bluuebunny/crossref_metadata_2025 huggingface dataset:
Small sex differences in song control dendrites are associated with minimal differences in song capacity
Authors: Devoogd T. J. , Brenowitz E. A. , Arnold A. P.
Published: January 2005

Previous work on canaries and zebra finches has shown that large differences between the sexes exist in the structure of dendrites in n. robustus archistriatalis (RA), one of the principal nuclei involved in the control of song. This sex difference is associated with a general or complete absence of song in females. If dendritic morphology in RA is causally related to capacity for song, large sex differences in structure should not occur in avian species in which both sexes sing. We now report this prediction confirmed for buff‐breasted wrens (Thryothorus leucotis), a species in which the members of a breeding pair sing duets with each other. Total dendritic length and number of dendritic branches in RA do not differ in this species. Dendrites from males project about 8 μm further from the cell body than dendrites from females, apparently because of longer dendritic segments near the cell body. We argue that this suggests that differential influences on the structure of RA occurred early in the lives of the wrens.
The release of axonally transported material from an in vitro amphibian sciatic nerve preparation
Authors: Snyder R. E.
Published: January 2005

The rapid axonal transport of a pulse of [35S]methionine‐labelled material was used to study the release of transported material from amphibian nerve maintained in vitro. Following creation of a moving pulse of activity in a dorsal root ganglion‐sciatic nerve preparation, the ganglion was removed and the nerve placed in a three‐compartment tray, the section of nerve in the middle compartment containing no truncated branches (unbranched section). All three compartments were filled with a saline solution that in some studies contained nonradioactive methionine (1.0 mmol/L). Analysis of studies in which nonradioactive methionine was absent revealed that labelled material appeared in the bathing solution of the end compartments that contained truncated branches, but not in the solution of the middle (unbranched) compartment. The quantity of label released in the branched compartments was approximately 6% of that remaining in the corresponding section of nerve following an 18–20 h incubation period. However, when nonradioactive methionine was present, all compartments showed an additional activity in the bathing solution of approximately 10% of that remaining in the nerve. In another study in which a position‐sensitive detector of ionizing radiation was used to monitor progress of the pulse, it was found that activity did not enter the bathing solution of a compartment prior to the pulse of activity. It is concluded that in the absence of methionine from the bathing solution, axonally transported material is released only from regions of nerve that contain severed axons; however, the presence of methionine allows transported material to be released from nerve containing intact axons. Ultrafiltration studies and thin‐layer chromatography revealed the majority of material released to be of low‐molecular weight (≤ 30,000 daltons) and not free [35S]methionine.
Sex differences in the motor nucleus of cranial nerve IX‐X in Xenopus laevis: A quantitative Golgi study
Authors: Kelley Darcy B. , Fenstemaker Suzanne , Hannigan Patricia , Shih Scott
Published: January 2005

In the clawed frog (Xenopus laevis), motor neurons in cranial nerve nucleus IX‐X control contraction of laryngeal muscles responsible for sexually dimorphic vocal behaviors. We examined sex differences in dendritic arbors of n.IX‐X cells using the Golgi–Cox method. Three morphological classes of somal types (ovoid, triangular, and elongate) are present in similar frequencies in n.IX‐X of both males and females. The male n.IX‐X neuron is a more complex and hypertrophied version of the female n.IX‐X cell. The number of primary dendrites is the same for both sexes, but males have more total dendritic segments. The overall dendritic length of male n.IX‐X neurons is two to three times that of the female. Males have longer dendritic segments between all branch points.

Male and female frogs differ in levels of circulating androgens; neurons of n.IX‐X are targets for androgenic steroids. To determine if androgen can affect dendritic morphology in adult females, we examined Golgi‐impregnated cells in n.IX‐X from ovariectomized females treated with testosterone for 1 month. The total number of dendritic segments was reduced by androgen treatment due to reduction in the number of higher order dendritic segments; the number of primary dendritic segments was unchanged. Androgen treatment may induce resorption of higher order dendritic branches. The overall dendritic length of androgen‐treated female n.IX‐X neurons was unchanged, and dendritic segments were longer. Thus, although androgen can alter dendrites of n.IX‐X cells in adult females, this short‐term treatment does not produce a masculine dendritic architecture.
Neural attrition following limb loss and regeneration in juvenile lobsters
Authors: Govind C. K. , Pearce J. , Potter D. J.
Published: January 2005

Lobsters have considerable regenerative capacity, being able to regrow an entire, albeit smaller, limb in one intermolt. Whether there is a corresponding downscaling in the hemiganglion and its nerves to the regenerate side compared with its contralateral intact side was examined in juvenile lobsters which had undergone single or multiple (2, 4, and 6) cycles of limb loss and regeneration on the one side. The limbs studied were the enlarged thoracic chelipeds or claws which appeared as paired symmetrical cutter‐type claws. The size of the regenerate limb, as indicated by its propus length, was approximately 30% smaller than its intact counterpart. Correspondigly, the total number of axons in the nerves to the regenerate side was smaller than on the intact, contralateral side. Such attrition was also by about 30% in lobsters experiencing a single cycle of limb loss and regeneration, but was considerably greater with multiple cycles. Tissue degeneration was occasionally seen in the nerves to the regenerate side but not in the ganglion. The paired hemiganglia were equivalent in all respects except in the size of the neuropil, which was smaller on the regenerate side compared with the contralateral intact side. Neuropil attrition was most marked with multiple cycles of limb loss and regeneration. Such attrition in nerve and neuropil are most likely due to the reduced number of sensory elements in the newly regenerated, but smaller, limb.
Structural plasticity at crustacean neuromuscular synapses
Authors: Govind C. K. , Walrond J. P.
Published: January 2005

