bluuebunny/crossref_metadata_2025 huggingface dataset:
Distribution and developmental change in [3H]MK‐801 binding within zebra finch song nuclei
Authors: Aamodt Sandra M. , Kozlowski Michael R. , Nordeen Ernest J. , Nordeen Kathy W.
Published: January 2005

In many songbirds, vocal learning depends upon appropriate auditory experience during a sensitive period that coincides with the formation and reorganization of song‐related neural pathways. Because some effects of early sensory experience on neural organization and early learning have been linked to activation of N‐methyl‐d‐aspartate (NMDA) receptors, we measured binding to this receptor within the neural system controlling song behavior in zebra finches. Quantitative autoradiography was used to measure binding of the noncompetitive antagonist [3H]MK‐801 (dizocilpine) in the brains of both adult and juvenile male zebra finches, focusing on four telencephalic regions implicated in song learning and production. Overall, the pattern of MK‐801 binding in zebra finches was similar to the pattern found in rats (Monaghan and Cotman, 1985, J. Neurosci. 5:2909–2919; Sakurai, Cha, Penney, and Young, 1991, Neuroscience 40:533–543). That is, binding was highest in the telencephalon, intermediate in thalamic regions, and virtually absent from the brain stem and cerebellum. The telencephalic song areas exhibited intermediate levels of binding, and binding in the juveniles was not significantly different from adult levels in most song nuclei. However, in the lateral magnocellular nucleus of the anterior neostriatum (IMAN), binding at 30 days of age was significantly higher than binding in adults. Given the established role of NMDA receptors in other developing neural systems, both their presence in song control nuclei and their developmental regulation within a region implicated in song learning suggest that NMDA receptors play a role in mediating effects of auditory experience on the development of song behavior.
Hypertrophy of gonadotropin releasing hormone‐containing neurons after castration in the teleost, Haplochromis burtoni
Authors: Francis Richard C. , Jacobson Ben , Wingfield John C. , Fernald Russell D.
Published: January 2005

In the African cichlid fish, Haplochromis burtoni, males are either territorial or nonterritorial. Territorial males suppress reproductive function in the nonterritorial males, and have larger gonads and larger gonadotropin‐releasing hormone‐ (GnRH) containing neurons in the preoptic area (POA). We describe an experiment designed to establish the causal relationship between large GnRH neurons and large testes in these males by determining the feedback effects of gonadal sex steroids on the GnRH neurons. Territorial males were either castrated or sham‐operated, 4 weeks after which they were sacrificed. Circulating steroid levels were measured, and the GnRH‐containing neurons were visualized by staining sagittal sections of the brains with an antibody to salmon GnRH. The soma areas of antibody‐stained neurons were measured with a computer‐aided imaging system. Completely castrated males had markedly reduced levels of circulating sex steroids [11‐ketotestosterone (11 KT) and testosterone (T)], as well as 17β‐estradiol (E2). POA GnRH neurons in castrates showed a significant increase in mean soma size relative to the intact territorial males. Hence, in mature animals, gonadal steroids act as a brake on the growth of GnRH‐containing neurons, and gonadal products are not responsible for the large GnRH neurons characteristic of territorial males. © 1992 John Wiley & Sons, Inc.
Ipsilateral retinopetal projection of the nucleus olfactoretinalis (NOR) during development and regeneration: A dil study in a cichlid fish
Authors: Wilm Claudia , Fritzsch Bernd
Published: January 2005

The development and regeneration of the ipsilateral retinopetal projection of the nucleus olfactoretinalis (NOR) in the cichlid fish Haplochromis burtoni was studied with 1,1′‐dioctadecyl‐3,3,3′,3′‐tetramethyl indocarbocyanine perchlorate (DiI) in fixed tissue. Through out development most NOR cells projected to the contralateral retina. Only an insignificant, transient elevation of a projection to the ipsilateral retinawas found in a few animals; however, after severing the contralateral processes of NOR cells by either enucleation or nerve crush, many animals had significantly more NOR cells with a regenerated process to the ipsilateral retina. Nevertheless, within a few weeks of surgery, the number of animals with ipsilaterally projecting cells were reduced to control values. The transiently enhanced ipsilateral projections to the retina imply changes in the guiding mechanism after these operations and the existence of control mechanisms against unusual connections to the retina in this bony fish. © 1993 John Wiley & Sons, Inc.
Cell lineage analysis in neural crest ontogeny
Authors: Le Douarin Nicole M. , Dupin Elisabeth
Published: January 2005

The neural crest is a transitory and pluripotent structure of the vertebrate embryo composed of cells endowed with developmentally regulated migratory properties. We review here a series of studies carried out both in vivo and in vitro on the ontogeny of the neural crest in the avian embryo. Through in vivo studies we established the fate map of the neural crest along the neuraxis prior to the onset of the migration and we demonstrated the crucial role played by the tissue environment in which the crest cells migrate in determining their fate. Moreover, the pathways of neural crest cell migration could also be traced by the quail‐chick marker system and the use of the HNK1/NC1 monoclonal antibody (Mab).

