Coinage Metal Bis(amidinate) Complexes as Building Blocks for Self-Assembled One-Dimensional Coordination Polymers.

The pyridyl functionalized amidinate [{PyC≡CC(NDipp)2 }Li(thf)2 ]n was used to synthesize a series of bis-amidinate complexes [{PyC≡CC(NDipp)2 }2 M2 ] (M=Cu, Ag, Au) with fully supported metallophilic interactions. These metalloligands were then used as building blocks for the synthesis of one-dimensional heterobimetallic coordination polymers using Zn(hfac)2 (hfac=hexaflouroacetylacetonate) for self-assembly. Interestingly, the three coordination polymers [{PyC≡CC(NDipp)2 }2 M2 ][Zn(hfac)2 ] (M=Cu, Ag, Au), exhibit a zig zag shape in the solid state. To achieve linear coordination geometry other connectors such as M'(acac) (M'=Ni, Co) (acac=acetylacetonate) were investigated. The thus obtained compounds [{PyC≡CC(NDipp)2 }2 Cu2 ][M'(acac)2 ] (M'=Ni, Co) are indeed linear heterobimetallic coordination polymers featuring a metalloligand backbone with fully supported metallophilic interactions.

Enantiopure Calcium Iminophosphonamide Complexes: Synthesis, Photoluminescence, and Catalysis.

The synthesis of calcium complexes ligated by three different chiral iminophosphonamide ligands, L-H (L=[Ph2 P{N(R)CH(CH3 )Ph}2 ]), L'-H (L'=[Ph2 P{NDipp}{N(R)CH(CH3 )Ph}]), (Dipp=2,6-i Pr2 C6 H3 ), and L''-H (L''=[Ph2 P{N(R)CH(CH3 )naph}2 ]), (naph=naphthyl) is presented. The resulting structures [L2 Ca], [L'2 Ca], and [L''2 Ca] represent the first examples of enantiopure homoleptic calcium complexes based on this type of ligands. The calcium complexes show blue-green photoluminescence (PL) in the solid state, which is especially bright at low temperatures. Whereas the emission of [L''2 Ca] is assigned to the fluorescence of naphthyl groups, the PL of [L2 Ca] and [L'2 Ca] is contributed by long-lived phosphorescence and thermally activated delayed fluorescence (TADF), with a strong variation of the PL lifetimes over the temperature range of 5-295 K. Furthermore, an excellent catalytic activity was found for these complexes in hydroboration of ketones at room temperature, although no enantioselectivity was achieved.

Alkali Metal Complexes of a Bis(diphenylphosphino)methane Functionalized Amidinate Ligand: Synthesis and Luminescence.

A novel bis(diphenylphosphino)methane (DPPM) functionalized amidine ligand (DPPM-C(N-Dipp)2 H) (Dipp=2,6-diisopropylphenyl) was synthesized. Subsequent deprotonation with suitable alkali metal bases resulted in the corresponding complexes [M{DPPM-C(N-Dipp)2 }(Ln )] (M=Li, Na, K, Rb, Cs; L=thf, Et2 O). The alkali metal complexes form monomeric species in the solid state, exhibiting intramolecular metal-π-interactions. In addition, a caesium derivative [Cs{PPh2 CH2 -C(N-Dipp)2 }]6 was obtained by cleavage of a diphenylphosphino moiety, forming an unusual six-membered ring structure in the solid state. All complexes were fully characterized by single crystal X-ray diffraction, NMR spectroscopy, IR spectroscopy as well as elemental analysis. Furthermore, the photoluminescent properties of the complexes were thoroughly investigated, revealing differences in emission with regards to the respective alkali metal. Interestingly, the hexanuclear [Cs{PPh2 CH2 -C(N-Dipp)2 }]6 metallocycle exhibits a blue emission in the solid state, which is significantly red-shifted at low temperatures. The bifunctional design of the ligand, featuring orthogonal donor atoms (N vs. P) and a high steric demand, is highly promising for the construction of advanced metal and main group complexes.

Thermally Activated Delayed Fluorescence and Phosphorescence Quenching in Iminophosphonamide Copper and Zinc Complexes.