Crustacean motor axons innervate muscle fibers via a multiplicity of synaptic terminals which release small but variable amounts of transmitter. Differences in release performance appear to be correlated with the size of synaptic contacts and presynaptic dense bars (active zones). These structural parameters proliferate via sprouting from existing synaptic terminals and relocate to ever more distal sites during development and growth of an identified axon. Moreover, alterations in number of synaptic contacts and active zones occur in adults following stimulation or decentralization, demonstrating structural plasticity of crustacean neuromuscular synapses.
Premotor neurons in the feeding system of Aplysia californica
Authors: Kirk Mark D.
Published: January 2005

Central pattern generator (CPG) circuits control cyclic motor output underlying rhythmic behaviors. Although there have been extensive behavioral and cellular studies of food‐induced feeding arousal as well as satiation in Aplysia, very little is known about the neuronal circuits controlling rhythmic consummatory feeding behavior. However, recent studies have identified premotor neurons that initiate and maintain buccal motor programs underlying ingesion and egestion in Aplysia. Other newly identified neurons receive synaptic input from feeding CPGs and in turn synapse with and control the output of buccal motor neurons. Some of these neurons and their effects within the buccal system are modulated by endogenous neuropeptides. With this information we can begin to understand how neuronal networks control buccal motor output and how their activity is modulated to produce flexibility in observed feeding behavior.
Regulation of high affinity choline uptake
Authors: Breer H. , Knipper M.
Published: January 2005

High affinity uptake of choline, the rate‐limiting, regulatory step for the synthesis of acetylcholine (ACh), was found to be regulated via presynaptic auto‐ and hetero‐receptors. The transport rate was reduced by a muscarinic agonist and neuropeptides, but was significantly enhanced by octopamine. Intracellular messengers, including cyclic nucleotides, appear to modulate the transport activity, apparently by activating specific protein kinases.
Depolarization regulates expression of a synaptic vesicle protein in rat superior cervical ganglia in vitro
Authors: Linderman Karen M. , Greif Karen F.
Published: January 2005

The role of membrane depolarization in the regulation of expression of a neuron specific protein was evaluated by culturing superior cervical ganglia from neonatal rats in defined medium and manipulating neuronal activity by depolarizing agents. P65 is an integral membrane protein of synaptic vesicles and can be used as a marker for general neuronal maturation. P65 antigen levels were quantified by indirect radioimmunoassay, using monoclonal antibodies. The expression of p65 in ganglion explants increased by 40–100% when the cultures were treated with the depolarizing agents, veratridine or high potassium. The veratridine effect could be blocked by simultaneous treatment with the sodium channel blocker, tetrodotoxin (TTX). The rise in p65 was not evident until 36 h after depolarizing treatment had begun and reached peak levels after 48 h, with no further increases observed with sustained treatment. After removal of the depolarizing treatment, p65 levels returned to control values after 24 h. P65 joins a growing number of molecules whose expression is regulated by membrane depolarization.
Giant Drosophila neurons differentiated from cytokinesis‐arrested embryonic neuroblasts
Authors: Wu Chun‐Fang , Sakai Kuniyoshi , Saito Mitsuyoshi , Hotta Yoshiki
Published: January 2005

The relative contributions of the intrinsic and extrinsic factors in determining neuronal differentiation are not fully understood yet. We found that isolated neuroblasts from Drosophila gastrulae were able to differentiate neuron‐specific properties in culture even when cell divisions were inhibited. The resultant giant multinucleated neurons displayed thickened neurites with a variety of distinct branching patterns. Neuronal antigens were expressed as in normal cultured neurons, and action potentials could be evoked by current injection within two days after plating. These results indicate that the factors for initiating specific differentiation programs for basic neuronal form and function are present in a neuroblast already. The cells of increased sizes in this culture system are more accessible to physiological and cell biological analyses and could facilitate future studies of the Drosophila nervous system.
Patterns of appearance of serotonin and proctolin immunoreactivities in the developing nervous system of the American lobster
Authors: Beltz Barbara S. , Pontes Manuel , Helluy Simone M. , Kravitz Edward A.
Published: January 2005