A large series of clonal cultures of isolated neural crest cells showed that, at migration time, most crest cells are pluripotent. Some, however, are already committed to a particular pathway of differentiation. The differentiation capacities of the pluripotent progenitors are highly variable from one to the other cell. Rare totipotent progenitors able to give rise to representatives of all the phenotypes (neuronal, glial, melanocytic, and mesectodermal) encountered in neural crest derivatives were also found. As a whole we propose a model according to which totipotent neural crest cells become progressively restricted (according to a stochastic rather than a sequentially ordered mechanism) in their potentialities, while they actively divide during the migration process. At the sites of gangliogenesis, selective forces allow only certain crest cells potentialities to be expressed in each type of peripheral nervous system (PNS) ganglia. © 1993 John Wiley & Sons, Inc.
Cell fate determination in the peripheral nervous system: The sympathoadrenal progenitor
Authors: Anderson David J.
Published: January 2005

Studies of postnatal chromaffin cells, sympathetic neurons and Small Intensely Fluorescent (SIF) cells have suggested that these cells develop from a common progenitor, the sympathoadrenal (SA) progenitor, whose fate is determined by the relative levels of nerve growth factor (NGF) and glucocorticoid (GC) in its environment (Unsicker et al., 1978, Proc. Natl. Acad. Sci. USA 75:3498–3502; Doupe et al., 1985a, J. Neurosci. 5:2119–2142). Recent studies have identified such a bipotential SA progenitor in the rat embryo. Surprisingly, this progenitor is initially unresponsive to NGF; neuronal differentiation is instead promoted by fibroblast growth factor (FGF). However, FGF appears to promote NGF responsiveness, suggesting that neuronal differentiation involves a relay or cascade of growth factor action. Furthermore, chromaffin cell differentiation appears to involve two sequential, GC‐dependent events: the inhibition of neuronal differentiation and the induction of epinephrine synthesis. The former event is a prerequisite to the latter. Thus both the chromaffin and neuronal pathways of differentiation follow a series of dependent events, involving changes in the responsiveness of SA progenitors to environmental factors. Such changes correlate with changes in antigenic marker expression that can be observed in vivo. In addition to choosing between neuronal and endocrine fates, SA progenitors must also express an appropriate neurotransmitter phenotype. For example, sympathetic neurons can become either noradrenergic or cholinergic. This cholinergic potential is already present in uncommitted SA progenitors, as evidenced by their ability to synthesize acetylcholine. Recent studies suggest that these cells may have yet other developmental capacities, including the ability to synthesize serotonin. This capacity is consistent with the hypothesis that SA progenitors are closely related to progenitors of enteric neurons, an idea supported by recent observations using novel antigenic markers. The SA progenitor may be, therefore, a “master” neuroendocrine progenitor for the peripheral nervous system. © 1993 John Wiley & Sons, Inc.
Regulation of substance P is similar to that of vasoactive intestinal peptide after axotomy or explantation of the rat superior cervical ganglion
Authors: Rao M. S. , Sun Y. , Vaidyanathan U. , Landis S. C. , Zigmond R. E.
Published: January 2005

The regulation of the expression of substance P (SP) in the rat superior cervical ganglion was compared to that of vasoactive intestinal peptide (VIP) in vivo after axotomy and in vitro after explantation. Previous studies have demonstrated that both neuropeptides increase after explantation, depolarization, and decentralization; however, whereas VIP expression increases after postganglionic axotomy, SP expression reportedly does not. To compare the effect of axotomy on these two peptides directly, the content of both was determined in individual ganglia at various times after surgery. The level of VIP‐like immunoreactivity (IR) is increased at 2 days, reaches a peak at 6 days, and then declines by 14 days to approximately half its peak value. The level of SP‐IR also increases 2 days after axotomy, but returns to control values by day 6. The increase in SP‐IR is accompanied by an increase in β‐preprotachykinin mRNA, suggesting that the elevation in SP content is due, at least in part, toenhanced peptide synthesis. Immunocytochemical localization of SP‐IR revealed the presence of immunoreactive principal neurons in axotomized, but not in sham‐operated ganglia. Similarities in the regulation of these two neuropeptides were also investigated in organ culture by examining the effects of dexamethasone and interleukin‐1β on VIP content, since the former has been shown to prevent the increase in SP in culture, while the latter has been found to enhance this increase (Kessler, Adler, Bell, et al., 1983, Neuroscience 9:309–321; Freidin and Kessler, 1991, Proc. Natl. Acad. Sci. USA 88:3200–3203; Hart, Shadiack, and Jonakait, 1991, J. Neurosci. Res. 29:282–291). As with SP expression, dexamethasone reduces the increases in VIP expression, while interleukin‐1β increases it. Thus, both in vivo and in vitro, similar changes in VIP and SP expression are observed following a number of experimental manipulations, suggesting that expression of the two peptides is regulated by qualitatively similar mechanisms in sympathetic neurons. © 1993 John Wiley & Sons, Inc.
Accommodation of mouse DRG growth cones to electrically induced collapse: Kinetic analysis of calcium transients and set‐point theory
Authors: Fields R. Douglas , Guthrie Peter B. , Russell James T. , Kater Stanley B. , Malhotra Bithika S. , Nelson Phillip G.
Published: January 2005

