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Leslie C Griffith

Publications and source records attributed to Leslie C Griffith.

At least 19 recordsLinked to original sources
PubMed2006

Cholinergic neurons mediate CaMKII-dependent enhancement of courtship suppression.

In Drosophila, calcium/calmodulin-dependent protein kinase II (CaMKII) activity is crucial in associative courtship conditioning for both memory formation and suppression of courtship during training with a mated female. We have previously shown that increasing levels of constitutively active CaMKII, but not calcium-dependent CaMKII, in a subset of neurons can decrease the initial level of courtship and enhance the rate of suppression of courtship in response to a mated female. In this study, we demonstrate that a subpopulation of noncholinergic, nondopaminergic, non-GABAergic neurons can cause CaMKII-dependent reductions in initial courtship, but only cholinergic neurons enhance training-dependent suppression. These data suggest that processing of pheromonal signals in two subpopulations of neurons, likely antennal lobe projection neurons, is critical for behavioral plasticity.

Adaptation, Psychological↗
PubMed2006

Activity-dependent gating of CaMKII autonomous activity by Drosophila CASK.

The ability of CaMKII to act as a molecular switch, becoming Ca(2+) independent after activation and autophosphorylation at T287, is critical for experience-dependent plasticity. Here, we show that the Drosophila homolog of CASK, also known as Camguk, can act as a gain controller on the transition to calcium-independence in vivo. Genetic loss of dCASK significantly increases synapse-specific, activity-dependent autophosphorylation of CaMKII T287. In wild-type adult animals, simple and complex sensory stimuli cause region-specific increases in pT287. dCASK-deficient adults have a reduced dynamic range for activity-dependent T287 phosphorylation and have circuit-level defects that result in inappropriate activation of the kinase. dCASK control of the CaMKII switch occurs via its ability to induce autophosphorylation of T306 in the kinase's CaM binding domain. Phosphorylation of T306 blocks Ca(2+)/CaM binding, lowering the probability of intersubunit T287 phosphorylation, which requires CaM binding to both the substrate and catalytic subunits. dCASK is the first CaMKII-interacting protein other than CaM found to regulate this plasticity-controlling molecular switch.

Animals↗
PubMed2006

Electrophysiological and anatomical characterization of PDF-positive clock neurons in the intact adult Drosophila brain.

Daily biological rhythms in both prokaryotes and eukaryotes are controlled by circadian clocks. In Drosophila, there is a good basic understanding of both the molecular and anatomical components of the clock. In this study we directly measure, for the first time, electrophysiological properties and anatomy of individual filled large lateral PDF-positive clock neurons, a cell group believed to be involved in synchronization of the clock in constant conditions. We find that the large PDF-positive neurons are morphologically homogeneous and that their resting membrane potential is modulated both by the clock and by light inputs. Expression of a leak channel, dORK-deltaC, which has been shown to disrupt circadian locomotor rhythms, hyperpolarizes these neurons, and blocks firing. These data imply that the firing properties of large PDF neurons are both regulated by and critical for clock function.

Action Potentials↗
PubMed2006

Role for calcium/calmodulin-dependent protein kinase II in the p75-mediated regulation of sympathetic cholinergic transmission.

Neurotrophins regulate sympathetic neuron cotransmission by modulating the activity-dependent release of norepinephrine and acetylcholine. Nerve growth factor promotes excitatory noradrenergic transmission, whereas brain-derived neurotrophic factor (BDNF), acting through the p75 receptor, increases inhibitory cholinergic transmission. This regulation of corelease by target-derived factors leads to the functional modulation of myocyte beat rate in neuron-myocyte cocultures. Calcium/calmodulin-dependent protein kinase II (CaMKII) has been implicated in the control of both pre- and postsynaptic mechanisms of synaptic plasticity. We demonstrate that CaMKII acts in conjunction with p75 signaling to regulate cholinergic transmission between sympathetic neurons and heart cells. Inhibition of presynaptic CaMKII prevents the BDNF-dependent shift to inhibitory neurotransmission, whereas presynaptic expression of a constitutively active CaMKII results in inhibitory neurotransmission in the absence of added BDNF, suggesting that activation of presynaptic CaMKII is both necessary and sufficient for a shift from excitatory to inhibitory transmission. Several isozymes of CaMKII are expressed in sympathetic neurons, with the delta-CaMKII being activated by BDNF and nerve growth factor. Activated CaMKII is less effective at promoting cholinergic transmission in the absence of p75 signaling, demonstrating that p75 and CaMKII act to coordinate neurotransmitter selection in sympathetic neurons.

