bluuebunny/crossref_metadata_2025 huggingface dataset:
Postsynaptic potentials in pacemaker cells: A correlate of behavior in command cells of an electric fish
Authors: Feng Albert S. , Bullock Theodore H.
Published: January 2005

Intracellular recordings were made from pacemaker‐command cells of the electric organ discharge (EOD) of the weakly electric fish Eigenmannia virescens. The fish was immobilized with gallamine triethiodide (Flaxedil) which silenced the EOD. A simulated EOD of this fish (ca. 300 Hz) and a sine wave simulating a neighbor, a few Hz higher (+ΔF) or lower (‐ΔF) were introduced into the bath to elicit the “jamming avoidance response” (JAR), monitored through the pacemaker potential. We observed that accompanying the JAR there is a minute hyperpolarizing postsynaptic potential (hpsp) superimposed on the pacemaker potential. A shift in the phase of the hpsp occurs with a change in the sign of ΔF, and therefore of the JAR. Assuming that the behaviorally correlated hpsp is inhibitory, it suggests that mutual inhibition may play a role in regulating the synchronous firing frequency of command neurons, which are electrically coupled with one‐another. Scheich and Bullock (1974) proposed a neuronal scheme for the JAR in which they suggest that two systems (P and T) operate together in the nervous system. The T system affects the pacemaker cells at a precise, variable phase of the pacemaker cycle. Although the present results indeed reveal a shift in the hpsp with a change in the sign of ΔF, the actual significance of this shift remains to be evaluated. The unexpected direction of the shift suggests either that the hpsp is excitatory at the phases when it occurs, or that effectiveness of inhibition decreases at later phases in this case instead of increasing as in other cases, or that the hpsp opposes the JAR. The parallel P system is probably more important in explaining the JAR, acting by a DC level control rather than a phase control.
Biosynthesis and processing of presumed neurosecretory proteins in single identified neurons of Aplysia californica
Authors: Aswad Dana W.
Published: January 2005

The biosynthesis and processing of low molecular weight protein (presumed neurosecretory protein) in cells R15, R14 and L11 of Aplysia californica was studied at high resolution by polyacrylamide slab gel electrophoresis in sodium dodecylsulfate. The number of low molecular weight proteins detected in each cell ranges from 3 in R14 and L11 to 5 or 6 in R15. In each of the cells studied, the low molecular weight protein consists of a primary precursor of ca. 12,000 daltons, and its proteolytic processing products. In each cell, the smallest protein, or in the case of R14, one of the two smallest proteins, accumulates to a significant extent, suggesting that it might correspond to a final processed neurohormone. In cell R15, the biosynthesis of the primary precursor and its subsequent processing to smaller peptides is largely unaffected by removal of extracellular calcium, by replacement of calcium with cobalt or by inhibition of spontaneous bursting via stimulation of the brachial nerve.
Developmental abnormalities of identifiable neurons in the crayfish Procambarus simulans
Authors: Ballinger Martis L. , Bittner George D.
Published: January 2005

We report anomalies of lateral giant neurons in field‐caught animals. In one case, both lateral giant neurons arising from the fifth abdominal ganglion did not terminate in the next‐most anterior ganglion, but rather continued to the third abdominal ganglion. In another case, an additional large neuron arising in the fifth abdominal ganglion coursed in a posterior direction. All other CNS structures appeared normal in animals having either anomaly.
Serial synapses in Aplysia
Authors: Graubard Katherine
Published: January 2005

Serial synapses occur between small profiles in the neuropil of Aplysia abdominal ganglion. Material was fixed in phosphate buffered OsO4, embedded in epon, and sections were stained with uranyl acetate and lead citrate. A class of synapses had the following characteristics: (1) synaptic vesicles clustered against the presynaptic membrane, (2) a widened extracellular space of about 20 nm containing electron‐dense material, (3) straightening of the pre‐ and postsynaptic membranes, and (4) no postsynaptic membrane specialization. Some density between the presynaptic membrane and the adjacent synaptic vesicles was occasionally observed. Synapses occurred between small profiles in the neuropil (typical profile diameters were 1–3 m̈m).

In this sample of approximately 100 synapses, four serial synapses were identified. The serial synaptic profiles were all small. In addition to the finding of serial synapses, 40% of the postsynaptic profiles contained vesicles similar to the synaptic vesicles seen in presynaptic profile. Serial synapses may be the anatomical substrate of presynaptic inhibition and facilitation and of dishabituation.
Effect of experimental colchicine encephalopathy on brain protein synthesis and tubulin metabolism
Authors: McMartin Donald N. , Schedlbauer Lewis M.
Published: January 2005

