Since its design 25 years ago (Olton & Samuelson, 1976), the eight-arm radial maze has become very popular and is now widely used to assess spatial memory in rodents. Two versions of the full-baited maze protocol are present in the literature: with or without confinement between the visit of each arm. The confinement was introduced by Olton himself as early as 1977 (Olton, Collison, & Werz, 1977) to eliminate stereotypic behaviors that he had previously observed. It is widely regarded that the confinement prevents rodents from developing these response patterns, and as such it is considered an improved procedure to test spatial memory. Surprisingly, to the best of our knowledge, no study has been especially designed to demonstrate the efficacy of the confinement in blocking the stereotypic behaviors of the animals. The present study compares the strategies of rats trained with or without a confinement procedure. The results show that, after nine days of training, rats submitted to a 5- or a 10-s confinement reach the same level of performance as rats without confinement. The confinement totally prevents stereotypic behaviors like clockwise serial searching strategies which are often observed without confinement. Even a 0-s confinement is sufficient to prevent clockwise strategies, but rats seem to develop other stratagems which do not imply spatial memory. Furthermore, rats previously trained without confinement are unable to perform the task when confinement is introduced on a test day. In contrast, rats previously trained with confinement perform the task correctly when the confinement is no longer present. Thus, without confinement, good levels of performance can be achieved without precise spatial representations.
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Title:
Value of water mazes for assessing spatial and egocentric learning and memory in rodent basic research and regulatory studies.
Maneuvering safely through the environment is central to survival of all animals. The ability to do this depends on learning and remembering locations. This capacity is encoded in the brain by two systems: one using cues outside the organism (distal cues), allocentric navigation, and one using self-movement, internal cues and sometimes proximal cues, egocentric navigation. Allocentric navigation involves the hippocampus, entorhinal cortex, and surrounding structures (e.g., subiculum); in humans this system encodes declarative memory (allocentric, semantic, and episodic, i.e., memory for people, places, things, and events). This form of memory is assessed in laboratory animals by many methods, but predominantly the Morris water maze (MWM). Egocentric navigation involves the dorsal striatum and connected structures; in humans this system encodes routes and integrated paths and when over-learned becomes implicit or procedural memory. Several allocentric methods for rodents are reviewed and compared with the MWM with particular focus on the Cincinnati water maze (CWM). MWM advantages include minimal training, no food deprivation, ease of testing, reliable learning, insensitivity to differences in body weight and appetite, absence of non-performers, control methods for performance effects, repeated testing capability and other factors that make this test well-suited for regulatory studies. MWM limitations are also reviewed. Evidence-based MWM design and testing methods are presented. On balance, the MWM is arguably the preferred test for assessing learning and memory in basic research and regulatory studies and the CWM is recommended if two tests can be accommodated so that both allocentric (MWM) and egocentric (CWM) learning and memory can be effectively and efficiently assessed.
ID:
Title:
Value of water mazes for assessing spatial and egocentric learning and memory in rodent basic research and regulatory studies.
The conditioned place preference paradigm is a standard preclinical behavioral model used to study the rewarding and aversive effects of drugs. Although a number of different designs and apparatuses are used in this model, the basic characteristics of this task involve the association of a particular environment with drug treatment, followed by the association of a different environment with the absence of the drug (i.e., the drug’s vehicle). A common variation of this design consists of a three-compartment chamber with the outer compartments being designed to have different characteristics (e.g., white vs. black walls, pine vs. corn bedding, horizontal grid vs. cross-grid flooring). The center compartment has no special characteristics and is not paired with a drug, and the gates between the compartments can be opened to allow an animal to pass freely between them. During training, an animal (typically a rat or mouse) is given an injection of a drug with potentially rewarding or aversive properties, and is then placed into one of the outer compartments for several minutes. On the following day, the rat is injected with the drug’s vehicle and then placed in the opposite compartment. Generally, these daily sessions alternate between drug and vehicle for 2 or 3 days each. Afterward, a test session is conducted, which consists of placing the animal in the center compartment and then, after opening the gates to both of the outer compartments, recording the time the animal spends in each of the outer compartments during the session. A conditioned place preference (CPP) is found if the animals spend significantly more time in the drug-paired compartment versus the vehicle-paired compartment. On the other hand, if the animals spend significantly more time in the vehicle-paired compartment versus the drug-paired compartment, then this is considered a conditioned place aversion (CPA). Typically, drugs of abuse, such as cocaine, produce CPP, and drugs that elicit aversive effects, such as lithium chloride, produce CPA. As with other behavioral models used in pharmacology research, the behavioral effects of drugs used in the CPP paradigm depend on species, strain, route of administration, time interval of drug administration, dose concentration, and the CPP apparatus used. Many drugs of abuse produce both CPP and CPA, depending on the dose administered. In drug-dependent animals, withdrawal effects generally produce CPA. Because the CPP paradigm generally provides a reliable indicator for studying the rewarding effects of drugs that require relatively little training compared to self-administration paradigm, the CPP paradigm has been commonly used in conjunction with standard neuroscience techniques to elucidate the subjective effects of drugs (Table 4.1).
