bluuebunny/crossref_metadata_2025_split huggingface dataset:
Posttranslational modification of neurofilament polypeptides in rabbit retina
Authors: Glicksman Marcie A. , Soppet Daniel , Willard Mark B. 
Published: January 2005

AbstractThree 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

AbstractSCP‐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

AbstractTo 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractWe 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

AbstractMale 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

AbstractIt 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

AbstractHow 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

AbstractUsing 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

AbstractIn 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

AbstractThe 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

AbstractInjecting 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

AbstractThe 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.