The synthesis of copper and zinc complexes of four variably substituted iminophosphonamide ligands is presented. While the copper complexes form ligand-bridged dimers, the zinc compounds are monomeric. Due to different steric demand of the ligand the arrangement of the ligands within the dimeric complexes varies. Similar to the structurally related iminophosphonamide complexes of alkali metals and calcium, the steady-state and time-resolved photoluminescence (PL) of four of the seven compounds studied here as solids in a temperature range of 5-295 K can be described within the scheme of thermally activated delayed fluorescence (TADF). Accordingly, they exhibit bright blue-green phosphorescence at low temperatures (<100 K), which turns into delayed fluorescence by increasing the temperature. However, unusually, the fluorescence is practically absent in two copper complexes which otherwise still conform to the TADF scheme. In these cases, the excited singlet states decay essentially non-radiatively and their thermal population from the corresponding low-lying triplet states efficiently quenches PL (phosphorescence). Three other copper and zinc complexes only exhibit prompt fluorescence, evidencing a wide variation of photophysical properties in this class of compounds. The excited states of the copper complex with especially pronounced phosphorescence quenching were also investigated by low-temperature time-resolved infrared spectroscopy and quantum chemical calculations.

Efficient Blue Phosphorescence in Gold(I)-Acetylide Functionalized Coinage Metal Bis(amidinate) Complexes.

The synthesis of linear symmetric ethynyl- and acetylide-amidinates of the coinage metals is presented. Starting with the desilylation of the complexes [{Me3 SiC≡CC(NDipp)2 }2 M2 ] (Dipp=2,6-diisopropylphenyl) (M=Cu, Au) it is demonstrated that this compound class is suitable to serve as a versatile metalloligand. Deprotonation with n-butyllithium and subsequent salt metathesis reactions yield symmetric tetranuclear gold(I) acetylide complexes of the form [{(PPh3 )AuC≡CC(NDipp)2 }2 M2 ] (M=Cu, Au). The corresponding Ag complex [{(PPh3 )AuC≡CC(NDipp)2 }2 Ag2 ] was obtained by a different route via metal rearrangement. All compounds show bright blue or blue-green microsecond long phosphorescence in the solid state, hence their photophysical properties were thoroughly investigated in a temperature range of 20-295 K. Emission quantum yields of up to 41 % at room temperature were determined. Furthermore, similar emissions with quantum yields of 15 % were observed for the two most brightly luminescent complexes in thf solution.

Electrocorticographic and neurochemical findings after local cortical valproate application in patients with pharmacoresistant focal epilepsy.

Because oral pharmacological treatment of neocortical focal epilepsy is limited due to common systemic side effects and relatively low drug concentrations reached at the epileptic foci locally, application of antiepileptic agents directly onto the neocortical focus may enhance treatment tolerability and efficacy. We describe the effects of cortically applied sodium valproate (VPA) in two patients with pharmacoresistant neocortical focal epilepsy who were selected for epilepsy surgery after a circumscribed epileptic focus had been determined by invasive presurgical evaluation using subdural electrodes. Local VPA modified epileptic activity as electrocorticographically recorded from the chronic focus in both patients. In addition, VPA induced local increase of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) in cortical tissue samples, whereas the excitatory glutamate was possibly decreased. In this clinical pilot study, we could show antiepileptic effects of cortically applied VPA in humans by electrocorticographic and neurochemical parameters.

Size Matters: From Two-Dimensional AuI -TlI Metallopolymers to Molecular Complexes by Simple Variation of the Steric Demand.

Bis(acetylido) aurates(I) and thallium(I) trifluoromethylsulfonates were used to synthesize AuI -TlI metallopolymers, displaying novel and unusual structural motifs of the metal-metal backbones in the solid state: a discrete molecular cluster, 1D chains of interconnected dimers, tetramers, or dodecamers of Au-Tl units, and a 2D-plane network, consisting of alternating edge-linked (AuTl)6 and (AuTl)4 cycles. The formation of the different architectures was primarily controlled by the steric demand of the acetylide-substituent groups. Thus, the bulkiest 2,6-diisopropylphenyl derivative yielded a molecular cluster [Tl2 Au3 ]. Most compounds showed bright visible photoluminescence with quantum yields of up to 25 % at ambient temperature. The color of the emitted light significantly differs with the network structure. Furthermore, theoretical studies of singlet excitations in the molecular cluster, as well as NMR and mass-spectrometric investigations of the fragmentation of the metallopolymers in solution are described in detail.

Investigating the Photochemistry of Spiropyran Metal Complexes with Online LED-NMR.

