bluuebunny/crossref_metadata_2025 huggingface dataset:
Fast axonal transport in central nervous system and peripheral nervous system axons following axotomy
Authors: Redshaw J. D. , Bisby M. A.
Published: January 2005

After axotomy, changes in the composition of fast axonally transported proteins (FTP) within the peripheral nervous system (PNS) axons have been reported. The most significant and reproducible changes involved polypeptides found within the molecular weight range of 31.0 to 14.5 kilodaltons (Bisby, 1980). We wished to determine whether similar changes following axotomy occur in axons of the central nervous system (CNS). Intracranial axotomy of the left optic tract was performed stereotaxically in rats. Six days post axotomy 50 μCi 35[S]‐methionine was injected into the vitreous body of both eyes. FTP were isolated within the optic nerves 2 h after isotope injection. The nerve segments were processed for SDS‐PAGE, fluorography, and compared to similarly prepared fluorographs of normal and eight day postaxotomy sciatic nerve segments. The labelling of 5 major polypeptide bands (S1, MW ≃ 28,000; S2a, MW ≃ 25,000; S2b, MW ≃ 23,000; T1, MW ≃ 20,200; and T2, MW ≃ 17,000) was studied by laser densitometry. Band S2b showed a highly significant (p < 0.001) increase in concentration, while bands S1 and T1 demonstrated highly significant decreases in concentration following axotomy of the sciatic nerve. In contrast, after axotomy of the retinal ganglion cell axons the only significant change was a decrease (p < 0.05) in T1. We suggest that failure of CNS axons to respond similarly to PNS axons following axotomy may be related to the failure of CNS axons to regenerate.
Neuromuscular modulation in Limulus by both octopamine and proctolin
Authors: Rane Stanley G. , Gerlach Peter H. , Wyse Gordon A.
Published: January 2005

Both octopamine and proctolin potentiate nerve‐evoked skeletal muscle contractions in the horseshoe crab, Limulus. The threshold concentration for octopamine was 10−9 to 10−8M, while for proctolin it was 3 × 10−9M. Norepinephrine and dopamine produced effects similar to octopamine but at higher thresholds; tyramine and serotonin were ineffective. Octopamine caused significant increases in amplitudes of excitatory postsynaptic potentials (epsps) of muscle fibers, but had little effect on muscle fiber input resistance or membrane potential. Also, octopamine did not affect depolarization of muscle fibers and subsequent contraction due to the direct action of exogenously applied glutamate. These results suggest that octopamine potentiates nerve‐evoked contractions primarily by facilitating release of neuromuscular transmitter. At concentrations above 10−7M, however, octopamine sometimes caused muscle spikes in response to motoneuron stimulation, a finding that suggests that octopamine may also have some postsynaptic action. Proctolin potentiated the muscle contractions evoked by glutamate but had little effect on glutamate‐evoked muscle fiber depolarization, muscle fiber input resistance, or membrane potential. Thus, proctolin appears to act directly on skeletal muscle to enhance contractility. The proctolin‐induced potentiations of contraction were sometimes accompanied by modest increases in epsp amplitude, so that unlike lobster skeletal and Limulus cardiac neuromuscular preparations, proctolin may have a secondary direct synaptic effect. Both octopamine and proctolin have been found in Limulus cardiac ganglion. This potential access to the hemolymph and the relatively low threshold concentrations needed for physiological action suggest that octopamine and proctolin could function as hormonal modulators of neuromuscular function in Limulus.
Depression of fast axonal transport produced by tullidora
Authors: Muñoz‐Martínez E. J. , Massieu D. , Ochs S.
Published: January 2005

The fast axoplasmic transport of labeled proteins was studied in cats showing hindlimb paralysis 4–7 weeks after a single oral dose of tullidora (Karwinskia humboldtiana) toxins. The isotope (3H‐leucine) was injected into the spinal ganglion and the contralateral spinal cord of the seventh lumbar segment in order to study transport in sensory and motor fibers.

The axoplasmic transport in motor fibers of the sciatic nerve was clearly altered in tullidora‐treated cats. The majority of these animals showed a gradual decline of radioactivity from the cord to the periphery instead of the clear‐cut wave front always seen in normal cats. An apparent wave was seen in three treated cats but the wave peak was behind the normal position and the slope of the wave front was reduced. While the rate of transport indicated by the farthest extent of the foot of the slope was not in all cases significantly changed, the results all indicated a hindered transport by the reduced slope front in the distal segments of the motor axons. In contrast, the axoplasmic transport appeared normal in the sensory fibers of all but one tullidora‐treated cat.