Electrical stimulation causes growth cones of mouse dorsal root ganglion neurons to collapse. During chronic stimulation, however, growth cones resume motility. In addition, these growth cones are now resistant to the collapsing effects of subsequent stimulation, a process we term accommodation. We compared the kinetics of electrically induced Ca2+ transients in naive and accommodated growth cones in order to determine whether the accommodation process results from a change in the Ca2+ transient, or a change in the Ca2+ sensitivity of the growth cones. Three kinetics were determined: (1) the initial increase to peak Ca2+ levels produced by 10 Hz stimulation; (2) recovery from peak Ca2+ levels during stimulus trains lasting 15 min; and (3) clearing of Ca2+ from growth cones after terminating the stimulus. These kinetics were analyzed using single exponential fits to changes in fura‐2 fluorescence ratios. The electrically evoked increase in Ca2+ was significantly slower in accommodated growth cones (τ = 6.0 s) compared to naive growth cones (τ = 1.4 s). Desptie the slower increase of [Ca2+]i in accommodated growth cones, peak [Ca2+]i was similar to that reached in naive growth cones, and the steady‐state Ca2+ level was significantly elevated after chronic stimulation. Thus, accommodated growth cones maintained outgrowth at [Ca2+]i that caused collapse initially. Time course experiments show that accommodation is a slow process (t1/2 = about 3 h). Accommodation did not induce measurable changes in the rates of Ca2+ homeostasis during or after stimulus trains. The kinetics of Ca2+ recovery during (τ = 90 s) and after 15 min of stimulation (τ = 8.5 s) was not significantly different in accommodated versus naive growth cones. Rates of 45Ca2+ efflux were also similar in both types of growth cones. These results suggest two regulatory processes contributing to growth cone motility during chronic stimulation: (1) recovery of [Ca2+]i to levels permissive to neurite outgrowth, and (2) an increase in the range of optimal [Ca2+]i for growth cone motility. These adaptive responses of mammalian growth cones to chronic stimulation could be involved in the modulation of CNS development by electrical activity of neurons. © 1993 John Wiley & Sons, Inc.

This article is a US Government work and, as such, is in the public domain in the United States of America.
Differential sensitivity to androgens within a sexually dimorphic muscle of male frogs (Xenopus laevis)
Authors: Regnier Michael , Herrera Albert A.
Published: January 2005

Male frogs use their forelimb flexor muscles to clasp females during the mating behavior known as amplexus. We investigated the effects of testosterone on a principal forelimb flexor, the flexor carpi radialis muscle (FCR), using morphological and histochemical techniques. Male Xenopus laevis were surgically manipulated to produce high or low levels of circulating testosterone for an 8‐week period. After this treatment, measurement of fibers in muscle cross‐sections revealed that average fiber size was positively correlated with testosterone level. This effect was not the same for all muscle fibers, however. Fibers in the shoulder region were more sensitive to testosterone than fibers in other regions of the muscle. Histochemical staining of cross‐sections showed that the patterns of staining for myosin ATPase or succinic dehydrogenase (SDH) were not influenced by testosterone levels, but total SDH activity was increased by testosterone treatment. When sensitivity to testosterone was correlated with ATPase activity, fibers with high ATPase activity were found to be more sensitive to testosterone than fibers with low activity, regardless of position within the muscle. Most fibers with high ATPase activity were located in the shoulder region of the muscle. These fibers are innervated by different motor axons than are fibers in the elbow region of the muscle, and contractions of shoulder (but not elbow) region fibers, elicited by stimulation of motor axons, are slowed by testosterone treatment (Regnier and Herrera, 1993, J. Physiol. 461:565–581). © 1993 John Wiley & Sons, Inc.
Emx and Otx homeobox genes in the developing mouse brain
Authors: Boncinelli Edoardo , Gulisano Massimo , Broccoli Vania
Published: January 2005

We have analyzed the expression of four mouse homeobox genes related to two Drosophila genes expressed in the developing head of the fly. Two of these genes, Emx1 and Emx2, are related to empty spiracles, and two genes, termed Otx1 and Otx2, are related to orthodenticle. These genes are all expressed in the developing rostral brain of E10 mouse embryos and their expression domains can be compared. Otx2 is expressed in all dorsal and most ventral regions of telencephalon, diencephalon, and mesencephalon. The Otx1 expression domain is similar to that of Otx2, but smaller and contained within it. The Emx2 expression domain is comprised of dorsal telencephalon and small diencephalic regions, both dorsally and ventrally. Finally, Emx1 expression is exclusively confined to the dorsal telencephalon. At the time when regional specification of major brain regions takes place, the expression domains of the four genes appear to be continuous regions contained within each other in the sequence Emx1 <Emx2 < Otx1 < Otx2. The first appearance of transcripts of the four genes is also sequential: Otx2 is expressed first (E5.5), followed by Otx1 and Emx2 (E8–8.5), and finally by Emx1 (E9.5). It is tempting to speculate about a possible role of the four genes in establishing and/or signalling the limits of the various embryonic brain regions in a discrete progressive process with its center in the dorsal telencephalon. © 1993 John Wiley & Sons, Inc.
Synapse elimination from the mouse neuromuscular junction in vitro: A non‐hebbian activity‐dependent process
Authors: Nelson Phillip G. , Fields R. Douglas , Yu Chang , Liu Yuan
Published: January 2005

