Human polyhomeotic homolog 3 (PHC3) sterile alpha motif (SAM) linker allows open-ended polymerization of PHC3 SAM

Sterile alpha motifs (SAMs) are frequently found in eukaryotic genomes. An intriguing property of many SAMs is their ability to self-associate, forming an open-ended polymer structure whose formation has been shown to be essential for the function of the protein. What remains largely unresolved is how polymerization is controlled. Previously, we had determined that the stretch of unstructured residues N-terminal to the SAM of a Drosophila protein called polyhomeotic (Ph), a member of the polycomb group (PcG) of gene silencers, plays a key role in controlling Ph SAM polymerization. Ph SAM with its native linker created shorter polymers compared to Ph SAM attached to either a random linker or no linker. Here, we show that the SAM linker for the human Ph ortholog, polyhomeotic homolog 3 (PHC3), also controls PHC3 SAM polymerization but does so in the opposite fashion. PHC3 SAM with its native linker allows longer polymers to form compared to when attached to a random linker. Attaching the PHC3 SAM linker to Ph SAM also resulted in extending Ph SAM polymerization. Moreover, in the context of full-length Ph protein, replacing the SAM linker with PHC3 SAM linker, intended to create longer polymers, resulted in greater repressive ability for the chimera compared to wild-type Ph. These findings show that polymeric SAM linkers evolved to modulate a wide dynamic range of SAM polymerization abilities and suggest that rationally manipulating the function of SAM containing proteins through controlling their SAM polymerization may be possible.

The growth-suppressive function of the polycomb group protein polyhomeotic is mediated by polymerization of its sterile alpha motif (SAM) domain

Polyhomeotic (Ph), a member of the Polycomb Group (PcG), is a gene silencer critical for proper development. We present a previously unrecognized way of controlling Ph function through modulation of its sterile alpha motif (SAM) polymerization leading to the identification of a novel target for tuning the activities of proteins. SAM domain containing proteins have been shown to require SAM polymerization for proper function. However, the role of the Ph SAM polymer in PcG-mediated gene silencing was uncertain. Here, we first show that Ph SAM polymerization is indeed required for its gene silencing function. Interestingly, the unstructured linker sequence N-terminal to Ph SAM can shorten the length of polymers compared with when Ph SAM is individually isolated. Substituting the native linker with a random, unstructured sequence (RLink) can still limit polymerization, but not as well as the native linker. Consequently, the increased polymeric Ph RLink exhibits better gene silencing ability. In the Drosophila wing disc, Ph RLink expression suppresses growth compared with no effect for wild-type Ph, and opposite to the overgrowth phenotype observed for polymer-deficient Ph mutants. These data provide the first demonstration that the inherent activity of a protein containing a polymeric SAM can be enhanced by increasing SAM polymerization. Because the SAM linker had not been previously considered important for the function of SAM-containing proteins, our finding opens numerous opportunities to manipulate linker sequences of hundreds of polymeric SAM proteins to regulate a diverse array of intracellular functions.

Identification of nucleic acid binding residues in the FCS domain of the polycomb group protein polyhomeotic

Polycomb group (PcG) proteins maintain the silent state of developmentally important genes. Recent evidence indicates that noncoding RNAs also play an important role in targeting PcG proteins to chromatin and PcG-mediated chromatin organization, although the molecular basis for how PcG and RNA function in concert remains unclear. The Phe-Cys-Ser (FCS) domain, named for three consecutive residues conserved in this domain, is a 30-40-residue Zn(2+) binding motif found in a number of PcG proteins. The FCS domain has been shown to bind RNA in a non-sequence specific manner, but how it does so is not known. Here, we present the three-dimensional structure of the FCS domain from human Polyhomeotic homologue 1 (HPH1, also known as PHC1) determined using multidimensional nuclear magnetic resonance methods. Chemical shift perturbations upon addition of RNA and DNA resulted in the identification of Lys 816 as a potentially important residue required for nucleic acid binding. The role played by this residue in Polyhomeotic function was demonstrated in a transcription assay conducted in Drosophila S2 cells. Mutation of the Arg residue to Ala in the Drosophila Polyhomeotic (Ph) protein, which is equivalent to Lys 816 in HPH1, was unable to repress transcription of a reporter gene to the level of wild-type Ph. These results suggest that direct interaction between the Ph FCS domain and nucleic acids is required for Ph-mediated repression.

