Small phenolic and indolic gut-dependent molecules in the primate central nervous system: levels vs. bioactivity.

INTRODUCTION: A rapidly growing body of data documents associations between disease of the brain and small molecules generated by gut-microbiota (GMB). While such metabolites can affect brain function through a variety of mechanisms, the most direct action would be on the central nervous system (CNS) itself. OBJECTIVE: Identify indolic and phenolic GMB-dependent small molecules that reach bioactive concentrations in primate CNS. METHODS: We conducted a PubMed search for metabolomic studies of the primate CNS [brain tissue or cerebrospinal fluid (CSF)] and then selected for phenolic or indolic metabolites that (i) had been quantified, (ii) were GMB-dependent. For each chemical we then conducted a search for studies of bioactivity conducted in vitro in human cells of any kind or in CNS cells from the mouse or rat. RESULTS: 36 metabolites of interests were identified in primate CNS through targeted metabolomics. Quantification was available for 31/36 and in vitro bioactivity for 23/36. The reported CNS range for 8 metabolites 2-(3-hydroxyphenyl)acetic acid, 2-(4-hydroxyphenyl)acetic acid, 3-(3-hydroxyphenyl)propanoic acid, (E)-3-(3,4-dihydroxyphenyl)prop-2-enoic acid [caffeic acid], 3-hydroxybenzoic acid, 4-hydroxybenzoic acid, 2-acetamido-3-(1H-indol-3-yl)propanoic acid [N-acetyltryptophan], 1H-indol-3-yl hydrogen sulfate [indoxyl-3-sulfate] overlapped with a bioactive concentration. However, the number and quality of relevant studies of CNS neurochemistry as well as of bioactivity were highly limited. Structural isomers, multiple metabolites and potential confounders were inadequately considered. CONCLUSION: The potential direct bioactivity of GMB-derived indolic and phenolic molecules on primate CNS remains largely unknown. The field requires additional strategies to identify and prioritize screening of the most promising small molecules that enter the CNS.

Bacteria Invade the Brain Following Sterile Intracortical Microelectrode Implantation.

Brain-machine interface performance is largely affected by the neuroinflammatory responses resulting in large part from blood-brain barrier (BBB) damage following intracortical microelectrode implantation. Recent findings strongly suggest that certain gut bacterial constituents penetrate the BBB and are resident in various brain regions of rodents and humans, both in health and disease. Therefore, we hypothesized that damage to the BBB caused by microelectrode implantation could amplify dysregulation of the microbiome-gut-brain axis. Here, we report that bacteria, including those commonly found in the gut, enter the brain following intracortical microelectrode implantation in mice implanted with single-shank silicon microelectrodes. Systemic antibiotic treatment of mice implanted with microelectrodes to suppress bacteria resulted in differential expression of bacteria in the brain tissue and a reduced acute inflammatory response compared to untreated controls, correlating with temporary improvements in microelectrode recording performance. Long-term antibiotic treatment resulted in worsening microelectrode recording performance and dysregulation of neurodegenerative pathways. Fecal microbiome composition was similar between implanted mice and an implanted human, suggesting translational findings. However, a significant portion of invading bacteria was not resident in the brain or gut. Together, the current study established a paradigm-shifting mechanism that may contribute to chronic intracortical microelectrode recording performance and affect overall brain health following intracortical microelectrode implantation.

Changes in the Serum Metabolome of Patients Treated With Broad-Spectrum Antibiotics.