Light and electron microscopy of medial gastrocnemius and sural (cutaneous) nerves revealed axonal constrictions and axolemal irregularities associated with organelle retention after tullidora treatment. Also, some mitochondria appeared swollen. These changes were more frequent and intense in the motor nerve fibers than in the cutaneous nerve fibers.
Sprouting and functional regeneration of an identified serotonergic neuron following axotomy
Authors: Murphy A. Don , Barker David L. , Loring Jeanne F. , Kater S. B.
Published: January 2005

An identified serotonergic neuron (C1) in the cerebral ganglion of Helisoma trivolvis sprouts following axotomy and rapidly (seven to eight days) regenerates to recover its regulation of feeding motor output from neurons of the buccal ganglia. The morphologies of normal and regenerated neurons C1 were compared. Intracellular injection of the fluorescent dye, Lucifer Yellow, into neuron C1 was compared with serotonin immunofluorescent staining of the cerebral and buccal ganglia. The two techniques revealed different and complimentary representations of the morphology of neuron C1. Lucifer Yellow provided optimal staining of the soma, major axon branches, and dendritic arborization. Immunocytochemical staining revealed terminal axon branches on distant targets and showed an extensive plexus of fine fibers in the sheaths of ganglia and nerve trunks. In addition to C1, serotonin‐like immunoreactivity was localized in approximately 30 other neurons in each of the paired cerebral ganglia. Only cerebral neurons C1 had axons projecting to the buccal ganglia. No neuronal somata in the buccal ganglia displayed serotonin‐like immunoreactivity.

Observations of regenerating neurons C1 demonstrated: (1) Actively growing neurites, both in situ and in cell culture, displayed serotonin‐like immunoreactivity; (2) severed distal axons of C1 retained serotonin‐like immunoreactivity for up to 28 days; (3) axotomized neurons C1 regenerated to restore functional control over the feeding motor program.
Modulation of a respiratory motor program by peptide‐secreting neurons in Aplysia
Authors: Schaefer Mark , Brownell Philip H.
Published: January 2005

Respiratory pumping of the gill and siphon of Aplysia californica is a fixed‐action pattern coordinated by a defined set of interneurons and motor neurons. In semi‐intact preparations of the gill and siphon innervated by the abdominal ganglion, respiratory pumping is facilitated for a prolonged period following activation of the peptidergic bag cell neurons. The induced changes in contractile behavior of the gill and siphon correlate with cell specific actions of the bag cells on motor neurons regulating these organs. Our results suggest that peptidergic neurons can alter the expression of a fixed pattern of behavior by modulating the excitability of motor neurons controlling the behavior.
Steroid interactions with structure and function of avian song control regions
Authors: DeVoogd Timothy J.
Published: January 2005

Following the pioneering work of Nottebohm, the brain regions involved in song production in songbirds have become a focus of extensive research in several laboratories. As both singing behavior and the neuroanatomy of song control regions are strongly affected by sex steroids in many songbird species, this system has become regarded as an ideal model system in which one can potentially determine how steroids affect neuronal anatomy, how altered anatomy leads to altered physiology, and how the altered physiology causes changes in singing. In the initial part of this review, I shall focus on canaries and zebra finches as most of our knowledge of the song system has been obtained from these two species. I shall describe singing behavior, the constituents of the song system, what is known of how these nuclei contribute to song, and how each is affected by steroid fluctuations. I shall then speculate on new ways of posing questions on hormone—anatomy interaction in this system (which I will illustrate with preliminary data from my own lab). This review will be brief as several reviews of aspects of the song system have recently been published (Arnold, 1982; Nottebohm, 1984; Arnold and Gorski, 1984; DeVoogd, 1984; Konishi, 1985).
Effects of octopamine on miniature excitatory junction potentials from developing and adult moth muscle
Authors: Klaassen Leland W. , Kammer Ann E. , Fitch Greg K.
Published: January 2005

Intracelluar recordings of excitatory junction potentials (EJPs) and miniature EJPs (MEJPs) were made from the dorsal longitudinal muscle of Manduca sexta to determine the sites of action of octopamine. MEJPs increased in amplitude and frequency as the moth developed during the 3 days before eclosion. DL‐Octopamine (5 × 10−6M) increased the amplitude of excitatory junction potentials in both immature moths (one day before eclosion) and adults. Octopamine (10−5M) also increased the amplitude and frequency of MEJPs from immature animals (one and two days before eclosion) but had the opposite effect on adults and pharate adults ready to eclose. Treatment with octopamine (10−5M) resulted in a decrease in input resistance and a hyperpolarization in both immature and adult muscle fibers.

The results suggest that octopamine acts both presynaptically and postsynaptically but that the increase in the amplitude of the evoked response is due primarily to influences on presynaptic processes.
Serotonin immunoreactivity of neurons in the gastropod Aplysia californica
Authors: Longley Roger D. , Longley Alison J.
Published: January 2005

Serotonergic neurons and axons were mapped in the central ganglia of Aplysia californica using antiserotonin antibody on intact ganglia and on serial sections. Immunoreactive axons and processes were present in all ganglia and nerves, and distinct somata were detected in all ganglia except the buccal and pleural ganglia. The cells stained included known serotonergic neurons: the giant cerebral neurons and the RB cells of the abdominal ganglion. The area of the abdominal ganglion where interneurons are located which produced facilitation during the gill withdrawal reflex was carefully examined for antiserotonin immunoreactive neurons. None were found, but two bilaterally symmetric pairs of immunoreactive axons were identified which descend from the contralateral cerebral or pedal ganglion to the abdominal ganglion. Because of the continuous proximity of this pair of axons, they could be recognized and traced into the abdominal ganglion neuropil in each preparation. If serotonin is a facilitating transmitter in the abdominal ganglion, these and other antiserotonin immunoreactive axons in the pleuroabdominal connectives may be implicated in this facilitation.
Silencing normal input permits regenerating foreign afferents to innervate an identified crayfish sensory interneuron
Authors: Krasne Franklin B.
Published: January 2005