The effect of action potentials on elimination of mouse neuromuscular junctions (NMJ) was studied in a three compartment cell culture preparation. Axons from superior cervical ganglion or ventral spinal cord neurons in two lateral compartments formed multiple neuromuscular junctions with muscle cells in a central compartment. The loss of synapses over a 2–7‐day period was determined by serial electrophysiological recording and a functional assay. Electrical stimulation of axons from one side compartment during this period, using 30‐Hz bursts of 2‐s duration, repeated at 10‐s intervals, caused a significant increase in synapse elimination compared to unstimulated cultures (p< 0.001). The extent of homosynaptic and heterosynaptic elimination was comparable, i. e., of the 226 functional synapses of each type studied, 111 (49%) of the synapses that had been stimulated were eliminated, and 87 (39%) of unstimulated synapses on the same muscle cells were eliminated. Also, simultaneous bilateral stimulation caused significantly greater elimination of synapses than unilateral stimulation (p< 0.005). These observations are contrary to the Hebbian hypothesis of synaptic plasticity. A spatial effect of stimulus‐induced synapse elimination was also evident following simultaneous bilateral stimulation. Prior to stimulation, most muscle cells were innervated by axons from both side compartments, but after bilateral stimulation, muscle cells were predominantly unilaterally innervated by axons from the closer compartment. These experiments suggest that synapse elimination at the NMJ is an activity‐dependent process, but it does not follow Hebbian or anti‐Hebbian rules of synaptic plasticity. Rather, elimination is a consequence of postsynaptic activation and a function of location of the muscle cell relative to the neuron. An interaction between spatial and activity‐dependent effects on synapse elimination could help produce optimal refinement of synaptic connections during postnatal development. © 1993 John Wiley & Sons, Inc.
Calcium‐dependent postsynaptic exocytosis: A possible mechanism for activity‐dependent synaptic modulation
Authors: Dan Yang , Poo Mu‐ming
Published: January 2005

Elevation of cytosolic Ca2+ level in the postsynaptic cell is critical for the induction of many forms of activity‐dependent synaptic modulation. Based on our recent evidence that in muscle cells and fibroblasts constitutive exocytosis is increased by elevating cytosolic Ca2+ levels, we hypothesize that Ca2+ ‐dependent exocytosis at the postsynaptic site may provide a mechanism for a localized, activitt‐dependent synaptic modulation. 1994 John Wiley & Sons, Inc.
Regeneration and molting effects on a proprioceptor organ in the dungeness crab, Cancer magister
Authors: Hartman H. Bernard , Cooper Robin L.
Published: January 2005

Decapoda Crustacea molt in order to grow; some species, such as the Dungeness crab Cancer magister, achieve a very large size. Does sendory neuron hyperplasia in internal proprioceptors accompany this growth? To determine this, neurons in propodite‐dactylopodite (PD) chordotonal organs were counted in first walking legs of juvenile (5th through 9th instar) and adult (10th through 13th instar) C. magister. We found that the PD organs of J5 crabs have about 56 neurons; the number increases to about 61 neurons in J6 crabs. Significant hyperplasia now occurs because an average of 79 neurons are found in the PD organs of J7 crabs. Little to no hyperplasia accompanies the several succeeding juvenile and adult molts (ca. 82–86 neurons are present). Because autotomized limbs are regenerated upon molting, we also examined how the number of PD organ neurons in regenerated legs compare with those of pristine legs. Newly regenerated legs (termed 1st stage regenerates) have fewer sensory neurons than do their contralateral pristine partners (65 vs 81); larger regenerated legs which have attained nearly normal size as a result of additional molts (2nd stage regenerates) still have fewer neurons than their pristine partners (69 vs 81). Additionally, in contrast to those of pristine walking legs, the elastic strand of PD organs from 1st stage regenerates is a misshapen sheet containing a cluster of small neurons with no obvious functional organization. Nonetheless, neurophysiological recordings indicate that all the receptor types typical for pristine legs (movement and position cells) are represented. The PD organs of 2nd stage regenerates differentiate to the shape and neuronal organization of pristine legs. © 1994 John Wiley & Sons, Inc.
Thyroxine treatment and the recovery of pyramidal cells of the cerebral cortex from changes induced by juvenile‐onset hypothyroidism
Authors: Ruiz‐Marcos Antonio , Cartagena‐Abella Pedro , Martinez‐Galan Juan Ramón , Calvo Rosa , de Escobar Gabriela Morreale , del Rey Francisco Escobar
Published: January 2005

In contrast to the permanent alterations resulting from neonatal hypothyroidism, the effects of juvenile‐onset hypothyroidism on the number and distribution of spines along the apical shaft by pyramidal neurons of the visual cortex appeared to be potentially reversible with adequate thyroxine (T4) therapy (Ruiz‐Marcos et al., 1980, Brain Res. 185:91–102 and 1982, Brain Res. 239:559–574). Treatment with 0.20 or 1.50 μg T4/100 g body weight per day had, however, only partially reversed the changes induced by juvenile‐onset hypothyroidism. We here study whether or not a higher dose of T4 would totally reverse these effects. A group of rats were thryoid‐ectomized at 40 days of age, and injected once daily with placebo or T4 (1.75 μg/100 g BW per day) from 70 to 90 days of age, a group on 1.50 μg being included to compare with previous results. Spine number and distribution‐were measured, as well as the concentrations of T4 and triidothyronine (T3) in plasma, liver and brain. The activities of two hepatic enzymes were measured as thyroid hormone‐sensitive biological end points. The 1.75‐μg dose restored spine number to 88% of normal values and was markedly more effective than the 1.50‐μg dose, which increased it to 68%. The degree of restoration appeared related to the concentration of T3. It is concluded that the changes caused by juvenile‐onset hypothyroidism in the number and distribution of dendritic spines along the apical shafts of pyramidal neurons are reversible, although complete restoration might require a higher dose of T4, a continuous mode of administration, or longer period of treatment. 1994 John Wiley & Sons, Inc.
Sexual differentiation of brain and behavior in the zebra finch: Critical periods for effects of early estrogen treatment
Authors: Adkins‐Regan E. , Mansukhani V. , Seiwert C. , Thompson R.
Published: January 2005

