Feeding high amounts of almond hulls to lactating cows.

California is the leading state for the production of almonds, with more than 400,000 bearing hectares of orchards that produced approximately 1 billion kilograms of shelled nuts in 2017. Almond hulls (AH) are a regional by-product feedstuff fed predominantly to dairy cattle in California. A 2012 study surveyed 40 dairy farms in California and found that 39 out of 104 total mixed rations contained AH, with a mean daily feeding rate of 1.45 kg/cow. In 2017, approximately 2 billion kilograms of AH was produced. At a feeding rate of 1.45 kg/cow daily, even if all 1.7 million lactating cows in California are consuming AH, there will be a surplus of AH on the market as the approximately 130,000 nonbearing hectares come into nut production. Therefore, the potential of feeding varying amounts of AH to lactating dairy cows was investigated using 12 Holstein cows with 4 primiparous and 8 multiparous cows. The dietary treatments were 4 total mixed rations containing 0, 7, 13, or 20% AH. The AH used contained 12.8% crude fiber (as-is basis), which was below the 15% legal limit set by state feed regulations. Diets were formulated so that as the inclusion rate of AH increased, the amount of steam-flaked corn and soyhull pellets decreased and soybean meal inclusion increased. Experimental design was a replicated 4 × 4 Latin square. Diet had a cubic effect on actual milk yield, energy-corrected milk yield, and dry matter intake, with the 7% AH diet having the highest values and the 13% AH diet having the lowest. The percent and yield of total solids and the yields of lactose and fat did not differ with diet, but percent and yield of protein declined linearly with increased AH inclusion, and fat percent increased linearly. Apparent total-tract digestibilities of dry matter and organic matter were higher with the inclusion of AH in the diet. Total percentage of the day spent ruminating increased linearly with higher amounts of AH. Overall, this work demonstrated that AH can be fed at varying amounts, up to 20% of the diet, to lactating dairy cows to support high levels of milk production and that increasing amounts of AH (up to 20%) in the diet could lead to improved digestibility and milk fat percentage but decreased milk protein production.

Neurovascular Manifestations of Hereditary Hemorrhagic Telangiectasia: A Consecutive Series of 376 Patients during 15 Years.

BACKGROUND AND PURPOSE: Hereditary hemorrhagic telangiectasia is associated with a wide range of neurovascular abnormalities. The aim of this study was to characterize the spectrum of cerebrovascular lesions, including brain arteriovenous malformations, in patients with hereditary hemorrhagic telangiectasia and to study associations between brain arteriovenous malformations and demographic variables, genetic mutations, and the presence of AVMs in other organs. MATERIALS AND METHODS: Consecutive patients with definite hereditary hemorrhagic telangiectasia who underwent brain MR imaging/MRA, CTA, or DSA at our institution from 2001 to 2015 were included. All studies were re-evaluated by 2 senior neuroradiologists for the presence, characteristics, location, and number of brain arteriovenous malformations, intracranial aneurysms, and nonshunting lesions. Brain arteriovenous malformations were categorized as high-flow pial fistulas, nidus-type brain AVMs, and capillary vascular malformations and were assigned a Spetzler-Martin score. We examined the association between baseline clinical and genetic mutational status and the presence/multiplicity of brain arteriovenous malformations. RESULTS: Three hundred seventy-six patients with definite hereditary hemorrhagic telangiectasia were included. One hundred ten brain arteriovenous malformations were noted in 48 patients (12.8%), with multiple brain arteriovenous malformations in 26 patients. These included 51 nidal brain arteriovenous malformations (46.4%), 58 capillary vascular malformations (52.7%), and 1 pial arteriovenous fistula (0.9%). Five patients (10.4%) with single nidal brain arteriovenous malformation presented with hemorrhage. Of brain arteriovenous malformations, 88.9% (88/99) had a Spetzler-Martin score of ≤2. Patients with brain arteriovenous malformations were more likely to be female (75.0% versus 57.6%, P = .01) and have a family history of hereditary hemorrhagic telangiectasia (95.8% versus 84.8%, P = .04). The prevalence of brain arteriovenous malformation was 19.7% in endoglin (ENG) mutations and 12.5% in activin receptor-like kinase (1ACVRL1) mutations. CONCLUSIONS: Our study of 376 patients with hereditary hemorrhagic telangiectasia demonstrated a high prevalence of brain arteriovenous malformations. Nidal brain arteriovenous malformations and capillary vascular malformations occurred in roughly equal numbers.

