Rewarding Capacity of Optogenetically Activating a Giant GABAergic Central-Brain Interneuron in Larval Drosophila.

Larvae of the fruit fly Drosophila melanogaster are a powerful study case for understanding the neural circuits underlying behavior. Indeed, the numerical simplicity of the larval brain has permitted the reconstruction of its synaptic connectome, and genetic tools for manipulating single, identified neurons allow neural circuit function to be investigated with relative ease and precision. We focus on one of the most complex neurons in the brain of the larva (of either sex), the GABAergic anterior paired lateral neuron (APL). Using behavioral and connectomic analyses, optogenetics, Ca2+ imaging, and pharmacology, we study how APL affects associative olfactory memory. We first provide a detailed account of the structure, regional polarity, connectivity, and metamorphic development of APL, and further confirm that optogenetic activation of APL has an inhibiting effect on its main targets, the mushroom body Kenyon cells. All these findings are consistent with the previously identified function of APL in the sparsening of sensory representations. To our surprise, however, we found that optogenetically activating APL can also have a strong rewarding effect. Specifically, APL activation together with odor presentation establishes an odor-specific, appetitive, associative short-term memory, whereas naive olfactory behavior remains unaffected. An acute, systemic inhibition of dopamine synthesis as well as an ablation of the dopaminergic pPAM neurons impair reward learning through APL activation. Our findings provide a study case of complex circuit function in a numerically simple brain, and suggest a previously unrecognized capacity of central-brain GABAergic neurons to engage in dopaminergic reinforcement.SIGNIFICANCE STATEMENT The single, identified giant anterior paired lateral (APL) neuron is one of the most complex neurons in the insect brain. It is GABAergic and contributes to the sparsening of neuronal activity in the mushroom body, the memory center of insects. We provide the most detailed account yet of the structure of APL in larval Drosophila as a neurogenetically accessible study case. We further reveal that, contrary to expectations, the experimental activation of APL can exert a rewarding effect, likely via dopaminergic reward pathways. The present study both provides an example of unexpected circuit complexity in a numerically simple brain, and reports an unexpected effect of activity in central-brain GABAergic circuits.

Learning and Memory in Drosophila Larvae.

The Drosophila larva has become an attractive model system for studying fundamental questions in neuroscience. Although the focus was initially on topics such as the structure of genes, mechanisms of inheritance, genetic regulation of development, and the function and physiology of ion channels, today it is often on the cellular and molecular principles of naive and learned behavior. Drosophila larvae have developed different mechanisms, often widespread in similar manifestations in the animal kingdom, to orient themselves toward olfactory, gustatory, mechanosensory, thermal, and visual stimuli to coordinate their locomotion appropriately. To adapt to changes in the environment, larvae are able to learn to categorize some of these sensory impressions as "good" or "bad." Depending on their relevance and reliability, the larva learns them and constantly updates these memories. Laboratory experiments allow us to parametrically study and describe many of these processes (e.g., olfactory appetitive and aversive memory or visual appetitive and aversive memory). Combining behavioral tests with various neurogenetic techniques allows us to thermally or optogenetically activate or inhibit individual cells during learning, memory consolidation, and memory retrieval. The molecular and genetic bases of larval learning can be analyzed by using specific mutants. The CRISPR-Cas method has established extensive new directions in this area, in addition to the already wide-ranging traditional approaches, like the GAL4/UAS system. The combination of these genetic methods with the simplicity and cost-effectiveness of the introduced behavioral assay provides a platform for discovering the fundamental mechanisms underlying learning and memory formation in the rather simple larval brain.

The Analysis of Aversive Olfactory-Taste Learning and Memory in Drosophila Larvae.

Drosophila larvae are able to associate an odor stimulus with a temporally overlapping teaching signal encoding reward or punishment. Here, we describe a standardized experimental setup that allows the analysis of larval aversive-odor-taste learning and memory. This is a Pavlovian learning experiment with a single training trial in which larvae are presented with two specific odors in succession, one odor together with salt at a high concentration that is harmful to the larva. In the subsequent test, the trained larvae then show avoidance of the salt-paired odor and spend more time near the unpaired odor. To rule out nonassociative effects (such as naive preferences for odors, exposure, or handling effects), two independent groups of larvae are reciprocally trained. Subsequently, the average of the two individual preference values is determined and quantified as a Performance Index (PI), which assigns a numerical value to the larvae's shown behavioral change.

Olfactory stimuli and moonwalker SEZ neurons can drive backward locomotion in Drosophila.