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Title:
Development of CGRP-dependent pain and headache related behaviours in a rat model of concussion: Implications for mechanisms of post-traumatic headache.
Posttraumatic headache (PTH) is one of the most common, debilitating and difficult symptoms to manage after a mild traumatic brain injury, or concussion. However, the mechanisms underlying PTH remain elusive, in part due to the lack of a clinically relevant animal model. Here, we characterized for the first time, headache and pain-related behaviours in a rat model of concussion evoked by a mild closed head injury (mCHI) - the major type of military and civilian related trauma associated with PTH - and tested responses to current and novel headache therapies.Concussion was induced in adult male rats using a weight-drop device. Characterization of headache and pain related behaviours included assessment of cutaneous tactile pain sensitivity, using von Frey monofilaments, and ongoing pain using the conditioned place preference or aversion (CPP/CPA) paradigms. Sensitivity to headache/migraine triggers was tested by exposing rats to low-dose glyceryl trinitrate (GTN). Treatments included acute systemic administration of sumatriptan and chronic systemic administration of a mouse anti-CGRP monoclonal antibody.Concussed rats developed cephalic tactile pain hypersensitivity that was resolved by two weeks post-injury and was ameliorated by treatment with sumatriptan or anti-CGRP monoclonal antibody. Sumatriptan also produced CPP seven days post mCHI, but not in sham animals. Following the resolution of the concussion-evoked cephalic hypersensitivity, administration of GTN produced a renewed and pronounced cephalic pain hypersensitivity that was inhibited by sumatriptan or anti-CGRP antibody treatment as well as a CGRP-dependent CPA. GTN had no effect in sham animals.Concussion leads to the development of headache and pain-related behaviours, in particular sustained enhanced responses to GTN, that are mediated through a CGRP-dependent mechanism. Treatment with anti-CGRP antibodies may be a useful approach to treat PTH.
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Title:
Methamphetamine-induced conditioned place preference is facilitated by estradiol pretreatment in female mice.
Ovarian hormones were well documented to modulate the dopamine release in the central dopaminergic systems. The dopamine-releasing effects in the nucleus accumbens, a major target of the mesolimbicortical dopaminergic system, were closely associated with the reinforcing effects of two psychomotor stimulants, cocaine and methamphetamine. This study aimed to examine the sex differences in the cocaine- and methamphetamine-reinforcing behavior, conditioned place preference. In addition, the modulating effects of estradiol and progesterone on methamphetamine-induced conditioned place preference were investigated in both sexes of adult gonadectomized mice. There was no sex difference in the sensitivity to the cocaine (5 mg/kg)-induced conditioned place preference. However, female mice exhibited a more potent methamphetamine (1 mg/kg)-induced conditioned place preference than did male mice. Moreover, pretreatment with estradiol for two consecutive days before the beginning of the conditioning and throughout the four daily conditionings (0.47 microg/day for totally six days) effectively facilitated methamphetamine-induced conditioned place preference in gonadectomized female mice, but not in gonadectomized male mice. Progesterone, under a similar treatment regimen (0.47 microg/day for six consecutive days), did not alter the methamphetamine-induced conditioned place preference in either sex of gonadectomized mice. Taken together, we conclude that the facilitating effects of estradiol on methamphetamine-induced conditioned place preference could be sex-dependent with an eminent sensitivity associated with the adult female mice.
