Plasticity of the Rufous-winged Sparrow, Aimophila carpalis, song control regions during the monsoon-associated summer breeding period

In most temperate zone songbirds, exposure to increasing photoperiod in the spring stimulates the reproductive system and induces reproductive behaviors. Additionally, the brain regions that control singing (song control regions; SCRs) are larger during the breeding season, thus paralleling changes in the activity of the reproductive system. However, in some birds, environmental factors other than photoperiod initiate breeding. For example, free-living male Rufous-winged Sparrows develop their testes in March due to increasing photoperiod, but have relatively low plasma T until after they begin to breed, usually in July, during the monsoon period when day length is declining. We tested the hypothesis that SCRs grow and singing behavior increases after the monsoon rains begin. We captured adult male Rufous-winged Sparrows in July 2002, 7 days before and 20 days after the monsoon rains began, euthanized birds in the field, collected their brains, and measured SCR volumes from sections immunostained for the neuronal marker NeuN. In June and July 2006, we measured song rates in the field before and after the monsoon rains. SCR volumes were larger and singing behavior increased after the onset of the monsoon rains, coinciding with the initiation of breeding. Unlike in other species studied so far, SCR volumes grew as day length was decreasing. Comparative studies utilizing species that do not breed when day length is increasing may provide information on the relative contributions of various environmental factors to SCR neuroplasticity.     

Experimental induction of social instability during early breeding does not alter testosterone levels in male black redstarts,a socially monogamous songbird

Testosterone plays an important role in territorial behavior of many male vertebrates and the Challenge Hypothesis has been suggested to explain differences in testosterone concentrations between males. For socially monogamous birds, the challenge hypothesis predicts that testosterone should increase during male–male interactions. To test this, simulated territorial intrusion (STI) experiments have been conducted, but only about a third of all bird species investigated so far show the expected increase in testosterone. Previous studies have shown that male black redstarts (Phoenicurus ochruros) do not increase testosterone during STIs or short-term male–male challenges. The aim of this study was to evaluate whether black redstarts modulate testosterone in an experimentally induced longer-term unstable social situation. We created social instability by removing males from their territories and compared the behavior and testosterone concentrations of replacement males and neighbors with those of control areas. Testosterone levels did not differ among replacement males, neighbors and control males. Injections with GnRH resulted in elevation of testosterone in all groups, suggesting that all males were capable of increasing testosterone. We found no difference in the behavioral response to STIs between control and replacement males. Furthermore, there was no difference in testosterone levels between replacement males that had expanded their territory and new-coming males. In combination with prior work these data suggest that testosterone is not modulated by male–male interactions in black redstarts and that testosterone plays only a minor role in territorial behavior. We suggest that territorial behavior in species that are territorial throughout most of their annual life-cycle may be decoupled from testosterone.     

Breeding-context-dependent relationships between song and cFOS labeling within social behavior brain regions in male European starlings (Sturnus vulgaris)

Male European starlings (Sturnus vulgaris) sing throughout the year, but the social factors that motivate singing behavior differ depending upon the context in which song is produced. In a non-breeding context (when testosterone concentrations are low), starlings form large, mixed-sex flocks and song is involved in flock cohesion and perhaps maintenance of social hierarchies. In contrast, in a breeding context (when testosterone concentrations are high), male song plays a direct role in mate attraction. How the nervous system ensures that song production occurs in an appropriate context in response to appropriate stimuli is not well understood. The song control system regulates song production, learning, and, to some extent, perception; however, these nuclei do not appear to regulate the social context in which song is produced. A network of steroid hormone sensitive nuclei of the basal forebrain and midbrain regulates social behavior. The present study used the immediate early gene cFOS to explore possible involvement of these regions in context-dependent song production. Numbers of cFOS-labeled cells in the medial bed nucleus of the stria terminalis, anterior hypothalamus, and ventromedial nucleus of the hypothalamus related positively only to song produced in a breeding context. In contrast, numbers of cFOS-labeled cells in three zones of the lateral septum related positively only to song produced in a non-breeding context. Taken together, these data suggest differential regulation of male starling song by social behavior nuclei depending upon the breeding context in which it is produced.     

Lack of resistance against the tick Ixodes ricinus in two related passerine bird species

Although many wild bird species may act as reservoir hosts for tick-transmitted diseases and/or support long-distance dispersal of infected ticks, to date no research has been done on the extent to which songbirds may acquire resistance to ixodid ticks. Here we investigate whether two passerine species belonging to the family Paridae, the blue tit (Cyanistes caeruleus) and the great tit (Parus major), are able to acquire resistance after repeated infestations with Ixodes ricinus nymphs. As blue tits are less frequently exposed to I. ricinus in the wild than great tits, we expected I. ricinus to be less adapted towards the blue tit’s resistance mechanisms. Over the three infestation sessions we observed consistently high tick attachment rates and yields, high engorgement weights, and short engorgement and moulting durations, indicating that neither of the two songbird species is able to mount effective immune responses against I. ricinus nymphs after repeated infestations. As a consequence of the lack of resistance, birds were unable to prevent the direct harm (acute blood depletion) caused by tick feeding. Birds compensated the erythrocyte loss without reduction in general body condition (body mass corrected for tarsus length). The lack of resistance suggests that I. ricinus has a long co-evolutionary history with both avian hosts, which enables the tick to avoid or suppress the host’s resistance responses.     

