Auditory-vocal cholinergic pathway in the songbird brain

Male zebra finches learn to imitate a tutor's song through auditory and motor learning. The two main song control nuclei in the zebra finch forebrain, the higher vocal center (HVC) and the robust nucleus of the archistriatum (RA), receive cholinergic innervation from the ventral paleostriatum (VP) of the basal forebrain which may play a key role in song learning. By injecting neuroanatomical tracers, we found a topographically segregated pathway from nucleus ovoidalis (Ov) to VP that in turn projects in a topographic fashion to HVC and RA. Ov is a major relay in the main ascending auditory pathway. The results suggest that the cholinergic neurons in the VP responsible for song learning are regulated by auditory information from the Ov.     

Temporal patterning of song production: Participation of nucleus uvaeformis of the thalamus

Birdsong is a learned vocal behavior used in intraspecific communication. The motor pathway serving learned vocalizations includes the forebrain nuclei NIf, HVC, and RA; RA projects to midbrain and brain stem areas that control the temporal and acoustic features of song. Nucleus Uvaeformis of the thalamus (Uva) sends input to two of these forebrain nuclei (NIf and HVC) but has not been thought to be important for song production. We used three experimental approaches to reexamine Uva's function in adult male zebra finches. (1) Electrical stimulation applied to Uva activated HVC and the vocal motor pathway, including tracheosyringeal motor neurons that innervate the bird's vocal organ. (2) Bilateral lesions of Uva including the dorso-medial portion of the nucleus affected the normal temporal organization of song. (3) Chronic multiunit recordings from Uva during normal song and calls show bursts of premotor activity that lead the onset of some song components, and also larger bursts that mark the end of complete song motifs. These results implicate Uva in the production of learned vocalizations, and further suggest that Uva contributes more to the temporal structure than to the acoustic characteristics of song. © 1993 John Wiley & Sons, Inc.     

Cellular analyses of hormone influence on motoneuronal development and function

The striated bulbocavernosus (BC) muscles of the rodent perineum are innervated by motoneurons in the spinal nucleus of the bulbocavernosus (SNB). In adulthood, the BC muscles are present in males only. However, newborn female rats have BC muscles, and SNB cells have made both anatomical and functional contact with them. Nevertheless, both motoneurons and muscles will degenerate unless androgens are administered perinatally. Such androgen treatment appears to be acting primarily on the BC muscles themselves, since the muscles are spared by androgen even after the loss of supraspinal neural afferents or even the entire lumbosacral spinal cord. Furthermore, androgen can spare SNB motoneurons that are themselves androgen insensitive. Perinatal steroid treatments can also alter the final spinal location of SNB cells as determined by retrograde tracing studies. Androgen continues to modify the morphology of the SNB system in adulthood, altering the size of both motoneurons and targets, which may be important for the reproductive function of BC muscles. Finally, the sexually dimorphic character of motoneuronal groups innervating perineal muscles seems to be common in mammals, since the homologue of the SNB, Onuf's nucleus, has more cells in males than in females in both dogs and humans.     

新纹状体巨细胞核外侧部（LMAN）与鸣禽鸣唱学习可塑性

鸣禽鸣唱控制系统的前端脑通路（anterior forebrain pathway, AFP）在鸣唱学习中发挥着重要作用。新纹状体巨细胞核外侧部（lateral magnocellular nucleus of the anterior neostriatum, LMAN）是AFP的最后一级输出核团,AFP中的信号通过LMAN传导到弓状皮质栎核（robust nucleus of the arcopallium, RA）,与高级发声中枢（high vocal centre,HVC）共同调节RA的活动,从而影响鸣禽的发声行为。LMAN可能通过其与RA的单突触连接来影响鸣唱可塑性。文章对近年来LMAN在鸣唱学习可塑性方面的研究进行综述。     

Bilateral feedback projections to the forebrain in the premotor network for singing in zebra finches