In order to determine the critical period(s) during which estrogen alters sexually dimorphic behavior and neuroanatomy in zebra finches (Poephila guttata), nestlings were injected daily 20 μg estradiol benzoate (EB) during posthatching week 1, week 2, week 3, or weeks 1, 2, and 3. At 7 months of age, birds were implanted with testosterone propionate and tested with female partners for singing, dancing, and copulatory mounting. Brains were subsequently processed for morphometry, and the volumes of the song system nuclei HVC, area X, and RA and the soma sizes and densities of neurons in RA were determined. Males given EB during week 1 failed to mount. Females given EB during week 1 were fully masculinized with respect to dancing and RA neuron soma size and density, and were partially masculinized with respect to song nuclei volumes and singing. Treatment beginning after week 1 was ineffective or less effective for all measures. Only for RA neuron measures was treatment for all three weeks more effective than week 1 treatment. Thus the first post‐hatching week is the most influential period of those tested for effects of exogenous estrogen on sexual differentiation in this species, and is a period during which both masculinization of females and demasculinization of males is possible. 1994 John Wiley & Sons, Inc.
Differential neural regulation of a neuromuscular junction‐associated antigen in muscle fibers and Schwann cells
Authors: Astrow Stephanie H. , Son Young‐Jin , Thompson Wesley J.
Published: January 2005

Monoclonal antibodies 3G2 and 4E2 recognize a postsynaptic component of rat neuromuscular junctions. In contrast to many other postsynaptic junctional antigens, expression of this antigen is nerve‐dependent: immunoreactivity disappears form junctions following denervation and returns upon reinnervation (Astrow et al., 1992 J. Neurosci. 12:1602–1615). Here we show that the epitope is also expressed by Schwann cells and that this expression is also neurally regulated. Weak mAb 3G2/4E2 immunoreactivity was found in myelinating Schwann cells but was not detected in either nonmyelinating Schwann cells or in terminal Schwann cells at the neuromuscular junction. Following axotomy, immunoreactivity increased in myelinating Schwann cells, and nonmyelinating and terminal Schwann cells became immmunopositive. Moreover, the immunoreactivity in terminal Schwann cells revealed their extensive sprouting in response to denervation (Reynolds and Woolf, 1992, J. Neurocytol. 21:50–66). After nerve regeneration, mAb 3G2/4E2 immunoreactivity in all Schwann cells returned towards normal: it disappeared from temrinal Schwann cells, returned to low levels in myelinating Schwann cells, and decreased in nonmyelinating Schwann cells. Immunoblots of axotomized nerve and cultured muscle fibers revealed the same set of immunoreactive bands. Therefore, Schwann cells and muscle fibers share the expression of an epitope that is under neural control, but is regulated differently at each site. In Schwann cells, the presence of the nerve suppresses expression of the epitope, whereas in muscle fibers, the nerve terminal promotes this expression. The differential regulation of mAb 3G2/4E2 immunoreactivity in terminal Schwann cells and muscle fibers suggests that the epitope may be involved in interactions between nerve terminals and these cells. 1994 John Wiley & Sons, Inc.
Cell surface contact mediates neuronal recognition and synapse formation between two identified leech neurons
Authors: Merz David C. , Drapeau Pierre
Published: January 2005

An early event in the formation of the serotonergic synapse by the Retzius (R) onto the pressure‐sensitive (P) neurons of the leech is the elimination of an extrasynaptic response to transmitter from sites of contact on the postsynaptic cell. This event during synapse formation is cell‐specific in that it is elicited in vitro by contact with the presynaptic R cell but not with other neurons. In the study reported here, we investigated the nature of this interaction between R and P neurons. The loss of the extrasynaptic response of the P cell was elicited by contact with R cells fixed in a mild paraformaldehyde solution, but not by R cells treated with the proteolytic enzyme trypsin prior to fixation. As well, a variety of lectins were assayed for their ability to interfere with synapse formation. The transmitter responses of P cells plated on lectin‐coated substrates were unaffected. However, exposure of the R cell to the lectin wheat germ agglutinin (WGA), but not to other lectins, prior to pairing prevented the loss of the extrasynaptic response in contacted P cells and blocked the formation of the RP synapse in culture. We conclude that recognition by the P cell of the R cell during synapse formation may be mediated by an R cell‐specific surface protein which binds wheat germ agglutinin. 1994 John Wiley & Sons, Inc.
Identification of CDK‐ and cyclin‐like proteins in the eye of Bulla gouldiana
Authors: Krucher Nancy A. , Roberts Michael H.
Published: January 2005

