Factors affecting the cholinomimetic activity of alkyltrimethylammonium compounds in experiments on isolated neurons of the mollusk Planorbarius corneus

It has been shown that the elementary current is independent whereas the duration of channel opening is slightly dependent on the number of methylene groups (from 1 to 9) in the molecule of alkyltrimethylammonium compounds. However, substances with more than 4 methylene groups exhibit lower cholinomimetic activity (i.e. the ability to increase the membrane current) and higher values of Q10 for the reaction with cholinoreceptor. It is suggested that lower activity of these compounds is due to a low rate of formation of a complex with cholinoreceptor because of the higher potential energy barrier.     

Demonstration of different type cholinoreceptors on the membrane of an isolated Planorbarius corneus mollusk membrane

In experiments on isolated and identified neurones of the pedal ganglion of the gastropod mollusc P. corneus, it was demonstrated that biphasic response to ACh may be obtained both to superfusion and electrophoretic application. Fast (depolarizing) phase may be imitated by a nicotinomimetic drug, suberyldicholine, and blocked by d-tubocurarine. These data indicate that this phase results from activation of nicotinic cholinoreceptors. Slow (hyperpolarizing) phase may be evoked by a muscarinomimetic, dioxolane F-2268, which is taken as an indication of the muscarinic nature of cholinoreceptors responsible for this phase. Experiments on completely isolated neurones directly show that both kinds of cholinoreceptors belong to the same neurone. Biphasic pattern of the response depends on the level of the membrane potential and on the conditions of ACh application. The fast phase is more evident at membrane hyperpolarization, the slow one--at depolarization. The fast phase is more readily obtained by superfusion by high concentrations of ACh or at close position of electrophoretic micropipette to neuronal surface, whereas the slow phase may be easily obtained by superfusion with low concentrations of ACh or when the micropipette is not attached so closely to the cell.     

Effect of inhibitors of energy metabolism on potassium accumulation in the neurons of the mollusk Planorbarius corneus

Studies have been made of the effect of inhibitors of energy metabolism on maintenance of Na and K concentrations, as well as on accumulation of Rb (as an analogue of K) in single neurones of the mollusc P. corneus. Concentrations of Na, K and Rb in cells were determined by X-ray spectral microanalysis. Monoiodoacetate, an inhibitor of glycolysis, decreased concentration gradients of K and Na between cells and the external medium, decreasing accumulation of Rb. Cyanide, which is used as an antirespiratory drug, did not significantly affect neither K and Na content, nor Rb accumulation in the neurones of the mollusc, these data being different from those obtained on the nervous tissue of other animals. Monovalent T1 which is capable of inhibiting the respiratory chain and destroying mitochondrial structure, significantly inhibited Rb accumulation in the neurones. The decrease in accumulation of Rb by monoiodoacetate and T1 was less significant as compared with that produced by a specific blocker of Na/K-pump, ouabain.     

Changes in the neuronal membrane potential of the mollusk Planorbarius corneus under the action of cardiac glycosides

In experiments on isolated neurones from the gastropod mollusc P. corneus, strophantin and digoxin in low concentrations produce slow hyperpolarization, in higher ones--depolarization; at concentrations about 1 mM, hyperpolarization was more evident. In all cases, the decrease in membrane resistance was observed. Presumably, membrane permeability for potassium ions increases. During application of the drugs in concentrations 10-100 microM, hyperpolarization may be masked by depolarization due to block of Na,K-pump. Higher concentrations, increasing potassium permeability of the membrane, may result in substitution of depolarization by hyperpolarization.     

Neuronal mechanisms of defense reaction to statocyst receptor stimulation in the freshwater snail Planorbarius corneus

Tilting of the freshwater snailPlanorbarius corneus triggering dynamic statocyst receptor response resulted in defense reaction attended by rapid lowering of the shell over the head, foreshortening of the foot, and inhibited locomotion and buccal apparatus operation. Large numbers of neurons from different ganglia were found to take part in this reaction in isolated nervous system preparations. The response usually followed an "all or none" pattern and did not depend on which statocyst receptors had been stimulated. Each successive response arose no sooner than 10–20 sec after the previous reaction to tilting the preparation. It is deduced that defense reaction to statocyst receptor stimulation takes the form of a "fixed action" governed by a special central mechanism. It was found during the process of investigating interaction between response to statocyte receptor and cutaneous nerve stimulation that the same central mechanism serves to produce defense reactions evoked by presentation of different stimuli.     

Neuron-microglia communication in the CNS of the freshwater snail Planorbarius corneus

The aim of the present study was to identify molecules that may be involved in neuron-microglia communication in the CNS of freshwater snail Planorbarius corneus. Messenger molecules are exchanged in normal and pathological conditions and we tried to identify some of them by immunocytochemistry on whole ganglia and cell cultures. In particular, we examined neurons and microglia for the expression of some cytokines, IL-1alpha, IL-1beta, IL-6 and TNF-alpha and the neurotransmitter glutamate. These substances may be released by suffering or injured neurons and communicate to microglia the damaging event. Even microglia, on own turn, once activated, express and released the same or other substances in order to reestablish the system homeostasis, depending on modalities and times of activation. We discuss the possibility that hyperactivated microglia can shift from neuroprotective to neurodegenerative. Moreover, we examined in neuron-microglia co-coltures the direct interaction effects in terms of neuronal survival and improved neurite regeneration.     