A discrete neural circuit mediates the production of learned vocalizations in oscine songbirds. Although this circuit includes some bilateral pathways at midbrain and medullary levels, the forebrain components of the song control network are not directly connected across the midline. There have been no previous reports of bilateral projections from medullary and midbrain vocal control nuclei back to the forebrain song system, but the existence of such bilateral corollary discharge pathways was strongly suggested by the recent observation that unilateral stimulation of a forebrain song nucleus during singing leads to a rapid readjustment of premotor activity in the contralateral forebrain. In the present study, we used neuroanatomical tracers to demonstrate bilateral projections from (a) the rostral ventrolateral medulla (RVL), which may control respiratory aspects of vocalization, to nucleus uvaeformis (Uva), and (b) the dorsomedial intercollicular nucleus (DM), a midbrain vocal control region, to Uva. Both RVL and DM receive descending projections from the forebrain song nucleus robustus archistriatalis, and Uva projects directly to the forebrain song nuclei interfacialis and high vocal center. We suggest that the bilateral feedback projections from DM and RVL to Uva function to coordinate the two hemispheres during singing in adult songbirds and to convey internal feedback of premotor signals to the forebrain in young birds that are learning to sing. © 1998 John Wiley & Sons, Inc. J Neurobiol 34: 27–40, 1998     

10种鸣禽控制鸣啭神经核团大小与鸣唱复杂性的相关性

为进一步揭示鸣禽鸣唱行为的神经生物学机制 ,本实验先对 8个科 10种鸣禽的鸣唱行为进行了观察和录音 ,并借助声谱软件分析了每种鸣禽的鸣唱复杂性。鸣唱语句复杂性的评价指标包括 :短语总数、每个短语中所含的平均音节数及音节种类数、所有短语的总音节数及音节种类数、最长短语的音节数及音节种类数。然后 ,测定了前脑三个鸣啭学习控制核团和一个与发声无关的视觉参考核团体积 ,分析了鸣唱语句复杂性和这些核团大小间的相关关系。结果表明 :1)HVC和HVC/Rt与 7种鸣唱语句复杂性指标无关 ;RA和RA/Rt与总音节种类数相关 ;AreaX与总音节数及音节种类数相关 ;2 )HVC/RA和HVC/X比值与多个鸣唱语句复杂性指标相关。结果提示 :鸣禽鸣唱复杂性不同特征可能受不同神经控制     

HVC microlesions do not destabilize the vocal patterns of adult male zebra finches with prior ablation of LMAN

The songs of adult male zebra finches (Taeniopygia guttata) arise by an integration of activity from two neural pathways that emanate from the telencephalic nucleus HVC (proper name). One pathway descends directly from HVC to the vocal premotor nucleus RA (the robust nucleus of the arcopallium) whereas a second pathway descends from HVC into a basal ganglia circuit (the anterior forebrain pathway, AFP) that also terminates in RA. Although HVC neurons that project directly to RA outnumber those that contribute to the AFP, both populations are distributed throughout HVC. Thus, partial ablation (microlesion) of HVC should damage both pathways in a proportional manner. We report here that bilateral HVC microlesions in adult male zebra finches produce an immediate loss of song stereotypy from which birds recover, in some cases within 3 days. The contribution of the AFP to the onset of song destabilization was tested by ablating the output nucleus of this circuit (LMAN, the lateral magnocellular nucleus of the anterior nidopallium) prior to bilateral HVC microlesions. Song stereotypy was largely unaffected. Together, our findings suggest that adult vocal production involves nonproportional integration of two streams of neural activity with opposing effects on song--HVC's direct projection to RA underlies production of stereotyped song whereas the AFP seems to facilitate vocal variation. However, the rapid recovery of song in birds with HVC microlesions alone suggests the presence of dynamic corrective mechanisms that favor vocal stereotypy.     