白腰文鸟发声相关核团体积在发育中的变化及神经机制

首先研究了5-120日龄雌雄白腰文鸟（Lonchura striata swinhoei)4个主要发声核团（RA,LMAN,AreaX和HVC）的体积变化,再通过神经示踪技术研究这些核团与其他核团神经联系的建立时间,以了解发声核团发育及性别分化的神经机制,结果表明：（1）雌雄RA体积均在20,30日龄前后表现出急剧的变化和雌雄差异;雌雄RA在15和25日龄分别接受LMAN和HVC的神经支配,（2）雌雄LMAN体积分别在20,30日龄前先增长,之后均缩小,雌雄LMAN的神经元大小均在15和20日龄间急剧增长,但在该时段之后,不再发生明显变化,雌雄LMAN均在15日龄接受RA的神经支配。（3）AreaX核体积,神经元大小最明显的变化位于20-25日龄间;雌雄AreaX核均在15日龄时接受HVC的神经支配,（4）AreaX核体积,神经元大小最明显的变化位于20-25日龄间;雌雄AreaX核均在15日龄时接受HVC的神经支配,（4）雌雄HVC体积变化的最大值在20和30日龄前后,雄乌HVC的神经元大小在20,30日龄前后,雌鸟在15-20日龄发生较大的变化,其余组间变化小或不明显,雌雄HVC分别在15,25日龄同AreaX核,RA建立神经联系,因此,4个发声核团组织学的明显变化与核团间神经联系的建立相关,说明发声核团间的神经联系可能影响和决定了核团体积在发育中的变化。     

鸣禽前脑X区结构功能的研究进展

鸣禽鸣唱与人类说话一样,都是在教习和听觉反馈下形成的感知运动学习过程。鸣禽鸣唱的发育和成熟巩固依赖于发声通路和前端脑通路组成的鸣唱系统的完整。前端脑通路中的X区在鸣唱学习记忆中扮演着重要角色。本文就X区的形态组织结构、在鸣唱发育与成熟巩固中的作用、突触可塑性的研究进展进行了综述,并且将X区与哺乳动物基底神经节的学习记忆功能做了比较。     

Coordinated and dissociated effects of testosterone on singing behavior and song control nuclei in canaries (Serinus canaria)

Temperate zone songbirds that breed seasonally exhibit pronounced differences in reproductive behaviors including song inside and outside the breeding season. Springlike long daylengths are associated with increases in plasma testosterone (T) concentrations, as well as with increases in singing and in the volume of several brain nuclei known to control this behavior. The mechanisms whereby T can induce changes in behavior and brain, and whether or not these effects are differentially regulated, have recently begun to be examined, as has the question of the relative contributions of T and its androgenic and estrogenic metabolites to the regulation of this seasonal behavioral and neural plasticity. In this experiment, we examined the effects of T, 5alpha-dihydrotestosterone, or 17beta-estradiol treatment on castrated male canaries housed on short days and compared neural and behavioral effects in these males to similarly-housed males given only blank implants. We observed that only T treatment was effective in eliciting significant increases in singing behavior after 11 days of hormone exposure. In addition, T alone was effective in increasing the volume of a key song production nucleus, HVC. However, at this time, none of the steroids had any effects on the volumes of two other song control nuclei, Area X of the medial striatum and the robust nucleus of the arcopallium (RA), that are efferent targets of HVC, known to be regulated by androgen in canaries and also to play a role in the control of adult song. T can thus enhance singing well before concomitant androgen-induced changes in the song control system are complete.     

Individual differences in the motivation to communicate relate to levels of midbrain and striatal catecholamine markers in male European starlings

Individuals display dramatic differences in social communication even within similar social contexts. Across vertebrates dopaminergic projections from the ventral tegmental area (VTA) and midbrain central gray (GCt) strongly influence motivated, reward-directed behaviors. Norepinephrine is also rich in these areas and may alter dopamine neuronal activity. The present study was designed to provide insight into the roles of dopamine and norepinephrine in VTA and GCt and their efferent striatal target, song control region area X, in the regulation of individual differences in the motivation to sing. We used high pressure liquid chromatography with electrochemical detection to measure dopamine, norepinephrine and their metabolites in micropunched samples from VTA, GCt, and area X in male European starlings (Sturnus vulgaris). We categorized males as sexually motivated or non-sexually motivated based on individual differences in song produced in response to a female. Dopamine markers and norepinephrine in VTA and dopamine in area X correlated positively with sexually-motivated song. Norepinephrine in area X correlated negatively with non-sexually-motivated song. Dopamine in GCt correlated negatively with sexually-motivated song, and the metabolite DOPAC correlated positively with non-sexually-motivated song. Results highlight a role for evolutionarily conserved dopaminergic projections from VTA to striatum in the motivation to communicate and highlight novel patterns of catecholamine activity in area X, VTA, and GCt associated with individual differences in sexually-motivated and non-sexually-motivated communication. Correlations between dopamine and norepinephrine markers also suggest that norepinephrine may contribute to individual differences in communication by modifying dopamine neuronal activity in VTA and GCt.     

Intrinsic bursting enhances the robustness of a neural network model of sequence generation by avian brain area HVC

Avian brain area HVC is known to be important for the production of birdsong. In zebra finches, each RA-projecting neuron in HVC emits a single burst of spikes during a song motif. The population of neurons is activated in a precisely timed, stereotyped sequence. We propose a model of these burst sequences that relies on two hypotheses. First, we hypothesize that the sequential order of bursting is reflected in the excitatory synaptic connections between neurons. Second, we propose that the neurons are intrinsically bursting, so that burst duration is set by cellular properties. Our model generates burst sequences similar to those observed in HVC. If intrinsic bursting is removed from the model, burst sequences can also be produced. However, they require more fine-tuning of synaptic strengths, and are therefore less robust. In our model, intrinsic bursting is caused by dendritic calcium spikes, and strong spike frequency adaptation in the soma contributes to burst termination.