BACKGROUND: The gut microbiome (GMB) generates numerous small chemicals that can be absorbed by the host and variously biotransformed, incorporated, or excreted. The resulting metabolome can provide information about the state of the GMB, of the host, and of their relationship. Exploiting this information in the service of biomarker development is contingent on knowing the GMB-sensitivity of the individual chemicals comprising the metabolome. In this regard, human studies have lagged far behind animal studies. Accordingly, we tested the hypothesis that serum levels of chemicals unequivocally demonstrated to be GMB-sensitive in rodent models would also be affected in a clinical patient sample treated with broad spectrum antibiotics. METHODS: We collected serum samples from 20 hospitalized patients before, during, and after treatment with broad-spectrum antibiotics. We also collected samples from 5 control patients admitted to the hospital but not prescribed antibiotics. We submitted the samples for a non-targeted metabolomic analysis and then focused on chemicals known to be affected both by germ-free status and by antibiotic treatment in the mouse and/or rat. RESULTS: Putative identification was obtained for 499 chemicals in human serum. An aggregate analysis did not show any time x treatment interactions. However, our literature search identified 10 serum chemicals affected both by germ-free status and antibiotic treatment in the mouse or rat. Six of those chemicals were measured in our patient samples and additionally met criteria for inclusion in a focused analysis. Serum levels of 5 chemicals (p-cresol sulfate, phenol sulfate, hippurate, indole propionate, and indoxyl sulfate) declined significantly in our group of antibiotic-treated patients but did not change in our patient control group. CONCLUSIONS: Broad-spectrum antibiotic treatment in patients lowered serum levels of selected chemicals previously demonstrated to be GMB-sensitive in rodent models. Interestingly, all those chemicals are known to be uremic solutes that can be derived from aromatic amino acids (L-phenylalanine, L-tyrosine, or L-tryptophan) by anaerobic bacteria, particularly Clostridial species. We conclude that judiciously selected serum chemicals can reliably detect antibiotic-induced suppression of the GMB in man and thus facilitate further metabolome-based biomarker development.

The phenolic interactome and gut microbiota: opportunities and challenges in developing applications for schizophrenia and autism.

Schizophrenia and autism spectrum disorder have long been associated with elevated levels of various small phenolic molecules (SPMs). In turn, the gut microbiota (GMB) has been implicated in the kinetics of many of these analytes. Unfortunately, research into the possible relevance of GMB-mediated SPMs to neuropsychiatry continues to be limited by heterogeneous study design, numerous sources of variance and technical challenges. Some SPMs have multiple structural isomers and most have conjugates. Without specialized approaches, SPMs can be incorrectly assigned or inaccurately quantified. In addition, SPM levels can be affected by dietary polyphenol or protein consumption and by various medications and diseases. Nonetheless, heterotypical excretion of various SPMs in association with schizophrenia or autism continues to be reported in independent samples. Recent studies in human cerebrospinal fluid demonstrate the presence of many SPMs A large number of these are bioactive in experimental models. Whether such mechanisms are relevant to the human brain in health or disease is not known. Systematic metabolomic and microbiome studies of well-characterized populations, an appreciation of multiple confounds, and implementation of standardized approaches across platforms and sites are needed to delineate the potential utility of the phenolic interactome in neuropsychiatry.

Urinary Metabolites of Green Tea as Potential Markers of Colonization Resistance to Pathogenic Gut Bacteria in Mice.

BACKGROUND: The gut microbiome (GMB) generates numerous chemicals that are absorbed systemically and excreted in urine. Antibiotics can disrupt the GMB ecosystem and weaken its resistance to colonization by enteric pathogens such as Clostridium difficile. If the changes in GMB composition and metabolism are sufficiently large, they can be reflected in the urinary metabo-lome. Characterizing these changes could provide a potentially valuable biomarker of the status of the GMB. While preliminary studies suggest such a possibility, the high level of data variance presents a challenge to translational applications. Since many GMB-generated chemicals are derived from the biotransformation of plant-derived dietary polyphenols, administering an oral precursor challenge should amplify GMB-dependent changes in urinary metabolites. METHODS: A course of antibiotics (clindamycin, piperacillin/tazobactam, or aztreonam) was administered SC daily (days 1 and 2) to mice receiving polyphenol-rich green tea in drinking water. Urine was collected at baseline as well as days 3, 7, and 11. Levels of pyrogallol and pyrocatechol, two phenolic molecules unequivocally GMB-dependent in humans but that had not been similarly examined in mice, were quantified. RESULTS: In confirmation of our hypothesis, differential changes in murine urinary pyrogallol levels identified the treatments (clindamycin, piperacillin/tazobactam) previously associated with a weakening of colonization resistance to Clostridium difficile. The changes in pyrocatechol levels did not withstand corrections for multiple comparisons. CONCLUSIONS: In the mouse, urinary pyrogallol and, in all likelihood, pyrocatechol levels, are GMB-dependent and, in combination with precursor challenge, deserve further consideration as potential metabolomic biomarkers for the health and dysbiotic vulnerability of the GMB.