The ocular circadian rhythm in the eye of Bulla gouldiana is generated by a rhythm in membrane potential of retinal neurons that is driven by alterations in potassium conductance. Since potassium conductance may be modulated by the phosphorylation of potassium channels, the circadian rhythm may reflect rhythmic changes in protein kinase activity. Furthermore, the circadian rhythm recorded from the Bulla eye can be phase shifted by agents that affect protein synthesis and protein phosphorylation on tyrosine residues. Interestingly, the eukaryotic cell division residues. Interestingly, the eukaryotic cell division cycle is generated by similar processes. Rhythmic cell division is regulated by periodic synthesis and degradation of a protein, cyclin, and periodic tyrosine phosphorylation of a cyclin‐dependent kinase (cdk), p34cdc2. The interaction between these two proteins results in rhythmic kinase activity of p34cdc2. Both cyclin and p34cdc2 are pat of two diverse gene families, some of whose members have been localized to postmitotic cell types with no function yet determined. In the current work, we identify proteins similar to the cdks and cyclin in the eye of Bulla. Neither of these ocular proteins are found in mitotic cells in Bulla, and the cdk‐like protein (p40) is specific to the eye. Furthermore, the concentration of the cyclin‐like protein (p66) is affected by treatments that phase shift the circadain rhythm. The identification of cdk and cyclin‐like proteins in the Bulla eye is consistent with the hypothesis that the biochemical mechanism responsible for generating the ocular circadian rhythm in Bulla is related to the biochemical mechnism that regulates the eukaryotic cell division cycle. 1994 John Wiley & Sons, Inc.
Activity‐dependent and hormonal regulation of neurotrophin mRNA levels in brain–implications for neuronal plasticity
Authors: Lindholm Dan , Castrén Eero , Berzaghi Maria , Blöchl Andrea , Thoenen Hans
Published: January 2005

The neurotrophins exhibit neurotrophic effects on specific, partially overlapping populations of neurons both in the peripheral and the central nervous system (CNS). In the periphery, they are synthesized by a variety of nonneuronal cells, and their synthesis seems to be independent of the neuronal input. In contrast, in the CNS all neurotrophins are expressed under physiological conditions primarily by neurons. The production of NGF and BDNF is controlled by neuronal activity: up‐regulation by glutamate and acetylcholine, down‐regulation by gamma‐aminobutyric acid. In contrast, NT‐3 regulation is independent of neuronal activity, but it is up‐regulated by thyroid hormones and BDNF. The latter observation suggests that NT‐3 might be controlled indirectly by neuronal activity via BDNF. In peripheral nonneuronal tissues, glucocorticoid hormones down‐regulate NGF mRNA levels both in vitro and in vivo. In contrast, in the CNS, neuronal production of NGF is enhanced by glucocorticoids. The rapid regulation of NGF and BDNF by subtle physiological stimuli together with the recent demonstration that the neurotrophin release neurotransmitters such as acetylcholine opens up interesting perspectives for the function of neurotrophins as mediators of neuronal plasticity. 1994 John Wiley & Sons, Inc.
Dorsoventral patterning of the avian mesencephalon/metencephalon: Role of the notochord and floor plate in suppressing Engrailed‐2
Authors: Darnell Diana K. , Schoenwolf Gary C.
Published: January 2005

Transcription factors that are spatially and temporally restricted within the embryo may be used for dorsoventral and rostrocaudal positional information during development. The Engrailed‐2 (En‐2) gene is expressed across the mesencephalon/metencephalon (mes/met) boundary in the cerebellar primordium with strong dorsolateral expression and limited expression in the floor plate. In a previous experiment we demonstrated that, after removal of Hensen's node, embryos lacked a notochord in the head and the pattern of En‐2 expression was normal rostrocaudally, but it was expanded into the ventral midline of the neural tube. This suggested that the notochord suppresses En‐2 in the ventral neural tube during normal development. To test further the ability of the notochord (and floor plate) to suppress En‐2, we transplanted ventral midline tissues from HH 5–9 quail embryos beneath the rostral neural plate of HH 4–6 chick embryos. After 24 hours in culture, 90% of the embryos with quail notochord or floor plate near the mes/met of the host lacked En‐2 expression adjacent to the graft, and suppression was distance dependent. Enzymatically isolated notochords also suppressed En‐2 (71%), but the results from isolated floor plates were inconclusive. Other grafts served as controls and included tissues from the trunk ventral midline, mes/met level dorsolateral neural plate, and trunk dorsolateral neural plate/somite. Collectively, the results suggest that during normal development the notochord and possibly the floor plate are important regulators of normal En‐2 expression. © 1995 John Wiley & Sons, Inc.
Development of wing sensory axons in the central nervous system of Drosophila during metamorphosis
Authors: Whitlock Kathleen E. , Palka John
Published: January 2005

