Molecular characterization of Plasmodium falciparum S-adenosylmethionine synthetase.

S-Adenosylmethionine (AdoMet) synthetase (SAMS: EC 2.5.1.6) catalyses the formation of AdoMet from methionine and ATP. We have cloned a gene for Plasmodium falciparum AdoMet synthetase (PfSAMS) (GenBank accession no. AF097923), consisting of 1209 base pairs with no introns. The gene encodes a polypeptide (PfSAMS) of 402 amino acids with a molecular mass of 44844 Da, and has an overall base composition of 67% A+T. PfSAMS is probably a single copy gene, and was mapped to chromosome 9. The PfSAMS protein is highly homologous to all other SAMS, including a conserved motif for the phosphate-binding P-loop, HGGGAFSGKD, and the signature hexapeptide, GAGDQG. All the active-site amino acids for the binding of ADP, P(i) and metal ions are similarly preserved, matching entirely those of human hepatic SAMS and Escherichia coli SAMS. Molecular modelling of PfSAMS guided by the X-ray crystal structure of E. coli SAMS indicates that PfSAMS binds ATP/Mg(2+) in a manner similar to that seen in the E. coli SAMS structure. However, the PfSAMS model shows that it can not form tetramers as does E. coli SAMS, and is probably a dimer instead. There was a differential sensitivity towards the inhibition by cycloleucine between the expressed PfSAMS and the human hepatic SAMS with K(i) values of 17 and 10 mM, respectively. Based on phylogenetic analysis using protein parsimony and neighbour-joining algorithms, the malarial PfSAMS is closely related to SAMS of other protozoans and plants.

6,7,8,9-Tetrahydro-3-methyl-1H-pyrano-[4,3-b]quinolin-1-one.

The condensation reaction of 4-amino-6-methyl-2-pyrone with 1-cyclohexenecarboxaldehyde and a catalytic amount of (S)-(+)-10-camphorsulfonic acid in toluene at 358 K gave a 1:2.5 ratio of the title compound, (1) (C13H13NO2), and 7,8,9,10-tetrahydro-1H-pyrano[4,3-c]isoquinoline-1-one, (2). The formation of (2) presumably proceeds through an intermediate imine. Both (1) and (2) show inhibitory activities against acetylcholinesterase and human aldose reductase. Of the three linear-fused rings of (1), both ring A and ring B are planar and the angle between these planes is 0.46 (13) degrees. While the two C atoms of cyclohexane ring C attached to its common atoms with ring B are in the plane of the latter, as expected, the remaining two C atoms of ring C are out of this plane, by 0.342 (4) and -0.402 (3) A, respectively.

Comparing predictability between eyes after bilateral laser in situ keratomileusis: a theoretical analysis of simultaneous versus sequential procedures.

