Sensitization to caffeine and cross-sensitization to amphetamine: influence of individual response to caffeine

The present study evaluated the ability of a subchronic intermittent administration of caffeine to induce a sensitized motor response and correlated the individual susceptibility of rats to acute caffeine to the development of sensitization. Moreover, individual susceptibility to caffeine and development of motor behaviour sensitization were correlated to the behavioural response obtained after a challenge with amphetamine. To this end, rats were subdivided in "low" and "high" responders according to their individual susceptibility to acute caffeine established on the basis of the motor activity observed after the first caffeine administration. "Low" and "high" responder rats were then repeatedly and intermittently treated with caffeine (15 mg/kg, i.p.), or vehicle, every other day for fourteen days. Three days after treatment discontinuation, behavioural activation induced by acute amphetamine (0.5 mg/kg, s.c.) was measured in vehicle- and caffeine-pretreated rats. Subchronic caffeine resulted in motor sensitization of a variable degree among rats and no difference were observed between "low" and "high" responders. Moreover, caffeine pretreatment potentiated the behavioural effects of amphetamine according to the degree of caffeine sensitization but not to individual susceptibility to acute caffeine. These results demonstrate that individual susceptibility to acute caffeine does not influence the modifications in caffeine motor effects produced by its subchronic administration and does not affect the enhancement of acute behavioural effects of amphetamine in caffeine-pretreated rats, rather sensitization to subchronic caffeine administration critically influences the behavioural effects of amphetamine.     

Review: Microglia of the aged brain: primed to be activated and resistant to regulation

Innate immunity within the central nervous system (CNS) is primarily provided by resident microglia. Microglia are pivotal in immune surveillance and also facilitate the co‐ordinated responses between the immune system and the brain. For example, microglia interpret and propagate inflammatory signals that are initiated in the periphery. This transient microglial activation helps mount the appropriate physiological and behavioural response following peripheral infection. With normal ageing, however, microglia develop a more inflammatory phenotype. For instance, in several models of ageing there are increased pro‐inflammatory cytokines in the brain and increased expression of inflammatory receptors on microglia. This increased inflammatory status of microglia with ageing is referred to as primed, reactive or sensitized. A modest increase in the inflammatory profile of the CNS and altered microglial function in ageing has behavioural and cognitive consequences. Nonetheless, there are major differences in microglial biology between young and old age when the immune system is challenged and microglia are activated. In this context, microglial activation is amplified and prolonged in the aged brain compared with adults. The cause of this amplified microglial activation may be related to impairments in several key regulatory systems with age that make it more difficult to resolve microglial activation. The consequences of impaired regulation and microglial hyper‐activation following immune challenge are exaggerated neuroinflammation, sickness behaviour, depressive‐like behaviour and cognitive deficits. Therefore the purpose of this review is to discuss the current understanding of age‐associated microglial priming, consequences of priming and reactivity, and the impairments in regulatory systems that may underlie these age‐related deficits.     

Semiology: witness to a seizure--what to note and how to report

This article reviews the Cleveland Epilepsy Classification (CEC) of seizure semiology. It defines the concept of semiology, and reviews its importance in epilepsy in defining the Symptomatogenic Zone, one of the five zones that make up the Epileptogenic Zone. It details the four broader spheres that contain all of the possible patient signs and symptoms (cognitive, autonomic, consciousness, and motor spheres), and reviews the specific seizure types that are classified within those spheres. Evidence-based information on usefulness of semiology for localization and lateralization is reviewed. A "user-friendly" reference table is provided.     

Pathways to relapse: the neurobiology of drug- and stress-induced relapse to drug-taking

