Evidence that dopamine within motivation and song control brain regions regulates birdsong context-dependently

Vocal communication is critical for successful social interactions among conspecifics, but little is known about how the brain regulates context-appropriate communication. The neurotransmitter dopamine (DA) is involved in modulating highly motivated, goal-directed behaviors (including sexually motivated singing behavior), and emerging data suggest that the role of DA in vocal communication may differ depending on the context in which it occurs. To address this possibility, relationships between immunolabeled tyrosine hydroxylase (TH, the rate-limiting enzyme in catecholamine synthesis) and song produced within versus outside of a breeding context were explored in male European starlings (Sturnus vulgaris). Immunocytochemistry for dopamine beta-hydroxylase (DBH; the enzyme that converts DA to norepinephrine) was also performed to provide insight into whether relationships between song and TH immunoreactivity reflected dopaminergic or noradrenergic neurotransmission. Measures of TH and DBH were quantified in song control regions (HVC, Area X, robust nucleus of the acropallium) and regions implicated in motivation (medial preoptic nucleus (POM), ventral tegmental area (VTA), and midbrain central gray). In Area X, POM, and VTA measures of TH correlated with song produced within, but not outside of a breeding context. DBH in these regions did not correlate with song in either context. Together, these data suggest DA in both song control and motivation brain regions may be more tightly linked to the regulation of highly goal-directed, sexually motivated vocal behavior.     

Sex differences in the densities of alpha 2-adrenergic receptors in the song control system,but not the medial preoptic nucleus in zebra finches

In songbirds, song is regulated by a specialized group of brain nuclei known as the song system. Other aspects of courtship, such as male sexual interest in a female, are likely regulated by the medial preoptic nucleus (POM). The song control system and the POM are rich in norepinephrine, which appears to regulate courtship behaviors, including song. Zebra finches (Taeniopygia guttata) exhibit an extreme sexual dimorphism in song behavior; males sing, primarily to attract or maintain mates, and females do not. We explored possible sex differences in the distribution and density of the alpha(2)-adrenergic receptors in the song system and POM of zebra finches. Receptors were labeled with the selective ligand, [(3)H] RX821002, via autoradiographic procedures. In males, dense alpha(2)-receptors were observed in the song system (Area X, the high vocal center (HVc), the lateral portion of the magnocellular nucleus of the anterior neostriatum, and the robust nucleus of the archistriatum). In contrast, in females neither the lateral portion of the magnocellular nucleus of the anterior neostriatum nor the HVc could be identified based on alpha(2)-receptor binding. Females lack Area X and indeed differential alpha(2)-binding was not observed within the female lobus parolfactorius. The robust nucleus of the archistriatum contained less dense alpha(2)-binding in females compared to males. Alpha(2)-binding in the POM was similar in males and females. The dimorphism in alpha(2)-binding in nuclei of the song system likely relates to the dimorphism in song behavior observed in male and female zebra finches.     

Pattern of interhemispheric synchronization in HVc during singing correlates with key transitions in the song pattern

Many complex voluntary behaviors require that motor commands be tightly coordinated between cerebral hemispheres. The neural mechanisms underlying such coordination, however, remain poorly understood. Song production in birds is a highly stereotyped learned motor behavior that requires finely tuned coordination between hemispheres. In the present study, neural activity was recorded simultaneously from the song control nucleus HVc in each hemisphere of singing adult male zebra finches (Taeniopygia guttata). In all cases, the pattern of recorded multiunit activity in each hemisphere was highly correlated during short segments of the song motor pattern. These correlated segments often consisted of multiple short bursts of activity. Because of the absence of interhemispheric connections between song control nuclei, these observations suggest that HVc activity is "synchronized" by common inputs to both hemispheres. Using sliding-window cross-covariance analyses, periods of high interhemispheric synchronization were found to be time-locked to the acoustic onset of syllables and notes. In some cases, precisely synchronized bursts in both hemispheres were also observed during periods associated with the intersyllable silent interval. In all cases, activity was correlated between hemispheres independently of the recording site, suggesting that all regions of HVc may be globally synchronized during these short segments of the song. Given the anatomical organization of the song system, inputs originating from either thalamus or midbrain are proposed to act as timing signals that initiate and synchronize intrinsic motor networks within each HVc thus allowing for the precise coordination of motor commands across hemispheres.     

