anisomycin and adenosine-3--5--cyclic-phosphorothioate

Extinction is the learned inhibition of retrieval. Recently it was shown that a brief exposure to a novel environment enhances the extinction of contextual fear in rats, an effect explainable by a synaptic tagging-and-capture process. Here we examine whether this also happens with the extinction of another fear-motivated task, inhibitory avoidance (IA), and whether it depends on dopamine acting on D1 or D5 receptors. Rats were trained first in IA and then in extinction of this task. The retention of extinction was measured 24 h later. A 5-min exposure to a novel environment 30 min before extinction training enhanced its retention. Right after exposure to the novelty, animals were given bilateral intrahippocampal infusions of vehicle (VEH), of the protein synthesis inhibitor anisomycin, of the D1/D5 dopaminergic antagonist SCH23390, of the PKA inhibitor Rp-cAMP or of the PKC inhibitor Gö6976, and of the PKA stimulator Sp-cAMP or of the PKC stimulator PMA. The novelty increased hippocampal dopamine levels and facilitated the extinction, which was inhibited by intrahippocampal protein synthesis inhibitor anisomysin, D1/D5 dopaminerdic antagonist SCH23390, or PKA inhibitor Rp-cAMP and unaffected by PKC inhibitor Gö6976; additionally, the hippocampal infusion of PKA stimulator Sp-cAMP reverts the effect of D1/D5 dopaminergic antagonist SCH 23390, but the infusion of PKC stimulator PMA does not. The results attest to the generality of the novelty effect on fear extinction, suggest that it relies on synaptic tagging and capture, and show that it depends on hippocampal dopamine D1 but not D5 receptors.

Topics: Animals; Anisomycin; Behavior, Animal; Benzazepines; Carbazoles; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Dopamine; Extinction, Psychological; Fear; Hippocampus; Learning; Male; Memory; Memory Disorders; Protein Kinase C; Rats; Rats, Wistar; Receptors, Dopamine D1; Receptors, Dopamine D5; Stress, Physiological; Thionucleotides; Time Factors

During the development of neuronal circuits, axonal growth cones can contact many inappropriate targets before they reach an appropriate postsynaptic partner. Although it is well known that the contact with synaptic partners upregulates the secretory machinery of the presynaptic neuron, little is known about the signaling mechanisms involved in preventing the formation of connections with inappropriate target cells. Here, we show that the contact with a nonphysiological postsynaptic target inhibits neurotransmitter release from axonal terminals of the Helix serotonergic neuron C1 by means of an active mechanism requiring ongoing protein synthesis and leading to the inhibition of cAMP-dependent protein kinase (PKA) and mitogen-activated protein kinase (MAPK)-extracellular signal-related kinase (Erk) pathways. The reversal of the inhibitory effect of the nonphysiological target by blockade of protein synthesis was prevented by cAMP-PKA or MAPK-Erk inhibitors, whereas disinhibition of neurotransmitter release promoted by cAMP-PKA activation was not affected by MAPK-Erk inhibitors. The data indicate that the inhibitory effect of the nonphysiological target on neurotransmitter release is an active process that requires protein synthesis and involves the downregulation of the MAPK-Erk and cAMP-PKA pathways, the same protein kinases that are activated after contact with a physiological target neuron. These mechanisms could play a relevant role in the prevention of synapse formation between inappropriate partners by modulating the neurotransmitter release capability of growing nerve terminals according to the nature of the targets contacted during their development.

Topics: Animals; Anisomycin; Cells, Cultured; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Cycloheximide; Enzyme Activation; Helix, Snails; Mitogen-Activated Protein Kinase Kinases; Mitogen-Activated Protein Kinases; Neurons; Neurotransmitter Agents; Protein Synthesis Inhibitors; Protein-Tyrosine Kinases; Signal Transduction; Thionucleotides

To test for a role for the cellular prion protein (PrP(c)) in cell death, we used a PrP(c)-binding peptide. Retinal explants from neonatal rats or mice were kept in vitro for 24 h, and anisomycin (ANI) was used to induce apoptosis. The peptide activated both cAMP/protein kinase A (PKA) and Erk pathways, and partially prevented cell death induced by ANI in explants from wild-type rodents, but not from PrP(c)-null mice. Neuroprotection was abolished by treatment with phosphatidylinositol-specific phospholipase C, with human peptide 106-126, with certain antibodies to PrP(c) or with a PKA inhibitor, but not with a MEK/Erk inhibitor. In contrast, antibodies to PrP(c) that increased cAMP also induced neuroprotection. Thus, engagement of PrP(c) transduces neuroprotective signals through a cAMP/PKA-dependent pathway. PrP(c) may function as a trophic receptor, the activation of which leads to a neuroprotective state.

