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Learning & Memory (Cold Spring Harbor,... May 2024Associative learning enables the adaptive adjustment of behavioral decisions based on acquired, predicted outcomes. The valence of what is learned is influenced not only...
Associative learning enables the adaptive adjustment of behavioral decisions based on acquired, predicted outcomes. The valence of what is learned is influenced not only by the learned stimuli and their temporal relations, but also by prior experiences and internal states. In this study, we used the fruit fly to demonstrate that neuronal circuits involved in associative olfactory learning undergo restructuring during extended periods of low-caloric food intake. Specifically, we observed a decrease in the connections between specific dopaminergic neurons (DANs) and Kenyon cells at distinct compartments of the mushroom body. This structural synaptic plasticity was contingent upon the presence of allatostatin A receptors in specific DANs and could be mimicked optogenetically by expressing a light-activated adenylate cyclase in exactly these DANs. Importantly, we found that this rearrangement in synaptic connections influenced aversive, punishment-induced olfactory learning but did not impact appetitive, reward-based learning. Whether induced by prolonged low-caloric conditions or optogenetic manipulation of cAMP levels, this synaptic rearrangement resulted in a reduction of aversive associative learning. Consequently, the balance between positive and negative reinforcing signals shifted, diminishing the ability to learn to avoid odor cues signaling negative outcomes. These results exemplify how a neuronal circuit required for learning and memory undergoes structural plasticity dependent on prior experiences of the nutritional value of food.
Topics: Animals; Mushroom Bodies; Drosophila melanogaster; Neuronal Plasticity; Dopaminergic Neurons; Eating; Optogenetics; Association Learning; Smell; Olfactory Perception; Reward; Animals, Genetically Modified
PubMed: 38862177
DOI: 10.1101/lm.053997.124 -
Learning & Memory (Cold Spring Harbor,... May 2024Across animal species, dopamine-operated memory systems comprise anatomically segregated, functionally diverse subsystems. Although individual subsystems could operate... (Review)
Review
Across animal species, dopamine-operated memory systems comprise anatomically segregated, functionally diverse subsystems. Although individual subsystems could operate independently to support distinct types of memory, the logical interplay between subsystems is expected to enable more complex memory processing by allowing existing memory to influence future learning. Recent comprehensive ultrastructural analysis of the mushroom body revealed intricate networks interconnecting the dopamine subsystems-the mushroom body compartments. Here, we review the functions of some of these connections that are beginning to be understood. Memory consolidation is mediated by two different forms of network: A recurrent feedback loop within a compartment maintains sustained dopamine activity required for consolidation, whereas feed-forward connections across compartments allow short-term memory formation in one compartment to open the gate for long-term memory formation in another compartment. Extinction and reversal of aversive memory rely on a similar feed-forward circuit motif that signals omission of punishment as a reward, which triggers plasticity that counteracts the original aversive memory trace. Finally, indirect feed-forward connections from a long-term memory compartment to short-term memory compartments mediate higher-order conditioning. Collectively, these emerging studies indicate that feedback control and hierarchical connectivity allow the dopamine subsystems to work cooperatively to support diverse and complex forms of learning.
Topics: Animals; Dopamine; Mushroom Bodies; Drosophila; Feedback, Physiological; Memory Consolidation; Nerve Net; Dopaminergic Neurons; Neural Pathways
PubMed: 38862171
DOI: 10.1101/lm.053807.123 -
Learning & Memory (Cold Spring Harbor,... May 2024Octopamine, the functional analog of noradrenaline, modulates many different behaviors and physiological processes in invertebrates. In the central nervous system, a few... (Review)
Review
Octopamine, the functional analog of noradrenaline, modulates many different behaviors and physiological processes in invertebrates. In the central nervous system, a few octopaminergic neurons project throughout the brain and innervate almost all neuropils. The center of memory formation in insects, the mushroom bodies, receive octopaminergic innervations in all insects investigated so far. Different octopamine receptors, either increasing or decreasing cAMP or calcium levels in the cell, are localized in Kenyon cells, further supporting the release of octopamine in the mushroom bodies. In addition, different mushroom body (MB) output neurons, projection neurons, and dopaminergic PAM cells are targets of octopaminergic neurons, enabling the modulation of learning circuits at different neural sites. For some years, the theory persisted that octopamine mediates rewarding stimuli, whereas dopamine (DA) represents aversive stimuli. This simple picture has been challenged by the finding that DA is required for both appetitive and aversive learning. Furthermore, octopamine is also involved in aversive learning and a rather complex interaction between these biogenic amines seems to modulate learning and memory. This review summarizes the role of octopamine in MB function, focusing on the anatomical principles and the role of the biogenic amine in learning and memory.
