NYX-458 Improves Cognitive Performance in a Primate Parkinson's Disease Model.

BACKGROUND: NYX-458 is a N-methyl-d-aspartate receptor (NMDAR) modulator that enhances synaptic plasticity. Dopaminergic cell loss in Parkinson's disease (PD) leads to NMDAR dysregulation in the cortico-striato-pallidal-thalmo-cortical network and altered plasticity in brain regions important to cognitive function. We hypothesize that targeting the NMDAR may be an efficacious approach to treating cognitive impairment in PD. OBJECTIVES: NYX-458 was evaluated in 2 nonhuman primate models of PD. The first, a chronic low-dose 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-administration model, was used to assess the effects of NYX-458 on cognitive domains impacted early in PD including attention, working memory, executive function, and visuospatial learning. The second, a high-dose MPTP-administration model, was used to assess potential for NYX-458 induced change in motor symptoms. METHODS: NYX-458 was evaluated in the chronic low-dose MPTP model using the variable delayed response measure to assess attention and working memory and simple discrimination reversal to assess executive function. NYX-458 was also assessed in the high-dose MPTP model as a monotherapy and in combination with low-dose or high-dose levodopa to assess potential impact on motor symptoms. RESULTS: NYX-458 administration resulted in rapid and long-lasting improvement in cognitive function across the domains of attention, working memory, and executive function. Dose levels effective in improving cognitive performance had no effect on PD motor symptoms, the antiparkinsonian benefit of levodopa, or dyskinesia. CONCLUSIONS: NYX-458 provides benefit in specific domains known to be impaired in PD in a dopamine depletion model of PD-like cognitive impairment. These data support the continued evaluation of NYX-458 as a potential therapeutic for cognitive decline in PD. © 2020 International Parkinson and Movement Disorder Society.

Regional changes in gene expression after limbic kindling.

Repeated electrical stimulation results in development of seizures and a permanent increase in seizure susceptibility (kindling). The permanence of kindling suggests that chronic changes in gene expression are involved. Kindling at different sites produces specific effects on interictal behaviors such as spatial cognition and anxiety, suggesting that causal changes in gene expression might be restricted to the stimulated site. We employed focused microarray analysis to characterize changes in gene expression associated with amygdaloid and hippocampal kindling. Male Long-Evans rats received 1 s trains of electrical stimulation to either the amygdala or hippocampus once daily until five generalized seizures had been kindled. Yoked control rats carried electrodes but were not stimulated. Rats were euthanized 14 days after the last seizures, both amygdala and hippocampus dissected, and transcriptome profiles compared. Of the 1,200 rat brain-associated genes evaluated, 39 genes exhibited statistically significant expression differences between the kindled and non-kindled amygdala and 106 genes exhibited statistically significant differences between the kindled and non-kindled hippocampus. In the amygdala, subsequent ontological analyses using the GOMiner algorithm demonstrated significant enrichment in categories related to cytoskeletal reorganization and cation transport, as well as in gene families related to synaptic transmission and neurogenesis. In the hippocampus, significant enrichment in gene expression within categories related to cytoskeletal reorganization and cation transport was similarly observed. Furthermore, unique to the hippocampus, enrichment in transcription factor activity and GTPase-mediated signal transduction was identified. Overall, these data identify specific and unique neurochemical pathways chronically altered following kindling in the two sites, and provide a platform for defining the molecular basis for the differential behaviors observed in the interictal period.

Using rat ultrasonic vocalization to study the neurobiology of emotion: from basic science to the development of novel therapeutics for affective disorders.

The use of ultrasonic vocalizations as an experimental tool for studying emotional states in rodents has led to an increased understanding of the basic science of affect as well as the development of novel diagnostics and therapeutics for the treatment of affective disorders. At the behavioral level, the rules that govern the generation of affective 'feeling' states are similar to those of the psychophysics of sensory perception. Emotions are elicited primarily in response to active social stimuli. A linear increase in affective response requires a logarithmic increase in stimulation and habituation of a given affective response allows for transition across the cycle of emotional/affective states (approach→consummatory phase→avoidance). At the neuronal level, the coordinated expression of affective responses in the medial prefrontal cortex is orchestrated by rhythmic activity, which is initiated and maintained by a variety of short-term and long-term synaptic plasticity processes. An objective measure of affective states may emerge from these psychophysical and neuronal properties of emotion. Enhancing synaptic plasticity with pharmacological agents that modulate NMDA receptor activity as well as IGFI receptor activity may have therapeutic potential for the treatment of affective disorders.

