Acute alcohol administration improves skilled reaching success in intact but not 6-OHDA dopamine depleted rats: a subsystems analysis of the motoric and anxiolytic effects of alcohol

The Home-Cage Automated Skilled Reaching Apparatus (HASRA): Individualized Training of Group-Housed Mice in a Single Pellet Reaching Task

The single pellet reaching task is commonly used in rodents to assess the acquisition of fine motor skill and recovery of function following nervous system injury. Although this task is useful for gauging skilled forelimb use in rodents, the process of training animals is labor intensive and variable across studies and labs. To address these limitations, we developed a single pellet reaching paradigm for training and testing group housed mice within their home cage. Mice enter a training compartment attached to the outside of the cage and retrieve millet seeds presented on a motorized pedestal that can be individually positioned to present seeds to either forelimb. To identify optimal training parameters, we compared task participation and success rates between groups of animals that were presented seeds at two different heights (floor vs mouth height) and at different intervals (fixed-time vs trial-based). The mouth height/fixed interval presentation style was most effective at promoting reaching behavior as all mice reached for seeds within 5 d. Using this paradigm, we assessed stroke-induced deficits in home-cage reaching. Following three weeks of baseline training, reaching success rate was ∼40%, with most trials performed during the dark cycle. A forelimb motor cortex stroke significantly decreased interaction with presented seeds within the first 2 d and impaired reaching success rates for the first 7 d. Our data demonstrate that group-housed mice can be efficiently trained on a single pellet reaching task in the home cage and that this assay is sensitive to stroke induced motor impairments.

The Impact of Acute Stress Physiology on Skilled Motor Performance: Implications for Policing

Investigations of police performance during acutely stressful situations have primarily focused on higher-order cognitive processes like attention, affect or emotion and decision-making, and the behavioral outcomes of these processes, such as errors in lethal force. However, behavioral outcomes in policing must be understood as a combination of both higher-order processes and the physical execution of motor skills. What is missing from extant police literature is an understanding of how physiological responses to acute stress contribute to observed decrements in skilled motor performance at the neuromuscular level. The purpose of the current paper is to fill this knowledge gap in the following ways: (1) review scientific evidence for the physiological (i.e., autonomic, endocrine, and musculoskeletal) responses to acutely stressful exposures and their influence on skilled motor performance in both human and animal models, (2) review applied evidence on occupationally relevant stress physiology and observed motor decrements in performance among police, and (3) discuss the implications of stress physiology for police training and identify future directions for applied researchers. Evidence is compelling that skill decay is inevitable under high levels of acute stress; however, robust evidence-informed training practices can help mitigate this decay and contribute to officer safety.

Task-specific compensation and recovery following focal motor cortex lesion in stressed rats

One reason for the difficulty to develop effective therapies for stroke is that intrinsic factors, such as stress, may critically influence pathological mechanisms and recovery. In cognitive tasks, stress can both exaggerate and alleviate functional loss after focal ischemia in rodents. Using a comprehensive motor assessment in rats, this study examined if chronic stress and corticosterone treatment affect skill recovery and compensation in a task-specific manner. Groups of rats received daily restraint stress or oral corticosterone supplementation for two weeks prior to a focal motor cortex lesion. After lesion, stress and corticosterone treatments continued for three weeks. Motor performance was assessed in two skilled reaching tasks, skilled walking, forelimb inhibition, forelimb asymmetry and open field behavior. The results revealed that persistent stress and elevated corticosterone levels mainly limit motor recovery. Treated animals dropped larger amounts of food in successful reaches and showed exaggerated loss of forelimb inhibition early after lesion. Stress also caused a moderate, but non-significant increase in infarct size. By contrast, stress and corticosterone treatments promoted reaching success and other quantitative measures in the tray reaching task. Comparative analysis revealed that improvements are due to task-specific development of compensatory strategies. These findings suggest that stress and stress hormones may partially facilitate task-specific and adaptive compensatory movement strategies. The observations support the notion that hypothalamic-pituitary-adrenal axis activation may be a key determinant of recovery and motor system plasticity after ischemic stroke.