Colchicine blocks axoplasmic flow and produces neurofibrillary degeneration. Brain slices from mice injected intracerebrally with colchicine incorporated more [14C]leucine into protein and had a decreased uptake of [14C]leucine into the perchloric acid‐soluble pool than did their controls. Brain RNA content was decreased and free leucine increased by colchicine‐induced encephalopathy. The specific activities of proteins from subcellular fractions of colchicine‐injected brain were increased in the nuclear fraction, the 100,000‐g supernatant, and its vinblastine‐precipitable tubulin. The ratio of the specific activity of the crude mitochondrial fraction to that of the total homogenate was decreased, as would consistent with impaired movement of newly labeled protein into synaptosomes. Colchicine‐injected brain extracts contained one or more cytosol fractions that stimulated ribosomal incorporation of [14C]leucine into protein in a cell‐free system. Colchicine‐binding‐activity measurements indicated loss of soluble and particulate tubulin in colchicine‐injected brains; the decrease of soluble tubulin was verified by its selective precipitation with vinblastine. Colchicine encephalopathy did not affect the rate of spontaneous breakdown of in vitro colchicine binding activity. Similarities of colchicine encephalopathy to the neuron's response to axonal damage suggest that colchicine‐induced increase in protein synthesis may, in part, reflect a neuronal response to blockage of neuroplasmic transport.
Taurine in the developing rabbit visual system: Changes in concentration and axonal transport including a comparison with axonally transported proteins
Authors: Sturman John A.
Published: January 2005

[35S]Taurine injected intravitreally into rabbits was transported axonally to the optic nerve terminals. Considerably more [35S]taurine was transported in young rabbits than in mature rabbits. The time course of taurine transport did not parallel that of proteins labeled with [3H]proline in the same system. The concentration of taurine in all components of the visual system, except retina, was greater in young animals than in mature animals, and was especially high in optic nerve. The possible functions of the high concentrations of taurine and the greater amount of axonally transported taurine in developing mammalian CNS are discussed.
Central inhibition of an identified mechanosensory interneuron in the crayfish
Authors: Wilkens Lon A. , Marzelli George A.
Published: January 2005

Inhibitory input from crayfish mechanoreceptors is mediated polysynaptically to sensory interneurons. An identifiable sensory interneuron, the caudal photoreceptor (CPR), has been used as a model system to characterize inhibitory intermediate cells. A survey of the abdominal connectives, by antidromic stimulation, has identified eleven inhibitory cells, some of which also function as ascending sensory interneurons. These results indicate that lateral interactions within networks of mechanosensory interneurons form an integral part of the information processing mechanisms.
Cobalt mapping of the nervous system: Evidence that cobalt can cross a neuronal membrane
Authors: Fredman Steven M. , Jahan‐Parwar Behrus
Published: January 2005

Exposing intact nerves of Aplysia to exogenous CoCl2 was sufficient to fill neurons by axonal iontophoresis. There were no significant differences between filling intact nerves and nerves whose ends had been cut. Nonneuronal elements were not filled appreciably. These results show that Co2+ can cross intact axonal membranes and suggest that in tracing neuronal pathways Co2+ may not remain confined to neurons whose interiors are directly exposed to it.
Electric membrane properties of adult mouse DRG neurons and the effect of culture duration
Authors: Scott Brian S. , Edwards Beverley A. V.
Published: January 2005

The electrical membrane properties (EMP) of adult mouse dorsal root ganglion (DRG) neurons were characterized by an extensive electrophysiological investigation of 450 cells. The neurons were divided into two types: an M‐type having an action potential with monophasic falling phase and a B‐type with a more complex biphasic or triphasic falling phase. Compared to M‐type, B‐type were “slow” neurons with a higher specific membrane resistance (Rm), and a longer time constant (τ), duration of action potential (Δt), and absolute refractory period (ARP). B‐type also had a larger amplitude action potential, afterhyperpolarization and positive overshoot. The action potential of the M‐type neuron had only a Na+ component while that of the B‐type had both a Na+ and a Ca2+ component. After two days in culture, M‐type neurons exhibited phase bright cytoplasmic granules, which were seldom observed for B‐type neurons. Although neuron survival remained constant during the first six days in culture (DIV), the relative frequency of occurrence of the M‐type decreased from 82 to 50%. Thereafter, it decreased more gradually to a final value of approximately 20% after 40 DIV. It was concluded that at least during the first 6 DIV and possibly through to 40 DIV, M‐type neurons transformed into B‐type. Both M‐ and B‐type neurons showed significant and similar changes in their EMP with increasing DIV (up to 40 DIV). For M‐ and B‐types combined, Rm increased approximately 142%, τ by 204%, and no significant change in specific membrane capacitance was observed. Rheobasic threshold depolarization decreased 58%, while the resting membrane potential decreased by only 19%. These changes in the EMP of adult neurons are strikingly similar to changes in EMP observed in adult denervated muscle and in cultures of either embryonic nerve or muscle. This similarity suggested that the adult DRG neurons in cell culture undergo progressive dedifferentiation because of isolation from their usual trophic interactions. Determination of neuronal membrane electrical characteristics provides a new method for evaluating the effects of various possible trophic agents, e.g., hormones and tissue extracts, on the state of differentiation of neurons in cell culture.
Learning, using natural reinforcements, in insect preparations that permit cellular neuronal analysis
Authors: Hoyle Graham
Published: January 2005