Tyrosine availability modulates potassium-induced striatal catecholamine efflux in vivo.

The relationship between tyrosine availability and high potassium (K+) induced dopamine (DA) and norepinephrine (NE) efflux was examined in striatum using in vivo microdialysis. High K+ (80 mM) was included in perfusate for two 30 min periods, 2.5 h apart. After the first high-K+ perfusion, a tyrosine- and phenylalanine-free mixture of large neutral amino acids (LNAA(-)) was administered (IP) to lower brain tyrosine. Tyrosine (0, 25, 50 or 100 mg/kg IP) was administered 30 min prior to the second high-K+ perfusion. The ratio of catecholamine efflux during the two perfusions (P2/P1) was compared between groups. LNAA(-) significantly lowered P2/P1 for both DA and NE. Tyrosine 25-50 mg/kg blocked the LNAA(-) effect. We conclude that catecholamine efflux during prolonged depolarization is tyrosine dependent. Analyses of LNAA levels suggest that availability of tyrosine for tyrosine hydroxylation may be modulated by competition between LNAAs within brain extracellular fluid.

Tyrosine depletion lowers dopamine synthesis and desipramine-induced prefrontal cortex catecholamine levels.

The relationship between limited tyrosine availability, DA (dopamine) synthesis and DA levels in the medial prefrontal cortex (MPFC) of the rat was examined by in vivo microdialysis. We administered a tyrosine- and phenylalanine-free mixture of large neutral amino acids (LNAA-) IP to lower brain tyrosine, and the norepinephrine transporter inhibitor desipramine (DMI) 10 mg/kg IP to raise MPFC DA levels without affecting DA synthesis. For examination of DOPA levels, NSD-1015 20 microM was included in perfusate. Neither NSD-1015 nor DMI affected tyrosine levels. LNAA- lowered tyrosine levels by 45%, and lowered DOPA levels as well; this was not additionally affected by concurrent DMI 10 mg/kg IP. In parallel studies DMI markedly increased extracellular levels of DA (420% baseline) and norepinephrine (NE) (864% baseline). LNAA- had no effect on baseline levels of DA or NE but robustly lowered DMI-induced DA (176% baseline) as well as NE (237% baseline) levels. Even when DMI (20 microM) was administered in perfusate, LNAA- still lowered DMI-induced DA and NE levels. We conclude that while baseline mesocortical DA synthesis is indeed dependent on tyrosine availability, the MPFC maintains normal extracellular DA and NA levels in the face of moderately lower DA synthesis. During other than baseline conditions, however, tyrosine depletion can lower ECF DA and NE levels in MPFC. These data offer a potential mechanism linking dysregulation of tyrosine transport and cognitive deficits in schizophrenia.

Gamma-butyrolactone-induced dopamine accumulation in prefrontal cortex is affected by tyrosine availability.

Gamma-butyrolactone (GBL) elevates striatal and prefrontal cortex dopamine levels; only the striatal dopamine levels are elevated by increased dopamine synthesis. If increased dopamine synthesis is necessary in order for dopamine levels to be affected by tyrosine availability, then GBL-induced prefrontal cortex dopamine levels should be tyrosine insensitive. Rats received either vehicle, tyrosine (50 or 200 mg/kg i.p.) or a tyrosine-depleting mixture prior to GBL 750 mg/kg i.p.. GBL-induced dopamine levels in prefrontal cortex were lowered by tyrosine depletion. GBL-induced striatal dopamine levels were not affected. Hence, increased dopamine synthesis may not be necessary in order for tyrosine availability to affect pharmacologically elevated prefrontal cortex dopamine levels.

Quantification of phenolic acid metabolites in humans by LC-MS: a structural and targeted metabolomics approach.

