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ABSTRACT: A prior screen identified dozens of Drosophila melanogaster mutants that possess defective long-term memory (LTM). Using spaced olfactory conditioning, we trained 26 of these mutant lines to associate an odor cue with electric shock and then examined the memory of this conditioning 24 h later. All of the mutants tested revealed a deficit in LTM compared to the robust LTM observed in control flies. We used in vivo functional optical imaging to measure the magnitude of a previously characterized LTM trace, which is manifested as increased calcium influx into the axons of α/β mushroom body neurons in response to the conditioned odor. This memory trace was defective in all 26 of the LTM mutants. These observations elevate the significance of this LTM trace given that 26 independent mutants all exhibit a defect in the trace, and further suggest that the calcium trace is a fundamental mechanism underlying Drosophila LTM.
Journal of Neuroscience 04/2011; 31(15):5643-7. · 7.11 Impact Factor
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ABSTRACT: Using functional optical imaging in vivo, we demonstrate that the γ mushroom body (MB) neurons of Drosophila melanogaster respond with axonal calcium influx when odors or electric shock stimuli are presented to the fly. Pairing of odor and electric shock stimuli in a single training trial or multiple, massed training trials failed to modify the odor-evoked calcium signal when flies were tested at several different times after training. In contrast, animals that received multiple but spaced odor-shock pairings exhibited a robust increase in calcium influx into the MB axons when tested between 18 and 48 h after training. This time window for the γ neuron memory trace is displaced relative to the modifications that occur between 9 and 24 h after training in the α branch of the α/β MB neurons. The α/β and the γ neuron long-term memory traces were both blocked by expressing a repressor of the transcription factor cAMP response element-binding protein or a calcium/calmodulin-dependent kinase II hairpin RNA. These results demonstrate that behavioral long-term olfactory memory is encoded as modifications of calcium influx into distinct MB neurons during overlapping but different windows of time after training.
Journal of Neuroscience 12/2010; 30(49):16699-708. · 7.11 Impact Factor
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ABSTRACT: Cyclic AMP signaling in Drosophila mushroom body neurons, anchored by the adenylyl cyclase encoded by the rutabaga gene, is indispensable for olfactory memory formation. From a screen for new memory mutants, we identified alleles of the gilgamesh (gish) gene, which encodes a casein kinase Iγ homolog that is preferentially expressed in the mushroom body neurons. The gish-encoded kinase participates in the physiology of these neurons underlying memory formation since the mutant memory deficit was rescued with expression of a gish cDNA in these neurons only during adulthood. A cellular memory trace, detected as increased calcium influx into the α'/β' neuron processes in response to the odor used for conditioning, was disrupted in gish mutants. Epistasis experiments indicated a lack of genetic interactions between gish and rutabaga. Therefore, gish participates in a rutabaga-independent pathway for memory formation and accounts for some of the residual learning that occurs in rutabaga mutants.
Neuron 09/2010; 67(5):810-20. · 14.74 Impact Factor
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ABSTRACT: Nonspecific cognitive impairments are one of the many manifestations of neurofibromatosis type 1 (NF1). A learning phenotype is also present in Drosophila melanogaster that lack a functional neurofibromin gene (nf1). Multiple studies have indicated that Nf1-dependent learning in Drosophila involves the cAMP pathway, including the demonstration of a genetic interaction between Nf1 and the rutabaga-encoded adenylyl cyclase (Rut-AC). Olfactory classical conditioning experiments have previously demonstrated a requirement for Rut-AC activity and downstream cAMP pathway signaling in neurons of the mushroom bodies. However, Nf1 expression in adult mushroom body neurons has not been observed. Here, we address this discrepancy by demonstrating (1) that Rut-AC is required for the acquisition and stability of olfactory memories, whereas Nf1 is only required for acquisition, (2) that expression of nf1 RNA can be detected in the cell bodies of mushroom body neurons, and (3) that expression of an nf1 transgene only in the alpha/beta subset of mushroom body neurons is sufficient to restore both protein synthesis-independent and protein synthesis-dependent memory. Our observations indicate that memory-related functions of Rut-AC are both Nf1-dependent and -independent, that Nf1 mediates the formation of two distinct memory components within a single neuron population, and that our understanding of Nf1 function in memory processes may be dissected from its role in other brain functions by specifically studying the alpha/beta mushroom body neurons.