The brain mapping of the retrieval of conditioned taste aversion memory using manganese-enhanced magnetic resonance imaging in rats

Manganese-enhanced MRI (MEMRI) is a newly developed noninvasive imaging technique of brain activities. The signal intensity of MEMRI reflects cumulative activities of the neurons. To validate the use of MEMRI technique to investigate the neural mechanisms of learning and memory, we tried to map brain areas involved in the retrieval of conditioned taste aversion (CTA) memory. CTAs were established to saccharin (conditioned stimulus: CS) by pairing its ingestion with an i.p. injection of LiCl (unconditioned stimulus: US). LiCl solutions (as a robust aversion chemical) of 0.15 M were injected i.p. 15 min after drinking the saccharine solution (CS). After the two times conditionings, these rats showed a robust aversion to the saccharine solution (CS). Rats of the control group were injected saline i.p. instead of LiCl solutions. The MRI signal intensities at the gustatory cortex (GC), the core subregion of the nucleus accumbens (NAcC), the shell subregion of the nucleus accumbens (NAcSh), the ventral pallidum (VP), the central nucleus of amygdala (CeA), the lateral hypothalamus (LH), and the basolateral nucleus of amygdala (BLA) of the conditioned group were higher than those of the control group. There were no significant differences between the conditioned and the control groups in the intensities for other regions, such as the striatum area, motor cortex, cingulate cortex, interstitial nucleus of the posterior limb of the anterior commissure and hippocampus. These indicate that the GC, NAcC, NAcSh, VP, CeA, LH and BLA have important roles in the memory retrieval of CTA.     

Sex- and age-related differences in ribosomal proteins L17 and L37, as well as androgen receptor protein, in the song control system of zebra finches

The zebra finch song system is sexually dimorphic--only males sing, and the morphology of forebrain regions controlling the learning and production of this song is greatly enhanced in males compared to females. Masculinization appears to involve effects of steroid hormones as well as other factors, perhaps including the expression of sex chromosome genes (males: ZZ, females: ZW). The present study investigated three proteins--two encoded by Z-linked genes, ribosomal proteins L17 and L37 (RPL17 and RPL37), including their co-localization with androgen receptor (AR), from post-hatching day 25 to adulthood. Extensive co-expression of AR with the ribosomal proteins was detected in the three song nuclei investigated (HVC, robust nucleus of the arcopallium (RA), and Area X) across these ages. In general, more cells expressed each of these proteins in males compared to females, and the sex differences increased as animals matured. Specific patterns differed across regions and between RPL17 and RPL37, which suggest potential roles of one or both of these proteins in the incorporation and/or differentiation of song system cells.     

Activity in a cortical-basal ganglia circuit for song is required for social context-dependent vocal variability

Variability in adult motor output is important for enabling animals to respond to changing external conditions. Songbirds are useful for studying variability because they alter the amount of variation in their song depending on social context. When an adult zebra finch male sings to a female ("directed"), his song is highly stereotyped, but when he sings alone ("undirected"), his song varies across renditions. Lesions of the lateral magnocellular nucleus of the anterior nidopallium (LMAN), the output nucleus of a cortical-basal ganglia circuit for song, reduce song variability to that of the stereotyped "performance" state. However, such lesions not only eliminate LMAN's synaptic input to its targets, but can also cause structural or physiological changes in connected brain regions, and thus cannot assess whether the acute activity of LMAN is important for social modulation of adult song variability. To evaluate the effects of ongoing LMAN activity, we reversibly silenced LMAN in singing zebra finches by bilateral reverse microdialysis of the GABA(A) receptor agonist muscimol. We found that LMAN inactivation acutely reduced undirected song variability, both across and even within syllable renditions, to the level of directed song variability in all birds examined. Song variability returned to pre-muscimol inactivation levels after drug washout. However, unlike LMAN lesions, LMAN inactivation did not eliminate social context effects on song tempo in adult birds. These results indicate that the activity of LMAN neurons acutely and actively generates social context-dependent increases in adult song variability but that social regulation of tempo is more complex.     