AIM: Co-metabolism between a human host and the gastrointestinal microbiota generates many small phenolic molecules such as 3-hydroxy-3-(3-hydroxyphenyl)propanoic acid (3,3-HPHPA), which are reported to be elevated in schizophrenia and autism. Characterization of these chemicals, however, has been limited by analytic challenges. METHODOLOGY/RESULTS: We applied HPLC to separate and quantify over 50 analytes, including multiple structural isomers of 3,3-HPHPA in human cerebrospinal fluid, serum and urine. Confirmation of identity was provided by NMR, by MS and other detection methods. The highly selective methods support rapid quantification of multiple metabolites and exhibit superior chromatographic behavior. CONCLUSION: An improved ultra-HPLC-MS/MS and structural approaches can accurately quantify 3,3-HPHPA and related analytes in human biological matrices.

L-Tyrosine availability affects basal and stimulated catecholamine indices in prefrontal cortex and striatum of the rat.

We previously found that L-tyrosine (L-TYR) but not D-TYR administered by reverse dialysis elevated catecholamine synthesis in vivo in medial prefrontal cortex (MPFC) and striatum of the rat (Brodnik et al., 2012). We now report L-TYR effects on extracellular levels of catecholamines and their metabolites. In MPFC, reverse dialysis of L-TYR elevated in vivo levels of dihydroxyphenylacetic acid (DOPAC) (L-TYR 250-1000 µM), homovanillic acid (HVA) (L-TYR 1000 µM) and 3-methoxy-4-hydroxyphenylglycol (MHPG) (L-TYR 500-1000 µM). In striatum L-TYR 250 µM elevated DOPAC. We also examined L-TYR effects on extracellular dopamine (DA) and norepinephrine (NE) levels during two 30 min pulses (P2 and P1) of K+ (37.5 mM) separated by t = 2.0 h. L-TYR significantly elevated the ratio P2/P1 for DA (L-TYR 125 µM) and NE (L-TYR 125-250 µM) in MPFC but lowered P2/P1 for DA (L-TYR 250 µM) in striatum. Finally, we measured DA levels in brain slices using ex-vivo voltammetry. Perfusion with L-TYR (12.5-50 µM) dose-dependently elevated stimulated DA levels in striatum. In all the above studies, D-TYR had no effect. We conclude that acute increases within the physiological range of L-TYR levels can increase catecholamine metabolism and efflux in MPFC and striatum. Chronically, such repeated increases in L-TYR availability could induce adaptive changes in catecholamine transmission while amplifying the metabolic cost of catecholamine synthesis and degradation. This has implications for neuropsychiatric conditions in which neurotoxicity and/or disordered L-TYR transport have been implicated.

In rats chronically treated with clozapine, tyrosine depletion attenuates the clozapine-induced in vivo increase in prefrontal cortex dopamine and norepinephrine levels.

We previously reported that depletion of brain tyrosine attenuated the acute clozapine (CLZ)-induced increase in medial prefrontal cortex (MPFC) dopamine (DA) levels. This effect was now examined after chronic CLZ treatment. Male rats received CLZ (10 mg kg(-1) day(-1)) in drinking water for 21 days. On day 18, a cannula was stereotaxically implanted over the MPFC. A microdialysis probe was inserted on day 20. On day 21 after a stable baseline was reached, rats received an acute injection of vehicle (VEH) or a tyrosine- and phenylalanine-free mixture of neutral amino acid [NAA(-)] (total 1 g kg(-1), i.p., two injections, 1 h apart) followed by CLZ (10 mg kg(-1), i.p.) or VEH. Basal tyrosine or norepinephrine (NE) levels were not different between the groups, but basal DA was higher in the group treated chronically with CLZ (p<0.05). Acute CLZ (10 mg kg(-1), i.p.) increased MPFC DA and NE levels to 370% and 510% of baseline, respectively, and similarly in rats chronically pretreated with CLZ or VEH. NAA(-) did not affect basal MPFC DA or NE levels but significantly attenuated acute CLZ-induced DA (220% of baseline) and NE (330% of baseline) levels (p<0.01) in rats pretreated chronically with CLZ or with VEH. These data demonstrate that even after chronic CLZ administration, the acute CLZ-induced increases in MPFC DA and NE levels depend on the availability of brain tyrosine. Judicious manipulation of brain tyrosine levels may provide a useful probe as well as a mechanism for enhancing psychotropic drug actions.