Topics: Animals; Animals, Newborn; Anisomycin; Antibodies, Monoclonal; Apoptosis; Colforsin; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Enzyme Inhibitors; Eye Proteins; Flavonoids; Gene Expression Regulation, Developmental; Immune Sera; MAP Kinase Signaling System; Mice; Mice, Inbred C57BL; Mice, Knockout; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinases; Neurons; Organ Culture Techniques; Peptide Fragments; Phosphatidylinositol Diacylglycerol-Lyase; Phosphoinositide Phospholipase C; Phosphorylation; Protein Processing, Post-Translational; PrPC Proteins; Rats; Rats, Inbred Strains; Retina; Signal Transduction; Thionucleotides; Type C Phospholipases

cAMP induces a protein-synthesis-dependent late phase of long-term potentiation (LTP) at CA3-CA1 synapses in acute hippocampal slices. Herein we report cAMP-mediated LTP and long-term depression (LTD) at monosynaptic CA3-CA1 cell pairs in organotypic hippocampal slice cultures. After bath application of the membrane-permeable cAMP analog adenosine 3',5'-cyclic monophosphorothioate, Sp isomer (Sp-cAMPS), synaptic transmission was enhanced for at least 2 h. Consistent with previous findings, the late phase of LTP requires activation of cAMP-dependent protein kinase A and protein synthesis. There is also an early phase of LTP induced by cAMP; the early phase depends on protein kinase A but, in contrast to the later phase, does not require protein synthesis. In addition, the cAMP-induced LTP is associated with a reduction of paired-pulse facilitation, suggesting that presynaptic modification may be involved. Furthermore, we found that Sp-cAMPS induced LTD in slices pretreated with picrotoxin, a gamma-aminobutyric acid type A (GABA(A)) receptor antagonist. This form of LTD depends on protein synthesis and protein phosphatase(s) and is accompanied by an increased ratio of failed synaptic transmission. These results suggest that GABA(A) receptors can modulate the effect of cAMP on synaptic transmission and thus determine the direction of synaptic plasticity.

Topics: Animals; Anisomycin; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Enzyme Activation; Excitatory Postsynaptic Potentials; GABA Antagonists; GABA-A Receptor Antagonists; Hippocampus; Long-Term Potentiation; Marine Toxins; Organ Culture Techniques; Oxazoles; Phosphoprotein Phosphatases; Picrotoxin; Protein Biosynthesis; Rats; Receptors, GABA-A; Synapses; Synaptic Transmission; Thionucleotides

Previous studies have shown that long-term potentiation (LTP) can be induced in the lateral nucleus of the amygdala (LA) after stimulation of central auditory pathways and that auditory fear conditioning modifies neural activity in the LA in a manner similar to LTP. The present experiments examined whether intra-LA administration of inhibitors of protein synthesis or protein kinase A (PKA) activity, treatments that block LTP in hippocampus, interfere with memory consolidation of fear conditioning. In the first series of experiments, rats received a single conditioning trial followed immediately by intra-LA infusions of anisomycin (a protein synthesis inhibitor) or Rp-cAMPS (an inhibitor of PKA activity) and were tested 24 hr later. Results indicated that immediate post-training infusion of either drug dose-dependently impaired fear memory retention, whereas infusions 6 hr after conditioning had no effect. Additional experiments showed that anisomycin and Rp-cAMPS interfered with long-term memory (LTM), but not short-term memory (STM), of fear and that the effect on LTM was specific to memory consolidation processes rather than to deficits in sensory or performance processes. Findings suggest that the LA is essential for memory consolidation of auditory fear conditioning and that this process is PKA and protein-synthesis dependent.

Topics: Acoustic Stimulation; Amygdala; Animals; Anisomycin; Behavior, Animal; Conditioning, Classical; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Dose-Response Relationship, Drug; Electroshock; Enzyme Inhibitors; Fear; Infusions, Parenteral; Male; Memory; Memory, Short-Term; Nerve Tissue Proteins; Protein Synthesis Inhibitors; Rats; Rats, Sprague-Dawley; Retention, Psychology; Thionucleotides; Time Factors

Long-term forms of synaptic plasticity that may underlie learning and memory have been suggested to depend on changes in the number of synapses between presynaptic and postsynaptic neurons. Here we have investigated a form of synaptic plasticity in cultures of hippocampal CA3 and CA1 neurons related to the late phase of long-term potentiation, which depends on cAMP and protein synthesis. Using the fluorescent dye FM 1-43 to label active presynaptic terminals, we find that a membrane permeable analog of cAMP enhances the number of active presynaptic terminals and that this effect requires protein synthesis.

Topics: Animals; Anisomycin; Cells, Cultured; Cyclic AMP; Excitatory Amino Acid Antagonists; Fluorescent Dyes; Hippocampus; Long-Term Potentiation; Neuronal Plasticity; Neurons; Presynaptic Terminals; Protein Synthesis Inhibitors; Pyridinium Compounds; Quaternary Ammonium Compounds; Rats; Rats, Sprague-Dawley; Receptors, Glutamate; Thionucleotides

Memory storage has a short-term phase that depends on preexisting proteins and a long-term phase that requires new protein and RNA synthesis. Hippocampal long-term potentiation (LTP) is thought to contribute to memory storage. Consistent with this idea, a cellular representation of these phases has been demonstrated in NMDA receptor-dependent LTP. By contrast, little is known about the NMDA receptor-independent LTP of the mossy fiber pathway. We find that mossy fiber LTP also has phases. Only late phase is blocked by protein and RNA synthesis inhibitors, but both phases are blocked by inhibitors of cAMP-dependent protein kinase, and both are stimulated by forskolin and Sp-cAMPS. During early phase, paired-pulse facilitation is occluded. This occlusion decays with the onset of late phase, consistent with its using a different mechanism. Thus, although Schaffer collateral and mossy fiber pathways use very different mechanisms for early phase, both use a cAMP-mediated mechanism for late phase.

Topics: Animals; Anisomycin; Colforsin; Cyclic AMP; Dactinomycin; Electric Stimulation; Hippocampus; Long-Term Potentiation; Nerve Fibers; Nerve Tissue Proteins; Protein Kinase Inhibitors; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Retention, Psychology; RNA, Messenger; Second Messenger Systems; Thionucleotides