Polycomb group targeting through different binding partners of RING1B C-terminal domain

RING1B, a Polycomb Group (PcG) protein, binds methylated chromatin through its association with another PcG protein called Polycomb (Pc). However, RING1B can associate with nonmethylated chromatin suggesting an alternate mechanism for RING1B interaction with chromatin. Here, we demonstrate that two proteins with little sequence identity between them, the Pc cbox domain and RYBP, bind the same surface on the C-terminal domain of RING1B (C-RING1B). Pc cbox and RYBP each fold into a nearly identical, intermolecular beta sheet with C-RING1B and a loop structure which are completely different in the two proteins. Both the beta sheet and loop are required for stable binding and transcription repression. Further, a mutation engineered to disrupt binding on the Drosophila dRING1 protein prevents chromatin association and PcG function in vivo. These results suggest that PcG targeting to different chromatin locations relies, in part, on binding partners of C-RING1B that are diverse in sequence and structure.

Backbone resonance assignments of the 48 kDa dimeric putative 18S rRNA-methyltransferase Nep1 from Methanocaldococcus jannaschii

Nep1 from Methanocaldococcus jannaschii is a 48 kDa dimeric protein belonging to the SPOUT-class of S-adenosylmethionine dependent RNA-methyltransferases and acting as a ribosome assembly factor. Mutations in the human homolog are the cause of Bowen-Conradi syndrome. We report here 1H, 15N and 13C chemical shift assignments for the backbone of the protein in its apo state.

The crystal structure of Nep1 reveals an extended SPOUT-class methyltransferase fold and a pre-organized SAM-binding site

Ribosome biogenesis in eukaryotes requires the participation of a large number of ribosome assembly factors. The highly conserved eukaryotic nucleolar protein Nep1 has an essential but unknown function in 18S rRNA processing and ribosome biogenesis. In Saccharomyces cerevisiae the malfunction of a temperature-sensitive Nep1 protein (nep1-1(ts)) was suppressed by the addition of S-adenosylmethionine (SAM). This suggests the participation of Nep1 in a methyltransferase reaction during ribosome biogenesis. In addition, yeast Nep1 binds to a 6-nt RNA-binding motif also found in 18S rRNA and facilitates the incorporation of ribosomal protein Rps19 during the formation of pre-ribosomes. Here, we present the X-ray structure of the Nep1 homolog from the archaebacterium Methanocaldococcus jannaschii in its free form (2.2 A resolution) and bound to the S-adenosylmethionine analog S-adenosylhomocysteine (SAH, 2.15 A resolution) and the antibiotic and general methyltransferase inhibitor sinefungin (2.25 A resolution). The structure reveals a fold which is very similar to the conserved core fold of the SPOUT-class methyltransferases but contains a novel extension of this common core fold. SAH and sinefungin bind to Nep1 at a preformed binding site that is topologically equivalent to the cofactor-binding site in other SPOUT-class methyltransferases. Therefore, our structures together with previous genetic data suggest that Nep1 is a genuine rRNA methyltransferase.

