The calyx of Held is probably the largest synaptic terminal in the brain, forming a unique one-to-one connection in the auditory ventral brainstem. During early development, calyces have many collaterals, whose function is unknown. Using electrophysiological recordings and fast-calcium imaging in brain slices, we demonstrate that these collaterals are involved in synaptic transmission. We show evidence that the collaterals are pruned and that the pruning already begins 1 week before the onset of hearing. Using two-photon microscopy to image the calyx of Held in neonate rats, we report evidence that both axons and nascent calyces are structurally dynamic, showing the formation, elimination, extension, or retraction of up to 65% of their collaterals within 1 hour. The observed dynamic behavior of axons may add flexibility in the choice of postsynaptic partners and thereby contribute to ensuring that each principal cell eventually is contacted by a single calyx of Held.auditory system ͉ medial nucleus of the trapezoid body ͉ two-photon imaging ͉ structural plasticity ͉ axon collateral S tudying the formation of individual, identified synapses in the CNS presents a formidable challenge because of their small size, their incredibly high density, and their protracted formation period (1). Imaging studies in living animals have provided insights into the structural changes that presynaptic axons undergo during development, which complements our understanding of how specific brain connections form (2). An emerging view from these studies is that axonal dynamics are age-and cell type-dependent (3) and strongly correlated with the formation of synaptic contacts, which may ultimately guide the growth of the axonal arbor (2, 4-6).Here, we study the development of a CNS synapse that can be identified relatively easily because it is probably the largest synaptic contact in the mammalian brain (7). The calyx of Held connects the globular bushy cells of the anteroventral cochlear nucleus and the principal cells of the medial nucleus of the trapezoid body (MNTB) in the brainstem. Studies in rodents have shown that shortly before birth, the principal cells of the MNTB are innervated by small glutamatergic boutons (8). Morphological and functional identification of nascent calyces is possible between postnatal days 3 and 5 (8-10), which suggests that the characteristic one-to-one innervation observed in mature animals is achieved very rapidly (10). However, previous studies have not been able to study the dynamic aspects of the calyx of Held development.As a first step toward elucidating the cellular mechanisms that ensure that each MNTB principal cell is always innervated by only a single calyx of Held, we sought an imaging approach. Because it has not been possible to study this unique synapse in culture, we carried out studies in vivo. We developed a surgical procedure to label brainstem axons in anesthetized rat pups and imaged them with a two-photon microscope. Using this approach, we provide evidence of structural dynamics r...

BackgroundHearing depends on correct functioning of the cochlear hair cells, and their innervation by spiral ganglion neurons. Most of the insight into the embryological and molecular development of this sensory system has been derived from animal studies. In contrast, little is known about the molecular expression patterns and dynamics of signaling molecules during normal fetal development of the human cochlea. In this study, we investigated the onset of hair cell differentiation and innervation in the human fetal cochlea at various stages of development.ResultsAt 10 weeks of gestation, we observed a prosensory domain expressing SOX2 and SOX9/SOX10 within the cochlear duct epithelium. In this domain, hair cell differentiation was consistently present from 12 weeks, coinciding with downregulation of SOX9/SOX10, to be followed several weeks later by downregulation of SOX2. Outgrowing neurites from spiral ganglion neurons were found penetrating into the cochlear duct epithelium prior to hair cell differentiation, and directly targeted the hair cells as they developed. Ubiquitous Peripherin expression by spiral ganglion neurons gradually diminished and became restricted to the type II spiral ganglion neurons by 18 weeks. At 20 weeks, when the onset of human hearing is thought to take place, the expression profiles in hair cells and spiral ganglion neurons matched the expression patterns of the adult mammalian cochleae.ConclusionsOur study provides new insights into the fetal development of the human cochlea, contributing to our understanding of deafness and to the development of new therapeutic strategies to restore hearing.

Sensorineural hearing loss (SNHL) is one of the most common congenital disorders in humans, afflicting one in every thousand newborns. The majority is of heritable origin and can be divided in syndromic and nonsyndromic forms. Knowledge of the expression profile of affected genes in the human fetal cochlea is limited, and as many of the gene mutations causing SNHL likely affect the stria vascularis or cochlear potassium homeostasis (both essential to hearing), a better insight into the embryological development of this organ is needed to understand SNHL etiologies. We present an investigation on the development of the stria vascularis in the human fetal cochlea between 9 and 18 weeks of gestation (W9–W18) and show the cochlear expression dynamics of key potassium‐regulating proteins. At W12, MITF+/SOX10+/KIT+ neural‐crest‐derived melanocytes migrated into the cochlea and penetrated the basement membrane of the lateral wall epithelium, developing into the intermediate cells of the stria vascularis. These melanocytes tightly integrated with Na+/K+‐ATPase‐positive marginal cells, which started to express KCNQ1 in their apical membrane at W16. At W18, KCNJ10 and gap junction proteins GJB2/CX26 and GJB6/CX30 were expressed in the cells in the outer sulcus, but not in the spiral ligament. Finally, we investigated GJA1/CX43 and GJE1/CX23 expression, and suggest that GJE1 presents a potential new SNHL associated locus. Our study helps to better understand human cochlear development, provides more insight into multiple forms of hereditary SNHL, and suggests that human hearing does not commence before the third trimester of pregnancy. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 75: 1219–1240, 2015

On the basis of this review, we conclude that children with migraine at referral to a specialist do not exhibit more psychological dysfunctioning and (to a lesser extent) do not exhibit more psychiatric comorbidity compared with healthy controls.

In this group of children with migraine, there is no evidence that 50 mg riboflavin has a prophylactic effect on migraine attacks. We found some evidence that 50 mg riboflavin may have a prophylactic effect on interval headaches that may correspond to mild migraine attacks or tension-type headache attacks in children with migraine.