Survival in portopulmonary hypertension: Mayo Clinic experience categorized by treatment subgroups.

To determine the natural history of portopulmonary hypertension (POPH), a retrospective screening-right heart catheterization-survival analysis of patients was performed. We categorized patients by three treatment subgroups: (1) no therapy for pulmonary hypertension (PH) or liver transplantation (LT), (2) therapy for PH alone and (3) therapy for PH followed by LT. Seventy-four patients were identified between 1994 and 2007. Nineteen patients received no therapy for PH and no LT representing the natural history of POPH. Five-year survival was 14%, and 54% had died within 1 year of diagnosis. Five-year survival in 43 patients receiving therapy for PH but no LT was 45%, and 12% had died within 1 year of diagnosis. Twelve patients underwent LT and 5-year survival for the nine receiving therapy for PH was 67% versus 25% in the three who were not pretreated with prostacyclin therapy. The survival of untreated patients with POPH was poor. Subgroups of patients selected to medical treatment with or without LT had better long-term survival. Mortality did not correlate with baseline hemodynamic variables, type of liver disease or severity of hepatic dysfunction. Medical therapy for POPH should be considered in all patients with POPH, but the treatment effects and impact on those considered for LT still requires well-designed, prospective study before practice guidelines can be suggested.

Tracheobronchial foreign bodies.

Aspiration of tracheobronchial foreign bodies occurs more commonly in children, but under certain circumstances, it also can occur in adults. The most common symptoms are choking followed by a protracted cough. Physical examination findings include fever, stridor, retractions, and decreased breath sounds. Radiographic imaging can be helpful if the object aspirated is radiopaque or if there are signs of hyperexpansion on expiration. Negative-imaging studies, however, do not exclude the presence of a foreign body in the airway. The longer a foreign body resides in the airway, the more likely it is to migrate distally. When this occurs, symptoms of chronic cough and wheezing may mimic an asthmalike condition. Bronchoscopy is indicated in this situation to evaluate the airway thoroughly. If a foreign body is present, extraction can be performed with flexible or rigid bronchoscopy. If flexible bronchoscopy is attempted, it is imperative that the bronchoscopist is familiar with rigid bronchoscopy and has the equipment immediately available should danger to the airway occur. The procedure is generally safe and well tolerated. Many patients are managed under general anesthesia, but foreign bodies often can be removed with a flexible bronchoscope with the patient under local anesthesia. Surgery should be performed only as a last resort and rarely is necessary.

Pulmonary arteriovenous fistulas: Mayo Clinic experience, 1982-1997.

