Philipp Görtz

Implications for hyperhomocysteinemia: not homocysteine but its oxidized forms strongly inhibit neuronal network activity

Severe hyperhomocysteinemia (50-200 microM) often presents itself with acute neuronal dysfunction including seizures and psychosis. Its moderate form (15-50 microM) is associated with cognitive impairment and dementia. We investigated the neuropharmacological effects of homocysteine and its oxidized forms, homocysteinesulfinic acid (HCSA) and homocysteic acid (HCA), on neuronal network function utilizing dissociated cortical neurons from embryonic Wistar rats on microelectrode arrays. All substances inhibited dose-dependently and reversibly spontaneous neuronal network activity within seconds: L-HCSA and L-HCA blocked spontaneous spike rate (SSR) significantly at very low concentrations, with an IC50 of 1.9 and 1.3 microM, respectively; whereas the dose-response curve of D,L-homocysteine revealed an IC50 of 401 microM. These effects were antagonized by 2-amino-5-phosphonovaleric acid (APV) pointing to the NMDA receptor as mediator of this fast and reversible inhibition of network activity. We conclude that a neuronal dysfunction observed in hyperhomocysteinemia is likely due to HCSA and HCA since effective concentrations of homocysteine are not reached in patients.

Cryopreserved rat cortical cells develop functional neuronal networks on microelectrode arrays

Neurons growing on microelectrode arrays (MEAs) are promising tools to investigate principal neuronal network mechanisms and network responses to pharmaceutical substances. However, broad application of these tools, e.g. in pharmaceutical substance screening, requires neuronal cells that provide stable activity on MEAs. Cryopreserved cortical neurons (CCx) from embryonic rats were cultured on MEAs and their immunocytochemical and electrophysiological properties were compared with acutely dissociated neurons (Cx). Both cell types formed neuritic networks and expressed the neuron-specific markers microtubule associated protein 2, synaptophysin, neurofilament and gamma-aminobutyric acid (GABA). Spontaneous spike activity (SSA) was recorded after 9 up to 74 days in vitro (DIV) in CCx and from 5 to 30 DIV in Cx, respectively. Cx and CCx exhibited synchronized burst activity with similar spiking characteristics. Tetrodotoxin (TTX) abolished the SSA of both cell types reversibly. In CCx SSA-inhibition occurred with an IC50 of 1.1 nM for TTX, 161 microM for magnesium, 18 microM for D,L-2-amino-5-phosphonovaleric acid (APV) and 1 microM for GABA. CCx cells were easy to handle and developed long living, stable and active neuronal networks on MEAs with similar characteristics as Cx. Thus, these neurochips seem to be suitable for studying neuronal network properties and screening in pharmaceutical research.

Neuronal network properties of human teratocarcinoma cell line-derived neurons

Understanding the structural and functional development of neurons in networks has a high impact to estimate the potentials for restorative therapies. Neurons derived from the human NT2 cell line (hNT) formed networks with a clustered neuritic architecture in vitro, whereas primary dissociated embryonic rat cortical neurons (Cx) displayed a more homogenous cell assembly. Spontaneous spikes of both cell types were recorded on microelectrode arrays within 2 weeks after seeding, but hNT showed a mostly uncorrelated firing pattern in contrast to Cx with highly synchronized bursting. hNT neurons were less sensitive to TTX (IC50 = 5.7 +/- 0.1 nM vs. IC50 = 1.1 +/- 0.2 nM), magnesium (IC50 = 1.83 +/- 0.01 mM vs. IC50 = 0.161 +/- 0.023 mM), and APV (IC50 > 100 microM vs. IC50 = 18 microM). We conclude that embryonic cortical neurons and hNT neurons have different network properties. This should be carefully considered before hNT neurons are used in therapeutic approaches, e g., central nervous system (CNS) grafting.

Transient reduction of spontaneous neuronal network activity by sublethal amyloid β (1–42) peptide concentrations

Soluble amyloid β1–42 (Aβ1–42) peptide has recently been assigned a key role in early Alzheimer’s disease (AD) pathophysiology accounting for synaptic dysfunction before amyloid plaque formation and neurodegeneration can occur. Following sublethal Aβ1–42 administration, we observed an acute but transient reduction of the spike and burst rate of spontaneously active cortical networks cultured on microelectrode arrays. This simple experimental system appears suitable for future long-term pharmacological and genetic studies of Aβ1–42 signaling, thus providing a valuable new tool in AD research.