A translational EEG-based approach to assess modulation of long-lasting NMDAR-dependent synaptic plasticity.

BACKGROUND: NYX-2925 is a novel N-methyl-D-aspartate receptor (NMDAR) modulator that has been shown to facilitate both NMDAR-dependent long-term potentiation (LTP) in vitro and learning and memory in vivo. OBJECTIVE: The present studies examine the effects of NYX-2925 on NMDAR-dependent auditory LTP (aLTP) in vivo. METHODS: NMDAR-dependent aLTP and NMDAR-dependent auditory mismatch negativity (MMN) was measured, as well as changes in resting-state qEEG power. RESULTS: NYX-2925 (1, 10 mg/kg PO) increased aLTP 1 h after auditory tetanus measured by the post- minus pre-tetanus difference waveform 140-180 ms post tone onset. NYX-2925 (0.1, 1 mg/kg PO) facilitated MMN measured by the difference waveform (i.e., deviant minus standard tones). NYX-2925 (0.1, 1, 10 mg/kg PO) also enhanced resting-state alpha qEEG power. Conversely, the NMDAR glutamate site antagonist CPP (10 mg/kg IP) reduces alpha power and MMN and produces an opposite effect as NYX-2925 on aLTP. CONCLUSIONS: Together, these data suggest that the activation of the NMDAR by NYX-2925 enhances synaptic plasticity in vivo, which may both reduce symptoms of neurological disorders and serve as a biomarker for drug effects. This is the first demonstration of a long-lasting (1-h post-tetanus) effect of NMDAR modulation on synaptic plasticity processes in vivo using a noninvasive technique in freely behaving animals.

Rats selectively bred for low levels of 50 kHz ultrasonic vocalizations exhibit alterations in early social motivation.

In rats, the rates of 50 kHz ultrasonic vocalizations (USVs) can be used as a selective breeding phenotype and variations in this phenotype can be an indicator of affective states. The 50 kHz USV is elicited by rewarding stimuli (e.g., food, sexual behavior) and therefore can express a positive affective state. Conversely, the 22 kHz USV is elicited by aversive stimuli (e.g., presence of a predator, social defeat) indicating a negative affective state. In the present study, we tested the effect of selectively breeding for 50 kHz USVs on a variety of maternal social/emotional behaviors in young rat pups (PND 10-12). These measures consisted of an assessment of isolation calls and conditioned odor preference paradigm. Results indicate that animals selected for low levels of 50 kHz USVs show the greatest alterations in social behaviors compared to the control animals. The low line animals had an increase in isolation calls tested during place preference conditioning and a decrease in 50 kHz ultrasonic calls in all conditions. These same low line animals failed to show a typical preference for a maternally-associated odor during the place preference test. The different social behaviors of the high line animals did not consistently vary from those of the control group. These results have important implications for the study of genetic and epigenetic mechanisms underlying emotional states, and possibly contribute to the research underlying the emotional changes in developmental disorders such as autistic spectrum disorder by providing a novel animal model that displays communication deficits that are interdependent with significant social behavioral impairments.

Modeling depression: social dominance-submission gene expression patterns in rat neocortex.