OBJECTIVE: To describe the results of analysis of clinical, physiologic, diagnostic, and therapeutic aspects and complications in patients with pulmonary arteriovenous fistulas (PAVFs). PATIENTS AND METHODS: Retrospective review of medical records of all patients with the diagnosis of PAVF evaluated at Mayo Clinic Rochester from 1982 through 1997. Demographic characteristics, presence or absence of hereditary hemorrhagic telangiectasia, clinical features, and results of imaging studies and blood gas analyses, treatments, and complications related to PAVFs were reviewed. RESULTS: Among the 93 patients, 44 were male and 49 female. The mean age at the time of evaluation was 40 years (range, 5-83 years). Fifteen patients (16%) were asymptomatic. History of hereditary hemorrhagic telangiectasia was present in 52 patients (56%). Notable clinical findings included epistaxis in 46 (49%), hemoptysis in 14 (15%), cyanosis in 27 (29%), clubbing in 18 (19%), dyspnea in 53 (57%), and pulmonary bruits/murmurs in 32 (34%). Chest x-ray films with or without tomograms showed abnormal findings in 87 (94%), of which 68 (73%) suggested PAVF. Polycythemia was detected in 12 (13%). Pretherapy arterial PO2 measured on room air averaged 56 mm Hg (range, 32-95 mm Hg), and the posttherapy PO2 averaged 77 mm Hg (range, 46-110 mm Hg). Echocardiography with indocyanine green dye was diagnostic of extracardiac right-to-left shunt in 26 (90%) of 29 patients tested. Diagnostic studies revealed single lesions in 32 patients (34%) and multiple lesions in 61 (66%). The most prominent complications of the disease were neurologic events in 34 patients (37%). These complications included transient ischemic attacks, hemiplegia, brain abscesses, and seizures. Surgical resection alone was carried out in 18 patients (19%), embolization therapy alone in 41 (44%), and both therapies in 7 (8%). The 48 patients treated with embolization required 78 embolization sessions with more than 200 lesions occluded. Complications of treatment included postembolization hemothorax in 1 patient and right-sided hemiparesis in another patient. Follow-up disclosed that 1 patient died from PAVF-related complications. CONCLUSIONS: Among our patients with PAVFs, hereditary hemorrhagic telangiectasia was observed in more than half and neurologic complications in more than one third. Because of the considerable risk of neurologic and other complications, definitive treatment should be considered in patients with PAVFs. Embolization is currently the preferred treatment in most patients. Frequent follow-up of treated patients is necessary because PAVFs tend to increase both in number and in size over time.

Strychnine: a potent competitive antagonist of alpha-bungarotoxin-sensitive nicotinic acetylcholine receptors in rat hippocampal neurons.

In our study, evidence is provided that strychnine, a competitive antagonist at glycine-gated Cl- channels, is also a potent competitive antagonist at native alpha-7-containing, alpha-bungarotoxin-sensitive nicotinic acetylcholine receptor (nAChRs). To address the effects of strychnine on two types of nicotinic responses, the whole-cell mode of the patch-clamp technique was applied to rat hippocampal neurons in culture. Type IA and type II nicotinic currents evoked by acetylcholine (ACh) were inhibited by strychnine in a concentration-dependent manner with IC50S of 1.2 and 38 microM, respectively. Strychnine (2 microM) decreased the peak amplitude of the alpha-bungarotoxin-sensitive type IA current in a voltage-independent manner and prolonged the decay phase of this current. The concentration-response curve for ACh in evoking type IA current showed a parallel shift to the right in the presence of strychnine (2 microM); the EC50 for ACh was increased from 0.4 to 0.8 mM. These findings suggest that strychnine acts as a competitive antagonist of ACh at the alpha 7 nAChRs that subserve type IA current. In contrast, the inhibition by strychnine of type II current was strongly voltage dependent, and the decay phase of this current was markedly accelerated by the toxin, suggesting an open-channel blockade by strychnine of the alpha 4 beta 2 nAChRs subserving type II currents. Preexposure of the neurons to strychnine enhanced its ability to decrease the peak amplitude of type II currents, indicating that the toxin may also act on alpha 4 beta 2 nAChR channels that are not open. It is concluded that strychnine is a potent competitive antagonist of ACh at neuronal alpha 7 nAChRs and a noncompetitive antagonist at the alpha 4 beta 2 nAChR.

Amantadine inhibits nicotinic acetylcholine receptor function in hippocampal neurons.

