Awake Animals Research Articles

Encoding of limb state by single neurons in the cuneate nucleus of awake monkeys.

The cuneate nucleus (CN) is among the first sites along the neuraxis where proprioceptive signals can be integrated, transformed, and modulated. The objective of the study was to characterize the proprioceptive representations in CN. To this end, we recorded from single CN neurons in three monkeys during active reaching and passive limb perturbation. We found that many neurons exhibited responses that were tuned approximately sinusoidally to limb movement direction, as has been found for other sensorimotor neurons. The distribution of their preferred directions (PDs) was highly nonuniform and resembled that of muscle spindles within individual muscles, suggesting that CN neurons typically receive inputs from only a single muscle. We also found that the responses of proprioceptive CN neurons tended to be modestly amplified during active reaching movements compared to passive limb perturbations, in contrast to cutaneous CN neurons whose responses were not systematically different in the active and passive conditions. Somatosensory signals thus seem to be subject to a "spotlighting" of relevant sensory information rather than uniform suppression as has been suggested previously.NEW & NOTEWORTHY The cuneate nucleus (CN) is the somatosensory gateway into the brain, and only recently has it been possible to record these signals from an awake animal. We recorded single CN neurons in monkeys. Proprioceptive CN neurons appear to receive input from very few muscles, and their sensitivity to movement changes reliably during reaching relative to passive arm perturbations. Sensitivity is generally increased, but not exclusively so, as though CN "spotlights" critical proprioceptive information during reaching.

Low Dose Ampakine Stimulates Diaphragm Activity and Increases Tidal Volume following Cervical Spinal Cord Injury in Non‐Anesthetized Freely Behaving Rats

Sabhya Rana1, 2, 3, Michael D. Sunshine1, 2, 3, David D. Fuller1, 2, 3 1Department of Physical Therapy, 2Center for Respiratory Research and Rehabilitation, 3McKnight Brain Institute, University of Florida, Gainesville, FL Ampakines are allosteric modulators of AMPA receptor channel kinetics, and can stimulate breathing during hypoventilation such as following opioid overdose or in neuromuscular disorders. Our laboratory has shown that acute treatment with an ampakine, CX717 can increase inspiratory phrenic motor output in rat models of incomplete cervical spinal cord injury (SCI), when studied under anesthesia. The next step in the translational pathway to is to determine if the drugs are safe and effective in the awake animal. The goal of the current work was to evaluate the effect of two low impact ampakines (CX717 and CX1739) on diaphragm muscle activation and breathing in freely moving non-anesthetized rats following SCI. Ventilation and metabolic rate (VCO2) were measured using whole body plethysmography and diaphragm EMG was assessed using in-dwelling muscle electrodes. At 4 and 14 days following C2 spinal hemisection injury (C2Hx), rats were given a single intravenous bolus of CX717 (5 mg/kg, n=8), CX1739 (5 mg/kg, n=8) or vehicle (2-hydroxypropyl-beta-cyclodextrin; HPCD; n=8). At the 4-day time point, infusion of CX717 or CX1739 increased peak diaphragm EMG (recorded ipsilateral to C2Hx) by 40-60% compared to vehicle. However, only the CX1739 group showed an accompanying increase in tidal volume (20%). During an acute respiratory challenge with hypoxia-hypercapnia (10% O2, 7% CO2), both the CX717 and CX1739 groups showed increased diaphragm EMG compared to vehicle (65-75%); the CX1739 group showed a larger increase in tidal volume. At 14 days post injury, CX717 infusion increased the peak inspiratory ipsilateral diaphragm EMG activity (~30%) and tidal volume (~20%) during baseline breathing. In contrast, CX1739 was less effective at 14 days and produced an increase in ipsilateral diaphragm EMG activity of ~10% with no change in tidal volume. During the hypoxia-hypercapnia challenge, both the CX1739 and CX717 groups showed increased ipsi-lesional diaphragm EMG (25-35%) but no increase in tidal volume as compared to vehicle group. Neither ampakine had an impact on respiratory rate at either time point, suggesting a spinal (vs. medullary) mechanism of action. Additionally, no adverse off-target effects (e.g., changes in heart rate or hypoactive state) were apparent. Improved respiratory muscle activation is often a desirable therapeutic outcome after incomplete cervical SCI. Our data indicate that low dose, low impact ampakine treatment can increase diaphragm muscle output after cervical SCI, and therefore may provide a pharmacologic strategy that could be useful in the context of respiratory rehabilitation. The divergent response to CX717 vs. CX1739 at 4 vs. 14 days post-injury merits further study; one possibility is that ongoing neuroplastic changes in AMPA receptor expression after SCI may differentially influence the efficacy of different ampakines.