Interneuron A, an identified first‐order sensory interneuron that is innervated by mechanoreceptors on one side of the crayfish tailfan, normally resists extra innervation by regenerating contralateral mechanoreceptor axons. However, if its normal innervation is silenced by covering mechanosensory hairs with a surgical glue, it accepts contralateral innervation. This finding on an arthropod provides evidence for the generality and antiquity of the principle, critical in development of the vertebrate nervous system, that activity of one set of afferents can control whether other afferents form synapses on a target.
Posttranslational modification of neurofilament polypeptides in rabbit retina
Authors: Glicksman Marcie A. , Soppet Daniel , Willard Mark B.
Published: January 2005

Three polypeptides that compose neurofilaments, designated H, M, and L, are synthesized in the cell bodies of neurons and subsequently conveyed down their axons by the process of slow axonal transport. The axonal form of H, which is a component of the cross bridges between the neurofilaments, is antigenically different from the form in the cell bodies and dendrites. To understand how this special form of H is directed to the axon, and more generally how intracellular differentiation is established and maintained by the selective delivery of different molecular species to different compartments of a cell, we have studied the events that occur immediately after the synthesis of the three neurofilament polypeptides in the retinas of rabbits. We observed that H and M are synthesized in the retina as precursor polypeptides, EH and EM, that migrate markedly faster on SDS polyacrylamide gels than their mature axonal forms. The maturation of these precursors requires more than one day and appears to involve their phosphorylation. Only the electrophoretically mature forms appear in the axons of the retinal ganglion cells in the optic nerve. We consider the following interpretation of these observations. Shortly after they are translated in the cell body, the neurofilament polypeptides become phosphorylated at multiple sites. However, only after they have moved a distance of several hundred micrometers down the axon, H and M are phosphorylated at additional sites, causing their conformation or binding properties to change. This change, which is reflected in the reduction of their electrophoretic mobility and the appearance of new antigenic determinants, may function to alter the H‐mediated crossbridges and produces the morphological and structural properties of the neurofilament lattice that is characteristic of axons.
A simple neuronal system characterized by a monoclonal antibody to SCP neuropeptides in embryos and larvae of tritonia diomedea (gastropoda, nudibranchia)
Authors: Kempf Stephen C. , Masinovsky Boris , Willows A. O. Dennis
Published: January 2005

SCP‐like antigenicity is first present in Tritonia diomedea in small cells of the cerebral ganglia and a single axon crossing the cerebral commissure of 8‐day‐old embryos. Other axons and neurons become antigenic as the larva develops. At 4–9 days after larvae hatch from the egg mass, 2 additional pairs of neurons are labeled. Axons extend from one pair to the left cerebral ganglion and from the other to the right. A second labeled axon is present across the cerebral commissure. In metamorphically competent larvae the cerebral and pedal neuropils, as well as two neurons in the buccal ganglia with axon(s?) across the commissure, are antigenic. The change in antigenicity as the larva becomes competent is presumably preparatory for juvenile life. The labeled buccal neurons may be B12, which are known to contain SCPs, extend an axon across the buccal commissure, and function in adult feeding behavior. The two large neurons strongly labeled by rabbit polyclonal antibodies against FMRFamide are clearly different from neurons labeled by monoclonal antibody against SCPs. This result supports the contention that different antigens are labeled by these two immune probes.
Extension and retraction of axonal projections by some developing neurons in the leech depends upon the existence of neighboring homologues. II. The AP and AE neurons
Authors: Gao Wei‐Qiang , Macagno Eduardo R.
Published: January 2005

To assess the generality of our previous finding (Gao and Macagno, 1987) that segmental homologues play a role in the establishment of the pattern of axonal projections of the heart accesory HA neurons, we have extended our studies to two other identified leech neurons: the anterior pagoda (AP) neurons and the annulus erector (AE) motor neurons. Bilateral pairs of AP neurons are found in the first through the twentieth segmental ganglia (SG1 through SG20) of the leech ventral nerve cord. All AP neurons initially extend axonal projections to the contralateral periphery as well as longitudinal projections along the contralateal interganglionic connective nerves toward anterior and posterior neighboring ganglia. Although the peripheral projections are maintained by all AP neurons throughout the life of the animal, the longitudinal projections disappear in all but two segments: the AP neurons in SG1 maintain their anterior projections and extend them into the head ganglion, and those in SG20 maintain their posterior projections and extend them into SG21 and the tail ganglion. When single AP neurons are delted anywhere along the nerve cord before processes begin to atrophy, however, the longtudinal projections are retained by their ipsilateral homologues in adjacent ganglia. The rescued processes appear to take over the projections of the deleted neurons. In cases where two or more AP neurons on the same side of the nerve cord are deleted from adjacent ganglia, a contralateral homologue sometimes extends projections to the periphery ipsilaterally or on both sides. We obtained similar results when we deleted single AE neurons from midbody ganglia. Thus, our experiments with three different identified neurons consistently show that the initial pattern of projections is the same in all ganglia, but that the existence of homologues in adjacent ganglia leads to the pruning of some of the initial projections. A consequence of this homologue‐dependent process retraction is that neurons normally lacking neighboring homologues will have patterns of projections different from those neurons that do have such neighbors.
Presynaptic modulation by octopamine at a single neuromuscular junction in the mealworm (Tenebrio molitor)
Authors: Hidoh O. , Fukami J.
Published: January 2005