Journal of Neuroscience 07/2010; 30(30):10135-43. · 7.11 Impact Factor
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ABSTRACT: Functional imaging with genetically encoded calcium and cAMP reporters was used to examine the signal integration underlying learning in Drosophila. Dopamine and octopamine modulated intracellular cAMP in spatially distinct patterns in mushroom body neurons. Pairing of neuronal depolarization with subsequent dopamine application revealed a synergistic increase in cAMP in the mushroom body lobes, which was dependent on the rutabaga adenylyl cyclase. This synergy was restricted to the axons of mushroom body neurons, and occurred only following forward pairing with time intervals similar to those required for behavioral conditioning. In contrast, forward pairing of neuronal depolarization and octopamine produced a subadditive effect on cAMP. Finally, elevating intracellular cAMP facilitated calcium transients in mushroom body neurons, suggesting that cAMP elevation is sufficient to induce presynaptic plasticity. These data suggest that rutabaga functions as a coincidence detector in an intact neuronal circuit, with dopamine and octopamine bidirectionally influencing the generation of cAMP.
Neuron 11/2009; 64(4):510-21. · 14.74 Impact Factor
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ABSTRACT: Assigning a gene's function to specific pathways used for classical conditioning, such as conditioned stimulus (CS) and unconditioned stimulus (US) pathway, is important for understanding the fundamental molecular and cellular mechanisms underlying memory formation. Prior studies have shown that the GABA receptor RDL inhibits aversive olfactory learning via its role in the Drosophila mushroom bodies (MBs). Here, we describe the results of further behavioral tests to further define the pathway involvement of RDL. The expression level of Rdl in the MBs influenced both appetitive and aversive olfactory learning, suggesting that it functions by suppressing a common pathway used for both forms of olfactory learning. Rdl knock down failed to enhance learning in animals carrying mutations in genes of the cAMP signaling pathway, such as rutabaga and NF1, suggesting that RDL works up stream of these functions in CS/US integration. Finally, knocking down Rdl or over expressing the dopamine receptor dDA1 in the MBs enhanced olfactory learning, but no significant additional enhancement was detected with both manipulations. The combined data suggest that RDL suppresses olfactory learning via CS pathway involvement.
Journal of Neuroscience 03/2009; 29(5):1573-9. · 7.11 Impact Factor
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ABSTRACT: Participation of RAS, RAF, and mitogen-activated protein kinase (MAPK) in learning and memory has been demonstrated in a number of studies, but the molecular events requisite for cascade activation and regulation have not been explored. We demonstrate that the adapter protein DRK (downstream of receptor kinase) which is essential for signaling to RAS in developmental contexts, is preferentially distributed in the adult mushroom bodies, centers for olfactory learning and memory. We demonstrate that drk mutant heterozygotes exhibit deficits in olfactory learning and memory, apparent under limited training conditions, but are not impaired in sensory responses requisite for the association of the stimuli, or brain neuroanatomy. Furthermore, we demonstrate that the protein is required acutely within mushroom body neurons to mediate efficient learning, a process that requires RAF activation. Importantly, 90 min memory remained impaired, even after differential training yielding equivalent learning in animals with compromised DRK levels and controls and did not require RAF. Sustained MAPK activation is compromised in drk mutants and surprisingly is negatively regulated by constitutive RAF activity. The data establish a role for DRK in Drosophila behavioral neuroplasticity and suggest a dual role for the protein, first in RAF activation-dependent learning and additionally in RAF-inhibition dependent sustained MAPK activation essential for memory formation or stability.