The development of new, adult‐specific axonal pathways in the central nervous system (CNS) of insects during metamorphosis is still largely uncharacterized. Here we used axonal labeling with DiI to describe the timing and pattern of growth of sensory axons originating in the wing of Drosophila as they establish their adult projection pattern in the CNS during pupal life. The wing of Drosophila carries a small number of readily identifiable sensory organs (sensilla) whose neurons are located in the periphery and whose axons travel along specific routes within the adult CNS. The neurons are born and undergo axonogenesis in a characteristic order. The order of axon arrival in the CNS appears to be the same as that of their development in the periphery. Within the CNS, the formation of four prominent axon bundles leading to distant termination sites is followed by the formation of a compact axon termination site near the point of wing nerve entry into the CNS. This sensillum‐specific pattern persists into adulthood without discernible modification. We also find a small number of axons filled with DiI prior to the formation of the four permanent bundles. We have only been able to fill them for a few hours in early pupal life and therefore consider them to be transient. The bundles of wing sensory axons travel within tracts that contain other axons as well. Using immunocytochemistry, the tracts start to be histologically identifiable at around 12 h after pupariation (AP), and grow substantially as metamorphosis proceeds. Wing sensory neurons are found in the tracts by 18–20 h AP and the full adult pattern is established by 48 h AP. When sensory axons first enter the CNS, they fan out in the region where their appropriate tracts are located, but they do not wander extensively. They quickly form bundles that become increasingly compact over time. Calculations show that the rate of axon extension within the CNS varies from bundle to bundle and is equal to or greater than that of the same axons growing through wing tissue. © 1995 John Wiley & Sons, Inc.
Postnatal maturation of gamma‐aminobutyric acidA and B‐mediated inhibition in the CA3 hippocampal region of the rat
Authors: Gaiarsa Jean‐Luc , McLean Heather , Congar Patrice , Leinekugel Xavier , Khazipov Rustem , Tseeb Vadim , Ben‐Ari Yehezkel
Published: January 2005

In the adult central nervous system, GABAergic synaptic inhibition is known to play a crucial role in preventing the spread of excitatory glutamatergic activity. This inhibition is achieved by a membrane hyperpolarization through the activation of postsynaptic γ‐aminobutyric acidA (GABAA) and GABAB receptors. In addition, GABA also depress transmitter release acting through presynaptic GABAB receptors. Despite the wealth of data regarding the role of GABA in regulating the degree of synchronous activity in the adult, little is known about GABA transmission during early stages of development. In the following we report that GABA mediates most of the excitatory drive at early stages of development in the hippocampal CA3 region. Activation of GABAA receptors induces a depolarization and excitation of immature CA3 pyramidal neurons and increases intracellular Ca2+ ([Ca2+]i) during the first postnatal week of life. During the same developmental period, the postsynaptic GABAB‐mediated inhibition is poorly developed. In contrast, the presynaptic GABAB‐mediated inhibition is well developed at birth and plays a crucial role in modulating the postsynaptic activity by depressing transmitter release at early postnatal stages. We have also shown that GABA plays a trophic role in the neuritic outgrowth of cultured hippocampal neurons. © 1995 John Wiley & Sons, Inc.
Retrograde but not anterograde bead movement in intact axons requires dynein
Authors: Wang Chang , Asai David J. , Robinson Kenneth R.
Published: January 2005

Dynein and kinesin have been implicated as the molecular motors that are responsible for the fast transport of axonal membranous organelles and vesicles. Experiments performed in vitro with partially reconstituted preparations have led to the hypothesis that kinesin moves organelles in the anterograde direction and dynein moves them in the retrograde direction. However, the molecular basis of transport directionality remains unclear. In the experiments described here, carboxylated fluorescent beads were injected into living Mauthner axons of lamprey and the beads were observed to move in both the anterograde and retrograde directions. The bead movement in both directions required intact microtubules, occurred at velocities approaching organelle fast transport in vivo, and was inhibited by vanadate at concentrations that inhibit organelle fast transport. When living axons were injected with micromolar concentrations of vanadate and irradiated at 365 nm prior to bead injections, a treatment that results in the V1 photolysis of dynein, the retrograde movement of the beads was specifically abolished. Neither the ultraviolet irradiation alone nor the vanadate alone produced the retrograde‐specific inhibition. These results support the hypothesis that dynein is required for retrograde, but not anterograde, transport in vivo. © 1995 John Wiley & Sons, Inc.
Regionalization and segmentation of the leech
Authors: Wedeen Cathy J.
Published: January 2005

Regionalization and segmentation of the leech body plan have been examined by numerous approaches over the years. A wealth of knowledge has accumulated regarding the normally invariant cell lineages of the leech and the degree of developmental plasticity that is possible in each cell line in early development and in neurogenesis. Homologues of genes that control regionalization and segmentation in Drosophila have been cloned from the leech and the expression patterns reveal conserved features with those in Drosophila and other organisms. Possible developmental functions of the en‐class proteins in spatial and temporal modes of segment formation are discussed in light of leech and Drosophila development. Annelida and Arthropoda cell lineages of engrailed‐class gene expression are compared in leech blast cell clones and crustacean parasegments. In addition, future directions for molecular analysis of segmentation of the leech are summarized. © 1995 John Wiley & Sons, Inc.
Development of midbrain and anterior hindbrain ocular motoneurons in normal and Wnt‐1 knockout mice
Authors: Fritzsch B. , Nichols D. H. , Echelard Y. , McMahon A. P.
Published: January 2005

