J. Hamil. Union College, Barbourville KY.
Signal Transduction Mechanisms in LTP Expression Mechanisms and LTP A bewildering array of signal transduction molecules has been suggested to play a role in translating the calcium signal In the 1990s generic prandin 1 mg without prescription diabetes 10, tremendous confusion and controversy sur- that is required to trigger LTP into a long-lasting increase rounded the seemingly simple issue of whether LTP is in synaptic strength (28) order prandin 2mg free shipping diabetes mellitus type 2 icd code. However 1 mg prandin fast delivery diabetic videos, for only a few of these caused primarily by presynaptic or postsynaptic modifica- has compelling evidence of a mandatory role in LTP been tions 1mg prandin with visa diabetes test no blood. The great challenge to answering this question largely presented. A major limitation of much of the work on this stemmed from the great technical difficulties inherent in topic is that investigators have not adequately distinguished examining the changes the occur at individual synapses that molecules that are key components of the signal transduc- are embedded in a complex network in which each cell tion machinery absolutely required for LTP from biochemi- receives 10,000 or more synapses. Most neurobiologists cal processes that modulate the ability to generate LTP or studying this question agree that the simplest postsynaptic play a permissive role. For example, any manipulation that change that could cause LTP would be a change in AMPA modifies the activity of NMDA receptors may affect LTP. First, it must be activated Most studies examining this issue have used electrophysi- or produced by stimuli that trigger LTP but not by stimuli ologic assays, and most of these are inconsistent with the that fail to do so. Second, inhibition of the pathway in hypothesis that the release of glutamate increases signifi- which the molecule participates should block the generation cantly during LTP (23,39). Third, activation of the pathway should lead to mitter release probability invariably influence various forms LTP. To pendent protein kinase II (CaMKII) fulfills these require- measure glutamate release more directly, two approaches ments and is a key component of the molecular machinery were used. One took advantage of the finding that glial for LTP. Inhibiting its activity pharmacologically by directly cells tightly ensheath synapses and respond to synaptically loading postsynaptic cells with CaMKII inhibitors or ge- released glutamate by activation of electrogenic transporters netic knockout of a critical CaMKII subunit blocks the that generate a current directly proportional to the amount ability to generate LTP (29–31). Conversely, acutely in- of glutamate released (40,41). The other took advantage of creasing the postsynaptic concentration of active CaMKII use-dependent antagonists of the NMDA receptor or of a increases synaptic strength and occludes LTP (32,33). Fur- mutant AMPA receptor that lacks the GluR2 subunit. That this autophosphoryla- directly proportional to the probability of transmitter release tion is required for LTP was demonstrated by the finding (42,43). LTP had no discernible effect on these measures, that genetic replacement of endogenous CaMKII with a even though they were affected in the predicted fashion by form lacking the autophosphorylation site prevented LTP manipulations known to increase transmitter release. In addition to these negative findings, certain electro- Several other protein kinases have also been suggested to physiologic and biochemical measures were found to in- play roles in the triggering of LTP, but the experimental crease during LTP. An increase in the amplitude of minia- evidence supporting their role is considerably weaker than ture electrophysiologic synaptic currents (mEPSCs), which for CaMKII. Activation of the cyclic adenosine monophos- represent the postsynaptic response to the spontaneous re- phate–dependent protein kinase (PKA), perhaps by activa- lease of a single quantum of neurotransmitter, normally in- tion of a calmodulin-dependent adenylyl cyclase, has been dicates an increase in the number or function of postsynap- suggested to boost the activity of CaMKII indirectly by tic neurotransmitter receptors. Such an increase occurs decreasing competing protein phosphatase activity (37,38). A more direct way 1, an endogenous protein phosphatase inhibitor (see section of monitoring changes in AMPA receptors is to measure on LTD later). Protein kinase C may play a role analogous the postsynaptic response to direct application of agonist, Chapter 11: Synaptic Plasticity 151 and such responses have also been reported to increase, al- beit gradually (47). That LTP is caused by a modification of AMPA receptors is supported by the finding that LTP causes an increase in the phosphorylation of the AMPA receptor subunit GluR1 at the site that is known to be phosphorylated by CaMKII (as well as PKC) (35,48,49). Using expression systems, this phosphorylation has been shown to increase the single- channel conductance of AMPA receptors (50). Because an increase in single-channel conductance