Journal of Neuroscience 03/2009; 29(8):2611-25. · 7.11 Impact Factor
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ABSTRACT: We examined tyrosine hydroxylase (TH-GAL4) expression and anti-TH immunoreactivity in the Drosophila protocerebrum and characterized single cell clones of the TH-GAL4 neurons. Eight clusters of putative dopaminergic neurons were characterized. Neurons in three of the clusters project to the mushroom body neuropil: PAM neurons project to the medial portion of the horizontal lobes; PPL1 neurons project to the vertical lobes, the junction area, the heel and distal peduncle; and PPL2ab neurons project to the calyx. Five types of PPL1 neurons were discovered that innervate different zones of the mushroom body lobes. Functional imaging experiments showed that the dopaminergic processes in four of the zones differ in response properties to odor, electric shock, or following the pairing of odor and electric shock. These results indicate that distinct dopaminergic neurons define separate zones of the mushroom body lobes and are probably involved in different functions. Differences in functional response properties of these neurons suggest that they are involved in different behavioral processes.
Frontiers in Neural Circuits 02/2009; 3:5. · 5.10 Impact Factor
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ABSTRACT: GABAergic neurotransmitter systems are important for many cognitive processes, including learning and memory. We identified a single neuron in each hemisphere of the Drosophila brain, the anterior paired lateral (APL) neuron, as a GABAergic neuron that broadly innervated the mushroom bodies. Reducing GABA synthesis in the APL neuron enhanced olfactory learning, suggesting that the APL neuron suppressed learning by releasing the inhibitory neurotransmitter GABA. Functional optical-imaging experiments revealed that the APL neuron responded to both odor and electric-shock stimuli that was presented to the fly with increases of intracellular calcium and released neurotransmitter. Notably, a memory trace formed in the APL neuron by pairing odor with electric shock. This trace was detected as a reduced calcium response in the APL neuron after conditioning specifically to the trained odor. These results demonstrate a mutual suppression between the GABAergic APL neuron and olfactory learning, and emphasize the functional neuroplasticity of the GABAergic system as a result of learning.
Nature Neuroscience 12/2008; 12(1):53-9. · 15.53 Impact Factor
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Nature 07/2008; 453(7199):1192-4. · 36.28 Impact Factor
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ABSTRACT: In Drosophila, the neuropeptide PDF is required for circadian rhythmicity, but it is unclear where PDF acts. In this issue of Neuron, Shafer et al. use a novel bioimaging methodology to demonstrate that PDF elevates cAMP in nearly all clock neurons. Thus, PDF apparently exerts more widespread effects on the circadian clock network than suggested by previous studies of PDF receptor expression.
Neuron 05/2008; 58(2):161-3. · 14.74 Impact Factor
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ABSTRACT: In Drosophila, the fruit fly, coincident exposure to an odor and an aversive electric shock can produce robust behavioral memory. This behavioral memory is thought to be regulated by cellular memory traces within the central nervous system of the fly. These molecular, physiological, or structural changes in neurons, induced by pairing odor and shock, regulate behavior by altering the neurons' response to the learned environment. Recently, novel in vivo functional imaging techniques have allowed researchers to observe cellular memory traces in intact animals. These investigations have revealed interesting temporal and spatial dynamics of cellular memory traces. First, a short-term cellular memory trace was discovered that exists in the antennal lobe, an early site of olfactory processing. This trace represents the recruitment of new synaptic activity into the odor representation and forms for only a short period of time just after training. Second, an intermediate-term cellular memory trace was found in the dorsal paired medial neuron, a neuron thought to play a role in stabilizing olfactory memories. Finally, a long-term protein synthesis-dependent cellular memory trace was discovered in the mushroom bodies, a structure long implicated in olfactory learning and memory. Therefore, it appears that aversive olfactory associations are encoded by multiple cellular memory traces that occur in different regions of the brain with different temporal domains.
