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Due MR, Wang Y, Barry MA, Jing J, Reaver CN, Weiss KR, Cropper EC. Convergent effects of neuropeptides on the feeding central pattern generator of Aplysia californica. J Neurophysiol 2022; 127:1445-1459. [PMID: 35507477 PMCID: PMC9142162 DOI: 10.1152/jn.00025.2022] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Modulators that induce distinct motor programs act divergently on neural networks to specify output. We study a situation where modulators that act divergently also act convergently. We focus on an interneuron (B63) that is part of the feeding central pattern generator (CPG) in Aplysia californica. Previous work has established that B63 is critical for program initiation regardless of the type of evoked activity. B63 receives input from a number of different elements of the feeding circuit. Program initiation occurs reliably when some are activated, but we show it does not occur reliably with activation of others. When program initiation is reliable, modulatory neuropeptides are released. For example, previous work has established that an ingestive input to the feeding CPG, cerebral buccal interneuron 2 (CBI-2), releases feeding circuit activating peptide (FCAP) and cerebral peptide 2 (CP-2). Afferents with processes in the esophageal nerve (EN) that trigger egestive motor programs release small cardioactive peptide (SCP). Previous studies have described divergent effects of FCAP/CP-2 and SCP on the feeding circuit that specify motor activity. Here, we show that FCAP/CP-2 and SCP increase the B63 excitability. Thus, we show that peptides that have well characterized divergent effects on the feeding circuit additionally act convergently at the level of a single neuron. Since convergent effects of neuromodulators are not necessary for specifying network output, we ask why they might be important. Our data suggest that they have an impact during a task switch.
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Affiliation(s)
- Michael R Due
- Department of Neuroscience and Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | - Yanqing Wang
- Department of Neuroscience and Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | - Michael A Barry
- Department of Neuroscience and Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | - Jian Jing
- Department of Neuroscience and Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, NY, United States.,State Key Laboratory of Pharmaceutical Biotechnology, Institute for Brain Sciences, Chemistry and Biomedicine Innovation Center, Jiangsu Engineering Research Center for MicroRNA Biology and Biotechnology, Advanced Institute for Life Sciences, School of Life Sciences, Nanjing University, Nanjing, Jiangsu, China
| | - Carrie N Reaver
- Department of Neuroscience and Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | - Klaudiusz R Weiss
- Department of Neuroscience and Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | - Elizabeth C Cropper
- Department of Neuroscience and Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, NY, United States
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Wright WG, Kirschman D, Rozen D, Maynard B. PHYLOGENETIC ANALYSIS OF LEARNING‐RELATED NEUROMODULATION IN MOLLUSCAN MECHANOSENSORY NEURONS. Evolution 2017; 50:2248-2263. [DOI: 10.1111/j.1558-5646.1996.tb03614.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/1995] [Accepted: 06/05/1996] [Indexed: 12/30/2022]
Affiliation(s)
- William G. Wright
- Department of Biology Colorado State University Fort Collins Colorado 80523
| | - David Kirschman
- Department of Biology Colorado State University Fort Collins Colorado 80523
| | - Danny Rozen
- Department of Biology Colorado State University Fort Collins Colorado 80523
| | - Barbara Maynard
- Department of Biology Colorado State University Fort Collins Colorado 80523
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Svensson E, Evans CG, Cropper EC. Repetition priming-induced changes in sensorimotor transmission. J Neurophysiol 2016; 115:1637-43. [PMID: 26763783 DOI: 10.1152/jn.01082.2015] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2015] [Accepted: 01/13/2016] [Indexed: 12/19/2022] Open
Abstract
When a behavior is repeated performance often improves, i.e., repetition priming occurs. Although repetition priming is ubiquitous, mediating mechanisms are poorly understood. We address this issue in the feeding network ofAplysia Similar to the priming observed elsewhere, priming inAplysiais stimulus specific, i.e., it can be either "ingestive" or "egestive." Previous studies demonstrated that priming alters motor and premotor activity. Here we sought to determine whether sensorimotor transmission is also modified. We report that changes in sensorimotor transmission do occur. We ask how they are mediated and obtain data that strongly suggest a presynaptic mechanism that involves changes in the "background" intracellular Ca(2+)concentration ([Ca(2+)]i) in primary afferents themselves. This form of plasticity has previously been described and generated interest due to its potentially graded nature. Manipulations that alter the magnitude of the [Ca(2+)]iimpact the efficacy of synaptic transmission. It is, however, unclear how graded control is exerted under physiologically relevant conditions. In the feeding system changes in the background [Ca(2+)]iare mediated by the induction of a nifedipine-sensitive current. We demonstrate that the extent to which this current is induced is altered by peptides (i.e., increased by a peptide released during the repetition priming of ingestive activity and decreased by a peptide released during the repetition priming of egestive activity). We suggest that this constitutes a behaviorally relevant mechanism for the graded control of synaptic transmission via the regulation of the [Ca(2+)]iin a neuron.
