The impact of Hodgkin-Huxley models on dendritic research.

For the past seven decades, the Hodgkin-Huxley (HH) formalism has been an invaluable tool in the arsenal of neuroscientists, allowing for robust and reproducible modelling of ionic conductances and the electrophysiological phenomena they underlie. Despite its apparent age, its role as a cornerstone of computational neuroscience has not waned. The discovery of dendritic regenerative events mediated by ionic and synaptic conductances has solidified the importance of HH-based models further, yielding new predictions concerning dendritic integration, synaptic plasticity and neuronal computation. These predictions are often validated through in vivo and in vitro experiments, advancing our understanding of the neuron as a biological system and emphasizing the importance of HH-based detailed computational models as an instrument of dendritic research. In this article, we discuss recent studies in which the HH formalism is used to shed new light on dendritic function and its role in neuronal phenomena.

Mechanisms underlying homeostatic plasticity in the Drosophila mushroom body in vivo.

Neural network function requires an appropriate balance of excitation and inhibition to be maintained by homeostatic plasticity. However, little is known about homeostatic mechanisms in the intact central brain in vivo. Here, we study homeostatic plasticity in the Drosophila mushroom body, where Kenyon cells receive feedforward excitation from olfactory projection neurons and feedback inhibition from the anterior paired lateral neuron (APL). We show that prolonged (4-d) artificial activation of the inhibitory APL causes increased Kenyon cell odor responses after the artificial inhibition is removed, suggesting that the mushroom body compensates for excess inhibition. In contrast, there is little compensation for lack of inhibition (blockade of APL). The compensation occurs through a combination of increased excitation of Kenyon cells and decreased activation of APL, with differing relative contributions for different Kenyon cell subtypes. Our findings establish the fly mushroom body as a model for homeostatic plasticity in vivo.

The receptor tyrosine kinase Alk controls neurofibromin functions in Drosophila growth and learning.

Anaplastic Lymphoma Kinase (Alk) is a Receptor Tyrosine Kinase (RTK) activated in several cancers, but with largely unknown physiological functions. We report two unexpected roles for the Drosophila ortholog dAlk, in body size determination and associative learning. Remarkably, reducing neuronal dAlk activity increased body size and enhanced associative learning, suggesting that its activation is inhibitory in both processes. Consistently, dAlk activation reduced body size and caused learning deficits resembling phenotypes of null mutations in dNf1, the Ras GTPase Activating Protein-encoding conserved ortholog of the Neurofibromatosis type 1 (NF1) disease gene. We show that dAlk and dNf1 co-localize extensively and interact functionally in the nervous system. Importantly, genetic or pharmacological inhibition of dAlk rescued the reduced body size, adult learning deficits, and Extracellular-Regulated-Kinase (ERK) overactivation dNf1 mutant phenotypes. These results identify dAlk as an upstream activator of dNf1-regulated Ras signaling responsible for several dNf1 defects, and they implicate human Alk as a potential therapeutic target in NF1.

Nutritional value-dependent and nutritional value-independent effects on Drosophila melanogaster larval behavior.

Gustatory stimuli allow an organism not only to orient in its environment toward energy-rich food sources to maintain nutrition but also to avoid unpleasant or even poisonous substrates. For both mammals and insects, sugars-perceived as "sweet"-potentially predict nutritional benefit. Interestingly, even Drosophila adult flies are attracted to most high-potency sweeteners preferred by humans. However, the gustatory information of a sugar may be misleading as some sugars, although perceived as "sweet," cannot be metabolized. Accordingly, in adult Drosophila, a postingestive system that additionally evaluates the nutritional benefit of an ingested sugar has been shown to exist. By using a set of seven different sugars, which either offer (fructose, sucrose, glucose, maltodextrin, and sorbitol) or lack (xylose and arabinose) nutritional benefit, we show that Drosophila, at the larval stage, can perceive and evaluate sugars based on both nutrition-dependent and -independent qualities. In detail, we find that larval survival and feeding mainly depend on the nutritional value of a particular sugar. In contrast, larval choice behavior and learning are regulated in a more complex way by nutrition value-dependent and nutrition value-independent information. The simplicity of the larval neuronal circuits and their accessibility to genetic manipulation may ultimately allow one to identify the neuronal and molecular basis of the larval sugar perception systems described here behaviorally.

Novel Software for Pain Drawing Analysis.

