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The Biological Bulletin Jun 2006Until recently, investigations of the neurobiological substrates of simple forms of learning and memory in the marine snail Aplysia have focused mostly on plastic... (Review)
Review
Until recently, investigations of the neurobiological substrates of simple forms of learning and memory in the marine snail Aplysia have focused mostly on plastic changes that occur within the presynaptic sensory neurons. Here, I summarize the results of recent studies that indicate that exclusively presynaptic processes cannot account for simple forms of learning in Aplysia. In particular, I present evidence that postsynaptic mechanisms play a far more important role in nonassociative learning in Aplysia than has been appreciated before now. Moreover, I describe recent data that suggests the intriguing hypothesis that the persistent, learning-induced changes in Aplysia sensory neurons might depend critically on postsynaptic signals for their induction. Finally, I discuss the potential applicability of this hypothesis to learning-related synaptic plasticity in the mammalian brain.
Topics: Animals; Aplysia; Excitatory Postsynaptic Potentials; Habituation, Psychophysiologic; Learning; Models, Neurological; Neuronal Plasticity; Neurons, Afferent; Receptors, Glutamate; Synapses
PubMed: 16801500
DOI: 10.2307/4134563 -
ACS Chemical Neuroscience Aug 2018When individual neurons in a circuit contain multiple neuropeptides, these peptides can target different sets of follower neurons. This endows the circuit with a certain...
When individual neurons in a circuit contain multiple neuropeptides, these peptides can target different sets of follower neurons. This endows the circuit with a certain degree of flexibility. Here we identified a novel family of peptides, the Aplysia SPTR-Gene Family-Derived peptides (apSPTR-GF-DPs). We demonstrated apSPTR-GF-DPs, particularly apSPTR-GF-DP2, are expressed in the Aplysia CNS using immunohistochemistry and MALDI-TOF MS. Furthermore, apSPTR-GF-DP2 is present in single projection neurons, e.g., in the cerebral-buccal interneuron-12 (CBI-12). Previous studies have demonstrated that CBI-12 contains two other peptides, FCAP/CP2. In addition, CBI-12 and CP2 promote shortening of the protraction phase of motor programs. Here, we demonstrate that FCAP shortens protraction. Moreover, we show that apSPTR-GF-DP2 also shortens protraction. Surprisingly, apSPTR-GF-DP2 does not increase the excitability of retraction interneuron B64. B64 terminates protraction and is modulated by FCAP/CP2 and CBI-12. Instead, we show that apSPTR-GF-DP2 and CBI-12 increase B20 excitability and B20 activity can shorten protraction. Taken together, these data indicate that different CBI-12 peptides target different sets of pattern-generating interneurons to exert similar modulatory actions. These findings provide the first definitive evidence for SPTR-GF's role in modulation of feeding, and a form of molecular degeneracy by multiple peptide cotransmitters in single identified neurons.
Topics: Amino Acid Sequence; Animals; Aplysia; Computational Biology; Eating; Ganglia, Invertebrate; Male; Membrane Potentials; Motor Activity; Neurons; Neuropeptides; Protein Processing, Post-Translational; Rats, Sprague-Dawley; Sequence Alignment
PubMed: 29543430
DOI: 10.1021/acschemneuro.7b00513 -
Analytical Chemistry Dec 2016A receptor binding class of d-amino acid-containing peptides (DAACPs) is formed in animals from an enzymatically mediated post-translational modification of ribosomally...