Gene expression profiles in the cortex of adult Long-Evans rats as a function of a stressful social loss and victory in inter-male fighting encounters were examined. This social dominance and subordination model has been postulated to simulate early changes in the onset of depression in the losers. Microarrays were fabricated containing 45mer oligonucleotides spotted in quadruplicate and representing 1178 brain-associated genes. Dynamic range, discrimination power, accuracy and reproducibility were determined with standard mRNA "spiking" studies. Gene expression profiles in dominant and subordinate animals were compared using a "universal" reference design [Churchill GA (2002) Fundamentals of experimental design for cDNA microarrays. Nat Genet 32 (Suppl):490-495]. Data were analyzed by significance analysis of microarrays using rank scores [Tusher VG, Tibshirani R, Chu G (2001) Significance analysis of microarrays applied to the ionizing radiation response. Proc Natl Acad Sci USA 98:5116-5121; van de Wiel MA (2004) Significance analysis of microarrays using rank scores. Kwantitatieve Methoden 71:25-37]. Ontological analyses were then performed using the GOMiner algorithm [Zeeberg BR, Feng W, Wang G, Wang MD, Fojo AT, Sunshine M, Narasimhan S, Kane DW, Reinhold WC, Lababidi S, Bussey KJ, Riss J, Barrett JC, Weinstein JN (2003) GoMiner: a resource for biological interpretation of genomic and proteomic data. Genome Biol 4(4):R28]. And finally, genes of special interest were further studied using quantitative reverse transcriptase polymerase chain reaction. Twenty-two transcripts were statistically significantly differentially expressed in the neocortex between dominant and subordinate animals. Ontological analyses revealed that significant gene changes were clustered primarily into functional neurochemical pathways associated with protein biosynthesis and cytoskeletal dynamics. The most robust of these were the increased expression of interleukin-18, heat shock protein 27, beta3-tubulin, ribosome-associated membrane protein 4 in subordinate animals. Interleukin-18 has been found to be over-expressed in human depression and panic disorder as well as other physiological stress paradigms [Takeuchi M, Okura T, Mori T, Akita K, Ohta T, Ikeda M, Ikegami H, Kurimoto M (1999) Intracellular production of interleukin-18 in human epithelial-like cell lines is enhanced by hyperosmotic stress in vitro. Cell Tissue Res 297(3):467-473] and heat shock proteins have been shown to be involved in the pathogenesis of many neurodegenerative and psychiatric disorders [Iwamoto K, Kakiuchi C, Bundo M, Ikeda K, Kato T (2004) Molecular characterization of bipolar disorder by comparing gene expression profiles of postmortem brains of major mental disorders. Mol Psychiatry 9(4):406-416; Pongrac JL, Middleton FA, Peng L, Lewis DA, Levitt P, Mirnics K (2004) Heat shock protein 12A shows reduced expression in the prefrontal cortex of subjects with schizophrenia. Biol Psychiatry 56(12):943-950]. Thus, the gene expression changes that we have observed here are consistent with and extend the observations found in the clinical literature and link them to the animal model used here thereby reinforcing its use to better understand the genesis of depression and identify novel therapeutic targets for its treatment.

Alpha2,6-sialylation of cell-surface N-glycans inhibits glioma formation in vivo.

Human gliomas express very high levels of cell-surface alpha2,3-linked terminal sialic acids on glycoproteins bearing N-linked oligosaccharides, most notably on alpha3beta1 integrin, which is the predominant integrin found in these tumors. Alpha2,6-linked terminal sialic acids, however, are not expressed. Two stable transfectants were made using a tumorigenic human glioma cell line, U-373 MG. Galbeta1,4GlcNAc alpha2,6-sialyltransferase (ST6Gal I) transfectants were made to replace the endogenous alpha2,3-linked sialic acids with alpha2,6-linked sialic acids. And Galbeta1,3(4)GlcNAc alpha2,3-sialyltransferase (ST3Gal III) transfectants were made to increase further the expression of cell-surface, N-glycan, alpha2,3-linked sialic acids. Although ST3Gal III transfection resulted in increased invasivity when compared with parental U-373 MG and vector-transfected control cells in vitro, ST6Gal I transfection abolished invasion in vitro and induced alterations in both cell morphology, cell-spreading, and adhesion-mediated protein tyrosine phosphorylation. Furthermore, the ST6Gal I transfectants produced no intracranial tumors in severe combined immunodeficient mice, whereas parental U-373 MG cells, the vector-transfected control cells, and ST3Gal III-transfected U-373 MG cells did. These results suggest that both the linkage and expression levels of the terminal sialic acids of alpha3beta1 integrin N-glycans play an important role in glioma cell-extracellular matrix interactions. Thus, manipulating ST6Gal I gene expression may have therapeutic potential for the treatment of malignant gliomas.

