By P. Nafalem. Northwestern College, Iowa. 2018.
There is an increasing consensus that the reinforcing ef- Studies have been conducted in animals with deletion fects of drugs of abuse buy 60caps ayurslim fast delivery herbals for blood pressure, along with possibly physical depen- of the dopamine transporter gene 60 caps ayurslim overnight delivery herbals definition, which many researchers dence, are not directly related to tolerance, and they also had hypothesized would eliminate cocaine self-administra- may not be directly related to any changes in receptor den- tion because of the very high constant levels of dopamine sity, number, desensitization, internalization, G-protein un- and the lack of further effects by superimposed cocaine (63). These findings are further supported by the report transporter knockout mice were found unequivocally to of Bohn, Lefkowitz, Caron, and colleagues that, in studies self-administer cocaine, although the acquisition of that be- in -arrestin knockout mice, one sees enhancement and havior was slower than in the wild-type mice (64). Thus, persistence of the antinociceptive effects of morphine (60). In that same animal model, the dopamine tion of opiates and no rewarding effects of opiates (reviewed reuptake transporter knockout mice, it has been found, in ref. Hemby and Smith in dopamine D1 mRNA levels, was found at the end of the and their colleagues also found a synergistic elevation of 6 days of morphine exposure (70). The mRNA levels for extracellular dopamine when cocaine was added to heroin both dopamine D1 and D2 receptors was reduced after 1 in self-administration studies (66). These findings may ex- day of withdrawal, and both returned toward normal by plain, in part, the common co-dependency in humans of the third day after drug withdrawal. These findings may be both heroin and cocaine addictions. However, curiously in this neurons completely in discrete brain regions by use of a study, but not in other studies, reductions of mRNA levels neurotoxin, 6-hydroxydopamine, self-administration of for dynorphin and enkephalin genes were found during morphine proceeded normally as in unlesioned animals. In contrast, enhanced dynorphin However, in such animals, cocaine self-administration was mRNA levels have been found at least after acute single and eliminated. Further studies will be needed to determine the time instance, in one study using the technique of in vivo fast course of dynorphin mRNA level changes during morphine cyclic voltammetry, it was found that heroin caused a dose- exposure. Trujillo, Akil, and their colleagues showed that dependent increase in dopamine in the nucleus accumbens chronic injection or infusion of morphine caused increases during heroin self-administration, and co-administration of in levels of dynorphin peptides in the dorsal striatum (cau- a -agonist (U-50,488 H) with the heroin, or alternatively, date putamen) but not in the ventral striatum (nucleus ac- intracerebroventricular administration of dynorphin A, sig- cumbens) (73). Moreover, installation of the -synthetic compound or only a few (approximately 20%) nucleus accumbens neu- natural ligand dynorphin A alone decreased basal dopamine rons seem to exhibit an inhibitory response after heroin self- release, as had also been shown by Claye and others (68). Thus, the multiple -agonist morphine activates the mesolimbic-mesocortical changes in signal transduction observed and discussed ear- dopaminergic pathway and that -opioid-receptor activa- lier, including the effects of chronic morphine administra- 35 tion offsets, or counterregulates, that activation (67). In related studies, these investigators result from a direct opiate effect or an indirect effect by found, as have numerous others, that cocaine caused a strik- alteration of the dopaminergic system (40,42). Similar find- ing increase in extracellular dopamine concentrations in the ings were made by the group of Sim-Selley, Selley, Childers, nucleus accumbens, and, moreover, the combination of co- and colleagues after chronic heroin self-administration, with caine and heroin caused a synergistic elevation (66). Their the greatest decrease in -opioid-receptor–stimulated 35 finding that heroin alone failed to cause an increase in dopa- [ S]GTP S binding in the brainstem and the lowest altera- mine in the nucleus accumbens complemented several ear- tions in binding in the striatum and cortex (42). Because lier findings that heroin self-administration is not attenu- the changes of dopamine D1-receptor activation would act ated by administration of dopamine antagonists, as well as in one direction and dopamine D2-receptor activation even earlier studies showing that integrity of dopamine would act in the opposite direction on adenylyl cyclase activ- pathways in the nucleus accumbens is not essential for her- ity, the effects on these receptors could also influence the oin self-administration. These findings document further effects of -opioid-receptor activation, and the changes that the early hypothesis of the Kreek laboratory, and many oth- have been observed may result exclusively from the opioid ers, that the reinforcing properties of heroin are mediated effects acting at the -opioid receptors or also secondary primarily by dopamine-independent mechanisms and prob- indirect effects on dopamine