OBJECTIVE: To compare the predictability of laser in situ keratomileusis (LASIK) between eyes of individuals to determine whether the refractive result of the first eye is useful in improving fellow eye outcomes. DESIGN: Single-center case series. PARTICIPANTS: One surgeon and 196 eyes of 98 patients. INTERVENTION: All patients received sequential bilateral LASIK. The mean time between procedures was 11.6 days. Attempted corrections ranged from 2.30 to 12.00 diopters (D). MAIN OUTCOME MEASURES: Predictability (achieved minus attempted correction), postoperative manifest refraction, and theoretical postoperative manifest refraction, using a proposed attempted correction on the second eye based on first eye results, were analyzed. RESULTS: At 1 week, 1 month, and 3 months, predictability of the first operated eye was correlated with predictability of the fellow eye (1 week: mean 1st = 0.33 D, mean 2nd = 0.33 D, Pearson coefficient = 0.46, P < 0.0005; 1 month: mean 1st = 0.028 D, mean 2nd = -0.020 D, Pearson coefficient = 0.43, P < 0.0005; 3 months: mean 1st = -0.22 D, mean 2nd = -0.12 D, Pearson coefficient = 0.52, P < 0.0005). At the 3-month follow-up of the second eye, comparing the actual distance from emmetropia with that calculated using a theoretical proposed attempted correction based on the first eye refraction, distance from emmetropia was closer in the theoretical correction group. This finding was stronger in patients with preoperative myopia less than 5.5 D (P = 0.03). For this group, 93% of patients in the proposed attempted correction group would fall within 1.0 D of emmetropia compared to 80% found in the actual outcomes. CONCLUSIONS: The refractive predictability between the two eyes of an individual after LASIK is correlated. Theoretically, therefore, one may be able to achieve correction closer to emmetropia in the second eye by applying the refractive predictability results from the first operated eye. In this study, using a theoretical proposed attempted correction in the second eye based on the first eye outcome, we have shown that better outcomes in the second eye are possible, particularly in low myopes. Thus, it may be advantageous to perform bilateral LASIK sequentially rather than simultaneously, using predictability outcomes from the first operated eye in planning fellow eye treatment. Moreover, waiting approximately 1 week was found to be potentially as effective as waiting longer periods of time between treatments. Further studies are necessary to better assess the actual clinical significance of these findings.

Encephalocoele as a complication of intranasal sinus surgery: optimal evaluation with magnetic resonance imaging.

We report a case of post-operative frontal basal encephalocoele evaluated using a new magnetic resonance imaging (MRI) sequence, fast inversion recovery for myelin suppression (FIRMS). FIRMS was developed to enhance the differentiation between grey and white matter. In this case, the sequence was beneficial in distinguishing the encephalocoele from adjacent nasal mucosa and secretions.

Biological effects of inhibitors of S-adenosylhomocysteine hydrolase.

S-Adenosylhomocysteine (AdoHcy), formed after the donation of the methyl group of S-adenosylmethionine to a methyl acceptor, is hydrolyzed to adenosine and homocysteine by AdoHcy hydrolase physiologically. The administration of the inhibitors of AdoHcy hydrolase to cells or animals normally results in an accumulation of cellular AdoHcy higher than those found in controls, which is often accompanied by a simultaneous rise in S-adenosylmethionine because of the feedback inhibition by AdoHcy on most methylation reactions. AdoHcy hydrolase has become a tantalizing pharmacological target for inhibition since its blockade can affect cellular methylation of phospholipids, proteins, small molecules, DNA, and RNA. Indeed, all of these different methylation reactions have been found to be inhibitable by the nucleoside inhibitors/substrates of AdoHcy hydrolase. Among the interesting effects are the activation of genes, induction of cellular differentiation, increased expression of transcription factors, and sometimes the repression of genes. Furthermore, some of the nucleosides show remarkable antiviral activities in vitro and in vivo. However, the mode of action of the inhibitors appears complex. Although the inhibition of methylation might account for some of the biological effects, the ability of some of the nucleoside inhibitors to undergo metabolic phosphorylation to nucleotides may account for part of their biological activities. The defining mode of action responsible for their biological effects still awaits biochemical elaboration, especially regarding their antiviral effects, induction of genes, or cellular differentiation.

Fast inversion recovery for myelin suppression (FIRMS). A new magnetic resonance pulse sequence.

Fast inversion recovery for myelin suppression is a new magnetic resonance sequence with the ability to increase gray-white matter contrast. This can improve the definition of normal anatomical structures.

Apoptosis of L1210 Leukemia Cells Induced by 3-Deazaadenosine Analogs: Differential Expression of c-myc, NF-Kappa B and Molecular Events.