Topics: Octopamine; Mushroom Bodies; Animals; Memory; Learning; Dopamine; Insecta; Neurons
PubMed: 38862169
DOI: 10.1101/lm.053839.123 -
Molecular Brain Jun 2024Chronic perturbations of neuronal activity can evoke homeostatic and new setpoints for neurotransmission. Using chemogenetics to probe the relationship between neuronal...
Chronic perturbations of neuronal activity can evoke homeostatic and new setpoints for neurotransmission. Using chemogenetics to probe the relationship between neuronal cell types and behavior, we recently found reversible decreases in dopamine (DA) transmission, basal behavior, and amphetamine (AMPH) response following repeated stimulation of DA neurons in adult mice. It is unclear, however, whether altering DA neuronal activity via chemogenetics early in development leads to behavioral phenotypes that are reversible, as alterations of neuronal activity during developmentally sensitive periods might be expected to induce persistent effects on behavior. To examine the impact of developmental perturbation of DA neuron activity on basal and AMPH behavior, we expressed excitatory hM3D(Gq) in postnatal DA neurons in TH-Cre and WT mice. Basal and CNO- or AMPH-induced locomotion and stereotypy was evaluated in a longitudinal design, with clozapine N-oxide (CNO, 1.0 mg/kg) administered across adolescence (postnatal days 15-47). Repeated CNO administration did not impact basal behavior and only minimally reduced AMPH-induced hyperlocomotor response in adolescent TH-Cre mice relative to WT littermate controls. Following repeated CNO administration, however, AMPH-induced stereotypic behavior robustly decreased in adolescent TH-Cre mice relative to controls. A two-month CNO washout period rescued the diminished AMPH-induced stereotypic behavior. Our findings indicate that the homeostatic compensations that take place in response to chronic hM3D(Gq) stimulation during adolescence are temporary and are dependent on ongoing chemogenetic stimulation.
Topics: Animals; Amphetamine; Dopaminergic Neurons; Stereotyped Behavior; Clozapine; Locomotion; Mice; Male; Motor Activity; Mice, Transgenic; Tyrosine 3-Monooxygenase; Behavior, Animal; Integrases
PubMed: 38858755
DOI: 10.1186/s13041-024-01110-9 -
ELife Jun 2024Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common genetic cause of Parkinson's disease (PD). However, whether LRRK2 mutations cause PD and...
Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common genetic cause of Parkinson's disease (PD). However, whether LRRK2 mutations cause PD and degeneration of dopaminergic (DA) neurons via a toxic gain-of-function or a loss-of-function mechanism is unresolved and has pivotal implications for LRRK2-based PD therapies. In this study, we investigate whether and its functional homolog play a cell-intrinsic role in DA neuron survival through the development of DA neuron-specific conditional double knockout (cDKO) mice. Unlike germline DKO mice, DA neuron-restricted cDKO mice exhibit normal mortality but develop age-dependent loss of DA neurons, as shown by the progressive reduction of DA neurons in the substantia nigra pars compacta (SNpc) at the ages of 20 and 24 months. Moreover, DA neurodegeneration is accompanied with increases in apoptosis and elevated microgliosis in the SNpc as well as decreases in DA terminals in the striatum, and is preceded by impaired motor coordination. Taken together, these findings provide the unequivocal evidence for the cell-intrinsic requirement of LRRK in DA neurons and raise the possibility that LRRK2 mutations may impair its protection of DA neurons, leading to DA neurodegeneration in PD.
