Biology subjects

Arbab, T.

Publications and source records attributed to Arbab, T..

4 recordsLinked to original sources

bioRxiv2022

Anticipation of appetitive operant action induces sustained dopamine release in the nucleus accumbens

The mesolimbic dopamine system is implicated in signaling reward-related information as well as in actions that generate rewarding outcomes. These implications are commonly investigated in either Pavlovian or operant reinforcement paradigms, where only the latter requires instrumental action. To parse contributions of reward- and action-related information to dopamine signals, we directly compared the two paradigms: rats underwent either Pavlovian or operant conditioning while dopamine release was measured in the nucleus accumbens, a brain region central for processing this information. Task conditions were identical with the exception of the operant-lever response requirement. Rats in both groups released the same quantity of dopamine at the onset of the reward-predictive cue. However, only the operant-conditioning group showed a subsequent, sustained plateau in dopamine concentration throughout the entire five-second cue presentation (preceding the required action). This dopamine "ramp" was unaffected by probabilistic reward delivery, occurred exclusively prior to operant actions, and was not related to task performance or task acquisition, as it persisted throughout the two-week daily behavioral training. Instead, the ramp flexibly increased in duration with longer cue presentation, seemingly modulating the initial cue-onset triggered dopamine release (i.e., the reward-prediction error (RPE) signal), as both signal amplitude and sustain diminished when reward timing was made more predictable. Thus, our findings suggest that RPE and action components of dopamine release can be differentiated temporally into phasic and ramping/sustained signals, respectively, where the latter depends on the former and presumably reflects the anticipation or incentivization of appetitive action, conceptually akin to motivation. Significance StatementIt is unclear whether the components of dopamine signals that are related to reward-associated information and reward-driven approach behavior can be separated. Most studies investigating the dopamine system utilize either Pavlovian or operant conditioning, which both involve the delivery of reward and necessitate appetitive approach behavior. Thus, used exclusively, neither paradigm can disentangle the contributions of these components to dopamine release. However, by combining both paradigms in the same study, we find that anticipation of a reward-driven operant action induces a modulation of reward-prediction-associated dopamine release, producing so-called "dopamine ramps". Therefore, our findings provide new insight into dopamine ramps, and suggest that dopamine signals integrate reward and appetitive action in a temporally distinguishable, yet dependent, manner.

neuroscience↗

bioRxiv2021

A novel automated approach for improving standardization of the marble burying test enables quantification of burying bouts and activity characteristics

The marble burying test is a commonly used paradigm to screen phenotypes in mouse models of neurodevelopmental and psychiatric disorders. The current methodological approach relies solely on reporting the number of buried marbles at the end of the test. By measuring the proxy of the behavior (buried marbles), rather than the behavior itself (burying bouts), many important characteristics regarding the temporal aspect of this assay are lost. Here we introduce a novel, automated method to quantify mouse behavior throughout the duration of the marble burying test with the focus on the burying bouts. Using open-source software packages, we trained a supervised machine learning algorithm (the "classifier") to distinguish burying behavior in freely moving mice. In order to confirm the classifiers accuracy and uncover the behavioral meaning of the marble burying test, we performed marble burying test in three mouse models: Ube3am-/p+ (Angelman Syndrome model), Shank2-/- (autism model), and Sapap3-/- (obsessive-compulsive disorder model) mice. The classifier scored burying behavior accurately and consistent with the literature in the Ube3am-/p+ mice, which showed decreased levels of burying compared to controls. Shank2-/- mice showed a similar pattern of decreased burying behavior, which was not found in Sapap3-/- mice. Tracking mouse behavior throughout the test enabled us to quantify activity characteristics, revealing hypoactivity in Ube3am-/p+ and hyperactivity in the Shank2-/- mice, indicating that mouse activity is unrelated to burying behavior. Together, we demonstrate that our classifier is an accurate method for the analysis of the marble burying test, providing more information than the currently used methods. Significance StatementThe marble burying test is widely used in phenotyping neurodevelopmental and neuropsychiatric disorder mouse models. Currently, its analysis consists of manually scoring the number of buried marbles upon the completion of the assay. This approach is not standardized across laboratories, and leaves out important variables such as movement characteristics and information about the burying bouts. This leads to divergent interpretations of the marble burying test, ranging from anxiety to cognitive impairment. We introduce a method that reliably tracks mouse behavior throughout the experiment, classifies the duration and number of the burying bouts, and is generalizable across laboratories. Using machine learning for measuring the actual burying behavior standardizes this method, and provides rich information about the burying characteristics.

neuroscience↗

bioRxiv2021

Nucleus-accumbens dopamine tracks aversive-stimulus duration and prediction but not value or prediction error

There is active debate on the role of dopamine in processing aversive stimuli, where inferred roles range from no involvement at all, to signaling an aversive-prediction error (APE). Here, we systematically investigate dopamine release in the nucleus-accumbens core (NAC), which is closely linked to reward-prediction errors, in rats exposed to white noise (WN, a versatile, underutilized, aversive stimulus) and its predictive cues. Both induced a negative dopamine ramp, followed by slow signal recovery upon stimulus cessation. In contrast to reward conditioning, this dopamine signal was unaffected by WN value, context valence, or probabilistic contingencies, and the WN dopamine-response shifted only partially towards its predictive cue. However, unpredicted WN provoked slower post-stimulus signal recovery than predicted WN. Despite differing signal qualities, dopamine responses to simultaneous presentation of rewarding and aversive stimuli were additive. Together, our findings demonstrate that instead of an APE, NAC dopamine primarily tracks prediction and duration of aversive events.

neuroscience↗

bioRxiv2017

Impaired hippocampal representation of place in the Fmr1-knockout mouse model of Fragile X syndrome

Fragile X syndrome (FXS) is an X-chromosome linked intellectual disability and the most common genetic cause of autism spectrum disorder (ASD). Building upon demonstrated deficits in neuronal plasticity and spatial memory in FXS, we investigated how spatial information processing is affected in vivo in an FXS mouse model (Fmr1-KO). Healthy hippocampal neurons (so-called place cells) exhibit place-related activity during spatial exploration, and the stability of these spatial representations can be taken as an index of memory function. We find impaired stability and reduced specificity of Fmr1-KO spatial representations. This is a potential biomarker for the cognitive dysfunction observed in FXS, informative on the ability to integrate sensory information into an abstract representation and successfully retain this conceptual memory. Our results provide key insight into the biological mechanisms underlying cognitive disabilities in FXS and ASD, paving the way for a targeted approach to remedy these.

animal behavior and cognition↗