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Affiliation(s)
- Erik Svensson
- Department of Neuroscience and Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, New York
| | - Colin G Evans
- Department of Neuroscience and Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, New York
| | - Elizabeth C Cropper
- Department of Neuroscience and Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, New York
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Kuznetsova LA, Plesneva SA, Sharova TS, Pertseva MN, Shpakov AO. Regulation of adenylyl cyclase signaling system by insulin, biogenic amines and glucagon at their separate and combined action in muscle membranes of mollusc Anodonta cygnea. J EVOL BIOCHEM PHYS+ 2013. [DOI: 10.1134/s0022093013020035] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Wan Q, Jiang XY, Negroiu AM, Lu SG, McKay KS, Abrams TW. Protein kinase C acts as a molecular detector of firing patterns to mediate sensory gating in Aplysia. Nat Neurosci 2012; 15:1144-52. [PMID: 22772333 PMCID: PMC4228944 DOI: 10.1038/nn.3158] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2012] [Accepted: 06/06/2012] [Indexed: 11/24/2022]
Abstract
Habituation of a behavioral response to a repetitive stimulus enables animals to ignore irrelevant stimuli and focus on behaviorally important events. In Aplysia, habituation is mediated by rapid depression of sensory synapses, which could leave an animal unresponsive to important repetitive stimuli, making it vulnerable to injury. We identified a form of plasticity that prevents synaptic depression depending on the precise stimulus strength. Burst-dependent protection from depression is initiated by trains of 2-4 action potentials and is distinct from previously described forms of synaptic enhancement. The blockade of depression is mediated by presynaptic Ca2+ influx and protein kinase C (PKC) and requires localization of PKC via a PDZ domain interaction with Aplysia PICK1. During protection from depression, PKC acts as a highly sensitive detector of the precise pattern of sensory neuron firing. Behaviorally, burst-dependent protection reduces habituation, enabling animals to maintain responsiveness to stimuli that are functionally important.