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Title:
Effects of test conditions on the outcome of place conditioning with morphine and naltrexone in mice.
URI:
https://www.ncbi.nlm.nih.gov/pubmed/?term=9952035
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Language Code:
en-us
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Drug administration during test trials can increase the expression of place conditioning, offering an opportunity to determine the specificity of this enhanced response. Prior to training, Swiss-Webster mice spent similar durations in each of the distinctive compartments of a two-compartment box during three 900-s tests. During a 4-day conditioning period, daily injections of morphine (5-20 mg/kg, SC) or vehicle were differentially paired with one of two compartments of the box using an unbiased place conditioning procedure. Post-conditioning tests were conducted 2 and 3 days after the last conditioning day. Mice pre-treated during post-conditioning tests with vehicle did not show significant preference for the morphine-paired compartment when conditioned with morphine. Pretreatment with morphine (2.5-30 mg/kg, SC) led to a dose-dependent increase in time spent in the morphine-paired compartment. Post-conditioning tests in other groups of mice were conducted with heroin (0.1-3 mg/kg), fentanyl (0.01-0.3 mg/kg), cocaine (10-30 mg/kg) and pentobarbital (10-30 mg/kg), and results suggested that none of the tested drugs facilitated the expression of the morphine-conditioned place preference. In another experiment, naltrexone (0.1-10 mg/kg, SC) was administered as the conditioning drug. When tested with naltrexone (0.1-10 mg/kg), there was a dose-dependent avoidance of the naltrexone-paired compartment. Overall, the present data indicated that: (1) failure to exhibit place preference or place aversion when tested in a drug-free state does not imply the failure of conditioning procedure; and (2) effects of the morphine cue reinstatement during the post-conditioning tests appeared to be related to the unique pharmacological profile of the morphine stimulus.
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Title:
Assessment of Cocaine-induced Behavioral Sensitization and Conditioned Place Preference in Mice.
It is thought that rewarding experiences with drugs create strong contextual associations and encourage repeated intake. In turn, repeated exposures to drugs of abuse make lasting alterations in the brain function of vulnerable individuals, and these persistent alterations likely serve to maintain the maladaptive drug seeking and taking behaviors characteristic of addiction/dependence(2). In rodents, reward experience and contextual associations are frequently measured using the conditioned place preference assay, or CPP, wherein preference for a previously drug-paired context is measured. Behavioral sensitization, on the other hand, is an increase in a drug-induced behavior that develops progressively over repeated exposures. Since sensitized behaviors can often be measured after several months of drug abstinence, depending on the dose and length of initial exposure, they are considered observable correlates of lasting drug-induced plasticity. Researchers have found these assays useful in determining the neurobiological substrates mediating aspects of addiction as well as assessing the potential of different interventions in disrupting these behaviors. This manuscript describes basic, effective protocols for mouse CPP and locomotor behavioral sensitization to cocaine.
ID:
Title:
Novel approach to data analysis in cocaine-conditioned place preference.
Only a subgroup of human drug users progress from initial drug taking to drug addiction. The learned associations between the effects of the drug and the environment in which it is experienced is an important aspect of the progression to continued drug taking and drug seeking. These associations can be modeled using the conditioned place preference (CPP) paradigm, although no current method of CPP analysis allows for the identification of within-group variability among subjects. In this study, we adapted a 'criterion' method of analysis to separate 'CPP expressing' from 'non-CPP expressing' rats to study more directly within-group variability in the CPP paradigm. Male Sprague-Dawley rats were conditioned with cocaine (5, 10, 20 mg/kg) or saline in an unbiased three-chamber CPP apparatus in either a single-trial or four-trial CPP procedure. A classification and regression tree analysis of time spent in the cocaine-paired chamber established a time of 324 s spent in the cocaine-paired chamber as the criterion for cocaine CPP expression. This criterion effectively discriminated control from cocaine-conditioned rats and was reliable for rats trained in both single trial and four-trial CPP procedures. The criterion method showed an enhanced ability to detect effective doses of cocaine in the single-trial CPP procedure and a blockade of CPP expression by MK 212 (0.125 mg/kg) treatment in a subgroup of rats. These data support the utility of the criterion analysis as an adjunct to traditional methods that compare group averages in CPP.