Blockade of mineralocorticoid and glucocorticoid receptors reverses stress-induced motor impairments

AIM

Stress and glucocorticoids can influence movement performance and pathologies of the motor system. The classic notion assumes that the glucocorticoid receptor (GR) mediates the majority of stress-induced behavioral changes. Nevertheless, recent findings have attributed a more prominent role to the mineralocorticoid receptor (MR) in modulating behavior. The purpose of this study was to dissociate the impact of MR versus GR activation in movement and stress-associated motor disruption.

METHODS

Groups of male and female rats were tested in skilled reaching and open field behavior and treated peri-orally with either agonists or antagonists for MR and GR, respectively.

RESULTS

Selective acute activation of MR (aldosterone) and GR (dexamethasone) decreased movement success with a magnitude similar to stress-induced impairment in male and female animals. By contrast, antagonist treatment to block MR (RU-28318) or GR (Mifepristone, RU-486) prevented motor impairments caused by acute restraint stress or corticosterone treatment. Moreover, both antagonists reversed chronic stress- and glucocorticoid-induced motor impairments to values comparable to baseline levels. Higher success rates in treated animals were accompanied by improved performance of skilled limb movements. In addition, combined treatment with MR and GR antagonists had additive benefit on aim and advance towards the reaching target.

CONCLUSION

These observations suggest that MR or GR equally influence motor system function with partially synergistic effects. Males and females show comparable responses to MR and GR activation or blockade. The need for balanced activation of MRs and GRs in motor control requires consideration in intervention strategies to improve performance in health and disease.

Predictable stress versus unpredictable stress: a comparison in a rodent model of stroke

Previous studies have associated stress with poor outcome in individuals affected by stroke. It was suggested that the effects of stress depend on the stressor's type and strength. Here we compare the effects of chronic predictable restraint stress and chronic unpredictable variable stress on motor recovery after focal lesion in the rat motor cortex. Adult male rats were pre-trained and tested in skilled reaching and skilled walking tasks. Animals were assigned to daily treatments of either restraint stress or variable stress starting 1 week prior to lesion up to 2 weeks post-lesion. One group served as lesion only control. The results revealed a distinct pattern of recovery and compensation of skilled movement. Animals exposed to predictable restraint stress had significantly lower reaching success at both pre- and post-lesion time points, and higher error rates in skilled walking when compared to lesion controls. Overall, restraint stress induced more pronounced motor impairments prior to and after injury than variable stress. Variable stress increased the number of attempts required to grasp food pellets and changed movement pattern performance. By contrast, variable stress improved limb placement accuracy when compared to lesion controls. The behavioural changes were not accompanied by differences in infarct size. These findings are in agreement with other studies reporting that both chronic predicable restraint stress and unpredictable variable stress influence the course of recovery following stroke, however, restraint stress might affect stroke recovery through a different route than variable stress.

Sex differences in skilled movement in response to restraint stress and recovery from stress

Sex differences exist in skilled movement, and skilled motor performance is also influenced by stress. As shown for cognitive function, the effects of stress are usually characterized by considerable sexual dimorphism. The purpose of this study was to investigate sex differences in skilled motor function in response to stress. Male and female Long-Evans rats were trained and tested in skilled reaching and skilled walking tasks. Both groups of animals were then exposed to daily restraint stress for 15 days. Recovery from daily stress was assessed by comparing reaching performance at 10 min versus 60 min after restraint stress, and recovery from chronic stress was tested for 21 days after cessation of stress. Animals were tested daily in skilled reaching for the entire period. Observations showed that females performed significantly better than males during the stress period in terms of reaching success and number of attempts needed to grasp a food pellet. No difference between testing at 10 or 60 min after daily stress was found. Analysis of movement patterns and recovery from stress indicated that males and females use different strategies to overcome stress-induced motor disturbance. While male rats preferred to use original movement patterns, females tended to modify these patterns in order to increase reaching success. Modification of movement patterns in female rats was accompanied by a faster recovery in success rate after the cessation of stress. These results indicate sex differences in skilled reaching in response to stress, and in the recovery period after stress.

