Donna L. Maney

Central administration of chicken gonadotropin-releasing hormone-II enhances courtship behavior in a female sparrow

Like most vertebrates, birds have two forms of gonadotropin-releasing hormone (GnRH). Chicken GnRH-I (cGnRH-I) is released at the median eminence to elicit gonadotropin release; chicken GnRH-II (cGnRH-II) is thought to be non-hypophysiotropic and its function is unclear. Both forms are hypothesized to act as neurotransmitters in the control of reproductive behavior. In the present study, we implanted chronic cannulae aimed at the third ventricle in female white-crowned sparrows (Zonotrichia leucophrys gambelii) to test the effects of both forms of GnRH on copulation solicitation, a female courtship behavior. This behavior can be elicited in captive, estrogen-primed females by playing a recording of male song. We quantified the behavioral response to recorded song 30, 60, and 90 min after intracerebroventricular infusion of cGnRH-I, -II, or saline. cGnRH-II, but not cGnRH-I, increased solicitation behavior compared with saline 30 min after infusion. Under control conditions, responses to the playback diminish from the 30-min to the 90-min time point. Responses after cGnRH-II infusion followed a similar pattern, whereas after cGnRH-I, there was no significant response decrement. cGnRH-I appears to maintain the level of solicitation seen at 30 min after infusion. Our results suggest a behavioral role for cGnRH-II that may be independent of cGnRH-I.

Effects of temperature on photoperiodically induced reproductive development, circulating plasma luteinizing hormone and thyroid hormones, body mass, fat deposition and molt in mountain white-crowned sparrows, Zonotrichia leucophrys oriantha.

The mountain white-crowned sparrow, Zonotrichia leucophrys oriantha, breeds in subalpine meadows throughout many mountainous regions of western North America. Mathematical analysis of 20 years of egg-laying dates at Tioga Pass, California (3030m elevation) indicated a highly predictable breeding season suggesting that precise environmental cues such as the annual change in day length were important for regulating reproductive function. Additionally, it appeared that there was sufficient yearly variation in the timing of breeding to suggest that other environmental cues may also be important for regulating adjustments in reproductive development and regression. Captive populations of Z. l. oriantha showed strong responses in gonadal development following transfer to longs days (15L 9D) and low temperature (5 degrees C) slowed down photoperiodically induced gonadal growth and subsequent regression, in both males and females. High temperature of 30 degrees C tended to accelerate gonadal development and regression whereas gonadal development was intermediate in a group exposed to 20 degrees C. Prior exposure to these temperature regimes while on short days (9L 15D) had no effect on body mass, fat, or plasma levels of luteinizing hormone (LH) and thyroid hormones. Curiously there was no effect of temperature on photoperiodically induced rises in LH in either sex despite marked effects on gonadal growth. Brood patch development was also enhanced in females exposed to 30 degrees C. Corticosterone levels measured in a subset of plasma samples from this experiment indicated no effect of temperature suggesting that the retarded gonadal development at 5 degrees C was not a result of thermal stress. Although there was a robust effect of photostimulation on thyroid hormone levels in blood of both sexes, temperature treatment had no effect on tri-iodothyronine (T3) concentrations. However, plasma levels of thyroxine (T4) were lower initially at 5 degrees C versus 20 and 30 degrees C treatments. This may be related to the protracted gonadal cycle at 5 degrees C versus the truncated gonadal cycle at 30 degrees C. Molt score, an indication of post-reproductive state and onset of photorefractoriness, was delayed in birds exposed to 5 degrees C. Body mass, and to a lesser extent fat score, tended to be lowest in birds exposed to 5 degrees C compared with those at 20 and 30 degrees C. These results demonstrate that ambient temperature significantly affected photoperiodically induced gonadal development and regression in these birds. The endocrine mechanisms underlying these effects require further study.

Intraventricular infusion of arginine vasotocin induces singing in a female songbird.

Arginine vasotocin (AVT) has been implicated in the activation of courtship and aggressive behaviors in many vertebrate taxa. Here, we tested its effect on singing and other vocal behavior in a songbird. Female white‐crowned sparrows (Z. l. gambelii) were implanted with chronic cannulae aimed at the third ventricle. Infusions of AVT dramatically increased the number of songs and other vocalizations during a 40u2003min period following infusion. Half of the subjects sang full song following AVT treatment. No bird sang after treatment with saline; any type of vocalization after saline treatment was rare. Female white‐crowned sparrows are known to sing in both spring and winter in the wild; this behavior is thought to be aggressive, functioning in dominance interactions and territoriality. Central infusion of AVT induced singing and other vocalizations in estrogen‐primed, photostimulated subjects as well as in non‐reproductive subjects housed on short photoperiods. Thus, the effects of AVT on vocal behavior may not require breeding levels of gonadal steroids and are probably not seasonal. We hypothesize that both in the breeding and non‐breeding seasons, AVT increases motivation to sing.