A general paradigm is described that permits testing the ability of an arthropod to learn (by operant conditioning) to alter the position of a single leg segment in order to relate to behaviorally appropriate reinforcement. The paradigm was designed so that intracellular recording from identified neurons involved would be possible during the training of a locust or grasshopper, for which extensive neuron maps are available. As a prelude to such studies, electromyograms were made from the antagonistic muscles that move the conditioned limb, which in the present experiments was the tibia of the metathoracic leg. Negative (aversive) reinforcement was provided by a loud sound/vibration and positive (reward) reinforcement by food in the form of sugar‐water or fresh‐growing grass. In the aversive reinforcement experiments the sound, which reflexly caused flexion, was on continually except when the tibia of one hind leg was voluntarily placed in an electronically set position “window” displaced, in extension, away from the preferred position. In feeding experiments, food was brought automatically to the mouth by a motor‐driven arm when the tibia was held within a position window set away from the preferred position in either extension or flexion. Whole or headless insects learned to turn off the sound permanently, except for sporadic brief interruptions, by tonic shifting of tibial position. Insects learned to bring food to the mouth by modifying the plateau phase of a position displacement lasting for a few minutes, that was found to occur from time to time also in controls. In aversive learning, minimum times to turn off the sound were 22 sec for the easiest position and 4 min for the most difficult. The longest time in the easiest position was 1 min 40 sec and in the most difficult 39 min; excluding measurement for individuals that did not learn. In reward learning, the minimum time in the easiest position was just under 1 min, and 12 min in the most difficult position. The longest times were about 8 hr regardless of difficulty.
Primary cultures of dispersed hypothalamic cells from fetal rats: Morphology, electrical activity, and peptide content
Authors: Vaccaro Dennis E. , Leeman Susan E. , Messer Anne , Dichter Marc A.
Published: January 2005

Cultures prepared from dispersed fetal hypothalamic tissue have cells which can be identified as neurons by their morphology and electrical activity. The elongation of neuritic processes in these cultures is increased by treatment with 1‐β‐D‐arabinofuranosylcytosine (ara‐C). Hypothalamic cultures have measurable quantities of immunoreactive substance P and neurotensin, and the neurons can accumulate (3H)GABA.
GABA inactivation at the crayfish neuromuscular junction
Authors: Horwitz I. S. , Orkand R. K.
Published: January 2005

Changes in the effective membrane resistance of the abductor muscle of the dactylopodite of the crayfish were used to indicate changes in the GABA concentration in the synaptic cleft. Following bath application of GABA (10−5 to 5 × 10−5M), the muscle membrane resistance decreased and then increased slowly over the next few minutes. Renewing the solution or stirring the bath restored the GABA effect. Higher GABA concentrations produced a large stable decrease in membrane resistance. An active uptake system for GABA in the junctional region is suggested by the observation that the slow increase in membrane resistance following GABA application was decreased by cooling to 2°C or by the addition of known GABA uptake blockers such as L‐DABA, β‐guanidinopropionic acid, or nipecotic acid. The transport inhibitors, PCMBS and chlorpromazine, produced irreversible decreases in muscle membrane resistance, which precluded examining their effects on GABA inactivation. The decrease in GABA effect was not dependent on the external sodium concentration or on the degree of receptor activation. Nipecotic acid, which blocked GABA inactivation, did not affect the decay of the neurally evoked inhibitory junctional potential.
Effects of p‐chloroamphetamine, a serotonin‐depleting drug, on the median eminence and pituitary pars intermedia
Authors: Saland L. C. , Dail W. G. , Reyes E.
Published: January 2005

p‐Chloroamphetamine (PCA), an agent known to cause depletion of levels of brain serotonin in rodents, was administered to rats in three sequential injections (10 mg/kg) to study effects on the hypothalamic median eminence and pituitary gland. One week following the initial sequence of injections of PCA, light and electron micrographs revealed degenerate fibers in the outer zone of the median eminence. Lower drug doses or single 10‐mg/kg doses did not lead to morphologic changes. Neuronal processes located in the pituitary intermediate lobe appeared normal, although there was a significant increase in the numbers of secretory granules contained within intermediate lobe cells of drug‐treated rats, as compared to controls. Fluorometric analysis of levels of catecholamine and indoleamine showed a decrease in serotonin in median eminence and pons‐medulla, but no change in that of the pituitary. Levels of dopamine and norepinephrine remained unchanged after PCA treatment. The data suggest that fibers affected in the median eminence contain serotonin. Processes in the intermediate lobe may be resistant to the serotonin‐lowering effects of PCA observed in brain tissue. In addition, PCA may directly affect granule release from pituitary cells, or may alternatively act on hypothalamic regions which affect the release of intermediate lobe cell hormones.
Excitatory neuromuscular transmission in crayfish: Calcium dependence is unaffected by picrotoxin
Authors: Staggs D. R. , Pofcher E. , L'Heureux Ramona , Ortiz C. L. , Orkand R. K.
Published: January 2005

Picrotoxin, 1 × 10−5M to 1.6 × 10−3M, had little or no effect on the amplitude of intracellularly recorded excitatory junctional potentials (EJPs) at extracellular calcium concentrations [Ca2+]0 ranging from 0.5 to 15 mM. The slope of the log EJP vs. log[Ca2+]0 relationship was approximately 1 with or without picrotoxin. The reduction of EJP amplitude resulting from the addition of 5 × 10−5M GABA was largely reversed by 10−5M picrotoxin.
Identification and localization of catecholamines in the nervous system of Limulus polyphemus
Authors: O'Connor Edward F. , Watson Winsor H. , Wyse Gordon A.
Published: January 2005