Prevention of metastases with a Mage-b DNA vaccine in a mouse breast tumor model: potential for breast cancer therapy

Anti-tumor vaccines are a relatively non-toxic alternative to conventional chemotherapeutic strategies to control breast cancer. Immunization with tumor-associated antigens (TAAs) triggers anti-tumor cytotoxic T lymphocytes (CTL), which can limit tumor progression. Here we report on the development and effectiveness of a TAA-based DNA vaccine encoding Mage-b1/2, the mouse homologue of the human MAGE-B1/2. As model system, we used immune competent Balb/c mice with syngeneic non-metastatic (64pT) or metastatic (4TO7cg) breast tumors. First, the presence of Mage-btranscripts in the 64pT and 4TO7cg breast tumors and metastases was demonstrated by RT-PCR, Southern blotting, and DNA sequencing. A DNA-based vaccine was developed from transcripts of one of the 64pT tumors, encoding the complete Mage-b1/2 protein, and subsequently tested for its preventive efficacy in both breast tumor models. Mice were immunized two times intramuscularly with the vaccine (pcDNA3.1-Mage-b1/2-V5), the control vector (pcDNA3.1-V5), or saline. Two weeks after the last immunization, the syngeneic 4TO7cg or 64pT tumor cell lines were injected in a mammary fat pad. Mice were monitored during the next 4 weeks for tumor formation, latency and size, and subsequently sacrificed for analysis. While the Mage-b1/2 vaccine had only a minor effect on the latency and growth of primary tumors, a significant and reproducible reduction in the number of 4TO7cg metastases was observed (vaccine versus control vector, p=0.0329; vaccine versus saline, p=0.0128). The observed protective efficacy of the Mage-b DNA vaccine correlated with high levels of vaccine-induced IFNgamma in spleen and lymph nodes upon re-stimulation in vitro. These results demonstrate the potential of TAA-based DNA vaccines in controlling metastatic disease in breast cancer patients.

Caspase-mediated apoptosis and caspase-independent cell death induced by irofulven in prostate cancer cells

Irofulven (hydroxymethylacylfulvene) is a novel antitumor drug, which acts by alkylating cellular macromolecular targets. The drug is a potent inducer of apoptosis in various types of tumor cells, whereas it is nonapoptotic in normal cells. This study defined molecular responses to irofulven involving mitochondrial dysfunction and leading to death of prostate tumor LNCaP-Pro5 cells. Irofulven caused early (2-5 hours) translocation of the proapoptotic Bax from cytosol to mitochondria followed by the dissipation of mitochondrial membrane potential and cytochrome c release at 4 to 12 hours. These effects preceded caspase activation and during the first 6 hours were not affected by caspase inhibitors. Processing of caspase-9 initiated the caspase cascade at approximately 6 hours and progressed over time. The activation of the caspase cascade provided a positive feedback loop that enhanced Bcl-2-independent translocation and cytochrome c release. General and specific caspase inhibitors abrogated irofulven-induced apoptotic DNA fragmentation with the following order of potency: pan-caspase > or = caspase-9 > caspase-8/6 > caspase-2 > caspase-3/7 > caspase-1/4. Abrogation of caspase-mediated DNA fragmentation failed to salvage irofulven-treated cells from growth inhibition and loss of viability, demonstrating a substantial contribution of a caspase-independent cell death. Monobromobimane, an inhibitor of alternative caspase-independent apoptotic pathway that is mediated by mitochondrial permeability transition, antagonized both apoptosis, measured as phosphatidylserine externalization, and cytotoxicity of irofulven. Collectively, the results indicate that irofulven-induced signaling is integrated at the level of mitochondrial dysfunction. The induction of both caspase-dependent and caspase-independent death pathways is consistent with pleiotropic effects of irofulven, which include targeting of cellular DNA and proteins.

Caspase-mediated apoptosis and caspase-independent cell death induced by irofulven in prostate cancer cells