Serotonin (5‐HT) and proctolin, neurohormones widely distributed in the lobster nervous system, have been implicated in a variety of behaviors and also are known to coexist in large pairs of identified neurons in the fifth thoracic (T5) and first abdominal ganglia (A1) of adults (Siwicki, Beltz, and Kravitz, 1987). Earlier studies also have shown that these paired neurons already contain 5‐HT in embryos approximately halfway through development, whereas protolin immunoreactivity does not appear in these cells until near the time of hatching (Beltz and Kravitz, 1987a). In the current studies, the brain and ventral nerve cord have been screened for the appearance of serotonin and proctolin immunoreactivities using immunocytochemical and biochemical methods, in order to determine whether the late appearance of proctolin in the paired T5 and A1 cells is a general feature of development in other neurons as well. In embryos approximately halfway through development, the adult complement of 5‐HT‐staining cells is already present. In several cases, embryonic serotonin cells are proportionally very large and prominent, suggesting possible developmental roles. In contrast to serotonin, fewer than 10% of the proctolin‐staining neurons of juvenile animals are seen in embryos halfway through development. The number of immunoreactive cells gradually increases, but even by the sixth larval stage only half the number of cells that will eventually stain for proctolin are observed. Therefore, the developmental appearance of proctolin in lobster neurons, assayed using immunocytochemical methods, is relatively late and protracted compared to the appearance of serotonin. Quantitative measurements for 5‐HT in lobster larvae were performed using high pressure liquid chromatography (HPLC) with dual electrochemical detection, and for proctolin using radioimmunoassay. A gradual, probably growth‐related increase in the amounts of serotonin and proctolin were seen during larval development. The implications of the biochemical data, in light of the immunocytochemical studies, are discussed.
Coexpression of sensory and autonomic neurotransmitter traits by avian neural crest cells in vitro
Authors: Leblanc Gabrielle G.
Published: January 2005

This study shows that explants of quail neural crest cultured in a medium containing serum and chick embryo extract give rise to large numbers of cells expressing immunoreactivity for substance P (SP), a neuropeptide found in sensory neurons. These cells arise from cycling precursors, but do not appear to divide after expressing SP. The SP‐positive cells in cranial neural crest cultures express both neurofilament and the Q211 antigen, but those in trunk cultures express only the Q211 antigen. In both cranial and trunk cultures, large subpopulations of the SP‐positive cells express tyrosine hydroxylase and/or choline acetyltransferase, neurotransmitter markers characteristic of autonomic neurons. This finding argues against the idea that SP expression necessarily indicates commitment to the sensory neuron lineage. I further show that embryonic dorsal root ganglion (DRG) cells retain the ability to coexpress SP and tyrosine hydroxylase in vitro although to a lesser extent than do neural crest cells.
Neuron‐specific modulation by serotonin of regenerative outgrowth and intracellular calcium within the CNS of Helisoma trivolvis
Authors: Murrain Michelle , Murphy A. Don , Mills Linda R. , Kater Stanley B.
Published: January 2005

We have investigated the cell‐specific effect of serotonin (5‐HT) on regenerating neurons within the adult central nervous system of the pond snail, Helisoma trivolvis. In culture, 5‐HT arrests outgrowth of buccal neurons B19 but not neurons B5 (Haydon, McCobb, and Kater, 1984). After axotomy, neurons within the Helisoma nervous system typically exhibit profuse regenerative outgrowth. This study, on neurons within the CNS, shows that 5‐HT selectively inhibits the outgrowth of specific identified neurons, and also causes significant elevations in intracellular calcium concentrations as measured by the calcium indicator dye, Fura‐2. The outgrowth of neurons B19 and C1 was selectively inhibited when ganglia were incubated in 5 × 10−5M 5‐HT. The outgrowth of buccal neurons B5, however, was not affected. Moreover, 5‐HT caused significant transient elevations of calcium concentrations in neurons B19 over 30 minutes, but neurons B5 did not show any increases in calcium concentrations with the addition of 5‐HT. These results suggest that the effect of 5‐HT upon outgrowth of regenerating neurons may be due to an increase in the intracellular calcium concentration.
Ontogeny of the sexually dimorphic male nucleus in the preoptic / anterior hypothalamus of ferrets and its manipulation by gonadal steroids
Authors: Cherry James A. , Basham Mark E. , Weaver Charles E. , Krohmer Randolph W. , Baum Michael J.
Published: January 2005

A sexually dimorphic nucleus exists in the dorsal region of the ferret preoptic / anterior hypothalamic area (POA / AH), and is called the male nucleus of the POA / AH (MN‐POA / AH) because it is found only in males. Development of the MN‐POA / AH was studied in male ferrets, and for comparison a sexually nondimorphic ventral POA / AH nucleus was studied in both sexes. The MN‐POA / AH was conspicuous in males as early as embryonic day 37 (E37) of a 41‐day gestation, and its volume increased until postnatal day 56 (P56). No nucleus was present in the dorsal POA / AH of females at any age. The densities and average somal areas of cells in the dorsal POA / AH were similar in males and females at E33, before the MN‐POA / AH could be visualized. However, at E37 and E41 dorsal cells were greater in density and / or somal area in males than in females, accounting for the appearance of a nucleus in males at these ages. To insure that the dorsal POA / AH necleus seen in males at E37 andE41 was the presumptive MN‐POA / AH present in adult males, pregnant ferrets were given progesterone and either implanted subcutaneously (s.c.) with testosterone (T) or ovariectomized and implanted s.c. with the aromatase inhibitor, 1,4,6‐androstatriene‐3,17‐dione (ATD), on day 30 of gestation. As predicted from previous studies in which subjects were sacrificed in adulthood, formation of a dorsal POA / AH nucleus was promoted in female ferrets by T, and blocked in males by maternal ovariectomy and ATD treatment for animals sacrificed at E41. Much evidence suggests that behavioral sexual differentiation is accomplished in the male ferret between age E28 and P20. The MN‐POA / AH is present and potentially functional in males during a considerable portion of this perinatal period.
Neurometamorphosis
Authors: Harris William A.
Published: January 2005