Animals↗
PubMed2006

Watching the fly brain learn.

The peptidergic dorsal paired medial (DPM) neurons, which innervate the mushroom bodies in Drosophila, have been widely hypothesized to be part of the unconditioned stimulus (US) pathway of odor-shock classical conditioning. In the December 2 issue of Cell, Yu et al., using functional imaging techniques, report the surprising finding that DPMs contain odor-specific memory traces and send integrated information about the conditioned stimulus (CS) to the mushroom bodies. These findings provide important new insight into the circuitry of learning in Drosophila.

Animals↗
PubMed2005

Sequential learning of pheromonal cues modulates memory consolidation in trainer-specific associative courtship conditioning.

BACKGROUND: Associative memory formation requires that animals choose predictors for experiences they need to remember. When an artificial odor is paired with an aversive experience, that odor becomes the predictor. In more natural settings, however, animals can have multiple salient experiences that need to be remembered and prioritized. The mechanisms by which animals deal with multiple experiences are incompletely understood. RESULTS: Here we show that Drosophila males can be trained to discriminate between different types of female pheromones; they suppress courtship specifically to the type of female that was associated with unsuccessful courtship. Such "trainer-specific" learning is mediated by hydrocarbon olfactory cues and modifies the male's processing of those cues. Animals that are unable to use olfactory cues can still learn by using other sensory modalities, but memory in this case is not specific to the trainer female's maturation state. Concurrent and serial presentation of different pheromones demonstrates that the ability to consolidate memory of pheromonal cues can be modified by the temporal order in which they appear. CONCLUSION: Suppression of memory by new learning demonstrates that the dynamics of memory consolidation are subject to plasticity in Drosophila. This type of metaplasticity is essential for navigation of experience-rich natural environments.

Age Factors↗
PubMed2005

Shaw potassium channel genes in Drosophila.

Drosophila Shaw encodes a voltage-insensitive, slowly activating, noninactivating K(+) current. The functional and developmental roles of this channel are unknown. In this study, we use a dominant transgenic strategy to investigate Shaw function and describe a second member of the Shaw family, Shawl. In situ hybridization showed that the two Shaw family genes, Shaw and Shawl, have largely nonoverlapping expression patterns in embryos. Shaw is expressed mainly in excitable cells of the CNS and PNS of late embryos. Shawl is expressed in many nonexcitable cell types: ubiquitously in embryos until the germband extends, then transiently in the developing CNS and PNS, becoming restricted to progressively smaller subsets of the CNS. Ectopic full-length and truncated Shaw localize differently within neurons, and produce uneclosed small pupae and adults with unfurled wings and softened cuticle. This phenotype was mapped to the crustacean cardioactive peptide (CCAP)-neuropeptide circuit. Widespread expression of Shaw in the nervous system results in a reduction in body mass, ether-induced shaking, and lethality. Expression of full-length Shaw had more extreme phenotypic consequences and caused earlier lethality than expression of truncated Shaw in a given GAL4 pattern. Whole cell recordings from ventral ganglion motor neurons expressing the truncated Shaw protein suggest that a major role of Shaw channels in these cells is to contribute to the resting potential.

Amino Acid Sequence↗
PubMed2004

Calcium-independent calcium/calmodulin-dependent protein kinase II in the adult Drosophila CNS enhances the training of pheromonal cues.

