Induction of plastic changes in the excitability of neuronal electrogenic membranes during habituation

Habituation of the postsynaptic response of a turtle cortical neurone to an orthodromic stimulus, induces enhanced excitability of the electro-excitable membrane which does not generate action potentials during habituation. Single excitation of the electro-excitable membrane by intracellular stimulation during this period, facilitates transmitter sensitivity of the chemoreceptor membrane. Habituation of the action potential to the intracellular electrical stimulus induces enhanced sensitivity of the chemoreceptor membrane. Single excitation of the chemoreceptor membrane during this period results in enhanced excitability of the electro-excitable membrane. Plastic changes during habituation involve the whole neurone membrane, although the monotonous stimulus activates only its local area.     

Colistin heteroresistance in Enterobacter cloacae is regulated by PhoPQ‐dependent 4‐amino‐4‐deoxy‐l‐arabinose addition to lipid A

The Enterobacter cloacae complex (ECC) consists of closely related bacteria commonly associated with the human microbiota. ECC are increasingly isolated from healthcare‐associated infections, demonstrating that these Enterobacteriaceae are emerging nosocomial pathogens. ECC can rapidly acquire multidrug resistance to conventional antibiotics. Cationic antimicrobial peptides (CAMPs) have served as therapeutic alternatives because they target the highly conserved lipid A component of the Gram‐negative outer membrane. Many Enterobacteriaceae fortify their outer membrane with cationic amine‐containing moieties to prevent CAMP binding, which can lead to cell lysis. The PmrAB two‐component system (TCS) directly activates 4‐amino‐4‐deoxy‐l ‐arabinose (l ‐Ara4N) biosynthesis to result in cationic amine moiety addition to lipid A in many Enterobacteriaceae such as E. coli and Salmonella. In contrast, PmrAB is dispensable for CAMP resistance in E. cloacae. Interestingly, some ECC clusters exhibit colistin heteroresistance, where a subpopulation of cells exhibit clinically significant resistance levels compared to the majority population. We demonstrate that E. cloacae lipid A is modified with l ‐Ara4N to induce CAMP heteroresistance and the regulatory mechanism is independent of the PmrAB_Ecl TCS. Instead, PhoP_Ecl binds to the arnB_Ecl promoter to induce l ‐Ara4N biosynthesis and PmrAB‐independent addition to the lipid A disaccharolipid. Therefore, PhoPQ_Ecl contributes to regulation of CAMP heteroresistance in some ECC clusters.     

Effects of SEPYLRFamide on acetylcholine-induced currents of Helix aspersa neurones: role of ryanodine receptors

The possible participation of ryanodine receptors in the modulatory effects of the endogenous Helix heptapeptide, SEPYLRFamide, on the acetylcholine-induced currents (ACh-currents) of Helix aspersa neurones was studied using the two-electrode voltage clamp technique. SEPYLRFamide (bath application) caused a reduction of the ACh-currents of D1, D2, F1, F2, F76 and F77 neurones. Ryanodine (10 microM; bath application), which modifies ryanodine-controlled Ca(2+) channels, potentiated the inhibitory effect of SEPYLRFamide on the ACh-current. An antagonist of cyclic adenosine diphosphate ribose (cADPR) and ryanodine receptors, ruthenium red (1 mM; intracellular injection), reduced the inhibitory effects of SEPYLRFamide on the ACh-current. Ryanodine (10 microM) did not change the inhibitory effect of SEPYLRFamide on the ACh-current after intracellular injection of ruthenium red. An agonist of ryanodine receptors, caffeine (5 mM; bath application), reduced the ACh-current. Ryanodine (10 microM) did not change the reduction of ACh-currents induced by the first application of caffeine but decreased the reduction of ACh-currents induced by subsequent applications of caffeine. It is proposed that ryanodine receptors are involved in the inhibitory modulatory effects of SEPYLRFamide on somatic cholinergic receptors of Helix aspersa neurones.     

Polysystemic assessment of the state of sanogenesis in workers employed in nuclear fuel plants. The analysis of functional state of cardiovascular, respiratory, and psychomotor systems

The state of the cardiovascular, respiratory, and psychomotor systems of workers employed in nuclear fuel plant was evaluated using a computer-assisted laboratory complex. It was found that neuroendocrine regulation of the peripheral circulation and muscular activity responsible for fine motions are most vulnerable to industrial hazardous factors.     

Neuronal assemblies: single cortical neurons are obedient members of a huge orchestra

Spontaneous cortical activity of single neurons is often either dismissed as noise, or is regarded as carrying no functional significance and hence is ignored. Our findings suggest that such concepts should be revised. We explored the coherent population activity of neuronal assemblies in primary sensory area in the absence of a sensory input. Recent advances in real-time optical imaging based on voltage-sensitive dyes (VSDI) have facilitated exploration of population activity and its intimate relationship to the activity of individual cortical neurons. It has been shown by in vivo intracellular recordings that the dye signal measures the sum of the membrane potential changes in all the neuronal elements in the imaged area, emphasizing subthreshold synaptic potentials and dendritic action potentials in neuronal arborizations originating from neurons in all cortical layers whose dendrites reach the superficial cortical layers. Thus, the VSDI has allowed us to image the rather illusive activity in neuronal dendrites that cannot be readily explored by single unit recordings. Surprisingly, we found that the amplitude of this type of ongoing subthreshold activity is of the same order of magnitude as evoked activity. We also found that this ongoing activity exhibited high synchronization over many millimeters of cortex. We then investigated the influence of ongoing activity on the evoked response, and showed that the two interact strongly. Furthermore, we found that cortical states that were previously associated only with evoked activity can actually be observed also in the absence of stimulation, for example, the cortical representation of a given orientation may appear without any visual input. This demonstration suggests that ongoing activity may also play a major role in other cortical function by providing a neuronal substrate for the dependence of sensory information processing on context, behavior, memory and other aspects of cognitive function.     