of AMPA receptors has been reported to occur during LTP (51), one mecha- nism that seems likely to contribute to LTP is CaMKII- dependent phosphorylation of GluR1. Consistent with this idea, genetic knockout of GluR1 has been found to prevent the generation of LTP (52). A syn- Transmission apse is functionally silent when it expresses NMDA receptors but notAMPAreceptorsinitsplasma membrane(bottom). Theinduc- Although the evidence presented thus far makes a strong tion of LTPcauses the insertion of AMPA receptors (top) from a case for postsynaptic changes contributing to LTP, there putative cytosolic pool. To the right of each diagram are the syn- remained one reproducible experimental result that was dif- aptic currents (i. This result derived from experiments that took advantage of the finding that the action potential-dependent release of quanta of neurotrans- mitter at individual synapses is probabilistic, and therefore release occurs only 10% to 40% of the time. Therefore, if protocol at such synapses causes the rapid appearance of a single synapse or a very small number of synapses is acti- AMPA receptor-mediated EPSCs (55,56). Second, immu- vated once every few seconds, on some of the trials no post- nocytochemical analysis demonstrates that AMPA receptors synaptic response is recorded, that is, a so-called failure oc- are not found at a significant percentage of hippocampal curs. An extensively replicated finding is that LTP causes a synapses, whereas all synapses appear to contain NMDA decrease in the proportion of failures that occur (see 53 for receptors (see 23 for references). Because these failures were assumed to result from to cause the delivery of green fluorescent protein (GFP)- failures of neurotransmitter release, it was concluded that tagged AMPA receptors to dendritic spines and the insertion LTP involves an increase in the probability of transmitter of recombinant AMPA receptors into the synaptic plasma release. Fourth, AMPA and NMDA receptors How can this result be reconciled with all the evidence interact with different proteins at the synapse (59), a finding suggesting that LTP is caused by modulation of AMPA suggesting that they are regulated independently. Fifth, in- receptors and is not accompanied by an increase in gluta- terference with membrane fusion and presumably exocytosis mate release? One straightforward idea to explain this appar- in the postsynaptic cells impairs LTP (60) and AMPA recep- ent discrepancy is the silent synapse hypothesis (54), which tors can interact with proteins involved in membrane fusion predicts that some synapses express only NMDA receptors, (61). These findings are consistent with the idea that mem- whereas others express both AMPA and NMDA receptors brane fusion may be an important mechanism for the deliv- (Fig. Synapses with only NMDA receptors would be ery of AMPA receptors to the synaptic plasma membrane. However, LTP at such silent synapses could by the phosphorylation of AMPA receptors and the delivery occur by the rapid expression of AMPA receptors, and such or clustering of AMPA receptors within the synaptic plasma a mechanism would account for the apparent change in membrane (23). These events will presumably occur both failure rate. First, it is possible to record EPSCs that are mediated appears to involve the converse process, that is, the removal solely by NMDA receptors, and applying an LTP induction or endocytosis of AMPA receptors. At the end of this chap- 152 Neuropsychopharmacology: The Fifth Generation of Progress ter, I discuss how these changes in the number of AMPA pattern of synaptic activity, with LTD requiring a modest receptors at individual synapses may lead to more perma- rise in calcium (67) and LTP requiring a large rise beyond nent structural changes, which, in turn, may mediate long- some critical threshold value (68). The temporal characteris- lasting forms of experience-dependent plasticity. Long-Term Depression Signal Transduction Mechanisms in LTD: A Role Like LTP, LTD has been demonstrated in a large number for Protein Phosphatases of different brain regions and comes in a variety of different If calcium is the critical triggering signal for LTD, it must forms (62–64). This section focuses on the NMDA recep- tor-dependent form of LTD found at excitatory synapses be capable of activating biochemical processes that reverse on CA1 pyramidal cells and that appears to result, in large LTP. Because LTP results, at least in part, from activation part, from a reversal of the processes that mediate LTP. This idea was first proposed in a theoretic article Triggering of LTD: A Critical Role for NMDA (70) that presented a specific model that accounted for the Receptors and Calcium bidirectional control of synaptic strength by calcium (Fig. LTD is normally generated by prolonged (3- to 15-minute) 11. It proposed that a balance between CaMKII activity low-frequency (1- to 5-Hz) afferent stimulation or by a pair- and protein phosphatase 1 (PP1) influenced synaptic ing protocol during which the cell is held at approximately strength by controlling the phosphorylation state of uniden- 50mV. It shares many features with LTP including input tified synaptic phosphoproteins. Small rises in calcium fa- specificity, and it can completely reverse LTP, a process vored activation of PP1, whereas large rises were required often termed depotentiation. Surprisingly, the triggering of to increase CaMKII activity. Because PP1 is not directly LTD requires NMDA receptor activation and an increase in influenced by calcium, a well-established calcium-depen- postsynaptic calcium concentration (65,66).