A receptor binding class of d-amino acid-containing peptides (DAACPs) is formed in animals from an enzymatically mediated post-translational modification of ribosomally translated all-l-amino acid peptides. Although this modification can be required for biological actions, detecting it is challenging because DAACPs have the same mass as their all-l-amino acid counterparts. We developed a suite of mass spectrometry (MS) protocols for the nontargeted discovery of DAACPs and validated their effectiveness using neurons from Aplysia californica. The approach involves the following three steps, with each confirming and refining the hits found in the prior step. The first step is screening for peptides resistant to digestion by aminopeptidase M. The second verifies the presence of a chiral amino acid via acid hydrolysis in deuterium chloride, labeling with Marfey's reagent, and liquid chromatography-mass spectrometry to determine the chirality of each amino acid. The third involves synthesizing the putative DAACPs and comparing them to the endogenous standards. Advantages of the method, the d-amino acid-containing neuropeptide discovery funnel, are that it is capable of detecting the d-form of any common chiral amino acid, and the first two steps do not require peptide standards. Using these protocols, we report that two peptides from the Aplysia achatin-like neuropeptide precursor exist as GdYFD and SdYADSKDEESNAALSDFA. Interestingly, GdYFD was bioactive in the Aplysia feeding and locomotor circuits but SdYADSKDEESNAALSDFA was not. The discovery funnel provides an effective means to characterize DAACPs in the nervous systems of animals in a nontargeted manner.
Topics: Amino Acids; Animals; Aplysia; CD13 Antigens; Mass Spectrometry; Neurons; Neuropeptides
PubMed: 27788334
DOI: 10.1021/acs.analchem.6b03658 -
Journal of Visualized Experiments : JoVE Apr 2022Post-transcriptional modifications (PTMs) of RNA represent an understudied mechanism involved in the regulation of translation in the central nervous system (CNS)....
Post-transcriptional modifications (PTMs) of RNA represent an understudied mechanism involved in the regulation of translation in the central nervous system (CNS). Recent evidence has linked specific neuronal RNA modifications to learning and memory paradigms. Unfortunately, conventional methods for the detection of these epitranscriptomic features are only capable of characterizing highly abundant RNA modifications in bulk tissues, precluding the assessment of unique PTM profiles that may exist for individual neurons within the activated behavioral circuits. In this protocol, an approach is described-single-neuron RNA modification analysis by mass spectrometry (SNRMA-MS)-to simultaneously detect and quantify numerous modified ribonucleosides in single neurons. The approach is validated using individual neurons of the marine mollusk, Aplysia californica, beginning with surgical isolation and enzymatic treatment of major CNS ganglia to expose neuron cell bodies, followed by manual single-neuron isolation using sharp needles and a micropipette. Next, mechanical and thermal treatment of the sample in a small volume of buffer is done to liberate RNA from an individual cell for subsequent RNA digestion. Modified nucleosides are then identified and quantified using an optimized liquid chromatography-mass spectrometry method. SNRMA-MS is employed to establish RNA modification patterns for single, identified neurons from A. californica that have known morphologies and functions. Examples of qualitative and quantitative SNRMA-MS are presented that highlight the heterogeneous distribution of RNA modifications across individual neurons in neuronal networks.
Topics: Animals; Aplysia; Chromatography, Liquid; Mass Spectrometry; Neurons; RNA; RNA Processing, Post-Transcriptional
PubMed: 35532275
DOI: 10.3791/63940 -
Neural Plasticity 2015Brain functions are strictly dependent on neural connections formed during development and modified during life. The cellular and molecular mechanisms underlying... (Review)
Review
Brain functions are strictly dependent on neural connections formed during development and modified during life. The cellular and molecular mechanisms underlying synaptogenesis and plastic changes involved in learning and memory have been analyzed in detail in simple animals such as invertebrates and in circuits of mammalian brains mainly by intracellular recordings of neuronal activity. In the last decades, the evolution of techniques such as microelectrode arrays (MEAs) that allow simultaneous, long-lasting, noninvasive, extracellular recordings from a large number of neurons has proven very useful to study long-term processes in neuronal networks in vivo and in vitro. In this work, we start off by briefly reviewing the microelectrode array technology and the optimization of the coupling between neurons and microtransducers to detect subthreshold synaptic signals. Then, we report MEA studies of circuit formation and activity in invertebrate models such as Lymnaea, Aplysia, and Helix. In the following sections, we analyze plasticity and connectivity in cultures of mammalian dissociated neurons, focusing on spontaneous activity and electrical stimulation. We conclude by discussing plasticity in closed-loop experiments.