As one of the best studied photoswitches, spiropyrans (SPs) have attracted significant interest in the scientific community. Among the many stimuli to alter the isomerization into the merocyanine (MC) isomer, such as temperature, pH, solvent polarity, redox potential, or mechanical force, the ability of the MC form to act as a ligand site for metal complexation has recently raised new attention. We herein synthesize hitherto undescribed coordination compounds of 8-methoxy-1',3',3'-trimethyl-6-nitrospiro-[chromene-2,2'-indoline] with s-block ([Ca(MC)4](ClO4)2), d-block ([Zn(MC)2(MeCN)2](ClO4)2, [Ni(MC)2(MeCN)2](ClO4)2), as well as f-block ([La(NO3)3(MC)2]) metals. All complexes are structurally described by X-ray crystallography and systematically investigated in solution via Job's method of continuous variations (Job plots), as well as online NMR spectroscopic kinetic experiments with in situ irradiation of the analyte solution inside the NMR spectrometer (LED-NMR). We can unambiguously identify the photoresponsive nature of the complexes in solution, which is a crucial step toward the application of these promising molecules in material science.

Synthesis, Spectroscopy, and Redox Studies of Ferrocene-Functionalized Coinage Metal Alkyne Complexes.

Ethynylferrocene (FcC≡CH) was utilized as a redox-active metalloligand for the synthesis of polynuclear coinage metal complexes. The reaction of [FcC≡CLi] with tri- tert-butylphosphine metal chlorides [tBu3P-MCl] (M = Au, Ag, Cu) yielded different heteronuclear ferrocene-funtionalized alkyne complexes featuring metallophilic interactions. Furthermore, the redox properties of the ferrocenyl-functionalized tetracopper complex were investigated by cyclic voltammetry and UV-vis-near-IR spectroelectrochemistry. They indicate the compounds' redox-rich nature and a weak electronic coupling between the redox-active ferrocenyl units over a large distance.

Spatially-Resolved Multiple Metallopolymer Surfaces by Photolithography.

A tetrazole-based photoligation protocol for the spatially-resolved encoding of various defined metallopolymers onto solid surfaces is introduced. By using this approach, fabrication of bi- and trifunctional metallopolymer surfaces with different metal combinations were achieved. Specifically, α-ω-functional copolymers containing bipyridine as well as triphenylphosphine ligands were synthesized through reversible addition-fragmentation chain transfer (RAFT) polymerization, and subsequently metal loaded to afford metallopolymers of the widely-used metals gold, palladium, and platinum. Spatially-resolved surface attachment was achieved by means of a nitrile imine-mediated tetrazole-ene cycloaddition (NITEC) based photoligation protocol, exploiting tethered tetrazoles and metallopolymers equipped with a maleimide chain terminus. Metallopolymer coated surfaces with three different metals were prepared and characterized by time-of-flight secondary ion mass spectrometry (ToF-SIMS) and spatially-resolved X-ray photoelectron spectroscopy (XPS) mapping, supporting the preserved chemical composition of the surface-bound metallopolymers. The established photochemical technology platform for arbitrary spatially-resolved metallopolymer surface designs enables the patterning of multiple metallopolymers onto solid substrates. This allows for the assembly of designer metallopolymer substrates.

Dimolybdenum Paddlewheel as Scaffold for Heteromultimetallic Complexes: Synthesis and Photophysical Properties.

A diphenylphosphine functionalized benzoic acid was applied for the synthesis of a homoleptic dimolybdenum-based metalloligand, exhibiting four symmetrically placed phosphine donor sites. This allowed subsequent treatment with gold(I), rhodium(I), and iridium(I) precursors to obtain early-late heterometallic complexes as well as Lewis acid-base adducts with BH3. The compounds were in-depth investigated by spectroscopic techniques, single-crystal X-ray diffraction, and femtosecond laser spectroscopy. The coordination of different metal fragments to the dimolybdenum metalloligand leads to a fine-tuning of the system's optical properties, which correlates well with fluorescence quantum yield measurements. Nevertheless, triplet dynamics still remain the dominating channel in these systems with an intersystem crossing time constant below 1 ps.

Intensely Photoluminescent Diamidophosphines of the Alkaline-Earth Metals, Aluminum, and Zinc.

