A model of naturalistic decision making in preference tests

Decisions as to whether to continue with an ongoing activity or to switch to an alternative are a constant in an animal’s natural world, and in particular underlie foraging behavior and performance in food preference tests. Stimuli experienced by the animal both impact the choice and are themselves impacted by the choice, in a dynamic back and forth. Here, we present model neural circuits, based on spiking neurons, in which the choice to switch away from ongoing behavior instantiates this back and forth, arising as a state transition in neural activity. We analyze two classes of circuit, which differ in whether state transitions result from a loss of hedonic input from the stimulus (an “entice to stay” model) or from aversive stimulus-input (a “repel to leave” model). In both classes of model, we find that the mean time spent sampling a stimulus decreases with increasing value of the alternative stimulus, a fact that we linked to the inclusion of depressing synapses in our model. The competitive interaction is much greater in “entice to stay” model networks, which has qualitative features of the marginal value theorem, and thereby provides a framework for optimal foraging behavior. We offer suggestions as to how our models could be discriminatively tested through the analysis of electrophysiological and behavioral data.

Specialized Metabolites in Floral Resources: Effects and Detection in Buff-Tailed Bumblebees

The selection of appropriate food resources by bees is a critical aspect for the maintenance of their populations, especially in the current context of global change and pollinator decline. Wild bees have a sophisticated ability to forage selectively on specific resources, and can assess the quality of pollen using contact chemosensory perception (taste). While numerous studies have investigated the detection of pollen macronutrients in bees and their impact on bee health and reproductive success, only a few studies have described the gustatory responses of bees toward specialized metabolites. In addition, these studies mostly focused on the response to nectar and neglected pollen, which is the main food resource for both bee imagines and larvae. Whether bees have the ability to detect specialized toxic metabolites in pollen and then rapidly adapt their foraging behavior to avoid them is very little studied. In this study, we tested whether pollen specialized metabolites affect bumblebees at both the micro-colony and individual levels (i.e., bioassays using supplemented pollen), and whether foragers detect these specialized metabolites and potentially display an avoidance behavior (i.e., preference tests using supplemented syrup). Bumblebees were fed with either amygdalin-, scopolamine- or sinigrin-supplemented pollen diets in ratios that mimic 50%, 100%, and 200% of naturally occurring concentrations. We found no effect of these specialized metabolites on resource collection, reproductive success and stress response at the micro-colony level. At the individual level, bumblebees fed on 50%-amygdalin or 50%-scopolamine diets displayed the highest scores for damage to their digestive systems. Interestingly, during the preference tests, the solution with 50%-scopolamine displayed a phagostimulatory activity, whereas solution with 50%-amygdalin had a deterrent effect and could trigger an active avoidance behavior in bumblebees, with a faster proboscis retraction. Our results suggest that regulation of toxin intake is not as well-established and effective as the regulation of nutrient intake in bees. Bees are therefore not equally adapted to all specialized pollen metabolites that they can come into contact with.

O mouse, where art thou? The Mouse Position Surveillance System (MoPSS)—an RFID-based tracking system

Existing methods for analysis of home cage-based preference tests are either time-consuming, not suitable for group management, expensive, and/or based on proprietary equipment that is not freely available. To correct this, we developed an automated system for group-housed mice based on radio frequency identification: the Mouse Position Surveillance System (MoPSS). The system uses an Arduino microcontroller with compatible components; it is affordable and easy to rebuild for every laboratory because it uses free and open-source software and open-source hardware with the RFID readers as the only proprietary component. The MoPSS was validated using female C57BL/6J mice and manual video comparison. It proved to be accurate even for fast-moving mice (up to 100% accuracy after logical reconstruction), and is already implemented in several studies in our laboratory. Here, we provide the complete construction description as well as the validation data and the results of an example experiment. This tracking system will allow group-based preference testing with individually identified mice to be carried out in a convenient manner. This facilitation of preference tests creates the foundation for better housing conditions from the animals’ perspective.

