The role of androgen receptors in regulating territorial aggression in male song sparrows.

This paper examines the role that androgen receptors (ARs) play in modulating aggressive behavior in male song sparrows, Melospiza melodia morphna. Song sparrows are seasonally breeding, territorial birds that maintain year-round territories with male-female pair bonds formed during the spring breeding season. Plasma testosterone levels peak as territories are established and mates acquired.

Influence of sex steroid hormones on spatial memory in a songbird.

In mammals, sex steroid hormones influence spatial learning and memory abilities but there are few data regarding such effects in birds. We investigated whether non-invasive sex steroid hormone treatment would affect spatial memory task performance of great tits (Parus major). For five consecutive days, birds were fed wax moth larvae injected with either 80 microg testosterone or 80 microg estradiol carried in peanut oil immediately prior to behavioral testing.

Impacts of frequent, acute pulses of corticosterone on condition and behavior of Gambel's white-crowned sparrow (Zonotrichia leucophrys gambelii).

Little is known about how frequent, acute stressors affect wild animals. We present two experiments conducted on captive, Gambel's white-crowned sparrow (Zonotrichia leucophrys gambelii) that explore how frequent, acute doses of corticosterone (CORT) affect condition and behavior. CORT was administered either once or three times a day to birds in pre-breeding, early-breeding, or late-breeding life-history stages.

Effects of repeated, short-term, corticosterone administration on the hypothalamo-pituitary-adrenal axis of the white-crowned sparrow (Zonotrichia leucophrys gambelii).

Our knowledge of glucocorticoid actions in vertebrates comes primarily from laboratory studies, which are often conducted with little consideration of how animals experience changes in glucocorticoid secretion in natural contexts. Typically, free-living animals are exposed to acute perturbations of the environment, ranging from a few minutes to a few hours duration, with varying frequency. The cumulative effects of these perturbations and their resultant glucocorticoid surges are not well known.

Fish on Prozac: a simple, noninvasive physiology laboratory investigating the mechanisms of aggressive behavior in Betta splendens.

The neuromodulator serotonin is an important regulator of aggressive behavior in vertebrates. Experimentally increasing synaptic levels of serotonin with fluoxetine, a selective serotonin reuptake inhibitor, has been shown to reliably decrease the expression of aggressive behavior. Here, we describe a method by which fluoxetine can be noninvasively administered to male Betta splendens (an attractive model for the study of aggressive behavior) and describe a simple laboratory exercise that allows students to experimentally investigate the physiological mechanisms of aggressive behavior.

Increased sensitivity of the serotonergic system during the breeding season in free-living American tree sparrows.

In order to understand the physiological role of serotonin in regulating aggressive behaviour it is important to understand how this neuromodulator acts within the context of a naturally fluctuating social and physical environment. To accomplish this, we examined the effect of the selective serotonin reuptake inhibitor fluoxetine during the breeding season in free-living male American tree sparrows (Spizella arborea) in Northern Alaska. During this time period males are maximally aggressive towards territorial intruders.

Latitudinal variation in plasma testosterone levels in birds of the genus Zonotrichia.

Birds breeding in northern latitudes generally have elevated plasma testosterone levels throughout the breeding season with a peak at the onset of the breeding season. In contrast, tropical birds tend to have extremely low plasma testosterone levels year round with only a slight increase during breeding. While these patterns have been consistent in the species investigated, closely related species have not been investigated across a range of latitudes.

Regulation of androgen receptors in Atlantic croaker brains by testosterone and estradiol.

A nuclear androgen receptor (AR1), distinctly different from the mammalian AR, has previously been identified in the brain of the Atlantic croaker, Micropogonias undulatus. Interestingly, brain AR1 levels were higher in gonadally recrudesced than in regressed fish. Therefore, the possible involvement of gonadal steroids in the regulation of brain AR1 levels was investigated in the present study.