Calcium/calmodulin-dependent protein kinase II (CaMKII) is abundant in the CNS and is crucial for cellular and behavioral plasticity. It is thought that the ability of CaMKII to autophosphorylate and become Ca2+ independent allows it to act as a molecular memory switch. We have shown previously that inhibition of Drosophila CaMKII leads to impaired performance in the courtship conditioning associative memory assay, but it was unknown whether the constitutive form of the kinase had a special role in learning. In this study, we use a tripartite transgenic system combining GAL4/UAS with the tetracycline-off system to spatially and temporally manipulate levels of Ca2+-independent CaMKII activity in Drosophila. We find an enhancement of information processing during the training period with Ca2+-independent, but not Ca2+-dependent, CaMKII. During training, control animals have a lag before active suppression of courtship begins. Animals expressing Ca2+-independent CaMKII have no lag, implying that there is a threshold level of Ca2+-independent activity that must be present to suppress courtship. This is the first demonstration, in any organism, of enhanced behavioral plasticity with overexpression of constitutively active CaMKII. Anatomical studies indicate that transgene expression in antennal lobes and extrinsic mushroom body neurons drives this behavioral enhancement. Interestingly, immediate memory was unaffected by expression of T287D CaMKII in mushroom bodies, although previous studies have shown that CaMKII activity is required in this brain region for memory formation. These results suggest that the biochemical mechanisms of CaMKII-dependent memory formation are threshold based in only a subset of neurons.

Animals↗
PubMed2004

Receptor clustering: nothing succeeds like success.

By experimentally limiting the amount of receptor molecules available in a postsynaptic neuron in Drosophila, it has been shown that receptors can preferentially cluster opposite active zones with a high release probability. This asymmetry in receptor distribution can alter the apparent probability and calcium-dependence of neurotransmitter release.

Animals↗
PubMed2004

Unconventional sex: fresh approaches to courtship learning.

Understanding the complex array of genes, proteins and cells involved in learning and memory is a major challenge for neuroscientists. Using the genetically powerful model system, Drosophila melanogaster, and its well-studied courtship behavior, investigators have begun to delineate essential elements of associative and nonassociative behavioral plasticity. Advances in transgenic tools and developments in behavioral assays have increased the power of studying courtship learning in the fruit fly.

Animals↗
PubMed2003

The eag potassium channel binds and locally activates calcium/calmodulin-dependent protein kinase II.

Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) has been implicated in the regulation of neuronal excitability in many systems. Recent studies suggest that local regulation of membrane potential can have important computational consequences for neuronal function. In Drosophila, CaMKII regulates the eag potassium channel, but if and how this regulation was spatially restricted was unknown. Using coimmunoprecipitation from head extracts and in vitro binding assays, we show that CaMKII and Eag form a stable complex and that association with Eag activates CaMKII independently of CaM and autophosphorylation. Ca(2+)/CaM is necessary to initiate binding of CaMKII to Eag but not to sustain association because binding persists when CaM is removed. The Eag CaMKII-binding domain has homology to the CaMKII autoregulatory region, and the constitutively active CaMKII mutant, T287D, binds Eag Ca(2+)-independently in vitro and in vivo. These results favor a model in which the CaMKII-binding domain of Eag displaces the CaMKII autoinhibitory region. Displacement results in autophosphorylation-independent activation of CaMKII which persists even when Ca(2+) levels have gone down. Activity-dependent binding to this potassium channel substrate allows CaMKII to remain locally active even when Ca(2+) levels have dropped, providing a novel mechanism by which CaMKII can regulate excitability locally over long time scales.

Amino Acid Sequence↗
PubMed2003

Electrophysiological and morphological characterization of identified motor neurons in the Drosophila third instar larva central nervous system.