A new class of potent apogens (apoptosis-inducing agents) has been identified, consisting of 3-deazaadenosine (DZA), 3-deaza-(+/-)aristeromycin (DZAri) and 1-beta-D-arabinofuranosyl-1H-imidazo[4,5-&cumacr;]pyridine (ara-3-deazaadenine; DZAra-A). They are inhibitors of S-adenosylhomocysteine hydrolase and indirect inhibitors of methylation. Furthermore, they have also been found to form 3-deaza-nucleotide analogs. The DZA analogs, DZA, DZAri, and DZAra-A, induced DNA fragmentation in a dose- and time-dependent manner, reaching a maximum at 250 &mgr;M after 72 h. Cycloheximide at 0.5 &mgr;g/ml completely blocked the DNA fragmentation induced by 250 &mgr;M of each of the analogs. Interestingly, exogenous 100 &mgr;M L-homocysteine thiolactone abrogated the DNA fragmentation caused by DZAri and DZAra-A, but not by DZA. Flow cytometric analysis showed that DZA arrested the cells in the G(2)/M phase, whereas the S phase was arrested by DZAri. Correlated with the effect of DZA was a rapid decrease in the expression of c-myc, whereas nur77 and GAPDH were unaffected. In comparison, there was an elevated expression of IFN-gamma mRNA without apparent change in bax, p53 or GAPDH mRNA after 24 h. After treatment with DZA, there was an elevated expression of NF-kappaB DNA binding activity, which became more pronounced at 24 h. Simultaneously, there was an apparent disappearance of AP-1 activity. Thus, DZA most likely inhibited the RNA synthesis of c-myc, a reduction of which could trigger a cascade of gene transcription leading to apoptosis in L1210 cells. Copyright 1997 S. Karger AG, Basel

Induction of proto-oncogenes during 3-deazaadenosine-stimulated differentiation of 3T3-L1 fibroblasts to adipocytes: mimicry of insulin action.

3-Deazaadenosine (DZA) mimicked the molecular action of insulin in the induction of 3T3-L1 fibroblasts to differentiate into adipocytes. The molecular effects of DZA were compared with insulin, which served as a positive control, on the expression of proto-oncogenes during the initial stage of differentiation of 3T3-L1 fibroblasts. Treatment of confluent 3T3-L1 fibroblasts with DZA or insulin produced a rapid but-transient expression of mRNA for proto-oncogenes c-fos and c-jun within 30-60 min. The mRNA of c-myc increased for 2 h and then decreased 4 h after treatment. Electrophoretic mobility shift assays showed a heightened increase in the appearance of transcription factors AP-1 and AP-2. The increase was detectable as early as 1 h after the treatment with either DZA or insulin and was maintained for 6 h. 3T3-L1 cells stably transfected with the promotor of c-fos linked to a CAT reporter gene showed an increase in CAT activity in response to DZA in a time- and dose-dependent manner. In cells stably transfected with antisense c-fos, neither DZA nor insulin was able to induce a differentiation response. The early transcription of c-fos, c-jun, and c-myc proto-oncogenes and the increased expression of transcription factors AP-1 and AP-2, induced by DZA and insulin, appear to be crucial events in the differentiation of the 3T3-L1 fibroblasts to adipocytes.

Antihuman Immunodeficiency Virus (HIV-1) Activities of Inhibitors of Polyamine Pathways.

Four inhibitors of polyamine biosynthetic pathways were tested for their effect on HIV-1 replication in phytohemagglutinin-stimulated human peripheral blood mononuclear cells. Methyl acetylenic putrescine (MAP) and alpha-monofluoromethyldehydroornithine methyl ester, irreversible inhibitors of ornithine decarboxylase, inhibited the production of p24 antigen in phytohemagglutinin-stimulated peripheral blood mononuclear cells by clinical HIV-1 strains isolated from HIV-infected patients with IC(50) values of about 1-2 &mgr;M. 5'--5'-deoxyadenosine (MDL 73811), an enzyme-activated irreversible inhibitor of S-adenosyl-L-methionine (AdoMet) decarboxylase, also inhibited the production of p24 antigen by HIV-1 strains in peripheral blood mononuclear cells with IC(50) values of 1-2 &mgr;M. The least potent was 1-aminoxyethylamine which is another inhibitor of AdoMet decarboxylase. MAP showed the best therapeutic index of 500-1,000. Copyright 1996 S. Karger AG, Basel

S-Adenosylmethionine and methylation.

