Adaptive robustness through incoherent signaling mechanisms in a regenerative brain.

Animal behavior emerges from collective dynamics of neurons, making it vulnerable to damage. Paradoxically, many organisms exhibit a remarkable ability to maintain significant behavior even after large-scale neural injury. Molecular underpinnings of this extreme robustness remain largely unknown. Here, we develop a quantitative pipeline to measure long-lasting latent states in planarian flatworm behaviors during whole-brain regeneration. By combining >20,000 animal trials with neural network modeling, we show that long-range volumetric peptidergic signals allow the planarian to rapidly restore coarse behavior output after large perturbations to the nervous system, while slow restoration of small-molecule neuromodulator functions refines precision. This relies on the different time and length scales of neuropeptide and small-molecule transmission to generate incoherent patterns of neural activity that competitively regulate behavior. Controlling behavior through opposing communication mechanisms creates a more robust system than either alone and may serve as a generalizable approach for constructing robust neural networks.

Adaptive robustness through incoherent signaling mechanisms in a regenerative brain.

Animal behavior emerges from collective dynamics of interconnected neurons, making it vulnerable to connectome damage. Paradoxically, many organisms maintain significant behavioral output after large-scale neural injury. Molecular underpinnings of this extreme robustness remain largely unknown. Here, we develop a quantitative behavioral analysis pipeline to measure previously uncharacterized long-lasting latent memory states in planarian flatworms during whole-brain regeneration. By combining >20,000 animal trials with neural population dynamic modeling, we show that long-range volumetric peptidergic signals allow the planarian to rapidly reestablish latent states and restore coarse behavior after large structural perturbations to the nervous system, while small-molecule neuromodulators gradually refine the precision. The different time and length scales of neuropeptide and small-molecule transmission generate incoherent patterns of neural activity which competitively regulate behavior and memory. Controlling behavior through opposing communication mechanisms creates a more robust system than either alone and may serve as a generic approach to construct robust neural networks.

Cellular diversity and developmental hierarchy in the planarian nervous system.

Our ability to dissect cell type diversity, development, and plasticity in the nervous system has been transformed by the recent surge of massive sequencing studies at the single-cell level. A large body of this work has focused primarily on organisms with nervous systems established early in development. Using planarian flatworms in which neurons are constantly respecified, replenished, and regenerated, we analyze several existing single-cell transcriptomic datasets and observe features in neuron identity, differentiation, maturation, and function that may provide the planarian nervous system with high levels of adaptability required to respond to various cues including injury. This analysis allows us to place many prior observations made by functional characterizations in a general framework and provide additional hypothesis and predictions to test in future investigations.

Ketogenic diet effects on inflammatory allodynia and ongoing pain in rodents.

Ketogenic diets are very low carbohydrate, high fat, moderate protein diets used to treat medication-resistant epilepsy. Growing evidence suggests that one of the ketogenic diet's main mechanisms of action is reducing inflammation. Here, we examined the diet's effects on experimental inflammatory pain in rodent models. Young adult rats and mice were placed on the ketogenic diet or maintained on control diet. After 3-4 weeks on their respective diets, complete Freund's adjuvant (CFA) was injected in one hindpaw to induce inflammation; the contralateral paw was used as the control. Tactile sensitivity (von Frey) and indicators of spontaneous pain were quantified before and after CFA injection. Ketogenic diet treatment significantly reduced tactile allodynia in both rats and mice, though with a species-specific time course. There was a strong trend to reduced spontaneous pain in rats but not mice. These data suggest that ketogenic diets or other ketogenic treatments might be useful treatments for conditions involving inflammatory pain.

Mechanical expansion microscopy.

This chapter describes two mechanical expansion microscopy methods with accompanying step-by-step protocols. The first method, mechanically resolved expansion microscopy, uses non-uniform expansion of partially digested samples to provide the imaging contrast that resolves local mechanical properties. Examining bacterial cell wall with this method, we are able to distinguish bacterial species in mixed populations based on their distinct cell wall rigidity and detect cell wall damage caused by various physiological and chemical perturbations. The second method is mechanically locked expansion microscopy, in which we use a mechanically stable gel network to prevent the original polyacrylate network from shrinking in ionic buffers. This method allows us to use anti-photobleaching buffers in expansion microscopy, enabling detection of novel ultra-structures under the optical diffraction limit through super-resolution single molecule localization microscopy on bacterial cells and whole-mount immunofluorescence imaging in thick animal tissues. We also discuss potential applications and assess future directions.

Ketogenic diet alters dopaminergic activity in the mouse cortex.

The present study was conducted to determine if the ketogenic diet altered basal levels of monoamine neurotransmitters in mice. The catecholamines dopamine (DA) and norephinephrine (NE) and the indolamine serotonin (5HT) were quantified postmortem in six different brain regions of adult mice fed a ketogenic diet for 3 weeks. The dopamine metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) and the serotonin metabolite 5-hydroxyindole acetic acid (5HIAA) were also measured. Tissue punches were collected bilaterally from the motor cortex, somatosensory cortex, nucleus accumbens, anterior caudate-putamen, posterior caudate-putamen and the midbrain. Dopaminergic activity, as measured by the dopamine metabolites to dopamine content ratio - ([DOPAC]+[HVA])/[DA] - was significantly increased in the motor and somatosensory cortex regions of mice fed the ketogenic diet when compared to those same areas in brains of mice fed a normal diet. These results indicate that the ketogenic diet alters the activity of the meso-cortical dopaminergic system, which may contribute to the diet's therapeutic effect in reducing epileptic seizure activity.