Introduction Pain drawings (PDs) are an important component of the assessment of a patient with pain. Although analog pain drawings (APDs), such as pen-on-paper drawings, have been extensively used in clinical assessment and clinical research, there is a lack of digital pain drawing (DPD) software that would be able to quantify and analyze the digital pain distribution obtained by the patients. The aim of this work is to describe a method that can quantify the extent and location of pain through novel custom-built software able to analyze data from the digital pain drawings obtained from the patients. Methods The application analysis and software specifications were based on the information gathered from the literature, and the programmers created the custom-built software according to the published needs of the pain scientific community. Results We developed a custom-built software named "Pain Distribution," which, among others, automatically calculates the number of the pixels the patient has chosen and therefore quantifies the pain extent, provides the frequency distribution from a group of images, and has the option to select the threshold over which the patient is considered with central sensitization (CS). Additionally, it delivers results and statistics for both every image and the frequency distribution, providing mean values, standard deviations, and CS indicators, as well as the ability to export them in *.txt file format for further analysis. Conclusion A novel Pain Distribution application was developed, freely available for use in any setting, clinical, research, or academic.

Localized inhibition in the Drosophila mushroom body.

Many neurons show compartmentalized activity, in which activity does not spread readily across the cell, allowing input and output to occur locally. However, the functional implications of compartmentalized activity for the wider neural circuit are often unclear. We addressed this problem in the Drosophila mushroom body, whose principal neurons, Kenyon cells, receive feedback inhibition from a non-spiking interneuron called the anterior paired lateral (APL) neuron. We used local stimulation and volumetric calcium imaging to show that APL inhibits Kenyon cells' dendrites and axons, and that both activity in APL and APL's inhibitory effect on Kenyon cells are spatially localized (the latter somewhat less so), allowing APL to differentially inhibit different mushroom body compartments. Applying these results to the Drosophila hemibrain connectome predicts that individual Kenyon cells inhibit themselves via APL more strongly than they inhibit other individual Kenyon cells. These findings reveal how cellular physiology and detailed network anatomy can combine to influence circuit function.

Inhibitory muscarinic acetylcholine receptors enhance aversive olfactory learning in adult Drosophila.

Olfactory associative learning in Drosophila is mediated by synaptic plasticity between the Kenyon cells of the mushroom body and their output neurons. Both Kenyon cells and their inputs from projection neurons are cholinergic, yet little is known about the physiological function of muscarinic acetylcholine receptors in learning in adult flies. Here, we show that aversive olfactory learning in adult flies requires type A muscarinic acetylcholine receptors (mAChR-A), particularly in the gamma subtype of Kenyon cells. mAChR-A inhibits odor responses and is localized in Kenyon cell dendrites. Moreover, mAChR-A knockdown impairs the learning-associated depression of odor responses in a mushroom body output neuron. Our results suggest that mAChR-A function in Kenyon cell dendrites is required for synaptic plasticity between Kenyon cells and their output neurons.

Caffeine Taste Signaling in Drosophila Larvae.

The Drosophila larva has a simple peripheral nervous system with a comparably small number of sensory neurons located externally at the head or internally along the pharynx to assess its chemical environment. It is assumed that larval taste coding occurs mainly via external organs (the dorsal, terminal, and ventral organ). However, the contribution of the internal pharyngeal sensory organs has not been explored. Here we find that larvae require a single pharyngeal gustatory receptor neuron pair called D1, which is located in the dorsal pharyngeal sensilla, in order to avoid caffeine and to associate an odor with caffeine punishment. In contrast, caffeine-driven reduction in feeding in non-choice situations does not require D1. Hence, this work provides data on taste coding via different receptor neurons, depending on the behavioral context. Furthermore, we show that the larval pharyngeal system is involved in bitter tasting. Using ectopic expressions, we show that the caffeine receptor in neuron D1 requires the function of at least four receptor genes: the putative co-receptors Gr33a, Gr66a, the putative caffeine-specific receptor Gr93a, and yet unknown additional molecular component(s). This suggests that larval taste perception is more complex than previously assumed already at the sensory level. Taste information from different sensory organs located outside at the head or inside along the pharynx of the larva is assembled to trigger taste guided behaviors.

Taste processing in Drosophila larvae.

The sense of taste allows animals to detect chemical substances in their environment to initiate appropriate behaviors: to find food or a mate, to avoid hostile environments and predators. Drosophila larvae are a promising model organism to study gustation. Their simple nervous system triggers stereotypic behavioral responses, and the coding of taste can be studied by genetic tools at the single cell level. This review briefly summarizes recent progress on how taste information is sensed and processed by larval cephalic and pharyngeal sense organs. The focus lies on several studies, which revealed cellular and molecular mechanisms required to process sugar, salt, and bitter substances.