This article introduces this special issue of the Journal of Neurobiology by reviewing several basic issues in metamorphosis as they specifically relate to the nervous system. It promotes the idea that metamorphic changes in the nervous system (neurometamorphosis) represent adaptive restructurings rather than recapitulations of evolutionary transitions. It introduces, but leaves unresolved, the question of whether neurometamorphosis is achieved primarily as a delayed phase of embryonic neurogenesis or as a special neurogenic period. It points out that respecification of old neurons and the addition of new neurons are the main contributory pathway of neural restructuring at metamorphosis, that respecification can be dramatic and seems to be preferred over the elimination and replacement of particular neurons. It also highlights the question of how much the central rewiring during metamorphosis is driven by trophic interactions with the changing body of the metamorphic animal and to what extent neurometamorphosis is driven by the direct action of metamorphic hormones on the neural elements themselves. Finally, this article introduces the question of the cellular and molecular pathways of neurometamorphosis, from the role of the nervous system in triggering the event to the receptor mediated changes in gene expression. Further details on all of these issues are to be found in the articles that make up the rest of this special issue.
Metamorphosis of the amphibian eye
Authors: Hoskins Sally G.
Published: January 2005

For many metamorphosing amphibians, the visual system must remain functional as the animal changes from an aquatic to a terrestrial habitat. Thyroid hormone, the trigger for metamorphosis, brings about changes at all levels of the animal, and profoundly alters the visual system, from cellular changes within the eye to new central connections subserving the binoculr vision that develops during metamorphosis in some species. I will survey the alterations in the visual system in the metamorphosis of several Amphibian groups, and consider the role of thyroid hormone in bringing about these transformations through action at the molecular level.
Mesencephalic fifth nucleus cell responses to thyroid hormone: One population or two?
Authors: Kollros Jerry J. , Bovbjerg Ann M.
Published: January 2005

Hypophysectomized Rana pipiens tadpoles 3–6 months old were placed in dl‐thyroxine (T4) solutions of 4 to 200 μg/l for 1–18 days and fixed 1 day after removal from the hormone solution. Exposure times varied inversely with T4 concentration. Mesencephalic fifth nucleus (M‐V) cells were counted on both sides, and cell and nuclear sizes were drawn and measured for each tadpole. Changes in M‐V cell characteristics correlated well with T4 exposure times and concentrations, as did changes in external tadpole morphology. All T4 concentrations were effective. Cells and nuclei were distinctly larger in all T4‐treated groups. The changes were greatest for cell sizes, less for nuclear dimensions, and still less for nucleo‐cytoplasmic ratios. Significant changes were seen for minimum and maximum sizes as well as for the mean values. The greatest mean changes were seen at dosages of 50 μg/l for 7–9 days.

Mean M‐V cell numbers are significantly smaller in hypophysectomized tadpoles than in controls (about 420 vs. 650). Thyroid hormone treatment of the hypophysectomized animals abolishes much of the deficit, though M‐V cell deaths at the higher concentrations and longer treatment times reduce the apparent increase in numbers. Are the additional cells obtained through cell division, or do they represent a preexisting subpopulation of prospective M‐V cells that require stimulation by thyroid hormone for their full differentiation?
The gastropod nervous system in metamorphosis
Authors: Marois Rene , Carew Thomas J.
Published: January 2005

Many gastropods, including the sea hare Aplysia californica, undergo metamorphosis in passing from the larval to the juvenile phases of their life cycle. During metamorphosis, the gastropod nervous system is affected by both progressive and regressive neuronal events. In addition to this metamorphic reorganization, the nervous system appears to be centrally involved in initiating metamorphosis. We propose that gastropods not only possess temprally distinct neuronal adaptations for the specific needs of the larval and juvenile phases, but also another transient neuronal adaptation specialized to subserve the metamorphic episode.
Metamorphic‐like changes in the nervous system of the nematode Caenorhabditis elegans
Authors: Walthall W. W.
Published: January 2005

During postembryonic development of the nematode Caenorhabditis elegans, one class of embryonic motoneurons, the DD cells, respecifies its pattern of synaptic connections. At the same time, a closely related set of postembryonic motoneurons, the VD cells, complete differentiation and assume a pattern of connections equivalent to the original pattern of the DD cells. These types of changes are reminiscent of changes observed in the nervous systems of animals as they undergo metamorphosis. The DD and VD neurons arise through different lineage mechanisms and in the adult, receive different synaptic inputs and make different outputs. The embryonic DD motoneurons are clonally related to one another; whereas the postembryonic VD motoneurons are produced by a repeated sublineage in which each stem cell generates four or five cell types in addition to the VD cells. In spite of these differences, it has been possible to identify only one gene by mutation that effects one of the two motoneuronal classes. Mutations in the gene unc‐55 (unc meaning uncoordinated) cause the VD cells to become essentially identical to the DD cells; thus the unc‐55 gene product appears necessary and sufficient to transform homeotically the pattern of synaptic connections of an entire class of motoneuron.
The developing visual system and metamorphosis in the lamprey
Authors: Rubinson Kalman
Published: January 2005

