Abstract A29: A selective HDAC3 inhibitor synergizes with 5-azacytidine in diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL) is an aggressive lymphoma, with 40% of patients relapsing or refractory to the conventional chemotherapy treatment, usually with fatal consequences. Therefore, more targeted therapies are needed. DLBCL are characterized by profound alterations in the epigenome (histone modifications and DNA methylation) that are correlated with poor survival. While epigenetic drugs are used as anti-cancer treatments, their full potential has not been achieved. One limitation for the implementation of epigenetic-based therapies in the clinic has been its use as single agents; therefore, we explored new combinatorial therapies with the goal to increase efficacy. Our previous studies showed that lymphoma epigenetic programming involves repression of BCL6 target genes. This BCL6-mediated gene silencing in DLBCL is driven by 1) reduced H3K27 acetylation through recruitment of histone deacetylase 3 (HDAC3) and 2) reduced 5-hydroxymethylcytosine (5hmC). We thus tested a therapy consisting of the hypomethylating agent 5-azacytidine (5-Aza) and a specific HDAC3 inhibitor (HDAC3i). DLBCL cell line MD901 was treated with 200nM 5-Aza or vehicle daily for 5 days, with 10uM HDAC3i or vehicle added at days 3 and 5. Analysis at day 8 showed that whereas single agent did not induce cell death based on propidium iodide (PI) staining (vehicle=13.5%, 5-Aza=18%, HDAC3i=14.8% PI+ cells), the combination induced significantly higher cell death (5-Aza+HDAC3i=43.6% PI+ cells). We observed similar increased efficacy of 5-Aza+HDAC3i in OCI-Ly7 and SUDHL-4 cells. We also demonstrated that 5-Aza+HDAC3i acted synergistically in MD901, OCI-Ly7 and SUDHL-4 (combination index (CI)<1), with a dose-reduction index (DRI)=3.1 for 5-Aza and DRI=2.6 for HDAC3i to achieve 50% cell death in MD901; similar results were obtained in the other cell lines tested. We established xenografts -transplanting lymphoma cells in NSG mice through intraperitoneal injection- to test the efficacy of the combinatorial therapy in vivo. Mice engrafted with OCI-Ly7 cells received daily treatment with 1mg/kg 5-Aza or vehicle for 1 week, and were also treated with 25mg/kg HDAC3i or vehicle for other 3 weeks. 80% mice treated with 5-Aza+HDAC3i survived after 150 days, compared to 50% mice treated with HDAC3i alone; 5-Aza did not induce survival advantage compared to vehicle-treated mice. At the molecular level, we found that 5-Aza as single agent reduced global 5hmC levels compared to vehicle-treated cells; interestingly, this was also observed when cells were treated with HDAC3i alone. Intriguingly, the level of 5hmC when combining 5-Aza+HDAC3i was comparable to vehicle-treated cells. In summary, we demonstrate superior efficacy of 5-Aza in combination with HDAC3i in DLBCL. We are currently performing genome-wide assays to dissect the molecular mechanisms underpinning this synergistic anti-tumor activity. At the same time, we are generating xenograft models with primary DLBCL samples to confirm the potential of this new therapeutic approach to improve the outcomes of DLBCL patients.

Citation Format: Pilar M Dominguez, Leonie A Cluse, Noura Tawfic, Peter J Fraser, Sophia Rutaquio, Rachel Lim, Giorgio Inghirami, Gareth Gregory, Michael Dickinson, Ari M Melnick, Ricky W Johnstone. A selective HDAC3 inhibitor synergizes with 5-azacytidine in diffuse large B-cell lymphoma [abstract]. In: Proceedings of the Third AACR International Meeting: Advances in Malignant Lymphoma: Maximizing the Basic-Translational Interface for Clinical Application; 2022 Jun 23-26; Boston, MA. Philadelphia (PA): AACR; Blood Cancer Discov 2022;3(5_Suppl):Abstract nr A29.