The effects of amantadine on nicotinic acetylcholine receptors (nAChRs) of hippocampal neurons were studied by recording three types of acetylcholine (ACh)-evoked currents, using the whole-cell patch-clamp technique. The rapidly desensitizing type IA nicotinic current, which is alpha-bungarotoxin-sensitive and is mediated by nAChRs bearing alpha 7 subunits, was inhibited by application of amantadine to neurons for 10 min (IC50 = 6.5 microM), but the potency of ACh (EC50 = 0.27 mM) was not affected by the drug. Amantadine (30-50 microM) attenuated the peak current amplitude in a voltage-dependent manner, with greater effect at negative than at positive membrane potentials. In contrast, the decay phase of the currents was shortened in a voltage-independent manner. When amantadine was coapplied briefly with ACh, the drug was markedly less potent (IC50 = 130 microM). Thus, the noncompetitive effects of amantadine on the type IA nicotinic current are complex, involving actions on the closed and desensitized states of the alpha 7 nAChR. The slowly desensitizing, alpha-bungarotoxin-insensitive nicotinic currents of type II, which is inhibited by dihydro-beta-erythroidine and is mediated by alpha 4 beta 2 nAChRs, and of type III, which is inhibited by mecamylamine and is mediated by alpha 3 beta 4 nAChRs, were also sensitive to inhibition by amantadine. The peak amplitude of type II current was reduced only slightly by 10 microM amantadine coapplied with ACh, but the decay-time constant and amplitude of the sustained current were markedly reduced. Type III current was also inhibited when amantadine was briefly coapplied with ACh. In contrast to its effects on nicotinic currents, amantadine at 10 microM did not affect currents evoked by N-methyl-D-aspartate plus glycine, gamma-aminobutyric acid, glycine or kainate. Thus, on cultured hippocampal neurons, amantadine preferentially inhibits nicotinic currents.

Glycine and calcium-dependent effects of lead on N-methyl-D-aspartate receptor function in rat hippocampal neurons.

The effects of lead (Pb++) on N-methyl-D-aspartate (NMDA) receptor function of rat hippocampal neurons in culture were studied by use of the whole-cell patch-clamp technique. Currents activated by NMDA (100 microM) in the presence of nonsaturating concentrations of glycine (0.01-0.05 microM) were potentiated in a voltage-independent manner by Pb++ (1-10 microM), and the potentiation was antagonized by 50 microM kynurenic acid. Increasing extracellular Ca++ from 1 to 10 mM similarly potentiated the NMDA-activated currents in the presence of a nonsaturating concentration of glycine (0.2 microM). The potentiation of NMDA-activated currents by low micromolar concentrations of Pb++ may be mediated by this cation's ability to increase the affinity of the NMDA receptor for glycine. In the presence of 10 microM glycine and 2 mM Ca++, Pb++ reduced the peak amplitudes of currents activated by NMDA (100 microM) in a voltage-independent manner (IC50 = 5.9 microM Pb++, Hill coefficient (nH) = 1.2). Also, steady-state currents activated by NMDA (50 microM) were inhibited by rapid application of Pb++ (IC50 = 3.2 microM, nH = 0.7). Increasing extracellular Ca++, in the presence of 10 microM glycine, reduced the NMDA-activated currents and shifted the Pb++ concentration-response curves to the right: at 0.2, 2 and 20 mM Ca++, the IC50 values of Pb++ were 3.0, 5.9 and 12.5 microM and the nH values were 0.9, 1.2 and 1.1, respectively. The finding that external Ca++ antagonized the inhibitory effect of Pb++ suggests that the noncompetitive inhibitory action of Pb++ with respect to glycine and NMDA may be mediated by Pb++ competition with Ca++ for a site on the NMDA receptor.

Paraoxon: cholinesterase-independent stimulation of transmitter release and selective block of ligand-gated ion channels in cultured hippocampal neurons.