The concentrations of various catecholamines in the nervous system of the horseshoe crab Limulus polyphemus have been determined by high‐performance liquid chromatography with electrochemical detection. Dopamine, norepinephrine, epinephrine, and their precursor L‐Dopa were present in appreciable quantities in discrete regions of the central nervous system and cardiac ganglion. The catecholamines were localized more precisely by use of the glyoxylic‐acid‐histofluorescence technique of de la Torre and Surgeon (1976). Catecholamine fluorescence appeared in protocerebral and tritocerebral neuropile, including regions of the central body and optic medulla. Posterior to these brain areas, tracts extended through the circumesophageal ganglionic ring and laterally out each of the pedal ganglia. Small clusters of large fluorescent somata were present in the protocerebrum. No fluorescence was observed in the corpora pedunculata.
Gangliosides associated with microsomal subfractions of brain: Comparison with synaptic plasma membranes
Authors: Skrivanek J. A. , Ledeen R. W. , Margolis R. U. , Margolis R. K.
Published: January 2005

To study ganglioside distribution within subcellular components and test the hypothesis that they are localized at the nerve ending, microsomes and synaptic plasma membranes were isolated from young adult rat brains and compared with respect to ganglioside composition. These were shown to be heterogeneous preparations by fractionation on a discontinuous sucrose gradient into subfractions which had differing ganglioside concentrations. The highest ganglioside concentrations occurred in membranes banding at the 0.8M/1.0M and 1.0M/1.3M interfaces for both microsomes and synaptic plasma membranes. These subfractions had closely similar ganglioside concentrations and pattern distributions. In addition, the kinetics of ganglioside labeling following administration of [3H]‐glucosamine were similar for the two preparations. The fact that microsomal subfractions representing heterogeneous mixtures of brain cell membranes showed close similarity to synaptosomal plasma membranes argues against localization of gangliosides at the nerve ending. These results, together with other lines of evidence, support the concept that gangliosides are distributed over large portions of the neuron (and perhaps other brain cells). Data concerning the labeling of gangliosides in different microsomal subfractions indicated a movement of label over time from the more dense to the less dense membranes, as was also noted for the glycoproteins in the same subfractions. Specific radioactivity of the gangliosides increased relative to that of the glycoproteins with time.
The ionic dependence of black widow spider venom action at the stretch receptor neuron and neuromuscular junction of crustaceans
Authors: Fritz L. C. , Mauro A.
Published: January 2005

The effects of black widow spider venom (BWSV) on the crayfish stretch receptor and the lobster neuromuscular junction were examined. In crayfish stretch receptor neurons, BWSV caused a slight hyperpolarization followed by a large depolarization. The venom‐induced depolarization of the strech receptor was caused by an increase in membrane conductance to Na+ and Ca2+. Black widow spider venom also caused an increase in the frequency of miniature inhibitory postsynaptic potentials recorded in the strech receptor. The ability of BWSV to increase the frequency of miniature excitatory postsynaptic potentials (MEPSPs) at the lobster neuromuscular junction was dependent on the divalent cation composition of the bathing medium. Ringer solutions containing Ca2+ supported the greatest venom‐induced increase in MEPSP frequency, Mg2+ and Mn2+ supported a moderate increase in MEPSP frequency, while Co2+ and Zn2+ blocked this venom effect entirely. Black widow spider venom did not block axonal conduction in lobster walking leg axons or in the axon of the crayfish stretch receptor. The results suggest that in crustaceans, BWSV interacts specifically with membrane of the soma‐dendritic region of the stretch receptor and with nerve terminal membrane, causing an increase in Na+ and Ca2+ conductance.
UV–visible antagonism in extraocular photosensitive neurons of the anthomedusa, spirocodon saltatrix (tilesius)
Authors: Ohtsu Kohzoh
Published: January 2005

Attempts were made to identify extraocular photosensitive cells in the subtentacular region (the area between the ocelli and the nerve ring) and around the inner‐nerve ring of the anthomedusan Spirocodon saltatrix. Irradiation with ultraviolet light (UV) led to inhibition of spontaneous impulses and after UV‐off, an afterinhibition which lasted for a few minutes. This afterinhibition was rapidly overcome by exposure to visible light (VIS). UV–VIS antagonism of this type was identified in six different impulse systems monitored in extracellular recordings. Intracellular recordings from two of the six cell types showed that UV irradiation causes hyperpolarization which inhibits spontaneous activity. The other cell types showed no membrane potential changes during UV irradiation even though the cells' spontaneous outputs were inhibited. It was concluded that the photosensitivity lies in three kinds of nerves which are distributed widely through the subtentacular region and the nerve ring.
Enhancement of inward current by serotonin in neurons of Aplysia
Authors: Pellmar Terry C.
Published: January 2005