Stress enhances hippocampal neuronal synchrony and alters ripple-spike interaction

Adverse effects of chronic stress include anxiety, depression, and memory deficits. Some of these stress-induced behavioural deficits are mediated by impaired hippocampal function. Much of our current understanding about how stress affects the hippocampus has been derived from post-mortem analyses of brain slices at fixed time points. Consequently, neural signatures of an ongoing stressful experiences in the intact brain of awake animals and their links to later hippocampal dysfunction remain poorly understood. Further, no information is available on the impact of stress on sharp-wave ripples (SPW-Rs), high frequency oscillation transients crucial for memory consolidation. Here, we used in vivo tetrode recordings to analyze the dynamic impact of 10 days of immobilization stress on neural activity in area CA1 of mice. While there was a net decrease in pyramidal cell activity in stressed animals, a greater fraction of CA1 spikes occurred specifically during sharp-wave ripples, resulting in an increase in neuronal synchrony. After repeated stress some of these alterations were visible during rest even in the absence of stress. These findings offer new insights into stress-induced changes in ripple-spike interactions and mechanisms through which chronic stress may interfere with subsequent information processing.

State-space optimal feedback control of optogenetically driven neural activity

Objective. The rapid acceleration of tools for recording neuronal populations and targeted optogenetic manipulation has enabled real-time, feedback control of neuronal circuits in the brain. Continuously-graded control of measured neuronal activity poses a wide range of technical challenges, which we address through a combination of optogenetic stimulation and a state-space optimal control framework implemented in the thalamocortical circuit of the awake mouse. Approach. Closed-loop optogenetic control of neurons was performed in real-time via stimulation of channelrhodopsin-2 expressed in the somatosensory thalamus of the head-fixed mouse. A state-space linear dynamical system model structure was used to approximate the light-to-spiking input-output relationship in both single-neuron as well as multi-neuron scenarios when recording from multielectrode arrays. These models were utilized to design state feedback controller gains by way of linear quadratic optimal control and were also used online for estimation of state feedback, where a parameter-adaptive Kalman filter provided robustness to model-mismatch. Main results. This model-based control scheme proved effective for feedback control of single-neuron firing rate in the thalamus of awake animals. Notably, the graded optical actuation utilized here did not synchronize simultaneously recorded neurons, but heterogeneity across the neuronal population resulted in a varied response to stimulation. Simulated multi-output feedback control provided better control of a heterogeneous population and demonstrated how the approach generalizes beyond single-neuron applications. Significance. To our knowledge, this work represents the first experimental application of state space model-based feedback control for optogenetic stimulation. In combination with linear quadratic optimal control, the approaches laid out and tested here should generalize to future problems involving the control of highly complex neural circuits. More generally, feedback control of neuronal circuits opens the door to adaptively interacting with the dynamics underlying sensory, motor, and cognitive signaling, enabling a deeper understanding of circuit function and ultimately the control of function in the face of injury or disease.

Effect of the combined administration of metoprolol and dihydroquercetin on the rheological properties of blood in spontaneously hypertensive rats (SHRs)