receptors. This hypothesis has These and other findings suggest that opiates may act 1496 Neuropsychopharmacology: The Fifth Generation of Progress directly to alter dopaminergic systems both in the ventrome- that is, the neuroplasticity after chronic opiate administra- dial striatum, that is, the core and shell of the nucleus ac- tion that results in impairment of normal neural integrity. Clearly, there are abundant - regulatory events may alter neural growth, development, opioid receptors as well as -opioid receptors in those re- and synapse formation, signal transduction, and overall sys- gions (26,75–77). Work from the Kreek laboratory showed tem integrity (24,79). There have been no similar expression, as well as more direct effects of enhanced tran- findings with respect to increasing -opioid-receptor den- scription factors on dynorphin gene expression, may be sity after chronic opioid administration, however. It is not again important counterregulatory events, which also repre- really known to what extent reinforcement or reward result- sent examples of profound neuroplasticity of the brain. Such ing from heroin and morphine occurs because of activation findings have also been made during binge pattern cocaine directly in these areas, especially the nucleus accumbens and administration (80,81). Enhanced dynorphin peptides, in possibly also the amygdala, as contrasted to indirect effects turn, acting at -opioid receptors, may reduce dopaminergic on the ventral tegmental area. The effects on dopamine tone in many brain regions, including those involved in in each of these different locations and also the different reward and also locomotor activity, and they may also atten- mechanisms involved have not yet been fully elucidated uate opioid withdrawal in dependent animals or humans using a model of chronic, high-dose, intermittent but evenly (6,8,9–11,16). Again, these events must be considered to spaced opiate administration, mimicking the human pattern be a direct result of neuroplasticity and are counterregula- of heroin or morphine abuse and addiction, and also after tory, the attempt to attenuate, modulate, or even brake the withdrawal, as well as during reexposure after such opiate events caused by the rapid changes in dopaminergic tone administration. During chronic binge pattern cocaine ad- brought about especially by stimulants such as cocaine, but ministration, a pattern mimicking the human condition, also to a lesser extent also by opiates.
Drugs that produce conditioned preferences development of procedures that provide a measure of reward for the drug-associated environment are those that function threshold that is unconfounded by influences on motor and as positive reinforcers in other paradigms purchase 60 caps ayurslim fast delivery herbals himalaya. These are the rate-frequency curve- aversions also are observed in response to drugs that are shift procedure 60 caps ayurslim fast delivery wise woman herbals 1, and the discrete-trial, current-intensity pro- negative reinforcers or produce aversive or dysphoric states cedure (28,47,64). These have been reviewed in detail previ- in human subjects (34,66). Potential Pitfalls Potential Pitfalls In place conditioning studies, the drug is administered non- Brain stimulation reward has the advantage of directly inter- contingently and there is evidence that the behavioral and facing with brain reward circuits and as such eliminates any neurochemical effects of abused drugs differ depending on interference with consummatory-like behaviors. In addi- whether drug administration is controlled by the subject. Route of drug administration, number of environmental Potential pitfalls, however, include the requirement for sur- Chapter 97: Recent Advances in Animal Models of Drug Addiction 1385 gery (e. The surgery itself Reliability and Predictability of Drug is routine but does require specialized equipment. Another Discrimination Procedures variable in this domain is the brain site selected. Some brain Drug discrimination offers both reliability and predictive regions support higher rates of brain stimulation reward validity. The dependent variable is very reliable as a measure than others and there may be different circuits activated by of the interoceptive effects of drugs. Drug discrimination also has This training requirement and the extensive surgical re- predictive validity in that drugs that produce discriminative quirements virtually force the use of within-subject designs. Potential Pitfalls Animal Models of the Subjective Effects Generalization gradients are dependent on the dose of drug of Drugs: Drug Discrimination used for training. Certain neurotransmitter antagonists at- The use of the drug discrimination paradigm in studies of tenuate the discriminative stimulus effects of a drug when drug addiction is based on two hypotheses. Second, discriminative stimulus effects of drugs may con- Similarly, generalization to partial agonists or mixed ago- tribute to drug taking in intermittent users and to relapse nists/antagonists can differ depending on the training dose of addiction in former drug addicts. In this latter view, employed (19); therefore, the use of multiple training doses discriminative stimuli signal the availability of a reinforcer is essential. Evidence responding on the lever on which the