How different sensory stimuli are collected, processed, and further transformed into a coordinated motor response is a fundamental question in neuroscience. In particular, the internal and external conditions that drive animals to switch to backward walking and the mechanisms by which the nervous system supports such behavior are still unknown. In fruit flies, moonwalker descending neurons (MDNs) are considered command-type neurons for backward locomotion as they receive visual and mechanosensory inputs and transmit motor-related signals to downstream neurons to elicit backward locomotion. Whether other modalities converge onto MDNs, which central brain neurons activate MDNs, and whether other retreat-driving pathways exist is currently unknown. Here, we show that olfactory stimulation can elicit MDN-mediated backward locomotion. Moreover, we identify the moonwalker subesophageal zone neurons (MooSEZs), a pair of bilateral neurons, which can trigger straight and rotational backward locomotion. MooSEZs act via postsynaptic MDNs and via other descending neurons. Although they respond to olfactory input, they are not required for odor-induced backward walking. Thus, this work reveals an important modality input to MDNs, a novel set of neurons presynaptic to MDNs driving backward locomotion and an MDN-independent backward locomotion pathway.

Left atrial appendage closure with the watchman device reduces atrial fibrillation management costs.

AIMS: To report hospitalization costs of patients with non-valvular atrial fibrillation (AF) submitted to percutaneous left atrial appendage closure (LAAC) with the Watchman device. METHODS: Pre- and post-procedural hospitalization AF-related costs were calculated using the DRG system (diagnosis-related groups) and compared. RESULTS: Between 2012 and 2016, 677 non-valvular AF patients underwent LAAC. Median time from first cardiac hospitalization to LAAC was 5.9 years (IQR 1.6-9.1) and median follow-up after LAAC was 4.8 years (IQR 3.6-5.6). LAAC mortality was 1.3% and follow-up mortality 16.9%. Median pre-LAAC hospitalization cost was € 17,867 (IQR € 7512-35,08) and post-LAAC € 8772 (IQR € 1183-25,159) (p < 0.0001). Annualized cost pre-LAAC was 3773 € (IQR € 1644-8,493) and post-LAAC 2,001 € (IQR € 260-6913) (p < 0.0001). Follow-up survivors had significantly lower post-LAAC costs (p < 0.0001) and after a survival cut-off time of 4.6 years LAAC procedural and post-procedural hospitalization costs achieved parity with pre-LACC costs (AUC 0.64; p = 0.02). CHA2DS2-VASc score (B = 0.04; p = 0.02; 95% CI 0.006-0.08), and HAS-BLED score (B = 0.08; p = 0.004; 95% CI 0.02-0.14) were independent determinants for annualized hospitalization costs post-LAAC. At Cox-regression analysis the DRG mean clinical complexity level (CCL) was the only independent determinant for follow-up mortality (OR = 2.2; p < 0.0001; 95% CI 1.6-2.8) with a cut-off value of 2.25 to predict follow-up mortality (AUC 0.72; p < 0.0001; Spec. 70%; Sens. 70%). CONCLUSION: Hospitalization costs pre-LAAC are consistent, and after LAAC, they are significantly reduced. Costs seem related to the patient's risk profile at the time of the procedure. With the increase in post-LAAC survival time, the procedure becomes economically more profitable.

Actual management costs of patients with non-valvular atrial fibrillation treated with percutaneous left atrial appendage closure or oral anticoagulation.

AIMS: Comparing actual management costs in patients with non-valvular atrial fibrillation (AF) treated with percutaneous left atrial appendage closure (LAAC) or OAC only. METHODS AND RESULTS: Patients undergoing percutaneous LAAC and AF patients treated with OAC only were matched for gender, age, and diagnosis related groups (DRG) clinical complexity level (CCL). Costs for cardiovascular outpatient clinic visits and hospitalizations were derived from the actual reimbursement records. Between 1/2012 and 12/2016, 8478 patients were referred: 7801 (92%) managed with OAC and 677 (8%) with percutaneous LAAC. Matching resulted in 558 patients (279 per group) for final analysis. Age was 74.9 ± 7.5 years, 244 were female (43.7%), and DRG CCL was 1.8 ± 1.1. Annualized management cost before percutaneous LAAC was € 3110 (IQR: € 1281-8127). After 4.5 ± 1.4 years follow-up, annualized management cost was € 1297 (IQR: € 607-2735) in OAC patients and € 1013 (IQR: € 0-4770) in patients after percutaneous LAAC (p = 0.003). Percutaneous LAAC was the strongest independent determinant to reduce follow-up costs (B = -0.8; CI: -1.09 ̶̶̶̶̶ -0.6; p < 0.0001). Estimated 3-year survival was 92% in percutaneous LAAC and 90% in OAC patients (p = 0.7). CONCLUSION: Percutaneous LAAC significantly reduces management costs. Management costs are significantly higher for patients treated with only OAC compared to patients after percutaneous LAAC. In spite of their complex comorbid profile, percutaneous LAAC patients show a follow-up survival rate similar to patients solely treated with OAC. Future studies are necessary to investigate the potential net economic and clinical benefit of percutaneous LAAC in patients treated with OAC only.

Food restriction reconfigures naïve and learned choice behavior in Drosophila larvae.