Neuromechanisms of reciprocal interrelation between jaw-opening and jaw-closing muscles in the cat (author's transl)]

Neural controlling mechanisms between the digastric (jaw-opening) and masseter (jaw-closing) muscles were studied in the cat. High threshold afferent impulses from the anterior belly of the digastric muscle to masseteric montoneurons in the trigeminal motor nucleus induced an EPSP-IPSP sequence of potentials with long latency, and high threshold afferent impulses from the masseter muscle also exerted a similar effect on digastric motoneurons in the same nucleus innervating the anterior belly of the digastric muscle. These results suggest that reciprocal inhibition via Ia interneurons as observed between the flexor and extensor muscles in the spinal cord does not exist between the digastric and masseter muscles in the cat. However, the respective motoneurons innervating the masseter and digastric muscles receive inputs of early excitation-late inhibition via high threshold afferent nerve fibers from each antagonistic muscle. As such, since EPSPs preceding IPSPs are recognized, these high threshold afferent impulses may exert not only a reciprocal inhibitory effect, but also a synchronous excitatory or inhibitory effect on the antagonistic motoneurons.     

Acetylcholinesterase in central vocal control nuclei of the zebra finch (<Emphasis Type="Italic">Taeniopygia guttata</Emphasis>)

The distribution of acetylcholinesterase (AChE) in the central vocal control nuclei of the zebra finch was studied using enzyme histochemistry. AChE fibres and cells are intensely labelled in the forebrain nucleus area X, strongly labelled in high vocal centre (HVC) perikarya, and moderately to lightly labelled in the somata and neuropil of vocal control nuclei robust nucleus of arcopallium (RA), medial magnocellular nucleus of the anterior nidopallium (MMAN) and lateral magnocellular nucleus of the anterior nidopallium (LMAN). The identified sites of cholinergic and/or cholinoceptive neurons are similar to the cholinergic presence in vocal control regions of other songbirds such as the song sparrow, starling and another genus of the zebra finch (Poephila guttata), and to a certain extent in parallel vocal control regions in vocalizing birds such as the budgerigar. AChE presence in the vocal control system suggests innervation by either afferent projecting cholinergic systems and/or local circuit cholinergic neurons. Co-occurrence with choline acetyltransferase (ChAT) indicates efferent cholinergic projections. The cholinergic presence in parts of the zebra finch vocal control system, such as the area X, that is also intricately wired with parts of the basal ganglia, the descending fibre tracts and brain stem nuclei could underlie this circuitry’s involvement in sensory processing and motor control of song.     

Immediate early gene activity in song control nuclei and brain areas regulating motivation relates positively to singing behavior during, but not outside of, a breeding context

In some species, such as songbirds, much is known about how the brain regulates vocal learning, production, and perception. What remains a mystery is what regulates the motivation to communicate. European starlings (Sturnus vulgaris) sing throughout most of the year, but the social and environmental factors that motivate singing behavior differ seasonally. Male song is highly sexually motivated during, but not outside of, the breeding season. Brain areas outside the song control system, such as the medial preoptic nucleus (POM) and ventral tegmental area (VTA), have been implicated in regulating sexually motivated behaviors in birds, including song. The present study was designed to explore whether these regions, as well as three song control nuclei [area X, the high vocal center (HVC), and the robust nucleus of the arcopallium (RA)], might be involved differentially in song produced within compared to outside of a breeding context. We recorded the behavioral responses of breeding and nonbreeding condition male starlings to the introduction of a female conspecific. Males did not show context-dependent differences in the overall amount of song sung. However, immunocytochemistry for the protein product of the immediate early gene cFOS revealed a positive linear relationship between the total amount of songs sung and number of cFOS-labeled cells in POM, VTA, HVC, and RA for birds singing during, but not outside of, a breeding context. These results suggest that these regions differentially regulate male song production depending on reproductive context. Overall the data support the hypothesis that the POM and VTA interact with the song control system, specifically HVC and RA, to regulate sexually motivated vocal communication in songbirds.     

