Is cholinergic activity of the caudate nucleus involved in memory?

A review was made of experiments dealing with the involvement of cholinergic activity of the caudate nucleus in memory processes. Injections of acetylcholine-receptor blockers or of neurotoxins against cholinergic interneurons into the striatum produce marked impairments in acquisition and retention of instrumental tasks while injections of acetylcholine or choline into the caudate produce the opposite effect. However, after a period of overtraining cholinergic blockade or interference with neural activity of the caudate does not produce significant deficits in retention. It is concluded that striatal cholinergic activity is critically involved in memory of recent events and that long-term memory is mediated by different neurochemical systems outside the caudate nucleus.     

Cyclic AMP independent protein kinase activity in rat cerebral cortex synaptic vesicles—Partial characterization

The intrinsic protein kinase activity of a highly purified synaptic vesicle preparation was characterized. The time-course of the reaction was found to be rapid and linear for about 1 min, but plateaued after 30 min by which time approximately 1 nmol of³²P pering protein was incorporated into trichloroacetic acid precipitated vesicular protein. The enzyme was optimally active at pH 6.0 (37°C), and had apparentK _m values of 40 and 88 M for ATP and GTP respectively. The enzyme was not stimulated by cAMP or cGMP. Mg²⁺ was required for maximal activity. The reaction was inhibited by free Ca²⁺, and non-selectively by Na⁺, K⁺, and NH₄ ⁺.Deceased.     

Is a Ca2+ -ATPase involved in Ca2+ regulation during capacitation and the acrosome reaction of guinea-pig spermatozoa?

The Ca2+-ATPase antagonists quercetin and ethacrynic acid accelerated the onset of the acrosome reaction in guinea-pig spermatozoa incubated in the continuous presence of Ca2+, whereas furosemide had no effect, and sodium orthovanadate only affected sperm motility. When spermatozoa were preincubated in a 'Ca2+-free' medium, quercetin and ethacrynic acid shortened capacitation time: spermatozoa incubated for 1 h in 100-200 microM-ethacrynic acid showed 60-80% acrosome reactions when Ca2+ was added. Such spermatozoa were able to fertilize zona-free hamster eggs. Our results therefore point to the possible involvement of a Ca2+-ATPase in the regulation of intracellular Ca2+ in spermatozoa. Cysteine and dithiothreitol, both disulphide reducing agents, prevented the effects of quercetin and ethacrynic acid, suggesting that sulphydryl groups may be important for the expression of Ca2+-ATPase activity. Lysophosphatidylserine (LS) also prevented the stimulatory effect of ethacrynic acid, an effect similar to that shown by LS on lysophosphatidylcholine (LC). It is argued that both LS and LC could exert their action through an effect on the Ca2+-ATPase.     

Is neurotensin in the brain involved in thermoregulation of the monkey?

Cannulae for intracerebroventricular (ICV) infusion were implanted stereotaxically in monkeys (Macaca fasicularis) maintained post-operatively in a primate restraint chair. During each experiment, a series of physiological measures was recorded simultaneously on a polygraph which included colonic temperature, vasomotor tone, heart rate, respiratory rate, and basal metabolism as reflected by O₂ uptake. The ICV infusion in a volume of 0.5 ml of neurotensin (NT) in doses ranging from 3–150 μg produced neither a statistically significant nor consistent change in body temperature or vasomotor response. Although the highest dose of 450 μg NT infused ICV caused an immediate bradycardia and a concomitant decline in metabolic and respiratory rates, an average decline in core temperature of 0.6°C and the accompanying cutaneous vasodilation often had a latency as long as 1.0 hr. In contrast to the typical hypothermia in this species following an ICV infusion of catecholamines, implicated in the central pathways underlying thermoregulation, NT failed to elicit a coordinated set of physiological responses for heat dissipation in the monkey. Therefore, it is unlikely that this tridecapeptide plays a role in the central mechanisms mediating the control of body temperature of this primate species.     

Is endothelial-nitric-oxide-synthase-derived nitric oxide involved in cardiac hypoxia/reoxygenation-related damage?

Nitric oxide (NO) has been reported to act both as a destructive and a protective agent in the pathogenesis of the injuries that occur during hypoxia/reoxygenation (H/R). It has been suggested that this dual role of NO depends directly on the isoform of NO synthase (NOS) involved. In this work, we investigate the role that NO derived from endothelial NOS (eNOS) plays in cardiac H/R-induced injury. Wistar rats were submitted to H/R (hypoxia for 30 min; reoxygenation of 0 h, 12 h and 5 days), with or without prior treatment using the selective eNOS inhibitor l-NIO (20 mg/kg). Lipid peroxidation, apoptosis and protein nitration, as well as NO production (NOx), were analysed. The results showed that l-NIO administration lowered NOx levels in all the experimental groups. However, no change was found in the lipid peroxidation level, the percentage of apoptotic cells or nitrated protein expression, implying that eNOS-derived NO may not be involved in the injuries occurring during H/R in the heart. We conclude that l-NIO would not be useful in alleviating the adverse effects of cardiac H/R.     