Progress in brain research 02/2008; 169:293-304. · 3.04 Impact Factor
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ABSTRACT: In both mammals and insects, neurons involved in learning are strongly modulated by the inhibitory neurotransmitter GABA. The GABAA receptor, resistance to dieldrin (Rdl), is highly expressed in the Drosophila mushroom bodies (MBs), a group of neurons playing essential roles in insect olfactory learning. Flies with increased or decreased expression of Rdl in the MBs were generated. Olfactory associative learning tests showed that Rdl overexpression impaired memory acquisition but not memory stability. This learning defect was due to disrupting the physiological state of the adult MB neurons rather than causing developmental abnormalities. Remarkably, Rdl knockdown enhanced memory acquisition but not memory stability. Functional cellular imaging experiments showed that Rdl overexpression abolished the normal calcium responses of the MBs to odors while Rdl knockdown increased these responses. Together, these data suggest that RDL negatively modulates olfactory associative learning, possibly by gating the input of olfactory information into the MBs.
Neuron 01/2008; 56(6):1090-102. · 14.74 Impact Factor
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ABSTRACT: Integrins comprise a large family of heterodimeric, transmembrane cell adhesion receptors that mediate diverse neuronal functions in the developing and adult CNS. Recent pharmacological and genetic studies have suggested that beta1-integrins are critical in synaptic plasticity and memory formation. To further define the role of integrins in these processes, we generated a postnatal forebrain and excitatory neuron-specific knockout of alpha3-integrin, one of several binding partners for beta1 subunit. At hippocampal Schaffer collateral-CA1 synapses, deletion of alpha3-integrin resulted in impaired long-term potentiation (LTP). Basal synaptic transmission and paired-pulse facilitation were normal in the absence of alpha3-integrin. Behavioral studies demonstrated that the mutant mice were selectively defective in a hippocampus-dependent, nonmatch-to-place working memory task, but were normal in other hippocampus-dependent spatial tasks. The impairment in LTP and working memory is similar to that observed in beta1-integrin conditional knockout mice, suggesting that alpha3-integrin is the functional binding partner for beta1 for these processes in the forebrain.
Learning & memory (Cold Spring Harbor, N.Y.) 10/2007; 14(9):606-15. · 4.08 Impact Factor
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Ronald L Davis
Neuron 05/2007; 54(1):14-6. · 14.74 Impact Factor
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ABSTRACT: The molecular mechanisms occurring in the nervous system that underlie behavioral responses to ethanol remain poorly understood. Here, we report that molecular requirements for two of these responses, initial sensitivity and the development of rapid tolerance, comap to the same small set of neurons. We show that null homer mutant flies exhibit both increased sensitivity to the sedative effects of ethanol and failure to develop normal levels of rapid tolerance. Both the sensitivity and rapid tolerance phenotypes of the homer mutants are rescued by the expression of wild-type homer in a subset of neurons that include the ellipsoid body. Thus, some of the molecular- and systems-level requirements for these two behavioral responses to ethanol are identical.
Journal of Neuroscience 05/2007; 27(17):4541-51. · 7.11 Impact Factor
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ABSTRACT: When Drosophila adults are placed into an open field arena, they initially exhibit an elevated level of activity followed by a reduced stable level of spontaneous activity. We have found that the initial elevated component arises from the fly's interaction with the novel arena since: (1) the increased activity is independent of handling prior to placement within the arena, (2) the fly's elevated activity is proportional to the size of the arena, and (3) the decay in activity to spontaneous levels requires both visual and olfactory input. These data indicate that active exploration is the major component of elevated initial activity. There is a specific requirement for the kurtz nonvisual arrestin in the nervous system for both the exploration stimulated by the novel arena and the mechanically stimulated activity. kurtz is not required for spontaneous activity; kurtz mutants display normal levels of spontaneous activity and average the same velocities as wild-type controls. Inhibition of dopamine signaling has no effect on the elevated initial activity phase in either wild-type or krz(1) mutants. Therefore, the exploratory phase of open field activity requires kurtz in the nervous system, but is independent of dopamine's stimulation of activity.