Topics: Animals; Dopaminergic Neurons; Leucine-Rich Repeat Serine-Threonine Protein Kinase-2; Mice, Knockout; Mice; Cell Survival; Protein Serine-Threonine Kinases; Parkinson Disease; Apoptosis
PubMed: 38856715
DOI: 10.7554/eLife.92673 -
BioRxiv : the Preprint Server For... May 2024The capacity to deal with stress declines during the aging process, and preservation of cellular stress responses is critical to healthy aging. The unfolded protein...
The capacity to deal with stress declines during the aging process, and preservation of cellular stress responses is critical to healthy aging. The unfolded protein response of the endoplasmic reticulum (UPR) is one such conserved mechanism, which is critical for the maintenance of several major functions of the ER during stress, including protein folding and lipid metabolism. Hyperactivation of the UPR by overexpression of the major transcription factor, , solely in neurons drives lifespan extension as neurons send a neurotransmitter-based signal to other tissue to activate UPR in a non-autonomous fashion. Previous work identified serotonergic and dopaminergic neurons in this signaling paradigm. To further expand our understanding of the neural circuitry that underlies the non-autonomous signaling of ER stress, we activated UPR solely in glutamatergic, octopaminergic, and GABAergic neurons in and paired whole-body transcriptomic analysis with functional assays. We found that UPR-induced signals from glutamatergic neurons increased expression of canonical protein homeostasis pathways and octopaminergic neurons promoted pathogen response pathways, while minor, but statistically significant changes were observed in lipid metabolism-related genes with GABAergic UPR activation. These findings provide further evidence for the distinct role neuronal subtypes play in driving the diverse response to ER stress.
PubMed: 38854121
DOI: 10.1101/2024.05.27.595950 -
BioRxiv : the Preprint Server For... Jun 2024Age-related dopamine (DA) neuron loss is a primary feature of Parkinson's disease. However, it remains unclear whether similar biological processes occur during healthy...
Age-related dopamine (DA) neuron loss is a primary feature of Parkinson's disease. However, it remains unclear whether similar biological processes occur during healthy aging, albeit to a lesser degree. We therefore determined whether midbrain DA neurons degenerate during aging in mice and humans. In mice, we identified no changes in midbrain neuron numbers throughout aging. Despite this, we found age-related decreases in midbrain mRNA expression of tyrosine hydroxylase (), the rate limiting enzyme of DA synthesis. Among midbrain glutamatergic cells, we similarly identified age-related declines in vesicular glutamate transporter 2 () mRNA expression. In co-transmitting / neurons, and transcripts decreased with aging. Importantly, striatal Th and Vglut2 protein expression remained unchanged. In translating our findings to humans, we found no midbrain neurodegeneration during aging and identified age-related decreases in and mRNA expression similar to mouse. Unlike mice, we discovered diminished density of striatal TH dopaminergic terminals in aged human subjects. However, TH and VGLUT2 protein expression were unchanged in the remaining striatal boutons. Finally, in contrast to and mRNA, expression of most ribosomal genes in neurons was either maintained or even upregulated during aging. This suggests a homeostatic mechanism where age-related declines in transcriptional efficiency are overcome by ongoing ribosomal translation. Overall, we demonstrate species-conserved transcriptional effects of aging in midbrain dopaminergic and glutamatergic neurons that are not accompanied by marked cell death or lower striatal protein expression. This opens the door to novel therapeutic approaches to maintain neurotransmission and bolster neuronal resilience.
PubMed: 38854057
DOI: 10.1101/2024.06.01.596950 -
Research Square May 2024Parkinson's disease (PD) is the most common progressive neurodegenerative movement disorder and results from the selective loss of dopaminergic neurons in the substantia...