S-Adenosylmethionine (AdoMet or SAM) plays a pivotal role as a methyl donor in a myriad of biological and biochemical events. Although it has been claimed that AdoMet itself has therapeutic benefits, it remains to be established whether it can be taken up intact by cells. S-Adenosylhomocysteine (AdoHcy), formed after donation of the methyl group of AdoMet to a methyl acceptor, is then hydrolyzed to adenosine and homocysteine by AdoHcy hydrolase. This enzyme has long been a target for inhibition as its blockade can affect methylation of phospholipids, proteins, DNA, RNA, and other small molecules. Protein carboxymethylation may be involved in repair functions of aging proteins, and heat shock proteins are methylated in response to stress. Bacterial chemotaxis involves carboxymethylation and demethylation in receptor-transducer proteins, although a similar role in mammalian cells is unclear. The precise role of phospholipid methylation remains open. DNA methylation is related to mammalian gene activities, somatic inheritance, and cellular differentiation. Activation of some genes has been ascribed to the demethylation of critical mCpG loci, and silencing of some genes may be related to the methylation of specific CpG loci. Viral DNA genomes exist in cells as extrachromosomal units and are generally not methylated, although once integrated into host chromosomes, different patterns of methylation are correlated with altered paradigms of transcriptional activity. Some viral latency may be related to DNA methylation. Cellular factors have been found to interact with methylated DNA sequences. Methylation of mammalian ribosomal RNAs occurs soon after the synthesis of its 47S precursor RNA in the nucleolus before cleavage to smaller fragments. Inhibition of the methylation of rRNA affects its processing to mature 18S and 28S rRNAs. The methylation of 5'-terminal cap plays an important role in mRNA export from the nucleus, efficient translation, and protection of the integrity of mRNAs. Another important function of AdoMet is that it serves as the sole donor of an aminopropyl group that is conjugated with putrescine to form, first, the polyamine spermidine, and then spermine.

Induction of Apoptosis and c-myc in L1210 Lymphocytic Leukemia Cells by Adenosine.

High concentrations of adenosine (Ado), when added to L1210 lymphocytic leukemia cells, resulted in apoptosis or programmed cell death. The apoptotic process was accompanied by distinct morphological changes including chromatin condensation and blebbing of plasma membranes. Extensive DNA fragmentation was correlated with Ado concentrations. Furthermore, apoptosis in these cells was preceded by an early but transient expression of c-myc proto-oncogene, and was not influenced by homocysteine thiolactone added to the cells. Since severe combined immunodeficiency (SCID) is associated with a deficiency of adenosine deaminase, leading to defects in both cellular and humoral immunity, Ado-induced apoptosis may thus be a contributing factor in the pathology of SCID. Copyright 1994 S. Karger AG, Basel

Monoclonal antibody AE-2 modulates carbamate and organophosphate inhibition of fetal bovine serum acetylcholinesterase.

The monoclonal antibody AE-2, raised against the human erythrocyte acetylcholinesterase (AChE) dimer (acetylcholine acetylhydrolase, EC 3.1.1.7), binds to other mammalian AChEs, including the tetramer that occurs in fetal bovine serum (FBS). AE-2 partially inhibited the rate of hydrolysis of the charged substrate acetylthiocholine by FBS AChE, whereas it increased the rate of hydrolysis of the neutral substrate indophenyl acetate. Present results show that AE-2 decreases the rate of inhibition of FBS AChE by the positively charged organophosphate amiton-p-toluene sulfonate and the positively charged carbamates pyridostigmine and neostigmine but accelerates inhibition of FBS AChE by the neutral organophosphates paraoxon and diisopropylfluorophosphate. Results suggest that AE-2 may allosterically modulate an anionic site in the catalytic center of FBS AChE.