Metamorphosis of the sea lamprey, Petromyzon marinus, is a true metamorphosis. The larval lamprey is a filter‐feeder who dwells in the silt of freshwater streams and the adult is an active predator found in large lakes or the sea. The transformation usually occurs in the fifth or sixth year of life. Enlargement of the eye has been long accepted as a distinctive indication of metamorphosis in the sea lamprey, but it had been thought that this was because eye development in the larva was arrested after the formation of only the small central region. Recent studies indicate that all of the retina begins its development in the larva and that ganglion, amacrine, and horizontal cells differentiate in the peripheral retina of the larva. Retinal development is arrested during the premetamorphic period, to be resumed during metamorphosis. Metamorphic contributions include the differentiation of photoreceptor and bipolar cells. With the early appearance of ganglion cells, retinal pathways to the thalamus and tectum are established in larvae, as is a centripetal pathway. Tectal development spans the larval period but a spurt in tectal growth and differentiation is correlated with the completion of the retinal circuitry late in metamorphosis. The metamorphic changes in retina and tectum complete the functional development of the visual system and provide for the adult lamprey's predatory and reproductive behavior.
Developmental expression of the GABAA receptor α1 subunit mRNA in the rat brain
Authors: Gambarana Carla , Pittman Robin , Siegel Ruth E.
Published: January 2005

Recent studies have suggested that the GABAA, receptor complex, the site of action of the inhibitory neurotransmitter gamma amino‐butyric acid (GABAA) and the anxiolytic benzodiazepines, is heterogeneous. Moreover, its composition may change during development. To better understand the molecular basis of receptor heterogeneity, the levels and distribution of the mRNA encoding the α1 receptor subunit were examined in the developing and adult rat brain with quantitative in situ hybridization histochemistry. Our studies demonstrate that α1 subunit mRNA expression changes during ontogeny. At late embryonic stages and in the first postnatal week, low levels of the mRNA were detected in the cortex, inferior colliculus, and hippocampus. The mRNA levels in these regions increased during the second and third postnatal weeks. Furthermore, a dramatic change in the distribution of the α1 subunit mRNA was seen in the second postnatal week when the message first became detectable in the cerebellar cortex. During subsequent development and in the mature brain, the α1 subunit mRNA was most abundant in the cerebellum, olfactory bulb, and inferior colliculus, although the absolute levels of mRNA varied by as much as sixfold in selected brain regions. The mature distribution of α1 subunit mRNA, along with its temporal appearance in the cerebellum, suggests that this subunit is a constituent of the Type 1 benzodiazepine site of the GABAA receptor complex. Furthermore, the onset of α1 subunit mRNA expression in the cerebellar cortex coincides with a period of extensive synapse formation, raising the possibility that synaptic interactions modulate the appearance of this GABAA receptor subunit in the cerebellum.
Elevated levels of polyneuronal innervation persist for as long as two years in reinnervated frog neuromuscular junctions
Authors: Werle Michael J. , Herrera Albert A.
Published: January 2005

When the nerve to an adult frog sartorius muscle is crushed, and axons are allowed to regenerate, the level of polyneuronal innervation at reinnervated neuromuscular junctions is higher than normal. With time, much of this polyneuronal innervation is reduced by the process of synapse elimination (Werle and Herrera, 1988). Using intracellular recording, we estimated the level of polyneuronal innervation in adult frog (Rana pipiens) sartorius muscles 2 years (range: 1.7–2.4 years) after crushing the sartorius nerve. We found that 27% (S.E. = 1.4%) of the junctions in muscles 2 years after reinnervation were polyneuronally innervated, whereas only 10% (S.E. = 1.2%) of the junctions in normal frog muscles were polyneuronally innervated. Thus, the synapse elimination that occurs following reinnervation does not restore the normal level of polyneuronal innervation. Histological comparisons of junctional structure between muscles 2 years after reinnervation and normal muscles revealed substantial differences. Reinnervated junctions had a greater length of synaptic gutter apposed by nerve terminal processes, more axonal inputs, more empty synaptic gutter, more instances of single synaptic gutters innervated by more than one axon, and longer lengths of nerve terminal processes that connect synaptic gutters within a junction. On the basis of this physiological and anatomical evidence, we conclude that nerve injury causes persistent changes in the pattern of muscle innervation.
Using fluorescence photoablation to study the regeneration of singly cut leech axons
Authors: Camhi Jeffrey M. , Macagno Eduardo
Published: January 2005

