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Biomedical subjects

K M Johnson

Publications and source records attributed to K M Johnson.

At least 19 recordsLinked to original sources
PubMed2002

Adaptation to chronic PCP results in hyperfunctional NMDA and hypofunctional GABA(A) synaptic receptors.

Schizophrenia is currently thought to be associated with a hypoglutamatergic state that is mimicked by acute phencyclidine (PCP), an antagonist of the N-methyl-D-aspartate (NMDA) receptor subtype. In this study we tested the hypothesis that chronic treatment of rats with this antagonist may be a more appropriate animal model than acute exposure since it could result in adaptive synaptic responses that would model certain aspects of the schizophrenic state in humans. In vitro intracellular electrophysiological recordings employing brain slices from rats treated chronically in vivo with PCP demonstrated that chronic PCP caused a substantial increase in synaptic responses mediated by NMDA receptors without any significant changes in alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/kainate-mediated synaptic responses. At the same time, GABA(A) receptor-mediated inhibitory responses were depressed significantly. Pharmacological and paired-pulse facilitation experiments demonstrated that these adaptive responses following chronic PCP administration were not the result of altered glutamate or GABA release. Immunoblot analyses suggest that the hyperfunctional NMDA response is at least partially mediated by an increased synthesis of NR1 and NR2A subunits as well as a change in the subunit stoichiometry of the NMDA receptor. This change in receptor composition was also supported by pharmacological experiments with a subunit selective NMDA antagonist. Our data support a reconsideration of NMDA and GABA(A) receptor responsiveness following a chronic, not acute, exposure to PCP and the adaptations that persist after such a regimen.

Animals↗
PubMed2001

Eukaryotic transcription: the core of eukaryotic gene activation.

Gene expression is controlled by interactions between activators and coactivators. These interactions in turn are regulated by signaling pathways and by chromatin remodeling events. Recent studies indicate that the final arbiter of gene regulation is a coactivator scaffold at the promoter.

Animals↗
PubMed2001

Mass transport effects on the kinetics of nitrobenzene reduction by iron metal.

To evaluate the importance of external mass transport on the overall rates of contaminant reduction by iron metal (Fe0), we have compared measured rates of surface reaction for nitrobenzene (ArNO2) to estimated rates of external mass transport in a permeable reactive barrier (PRB). The rate of surface reaction was measured at a polished Fe0 rotating disk electrode (RDE) in an electrochemical cell, and the rate of mass transport was estimated from a correlation for mass transport in packed-bed reactors. The kinetics of ArNO2 reduction were studied in pH 8.4 borate buffer at a potential below which an oxide film would form. The cathodic current measured in this system was dependent on the electrode rotation rate, and the measured first-order heterogeneous rate coefficient for surface reaction [krxn = (1.7 +/- 0.2) x 10(-3) cm s-1] was about 10 times faster than the first-order mass transport rate coefficient (kmt approximately 2 x 10(-4) cm s-1) estimated for PRBs. The similarity between rates of surface reaction and mass transport suggest that it may be important to consider mass transport processes in the design of PRBs for contaminants such as nitroaromatics that are highly reactive with Fe0.

Chemical Phenomena↗
PubMed2001

Pharmacological and behavioral analysis of the effects of some bivalent ligand-based monoamine reuptake inhibitors.

Novel piperidine-based bivalent ligands were prepared in enantiomerically pure form and evaluated for their ability to inhibit reuptake of dopamine (DA), serotonin (5-HT), and norepinephrine (NE) into rat brain nerve endings (synaptosomes). In this study, we have succeeded in using (1) the length of the linking chain connecting the two piperidine-based monomer units and (2) the absolute configuration of the piperidine monomer as a means to tailor activity and selectivity at the three monoamine transporters tested. In this series, the bivalent ligand 16, comprised of two (+)-trans-piperidine units linked by a pentamethylene spacer, exhibits a combination of high DA transporter (DAT) and 5-HT transporter (SERT) activity (K(i) = 39 nM and 7 nM, respectively). Piperidine 16 is capable of reducing cocaine's locomotor effects in mice while not having any effect on locomotion when tested alone. Additionally, compound 16 (1-10 mg/kg) does not substitute for cocaine in drug discrimination studies in rats. However, the analogous bivalent ligand 15 comprised of two (-)-trans-piperidine units, which is SERT selective, was less effective in antagonizing cocaine's locomotor stimulant activity. The piperidine-based bivalent inhibitors described herein constitute a new class of monoamine reuptake inhibitors that exhibit varying levels of monoamine transporter activity and selectivity, and these ligands may serve as lead candidates in the discovery of new therapeutics to treat a range of neurological disorders including cocaine addiction.