In RB cells of Aplysia, serotonin, in the presence of TEA, 4AP and Ba, elicits a voltage‐dependent inward current. In Ba‐TEA‐4AP seawater, RB cells showed a negative slope region (NSR) in their current‐voltage (I‐V) relationship when measured at the end of 2‐s commands from a holding potential of −60 mV. Addition of serotonin to the bathing solution enhanced the NSR. When holding potential was lowered to −10 mV, the NSR as well as the effects of serotonin were greatly reduced. Addition of 20 mM cobalt to the bathing solution blocked both the NSR and the inward current produced by serotonin. Changes in potassium concentration produced no consistent shift in voltage sensitivity nor change in amplitude of the current elicited by serotonin. Intracellular injection of cesium sufficient to broaden action potentials did not block the enhancement of NSR by serotonin. These results support the conclusion that in RB cells, serotonin produces a voltage‐dependent current carried by calcium ions.
Scanning and freeze‐fracture study of larval nerves and neuromuscular junctions in Manduca sexta
Authors: Schaner Pamela J. , Rheuben Mary B.
Published: January 2005

The nerves and nerve terminals to tonic larval muscle fibers in third and fifth instar caterpillars were studied to compare them with those formed by the same motor neurons on phasic flight muscles in adult moths.

Scanning micrographs showed a primary nerve branch running the length of each fiber, with secondary nerve branches extending from it at intervals. There was a great deal of variability in both the length of the branches and the distance from the nerve at which the neuromuscular junctions were formed. The rapid increase in muscle fiber size during larval development may be responsible for this variability. The nerves and junctions were often found to be obscure by overlying fibroblasts and tracheoblasts or entering the deep muscle clefts. Those examined were similar in appearance to the adult junctions formed by the same neurons, although some may have formed single branches instead of y‐shapes.

The membrane specializations of the synapse seen in freeze‐fractured specimens were similar to those of the adult junction. However, the overall shape of the nerve terminal within the junction differed. The larval nerve terminals appeared varicose instead of having a uniform diameter. The spacing of the nerve plaques varied, in contrast with the relatively straight alignment and even spacing of plaques found in adult junctions. Such differences could result from an interaction between the motor neuron and the two different types of muscle fiber that it innervates, an intrinsic change in the motor neurons themselves that occurs with metamorphosis, or a plastic functional response that occurs as a result of the different types of motor patterns that are used in the two stages.
Unresponsive, a behavioral mutant in Xenopus laevis: Electrophysiological studies of the neuromuscular system
Authors: Dudek F. Edward , Ide Charles F. , Tompkins Robert
Published: January 2005

Normal Xenopus laevis embryos begin movements at 1 day after fertilization. Embryos homozygous for the unresponsive mutation fail to move until 4 days after fertilization (just prior to feeding), after which they recover slowly. Electrophysiological studies were undertaken to determine the focus of this mutation. Formamide treatment of normal embryos was used to produce a phenocopy of the unresponsive condition, permitting direct comparisons between mutant and normal embryos. Intracellular recordings from muscle cells were obtained in formamide‐treated and untreated preparations with both normal and unresponsive animals. Local electrical stimulation evoked either isolated endplate potentials and action potentials or after‐discharges of these events in all preparations. A decrease in illumination also caused a burst of endplate potentials and action potentials. Therefore, the electrophysiology of the neuromuscular junction in unresponsive appears qualitatively normal; the effect of the mutation on the motor system is probably distal to the neuromuscular junction, either at or subsequent to excitation‐contraction coupling.
Estrogen accumulation in zebra finch song control nuclei: Implications for sexual differentiation and adult activation of song behavior
Authors: Nordeen K. W. , Nordeen E. J. , Arnold A. P.
Published: January 2005

In zebra finches the gonadal steroid estradiol (E2) directs the sexual differentiation of neural regions controlling song and synergizes with androgens to stimulate song in adulthood. To identify regions where E2 may act to exert these effects, steroid autoradiographic techniques were used to assess cellular accumulation of 3[H]‐E2 or its metabolites within various nuclei of the zebra finch brain. In Experiment 1 we examined brains from juvenile females, still within the critical period for E2's effect on sexual differentiation. In Experiment 2 the pattern and extent of labeling in adult male brains was determined following injection of 3[H]‐E2, 3[H]‐testosterone, or 3[H]‐dihydrotestosterone. The results suggest that, both during development and in adulthood, most song‐control nuclei contain few E2‐accumulating cells. In contrast, many cells densely labeled by 3[H]‐E2 or its metabolites are present in the hypothalamus and in close proximity to one song‐control region, the hyperstriatum ventralis pars caudalis (HVc). The distribution of these latter cells overlaps with cells that project to another song‐related nucleus, Area X. Thus, in Experiment 3 fluourescent retrograde tracing and steroid autoradiographic techniques were combined to determine if E2‐accumulating cells project to Area X in adult males. Although a few retrogradely labeled cells were lightly labeled by 3[H]‐E2 or its metabolites, for the most part these appear to be two distinct populations of cells. The sparse accumulation of E2 in the zebra finch song system contrasts with that described in other song birds and has important implications as to the mechanism of E2 action on the developing and mature song system.
Activity sharpens the regenerating retinotectal projection in goldfish: Sensitive period for strobe illumination and lack of effect on synaptogenesis and on ganglion cell receptive field properties
Authors: Eisele Leslie E. , Schmidt John T.
Published: January 2005