The effect of homozygotic Wnt‐1−/− mutations on the development of ocular motoneurons was examined with the lipophilic dye DiI and compared to control and phenotypic wild‐type mouse embryos. A piece of DiI‐soaked filter paper was inserted into the orbit, the midbrain, or rhombomere 5 of the hindbrain in six paraformaldehydefixed litters (10.5, 12.5, and 14.5 days postcoitum) containing Wnt‐1, Wnt+/−, and Wnt‐1+/+ individuals and three control litters. We labeled all ocular motoneurons retrogradely and all relevant nerves anterogradely in all control and phenotypic wild‐type animals. In all phenotypically identified Wnt‐1−/− mutants we could always label the abducens nerve and motoneurons and the optic fibers to the thalamus, but we were unable to lable oculomotor or trochlear nerves or motoneurons. In addition to Wnt‐1 knockout mutants, we also labeled mice from the WZT9B transgenic line carrying a lacZ reporter gene driven by the Wnt‐1 gene enhancer. In these embryos we tested for co‐localization of Wnt‐1 expression in biotinylated dextran amine‐labeled ocular motoneurons using a newly developed technique. In younger embryos we obtained evidence for co‐localization of the β‐galactosidase reaction product derived from lacZ gene activity in some retrogradely filled oculomotor motoneurons and adjacent to other oculomotor and the trochlear motoneurons. Acetylcholine esterase, a marker of early differentiating cholinergic neurons, showed a similar topology with respect to the lacZ reaction product. Thus, at least some future oculomotor motoneurons express Wnt‐1, whereas others and the trochlear motoneurons caudal to the ventral midbrain expression of Wnt‐1 may be exposed to the short range diffusion of the Wnt‐1 gene product. Thus, the Wnt‐1−/− mutation precludes formation or survival of midbrain and anterior hindbrain neurons, including oculomotor and trochlear motoneurons. © 1995 John Wiley & Sons, Inc.
Role of local nonspiking interneurons in the generation of rhythmic motor activity in the stick insect
Authors: Büschges Ansgar
Published: January 2005

Local nonspiking interneurons in the thoracic ganglia of insects are important premotor elements in posture control and locomotion. It was investigated whether these interneurons are involved in the central neuronal circuits generating the oscillatory motor output of the leg muscle system during rhythmic motor activity. Intracellular recordings from premotor nonspiking interneurons were made in the isolated and completely deafferented mesothoracic ganglion of the stick insect in preparations exhibiting rhythmic motor activity induced by the muscarinic agonist pilocarpine. All interneurons investigated provided synaptic drive to one or more motoneuron pools supplying the three proximal leg joints, that is, the thoraco‐coxal joint, the coxa‐trochanteral joint and the femur‐tibia joint. During rhythmicity in 83% (n=67) of the recorded interneurons, three different kinds of synaptic oscillations in membrane potential were observed: (1) Oscillations were closely correlated with the activity of motoneuron pools affected; (2) membrane potential oscillations reflected only certain aspects of motoneuronal rhythmicity; and (3) membrane potential oscillations were correlated mainly with the occurrence of spontaneous recurrent patterns (SRP) of activity in the motoneuron pools. In individual interneurons membrane potential oscillations were associated with phase‐dependent changes in the neuron's membrane conductance. Artificial changes in the interneurons' membrane potential strongly influenced motor activity. Injecting current pulses into individual interneurons caused a reset of rhythmicity in motoneurons. Furthermore, current injection into interneurons influenced shape and probability of occurrence for SRPs. Among others, identified nonspiking interneurons that are involved in posture control of leg joints were found to exhibit the above properties. From these results, the following conclusions on the role of nonspiking interneurons in the generation of rhythmic motor activity, and thus potentially also during locomotion, emerge: (1) During rhythmic motor activity most nonspiking interneurons receive strong synaptic drive from central rhythm‐generating networks; and (2) individual nonspiking interneurons some of which underlie sensory‐motor pathways in posture control, are elements of central neuronal networks that generate alternating activity in antagonistic leg motoneuron pools. © 1995 John Wiley & Sons, Inc.
Differential regulation of motor neuron survival and choline acetyltransferase expression following axotomy
Authors: Kou Shi‐Ying , Chiu Arlene Y. , Patterson Paul H.
Published: January 2005

Although it is well known that motor neuron survival following axotomy is enhanced with maturation, the ability of surviving neurons to express the cholinergic enzyme choline acetyltransferase (ChAT) following axotomy has not been closely examined. Moreover, the utility of the facial nucleus in studies of motoneuron response to injury and to trophic factors, coupled with the increasing importance of the mouse in gene targeting, compelled us to investigate the age dependence of neuronal survival and ChAT expression in the mouse facial nucleus following axotomy. We cut the facial nerve at postnatal day (P)4, 7, 14, 21, and 28 or in the adult and used Nissl staining and ChAT immunocytochemistry to quantitate survival and ChAT expression, respectively, following 1, 2, or 3 weeks' survival at each age. We confirm in this model that the rate and extent of motor neuron death following axotomy is reduced with increasing maturity. The surviving neurons maintain a high ChAT content through P21; however, axotomy from P28 through adulthood results in a striking reduction in ChAT immunoreactivity. That is, although axotomy at P21 results in 61% motor neuron survival, with virtually all of the surviving neurons being ChAT positive, axotomy in the adult results in 72% survival but only 9% of the neurons are ChAT positive. Thus, surviving motor neurons in the adult animals are only weakly cholinergic. These results indicate that a change in the regulation of ChAT expression occurs following P21 so that cell survival and enzyme levels are uncoupled. We suggest that the putative factor or factors that enhances motor neuron survival in maturity is not capable of maintaining ChAT expression. © 1995 John Wiley & Sons, Inc.