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Affiliation(s)
- Qin Wan
- Department of Pharmacology, University of Maryland School of Medicine, 655 West Baltimore Street, Baltimore, MD 21201-1559
| | - Xue-Ying Jiang
- Department of Pharmacology, University of Maryland School of Medicine, 655 West Baltimore Street, Baltimore, MD 21201-1559
| | - Andreea M. Negroiu
- Department of Pharmacology, University of Maryland School of Medicine, 655 West Baltimore Street, Baltimore, MD 21201-1559
| | - Shao-Gang Lu
- Department of Pharmacology, University of Maryland School of Medicine, 655 West Baltimore Street, Baltimore, MD 21201-1559
| | - Kimberly S. McKay
- Program in Neuroscience, University of Maryland School of Medicine, 655 West Baltimore Street, Baltimore, MD 21201-1559
| | - Thomas W. Abrams
- Department of Pharmacology, University of Maryland School of Medicine, 655 West Baltimore Street, Baltimore, MD 21201-1559
- Program in Neuroscience, University of Maryland School of Medicine, 655 West Baltimore Street, Baltimore, MD 21201-1559
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Dumitriu B, Cohen JE, Wan Q, Negroiu AM, Abrams TW. Serotonin receptor antagonists discriminate between PKA- and PKC-mediated plasticity in aplysia sensory neurons. J Neurophysiol 2005; 95:2713-20. [PMID: 16236785 DOI: 10.1152/jn.00642.2005] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Highly selective serotonin (5-hydroxytryptamine, 5-HT) receptor antagonists developed for mammals are ineffective in Aplysia due to the evolutionary divergence of neurotransmitter receptors and because the higher ionic strength of physiological saline for marine invertebrates reduces antagonist affinity. It has therefore been difficult to identify antagonists that specifically block individual signaling cascades initiated by 5-HT. We studied two broad-spectrum 5-HT receptor antagonists that have been characterized biochemically in Aplysia CNS: methiothepin and spiperone. Methiothepin is highly effective in inhibiting adenylyl cyclase (AC)-coupled 5-HT receptors in Aplysia. Spiperone, which blocks phospholipase C (PLC)-coupled 5-HT receptors in mammals, does not block AC-coupled 5-HT receptors in Aplysia. In electrophysiological studies, we explored whether methiothepin and spiperone can be used in parallel to distinguish between the AC-cAMP and PLC-protein kinase C (PKC) modulatory cascades that are initiated by 5-HT. 5-HT-induced broadening of the sensory neuron action potential in the presence of tetraethylammonium/nifedipine, which is mediated by modulation of the S-K+ currents, was used an assay for the AC-cAMP cascade. Spike broadening initiated by 5 microM 5-HT was unaffected by 100 microM spiperone, whereas it was effectively blocked by 100 microM methiothepin. Facilitation of highly depressed sensory neuron-to-motor neuron synapses by 5-HT was used as an assay for the PLC-PKC cascade. Spiperone completely blocked facilitation of highly depressed synapses by 5 microM 5-HT. In contrast, methiothepin produced a modest, nonsignificant, reduction in the facilitation of depressed synapses. Interestingly, these experiments revealed that the PLC-PKC cascade undergoes desensitization during exposure to 5-HT.
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Affiliation(s)
- Bogdan Dumitriu
- Department of Pharmacology, University of Maryland School of Medicine, Baltimore, MD 21201-1559, USA
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Buttner N, Siegelbaum SA. Antagonistic modulation of a hyperpolarization-activated Cl(-) current in Aplysia sensory neurons by SCP(B) and FMRFamide. J Neurophysiol 2003; 90:586-98. [PMID: 12724359 DOI: 10.1152/jn.00007.2003] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Whole cell voltage-clamp recordings from Aplysia mechanosensory neurons obtained from the pleural ganglion were used to investigate the actions on membrane currents of the neuropeptides SCP(B) and FMRFamide. At the start of whole cell recording, SCP(B) typically evoked an inward current at a holding potential of -40 mV, due to the cAMP-mediated closure of the S-type K+ channel, whereas FMRFamide evoked an outward current, due to the opening of the S-type K+ channels mediated by 12-lipoxygenase metabolites of arachidonic acid. However, after several minutes of whole cell recording with a high concentration of chloride in the whole cell patch pipette solution, the responses to SCP(B) and FMRF-amide at -40 mV were inverted; SCP(B) evoked an outward current, whereas FMRFamide and YGGFMRFamide evoked inward currents. Ion substitution experiments and reversal potential measurements revealed that these responses were due to the opposing regulation of a Cl(-) current, whose magnitude was greatly enhanced by dialysis with the high Cl(-) - containing pipette solution. SCP(B) inhibited this Cl(-) current through production of cAMP and activation of PKA. YGGFMRFamide activated this Cl(-) current by stimulating a cGMP-activated phosphodiesterase that hydrolyzed cAMP. Thus a cAMP-dependent Cl(-) current undergoes antagonistic modulation by two neuropeptides in Aplysia sensory neurons.