Increased striatal dopamine synthesis is associated with decreased tissue levels of tyrosine.

Tyrosine levels do not generally affect indices of dopamine (DA) synthesis or efflux under basal conditions, but can do so when DA synthesis is increased. One possibility is that a high rate of DA synthesis depletes the normally adequate pool of endogenous tyrosine. To study this, we administered drugs known to preferentially increase striatal DA synthesis and examined DOPA levels in striatal microdialysate during perfusion with NSD-1015. In additional groups, we also measured DA, tyrosine and large neutral amino acids in striatal microdialysate, as well as in tissue from striatum and medial prefrontal cortex (MPFC). gamma-butyrolactone (GBL) (750 mg/kg i.p.) increased DOPA levels in striatal microdialysate, increased tissue DA levels in the MPFC and striatum, but lowered tissue tyrosine levels only in striatum. In striatal microdialysate, GBL markedly lowered DA levels; tyrosine levels were only marginally lower. Haloperidol (HAL) (1.0 mg/kg s.c.)+/-amfonelic acid (AFA) (5 mg/kg i.p.) increased striatal DOPA accumulation, increased striatal DA efflux, lowered striatal tissue tyrosine levels, but did not affect microdialysate tyrosine levels. There were no consistent changes in levels of other large neutral amino acids. We conclude that increased tyrosine hydroxylation can significantly deplete the endogenous pool of tyrosine. Under such conditions, near normal extracellular tyrosine levels are maintained despite lower tissue levels. The data are consistent with a net transfer of tyrosine from non-DAergic cells to DA terminals in support of DA synthesis.

Large neutral amino acids levels in primate cerebrospinal fluid do not confirm competitive transport under baseline conditions.

In rodents, transport of large neutral amino acids (LNAAs) across the blood brain barrier (BBB) and blood-cerebrospinal fluid (CSF) barrier is mediated by high affinity carriers. Net brain LNAA levels are thought to be determined mainly by this competitive transport from plasma. Since the affinity for LNAA transport at the BBB in primates is considerably higher than in rodents, brain influx and by extension LNAA brain levels, should be even more dependent on competitive transport. Given that LNAA levels in CSF and brain interstitial fluid are usually similar, we analyzed serum and CSF of fasted subjects (n=24) undergoing spinal anesthesia and calculated brain influx and transporter occupancy using a conventional model of transport. Despite predicted near-full transporter saturation (99.7%), correlations between CSF levels and brain influx were modest, limited to tyrosine (r=0.60, p<0.002) and tryptophan (r=0.50, p<0.01) and comparable to correlations between CSF and serum levels. We also analyzed serum and CSF in (n=5) fasted vervet monkeys. Tyrosine and phenylalanine levels in CSF were positively correlated with those in serum, but correlations with calculated brain influx, which takes competition into account, were weaker or absent. We conclude that in primates i) baseline CSF LNAA levels do not confirm competitive transport, ii) brain LNAA levels should not be estimated on the basis of serum indices alone. This has implications for amino acid challenge studies and for neuropsychiatric disorders associated with dysregulated LNAA transport in which quantitative information about brain LNAA levels is needed.

Clozapine-induced dopamine release in the medial prefrontal cortex is augmented by a moderate concentration of locally administered tyrosine but attenuated by high tyrosine concentrations or by tyrosine depletion.

