE. However, in DSP-4-treated males, NE levels in specific vocal-control nuclei showed high positive correlations with courtship singing. There were no significant correlations between NE levels in hypothalamic nuclei and any behavior or DA or 5-HT levels in any nuclei and any behavior. DSP-4-treated males took longer to begin singing and performed fewer song bouts and courtship displays, but their songs could not be differentiated from those of control males. This suggests that their behavioral deficits resulted from deficits in attention rather than an inability to sing.

Differential modulation of monoamine levels and turnover rates by estrogen and/or androgen in hypothalamic and vocal control nuclei of male zebra finches.

Sexual behaviors, including singing, in male zebra finches are under the combined control of androgens and estrogens. Treating castrates with androstenedione (AE), a hormone which provides both androgenic and estrogenic metabolites, restores catecholamine (CA; i.e., norepinephrine (NE) and dopamine (DA] function in brain areas known to be involved in the control of these behaviors. Since these behaviors can only be activated by the combined action of androgens and estrogens, the present study determined whether estrogen alone, androgen alone, or only their combination would restore CA function in these brain areas. Males were castrated for at least three weeks and then received one of three hormone implants: (1) estradiol (E) alone, (2) dihydrotestosterone (DHT) alone, or (3) E + DHT. Each male was then housed with a female for at least one week. Levels of NE, DA, epinephrine, serotonin and the latter's primary metabolite, 5-hydroxyindoleacetic acid, were measured in 3 hypothalamic, one auditory and 6 vocal control areas in their brains. NE and DA turnover in these areas were also estimated using alpha-methylparatyrosine. CA function proved to be hormone sensitive in 64% of the comparisons in the three hypothalamic and six vocal control nuclei examined. As expected, the treatment which provided both estrogenic + androgenic stimulation (E + DHT) restored CA function in all of these cases. Although E + DHT restored CA function in these areas, only 22% required both estrogenic + androgenic stimulation to restore normal CA function. For 57% of the comparisons, treatment with E alone also restored normal function, while in the remaining 22%, DHT alone was sufficient. All hormone-induced changes in noradrenergic neurotransmission were estrogen dependent; while modulation of DA function was much more variable, and frequently androgen dependent. To the best of our knowledge, this is the first time that these types of functional differences in the role of estrogen versus androgen in the modulation of neurotransmitter systems has been demonstrated.

Androstenedione modulation of monoamine levels and turnover in hypothalamic and vocal control nuclei in the male zebra finch: steroid effects on brain monoamines.

Levels of norepinephrine (NE), dopamine (DA), serotonin and the latter's primary metabolite, 5-hydroxyindoleacetic acid, were measured in two hypothalamic and 6 vocal control areas in the brains of male zebra finches. NE and DA turnover in these areas were also estimated using alpha-methylparathyrosine. Males were castrated for at least 3 weeks and then received an implant of androstenedione (AE) or a control implant of cholesterol. Each male was then housed with a female for at least one week. significant quantities of the 4 monoamines were found in all brain areas examined; steady-state levels varied significantly across brain areas. Hormone treatment affected steady-state monoamine levels in the preoptic area (POA), the magnocellular paraventricular nucleus and the vocal control area, area X. Hormone treatment altered both NE and DA turnover in the POA, area X and a second vocal control area, nucleus robustus archistriatalis. NE turnover as altered by hormone treatment ina third vocal area, the dorsomedial portion of the intercollicular nucleus. These data suggest that monoaminergic neurotransmitters may be involved in the mediation of steroid-dependent changes in singing behavior in passerine birds.

Administration of estradiol-17 beta in pulses to female guinea pigs: self-priming effects of estrogen on brain tissues mediating lordosis.

Lordosis behavior in ovariectomized guinea pigs is facilitated by the sequential action of estradiol-17 beta (E) and progesterone (P). The present study was designed to explore the possibility that administration of E in a pulsatile manner is more efficacious than a single injection of E with respect to lordosis facilitation in ovariectomized guinea pigs. The data indicate that pulse administration of unesterified E is more effective than a single large dose of E for the facilitation of lordosis behavior. Three injections of as little as 0.5 microgram E at 0, 19 and 28 hr followed by 0.5 mg P at 39 hr was more effective (63.6% responding with lordosis) than a single injection of as much as 15 micrograms E at hr 0 followed by vehicle injections at 19 and 28 hr and 0.5 mg P at 39 hr (0% responding). We also demonstrated that the 19 hr E injection could be eliminated and that two injections of E (0.5 microgram at hr 0 and 1.0 microgram at hr 28 followed by 0.5 mg P at hr 39) was at least as effective (69.0% responding) as three split injections in facilitating lordosis. This behaviorally effective pulse administration of E also resulted in significant induction of cytoplasmic progestin receptors in hypothalamic tissue. Further experiments indicated that a 28 hr interval between E pulses was optimal in terms of percent animals displaying lordosis. The data suggest that pulsatile E stimulation of brain tissues mediating lordosis is a highly effective mode of stimulation, and that an initial pulse of E sensitizes neural tissues to subsequent E administration.