Unexpected cardiac arrest after cardiac surgery: incidence, predisposing causes, and outcome of open chest cardiopulmonary resuscitation.

STUDY OBJECTIVES: To assess the incidence of acute mechanical causes precipitating sudden cardiac arrest in cardiac surgery patients during the immediate postoperative period. In addition, we report the success rate of cardiopulmonary resuscitation (CPR) in which open-chest CPR was employed at an early stage of the resuscitation effort. METHODS: Data on all cardiac surgical patients who suffered a sudden cardiac arrest during the first 24 h after surgery were collected prospectively. CPR consisted of conventional closed-chest CPR initially and was followed within 3 to 5 min, if needed, by open-chest CPR. RESULTS: Of 3,982 patients undergoing cardiac surgery over a 30-month period, 29 patients (0.7%) had a sudden cardiac arrest. Of these, 13 patients (45%) were successfully resuscitated with closed-chest CPR, 14 (48%) with open-chest CPR, and 2 (7%) died despite closed- and open-chest CPR. Four CPR survivors died subsequently in the ICU, yielding an overall hospital discharge rate of 79%. Perioperative myocardial infarction was the underlying cause of sudden cardiac arrest in 14 patients (48%), and mechanical impediments to cardiac function (tamponade or graft malfunction) in another 8 (28%) patients; in the remaining 7 patients (24%), no underlying cause was found. The length of ICU stay was 6+/-1 (mean+/-SE) days. None of the patients developed wound infection and all were neurologically intact at hospital discharge. CONCLUSION: Mechanical factors account for a substantial portion (28%) of causes of sudden cardiac arrest occurring in hemodynamically stable patients during the immediate postoperative period. This high incidence, in conjunction with the high survival rate achieved by open CPR, supports an early approach to open-chest CPR in this group of patients.

Effects of positive end-expiratory pressure (PEEP) in cardiac surgery patients.

The role of positive end-expiratory pressure (PEEP) in the postoperative course of cardiac surgery patients remains questionable. In this prospective study, we examined the effect of different levels of PEEP on arterial oxygenation, SvO2 and PvO2 values, and on haemodynamic indices, during the early postoperative period in cardiac surgery patients. Upon transfer to the ICU, 67 adult patients with normal preoperative respiratory status were randomly assigned to receive zero PEEP (Group A), 5 cmH2O (Group B), or 10 cmH2O PEEP (Group C) during mechanical ventilatory support. PaO2/FIO2 ratio, mixed venous PvO2 and SvO2, and cardiac index, were measured 30 min, 4 h and 8 h after application of mechanical ventilation in the ICU, just prior to extubation, half an hour after extubation, and 4 h post-extubation. We found no statistically significant differences (P = n.s.) in arterial oxygenation expressed by PaO2/FIO2 ratio, SvO2 and PvO2 values, and in cardiac index among the three groups at any study interval. We conclude that low levels of PEEP have no advantage over zero PEEP in improving gas exchange in the early postoperative course of patients following open heart surgery.

The neuronal and molecular basis of quinine-dependent bitter taste signaling in Drosophila larvae.

The sensation of bitter substances can alert an animal that a specific type of food is harmful and should not be consumed. However, not all bitter compounds are equally toxic and some may even be beneficial in certain contexts. Thus, taste systems in general may have a broader range of functions than just in alerting the animal. In this study we investigate bitter sensing and processing in Drosophila larvae using quinine, a substance perceived by humans as bitter. We show that behavioral choice, feeding, survival, and associative olfactory learning are all directly affected by quinine. On the cellular level, we show that 12 gustatory sensory receptor neurons that express both GR66a and GR33a are required for quinine-dependent choice and feeding behavior. Interestingly, these neurons are not necessary for quinine-dependent survival or associative learning. On the molecular receptor gene level, the GR33a receptor, but not GR66a, is required for quinine-dependent choice behavior. A screen for gustatory sensory receptor neurons that trigger quinine-dependent choice behavior revealed that a single GR97a receptor gene expressing neuron located in the peripheral terminal sense organ is partially necessary and sufficient. For the first time, we show that the elementary chemosensory system of the Drosophila larva can serve as a simple model to understand the neuronal basis of taste information processing on the single cell level with respect to different behavioral outputs.

Composition of agarose substrate affects behavioral output of Drosophila larvae.