Epigenetic Activation of Plasmacytoid DCs Drives IFNAR-Dependent Therapeutic Differentiation of AML

Pharmacologic inhibition of epigenetic enzymes can have therapeutic benefit against hematologic malignancies. In addition to affecting tumor cell growth and proliferation, these epigenetic agents may induce antitumor immunity. Here, we discovered a novel immunoregulatory mechanism through inhibition of histone deacetylases (HDAC). In models of acute myeloid leukemia (AML), leukemia cell differentiation and therapeutic benefit mediated by the HDAC inhibitor (HDACi) panobinostat required activation of the type I interferon (IFN) pathway. Plasmacytoid dendritic cells (pDC) produced type I IFN after panobinostat treatment, through transcriptional activation of IFN genes concomitant with increased H3K27 acetylation at these loci. Depletion of pDCs abrogated panobinostat-mediated induction of type I IFN signaling in leukemia cells and impaired therapeutic efficacy, whereas combined treatment with panobinostat and IFNα improved outcomes in preclinical models. These discoveries offer a new therapeutic approach for AML and demonstrate that epigenetic rewiring of pDCs enhances antitumor immunity, opening the possibility of exploiting this approach for immunotherapies.

SIGNIFICANCE

We demonstrate that HDACis induce terminal differentiation of AML through epigenetic remodeling of pDCs, resulting in production of type I IFN that is important for the therapeutic effects of HDACis. The study demonstrates the important functional interplay between the immune system and leukemias in response to HDAC inhibition. This article is highlighted in the In This Issue feature, p. 1397.

Increase in CFC-11 emissions from eastern China based on atmospheric observations

The recovery of the stratospheric ozone layer relies on the continued decline in the atmospheric concentrations of ozone-depleting gases such as chlorofluorocarbons¹. The atmospheric concentration of trichlorofluoromethane (CFC-11), the second-most abundant chlorofluorocarbon, has declined substantially since the mid-1990s². A recently reported slowdown in the decline of the atmospheric concentration of CFC-11 after 2012, however, suggests that global emissions have increased^3,4. A concurrent increase in CFC-11 emissions from eastern Asia contributes to the global emission increase, but the location and magnitude of this regional source are unknown³. Here, using high-frequency atmospheric observations from Gosan, South Korea, and Hateruma, Japan, together with global monitoring data and atmospheric chemical transport model simulations, we investigate regional CFC-11 emissions from eastern Asia. We show that emissions from eastern mainland China are 7.0 ± 3.0 (±1 standard deviation) gigagrams per year higher in 2014-2017 than in 2008-2012, and that the increase in emissions arises primarily around the northeastern provinces of Shandong and Hebei. This increase accounts for a substantial fraction (at least 40 to 60 per cent) of the global rise in CFC-11 emissions. We find no evidence for a significant increase in CFC-11 emissions from any other eastern Asian countries or other regions of the world where there are available data for the detection of regional emissions. The attribution of any remaining fraction of the global CFC-11 emission rise to other regions is limited by the sparsity of long-term measurements of sufficient frequency near potentially emissive regions. Several considerations suggest that the increase in CFC-11 emissions from eastern mainland China is likely to be the result of new production and use, which is inconsistent with the Montreal Protocol agreement to phase out global chlorofluorocarbon production by 2010.

Fine tuning of globin gene expression by DNA methylation

Expression patterns in the globin gene cluster are subject to developmental regulation in vivo. While the γ^A and γ^G genes are expressed in fetal liver, both are silenced in adult erythrocytes. In order to decipher the role of DNA methylation in this process, we generated a YAC transgenic mouse system that allowed us to control γ^A methylation during development. DNA methylation causes a 20-fold repression of γ^A both in non-erythroid and adult erythroid cells. In erythroid cells this modification works as a dominant mechanism to repress γ gene expression, probably through changes in histone acetylation that prevent the binding of erythroid transcription factors to the promoter. These studies demonstrate that DNA methylation serves as an elegant in vivo fine-tuning device for selecting appropriate genes in the globin locus. In addition, our findings provide a mechanism for understanding the high levels of γ-globin transcription seen in patients with Hereditary Persistence of Fetal Hemoglobin, and help explain why 5azaC and butyrate compounds stimulate γ-globin expression in patients with β-hemoglobinopathies.

Effects of gravity, hypergravity and microgravity on vestibular neurones of the crab

Recordings were made from identified balancing system interneurones using implanted electrodes in crabs oscillated at 0.3 Hz during bouts of Parabolic flight. Repeatable non stabilized patterns of response firing were seen in head up and head down interneurones. During the hypergravity phases, the ratio of firing frequencies in the two directional categories of interneurones was altered showing that hypergravity produced effects normally seen during tilting of the crab, implying greater bending of the sensory thread hairs. During microgravity, firing levels remained low and constant or changed slowly towards initial firing levels.

