bluuebunny/crossref_metadata_2025 huggingface dataset:
Behavioral recovery associated with central nervous system regeneration in the snail Melampus
Authors: Moffett Stacia , Snyder Keith
Published: January 2005

The pulmonate snail Melampus bidentatus regenerates central nervous tracts following commissurotomy, connective transection, and cerebral ganglion ablation. Our goal was to determine whether or not neural regrowth within the central nervous system restored behaviors disrupted by lesions. One behavior that is disrupted by commissurotomy is retraction of facial structures that are contralateral to a stimulated facial region, a response that normally accompanies the ipsilateral retraction. Tentacle withdrawal on the side contralateral to stimulation reappeared on a timescale that was correlated with growth of a commissural link (8–19 days post‐lesion). Electrophysiological recordings from a labial nerve pathway that has a contralateral component similar to the contralateral tentacle response showed that development or strengthening of an alternative pathway could also mediate contralateral responses. Thus, a major conclusion of this study was that both tract regeneration and changes in existing CNS pathways can underlie recovery. The percentage (approx. 75%) of snails that regenerate the cerebral commissure and show behavioral recovery is established early in the period following commissure transection. Behavioral recovery and anatomical evidence of regeneration were also correlated in the other two operations: single cerebral ganglion removal and unilateral cerebropleural and cerebropedal connective transection. We conclude that Melampus is able to regenerate neuronal connectivity that can restore normal behavior.
Octopamine enhances neuromuscular transmission in developing and adult moths, Manduca sexta
Authors: Klaassen Leland W. , Kammer Ann E.
Published: January 2005

The effect of octopamine on neuromuscular transmission was examined in developing and adult Manduca sexta. Intracellular recordings were made from the dorsal longitudinal muscle (DLM), superfused with solutions containing DL‐octopamine or other amines. In untreated adult moths and pharate adults nearly ready to eclose (stage Day 19), stimulation of the motor nerve evokes a large excitatory junction potential (EJP), an active membrane respons, and a twitch. In adults and Day 19 animals DL‐octopamine (10−7 to 10−4 M) has no effect on the amplitude and rise‐time of the electrical response in normal saline, but 10−6 to 10−4 M DL‐octopamine increases the amplitude of the excitatory junction potential recorded in saline containing one‐third the normal calcium concentration. Immature (Day 16) muscle, which normally produces only small EJPs following stimulation of its motor nerve, responds to 10−6 to 10−4 M DL‐octopamine by an increase in the EJP above threshold for an active membrane response and a contraction. When the muscle has developed sufficiently to spike and contract in response to nerve stimulation in the absence of exogenous octopamine (Days 17 and 18), application of DL‐octopamine increases the maximum rate at which the muscle contracts in response to each stimulus in a train (designated the maximum following frequency, MFF). The threshold dose for an effect on the MFF of Day 18 immature moths is less than 10−10 M. At this stage 10−8 M DL‐octopamine increases the MFF four‐fold. The effect on the MFF is dose‐dependent over the range 10−10 M to 10−6 M.

The biogenic amines DL‐epinephrine, DL‐norepinephrine, tyramine, DL‐phenylethanolamine, 2‐phenylethylamine, and dopamine, applied at concentrations of 10−8 or 10−4 M, do not change the MFF. Both DL‐synephrine (10−8 M) and serotonin (10−7 M) mimic the action of 10−10 M DL‐octopamine on the MFF. The action of DL‐octopamine (10−7 M) is blocked by phentolamine (10−4 M) but not by propranolol (10−4 M).

The octopamine content of hemolymph was determined with a radioenzymtic assay. The concentration of octopamine in the hemolymph increases 3.6‐fold, from 5 × l0−8 M on Day 18 (duration of adult development is 19 days) to 1.85 × 10−7M one day following eclosion. The concentration of octopamine in the hemolymph on Days 14 and 16 is not significantly different from that on Day 18. This concentration is sufficient to increase the MFF of Day 18 preparations.

These data provide evidence for a modulatory role of octopamine on developing neuromuscular junctions of a fast flight muscle.
Central and peripheral neurosecretory pathways to an insect flight motor nerve
Authors: Wasserman Arthur J.
Published: January 2005

Ultrastructural examination of the IIN1b nerve to the dorsal longitudinal flight muscle of Manduca sexta L. verified the presence of neurosecretory processes. Subspherical and irregular vesicles were found where the nerve enters the muscle, while spherical vesicles were found in the proximal region only. A dorsal unpaired median (DUM) cell, the median nervous system, and two or more peripheral cells are the sources of these neurosecretory inclusions.

Light the electron microscopy CoCl2 backfills of the transverse nerve produced intensification of a peripheral neuron (#1) and processes in nerves IIN1a and IIN1b. Similar backfills of nerve IIN1b produced intensification of a DUM cell, a second peripheral neuron (#2), and processes in the transverse nerve and nerve IIN1a. Neuron #1 contained large spherical electron‐dense vesicles while neuron #2 contained smaller subspherical vesicles. These cells were situated upon the link and/or transverse nerves.