Is cyclic AMP involved in the defibrillating effect of sotalol ?

Ventricular fibrillation induced in animals pretreated with sotalol, a class III antiarrhythmic agent, would spontaneously terminate and revert into a sinus rhythm. This phenomenon has been atributed to the class III action of this Drug, I.e., prolongation of myocardial action potential duration and effective refractory period. Since various observations suggested that these alone cannot explain the defibrillating phenomenon, we hypothesised that sotalol affeced ventricular intercellular synchronization by increasing intercellular coupling. Our recent experimental studies have shown that sotalol antagonized the cellular decoupling to guinea pig ventricular muscle strip caused by perfusion with either a hypoxic normal Tyrode's solution or an oxygenated high Ca2+ Tyrode's solution. We assumed that the most likely mechanism for the restoration of intercellular coupling would be by increasing intracellular cAMP concentration. In order to test this hypothesis, we studied the modification of this sotalol-induced recoupling by a cAMP dependent protein kinase inhibitor. The results clearly supported our assumption since the addition of Arg-Gly-Tyr-Ala-Leu-Gly (pure A- kinase inhibitor) prevented the aforementioned cellular recoupling action of sotalol in a dose-dependent manner. It can thus be concluded that changes in intracellular cAMP level are involved in the synchronizing /defibrillating effect of sotalol.     

Is a ferroxidase involved in the high-affinity iron uptake in Chlamydomonas reinhardtii?

In phosphorus deficient soils and under smallscale farming systems, the development of efficient management strategies for P fertilizers is crucial to sustain food production. A field experiment was conducted on a P-fixing Acrisol in western Kenya to study possibilities of replenishing soil P with seasonal additions of small rates of P fertilizers. Triple superphosphate was applied at 0, 10, 25, 50 and 150 kg P ha^–1 for 5 consecutive maize growing seasons followed by 4 seasons of residual crops. Maize yields and soil P fractions were determined. Although maize responded to additions of 10 kg P ha^–1 with a cumulative grain yield of 16.8 Mg ha^–1, at the end of the experiment, compared to 8.8 Mg ha^–1 in the non-P fertilized plots, soil labile P did not increase correspondingly. Seasonal additions of 150 kg P ha^–1 increased maize yields to a cumulative value of 39 Mg ha^–1 at the end of the experiment, and increased all soil inorganic P fractions. At the third season of residual phase, treatment with a cumulative addition of 750 kg P ha^–1 gave the highest yields compared to treatments in the same residual stage, but these yields were considered less than the maximum yield of the season. This indicates that the large build up of soil P was not available for crop uptake. The inorganic P fraction extracted by NaHCO₃ was the most affected by changes in management, increasing during the input phase and decreasing after interruption of P addition, for all P rates. The decrease in this pool during the residual phase could be explained by the maize uptake. This study showed that seasonal additions of 25 kg P ha^–1 can increase maize yield with gradual replenishment of soil P.     

Is the epithelium-derived inhibitory factor in guinea-pig trachea a prostanoid?

To examine further the possible prostanoid involvement in the influence of the epithelium on guinea-pig tracheal smooth muscle responsiveness, we have analyzed the effects of LTD4, methacholine and histamine on the level of airway smooth muscle tone and on the amounts of PGE2, PGF2 alpha and PGI2 (determined by radioimmunoassay) in the presence and absence of the epithelium. Removal of the epithelium increased the sensitivity of guinea-pig trachea to the contractile effects of LTD4, methacholine and histamine. LTD4 (3-100 nM), methacholine (0.1-10 microM) or histamine (0.3-30 microM) did not increase prostanoid release above control values in either the presence or absence of the epithelium. The unstimulated release of PGE2 and PGF2 alpha, but not PGI2, was decreased in tissues lacking epithelium. Indomethacin (1 microM) reduced the baseline tone to a smaller extent in the absence of epithelium. In the presence but not the absence of the epithelium, indomethacin increased the sensitivity of preparations to the contractile effect of methacholine. The results support the postulate of an epithelium-derived inhibitory factor modulating guinea-pig tracheal smooth muscle responsiveness. The identity of this factor is not known but is not PGI2 and is unlikely to be PGF2 alpha or PGE2. However, the possibility remains that the basal release of PGE2 and/or PGF2 alpha derived from the epithelium may markedly affect the responsiveness of guinea-pig tracheal smooth muscle. Furthermore, the epithelium is a significant source of PGE2 and PGF2 alpha which may be involved in the maintenance of baseline tone.     