An Ultrasensitive Assay for Diagnosis of Alzheimer's Disease

Alzheimers disease (AD) is a chronic neurodegenerative disorder and the most common cause of dementia. Aging is among the most significant risk factors. Today, AD can be diagnosed with certainty only post mortem, detecting insoluble beta-amyloid peptide (Abeta) aggregates in the patients brain tissue. We have developed an ultrasensitive assay for early and non-invasive diagnosis of AD. This highly specific and sensitive assay uses fluorescence correlation spectroscopy (FCS) and is sensitive enough to detect even single aggregates in body fluids of AD patients. We investigate the correlation of aggregated Abeta concentrations in body fluids with clinical symptoms of AD.

Disturbance of Cultured Rat Neuronal Network Activity Depends on Concentration and Ratio of Leucine and α-Ketoisocaproate: Implication for Acute Encephalopathy of Maple Syrup Urine Disease

Increased concentrations of leucine and its respective ketoacid α-ketoisocaproate (KIC) in plasma and cerebrospinal fluid are related to acute and reversible encephalopathy in patients with maple syrup urine disease. We studied electrophysiological properties of primary dissociated rat neurons at increased extracellular concentrations of leucine and KIC (1-10 mM). Spontaneous neuronal network activity was reversibly reduced or blocked by leucine as well as by KIC in a dose-dependent manner. Simultaneous incubation with both substances led to a minor inhibition compared to the effect of each substance alone. Neuronal resting potential, voltage dependent Na+ (INa) and K+ (IK) currents, the GABA- and glycine-elicited membrane currents, and glutamate-induced intracellular Ca2+ increase of single neurons, however, were unaffected by both substances. We conclude that acute neuronal network dysfunction in maple syrup urine disease is mainly based on an imbalance of the presynaptic glutamatergic/GABAergic neurotransmitter concentrations or their release.

Multielectrode array analysis of cerebrospinal fluid in Alzheimer’s disease versus mild cognitive impairment: A potential diagnostic and treatment biomarker

Pathological cerebrospinal fluid (CSF) alterations like changes in amyloid-β1-42 and tau protein concentration are typical in Alzheimers disease (AD). However, it remains unclear, if the composition of known or unknown pathological factors in native CSF has a functional significance in AD. In this pilot study, we used multielectrode array (MEA) neurochips to determine whether CSF of individuals with AD (AD-CSF) may have distinct neurofunctional properties that may distinguish it from that of individuals with mild cognitive impairment (MCI) - a differential diagnosis of high clinical importance. MEAs are neuronal cultures coupled to a multisite electrical recording system with the ability to reflect pharmacological or toxicological alterations on the functional level of whole neuronal networks. Collective rhythmical electrical activity was substantially enhanced after exposure to CSF of cognitively healthy subjects (controls) and of MCI individuals (MCI-CSF) alike. However, this activity increment was significantly reduced when MEAs were exposed to AD-CSF compared to MCI-CSF. Moreover, following AD-CSF exposure, networks showed significantly enhanced burst durations and less synchronous bursting, respectively. Thus, AD-CSF and MCI-CSF could be distinguished by characteristic changes of the network firing pattern on MEAs. When data of MCI individuals and AD patients were pooled, the network suppression correlated significantly with the degree of cognitive decline. The findings of this pilot study may set the stage for a unique and straightforward diagnostic bioassay of AD with particular value in the differential diagnosis to MCI and as a much needed biomarker for clinical trials.

Assessment-based Home Treatment for People with Schizophrenia Spectrum Disorder

Introduction There is a growing evidence for clinical effectiveness of Home Treatment for patients with severe psychotic disorders . Here we present the development and implementation of a manualised assessment-based Home Treatment in Germany. Objectives We compared the 6-month effectiveness of an assessment-based Home Treatment in patients with schizophrenia spectrum disorder to standard care in a catchment area design. Aims The primary outcome criteria was the rehospitalisation rate. Secondary outcomes comprised improvement of symptoms, functioning, quality of life, medication adherence and satisfaction with care. Methods Assessments were carried out at baseline and at 3 and 6 month. Inpatient admission and treatment contacts were assessed from the hospital database. Results We visited 20 patients with severe psychotic disorder (ICD10: F2.x) almost 400 times in twelve months. The median was 15.5 visits per patient. The intervention resulted in a highly significant reduction of the rehospitalisation rate (−51%, P Conclusions Applying assessment-based Home Treatment for patients with severe psychotic disorders is an alternative treatment compared with standard care resulting in a significant lower rehospitalisation rate with an equivalent clinical outcome.