Physiological insights into the social-context-dependent changes in the rhythm of the song motor program

Precisely timed behaviors are central to the survival of almost all organisms. Song is an example of a learned behavior under exquisite temporal control. Song tempo in zebra finches (Taeniopygia guttata) is systematically modified depending on social context. When male zebra finches sing to females (directed), it is produced with a faster motor pattern compared with when they sing in isolation (undirected). We measured heart rate and air sac pressure during directed and undirected singing to quantify motivation levels and respiratory timing. Heart rate was significantly higher when male birds sang to females and was negatively correlated with song duration. The change in song tempo between directed and undirected song was accounted for by varying the duration of vocal expiratory events, whereas the duration of silent inspirations was unchanged. Song duration increased with repeated singing during directed song bouts, which was caused by a uniform increase in the duration of both expirations and inspirations. These results illustrate the importance of motivational state in regulating song tempo and demonstrate that multiple timing oscillators are necessary to control the rhythm of song. At least two different neural oscillators are required to control context-dependent changes in song tempo. One oscillator controlling expiratory duration varies as function of social context and another controlling inspiratory duration is fixed. In contrast, the song tempo change affecting expiratory and inspiratory duration within a directed bout of song could be achieved by slowing the output of a single oscillator.     

Expression of reelin, its receptors and its intracellular signaling protein, Disabled1 in the canary brain: relationships with the song control system

Songbirds produce learned vocalizations that are controlled by a specialized network of neural structures, the song control system. Several nuclei in this song control system demonstrate a marked degree of adult seasonal plasticity. Nucleus volume varies seasonally based on changes in cell size or spacing, and in the case of nucleus HVC and area X on the incorporation of new neurons. Reelin, a large glycoprotein defective in reeler mice, is assumed to determine the final location of migrating neurons in the developing brain. In mammals, reelin is also expressed in the adult brain but its functions are less well characterized. We investigated the relationships between the expression of reelin and/or its receptors and the dramatic seasonal plasticity in the canary (Serinus canaria) brain. We detected a broad distribution of the reelin protein, its mRNA and the mRNAs encoding for the reelin receptors (VLDLR and ApoER2) as well as for its intracellular signaling protein, Disabled1. These different mRNAs and proteins did not display the same neuroanatomical distribution and were not clearly associated, in an exclusive manner, with telencephalic brain areas that incorporate new neurons in adulthood. Song control nuclei were associated with a particular specialized expression of reelin and its mRNA, with the reelin signal being either denser or lighter in the song nucleus than in the surrounding tissue. The density of reelin-immunoreactive structures did not seem to be affected by 4 weeks of treatment with exogenous testosterone. These observations do not provide conclusive evidence that reelin plays a prominent role in the positioning of new neurons in the adult canary brain but call for additional work on this protein analyzing its expression comparatively during development and in adulthood with a better temporal resolution at critical points in the reproductive cycle when brain plasticity is known to occur.     

Radio-anatomic study of the pancreatic duct by MR cholangiopancreatography

To compare the performance of MR-cholangiopancreatography (MRCP) and that of classical anatomy in the depiction of the main pancreatic duct, 50 MRCP examinations were done in patients free of pancreatic disease. Axial and coronal sections 20 mm thick were obtained in a Single Shot Fast Spin Echo (SSFSE) sequence. The following were analyzed: (1) visibility of pancreatic duct structures, (2) form of the main pancreatic duct, (3) various angulations of the duct and (4) diameter of the duct. Anatomic variants were noted. These findings were compared with anatomic and radio-anatomic (ERCP) data in the literature. The main pancreatic duct was visualized in 100% of cases and the accessory pancreatic duct in 61%. The form, diameter and angulations of the various segments of the pancreatic duct were similar to those reported in the literature. These findings are reported in the axial and coronal planes. Comparison with major anatomic classifications was not possible. MRCP enables in vivo anatomic exploration of the main pancreatic duct. Horizontal sections provided new radio-anatomic information. The technique nevertheless remains limited by poor spatial resolution.     