Based on these results, we suspect central and peripheral neurosecretory processes reach nerve IIN1b as follows: the link nerve projects prothoracic median nervous system and neuron #2 processes, nerve IIN1a projects neuron #1 processes, and nerve IIN1 projects mesothoracic DUM cell processes, although this latter pathway was less clear.
Innervation of the limb accessory flexor muscle in several decapod crustaceans. II. Electrophysiology
Authors: Wiens T. J. , Govind C. K.
Published: January 2005

The innervation of the distal and proximal heads of the accessory flexor muscle in three portunid crabs and two non‐portunid decapods was studied electrophysiologically. In all species studied, the proximal head received only the two previously reported accessory flexor axons, an excitor and an inhibitor. The same two axons also innervated the distal head in all species, but in the portunids the distal head also received excitation from at least three, and probably sometimes four, of the main flexor excitor efferents. The accessory inhibitor exertend very strong effects in the tonic muscle fibers found in the proximal head and in the most proximal bundle of the distal head. The newly described inhibitory and excitatory distributions may have important implications for locomotory behavior.
Differential ability of two adult molluscan neurons to regenerate electrical synapses
Authors: Bulloch A. G. M.
Published: January 2005

The ability of two electrical synapses (neuron L4‐R4 and neuron L19‐R19) to regenerate in the adult Helisoma nervous system was examined. The L4‐R4 electrical connection exhibited rapid restoration to 50% of normal strength, whereas L19‐R19 reconnection was weak or absent. This disparity is attributable to the inability of neuron 19 to sprout effectively across a crush site in the buccal commissure, although peripheral sprouting was pronounced. The factors which underlie the inability of neuron 19 (but not neuron 4) to sprout into a central environment are unknown, but dictate differential synapse restoration in this adult nervous system.
Crayfish motor nerve terminal's response to serotonin examined by intracellular microelectrode
Authors: Dixon D. , Atwood H. L.
Published: January 2005

Measurements of resting potential and action potential in presynaptic branches of the excitatory motor axon to the crayfish opener muscle were made with intracellular microelectrodes during application of serotonin (10−9–10−3 M). A 5‐min exposure to 10−6 M serotonin produced enhancement of excitatory junction potentials (EJPs) lasting about 1 h. The membrane potential of the presynaptic terminals was depolarized by about 5 mV; the depolarization subsided within 1/2 h. Concomitant reduction in amplitude of the presynaptic action potential, not accompanied by spike broadening, was observed. The presynaptic depolarization, and the enhancement of EJPs, were dependent on the presence of extracellular sodium but not extracellular calcium. A possible mechanism for serotonin's effect involves initial entry of sodium into the nerve terminal, with consequent increased availability of intracellular calcium. The subsequent long‐lasting phase of EJP enhancement may result from an additional effect on the metabolism of the nerve terminal.
A comparative study of soluble calcium‐dependent proteolytic activity in brain
Authors: Baudry Michel , Simonson Lisa , Dubrin Richard , Lynch Gary
Published: January 2005

Recent studies have shown that soluble calcium activated proteases (calpains) in brain degrade proteins associated with the cytoskeleton and vary markedly in activity across regions and as a function of development. It was suggested that the observed differences in calpain activity reflect differences in the turnover rate of structural elements. The present study extends this analysis by measuring the properties and activity of calpain in representatives of the five classes of vertebrates with particular emphasis on the mammals.

No evidence for proteolysis was found in soluble fractions of fish brains at neutral pH in the presence or absence of added calcium. A substantial calcium‐independent proteolytic activity was found in amphibian brains—the effects of a variety of protease inhibitors indicated that it is also a neurtral thiol (cysteine) protease. Reptilian brains exhibited both calcium‐independent and calcium‐dependent proteolytic activity. Virtually all proteolytic activity in birds (5 species) and mammals (9 species) measured at neutral pH was calcium‐dependent. The endogenous substrates for the calcium activated proteases were very similar in several species of birds and mammals as were the effects of a variety of protease inhibitors. However, the activity of the enzyme, expressed per mg of soluble protein, was highly and negatively correlated with brain size in the mammals. The allometric expression for this relationship was similar to that found for the density of neurons in cerebral cortex as a function of absolute brain size. These results indicate that soluble proteolytic enzymes in brain are differentially expressed among classes of vertebrates and suggest that the turnover of cytoskeletal elements in birds and mammals differs in important ways from that found in fish and amphibians. The results obtained for mammals raise the possibility of a relationship between brain size and the rate at which structural elements are broken down and replaced in this vertebrate class.
In vitro classical conditioning of a gill withdrawal reflex in Aplysia: Neural correlates and possible neural mechanisms
Authors: Lukowiak Ken
Published: January 2005

An in vitro preparation consisting of the siphon, mantle, gill, and abdominal ganglion undergoes classical conditioning when a weak tactile stimulus (CS) applied to the siphon is paired with a strong tactile stimulus to the gill (UCS). When the stimuli are paired, the CS comes to evoke a gill withdrawal reflex (GWR) which increases in amplitude with training. Only when the stimuli are paired in a classical conditioning paradigm does the CS come to evoke a GWR. With classical conditioning training there is an alteration in the synaptic efficacy between central sensory neurons and central gill motor neurons. Moreover, these changes can be observed in sensory neurons not activated by the CS. The changes observed, as evidenced by the number of action potentials evoked in the gill motor neuron do not completely parallel the observed behavioral changes. It is suggested that in addition to changes in the synaptic efficacy at the sensory‐motor neuron synapse, other changes in neuronal activity occur at other loci which lead to the observed behavioral changes.
Generation of subunit‐specific antibody probes for Torpedo acetylcholinesterase: Cross‐species reactivity and use in cell‐free translations
Authors: Lappin Richard I. , Rubin Lee L. , Lieberburg Ivan M.
Published: January 2005

