Biology subjects

Thornquist, S. C.

Publications and source records attributed to Thornquist, S. C..

4 recordsLinked to original sources

bioRxiv2024

A green lifetime biosensor for calcium that remains bright over its full dynamic range

Fluorescent biosensors toggle between two states and for the vast majority of biosensors one state is bright and the other state is dim. As a consequence, there is a substantial difference in the signal-to-noise ratio (SNR) for the two states. The dim state has a low signal-to-noise ratio, which is problematic when precise, quantitative measurements are needed. During the engineering of a red-shifted variant of an mTurquoise-based calcium sensor, we serendipitously generated a green-emitting sensor that shows high brightness in both the calcium-bound and -unbound state, while still showing a calcium dependent lifetime change of >1 nanosecond. This sensor, named G-Ca-FLITS, is comparable in brightness to the bright state of GCaMP3 and jGCaMP7c in mammalian cells. The calcium induced loss in fluorescence intensity is only around 30% and therefore we observe little variation in the SNR when calcium levels change. G-Ca-FLITS shows negligible sensitivity to pH in the physiological range, like its turquoise parent. Using fluorescence lifetime imaging (FLIM), we measured the calcium concentration with G-Ca-FLITS in various organelles and observed in HeLa cells transient and spatially heterogeneous calcium elevations in mitochondria. Finally, we evaluated the use of G-Ca-FLITS and its turquoise predecessor for two-photon FLIM in Drosophila brains. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=120 SRC="FIGDIR/small/622032v2_ufig1.gif" ALT="Figure 1"> View larger version (55K): org.highwire.dtl.DTLVardef@1caf016org.highwire.dtl.DTLVardef@586996org.highwire.dtl.DTLVardef@7c15cdorg.highwire.dtl.DTLVardef@7b6f03_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2024

Molecular control of temporal integration matches decision-making to motivational state

Motivations bias our responses to stimuli, producing behavioral outcomes that match our needs and goals. We describe a mechanism behind this phenomenon: adjusting the time over which stimulus-derived information is permitted to accumulate toward a decision. As a Drosophila copulation progresses, the male becomes less likely to continue mating through challenges. We show that a set of Copulation Decision Neurons (CDNs) flexibly integrates information about competing drives to mediate this decision. Early in mating, dopamine signaling restricts CDN integration time by potentiating CaMKII activation in response to stimulatory inputs, imposing a high threshold for changing behaviors. Later into mating, the timescale over which the CDNs integrate termination-promoting information expands, increasing the likelihood of switching behaviors. We suggest scalable windows of temporal integration at dedicated circuit nodes as a key but underappreciated variable in state-based decision-making.

neuroscience↗

bioRxiv2020

Biochemical computation underlying behavioral decision-making

Computations in the brain are broadly assumed to emerge from patterns of fast electrical activity. Challenging this view, we show that a male flys decision to persist in mating, even through a potentially lethal threat, hinges on biochemical computations that enable processing over minutes to hours. Each neuron in a recurrent network measuring time into mating contains slightly different internal molecular estimates of elapsed time. Protein Kinase A (PKA) activity contrasts this internal measurement with input from the other neurons to represent evidence that the networks goal has been achieved. When consensus is reached, PKA pushes the network toward a large-scale and synchronized burst of calcium influx, which we call an eruption. The eruption functions like an action potential at the level of the network, transforming deliberation within the network into an all-or-nothing output, after which the male will no longer sacrifice his life to continue mating. We detail the continuous transformation between interwoven molecular and electrical information over long timescales in this system, showing how biochemical activity, invisible to most large scale recording techniques, is the key computational currency directing a life-or-death decision.

neuroscience↗

bioRxiv2020

Behavioural choice emerges from nonlinear all-to-all interactions between drives

Under the right conditions any drive can overcome nearly any other, yet studies of behavioural selection predominantly focus on only one, or occasionally two behaviours. We present an experimental and computational framework that captures and explains the resolution of conflicts between several competing motivations. We characterize neurons that integrate information from all rival drives to generate an aggregate signal that urges male Drosophila to transition out of mating. Experimental investigation of these Drive Integrating Neurons (DINs) revealed time-varying, supralinear interactions among competing drives that stimulate the DINs and induce a change in behaviour. Extending these findings to model the interactions between all of an animals motivations led to the surprising prediction that, under many conditions, all-to-all interactions actually buffer the dominant drive against challengers. We experimentally validated this prediction, showing that weak drives for a variety of tertiary goals can have a profound stabilizing effect on the ongoing behaviour. These results emerge only if non-linear integration of other motivations occurs for each of an animals drives, suggesting the potential universality of this mechanism. Our findings emphasize the interconnectedness of motivational systems and the consequent importance of considering the full motivational state of an animal to understand its behaviour.

neuroscience↗