In many animals, the establishment and expression of food-related memory is limited by the presence of food and promoted by its absence, implying that this behavior is driven by motivation. In the past, this has already been demonstrated in various insects including honeybees and adult Drosophila. For Drosophila larvae, which are characterized by an immense growth and the resulting need for constant food intake, however, knowledge is rather limited. Accordingly, we have analyzed whether starvation modulates larval memory formation or expression after appetitive classical olfactory conditioning, in which an odor is associated with a sugar reward. We show that odor-sugar memory of starved larvae lasts longer than in fed larvae, although the initial performance is comparable. 80 minutes after odor fructose conditioning, only starved but not fed larvae show a reliable odor-fructose memory. This is likely due to a specific increase in the stability of anesthesia-resistant memory (ARM). Furthermore, we observe that starved larvae, in contrast to fed ones, prefer sugars that offer a nutritional benefit in addition to their sweetness. Taken together our work shows that Drosophila larvae adjust the expression of learned and naïve choice behaviors in the absence of food. These effects are only short-lasting probably due to their lifestyle and their higher internal motivation to feed. In the future, the extensive use of established genetic tools will allow us to identify development-specific differences arising at the neuronal and molecular level.

Reversal learning in Drosophila larvae.

Adjusting behavior to changed environmental contingencies is critical for survival, and reversal learning provides an experimental handle on such cognitive flexibility. Here, we investigate reversal learning in larval Drosophila Using odor-taste associations, we establish olfactory reversal learning in the appetitive and the aversive domain, using either fructose as a reward or high-concentration sodium chloride as a punishment, respectively. Reversal learning is demonstrated both in differential and in absolute conditioning, in either valence domain. In differential conditioning, the animals are first trained such that an odor A is paired, for example, with the reward whereas odor B is not (A+/B); this is followed by a second training phase with reversed contingencies (A/B+). In absolute conditioning, odor B is omitted, such that the animals are first trained with paired presentations of A and reward, followed by unpaired training in the second training phase. Our results reveal "true" reversal learning in that the opposite associative effects of both the first and the second training phase are detectable after reversed-contingency training. In what is a surprisingly quick, one-trial contingency adjustment in the Drosophila larva, the present study establishes a simple and genetically easy accessible study case of cognitive flexibility.

Influence on ICU course, outcome and costs for lung transplantation after implementation of the new Swiss transplantation law.

BACKGROUND: The Swiss organ allocation system for donor lungs was implemented on 1 July 2007. The effects of this implementation on patient selection, intensive care unit course, outcomes and intensive care costs are unknown. METHODS: The first 37 consecutive lung transplant recipients following the implementation of the new act were compared with the previous 42 lung transplant recipients. RESULTS: Following implementation of the new law, baseline characteristics and cumulative one-year patient survival were comparable in both groups (88.1% vs 83.8%, P = 0.58). The costs for each case increased by 35,000 euros after adoption of the new law. Stratifying patients after implementation of the law according to urgency status shows that urgent patients required longer mechanical ventilation (P = 0.04), a longer ICU stay (P = 0.045) and a longer hospital stay (P = 0.04) and ICU costs (median 64,050 euros) were higher compared to regular patients. CONCLUSION: The new transplantation law has increased ICU costs with the implementation of the Swiss organ allocation system. Patients listed as 'urgent' contribute significantly to the increase in ICU costs.

Association of intraoperative transfusion of blood products with mortality in lung transplant recipients.

BACKGROUND: The impact of intraoperative transfusion on postoperative mortality in lung transplant recipients is still elusive. METHODS: Univariate and multivariate analysis were performed to investigate the influence of red blood cells (RBCs) and fresh frozen plasma (FFP) on mortality in 134 consecutive lung transplants recipients from September 2003 until December 2008. RESULTS: Intraoperative transfusion of RBCs and FFP was associated with a significant increase in mortality with odds ratios (ORs) of 1.10 (1.03 to 1.16, P = 0.02) and 1.09 (1.02 to 1.15, P = 0.03), respectively. For more than four intraoperatively transfused RBCs multivariate analysis showed a hazard ratio for mortality of 3.8 (1.40 to 10.31, P = 0.003). Furthermore, non-survivors showed a significant increase in renal replacement therapy (RRT) (36.6% versus 6.9%, P <0.0001), primary graft dysfunction (PGD) (39.3% versus 5.9%, P <0.0001), postoperative need of extracorporeal membrane oxygenation (ECMO) (26.9% versus 3.1%, P = 0.0019), sepsis (24.2% versus 4.0%, P = 0.0004), multiple organ dysfunction syndrome (MODS) (26.9% versus 3.1%, P <0.0001), infections (18.1% versus 0.9%, P = 0.0004), retransplantation (12.1% versus 6.9%, P = 0.039) and readmission to the ICU (33.3% versus 12.8%, P = 0.024). CONCLUSIONS: Intraoperative transfusion is associated with a strong negative influence on outcome in lung transplant recipients.