Effect of retinoic acid and phorbol-12-myristate-13-acetate on glycosyltransferase activities in normal and transformed cells.

Retinoic acid was found to increase the activity of cytidine monophosphosialic acid:lactosylceramide sialyltransferase activity in a nontransformed clonal hamster cell line, NIL 8, and a virally transformed clone, NIL 8-HSV. The potent tumor promoter phorbol-12-myristate-13-acetate (PMA) had no significant effect on sialyltransferase activity in NIL 8 cells but stimulated this activity almost 6-fold when added to NIL 8-HSV cells. There was a synergistically additive effect on sialyltransferase activity when PMA was added to NIL 8 cells in concert with retinoic acid. On the other hand neither PMA nor retinoic acid had an appreciable effect on two other glycosyltransferases measured, uridine diphospho-N-acetylgalactosamine:globotriaosylceramide N-acetylgalactosaminyl-transferase and uridine diphosphogalactose:asialoagalactofetuin galactosyltransferase. Examination of sialyltransferase activity in a human epidermoid carcinoma cell line showed a large increase in enzyme activity in response to retinoic acid administration. Two nontransformed hamster cell lines had less basal sialyltransferase activity but also showed marked elevations after retinoic acid treatment. It is proposed that one of the molecular mechanisms underlying the biological effects of retinoic acid and PMA may be an increase in sialyltransferase activity. Possible regulatory mechanisms are discussed.

Sialidase gene transfection enhances epidermal growth factor receptor activity in an epidermoid carcinoma cell line, A431.

Glycosphingolipids expressed in cancer cells have been implicated in the modulation of tumor cell growth through their interaction with transmembrane signaling molecules such as growth factor receptors. For glycosphingolipids to interact with growth factor receptors, the presence of sialic acid seems to be essential. Stable transfection of a gene encoding a soluble Mr 42,000 sialidase into a human epidermoid carcinoma cell line (A431) provided an approach by which the level of terminal lipid-bound sialic acid on the cell surface could be altered. In the sialidase-positive clones, the level of ganglioside GM3 was diminished, and little change was observed in protein sialylation. Sialidase-transfected cells grew faster than control cells. Sialidase expression did not modify the binding of epidermal growth factor (EGF) to its receptor but enhanced EGF receptor (EGFR) tyrosine autophosphorylation as compared to that of parental cells or cells transfected with the vector (pcDNA3) alone. Moreover, the phosphorylation of the EGFR, as well as other protein substrates, was observed at low EGF concentrations, suggesting an increase in the receptor kinase sensitivity. These data provided evidence that changes in ganglioside expression in cancer cells by appropriate gene transfection can dramatically affect EGFR kinase activity. Hence, the modulation of ganglioside expression may represent an approach to alter tumor cell growth.

Beta1,6-N-acetylglucosamine-bearing N-glycans in human gliomas: implications for a role in regulating invasivity.

The metastatic potential of tumor cells has been shown to be correlated with the expression of tri- and tetra-antennary beta1,6-N-acetylglucosamine (beta1,6-GlcNAc)-bearing N-glycans, which are recognized by Phaseolus vulgaris leukoagglutinating lectin (L-PHA). The expression of beta1,6-GlcNAc-bearing N-glycans also has been used as a marker of tumor progression in human breast and colon cancers. In this report, the role of N-glycan branching in regulating glioma migration and invasion was examined. The expression of beta1,6-GlcNAc-bearing N-glycans was found in human glioma specimens, whereas astrocytes from normal adult brain were negative. The expression of N-acetylglucosaminyltransferase V (GnT-V) mRNA, which is responsible for the biosynthesis of beta1,6-GlcNAc-bearing N-glycans, was high in glioma cell lines with robust ets-1 expression. To study the molecular mechanism of GnT-V expression in human glioma cells, an inducible ets-1 gene was stably transfected into SNB-19 cells using a tetracycline repressor system. GnT-V mRNA expression was increased by the induction of c-ets-1, suggesting that the Ets-1 transcription factor directly regulates the transcription of GnT-V. Stable transfection of GnT-V into human glioma U-373 MG cells resulted in changes in cell morphology and focal adhesions and a marked increase in glioma invasivity in vitro. L-PHA has little effect on cell migration. On the contrary, Phaseolus vulgaris erythroagglutinating lectin (E-PHA), which recognizes bisecting beta1,4-GlcNAc-bearing N-glycans, strongly inhibits cell migration (haptotaxis) on a fibronectin substrate in U-373 MG transfectants and other glioma cell lines tested. These results suggest that the increased beta1,6-GlcNAc-bearing N-glycan expression found in malignant gliomas is modulated by GnT-V through the Ets-1 transcription factor, and that the branching of complex type N-glycans plays a major role in glioma invasivity.