The effect of octopamine on the neuromuscular junction of the mealworm (Tenebrio molitor) was examined. Octopamine potentiated excitatory junctional potentials (EJPs) recorded intracellularly and extracellularly from ventral longitudinal muscle fibers. The potentiating action of octopamine was blocked in the presence of the α‐adrenergic blocking agent, phentolamine, but not in the presence of another α‐blocker, phenoxybenzamine, or the ß‐blockers propranolol and dichloroisoproterenol. The resting membrane potential, membrane input resistance, reversal potential of EJP, glutamate potentials, and spontaneous miniature EJPs were found to be unaffected by octopamine. In contrast, quantal contents estimated by the extracellularly recorded EJP failures were greatly increased by octopamine. These results suggest that octopamine acted on the presynaptic terminals via α‐adrenoceptor‐like receptors (octopamine receptors) at the Tenebrio neuromuscular junctions to enhance the transmitter release associated with the motor nerve impulses.
Evidence for differential DNA endoreplication during the development of a molluscan brain
Authors: Chase Ronald , Tolloczko Barbara
Published: January 2005

The DNA content of neurons in the cerebral ganglion of Achatina fulica was determined by the two‐wavelength method of microspectrophotometry using Feulgen‐stained sections. DNA measurements of mouse hepatocytes were used as a control of the methods. All sampled neurons with a nuclear diameter > 7 m̈m were polyplid. The shape of the frequency histogram of DNA contents is not compatible with an interpretation that assumes one or more simple duplications of the genome. It is suggested, instead, that the results are due to either the underreplication of some DNA sequences or the selective amplification of genes. Additional experiments using [3H]‐thymidine autoradiography showed that the incidence of neuronal DNA synthesis is highest during the period of the animal's greatest growth and then declines rapidly near the onset of sexual maturity. The mesocerebrum incorporated greater amounts of [3H]‐thymidine than the rest of the brain, whereas the procerebrum remained diploid throughout the course of the study.
FMRF‐amide‐like immunoreactive efferent fibers and FMRF‐amide suppression of pacemaker neurons in eyes of Bulla
Authors: Jacklet Jon W. , Klose Monika , Goldberg Mark
Published: January 2005

The eyes of certain marine gastropods, including Aplysia and Bulla, contain circadian pacemakers, which produce a circadian rhythm of autogenous compound action potential (CAP) activity. The CAPs are generated by the synchronous spike discharge of a distinctive population of retinal pacemaker neurons whose axons convey the CAP activity to the CNS. When CAP activity is recorded from a preparation with eyes attached to the CNS, the CAP activity is modulated by efferent activity. In this study we have identified FMRF‐amide‐like immunoreactive efferent axons in the optic nerves of Bulla. These axons arborize in the basal retinal neuropil adjacent to the pacemaker neurons and are in a position to make synaptic contacts with their dendrites. Similar immunoreactive fibers are not observed in Aplysia eyes. Exogenous FMRF‐amide at micromolar concentrations suppresses ongoing CAP activity in isolated eyes but does not suppress the ERG or phase shift the circadian rhythm of CAP activity. Intracellular recordings from the retinal pacemaker neurons reveal that FMRF‐amide hyperpolarizes the membrane potential, suppresses spike discharge, and decreases the input resistance, suggesting that a K conductance is increased. Electrical stimulation of the region of the cerebral ganglion that contains FMRF‐amide immunoreactive neurons suppresses ongoing CAP activity. All these results are consistent with the idea that the FMRF‐amide immunoreactive central neurons and their axons provide a pathway for efferent modulation of the CAP rhythm generated by the retinal pacemaker neurons.
Lead‐dependent deposits in diverse synaptic vesicles: Suggestive evidence for the presence of anionic binding sites
Authors: Sulzer David , Piscopo Irene , Ungar Florette , Holtzman Eric
Published: January 2005

We have observed electron dense deposits dependent on incubation of aldehyde‐fixed tissues with lead ions within synaptic vesicles of several types of neurons that differ in the neurotransmitters utilized and in the secretory granules of the adrenal medulla. Evidently, vesicle components that can interact with lead ions are widespread. A plausible explanation for the occurrence of the deposits is the presence of anionic binding sites within the vesicles. This would agree well with other biochemical, cytochemical, and immunocytochemical evidence, such as that indicating the presence of sulfated macromolecules in certain synaptic vesicles. Anionic binding sites could play significant roles by participating in processes such as Ca2+ storage, stabilization of pH gradients, or the control of osmotic phenomena.
Correlations between song acquisition, song production, and plasma levels of testosterone and estradiol in sparrows
Authors: Marler Peter , Peters Susan , Wingfield John
Published: January 2005