PET and precision heretofore unavailable with electrophysiologic fMRI allow localization of the brain regions that work to- methods order 0.5 mg prandin mastercard diabetes mellitus weight loss. On the other hand purchase 0.5mg prandin blood sugar 600 emergency, EEG and MEG TECHNICAL PERSPECTIVE have relatively poorer spatial resolution prandin 1 mg mastercard diabetes mellitus type 1 journal, but provide fine time resolution (i cheap prandin 0.5mg with mastercard diabetes youth foundation of indiana. Combining these meth- As can be seen in the preceding brief history, over the years ods, together with the application of the advanced computa- the sophistication of the questions that could be asked and tional cross-registration and source localization techniques the hypotheses about schizophrenia that could be tested that now exist, provides exponentially more information have paralleled the development of new brain imaging tech- than any of these techniques alone. For example, this allows nologies and analytic methods. This parallel development the determination of the sequence in which various finely is evident in the evolution of the science from the search localized regions are activated during cognition and the test- for regionally specific pathologic function to that in neural ing of the hypothesis that this sequence of events is altered systems, and from measures sensitive only to static patho- in schizophrenia. Although this specific multimodal ap- physiology to explorations of the dynamic interplay among proach has not been applied in schizophrenia, other exam- regions in those neural systems. Therefore, a brief discussion ples are described in the following. New Vistas in Data Analysis The analytic approaches for the two data collection modali- New Vistas in Data Acquisition ties discussed, event-related fMRI and fusion of spatial and Event-related fMRI is a relatively recent class of experimen- temporal neurofunctional data (i. Another recent set of analytic methods ad- fMRI and PET approaches that blocked together relatively dresses the growing appreciation that the transduction be- long (e. This approach has much in common with tradi- uted components of neural systems (interregional integra- tional evoked-potential electrophysiology and offers advan- tion of neural function). Questions about functional tages in experimental design. Because different trial types integration and coordinated interregional activity are likely can be randomly intermixed and then separated for analysis, to have particular relevance for schizophrenia, as discussed order effects and habituation can not only be controlled in later sections. Although the segregational view can be Chapter 54: Functional Neuroimaging in Schizophrenia 747 tested with univariate statistics (multiple t-tests or ANO- tients tend to be different from normal controls. In particu- VAs), hypotheses about interregional integration require lar, they show abnormal prefrontal activity (8) during tests multivariate approaches. The influence that one brain re- involving working memory (i. They amined via the correlations between brain activity measures show deficits in cingulate cortex as well as alterations in for the two anatomic structures; as an operational definition frontal–temporal and other intracortical functional rela- two brain regions can be considered to be functionally cou- tionships (12,13) during other cognitive tasks, such as cued pled if their activities are correlated (3); however, this ap- verbal recall (9) and the Stroop test (10), and in some studies proach cannot elucidate how other nodes in the network at rest (11). In general, most of these findings have been mediate these relationships. To model this mediation re- reproduced in acute, untreated patients, thus excluding a quires analysis of the covariance matrix of regions studied primary role for medication artifacts. More recent functional brain imaging studies in schizo- These include structural equation modeling (SEM) and phrenia have focused on: (a) further characterization of the eigenimage analysis. SEM, used in conjunction with ac- locales and cognitive and behavioral context of neurophysio- knowledged anatomical models, can characterize and quan- logic deficits in schizophrenia; (b) delineation of the rela- tify the 'functional connectivity' among the multiple com- tionship of the deficits to clinical symptoms and other neu- ponents of neural systems. A model of known or robiological features of the illness; and, most important; (c) hypothesized anatomic pathways is defined first; then a attempts to elucidate the pathophysiologic mechanism(s) of functional model of interest is tested against this