鸣禽锡嘴雀(Coccothraustes coccothraustes)发声中枢的定位研究

用常规组织学,HRP 逆行示踪,电生理等方法确定了鸣禽锡嘴雀控制发声的神经核团及这些核团的定位坐标值。锡嘴雀控制发声的神经通路由四级神经核团组成。位于端脑上纹状体腹侧的尾部区域(HVc)是控制鸣禽发声的高位中枢,它发出的神经纤维投射到端脑原纹状体腹内侧的粗核(RA),由 RA 又发出两束纤维,分別投射到中脑丘间核(ICo)和延脑的中间核(IM)。左右侧发声控制神经通路并非严格单侧性,每侧气管鸣管肌群分別受双侧发声中枢的交叉控制。中脑 ICo 在控制发声行为中具有相对独立性。各级发声核团的定位坐标值为,HVc∶p1.3,L/R2.4,H0.8;RA∶1.4,L/R3.2,H6.0;ICo∶p0.3,L/R2.6,H8.5:IM∶P3.1,L/R1.0,H∶7.8。     

鸣禽锡嘴雀（Coccothraustes coccothraustes）发声中枢...

Vocal-control nuclei in hawfinch (Coccothraustes coccothraustes) were studied by HRP retrograde tracing and electrophysiological methods. Vocal control centres in hawfinch consist of four discrete nuclei. Hyperstriatum ventral, pars caudale (HVc) is the highest nucleus, with its efferent fibers projecting to the rubust nucleus of archistriatum (RA), which in turn projects to the nucleus intercollicularis (ICo) of midbrain and the nucleus intermedius (IM) of medulla oblongata IM innervating vocal organ (syrinx) also receives input from ICo. The both vocal control pathways are not strictly unilateral. ICo plays a relative independent role in vocal control. The stereotaxic coordinates for HVc RA, ICo, IM are tabulated in Table 2.     

成年雄性斑胸草雀前脑与中脑对习得性发声控制的侧别差异

成年雄性鸣禽的习得性发声信号——长鸣(long call)和鸣唱(song)是由前脑高级发声中枢启动,以及由前脑最后一级输出核团弓状皮质栎核(robust nucleus of the arcopallium,RA)整合输出.RA投射神经元与位于中脑的基本发声中枢丘间复合体背内侧核(dorsomedial nucleus of the intercollicular,DM)形成突触连接.该文采用电损毁与声谱分析相结合的方法,通过依次损毁成年雄性斑胸草雀(Taeniopygia guttata)单侧RA和DM核团,探讨了前脑和中脑对习得性发声的影响.结果提示,RA核团与DM核团共同参与了对雄性斑胸草雀习得性声音的调控,而且这种控制具有右侧优势.     

Breeding status affects motoneuron number and muscle size in naked mole-rats: recruitment of perineal motoneurons?

Naked mole-rats live in large colonies and exhibit a strict reproductive hierarchy. Each colony has one breeding female and one to three breeding males; all other individuals are nonreproductive subordinates. Subordinates show a remarkable lack of sex differences in behavior and anatomy, but can become reproductive if removed from the colony. We recently reported that the striated perineal muscles and their innervating motoneurons, which are sexually dimorphic in all other mammals examined to date, are not dimorphic in subordinate naked mole-rats. Here we asked whether sexual differentiation of this neuromuscular system occurs when a subordinate becomes a breeder. The size and number of cells within Onuf's nucleus (homologue of the rat spinal nucleus of the bulbocavernosus) as well as perineal muscle volume were examined in subordinate and breeding naked mole-rats of both sexes. Sex differences in perineal motoneurons were not observed, regardless of social status. To our surprise, however, counts of motoneurons in Onuf's nucleus were increased approximately 30% in breeders of both sexes. This was accompanied by a reciprocal decrease in cells in Onuf's nucleus that were characterized by small soma size, and lacked a clear nucleus or nucleolus. Although not exhibiting typical motoneuron morphology, some of these small cells were positive for the motoneuron marker, SMI-32. The neuronal changes correlate with increased perineal muscle volumes in breeders. We propose that small, relatively undifferentiated cells are recruited to the pool of large Onuf's nucleus motoneurons when subordinate naked mole-rats become breeders.     

Breeding status affects motoneuron number and muscle size in naked mole‐rats: Recruitment of perineal motoneurons?

