Biology subjects

Eiting, T. P.

Publications and source records attributed to Eiting, T. P..

6 recordsLinked to original sources

bioRxiv2026

Functional tradeoffs promote morphological disparity in the bat nasal cavity

Multifunctional anatomical structures must accommodate potentially competing performance demands, leading to functional tradeoffs. The mammal rostrum (snout) is involved in multiple functions, including feeding, respiratory conditioning, olfaction, and, in most bats, echolocation. Therefore, it serves as an ideal system to investigate whether and how functional tradeoffs promote or constrain morphological diversification. While the external morphology of the rostrum has been linked with mechanical demands of feeding in bats, the factors and processes influencing its internal morphology, including the turbinals in the nasal cavity, remain comparatively unexplored. Here we investigate how internal rostral morphology reflects specialization and tradeoffs among respiratory air conditioning, echolocation, and olfaction by quantifying turbinal morphological diversity in a phylogenetically and ecologically diverse sample of bat species. We find that echolocation mode predominantly influences both the ethmoturbinal complex (ETc) and maxilloturbinal (MT) systems, with nasal-emitting bats having reduced and less complex turbinals compared to oral and non-laryngeally echolocating bat species. MT complexity and surface area are not associated with bioclimatic variables representing thermal variability and aridity. However, the ETc exhibits higher complexity in plantivorous bats than faunivorous bats, suggesting higher olfactory reliance. While MT morphological disparity was predominantly explained by echolocation mode, ETc morphological disparity was associated with both echolocation mode and diet, suggesting potentially opposing demands favoring turbinal reduction for sound transmission and elaboration for olfaction. Among nasal emitters, which must accommodate both demands within the nasal cavity, ETc complexity exhibited higher relative disparity compared to MT complexity. These patterns suggest that competing functional demands may promote or maintain morphological diversity, possibly through ecological specialization and/or many-to-one mapping between morphology and performance.

evolutionary biology↗

bioRxiv2022

Mapping odorant sensitivities reveals a sparse but structured representation of olfactory chemical space by sensory input to the mouse olfactory bulb.

In olfactory systems, convergence of sensory neurons onto glomeruli generates a map of odorant receptor identity. How glomerular maps relate to sensory space remains unclear. We sought to better characterize this relationship in the mouse olfactory system by defining glomeruli in terms of the odorants to which they are most sensitive. Using high-throughput odorant delivery and ultrasensitive imaging of sensory inputs, we imaged responses to 185 odorants presented at concentrations determined to activate only one or a few glomeruli across the dorsal olfactory bulb. The resulting datasets defined the tuning properties of glomeruli - and, by inference, their cognate odorant receptors - in a low-concentration regime, and yielded consensus maps of glomerular sensitivity across a wide range of chemical space. Glomeruli were extremely narrowly tuned, with ~25% responding to only one odorant, and extremely sensitive, responding to their effective odorants at sub-picomolar to nanomolar concentrations. Such narrow tuning in this concentration regime allowed for reliable functional identification of many glomeruli based on a single diagnostic odorant. At the same time, the response spectra of glomeruli responding to multiple odorants was best predicted by straightforward odorant structural features, and glomeruli sensitive to distinct odorants with common structural features were spatially clustered. These results define an underlying structure to the primary representation of sensory space by the mouse olfactory system.

neuroscience↗

bioRxiv2021

Circuit contributions to sensory-driven glutamatergic drive of olfactory bulb mitral and tufted cells during odorant inhalation

In the mammalian olfactory bulb (OB), mitral/tufted (MT) cells respond to odorant inhalation with diverse temporal patterns that are thought to encode odor information. Much of this diversity is already apparent at the level of glutamatergic input to MT cells, which receive direct, monosynaptic excitatory input from olfactory sensory neurons (OSNs) as well as multisynaptic excitatory drive via glutamatergic interneurons. Both pathways are also subject to modulation by inhibitory circuits in the glomerular layer of the OB. To understand the role of direct OSN input versus postsynaptic OB circuit mechanisms in shaping diverse dynamics of glutamatergic drive to MT cells, we imaged glutamate signaling onto MT cell dendrites in anesthetized mice while blocking multisynaptic excitatory drive with ionotropic glutamate receptor antagonists and blocking presynaptic modulation of glutamate release from OSNs with GABAB receptor antagonists. GABAB receptor blockade increased the magnitude of inhalation-linked glutamate transients onto MT cell apical dendrites without altering their inhalation-linked dynamics, confirming that presynaptic inhibition impacts the gain of OSN inputs to the OB. Surprisingly, blockade of multisynaptic excitation only modestly impacted glutamatergic input to MT cells, causing a slight reduction in the amplitude of inhalation-linked glutamate transients in response to low odorant concentrations and no change in the dynamics of each transient. Postsynaptic blockade also modestly impacted glutamate dynamics over a slower timescale, mainly by reducing adaptation of the glutamate response across multiple inhalations of odorant. These results suggest that direct glutamatergic input from OSNs provides the bulk of excitatory drive to MT cells, and that diversity in the dynamics of this input may be a primary determinant of the temporal diversity in MT cell responses that underlies odor representations at this stage.