Irofulven (hydroxymethylacylfulvene) is a novel antitumor drug, which acts by alkylating cellular macromolecular targets. The drug is a potent inducer of apoptosis in various types of tumor cells, whereas it is nonapoptotic in normal cells. This study defined molecular responses to irofulven involving mitochondrial dysfunction and leading to death of prostate tumor LNCaP-Pro5 cells. Irofulven caused early (2–5 hours) translocation of the proapoptotic Bax from cytosol to mitochondria followed by the dissipation of mitochondrial membrane potential and cytochrome c release at 4 to 12 hours. These effects preceded caspase activation and during the first 6 hours were not affected by caspase inhibitors. Processing of caspase-9 initiated the caspase cascade at ∼6 hours and progressed over time. The activation of the caspase cascade provided a positive feedback loop that enhanced Bcl-2-independent translocation and cytochrome c release. General and specific caspase inhibitors abrogated irofulven-induced apoptotic DNA fragmentation with the following order of potency: pan-caspase ≥ caspase-9 > caspase-8/6 > caspase-2 > caspase-3/7 > caspase-1/4. Abrogation of caspase-mediated DNA fragmentation failed to salvage irofulven-treated cells from growth inhibition and loss of viability, demonstrating a substantial contribution of a caspase-independent cell death. Monobromobimane, an inhibitor of alternative caspase-independent apoptotic pathway that is mediated by mitochondrial permeability transition, antagonized both apoptosis, measured as phosphatidylserine externalization, and cytotoxicity of irofulven. Collectively, the results indicate that irofulven-induced signaling is integrated at the level of mitochondrial dysfunction. The induction of both caspase-dependent and caspase-independent death pathways is consistent with pleiotropic effects of irofulven, which include targeting of cellular DNA and proteins.

Influence of radiotherapy on 6-sulphatoxymelatonin levels in the urine of brain cancer patients

OBJECTIVES: The synthesis of melatonin, an endogenous compound synthesized by the pineal gland in the brain, is reported to be depressed in patients with primary cancers of the breast, prostate, stomach and rectum. It is not known whether patients with brain cancer exhibit altered melatonin synthesis. Also unknown is whether radiotherapy given to the region of the brain where the pineal gland is located affects the synthesis of melatonin. This information could be relevant to the clinician for the successful treatment of brain cancer patients since melatonin has been reported to be a potent oncostatic agent. METHODS: Urinary levels of 6-sulphatoxymelatonin, the chief metabolite of melatonin, are routinely used as an index of pineal melatonin production and secretion. In this study, the concentrations of 6-sulphatoxymelatonin (aMT6S) excreted in the urine before and during radiotherapy of patients with primary or metastatic brain cancer were determined and compared with the values obtained in breast or lung cancer patients who also received radiotherapy (excluding exposure of the brain where the pineal gland is located). RESULTS: The results showed a wide variation in the mean concentration of aMT6S excreted in the urine. CONCLUSION: The data from this preliminary study suggested that radiotherapy given to the region of human brain, where the pineal gland is located, does not significantly affect the excretion of aMT6S, the chief metabolite of melatonin.

Cytogenetic studies in human blood lymphocytes exposed in vitro to radiofrequency radiation at a cellular telephone frequency (835.62 MHz, FDMA)

Freshly collected peripheral blood samples from four healthy human volunteers were diluted with RPMI 1640 tissue culture medium and exposed in sterile T-75 tissue culture flasks in vitro for 24 h to 835.62 MHz radiofrequency (RF) radiation, a frequency employed for customer-to-base station transmission of cellular telephone communications. An analog signal was used, and the access technology was frequency division multiple access (FDMA, continuous wave). A nominal net forward power of 68 W was used, and the nominal power density at the center of the exposure flask was 860 W/m(2). The mean specific absorption rate in the exposure flask was 4.4 or 5.0 W/kg. Aliquots of diluted blood that were sham-exposed or exposed in vitro to an acute dose of 1.50 Gy of gamma radiation were used as negative or positive controls. Immediately after the exposures, the lymphocytes were stimulated with a mitogen, phytohemagglutinin, and cultured for 48 or 72 h to determine the extent of genetic damage, as assessed from the frequencies of chromosomal aberrations and micronuclei. The extent of alteration in the kinetics of cell proliferation was determined from the mitotic indices in 48-h cultures and from the incidence of binucleate cells in 72-h cultures. The data indicated no significant differences between RF-radiation- and sham-exposed lymphocytes with respect to mitotic indices, incidence of exchange aberrations, excess fragments, binucleate cells, and micronuclei. In contrast, the response of the lymphocytes exposed to gamma radiation was significantly different from both RF-radiation- and sham-exposed cells for all of these indices. Thus, under the experimental conditions tested, there is no evidence for the induction of chromosomal aberrations and micronuclei in human blood lymphocytes exposed in vitro for 24 h to 835.62 MHz RF radiation at SARs of 4.4 or 5.0 W/kg.

