Glutamic acid diethyl ester induces catalepsy in rats. A new model for schizophrenia?

Aspects of Piaget's cognitive developmental psychology and neurobiology of psychotic disorders - an integrative model

Psychological, neurobiological and neurodevelopmental approaches have frequently been used to provide pathogenic concepts on psychotic disorders. However, aspects of cognitive developmental psychology have hardly been considered in current models. Using a hypothesis-generating approach an integration of these concepts was conducted. According to Piaget (1896-1980), assimilation and accommodation as forms of maintenance and modification of cognitive schemata represent fundamental processes of the brain. In general, based on the perceived input stimuli, cognitive schemata are developed resulting in a conception of the world, the realistic validity and the actuality of which is still being controlled and modified by cognitive adjustment processes. In psychotic disorders, however, a disproportion of environmental demands and the ability to activate required neuronal adaptation processes occurs. We therefore hypothesize a failure of the adjustment of real and requested output patterns. As a consequence autonomous cognitive schemata are generated, which fail to adjust with reality resulting in psychotic symptomatology. Neurobiological, especially neuromodulatory and neuroplastic processes play a central role in these perceptive and cognitive processes. In conclusion, integration of cognitive developmental psychology into the existing pathogenic concepts of psychotic disorders leads to interesting insights into basic disease mechanisms and also guides future research in the cognitive neuroscience of such disorders.

Modulation of NMDA and dopaminergic neurotransmissions by sigma ligands: possible implications for the treatment of psychiatric disorders

Sigma (sigma) receptors, improperly classified as belonging to the opiate receptor family when discovered in 1976, were subsequently confused with phencyclidine binding sites for several years. It's only recently, with the emergence of new selective ligands that their functional significance could be meaningfully addressed. Several subtypes of sigma receptors are present in high densities in the limbic structures as well as in motor-related areas of the CNS. Different lines of evidence suggest that a major role for sigma receptors might be to regulate the activity of the glutamatergic system via the modulation one of its subtype of receptor, the NMDA receptor. This modulation of the glutamatergic system could in turn interfere with the dopaminergic neurotransmission with which, however, sigma ligands could also interact directly. The potential involvement of sigma receptors in schizophrenia has been considered ever since their discovery. The initial suggestion to this respect emerged from the observation that several of the earliest sigma ligands induced psychotomimetic symptoms such as delusions, hallucinations and depersonalization. This link was later reinforced with the demonstration that several neuroleptics, such as haloperidol, have a high affinity for sigma receptors, whereas, some new molecules with a high affinity for sigma receptors, but a low affinity for dopaminergic receptors demonstrated a "neuroleptic-like" pharmacological profile. However, the therapeutic efficacy of selective sigma ligands in schizophrenia has not yet been established and it has even been suggested that sigma receptors might be responsible for some side effects of the classical neuroleptics. The possible implication of sigma receptors in affective disorders has also been suggested by reports showing that some antidepressant drugs have a high affinity for sigma receptors and that long-term treatments with anti- depressant drugs, even with those devoid of affinity for sigma receptors, modify their binding characteristics. In conclusion, indirect evidence suggests possible etiological and/or therapeutic roles for sigma receptors in some psychiatric disorders. However, despite several attempts, no clear indications of a therapeutic efficacy of sigma ligands has yet emerged. More selective ligands and fundamental studies on the respective role of the different subtypes of sigma receptors are needed before clear concepts can be formulated. p3

Voltage-gated and synaptic currents in rat Purkinje cells in dissociated cell cultures

The electrical properties of rat Purkinje cells and synapses from granule cells were studied in dissociated cell cultures. To identify the cells we used an immunohistochemical method and recorded voltage-gated and synaptic currents with the patch-clamp technique (the whole-cell mode). Cultured Purkinje cells generated action potentials similar to those recorded from in vitro slices or in vivo preparations. Early Na, late Ca inward current, and K outward currents were distinguished by ion substitution under voltage clamp. We also recorded spontaneous synaptic currents in Purkinje cells cultured with granule cells. These synaptic currents reversed direction at the membrane potential of 2.5 mV, which was similar to currents induced by L-glutamate. Therefore, these are most likely excitatory synaptic currents from granule cells. Since these properties of Purkinje cells examined here are similar to those in situ, the cells in dissociated cell cultures offer a great opportunity to study biophysical properties of identified neurons in the central nervous system.