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Affiliation(s)
- Ned Buttner
- Center for Neurobiology and Behavior, Department of Pharmacology, Howard Hughes Medical Institute, Columbia University, New York City, New York 10032, USA
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Chang DJ, Lim CS, Lee JA, Kaang BK. Synaptic facilitation by ectopic octopamine and 5-HT receptors in Aplysia. Brain Res Bull 2003; 60:73-9. [PMID: 12725895 DOI: 10.1016/s0361-9230(03)00016-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The cAMP pathway plays a critical role in synaptic plasticity. We assessed using the ectopic expression of octopamine (OA) receptor, the contribution of the cAMP pathway to short-term facilitation of sensory-motor synapses in Aplysia. When synaptic connections were depressed to 20-30% of their initial EPSP amplitude, the application of OA to sensory cells expressing OA receptor showed significant synaptic facilitation, but this was less than the synaptic facilitation shown by 5-HT treatment. We also found that synaptic facilitation was further enhanced when OA was treated in the presence of 5-HT at non-depressed synapses, but not at depressed synapses. These results imply that the role of cAMP in synaptic facilitation is reduced as the synapse becomes depressed due to repeated activity.
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Affiliation(s)
- Deok-Jin Chang
- National Research Laboratory of Neurobiology, Institute of Molecular Biology and Genetics, School of Biological Sciences, College of Natural Sciences, Seoul National University, San 56-1 Silim-dong Kwanak-gu, Seoul 151-742, South Korea
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Cohen JE, Onyike CU, McElroy VL, Lin AH, Abrams TW. Pharmacological characterization of an adenylyl cyclase-coupled 5-HT receptor in aplysia: comparison with mammalian 5-HT receptors. J Neurophysiol 2003; 89:1440-55. [PMID: 12611939 DOI: 10.1152/jn.01004.2002] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We attempted to identify compounds that are effective in blocking the serotonin (5-hydroxytryptamine, 5-HT) receptor(s) that activate adenylyl cyclase (AC) in Aplysia CNS. We call this class of receptor 5-HT(apAC). Eight of the 14 antagonists tested were effective against 5-HT(apAC) in CNS membranes with the following rank order of potency: methiothepin > metergoline approximately fluphenazine > clozapine > cyproheptadine approximately risperidone approximately ritanserin > NAN-190. GR-113808, olanzapine, Ro-04-6790, RS-102221, SB-204070, and spiperone were inactive. Methiothepin completely blocked 5-HT stimulation of AC with a K(b) of 18 nM. Comparison of the pharmacological profile of the 5-HT(apAC) receptor with those of mammalian 5-HT receptor subtypes suggested it most closely resembles the 5-HT(6) receptor. AC stimulation in Aplysia sensory neuron (SN) membranes was also blocked by methiothepin. Methiothepin substantially inhibited two effects of 5-HT on SN firing properties that are mediated by a cAMP-dependent reduction in S-K(+) current: spike broadening in tetraethylammonium/nifedipine and increased excitability. Consistent with cyproheptadine blocking 5-HT stimulation of AC, cyproheptadine also blocked the 5-HT-induced increase in SN excitability. Methiothepin was less effective in blocking AC-mediated modulatory effects of 5-HT in electrophysiological experiments on SNs than in blocking AC stimulation in CNS or SN membranes. This reduction in potency appears to be due to effects of the high ionic strength of physiological saline on the binding of this antagonist to the receptor. Methiothepin also antagonized AC-coupled dopamine receptors but not AC-coupled small cardioactive peptide receptors. In conjunction with other pharmacological probes, this antagonist should be useful in analyzing the role of 5-HT in various forms of neuromodulation in Aplysia.
