Neuroscience

Using animal models in addiction and pain research is pivotal to unravel new pathways and mechanisms for the treatment of these disorders. Reward devaluation through a consummatory successive negative contrast (cSNC) task has shown the ability to reduce physical pain sensitivity (hypoalgesia) and increase oral ethanol consumption in rats. The procedure is based on exposing the experimental animals to a 32% sucrose solution during several sessions (preshift sessions) followed by a devaluation to 4% sucrose during the next few sessions (postshift sessions). The cSNC effect can be monitored by comparing the experimental group to an unshifted control that had access to 4% sucrose throughout the entire experiment (preshift and postshift sessions). The cSNC phenomenon is defined by lower consumption of sucrose in the downshifted group than in the unshifted group during postshfit sessions.

The Classic Labyrinth Test (CLT) is a simple way to evaluate behaviors in rodents such as learning ability, memory, and anxiety. The protocol presented here describes the procedure for use with rats, but the protocol can also be adapted for use in mice if a smaller device is used. In short, the CLT uses a square-shaped maze with a starting point and a stopping point. After the animal is trained, the animal is allowed to view and explore the labyrinth freely for 10 min. During this time, all of the animal's vertical and horizontal movements within the labyrinth are recorded. This is a very challenging task because it requires the animal to remember the quickest path between the starting points and the end. In cases where the labyrinth is designed so that the animal only needs to walk forward, it is quite easy for healthy rats, but for rats exposed to neuro-xenobiotics (drugs, pesticides) there will be disturbances in their path. Researchers use many different versions of this test and the procedure for each version can vary significantly. Here, we present a working protocol that enables the detection of traces of some toxic substances that may be exposed to individuals over a long period and in very small amounts under specific conditions such as drugs, medicines and pesticides.

Working memory is short-term memory, so temporal improvement does not reflect the consolidation of a memory trace, rather the functionality of the underlying neuronal circuits and molecular signaling cascades. The administration of drugs–either one-time or through daily injection–can elucidate the underlying mechanisms. The T-maze is especially suitable for studying dopamine-dependent working memory, since it is less stressful than other tests, for example, water maze-based paradigms (Bezu et al., 2016 and 2017). Here, we present a training protocol for evaluating the underlying mechanisms that lead to the development of spatial working memory in rats. Our approach uses a T-maze, and it can be used to get high temporal resolution.

The Traveling Salesman Problem (TSP) is a behavioral test used to measure the efficiency of spatial navigation. It is an optimization problem, in which a number of baited targets are placed in an arena, and as the subject travels between the targets, the route is recorded and compared to chance and optimal routes. The TSP is appealing for the study of learning, memory, and executive function in nonhuman animals because the memory requirements can easily be modified with minor adjustments to task parameters. In the standard version of the task, rats are initially pre-trained to forage for bait in the arena. Once the animals consistently retrieve the bait, they are tested with a set of novel target configurations, and their behavior is recorded. The videos are then scored to produce several measures of performance.

Permanent occlusion of bilateral common carotid arteries (2VO) in rat is considered as a suitable animal model to mimic chronic brain hypoperfusion status, which is proved to be a risk factor to precede the Alzheimer’s disease or/and vascular dementia. In this protocol, we describe how to successfully ligate the bilateral common carotid arteries covered by anterior cervical muscle group, and provide the details for understanding the surgical procedures of 2VO.

Pain is a complex experience. The aversive component of pain has been assessed through conditioned place aversion in rodents. However, this behavioral test does not allow the evaluation of the aversion of an acute pain stimulus. In Zhang et al. (2017), we provide an updated version of a Conditioned Place Aversion paradigm to address this challenge. In this protocol, a detailed version of this method is described.

The Hargreaves test is specifically designed to assess thermal pain sensation in rodents such as rats and mice. This test has been used in experiments involving pain sensitization or recovery of thermal pain response following neural injury and regeneration. We present here a step-by-step protocol highlighted with important notes to guide first-time users through the learning process. Additionally, we have also included representative data from a rat model of sensory denervation showing how the data can be analysed to obtain meaningful results. We hope that this protocol can also assist potential users in deciding whether the Hargreaves test is a suitable test for their experiment.

