By U. Myxir. Crichton College.
Clozapine is unique in causing neutropenia (potentially fatal) in 1-2% of patients proven floxin 200mg antibiotic strep throat. Other side-effects include significant weight gain generic floxin 200 mg otc virus 5 days of fever, hypotension and tachycardia floxin 400 mg amex infection vs inflammation. Hypersalivation (unknown with the FGAs) can be troublesome with clozapine (and rarely with some other atypicals, such as olanzapine). This is a formidable array of side-effects, but the antipsychotic benefits are substantial. Risperidone Risperidone is an effective antipsychotic. At high doses (8 mg and above) it loses some of its advantages over FGAs, insofar, as acute EPS readily appear. A major disadvantage is the elevation of prolactin levels. A preparation which dissolves in the mouth is available. Risperidone has an advantage over some other SGAs as an IMI depot (long-acting) preparation is available. This can be administered once per fortnight during the maintenance phase, somewhat reducing compliance problems. Paliperidone Paliperidone is the active metabolite of risperidone, which was released when the patent of the parent chemical was about to expire. There is less weight gain, but more EPS problems, and the elevation of prolactin remains problematic. The dosing strategy is simpler, a single daily dose is possible. Recently a paliperidone depot has become available which need only be repeated monthly (a great advantage over 2/52 injection). Olanzapine Olanzapine is an effective antipsychotic which has gained acceptance as a mood stabilizer (used in the prophylaxis of mood disorder; Tohen et al, 2005). It has a pharmacological action and side-effect profile similar to clozapine (except, it is not associated with blood dyscrasia). The most troublesome side-effects are weight gain and sedation. The risks of diabetes and hyperlipidemia need to be monitored. An occasional side-effect, which is seen more regularly with clozapine, is hypersalivation. Olanzapine does not elevate prolactin to a significant degree. The sedating/calming effect of olanzapine is useful in acute disturbance. Olanzapine has an advantage of over some other SGAs in being available in an IMI form for acute Pridmore S. A preparation which dissolves in the mouth is available. A long-acting depot form is available but because physiological response is variable, the patient must be observed for 3 hours following every injection (which is proving to be a disincentive). Quetiapine Quetiapine is an effective antipsychotic which has a receptor binding profile similar to clozapine, but with relatively lower affinity for all receptors. The side-effect profile is favourable, 75% of respondents denying any side-effects (Hellewell et al, 1999). Sedation and hypotension are reported, especially during the commencement phase. Weight gain, and the risk of diabetes and hyperlipidemia need to be considered. Quetiapine has little affinity for muscarinic receptors so that blurred vision and difficulty with micturition are rarely problems. The rate of EPS symptoms is similar to placebo and there is no significant elevation of prolactin. Amisulpride Amisulpride is a useful antipsychotic which has effects (potent antagonist) only at D2 and D3 receptors, and no effect on serotonin receptors. Thus, it could be considered an FGA, which was released in the age of the SGAs. At recommended doses it appears to be selective for limbic (rather than extra-pyramidal system) receptors (Xiberas et al, 2001). Unfortunately, when higher doses are required, EPS side-effects may become a problem. Amisulpride is less likely to cause weight gain than the other SGAs, but it produces robust elevation of prolactin levels, thus breast development and lactation in both men and women and amenorrhoea in women may be bothersome side effects (Leucht et al, 2013). Some guidelines list amisulpride as benign with respect to QTc prolongation and sudden death (Hasan et al, 2012). It has low sedation effects, and discontinuation rate, suggesting it is well tolerated. Aripiprazole Aripiprazole is unusual - rather than an antagonist of dopamine receptors, it appears to be a high affinity partial agonist at presynaptic D2 receptors and an antagonist at postsynaptic D2 receptors. It has little affinity for D3, D4 and D1-like receptors, and its affinity for 5HT-2A receptors is low. There is some alph-1 blockade and orthostatic hypotension has been reported. The efficacy appears similar to risperidone and less than olanzapine, but the side-effect profile appears favourable at manufacturer recommended doses, with minimal elevation of prolactin (Komossa et al, 2009). However, a recent review demonstrated no clear advantage over many other SGAs (Khanna et al, 2013). Aripiprazole has a role as a mood stabilizer (Keck et al, 2007). It appears to be an effective antipsychotic (compared to