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Title:
Disruption of morphine-conditioned place preference by a delta2-opioid receptor antagonist: study of mu-opioid and delta-opioid receptor expression at the synapse.
The addictive properties of morphine limit its clinical use. Learned associations that develop between the abused opiate and the environment in which it is consumed are engendered through Pavlovian conditioning processes. Disruption of the learned associations between the opiate and environmental cues may be a therapeutic approach to prevent morphine dependence. Although a role for the delta-opioid receptor in the regulation of the rewarding properties of morphine has already been shown, in this study we further characterized the role of the delta-opioid receptor in morphine-induced conditioned responses by examining the effect of a selective delta2-opioid receptor antagonist (naltriben), using a conditioned place preference paradigm in rats. Additionally, we used a subcellular fractionation technique to analyze the synaptic localization of mu-opioid and delta-opioid receptors in the hippocampus, in order to examine the molecular mechanisms that may underlie this morphine-induced conditioned behavior. Our data show that the administration of 1 mg/kg naltriben (but not 0.1 mg/kg) prior to morphine was able to block morphine-induced conditioned place preference. Interestingly, this naltriben-induced disruption of morphine conditioned place preference was associated with a significant increase in the expression of the delta-opioid receptor dimer at the postsynaptic density. In addition, we also observed that morphine conditioned place preference was associated with an increase in the expression of the mu-opoid receptor in the total homogenate. Overall, these results suggest that modulation of the delta-opioid receptor expression and its synaptic localization may constitute a viable therapeutic approach to disrupt morphine-induced conditioned responses.
ID:
Title:
Contextually Induced Drug Seeking During Protracted Abstinence in Rats.
Over the past half century great strides have been made in the development of useful animal models for the drug abuse triad—self-administration, physical or psychological dependence, and withdrawal. In fact, the compulsion to self-administer cocaine even in the face of adverse consequences is not limited to human beings [1,2]. Practically, it is not that difficult to detoxify a drug addict, but the problem lies in the propensity for former addicts to relapse to drug-seeking behavior, a risk factor that does not appear to decrease in potency over time. Recently there has been an increasing focus on the issue of protracted withdrawal. This feature of drug addiction mirrors classical conditioning in that certain contextual cues or environmental stimuli associated with drug taking can readily initiate a form of withdrawal or craving in addicts that often leads to renewed drug seeking and relapse (for review, see [3–5]). Indeed, both the rat and human share common triggers of relapse, including the drug of abuse itself, stress, and stimuli or the environment conditioned to the drug of abuse [6]. Rodent models of human drug craving and relapse have used paradigms of extinction and reinstatement. Such models have shown predictive validity by demonstrating that clinically effective anti-craving drugs reduce drug-seeking behavior as a component of the model [7].
ID:
Title:
Transgenic Mouse Models of Alzheimer’s Disease: Behavioral Testing and Considerations.
