bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transfer of habituation in Aplysia: Contribution of heterosynaptic pathways in habituation of the gill‐withdrawal reflex
Authors: Goldberg Jeff I. , Lukowiak Ken 
Published: January 2005

AbstractHabituation of the Aplysia gill‐withdrawal reflex (and siphon‐withdrawal reflex) has been attributed to low‐frequency homosynaptic depression at central sensory–motor synapses. The recent demonstration that transfer of habituation between stimulation sites occurs in this model system has prompted the hypothesis that heterosynaptic inhibitory pathways also play a role in the mediation of habituation behavior. To test this hypothesis, the sites and mechanisms of neural plasticity which underlie transfer of habituation in Aplysia were examined. Transfer of habituation is a reduction in the reflex evoked at one stimulation site (siphon) due to repeated presentation of a stimulus to a second site (gill). Centrally mediated transfer of habituation, measured in a preparation lacking the siphon–gill peripheral nervous system (PNS), was associated with a reduced excitatory response in central motor neurons. Repeated tactile stimulation of the gill did not attenuate the gill response evoked by electrical stimulation of the branchial nerve nor the mechanoreceptor response recorded in LE sensory neurons. In contrast, repeated stimulation of siphon or gill at a site which was “off” the sensory field of a specific mechanoreceptor led to a diminution in synaptic transmission between that sensory neuron and its followers (motor neurons and interneurons). These data demonstrate that centrally mediated transfer of habituation results from heterosynaptic modulation of synaptic transmission at the sensory–motor (and sensory–interneuron) synapses. Therefore, habituation behavior in Aplysia is mediated through the conjoint action of homosynaptic and heterosynaptic inhibitory processes.
Photoreceptors and visual interneurons in the medicinal leech
Authors: Peterson Eric L. 
Published: January 2005

AbstractThe medicinal leech has five pairs of eyes, each with about 50 photoreceptors. Receptors produce propagating impulses which constitute their output to second order neurons in the CNS. Within the eye, receptors have diverse thresholds, and thus the aggregate output of the eye is graded with light intensity. By having many receptors in parallel, the eye may achieve better intensity discrimination and temporal response than would be predicted from the relatively poor characteristics of individual receptors. Receptors in eyes 3–5 on one side of the animal excite the ipsilateral LV (lateral visual) cell, an interneuron in the first segmental ganglion. By physiological tests the receptor axons are electrically coupled to the LV cell. Moreover, the LV cell is Lucifer Yellow dye‐coupled to many fine fibers that appear to be receptor axons of the ipsilateral eyes 3–5. The receptors of the contralateral eyes 3–5, and those of the photosensitive sensilla lining the body inhibit the LV cell via polysynaptic pathways. Thus, the LV cells are central elements of the neural circuit processing input from the leech's spatially distributed visual system.
Membrane mechanism of neuroendocrine caudo‐dorsal cell inhibition by the ring neuron in the pond snail Lymnaea stagnalis
Authors: Jansen R. F. , Maat A. Ter , Bos N. P. A. 
Published: January 2005

AbstractOvulation in the pond snail Lymnaea stagnalis is controlled by the neuroendocrine caudo‐dorsal cells (CDCs) in the cerebral ganglia, which release an ovulation hormone during a period of impulse activity. Firing of the single RN in the right cerebral ganglion hyperpolarizes the CDCs. This hyperpolarization is caused by the opening of potassium channels in the axons that connect both the CDC clusters. By this action, that presumably is mediated by axonal branches of the RN in the intercerebral commissure closely associated with these CDC axons, the RN decouples both the CDC clusters. Although the RN has negative feedback on the CDC, it does not control afterdischarge characteristics. The authors suggest that the RN, next to the egg‐laying behavior, is involved in another behavior, not compatible with ovulation. Male reproductive activity is presented as a possible candidate for such behavior.
Regulation of calcium influx into buccal muscles of Aplysia by acetylcholine and serotonin
Authors: Ram Jeffrey L. , Parti Rajesh 
Published: January 2005

AbstractAcetylcholine (ACh) causes contraction of Aplysia buccal muscles E1 and I5, and serotonin (5‐hydroxytryptamine, 5‐HT) enhances ACh‐elicited contractions of these muscles. Possible roles of calcium influx in mediating these responses were examined by studying influx of 45Ca++. 5‐HT increased calcium influx into both I5 and E1. Maximal influx occurred at 10−6M 5‐HT and the increased influx could be sustained in the presence of 5‐HT for at least 10 min. ACh also caused calcium influx, and calcium influx increased approximately in proportion to log[ACh] from 10−5M to 10−3M ACh. 5‐HT and ACh probably bring about calcium influx by different mechanisms since the effect of ACh was additive to a maximal 5‐HT response, and 10−4M hexamethonium bromide inhibited the increased influx caused by ACh but did not affect influx caused by 5‐HT. Cyclic AMP analogues and forskolin neither caused an increase in calcium influx nor an increase in the influx caused by ACh. The data support a model in which ACh‐elicited contractions of I5 and E1 are due primarily to calcium entry across the extracellular membrane, and 5‐HT can “load” an intracellular site by a mechanism different from that activated by ACh. The data do not support a role for cyclic AMP in mediating the calcium influx response to 5‐HT.
Behavioral recovery associated with central nervous system regeneration in the snail Melampus
Authors: Moffett Stacia , Snyder Keith 
Published: January 2005

AbstractThe 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

AbstractThe 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

AbstractUltrastructural 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

AbstractThe 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

AbstractThe 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

AbstractMeasurements 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

AbstractRecent 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

AbstractAn 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

AbstractThe 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

AbstractRat 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

AbstractIdentified 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.