3. Because we’re all about that mouse, ‘bout that mouse, and gerbil….. ♫ ‘
There is a growing awareness of the link between compromised heart function and nervous system abnormalities. This point is beautifully conveyed in a poster presented by Dr. Anand Pandey and colleagues this coming Sunday at SfN. We are particularly excited to see how treadmill locomotion in rats is affected after cardiac arrest.
Often, non-invasive in vivo data about the cardiovascular system in awake laboratory animals are absent from many studies. For example, a recent publication described heart failure in diabetic mice to demonstrate that early down regulation of pro-survival protein Pim-1 plays a major role in accelerating the progression of cardiomyopathy (1). In vivo heart monitoring could have revealed whether the cardiomyopathy was associated with reductions in heart rate (HR) variability (HRV), as seen in patients with heart failure (2). Another recent publication studied mice after transaortic artery constriction-induced heart failure to demonstrate that inhibition of miR-25 improves cardiac contractility(3). Here again, this beautiful study could easily have incorporated elegantly collected electrocardiographic data to further characterize the extent of heart failure in awake animals.
The absence of awake preclinical electrocardiographic data may be due to the perception that recording the ECG in awake mice requires expensive instrumentation, anesthetic, and surgery. The ECGenie, however, makes it incredibly simple to make ECG recordings in awake lab animals. When you or I enter the physician’s office for a checkup, we do not expect to be anesthetized to have our ECG recorded. Many researchers, however, believe they need to resort to anesthesia, and surgical implantation of radio transmitters, for recording ECG in conscious mice. However, this if often not possible in fragile mice, and in any case requires up to 3 weeks for the animals to recover from the painful surgery. Moreover, a recent study suggests that the implanted transmitters themselves may result in an immune response and infection (4). With the ECGenie, it is no longer necessary to anesthetize or perform surgery on laboratory animals to obtain a complete set of ECG data, including heart rate, all of the PQRST interval durations, and heart rate variability, in the time and frequency domains. The ECGenie provides the same ECG data as provided by surgically implanted transmitters, but faster, sooner, in tiny lab animals at a fraction of the cost.
“… ‘bout that mouse, and gerbil….
“Mouse Specifics” has a better “ring” to the company’s name than does “Gerbil Specifics”, though MSI’s life sciences instrumentation applies to the non-invasive study of numerous small animals, including gerbils. Because researchers have described extensive complications, morbidity, and mortality associated with the implantation of radiotransmitters in small gerbils (5) we have extended the ECGenie instrumentation to non-invasively record ECG in awake gerbils as well. The Mongolian gerbil provides an excellent model of iron-overload cardiomyopathy (6). Cardiac disease with arrhythmia or heart failure is the leading cause of death in patients with thalassemia major and a complication of other forms of iron overload (7). Several poster presentations at the upcoming SfN 2014 congress describe the role of iron accumulation in animal models of stroke [Program#/Poster#: 143.19/V5], Huntington’s disease [Program#/Poster#: 46.17/L1], and ALS [Program#/Poster#: 696.08/F9]. Iron overload via injections of iron-dextran in gerbils produced prolongation of the PR interval and bradycardia in early stages and prolongation of the QT interval, premature ventricular contractions, variable degrees of atrioventricular block, changes in the ST segment, and T-wave inversion at later stages coinciding with the development of heart failure (8). Iron overload in mice also results in cardiac rhythm changes and electrocardiographic abnormalities (9) detectable by the ECGenie.
The gerbil is also used extensively in stroke research because of its organization of its cerebral circulation in that it does not have a circle of Willis, unlike other laboratory animals. The brain of the gerbil, therefore, can be made more completely and uniformly ischemic by carotid artery occlusion. For example, the iridoid glycoside catalpol was recently shown to be neuroprotective in gerbils following stroke (10). At the upcoming SfN 2014 meeting, Dr. Kim and colleagues from Seoul demonstrate the protective benefits of garlic after stroke in the gerbil. Changes in heart rate were shown to be prognostic of survival following ligation of one common carotid artery in gerbils (11). The ECGenie, therefore, could be a useful instrument for monitoring stroke outcome in gerbils, as it has been for mice (12).