Primary DNA damage in human blood lymphocytes exposed in vitro to 2450 MHz radiofrequency radiation

Human peripheral blood samples collected from three healthy human volunteers were exposed in vitro to pulsed-wave 2450 MHz radiofrequency (RF) radiation for 2 h. The RF radiation was generated with a net forward power of 21 W and transmitted from a standard gain rectangular antenna horn in a vertically downward direction. The average power density at the position of the cells in the flask was 5 mW/cm(2). The mean specific absorption rate, calculated by finite difference time domain analysis, was 2.135 (+/-0.005 SE) W/kg. Aliquots of whole blood that were sham-exposed or exposed in vitro to 50 cGy of ionizing radiation from a (137)Cs gamma-ray source were used as controls. The lymphocytes were examined to determine the extent of primary DNA damage (single-strand breaks and alkali-labile lesions) using the alkaline comet assay with three different slide-processing schedules. The assay was performed on the cells immediately after the exposures and at 4 h after incubation of the exposed blood at 37 +/- 1 degrees C to allow time for rejoining of any strand breaks present immediately after exposure, i.e. to assess the capacity of the lymphocytes to repair this type of DNA damage. At either time, the data indicated no significant differences between RF-radiation- and sham-exposed lymphocytes with respect to the comet tail length, fluorescence intensity of the migrated DNA in the tail, and tail moment. The conclusions were similar for each of the three different comet assay slide-processing schedules examined. In contrast, the response of lymphocytes exposed to ionizing radiation was significantly different from RF-radiation- and sham-exposed cells. Thus, under the experimental conditions tested, there is no evidence for induction of DNA single-strand breaks and alkali-labile lesions in human blood lymphocytes exposed in vitro to pulsed-wave 2450 MHz radiofrequency radiation, either immediately or at 4 h after exposure.

Interaction of hyperthermia with Taxol in human MCF-7 breast adenocarcinoma cells

Hyperthermia treatments (43 degrees C, 1 h) were performed on exponentially growing MCF-7 breast adenocarcinoma cells at the beginning, middle, or end of 24 h incubations of the cells in vitro with Taxol (paclitaxel). When the cells were heated at the beginning or middle of the Taxol incubation, the hyperthermia treatment protected against the toxic effect of each of the Taxol concentrations examined (5, 10 and 100 nM). Consistent with earlier studies, Taxol treatment at 37 degrees C resulted in an accumulation of greater than 94% of the cells in G2/M at 24 h. Heating the cells at the middle or end of the Taxol treatment resulted in a similar accumulation. However, heat treatment during the first hour of Taxol exposure resulted in a significantly smaller percentage of cells (approximately 50%) in G2/M. HPLC analysis showed that at 37 degrees C, Taxol uptake into MCF-7 cells approached maximum within 0.25 h and increased only slightly more over the next 11.75 h. The parental Taxol level was markedly lower by 24 h. In contrast, 1 h hyperthermia treatments at the beginning or middle of the Taxol incubation resulted in higher Taxol concentrations at 12 and 24h, and higher intracellular concentrations overall than at 37 degrees C. These results indicate that hyperthermia inhibits Taxol related cell cycle effects and cytotoxicity, in spite of causing higher concentrations of Taxol to be present in heated cells.