Naked mole‐rats live in large colonies and exhibit a strict reproductive hierarchy. Each colony has one breeding female and one to three breeding males; all other individuals are nonreproductive subordinates. Subordinates show a remarkable lack of sex differences in behavior and anatomy, but can become reproductive if removed from the colony. We recently reported that the striated perineal muscles and their innervating motoneurons, which are sexually dimorphic in all other mammals examined to date, are not dimorphic in subordinate naked mole‐rats. Here we asked whether sexual differentiation of this neuromuscular system occurs when a subordinate becomes a breeder. The size and number of cells within Onuf's nucleus (homologue of the rat spinal nucleus of the bulbocavernosus) as well as perineal muscle volume were examined in subordinate and breeding naked mole‐rats of both sexes. Sex differences in perineal motoneurons were not observed, regardless of social status. To our surprise, however, counts of motoneurons in Onuf's nucleus were increased ～30% in breeders of both sexes. This was accompanied by a reciprocal decrease in cells in Onuf's nucleus that were characterized by small soma size, and lacked a clear nucleus or nucleolus. Although not exhibiting typical motoneuron morphology, some of these small cells were positive for the motoneuron marker, SMI‐32. The neuronal changes correlate with increased perineal muscle volumes in breeders. We propose that small, relatively undifferentiated cells are recruited to the pool of large Onuf's nucleus motoneurons when subordinate naked mole‐rats become breeders. © 2006 Wiley Periodicals, Inc. J Neurobiol, 2006     

Modifications of motoneuron development following transplantation of thoracic spinal cord to the lumbar region in the chick embryo: Evidence for target-derived signals that regulate differentiation

In order to examine the role of target cells in the development of spinal motoneurons, the neural tube from thoracic segments was transplanted to the lumbar region on embryonic day (E) 2, and allowed to innervate hindlimb muscles in the chick embryo. When examined at later stages of development, the proportion of white and gray matter in the thoracic transplant was altered to resemble normal lumbar cord. Many thoracic motoneurons were able to survive up to posthatching stages following transplantation. The branching and arborization of dendrites of thoracic motoneurons innervating hindlimb muscles, as well as motoneuron (soma) size, were also increased to an extent approximating that seen in normal lumbar motoneurons. In support of previous studies using a similar transplant model, we have also found that the peripheral (intramuscular) branching pattern of thoracic motoneuron axons innervating hindlimb muscles was similar to that of normal lumbar motoneurons. Axon size and the degree of myelination of transplanted thoracic motoneuron axons were also increased so that these parameters more closely resembled axons of normal lumbar than normal thoracic spinal motoneurons. Virtually all of the changes in motoneuron properties noted above were observed irrespective of whether or not the transplanted spinal cord had developed in anatomical continuity with the host rostral cord. Accordingly, it is unlikely that the changes in the development of transplanted thoracic motoneurons reported here are induced either entirely, or in part, by signals derived from the host central nervous system. Rather, these changes appear to be mediated by interactions between the transplanted motoneurons and the hindlimb. We favor the notion that retrograde trophic signals derived from the hindlimb act to modulate the development of innervating motoneurons. Whether this signal involves a diffusible trophic agent released from target cells, or acts by some other mechanism is presently unknown. © 1992 John Wiley & Sons, Inc.     

Modifications of motoneuron development following transplantation of thoracic spinal cord to the lumbar region in the chick embryo: evidence for target-derived signals that regulate differentiation.

In order to examine the role of target cells in the development of spinal motoneurons, the neural tube from thoracic segments was transplanted to the lumbar region on embryonic day (E) 2, and allowed to innervate hindlimb muscles in the chick embryo. When examined at later stages of development, the proportion of white and gray matter in the thoracic transplant was altered to resemble normal lumbar cord. Many thoracic motoneurons were able to survive up to posthatching stages following transplantation. The branching and arborization of dendrites of thoracic motoneurons innervating hindlimb muscles, as well as motoneuron (soma) size, were also increased to an extent approximating that seen in normal lumbar motoneurons. In support of previous studies using a similar transplant model, we have also found that the peripheral (intramuscular) branching pattern of thoracic motoneuron axons innervating hindlimb muscles was similar to that of normal lumbar motoneurons. Axon size and the degree of myelination of transplanted thoracic motoneuron axons were also increased so that these parameters more closely resembled axons of normal lumbar than normal thoracic spinal motoneurons. Virtually all of the changes in motoneuron properties noted above were observed irrespective of whether or not the transplanted spinal cord had developed in anatomical continuity with the host rostral cord. Accordingly, it is unlikely that the changes in the development of transplanted thoracic motoneurons reported here are induced either entirely, or in part, by signals derived from the host central nervous system. Rather, these changes appear to be mediated by interactions between the transplanted motoneurons and the hindlimb. We favor the notion that retrograde trophic signals derived from the hindlimb act to modulate the development of innervating motoneurons. Whether this signal involves a diffusible trophic agent released from target cells, or acts by some other mechanism is presently unknown.     