Male birdsong is a sexually dimorphic behavior characterized by learned dialects. In a combined study of learning in relation to steroid levels in the plasma, changes in estradiol and testosterone levels were correlated with the timing of the sensitive period for song acquisition and with successive stages in song development. Male swamp sparrows were trained with a changing series of live singing tutors from 26 days to 1 year of age. Song acquisition was concentrated between 26 and 47 days of age (57%). By 85 days of age 71% of acquisition was completed; some occurred as late as 300 days. There were two major periods when testosterone levels were elevated. The first, from 30–80 days, encompassed most of the period of song acquisition. The second, from 260 to at least 360 days of age, coincided with song development. Estradiol levels were elevated from 18 to 170 days of age, encompassing almost all of the period of song acquisition. A marked estradiol peak between 40 and 50 days coincided with a trough in testosterone levels and a hiatus in song acquisition. The strong correlation between the second period of elevated testosterone and song motor development suggests a causal connection, with levels peaking in mid‐development and declining during mature song production. Estradiol levels were elevated at the start of the study and remained so during early subsong production, from 30 to 165 days. They then fell to baseline, remaining there throughout the resumption of subsong and plastic song production at 250–326 days. Both estradiol and testosterone are candidates for possibly affecting song acquisition.
Evidence for an absence of estrogen‐concentration by CCK‐immunoreactive neurons in the hypothalamus of the female rat
Authors: Akesson Thomas R. , Micevych Paul E.
Published: January 2005

It is becoming increasingly clear that the neuropeptide cholecystokinin (CCK), widely distributed in the rat hypothalamus and limbic system, is subject to both organizational and activational influences of steroid hormones. Sex differences in numbers of CCK‐immunoreactive elements have been demonstrated in sexually dimorphic structures such as the bed nucleus of the stria terminalis, medial preoptic nucleus, and ventromedial nucleus of the hypothalamus. Steroid activation of CCK has been indicated by findings that hypothalamic CCK levels and binding capacity vary over the estrous cycle. These studies, in combination with evidence of CCK mediation of sexually differentiated functions, prompted us to test for estrogen concentration among CCK‐containing cells of the female rat hypothalamus by combining the techniques of immunohistochemistry and autoradiography.

A method employing 2‐week ovariectomies and perfusion fixation with 4% paraformaldehyde was compatible with the localization of both estrogen‐accumulating and CCK‐immunoreactive cell bodies. The maintenance of numbers of CCK‐positive cells after gonadectomy suggested that expression of this peptide may not be directly regulated by ovarian steroids in female rats. This suggestion was substantiated by the finding that, with rare exceptions, CCK‐immunoreactive cells did not concentrate estrogen in tissues collected from the anterior‐posterior extent of the bed nucleus of the stria terminalis, medial preoptic nucleus, anterior hypothalamic area, and paraventricular nucleus.
Parallel processing of short‐term memory for sensitization in Aplysia
Authors: Frost William N. , Clark Gregory A. , Kandel Eric R.
Published: January 2005

How is the short‐term memory for a single form of learing distributed among the various elements of a neuronal circuit? To answer this question, we examined the short‐term memory for sensitization, using the siphon component of the defensive gill‐ and siphon‐withdrawal reflex. We found that the memory for short‐term sensitization is represented by at least four sites of circuit modification, each involving a different type of plasticity. These include (1) presynaptic facilitation of the sensory neuron connections onto both interneurons and motorneurons; (2) presynaptic inhibition at the connections of the L30 inhibitory neurons onto the excitatory interneuron L29; (3) posttetanic potentiation of the excitatory connections made by L29 onto a specific subclass of siphon motorneurons, the LFS cells; and (4) an increase in the tonic firing rate of the LFS siphon motor neurons, resulting in neuromuscular facilitation. Each of the heterosynaptic changes seems to involve a common modulatory transmitter and to utilize a common second messenger system. Moreover, each of these sites seems capable of encoding a different component of the short‐term memory. Facilitation of the connections of sensory neurons should contribute to the increase in amplitude of the response; the disinhibition of the L29 interneurons and the posttetanic potentiation at L29 synapses should contribute to an increase in the duration of the response; and the increase in tonic firing of the LFS subclass of siphon motor neurons seems capable of contributing both to an increase in response amplitude and to changes in response topography.
Synapse elimination occurs late in the hormone‐sensitive levator ani muscle of the rat
Authors: Jordan Cynthia L. , Letinsky Michael S. , Arnold Arthur P.
Published: January 2005

Using tetranitroblue tetrazolium (TNBT) to stain neuromuscular synapses, we compared the development of the adult pattern of innervation in two fast‐twitch muscles in the rat: the androgen‐sensitive levator ani (LA) and the extensor digitorum longus (EDL), which is not thought to be androgen sensitive. We found that about 18% of adult LA muscle fibers, but only about 2% of adult EDL fibers, are multiply innervated. Moreover, synapse elimination occurs substantially later in the LA compared with the EDL. At 2 weeks after birth, the EDL is already predominantly singly innervated, whereas the LA is still predominantly multiply innervated. The apparent delay in the normal time course of synapse elimination in the LA corresponds to a similar delay in other aspects of neuromuscular development (the time course of appearance of axonal retraction bulbs, the growth of fibers, and the development of adult motor terminal morphology). Finally, motor terminals change during synapse elimination from morphologies resembling growth cones to the adult form of neuromuscular synapses. Because the period of synapse elimination is significantly different for muscles that differ in their androgen sensitivity, hormonal sensitivity may represent an important property of motoneurons or muscle fibers influencing the normal time course of neuromuscular synapse elimination in rats. Thus, androgen might regulate the normal ontogenetic process of synapse elimination.
Analysis of proprioceptive inputs to DPG interneurons in the cockroach
Authors: Murrain Michelle , Ritzmann Roy E.
Published: January 2005