neuroscience↗

bioRxiv2020

Differential impacts of repeated sampling on odor representations by genetically-defined mitral and tufted cell subpopulations in the mouse olfactory bulb

Sniffing--the active control of breathing beyond passive respiration--is used by mammals to modulate olfactory sampling. Sniffing allows animals to make odor-guided decisions within ~200 ms, but animals routinely engage in bouts of high-frequency sniffing spanning several seconds; the impact of such repeated odorant sampling on odor representations remains unclear. We investigated this question in the mouse olfactory bulb, where mitral and tufted cells (MTCs) form parallel output streams of odor information processing. To test the impact of repeated odorant sampling on MTC responses, we used two-photon imaging in anesthetized male and female mice to record activation of MTCs while precisely varying inhalation frequency. A combination of genetic targeting and viral expression of GCaMP6 reporters allowed us to access mitral (MC) and superficial tufted cell (sTC) subpopulations separately. We found that repeated odorant sampling differentially affected responses in MCs and sTCs, with MCs showing more diversity than sTCs over the same time period. Impacts of repeated sampling among MCs included both increases and decreases in excitation, as well as changes in response polarity. Response patterns across ensembles of simultaneously-imaged MCs reformatted over time, with representations of different odorants becoming more distinct. MCs also responded differentially to changes in inhalation frequency, whereas sTC responses were more uniform over time and across frequency. Our results support the idea that MCs and TCs comprise functionally distinct pathways for odor information processing, and suggest that the reformatting of MC odor representations by high-frequency sniffing may serve to enhance the discrimination of similar odors.

neuroscience↗

bioRxiv2019

Diverse dynamics of glutamatergic input underlie heterogeneous response patterns of olfactory bulb mitral and tufted cells in vivo

Mitral/tufted (MT) cells of the olfactory bulb (OB) show diverse temporal responses to odorant stimulation that are thought to encode odor information. To understand the role of sensory input dynamics versus OB circuit mechanisms in generating this diversity, we imaged glutamate signaling onto MT cell dendrites in anesthetized and awake mice. We found surprising diversity in the dynamics of these signals, including excitatory, suppressive, and biphasic responses as well as nonlinear changes in glutamate signaling across inhalations. Simultaneous imaging of glutamate and calcium signals from MT cell dendrites revealed highly correlated responses for both signals. Glutamate responses were only weakly impacted by blockade of postsynaptic activity, implicating sensory neurons as a primary source of glutamate signaling onto MT cells. Thus, the dynamics of sensory input alone, rather than emergent features of OB circuits, may account for much of the diversity in MT cell responses that underlies OB odor representations.

neuroscience↗

bioRxiv2018

A novel olfactometer for efficient and flexible odorant delivery

Understanding how sensory space maps to neural activity in the olfactory system requires efficiently and flexibly delivering numerous odorants within single experimental preparations. Such delivery is difficult with current olfactometer designs, which typically include limited numbers of stimulus channels and are subject to inter-trial and inter-channel contamination of odorants. Here, we present a novel olfactometer design that is easily constructed, modular, and capable of delivering an unlimited number of odorants with temporal precision and no detectable inter-trial or inter-channel contamination. The olfactometer further allows for flexible generation of odorant mixtures and flexible timing of odorant sequences. Odorant delivery from the olfactometer is turbulent but reliable from trial-to-trial, supporting operant conditioning of mice in an odorant discrimination task and permitting odorants and concentrations to be mapped to neural activity with a level of precision equivalent to that obtained with a flow dilution olfactometer. This novel design thus provides several unique advantages for interrogating olfactory perception and for mapping sensory space to neural activity in the olfactory system.

neuroscience↗