We have used dye fills and electrophysiological recordings to identify and characterize a cluster of motor neurons in the third instar larval ventral ganglion. This cluster of neurons is similar in position to the well-studied embryonic RP neurons. Dye fills of larval dorsomedial neurons demonstrate that individual neurons within the cluster can be reproducibly identified by observing their muscle targets and bouton morphology. The terminal targets of these five neurons are body wall muscles 6/7, 1, 14, and 30 and the intersegmental nerve (ISN) terminal muscles (1, 2, 3, 4, 9, 10, 19, 20). All cells except the ISN neuron, which has a type Is ending, display type Ib boutons. Two of these neurons appear to be identical to the embryonic RP3 and aCC cells, which define the most proximal and distal innervations within a hemisegment. The targets of the other neurons in the larval dorsomedial cluster do not correspond to embryonic targets of the neurons in the RP cluster, suggesting rewiring of this circuit during early larval stages. Electrophysiological studies of the five neurons in current clamp revealed that type Is neurons have a longer delay in the appearance of the first spike compared with type Ib neurons. Genetic, biophysical, and pharmacological studies in current and voltage clamp show this delay is controlled by the kinetics and voltage sensitivity of inactivation of a current whose properties suggest that it may be the Shal I(A) current. The combination of genetic identification and whole cell recording allows us to directly explore the cellular substrates of neural and locomotor behavior in an intact system.

4-Aminopyridine↗
PubMed2003

Regulation of the Ca2+/CaM-responsive pool of CaMKII by scaffold-dependent autophosphorylation.

CaMKII is critical for structural and functional plasticity. Here we show that Camguk (Cmg), the Drosophila homolog of CASK/Lin-2, associates in an ATP-regulated manner with CaMKII to catalyze formation of a pool of calcium-insensitive CaMKII. In the presence of Ca(2+)/CaM, CaMKII complexed to Cmg can autophosphorylate at T287 and become constitutively active. In the absence of Ca(2+)/CaM, ATP hydrolysis results in phosphorylation of T306 and inactivation of CaMKII. Cmg coexpression suppresses CaMKII activity in transfected cells, and the level of Cmg expression in Drosophila modulates postsynaptic T306 phosphorylation. These results suggest that Cmg, in the presence of Ca(2+)/CaM, can provide a localized source of active kinase. When Ca(2+)/CaM or synaptic activity is low, Cmg promotes inactivating autophosphorylation, producing CaMKII that requires phosphatase to reactivate. This interaction provides a mechanism by which the active postsynaptic pool of CaMKII can be controlled locally to differentiate active and inactive synapses.

Adenosine Triphosphate↗
PubMed2003

Activity-dependent remodeling of presynaptic inputs by postsynaptic expression of activated CaMKII.

Competitive synaptic remodeling is an important feature of developmental plasticity, but the molecular mechanisms remain largely unknown. Calcium/calmodulin-dependent protein kinase II (CaMKII) can induce postsynaptic changes in synaptic strength. We show that postsynaptic CaMKII also generates structural synaptic rearrangements between cultured cortical neurons. Postsynaptic expression of activated CaMKII (T286D) increased the strength of transmission between pairs of pyramidal neuron by a factor of 4, through a modest increase in quantal amplitude and a larger increase in the number of synaptic contacts. Concurrently, T286D reduced overall excitatory synaptic density and increased the proportion of unconnected pairs. This suggests that connectivity from some synaptic partners was increased while other partners were eliminated. The enhancement of connectivity required activity and NMDA receptor activation, while the elimination did not. These data suggest that postsynaptic activation of CaMKII induces a structural remodeling of presynaptic inputs that favors the retention of active presynaptic partners.

Alanine↗
PubMed2003

CaMKII, an enzyme on the move: regulation of temporospatial localization.

Calcium-calmodulin-dependent protein kinase II (CaMKII) is an important regulator of neuronal and behavioral plasticity. Studies in which the subcellular distribution of CaMKII has been altered argue that targeting of this enzyme to specific subcellular compartments is crucial to many of its roles. Understanding how a very abundant enzyme can achieve specificity of action over time and space requires an understanding of the functional diversity of the enzyme and its distribution. In this review we will discuss how structurally distinct isozymes, splice isoforms, and autophosphorylation states of CaMKII can affect kinase activity and localization. We will focus on the fast activity-dependent synaptic localization of the kinase and its association with postsynaptic proteins. The ability of enzyme activation to regulate protein-protein interactions with these binding partners and the potential for such binding interactions to regulate CaMKII activity in novel ways may represent new paradigm for CaMKII regulation.

Animals↗