Parkinson's disease (PD) is the most common progressive neurodegenerative movement disorder and results from the selective loss of dopaminergic neurons in the substantia nigra pars compacta. Pink1 and Parkin are proteins that function together in mitochondrial quality control, and when they carry loss-of-function mutations lead to familial forms of PD. While much research has focused on central nervous system alterations in PD, peripheral contributions to PD pathogenesis are increasingly appreciated. We report Pink1/Parkin regulate glycolytic and mitochondrial oxidative metabolism in peripheral blood mononuclear cells (PBMCs) from rats. Pink1/Parkin deficiency induces changes in the circulating lymphocyte populations, namely increased CD4 + T cells and decreased CD8 + T cells and B cells. Loss of Pink1/Parkin leads to elevated platelet counts in the blood and increased platelet-T cell aggregation. Platelet-lymphocyte aggregates are associated with increased thrombosis risk, and venous thrombosis is a cause of sudden death in PD, suggesting targeting the Pink1/Parkin pathway in the periphery has therapeutic potential.
PubMed: 38854001
DOI: 10.21203/rs.3.rs-4431604/v1 -
BioRxiv : the Preprint Server For... Jun 2024Cue reactivity is the maladaptive neurobiological and behavioral response upon exposure to drug cues and is a major driver of relapse. The leading hypothesis is that...
Cue reactivity is the maladaptive neurobiological and behavioral response upon exposure to drug cues and is a major driver of relapse. The leading hypothesis is that dopamine release by addictive drugs represents a persistently positive reward prediction error that causes runaway enhancement of dopamine responses to drug cues, leading to their pathological overvaluation compared to non-drug reward alternatives. However, this hypothesis has not been directly tested. Here we developed Pavlovian and operant procedures to measure firing responses, within the same dopamine neurons, to drug versus natural reward cues, which we found to be similarly enhanced compared to cues predicting natural rewards in drug-naïve controls. This enhancement was associated with increased behavioral reactivity to the drug cue, suggesting that dopamine release is still critical to cue reactivity, albeit not as previously hypothesized. These results challenge the prevailing hypothesis of cue reactivity, warranting new models of dopaminergic function in drug addiction, and provide critical insights into the neurobiology of cue reactivity with potential implications for relapse prevention.
PubMed: 38853878
DOI: 10.1101/2024.06.02.597025 -
Neurobiology of Disease Aug 2024Parkinson's disease is caused by a selective vulnerability and cell loss of dopaminergic neurons of the Substantia Nigra pars compacta and, consequently, striatal...
Parkinson's disease is caused by a selective vulnerability and cell loss of dopaminergic neurons of the Substantia Nigra pars compacta and, consequently, striatal dopamine depletion. In Parkinson's disease therapy, dopamine loss is counteracted by the administration of L-DOPA, which is initially effective in ameliorating motor symptoms, but over time leads to a burdening side effect of uncontrollable jerky movements, termed L-DOPA-induced dyskinesia. To date, no efficient treatment for dyskinesia exists. The dopaminergic and serotonergic systems are intrinsically linked, and in recent years, a role has been established for pre-synaptic 5-HT1a/b receptors in L-DOPA-induced dyskinesia. We hypothesized that post-synaptic serotonin receptors may have a role and investigated the effect of modulation of 5-HT4 receptor on motor symptoms and L-DOPA-induced dyskinesia in the unilateral 6-OHDA mouse model of Parkinson's disease. Administration of RS 67333, a 5-HT4 receptor partial agonist, reduces L-DOPA-induced dyskinesia without altering L-DOPA's pro-kinetic effect. In the dorsolateral striatum, we find 5-HT4 receptor to be predominantly expressed in D2R-containing medium spiny neurons, and its expression is altered by dopamine depletion and L-DOPA treatment. We further show that 5-HT4 receptor agonism not only reduces L-DOPA-induced dyskinesia, but also enhances the activation of the cAMP-PKA pathway in striatopallidal medium spiny neurons. Taken together, our findings suggest that agonism of the post-synaptic serotonin receptor 5-HT4 may be a novel therapeutic approach to reduce L-DOPA-induced dyskinesia.
Topics: Animals; Dyskinesia, Drug-Induced; Levodopa; Oxidopamine; Mice; Male; Mice, Inbred C57BL; Serotonin 5-HT4 Receptor Agonists; Antiparkinson Agents; Corpus Striatum; Receptors, Serotonin, 5-HT4; Parkinsonian Disorders; Pyridines; Neurons; Piperidines; Pyrimidines
PubMed: 38852753
DOI: 10.1016/j.nbd.2024.106559