model by the deficits. The following section reviews these areas of iterative fitting of the interregional correlational weights. The most enlightening of these re- It should be borne in mind that the regional components sults have emerged from experimental paradigms designed examined are preselected based on putative pathways and to actively engage neural systems in cognitive or other activi- the results from this approach are only as good as the model. Single value decomposition or principal component analysis is used to The frontal lobes have played a prominent role in formula- present the percentage of variance accounted for by different tions of schizophrenia since the conceptualization of the patterns of activity or spatial modes, and canonical variates illness. In earlier times this role was inferred by clinical anal- analysis, conceptually similar to factor analysis, can be used ogy with known frontal lobe disorders and findings in neu- to extract connectivity patterns across the entire brain that ropsychology and nonhuman primate studies. Substantial are most different between the studied groups. Thus, these indirect but compelling evidence from these multiple do- recently developed methods permit characterization of nor- mains conferred the status of best studied and most im- mal and altered neural connectivity using neuroimaging. Changes The explosion of functional neuroimaging studies of schizo- in rCBF in response to cognitive activation were also first phrenia has resulted in many 'findings' and many discrep- observed in these early studies; this approach has been ancies. Nonetheless, several trends spanning the various ex- greatly refined and now has largely replaced the inherently perimental and methodologic techniques were apparent ill-defined and variable resting state as the cornerstone of several years ago (4). First, when brain activity or metabo- functional brain imaging studies in schizophrenia. Second, when scanned during lobe findings (Table 54. Although patients may have Functional Alterations relatively normal regional patterns of resting brain activity, there appear to be associations between specific resting re- The relatively subtle prefrontal functional alterations ob- gional CBF patterns and symptom profiles (5). Changes in served in schizophrenia have been increasingly brought into lateralization of brain function also have been described (6, focus by recent advances in the available neuroimaging ar- 7). Third, when scanned during cognitive activation, pa- mamentarium. FRONTAL LOBE FINDINGS WITH ACTIVATION PARADIGMS IN SCHIZOPHRENIA SINCE 1985 First Author Publication Year Reference Number Imaging Technique Studies Reporting Decreased Frontal Lobe Activation in Schizophrenia Activation Paradigm Berman KF, et al. Chapter 54: Functional Neuroimaging in Schizophrenia 749 over the past 15 years that report frontal lobe results. The but with differing lifetime histories of neuroleptic intake, overwhelming majority of these investigations have detected found that in most pairs the twin with less exposure to abnormal prefrontal responses to a variety of cognitive ac- neuroleptics was actually the more hypofrontal of the pair tivities designed to access and/or control frontal neural cir- during a prefrontally linked task (18), a result opposite to cuitry, particularly working memory. The prefrontal site that expected if neuroleptics caused hypofrontality. Fourth, most commonly affected is the dorsolateral prefrontal cortex studies examining metabolic or rCBF changes occurring (DLPFC), and, until recently, the physiologic abnormality when patients go from the unmedicated to the medicated in this brain region was consistently seen as hyporesponsiv- state are quite inconsistent (4,8). However, the relative universality haps most conclusively, frontal lobe abnormalities during with which the schizophrenic prefrontal cortex had been cognition have been found in a number of studies of young reported to be hypofunctional, in the past several years, has patients who have never received neuroleptics (22–26). Most prominent among potential epiphenomena and con- This fact suggests that the anatomic and/or chemical pertur- founds examined has been the effect of poor performance. A variety of potential the poor performance—or differences in attention or effort epiphenomenological explanations for this pathophysiology and motivation—somehow cause the frontal pathophysiol- have been considered, and a number of neurobiologically ogy, rather than the more neurobiologically plausible expla- plausible mechanisms have been proposed. It is clear that if patients are simply not engaged in a cognitive task during scanning they will Effect of Neuroleptic Treatment not activate relevant brain regions; such results are obviously One potential epiphenomonological confound is the possi- artifactual. It is less clear what should be predicted if patients bility of a causative role of antipsychotic medications, an (or healthy subjects) are manifestly working at a task, but important consideration because the majority of functional performing it abnormally. However, taken as a whole, the literature provides