The assembly of the collagen tailed A12 form of acetylcholinesterase (AChE) is regulated by muscle contraction. To begin to study this regulation, we derived antibody probes for the three subunits (100 kd, catalytic, and collagen tail) of AChE purified from Torpedo californica electric tissue. These included a polyclonal antiserum that recognizes all 3 subunits and 19 monoclonal antibodies; 16 of the monoclonals recognized the catalytic subunit, 2 recognized the tail subunit, and 1 recognized the 100 kd subunit on Western blots. We used immunohistochemical procedures to show that several of the anticatalytic and one of the antitail monoclonals cross‐reacted with frog muscle AChE and Western blotting to show that several of the anticatalytic monoclonals cross‐react with rat brain AChE. These antibodies were then used to immunoprecipitate AChE precursors from a cell‐free translation system. There were generally three primary translation products, corresponding to the three enzyme subunits. Therefore, each subunit is probably derived from a separate mRNA. Occasionally there were two translation products corresponding to the catalytic subunit alone. The catalytic subunit was glycosylated following addition of canine microsomal membranes to the translation mix. The mRNA coding for this subunit appeared to be present in the poly(A)− RNA pool.
Development of rat soleus endplate membrane following denervation at birth
Authors: Moss Brenda L. , Schuetze Stephen M.
Published: January 2005

Rat soleus endplates develop some of their characteristic features before birth and others after birth. Specializations appearing before birth include a localized cluster of acetylcholine receptors (AChRs), an accumulation of acetylcholinesterase (AChE) in the synaptic basal lamina, and a cluster of nuclei near the endplate membrane. In contrast, postsynaptic membrane folds are elaborated during the first three weeks after birth. We denervated soleus muscles on postnatal day 1, before folds had appeared, and followed the subsequent development of endplate regions with light and electron microscopy. We found that the denervated endplates initiated fold formation on schedule and maintained their accumulations of AChRs, AChE, and endplate nuclei. However, the endplates stopped fold formation prematurely and eventually lost their rudimentary folds. At about the same time, the junctional AChR clusters were joined by ectopic patches of AChRs. The former endplate regions also became unusually elongated, possibly as a consequence of the lack of membrane folds. Apparently, endplate membranes have only a limited capacity for further development in the absence of both the nerve and muscle activity.
The regulation of neurite outgrowth, growth cone motility, and electrical synaptogenesis by serotonin
Authors: Haydon P. G. , McCobb D. P. , Kater S. B.
Published: January 2005

Identified neurons of the buccal ganglion of the snail Helisoma when isolated from their ganglionic environment and plated in cell culture grow new neurites that are tipped with motile growth cones. Addition of the neurotransmitter serotonin to the culture medium surrounding actively growing neurons causes an immediate, premature cessation of neurite elongation in specific identified neurons. Serotonin selectively inhibits neurite extension of neurons B19 and P5 while having no effect on the extension of neuron B5. Coincident with the serotonin evoked inhibition of neurite elongation is an inhibition of growth cone motile activities and a retraction of growth cone filopodia and lamellipodia. One site of serotonin's growth inhibitory actions is directly at the growth cone rather than at the neurites or cell body. A second area of this study concerns connectivity. In Helisoma neurons the formation of electrical synaptic connections critically relies on both potential partner neurons having a mutual interaction of actively growing neurites. Neurons in a nongrowing state do not form electrical synapses (Hadley et al., 1983). As a result of inhibiting neurite extension, serotonin is able to affect synaptogenesis by preventing certain neurons (neurons B19) from forming electrical synaptic connections with other neurons (neurons B5) that are themselves competent to interconnect. Thus, by inhibiting neurite extension, serotonin is capable of regulating both the development of arborizations and the formation of connectivity.
Acetylcholine activates cerebral interneurons and feeding motor program in Limax maximus
Authors: King Michael S. , Delaney Kerry , Gelperin Alan
Published: January 2005