the other available agents – but, none of them are much good). It has a lower profile of weight gain and adverse changes in glycemic or lipid profile (Bobo, 2013), which will be considered an advantage. It does not significantly increase prolactine (Leucht et al, 2013). However, dose related akathisia and oral hypoaesthesia, my be problematic. Blonanserin, Iloperidone, Lurasidone, and Sertindole Blonanserin has been released for use in Japan and Korea. It appears to be an effective anti-psychotic, which lowers the serum prolactin level (Kawabe et al, 2013. Iloperidone and Lurasidone have been released in the USA but their place in the clinical armamentarium remains to be determined. The question has been raised (Leucht et al, 2013) – with the earlier SGAs coming off patent – will these newer SGAs be cost-effective (good value for money). ACUTE AND LONGTERM ANTIPSYCHOTIC USE Acute treatment is straightforward if the patient is able to cooperate and accepts oral medication.
The major finding of these stud- cycling to neuroenergetics have provided several new and ies is that in normal conditions in nonactivated human cere- controversial insights into the relationship of brain metabo- bral cortex and in rodent models cheap floxin 400 mg amex virus 09, glucose oxidation in gluta- lism and function floxin 200mg line 3m antimicrobial filter. Contrary to the previous view of a sepa- matergic neurons accounts for between 60% and 80% of rate metabolic and neurotransmitter pool of glutamate cheap floxin 400mg on-line bacteria quizlet, glu- cerebral cortex energy consumption. The remaining 20% tamate release and recycling have been shown to be a major to 40% is primarily distributed between GABAergic neu- metabolic pathway. Another key finding is that the gluta- mate/glutamine cycle in the cerebral cortex is coupled in a Oxidation in Glutamatergic Neurons close to 1:1 ratio to neuronal (primarily glutamatergic) glu- The initial use of MRS to study brain metabolism was to cose oxidation above isoelectricity. This finding, in combi- measure glucose oxidation by following the flow of 13C nation with cellular studies, has led to a model for the coup- isotope from [1-13C] glucose into the C4 position of gluta- ling between functional neuroenergetics and glutamate mate (2,6). The coupling between neurotransmis- a [1-13C] glucose precursor to C4-glutamate and subse- sion and neuroenergetics provides a linkage between the quently C4-glutamine. Glucose is metabolized to pyruvate functional imaging signal and specific neuronal processes. The 318 Neuropsychopharmacology: The Fifth Generation of Progress The rate of neuronal glucose oxidation has been deter- mined in several studies from 13C MRS and 1H-13CMRS measurements of cerebral cortex glutamate turnover from a [1-13C] glucose precursor in animal models (2,14–17, 21,22,25–27) and humans (12,13,18,19,29,31,35,43,44). Comparison of the rates of neuronal glucose oxidation mea- sured in these studies with conventional arteriovenous (AV) difference and PET measurements of total glucose con- sumption found that the majority (between 70% and 90%) of total glucose oxidation in the rat and human brain is associated with the large glutamate pool, believed to reflect glutamatergic neurons, measured by MRS. In two recent 13C MRS studies of resting awake human occipital parietal FIGURE 25. The figure shows a 50- cortex, in which other pathways of glucose metabolism were minute accumulation 13C MRS spectrum obtained at 4 T approxi- directly measured, a similar range of between 60% (35) and mately 60 minutes after the start of a 1-13C glucose infusion. The 80% (29) of total glucose oxidation was calculated for the spectrum was obtained from a 72-mL volume centered on the midline in the occipital/parietal lobe. The large percentage of cortical syn- sion of regions of the bottom trace. Labeled resonances include apses that are glutamatergic and the high electrical activity the C2, C3, and C4 positions of glutamate, glutamine, aspartate, of glutamatergic pyramidal cells (4,45) may explain why and -aminobutyric acid (GABA) and the C3 position of lactate. As described in the text (see In Vivo 13C MRS Measurements of such a large fraction of total glucose oxidation is associated the Pathways of Glucose Oxidation: Findings and Validation), the with glutamatergic neurons. Local- ized in vivo 13C-NMR of glutamate metabolism in the human other neuron types, particularly GABAergic, the assignment brain: initial resultsat 4 tesla. DevNeurosci 1999;20:380–388, with of the fraction of glucose oxidation occurring in gluta- permission. In the future, the fraction of glutamate in glia may be measured more accurately through dynamic 13C MRS measurements of glutamate and glutamine labeling during the infusion of label is then transferred to the tricarboxylic acid cycle (TCA) labeled acetate that is incorporated into the brain