Fluorescence histochemical study on the noradrenergic control to the anterior column of the spinal lumbosacral segments of the rat and dog,with special reference to motoneurons innervating the perineal striated muscles (Onuf's nucleus)

Summary The organization of noradrenergic fibers in the lumbosacral anterior column of rats and dogs was examined in detail using a modification of a highly sensitive glyoxylic acid fluorescence histochemical method. In both rat and dog, there were greater concentrations of fluorescing noradrenergic fibers around the motoneurons innervating the perineal striated muscles (Onuf's nucleus) than around other motoneuronal groups. The preferential accumulation of noradrenergic fibers in Onuf's nucleus may indicate that the noradrenergic neuron system in the spinal cord of rodents and carnivores is closely related to the functional peculiarities of the perineal striated muscles, including the external anal and urethral sphincter muscles.     

Fluorescence histochemical study on the noradrenergic control to the anterior column of the spinal lumbosacral segments of the rat and dog, with special reference to motoneurons innervating the perineal striated muscles (Onuf's nucleus)

The organization of noradrenergic fibers in the lumbosacral anterior column of rats and dogs was examined in detail using a modification of a highly sensitive glyoxylic acid fluorescence histochemical method. In both rat and dog, there were greater concentrations of fluorescing noradrenergic fibers around the motoneurons innervating the perineal striated muscles (Onuf's nucleus) than around other motoneuronal groups. The preferential accumulation of noradrenergic fibers in Onuf's nucleus may indicate that the noradrenergic neuron system in the spinal cord of rodents and carnivores is closely related to the functional peculiarities of the perineal striated muscles, including the external anal and urethral sphincter muscles.     

Doublecortin is expressed in trigeminal motoneurons that innervate the velar musculature of lampreys: considerations on the evolution and development of the trigeminal system

Studies in lampreys have revealed interesting aspects of the evolution of the trigeminal system and the jaw. In the present study, we found a marker that distinguishes subpopulations of trigeminal motoneurons innervating two different kinds of oropharyngeal muscles. Immunofluorescence with an antibody against doublecortin (DCX; a neuron-specific phosphoprotein) enabled identification of the trigeminal motoneurons that innervate the velar musculature of larval and recently transformed sea lampreys. DCX-immunoreactive (-ir) motoneurons were observed in the rostro-lateral part of the trigeminal motor nucleus of these animals, but not in lampreys 1 month or more after metamorphosis. Combined double DCX/tubulin and serotonin/tubulin immunofluorescence and tract-tracing experiments with neurobiotin (NB) were also performed in larvae for further characterization of this system. Rich innervation by DCX-ir fibers was observed on the muscle fibers of the velum but not on the upper lip or lower lip muscles, which were innervated by tubulin-ir/DCX-negative fibers. No double-labelled DCX-ir motoneurons were observed in experiments in which the tracer NB was applied to the upper lip. Innervation of velar muscles by serotonergic fibers is also reported. The present results indicate that development of the trigeminal motoneurons innervating the velum differs from that of the trigeminal motoneurons innervating the lips, which is probably related to the dramatic regression of the velum during metamorphosis. The absence of data on a similar subsystem in the trigeminal motor nucleus of gnathostomes suggests that they may be lamprey-specific motoneurons. These results provide support for the "heterotopic theory" of jaw evolution and are inconsistent with the theories of a velar origin for the gnathostome jaw.