Is the epithelium-derived inhibitory factor in guinea-pig trachea a prostanoid?

To examine further the possible prostanoid involvement in the influence of the epithelium on guinea-pig tracheal smooth muscle responsiveness, we have analyzed the effects of LTD₄, methacholine and histamine on the level of airway smooth muscle tone and on the amounts of PGE_2α and PGI₂ (determined by radioimmunoassay) in the presence and absence of the epithelium. Removal of the epithelium increased the sensitivity of guinea-pig trachea to the contractile effects of LTD₄, methacholine and histamine. LTD₄ (3–100 nM), methacoline (0.1–10 μM) or histamine (0.3–30 μM) did not increase prostanoid release above control values in either the presence or absence of the epithelium. The unstimulated release of PGE₂ and PGF_2α but not PGI₂, was decreased in tissues lacking epithelium. Indomethacin (1 μM) reduced the baseline tone to a smaller extent in the absence of epithelium. In the presence but not the absence of the epithelium, indomethacin increased the sensitivity of preparations to the contractile effect of methacholine. The results support the postulate of an epithelium-derived inhibitory factor modulating guinea-pig tracheal smooth muscle responsiveness. The identity of this factor is not known but is not PGI₂ and is unlikely to be PGF_2α or PGE₂. However, the possibility remains that the basal release of PGE₂ and/or PGF_2α derived from the epithelium may markedly affect the responsiveness of guinea-pig tracheal smooth muscle. Furthermore, the epithelium is a significant source of PGE₂ and PGF_2α which may be involved in the maintenance of baseline tone.     

Is the Rsp5 ubiquitin ligase involved in the regulation of ribophagy?

Under nutrient limiting conditions, cytoplasmic components are randomly sequestered into double-membrane vesicles called autophagosomes and delivered to the lysosome/vacuole for degradation and recycling. In the last few years, however, it has been observed that several cytoplasmic components such as organelles, pathogens or specific protein complexes can also be selectively targeted for degradation by autophagy-related pathways (reviewed in reference 1). We have recently shown that in S. cerevisiae, mature ribosomes are subject to such selective degradation by autophagy under starvation conditions, in a process that we termed ‘ribophagy’.² By genetic screening, we found that selective degradation of 60S large ribosomal subunits depends on the ubiquitin protease Ubp3 and its cofactor Bre5, implying that ribophagy is regulated by ubiquitin-dependent steps. Interestingly, several ubiquitinated proteins accumulate in ribosome fractions isolated from ubp3? cells, suggesting that the regulation of ribophagy by ubiquitin may be direct. Here we present data on a potential role of the ubiquitin ligase Rsp5 as a positive regulator of ribophagy, and discuss the possible involvement of ubiquitin as a signaling molecule in this process.

Addendum to: Kraft C, Deplazes A, Sohrmann M, Peter M. Mature ribosomes are selectively degraded upon starvation by an autophagy pathway requiring the Ubp3p/Bre5p ubiquitin protease. Nat Cell Biol 2008; 10:602-10.     

Is the Rsp5 ubiquitin ligase involved in the regulation of ribophagy?

Under nutrient limiting conditions, cytoplasmic components are randomly sequestered into double-membrane vesicles called autophagosomes and delivered to the lysosome/vacuole for degradation and recycling. In the last few years, however, it has been observed that several cytoplasmic components such as organelles, pathogens or specific protein complexes can also be selectively targeted for degradation by autophagy-related pathways (reviewed in ref. 1). We have recently shown that in S. cerevisiae, mature ribosomes are subject to such selective degradation by autophagy under starvation conditions, in a process that we termed 'ribophagy.'(2) By genetic screening, we found that selective degradation of 60S large ribosomal subunits depends on the ubiquitin protease Ubp3 and its cofactor Bre5, implying that ribophagy is regulated by ubiquitin-dependent steps. Interestingly, several ubiquitinated proteins accumulate in ribosome fractions isolated from ubp3Delta cells, suggesting that the regulation of ribophagy by ubiquitin may be direct. Here we present data on a potential role of the ubiquitin ligase Rsp5 as a positive regulator of ribophagy, and discuss the possible involvement of ubiquitin as a signaling molecule in this process.     

Is the salt marsh vegetation a determining factor in the sedimentation processes?