The regenerating optic nerve of goldfish first reestablishes a rough retinotopic map on the contralateral tectum and then sharpens it. Disruption of visual activity, either by blocking activity with intraocular tetrodotoxin (TTX; Schmidt and Edwards, 1983) or by synchronizing activity with strobe illumination (Schmidt and Eisele, 1985), disrupts the sharpening process: the map is correctly oriented but the multiunit receptive fields at each point average 25–40° in diameter. In order to test whether strobe and TTX interfere with the same mechanism, we have tested whether their sensitive periods are the same, and whether strobe, like TTX treatment, does not affect either ganglion cell receptive field properties or synaptogenesis. In parallel studies, we exposed fish to 2 weeks of either strobe illumination or intraocular TTX beginning at various times after crush and determined via electrophysiological recordings that the periods of sensitivity were nearly identical. There was no effect of either treatment during the first 2 weeks (before the fibers arrive at the tectum), maximal disruption of sharpening between 14 and 50 days (the period of rapid synaptogenesis), decreasing disruption between 50 and 125 days, and no effect beyond that point or in the normal projection. In addition, long strobe exposures of up to 142 days produced no greater disruptions than shorter 2–3‐week exposures, indicating no cumulative effect. The reestablishment of synaptic transmission in tectum, assayed by recording field potentials elicited by optic nerve shock, was not affected by stroboscopic illumination. Finally, individual ganglion cells, recorded intraretinally following long‐term strobe exposure, had receptive fields that were normal both in size and in their characteristic responses to light‐on, to light‐off, or to both on and off. These findings support the hypothesis that strobe‐like TTX prevents retinotopic refinement by preventing the correction of errors initially made by the ingrowing optic axons (Schmidt et al., 1988).
The role of the sexual organs in the generation of postembryonic neurons in the leech Hirudo medicinalis
Authors: Baptista Carlos A. , Macagno Eduardo R.
Published: January 2005

In adult Hirudo medicinalis, the segmental ganglia (SG) of the fifth and sixth body segments contain a few hundred more cells than the other segmental ganglia of the body (Macagno, 1980). These ganglia innervate the sex organs and are known as the sex SG. As shown here, these cells are stained by neuron‐specific antibodies. Cell counts at several developmental stages reveal that the extra cells are added exclusively to the sex SG, and that this addition occurs gradually and almost entirely postembryonically (embryogenesis ends at 30 days of development). Hence, we refer to them as PE cells. Until 16 days of development, deleting the male genitalia or disconnecting them from the sex ganglia results in a complete absence of the PE cells. From 16 days onward, the generation of the PE cells is independent of the male genitalia. No PE cells appear in non‐sex SG that innervate male genitalia transplanted to ectopic locations at 10 days or later, indicating that as early as about 10 days of development sex SG are different from other SG in their ability to acquire PE cells. These data suggest that the PE cells are generated within the sex SG, in a process that is triggered by an interaction with the male genitalia and mediated through the innervation of the organs by these ganglia.
Regenerative specificity of motor axons when reinnervation is partially suppressed
Authors: Farel Paul B. , Wray Sibyl E.
Published: January 2005

We asked whether regenerating hindlimb motor axons would innervate inappropriate hindlimb regions if competition from appropriate innervation were prevented. The three ventral roots that innervate the hindlimb in the bullfrog (Rana catesbeiana) tadpole were transected, and the two more rostral roots were ligated to prevent regeneration. The most caudal root, which primarily supplies more distal limb musculature in unoperated tadpoles, was left free to regnerate. The specificity of regeneration was assessed by retrogradely labeling spinal motoneurons with HRP placed in the ventral thigh, a region that receives most of its innervation from the ligated roots. Despite the lack of competition from appropriate innervation, the regenerating root did not provide substantial innervation to proximal limb musculature. The same result was obtained in tadpoles operated upon at stages when regeneration of motor axons is specific and in tadpoles at stages when regenerating motor axons do not reinnervate their appropriate targets (Farel and Bemelmans, 1986), although the mechanisms in each case are likely different.
Loss of material from the retrograde axonal transport system in frog sciatic nerve
Authors: Snyder R. E.
Published: January 2005

Rapid axonal transport was studied in sciatic nerve preparations of the amphibian Xenopus laevis maintained in vitro at 23.0 ± 0.2°C. A pulse of [25S]methionine‐labeled material was allowed to move in the anterograde direction until encountering a lesion, at which a portion of the pulse reversed directions and moved in the retrograde direction. By constricting the nerve during the course of the experiment, it was possible to prevent continuous return of label from the lesion, thus creating a retrogradely moving pulse that contained a defined quantity of radiolabel. Movement of both the anterograde and the retrograde pulse were monitored continuously for up to 24 h using a position‐sensitive detector of ionizing radiation. The front and the back edge of the anterograde pulse were found to move at the rates of (mm/day) 179.9 ± 3.9 (±SEM) and 149.9 ± 5.9, respectively, and the front and the back edge of the retrograde pulse moved at the rates of 155.8 ± 11.3 and 84.6 ± 2.9, respectively. By comparison of the quantity of label lost to the stationary phase to the quantity of label calculated to have been present in the anterrograde pulse, it was determined that 0.068 ± 0.009 of the anterograde pulse is lost to each 3.18‐mm region of nerve. Comparison of the quantity of label calculated to have been present in the retrograde pulse to that in the anterograde pulse revealed that 0.057 ± 0.014 of the retrograde pulse is lost to each 3.18‐mm region of nerve. It is concluded that protein originating in the cell body and which reverses its direction of transport at a lesion can be lost from the retrograde axonal transport system.
The importance of cnidarian synapses for neurobiology
Authors: Anderson Peter A. V. , Spencer Andrew N.
Published: January 2005