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Affiliation(s)
- Jonathan E Cohen
- Department of Pharmacology, University of Maryland School of Medicine, BRB 4-002, Baltimore 21201-1559, USA
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Liao X, Brou CG, Walters ET. Limited contributions of serotonin to long-term hyperexcitability of Aplysia sensory neurons. J Neurophysiol 1999; 82:3223-35. [PMID: 10601456 DOI: 10.1152/jn.1999.82.6.3223] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Serotonin (5-HT) has provided a useful tool to study plasticity of nociceptive sensory neurons in Aplysia. Because noxious stimulation causes release of 5-HT and long-term hyperexcitability (LTH) of sensory neuron somata and because 5-HT treatment can induce long-term synaptic facilitation of sensory neuron synapses, a plausible hypothesis is that 5-HT also induces LTH of the sensory neuron soma. Prolonged or repeated exposure of excised ganglia to 5-HT produced immediate hyperexcitability of sensory neurons that showed little desensitization, but the hyperexcitability decayed within minutes of washing out the 5-HT. Prolonged or repeated treatment of either excised ganglia or dissociated sensory neurons with various concentrations of 5-HT failed to induce significant LTH even when long-term synaptic facilitation was induced in the same preparations. Use of a high-divalent cation solution to reduce interneuron activity during 5-HT treatment failed to enable the induction of LTH in excised ganglia. Pairing 5-HT application with nerve shock failed to enhance LTH produced by nerve shock or to reveal covert LTH produced by 5-HT. The induction of LTH by nerve stimulation was enhanced rather than inhibited by treatment with methiothepin, a 5-HT antagonist reported to block various 5-HT receptors and 5-HT-induced adenylyl cyclase activation. This suggests that endogenous 5-HT may have inhibitory effects on the induction of LTH by noxious stimulation. Methiothepin blocked immediate hyperexcitability produced by exogenous 5-HT and also inhibited the expression of LTH induced by nerve stimulation when applied during testing 1 day afterward. At higher concentrations, methiothepin reduced basal excitability of sensory neurons by mechanisms that may be independent of its antagonism of 5-HT receptors. Several observations suggest that early release of 5-HT and consequent cAMP synthesis in sensory neurons is not important for the induction of LTH by noxious stimulation, whereas later release of 5-HT from persistently activated modulatory neurons, with consequent elevation of cAMP synthesis, may contribute to the maintenance of LTH.
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Affiliation(s)
- X Liao
- Department of Integrative Biology, Pharmacology and Physiology, University of Texas-Houston Medical School, Houston, Texas 77030, USA
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Baxter DA, Canavier CC, Clark JW, Byrne JH. Computational model of the serotonergic modulation of sensory neurons in Aplysia. J Neurophysiol 1999; 82:2914-35. [PMID: 10601429 DOI: 10.1152/jn.1999.82.6.2914] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Serotonergic modulation of the sensory neurons that mediate the gill- and tail-withdrawal reflexes of Aplysia is a useful model system for studies of neuronal plasticity that contributes to learning and memory. The effects of serotonin (5-HT) are mediated, in part, via two protein kinases (protein kinase A, PKA, and protein kinase C, PKC), which in turn, modulate at least four membrane currents, including a S ("serotonin-sensitive") K(+) current (I(K, S)), a steeply voltage-dependent K(+) current (I(K-V)), a slow component of the Ca(2+)-activated K(+) current (I(K,Ca-S)), and a L-type Ca(2+) current (I(Ca-L)). The present study investigated how the modulation of these currents altered the spike duration and excitability of sensory neurons and examined the relative contributions of PKA- and PKC-mediated effects to the actions of 5-HT. A Hodgkin-Huxley type model was developed that described the ionic conductances in the somata of sensory neurons. The descriptions of these currents and their modulation were based largely on voltage-clamp data from sensory neurons. Simulations were preformed with the program SNNAP (Simulator for Neural Networks and Action Potentials). The model was sufficient to replicate empirical data that describes the membrane currents, action potential waveform and excitability as well as their modulation by application of 5-HT, increased levels of adenosine cyclic monophosphate or application of active phorbol esters. In the model, modulation of I(K-V) by PKC played a dominate role in 5-HT-induced spike broadening, whereas the concurrent modulation of I(K,S) and I(K,Ca-S) by PKA primarily accounted for 5-HT-induced increases in excitability. Finally, simulations indicated that a PKC-induced increase in excitability resulted from decreases of I(K,S) and I(K,Ca-S), which was likely the indirect result of cross-talk between the PKC and PKA systems. The results provide several predictions that warrant additional experimental investigation and illustrate the importance of considering indirect as well as direct effects of modulatory agents on the modulation of membrane currents.