The cellular and network effects of acetylcholine (ACh) on the control system for feeding in Limax maximus were measured by intracellular recordings from feeding command‐like interneurons and whole nerve recordings from buccal ganglion motor nerve roots that normally innervate the ingestive feeding muscles. The buccal ganglion motor nerve root discharge pattern that causes rhythmic feeding movements, termed the feeding motor program (FMP), was elicited either by attractive taste solutions applied to the lip chemoreceptors or by ACh applied to the cerebral ganglia. The ability of exogeneous ACh applied to the cerebral ganglia to trigger FMP was blocked by the cholinergic antagonists curare and atropine. If the strength of the lip‐applied taste stimulus was in the range of 1–2 times threshold, cerebral application of the cholinergic antagonists blocked or greatly decreased the ability of lip‐applied taste solutions to trigger FMP (5 of 8 trials). The cerebral feeding interneurons, some of which activate FMP when stimulated intracellularly, are excited by small pulses of ACh applied directly to the cell body from an ACh‐filled micropipette. A pulse of ACh that activates several of the feeding interneurons simultaneously triggers FMP. The data suggest that under certain stimulus conditions an obligatory set of cholinergic synapses onto the feedininterneurons must be activated for taste inputs to trigger ingestion. The determination of ACh's action within the feeding control system is necessary for understanding how enhanced cholinergic transmission leads to prolonged associative memory retention (Sahley, et al., 1986).
Multiple transmitter neurons in Tritonia. II. Control of gut motility
Authors: Lloyd Philip E. , Willows A. O. Dennis
Published: January 2005

Two large multiple transmitter neurons are located in each buccal ganglion of Tritonia. One of these neurons (B11) contains large quantities of two neuropeptides and acetylcholine (ACh), whereas the other neuron (B12) appears to contain the same two peptides but no ACh. One of the peptides present in these neurons has recently been sequenced and is termed small cardioactive peptide B (SCPB). Both neurons regulate the motility of the gut. Stimulation of B11 produces a posteriorly directed peristalsis after a short latency. This gut movement may normally accompany swallowing. B11 stimulation also produces an increase in the rate of endogenous contractile activity that is similar to that produced by superfusion of the gut with low concentrations (10−8 M) of SCPB. Stimulation of B12 produces a vigorous longitudinal contraction of the gut, initiated in the posterior part of the gut and not peristaltic in nature. This movement appears incompatible with swallowing behavior and may be involved in regurgitation.
The molluscan neuropeptide, SCPB, increases the responsiveness of the feeding motor program of Limax maximus
Authors: Prior David J. , Watson Winsor H.
Published: January 2005

Small cardioactive peptide B (SCPB) has an excitatory effect on both buccal neurons and musculature in numerous molluscan species. The present study reports the effects of SCPB on the activity of specified buccal neurons and the expression of the feeding motor program of the terrestrial slug, Limax maximums. Superfusion of an isolated CNS preparation with 10−6 M SCPB results in a 3–4‐fold increase in the burst frequency of the fast salivary burster neuron (FSB), while having no effect on the activity of another endogenous burster, the bilateral salivary neuron (BSN). The response of the FSB to SCPB iS dose dependent, with a threshold concentration of 2 × 10−8M. The response of the FSB to SCPB showed no indication of desensitization, even after long‐term exposure (20 min).

The feeding motor program (FMP) in Limax is a discrete pattern of cyclical motor activity that can be initiated by lip nerve stimulation. In the presence of SCPB a previously subthreshold stimulus can initiate the full FMP. The pattern of the FMP, once initiated, appears unaffected by SCPB. Thus it is the responsiveness of the initiation process that is enhanced by SCPB. Histochemical studies revealed a number of buccal neuron somata and fibers that stain for SCPB‐like immunoreactive material (SLIM).
Acetylcholine receptor clustering and triton solubility: Neural effect
Authors: Podleski Thomas R. , Salpeter Miriam M.
Published: January 2005

Previous studies by Prives et al. (1980, 1982a and b) have shown that acetylcholine receptors (AchRs) are extracted from muscle cells in vitro by Triton X‐100 at different rates, and that clustered receptors extract most slowly. The present study was aimed at comparing the relative extractability of receptors in clusters with those in intercluster regions and the role of neural factors in regulating this extractability. Using primary rat muscle cells in vitro we confirmed that receptor extraction with Triton X‐100 does not fit a single exponential but has more than one rate, and that in control cells clustered receptors extract more slowly than do receptors in intercluster regions. The major new observation in this study was that neural extract lowered the overall Triton extraction rate of intercluster receptors to that of clustered receptors. Additional new observations include the findings that (1) both clustered and intercluster receptors show multiphasic extraction rates; (2) stabilization of AchRs against Triton extraction increases with time in the surface membrane; (3) the effect of neural extract on Triton extractability of AChR is dependent on factors that control RNA synthesis, cytoskeletal elements, and collagen; (4) fixation and/or buffer washes accelerate receptor extraction only incells that are treated with Triton, but not in control cells; (5) in control cells (not exposed to neural factors) Triton X‐100 causes new clusters to form. From experiments using Con A we suggest that the Tritoninduced new clusters may not be formed by a redistribution of receptorsbut are, most likely, due to the presence of groups of intercluster receptors with extraction rates lower than thoseof surrounding receptors.
Regeneration of goldfish retina: Rod precursors are a likely source of regenerated cells
Authors: Raymond Pamela A. , Reifler Michael J. , Rivlin Patricia K.
Published: January 2005