Effects of N-Methyl-d-Aspartate on Luteinizing Hormone Release and Fos-Like Immunoreactivity in the Male White-Crowned Sparrow (Zonotrichia leucophrys gambelii)

Seasonal breeding is terminated in the White-crowned sparrow by the onset of absolute photorefractoriness, a condition in which the reproductive system is switched off indefinitely until it is dissipated by short day lengths. Absolute photorefractoriness is controlled by the central nervous system; however, the mechanisms underlying GnRH quiescence in photorefractory birds have yet to be elucidated. Using the excitatory amino acid glutamate agonist N-methyl-d-aspartate (NMDA), plasma LH levels in White-crowned sparrows were significantly elevated regardless of the reproductive or photoperiodic condition. NMDA also significantly induced Fos-like immunoreactivity (FLI) within the infundibular nucleus and median eminence, regions previously shown to express FLI after a photoperiodically driven LH rise. NMDA did not induce FLI within GnRH I neurons; instead, it significantly activated cells within the organum vasculosum of the lamina terminalis in close proximity to GnRH I perikarya. These findings provide th...

Neuroendocrine Suppression of Female Courtship in a Wild Passerine: Corticotropin-Releasing Factor and Endogenous Opioids

During emergencies in their natural environments, vertebrates initiate coping mechanisms that redirect behavior away from nonessential activities and towards survival. Reproductive behaviors are suppressed. Evidence from field studies on passerine birds shows that this inhibition may not depend on the suppression of gonadal sex steroids, since during the breeding season they remain elevated despite activation of the stress response. We hypothesize that an alternate, central mechanism mediates the inhibition of reproductive behavior during stress in passerines. In this study, we tested the intracerebroventricular effects of endogenous opioids and corticotropin‐releasing factor (CRF), neuropeptides implicated in the stress response, on courtship behavior in wild‐caught female white‐crowned sparrows. β‐endorphin (β‐EN) significantly inhibited copulation solicitation, an estrogen‐dependent courtship display, 30u2003min after treatment. Naloxone, an opioid antagonist, enhanced the behavior. CRF caused a suppression of solicitation that was reversible by pretreatment with naloxone, suggesting an intermediary role for endogenous opioids in CRF‐induced suppression of courtship. The effects of β‐EN and CRF on solicitation appear to be independent of any general effects on locomotor activity. These results support our hypothesis that stress neuropeptides orchestrate coping behaviors in wild birds.

Regulation of Chicken Gonadotropin-Releasing Hormone-I mRNA in Incubating, Nest-Deprived and Laying Bantam Hens

Secretion of luteinizing hormone is decreased when hens start to incubate their eggs and is increased after nest deprivation or hatching of the eggs. The purpose of this study was to determine whether decreased luteinizing hormone (LH) secretion during incubation in the domestic hen is associated with a decrease in hypothalamic chicken gonadotropin-releasing hormone-I (cGnRH-I) mRNA or peptide. A semiquantitative competitive PCR assay was developed to measure cGnRH-I mRNA. Hypothalamic mRNA was quantified as the amount of GnRH cDNA obtained by reverse transcription of cGnRH-I mRNA. The amount of hypothalamic cGnRH-I mRNA was significantly higher in laying than in incubating hens (38.7 +/- 10.3 vs. 7.7 +/- 1.6 x 10(-17) mol cDNA, p = 0.01, n = 8). The hypothalamic GnRH peptide content was not significantly different between laying and incubating hens in either the preoptic area (286.9 +/- 24.01 vs. 269.3 +/- 29.3 pg, n = 8) or the basal hypothalamus (1.67 +/- 0.19 vs. 1.54 +/- 0.21 ng, n = 8). Five days after incubating hens were deprived of their eggs, the resulting increase in LH secretion was associated with a significant increase in hypothalamic content of cGnRH-I mRNA (22.8 +/- 2.2 vs. 6.7 +/- 1.7 x 10(-17) mol cDNA, p < 0.001, n = 8). These observations suggest that a decrease in the expression of the cGnRH-I gene is a major factor in maintaining depressed LH secretion in incubating domestic chickens.

Central Opioid Control of Feeding Behavior in the White-Crowned Sparrow,Zonotrichia leucophrys gambelii ☆

Many behavioral responses to stress do not appear to be mediated by glucocorticoids, suggesting another mechanism. We tested the effects of intracerebroventricular administration of beta-endorphin, a neuropeptide implicated in the stress response, on feeding behavior in captive, wild-caught white-crowned sparrows (Zonotrichia leucophrys gambelii). The amount of time spent feeding and the number of feeding bouts were higher after infusion with beta-endorphin than after saline infusion. Beta-endorphin decreased the latency to feed compared with saline. Naloxone, an opioid antagonist, suppressed feeding behavior and increased latency to feed. These results support our hypothesis that neuropeptides associated with stress may initiate adaptive responses to natural stressors in wild species.