Paraoxon (O,O-diethyl O-p-nitrophenyl phosphate) is the neurotoxic metabolite of the insecticide parathion (O,O-diethyl O-p-nitrophenyl phosphorothioate). The effects of organophosphorus compounds on peripheral synapses have been attributed to inhibition of cholinesterase and to direct actions on muscarinic and nicotinic receptors, but less is known about the actions of organophosphorus compounds, including paraoxon, in the central nervous system. We investigated initially the effects of paraoxon on spontaneous transmitter release by recording miniature postsynaptic currents (MPSCs) from cultured rat hippocampal neurons using the whole-cell mode of the patch-clamp technique. Paraoxon (0.3 microM) in the presence of tetrodotoxin (0.3 microM) and atropine (1 microM) caused a significant increase in the frequency of gamma-aminobutyric acid- and glutamate-mediated MPSCs, but did not change the peak amplitudes or decay-time constants of these MPSCs. In contrast, application of nicotinic agonists or antagonists did not change the MPSC frequency. The presynaptic effect of paraoxon shown here was not mediated by actions on muscarinic or nicotinic receptors, or by elevated acetylcholine levels secondary to inhibition of cholinesterase. In addition, agonists were applied to assess the postsynaptic effects of paraoxon on excitatory and inhibitory amino acid receptors. Paraoxon (30 microM-1 mM) blocked the ion channels of glycine, gamma-aminobutyric acidA, N-methyl-D-aspartic acid and nicotinic acetylcholine receptors, but not the ion channels of kalnate- and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-type glutamate receptors. The combined effects of paraoxon on spontaneous transmitter release and on the functions of several ligand-gated receptors may constitute mechanisms relevant to the neurotoxicity of paraoxon.

Diversity of nicotinic acetylcholine receptors in rat hippocampal neurons. IV. Regulation by external Ca++ of alpha-bungarotoxin-sensitive receptor function and of rectification induced by internal Mg++.

Applying the whole-cell mode of the patch-clamp technique to cultured hippocampal neurons, we demonstrated that extracellular Ca++ modulates the activation and inactivation of type IA nicotinic currents, ie., the currents subserved by alpha-bungarotoxin (alpha-BGT)-sensitive, alpha-7-containing nicotinic acetylcholine receptors (nAChRs). The rundown profile of acetylcholine (ACh)-induced type IA currents that were obtained using patch pipettes filled with F(-)-based internal solution had two components: the first component of rundown was counteracted by a more physiological internal solution containing an organic anion (malate or aspartate), suggesting energy dependence; the second component exhibited dependence on concentration of CaCl2 added to the external solution ([Ca++]o), with rundown minimized at 0.32 mM. The inward rectification of Ach-elicited type IA currents, induced by intracellular Mg++ was augmented by lowering [Ca++]o (from 2 to 0.32 mM). Moreover, extracellular Ca++ (0.01-10 mM) acted in a concentration-dependent manner (IC50 = 0.26 mM) to decrease the cooperativity induced by ACh (nH was reduced from 2.7 to 1). Extracellular Ca++ (EC50 = 0.1 mM) also increased the efficacy of ACh, but exposure to [Ca++]o from 1 to 32 mM decreased the efficacy of ACh and inactivated the alpha-BGT-sensitive nAChRs (IC50 = 11 mM). In conclusion, Ca++ regulates agonist efficacy and cooperativity at the alpha-BGT-sensitive neuronal nAChR, modulates rundown and counteracts Mg++ -dependent inward rectification of type IA currents. It is suggested that the regulation by Ca++ of the alpha-BGT-sensitive nAChR activity could modulate many neuronal functions.

Field and observer modes of remembering.

Nigro and Neisser (1983) contrasted two ways of remembering personal experiences: the rememberer may 'see' the event from his or her perspective as in normal perception, or 'see' the self engaged in the event as an observer would. Several factors contribute to the determination of perspective, but Nigro and Neisser also reported that many subjects claimed they could change to another perspective at will. We sampled personal memories from several life periods and assessed ability to change the initially reported perspective. Changing was easier for recent or vividly recalled events, harder for older and less vividly recalled events. Memory perspectives may differ in other aspects than their imagery. A second study was conducted to determine whether affective experience is altered when perspectives are changed. The affect experienced decreased when shifting from a field to an observer perspective, but did not change with the converse shift. These studies provide further evidence that remembering is more than retrieval. The information that enters awareness is determined by the information sources in memory and the organisational scheme adopted for recollection.