In this study we report on morphological and physiological analysis of proprioceptive sensory input to thoracic interneurons. Sensory neurons from leg proprioceptors were filled using cobalt chloride. The morphological location of these sensory neurons was compared with that of the DPG interneurons. The interneurons investigated were found to have morphological overlap with the sensory neurons of the specific proprioceptors, suggesting that they have the potential to receive direct input from these proprioceptors. Individual interneurons were recorded intracellularly and identified by intracellular injection of Lucifer Yellow, and the responses of these cells to mechanical stimulation of specific proprioceptors were analyzed. All of the DPG interneurons tested as well as other interneurons receive input from one or more of these proprioceptors. In addition, DPG interneurons have ipsilateral/contralateral biases in their responses to proprioceptors. Paired stimulation of proprioceptors resulted in enhancement or decrement of the response in the interneurons, depending upon which sensory structures were stimulated together. The results of this study show that proprioceptive information is processed by DPG interneurons.
Peptide B induction of bag‐cell activity in Aplysia: Localization of sites of action to the cerebral and pleural ganglia
Authors: Painter Sherry D. , Rock Michael K. , Nagle Gregg T. , Blankenship James E.
Published: January 2005

The bag cells of the marine mollusc Aplysia are model neuroendocrine cells involved in the initiation of egg laying and its associated behaviors, but the natural stimulus triggering bag‐cell activity is not known. The atrial gland of A. california, an exocrine organ in the reproductive tract, contains two structurally related peptides (A and B) which can induce an afterdischarge in vitro, and these peptides can be used to probe the central nervous system for sites where extrinsic excitatory input onto the bag‐cell system might occur. These sites were identified in a series of lesion and ablation experiments. The entire central nervous system was removed from an animal and placed in a chamber with two compartments which could be independently perfused, allowing peptides (atrial gland extract or purified peptide B) to be selectively applied to specific regions of the nervous system while bag‐cell activity was monitored using extracellular suction electrodes. Afterdischarges were consistently and reliably induced when peptides were applied to the cerebral ganglion, the pleural ganglia, the cerebropleural connectives, or the rostral 10–15% of the pleurovisceral connectives, provided that an intact neuronal pathway connected the site of peptide application with the bag cells. In contrast, afterdischarges were never observed when peptides were selectively applied to the buccal or pedal ganglia and only rarely observed when applied to the abdominal ganglion and caudal pleurovisceral connectives. These results support the hypothesis that bag‐cell processes and/or neuron(s) presynaptically excitatory to the bag cells are located in the pleural and cerebral ganglia and narrow the region of the central nervous system where the critical initiator element(s) can be identified.
The cyclic GMP‐induced inward current in neuron R14 of Aplysia californica: Similarity to a FMRFamide‐induced inward current
Authors: Ichinose Mitsuyuki , McAdoo David J.
Published: January 2005

Injecting cGMP into Aplysia neuron R14 induced an inward current similar to one elicited by application of FMRFamide to the outside of that cell. In contrast, injection of cAMP into R14 caused a long‐lasting outward current and conductance increase. Phosphodiesterase inhibitors increased the cGMP and FMRFamide‐induced inward currents in R14. The cGMP‐induced inward current is voltage dependent and is largely carried by Na+. It is also strongly and inversely dependent on both external [Ca2+] and [Cl−], although these ions are not significant current carriers. Changing external [K+] had no effect. Voltage and ion dependencies of the cGMP‐induced inward current are similar to those of an inward current induced by FMRFamide. Thus cGMP may be a second messenger to FMRFamide in producing a slow inward current in R14. cGMP does not appear to be a second messenger to FMRFamide in most Aplysia neurons.
A quantitative analysis of the development of the central nervous system in juvenile Aplysia californica
Authors: Cash Dave , Carew Thomas J.
Published: January 2005

The marine mollusc Aplysia californica has proved to be a useful preparation for analyzing the development of learning and memory on both behavioral and cellular levels. An important issue in this analysis concerns the anatomical substrate upon which learning is superimposed during development. As a first step in examining this question, in the present study we have determined the number of neurons in all the major central ganglia at each stage during juvenile development, a time when several forms of learning first emerge in Aplysia. We found that a large and highly nonlinear proliferation of neurons occurs during juvenile development, with the greatest increase in cell number occurring during a specific juvenile stage: Stage 12. The neuronal proliferation is system‐wide, occurring in each of the central ganglia simultaneously, suggesting the action of a general developmental signal or trigger (perhaps a hormone). Accompanying the increase in neuron number in Stage 12 there is a large increase in neuropilar volume (150‐fold), which significantly increases the opportunity for synaptic interactions late in juvenile development.
Catecholamine neurons in Aplysia: Improved light‐microscopic resolution and ultrastructural study using paraformaldehyde and glutaraldehyde (FaGlu) cytochemistry
Authors: Goldstein Ronald S. , Schwartz James H.
Published: January 2005