Stabilization of thymopentin and preservation of its pharmacological properties by 2-hydroxypropyl-beta-cyclodextrin.

Thymopentin prepared in 5, 15, and 20% 2-hydroxypropyl-beta-cyclodextrin (HPCD) was able to inhibit guinea-pig ileum contraction stimulated by anatoxin-a (3 x 10(-6) M) after fourteen months of storage at room temperature. Thus, in contrast to the instability of thymopentin prepared without HPCD, the pharmacological activity was retained and could be stored in a ready-to-use solution for extended periods without refrigeration.

Synthesis and antimuscarinic activity of 2-[N-(ethyl)-(N-beta-hydroxyethyl)]aminoethyl 2,2-diphenylpropionate, a metabolite of aprophen.

The preparation of 2-[N-(ethyl)-(N-beta-hydroxyethyl)]amino-ethyl 2,2-diphenylpropionate (1), a metabolite of aprophen [2-diethylaminoethyl 2,2-diphenylpropionate], is described. Hydrolysis of [2-(2-chloroethyl)ethylamino]ethyl acetate hydrochloride (2) in a basic solution, followed by acidic pH adjustment, gave the ethylcholineaziridinium ion (3) that upon treatment with 2,2-diphenylpropionic acid produced 1 in a 56% yield. Synthetic 1 was found to possess antimuscarinic activities, but was approximately 10-fold less potent than the parent compound aprophen.

Induced release of acetylcholine from guinea pig ileum longitudinal muscle-myenteric plexus by anatoxin-a.

Anatoxin-a (ANTX), a nicotinic agonist, has been shown to induce contraction of guinea pig ileum, which was abrogated by the muscarinic antagonist atropine and the nicotinic antagonists tubocurarine and hexamethonium. We showed here that the ganglionic nicotinic antagonist mecamylamine was a better inhibitor of the contraction of ileum induced by ANTX. The sodium channel blocker tetrodotoxin also abolished ANTX-induced contraction. In contrast, alpha-bungarotoxin, the muscle type nicotinic receptor blocker, had no effect on ANTX-induced contraction of guinea pig ileum. Longitudinal muscle-myenteric plexus prepared from guinea pig ileum, labeled with [3H]choline and then incubated with ANTX was shown for the first time to release [3H]acetylcholine (ACh) in a dose-dependent manner. Pretreatment of longitudinal muscle-myenteric plexus with tubocurarine, hexamethonium or mecamylamine blocked ANTX-induced release of [3H]ACh. In contrast, atropine was without effect. Mecamylamine was the most potent antagonist. As observed in ileum contraction, tetrodotoxin completely and potently blocked the release of [3H]ACh induced by ANTX. Neither alpha-bungarotoxin nor the neuromuscular junction blockers conotoxin G1 or M1 could inhibit the [3H]ACh release. Taken together, these results suggested that ANTX activated nicotinic receptors on ganglionic interneurons to trigger a release of ACh, which next stimulated muscarinic receptors and induced ileum contraction.

Prejunctional muscarinic receptors in the deep muscular plexus of canine ileum: comparison with smooth muscle receptors.