little healthy control subjects. Several studies have found signifi- evidence that neuroleptics generate the functional neuroim- cant correlations between prefrontal neural activity and cog- aging abnormalities. First, although additional longitudinal nitive function, suggesting that these two variables are para- investigations with newer techniques are necessary, an 18- digmatically linked, but both positive and negative (27) year follow up (15) showed that prefrontal hypofunction relationships have been described (8). The research chal- in chronic patients is remarkably stable over time and unaf- lenge has been to (a) understand this relationship and (b) fected by long-term consistent neuroleptic treatment. Sec- tease apart abnormal cognitive performance and abnormal ond, prefrontal abnormalities like those observed in schizo- brain activity in patients to determine which is primary. Third, a no single study alone can answer the question; however, study of monozygotic twins concordant for schizophrenia, convergent evidence derived from several different research 750 Neuropsychopharmacology: The Fifth Generation of Progress directions leads to the conclusion that prefrontal pathophys- described in the context of performance difficulties. Gold- iology cannot be accounted for as an epiphenomenon (8). Callicott and co- In principal, if the prefrontal physiologic deficit found in workers (1999) demonstrated that normal controls pushed patients with schizophrenia is an epiphenomenon of poor beyond their working memory capacities also demonstrate performance per se, then other subjects who perform as reduced DLPFC responses (36). Electrophysiologic record- poorly should have similar prefrontal function. These findings indicate that poor per- be seen as part of an expected curve between working mem- formance per se does not necessarily produce the pathophys- ory load and neural response—a dose–response curve that is iologic picture seen in schizophrenia. A second way to experimentally attack this 'chicken and Given the fact that other poorly performing patient popula- egg' question, and at least on the face of it the most direct tions with pathology that is different than schizophrenia do way, is to match patients and normal controls for level of not show the same prefrontal response one (28,30,31), this performance. However, ensuring good performance in pa- particular shift in the dose–response curve with poor perfor- tients (by using different versions of the task for patients mance is neither inevitable nor the only possible one. Thus, the strategy of employing 'easy' tasks that (27).
Overall order prandin 0.5 mg on line diabetes pathophysiology, this is a powerful paradigm for medica- HUMAN TESTING PARADIGMS FOR NEW tion development because of its potential to inform the MEDICATIONS clinical trials process with information about how the outpa- tients in a trial are likely to respond to the newmedication buy generic prandin 2 mg on line diabetes and diet 7up, Human Laboratory when a study participant uses a stimulant discount prandin 0.5 mg otc gestational diabetes diet youtube. Its utility as a The human laboratory setting in which cocaine or amphet- rapid screening procedure for eliminating medications from amine is administered to volunteer subjects has been a criti- further outpatient testing has yet to be demonstrated buy prandin 2 mg without prescription diabetes insipidus and diabetes mellitus, but 1464 Neuropsychopharmacology: The Fifth Generation of Progress this may be a future use of these highly controlled paradigms can be combined with self-reported use and compared to as we obtain gold standard agents with demonstrated effi- urine levels obtained prior to the urine in question to esti- cacy in outpatient trials. Although the goal of treatment is often com- potential medications is neuroimaging of either functional plete abstinence, the sensitivity of these urine tests can be activity or receptor and transporter occupancy (28). Thus, self-reported tional activity can involve either cerebral blood flow(CBF) decreases in stimulant use may be important as a treatment or metabolic activity using fluorodeoxyglucose (FDG). The outcome even when the goal may be abstinence initiation. In this study, selegiline reduced the available for intervention. Relapse that the cocaine-induced changes in metabolic activity were as defined by recurrent use or dependence after 'sustained blocked by the administration of selegiline (29). This surro- abstinence' first requires a definition of sustained absti- gate marker provided an interesting correlate of the attenua- nence, particularly among the binge users of stimulants. Because similar studies of subjective of the Diagnostic and Statistical Manual of Mental Disorders, effects alone have not had corresponding predictive validity fourth edition (DSM-IV) for stimulant dependence, the pe- for outpatient efficacy, these neuroimaging measures may riods of nonuse can manifest reasonable psychosocial func- have promise as a more rapid screening tool for medications. Simple definitions of sustained absti- roimaging focuses on the CBF defects that have been ob- nence