As Dr. Pandey and many presenters reveal, many neurological disorders present with both cardiac and motor function anomalies. It is important, therefore, to consider how deficits in cardiac function can affect motor function. Extending the ECGenie and DigiGait technologies to apply to all laboratory animals and numerous disease areas reflects our commitment to making our products as accessible and translatable as possible.
“Because you know we’re all about that mouse, …and gerbil!”
- Moore A, Shindikar A, Fomison-Nurse I, Riu F, Munasinghe PE, Ram TP, Saxena P, Coffey S, Bunton RW, Galvin IF, Williams MJ, Emanueli C, Madeddu P, Katare R. Rapid onset of cardiomyopathy in STZ-induced female diabetic mice involves the downregulation of pro-survival Pim-1. Cardiovasc Diabetol. 2014 Apr 1;13:68.
- Liu G, Wang L, Wang Q, Zhou G, Wang Y, Jiang Q. A new approach to detect congestive heart failure using short-term heart rate variability measures. PLoS One. 2014 Apr 18;9(4):e93399.
- Wahlquist C, Jeong D, Rojas-Muñoz A, Kho C, Lee A, Mitsuyama S, van Mil A, Park WJ, Sluijter JP, Doevendans PA, Hajjar RJ, Mercola M. Inhibition of miR-25 improves cardiac contractility in the failing heart. Nature. 2014 Apr 24;508(7497):531-5.
- Gaskill BN, Gordon CJ, Pajor EA, Lucas JR, Davis JK, Garner JP. Impact of nesting material on mouse body temperature and physiology. Physiol Behav. 2013 Feb 17; 110-111:87-95.
- Moons CP, Hermans K, Remie R, Duchateau L, Odberg FO. Intraperitoneal versus subcutaneous telemetry devices in young Mongolian gerbils (Meriones unguiculatus). Lab Anim. 2007 Apr;41(2):262-9.
- Carthew P, Dorman BM, Edwards RE, Francis JE, Smith AG. A unique rodent model for both the cardiotoxic and hepatotoxic effects of prolonged iron overload. Lab Invest. 1993 Aug;69(2):217-22.
- Laurita KR, Chuck ET, Yang T, Dong WQ, Kuryshev YA, Brittenham GM, Rosenbaum DS, Brown AM. Optical mapping reveals conduction slowing and impulse block in iron-overload cardiomyopathy. J Lab Clin Med. 2003 Aug;142(2):83-9.
- Obejero-Paz CA, Yang T, Dong WQ, Levy MN, Brittenham GM, Kuryshev YA, Brown AM. Deferoxamine promotes survival and prevents electrocardiographic abnormalities in the gerbil model of iron-overload cardiomyopathy. J Lab Clin Med. 2003 Feb;141(2):121-30.
- Rose RA, Sellan M, Simpson JA, Izaddoustdar F, Cifelli C, Panama BK, Davis M, Zhao D, Markhani M, Murphy GG, Striessnig J, Liu PP, Heximer SP, Backx PH. Iron overload decreases CaV1.3-dependent L-type Ca2+ currents leading to bradycardia, altered electrical conduction, and atrial fibrillation. Circ Arrhythm Electrophysiol. 2011 Oct;4(5):733-42.
- Liu YR, Li PW, Suo JJ, Sun Y, Zhang BA, Lu H, Zhu HC, Zhang GB. J Pharm Pharmacol. 2014 Sep;66(9):1265-70. Catalpol provides protective effects against cerebral ischaemia/reperfusion injury in gerbils.
- Laas R. Common carotid artery stump pressure in the gerbil stroke model. J Neurol Neurosurg Psychiatry. 1984 Apr;47(4):365-71.
- Lubjuhn J, Gastens A, von Wilpert G, Bargiotas P, Herrmann O, Murikinati S, Rabie T, Marti HH, Amende I, Hampton TG, Schwaninger M. Functional testing in a mouse stroke model induced by occlusion of the distal middle cerebral artery. J Neurosci Methods. 2009 Oct 30;184(1):95-103.