Antisense intergenic transcription in V(D)J recombination

Antigen receptor genes undergo variable, diversity and joining (V(D)J) recombination, which requires ordered large-scale chromatin remodeling. Here we show that antisense transcription, both genic and intergenic, occurs extensively in the V region of the immunoglobulin heavy chain locus. RNA fluorescence in situ hybridization demonstrates antisense transcription is strictly developmentally regulated and is initiated during the transition from DJ(H) to VDJ(H) recombination and terminates concomitantly with VDJ(H) recombination. Our data show antisense transcription is specific to the V region and suggest transcripts extend across several genes. We propose that antisense transcription remodels the V region to facilitate V(H)-to-DJ(H) recombination. These findings have wider implications for V(D)J recombination of other antigen receptor loci and developmental regulation of multigene loci.

Hydrostatic pressure effects on vestibular hair cell afferents in fish and crustacea

Following the discovery of a hydrostatic pressure sensor with no associated gas phase in the crab, and the knowledge that several systems of cells in culture show long term alterations to small changes in hydrostatic pressure, we show here that vestibular type II hair cells in a well known model system (the isolated elasmobranch labyrinth), are sensitive to hydrostatic pressure. This new finding for the vertebrate vestibular system may provide an explanation for low levels of resting activity in vertebrate hair cells and explain how fish without swim bladders sense hydrostatic cues. It could have implications for humans using their balancing systems in hypobaric or hyperbaric environments such as in aircraft or during space exploration. Although lacking the piston mechanism thought to operate in crab thread hairs which sense angular acceleration and hydrostatic pressure, the vertebrate system may use larger numbers of sensory cells with resultant improvement in signal to noise ratio. The main properties of the crab hydrostatic pressure sensing system are briefly reviewed and new experimental work on the isolated elasmobranch labyrinth is presented.

Hydrostatic pressure effects on vestibular hair cell afferents in fish and crustacea

Following the discovery of a hydrostatic pressure sensor with no associated gas phase in the crab, and the knowledge that several systems of cells in culture show long term alterations to small changes in hydrostatic pressure, we show here that vestibular type II hair cells in a well known model system (the isolated elasmobranch labyrinth), are sensitive to hydrostatic pressure. This new finding for the vertebrate vestibular system may provide an explanation for low levels of resting activity in vertebrate hair cells and explain how fish without swim bladders sense hydrostatic cues. It could have implications for humans using their balancing systems in hypobaric or hyperbaric environments such as in aircraft or during space exploration. Although lacking the piston mechanism thought to operate in crab thread hairs which sense angular acceleration and hydrostatic pressure, the vertebrate system may use larger numbers of sensory cells with resultant improvement in signal to noise ratio. The main properties of the crab hydrostatic pressure sensing system are briefly reviewed and new experimental work on the isolated elasmobranch labyrinth is presented.

Dogfish hair cells sense hydrostatic pressure

Many marine invertebrates and fish respond to hydrostatic pressure in order to regulate their depth and synchronize their behaviour to tidal cycles. Here we investigate the effect of hydrostatic pressure on the vestibular hair cells located in the labyrinth of the dogfish Scyliorhinus canicula, and find that it modulates their spontaneous activity and response to angular acceleration. This may explain not only the low resting activity of vertebrate hair cells but also how fish that do not have swim bladders can sense hydrostatic cues.

Evidence for substantial variations of atmospheric hydroxyl radicals in the past two decades

The hydroxyl radical (OH) is the dominant oxidizing chemical in the atmosphere. It destroys most air pollutants and many gases involved in ozone depletion and the greenhouse effect. Global measurements of 1,1,1-trichloroethane (CH3CCl3, methyl chloroform) provide an accurate method for determining the global and hemispheric behavior of OH. Measurements show that CH3CCl3 levels rose steadily from 1978 to reach a maximum in 1992 and then decreased rapidly to levels in 2000 that were lower than the levels when measurements began in 1978. Analysis of these observations shows that global OH levels were growing between 1978 and 1988, but the growth rate was decreasing at a rate of 0.23 +/- 0.18% year(-2), so that OH levels began declining after 1988. Overall, the global average OH trend between 1978 and 2000 was -0.64 +/- 0.60% year(-1). These variations imply important and unexpected gaps in current understanding of the capability of the atmosphere to cleanse itself.