This study describes regeneration of the neural retina in juvenile goldfish. The retina was destroyed with an intraocular injection of ouabain, a technique introduced by Wolburg and colleagues (Maier and Wolburg, 1979; Kurz‐Isler and Wolburg, 1982). We confirmed their observation that the level of damage produced by the toxin was graded, in that neurons in the inner retinal layers were preferentially destroyed, and only in the more severely affected retinas were cells in the outer nuclear layer (i.e., photoreceptor cells) damaged. Evidence of retinal regeneration could be seen beginning about 2 weeks after the injection of ouabain. In contrast to previous studies (Maier and Wolburg, 1979), we found that regeneration took place only in those retinas in which photoreceptors had been destroyed. In cases in which the outer nuclear layer was spared, no regeneration of inner layers occurred, even after 6 months. Thymidine autoradiography was used to document the regeneration of new retinal neurons and to show that rod precursors, like other dividing cells, were not destroyed by the oubain, but in contrast showed an increased mitotic activity. Regeneration did not proceed uniformly, but was initiated at neurogenic foci scattered across the retina. These foci consisted of clusters of dividing neuroepithelial‐like cells. The evidence is consistent with the proposal that these cells were derived from rod precursors. These results imply that rod precursors are capable of a wider range of developmental fates than they normally express.
Dissociation of the inhibition of fast axonal transport by chlorimipramine from an effect on axonal microtubules
Authors: Lavoie P.‐A. , Filion P. R. , Pharand M.
Published: January 2005

The effect of in vitro exposure of bullfrog spinal nerves to 0.2 mM chlorimipramine on the density of axonal microtubules was studied in an attempt to clarify the mechanism by which chlorimipramine inhibits fast axonal transport. A 17‐ h exposure to chlorimipramine reduced the density of microtubules in unmyelinated axons by only 18%; this microtubular loss does not reach the upper limit of the range of microtubule reduction associated with inhibition of fast axonal transport. A 23‐ h exposure to chlorimipramine, which had decreased microtubular density in unmyelinated axons by 40% in a previous study, did not decrease microtubular density in myelinated axons in the present study. These results rule out microtubular destruction as the mechanism responsible for inhibition of fast orthograde axonal transport by chorimipramine, and greatly reduce the likelihood that microtubular destruction plays a significant role in the inhibition of fast retrograde transport by chlorimipramine.
Neural and glial phenotypic expression by neural crest cells in culture: Effects of control and presumptive aganglionic bowel from ls/ls mice
Authors: Coulter H. David , Gershon Michael D. , Rothman Taube P.
Published: January 2005

The enteric nervous system is formed by cells that migrate to the bowel from the neural crest. Previous experiments have established that avian crest cells in vitro will colonize explants of murine bowel and there give rise to neurons. It has been proposed that phenotypic expression by the crest‐ derived precursors of enteric neurons and glia is critically influenced by the microenvironment these cells encounter within the gut. To test this hypothesis, quail crest cells were cocultured with explants of control or presumptive aganglionic bowel from the ls/ls mutant mouse, and the effects of the enteric tissue on five phenotypic markers of crest cell development were followed. Aganglionosis develops in the terminal region of the colon of the ls/ls mouse because viable crest‐ derived neural and glial precursors fail to colonize this tissue. Expression of the phenotypic markers in the cocultures was compared with that in cultures of crest alone, crest plus neural tube, and gut grown alone. The markers examined were melanogenesis and immunostaining with antisera to 5‐ hydroxytryptamine (5‐ HT) and tyrosine hydroxylase (TH) and the monoclonal antibodies, NC‐ 1 and GlN1. Explants of control, but not presumptive aganglionic ls/ls gut were found to increase the incidence of the expression of 5‐ HT and NC‐ 1 immunoreactivities; moreover, especially near the gut, the assumption of a neuronal morphology by 5‐ HT‐, NC‐1‐, and GlN1‐ immunoreactive cells was also increased. Coincidence of expression of 5‐ HT with NC‐ 1 and GlN1 immunoreactivities was observed. The effect of the bowel was selective in that the expression of TH immunoreactivity, which is not a marker of mature enteric neurons, was reduced rather than enhanced. The effect of enteric explants on crest cell development was specific in that it was not mimicked by explants of metanephros, which inhibited expression of 5‐ HT immunoreactivity and the acquisition of a neuritic form by NC‐ 1‐ immunoreactive cells. It is concluded that theenteric microenvironment affects the phenotypic expression of subsets of crest cells and that this action of the bowel.

Is manifested in vitro. The inability of presumptive aganglionic gut from ls/ls mice to influence neural phenotypic expression may be due to the failure of this tissue to produce putative factor(s) required for theeffector to the inability of the crest‐ derived precursor cells to migrate into the abnormal enteric tissue.
Wind‐activated thoracic interneurons of the cockroach: I. Responses to controlled wind stimulation
Authors: Westin Joanne , Ritzmann Roy E. , Goddard Donald J.
Published: January 2005

The cockroach escape response begins with a turn away from a wind puff such as that generated by an approaching predator. The presence and direction of that wind is detected by hairs on the animal's cerci, and this information is conducted to the thoracic ganglia via two populations of giant interneurons. In the thoracic ganglia, the giant interneurons excite a number of interneurons, at least some of which in turn excite motor neurons that control leg movement. In this paper we examine response properties of various thoracic neurons to wind stimuli originating from different directions.