can just be defined by a period of cocaine- or amphet- served in cocaine abusers and on the neuropsychological amine-free urines that lasts three, four, or perhaps ten times deficits that persist even during sustained abstinence (6,15, longer than the typical inter-binge interval. As reviewed below, these CBF defects may be respon- vestigations, an important prognostic stratification is evolv- sive to pharmacotherapy. The therapeutic implication is ing based on sustained abstinence; patients who are absti- that by resolving these CBF defects, cognitive functioning nent during the 2 to 5 weeks before entering a medication might improve, and the response to cognitive behavioral trial have better treatment outcomes than those who con- therapies also might be enhanced. Longer- term relapse prevention has also been an area where psycho- therapy may synergize with pharmacotherapy (32). For Outpatient Randomized Clinical Trials example, sustained abstinence with desipramine treatment Outpatient clinical trials remain the standard approach to for cocaine dependence was enhanced by relapse-prevention assessing efficacy of a medication. Although many principles cognitive behavioral therapy when examined at 6 and 12 of conducting randomized placebo-controlled clinical trials month follow-up. Relapse was significantly higher after at- in psychopharmacology apply to these studies, some specific taining abstinence with the medication alone than with both considerations are relevant to outcome measures that are not medication and the behavioral therapy. Urine toxicology is a most informative outcome that can be analyzed with both quantitative and qualitative approaches. The urines are typically obtained SPECIFIC MEDICATIONS three times per week for maximum sensitivity to repeated stimulant use based on the duration that detectable metabo- A large number of medications have been used for a variety lite levels remain after use. Analyses are most frequently of cocaine-related effects, including treatment of cocaine done with cutoff scores of 300 ng/mL, for example, with withdrawal or cocaine craving, and initiation and mainte- the cocaine metabolite benzoylecgonine, with any level nance of abstinence. Although many of these medications above this being considered an indication of cocaine use have appeared to be promising in open trials, randomized, within the last 3 days. More complex analyses have been placebo-controlled clinical trials have not shown any medi- proposed using quantitative levels either directly with gas cations to have substantial efficacy for cocaine dependence. This semiquantitation been hampered by large dropout rates. Diagnostic criteria Chapter 102: Pathophysiology and Treatment of Cocaine Dependence 1465 have varied across clinical trials (some studies enroll patients duction in both opioid and cocaine abuse with desipramine meeting diagnostic criteria for cocaine dependence or for (36). A recent report of desipramine in depressed cocaine cocaine abuse, and others do not specify patient diagnosis). Thus, these tricyclic anti- these patients tend to be more available for follow-up be- depressants do not have well-demonstrated utility even in cause of their need to report to a clinic daily for methadone the depressed cocaine abusers, who can be a substantial treatment, it is likely that they are different from patients subgroup comprising up to 40% of those presenting for with primary cocaine use disorders. Outcome clinical trials with fluoxetine have been conducted in pa- variables differ among clinical trials, making it difficult to tients with cocaine use disorders. Studies that utilized controlled, cocaine administration study examined the in- self-reports without confirmation by urine toxicology screen teraction of cocaine with fluoxetine at 0, 20, 40, or 60 mg may not be reflective of cocaine use by study participants. Fluoxetine has been utilized in outpatient clinical Antidepressants trials in both methadone-maintained, cocaine-dependent Desipramine, a tricyclic antidepressant agent, was one of patients and in patients with primary cocaine use disorders. It is one of the most extensively studied phar- dent patients found that fluoxetine at 45 mg daily signifi- macotherapies for cocaine dependence to date (4). The cantly reduced self-reported use and quantitative urine ben- initial study of desipramine suggested its efficacy based on zoylecgonine concentrations during 9 weeks of treatment self-report primarily, and two subsequent studies in metha- (39). More recently, fluoxetine has not reduced cocaine pos- done-maintained samples based on urine toxicology found itive urines more than placebo in either methadone-main- no difference from placebo (33–35). A large clinical trial tained or primary cocaine abusers (40). The consensus of examined the efficacy of desipramine and psychotherapy, these studies is that fluoxetine may not have a clinical role alone and in combination, as a treatment for ambulatory among unselected cocaine abusers, and side effects have lim- cocaine abusers (32). In this 12-week, double-blind, pla- ited its use in several studies. Al- vention plus placebo, and clinical