The positively charged and weakly polarizable s-block metals commonly do not usually have phosphine ligands in molecular complexes. Herein, we report mono- and dinuclear small diamidophosphine complexes of the alkaline-earth metals Mg, Ca, and Sr, which were prepared from simple precursors and a phosphine-functionalized diamine ligand N,N-bis(2-(diphenyl-phosphino)phenyl)ethane-1,2-diamine (PNHNHP). The alkaline-earth metal based complexes [(PNNP)Mg]2 and [(PNNP)M(thf)3 ] (M=Ca, Sr), exhibit unusual coordination spheres and show bright fluorescence, both in the solid state and in solution. For comparison, the even stronger luminescent Al and Zn complexes [(PNNP)Zn]2 and [(PNNP)AlCl] were prepared. Emission lifetimes in the nanosecond range and high photoluminescence quantum yields up to 93 % are observed at room temperature.

Neocortical GABA release at high intracellular sodium and low extracellular calcium: an anti-seizure mechanism.

In epilepsy, the GABA and glutamate balance may be disrupted and a transient decrease in extracellular calcium occurs before and during a seizure. Flow Cytometry based fluorescence activated particle sorting experiments quantified synaptosomes from human neocortical tissue, from both epileptic and non-epileptic patients (27.7% vs. 36.9% GABAergic synaptosomes, respectively). Transporter-mediated release of GABA in human and rat neocortical synaptosomes was measured using the superfusion technique for the measurement of endogenous GABA. GABA release was evoked by either a sodium channel activator or a sodium/potassium-ATPase inhibitor when exocytosis was possible or prevented, and when the sodium/calcium exchanger was active or inhibited. The transporter-mediated release of GABA is because of elevated intracellular sodium. A reduction in the extracellular calcium increased this release (in both non-epileptic and epileptic, except Rasmussen encephalitis, synaptosomes). The inverse was seen during calcium doubling. In humans, GABA release was not affected by exocytosis inhibition, that is, it was solely transporter-mediated. However, in rat synaptosomes, an increase in GABA release at zero calcium was only exhibited when the exocytosis was prevented. The absence of calcium amplified the sodium/calcium exchanger activity, leading to elevated intracellular sodium, which, together with the stimulation-evoked intracellular sodium increment, enhanced GABA transporter reversal. Sodium/calcium exchange inhibitors diminished GABA release. Thus, an important seizure-induced extracellular calcium reduction might trigger a transporter- and sodium/calcium exchanger-related anti-seizure mechanism by augmenting transporter-mediated GABA release, a mechanism absent in rats. Uniquely, the additional increase in GABA release because of calcium-withdrawal dwindled during the course of illness in Rasmussen encephalitis. Seizures cause high Na(+) influx through action potentials. A transient decrease in [Ca(2+)]e (seizure condition) increases GABA transporter (GAT)-mediated GABA release because of elevated [Na(+)]i. This amplifies the Sodium-Calcium-Exchanger (NCX) activity, further increasing [Na(+)]i and GABA release. The reduction in [Ca(2+)]e triggers a GAT-NCX related anti-seizure mechanism by augmenting GAT-mediated GABA release. This mechanism, obvious in humans, is absent in rats.

High-frequency electrical stimulation suppresses cholinergic accumbens interneurons in acute rat brain slices through GABA(B) receptors.

The nucleus accumbens is selected as a surgical target in deep brain stimulation for treating refractory obsessive-compulsive disorder (OCD). One of the therapeutic benefits of this procedure is that the abnormal hyper-functioning prefrontal cortex of patients with OCD is restored during stimulation. One hypothesis regarding the mechanism of deep brain stimulation is that the neuronal electrophysiological properties are directly altered by electrical stimulation; another hypothesis assumes that the stimulation induces selective neuron transmitter release, such as γ-aminobutyric acid (GABA). In this study, we used multi-electrode arrays with electrode size of 40 × 40 µm to record electrophysiological signals from the large nucleus accumbens neurons in acute rat brain slices while applying electrical stimulation simultaneously. We revealed that high-frequency stimulation (HFS, 140 Hz) suppressed the spontaneous neuronal firing rate significantly, whereas low-frequency stimulation (LFS, 10 Hz) did not. Both HFS and LFS have no effect on neuronal firing pattern or on neuronal oscillation synchrony. GABAB receptor antagonism reversed the HFS-provoked neuronal inhibition, whereas GABAA receptor blockade failed to affect it. The recorded neurons were pharmacologically identified to be cholinergic interneurons. We propose that HFS has a direct suppressive effect on the identified accumbal acetylcholine (ACh) interneurons by enhancing GABA release in the stimulated region. Potentially, suppressed ACh interneurons decrease the disinhibiting function of medium-sized spiny neurons in the striato-thalamo-cortical circuit. This finding might give an indication of the mechanism of the therapeutic effect of HFS in nucleus accumbens on restoring the abnormal hyperactive prefrontal cortex status in OCD.