Synaptic interactions underlying song-selectivity in the avian nucleus HVC revealed by dual intracellular recordings

Stimulus-dependent synaptic interactions underlying selective sensory representations in neural circuits specialized for sensory processing and sensorimotor integration remain poorly understood. The songbird telencephalic nucleus HVC is a sensorimotor area essential to learned vocal control with one projection neuron (PN) type (HVC(RA)) innervating a song premotor pathway, another PN (HVC(X)) innervating a basal ganglia pathway essential to vocal plasticity, and interneurons (HVC(Int)). Playback of the bird's own song (BOS), but not other songs, evokes action potential bursts from both PNs, but HVC(RA) and HVC(X) display distinct BOS-evoked subthreshold responses. To characterize synaptic interactions underlying HVC's BOS-selective responses and assess stimulus-evoked changes in functional interactions between HVC neurons, we made simultaneous in vivo intracellular recordings from various HVC neuron pairs in urethan-anesthetized zebra finches. Spike-triggered averaging revealed that all HVC neuron types receive common excitation and that the onset of this excitation occurs during a narrower time window in projection neurons during BOS playback. To distinguish local from extrinsic contributions to HVC subthreshold response patterns, we inactivated the HVC local circuit with GABA or occluded inhibition in single HVC(X) cells. After either treatment, BOS-evoked responses in HVC(X) neurons became purely depolarizing and subthreshold responses of HVC(X) and HVC(RA) cells became remarkably similar to one another while retaining BOS selectivity. Therefore both PN types receive a common extrinsic source of BOS-selective excitation, and local inhibition specifically alters processing of auditory information in HVC(X) cells. In HVC, excitatory and inhibitory synaptic interactions are recruited in a stimulus-dependent fashion, affecting auditory representations of the BOS locally and in other song nuclei important to song learning and production.     

黄眉鹀(Emberiza Chrysophrys)端脑发声控制核团的传入投射——HRP法研究

本文用HRP顺、逆行追踪方法,研究了黄眉鹀端脑发声控制中枢-上纹状体腹侧尾核及古纹状体粗核的传入投射。将HRP微电泳入上纹状体腹侧尾核,在同侧新纹状体前部巨细胞核的内侧部、新纹状体中部界面核、端脑听区-Field L、丘脑Uvacformis核及脑桥蓝斑等处见到密布的标记细胞,在古纹状体粗核及嗅叶的X区等处出现了密集成簇的标记终末。将HRP微电泳入古纹状体粗核,逆行标记细胞分布于同侧上纹状体腹侧尾核、新纹状体前部巨细胞核的外侧部、古纹状体带核及蓝斑等处。上述结果表明,上纹状体腹侧尾核接受新纹状体的前部巨细胞核内侧部、新纹状体中部界面核、端脑听区-Field L、丘脑Uvacformis核及脑桥蓝斑的传入投射。新纹状体前部巨细胞核、新纹状体中部界面核和Uvacformis核是参与发声学习与记忆的核团,L区是听觉的最高位中枢,蓝斑与植物性以及情绪性反应有关。提示上纹状体腹侧尾核也参与发声学习、听觉记忆以及植物性、情绪性反应的调节。古纹状体粗核接受上纹状体腹侧尾核、新纹状体前部巨细胞核外侧部、古纹状体带核及蓝斑的传入投射。     

An associational model of birdsong sensorimotor learning II. Temporal hierarchies and the learning of song sequence