A model of naturalistic decision making in preference tests

Decisions as to whether to continue with an ongoing activity or to switch to an alternative are a constant in an animal’s natural world, and in particular underlie foraging behavior and performance in food preference tests. Stimuli experienced by the animal both impact the choice and are themselves impacted by the choice, in a dynamic back and forth. Here, we present model neural circuits, based on spiking neurons, in which the choice to switch away from ongoing behavior instantiates this back and forth, arising as a state transition in neural activity. We analyze two classes of circuit, which differ in whether state transitions result from a loss of hedonic input from the stimulus (an “entice to stay” model) or from aversive stimulus input (a “repel to leave” model). In both classes of model, we find that the mean time spent sampling a stimulus decreases with increasing value of the alternative stimulus, a fact that we linked to the inclusion of depressing synapses in our model. The competitive interaction is much greater in “entice to stay” model networks, which has qualitative features of the marginal value theorem, and thereby provides a framework for optimal foraging behavior. We offer suggestions as to how our models could be discriminatively tested through the analysis of electrophysiological and behavioral data.Author summaryMany decisions are of the ilk of whether to continue sampling a stimulus or to switch to an alternative, a key feature of foraging behavior. We produce two classes of model for such stay-switch decisions, which differ in how decisions to switch stimuli can arise. In an “entice-to-stay” model, a reduction in the necessary positive stimulus input causes switching decisions. In a “repel-to-leave” model, a rise in aversive stimulus input produces a switch decision. We find that in tasks where the sampling of one stimulus follows another, adaptive biological processes arising from a highly hedonic stimulus can reduce the time spent at the following stimulus, by up to ten-fold in the “entice-to-stay” models. Along with potentially observable behavioral differences that could distinguish the classes of networks, we also found signatures in neural activity, such as oscillation of neural firing rates and a rapid change in rates preceding the time of choice to leave a stimulus. In summary, our model findings lead to testable predictions and suggest a neural circuit-based framework for explaining foraging choices.

Alternate without alternative: neither preference nor learning explains behaviour of C57BL/6J mice in the T-maze

In rodents, the T-maze is commonly used to investigate spontaneous alternating behaviour, but it can also be used to investigate preference between goods. However, for T-maze preference tests with mice there is no recommended protocol and researchers frequently report reproduction difficulties. Here, we tried to develop an efficient protocol with female C57BL/6J CrL mice for preference tests. We used two different designs, adapting habituation, cues and trial timing. However, in both experiments mice did not show any preference, although we used goods which we knew mice find rewarding. Instead, they alternated choices indicating that exploratory behaviour overruled preference. We argue that this behavioural strategy has evolved as an adaptive trait in saturated conditions where there is no need to take the reward immediately. Therefore, we deem the T-maze unsuitable for preference testing with the procedures we used here.

D-serine has antidepressant effects in mice through suppression of the BDNF signaling pathway and regulation of synaptic plasticity in the nucleus accumbens

Background and Purpose: D-serine is a crucial endogenous co-agonist of NMDARs in the central nervous system and can affect the function of the BDNF system, which plays an essential role in modulating synaptic plasticity. The aim of the current investigation was to systematically evaluate the role and mechanisms of D-serine in depressive behavior in NAc. Experimental Approach: D-Serine concentration in the CSDS model in NAc was measured by HPLC. The antidepressant-like effects of D-serine were identified by the FST and TST in control mice, and then assessed in the CSDS model. We applied social interaction and sucrose preference tests to identify the susceptibility of CSDS model. Western blotting was further performed to assess the changes of BDNF signaling cascade in NAc after CSDS and D-serine treatment. The BDNF signaling inhibitor (K252a) was also used to clarify the antidepressant mechanism of D-serine. Moreover, effects of D-serine on synaptic plasticity in NAc were investigated by electrophysiological methods. Key Results: D-serine injections into the NAc exhibited antidepressant effects in the FST, TST and CSDS model. Next, D-serine down-regulated the BDNF signaling pathway in NAc during the CSDS procedure. Moreover, K252a enhanced the antidepressant effects of D-serine. We also found that D-serine was essential for NMDARs-LTD. Conclusion and Implications: Our results provide the first evidence that D-serine exerts antidepressant effects in mice mediated through restraining the BDNF signaling pathway and regulating synaptic plasticity in NAc, which indicates that D-serine may be an effective therapeutic agent for depression. KEYWORDS D-serine, depression, NAc, BDNF, CSDS, LTD

TREK-1 Mediates The Alleviative Effects of GABAB Receptor Antagonism on Depression-Like Behavior in Chronic Unpredictable Stress Rats

GABAB receptor (GABAB R) antagonists are known to have antidepressant effects. TWIK-related potassium channel-1 (TREK-1) plays a role in GABAB R signaling. However, the role of TREK-1 in the antidepressant actions of GABAB R antagonist is still unclear. This study aimed to investigate whether TREK-1 mediates the antidepressant actions of GABAB R antagonist. To investigate this hypothesis, chronic unpredictable stress rats were treated with a GABAB R antagonist, GABAB R agonist, or TREK-1 blocker. Depression-like behavior was assessed by open field tests and sucrose preference tests. GABAB R and TREK-1 protein levels were measured by western blotting. The results demonstrated that the GABAB R antagonist alleviated depression-like behavior and reversed the decrease in hippocampal TREK-1 protein expression that characterizes chronic unpredictable stress rats. Conversely, the GABAB R agonist exacerbated depression-like behavior and further decreased hippocampal TREK-1 protein expression. In addition, the TREK-1 blocker alleviated the depression-like behavior of chronic unpredictable stress rats and increased hippocampal TREK-1 protein expression. These results suggest that the alleviative effects of the GABAB receptor antagonist on depression-like behavior in chronic unpredictable stress rats are at least partially mediated through TREK-1. These novel findings will be helpful for the clinical therapy of depression.