One hundred years ago, the German psychiatrist and neuropathologist Alois Alzheimer gave a lecture in which he identified a disease of the cerebral cortex [1] that would ultimately bear his name: Alzheimer’s disease (AD). In individuals with this condition, the cerebral cortex is thinner than normal and senile plaques, along with neurofibrillary tangles (NFTs), are found in the brain [2]. In the early 1980s, the biochemical characterization of senile plaques in patients with Down’s syndrome and AD led to the identification of amyloid-β (Aβ) peptide as a major component. Thereafter, it was determined that Aβ is a product of the Aβ protein precursor (APP). The importance of Aβ/APP in the pathogenesis of AD is evidenced by the fact that genetic mutations in the APP gene invariably cause AD in cases with the early onset familial form of the disease [3–5]. The relationship between APP and Aβ caused the research community to respond with quick enthusiasm for Aβ and laid the foundation for the amyloid cascade hypothesis [4,6]. The amyloid cascade hypothesis states that mutations in APP (or other genes) lead to an increase in Aβ and that this then leads to disease. While the original hypothesis [6] posited Aβ fibrils as the major mediator of the disease, a more recent incarnation of the hypothesis [4] proposes smaller oligomeric forms of Aβ as key. In both cases, Aβ is viewed as being important in mediating the neuronal and synaptic toxicity that leads to the deterioration of cognition [7]. Likewise, a steady influx of research began to elucidate the role of NFTs and their principal protein component, phosphorylated tau, in the brain and how these pathological entities related to the symptomatology of AD [8]. While the pathological significance of Aβ and NFTs in disease, as well as their interaction is still under much discussion [9,10], the majority of investigators in the field are convinced that they play fundamental roles in the onset and progression of AD. That said, other theories of AD, unrelated to NFTs and Aβ deposits, are also being actively pursued (for review see [11–15]). Nevertheless, the development of transgenic mouse models of AD over the last decade has primarily focused on the pathological markers (NFTs and senile plaques), and such transgenic models have become promising tools to decipher the mechanistic importance of tau phosphorylation and Aβ deposits, as well their relationship between each other and the other pathological changes. While seemingly obvious, it is important to remember that the validity of a mouse model of disease is tightly linked to the ability of the animal to mimic the signs of the disease—in the case of AD, cognitive decline. The aim of this review is to discuss cognitive function in transgenic mouse models focused predominantly on Aβ and tau models and, thereafter, the validity of these models to study AD and the mechanistic questions that have arisen based on their behavioral phenotype [16,17].
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Title:
The Revival of Scopolamine Reversal for the Assessment of Cognition-Enhancing Drugs.
Atropine and scopolamine are muscarinic receptor antagonists with amnestic properties that have been used for decades in experimental animals to induce impairment in their performance of a variety of tasks requiring intact working and reference memory [1–3]. As long as 30 years ago, scopolamine had been used in clinical research studies (e.g., see [4]). Scopolamine has also been used clinically (though less frequently than in past years) as an adjunct to surgical or obstetric procedures to induce sedation and post-procedural amnesia. Since the first reports of a central cholinergic deficit associated with Alzheimer’s disease, the connection had been made between the cognitive and memory deficits associated with this disease and the reversible amnestic effects induced by centrally acting muscarinic cholinergic antagonists. Indeed, blockade of central muscarinic receptors could induce a pattern of cognitive impairment even in young subjects reminiscent of that observed in the aged, or in individuals with Alzheimer’s disease. For many years, the amnestic action produced in animals by the administration of centrally acting muscarinic cholinergic antagonists, particularly scopolamine, has been a widely used model for the characterization of potential cognition-enhancing drugs [5]. For animal studies, however, pharmacological models of induced memory impairment have been suggested to be of limited value because they fail to replicate the pathological aspects and the progressive degenerative nature of Alzheimer’s disease [6]. Despite this limitation, scopolamine-induced memory impairment, particularly when coupled with a version of the inhibitory avoidance [7] task provides a relatively rapid phenotypic screening tool for drug discovery in the field of cognition enhancement. A criticism often leveled at what might be termed the scopolamine reversal test pertains to the lack of versatility in the model, since scopolamine’s actions are limited to the blockade of brain function mediated via cholinergic (muscarinic) receptors. In Alzheimer’s disease basal forebrain cholinergic neurons appear to be targeted primarily in early stages of the disease. However, other neurotransmitter systems can be affected [8,9]. Alzheimer’s disease attacks cholinergic neurons in specific brain regions where the disease process leads to the decreased expression of specific subtypes of muscarinic cholinergic receptors. Presynaptic M2 receptors (located on cholinergic basal forebrain projection neurons) are depleted more severely than postsynaptic M1 receptors [10]. Scopolamine, however, is relatively nonselective pharmacologically with respect to receptor subtypes, and the drug does not discriminate very much with respect to brain region. Scopolamine certainly would have little direct effect on