first schedule require- has been obtained that stimuli predictive of drug adminis- ment is completed) may yield different results depending tration elicit drug-seeking and -taking behavior and can re- on the variable used to measure generalization. As with all tard the extinction of responding for psychostimulants (24, animal models, species and strain differences as well as the 87,97) suggesting that the discriminative stimulus effects of experimental history of an animal can alter the discrimina- a drug contribute to the genesis of these behaviors. Finally, subtle differences In a typical experiment, animals are trained to emit a in the discriminative stimulus effects of a drug may occur particular response following administration of a fixed drug depending on whether appetitive or aversively maintained dose (e. Most commonly, an appetitively moti- ANIMAL MODELS OF THE NEGATIVE vated operant procedure is used in which animals are food REINFORCING EFFECTS OF DRUG or water deprived. Responding on the training-condition WITHDRAWAL appropriate lever results in the delivery of food or water. Training is continued until the animal reliably selects the Withdrawal from chronic drug administration usually is appropriate lever after drug or saline administration. Once characterized by responses opposite to the acute initial ac- trained, tests of stimulus generalization or antagonism are tions of the drug. Many of the overt physical signs associated implemented to determine whether other doses of the train- with withdrawal from drugs (e. However, motivational measures of ab- effects qualitatively similar to or different from that of the stinence have proven to be more sensitive measures of drug training drug. Dose 1 versus Operant Drug Self-Administration dose 2 and drug 1 versus drug 2 versus saline discriminations also can be employed. Details can be found in the following Drug self-administration can be conducted under condi- references (13,29,46,72). Although it is clear that animals will self-administer drugs in the absence of with- drawal, some evidence suggests that physical dependence can increase the reinforcing efficacy of a drug. Monkeys made physically dependent on morphine show increases in their progressive-ratio performance compared to animals that do not exhibit withdrawal symptomology (101). Also, baboons in a discrete-trials choice procedure for food and heroin showed significant behavioral plasticity when al- lowed periodic access to heroin or food (20).
A: [123I]Epidepride was given as a bolus (145 MBq) followed by constant infusion with bolus/infusion ratio of 6 buy ayurslim 60caps otc bajaj herbals fze. Note that equilibrium was achieved only in low-density regions (thalamus/hypothalamus and temporal cortex) order 60 caps ayurslim otc herbals world, not in a high-density region (striatum), with this bolus/infusion ratio. To achieve equilib- rium in all regions, including striatum, a higher bolus/infusion ratio and longer infusion are re- quired. B: [123I]Epidepride (371 MBq) was give as a bolus to a 24-year-old man. Kinetic and equilibrium analyses of [123I]epidepride binding. The major disadvantage of this technique is region would not be the same as that in the background that many hours of infusion may be required to achieve region. Depending on the kinetics of specific and nonspe- steady-state conditions in both plasma and brain. In addi- cific binding, the resulting discrepancy might be significant. Stable levels of drugs, 30 minutes) of a long infusion period (e. Thus, including radiotracers, can be achieved with constant activity measurements before and after the relatively brief (sometimes called continuous) intravenous infusion of the acquisition are not used, and the resulting radiation expo- drug (Fig. From a practical perspective, the total and free drug in plasma will subsequently be stable. In an analogy to in vitro receptor binding studies, this stable condition is a state of equilibrium receptor In summary, three basic methods can be used to estimate binding. The concentration of receptor- the target parameter is typically Bmax/Kd, which equals the bound tracer (B) can be estimated as target minus back- equilibrium value of B/F under tracer occupancy conditions ground. The level of free tracer in plasma (F) can be mea- (i. From a practical concentration of tracer in plasma is measured with the as- Chapter 31: In Vivo Molecular Imaging 417 sumption that free concentration in plasma equals that in surements of both the tracer and the competing displacer brain. An alternate out- in conjunction with D2-receptor imaging and a stimulant come measure for each of these three methods uses the non- challenge (25,26). Although D2-ligand displacement corre- displaceable activity in a background region of brain as a lated with the increase in extracellular dopamine measured value proportional to free tracer concentration. The reasons that the changes in binding are ESTIMATION OF ENDOGENOUS so much lower (although still, it is hoped, linear) relative NEUROTRANSMITTER LEVELS to the increase in extracellular dopamine are unclear. For exam- brain region occurs over a much slower time course than ple, a D2-receptor probe can be used not only to measure the relatively rapid changes in extracellular dopamine. Nevertheless, these stimulant-induced displacement studies