selectively by the actions of pyruvate dehydrogenase (PDH) and citrate in the glia (28,38,39). When the label reaches C4- -ketoglutarate it is transferred to the large neuronal glutamate pool by the high MRS Measurements of the Rate Glucose activity exchange reactions of the amino acid transaminases Oxidation in GABAergic Neurons and mitochondrial/cytosolic transporters. The large gluta- mate pool was first identified in 14C tracer studies (40). GABA is the major inhibitory neurotransmitter and may Based on kinetic and immunohistochemical staining stud- represent over 30% of the synapses in the cerebral cortex (4, ies, it is believed to correspond to the glutamate pool of 46,47). GABA is synthesized from glutamate in GABAergic glutamatergic neurons (18,41,42). Due to the rate of these neurons by the enzyme glutamic acid decarboxylase (GAD). Almost all of the brain GABA pool tion of 13C label into the trapping glutamate pool, and the is localized to GABAergic neurons under normal condi- kinetic curves analyzed by metabolic modeling to calculate tions. The labeling of the GABA pool from [1-13C] glucose the rate of the neuronal TCA cycle (18). The trapping pool provides a minimum estimate of the rate of glucose oxida- assumption is not essential to determine the rate of the tion in the GABAergic neuron. The estimate is a minimum TCA cycle because subsequent labeling in the C3 position because label may bypass GABA and continue from -keto- of glutamate can be measured to allow calculation of the glutarate/glutamate into the TCA cycle directly. Because glucose is the primary MRS analysis of cerebral cortex from extracts of rats infused fuel for neuronal oxidation, the measurements of the TCA with [1-13C] glucose has been used to measure the time cycle may be converted to measurements of glucose oxida- course of labeling in the GABA and glutamate pools (24, tion using known stoichiometries (17,18). Isotopic labeling of C4-glutamine by the glutamate/glutamine cycle from a [1-13C] glucose precursor. Infused [1-13C] glucose labels neuronal C3-pyruvate. This label is then incorpo- rated via the combined action of pyruvate dehydrogenase and the TCA cycle into -ketoglutarate, which is in rapid exchange with glutamate due to the action of several transaminases. The large glutamate pool in the neuron acts as a label trap with [4-13C]-glutamate accumulating at the rate of the neuronal TCA cycle. Released [4-13C] glutamate from the nerve terminal is taken up by glial transport and the 13C label is transferred to [4-13C] glutamine through the action of glutamine synthetase at the rate of the glutamate/glutamine cycle. Interpretation of glutamine labeling is complicated by 13C label entering by the astrocyte pyruvate dehydrogenase reaction. MRS studies using 15N ammonia, [2-13C] glucose, and [2-13C] acetate, as well as comparison with traditional measurementsof theuptake ofnet glutamineprecursors, haveshown thatthe majorityof labeling in glutamine from [1-13C] glucose is from the glutamate/glutamine cycle (27,36–39). Under conditions of -chloralose anesthesia studies of human cerebral cortex (13,29,35), the rate of the rate of glucose oxidation in GABAergic neurons was GABA synthesis, and by inference glucose oxidation in the estimated to be between 10% and 20% of total neuronal GABAergic pool, was estimated to be on the order of 10% glucose oxidation. This value is similar to previous estimates of total glucose oxidation, although no rates were given. In obtained using isotopic methods and by inhibiting the de- the future, with the higher sensitivity available using inverse gradative enzyme GABA transaminase (24). It should be MRS methods in combination with the development of noted that determination of the rate of GABA synthesis ultrahigh field magnets for human studies, measurements from isotopic methods depends on the assumption that the of the rate of glucose oxidation in GABAergic neurons glutamate precursor pool for GABA is severalfold lower in should be possible in humans. A long-term controversy in brain metabolism studies has been the rate of glucose oxidation in glial cells. Early esti- IN VIVO MRS MEASUREMENTS OF THE mates range from 10% to over 50% of glucose oxidation RATE OF THE GLUTAMATE/GLUTAMINE (49). MRS may be used to measure the rate of glial glucose CYCLE: FINDINGS AND VALIDATION oxidation based on the localization of the enzyme glutamine synthetase in the glia (50). This localization allows the rate The function of the glutamate/glutamine cycle is to prevent of the glial TCA cycle to be calculated from the labeling of depletion of the nerve terminal glutamate pool by synaptic glutamine from glial glutamate. Glial cells have a high capacity for transporting glu- findings were by Van den Berg and co-workers (40), who, tamate from the synaptic cleft in order to maintain a low using 14C isotopic labeling strategies, assigned