Biology subjects

Miller, D. M.

Publications and source records attributed to Miller, D. M..

23 records · Page 2Linked to original sources

bioRxiv2019

Responses of Neurons in the Rostral Ventrolateral Medulla (RVLM) of Conscious Felines to Anticipated and Passive Movements

Considerable evidence demonstrates that the vestibular system contributes to regulating sympathetic nerve activity and blood pressure. Initial studies in decerebrate animals showed that presumed pre-sympathetic neurons in the rostral ventrolateral medulla (RVLM) respond to small-amplitude (<10{degrees}) rotations of the body, as in other brain areas that process vestibular signals, despite the fact that such movements do not appreciably affect blood distribution in the body. However, a subsequent experiment in conscious animals showed that few RVLM neurons respond to small-amplitude movements. This study tested the hypothesis that vestibular inputs to RVLM neurons are modulated in conscious animals, such that vestibulosympathetic responses are only elicited when changes in body position are large enough to require changes in sympathetic nerve activity. The activity of approximately a third of RVLM neurons whose firing rate was related to the cardiac cycle, and thus likely received baroreceptor inputs, responded to vestibular inputs elicited by 40{degrees} head-up tilts in conscious cats, but not during 10{degrees} sinusoidal rotations in the pitch plane that affected the activity of neurons in brain regions providing inputs to the RVLM. These data suggest the existence of brain circuitry that suppresses vestibular influences on the activity of RVLM neurons and the sympathetic nervous system unless these inputs are physiologically warranted. We also determined that RVLM activity is not altered prior to tilts when a light cue is provided signaling the movement. The simplest interpretation of this findings is that feedforward cardiovascular responses are associated with active movement such as occurs during exercise, but not passive movements that require cardiovascular adjustments.

physiology↗

bioRxiv2019

Integration of vestibular and hindlimb inputs by vestibular nucleus neurons: Multisensory influences on postural control.

1.We recently demonstrated in both decerebrate and conscious cat preparations that hindlimb somatosensory inputs converge with vestibular afferent input onto neurons in multiple CNS locations that participate in balance control. While it is known that head position and limb state modulate postural reflexes, presumably through both vestibulospinal and reticulospinal pathways, the combined influence of the two inputs on the activity of neurons in these brainstem regions is unknown. In the present study, we evaluated the responses of vestibular nucleus (VN) neurons to vestibular and hindlimb stimuli delivered separately and together in conscious cats. We hypothesized that VN neuronal firing during activation of vestibular and limb proprioceptive inputs would be well-fit by an additive model. Extracellular single-unit recordings were obtained from neurons in the caudal aspects of the VN. Sinusoidal whole-body rotation in the roll plane was used as the search stimulus. Units responding to the search stimulus were tested for their responses to 10{degrees} ramp-and-hold roll body rotation, 10{degrees} extension hindlimb movement, and both movements delivered simultaneously. Composite response histograms were fit by a model of low and high pass filtered limb and body position signals using least squares nonlinear regression. We found that VN neuronal activity during combined vestibular and hindlimb proprioceptive stimulation in the conscious cat is well-fit by a simple additive model for signals with similar temporal dynamics. The mean R2 value for goodness of fit across all units was 0.74 {+/-} 0.17. It is likely that VN neurons that exhibit these integrative properties participate in adjusting vestibulospinal outflow in response to limb state.\n\nNew and NoteworthyVestibular nucleus neurons receive convergent information from hindlimb somatosensory inputs and vestibular inputs. In this study, extracellular single unit recordings of vestibular nucleus neurons during conditions of passively applied limb movement, passive whole-body rotations, and combined stimulation, were well fit by an additive model. The integration of hindlimb somatosensory inputs with vestibular inputs at the first stage of vestibular processing suggests vestibular nucleus neurons account for limb position in determining vestibulospinal responses to postural perturbations.