non-cholinergic neuronal pathways, although cholinergic neurons have functional interactions with a wide variety of neurotransmitter systems that could be affected indirectly by the drug. Despite these limitations, the amnestic responses elicited by scopolamine in humans appear to mimic very closely the cognitive deficits associated with Alzheimer’s disease [5]. Another advantage of scopolamine reversal as a model system for Alzheimer’s disease is that the induced memory impairment is reversible, which lends itself well to screening methods in drug discovery. The utility of the scopolamine model has been partially validated by the ability of centrally acting cholinomimetic drugs to reverse the effects of scopolamine on memory task performance. Studies with the centrally acting cholinesterase inhibitor physostigmine demonstrated consistent but partial reversal of scopolamine-induced memory deficits [11,12]. More recent studies with the currently prescribed Alzheimer’s drugs rivastigmine, donepezil, and galantamine have reported similar scopolamine reversal properties in the rat [13–16]. However, cholinomimetic drugs are not the only pharmacological class to reverse scopolamine-induced memory deficits [17–19], attesting perhaps to the greater than expected versatility of the model. Although the scopolamine reversal model is in wide use in preclinical stages of drug development, some examples of the model have been applied to clinical studies in young or healthy aged subjects. Indeed, a diverse set of compounds with unrelated pharmacological properties have shown efficacy in reversing the amnestic and sedating actions of scopolamine in clinical trials (Table 17.1). In preclinical studies, perhaps the two most widely used rodent tasks for studying or screening cognition-enhancing drugs are the inhibitory avoidance and the water maze tasks. However, clinical versions of these tasks are not well established. Computer-presented operant tasks designed for assessing the cognitive deficits associated with Alzheimer’s disease are available such as the CogState™ product [27,28] and the CANTAB™ product [29,30]. Computer presented cognitive test procedures are becoming more prevalent in the clinical cognitive testing domain. Therefore, there would be some advantage to having available preclinical models that are more relevant than those often used for preclinical drug screening.
“Attention” refers to a variety of hypothetical constructs by which the nervous system apprehends and organizes sensory input and generates coordinated behavior. Although it has been a subject of psychological investigation since William James introduced it to the field in the late 19th century, systematic assessment of attention in animals has a shorter history. As with any unobservable cognitive process, assessment of attention requires quantification of an observable phenomenon, such as the behavior of the animal or the electrical activity of its nervous system. To the extent that these events can be measured objectively, attention can be inferred equally readily in any animal species, including humans or other primates, rats, mice, or birds [1]. As James [2] pointed out, attention is not a unitary phenomenon, but rather a term that subsumes several different varieties of attentional processes. In the present discussion, we focus on three such processes: the ability to sustain attention over time, the ability to attend selectively to a subset of environmental information while filtering out extraneous stimuli, and the ability to shift attentional set. Accordingly, this chapter discusses three behavioral approaches to assessing attention in rodents. These approaches include multiple-choice serial reaction time tests that can be arranged to assess both sustained and selective attention, signal detection tests with blank trials that focus on sustained attention, and attentional set-shifting procedures. For each of these approaches, we present a commonly used method and then discuss design and analytic procedures that can help determine whether observed changes in performance can be attributed to the target attentional construct (see Sections 7.2–7.4). Section 7.5 discusses some guidelines for task selection. The appendix lists suppliers for necessary equipment.
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Title:
The Behavioral Assessment of Sensorimotor Processes in the Mouse: Acoustic Startle, Sensory Gating, Locomotor Activity, Rotarod, and Beam Walking.
Assessment of sensorimotor competence is an important part of the evaluation of animal behavior. Measurement of sensorimotor performance is of obvious importance in investigations of sensory or motor processes; however, the effects of experimental manipulations on sensorimotor performance have broader implications for behavioral neuroscience because behavioral experiments typically measure motor responses to sensory information. Thus, the results of behavioral experiments designed to assess other neurobiological processes often cannot be properly interpreted without considering concomitant effects on sensorimotor function. For example, if a lesion or genetic manipulation impairs performance on a spatial memory test, such as the radial arm maze, this impairment cannot be interpreted as evidence of cognitive dysfunction unless it is first established that it is not the result of sensorimotor deficits. Moreover, sensorimotor effects of manipulations can often be used in animal models as surrogates for effects that are more difficult to measure, and relatively simple variations of sensorimotor measures can be used as indices of performance in other behavioral domains, including cognition and emotion. A number of behavioral tasks have been designed to assess sensorimotor performance in rodents, and this chapter focuses on five general procedures—acoustic startle, sensory gating, open field exploration, rotarod, and beam walking.