Introduction. Hyperviscosity syndrome plays an important role in the pathogenesis of arterial hypertension and its complications associated with impaired microcirculation in target organs. Therefore, along with the use of antihypertensive drugs, it is important to pay attention to the correction of the hyperviscosity syndrome with means of hemorheological agents.The aimis to study the effect of metoprolol and its combined use with dihydroquercetin (DHQ) on the rheological parameters of blood in rats with spontaneous arterial hypertension.Materials and methods. The experiments were carried out on normotensive male Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs). SHRs of the experimental groups received metoprolol (50 mg/kg) or metoprolol and DHQ (50 mg/kg each) daily intragastrically for 6 weeks in 1 % starch mucus; SHRs of the control group and normotensive rats received 1 % starch mucus according to the same scheme. Systemic blood pressure was registered in awake animals. Blood was sampled from the catheterized right common carotid artery. Blood viscosity, plasma viscosity, hematocrit, erythrocyte aggregation and deformability were studied.Results. Compared with the parameters in normotensive rats, SHRs showed significant increase of blood viscosity, hematocrit, erythrocyte aggregation, and decrease of erythrocyte deformability. The course administration of metoprolol induced to a further increase in blood viscosity at low shear rates (15–45 s–1); plasma viscosity, hematocrit and micro-rheological parameters in rats of this group did not significantly differ from those in the control. With the combined administration of metoprolol and DHQ, blood viscosity at shear rates of 300 and 450 s–1and erythrocyte aggregation were significantly lower than in the control SHRs.Conclusions. The course administration of metoprolol increases the severity of the hyperviscosity syndrome in SHRs. The use of DHQ together with metoprolol partially eliminates adverse effects of the beta blocker on blood rheology parameters.

Orexin/Hypocretin and MCH Neurons: Cognitive and Motor Roles Beyond Arousal.

The lateral hypothalamus (LH) is classically implicated in sleep-wake control. It is the main source of orexin/hypocretin and melanin-concentrating hormone (MCH) neuropeptides in the brain, which have been both implicated in arousal state switching. These neuropeptides are produced by non-overlapping LH neurons, which both project widely throughout the brain, where release of orexin and MCH activates specific postsynaptic G-protein-coupled receptors. Optogenetic manipulations of orexin and MCH neurons during sleep indicate that they promote awakening and REM sleep, respectively. However, recordings from orexin and MCH neurons in awake, moving animals suggest that they also act outside sleep/wake switching. Here, we review recent studies showing that both orexin and MCH neurons can rapidly (sub-second-timescale) change their firing when awake animals experience external stimuli, or during self-paced exploration of objects and places. However, the sensory-behavioral correlates of orexin and MCH neural activation can be quite different. Orexin neurons are generally more dynamic, with about 2/3rds of them activated before and during self-initiated running, and most activated by sensory stimulation across sensory modalities. MCH neurons are activated in a more select manner, for example upon self-paced investigation of novel objects and by certain other novel stimuli. We discuss optogenetic and chemogenetic manipulations of orexin and MCH neurons, which combined with pharmacological blockade of orexin and MCH receptors, imply that these rapid LH dynamics shape fundamental cognitive and motor processes due to orexin and MCH neuropeptide actions in the awake brain. Finally, we contemplate whether the awake control of psychomotor brain functions by orexin and MCH are distinct from their “arousal” effects.

Towards chronic deep brain stimulation in freely moving hemiparkinsonian rats: applicability and functionality of a fully implantable stimulation system

Objective. This study aimed at investigating a novel fully implantable deep brain stimulation (DBS) system and its ability to modulate brain metabolism and behavior through subthalamic nucleus (STN) stimulation in a hemiparkinsonian rat model. Approach. Twelve male rats were unilaterally lesioned with 6-hydroxydopamine in the medial forebrain bundle and received a fully implantable DBS system aiming at the ipsilesional STN. Each rat underwent three cylinder tests to analyze front paw use: a PRE test before any surgical intervention, an OFF test after surgery but before stimulation onset and an ON test under DBS. To visualize brain glucose metabolism in the awake animal, two [18F]FDG scans were conducted in the OFF and ON condition. At least 4 weeks after surgery, an [18F]FDOPA scan was used to check for dopaminergic integrity. Main results. In general, STN DBS increased [18F]FDG uptake ipsilesionally and decreased it contralesionally. More specifically, bilateral orbitofrontal cortex, ipsilateral caudate putamen, sensorimotor cortex and nucleus accumbens showed significantly higher tracer uptake in ON compared to OFF condition. Contralateral cingulate and secondary motor cortex, caudate putamen, amygdala, hippocampus, retrosplenial granular cortex, superior colliculus, and parts of the cerebellum exhibited significantly higher [18F]FDG uptake in the OFF condition. On the behavioral level, stimulation was able improve use of the contralesional affected front paw suggesting an effective stimulation produced by the implanted system. Significance. The fully implantable stimulation system developed by us and presented here offers the output of arbitrary user-defined waveforms, patterns and stimulation settings and allows tracer accumulation in freely moving animals. It is therefore a suitable device for implementing behavioral PET studies. It contributes immensely to the possibilities to characterize and unveil the effects and mechanisms of DBS offering valuable clues for future improvements of this therapy.