Basic fibroblast growth factor-like activity and receptors are expressed in a human glioma cell line.

Basic fibroblast growth factor (bFGF), a potent mitogen and angiogenic peptide, has been examined as an autocrine regulator of glioma cell growth. The addition of purified bovine pituitary bFGF to an established human glioma cell line, SNB-19, doubled the density of these cells in chemically defined medium. Half-maximal stimulation occurred at 8.2 ng/ml (480 pM). Also, human recombinant bFGF (hr-bFGF) significantly enhanced the growth of SNB-19 cells in soft agar. SNB-19 cells expressed both high and low affinity binding sites for hr-bFGF. These cells expressed approximately 13,000 high affinity sites/cell (Kd = 16.6 +/- 1.7 pM) and 9.5 x 10(6) low affinity sites/cell (Kd = 61.2 +/- 4.1 nM). The results of cross-linking experiments with iodinated hr-bFGF demonstrated the presence of two bands with molecular masses of 145 and 130 kDa. High affinity receptors were also demonstrated in SNB-19 tumors grown in nude mice. SNB-19 cell extracts contained mitogenic activity that eluted from heparin-agarose with high salt (1.2-2 M NaCl) and exhibited many properties normally associated with authentic bFGF. This material cross-reacted with a monoclonal antibody to hr-bFGF, comigrated with hr-bFGF by Western blot analysis, competed with 125I-hr-bFGF in a radioreceptor assay, and stimulated SNB-19 cell growth. These results indicate that a human glioma cell line both expresses and utilizes a bFGF-like growth factor. Such a factor may be an important autocrine regulator of glioma cell growth and may also facilitate its neoplastic progression.

The long-lasting antidepressant effects of rapastinel (GLYX-13) are associated with a metaplasticity process in the medial prefrontal cortex and hippocampus.

Rapastinel (GLYX-13) is an N-methyl-d-aspartate receptor (NMDAR) modulator that has characteristics of a glycine site partial agonist. Rapastinel is a robust cognitive enhancer and facilitates hippocampal long-term potentiation (LTP) of synaptic transmission in slices. In human clinical trials, rapastinel has been shown to produce marked antidepressant properties that last for at least one week following a single dose. The long-lasting antidepressant effect of a single dose of rapastinel (3mg/kg IV) was assessed in rats using the Porsolt, open field and ultrasonic vocalization assays. Cognitive enhancement was examined using the Morris water maze, positive emotional learning, and contextual fear extinction tests. LTP was assessed in hippocampal slices. Dendritic spine morphology was measured in the dentate gyrus and the medial prefrontal cortex. Significant antidepressant-like or cognitive enhancing effects were observed that lasted for at least one week in each model. Rapastinel facilitated LTP 1day-2weeks but not 4weeks post-dosing. Biweekly dosing with rapastinel sustained this effect for at least 8weeks. A single dose of rapastinel increased the proportion of whole-cell NMDAR current contributed by NR2B-containing NMDARs in the hippocampus 1week post-dosing, that returned to baseline by 4weeks post-dosing. The NMDAR antagonist 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) blocked the antidepressant-like effect of rapastinel 1week post dosing. A single injection of rapastinel also increased mature spine density in both brain regions 24h post-dosing. These data demonstrate that rapastinel produces its long-lasting antidepressant effects via triggering NMDAR-dependent processes that lead to increased sensitivity to LTP that persist for up to two weeks. These data also suggest that these processes led to the alterations in dendritic spine morphologies associated with the maintenance of long-term changes in synaptic plasticity associated with learning and memory.