Stress as a modulator of motor system function and pathology

Stress is one of the most significant influences on behaviour and performance. The classical account is that stress mainly affects functions of the limbic system, such as learning, memory and emotion. Recent evidence, however, suggests that stress also modulates motor system function and influences the pathology of movement disorders. Most parts of the motor system show the presence of glucocorticoid receptors that render their circuits susceptible to the influence of stress hormones. Stress and glucocorticoids have been shown to modulate temporal and spatial aspects of motor performance. Skilled movements seem to be most prone to stress-induced disturbances, but locomotion and posture can also be affected. Stress can modulate movement through activation of the hypothalamic-pituitary-adrenal axis and via stress-associated emotional changes. The dopaminergic system seems to play a central role in mediating the effects of stress on motor function. This route might also account for the finding that stress influences the pathology of dopamine-related diseases of the motor system, such as Parkinson's disease. Clinical observations have indicated that stress might lead to the onset of Parkinsonian symptoms or accelerate their progression. Glucocorticoids are modulators of neuronal plasticity, thus determining the degree of structural and functional compensation of the damaged motor system. This may particularly affect slowly progressive neurodegenerative diseases, such as Parkinson's disease. That stress represents a significant modulator of motor system function in both the healthy and the damaged brain should be recognized when developing future therapies for neurodegenerative diseases.

Differential effects on forelimb grasping behavior induced by fetal dopaminergic grafts in hemiparkinsonian rats

Skilled forelimb movements depend on an intact dopaminergic (DA) neurotransmission and are substantially impaired in the unilateral rat model of Parkinson's disease. It has remained unclear, however, to what extent reaching and grasping movements can be influenced by intrastriatal transplantation of fetal DA neurons. Here an extensive behavioral assessment of skilled forelimb movement patterns in hemiparkinsonian and DA-grafted rats was carried out. Good DA graft survival was accompanied by a compensation of drug-induced rotational asymmetries. Interestingly, skilled forelimb use was significantly improved in transplanted animals as compared to lesion-only animals in the staircase test. Qualitative analysis of single forelimb reaching movement components revealed dissociable patterns of graft effects: while some movement components in grafted animals improved, others remained unchanged or even deteriorated. These findings provide novel insights into the complex interactions of graft-derived restoration of DA neurotransmission and skilled forelimb behavior.

Modulation of motor function by stress: a novel concept of the effects of stress and corticosterone on behavior

Stress and stress hormones affect a variety of behaviors and cognitive abilities. The influences of stress and glucocorticoids on motor function, however, have not been characterized although the presence of glucocorticoid receptors in the motor system has been documented. Here we demonstrate that stress and the stress hormone corticosterone influence motor system function in rats. Groups of adult female Long-Evans rats underwent either a daily stress-inducing procedure (immobilization or swimming in cold water) or oral corticosterone treatment. While these treatments continued, animals were tested in skilled reaching and skilled walking tasks for a period of 2 weeks. Both acute (day 1) and chronic (day 14) stress and corticosterone treatment reduced skilled movement accuracy in reaching and walking and increased performance speed. Furthermore, both chronic stress and chronic corticosterone treatment altered skilled movement patterns in the reaching task. These findings indicate that stress modulates motor system function and that these effects are partially mediated by glucocorticoids. To examine whether stress-induced changes might also derive from enhanced emotionality, rats were treated with the benzodiazepine diazepam. Based on an inverted U-shaped dose-response relationship, a moderate dose of diazepam significantly improved reaching success while at the same time reducing corticosterone levels. Thus, stress-associated emotional responses such as anxiety might account for diminished movement accuracy. These results suggest that stress affects the motor system both directly via hormonal changes and indirectly via changes in emotionality. These findings are discussed with respect to the role of stress in motor system function and movement disorders.