Animals↗
PubMed2001

Pharmacophore-based discovery of 3,4-disubstituted pyrrolidines as a novel class of monoamine transporter inhibitors.

3,4-Disubstituted pyrrolidines were discovered as a novel class of monoamine transporter inhibitors through 3-D database pharmacophore searching using a new pharmacophore model. The most potent analogue 12 has Ki values of 0.084 microM in [3H]mazindol binding, 0.20, 0.23, and 0.031 microM in inhibition of dopamine (DA), serotonin (SER), and norepinephrine (NE) reuptake, respectively. Functional antagonism testing in vitro showed that 11 and 12 are weak cocaine antagonists.

Biogenic Monoamines↗
PubMed2001

Pharmacophore-based discovery, synthesis, and biological evaluation of 4-phenyl-1-arylalkyl piperidines as dopamine transporter inhibitors.

Pharmacophore-based discovery, synthesis, and structure activity relationship (SAR) of a series of 4-phenyl-1-arylalkyl piperidines are disclosed. These compounds have been evaluated for their ability to inhibit reuptake of dopamine (DA) into striatal nerve endings (synaptosomes). The lead compound 5 and the most potent analogue 43 were found to have significant functional antagonism.

Animals↗
PubMed2001

Dysprosium-bearing red cells as potential transverse relaxation agents for MRI.

The cytosol of intact human red blood cells was loaded with 28.1 +/- 3.4 mM of dysprosium DTPA-BMA using a hypoosmotic technique. When loaded cells were diluted with saline and control cells to give an average dysprosium concentration of 3.3 +/- 0.5 mM, the transverse relaxation rate constants R(*)(2) and R(2) increased. R(*)(2) increased from 7.5 +/- 0.9 sec(-1) to 356 +/- 50 sec(-1), and R(2) increased from 7.4 +/- 0.7 sec(-1) to 148 +/- 40 sec(-1). After lysing, R(*)(2) was 6.0 +/- 0.6 sec(-1) in the control and 13.4 +/- 1.5 sec(-1) in the mixture; R(2) was 6.4 +/- 1.1 sec(-1) and 9.8 +/- 2.4 sec(-1), respectively. Thus, the relaxivity effects were enhanced by sequestration of the dysprosium within intact red cells, and this effect was lost after lysis. At a circulating whole-blood concentration of 0.81 +/- 0.15 mM in rats, the liver signal intensity dropped 29.9% +/- 3.7% and kidney signal intensity dropped 19.4% +/- 8.7%. Dysprosium-loaded cells might be useful in the study of perfusion and tissue blood volume.

Animals↗
PubMed2001

Engraftment of serotonergic precursors enhances locomotor function and attenuates chronic central pain behavior following spinal hemisection injury in the rat.

Spinal cord injury (SCI) results in abnormal locomotor and pain syndromes in humans. T13 spinal hemisection in the rat results in development of permanent mechanical allodynia and thermal hyperalgesia partially due to interruption of descending inhibitory modulators such as serotonin (5-HT). We hypothesize that lumbar transplantation of nonmitotic cells that tonically secrete antinociceptive and trophic compounds will reduce the pain-like behavior and enhance locomotor recovery after SCI. We used RN46A-B14 cells, a conditionally immortalized (SV40tsTag) rat neuronal cell line derived from E13 raphe bioengineered to secrete both 5-HT and BDNF in vitro at both permissive (33 degrees C) and nonpermissive (39 degrees C) temperatures. Three groups (n = 72) of 30-day-old male Sprague-Dawley rats were spinally hemisected at T13 and allowed 4 weeks for adequate recovery of locomotor function and development of allodynia and hyperalgesia. Immunosuppressed animals received either lumbar RN46A-B14 (n = 24) or control RN46A-V1 (n = 24) empty-vector transplants or no cell (n = 24) transplant. HPLC analysis of media and CSF demonstrated increases of both in vitro and in vivo 5-HT levels at 28 days in RN46A-B14 animals. ELISA demonstrated BDNF secretion in vitro and in vivo by RNA46A-B14 cells. Locomotor function (BBB scale) and nociceptive behaviors measured by paw withdrawals to von Frey filaments, radiant heat, and noxious pin stimuli were tested for 4 weeks posttransplant. Animals receiving RN46A-B14 cells demonstrated significantly improved locomotor function and reductions in both fore- and hindlimb mechanical allodynia and thermal hyperalgesia compared to controls receiving RN46A-V1 or no transplants. These effects were modulated by the 5-HT antagonist methysergide and reuptake inhibitor fluvoxamine. Bromodeoxyuridine and 5-HT immunoreactivity confirmed cell survival and graft location 4 weeks posttransplantation. These results support the therapeutic potential of bioengineered serotonin-secreting cell lines in reducing chronic central pain following spinal cord injury.