Prejunctional muscarinic receptors from the deep muscular plexus of canine ileum were studied, and their properties were compared with those of the postjunctional receptors of the circular smooth muscle. In the purified synaptosomal fraction (a fraction containing primarily the axonal varicosities of deep muscular plexus), the muscarinic ligand N-[3H]methylscopolamine labeled an apparently homogenous population of receptors (nH = 1) with a Kd of 2.7 nM and a Bmax of 195 +/- 44 fmol/mg protein (mean +/- S.D., n = 4). These receptors showed a high affinity for the M3/M1-selective antagonist 4-diphenylacetoxy-N-methylpiperidine methiodide (pKi = 7.41); in contrast, the pKi values of pirenzepine (5.60), methoctramine (5.65) and AF-DX 116 (5.21) implied little selectivity for these subtypes. The binding properties of muscarinic receptors in the synaptosomal fraction were different from the binding properties of muscarinic receptors in the purified circular smooth muscle plasma membranes. Most notably, the circular smooth muscle receptors had significantly lower affinity for N-[3H]methylscopolamine (Kd = 16 nM) with a Bmax value of 2088 +/- 276 fmol/mg. The affinities of the M2 subtype-selective muscarinic antagonists methoctramine and AF-DX 116 were similar in both membrane preparations. The receptor population associated with the deep muscular plexus synaptosomal fraction was linked to the inhibition of adenylate cyclase activity, as demonstrated by a concentration-dependent, atropine-sensitive inhibition of the forskolin-stimulated enzyme in the presence of muscarinic agonists carbachol and oxotremorine. Based on the pharmacological observations presented here, the prejunctional muscarinic receptors in the axonal varicosities of deep muscular plexus are different from the postjunctional receptors present in the circular smooth muscle.

Relationship of three-dimensional structure of muscarinic antagonists to antimuscarinic activity: structure of thiodeacylaprophen hydrochloride.

C20H28NS+.Cl-, 2-(diethylamino)ethyl 1,1-diphenylethyl sulfide hydrochloride (thiodeacylaprophen hydrochloride), M(r) = 349.9, orthorhombic, P2(1)2(1)2(1), a = 8.933 (2), b = 11.710 (3), c = 18.934 (4) A, V = 1980.6 (7) A3, Z = 4, Dx = 1.173 g cm-3, Cu K alpha, lambda = 1.54178 A, mu = 26.70 cm-1, F(000) = 752, room temperature, final R = 4.1% for 1417 reflections with /Fo/ greater than 3 sigma (F). Thiodeacylaprophen crystallized as a tertiary amine hydrochloride salt. The S--C--C--N+ segment adopts a trans configuration as does one of the Cphenyl--C--S--C segments. A comparison of the structure of thiodeacylaprophen with the crystal structures of potent antimuscarinic agents suggests that the relatively weak antimuscarinic activity of thiodeacylaprophen compared to atropine and aprophen may be substantially due to the short intramolecular S...N+ distance of 4.106 (6) A. Other contributing structural factors may include the direction of the N+--H bond and restricted accessibility of the sulfur atom for interatomic interactions.

Muscarinic receptor subtype specificity of (N,N-dialkylamino)alkyl 2-cyclohexyl-2-phenylpropionates: cylexphenes (cyclohexyl-substituted aprophen analogues).

A series of aprophen [(N,N-diethylamino)ethyl 2,2-diphenylpropionate] analogues, called cylexphenes, were synthesized with alterations in (1) the chain length of the amine portion of the ester, (2) the alkyl groups on the amino alcohol, and (3) a cyclohexyl group replacing one of the phenyl rings. The antimuscarinic activities of these analogues were assessed in two pharmacological assays: the inhibition of acetylcholine-induced contraction of guinea pig ileum, and the blocking of carbachol-stimulated release of alpha-amylase from rat pancreatic acinar cells. These two tissues represent the M3(ileum) and M3(pancreas) muscarinic receptor subtypes. In addition, the analogues were also evaluated for their competitive inhibition of the binding of [3H]NMS to selected cell membranes, each containing only one of the m1, M2, m3, or M4 muscarinic receptor subtypes. The m1 and m3 receptors were stably transfected into A9 L cells. The replacement of one phenyl group of aprophen with a cyclohexyl group increased the selectivity of all the analogues for the pancreatic acinar muscarinic receptor subtype over the ileum subtype by more than 10-fold, with the (N,N-dimethylamino)propyl analogue exhibiting the greatest selectivity for the pancreas receptor subtype, over 30-fold. The cylexphenes also showed a decrease in potency in comparison to the parent compound when examined for the binding of [3H]NMS to the M2 subtype. In agreement with the pharmacological data obtained from the pancreas, the (N,N-dimethylamino)propyl cylexphene 3 demonstrated the greatest selectivity for the m3 subtype, and additionally showed a preference for the m1 and M4 receptor subtypes over the M2 receptor subtype in the binding assay. Thus, this compound showed a potent selectivity according to the pharmacological and binding assays between the muscarinic receptor subtypes of the pancreas and ileum. In both the pharmacological and binding assays, the potency of the analogues decreased markedly when the chain length and the bond distance between the carbonyl oxygen and protonated nitrogen were increased beyond three methylene groups. When the structures of these analogues were analyzed using a molecular modeling program, the bond distance between the carbonyl oxygen and protonated nitrogen was deduced to be more important for the antagonist activity than subtype specificity.