Statocysts in crabs: short-term control of locomotion and long-term monitoring of hydrostatic pressure

Crabs show well-coordinated locomotion. They have proprioceptors similar to those of lobsters, but they differ in terms of their balancing systems and their condensed nervous system, which allows rapid interganglionic conduction. Typically they exhibit dynamically stable locomotion with a highly developed semicircular canal system that codes angular acceleration in each of three orthogonal planes (horizontal and vertical at 45 degrees and 135 degrees to the pitching plane). Left and right interneurons each code one direction of angular acceleration, carrying information between the brain and the thoracic ganglia. Cell A codes head-up vertical plane angular accelerations. Cell B codes rotations in the horizontal plane. Interneurons C and D code headdown vertical plane information, carrying it ipsilaterally and contralaterally respectively. These interneurons have a central role in locomotion. They are activated and have their responsiveness to angular acceleration enhanced before and during locomotion. Such simple activation pathways point to how an angular-acceleration-controlled robot (CRABOT) could be constructed. Hydrostatic pressure information carried by the thread hairs, which also sense angular acceleration, is filtered out from direct pathways onto the interneurons, but spectral analysis shows that it still has an influence via central pathways. Long-term recordings from equilibrium interneurons in free-walking crabs taken from the wild into constant conditions show tidally changing frequencies

The transduction of very small hydrostatic pressures

This paper reviews experiments in which cells, subjected to hydrostatic pressures of 20 kPa or less, (micro-pressures), demonstrate a perturbation in growth and or metabolism. Similarly, the behavioural responses of aquatic animals (lacking an obvious compressible gas phase) to comparable pressures are reviewed. It may be shown that in both cases the effect of such very low hydrostatic pressures cannot be mediated through the thermodynamic mechanisms which are invoked for the effects of high hydrostatic pressure. The general conclusion is that cells probably respond to micro-pressures through a mechanical process. Differential compression of cellular structures is likely to cause shear and strain, leading to changes in enzyme and/or ion channel activity. If this conclusion is true then it raises a novel question about the involvement of 'micro-mechanical' effects in cells subjected to high hydrostatic pressure. The responses of aquatic animals to micro-pressures may be accounted for, using the model case of the crab, by the mechanical, bulk, compression of hair cells in the statocysts, the organ of balance. If this is true, it raises the interesting question of why the putative cellular mechanisms of micro-pressure transduction appear to have been superseded by the statocyst.

Atmospheric Trends and Lifetime of CH3CCI3 and Global OH Concentrations

Determination of the atmospheric concentrations and lifetime of trichloroethane (CH(3)CCI(3)) is very important in the context of global change. This halocarbon is involved in depletion of ozone, and the hydroxyl radical (OH) concentrations determined from its lifetime provide estimates of the lifetimes of most other hydrogen-containing gases involved in the ozone layer and climate. Global measurements of trichloroethane indicate rising concentrations before and declining concentrations after late 1991. The lifetime of CH(3)CCI(3) in the total atmosphere is 4.8 +/- 0.3 years, which is substantially lower than previously estimated. The deduced hydroxyl radical concentration, which measures the atmosphere's oxidizing capability, shows little change from 1978 to 1994.

Specific pattern of gene expression during induction of mouse erythroleukemia cells

We have studied the expression of several characterized genes during induction of mouse erythroleukemia (MEL) cells with dimethyl sulfoxide (DMSO) and have observed a specific pattern of changes in transcriptional activity and steady-state RNA levels associated with erythroid differentiation. During induction there is a gradual, steady decrease in total transcriptional activity and RNA content per cell, which by day 3 of DMSO treatment amounts to less than 50% of the level in the uninduced cell. During this time we observe increases in transcriptional activity for 5-aminolevulinic acid synthase, carbonic anhydrase form II, and band 3 coordinate with the large increase in beta-globin gene transcription. The results also demonstrate an early decrease in transcription for carbonic anhydrase form I, which precedes decreases in transcription for glyceraldehyde phosphate dehydrogenase and rRNA genes. Changes in steady-state RNA levels reflected changes in transcriptional activity during induction except for carbonic anhydrase II mRNA. These results represent the first report characterizing the regulated expression at transcriptional and posttranscriptional levels of several known genes that are characteristically expressed in the erythrocyte. The results demonstrate that coordinate gene expression in erythroid differentiation occurs primarily at the level of transcription.