Specific regulation of vasoactive intestinal polypeptide biosynthesis by phorbol ester in bovine chromaffin cells.

Two neuropeptides, enkephalin and vasoactive intestinal polypeptide (VIP), are simultaneously increased in cultures of bovine chromaffin cells after diverse treatments including elevation of cAMP, application of nicotine, or chronic depolarization. We now show that phorbol esters can specifically elevate VIP in cultured chromaffin cells without changing the amount of enkephalin. Peptide histidine isoleucine, a VIP-related peptide, is also expressed concomitantly with VIP after treatment with phorbol ester. Immunocytochemical examination of drug-treated cells defines a subpopulation of chromaffin cells which are responsive to phorbol ester stimulation. The unique ability of phorbol esters to selectively regulate VIP expression indicates the presence of independent mechanisms for controlling the expression of individual neuropeptides in chromaffin cells.

The use of antibody engineering to create novel drugs that target N-methyl-D-aspartate receptors.

According to a recent World Health Organization survey, there are over four hundred million people worldwide suffering from mental and neurological disorders; schizophrenia affects some forty-five million people, and unipolar major depression ranked fifth in major causes of disability and death. Clearly it is of the utmost importance to develop new, effective, and safe neuro-pharmaceuticals with this increasing "global burden of disease". To this end, we have developed a strategy of generating monoclonal antibodies that act as modulators of the cell-surface central nervous system receptor-ion channel complexes. In this review we will focus on the generation and characterization of a monoclonal antibody that acts as a partial agonist to the N-methyl-D-aspartate receptor. The creation of peptide mimetics, derived from this monoclonal antibody, that may be useful as cognitive enhancers and protect neurons hypoxic and ischemic insults caused by stroke, will also be discussed.

Expression of Gal beta 1,4GlcNAc alpha 2,6-sialyltransferase and alpha 2,6-linked sialoglycoconjugates in normal human and rat tissues.

We performed histochemical studies on normal human and rat tissues using anti-Gal beta 1,4GlcNAc alpha 2,6-sialyltransferase (alpha 2,6-ST) antibody and Sambucus nigra agglutinin (SNA). alpha 2,6-ST and its products were detected in almost all tissues examined. However, the staining intensities varied significantly with different cell types. Some secretory epithelial cells, such as hepatocytes and choroid plexus cells, were vividly stained with either anti-alpha 2,6-ST or SNA. In several cell types the intensity of alpha 2,6-ST staining did not always correlate with SNA stainability. Neurons and gastrointestinal epithelia were rarely stained with SNA, even though they were positive for alpha 2,6-ST. In contrast, the endothelial cells of blood vessels strongly reacted with SNA despite their weak alpha 2,6-ST expression. The precise physiological roles played by alpha 2,6-linked sialylated glycoconjugates have been unclear. However, the findings described here lend further support to their important role in cell growth and differentiation, since immature blood cells, including megakaryocytes in bone marrow, were intensely stained with anti-alpha 2,6-ST and SNA, and SNA reaction products were primarily observed in the basal and suprabasal layers of the stratified epithelia rather than in the more differentiated upper layers. In view of the vivid reactivity of anti-alpha 2,6-ST in the decidual cells of the placenta, it seems likely that alpha 2,6-ST expression is under hormonal control.

The identification of novel therapeutic targets for the treatment of malignant brain tumors.

A two-step strategy was developed consisting of differential display reverse transcriptase polymerase chain reaction (DDRT-PCR) with cultured normal human fetal astrocytes and U-373MG glioma cells followed by reverse Northern analysis of normal brain and primary tumor tissues. hu-dek, alpha-NAC, ribosomal proteins L7a and L35a, and five novel genes were identified. Since none of these genes has been previously shown to be associated with malignant brain tumor formation, this approach may be useful to identify novel targets for the diagnosis and treatment of brain tumors.

Keratin expression in astrocytomas: an immunofluorescent and biochemical reassessment.