management plus pla- though a pilot study suggested efficacy, a large multicenter cebo. The mean dose of desipramine was 200 mg daily and study in methadone-maintained patients showed little bene- was adjusted by a nonblinded psychiatrist in response to fit in cocaine dependence (41). All groups showed significant improvement in Dopaminergic Agents (DA) treatment retention and a reduction in cocaine use at 12 weeks, but there were no significant main effects for psycho- The most widely accepted explanation of cocaine-induced therapy, pharmacotherapy, or the combination. Lower se- euphoria is that dopamine reuptake inhibition results in verity patients (cocaine use 1 to 2. Desi- limbic and mesocortical reward pathways in the brain (42). Although a laboratory study suggested attenuation response among depressed patients was confirmed among of cocaine effects by the D1 antagonist Schering 39166, a the depressed patients on methadone. A subsequent study multisite outpatient trial found no dose response and no by Nunes et al. The D2 antagonists such as halo- imipramine, but not placebo. They did not find a significant peridol and flupenthixol have had minimal effects on eu- effect in the nondepressed patients. Finally, a recent study phoria in human cocaine administration studies (44), and with desipramine in methadone- and buprenorphine-main- flupenthixol has not been superior to placebo in an outpa- tained cocaine- and opioid-dependent patients found a re- tient trial (45). Bromocriptine is primarily used in the treatment of childhood attention-defi- an agonist with high affinity for the D2 receptor. MP is a DA agonist with pharma- studies, pretreatment with either bromocriptine 2. Although early work supported (55) have reported that it does not increase cocaine use and its use, even in an early double-blind clinical trial, bromo- retains patients better than placebo, but have not shown a criptine at 5 to 7. In another small double-blind, placebo- Mazindol is a DA reuptake inhibitor that is without controlled trial Moscovitz et al. A report on the patients presenting to an emergency room for minor medi- effects of cocaine alone and in combination with mazindol cal complaints. They found no difference in retention (bro- at 1 or 2 mg orally in cocaine abusing volunteers found mocriptine group 43%, placebo group 31%), but those ran- that the combination significantly increased heart rate and domized to bromocriptine had more urine toxicology blood pressure (56). Mazindol did not alter the subjective screens negative for cocaine (67%) than those randomized effects of cocaine. One 12-week, double-blind, placebo-con- to placebo (31%). Cocaine administration studies have trolled clinical trial of mazindol 2 mg daily in cocaine- found a lack of effects with pergolide (49). A placebo-con- dependent subjects reported no difference from placebo trolled outpatient study of pergolide found no difference in (57). Mazindol was also not well tolerated, with 16 of 33 patients dropping out, and the average length of treatment cocaine use and significant side effects, in spite of early pilot was 5 weeks.
Imipramine treatment reversed this process by histone acetylation at the promoters order 0.5 mg prandin with mastercard diabetes chart. Thus 2 mg prandin free shipping blood glucose feedback loop, histone remodeling has been implicated in the pathophysiology and treatment of depression (Tsankova et al 2006) cheap 2 mg prandin mastercard diabetes signs of diabetes. In human inpatients with major depressive disorder increased methylation of the insulin dependent glucose transporter 1 (GLUT1) was demonstrated (Kahl et al cheap prandin 1 mg amex definition of diabetes type 1, 2016). After treatment, remitters (but not non-remitters) demonstrated significant lowering of GLUT1 methylation. Drug and alcohol addiction Findings of many epigenetic changes have been reported in association with addiction to many different agents. So far, many are from animal studies, however, Andersen et al (2015) have reviewed robust changes in DNA methylation in humans with a range of substance abuse disorders. In laboratory animals, Maze et al, (2010) described histone methylation in the nucleus accumbens (an important pleasure center) associated with cocaine use. Sun et al (2012) described similar molecular events in response to chronic morphine administration. Sakharkar et al (2016) demonstrated that intermittent alcohol consumption in adolescent rodents decreased histone acetylation which reduced brain-derived neurotrophic factor (BDNF) and neurogenesis in the hippocampus of adults. Vassoler et al (2013) described amazing transgenerational epigenetic effects in the offspring of male rats which have been self-administering cocaine. The male offspring (but not the females) display little interest in the self-administration of cocaine. These animals feature modification of histone acetylation and Bdnf promoter and increased BDNF in the medial prefrontal cortex (mPFC). Schizophrenia Wockner et al (2014) performed genome-wide DNA methylation analysis on post-mortem human brain tissue from patients with schizophrenia and controls. Two clusters