We have modified the formaldehyde‐glutaraldehyde (FaGlu) histofluorescence method of Furness, Costa, and Blessing (1977a) and Furness, Costa, and Wilson (1977b) to examine wholemounts and sections of both juvenile and adult ganglia as well as peripheral tissues of Aplysia californica. FaGlu fluorescence is the result of a reaction between formaldehyde and tissue catecholamines to produce water‐insoluble (fixed) fluorophores. In serially sectioned cerebral ganglia, 70–80 positive neurons were observed (many in clusters of 10–20 cells), many more than were found using the glyoxylic acid technique. Catecholamine‐containing varicosities were densely packed in localized portions of the neuropil of all central ganglia. Exclusive localization in the neuropil of presumed dopamine release sites is similar to that previously found for the neuropeptide SCP but differs form the widespread ramification of varicose neurites containing 5‐HT, FMRFamide, and ELH. The FaGlu technique also enabled us to study the ultrastructure of catecholamine‐containing neurons. In contrast to the larger vesicles found in serotonergic and histaminergic neurons, these dopaminergic neurons contain 70 nm dense‐cored vesicles.
Long‐term cultures of neurons from adult frog brain express GABA and glutamate‐activated channels
Authors: Wetzel D. M. , Lee V. M‐Y. , Erulkar S. D.
Published: January 2005

Cells from adult Xenopus laevis brainstem and spinal cord were dissociated with mild enzymatic treatment and grown in long‐term cell culture. These cells had specific attachment/substrate and medium/serum requirements. Cells with bipolar and multipolar morphology were positively identified as neurons using immunohistochemistry with monoclonal antibodies to rat and bovine neurofilament proteins which we show here cross‐react with similar amphibian proteins. Patch clamp recordings demonstrated that these neurons have populations of ionic channels which are activated by L‐glutamate or γ‐aminobutyric acid (GABA).

Abbreviations: ABC, avidin‐biotin‐complex; dHnO, distilled water; GABA, γ‐aminohutyric acid; L‐15, Leibovitz's 15 medium; NCM, zero calcium zero magnesium Ringers' solution; NF, neurofilament; NFRS, normal frog Ringers' solution; PAP, peroxidase antiperoxidase.

The characteristics of these channels were similar to those previously described for GABA‐ and glutamate‐activated channels in embryonic mammalian neurons isolated in culture. Cell cultures of neurons isolated from adult Xenopus laevis brain may be a useful and simple preparation with which to examine the modulation of neuronal properties by various agents over longer time intervals then has been previously possible.
Neuronal plasticity in the adult invertebrate nervous system
Authors: Bulloch A. G. M. , Ridgway R. L.
Published: January 2005

This essay provides a brief overview of neuronal plasticity in adult invertebrate nervous systems. Our discussion focuses on the factors which influence sprouting by adult neurons, i.e., (1) the nature of the neuron itself, (2) axon integrity, (3) the presence of targets, (4) diffusible factors, and (5) ageing. Evidence that the neurites of some adult neurons exhibit a dynamic equilibrium of expansion and retraction is presented, a topic which prompted us to speculate on the significance of such plasticity in altered behavioral states. We conclude with some suggestions as to specific questions that need to be addressed by future studies in this challenging area.
Structural plasticity at identified synapses during long‐term memory in Aplysia
Authors: Bailey Craig H. , Chen Mary
Published: January 2005

We have used the gill‐ and siphon‐withdrawal reflex of Aplysia californica to determine the morphological basis of the prolonged changes in synaptic effectiveness that underlie long‐term habituation and sensitization. We have found that clear structural changes accompany behavioral modification and have demonstrated that these can be detected at the level of identified sensory neuron synapses, a critical site of plasticity for the short‐term forms of both types of learning. These alterations occur at two different levels of synaptic organization and include (1) changes in focal regions of synaptic membrane specialization—the number, size and vesicle complement of sensory neuron active zones are larger in sensitized animals and smaller in habituated animals compared with controls—and (2) a parallel but more dramatic and global trend involving modulation of the total number of presynaptic varicosities per sensory neuron. Quantitative analysis of the time course over which these structural alterations occur during sensitization has further demonstrated that changes in the number of varicosities and active zones persist in parallel with the behavioral retention of the memory. This increase in the number of sensory neuron synapses during long‐term sensitization in Aplysia is similar to changes in the number of synapses in the mammalian brain following various forms of environmental manipulations and learning (Greenough, 1984). Therefore learning may involve a form of neuronal growth across a braod segment of the animal kingdom, thereby suggesting a role for structural synaptic plasticity during long‐term behavioral modifications.
Rapid introduction of long‐lasting synaptic changes at crustacean neuromuscular junctions
Authors: Atwood H. L. , Dixon D. , Wojtowicz J. M.
Published: January 2005