Despite being the most primitive organisms to possess a nervous system, cnidarians afford rare opportunities for studying various, general aspects of chemical synaptic transmission. This is made possible by the unique organization of their nervous systems and by the fact that in certain species the neurons and synapses are readily accessible for intracellular recordings and voltage clamp. The results obtained from such studies are summarized here, with particular emphasis on work with two species, Cyanea capillata (Scyphozoa) and Polyorchis pennicilatus (Hydrozoa). The potential of these preparations for providing additional data is also discussed.
Metamorphosis and fish vision
Authors: Evans Barbara I. , Fernald Russell D.
Published: January 2005

Many species of fish exhibit metamorphosis in which dramatic external transformations occur as a consequence of coordinated changes in gene expression within an organism. Because postembryonic development and change appears to be the rule rather than the exception in teleost fish species, we view metamorphosis as one of many developmental strategies in fish which have continued plasticity as a common theme. Metamorphic changes are manifested in the visual system by modification of photoreceptor peak sensitivity rod photoreceptor cell addition, and retinal reorganization. These changes correspond to significant changes in the natural habitat of the animal and in its visual capabilities as demonstrated behaviorally. Thyroxine is the main metamorphic hormone as has also been found in amphibia. The sequence of metamorphic events occur in all teleosts, but they are compressed in time in direct developing animals suggesting that such animals might prove useful for understanding the evolution of metamorphosis in fish. It seems likely that rod photoreceptors may have evolved in conjunction with the change from larval to juvenile stage through metamorphosis in indirect developing fishes. During evolution, the contraction and/or loss of the larval stage has resulted in earlier appearance of rod photoreceptors during development although they always arise later than cone photoreceptors. This ontogenetic developmental sequence supports Walls's (1942) proposal that cones are phylogenetically older than rods and suggests that rods may have evolved several times.
Slow transport of the cytoskeleton after axonal injury
Authors: McKerracher Lisa , Hirscheimer Andrea
Published: January 2005

The delivery of cytoskeletal proteins to the axon occurs by slow axonal transport. We examined how the rate of slow transport was altered after axonal injury. When retinal ganglion cell (RGC) axons regenerated through peripheral nerve grafts, an increase in the rate of slow transport occurred during regrowth of the injured axons. We compared these results to axonal injury in the optic nerve where no substantial regrowth occurs and found a completely different response. Slow transport was decreased approximately tenfold in rate in the proximal segment of crushed optic nerves. This decreased rate of slow transport was not induced immediately, but occurred about 1 week after injury. To explore whether a decrease in the rate of slow transport was induced when the regeneration of peripheral nerves was physically blocked, we examined slow transport in motor neurons after the sciatic nerve was transected and ligated. In this case, no change in the rate of the comigrating tubulin and neurofilament (NF) radioactive peaks were observed. We discuss how the changes in the rate of slow transport may reflect different neuronal responses to injury and speculate about the possible molecular changes in the expression of tubulin which may contribute to the observed changes. © 1992 John Wiley & Sons, Inc.
Biogenic amines modulate synaptic transmission between identified giant interneurons and thoracic interneurons in the escape system of the cockroach
Authors: Casagrand Janet L. , Ritzmann Roy E.
Published: January 2005

In the escape system of the cockroach, Periplaneta americana, a population of uniquely identifiable throacic interneurons (type A or TIAs) receive information about wind via chemical synapses from a population of ventral giant interneurons (vGIs). The TIAs are involved in the integration of sensory information necessary for orienting the animal during escape. It is likely that there are times in an animal's life when it is advantageous to modify the effectiveness of synaptic transmission between the vGIs and the TIAs. Given the central position of the TIAs inthe escape system, this would greatly alter associated motor outputs. We tested the ability of octopamine, serotonin, and dopamine to modulate synaptic transmission between vGIs and TIAs. Both octopamine and dopamine significantly increased the amplitude of vGI‐evoked excitatory postsynaptic potentials (EPSPs) in TIAs at 10−4−10−2 M, and 10−3 M, respectively. On the other hand, serotonin significantly decreased the vGI‐evoked EPSPs in TIAs at 10−4−10−3 M. These results indicate that octopamine, serotonin, and dopamine are capable of modulating the efficacy of transmission of important neural connections within this circuit. © 1992 John Wiley & Sons, Inc.
A real‐time analysis of growth cone–target cell interactions during the formation of stable contacts between hippocampal neurons in culture
Authors: Cooper Monica W. , Smith Stephen J.
Published: January 2005