RATIONALE: Tyrosine availability can affect indices of dopamine (DA) release in activated central DA systems. There are, however, inconsistencies between studies. One possibility is that the relationship between tyrosine availability and DA release is non-linear. OBJECTIVES: This study aimed to determine how tyrosine depletion as well as a range of administered tyrosine concentrations affect antipsychotic drug-induced extracellular DA levels in the MPFC or striatum. METHODS: A guide cannula was implanted over the medial prefrontal cortex or striatum of adult male rats. After a 24-h recovery period, a microdialysis probe was inserted. Microdialysate collection began on the following day. Some rats received vehicle or a tyrosine- and phenylalanine-free neutral amino acid solution NAA(-) (IP) prior to clozapine (CLZ 10 mg/kg IP). Others received vehicle, CLZ (10 mg/kg IP) or haloperidol (HAL) (1 mg/kg IP) while the probe was perfused with artificial cerebrospinal fluid containing tyrosine 0-200 mug/ml. RESULTS: NAA(-) reduced tyrosine levels in MPFC dialysate by 35%. This reduction did not affect basal MPFC DA levels but attenuated the peak of CLZ-induced MPFC DA levels. The NAA(-) effect could be reversed by administration of tyrosine. Infused tyrosine 12.5-200 mug/ml did not affect basal DA levels either in MPFC or striatum. Within the MPFC, tyrosine 50.0 mug/ml significantly increased CLZ-induced DA levels. Within the striatum, tyrosine 25.0 mug/ml significantly increased while 150.0 mug/ml significantly decreased HAL-induced DA levels. CONCLUSIONS: Basal extracellular levels of DA in the MPFC and striatum are not affected by wide changes in tyrosine availability. However, modestly increased brain tyrosine levels can augment CLZ-induced MPFC and HAL-induced DA levels. Very high tyrosine concentrations attenuate HAL-induced striatal DA levels. These data may explain inconsistencies in the literature and suggest that tyrosine availability could be exploited to modulate psychotropic drug-induced DA levels in the brain.

Tyrosine administration does not affect desipramine-induced dopamine levels as measured in vivo in prefrontal cortex.

Using in vivo microdialysis, we examined whether tyrosine administration would potentiate the desipramine (DMI)-induced elevation of medial prefrontal cortex (MPFC) dopamine (DA) levels. DMI (10 or 20 mg/kg IP) increased MPFC DA levels but not DOPA accumulation. Tyrosine (12.5-100 mug/ml) administered by reverse microdialysis did not affect DMI-induced MPFC DA levels. The data support our hypothesis that DA synthesis must be significantly increased in order for administered tyrosine to increase extracellular DA levels.

Pharmacokinetics of quetiapine in elderly patients with selected psychotic disorders.

OBJECTIVE: To assess the pharmacokinetics and tolerability of quetiapine in elderly patients with selected psychotic disorders. STUDY DESIGN: This was a multicentre, open-label, 27-day, rising multiple-dose trial. Descriptive statistics summarised plasma quetiapine concentrations and pharmacokinetic parameters by trial day. A two-way analysis of variance was used to evaluate all pharmacokinetic parameters, and 90% confidence intervals of the mean differences were calculated. METHODS: Antipsychotic drugs taken prior to the study period were discontinued on day 1. Quetiapine treatment began on day 3. Doses were increased stepwise, starting at 25mg three times daily and reaching 250mg three times daily by day 21. PATIENTS: Twelve patients (age 63-85 years) with schizophrenia, schizoaffective disorder or bipolar disorder. MAIN OUTCOME MEASURES AND RESULTS: Key assessments included quetiapine plasma concentrations, and neurological and safety evaluations. Under steady-state conditions, the 100 and 250mg doses of quetiapine were not significantly different in terms of dose-normalised area under the plasma concentration-time curve within an 8-hour dose administration interval, or in dose-normalised minimum plasma concentration (C(min)) at the end of a dose administration interval. The morning C(min) values for the seven discrete dose amounts evaluated also increased linearly with dose. The apparent oral clearance, volume of distribution and half-life did not change as a function of dose. There were no serious adverse events. The most common adverse events were postural hypotension (n = 6), dizziness (n = 5) and somnolence (n = 4). CONCLUSIONS: While quetiapine was well tolerated at doses up to 250mg three times daily, the potential for reduced clearance, as well as the adverse effects of postural hypotension and dizziness, indicated that quetiapine should be introduced at lower doses and titrated at a relatively slower rate in patients > or =65 years.

Phenylpropanolamine appears not to promote weight loss in patients with schizophrenia who have gained weight during clozapine treatment.