Understanding the neural mechanisms underlying serially ordered behavior is a fundamental problem in motor learning. We present a computational model of sensorimotor learning in songbirds that is constrained by the known functional anatomy of the song circuit. The model subsumes our companion model for learning individual song "syllables" and relies on the same underlying assumptions. The extended model addresses the problem of learning to produce syllables in the correct sequence. Central to our approach is the hypothesis that the Anterior Forebrain Pathway (AFP) produces signals related to the comparison of the bird's own vocalizations and a previously memorized "template." This "AFP comparison hypothesis" is challenged by the lack of a direct projection from the AFP to the song nucleus HVc, a candidate site for the generator of song sequence. We propose that sequence generation in HVc results from an associative chain of motor and sensory representations (motor --> sensory --> next motor. ) encoded within the two known populations of HVc projection neurons. The sensory link in the chain is provided, not by auditory feedback, but by a centrally generated efference copy that serves as an internal prediction of this feedback. The use of efference copy as a substitute for the sensory signal explains the ability of adult birds to produce normal song immediately after deafening. We also predict that the AFP guides sequence learning by biasing motor activity in nucleus RA, the premotor nucleus downstream of HVc. Associative learning then remaps the output of the HVc sequence generator. By altering the motor pathway in RA, the AFP alters the correspondence between HVc motor commands and the resulting sensory feedback and triggers renewed efference copy learning in HVc. Thus, auditory feedback-mediated efference copy learning provides an indirect pathway by which the AFP can influence sequence generation in HVc. The model makes predictions concerning the role played by specific neural populations during the sensorimotor phase of song learning and demonstrates how simple rules of associational plasticity can contribute to the learning of a complex behavior on multiple time scales.     

Noradrenergic and GABA B receptor activation differentially modulate inputs to the premotor nucleus RA in zebra finches

Neuromodulators can rapidly modify neural circuits, altering behavior. Songbirds provide an excellent system for studying the role of neuromodulation in modifying circuits that underlie behavior because song learning and production are mediated by a discrete set of interconnected nuclei. We examined the neuromodulatory effects of noradrenergic and GABA B receptor activation on synaptic inputs to the premotor robust nucleus of the arcopallium (RA) in zebra finches using whole cell voltage-clamp recording in vitro. In adults, norepinephrine strongly reduced input from the lateral magnocellular nucleus of the anterior nidopallium (LMAN) but only slightly reduced the input from nucleus HVC (proper name), the excitatory input from axon collaterals of other RA neurons, and input from GABAergic interneurons. The effect of norepinephrine was mimicked by the alpha2 adrenoceptor agonist UK14,304 and blocked by the alpha2 antagonist yohimbine. Conversely, the GABA B receptor agonist baclofen strongly decreased HVC, collateral, and GABAergic inputs to RA neurons while causing little reduction in the LMAN input. In juveniles undergoing song learning, norepinephrine reduced the LMAN input, caused only a small reduction in the HVC input, and greatly reduced the collateral and GABAergic inputs. Baclofen caused similar results in juvenile and adult birds, reducing HVC, collateral, and GABAergic inputs significantly more than the LMAN input. Significant increases in paired-pulse ratio accompanied all reductions in synaptic transmission, suggesting a presynaptic locus. The reduction in the LMAN input by norepinephrine may be important for mediating changes in song elicited by different social contexts and is well-placed to play a role in song learning.     

Cocaine‐induced locomotor sensitization in rats correlates with nucleus accumbens activity on manganese‐enhanced MRI

A long‐standing goal of substance abuse research has been to link drug‐induced behavioral outcomes with the activity of specific brain regions to understand the neurobiology of addiction behaviors and to search for drug‐able targets. Here, we tested the hypothesis that cocaine produces locomotor (behavioral) sensitization that correlates with increased calcium channel‐mediated neuroactivity in brain regions linked with drug addiction, such as the nucleus accumbens (NAC), anterior striatum (AST) and hippocampus, as measured using manganese‐enhanced MRI (MEMRI). Rats were treated with cocaine for 5 days, followed by a 2‐day drug‐free period. The following day, locomotor sensitization was quantified as a metric of cocaine‐induced neuroplasticity in the presence of manganese. Immediately following behavioral testing, rats were examined for changes in calcium channel‐mediated neuronal activity in the NAC, AST, hippocampus and temporalis muscle, which was associated with behavioral sensitization using MEMRI. Cocaine significantly increased locomotor activity and produced behavioral sensitization compared with saline treatment of control rats. A significant increase in MEMRI signal intensity was determined in the NAC, but not AST or hippocampus, of cocaine‐treated rats compared with saline‐treated control rats. Cocaine did not increase signal intensity in the temporalis muscle. Notably, in support of our hypothesis, behavior was significantly and positively correlated with MEMRI signal intensity in the NAC. As neuronal uptake of manganese is regulated by calcium channels, these results indicate that MEMRI is a powerful research tool to study neuronal activity in freely behaving animals and to guide new calcium channel‐based therapies for the treatment of cocaine abuse and dependence. Copyright © 2015 John Wiley & Sons, Ltd.     