Mechanisms of cell‐cell recognition and structural changes of growth cones (g.c.) and target membranes during contact formation are poorly understood. To examine these issues, we obtained a high magnification, realtime record of stale contact formation in cultured cells from the hippocampal CA1 area in the newborn rat. We used differential interference contrast (DIC) optics coupled to a video microscope for periods of over 24 h of continuous time‐lapse recording. Our goal was to observe the sequential changes exhibited by afferent and target cells as they form a stable contact. Understanding the process of how stable contacts are made is important because such contacts are the first step in synapse formation. Four principal observations emerged from our study: (1) The target cell was receptive to a contact on a specific patch on its surface defined by the presence of lamellae and filopodia. This specific patch (named target site) was invariably present on the target cell surface before the time the growth cone arrived. (2) Stable adhesion between filopodia on the two cells initiated events leading to cell–cell contact formation. Specifically, the remaining filopodia on the growth cone and target cell were redirected toward the adhering filopodia, and the growth cone size decreased dramatically. (3) The axonal process then grew at a significantly accelerated rate (up to 50 times its baseline growth rate). (4) In addition, a number of observations were obtained on axonal turns towards the target cell, induction of target sites, and architectural remodelling of cells after the formation of a new contact. Our findings indicate that in this neuronal system, filopodia are the means used by cells to interact at stages prior to and during contact formation. We speculate that the molecules involved in cell recognition and the machinery that initiates contact formation are embedded in the fine structure of filopodia. Finally, our results provide possible clues as to some of the stages that may be involved in synapse formation in the mammalian central nervous system. © 1992 John Wiley & Sons, Inc.
Developmental study of the expression of B50/GAP‐43 in rat retina
Authors: Reh T. A. , Tetzlaff W. , Ertlmaier A. , Zwiers H.
Published: January 2005

B50/GAP‐43 has been implicated in neural plasticity, development, and regeneration. Several studies of axonally transported proteins in the optic nerve have shown that this protein is synthesized by developing and regenerating retinal ganglion cells in mammals, amphibians, and fish. However, previous studies using immunohistochemistry to localize B50/GAP‐43 in retina have shown that this protein is found in the inner plexiform layer in adults. Since the inner plexiform layer contains the processes of amacrine cells, ganglion cells, and bipolar cells to determine which cells in the retina express B50/GAP‐43, we have now used in situ hybridization to localize the mRNA that codes for this protein in the developing rat retina. We have found that B50/GAP‐43 is expressed primarily by cells in the retinal ganglion cell layer as early as embryonic day 15, and until 3 weeks postnatal. Some cells in the inner nuclear layer, possibly a subclass of amacrine cells, also express B50/GAP‐43 protein and mRNA; however, the other retinal neurons–bipolar cells, photoreceptors, and horizontal cells express little, if any, B50/GAP‐43 at any stage in their development. Early in development, the protein appears in the somata and axons of ganglion cells, while later in development, B50/GAP‐43 becomes concentrated in the inner plexiform layer, where it continues to be expressed in adult animals. These results are discussed in terms of previous proposals as to the functions of this molecule. © 1993 John Wiley & Sons, Inc.
Mechanisms of early neurogenesis in Drosophila melanogaster
Authors: Campos‐Ortega José A.
Published: January 2005

The neuroectoderm of insects contains an initially indifferent population of cells which during later development will give rise to the progenitor cells of the neural and epidermal lineages. Experimental evidence indicates that cellular interactions determine which cells will adopt each one of these fates. Transplantation experiments suggest that a signal with neuralising character is required to stabilize the primary neural fate in 25% of all the neuroectodermal cells, which will develop as neuroblasts, and that an epidermalising signal contributes to suppress the neural fate in the remaining 75% of the cells, allowing in this way their development as epidermal progenitor cells. The invoked cell interactions are assumed to be mediated by the products of several genes forming a complex, not yet well understood network of interrelationships. Elements of this network are the proteins encoded by Delta and Notch, which appear to convey the regulatory signals between the cells; the proteins encoded by the achaete‐scute gene complex, which regulate neural development; and the proteins encoded by the Enhancer of split gene complex, which give neuroectodermal cells access to epidermal development. © 1993 John Wiley & Sons, Inc.
A putative nicotine pump at the metabolic blood–brain barrier of the tobacco hornworm
Authors: Murray Christine L. , Quaglia Michele , Arnason Jon T. , Morris Catherine E.
Published: January 2005

In mammals, P‐glycoprotein immunostaining at the blood–brain barrier has implicated the multidrug pump in the restricted movement of many cytotoxic agents into the central nervous system (NCS). Since many insects require as sophisticated blood–brain barrier system to protect their CNS from plant‐derived neurotoxins, we have investigated the possibility that a P‐glycoprotein homolog constitutes a component of the insect blood–brain barrier. We have used the nicotine‐resistant tobacco hornworm (Manduca sexta) to address this issue. Manduca has been previously shown, in physiological studies, to have an alkaloid (nicotine/morphine/atropine) pump at its excretory malpighian tubules. We show (1) that the tubules are P‐glycoprotein immunopositive, (2) that Manduca has a metabolic blood–brain barrier for nicotine, (3) that the barrier co‐localizes with P‐glycoprotein immunostaining, and (4) that detoxifying enzymes as well as the nicotine pump are likely to account for the metabolic blood–brain to nicotine. These findings may provide insights on two major fronts, the troublesome problem of multi‐insecticide resistance, a phenomenon that parallels multidrug resistance in tumor cells, and the problem of tolerance to addictive neuroactive drugs like nicotine or morphine. 1994 John Wiley & Sons, Inc.