Neonatal hypoxia-ischemia (HI) affects 60% of low birth weight infants and up to 40% of preterm births. Cell death and brain injury after HI have been shown to cause long-lasting neurological deficits. Two motor coordination tests on rats that had been exposed to HI on postnatal day 7 (P7) showed that HI in the P7 rat is associated with significant motor coordination impairment. These results call attention to the risks associated with perinatal ischemia and the need for proper treatment to reverse HI-induced deleterious effects.

Stress is a condition of human experience and an important factor in the onset of various diseases. There are numerous studies showing how stress can accelerate cell aging, immune senescence and some age-related diseases such as neurodegenerative disorders and osteoporosis. However, the effects of stress have different consequences depending on the type, duration or severity and predictability of the stressor applied. Although stress can be beneficial in its acute phase, repeated and severe stressful stimuli produce adverse effects. There are different models of stress depending on the exposure time; acute (when the stressor is applied for a short time, e.g. hours or days, and intensely) or chronic (when the stressor is applied for a long time, e.g. weeks or months, and less intensely. In these cases, the stressor can be repeated each time or different stressors can be used). The latter model is most frequently used to achieve similar conditions to those found in human diseases related to stress. Also, there are several different paradigms depending on the purpose of the study [development of drug therapies or modeling depressive behaviors; for the different paradigms see Dagnino-Subiabre, (2012)]. Here, we describe a 9-day variable-stressor paradigm with repeated and prolonged stimulation and a random daily stressor over days or weeks to minimize its predictability. This protocol has been adapted from other models of variable stress with significant modifications. The absence of predictability of the stressor applied is an important characteristic of this model compared to other models in which repeated stress is used. We avoid the use of a strong stressor, such as foot shock or tail pinch, and describe an easily reproducible new chronic mild stress model. Some models of chronic mild stress have been reported to lead to a wide range of behavioral disturbances and have been proposed as models of depression in animal studies (Cryan et al., 2005).

In order to survive, preterm and/or sick neonates need diagnostic and therapeutic measures that may cause discomfort, stress and pain during a critical period of intense growing and modeling of the central nervous system (Anand et al., 2013). Scientific interest in the long lasting effects of the Neonatal Intensive Care (NIC) experience, which provides a sensory experience completely different from the natural uterine environment, is growing (Jobe, 2014). The follow-up of critically ill newborn infants until adulthood indicated an association of early noxious stimuli with long lasting alterations in somatosensory and cognitive processing (Doesburg, 2013; Vinall et al., 2014; Vinall et al., 2013). However, one major limitation of the clinical studies is the difficulty to distinguish between long-term effects of pain suffered during neonatal intensive care and other confounding factors such as the presence of non-painful stress during hospital stay, the occurrence of acute and chronic morbidities, the post-natal environmental influences and family care. In this context, the understanding of the roles played by each factor and the interplay between these diverse variables require the use of animal models. The protocol described here is used to model the noxious stimulation in which premature newborns are subjected during treatment in the NIC. The current protocol models inflammatory nociceptive stimulation in neonatal rats, as previously demonstrated (Leslie et al., 2011; Lima et al., 2014; Malheiros et al., 2014). Complete Freund's adjuvant (CFA) is a solution of antigen emulsified in mineral oil and used as an immunopotentiator, causing a painful reaction that lasts 7-8 days after subcutaneous injection. It is effective in stimulating cell-mediated immunity. The rodent model of neonatal inflammatory stimulation with CFA is advantageous because at birth the formation of the central nervous system is incomplete in rat pups and corresponds to that of 24 week intra-uterine human preterm neonates (Anand et al., 1999), following similar patterns in the development of the pain system (Fitzgerald and Anand,1993). The first postnatal week in newborn rat pups corresponds to human premature infants from 24-36 weeks of gestation (Kim et al., 1996; Wilson, 1995), offering a suitable condition to model and compare preterm (rat pups on P1) to full term (rat pups on P8) infants subjected to noxious stimulation. In this paper, we present our methods to induce nociceptive inflammatory stimulation in neonatal rat pups as an attractive approach to study short- or long-term effects and the mechanisms underlying the behavioral repertoire of ex-premature infants or adolescents.