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Affiliation(s)
- D A Baxter
- Laboratories of Origin, Department of Neurobiology and Anatomy, W. M. Keck Center for the Neurobiology of Learning and Memory, The University of Texas-Houston Medical School, Houston, 77225, USA
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Lin AH, Onyike CU, Abrams TW. Sequence-dependent interactions between transient calcium and transmitter stimuli in activation of mammalian brain adenylyl cyclase. Brain Res 1998; 800:300-7. [PMID: 9685686 DOI: 10.1016/s0006-8993(98)00536-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Recent evidence implicates Ca2+/CaM-sensitive adenylyl cyclase (AC) as a molecular coincidence detector for temporally paired stimuli during associative learning. During conditioning in Aplysia, AC is optimally activated when Ca2+ influx, the cellular signal for the conditioned stimulus (CS), precedes binding of modulatory transmitter, the cellular signal for the unconditioned stimulus (US). This sequence preference of the AC for Ca2+-before-transmitter, parallels the CS-preceding-US pairing requirement of classical conditioning. In this study, we have examined the response of AC from rat cerebellum to brief exposures to Ca2+ and to transmitter in a perfused membrane assay. We observed modest synergism between Ca2+ and transmitter in activating AC. Activation was more effective when a Ca2+ stimulus immediately preceded a transmitter stimulus than when the two stimuli were delivered in the reverse order. Thus, rat cerebellar AC displayed a sequence preference for optimal activation by paired stimuli similar to that observed in Aplysia; this sequence dependence could contribute to the CS-US sequence requirement observed in most mammalian classical conditioning paradigms.
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Affiliation(s)
- A H Lin
- Department of Pharmacology, University of Maryland School of Medicine, BRB 4-002, 655 West Baltimore Street, Baltimore, MD 21201-1559, USA
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Abrams TW, Yovell Y, Onyike CU, Cohen JE, Jarrard HE. Analysis of sequence-dependent interactions between transient calcium and transmitter stimuli in activating adenylyl cyclase in Aplysia: possible contribution to CS--US sequence requirement during conditioning. Learn Mem 1998; 4:496-509. [PMID: 10701874 DOI: 10.1101/lm.4.6.496] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
An important recent insight in a number of neurobiological systems is that during learning, individual dually regulated proteins with associative properties function as critical sites of stimulus convergence. During conditioning in Aplysia, the Ca2+ /calmodulin-sensitive adenylyl cyclase (AC) in mechanosensory neurons serves as a molecular site of interaction between Ca2+ and serotonin [5-hydroxytryptamine (5-HT)]-two signals that represent the CS and US in these cells. Conditioning requires that the CS and US be paired within a narrow time window and in the appropriate sequence. AC shows an analogous sequence preference: It is more effectively activated when a pulse of Ca2+ precedes a pulse of 5-HT than when the 5-HT precedes Ca2+. One mechanism that contributes to this sequence preference is that Ca2+/calmodulin binding to AC accelerates the rate of AC activation by receptor-Gs. We have identified two additional properties of AC activation that would cause pairing with Ca2+ preceding 5-HT to be more effective than simultaneous pairing or pairing with the reciprocal sequence: (1) Activation of Aplysia AC by a Ca2+ pulse rose with a delay compared with activation by a 5-HT pulse. (2) A late pulse of Ca2+, which arrived after 5-HT, acted, via calmodulin, to accelerate the decay of AC activation by receptor-Gs. Together, these activation properties of AC may contribute to the CS-US sequence requirement of classical conditioning.