Three sets of thoracic neurons were distinguished on the basis of latency. Type A interneurons had short latencies to wind stimuli (1.3–2.25 ms). Type B interneurons had longer latencies (4–6 ms), and motor neurons had the longest latencies (5.6–17.0 ms). Individual type A interneurons either responded equally to wind from all directions or were biased in their response. Directionality was related to the presence of ventral branches near one or both sides of the midline of the ganglion. Cells with ventral median (VM) branches on either side tended to be omnidirectional or front‐rear biased, whereas cells with VM branches on only one side were biased to that side. Although several type B interneurons had strong wind responses and were directionally sensitive, they did not have VM branches. We hypothesize that the presence of VM branches in type A interneurons permits connection with ventral giant interneurons, and this connection accounts for their short latency and directional properties. This hypothesis will be tested in the companion paper.
Development and senescence of control of ciliary locomotion in a gastropod veliger
Authors: Arkett Stuart A.
Published: January 2005

The rhythmical ciliary arrest behavior characteristic of the veliger larvae of the prosobranch Calliostoma ligatum develops in a predictable sequence of events. Spontaneous, small‐amplitude (1–3 mV) postsynaptic potentials (PSPs) are first recorded intracellularly from prototrochal ciliated cells at about 45 h after fertilization. Prototrochal ciliated cells, which are precusors of the locomotory, preoral ciliated cells of mature veligers, are electrically coupled to each other. Cilia beat continuously and erratically at this stage. PSP amplitude and duration gradually increase with age, and at about 56 h, preoral ciliated cells become electrically excitable. A single regenerative action potential first occurs at this time and causes a velum‐wide, ciliary arrest. Between 56 and 72 h, the duration of the depolarizing phase of the preoral ciliated cell action potential decreases, the amplitude increases, and the hyperpolarizing undershoot develops. Preoral ciliated cell action potentials appear to be Ca2+‐dependent throughout development. Shortening of the action potential duration and development of the hyperpolarizing undershoot may be due to activation of later developing K+ channels. As veligers become competent to metamorphose, the preoral velar cells and their connections with the body deteriorate.
The effect of cyclic AMP on neuritic outgrowth in explant cultures of developing chick olfactory epithelium
Authors: Johnson Randall R. , Farbman Albert I. , Gonzales Federico
Published: January 2005

The effect of cyclic AMP (cAMP) analogs and phosphodiesterase (PDE) inhibitors on neurite outgrowth was studied in explant cultures of olfactory neurons. Nasal pits from 5‐ or 6‐day‐old chick embryos were minced, explanted into culture dishes, and grown in a serum‐free medium. One of the cyclic AMP analogs, dibutyryl cyclic AMP (dbcAMP) or 8‐bromo‐cyclic AMP (8‐Br‐cAMP), or one of the PDE inhibitors, theophylline or isobutylmethylxanthine (IBMX), was added to the culture medium. The explants were examined for neurite outgrowth after 2 days in vitro. Db‐cAMP Increased the number of explants expressing neurites by 25–35% over control cultures, whereas 8‐Br‐cAMP had essentially no effect at the same concentrations. Addition of dibutyryl cyclic GMP (dbcGMP) gave no increase in neurite out growth, thus indicating that the effect of enhancing neuritic growth is specific to cAMP and not cyclic nucleotides in general. The resulting increase in neurite outgrowth is due to the cyclic nucleotide component of dbcAMP, since both IBMX and theophylline, which elevate intracellular cAMP, also increased neurite outgrowth significantly. When forskolin was added to the culture medium, there was a trend to increased neurite outgrowth; this was significantly enhanced when a subthreshold concentration of theophylline was added in addition to the forskolin.
Inhibitor of protein synthesis blocks longterm behavioral sensitization in the isolated gill‐withdrawal reflex of Aplysia
Authors: Castellucci V. F. , Blumenfeld H. , Goelet P. , Kandel E. R.
Published: January 2005

To study the effect of protein synthesis inhibition on long‐term sensitization of the gill‐ and siphon‐withdrawal reflex of Aplysia, we have developed an isolated reflex preparation in which we could expose the inhibitor to only that part of the central nervous system involved in mediating the reflex and not to the other parts of the animal's central nervous system, thus minimizing the possible systemic side effects. We have found that long‐term sensitization can be obtained in the isolated gill reflex, and that this long‐term process, but not the short‐term process, is blocked selectively by anisomycin, a reversible inhibitor of protein synthesis. Moreover, to obtain this blockade of long‐term sensitization, this drug need only be applied during the training procedure.
ω‐Aga‐I: A presynaptic calcium channel antagonist from venom of the funnel web spider, Agelenopsis aperta
Authors: Bindokas Vytautas P. , Adams Michael E.
Published: January 2005

Spider venoms are proving to be important sources of specific ion channel toxins. Venom of Agelenopsis aperta, a funnel web spider, contains a class of polypeptide toxins which blocks neuromuscular synapses at nanomolar concentrations. Detailed physiological analyses of block caused by one of these toxins, ω‐Aga‐I show that it suppresses transmitter release at insect and frog neuromuscular junctions and blocks calcium spikes in insect neuronal cell bodies. ω‐Aga‐I may define a binding site on neuronal calcium channels which is common to both vertebrates and invertebrates.
Androgens modulate endplate size and ACh receptor density at synapses in rat levator ani muscle
Authors: Bleisch William V. , Harrelson Allan
Published: January 2005