The cholinomimetic activity of alkyltrimethylammonium compounds in experiments on the isolated mollusk neuron and on frog and chicken skeletal muscle

As revealed by contractile reaction of frog and chick muscles and by changes in the membrane current of isolated molluscan neurone, cholinomimetic activity of alkyltrimethylammonium compounds (ATMC) in the highest in drugs with 4 and 5 methylene groups in a molecule. The decrease in the activity with the decrease in the number of methylene groups was more evident in chick muscle; the decrease in the activity due to the increase in the number of these groups was most significant in experiments on molluscan neurone. Analysis of membrane current fluctuations showed that elementary current does not depend, whereas channel open time only slightly depends on the number of methylene groups in ATMC. However, with the increase of the number of methylene groups above 4, gradual decrease was observed in the ability of ATMC to increase at low (threshold) concentrations the membrane current (response) in the neurone. This decrease in the potency of ATMC correlated with the increase in Q10 value for neuronal response and calculated Q10 value for the reaction rate of ATMC with cholinoreceptor. The decrease in the activity of these ATMC is presumably due to a longer duration of complex formation with cholinoreceptor because of the higher energy barrier. ATMC with 8 and 9 methylene groups at high (saturating) concentrations elicited significantly smaller neuronal response with higher Q10 value. It is suggested that this phenomenon is due to a longer duration of complex formation with cholinoreceptor because of a higher energy cost.     

Eye Structure and Vision in the Freshwater Pulmonate Mollusc Planorbarius corneus

The structure of the mollusc Planorbarius corneus eye was studied using light and electron microscopy. The eye consists of the cornea, eye lens of non-spherical shape, and the vitreous body tightly bound to it, as well as of a monolayer non-inverted retina composed of photoreceptor and supporting (pigmented) cells. Its inner surface has two invaginations. The apices of several hundreds of photoreceptors directed to the vitreous body have groups of microvilli with a parallel orientation to each other. The eye optic system places the image into the base of the retinal microvillar layer. Its angle resolution provided by density of distribution of photoreceptor cells and the value of the index F = 1.71 is to be about 2.06° with a correction for the light spreading between microvilli of neighbor cells. Under conditions of a V-shaped labyrinth, the P. corneus molluscs show positive phototaxis by moving to the light source. The angular acuity of vision was assessed from differences in the choice by the molluscs of direction of movement to the pattern of vertical black bands with different periods of alternation. The differential threshold obtained is within an interval of 1.43–1.91°, which is close to the calculated value of angular resolution of the retina.     

Starvation and growth in the gastropod Planorbarius corneus (L.)

The effect of different degrees of partial starvation on growth was studied in the fresh-water gastropodPlanorbarius corneus (L.). Two indices of growth were used, fresh weight and shell diameter, and for both indices the rate of growth decreased proportionately at least as much as the proportion of time that food was absent. This suggests that growth is not regulated in this species, and some doubts are expressed about the validity of results with other invertebrate species that suggest growth is regulated.     

淡水蜗牛视觉系统的输入与输出通路(英文)

通过神经生物素在视神经上的逆行性传输对淡水蜗牛(Planorbarius corneus)视网膜及中央神经节的输入、输出神经元进行标记。由于没有发现突触联系,所以至少一部分光感受细胞的轴突可被视为直接参与形成视神经。这些神经元的轴突进入大脑神经节形成密集的细传入神经纤维束-视神经堆。传出神经元则存在于除颊部以外的所有神经节。一些上行轴突在大脑神经节处分叉,通过脑-脑联合,到达对侧眼并在眼杯处形成分枝。部分传出神经元的轴突也投射于不同的外周神经,如:n.n.intestinalis,pallialis dexter,pallialis sinister internus et externus。五羟色胺能纤维和FMRF-酰胺能纤维均存在于视神经上,且这些纤维隶属于只投射在同侧眼的中央神经元。它们形成了位于眼杯处的丰富曲张结构及视网膜核心层,并且可能有助于调节视网膜对光的敏感性。     

Individual Growth of Planorbarius corneus (Planorbidae,Gastropoda) in Postlarval Ontogenesis

Russian Journal of Developmental Biology - Individual growth of 15 great ramshorn snail Planorbarius corneus individuals was studied in aquaculture at 20°С starting from 2 weeks after...     

Energy Metabolism in Postlarval Ontogenesis of Planorbarius corneus (Planorbidae,Gastropoda)

Russian Journal of Developmental Biology - The change in the rate and mass-specific rate of oxygen consumption was studied during individual ontogenesis of nine Planorbarius corneus individuals...     

Microglia proliferation as a response to activation in the freshwater snail Planorbarius corneus: a BrdU incorporation study

Invertebrate microglia constitute a class of cells resident in the ganglionic nervous system which are activated after tissue injury or by the presence of pathogens. The microglia activation response includes graduated morpho-functional and biochemical changes and cell proliferation. In this study we verified in the freshwater snail Planorbarius corneus that an activation caused by a traumatic event may induce microglia division. Cell proliferation was assessed immunocytochemically using BrdU incorporation technique and documented on both ganglionic sections and microglia cultured cells at different experimental conditions and times after activation. In addition, we studied the possibility of increasing microglia proliferation by adding to the cultured medium the Macrophage-Colony Stimulating Factor (M-CSF) that has been shown to stimulate specifically this process in vertebrates.