Progress in understanding the nicotinic acetylcholine receptor function at central and peripheral nervous system synapses through toxin interactions.

The need to treat diseases affecting the nicotinic AChR is great, but therapeutic options are few. Through careful correlation of structure-activity relationships of AnTX analogs, we may ultimately be led to the development of diagnostic and therapeutic drugs with specific nicotinic agonist or antagonist activities in the central nervous system that would be of major importance in the treatment of Alzheimer's disease.

Homoanatoxin: a potent analogue of anatoxin-A.

The natural toxin anatoxin-a (AnTx) is a potent nicotinic agonist that is valuable for the study of nicotinic receptors. We have synthesized 2-(propan-1-oxo-1-yl)-9-azabicyclo[4.2.1]non-2-ene, the homologue of AnTx in which the side-chain is extended by one methylene unit from a methyl to an ethyl ketone. This chemistry would allow the generation of a tritiated product and the homologue, designated homoanatoxin (HomoAnTx), has been characterized here with that aim in mind. In competition binding assays at neuronal nicotinic ligand binding sites characterized by [3H]nicotine and [125I]-alpha bungarotoxin, HomoAnTx retained the same potency as the parent molecule, with Ki values of 7.5 nM and 1.1 microM, respectively. In contrast, it showed little inhibition of muscarinic binding defined by [3H]-quinuclidinyl benzilate. HomoAnTx is a potent nicotinic agonist in frog muscle contracture assays, having four times the potency of carbamylcholine and one tenth of the activity of AnTx itself. The N-methylated version of HomoAnTx was more than two orders of magnitude weaker in both functional and binding assays. The successful synthesis of HomoAnTx with retention of high nicotinic potency offers a route for the generation of novel, potent radiolabelled nicotinic ligands.

Nicotinic pharmacology of anatoxin analogs. I. Side chain structure-activity relationships at peripheral agonist and noncompetitive antagonist sites.

Anatoxin analogs were designed to evaluate the importance of H-bonding, planarity, size and steric configuration of the anatoxin side chain moiety with regard to nicotinic potency and efficacy. This report examines the actions of these analogs on the somatic nicotinic acetylcholine receptor at two different loci: the agonist recognition site and the ion channel site. Agonist effects were evaluated using stimulation of contracture and radioligand binding competition for [125I]alpha bungarotoxin sites in Rana pipiens muscle, and stimulation of [3H]perhydrohistrionicotoxin binding and competition for [125I]alpha bungarotoxin sites in Torpedo californica electric organ. Antagonist effects were evident in the inhibition of neurally evoked twitch of the frog sciatic nerve-sartorius muscle preparation and in inhibition of [3H]perhydrohistrionicotoxin binding to Torpedo receptors. The affinity of these analogs for the agonist locus was consistently associated with activation of the AChR. Our results show that side chain steric configuration has an important role in affinity of the (+)-anatoxin-a analogs for the nicotinic acetylcholine receptor ion channel sites. Several analogs also revealed stereospecific noncompetitive actions. The (+)-anatoxin-a-related structures are important probes for characterizing both agonist and ion channel target sites on the peripheral nicotinic receptor.

Nicotinic pharmacology of anatoxin analogs. II. Side chain structure-activity relationships at neuronal nicotinic ligand binding sites.