The dorsal bulbocavernosus or “levator ani” muscle of the rat is highly responsive to androgens. Both the muscle and the motoneurons which innervate it contain high concentrations of androgen receptors. The neuromuscular synapses in this muscle are also affected by changing androgen levels. In particular, the total number of ACh receptors (AChRs) in the muscle is lower in males that have been castrated, and it increases after treatment with the androgens, testosterone and 5 α‐dihydrotestosterone. An examination of individual endplates using histochemistry and quantitative autoradiography suggested that the reduction in AChR number following castration is caused by reductions in both the size of endplates and in the density of AChRs at each synapse.
Cell death of motoneurons in the chick embryo spinal cord. X. Synapse formation on motoneurons following the reduction of cell death by neuromuscular blockade
Authors: Okada A. , Furber S. , Okado N. , Homma S. , Oppenheim R. W.
Published: January 2005

Chronic treatment of chick embryos with neuromuscular blocking agents, such as curare, rescues motoneurons from naturally occurring cell death. In the present study, embryos treated with curare from E6 to E9 had 35% more motoneurons than controls on E10 and 42% more than controls on E16. Previous studies have shown that several aspects of motoneuron differentiation occur normally in curare‐treated embryos. We report here that dendrite growth and arborization is also unaltered on E10 and E16 following curare treatment. A quantitative analysis of afferent synapses on motoneurons shows that the packing density of both axosomatic and axodendritic synapses is also normal on E10 in curare‐treated embryos, despite the greater number of motoneurons present. This indicates that the interneurons that provide presynaptic input to motoneurons are able to compensate for the increased number of synaptic sites made available by curare treatment. However, by E16 the packing density of synapses is reduced by about half. Because motoneurons and their dendrites continue to grow between E10 and E16, the further increase in synaptic sites made available in curare‐treated embryos apparently exceeds the compensatory capacity of presynaptic interneurons on E16. One can conclude from these results that the increased survival of motoneurons in curare‐treated embryos in not owing to an increase in afferent synapses. Motoneurons in these embryos continue to survive in the face of either no change (E10) or a reduction (E16) in the number of axodendritic and axosomatic synapses. Therefore, increased motoneuron survival in this situation is very likely regulated primarily by motoneuron–target interactions.
The use of hormonally induced mosaics to study alterations in the synaptic connections made by persistent sensory neurons during insect metamorphosis
Authors: Levine Richard B. , Waldrop Brian , Tamarkin Dawn
Published: January 2005

During the initial phase of metamorphosis in the hawkmoth, Manduca sexta, persistent mechanosensory neurons expand their terminal arborizations within the CNS and evoke a reflex response in the pupa which is different than in the larva. In an effort to determine the contribution of sensory neuron modifications to the difference in reflex responses, manipulations of juvenile hormone and 20‐hydroxyecdysone were used to generate mosaic animals in which the sensory neurons were advanced or delayed developmentally with respect to the rest of the animal, including circuit components within the CNS. In the larval stage electrical stimulation of the sensory axons evokes a slow depolarization and a prolonged burst of action potentials in the ipsilateral intersegmental muscle motor neurons. By contrast, in pupal preparations the same motor neurons respond to an identical stimulus with a larger, more rapid depolarization which leads to a relatively brief, high‐frequency burst of action potentials. Motor responses on the contralateral side of the body are also altered during pupal development. In mosaic animals where larval‐like sensory neurons interact with a pupal CNS, a larval reflex response is generated. In the converse situation, pupal‐like sensory neurons interacting with a larval or prepupal CNS evoke a motor response that is typical of larvae or prepupae. We conclude, therefore, that pupal development of the sensory neurons is necessary, but not sufficient, for the production of the pupal reflex.
Synaptic plasticity at the crayfish opener neuromuscular preparation
Authors: Bittner George D.
Published: January 2005

The crayfish opener neuromuscular preparation exhibits most of the plasticities yet described for any synpase, including facilitation, long‐term potentiation, presynaptic inhibition, and modulation. Since the presynaptic terminals and postsynaptic muscle fibers can both be intracellularly penetrated, one can now more easily examine the cellular/molecular bases for these plasticities. Data from such studies suggest that facilitation may be influenced by something other than residual free calcium and that presynaptic inhibition is produced by a conductance increase to chloride in the terminals of the excitor axon. Several drugs (ethanol, pentobarbital) have significant effects on these synaptic plasticities over concentration ranges which produce obvious behavioral effects in crayfish and mammals. Hence, this preparation should be a useful model system to determine cellular/molecular bases for various synaptic plasticities and the effects of drugs on these plasticities.
Proctolin: A review with emphasis on insects
Authors: Orchard Ian , Belanger Jim H. , Lange Angela B.
Published: January 2005

The distribution, physiological role, mode of action, and pharmacology of the pentapeptide neuroregulator proctolin are reviewed, with special emphasis on insects. Whereas proctolin is distributed extensively throughout arthropods, its presence in molluscs, annelids, or chordates is not well established. In the arthropods, proctolin acts as a neuromodulator and possibly as a neurohormone. It does not appear to function as a conventional neurotransmitter. Two model proctolinergic systems are highlighted: motor control of the visceral muscles of the locust oviduct and of the skeletal muscles of the locust ovipositor. In these preparations proctolin is a cotransmitter acting to enhance neuromuscular transmission and muscular contraction.