Animals↗
PubMed2001

Novel monoamine transporter ligands reduce cocaine-induced enhancement of brain stimulation reward.

Six novel monoamine reuptake inhibitors were screened for their intrinsic effects on brain stimulation reward (BSR), as well as for their potential to reduce cocaine-induced reward-enhancement in that paradigm. Two of the compounds, nocaine-3B and 5-ara-74A (disubstituted piperidines) significantly reduced locus of rise (LOR), threshold measure of reward, at some doses. One compound, 1-RV-96A (a hybrid of the GBR and WIN-like agents) significantly reduced reward (increased LOR), but only at the highest dose tested. No effect of dose was found for MC9-20 (a GBR-like acyclic analogue of the N-bisarylmethoxyethyl-N'-phenylpropyl piperazine), nocaine-250B or 4-ara-42C (disubstituted piperidines). When cocaine (10 mg/kg, ip) and selected, hedonically neutral doses of novel compounds were combined, the following findings were obtained: MC9-20 (2.5 mg/kg, ip) showed a significant increase in cocaine-induced reward enhancement (0.2 log units or 53%). In contrast, nocaine-250B and 1-RV-96A (both at 10 mg/kg, ip) demonstrated a significant reduction (0.13 log units or 41%) in cocaine-induced reward enhancement (P<.01 and P<.05, respectively), as measured by changes in LOR. There were no differences in the maximum behavioral output (MAX) at either dose of each of the six drugs, or when selected doses were combined with cocaine. These results indicate that nocaine-250B and 1-RV-96A constitute two potential anticocaine compounds worthy of further behavioral and biochemical evaluation.

Animals↗
PubMed2001

Long-term behavioral and neurodegenerative effects of perinatal phencyclidine administration: implications for schizophrenia.

Both acute and chronic administration of N-methyl-D-aspartate (NMDA) receptor antagonists such as phencyclidine and dizocilpine have been proposed to mimic some of the symptoms of schizophrenia. The purposes of the present study were first, to characterize the long-term behavioral and neurodegenerative effects of subchronic administration of phencyclidine to perinatal rats and second, to determine whether pretreatment with olanzapine could attenuate these effects. On postnatal days 7, 9 and 11 rat pups were pretreated with either vehicle or olanzapine prior to administration of either saline or phencyclidine (10 mg/kg). Some pups were killed on postnatal day 12 for biochemical determinations and others were tested on postnatal days 24-28 for prepulse inhibition of acoustic startle, on postnatal day 42 for phencyclidine-induced locomotor activity and between postnatal days 33 and 70 for acquisition of a delayed spatial learning task. Phencyclidine treatment resulted in a substantial increase in fragmented DNA in the frontal and olfactory cortices consistent with neurodegeneration by an apoptotic mechanism. An increase in the NMDA receptor NR1 subunit mRNA was also observed in the cortex. Gel shift assays showed that phencyclidine also increased the nuclear translocation of nuclear factor-kappaB proteins in the prefrontal cortex. In tissue from the frontal cortex, western blot analysis revealed that phencyclidine treatment increased Bax and decreased Bcl-X(L) proteins. Later in development, it was observed that perinatal phencyclidine treatment significantly retarded baseline prepulse inhibition of acoustic startle measured shortly after weaning. In 42-day-old rats, it was found that challenge with 2 mg/kg phencyclidine increased locomotor activity to a significantly greater extent in the rats that had been pretreated with phencyclidine. Similarly, perinatal phencyclidine treatment significantly delayed the acquisition of a delayed spatial alternation task. Each of the aforementioned changes (except for the spatial learning task, which was not tested) was significantly inhibited by olanzapine pretreatment, an antipsychotic drug known to be effective against both positive and negative symptoms of schizophrenia. Further, olanzapine treatment for 12 days following the administration of phencyclidine was also able to reverse the phencyclidine-induced deficit in baseline prepulse inhibition. Together these data suggest that perinatal administration of phencyclidine results in long-term behavioral changes that may be mechanistically related to the apoptotic neurodegeneration observed in the frontal cortex. It is postulated that these deficits may model the hypofrontality observed in schizophrenia and that this model may be helpful in designing appropriate pharmacotherapy.