Altered transporter-mediated neocortical GABA release in Rasmussen encephalitis.

To learn whether epileptic seizures in Rasmussen encephalitis (RE) may be promoted by insufficient γ-aminobutyric acid (GABA) release. (3) H-GABA was released from neocortical synaptosomes through transporter reversal following intrasynaptosomal Na(+) accumulation by veratridine that prevents inactivation of Na(+) channels. Tissues of three RE patients were compared with those of nine non-RE. In RE, the release was markedly reduced. In non-RE, the extracellular Ca(2+) concentration ([Ca(2+) ]e ) was inversely related to the amount of release. In RE, the percental decline of additional release upon Cae 2+ withdrawal was linked with the presurgical duration of epilepsy. Permanent opening of Na(+) channels by veratridine resembles maximal frequency of action potentials corresponding to epileptic seizures. These are preceded by a fall in [Ca(2+) ]e . Zero [Ca(2+) ]e increased release through the Na(+) /Ca(2+) exchanger additionally elevating intrasynaptosomal Na(+) . This enhanced GABA release probably reflects an antiseizure mechanism. In RE, the additional release gets lost over epilepsy duration.

Luminescent early-late-hetero-tetranuclear group IV - Au(I) bisamidinate complexes.

The versatile metalloligand [{HCCC(NDipp)2}2Au2] (dipp = 2,6-diisopropylphenyl) was converted into early-late heterotetrametallic complexes [{ClCp2MCCC(NDipp)2}2Au2] (M = Ti, Zr). These compounds show photoluminescence with either remarkably different (Ti) or similar (Zr) features as compared to related solely coinage metal containing acetylide amidinate complexes.

ß1-Blockers Enhance Inotropy of Endogenous Catecholamines in Chronic Heart Failure.

Although ß1-blockers impressively reduce mortality in chronic heart failure (CHF), there are concerns about negative inotropic effects and worsening of hemodynamics in acute decompensated heart failure. May receptor theory dispel these concerns and confirm clinical practice to use ß1-blockers? In CHF, concentrations of catecholamines at the ß1-adrenoceptors usually exceed their dissociation constants (K Ds). The homodimeric ß1-adrenoceptors have a receptor reserve and display negative cooperativity. We considered the binomial distribution of occupied receptor dimers with respect to the interaction of an exogenous ß1-blocker and elevated endogenous agonist concentrations > [K Ds], corresponding to an elevated sympathetic tone. Modeling based on binomial distribution suggests that despite the presence of a low concentration of the antagonist, the activation of the dimer receptors is higher than that in its absence. Obviously, the antagonist improves the ratio of the dimer receptors with only single agonist activation compared with the dimer receptors with double activation. This leads to increased positive inotropic effects of endogenous catecholamines due to a ß1-blocker. To understand the positive inotropic sequels of ß1-blockers in CHF is clinically relevant. This article may help to eliminate the skepticism of clinicians about the use of ß1-blockers because of their supposed negative inotropic effect, since, on the contrary, a positive inotropic effect can be expected for receptor-theoretical reasons.

Molecular gold strings: aurophilicity, luminescence and structure-property correlations.

This review covers the compound class of one-dimensional gold strings. These compounds feature a formally infinite repetition of gold complexes as monomers/repeating units that are held together by aurophilic interactions, i.e. direct gold-gold contacts. Their molecular structures are primarily determined in the solid state using single crystal X-ray diffraction. The chemical composition of the employed gold complexes is diverse and furthermore plays a key role in terms of structure characteristics and the resulting properties. One of the most common features of gold strings is their photoluminescence upon UV excitation. The emission energy is often dependent on the distance of adjacent gold ions and the electronic structure of the whole string. In terms of gold strings, these parameters can be fine-tuned by external stimuli such as solvent, pH value, pressure or mechanical stress. This leads to direct structure-property correlations, not only with regard to the photophysical properties, but also electric conductivity for potential application in nanoelectronics. Concerning these correlations, gold strings, consisting of self-assembled individual complexes as building blocks, are the ideal compound class to look at, as perturbations by an inhomogeneity in the ligand sphere (such as the end of a molecule) can be neglected. Therefore, the aim of this review is to shed light on the past achievements and current developments in this area.