Relapse is a major characteristic of drug addiction, and remains the primary problem in treating drug abuse. Without an understanding of the factors that determine renewed drug-seeking, the urge to use drugs, and the persistent craving for them, it is unlikely that health care professionals can provide effective treatment. Using an animal model of relapse, the author and her team are studying factors that induce reinstatement of drug-taking behaviour after short and long periods of abstinence, and they are exploring the neurobiological basis of these effects. In their experiments, rats are trained to self-administer drugs intravenously by pressing 1 of 2 levers. During a subsequent period, the drug is no longer available, but the rats are free to try to obtain the drug (a period of "extinction training"). After extinction of responding, the investigators test for the ability of various events to reinitiate drug-seeking. On this background of renewed drug-seeking or relapse, the investigators search for pharmacological and neurochemical manipulations that might block or attenuate such behaviour. They have found that the 2 most effective events for reinstating responding after both short and long drug-free periods are re-exposure to the drug itself and exposure to a brief period of stress. The critical neurochemical pathways mediating drug-induced relapse are not identical to those mediating stress-induced relapse. Relapse induced by "priming" injections of heroin or cocaine involves activation of the mesolimbic dopaminergic pathways, whereas relapse induced by stress involves actions of corticotropin-releasing factor (CRF) in the brain, and of brain noradrenergic (NE) systems. In addition, evidence shows that CRF and NE may interact at the level of the bed nucleus of the stria terminalis in stress-induced relapse. By contrast, relapse induced by "priming" injections of drugs is relatively unaffected by manipulation of CRF and NE systems of the brain.     

Inflammation and lithium: clues to mechanisms contributing to suicide-linked traits

Suicide is one of the leading causes of death in the United States, yet it remains difficult to understand the mechanistic provocations and to intervene therapeutically. Stress is recognized as a frequent precursor to suicide. Psychological stress is well established to cause activation of the inflammatory response, including causing neuroinflammation, an increase of inflammatory molecules in the central nervous system (CNS). Neuroinflammation is increasingly recognized as affecting many aspects of CNS functions and behaviors. In particular, much evidence demonstrates that inflammatory markers are elevated in traits that have been linked to suicidal behavior, including aggression, impulsivity and depression. Lithium is recognized as significantly reducing suicidal behavior, is anti-inflammatory and diminishes aggression, impulsivity and depression traits, each of which is associated with elevated inflammation. The anti-inflammatory effects of lithium result from its inhibition of glycogen synthase kinase-3 (GSK3). GSK3 has been demonstrated to strongly promote inflammation, aggressive behavior in rodents and depression-like behaviors in rodents, whereas regulation of impulsivity by GSK3 has not yet been investigated. Altogether, evidence is building supporting the hypothesis that stress activates GSK3, which in turn promotes inflammation, and that inflammation is linked to behaviors associated with suicide, including particularly aggression, impulsivity and depression. Further investigation of these links may provide a clearer understanding of the causes of suicidal behavior and provide leads for the development of effective preventative interventions, which may include inhibitors of GSK3.     

Naturalistic stress and cortisol response to awakening: adaptation to seafaring

Study of the hypothalamic-pituitary adrenal (HPA) axis has been critical to advancing our understanding of human adaptation to stress. The cortisol response to awakening (CRA) is a potentially useful measure for understanding group and individual differences in HPA axis regulation. In this study, the CRA was examined in the context of a naturalistic stressor--a 6-week voyage of work and study aboard an oceangoing ship, including both experienced and novice sailors. Thirty-one subjects provided weekday and weekend baseline CRA data onshore prior to boarding, followed by three CRAs at sea and one shore leave CRA. Subjective measures of sleep, stress and control were also collected. Results suggest that novice sailors' cortisol response to awakening was elevated at sea relative to both a shoreside weekend and a shore leave during the voyage, but the most striking elevation was found during a workday onshore. Inexperienced students' profiles changed differently over the course of the voyage from those of professional crew. CRAs were not affected by sleep variables and were not predicted by subjective ratings. These data support the value of the cortisol response to awakening as a neuroendocrine marker of HPA regulatory responses to a naturalistic stressor, influenced by changes in work and living environment, and perhaps prior experience with the stressor.     

Capacity to consent to research: The evolution and current concepts

The ethical problem of the need to conduct research on the very conditions that impair the ability to consent to such research is widely acknowledged. People with cognitive impairment and mental illness have an equitable right to research being conducted in areas relevant to their treatment and care, and should be given an equitable opportunity to participate in such research, even if they lack capacity. They also have a right to adequate safeguards to protect their interests and respect their wishes in regards to research participation. Provisions for involvement in research of those who are unable to give consent have only developed over the last 50 years. Over this period we have witnessed a proliferation of policies, regulations and laws that govern research involving subjects unable to give consent. There has been a parallel increase in our understanding of the concepts of consent and capacity, specifically as it relates to the research context, with development of standards for research consent and instruments to guide capacity evaluation. We review the evolution of research governance and the underlying ethical principles that underpin such regulations, approaches to capacity evaluation and the use of proxies and advance research directives to facilitate research participation in adults who lack capacity.