Topics: Animals; Aplysia; Brain; Electrophysiological Phenomena; Electrophysiology; Helix, Snails; In Vitro Techniques; Invertebrates; Learning; Lymnaea; Memory; Microelectrodes; Nerve Net; Neuronal Plasticity; Neurons; Rats
PubMed: 25866681
DOI: 10.1155/2015/196195 -
Scientific Reports Mar 2021ATP and its ionotropic P2X receptors are components of the most ancient signaling system. However, little is known about the distribution and function of purinergic...
ATP and its ionotropic P2X receptors are components of the most ancient signaling system. However, little is known about the distribution and function of purinergic transmission in invertebrates. Here, we cloned, expressed, and pharmacologically characterized the P2X receptors in the sea slug Aplysia californica-a prominent neuroscience model. AcP2X receptors were successfully expressed in Xenopus oocytes and displayed activation by ATP with two-phased kinetics and Na-dependence. Pharmacologically, they were different from other P2X receptors. The ATP analog, Bz-ATP, was a less effective agonist than ATP, and PPADS was a more potent inhibitor of the AcP2X receptors than the suramin. AcP2X were uniquely expressed within the cerebral F-cluster, the multifunctional integrative neurosecretory center. AcP2X receptors were also detected in the chemosensory structures and the early cleavage stages. Therefore, in molluscs, rapid ATP-dependent signaling can be implicated both in development and diverse homeostatic functions. Furthermore, this study illuminates novel cellular and systemic features of P2X-type ligand-gated ion channels for deciphering the evolution of neurotransmitters.
Topics: Adenosine Triphosphate; Animals; Aplysia; Models, Molecular; Neurons; Phylogeny; Receptors, Purinergic P2X; Signal Transduction; Xenopus
PubMed: 33750901
DOI: 10.1038/s41598-021-84981-5 -
ELife Aug 2017The joint activity of neural populations is high dimensional and complex. One strategy for reaching a tractable understanding of circuit function is to seek the simplest...
The joint activity of neural populations is high dimensional and complex. One strategy for reaching a tractable understanding of circuit function is to seek the simplest dynamical system that can account for the population activity. By imaging 's pedal ganglion during fictive locomotion, here we show that its population-wide activity arises from a low-dimensional spiral attractor. Evoking locomotion moved the population into a low-dimensional, periodic, decaying orbit - a spiral - in which it behaved as a true attractor, converging to the same orbit when evoked, and returning to that orbit after transient perturbation. We found the same attractor in every preparation, and could predict motor output directly from its orbit, yet individual neurons' participation changed across consecutive locomotion bouts. From these results, we propose that only the low-dimensional dynamics for movement control, and not the high-dimensional population activity, are consistent within and between nervous systems.
Topics: Action Potentials; Animals; Aplysia; Brain; Locomotion; Models, Neurological; Motor Neurons; Nerve Net; Periodicity
PubMed: 28780929
DOI: 10.7554/eLife.27342 -
Scientific Reports Mar 2020The formation of appropriate neural connections during development is critical for the proper wiring and functioning of the brain. Although considerable research...
Specificity of synapse formation in Aplysia: paracrine and autocrine signaling regulates bidirectional molecular interactions between sensory and non-target motor neurons.
The formation of appropriate neural connections during development is critical for the proper wiring and functioning of the brain. Although considerable research suggests that the specificity of synapse formation is supported by complex intercellular signaling between potential presynaptic and postsynaptic partners, the extracellular factors and the intracellular signal transduction pathways engaged in this process remain largely unknown. Using the sensory-motor neural circuit that contributes to learning in defensive withdrawal reflexes in Aplysia californica, we investigated the molecular processes governing the interactions between sensory neurons and both target and non-target motor neurons during synapse formation in culture. We found that evolutionarily-conserved intercellular and intracellular signaling mechanisms critical for learning-related plasticity are also engaged during synaptogenesis in this in vitro model system. Our results reveal a surprising bidirectional regulation of molecular signaling between sensory neurons and non-target motor neurons. This regulation is mediated by signaling via both paracrine and autocrine diffusible factors that induce differential effects on transcription and on protein expression/activation in sensory neurons and in target and non-target motor neurons. Collectively, our data reveal novel molecular mechanisms that could underlie the repression of inappropriate synapse formation, and suggest mechanistic similarities between developmental and learning-related plasticity.