Several studies have shown that immunoenzymatic staining of formalin-fixed, paraffin-embedded astrocytomas with keratin antibodies frequently yields positive labelling, but no biochemical evidence of keratin expression in astrocytomas has been reported. We have investigated the presence of keratin in astrocytoma and normal brain tissues both by immunofluorescence on frozen sections and by 1D and 2D immunoblotting using seven monoclonal antibodies that, collectively, recognize most keratin polypeptides. Four of these antibodies did not stain neural tissues by immunofluorescence and were also negative by immunoblotting. The remaining three keratin antibodies stained normal brain and/or a high proportion of astrocytomas. Two of these three antibodies only stained glial fibrillary acidic protein (GFAP)-positive cells, while the third only stained GFAP-negative cells. 1D and 2D immunoblotting analysis showed that positive immunofluorescence staining of normal brain and/or astrocytomas seen with these three keratin antibodies was due to cross-reactivity with non-keratin proteins, such as GFAP. These results demonstrate that, contrary to earlier suggestions, keratin polypeptides are not frequently expressed in astrocytomas. Our studies also emphasize that keratin antibodies should be used cautiously for the differential diagnosis of undifferentiated gliomas from tumours of non-glial origin.

Diphenylhydantoin protects against hypoxia-induced impairment of hippocampal synaptic transmission.

The ability of diphenylhydantoin (DPH) to protect against hypoxia-induced neuronal damage was examined using electrophysiological recordings of extracellular evoked potentials from CA1 pyramidal neurons of rat hippocampal slices in vitro. In normal medium, a 15-min hypoxic insult (95% N2/5% CO2) produced rapid and complete loss of Schaffer collateral synaptic transmission, which only recovered to 20% of pre-hypoxia values after 90 min of reoxygenation. DPH (20 microM) bath applied prior to onset of hypoxia slowed the loss of transmission during hypoxia, and led to 75% recovery of evoked potentials upon reoxygenation. Thus, DPH appears to protect against hypoxia-induced loss of synaptic transmission, and may thereby lessen neuronal damage and cognitive dysfunction associated with stroke.

Photoendocrine transduction in cultured chick pineal cells: effects of light, dark, and potassium on the melatonin rhythm.

Several laboratories have demonstrated the persistence of photosensitive rhythms related to melatonin secretion in cultured chick pineals. We describe here a system using dispersed chick pineal cells in static culture, which displays a rhythm of melatonin release for at least two weeks under cyclic lighting conditions, and for at least 4 cycles under constant red light. Using a rapid and specific extraction assay for the [14C]melatonin formed (from [14C]tryptophan) and secreted by these cells, we have examined the effects of perturbations (light, dark, and potassium) on the amplitude, period, and phase of the melatonin rhythm. The period in constant red light was close to 20 h, but in constant white light (or 12:12 cycles) it was closer to 24 h. Four-hour pulses of white light (in otherwise constant red light) caused an acute fall in melatonin output, and phase-dependent phase shifts of the rhythm relative to controls. Pulses of darkness (in otherwise constant red light) tended to increase melatonin output, and caused phase-dependent phase shifts. Elevated potassium concentrations increased melatonin output and the amplitude of the rhythm, but did not change the period. Four-hour pulses of low (5.4 mM) potassium (in otherwise constant high potassium) mimicked the acute effect of light, reducing melatonin output, but did not induce appreciable phase shifts. Changes in membrane potential appear more likely to be involved in the regulation of melatonin output (and thus be regulated by the pacemaker) than to be involved in regulation of the pacemaker which generates the melatonin rhythm.

Diphenylhydantoin attenuates hypoxia-induced release of [3H]glutamate from rat hippocampal slices.

The ability of diphenylhydantoin (DPH) to prevent hypoxia-induced [3H]glutamate release was examined in perfused rat hippocampal slices. Hypoxia (25 min; 95% N2/5% CO2) caused a prolonged release of [3H]glutamate, which was reduced significantly if DPH (20 microM) was present from the beginning of the perfusion. Perfusion with oxygenated medium (reoxygenation) following hypoxia also caused a pronounced release of glutamate. A therapeutic concentration of DPH, added before, during, or after hypoxia, decreased this release of glutamate. These results suggest that DPH may protect against glutamate-mediated neurotoxicity associated with stroke.