Dietary restriction alters fine motor function in rats

A number of standard behavioral tasks in animal research utilize food rewards for positive reinforcement. In order to enhance the motivation to participate in these tasks, animals are usually placed on a restricted diet. While dietary restriction (DR) has been shown to have beneficial effects on recovery after brain injury, life span and aging processes, it might also represent a stressor. Since stress can influence a broad range of behaviors, the purpose of this study was to assess whether DR may have similar effects on skilled movement. Adult male Long-Evans rats were trained and tested in a skilled reaching task both prior to and during a mild food restriction regimen that maintained their body weights at 90-95% of baseline weight for eight days. The observations revealed that DR decreased reaching success and increased the number of attempts to grasp a single food pellet. The animals appeared to be more frantic when attempting to reach for food pellets, and the time taken to reach for 20 pellets decreased following the onset of DR. A second experiment investigating behaviors that do not require food rewards, including a ladder rung walking task and an open field test, confirmed that rats on DR display deficits in skilled movements and are hyperactive. These findings suggest that results obtained in motor tasks using food rewards need to be interpreted with caution. The findings are discussed with respect to stress associated with DR.

Ethanol, 3,4-methylenedioxymethamphetamine (ecstasy) and their combination: long-term behavioral, neurochemical and neuropharmacological effects in the rat

This study investigated long-term behavioral, neurochemical, and neuropharmacological effects of ethanol-(+/-)-3,4-methylenedioxymethamphetamine (MDMA, ecstasy) combinations. Over 4 consecutive days, male Long-Evans rats received 1.5 g/kg ethanol and/or 10 mg/kg MDMA, or saline. Rectal temperatures were taken in some rats. Starting 4 days after the last injection, we tested working memory, sensory-motor coordination, and anxiety. Subsequently, we measured cortical, striatal, septal, and hippocampal monoamines (last MDMA injection-euthanasia delay: 20 days), or electrically evoked release of serotonin (5-HT) in cortical and hippocampal slices, and its modulation in the presence of CP 93,129 (3-(1,2,5,6-tetrahydropyrid-4-yl)pyrrollo[3,2-b]pyrid-5-one) or methiotepin (last MDMA injection-euthanasia delays: 3-6 weeks). Ethanol attenuated the MDMA-induced hyperthermia, but only on the first day. In the long-term, MDMA reduced 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) content in most brain regions. The behavioral and neurochemical effects of the ethanol-MDMA combination were comparable to those of MDMA alone; sensory-motor coordination was altered after ethanol and/or MDMA. In hippocampal slices from rats given ethanol and MDMA, the CP 93,129-induced inhibition and methiotepin-induced facilitation of 5-HT release were stronger and weaker, respectively, than in the other groups. This is the first study addressing long-term effects of repeated MDMA and EtOH combined treatments in experimental animals. Whereas the drug combination produced the same behavioral and neurochemical effects as MDMA alone, our neuropharmacological results suggest that MDMA-EtOH interactions may have specific long-term consequences on presynaptic modulation of hippocampal 5-HT release, but not necessarily related to MDMA-induced depletion of 5-HT. Thus, it is likely that the psycho(patho)logical problems reported by ecstasy users drinking alcohol are not solely due to the consumption of MDMA.

Kindling modifies morphine, cocaine and ethanol place preference

Brailowsky and Garcia (1999) proposed the existence of a relationship between epilepsy and addiction. To prove this hypothesis, pentylenetetrazol kindled rats were tested in the conditioned place preference (CPP) paradigm for their reaction to various addictive drugs with different modes of action (morphine, cocaine and ethanol). In separate experiments, locomotor activity and body temperature after application of the same drugs were tested in kindled and non-kindled rats. In the CPP experiment there were significant differences between both groups of rats. Non-kindled animals showed place preference to morphine (5.0 mg/kg) or cocaine (20.0 mg/kg). This reaction was abolished in the kindled rats. Moreover, control rats demonstrated aversion to 2.0 g/kg ethanol. However, ethanol aversion was not detectable in kindled rats. Moreover, there was no difference between non-kindled and kindled rats in locomotor activity and body temperature after morphine (1.0 and 5.0 mg/kg), cocaine (10.0 and 20.0 mg/kg), or ethanol (0.5 and 2.0 g/kg) application. This suggests alterations in reward systems as a consequence of kindling. It is hypothesised that GABAergic neurones in the ventral tegmental area might play a major role in the alterations found.