In the last decade the Drosophila larva has evolved into a simple model organism offering the opportunity to integrate molecular genetics with systems neuroscience. This led to a detailed understanding of the neuronal networks for a number of sensory functions and behaviors including olfaction, vision, gustation and learning and memory. Typically, behavioral assays in use exploit simple Petri dish setups with either agarose or agar as a substrate. However, neither the quality nor the concentration of the substrate is generally standardized across these experiments and there is no data available on how larval behavior is affected by such different substrates. Here, we have investigated the effects of different agarose concentrations on several larval behaviors. We demonstrate that agarose concentration is an important parameter, which affects all behaviors tested: preference, feeding, learning and locomotion. Larvae can discriminate between different agarose concentrations, they feed differently on them, they can learn to associate an agarose concentration with an odor stimulus and change locomotion on a substrate of higher agarose concentration. Additionally, we have investigated the effect of agarose concentration on three quinine based behaviors: preference, feeding and learning. We show that in all cases examined the behavioral output changes in an agarose concentration-dependent manner. Our results suggest that comparisons between experiments performed on substrates differing in agarose concentration should be done with caution. It should be taken into consideration that the agarose concentration can affect the behavioral output and thereby the experimental outcomes per se potentially due to the initiation of an escape response or changes in foraging behavior on more rigid substrates.

Appetitive associative olfactory learning in Drosophila larvae.

In the following we describe the methodological details of appetitive associative olfactory learning in Drosophila larvae. The setup, in combination with genetic interference, provides a handle to analyze the neuronal and molecular fundamentals of specifically associative learning in a simple larval brain. Organisms can use past experience to adjust present behavior. Such acquisition of behavioral potential can be defined as learning, and the physical bases of these potentials as memory traces. Neuroscientists try to understand how these processes are organized in terms of molecular and neuronal changes in the brain by using a variety of methods in model organisms ranging from insects to vertebrates. For such endeavors it is helpful to use model systems that are simple and experimentally accessible. The Drosophila larva has turned out to satisfy these demands based on the availability of robust behavioral assays, the existence of a variety of transgenic techniques and the elementary organization of the nervous system comprising only about 10,000 neurons (albeit with some concessions: cognitive limitations, few behavioral options, and richness of experience questionable). Drosophila larvae can form associations between odors and appetitive gustatory reinforcement like sugar. In a standard assay, established in the lab of B. Gerber, animals receive a two-odor reciprocal training: A first group of larvae is exposed to an odor A together with a gustatory reinforcer (sugar reward) and is subsequently exposed to an odor B without reinforcement. Meanwhile a second group of larvae receives reciprocal training while experiencing odor A without reinforcement and subsequently being exposed to odor B with reinforcement (sugar reward). In the following both groups are tested for their preference between the two odors. Relatively higher preferences for the rewarded odor reflect associative learning--presented as a performance index (PI). The conclusion regarding the associative nature of the performance index is compelling, because apart from the contingency between odors and tastants, other parameters, such as odor and reward exposure, passage of time and handling do not differ between the two groups.

On the biocompatibility between TiO2 nanotubes layer and human osteoblasts.

Titanium and its alloys are the most popular biomaterials replacing hard tissues in implant surgeries. Clinicians are generally pleased by titanium mechanical properties and non-toxicity performances; on the other hand, there have been reported several cases of titanium implantation failure, phenomenon explained sometimes as "non adherence of human tissue to the metallic surface." Yet, researchers reported that titanium surfaces are favorable for osteoblasts adhesion. Therefore, titanium integration into the human body remains an unsolved problem. In the present study, biocompatibility tests were performed on titanium and TiO(2) nanotubes substrates, involving human bone marrow cells. The combination of a newly developed analytical model based on the hybrid interphase concept, applicable to systems consisting of inert materials when in contact with living tissues, together with experimental results, confirmed previous research studies and lead to the conclusion that osteoblasts adhere efficiently to titanium surfaces. However, the present results suggest that osteoblasts strong anchorage at the very first moment of their contact with the metallic material leads to their apoptosis. It is most probable that in several cases this is the reason of failed implantation surgeries involving titanium.

The serotonergic central nervous system of the Drosophila larva: anatomy and behavioral function.