were identified, one contained 88% of people with schizophrenia and 12 % of controls, and the other contained 27% of people with schizophrenia and 73% of controls. These findings indicate that differential DNA methylation is important in the etiology of schizophrenia. Eventually it may be possible to identify aberrant DNA methylation profiles which can be translated into a diagnostic test for use with blood or saliva samples. Montano et al (2016) studied 689 people with schizophrenia and found some overlap with the above study. Major psychosis In this section, schizophrenia and bipolar disorder are considered together. There is some evidence that these disorders may not be distinct (Craddock and Owen, 2005). However, to date, epigenetic studies support a distinction. Dempster et al (2011), conducted a genome-wide study of peripheral blood of monozygotic twins discordant for schizophrenia and bipolar disorder. They found differences in DNA methylation which they believe explained the different phenotypes. Rubin et al (2016) studied DNA methylation of the oxytocin receptor gene, and reported higher methylation in schizophrenia than bipolar disorder. Other psychiatric disorders It is probable that epigenetic modifications will be important in most psychiatric disorders. Eating disorders (Pjetri et al 2012), anxiety (Hunter & McEwen 2013), OCD (Nissen et al, 2016), ADHD (Schuch et al, 2015) and borderline personality disorder (Teschler et al, 2016) have all been studied or studies are in the planning stage. SUICIDE Suicide is not a mental disorder and is not always the result of mental disorder (Pridmore 2015). A postmortem study of the Wernicke area of suicide subjects found hypermethylation of the promoter of BDNF, which could explain the downregulation of BDNF expression in this population (Keller et al 2010). A recent genome-wide investigation of the brains of suicide subjects, demonstrated 366 promoters that were differentially methylated in the hippocampus of suicide completers compared to controls. The effects of these changes remain to be confirmed (Labonte et al 2013). Reviews (Lockwood et al, 2015) support a role for epigenetics in depression and suicide, but it is not clear whether identified changes are associated with depression, or suicide or both. GRAY MATTER VOLUME Methylation of the serotonin transporter gene is associated with hippocampal increased gray matter volume (hippocampal caudate, insula and caudate nucleus grey matter volumes). Thus, epigenetic processes can alter brain structure (Dannlowski et al, 2014). TREATMENT Changing epigenetic markers - a form of treatment There is great interest in finding ways to alter epigenetic status in the hope of therapeutic outcomes. Weaver et al (2004&5) (working with rodents) used central infusion of a histone deacetylase inhibitor to remove epigenetic marks and the effects of maternal care. Changing epigenetic markers – a consequence of treatment There is interest in understanding the impact of established treatments on the epigenome. These effects need to be taken into consideration when seeking to describe epigenetic patterns of particular disorders. Perroud et al (2013) have demonstrated that in borderline personality disorder, response to psychotherapy was associated with a decrease in methylation of the promoter of the BDNF gene. De Jong et al (2014) suggest that electroconvulsive seizure in animals (a model of ECT) has a robust impact on epigenetic mechanisms, which may be useful in the development of electrical treatments. Changes in DNA methylation changes have been demonstrated with valproic acid and quetiapine (Houtepen et al, 2016). Mentioned above, imipramine treatment reversed histone methylation associated with depression (Tsankova et al 2006). CONCLUSION Epigenetics is a most exciting development in biology. It promises to provide insights and even therapies for mental disorders – students are encouraged to take an active interest. References Andersen A, Dogan M, Beach S, Philibert R. Current and future prospects for epigenetic biomarkers of substance use disorders. The beginning of the end for the Kraepelinian dichotomy. Serotonin transporter gene methylation is associated with hippocampal gray matter volume. Dempster E, Pidsley R, Schalkwyk L, Owen S, Georgiades A, Kane F and Kalidini S. Disease- associated epigenetic changes in monozygotic twins discordant for schizophrenia and bipolar disorder. Nongeneomic transmission across generations of maternal behaiveor stress responses in the rat. DNA methylation signatures of mood stabilizers and antipsychotics in bipolar disorder. Stress and anxiety across the lifespan: structural plasticity and epigenetic regulation. Epigenetic regulation of gene expression: how the genome integrates intrinsic and environmental signals. Maternal plasma folate impacts differential methylation in an epigenome-wide meta-analysis of newborns. Altered DNA methylation of glucose transporter 1and glucose transporter 4 in patients with major depressive disorder. Keller S, Sarchiapone M, Zarrilli F, Videtic A, Ferraro A, Carli V. Increased BDNF promoter methylation in the Wernicke area of suicide subjects.