Participation of Na/Ca-exchange and intracellular mobilized Ca2+ in regulating depression of cholino-sensitive Helix lucorum neurons to a cellular analog of habituation

The role the Na/Ca-exchange and intracellular Ca2+ released from Ca(2+)-depots in the modulatory action of Na,K-pump inhibitor ouabain on cholinosensitivity in the command neurons of Helix lucorum was studied in a cellular analogue of habituation. The integral transmembrane inward currents in LPa2, LPa3, RPa3, and RPa2 neurons were recorded in Helix lucorum ganglia preparation using two-electrode voltage clamp technique. The reduction of cholinosensitivity of a neuron was estimated as a depth of the depression of the acetylcholine-induced inward currents during the rhythmic local acetylcholine applications (with the interstimulus interval of 2-4 min) on a somatic membrane. The inhibitor of the Na/Ca-exchange benzamil (the extracellular action, 15-35 mcM) and two specific inhibitors of Ca-ATPase in the sarcoplasmic and endoplasmic reticulum, cyclopiazonic acid and thapsigargin (intracellular injection by spontaneous diffusion, 0.1 mM) prevented the modification of the depression of acetylcholine-induced current by ouabain (100 mcM) during the rhythmic application of acetylcholine. A conclusion is drawn that the inhibitor of the Na,K-pump ouabain modifies the depression of neuron cholinosensitivity in the cellular analogue of habituation via the Na/Ca-exchange and intracellular Ca2+ released from Ca2+ depots.     

EPYLRFamide-mediated reduction of acetylcholine-induced inward currents in Helix lucorum-identified neurones: role of NAADP-dependent and IP3-dependent Ca2+ release from internal stores,calmodulin and Ca2+/calmodulin-dependent protein kinase II

The effect of seven compounds intracellularly applied by spontaneous diffusion were investigated on the EPYLRFamide-induced reduction of acetylcholine-induced inward current (ACh-current) recorded from identified neurones from Helix lucorum. Inward currents were recorded from neurones LPa2, LPa3, RPa3 and RPa2 in isolated ganglia preparations using two-electrode voltage clamp technique. ACh was applied ionophoretically. Heparin, an antagonist of IP(3) receptors (IP(3)Rs), and IP(3), the agonist of IP(3)Rs, decreased the effect of EPYLRFamide. Thio-NADP, a blocker of NAADP-induced Ca(2+) release, beta-NAADP, Ca(2+) releaser, R24571, W-7 (both calmodulin antagonists), and KN-62, a selective inhibitor of Ca(2+)/calmodulin-dependent protein kinase II, did not change the modulatory effect of EPYLRFamide. These data suggest that EPYLRFamide decreases ACh-current through elevation of the basal intracellular level of the putative endogenous agonist of IP(3)Rs which activates release of Ca(2+) from intracellular stores. It is concluded that intracellular free Ca(2+) acts on ACh receptor/ionic channel without activation of calmodulin and Ca(2+)/calmodulin-dependent protein kinase II.     

Unraveling nature's networks

A report on the meeting 'Unravelling Nature's Networks: from Microarray and Proteomic Analysis to Systems Biology', Sheffield, UK, 21-22 July 2003.     

Both the stimulation and inhibition of root hair growth induced by extracellular nucleotides in Arabidopsis are mediated by nitric oxide and reactive oxygen species

Root hairs secrete ATP as they grow, and extracellular ATP and ADP can trigger signaling pathways that regulate plant cell growth. In several plant tissues the level of extracellular nucleotides is limited in part by ectoapyrases (ecto-NTPDases), and the growth of these tissues is strongly influenced by their level of ectoapyrase expression. Both chemical inhibition of ectoapyrase activity and suppression of the expression of two ectoapyrase enzymes by RNAi in Arabidopsis resulted in inhibition of root hair growth. As assayed by a dose-response curve, different concentrations of the poorly hydrolysable nucleotides, ATPγS and ADPβS, could either stimulate (at 7.5–25 μM) or inhibit (at ≥ 150 μM) the growth rate of root hairs in less than an hour. Equal amounts of AMPS, used as a control, had no effect on root hair growth. Root hairs of nia1nia2 mutants, which are suppressed in nitric oxide (NO) production, and of atrbohD/F mutants, which are suppressed in the production of H₂O₂, did not show growth responses to applied nucleotides, indicating that the growth changes induced by these nucleotides in wild-type plants were likely transduced via NO and H₂O₂ signals. Consistent with this interpretation, treatment of root hairs with different concentrations of ATPγS induced different accumulations of NO and H₂O₂ in root hair tips. Two mammalian purinoceptor antagonists also blocked the growth responses induced by extracellular nucleotides, suggesting that they were initiated by a receptor-based mechanism.