Molecular evolution of the carbonic anhydrase genes: calculation of divergence time for mouse carbonic anhydrase I and II

A cDNA clone in pBR322 that cross-hybridizes with a mouse carbonic anhydrase form II (CAII) probe has been sequenced and identified as mouse carbonic anhydrase form I (CAI). The 1224-base-pair clone encodes the entire 260-amino-acid protein and appears to contain an Alu-like element in the 3' untranslated region. The deduced amino acid sequence exhibits 77% homology to human CAI and contains 17 of the 20 residues that are considered unique to and invariant for all mammalian CAI isozymes. The results of a detailed comparison of the nucleic acid sequences spanning the coding regions of mouse CAI and rabbit CAI have been used to calibrate an evolutionary clock for the carbonic anhydrases (CAs). These data have been applied to a comparison of the mouse CAI and CAII nucleic acid sequences to calculate the divergence time between the two genes. The divergence-time calculation provides the first estimation of the evolutionary relationship between CAs based entirely on nucleotide sequence comparison.

Cloning and structural characterization of a human non-erythroid band 3-like protein

Polypeptides which are immunologically related to the erythrocyte anion transport protein have been identified in a variety of non-erythroid cells. We describe two cDNA clones encoding a human non-erythroid band 3 protein (HKB3) and the mouse erythrocyte band 3 (MEB3) and show that these proteins are structurally similar. Comparison of the predicted amino acid sequences from HKB3 and MEB3 reveals a high degree of sequence homology (71%) and conservation of the overall topography of the transmembrane domain. Similar levels of homology are also observed in comparisons with published amino acid sequence from the human erythrocyte band 3. In addition, specific residues which have been demonstrated to be involved in erythroid anion transport are conserved in HKB3, suggesting that this non-erythroid band 3 protein functions in this respect. Although protein sequence homology within the cytoplasmic domain is considerably lower (35%), three specific regions in HKB3 are conserved, one of which may represent an ankyrin binding site. Northern blot analysis reveals transcripts that cross-hybridize with the HKB3 cDNA in a variety of non-erythroid cell lines but not in cells of erythroid lineage.

Microcomputers and neurobiology: a short review

A brief history of the application of computing techniques emphasizes the two-part development with expensive minicomputers available in a few laboratories being added to by inexpensive microcomputers ubiquitously available. Computers are used for microscope control and plotting, serial section reconstruction, morphometric measurement, stereology, video image analysis, photometry and fluorescence microscopy. Basic principles are exemplified by considering nerve cell reconstruction. General principles of computerized electrical measurement including filtering, averaging and stimulus generation are discussed. Computerized waveform selection as used for spike discrimination, when considered along with computer control of electrode position and the growing availability of multichannel recording arrays, suggests a possible advance in automatic analyses. With the ability to process more complex waveforms successfully, electrophysiological data such as compound extracellular potentials may usefully replace the cleaner, but more limited intracellular data. Success with multichannel feedback controlled stimulators making paraplegics stand and walk point to a developing application with much potential.

Oxidative addition of monosilanes to planar iridium(I) complexes and carbonylation of the resulting adducts

Silanes [R3SiH; R3 = Cl3, MeCl2, (EtO)3, Ph3] undergo irreversible oxidative addition to planar iridium(I) complexes IrClL3 (L = PPh3, PMePh2 or AsPh3) to give silyliridium(III) hydrides IrHCl(SiR3)Ln (n = 2 or 3). The yellow, five-coordinate, probably tetragonal pyramidal complexes(n = 2) are formed mainly when L = PPh3 or AsPh3, and also in the case of L = PmePh2, R = Ph, whereas the colourless, six-coordinate, presumably octahedral adducts are formed predominantly when L = PMePh2. Both five- and six-coordinate adducts can be isolated from the addition of dichloro(methyl)silane to IrCl(AsPh3)3. Most of the adducts react with carbon monoxide under ambient conditions to give silyliridium(III) hydrido carbonyls, IrHCl(SiR3)(CO)L2, which may undergo partial or complete reductive elimination to IrCl(CO)L2 and R3SiH; the ease with which this occurs depends on L (PPh3 > PMePh2 > AsPh3) and on R3 [Ph3 > (EtO)3 > Cl3 ≈ MeCl2]. The reactions of silanes with IrClL3, RhClL3 and IrCl(CO)(PPh3)2 are compared, and the trends observed in the case of IrClL3 are discussed in terms of electronic and steric effects in the silyl and Group 5 donors. Structural assignments for the new complexes are based on i.r., far-i.r. and 1H N.M.R. data.