The mode of action of proctolin is not well understood, although the second messengers cAMP, phosphatidyl inositol, and calcium have been implicated in various systems. Pharmacologically, the proctolin receptor has been examined with structure/activity studies, and the effects of a variety of amino acid substitutions and deletions of the pentapeptide are described. It is unfortunate that no specific antagonists of the proctolin receptor appear to be available and that no receptor‐binding studies have been reported.

The prospects are good for advances in our understanding of modulatory mechanisms, since proctolin appears to be emerging as the model for studies of this type.
Identification of protein‐bound oligosaccharides on the surface of growth cones that bind to muscle cells
Authors: Ambron Richard T. , Protic John , Den Halina , Gabel Christopher A.
Published: January 2005

In the accompanying paper (Gabel, Den, and Ambron, in press) it was shown that eight populations of glycopeptides are synthesized by single neurons of Aplysia californica. To see which glycopeptides might mediate interactions with target cells, we first identified glycopeptides that are transported selectively to synapses and growth cones. The giant neuron R2 was injected intrasomatically with 3H‐glucosamine. Twenty‐four hours later, 3H‐glycopeptides in the axon and cell body were isolated and resolved by serial lectin affinity chromatography. Of the eight populations, the biantennary‐type glycopeptides (GPbi) and those that bind to WGA (GPwga) were preferentially associated with rapidly transported glycoproteins. In contrast, the glycopeptide that consists of N‐acetylglucosamine O‐linked to ser/thr was mostly retained in the cell body. GPbi and GPwga were also preferentially transported to growth cones. Analyses of RUQ cells, exposed to 3H‐glucosamine in vitro for 36 h showed an enrichment of GPbi and GPwga at the growth cone relative to the cell body. The disposition of the various glycopeptides in growing neurons was also examined using FITC lectins. FITC‐coupled WGA, Vicia vellosa, and lentil lectin showed extensive staining of the cell body, but only WGA stained the growth cones.

To investigate if GPwga interacts specifically with target cells, these glycopeptides were isolated from the neurons of 180 abdominal ganglia. GPwga, other Aplysia glycopeptides, and glycopeptides prepared from ovalbumin were coupled separately to fluorescent spheres. The spheres were then added to muscle cells isolated from the auricle of the heart, which is innervated by many neurons from the ganglion. While spheres coupled to GPwga bound to the muscle cell surface, the other glycopeptides did not. These results indicate that glycopeptide class GPwga, found among rapidly transported glycoproteins and on the growth cone surface, is able to bind to muscle cells and may therefore play some role in neuron‐target interactions.
Giant fiber activation of flight muscles in Drosophila: Asynchrony in latency of wing depressor fibers
Authors: Hummon Margaret Raper , Costello Walter J.
Published: January 2005

In Drosophila, brain stimulation of the giant fiber pathway brings about highly stereotyped electrical responses in target muscles involved in the escape response. Both the order of muscle response and the latency of that response are predictable in wild‐type flies. The neuronal circuit to the targets is well defined and has been used in the analysis of a number of mutant phenotypes, including induced anomalies in temperature‐sensitive (ts) mutations such as shibire (shi). It has been assumed that the stereotyped response includes simultaneous activation of all six fibers of the wing depressor muscle, DLM, resulting in equal latencies for all fibers. We report here a small, but distinct, inherent difference in latency between two sets of DLM fibers in a proportion of two wild‐type strains as well as in a strain carrying the ts mutation shi. This difference may occur on one or both sides of an individual, is stable over time, and persists when the motor axon is stimulated peripherally. These results, due to the circuit leading to the target, suggest that the difference in latency arises peripherally. In flies reared at the shi permissive temperature (22°C), the difference is more common in shi than in wild‐type flies; however, in shi flies reared at 18°C, the prevalence resembles that of wild‐type flies. This indicates a subtle expression of the shi defect even at the presumed permissive temperature of 22°C. The difference in latency is similar to that induced in shi flies whose development is affected by pupal heat pulse. Thus, correct interpretation of differences in latency, e.g., in shi/wild‐type mosaic flies or in flies with mutations affecting the GF pathway, requires recognition of the inherent asynchrony that can occur between DLM fibers.
A role for cAMP in the development of functional neuromuscular transmission
Authors: Dubinsky J. M. , Fischbach G. D.
Published: January 2005

We have found that the incidence of functionally connected neuron‐myotube pairs in chick ciliary‐myotube cultures increases from 58% to more than 90% when the cells are treated for several hours with 8‐bromo‐cyclic adenosine monophosphate (8‐br‐cAMP) or with agents known to increase intracellular cAMP. The increase in connectivity was not accompanied by a change in neuron survival, or in the length of neurite‐myotube contact. Moreover, there was no change in the shape of the presynaptic action potential, in mean end plate potential (epp) amplitude or in the sensitivity of postsynaptic acetylcholine receptors (AChRs). One interpretation of these results is that a cAMP‐dependent phosphorylation acts as a trigger to activate a previously “silent” synapse.