a rate to glial ECF (extracellular fluid) concentration of glutamate (50, pyruvate dehydrogenase, which they referred to as the small 51). In vivo and in vitro studies indicate that glutamate glutamate pool, of 15% to 25% of total pyruvate dehydro- released by the neuron is taken up by the glia and converted genase (neuronal glial) activity. The pyruvate dehydro- to glutamine by glutamine synthetase (53,54), an enzyme genase rate is equal to the rate of complete glucose oxidation found exclusively in glia (52). Glutamine is transported by the TCA cycle plus the rate of net glial anaplerosis. These from the glia into the ECF where it is taken up by neurons measurements were performed using extract analysis of and converted back to glutamate through the action of whole brains. Two recent 13C MRS measurements of hu- phosphate-activated glutaminase (PAG) (55). Based on ex- mans have measured glial pyruvate dehydrogenase as ac- tensive data from isotopic labeling studies, immunohisto- counting for between 8% (29) and 15% (35) of total pyru- chemical staining of cortical cells for specific enzymes, iso- vate dehydrogenase activity in the occipital parietal lobe.
DL-PFC order 200 mg floxin with mastercard medicine for uti that turns pee orange, dorsolateral prefrontal cortex; IC purchase 200 mg floxin with amex antimicrobial chemotherapy, internal capsule; S floxin 400mg for sale virus fbi, shell; Snc, sub- stantia nigra, zona compacta; Snr, substantia nigra, zona reticulata; VTA, ventral tegmental area. Therefore, unlike acute exposure to stressful or noxious Increasing NO in the striatum by infusion of the substrate stimuli, chronic stress actually attenuates DA neuron base- for the synthetic enzyme nitric oxide synthetase (NOS), line activity. Such a decrease in baseline activity could enable coupled with striatal or cortical stimulation, was found to the system to show a magnified response to activating stim- increase the firing rate of striatal neuron DA neurons. This uli, thereby producing a sensitized DA response. In contrast, NOS inhibitors failed to affect REGULATION OF DA RELEASE baseline DA cell firing but did increase their response to stimulation (34); therefore, NO signaling in the striatum DA appears to be released by multiple factors within its facilitates DA neurotransmission by modulation of cortico- postsynaptic target; moreover, once it is released, there are striatal and striatonigral pathways. NO also appears to have several mechanisms that can modulate its site of action. In a role in regulating terminal DA release (see the following). Carbon fiber recordings, which plays a role both in acute behavioral responses and adapta- allow rapid measurement of DA overflow, show that stimu- tions to chronic stressful conditions. Although the nor- lation of DA axons causes rapid release of transmitter. More- adrenergic system has played a major role in these processes, over, the release varies with tissue content, with PFC show- recent evidence supports a role for the DA system as well. DA released by impulse differential increases in DA dynamics depending on the flow is then rapidly removed via the DA transporter, because brain regions involved. Thus, stressful stimuli tend to cause mice with knockouts of this transporter exhibit 300 times the largest increase in DA levels in the PFC region, with longer clearance half-life compared to controls (42). The markedly smaller changes in the limbic and dorsal striatal amount of DA released by impulses appears to depend on regions (35); however, this relationship is altered by lesions several factors. Previous volumes in the Generations of of different nuclei. Thus, stress causes release of DA in the Progress series have detailed how DA release can be modu- amygdala (36), and lesions of the amygdala tend to block lated by both synthesis- and release-modulating autorecep- stress-induced increases in PFC DA levels (37). It is becoming more evident that the PFC also affect this response. Studies in which the PFC heteroceptors also play a significant role in modulating DA DA innervation is lesioned show that subsequent stressors release (43). One is the DA that is released in a high-ampli- response (38). This suggests that PFC DA released in re- tude, brief pulsatile manner by means of action potentials, sponse to stress actually blunts the responsiveness of the and then is rapidly removed from the synaptic cleft via reup- subcortical limbic DA system. This has been termed the phasic component of DA of PFC DA levels were found to decrease the basal electro- release (44), and is believed to underlie most of the behav- physiologic activity of VTA DA neurons (39). The other is the level of basal DA levels in the accumbens are normal, one interpreta- DA present in the extrasynaptic space. This tonic DA exists tion is that the DA release system has adapted to the dimin- in very