Reactions of Mono- and Di-substituted acetylenes with planar iridium(I) complexes and carbonylation of the resulting adducts

Alk-1-ynes (RC2H; R = H, Pr, Bu, CH2CH2OH, Ph, CO2Me) undergo irreversible oxidative addition to the iridium(I) complex IrCl(PPh3)3 to give six-coordinate hydrido acetylides of iridium(III), IrHCl(C2R)(PPh3)3, the stereochemistry of which is deduced from 1H N.M.R. and infrared data. Isomers of the corresponding adduct of phenylacetylene with IrCl(PMePh2)3 can be isolated. Carbonylation of IrHCl(C2R)(PPh3)3 gives IrHCl(C2R)(CO)(PPh3)2, which can be isolated only when R = H, Ph or CO2Me; when R = Pr, Bu or CH2CH2OH, the complexes immediately decompose to IrCl(CO)(PPh3)2 and the alkyne. This reductive elimination also occurs to some extent for R = Ph. Diphenylacetylene and dimethyl acetylenedicarboxylate react with IrCl(PPh3)3 to give the known alkyne complex IrCl(PhC2Ph)(PPh3)2 and the known iridiacyclopentadiene complex IrCl-(MeO2CC2CO2Me)2(PPh3)2 respectively. The additions of alk-1-ynes to IrClL3 and to other lowvalent metal complexes are compared, and the relevance of the oxidative addition to catalysis of linear polymerization of alk-1-ynes is noted.

Pseudosymmetry in the structure of luteinizing hormone-releasing hormone. Studies on a series of novel analogs

Pseudosymmetry in the LH-RH structure is described. Eleven analogs of LH-RH (SMALLER THAN Glu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2) have been synthesized by the fragment condensation method and the repetitive excess mixed anhydride method. Multiple substitutions have been made in the LH-RH sequence, which retain the pseudosymmetry of the LH-RH molecule, while presenting fewer problems of synthesis than the corresponding residues in the natural decapeptide. Thus Trp3, Ser4, Tyr5, Gly6, Leu7, and Arg8 residues were replaced by amino acids having similar properties to the residues that they replace. In all but one of the peptides the Gly10-NH2 residue was replaced by ethylamide, while in the remaining peptide, 1-methyl-5-aminomethyltetrazole (AMT-Me) was substituted at position 10. The compounds were assayed in vitro and in vivo. The following analogs had in vivo and in vitro activities in the range 1-28 percent relative to LH-RH: I, smaller than Glu-His-Phe-Ala-Tyr-Gly-Leu-Arg-Pro-NHEt; II, smaller than Glu-His-Phe-Gly-Tyr-Gly-Leu-Arg-Pro-NHEt; VII, smaller than Glu-His-Phe-Ala-Tyr-Gly-Phe-Arg-Pro-NHEt; IX, smaller than Glu-His-Phe-Ala-Tyr-D-Ala-Leu-Arg-Pro-NHEt; XI, smaller than Glu-His-Phe-Gly-Tyr-Gly-Leu-Arg-Pro-AMT-Me.

Interneurones in Crab Connectives (Carcinus Maenas (L.)): Directional Statocyst Fibres

Five interneurones in each connective respond directionally to rotation of a crab. Each seems to be activated by one direction of fluid flow in one statocyst canal. The anatomy of two is known and correlates well with a direct input from the receptors of one statocyst. Three of the fibres have input from leg joint proprioceptors.

The swimming reflex and a complicated turning reflex are evoked on rotation of a minimally restrained crab. It is likely that the statocyst interneurones are involved in these and other behaviour patterns, including the rearing reflex and sideways walking.

Interneurones in Crab Connectives (Carcinus Maenas (L.)): Giant Fibres

Five interneurones with cell bodies and dendritic trees in the brain have axons 40-60µm diameter in one oesophageal connective. The fibres are phasic and multimodal, responding to visual and tactile stimuli. They have complex adaptation properties and two are suppressed completely during certain movements of the animal. The role of the fibres in overt behaviour has not been revealed by electrical stimulation or by examination of output in free walking animals. Several smaller interneurones in the connective are briefly described anatomically and physiologically.