Distributed chromatic processing at the interface between retina and brain in the larval zebrafish

Larval zebrafish (Danio rerio) are an ideal organism for studying color vision, as their retina possesses four types of cone photoreceptors, covering most of the visible range and into the UV.1,2 Additionally, their eye and nervous systems are accessible to imaging, given that they are naturally transparent.3-5 Recent studies have found that, through a set of wavelength-range-specific horizontal, bipolar, and retinal ganglion cells (RGCs),6-9 the eye relays tetrachromatic information to several retinorecipient areas (RAs).10-13 The main RA is the optic tectum, receiving 97% of the RGC axons via the neuropil mass termed arborization field 10 (AF10).14,15 Here, we aim to understand the processing of chromatic signals at the interface between RGCs and their major brain targets. We used 2-photon calcium imaging to separately measure the responses of RGCs and neurons in the brain to four different chromatic stimuli in awake animals. We find that chromatic information is widespread throughout the brain, with a large variety of responses among RGCs, and an even greater diversity in their targets. Specific combinations of response types are enriched in specific nuclei, but there is no single color processing structure. In the main interface in this pathway, the connection between AF10 and tectum, we observe key elements of neural processing, such as enhanced signal decorrelation and improved chromatic decoding.16,17 A richer stimulus set revealed that these enhancements occur in the context of a more distributed code in tectum, facilitating chromatic signal association in this small vertebrate brain.

Assessment of Corticospinal Excitability in Awake Rodents Using EMG-Controlled Intracortical Stimulation.

Assessment of corticospinal excitability (CSE) is an essential component of experiments designed to induce or study neuronal plasticity in the motor system. Common examples are paired associative stimulation (PAS), theta-burst stimulation (TBS), intensive motor training, or any methods aimed at potentiating the corticomotor system in the hope of promoting better recovery after neurological insult. To date, rodent models of CSE assessment have mostly been completed under anaesthesia, which greatly affects the level of CSE, as well as the mechanisms of plasticity. Experiments in awake animals are difficult because the ongoing state of behavior affects the excitability of the motor system and complicates the assessment of CSE. To address this issue, we have designed a novel approach for CSE assessment in awake behaving rodents, enabling a reliable measure of evoked motor responses obtained from cortical microstimulation in repeatable conditions of ongoing motor activity. The system relies on chronically implanted intracortical and intramuscular electrodes and a custom-made software control system, enabling the user to require that precise parameters of EMG activity be met before cortical stimulation probes are delivered. This approach could be used for further studies of PAS, TBS or other interventions requiring the assessment of CSE under repeatable conditions. We provide fabrication schematics and a list of materials for the implant, as well as instructions for running a custom-made MATLAB codebase, customizing the PAS protocol, and performing the complete analysis of experimental data. We hope these tools can further facilitate animal research in the field of neuroplasticity and neurorehabilitation.

Eosinophils in Asthma Models to House Dust Mite for Drug Development.

Murine models of asthma are developed to better understand the mechanisms of asthma including eosinophil recruitment in the airways with the aim of evaluating new therapeutic strategies. They are intended to model the typical features of human disease, in particular airway inflammation, hyperresponsiveness (AHR), and remodeling. The phenotype of inflammatory cells recovered from the bronchoalveolar lavage fluid (BAL) is studied with innovative flow cytometry techniques while airway obstruction is measured using the forced oscillation technique, and airway responsiveness approached by barometric plethysmography in awake and unconstrained animals. We here describe models of asthma of house dust mite (HDM) as a clinically relevant allergen: a short study design (8days) model of hypereosinophilic asthma and a chronic (31days) asthma model, both suitable to evaluate the potential of new drug candidates to prevent allergic asthma.

Impact of chronic transcranial random noise stimulation (tRNS) on GABAergic and glutamatergic activity markers in the prefrontal cortex of juvenile mice.