Functional characterization of muscarinic autoreceptors in rat and human neocortex.

Electrically evoked overflow of [(3)H]acetylcholine in slices of rat neocortex and of human neocortex (freshly obtained during neurosurgical treatment of epilepsy or deep-seated tumors) was used to functionally characterize the muscarinic receptor subtype, which mediates autoinhibition of acetylcholine release in these tissues. In the rat neocortex, the following pK(B) values [CI(95)] were calculated from the shifts to the right of the concentration-response curves of the full agonist oxotremorine in presence of subtype preferring muscarinic receptor antagonists: tripitramine: 9.1 [8.8, 9.4], tripinamide: 8.6 [8.5, 8.7], AQ-RA 741 (11-[[4-[4-(diethylamino)butyl]-1-piperidinyl]acetyl]-5,11-dihydro-6H-pyrido(2,3-b)[1,4]benzodiazepine-6-one): 8.2 [8.0, 8.4], himbacine: 8.0 [7.9, 8.1], 4-diphenylacetoxy-N-methylpiperidine methobromide: 8.0 [7.8, 8.1], methoctramine: 7.5 [7.4, 7.6], AF-DX 116 (11[[2-[(diethyl-amino)methyl]-1-piperidinyl] acetyl] 5,11-dihydro-6H-pyrido(2,3-b)[1,4]benzodiazepine-6-one): 7.1 [7.0, 7.3], hexahydro-sila-difenidol: 6.8 [6.7, 6.9], pirenzepine: 6.6 [6.4, 6.7], and 3,6a,11,14-tetrahydro-9-methoxy-2-methyl-12H-isoquino[1,2-b]pyrrolo[3,2-f] [1,3]benzoxazine-1-carboxylic acid ethyl ester (PD 102807): 6.0 [5.8, 6.2]. In the human neocortex the following values were found: tripitramine: 9.4 [9.3, 9.6], tripinamide: 9.0 [8.9, 9.2], AF-DX 116: 6.7 [6.4, 6.9], hexahydro-sila-difenidol: 6.6 [6.2, 6.9], and PD 102807: 6.5 [6.3, 6.6]. In correlation plots, these pK(B) values correspond best to published binding data on native or recombinant M(2) receptors but not to those on M(1), M(3), M(4), and M(5) receptors, suggesting that muscarinic autoreceptors of both the rat and human neocortex belong to the M(2) subtype. This observation lends further support to the development of M(2) receptor selective brain penetrating antagonists for application in Alzheimer's disease.

Inhibitory potency of choline esterase inhibitors on acetylcholine release and choline esterase activity in fresh specimens of human and rat neocortex.

Fresh specimens of human and rat neocortex were used to determine direct and indirect inhibitory potencies of choline esterase inhibitors (ChEIs) on ChE and the release of acetylcholine (ACh), respectively. Km values of ChE in homogenates of rat and human neocortex did not differ significantly, whereas the specific activity of ChE was > times higher in the rat. Butyryl ChE exhibited a higher Km and a lower specific activity than ACh esterase in human neocortex. Inhibition of ChE in rat and human tissue was similar [IC50 (nM; human): donepezil: 14, physostigmine: 22, tacrine: 95, galanthamine: 575, rivastigmine: 9120]. In neocortex slices preincubated with [3H]choline, the electrically evoked release of [3H]ACh was inhibited up to 60% by ChEIs (IC50 (nM, rat): donepezil: 30, physostigmine: 39, tacrine: 302, galanthamine: 646, rivastigmine: >10000). Similar IC50-values were also estimated for ACh release in human neocortex, although the maximal inhibitory effects were much smaller ( approximately 20%). We conclude that in comparison to rats: 1) neocortical ChE concentrations are lower and 2) that ChEIs have weaker indirect (muscarine receptor-mediated) presynaptic inhibitory effects in the human brain. We further suggest that a combination of ChEIs with brain-selective muscarine autoreceptor antagonists might help to improve their clinical efficacy.