Genetics 04/2007; 175(3):1197-212. · 4.01 Impact Factor
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ABSTRACT: Recent studies using functional optical imaging have revealed that cellular memory traces form in different areas of the insect brain after olfactory classical conditioning. These traces are revealed as increased calcium signals or synaptic release from defined neurons, and include a short-lived trace that forms immediately after conditioning in antennal lobe projection neurons, an early trace in dopaminergic neurons, and a medium-term trace in dorsal paired medial neurons. New molecular genetic tools have revealed that for normal behavioral memory performance, synaptic transmission from the mushroom body neurons is required only during retrieval, whereas synaptic transmission from dopaminergic neurons is required at the time of acquisition and synaptic transmission from dorsal paired medial neurons is required during the consolidation period. Such experimental results are helping to identify the types of neurons that participate in olfactory learning and when their participation is required. Olfactory learning often occurs alongside crossmodal interactions of sensory information from other modalities. Recent studies have revealed complex interactions between the olfactory and the visual senses that can occur during olfactory learning, including the facilitation of learning about subthreshold olfactory stimuli due to training with concurrent visual stimuli.
Current Opinion in Neurobiology 01/2007; 16(6):679-85. · 7.44 Impact Factor
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ABSTRACT: Functional optical imaging showed that odor or electric shock stimuli presented to the fly causes transient calcium influx into the two major axon branches of alpha/beta mushroom body (MB) neurons. One pairing of odor and electric shock stimuli or multiple, massed pairings did not alter odor-evoked calcium influx. In contrast, animals that received multiple, spaced pairings exhibited a robust increase in calcium influx into the MB axons when tested at 9 or 24 hr after training, but not at 3 hr. This modification occurred only in the alpha branch of the neurons and was blocked by mutation of the amnesiac gene, inhibition of protein synthesis, or the expression of a protein blocker of the transcription factor Creb. Thus, behavioral long-term olfactory memory appears to be encoded as a branch-specific modification of calcium influx into the alpha/beta MB neurons that occurs after spaced training in a protein synthesis-, Creb-, and amnesiac-dependent way.
Neuron 01/2007; 52(5):845-55. · 14.74 Impact Factor
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ABSTRACT: Nonvisual arrestins are a family of multifunctional adaptor molecules that regulate the activities of diverse families of receptors including G protein-coupled receptors, frizzled, and transforming growth factor-beta receptors. These activities indicate broad roles in both physiology and development for nonvisual arrestins. Drosophila melanogaster has a single nonvisual arrestin, kurtz, which is found at high levels within the adult olfactory receptor neurons (ORNs), suggesting a role for this gene in modulating olfactory sensitivity. Using heat-induced expression of a krz cDNA through development, we rescued krz(1) lethality. The resulting adults lacked detectable levels of krz in the olfactory system. The rescued krz(1) homozygotes have an incompletely penetrant antennal structural defect that was completely rescued by the neural expression of a krz cDNA. The krz(1) loss-of-function adults without visible antennal defects displayed diminished behavioral responsiveness to both aversive and attractive odors and also demonstrated reduced olfactory receptor potentials. Both the behavioral and electrophysiological phenotypes were rescued by the targeted expression of the krz cDNA within postdevelopmental ORNs. Thus, krz is required within the nervous system for antennal development and is required later in the ORNs for the maintenance of olfactory sensitivity in Drosophila. The reduced receptor potentials in krz(1) antenna indicate that nonvisual arrestins are required for the early odor-induced signaling events within the ORNs.
Chemical Senses 02/2006; 31(1):49-62. · 2.60 Impact Factor