BACKGROUND: Weight gain is a common side effect of clozapine treatment and may expose patients to obesity-associated health risks. We proposed that concomitant treatment with an appetite suppressant such as phenylpropanolamine (PPA) would lead to a decrease in appetite and therefore loss of weight. METHOD: This was a 12-week, double-blind, randomized, placebo-controlled trial of PPA, 75 mg/day, in outpatients with treatment-refractory schizophrenia (DSM-IV) who were stable on clozapine treatment for at least 4 months and had gained > 10% of their baseline body weight since starting clozapine. Patients were evaluated for adverse effects and weighed weekly. A Positive and Negative Syndrome Scale (PANSS) assessment, a short dietary quiz, and blood indices were completed monthly. RESULTS: Sixteen patients were equally randomly assigned to receive PPA or placebo. The groups did not differ in mean age, baseline weight, dose of clozapine, baseline PANSS scores, or the percent of weight gained since the start of clozapine. There was no significant effect of treatment on weight (t = 0.219, df = 10, p = .831). There was no significant change in either the total PANSS scores (t = -0.755, df = 10, p = .468), the positive or negative symptom cluster scores, or any of the remaining variables. CONCLUSION: Phenylpropanolamine 75 mg/day was well tolerated but was not effective in reversing established weight gain associated with clozapine treatment in stable outpatients with schizophrenia.

A meta-analysis of the response to chronic L-dopa in patients with schizophrenia: therapeutic and heuristic implications.

RATIONALE: While it is generally believed that administration of the dopamine precursor levodopa ( L-dopa) exacerbates symptoms of schizophrenia, numerous reports suggest that adjunctive L-dopa may be beneficial. This body of literature has not been critically reviewed. OBJECTIVES: On the basis of published studies, to determine whether L-dopa administered concomitantly with antipsychotic drugs provides a beneficial response in patients with schizophrenia. METHODS: This review examined 30 studies involving 716 patients. Due to wide methodological variability and limited statistical information, only five studies encompassing 160 patients could be included in a meta-analysis. The others were evaluated qualitatively. RESULTS: When L-dopa was added to antipsychotic drugs, the overall improvement was moderate ( d=0.71) and highly significant ( P<0.0001). There were 16 other studies in which L-dopa was added to antipsychotic drugs, but which did not meet criteria for inclusion in the meta-analysis. In these, worsening occurred in less than 20% of patients; the percentage of improved patients varied widely but had a central tendency around 50%. CONCLUSIONS: . In patients already on antipsychotic drugs, the addition of L-dopa can be beneficial. Dopamine agonists merit further consideration as adjuncts to antipsychotic drugs in the treatment of schizophrenia.

Brain tyrosine depletion attenuates haloperidol-induced striatal dopamine release in vivo and augments haloperidol-induced catalepsy in the rat.

RATIONALE: There are conflicting reports as to whether alterations in tyrosine levels affect functional indices of striatal dopamine (DA) transmission. Since the DA antagonist haloperidol (HAL) increases striatal DA release and induces catalepsy through its actions on striatal DA systems, it provides a useful paradigm to assess both neurochemical and behavioral effects of lowering brain tyrosine levels. OBJECTIVES: To determine how brain tyrosine depletion affects HAL-induced catalepsy and striatal DA release in awake, freely moving rats. METHODS: In male rats, a control or tyrosine- and phenylalanine-free neutral amino acid solution NAA(-) (IP) was administered 30-60 min prior to HAL (IP). In one cohort, striatal microdialysate was assayed for DA levels. In a parallel cohort, catalepsy was measured using the bar test. RESULTS: NAA (-) reduced striatal tyrosine levels by 60%. The latter did not affect basal striatal DA release, but consistently delayed the attainment of maximal HAL-induced (0.19 mg/kg and 0.25 mg/kg SC) striatal DA release; the latter was abolished by administration of tyrosine. NAA(-) also potentiated HAL-induced catalepsy. CONCLUSIONS: Acute brain tyrosine depletion attenuates HAL-induced striatal DA release and potentiates haloperidol-induced catalepsy. Both effects can be reversed by administration of tyrosine. Overall, the data indicate that tyrosine depletion affects both neurochemical and behavioral indices of striatal DA release.