Transcranial random noise stimulation (tRNS), a non-invasive neuromodulatory technique capable of altering cortical activity, has been proposed to improve the signal-to-noise ratio at the neuronal level and the sensitivity of the neurons following an inverted U-function. The aim of this study was to examine the effects of tRNS on vGLUT1 and GAD 65-67 and its safety in terms of pathological changes. For that, juvenile mice were randomly distributed in three different groups: "tRNS 1×" receiving tRNS at the density current used in humans (0.3A/m2, 20min), "tRNS 100×" receiving tRNS at two orders of magnitude higher (30.0A/m2, 20min) and "sham" (0.3A/m2, 15s). Nine tRNS sessions during 5 weeks were administered to the prefrontal cortex of awake animals. No detectable tissue macroscopic lesions were observed after tRNS sessions. Post-stimulation immunohistochemical analysis of GAD 65-67 and vGLUT1 immunoreactivity showed reduced GAD 65-67 immunoreactivity levels in the region directly beneath the electrode for tRNS 1× group with no significant effects in the tRNS 100× nor sham group. The observed results suggest an excitatory effect associated with a decrease in GABA levels in absence of major histopathological alterations providing a novel mechanistic explanation for tRNS effects.

Multimodal Functional Analysis Platform: 3. Spherical Treadmill System for Small Animals.

In the application of advanced neuroscience techniques including optogenetics to small awake animals, it is often necessary to restrict the animal's movements. A spherical treadmill is a beneficial option that enables virtual locomotion of body- or head-restrained small animals. Besides, it has a wide application range, including virtual reality experiments. This chapter describes the fundamentals of a spherical treadmill for researchers who want to start experiments with it. First, we describe the physical aspect of a spherical treadmill based on the simple mechanical analysis. Next, we explain the basics of data logging and preprocessing for behavioral analysis. We also provide simple computer programs that work for the purpose.

Motivated displacement assay distinguishes ALA neuron mutants from RIS neuron mutants during recovery from heat stress in Caenorhabditis elegans.

The interneurons ALA and RIS both regulate stress induced sleep in C. elegans but their roles in awake animal movement has been reported to differ. We describe the development of a motivated mobility-based assay that distinguishes between animals mutant for ALA function and those mutant for RIS function.

Dendritic coincidence detection in Purkinje neurons of awake mice.

Dendritic coincidence detection is fundamental to neuronal processing yet remains largely unexplored in awake animals. Specifically, the underlying dendritic voltage-calcium relationship has not been directly addressed. Here, using simultaneous voltage and calcium two-photon imaging of Purkinje neuron spiny dendrites, we show how coincident synaptic inputs and resulting dendritic spikes modulate dendritic calcium signaling during sensory stimulation in awake mice. Sensory stimulation increased the rate of postsynaptic potentials and dendritic calcium spikes evoked by climbing fiber and parallel fiber synaptic input. These inputs are integrated in a time-dependent and nonlinear fashion to enhance the sensory-evoked dendritic calcium signal. Intrinsic supralinear dendritic mechanisms, including voltage-gated calcium channels and metabotropic glutamate receptors, are recruited cooperatively to expand the dynamic range of sensory-evoked dendritic calcium signals. This establishes how dendrites can use multiple interplaying mechanisms to perform coincidence detection, as a fundamental and ongoing feature of dendritic integration in behaving animals.

Locus coeruleus in memory formation and Alzheimer's disease.

Catecholamine neurons of the locus coeruleus (LC) in the dorsal pontine tegmentum innervate the entire neuroaxis, with signaling actions implicated in the regulation of attention, arousal, sleep–wake cycle, learning, memory, anxiety, pain, mood, and brain metabolism. The co‐release of norepinephrine (NE) and dopamine (DA) from LC terminals in the hippocampus plays a role in all stages of hippocampal‐memory processing. This catecholaminergic regulation modulates the encoding, consolidation, retrieval, and reversal of hippocampus‐based memory. LC neurons in awake animals have two distinct firing modes: tonic firing (explorative) and phasic firing (exploitative). These two firing modes exert different modulatory effects on post‐synaptic dendritic spines. In the hippocampus, the firing modes regulate long‐term potentiation (LTP) and long‐term depression, which differentially regulate the mRNA expression and transcription of plasticity‐related proteins (PRPs). These proteins aid in structural alterations of dendritic spines, that is, structural long‐term potentiation (sLTP), via expansion and structural long‐term depression (sLTD) via contraction of post‐synaptic dendritic spines. Given the LC's role in all phases of memory processing, the degeneration of 50% of the LC neuron population occurring in Alzheimer's disease (AD) is a clinically relevant aspect of disease pathology. The loss of catecholaminergic regulation contributes to dysfunction in memory processes along with impaired functions associated with attention and task completion. The multifaceted role of the LC in memory and general task performance and the close correlation of LC degeneration with neurodegenerative disease progression together implicate it as a target for new clinical assessment tools.

