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.     

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.     

The reaction of the N-cholinoreceptors of the isolated neuron of the mollusk Planorbarius corneus to polymethylene-bis-trimethylammonium compounds

Experiments have been made on isolated giant neurones of the mollusc Planorbarius corneus using clamp technique at temperatures 10 and 20 degrees C. The effect of polymethylene-bis-trimethylammonium compounds with 7-18 methylene groups in the molecule (C7...C18) on N-cholinoreceptors with chloride ionic channels was investigated. All these drugs were found to be agonists. Their cholinomimetic activity depends on the number of methylene groups (up to a certain extent) in their structure. This finding stands true also for skeletal muscles of frog and chick, as it had been shown in our earlier experiments. Analysis of membrane current fluctuations showed that the elementary current, the channel opened time, temperature coefficient (Q10) of the neuronal response to application of an agonist and the calculated Q10 of the reaction rate of the agonist with cholinoreceptor did not significantly differ for C8...C18 from the reaction rate of the agonist with cholinoreceptor. As compared with C8, C12...C18 exhibited 30 ... 40 times higher cholinomimetic activity, all other parameters in them being similar. Presumably, this difference is explained by concentrating capacity of C12...C18 at the membrane site because of their higher hydrophobic properties.     

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.     

Characteristics of heterosynaptic facilitation in giant neurons of the cerebral ganglion of Planorbis corneus

Experiments on giant neurons of the cerebral ganglion of the molluskPlanorbis corneus showed that heterosynaptic facilitation even if evoked by a single uncombined stimulation of the pallial nerve, is more effective than facilitation achieved by a combination of stimulations of nerves directly entering the cerebral ganglion. The intensity of facilitation does not depend on the synaptic efficiency of the heterosynaptic input for the test neuron, but on the intensity of its connection with the other neurons surrounding the giant cell (conjecturally of neurosecretory type). This fact, and also the long latent period of manifestation and achievement of the maximum of facilitation, and its nonspecificity relative to several inputs all suggest that heterosynaptic facilitation is neurosecretory in its origin. Such a mechanism of a sharp increase in the efficiency of synaptic connections in a nerve center may play an important role in the animal's nervous activity as a whole and in the formation of temporary connections in particular, although it does not reflect the specificity of the conditioned reflex.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 5, pp. 498–507, September–October, 1980.     

Crossed and uncrossed afferent inputs of mesocerebral neurons of the mollusk Planorbis corneus

Experiments on the isolated ganglionic ring of the freshwater molluskPlanorbis corneus showed that more neurons (30%) in the ipsilateral mesocerebrum respond to stimulation of the left cerebral nerves than to stimulation of the opposite nerves (13%). A similar picture is observed for neurons of the right mesocerebrum, except that 11% of neurons respond to activation of the left cerebral nerves compared with 39% to stimulation of the ipsilateral right cerebral nerves. Ipsilateral connections of nerve of the visceral complex of ganglia are more clearly defined, as is exemplified by the left pallial nerve, during stimulation of which 68% of neurons in the ipsilateral mesocerebrum were activated, compared with 8% in the contralateral right mesocerebrum. Afferent fibers running in the visceral nerves cross at the level of the abdominal ganglion and not of the cerebral commissure, as might be expected from the structure of the ganglionic ring. The mesocerebral neurons themselves do not form synaptic connections between the mesocerebra, and excitation reaching one of them does not therefore induce any effects in the other.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 6, pp. 571–575, November–December, 1973.     

Analysis of heterosynaptic facilitation in identified giant neurons from cerebral ganglion of the pond snail Planorbis corneus.

1. The intracellular mechanism of heterosynaptic facilitation (HSF) formation in identified neurons from the snail Planorbis corneus has been studied. 2. Facilitation of excitatory postsynaptic currents (EPSC) were induced by (a) stimulation of pallial nerve, and (b) addition to extracellular saline of serotonin, NaF, papaverine, theophylline, caffeine or dibutril-cAMP. 3. A depression of EPSC in solutions containing tolbutamide, a cAMP-dependent protein kinase inhibitor was observed. 4. In some cases the similar facilitation or depression of the current induced by acetylcholine application (ACh-current) was found in the same neuron. 5. The effects on ACh-current were distorted in solutions containing caffeine, a well-known activator of calcium ions release from the intracellular depot. 6. According to our findings, we suggest that adenylate cyclase activity of postsynaptic cells could underlie the formation of HSF and it is likely that this activity was modulated by intracellular concentration of calcium ions.     

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.     

Ionic mechanisms of the fast (nicotinic) phase of the acetylcholine response of identified Planorbarius corneus neurons

Responses to electrophoretic application of acetylcholine and suberyldicholine were investigated in identified neurons (LPed-2 and LPed-3) isolated from the left pedal ganglion ofPlanorbarius corneus. When microelectrodes filled with potassium chloride were used the reversal potentials of responses to acetylcholine and suberyldicholine were less negative than when microelectrodes filled with potassium sulfate were used; these reversal potentials were shifted toward depolarization if chloride ions in the medium were replaced by sulfate. These facts indicate that the responses in both LPed-2 and LPed-3 depend on chloride ions. Reversal potentials for acetylcholine and suberyldicholine in LPed-3 were virtually identical (–51 and –50 mV respectively), but in LPed-2 they differed significantly (–46 and –62 mV respectively). Replacement of sodium ions by Tris ions shifted the reversal potential for acetylcholine in LPed-2 toward hyperpolarization but did not change the reversal potential for suberyldicholine. Benzohexonium had the same action. The reversal potential for acetylcholine in medium with a reduced sodium concentration or in the presence of benzohexonium was the same as for suberyldicholine. It is concluded that on neuron LPed-2 acetylcholine activates both acetylcholine receptors which control conductance for chloride ions and acetylcholine receptors which change conductance for sodium ions, whereas suberyldicholine acts only on acetylcholine receptors responsible for the chloride conductance of the membrane.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 12, No. 5, pp. 533–540, September–October, 1980.     

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.     

Structure and synaptic organization of the osphradium of the lamellibranch mollusk Unio pectorum

The osphradial organ has been studied in Lamellibranchia--Unio pectorum--by means of scanning and transmissive electron microscopy. On the surface of the distal part of this hemosensory organ there is a distinct division into zones. The central part of the osphradial torus is occupied by the receptory zone, formed predominantly by supporting cells with microvilli and by peripheral processes of the subepithelial receptory cells. The lateral surfaces are occupied with ciliar areas of the ciliar supporting cells. In the receptory zone two types of the peripheral processes of the receptory cells are identified; they differ by the number of kinocilia and by ultrastructural organization of the apical part. Axon-like processes of the receptory cells interact with axons and dendrites of the ganglionic cells, forming axo-axonal, axodendritic and axosomatic synapses. The facts revealed demonstrate a high level of specialization of the osphradial receptory surface, connected with polymodality of this organ.