Mismatch negativity generation in the human 5HT2A agonist and NMDA antagonist model of psychosis

RATIONALE: Many studies have reported deficits of mismatch negativity (MMN) in schizophrenic patients. Pharmacological challenges with hallucinogens in healthy humans are used as models for psychotic states. Previous studies reported a significant reduction of MMN after ketamine (N-methyl-D-aspartate acid [NMDA] antagonist model) but not after psilocybin (5HT2A agonist model). OBJECTIVES: The aim of the present study was to directly compare the two models of psychosis using an intraindividual crossover design. MATERIALS AND METHODS: Fifteen healthy subjects participated in a randomized, double-blind, crossover study with a low and a high dose of the 5HT2A agonist dimethyltryptamine (DMT) and the NMDA antagonist S-ketamine. During electroencephalographic recording, the subjects were performing the AX-version of a continuous performance test (AX-CPT). A source analysis of MMN was performed on the basis of a four-source model of MMN generation. RESULTS: Nine subjects completed both experimental days with the two doses of both drugs. Overall, we found blunted MMN and performance deficits in the AX-CPT after both drugs. However, the reduction in MMN activity was overall more pronounced after S-ketamine intake, and only S-ketamine had a significant impact on the frontal source of MMN. CONCLUSIONS: The NDMA antagonist model and the 5HT2A agonist model of psychosis display distinct neurocognitive profiles. These findings are in line with the view of the two classes of hallucinogens modeling different aspects of psychosis

Molecular biology of the blood-brain and the blood-cerebrospinal fluid barriers: similarities and differences

Efficient processing of information by the central nervous system (CNS) represents an important evolutionary advantage. Thus, homeostatic mechanisms have developed that provide appropriate circumstances for neuronal signaling, including a highly controlled and stable microenvironment. To provide such a milieu for neurons, extracellular fluids of the CNS are separated from the changeable environment of blood at three major interfaces: at the brain capillaries by the blood-brain barrier (BBB), which is localized at the level of the endothelial cells and separates brain interstitial fluid (ISF) from blood; at the epithelial layer of four choroid plexuses, the blood-cerebrospinal fluid (CSF) barrier (BCSFB), which separates CSF from the CP ISF, and at the arachnoid barrier. The two barriers that represent the largest interface between blood and brain extracellular fluids, the BBB and the BCSFB, prevent the free paracellular diffusion of polar molecules by complex morphological features, including tight junctions (TJs) that interconnect the endothelial and epithelial cells, respectively. The first part of this review focuses on the molecular biology of TJs and adherens junctions in the brain capillary endothelial cells and in the CP epithelial cells. However, normal function of the CNS depends on a constant supply of essential molecules, like glucose and amino acids from the blood, exchange of electrolytes between brain extracellular fluids and blood, as well as on efficient removal of metabolic waste products and excess neurotransmitters from the brain ISF. Therefore, a number of specific transport proteins are expressed in brain capillary endothelial cells and CP epithelial cells that provide transport of nutrients and ions into the CNS and removal of waste products and ions from the CSF. The second part of this review concentrates on the molecular biology of various solute carrier (SLC) transport proteins at those two barriers and underlines differences in their expression between the two barriers. Also, many blood-borne molecules and xenobiotics can diffuse into brain ISF and then into neuronal membranes due to their physicochemical properties. Entry of these compounds could be detrimental for neural transmission and signalling. Thus, BBB and BCSFB express transport proteins that actively restrict entry of lipophilic and amphipathic substances from blood and/or remove those molecules from the brain extracellular fluids. The third part of this review concentrates on the molecular biology of ATP-binding cassette (ABC)-transporters and those SLC transporters that are involved in efflux transport of xenobiotics, their expression at the BBB and BCSFB and differences in expression in the two major blood-brain interfaces. In addition, transport and diffusion of ions by the BBB and CP epithelium are involved in the formation of fluid, the ISF and CSF, respectively, so the last part of this review discusses molecular biology of ion transporters/exchangers and ion channels in the brain endothelial and CP epithelial cells