In vivo analysis of the spontaneous firing of cerebellar Purkinje cells in awake transgenic mice that model spinocerebellar ataxia type 2

Cerebellar Purkinje cells (PCs) fire spontaneously in a tonic mode, although the precision of this pacemaking activity is disturbed in many abnormal conditions involving cerebellar atrophy, such as many spinocerebellar ataxias (SCAs). In our previous studies we used the single-unit extracellular recording method to analyze spontaneous PC firing in vivo in the anesthetized SCA2-58Q transgenic mice. We realized that PCs from aging SCA2-58Q mice fire much less regularly compared to PCs from their wild type (WT) littermates and this abnormal activity can be reversed with an intraperitoneal (i. p.) injection of SK channel-positive modulator chlorzoxazone (CHZ). Here we used the same single-unit extracellular recording method to analyze the spontaneous firing in vivo in awake SCA2-58Q transgenic mice. For this purpose, we used the Mobile HomeCage (Neurotar, Finland) floating platform to immobilize the experimental animal's head during the recording sessions. We discovered that generally PCs from awake animals fired much more frequently and much less regularly than previously observed PCs from anesthetized animals. In vivo recordings from awake SCA2/WT mice revealed that complex spikes, which are generated by PCs in reply to the excitation coming by climbing fibers, as well as simple spikes, were much less frequent in SCA2 mice compared to their WT littermates. To test the effect of the SK channel positive modulation on the PCs firing activity in awake SCA2 mice and also the effect on their motor coordination, we started the CHZ trial in these mice. We discovered that the long-term i. p. injections of CHZ did not affect the spike generation in SCA2-58Q mice, however, they did recover the precision of this spontaneous pacemaking activity. Furthermore, we also showed that treatment with CHZ alleviated the age-dependent motor impairment in SCA2-58Q mice. We propose that the lack of precision in PC spike generation might be a key cause for the progression of ataxic symptoms in different SCAs and that the activation of calcium-activated potassium channels, including SK channels, can be used as a potential way to treat SCAs on the physiological level of the disease.

Transient loss of interhemispheric functional connectivity following unilateral cortical spreading depression in awake rats.

Growing evidence shows a critical role of network disturbances in the pathogenesis of migraine. Unilateral pattern of neurological symptoms of aura suggests disruption of interhemispheric interactions during the early phase of a migraine attack. Using local field potentials data from the visual and motor cortices, this study explored effects of unilateral cortical spreading depression, the likely pathophysiological mechanism of migraine aura, on interhemispheric functional connectivity in freely behaving rats. Temporal evolution of the functional connectivity was evaluated using mutual information and phase synchronization measures applied to local field potentials recordings obtained in homotopic points of the motor and visual cortices of the two hemispheres in freely behaving rats after induction of a single unilateral cortical spreading depression in the somatosensory S1 cortex and sham cortical stimulation. Cortical spreading depression was followed by a dramatic broadband loss of interhemispheric functional connectivity in the visual and motor regions of the cortex. The hemispheric disconnection started after the end of the depolarization phase of cortical spreading depression, progressed gradually, and terminated by 5 min after initiation of cortical spreading depression. The network impairment had region- and frequency-specific characteristics and was more pronounced in the visual cortex than in the motor cortex. The period of impaired neural synchrony coincided with post-cortical spreading depression electrographic aberrant activation of the ipsilateral cortex and abnormal behavior. The study provides the first evidence that unilateral cortical spreading depression induces a reversible loss of functional hemispheric connectivity in the cortex of awake animals. Given a critical role of long-distance cortical synchronization in sensory processing and sensorimotor integration, the post-cortical spreading depression breakdown of functional connectivity may contribute to neuropathological mechanisms of aura generation.