2-Amino-4-phosphonobutyric acid selectively blocks two-way avoidance learning in the mouse

There seems to be ample evidence supporting the view that glutamate plays a significant role in the mammalian brain as a neurotransmitter. It is considered to be a likely transmitter candidate in one or more hippocampal pathways. Recently it has been visualized in excitatory, possibly glutamatergic, neurons in the hippocampus. Glutamate has been proposed to mediate memory formation. We wanted to see if blocking glutamate action by a specific glutamate antagonist could result in reduction of learning ability. 2-Amino-4-phosphonobutyric acid (APB) is an analogue of glutamic acid and has been used as a glutamate antagonist in electrophysiological studies on invertebrate neuromuscular junction, retina and hippocampus. We tested the influence of APB on the acquisition of two way avoidance learning in the shuttle box and on learning in the water maze. Our results show that intraperitoneal injection of APB led to a reduction in avoidance learning, whereas learning in the water maze was unaffected.

Acidic amino acid binding sites in mammalian neuronal membranes: their characteristics and relationship to synaptic receptors

This review summarizes studies designed to label and characterize mammalian synaptic receptors for glutamate, aspartate and related acidic amino acids using in vitro ligand binding techniques. The binding properties of the 3 major ligands employed--L-[3H]glutamate, L-[3H]aspartate and [3H]kainate--are described in terms of their kinetics, the influence of ions, pharmacology, molecular nature, localization and physiological/pharmacological function. In addition, the binding characteristics are described of some new radioligands--[3H]AMPA, L-[3H]cysteine sulphinate, L-[35S]cysteate, D-[3H]aspartate, D,L-[3H]APB, D-[3H]APV and D,L-[3H]APH. Special emphasis is placed on recent findings which allow a unification of the existing binding data, and detailed comparisons are made between binding site characteristics and the known properties of the physiological/pharmacological receptors for acidic amino acids. Through these considerations, a binding site classification is suggested which differentiates 5 different sites. Four of the binding site subtypes are proposed to correspond to the individual receptor classes identified in electrophysiological experiments; thus, A1 = NMDA receptors; A2 = quisqualate receptors; A3 = kainate receptors; A4 = L-APB receptors; the fifth site is proposed to be the recognition site for a Na+-dependent acidic amino acid membrane transport process. An evaluation of investigations designed to elucidate regulatory mechanisms at acidic amino acid binding sites is made; hypotheses such as the Ca2+-activated protease hypothesis of long-term potentiation are assessed in terms of the new binding site/receptor classification scheme, and experiments are suggested which will clarify and expand this exciting area in the future.

Chemistry, physiology and neuropsychology of schizophrenia: towards an earlier diagnosis of schizophrenia I

Data supporting the glutamate hypothesis of schizophrenia are presented. The glutamate hypothesis is linked to the dopamine hypothesis by the fact that dopamine synapses inhibit the release of glutamate in the striate and mesolimbic system. The glutamate hypothesis of schizophrenia may open a way to find better drugs for treatment. The concept of schizophrenia I is described. It consists of "negative symptoms" such as disconcentration or reduction of energy. Schizophrenia I precedes and follows schizophrenia II with "positive symptoms," e.g. hallucinations and delusions. Schizophrenia I so far cannot be diagnosed as schizophrenia unless schizophrenia II appears. Chemical, physiological or neuropsychological methods for the diagnosis of schizophrenia I would render an earlier treatment of schizophrenia possible and thus make social and occupational rehabilitation more efficient. An objective diagnosis of schizophrenia I may also elucidate the mode of genetic transmission of schizophrenia. Several neuropsychological methods distinguish schizophrenic patients as a group from normals. Some of them are based on a specific disturbance of long term concentration. The EEG also distinguishes schizophrenics from normals when analyzed during voluntary movement. For schizophrenics it takes more effort to initiate a voluntary movement, and there are several features of the EEG correlated to this. Moreover, the longer motor reaction time of schizophrenics is paralleled by a longer duration of the Bereitschaftspotential in schizophrenia. Furthermore, there is a difference in the theta rhythm between schizophrenic patients and normals in a task which requires concentration. Some of the children of schizophrenic parents show a disturbance of concentration in both reaction time tasks and the d 2 test.(ABSTRACT TRUNCATED AT 250 WORDS)