low concentrations; too low to stimulate intrasynap- ished DA neuron drive, allowing normal levels of DA trans- tic DA receptors, but of sufficient level to activate extrasy- mission to occur. However, if a stimulus then causes an naptic receptors, including DA terminal autoreceptors increase in DA neuron firing, the compensated release (thereby causing feedback-inhibition of phasic DA release) mechanism would produce an augmented response. It is this tonic DA the magnitude of increase in action potential-dependent DA compartment that is sampled by slower measures of DA release into the accumbens that occurs in response to a chal- dynamics, such as microdialysis. Recently, evidence has lenge may be augmented when the PFC DA response is been advanced to define what factors may contribute to the attenuated (39). Repeated stress also has important clinical implications Although studies suggest that neuronal impulse flow is with regard to the DA system and exacerbation of schizo- necessary for DA overflow in the striatum, there is substan- phrenia. A recent study examined how chronic stress in the tial evidence that the released DA can be controlled locally form of cold exposure affects the discharge of VTA DA by a number of factors. Thus, after exposing rats to cold, there was a 64% inputs increases DA release within the striatum, and evi- decrease in the number of spontaneously active DA neurons, dence suggests that this can occur via afferents to DA cell with no significant alteration in their average firing rate. Thus, infusion of hibited excessive burst activity in the exposed rats (40). It is proposed that this subicular-driven DA re- striatum. Thus, implantation of a microdialysis probe was lease may be involved in the modulation of investigatory found to disrupt DA neuron depolarization block when DA response to novel and conditioned stimuli (45). Stimulation cell activity was assessed 24 hours following probe implanta- of the PFC also appears to result in impulse-dependent DA tion. However, if the probe was inserted via a preimplanted release in the striatum (28). On the other hand, there is guide cannula, depolarization block was maintained, and evidence suggesting that DA can be released in a manner the DA levels were found to be approximately 50% less not dependent on DA neuron firing via stimulation of the than in control conditions. Moreover, the relationship be- hippocampal afferents (46), or amygdala afferents (47) to tween DA neuron firing and release was altered. Thus, al- the accumbens, all of which use glutamate as a transmitter. There is also evidence that glutamate can release chronic antipsychotic drug (60). Thus, correlations between acetylcholine or serotonin in the striatum, which in turn cell firing patterns and DA levels postsynaptically appear to can trigger DA release (43). Glutamate may also stimulate depend on the state of the system. DA release via an action on other local systems, such as It is also possible that there may be local fluctuations in those producing NO. NO is known to be released from tonic DA stimulation that may be a consequence of in- striatal interneurons containing the enzyme NOS, and exert creases in DA neuron firing. Indeed, studies using voltamet- actions on neuronal elements in the vicinity of the release ric measures have shown that brief elevations in extracellular site. Infusion of NOS substrates or NO generator com- DA may occur as a consequence of rapid burst firing, over- pounds was found to facilitate the release of both glutamate whelming the DA uptake process (61). This relationship is and DA within the striatum in a calcium-dependent man- particularly important during administrations of drugs that ner, and is dependent on vesicular stores (52,53). Moreover, interfere with the uptake process, such as cocaine or amphet- the NO-induced efflux of striatal glutamate was found to amine (57,58). Such drugs would cause phasic DA release indirectly enhance extracellular DA levels in the striatum to rapidly augment tonic DA levels, leading to high extracel- in a manner dependent on NMDA and AMPA receptors lular DA and abnormal levels of down-regulation of spike- (53,54). Therefore, it is likely that excitatory amino acids dependent DA release. In a similar nature, in mice lacking and NO interact with DA neuron firing to regulate DA the DA transporter, the extracellular DA is already elevated release from presynaptic sites within the striatum. This tonic/ extracellular DA and glutamate within the striatum (55), phasic balance has been proposed to underlie normal and which would thereby increase in the behavioral response to dysfunctional DA regulation as it relates to the pathophysi- amphetamine (56). Thus, evidence indicates that alterations ology of schizophrenia, drug abuse, and the treatment of in tonic DA levels produced by cortical afferents can po- ADHD (44,57,58).