Subjective and physiological responses among racemic-methadone maintenance patients in relation to relative (S)- vs. (R)-methadone exposure

The definitive version is available at www.blackwell-synergy.comAIMS: To investigate the possibility that (S)-methadone influences therapeutic and adverse responses to rac-methadone maintenance treatment, by examining how subjective and physiological responses among rac-methadone maintenance patients vary in relation to relative exposure to (S)- vs. (R)-methadone. METHODS: Mood states (Profile of Mood States), opioid withdrawal (Methadone Symptoms Checklist), physiological responses (pupil diameter, heart rate, respiration rate, blood pressure), and plasma concentrations (CP) of (R)- and (S)-methadone were measured concurrently 11–12 times over a 24-h interdosing interval in 55 methadone maintenance patients. Average steady-state plasma concentrations (Cav) and pharmacodynamic responses were calculated using area under the curve (AUC). Linear regression was used to determine whether variability in pharmacodynamic responses was accounted for by (S)-methadone Cav controlling for (R)-methadone Cav and rac-methadone dose. Ratios of (S)-:(R)-methadone using AUCCP and trough values were correlated with pharmacodynamic responses for all subjects and separately for those with daily rac-methadone doses ≥ 100 mg. RESULTS: (S)-methadone Cav accounted for significant variability in pharmacodynamic responses beyond that accounted for by (R)-methadone Cav and rac-methadone dose, showing positive associations (partial r) with the intensity of negative mood states such as Tension (0.28), Fatigue (0.31), Confusion (0.32), and opioid withdrawal scores (0.30); an opposite pattern of relationships was evident for (R)-methadone. The plasma (S)-:(R)-methadone AUCCP ratio (mean ± SD 1.05 ± 0.21, range 0.65–1.51) was not significantly related to pharmacodynamic responses for the subjects as a whole but showed significant positive associations (r) with the intensity of negative mood states such as Total Mood Disturbance (0.61), Tension (0.69), Fatigue (0.65), Confusion (0.64), Depression (0.49) and heart rate (0.59) for the ≥ 100-mg dose range. CONCLUSIONS: These findings agree with previous evidence that (S)-methadone is associated with a significant and potentially adverse profile of responses distinct from that of (R)-methadone. Individual variability in relative (S)- vs. (R)-methadone exposure may be associated with variability in response to rac-methadone maintenance treatment.Timothy B. Mitchell, Kyle R. Dyer, David Newcombe, Amy Salter, Andrew A. Somogyi, Felix Bochner and Jason M. Whit

Lactate modulates the activity of primary cortical neurons through a receptor-mediated pathway.

Lactate is increasingly described as an energy substrate of the brain. Beside this still debated metabolic role, lactate may have other effects on brain cells. Here, we describe lactate as a neuromodulator, able to influence the activity of cortical neurons. Neuronal excitability of mouse primary neurons was monitored by calcium imaging. When applied in conjunction with glucose, lactate induced a decrease in the spontaneous calcium spiking frequency of neurons. The effect was reversible and concentration dependent (IC50 ∼4.2 mM). To test whether lactate effects are dependent on energy metabolism, we applied the closely related substrate pyruvate (5 mM) or switched to different glucose concentrations (0.5 or 10 mM). None of these conditions reproduced the effect of lactate. Recently, a Gi protein-coupled receptor for lactate called HCA1 has been introduced. To test if this receptor is implicated in the observed lactate sensitivity, we incubated cells with pertussis toxin (PTX) an inhibitor of Gi-protein. PTX prevented the decrease of neuronal activity by L-lactate. Moreover 3,5-dyhydroxybenzoic acid, a specific agonist of the HCA1 receptor, mimicked the action of lactate. This study indicates that lactate operates a negative feedback on neuronal activity by a receptor-mediated mechanism, independent from its intracellular metabolism