Biology subjects

Markov, D. A.

Publications and source records attributed to Markov, D. A..

4 recordsLinked to original sources

bioRxiv2025

Quantifying and modeling loss of steroid hormones in PDMS-based devices

Many polydimethylsiloxane (PDMS)-based devices, e.g., organ-on-chip or microphysiological systems, have been developed to investigate biological processes at a miniaturized scale. These devices typically culture cells under microfluidic perfusion to dynamically dose cells with chemicals of interest; however, PDMS is known to interact with hydrophobic compounds and can strongly limit such compounds in-device bioavailability. Here, we quantify chemical-PDMS interactions for three commonly used steroid hormones: aldosterone, estradiol, and progesterone. We find that aldosterone does not detectably interact with PDMS; estradiol interacts modestly; and progesterone interacts strongly. Based on these measured interactions, we computationally model dynamic dosing protocols based on pulsed/bolus delivery and circadian control. We show that interactions with PDMS can strongly disrupt these dynamic dosing protocols in a chemical-specific and flow-rate-dependent manner. These results have critical implications for the use of steroid hormones in PDMS-based devices.

bioengineering↗

bioRxiv2024

Toxicokinetics for organ-on-chip devices

Organ-on-chip (OOC) devices are an emerging New Approach Method in both pharmacology and toxicology. Such devices use heterotypic combinations of human cells in a micro-fabricated device to mimic in vivo conditions and better predict organ-specific toxicological responses in humans. One drawback of these devices is that they are typically made from polydimethylsiloxane (PDMS), a polymer known to interact with hydrophobic chemicals. Due to this interaction, the actual dose experienced by cells inside OOC devices can differ strongly from the nominal dose. To account for these effects, we have developed a comprehensive toxicokinetic approach to measure and model chemical-PDMS interactions, including partitioning into and diffusion through PDMS. We use these methods to characterize PDMS interactions for ten chemicals, ranging from fluorescent dyes to persistent organic pollutants to organophosphate pesticides. We further show that these methods return physical interaction parameters that can be used to accurately predict time-dependent doses under continuous-flow conditions, as would be present in an OOC device. These results demonstrate the validity of the methods and model across geometries and flow rates.

bioengineering↗

bioRxiv2021

Structural and functional organization of visual responses in the inferior olive of larval zebrafish

The olivo-cerebellar system plays an important role in vertebrate sensorimotor control. According to a classical theory of cerebellar cortex, the inferior olive (IO) provides Purkinje cells with error information which drives motor learning in the cerebellum. Here we investigate the sensory representations in the IO of larval zebrafish and their spatial organization. Using single-cell labeling of genetically identified IO neurons we find that they can be divided into at least two distinct groups based on their spatial location, dendritic morphology, and axonal projection patterns. In the same genetically targeted population, we recorded calcium activity in response to a set of visual stimuli using 2-photon imaging. We found that most IO neurons showed direction selective and binocular responses to visual stimuli and that functional properties were spatially organized within the IO. Light-sheet functional imaging that allowed for simultaneous activity recordings at the soma and axonal level revealed tight coupling between soma location, axonal projections and functional properties of IO neurons. Taken together, our results suggest that anatomically-defined classes of inferior olive neurons correspond to distinct functional types, and that topographic connections between IO and cerebellum contribute to organization of the cerebellum into distinct functional zones.

neuroscience↗

bioRxiv2020

The cerebellum recalibrates a feedback controller involved in motor control

Animals must adapt their behavior to survive in a changing environment. Behavioral adaptations can be evoked by two mechanisms: feedback control and internal-model-based control. Feedback controllers can maintain the sensory state of the animal at a desired level under different environmental conditions. In turn, internal models learn the relationship between behavior and resulting sensory consequences in order to modify the behavior when this relationship changes. Here, we present multiple perturbations in visual feedback to larval zebrafish performing the optomotor response and show that they react to these perturbations through a feedback control mechanism. In contrast, if a perturbation is long-lasting, fish adapt their behavior by updating a cerebellum-dependent internal model. We use modelling and functional imaging to show that neuronal requirements for these mechanisms are met in the larval zebrafish brain. Our results illustrate the role of the cerebellum in encoding internal models and how these can calibrate neuronal circuits involved in reactive behaviors depending on the interactions between animal and environment. HighlightsO_LIBehavioral reactions to unexpected changes in visual feedback are implemented by a feedback control mechanism C_LIO_LIA long-lasting change in visual feedback updates the state of the neuronal controller C_LIO_LIThe cerebellar internal model mediates this recalibration C_LI

neuroscience↗