Effect of melatonin on mitotic and proliferation indices, and sister chromatid exchange in human blood lymphocytes

Cells from human peripheral blood were cultured in vitro in the presence of 0.05 to 1.00 mM melatonin, 10(-7) M mitomycin C (positive control) and 0.5% ethanol (solvent control) for 72 h at 37 +/- 1 degree C. Lymphocytes were examined for mitotic and proliferation indices, and for the incidence of sister chromatid exchange. The results indicate that the lymphocytes which were cultured in the presence of > or = 0.20 mM concentrations of melatonin exhibited a significant and concentration-dependent decrease in mitotic index and alteration in proliferation kinetics. This was demonstrated by an increase in the frequency of lymphocytes in their first division, with a concomitant decrease in the second and third or later division cells. The incidence of sister chromatid exchange was similar in the lymphocytes exposed to 0.05 to 1.00 mM melatonin and untreated controls. Exposure of the cells to ethanol, the solvent used, did not alter either the mitotic or proliferation indices, or the frequency of sister chromatid exchange. The lymphocytes treated with mitomycin C showed the expected decrease in mitotic and proliferation indices, and an increased incidence of sister chromatid exchange. These observations indicate that melatonin, when continuously present in the cultures for 72 h at the concentrations tested, while not genotoxic as indicated by the sister chromatid exchange assay, inhibits the proliferation of mitogen stimulated (and proliferating) human blood lymphocytes at supraphysiological concentrations.

Variability in adaptive response to low dose radiation in human blood lymphocytes: consistent results from chromosome aberrations and micronuclei

The frequencies of chromosome aberrations and micronuclei were evaluated to assess the induction of adaptive response to low dose ionizing radiation in each of the blood samples collected from eight different individuals. Following stimulation with phytohemagglutinin, the cells were exposed to an adaptive dose of 1 cGy X-radiation at 24 hours and a challenge dose of 150 cGy gamma radiation at 48 hours. Lymphocytes were fixed at 54 hours to examine the incidence of chromosome aberrations and at 72 hours to examine the frequency of micronuclei in cytokinesis-blocked binucleated cells. Lymphocytes from five donors, i.e., "responders", exhibited the induction of adaptive response; their lymphocytes, which were pre-treated with 1 cGy had significantly fewer chromosome aberrations and micronuclei induced by the challenge dose of 150 cGy gamma radiation, as compared to the cells which did not receive the pre-treatment with 1 cGy. Such an induction of adaptive response was not observed in the remaining three donors, i.e., "non-responders"; the incidence of chromosome aberrations and micronuclei induced by the challenge dose of 150 cGy was not significantly different between the cells which were pre-exposed and un-exposed to 1 cGy. In all eight individuals, there was a strong positive correlation between the incidence of chromosome aberrations and micronuclei. Hence, whether or not an individual is a 'responder' or 'non-responder' could be assessed using either chromosome aberrations or micronuclei as the end-point. The overall pattern of response confirms the heterogeneity in adaptive response between individuals to ionizing radiation, which may in part be genetically controlled. Because of the simplicity of the technique and rapid assessment of the binucleated cells, we suggest the use of the micronucleus test as an alternative procedure in large scale population studies related to the adaptive response.

Marked reduction of radiation-induced micronuclei in human blood lymphocytes pretreated with melatonin

Human peripheral blood lymphocytes which were pretreated in vitro with melatonin, an endogenously synthesized pineal hormone, for 20 min at 37 +/- 1 degree C exhibited a significant and concentration-dependent reduction in the frequency of gamma-radiation-induced micronuclei compared with irradiated cells which did not receive the pretreatment. The extent of the reduction observed with 2.0 mM melatonin was similar to that found in lymphocytes pretreated for 20 min with 1.0 M dimethylsulfoxide, a known free radical scavenger. These observations indicate that melatonin may have an active role in protection of humans against genetic damage due to endogenously produced free radicals, and also may be of use in reducing damage due to exposure to physical and chemical mutagens and carcinogens which generate free radicals.