Behavioral Assessment of Visual Function via Optomotor Response and Cognitive Function via Y-Maze in Diabetic Rats.

The optomotor response and the Y-maze are behavioral tests useful for assessing visual and cognitive function, respectively. The optomotor response is a valuable tool to track changes in spatial frequency (SF) and contrast sensitivity (CS) thresholds over time in a number of retinal disease models, including diabetic retinopathy. Similarly, the Y-maze can be used to monitor spatial cognition (as measured by spontaneous alternation) and exploratory behavior (as measured by a number of entries) in a number of disease models that affect the central nervous system. Advantages of the optomotor response and the Y-maze include sensitivity, speed of testing, the use of innate responses (training is not needed), and the ability to be performed on awake (non-anesthetized) animals. Here, protocols are described for both the optomotor response and the Y-maze and examples of their use shown in models of Type I and Type II diabetes. Methods include preparation of rodents and equipment, performance of the optomotor response and the Y-maze, and post-test data analysis.

Non-contact capacitive sensing for ECG recording in small animals

Rat electrocardiography (ECG) is frequently used in biomedical research as a model for exploring heart function in a wide variety of experimental conditions. Subcutaneous ECG is a common approach to record rat heart rhythm using implanted needle electrodes to sense the rat ECG signals with the animal under deep anesthesia. However, such an invasive measurement could cause inconvenience due to cumbersome animal preparation, and the anesthetics are likely to interfere with the autonomic regulation of cardiac rhythm. Most studies used the galvanic contact between animal limb and electrode sensing surface to record cardiac signals from small animals. However, the non-contact approach of capacitive ECG sensing for small laboratory animals has not been extensively investigated. This study aims to develop a non-contact ECG system to promote the ECG measurement of laboratory animals for biomedical research. The method utilizes the capacitive coupling technique to detect cardiac signals in awake rats (R-wave amplitude of only 0.2 mV) through a non-conductive layer. The proposed system generates non-contact ECG signals with distinguishable R-peaks at a limb-electrode capacitance above 8.5 pF and maximum through-thickness of the non-conductive layer of 0.4 mm for heart rate assessment. In conclusion, this study provides non-contact ECG monitoring based on capacitive electrodes to improve the throughput of ECG measurement procedures for biomedical research and establish a lower bound of coupling capacitance for non-contact application to heart rate. The new method is ideally suited for the rapid evaluation of autonomic regulation of heart rhythm in awake laboratory small animals.

Neuroimaging reveals functionally distinct neuronal networks associated with high-level alcohol consumption in two genetic rat models.

Human imaging data suggest that the motivational processes associated with alcohol reward are reflected in the patterns of neural activation after alcohol or alcohol-related cues. In animal models of alcohol drinking, however, the changes in brain activation during voluntary alcohol ingestion are poorly known. In order to improve the translational utility of animal models, we examined alcohol-induced functional brain activation in Alko Alcohol (AA) and Marchigian-Sardinian alcohol-preferring (msP) rats that drink voluntarily high levels of alcohol, but exhibit widely different neurochemical and behavioral traits cosegregated with alcohol preference. Brain imaging was performed using manganese-enhanced MRI (MEMRI), which is based on accumulation of Mn2+ ions in activated neurons, allowing the identification of functional neuronal networks recruited during specific behaviors in awake animals during a subsequent imaging session under anesthesia. MEMRI was performed following 4 weeks of voluntary alcohol drinking, using water drinking as the control. Despite similar levels of alcohol drinking, strikingly different alcohol-induced neuronal activity patterns were observed in AA and msP rats. Overall, functional activation in the AA rats was more widespread, involving large cortical areas and subcortical structures, such as the bed nucleus of the stria terminalis, preoptic area, hypothalamus, periaqueductal grey, and substantia nigra. In the msP rats, however, alcohol-related activation was largely confined to prefrontal cortical regions and insular cortex, and olfactory areas. Overlapping areas of activation found in both rat lines included the nucleus accumbens, prelimbic, orbital, and insular cortex. In conclusion, our data reveal strikingly different brain circuits associated with alcohol drinking in two genetically different rat lines and suggest innately different motivational and behavioral processes driving alcohol drinking. These findings have important implications for the use of these lines in translational alcohol research.