neuroscience↗

bioRxiv2019

Machine learning prediction of emesis and gastrointestinal state in ferrets

Although electrogastrography (EGG) could be a critical tool in the diagnosis and treatment of patients with gastrointestinal (GI) disease, it remains under-utilized. The lack of spatial and temporal resolution using current EGG methods presents a significant roadblock to more widespread usage. Human and preclinical studies have shown that GI myoelectric electrodes can record signals containing significantly more information than can be derived abdominal surface electrodes. The current study sought to assess the efficacy of multi-electrode arrays, surgically implanted on the serosal surface of the GI tract, from gastric fundus to duodenum, in recording myoelectric signals. It also examines the potential for machine learning algorithms to predict functional states, such as retching and emesis, from GI signal features. Studies were performed using ferrets, a gold standard model for emesis testing. Our results include simultaneous recordings from up to six GI recording sites in both anesthetized and chronically implanted free-moving ferrets. Testing conditions to produce different gastric states included gastric distension, intragastric infusion of emetine (a prototypical emetic agent), and feeding. Despite the observed variability in GI signals, machine learning algorithms, including k nearest neighbors and support vector machines, were able to detect the state of the stomach with high overall accuracy (>80%). The present study is the first demonstration of machine learning algorithms to detect the physiological state of the stomach and onset of retching and could provide insight into methodologies to treat GI diseases and control symptoms such as nausea and vomiting.

neuroscience↗

bioRxiv2019

Dendritic spines on GABAergic neurons respond to cholinergic signaling in the Caenorhabditis elegans motor circuit.

Dendritic spines are specialized postsynaptic structures that detect and integrate presynaptic signals. The shape and number of dendritic spines are regulated by neural activity and correlated with learning and memory. Most studies of spine function have focused on the mammalian nervous system. However, spine-like protrusions have been previously reported in invertebrates, suggesting that the experimental advantages of smaller model organisms could be exploited to study the biology of dendritic spines. Here, we document the presence of dendritic spines in Caenorhabditis elegans motor neurons. We used super-resolution microscopy, electron microscopy, live-cell imaging and genetic manipulation to show that GABAergic motor neurons display functional dendritic spines. Our analysis revealed salient features of dendritic spines: (1) A key role for the actin cytoskeleton in spine morphogenesis; (2) Postsynaptic receptor complexes at the tips of spines in close proximity to presynaptic active zones; (3) Localized postsynaptic calcium transients evoked by presynaptic activity; (4) The presence of endoplasmic reticulum and ribosomes; (5) The regulation of spine density by presynaptic activity. These studies provide a solid foundation for a new experimental paradigm that exploits the power of C. elegans genetics and live-cell imaging for fundamental studies of dendritic spine morphogenesis and function.\n\nHIGHLIGHTS- Spines in C. elegans GABAergic motor neurons are enriched in actin cytoskeleton.\n- Spines are dynamic structures.\n- Spines display Ca++ transients coupled with presynaptic activation.\n- Spine density is regulated during development and is modulated by actin dynamics and cholinergic signaling.

neuroscience↗

bioRxiv2018

NATF (Native And Tissue-specific Fluorescence): A strategy for bright, tissue-specific GFP labeling of native proteins.

GFP labeling by genome editing can reveal the authentic location of a native protein but is frequently hampered by weak GFP signals and broad expression across a range cell types in multicellular animals. To overcome these problems, we engineered a Native And Tissue-specific Fluorescence (NATF) strategy which combines CRISPR/Cas-9 and split-GFP to yield bright, cell-specific protein labeling. We use CRISPR/Cas9 to insert a tandem array of seven copies of the GFP11 {beta}-strand (gfp11x7) at the genomic locus of each target protein. The resultant gfp11x7 knock-in strain is then crossed with separate reporter lines that express the complementing split-GFP fragment (gfp1-10) in specific cell types thus affording tissue-specific labeling of the target protein at its native level. We show that NATF reveals the otherwise undetectable intracellular location of the immunoglobulin protein, OIG-1, and demarcates a receptor auxiliary protein LEV-10 at cell-specific synaptic domains in the C. elegans nervous system.

cell biology↗