Animals↗
PubMed2001

Molecular modeling, structure--activity relationships and functional antagonism studies of 4-hydroxy-1-methyl-4-(4-methylphenyl)-3-piperidyl 4-methylphenyl ketones as a novel class of dopamine transporter inhibitors.

We previously disclosed the discovery of 4-hydroxy-1-methyl-4-(4-methylphenyl)-3-piperidyl 4-methylphenyl ketone (3) as a novel class of dopamine transporter (DAT) inhibitors and showed that (+/-)-3 has a significant functional antagonism against cocaine in vitro. Our previous preliminary structure-activity relationship study led to identification of a more potent DAT inhibitor [(+/-)-4] but this compound failed to show any significant functional antagonism. To search for more potent analogues than 3 but still displaying significant functional antagonism, further SARs, molecular modeling studies and in vitro pharmacological evaluation of this novel class of DAT inhibitors were performed. Sixteen new analogues were synthesized in racemic form and evaluated as DAT inhibitors. It was found that seven new analogues are reasonably potent DAT inhibitors with K(i) values of 0.041--0.30 and 0.052--0.16 microM in [(3)H]mazindol binding and inhibition of DA reuptake. Chiral isomers of several potent DAT inhibitors were obtained through chiral HPLC separation and evaluated as inhibitors at all the three monoamine transporter sites. In general, the (-)-isomer is more active than the (+)-isomer in inhibition of DA reuptake and all the (-)-isomers are selective inhibitors at the DAT site. Evaluation of cocaine's effect on dopamine uptake in the presence and absence of (+)-3 and (-)-3 showed that (-)-3 is responsible for the functional antagonism obtained with the original lead (+/-)-3. Out of the new compounds synthesized, analogue (+/-)-20, which is 8- and 3-fold more potent than (+/-)-3 in binding and inhibition of DA reuptake, appeared to have improved functional antagonism as compared to (+/-)-3.

Animals↗
PubMed2001

Strain and model differences in behavioral outcomes after spinal cord injury in rat.

Spinal cord injury (SCI) results in loss of function below the level of injury and the development of chronic central pain (CCP) syndromes. Since different strains may develop and express chronic pain behaviors differently, we evaluated behavioral outcomes (locomotor recovery and the development of mechanical and thermal allodynia) in three commonly used strains of rats (Long-Evans, Wistar, and Sprague-Dawley) using two models of SCI. The two models examined were contusion at T10 (NYU impactor, 12.5 mm height) and the T13 hemisection. Mechanical stimulation (von Frey filaments) revealed significantly lower baseline responses for Long-Evans rats and significantly higher baseline paw withdrawal latencies to thermal stimulation for Wistar rats compared to the other strains. Following contusion SCI, Long-Evans rats had the highest percentage of animals that developed mechanical allodynia (73%), while Sprague-Dawley rats had the highest percentages (75%) following hemisection SCI. Interestingly, the Sprague-Dawley rats had the highest percentage (87%) to develop thermal allodynia following contusion SCI, while 100% of both Long-Evans and Sprague Dawley rats developed thermal allodynia in the hemisection model. Locomotor recovery after SCI was similar for each model in that Long-Evans rats recovered slower and to a lesser extent than the other strains. In each model, Sprague-Dawley rats recovered faster and achieved greater function. Overall, the hemisection model produced a larger percentage of animals that developed CCP and had greater responses to mechanical stimulation. Thus, it appears that strain selection has a greater impact on locomotor recovery and model selection has a greater impact on the development of CCP following SCI. Furthermore, these results suggest that genetic factors may play a role in recovery following SCI.

Animals↗
PubMed2001

The child PTSD Symptom Scale: a preliminary examination of its psychometric properties.

Reports on the development and preliminary validation of the Child PTSD Symptom Scale (CPSS) for children and adolescents. The CPSS is a new instrument that was developed to assess the severity of Diagnostic and Statistical Manual of Mental Disorders (4th ed.; American Psychiatric Association, 1994) posttraumatic stress disorder symptoms in children exposed to trauma. The CPSS was administered to 75 school-age children approximately 2 years after the 1994 Northridge, California, earthquake. The psychometric properties of the CPSS show high internal consistency and test-retest reliability for both the total score and the three subscales. Convergent validity with the Child Post-Traumatic Stress Disorder Reaction Index (CPTSD-RI) was established. As expected, the correlations of the CPSS with depression and anxiety measures were lower than those with the CPTSD-RI, providing some support for discriminant validity of the CPSS. These results suggest that the CPSS is a useful tool for the assessment of posttraumatic stress disorder (PTSD) severity and for the screening of PTSD diagnosis among traumatized children.