In this review we present recent evidence implicating second‐messenger systems in two forms of long‐lasting synaptic change seen at crustacean neuromuscular junctions. Crustacean motor axons are endowed with numerous terminals, each possessing many individual synapses. Some synapses appear to be quiescent or impotent, but can be recruited in response to imposed functional demands. Supernormal impulse activity leads to long‐term facilitation (LTF) which persists for many hours. During the persistent phase, additional synapses are physiologically effective, and morphological changes in synapses are seen at the ultrastructural level. Pulsatile application of serotonin, a neuromodulator, also enhances synaptic transmission, but this enhancement declines more rapidly than LTF. Elevation of intraterminal Ca2+ is neither necessary nor sufficient for long‐lasting enhancement of transmission, but activation of A‐kinase is necessary. LTF is set in motion by an unknown depolarization‐dependent mechanism leading to A‐kinase activation, whereas serotonin facilitation depends for its initiation on the phosphatidylinositol system. The initial phase of serotonin facilitation may be accounted for by production of inositol triphosphate, whereas the secondary long‐lasting phase appears to require participation of both C kinase and A kinase. Neither LTF nor serotonin facilitation requires an intact neuron; both are presynaptic phenomena expressed by the nerve terminals. Brief comparison is made with long‐lasting synaptic changes in other systems.
Effect of putative neuromodulators on rhythmic buccal motor output in Lymnaea stagnalis
Authors: Kyriakides M. A. , McCrohan C. R.
Published: January 2005

The effects of a variety of neuromodulator substances on rhythmic motor output and activity in neurons in the feeding circuitry of Lymnaea stagnalis were examined. Each neuromodulator produced a unique combination of effects at different levels in the network: i.e., pattern‐generating interneurons (N1, N2, and N3), an identified higher‐order interneuron (cerebral giant cell, CGC), and buccal motoneurons. 5‐Hydroxytryptamine, acetylcholine, and FMRFamide all inhibited rhythmic motor activity. However, this was achieved in different ways. Dopamine changed the nature of rhythmic activity from one in which N2 interneuronal activity was predominant (“N2 rhythm”) to a feeding rhythm. Dopamine was the only substance capable of activating the feeding rhythm. Activity in the CGC was increased by 5‐hydroxytryptamine, dopamine, and acetylcholine and reduced by FMRFamide. Differential responses in buccal motoneurons were also observed. The results are discussed in relation to previous work on other species and also in terms of the selection of different patterns of motor output by neuromodulators.
ATP and calmodulin dependent actomyosin aggregates induced by cytochalasin D in goldfish retinal ganglion cell axons in vitro
Authors: Edmonds Brain T. , Koeing Edward
Published: January 2005

Growing retinal ganglion cell (RGC) axons of the goldfish have mobile varicosities, which play a role in rapid bulk redistribution of axoplasm (Koenig, Kinsman, Repasky, and Sultz, 1985; Edmonds and Koeing, 1987). Varicosities contain a tubulo‐vesicular SER embedded in an actin‐containing cytomatrix (Koenig et al., 1985). Cytochalasin D (CD) induces the formation of focal cytoskeletal aggregates throughout preterminal axons and especially in varicosities. The aggregates are visible when labelled with fluoroscein isothiocyanate (FITC)‐conjugated phalloidin. Double‐labelling experiments show that Texas red‐myosin or rhodamine isothiocyanate (RITC)‐calmodulin immunofluorescence co‐localizes with FITC‐phalloidin‐labelled aggregates. Formation of aggregates is blocked by calmidazolium, a calmodulin antagonist. Axon models permeabilized with digitonin retain the capacity to form focal aggregates in response to CD, when ATP or adenosine‐5′‐O(3‐thiotriphosphate) (ATP‐γS) is present in the permeabilization buffer, but not when 5′‐adenylylimidodiphosphate (AMP‐PNP) is present. The latter result indicates that formation of focal aggregates depends on ATP. The findings suggest that the formation of focal aggregates in immature axons is a manifestation of actomyosin interactions after free actin‐filament ends are generated by CD treatment.
A kinematic analysis of hindlimb motility in 9‐ and 10‐day‐old chick embryos
Authors: Watson Sandra J. , Bekoff Anne
Published: January 2005

Although chick embryonic leg movements appear jerky and disorganized, the underlying motor patterns are coordinated. This apparent conflict in results was investigated using kinematic analyses to provide detailed quantitative descriptions of leg movements during spontaneous motility in 9‐ and 10‐day‐old chick embryos. In many respects, hip, knee, and ankle movements were highly variable. There was variation in movement durations and in the number of leg joints that participated in a given movement. Motion could begin with either flexion or extension. Furthermore, the limb could return to its rest position between movements or move continuously to produce sequences of variable lengths. Patterns of interlimb coordination included alternating, synchronous and independent movements of the legs. We propose that these variable features account for the uncoordinated appearance of embryonic leg movements. In addition to variable features, however, some consistent characteristics were identified. For example, when more than one joint was active, activity typically began and ended synchronously. Furthermore, all active joints generally extended or flexed together and movements were symmetrical. These data are consistent with previous EMG results. Therefore, despite the variability in some parameters that results in the perception that embryonic leg movements are random and uncoordinated, our kinematic analyses show that an organized pattern of interjoint coordination is a prominent feature. This basic pattern shows some similarities to, but is less complex than, kinematic patterns found during a variety of posthatching behaviors.