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Affiliation(s)
- T W Abrams
- Department of Pharmacology, University of Maryland School of Medicine, Baltimore 21201-1559, USA
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Abstract
The synaptic connections between the sensory neurons of Aplysia and their follower neurons have been used as a model system for examining the cellular mechanisms contributing to neuronal and synaptic plasticity. Recent studies suggest that at least two protein kinases, protein kinase A (PKA) and protein kinase C (PKC), contribute to serotonin (5-HT)-induced short-term facilitation. The interaction between these two kinase cascades has not been examined, however. Using electrophysiological and biochemical approaches, we examined possible interactions between PKA and PKC cascades. The results indicated that prolonged activation of PKC by preincubation with phorbol esters attenuated PKA-mediated actions of 5-HT, including increases in sensory neuron excitability and spike broadening in the presence of tetraethylammonium (TEA) and nifedipine. Although phorbol esters also attenuated increases in excitability by an analog of cAMP and small cardioactive peptide B (SCPB), the degree of attenuation was smaller. In addition, phorbol esters did not attenuate broadening of TEA spikes by the cAMP analog and SCPB. Thus, phorbol esters appeared specifically to attenuate aspects of the 5-HT activation of the cAMP/PKA cascade. Measurements of cAMP levels with radioimmunoassays revealed that phorbol esters did not attenuate 5-HT-induced cAMP synthesis, however. Finally, the results indicated that phorbol esters themselves induced a small but significant increase in excitability as well as an increase in the level of cAMP. Our results suggest that there is crosstalk between the PKC and PKA cascades. The mechanisms by which phorbol esters specifically attenuate 5-HT-induced activation of the cAMP/PKA cascade are not known, however.
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Ferretti ME, Sonetti D, Pareschi MC, Buzzi M, Colamussi ML, Biondi C. Effect of serotonin and neuropeptides on adenylate cyclase of the central nervous system and peripheral organs of the freshwater snail Planorbarius corneus. Neurochem Int 1996; 28:417-24. [PMID: 8740449 DOI: 10.1016/0197-0186(95)00096-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The effect of serotonin, FMRFamide and the small cardioactive peptide B (SCPB) on adenylate cyclase activity of the central nervous system and some peripheral organs of the freshwater snail Planorbarius corneus was investigated. The amine and the cardioactive peptide stimulated the enzyme, although with different potencies, in all tissues studied and, when tested in combination, an additive activation was obtained. FMRFamide induced differential effects in the various targets: marked stimulation of adenylate cyclase, additive to that provoked by serotonin or SCPB, in salivary glands; inhibition of the enzyme, both alone and in combination with the other neuromediators, in the nervous tissue; whereas no influence was found in adenylate cyclase activity in the buccal mass. In the last of these tissues, the peptide might act through an intracellular second messenger other than cyclic AMP. The responsiveness of adenylate cyclase to these neuromediators in all the central ganglia suggested that they can exert an important role as neurotransmitters and/or neuromodulators in the central nervous system of the snail. Moreover, in the light of the differential sensitivity of adenylate cyclase in the salivary glands and buccal mass, we suggest that serotonin, FMRFamide and SCPB modulate the feeding behaviour of P. corneus in a complex way.
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Affiliation(s)
- M E Ferretti
- Dipartimento di Biologia, Università di Ferrara, Italy
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