2. Autism Spectrum Disorder and Gait Disturbances
There is increasing awareness of impairment of motor control and motor learning in subjects with Autism Spectrum Disorder (ASD). Observations of disturbed gait in autistic adults and children suggest cerebellar abnormalities may contribute to the aberrant motor symptoms. To investigate, Dr. Claire Piochon and her colleagues at the University of Chicago studied gait (The DigiGait Imaging System) in a mouse model for the human 15q11-13 duplication, one of the most frequent and penetrant genetic abnormalities in autism in humans. In mice with a paternally inherited duplication (patDp/+), ASD-resembling behaviors, including poor social interaction and behavioral inflexibility, have been described.
Here, Dr. Piochon et al. show that delay eye blink conditioning, a form of cerebellum-dependent associative motor learning, and gait control are impaired in patDp/+ mice. Long-term potentiation (LTP) at parallel fiber Purkinje cell synapses was intact, but long-term-depression (LTD) is prevented at these synapses; LTP is induced instead. The elimination of surplus climbing fiber inputs, a synaptic pruning process that provides a critical step in the development of cerebellar circuits, is impaired.
15q11-13 duplication, therefore, affects synaptic plasticity in the developing and adult cerebellum as well as cerebellum-dependent motor learning. These findings identify cerebellar abnormalities that may contribute to gait disturbances and possibly non-motor symptoms in autism. Deficits in synaptic pruning and plasticity may potentiate abnormal synapse and circuit development throughout the autistic brain. It may be interesting to study gait in these mice at a very young age (e.g., PND14) since the specificity of motor disturbances in autistic infants (e.g., postural asymmetry) is consistent with cerebellar involvement (1).
- Esposito G, Venuti P, Apicella F, Muratori F. Analysis of unsupported gait in toddlers with autism. Brain Dev. 2011 May;33(5):367-73.
- Cold Feet
Dr. Adam Thrasher and Raul Amador present very interesting data regarding sensory input impairment during walking in humans. Little is known regarding how reduced sensation and perturbations in proprioception affect ground reaction forces during the stance phase. Such is important to individuals with pathological conditions such as diabetic neuropathy or limb ischemia. It may also be of interest to space travel, shoe design, and ambulation in the elderly. High loading rates can cause injury so understanding and modulating such could be useful to prevent injuries.
Amador and Thrasher describe an elegant experiment in which they simply numbed, with ice cold water, the left plantar surface of healthy adults. The subjects walked barefoot at self-selected speeds on a split-belt treadmill embedded with force transducers, which measured the loading rates of the legs. Vertical instantaneous loading rate (VILR), average rate of loading (ROL), and heel strike transient (HST) percentage were measured for each leg. Numbing resulted in a lower VILR on the numbed side, and a higher ROL on the contralateral side. HST was unchanged. The data indicate that the reduced sensation affects ground reaction forces during the initial stance phase. Without appropriate afferent signals, subjects may load the unaffected limb more rapidly than the contralateral affected leg, possibly in an effort to amass more afferent information.
We performed a similar experiment with a few mice. We used the DigiGait Imaging System to study the gait of mice at baseline, and after numbing of the plantar surface of a paw. After imaging a baseline ventral view of the animal walking 60 cm/s, it was gently held such that only its right hind paw was immersed in ice cold water for ~2 minutes. Immediately afterwards, the subject repeated the treadmill walking at the same speed. Images were captured for ~5 seconds, representing ~25 consecutive strides. Figure 1 illustrates the ensemble averaged gait signals for the hind limbs of a mouse at baseline (top panel), and after numbing only of the right hind paw (bottom panel). The baseline gait signals, nearly superimposable, illustrate the symmetry in loading of the left and right hind limbs under normal conditions. The hind limb gait signals are usually characterized by a sharp upstroke during the initial stance phase, and more gradual down stroke during the propulsion phase. After numbing, there is a marked asymmetry in the gait signals – amplitude, braking, and propulsion are all affected by the change in afferent information. We are thankful to these presenters for inspiring us to develop an animal model, which may be of interest to conditions such as diabetic neuropathy, where afferent signaling is blunted (1).
- Höhne A, Ali S, Stark C, Brüggemann GP. Reduced plantar cutaneous sensation modifies gait dynamics, lower-limb kinematics and muscle activity during walking. Eur J Appl Physiol. 2012 Nov;112(11):3829-38.