The regeneration of the axons of leech Retzius cells was compared following two different methods of axonal severing: (1) a crush of the whole connective that includes the Retzius axon; and (2) photoablation of a small segment of only the Retzius axon. The photoablation was carried out after filling the Retzius cell with Lucifer Yellow (LY). Several tests were carried out to determine whether the photoablation actually severed the axon. These included (1) using the lipophilic membrane probe Dil as an indicator of membrane severance [Fig. 4 (A)]; (2) electron microscopic examination of the photoablated axon after filling it with horseradish peroxidase (HRP) (Fig. 7); and (3) filling the Retzius cell first with HRP, then photoablating, and looking for the disappearance of the HRP in the photoablated region (Figs. 5,6). These and other observations indicated that the photoablated axon was actually severed. Two differences were seen in the regeneration of the Retzius axon after crush versus after photoablation. First, the sprouting following crush was far more disorganized, and included significantly more lateral spread. Second, after photoablation, over 70% of the axons, upon refilling with LY after 3 days or more, showed the newly introduced LY suddenly extending far down the distal segment, indicating that the proximal and distal segments had become reconnected (Figs. 8,9). This was never seen following a crush (Fig. 1). The photoablated axons did not pass HRP into the distal segment, suggesting that the reconnection was not by fusion, but perhaps by a gap junction. The results show that axonal regeneration can take a dramatically different from than it does following a standard crush procedure if, instead, the axon is severed in a way that preserves the structural integrity of the surrounding tissue.
Nonspiking pathways antagonize the resistance reflex in the thoraco‐coxal joint of stick insects
Authors: Büschges Ansgar , Schmitz Josef
Published: January 2005

In the stick insect (Carausius morosus) imposed forward and backward movements of the coxa of the middle leg induce resistance reflexes in the retractor or protractor coxae muscles, depending on the direction of movement. The hairs of the ventral coxal hairplate (cxHPv) function as the primary transducer of the retractor part of the underlying feedback loop: bending of the hairs of the cxHPv during an imposed forward movement of the coxa leads to a reflex activation of the retractor motoneurones, whereas releasing of the hairs causes an inhibition of these motoneurones. Local nonspiking interneurones were investigated, which transmit information from the cxHPv onto the retractor motoneurones: (1) they are depolarized during bending of the hair sensilla of the cxHPv and (2) they decrease the activities of retractor motoneurones. In addition, four of the interneurones drive a protractor motoneurone, when they are depolarized. As bending stimuli at the cxHPv (mimicking an imposed forward movement of the leg) induce reflex activation of the retractor motoneurones and reflex inhibition of the protractor motoneurones, the physiology of the recorded interneurones appears to antagonize the resistance reflex in the thoraco‐coxal joint. The results indicate that these nonspiking interneurones take part in the shaping of the reflex response and that furthermore these interneurones are involved in the organization of the motor output to the two antagonistic sets of motoneurones. The possible role of these interneurones might be the adjustment of the gain and of the time constant in the thoraco‐coxal feedback loop.
Light‐adapting migration of the screening‐pigment in crayfish photoreceptors is a two‐stage movement comprising an all‐or‐nothing initial phase
Authors: Frixione Eugenio , Pérez‐Olvera Ofelia
Published: January 2005

The light‐adapting response of the screening‐pigment in crayfish retinal photoreceptors, previously described as a monophasic movement, was found to consist of two stages with different properties: (1) a rapid initial expansion that once started proceeds for at least half of the full distance, and (2) a slower and more variable continuation of the movement. The two components were resolved in isolated eyes stimulated under conditions expected to restrict Na+ influx into the photoreceptors. Only the second stage of the response to light was inhibited when Na+ was substituted with choline, or if the normal saline contained amiloride, a diuretic that hinders Na+ entry across many cell membranes. Amiloride in a medium without Na+ delayed, but did not curb, the first stage, whereas the rest of the movement was markedly restrained. Partial replacement of Na+ with Li+ blocked the second stage without affecting the rapid initial shift triggered by light. Exposure of dark‐adapted eyes to high Na+ levels or to ouabain in the presence of Na+ in the dark also elicited a two‐staged pigment dispersion to the light‐adapted position. Low Na+ concentrations or amiloride affected the latency, but not the rate or extent, of the first stage of migration in ouabain‐treated eyes. Consistent though less significant results were obtained with cyanide and the Na+ ionophore monensin. These observations suggest a differential control of pigment position over two defined domains along the photoreceptors, probably to integrate a double mechanism of light‐adaptation: an all‐or‐nothing partial shift of the pigment screen as a safety factor against overexposure, followed by a regulated adjustment according to stimulation intensity.
Glycoconjugates are stage‐ and position‐specific cell surface molecules in the developing olfactory system, 2: Unique carbohydrate antigens are topographic markers for selective projection patterns of olfactory axons
Authors: Schwarting Gerald A. , Deutsch Gail , Gattey Devin M. , Crandall James E.
Published: January 2005