Transition metal complexes of substituted alkynes. IX. Factors that influence the formation of Tris(alkyne)cobalt complexes

Reactions involving p-alkyne-hexacarbonyldioobalt complexes and an excess of an alkyne have been investigated systematically to determine some of the factors affecting the formation and stabilization of CO,(CO)~C,(CF,)~R,-, complexes. Systems have been studied in which the value of n has been varied through all values from 0 to 6. The new tris(a1kyne)tetracarbonyldioobalt complex CO,(CO),C,(CF,),(CH~)~- Hz, formed from Co,(CO),(CH,C,CH,) and an excess of CF,C=_CH, has been characterized by elementary and spectroscopic analysis. Tris(a1kyne)tetracarbonyldi- cobalt compIexes have not been isolated from the systems [Co,(CO),(CF3C,CF3)+2- CH,C=CCH,], [Co,(CO),(CF,C,CF,) + 2CH3CzCH], [Co,(CO),(CF,C,CH,) + 2CH3C~C- CH,], [Co,(CO),(CH,C,CH,) + 2CF3CKXF3], [Co,(CO),(CH3C,CH,) + 2CH3C~CCH3], and [Co,(CO),(CH3C,CH,)+2CH3C~CH]. Rather, significant amounts of various CF,- and/or CH,-substituted benzenes are obtained in these reactions. These sub- stituted benzenes are presumably formed by decomposition of unstable tris(a1kyne)- tetracarbonyldicobalt complexes. The accumulated results indicate that two principal factors influence the stability of the CO,(CO)~C,(CF,),R,-, complexes. Stable complexes are isolated only when (i) at least two CF, groups are incorporated as substituents in the C,-bridging fragment, and (ii) CF, substituents are attached to the two terminal carbon atoms of the bridging fragment.

Transition metal complexes of substituted alkynes. VIII. Complexes of cobalt derived from 1,1,1-Trifluorobut-2-yne

The complex Co4(CO)10(CF3C2CH3) is formed at room temperature from dodecacarbonyltetracobalt and 1,1,1-trifluorobut-2-yne. Another monoalkyne complex Co2(CO)6(CF3C2CH3) has been prepared from octacarbonyldicobalt and 1,1,1-trifluorobut-2-yne at room temperature. Treatment with triphenylphosphine converts the complex into Co2(CO)4[P(C6H5)3]2(CF3C2CH3). At 150�, reaction of Co2(CO)6(CF3C2CH3) and 1,1,1-trifluorobut-2-yne gives a small amount of a purple complex which is believed to be Co2(CO)4(CF3C2CH3)3. Similar reactions involving Co2(CO)4(CF3C2CH3) and the alkynes hexafluorobut-2-yne and 3,3,3-trifluoropropyne give the complexes Co2(CO)4(CF3C2CH3)(CF3C2CF3)2 and Co2(CO)4(CF3C2CH3)(CF3C2H)2. Spectroscopic studies have led to an assignment of the substitution pattern in these latter complexes. Tris-alkyne complexes were not isolated from similar reactions between 1,1,1-trifluorobut-2-yne and the complexes Co2(CO)6(CF3C2CF3) and Co2(CO)6(CF3C2H). Three isomers of the π-cyclopentadienone-π-cyclopentadienylcobalt complex, [(CF3C2CH3)2CO]Co(π-C5H5), were obtained from (π-C6H6)Co(CO)2 and 1,1,1-trifluorobut-2-yne after U.V. irradiation for several days. The isomers vary in the arrangement of the substituents attached to the cyclopentadienone ring. All reactions involving 1,1,1-trifluorobut-2-yne have been compared with similar reactions involving the related alkynes hexafluorobut-2-yne and but-2-yne.

Transition metal complexes of substituted alkynes. VI. Substituent arrangement in some bridging tris(alkyne)-cobalt complexes

The new organocobalt complex CO2(CO)4(CF3C2CF3)2(CF3C2H) has been isolated from the reaction of hexafluorobut-2-yne with p-trifluoropropyne-hexacarbonyldicobalt. In addition, a second isomer of the known complex CO2(CO)4(CF3C2CF3)2(CF3C2H)2 has been isolated from the reaction of 3,3,3-tri-fluoropropyne with p-hexafluorobut-2-yne-hexacarbonyldicobalt. A detailed study of the 1H and 19F N.M.R. spectra of these and the related complexes Co2(C0)4- (CF3C2CF3)3 and CO2(CO)4(CF3C2H)3 has led to an assignment of the substituent arrangement in all of these complexes.