Activation of collagen IV gene expression in F9 teratocarcinoma cells by 3-deazaadenosine analogs. Indirect inhibitors of methylation.

3-Deazaadenosine analogs can function as inhibitors and also as alternative substrates of S-adenosylhomocysteine (AdoHcy) hydrolase. In cells treated with the analogs, AdoHcy invariably accumulates, leading to inhibition of cellular methylation. F9 teratocarcinoma cells, stably transfected with two collagen (IV) promoter-enhancer-CAT constructs and treated with 10 microM 3-deazaadenosine, 3-deaza-(+-)-aristeromycin or 3-deazaneplanocin, showed a strong induction of CAT activities without affecting differentiation. In comparison, the same 3-deaza analogs did not affect the CAT activity in F9 cells transfected with the beta-actin promoter-CAT construct. Furthermore, Northern blot analysis of endogenous mRNA from wild-type F9 cells treated with the 3-deaza nucleosides all showed an induction of the collagen alpha 1(IV) chain mRNA. Thus, the 3-deaza analogs most likely affect DNA methylation because their results are consistent with the previous observation that the integrated collagen alpha 1(IV) promoter-enhancer constructs were activated with 5-azacytidine.

Behavioral effects of some diphenyl-substituted antimuscarinics: comparison with cocaine and atropine.

To more fully characterize the behavioral excitatory effects observed with certain diphenyl-substituted antimuscarinics, various behavioral effects of benactyzine, a prototype excitatory antimuscarinic, was evaluated in rats. These effects were compared to those of cocaine, atropine, and azaprophen, a muscarinic antagonist that contains both the diphenyl substituents of benactyzine and a ring isomeric with the tropane ring of atropine. Under a fixed-interval 5-min schedule of food presentation, cocaine and benactyzine increased response rates. Atropine and azaprophen only decreased responding. The muscarinic agonist oxotremorine attenuated the rate-increasing effects but did not alter the disruptions in the temporal patterning produced by benactyzine or shift the dose-effect function to the right. In rats discriminating 10 mg/kg cocaine from saline, benactyzine partially substituted for cocaine, producing a maximum of 50% cocaine-appropriate responses. Benactyzine fully substituted for scopolamine in rats discriminating 0.056 mg/kg scopolamine from saline. All antimuscarinics increased locomotor activity when activity levels were low in control animals, but the increases were less than those produced by cocaine. Cocaine increased both locomotor activity and fixed-interval responding at comparable doses, whereas 10-fold higher doses of benactyzine were required to increase locomotor activity. These results support the following conclusions: 1) In addition to its classical antimuscarinic behavioral profile, benactyzine has behavioral excitatory actions similar in some respects to those of cocaine; 2) the behavioral excitatory effects of benactyzine do not appear to be due solely to antagonism of muscarinic receptors; and 3) the alkyl-ester may be an important structural feature of diphenyl-substituted antimuscarinics for the induction of behavioral stimulation.