Adolescent↗
PubMed2001

Pharmacological characterization of locomotor sensitization induced by chronic phencyclidine administration.

Phencyclidine (PCP) administration in rats acutely in high doses or chronically in lower doses causes neurotoxicity characterized by neuronal vacuolization and apoptotic neuronal death, respectively. The purpose of this study was to determine whether drugs that previously had been reported to prevent either type of neurotoxicity were also able to prevent locomotor sensitization following chronic PCP administration. PCP (5 or 20 mg/kg) was administered once a day for 5 days following drug pretreatment. After withdrawal, rats were challenged with 3.2 mg/kg PCP and locomotor activity was assessed. Haloperidol and clozapine significantly attenuated sensitization elicited by PCP (20 mg/kg). The D(1)-like antagonist SCH23390 was much less effective than clozapine, showing a marginal inhibition. Risperidone, a D(2)/serotonin (5-HT(2)) antagonist, also resulted in a marginal attenuation of 15%. Ketanserin, a 5-HT(2) antagonist, had no effect. Atropine retarded sensitization by 35% and (+)-sulpiride caused a 50% reduction. The AMPA/kainate antagonist, 6,7-dinitroquinoxaline-2,3-dione, had no effect, but barbital sodium reduced sensitization by 54%. These data suggest that gamma-aminobutyric acid A, D(2), and muscarinic receptors play a major role in the complex pathway underlying sensitization to PCP, whereas D(1), 5-HT(2) and AMPA receptors have little or no relevance in the behavioral sensitization produced by 20 mg/kg PCP. In a model using 5 mg/kg PCP, the effects of sulpiride and SCH23390 replicated those observed with 20 mg/kg PCP and further showed that acute locomotor activation is not a strict requirement for the development of sensitization. These data argue that there is overlap, but nonidentity, between the mechanisms underlying PCP-induced sensitization and neurotoxicity.

Animals↗
PubMed2001

Surrogate end-point biomarkers in chemopreventive drug development.

Relevant and feasible surrogate end-points are needed for the evaluation of intervention strategies against cancer and other chronic, life-threatening diseases. Carcinogenesis can be viewed as a process of progressive disorganization. This process is characterized by the accumulation of genotypic lesions and corresponding tissue and cellular abnormalities, including loss of proliferation and apoptosis controls. Potential surrogate end-points for cancer incidence include both phenotypic and genotypic biomarkers of this progression. In the US National Cancer Institute chemoprevention programme, histological modulation of a precancer (intraepithelial neoplasia) has so far been the primary phenotypic surrogate end-point in chemoprevention trials. Additionally, high priority has been given to biomarkers measuring specific and general genotypic changes correlated with the carcinogenesis progression model for the targeted cancer (e.g., progressive genomic instability as measured by loss of heterozygosity or amplification at specific microsatellite loci). Other potential surrogate end-points include proliferation and differentiation indices, specific gene and general chromosome damage, cell growth regulatory molecules, and biochemical activities (e.g., enzyme inhibition). Serum biomarkers thought to be associated with cancer progression (e.g., prostate-specific antigen) are particularly appealing surrogate end-points because of accessibility. Potentially chemopreventive effects of the test agent may also be measured (e.g., tissue and serum estrogen levels in studies of steroid aromatase inhibitors). To establish chemopreventive efficacy, prevention of virtually all biomarker lesions, or of those lesions with particular propensity for progression, may be required. Ideally, the phenotype and genotype of any new or remaining precancers in the target tissue of chemopreventive agent-treated subjects would show less, and certainly no greater, potential for progression than those of placebo-treated subjects.

Anticarcinogenic Agents↗
PubMed2000

AIDA reduces glutamate release and attenuates mechanical allodynia after spinal cord injury.

Spinal cord injury (SCI) leads to an increase in extracellular excitatory amino acid (EAA) concentrations, resulting in glutamate receptor-mediated excitotoxicity and central sensitization. To test contributions of group I metabotropic glutamate receptors (mGluRs) in SCI induced release of glutamate and in behavioral outcomes of central sensitization following injury, we administered 1-aminoindan-1,5-dicarboxylic acid (AIDA; 0.1 nmol intraspinally), a potent group I mGluR antagonist, to rats immediately after spinal cord contusion injury. EAAs were collected by microdialysis and quantified using HPLC. AIDA significantly decreased extracellular glutamate but not aspartate concentrations and significantly attenuated the development of mechanical but not thermal allodynia. These results suggest mGluRs play an important role in injury-induced EAA release and in central sensitization following SCI.

Animals↗