The Drosophila larva has turned into a particularly simple model system for studying the neuronal basis of innate behaviors and higher brain functions. Neuronal networks involved in olfaction, gustation, vision and learning and memory have been described during the last decade, often up to the single-cell level. Thus, most of these sensory networks are substantially defined, from the sensory level up to third-order neurons. This is especially true for the olfactory system of the larva. Given the wealth of genetic tools in Drosophila it is now possible to address the question how modulatory systems interfere with sensory systems and affect learning and memory. Here we focus on the serotonergic system that was shown to be involved in mammalian and insect sensory perception as well as learning and memory. Larval studies suggested that the serotonergic system is involved in the modulation of olfaction, feeding, vision and heart rate regulation. In a dual anatomical and behavioral approach we describe the basic anatomy of the larval serotonergic system, down to the single-cell level. In parallel, by expressing apoptosis-inducing genes during embryonic and larval development, we ablate most of the serotonergic neurons within the larval central nervous system. When testing these animals for naïve odor, sugar, salt and light perception, no profound phenotype was detectable; even appetitive and aversive learning was normal. Our results provide the first comprehensive description of the neuronal network of the larval serotonergic system. Moreover, they suggest that serotonin per se is not necessary for any of the behaviors tested. However, our data do not exclude that this system may modulate or fine-tune a wide set of behaviors, similar to its reported function in other insect species or in mammals. Based on our observations and the availability of a wide variety of genetic tools, this issue can now be addressed.

Functional status and quality of life in long-term survivors of cardiac arrest after cardiac surgery.

OBJECTIVE: To assess long-term survival, functional status, and quality of life in patients who experienced cardiac arrest after cardiac surgery. DESIGN: Prospective, observational study. SETTING: An 18-bed, adult cardiac surgery intensive care unit in a tertiary teaching center. PATIENTS: Twenty-nine cardiac surgery patients who suffered an unexpected cardiac arrest in the immediate postoperative period. INTERVENTIONS: The New York Heart Association classification and a questionnaire based on the Nottingham Health Profile were used to evaluate functional status and quality of life 4 yrs after hospital discharge. MEASUREMENTS AND MAIN RESULTS: Of the 29 patients who experienced cardiac arrest during the first 24 hrs after cardiac surgery, 27 patients (93%) were successfully resuscitated and 23 patients (79%) survived to hospital discharge. Evaluation 4 yrs postdischarge showed that, of the 29 patients, 16 patients (55%) were still alive (long-term survivors). Functional status assessment of long-term survivors revealed that 12 patients (75%) were grouped in New York Heart Association class I, 3 patients (19%) in class II, and 1 patient (6%) in class III. None of them had a neurologic deficit. They all were living independently at home, without need of any nursing care. No patient reported any abnormal emotional reactions, and six patients (38%) had mild sleep disturbances, such as early awaking. Regarding activities of daily living, 20% returned to work, 94% were able to look after their home, 96% had a social life, 63% were sexually active, 81% were involved in their hobbies, and 75% had gone on holidays. CONCLUSIONS: Cardiac surgery patients who experience an unexpected cardiac arrest in the immediate postoperative period have a 55% chance of being alive 4 yrs postdischarge. The majority of these long-term survivors has a good outcome with respect to functional status and quality of life.

Protein S-100b serum levels in trauma-induced brain death.

OBJECTIVE: To analyze the time course of serum protein S-100b in patients with traumatic brain injury deteriorating to brain death and to investigate the predictive value of initial S-100b levels in relation to clinical and radiologic measures of injury severity with regard to brain death. METHODS: Forty-seven patients who sustained severe head injury were studied. Blood samples for measurement of S-100b were drawn on admission in the intensive care unit and every 24 hours thereafter for a maximum of 6 consecutive days or until brain death occurred. Variables related to outcome were recorded, including age, sex, Glasgow Coma Scale (GCS), and brain CT findings on admission. Outcome was defined as deterioration to brain death or not. RESULTS: Of the 47 patients studied, 17 deteriorated to brain death and 30 did not. On admission, patients who became brain dead had higher median serum S-100b levels compared with those who did not (2.32 microg/L vs 1.04 micro g/L, p = 0.0028). Logistic regression analysis showed that initial S-100b was an independent predictor of brain death (p = 0.041), in the presence of advanced age (p = 0.043) and low GCS score (p = 0.013). The odds ratio of 2.09 (95% CI, 1.03 to 4.25) indicates a more than doubling of the probability of deteriorating to brain death per 1- micro g/L increase in S-100b on admission. At clinical brain death, median S-100b was higher in patients with brain death compared with the peak S-100b value obtained over a 6-day period in those who did not become brain dead (6.58 microg/L vs 1.49 microg/L, p < 0.0001). CONCLUSIONS: Prediction of brain death after severe head injury can be improved by combining clinical and S-100b data; thus, serum S-100b determination deserves to be included in the neuromonitoring of patients with severe traumatic brain injury.