Lesions of an avian basal ganglia circuit prevent context-dependent changes to song variability

Trial-by-trial variability is important in feedback-based motor learning. Variation in motor output enables evaluation mechanisms to differentially reinforce patterns of motor activity that produce desired behaviors. Here, we studied neural substrates of variability in the performance of adult birdsong, a complex, learned motor skill used for courtship. Song performance is more variable when male birds sing alone (undirected) than when they sing to females (directed). We test the role of the anterior forebrain pathway (AFP), an avian basal ganglia-forebrain circuit, in this socially driven modulation of song variability. We show that lesions of the lateral magnocellular nucleus of the anterior nidopallium (LMAN), the output nucleus of the AFP, cause a reduction in the moment-by-moment variability in syllable structure during undirected song to the level present during directed song. This elimination of song modulation is immediate and long-lasting. We further show that the degree of syllable variability and its modulation are both attenuated in older birds, in concert with decreased variability of LMAN activity in these birds. In contrast to the requirement of LMAN for social modulation of syllable structure, we find that LMAN is not required for modulation of other features of song, such as the number of introductory elements and motif repetitions and the ordering of syllables or for other motor and motivational aspects of courtship. Our findings suggest that a key function of avian basal ganglia circuitry is to regulate vocal performance and plasticity by specifically modulating moment-by-moment variability in the structure of individual song elements.     

湖北襄阳2016—2017年埃可病毒11型流行株基因特征分析

目的:对2016—2017年中国湖北襄阳地区分离的埃可病毒11型(Echovirus 11,Echo11)基于VP1基因进行分子进化特征分析。方法:采集2016—2017年中国湖北襄阳地区手足口病患儿肛拭子或咽拭子标本,应用real-time RT-PCR技术对肠道病毒阳性样本进行筛选,对肛拭子或咽拭子样本进行病毒分离...     

Improved Assessment of Ex Vivo Brainstem Neuroanatomy With High‐Resolution MRI and DTI at 7 Tesla

The aim of the present work was to provide the topography of the main gray nuclei and white matter tracts of the human brainstem at 7 Tesla (7 T) high‐field magnetic resonance imaging (MRI) using structural imaging (T1) and diffusion tensor imaging (DTI). Both imaging techniques represent a new field of increasing interest for its potential neuroanatomic and neuropathologic value. Brainstems were obtained postmortem from human donors, fixated by intracarotid perfusion of 10% neutral buffered formalin, and scanned in a Bruker BioSpec 7 T horizontal scanner. 3D‐data sets were acquired using the modified driven equilibrium Fourier transform (MDEFT) sequence and Spin Echo‐DTI (SE‐DTI) sequence was used for DTI acquisition. High‐resolution structural MRI and DTI of the human brainstem acquired postmortem reveals its basic cyto‐ and myeloar‐chitectonic organization, only visualized to this moment by histological techniques and higher magnetic field strengths. Brainstem structures that are usually not observed with lower magnetic fields were now topographically identified at midbrain, pons, and medullar levels. The application of high‐resolution structural MRI will contribute to precisely determine the extension and topography of brain lesions. Indeed, the current findings will be useful to interpret future high‐resolution in vivo MRI studies in living humans. Anat Rec, 2011. © 2011 Wiley‐Liss, Inc.