Eighteen analogs of (+)-anatoxin-a were evaluated for nicotinic potency at two putative nicotinic acetylcholine receptor sites in the central nervous system. The affinities of the analogs for [3H]nicotine and [125I]alpha-bungarotoxin binding sites were compared. This series of analogs, with modifications to the side chain moieties of the parent structure, enables the importance (for nicotinic binding) of hydrogen bonding strength, planarity, size and steric configuration of this region of the molecule to be assessed. These studies confirm the importance of the side chain stereochemistry and the subordinate role of H-bonding strength of anatoxin analogs. Of all the analogs tested, the parent compound (+)-anatoxin-a is the most potent competitor of ligand binding. Although all analogs have higher affinity at the [3H](-)-nicotine site compared to the alpha-[125I]bungarotoxin site, the rank order of potency is generally the same at both central nervous system sites, and agrees with the order at the muscle nicotinic receptor. However, the simple methoxyamide and the isoxazolidide analogs appear more selective for the neuronal nicotinic receptor subtype identified by [3H](-)-nicotine, indicative of structural differences among the agonist recognition sites.

Red shift of absorption maxima in chlorobiineae through enzymic methylation of their antenna bacteriochlorophylls.

The bacteriochlorophyll d producing photosynthetic green sulfur bacteria Chlorobium vibrioforme forma thiosulfatophilum strain NCIB 8327 and C. vibrioforme strain B1-20 respond to reduced light conditions in culture by performing methylations at the 4- and 5-substituents, for example, converting the 4-Et into 4-n-Pr, 4-i-Bu, and even 4-neoPn. During this process, the absorption maximum in living cells of C. vibrioforme strain B1-20 red shifts from 714 to about 728 nm. Eventually, the C. vibrioforme forma thiosulfatophilum strain NCIB 8327 culture carries out a delta-methylation to produce the bacteriochlorophylls c (lambda max ca. 750 nm); the new UC Davis bacteriochlorophyll c culture is named C. vibrioforme forma thiosulfatophilum strain D. It is possible that the homologation process increases hydrophobic interactions between individual BChl molecules, giving rise to larger aggregates in the antenna system. Alternatively, the additional methyl units attached to the 4-position shift the absolute configuration of the 2-(1-hydroxyethyl) group from pure R in the case of 4-Et to pure S in the case of 4-neoPn, which in turn might determine the size of the in vivo aggregates due to the intrinsic nature of the pigment protein system. It is suggested that the bacteriochlorophylls c from Chloroflexus aurantiacus strain J-10-fl and the bacteriochlorophylls e from Chlorobium phaeovibrioides might have undergone similar meso methylation as a response to external environmental pressure such as low light intensity.

Molecular effects of dimethylanatoxin on the peripheral nicotinic acetylcholine receptor.

N,N-dimethylanatoxin (DMAnTX), the quaternary derivative of the potent nicotinic agonist (+)-anatoxin-a (AnTX), has been evaluated for potency and efficacy at nicotinic acetylcholine receptors of frog motor endplates and Torpedo electric organs. DMAnTX was only weakly effective in eliciting contracture of the frog rectus abdominis and was orders of magnitude less potent than AnTX. Biochemical assay showed that DMAnTX was a weak inhibitor of [125I]alpha-bungarotoxin binding to the receptors in frog muscle and Torpedo electroplaque membranes: the IC50 values were 60 and 14 microM, respectively. A low frequency of single channel currents recorded from isolated interosseal fibers at concentrations from 20 to 100 microM of DMAnTX and the stimulation of [3H]perhydrohistrionicotoxin [( 3H]H12-HTX) binding (half-maximal at 0.3 microM) confirmed the weak activation of the receptor. DMAnTX also exhibited antagonist effects. In muscle twitch assays, 100 microM of DMAnTX effectively decreased the tension induced by nerve stimulation, although DMAnTX did not affect muscle membrane action potentials. The binding of [3H] perhydrohistrionicotoxin was also inhibited at high micromolar concentrations of DMAnTX. Combination of DMAnTX with acetylcholine in single channel current experiments demonstrated that DMAnTX possesses ion channel blocking properties, which become apparent at low micromolar concentrations, and DMAnTX enhances the desensitization induced by acetylcholine above 10 microM AnTX. The difference in agonist potency between AnTX and DMAnTX may be attributed to a change in conformation of the molecular skeleton induced by the N-methyl groups.