Melatonin's inhibitory effect on growth of ME-180 human cervical cancer cells is not related to intracellular glutathione concentrations

The effects of various concentrations of melatonin on the growth of ME-180 human cervical cancer cells in vitro was examined. Melatonin at a concentration of 2 mM inhibited the growth of the cells after 48 h of melatonin treatment. At concentrations of 2 microM or 0.1 mM melatonin had no effect on cell proliferation. To determine whether the inhibitory effect of melatonin on the growth of the cervical cancer cells was linked to intracellular glutathione concentrations, experiments were performed in which intracellular glutathione levels were depressed by the addition of buthionine sulfoximine to the incubation medium 24 h before the addition of melatonin. The results show that 2 mM melatonin treatment still inhibits the growth of cells when glutathione levels are depressed by 95%. Even with depressed glutathione levels, 0.1 mM melatonin still had no effect on cell growth. Thus, melatonin's ability to inhibit ME-180 cervical cell growth in vitro may be independent of intracellular glutathione concentrations. It was also found that during one passage the intracellular glutathione levels of cervical cancer cells gradually decreases. When 4.5-day-old medium was replaced with new medium, intracellular glutathione levels partially recovered within 36 h. This suggests that the observed gradual reduction of cellular glutathione during incubation was a result of a reduction of some constituent in the medium after prolonged culture of the cells.

Neurobehavioral effects of repeated sublethal soman in primates

Juvenile male baboons were trained to perform a match-to-sample discrimination task; effects of repeated sublethal exposure to the organophosphate nerve gas, soman, upon task performance were then explored. Both acute and subchronic exposure schedules were employed, and soman potency was verified by assay of soman-induced inhibition of acetylcholinesterase activity in whole blood, plasma, and erythrocytes. A characteristic profile of behavioral effects encompassing immediate, persistent, and delayed effects was observed. Immediate dose-related effects of soman included: increases in mean session response time, increases in errors, and decreases in extra responses. Seizures were also observed at the highest dose of soman employed (5 micrograms/kg). The increase in mean session response time was due to intermittent lapses in responding to stimuli (attentional deficits). Both the attentional deficits and intermittent generalized seizures were also persistent effects, with both occurring randomly after acute exposure to 5 micrograms/kg soman. Preliminary evidence suggests that occurrence of attentional deficits was associated with the occurrence of generalized and/or focal seizures; and that these effects may reflect irreversible lesions which become more threatening to the animal with increasing time. An additional, delayed effect was a sudden marked increase in the incidence of extra inconsequential responses which occurred several weeks after cessation of soman exposures.

Acute soman effects in the juvenile baboon: effects on a match-to-sample discrimination task and on total blood acetylcholinesterase

Male juvenile baboons, trained on a match-to-sample operant discrimination task, were given acute intramuscular injections of soman (methyl pinacolyl phosphonofluoridate) at 1.0, 2.0, 3.0, 4.0, and 5.0 micrograms/kg. The different doses were given in a mixed order just before a behavioral test session. Just prior to administration of each soman dose and immediately following the 2-hr behavioral test session, a sample of blood (0.5 ml) was drawn from the baboon and analyzed for inhibition of acetylcholinesterase activity. Thereafter, blood sampling was accomplished at weekly intervals and soman was administered again only when whole blood acetylcholinesterase reached at least 80% of pre-soman control level. Behavioral effects of soman included a slowing of response times, a decrease in extra inconsequential responses, a decrease in responsiveness to the visual stimuli and an increase in errors. These effects were observed when acetylcholinesterase (AChE) levels fell to 25 mumoles/hr/ml blood or less. The threshold dose for behavioral effects was very close to the dose of soman which induced seizures.

Behavioral effects of drugs as a function of maternal polybrominated biphenyl body burden

Prior to breeding, female rats were dosed orally for 20 days with either 0.5 mg/kg polybrominated biphenyl (PBB), 5.0 mg/kg PBB, or the lecithin liposome vehicle. Male offspring of these 3 treatment groups did not differ with respect to the learning of an operant discrimination task. However, administration of phenobarbital or d-amphetamine impaired the behavior of the offspring of low-dose PBB dams less than that of the offspring of controls. The behavioral effects of the drugs were generally inversely related to levels of liver PBB and activities of liver aryl hydrocarbon hydroxylase (AHH).