Three monoclonal antibodies specific for different carbohydrate antigens were used to analyze the development of the olfactory system in rats. CC2 antibodies react with a subset of main olfactory neurons, their axons, and terminals in the olfactory bulb. CC2 antigens are expressed on dorsomedial neurons in the olfactory epithelium (OE) from embryonic (E) day 15 to adults. In the olfactory bulb (OB), only dorsomedially located glomeruli express CC2 glycoconjugates from postnatal day (P) 2 to adults. Thus CC2 defines a dorsomedially organized projection that is established early in embryonic development and continues in adults. P‐Path antibodies react with antigens that are expressed on the olfactory nerve in embryos, and are also detected on cell bodies in the neuroepithelium and in glomeruli of the OB at P2. At P14, P‐Path staining is weaker, but remains present on many cells in the epithelium and in many glomeruli in the bulb. Postnatally, P‐Path immunostaining continues to decrease in most regions of the OE and OB. At P35 and afterwards, only a few P‐Path‐positive neuronal cells can be detected in the OE. Furthermore, after P35 only two groups of glomeruli in the OB are P‐Path immunoreactive. One is situated adjacent to the accessory olfactory bulb (AOB) at the dorsocaudal surface of the OB. The other is adjacent to the AOB at the ventrocaudal surface of the OB. Thus, in adults, P‐Path glycoconjugates are expressed in neurons and axons that project only to a specific subset of caudal glomeruli of the OB. Monoclonal antibody 1B2, reacts with β‐galactose‐terminating glycolipids and glycoproteins. At P2, 1B2 immunoreactivity is seen on a subset of cell bodies that are distributed throughout the OE and is expressed in most glomeruli in the OB at this age. By P35 and in adults, 1B2 continues to be expressed on a subset of neurons in the OE that project to only a small subset of glomeruli in the OB. Unlike CC2 and P‐Path antigens that define specific groups of glomeruli, 1B2‐immunoreactive glomeruli do not have a detectable spatial pattern. It is more likely that 1B2 antigens define a specific stage in the maturation of connections between the OE and OB.
Inhibition of tyrosine phosphorylation potentiates substrate‐induced neurite growth
Authors: Bixby John L. , Jhabvala Perseus
Published: January 2005

Protein tyrosine kinases (PTKs) have major roles in signal transduction and growth control. There are several lines of evidence implicating PTKs in the regulation of axon growth, and this has led to the suggestion that they are centrally involved in the transduction of neuronal growth signals. To test this idea, we assayed the effect of the compounds genistein and lavendustin, specific inhibitors of PTKs, on neurite growth. We find that genistein greatly reduces phosphotyrosine in neurons, as expected from its action on other cells. Surprisingly, administration of genistein or lavendustin potentiated substrate‐induced neurite growth in at least several different neuronal types. Stimulation of neurite growth by genistein was abolished by vanadate, providing additional evidence that inhibition of PTKs is responsible for this effect. The potentiation of growth is rather general, in that it occurs on several different extracellular matrix substrates and on two different cell adhesion molecules. Both the initiation of neurite growth and the rate of neurite elongation appear to be potentiated. Our results do not provide evidence for models of substrate‐induced signal transduction that involve PTKs asa positive and necessary step, but suggest that such kinases play aregulatory role in neurite elongation. © 1992 John Wiley & Sons, Inc.
Modulation of growth of Aplysia neurons by an endogenous lectin
Authors: Wilson Monita P. , Carrow Grant M. , Levitan Irwin B.
Published: January 2005

We have purified and characterized a galactose‐binding lectin from the gonads of the mollusk Aplysia californica that modulates neurite outgrowth from cultured Aplysia neurons. Agglutination of sheep red blood cells (RBC) by this lectin, termed Aplysia gonad lectin (AGL), is inhibited strongly by galactose and to a lesser extent by fucose. On SDS‐PAGE, AGL appears as a single species with a molecular weight of 34 kD under reducing conditions, and 65 kD under nonreducing conditions. This suggests that AGL is a disulfide‐linked dimer in its native state. Amino terminal sequence analysis of purified AGL indicates a similarity to another galactose‐binding lectin, phytohemagglutinin‐E (E‐PHA), found in red kidney beans. By using polyclonal antibodies prepared against AGL, we have found that the lectin is present in the gonads and eggs but not in other tissues of adult Aplysia californica. We have examined biological actions of AGL on Aplysia neurons growing in primary cell culture. AGL affects several properties of these neurons. The addition of 100 nM AGL to cultured neurons enhances neurite outgrowth from the cell soma, resulting in a greater number of primary processes. In addition, AGL acts as a neurotrophic agent, increasing neurite viability in vitro. This trophic effect is not seen with concanavalin A (con A), another lectin known to affect several properties of cultured Aplysia neurons. The results are consistent with the suggestion that AGL may play a role in neuronal differentiation and/or maintenance of viability. © 1992 John Wiley & Sons, Inc.
Modification of the dystrophic phenotype after transient neonatal denervation: Role of MHC isoforms
Authors: Ontell Martin P. , Moschella Maria C. , Schiaffino Stefano , Butler‐Browne Gillian , Whalen Robert , Ontell Marcia
Published: January 2005