D2 receptors but also the extent of competition of this bind- appear to provide some reflection of changes in synaptic ing caused by endogenous dopamine. In fact, the most ex- dopamine levels because they are relatively well correlated tensively studied indirect measurements have been the inter- and because depletion of tissues levels of dopamine can action of dopamine with D2-receptor ligands. These studies block the effects of amphetamine (27). The percentage of unmasking reflects the Dopamine transmission in striatum is thought to occur in percentage of D2 receptors occupied by dopamine under two different modes, tonic and phasic (22,23). Dopamine depletion has been mine release represents the steady-state level of dopamine induced in both animals and humans, with a resulting in- in the extracellular space, which is estimated to be in the crease in D2 radiotracer binding (28,29). On the other hand, in phasic release, high of these studies, especially in humans, is the difficulty of extracellular concentrations of dopamine (millimolar range) knowing whether depletion is essentially complete, so that are released within or near a synapse during an action poten- the full extent of dopamine occupancy of the receptor has tial. Close relationships have been proposed between abnor- been measured. For example, if differences in unmasking malities in phasic and tonic dopamine release and the symp- are found in two subjects, does that reflect different levels toms of schizophrenia. Namely, excessive phasic release of endogenous dopamine—or just different levels of dopa- causes psychosis, and decreased tonic release causes cogni- mine depletion? A second limitation of this depletion para- tive deficits and negative symptoms (24). These agents elevate synaptic dopamine One mechanism to minimize this potential confound is to concentrations either by releasing dopamine in a reverse perform the measurements as soon after dopamine deple- manner via a dopamine transporter (amphetamine) or by tion as possible. However, one clear advantage of the deple- blocking dopamine transporter-mediated reuptake of dopa- tion paradigm in comparison with the stimulant-induced mine (methylphenidate).
New York purchase ayurslim 60caps line worldwide herbals, NY buy ayurslim 60 caps cheap herbals, Albert & Mary Lasker Foundation, 2000. Exceptional returns: the value of investing in health R&D in Australia II. Canberra, The Australian Society for Medical Research, 2008. Efect of a US National Institutes of Health programme of clinical trials on public health and costs. Systematic review of methods for evaluating healthcare research economic impact. Payback arising from research funding: evaluation of the Arthritis Research Campaign. An assessment of the impact of the NHS Health Technology Assessment Programme. Health Technology Assessment, 2007,11:iii-iv, ix–xi, 1–180. Assessing the impact of health technology assessment in the Netherlands. International Journal of Technology Assessment in Health Care, 2008,24:259-269. A systematic evaluation of payback of publicly funded health and health services research in Hong Kong. How can payback from health services research be assessed? Journal of Health Services Research & Policy, 1996,1:35-43. The economic and social benefts of HRB funded research. The role of public-sector research in the discovery of drugs and vaccines. The New England Journal of Medicine, 2011,364:535-541. Strengthening capacity for health research in Africa. Best days for public health are ahead of us, says WHO Director-General. Address to the Sixty-ffth World Health Assembly, Geneva, 21 May 2012. Overcoming gaps to advance global health equity: a symposium on new directions for research. South-South collaboration in health biotechnology: growing partnerships amongst developing coun- tries. New Delhi and Ottawa, Academic Foundation and International Development Research Centre, 2012. The yellow on the armband indicates that the child is malnourished (© UNICEF/NYHQ2011-2139/Esteve). Key points ■ Research illuminates the path to universal health coverage and to better health. This chapter illustrates this with 12 case-studies which investigate questions on issues ranging from the prevention and control of specific diseases to the functioning of health systems. Second, what specifc question is being asked, and where is this question placed in the cycle of research from understanding causes to applying solutions? Tird, what is the most appropriate study design for addressing the question at hand? In particular, they highlight the range of methods that are commonly used in health research, from observational studies to randomized controlled trials. They illustrate the diversity of problems for which research can offer solutions, the benefits of having evidence from multiple sources, the nature of the research cycle, the relationship between study design and strength of inference, the challenge of applying research findings from one setting to another, and the link between research, policy and practice. Turning now to the fndings of research, this chapter illustrates, with selected case-studies, how research can address a wide range of questions about universal health coverage and provide answers that can guide health policy and practice.
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