Many authors have referred to the important role of vegetation in the consolidation of salt marsh sediments, but experiments previously carried out by us have shown results that do not always agree with these statements. In other words, the type of salt marsh surface coverage is not the main factor that contributes to the consolidation of sediments. To test this hypothesis different Portuguese salt marsh stations (species/unvegetated areas) from two sites, Tagus estuary (Corroios and Pancas) and Ria de Aveiro (Barra and Verdemilho), were compared to evaluate their influence on suspended matter deposition on the salt marsh surface. A short-term sedimentation study was performed within stands of Spartina maritima, Halimione portulacoides, Sarcocornia perennis subsp. perennis and unvegetated areas, by analysing the deposition of sediment material on nylon filters anchored to the marsh surface. Numerical results obtained from hydrodynamic models coupled to a Lagrangean module implemented for the Ria de Aveiro and the Tagus Estuary, namely the root-mean square velocity (V _rms) and residual velocity of tides, were also used. Average sedimentation rates (mean value between the different surface cover in a salt marsh) showed a seasonal trend more or less defined but with significantly different values between sites and salt marshes. Sedimentation rates varied between marshes: there are significant differences between Pancas and the other three marshes, but only significant differences in sedimentation rates between Spartina and Sarcocornia. Despite the important role of vegetation in the consolidation of salt marsh sediments, our results suggest that, the position of stations and related abiotic conditions in the salt marshes are determining factors of variation to take into account in the studies related with the stabilization and survival of salt marshes facing sea level rise. Handling editor: P. Viaroli     

Is CYP1B1 involved in the metabolism of dioxins in the pig?

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is the most difficult to biodegradate and the most toxic dioxin congener. Previously, we demonstrated in silico the ability of pig CYP1A1 to hydroxylate 2,7-dichlorodibenzo-p-dioxin (DiCDD), but not TCDD. To increase our knowledge concerning the low effectiveness of TCDD biodegradability, we analyzed in silico the binding selectivity and affinity between pig CYP1B1 and the two dioxins by means of molecular modeling. We also compared the effects of TCDD and DiCDD on CYP1B1 gene expression (qRT-PCR) and catalytic (EROD) activity in porcine granulosa cells. It was found that DiCDD and TCDD were stabilized within the pig CYP1B1 active site by hydrophobic interactions. The analysis of substrate channel availability revealed that both dioxins opened the exit channel S, allowing metabolites to leave the enzyme active site. Moreover, DiCDD and TCDD increased the CYP1B1 gene expression and catalytic activity in porcine granulosa cells. On the other hand, TCDD demonstrated higher than DiCDD calculated affinity to pig CYP1B1, hindering TCDD exit from the active site. The great distance between CYP1B1's heme and TCDD also might contribute to the lower hydroxylation effectiveness of TCDD compared to that of DiCDD. Moreover, the narrow active site of pig CYP1B1 may immobilize TCDD molecule, inhibiting its hydroxylation. The results of the access channel analysis and the distance from pig CYP1B1's heme to TCDD suggest that the metabolizing potential of pig CYP1B1 is higher than that of pig CYP1A1. However, this potential is probably not sufficiently high to considerably improve the slow TCDD biodegradation.     

α-adrenergic receptor regulation of Ca2+/Mg2+-ATPase in brain synaptic membranes

The effects of ₁ and ₂ receptor ligands on Ca²⁺/Mg²⁺-ATPase have been studied using synaptosomal plasma membranes isolated from rat brain cortex. Both phenylephrine and clonidine inhibited Ca²⁺/Mg²⁺-ATPase, in a concentration-dependent fashion. IC₅₀ values for half-maximal inhibition for phenylephrine and clonidine were 29 M and 18 M, respectively. The inhibitory effect of phenylephrine was reversed by the alpha antagonist prazosin while yohimbine and rauwolscine reversed the inhibition of enzyme activity by clonidine. The two antagonist subtypes were effective only against the respective agonist subtypes, demonstrating distinct subtype preferences. Analysis of the kinetics of enzyme inhibition indicate both agonists to be noncompetitive. Some evidence suggests that yohimbine may exhibit mixed agonist/antagonist properties which depend on [Ca²⁺]. The present study provides biochemical evidence to support auto receptor adrenergic receptor regulation of neurotransmitter release.     

Is the ClC-2 chloride channel involved in the Cl- secretory mechanism of gastric parietal cells?

It has been controversial whether the ClC-2 chloride channel is involved in hydrochloric acid secretion of gastric parietal cells. Here, we investigated whether ClC-2 is the apical Cl- channel associated with gastric acid secretion. Two anti-ClC-2 antibodies used in this study reacted with cloned ClC-2 protein expressed in HEK293 cells. In isolated rabbit gastric glands, significant expression of ClC-2 mRNA was observed, but the presence of ClC-2 protein was not clear. Furthermore, no expression of ClC-2 protein was observed in isolated rat and human gastric mucosa. Immunohistochemistry on the rat gastric mucosa showed no significant expression of ClC-2 protein in the parietal cells which showed abundant expression of H+,K+-ATPase. These results indicate that ClC-2 may not be a Cl- -transporting protein for gastric acid secretion in parietal cells.