While it recently has been demonstrated that it is possible to modify the phenotypic expression of murine dystrophy (dy/dy) (i.e., prevent myofiber loss) by subjecting the extensor digitorum longus (EDL) muscle of 14‐day‐old dy/dy mice to transient neonatal denervation (Moschella and Ontell, 1987), the mechanism responsible for this phenomenon has not been determined. Since it has been suggested that the effects of dystrophy vary according to fiber type, the fiber type frequency in 100‐day‐old normal (+/+) and dy/dy EDL muscles subjected to transient neonatal denervation has been determined by immunohistochemical analysis of their myosin heavy chain (MHC) composition. This frequency has been compared with that found in the EDL muscles of 14 ‐and 100‐day‐old unoperated +/+ and dy/dy mice, in order to determine whether the reinnervation of transiently denervated neonatal muscle results in a preponderance of fibers of the type that might be spared dystrophic deterioration. In unoperated dy/dy muscle there is a progressive decrease in the frequency and in the absolute number of fibers that express MHC2B, with 100‐day‐old dy/dy muscles having ∼32% of the number of myofibers fibers containing MHC2B as is found in age‐matched +/+ muscles. The number of fibers containing the other fast isoforms (MHC2A and MHC2X) is similar in +/+ and dy/dy muscles at this age, indicating that fibers with MHC2B are most affected by the dystrophic process. Reinnervation following transient neonatal denervation of both the +/+ and the dy/dy EDL muscles results in a similar decrease (∼62%) in the number of myofibers containing MHC2B and an increase in myofibers containing the other fast MHC isoforms (MHC2A and MHC2X). The selective effect of dy/dy on fibers containing MHC2B and the sparing of myofibers in transiently denervated dy/dy muscle (which contains a reduced frequency of fibers containing MHC2B) are consistent with, although not direct proof of, the hypothesis that alterations in the fiber type may play a role in the failure of myofibers in transiently denervated dy/dy muscles to undergo dystrophic deterioration. Evidence is presented suggesting that neurons that supply myofibers containing MHC2B may be at a selective disadvantage in their ability to reinnervate neonatally denervated muscles. © 1992 John Wiley & Sons, Inc.
Formation and preservation of cortical layers in slice cultures
Authors: Götz Magdalena , Bolz Jürgen
Published: January 2005

During cortical development, neurons generated at the same time in the ventricular zone migrate out into the cortical plate and form a cortical layer (Berry and Eayrs, 1963, Nature 197:984–985; Berry and Rogers, 1965, J. Anat. 99:691–709). We have been studying both the formation and maintenance of cortical layers in slice cultures from rat cortex. The bromodexyuridine (BrdU) method was used to label cortical neurons on their birthday in vivo. When slice cultures were prepared from animals at different embryonic and postnatal ages, all cortical layers that have already been established in vivo remained preserved for several weeks in vitro. In slice cultures prepared during migration in the cortex, cells contiuned to migrate towards the pial side of the cortical slice, however, migration ceased after about 1 week in culture. Thus, cortical cells reached their final laminar position only in slice cultures from postnatal animals, whereas in embryonic slices, migrating cells became scattered throughout the cortex. Previous studies demonstrated that radial glia fibers are the major substrate for migrating neurons (Rakic, 1972, J. Comp. Neurol. 145:61–84; Hatten and Mason, 1990, Experientia 46:907–916). Using antibodies directed against the intermediate filament Vimentin, radial glial cells were detected in all slice cutures where cell migration did occur. Comparable to the glia development in vivo, radial glial fibers disappeared and astrocytes containing the glia fibrillary‐associated protein (GFAP) differentiated in slice cultures from postnatal cortex, after the neurons have completed their migration. In contrast, radial glial cells were detected over the whole culture period, and very few astrocytes differentiated in embryonic slices, where cortical neurons failed to finish their migration. The results of this study indicate that the local environment is sufficient to sustain the layered organization of the cortex and support the migration of cortical neurons. In addition, our results reveal a close relationship between cell migration and the developmental status of glial cells. © 1992 John Wiley & Sons, Inc.
A specific brain tract guides follower growth cones in two regions of the zebrafish brain
Authors: Chitnis Ajay B. , Patel Chetan K. , Kim Stennis , Kuwada John Y.
Published: January 2005

Neurons of the nucleus of the posterior commissure (nuc PC), an identifiable cluster of neurons in the embryonic zebrafish brain, project growth cones ventrally along the posterior commissure to the anterior tegmentum where the PC intersects two longitudinal tracts, the tract of the postoptic commissure (TPOC) and the medial longitudinal fasciculus (MLF). Once at the intersection, nuc PC growth cones turn posteriorly onto the TPOC in the dorsal tegmentum and follow it to the hindbrain. Previously we showed that in the absence of the TPOC, nuc PC growth cones often extended along aberrant path ways suggesting that fasciculation, that is, contact with TPOC axons is an important factor in guiding growth cones along their normal pathway. However, a significant number of nuc PC growth cones also followed their normal pathway suggesting that cues associated with the dorsolateral tegmentum, independent of the TPOC, can also guide nuc PC growth cones. We have now confirmed using electron microscopy that nuc PC growth cones fasciculate with axons in the TPOC. In the absence of the TPOC, the nuc PC growth cones that extend along their normal pathway do so in contact with dorsolateral neuroepithelial cells. This suggests that cues associated with these cells can also guide the nuc PC growth cones. Furthermore, in the absence of the TPOC axons, these growth cones now inappropriately turn onto axons that normally intersect the TPOC near the border of the midbrain and hindbrain, that is, at a second intersection of tracts. This suggests that fasciculation with TPOC axons may also guide nuc PC growth cones in this second region of the brain. © 1992 John Wiley & Sons, Inc.