Topics: Animals; Aplysia; Autocrine Communication; Coculture Techniques; Cyclic AMP Response Element-Binding Protein; Extracellular Signal-Regulated MAP Kinases; Motor Neurons; Neuronal Plasticity; Neuropeptides; Paracrine Communication; Receptor, trkB; Sensory Receptor Cells; Signal Transduction; Single-Cell Analysis; Synapses
PubMed: 32251363
DOI: 10.1038/s41598-020-62099-4 -
Scientific Reports Oct 2019Insulin-like growth factor II (IGF2) enhances memory in rodents via the mannose-6-phosphate receptor (M6PR), but the underlying mechanisms remain poorly understood. We...
Insulin-like growth factor II (IGF2) enhances memory in rodents via the mannose-6-phosphate receptor (M6PR), but the underlying mechanisms remain poorly understood. We found that human IGF2 produces an enhancement of both synaptic transmission and neurite outgrowth in the marine mollusk Aplysia californica. These findings were unexpected since Aplysia lack the mammal-specific affinity between insulin-like ligands and M6PR. Surprisingly, this effect was observed in parallel with a suppression of neuronal excitability in a well-understood circuit that supports several temporally and mechanistically distinct forms of memory in the defensive withdrawal reflex, suggesting functional coordination between excitability and memory formation. We hypothesize that these effects represent behavioral adaptations to feeding that are mediated by the endogenous Aplysia insulin-like system. Indeed, the exogenous application of a single recombinant insulin-like peptide cloned from the Aplysia CNS cDNA replicated both the enhancement of synaptic transmission, the reduction of excitability, and promoted clearance of glucose from the hemolymph, a hallmark of bona fide insulin action.
Topics: Adaptation, Physiological; Animals; Aplysia; Homeostasis; Humans; Insulin-Like Growth Factor II; Neuronal Outgrowth; Synapses
PubMed: 31591438
DOI: 10.1038/s41598-019-50923-5 -
The Journal of Neuroscience : the... Jan 1989We prepared and characterized subcellular membrane fractions from the CNS of Aplysia californica that are enriched in isolated nerve terminals (synaptosomes). Ganglia...
We prepared and characterized subcellular membrane fractions from the CNS of Aplysia californica that are enriched in isolated nerve terminals (synaptosomes). Ganglia were homogenized in 1.1 M sucrose and fractionated on a 2-step sucrose gradient, yielding 50 micrograms protein/animal in the synaptosomal fraction (P3), which was enriched 3-fold in plasma membrane as compared with the initial homogenate. Quantitative morphometry of electron micrographs revealed that P3 contained 25% intact synaptosomes, a 5-fold enrichment over the homogenate. Although fractionation on a 5-step sucrose gradient reduced the yield of protein in the synaptosomal fraction to 40 micrograms/animal, this fraction (the 0.35 M/0.75 M interface) was more enriched in plasma membrane than P3 and was less contaminated by lysosomes and free mitochondria. By electron microscopy, the 0.35 M/0.75 M interface contained up to 50% synaptosomes. Synaptosomal fractions contained cAMP-, Ca2+/calmodulin-, and Ca2+/phospholipid-dependent protein kinase activities and were enriched in a Mr 40,000 pertussis toxin substrate, Gi/o. In the accompanying paper, we show that these synaptosomes retain the ability to release transmitters.
Topics: Animals; Aplysia; Central Nervous System; Centrifugation, Density Gradient; Ganglia; Membranes; Pertussis Toxin; Protein Kinases; Subcellular Fractions; Synaptosomes; Virulence Factors, Bordetella
PubMed: 2913212
DOI: 10.1523/JNEUROSCI.09-01-00038.1989