Biomedical subjects
Publications and source records attributed to D B Logunov.
In the present work the reactions of identified neurones of Helix lucorum L. to food were analysed depending on preliminary feeding and illumination.
Degree of the EPSP depression in different command neurons of the snail defensive reaction during the repeated rhythmic stimulation of presynaptic neuron LPa7 is found to be diverse. A decrease in responses of neurons to microiontophoretic applications of acetylcholine is also significantly different. It is suggested that differences in the EPSP depression are closely connected with the heterogeneity of the chemoreceptive membrane properties.
Posttetanic potentiation (PTP) of the identified synapse (LPa9-LPa3) in the central nervous system of snail (Helix lucorum L.) was investigated. PTP was observed both after tetanization of presynaptic neuron LPa9 by intracellular current pulses and after tetanization of the same presynaptic neuron by extracellular stimulation of its axonal branch.
Desensitization of receptors by the rhythmic application of acetylcholine (AC) was studied in Helix lucorum command neurons PPa2, PPa3, LPa2, LPa3. Application of AC induced in them monophasic depolarization wave. Repetitive AC stimulation with intervals less than 1-2 min induced a decrement of the response which gradually reached plato. Rate and degree of desensitization were constant in every following series and did not depend on preceding periods of depression. Response restoration was unchanged if intervals between series were equal. Stimulation with higher frequencies induced more considerable desensitization. Desensitization was specific to the locus of the membrane, on which AC was applied. Extrastimulation (intracellular stimulation and application of AC) did not lead to restoration of the response. It is supposed that desensitization is a short-term process and results from changes in receptors. The obtained data are explained by means of the Katz-Thesleff model of desensitization. As certain characteristics of synaptic depression and desensitization are similar, a suggestion is put forward that postsynaptic receptors can participate in the processes of synaptic effectiveness decrement during habituation.
The amplitude of EPSP arising in different command neurons (LPa2, LPa3 and PPa3) of the snail Helix lucorum after stimulation of presynaptic element LPa7 fluctuated synchronously. Synchronous application of acetylcholine on two command neurons showed that synchronous EPSP fluctuations were connected not with postsynaptic but with presynaptic mechanisms. The existence of a special modulating neuron is suggested.
Perfusion of the snail (Helix lucorum L.) CNS with DG-AVP (concentration 10(-6) M) in the course of low frequency intracellular stimulation (2-4-minute interval) of the defensive reflex command neurons led to an increase in the excitability. It was expressed both in the reduction of the spike generation latency, in the increased number of spikes in response to fixed stimuli, and in the activation of pacemaker potentials. If DG-AVP was added to the medium during endoneuronal habituation, there was no increase in the excitability. It is supposed that modification of the neuronal excitability may be caused by the DG-AVP effect on the pacemaker mechanism.
Spontaneous and evoked synaptic activity of the command neurons of the snail defensive reaction were studied by means of simultaneous intracellular recording. The spontaneous synaptic potentials and monosynaptic EPSP evoked by stimulation of presynaptic neurons were investigated. A mathematical model of a two-layered neuronal net of the defensive reaction was developed and constructed on the basis of the neurophysiological data. In this model the neurons of the afferent layer have local but overlapping receptive fields. Each afferent neuron is monosynaptically connected with all efferent neurons but the efficiency of the connections is different (each efferent neuron has the most effective connection with one afferent neuron only). The number of spikes of each afferent neuron appearing after stimulation of different points of its receptive field as well as efficiency of synaptic connections of each afferent neuron with efferent neurons are described by the normal low. Such neuronal net acquires the following principal property: different stimuli result in different one-model "excitation profiles" of efferent neurons.
A simple two-layered neuronal network model consisting of afferent and efferent neurons was constructed on the basis of a study of neuronal structure of defensive reactions in snail. Synaptic and spike reactions of the efferent neurons in response to stimulation of the receptive fields of afferent neurons were studied. It has been shown that a reduction in the distance between two points of stimulation results in a gradual transformation of a bimodal distribution of synaptic and spike reactions of the efferent neurons to the one-modal. These changes in synaptic and spike reactions were in agreement with the reaction of the snail leg muscle to two tactile stimuli simultaneously applied to the skin of the leg. The ablation of the snail central nervous systems resulted in a more diffuse contractile reaction. It is suggested that the central and peripheral neuronal networks differ in the exactness of defensive reflex realizations.
A defensive reaction of closing the pneumostome was rhythmically induced (with 2 or 3 min intervals) in a semi-intact preparation of Helix locorum by activation of a burst of action potentials in the command neurone with a suprathreshold depolarizing current (lasting 2 to 5 s). After 10 to 30 stimulations of the command neurone, defensive reactions of closing pneumostome appeared preceding the next stimulus and setting in after an omission of the stimulus. During this period, spike reactions to time appeared in non-stimulated neurones (the command neurone and neurones of the visceral ganglion) and sometimes in the stimulated command neurone. Their appearance was preceded by augmentation of synaptic activity. Since most of the synaptic inputs on the command neurone are sensory, it may be assumed that the leading role in the formation of reaction to time belongs to changes in the afferent link of the unconditioned reflex.
Unitary EPSP were recorded in two identified neurons of the snail ganglia after stimulation of an identified presynaptic neuron. Low-frequency EPSP depression was found in the course of repetitive stimulation (0.1-0.5/s). Transmitter release at two synapses was analyzed in terms of the depletion model using known and modified methods. The fraction of available pool (F) released by a presynaptic impulse was not significantly different at synapses of two different target neurons. The available pool of transmitter (C) and the rate constant of demobilization (k) in the RPa3 neuron were found to be 2-3 times and mobilization (M) 10 times as high as in the LPa2 neuron. Deviations of the depletion model from the experimental data were found. A new method was developed permitting k to be determined and any change in F to be postulated. No significant correlation was found between parameters of the depletion model F and C and the binomial parameters p and n calculated on the basis of the quantal hypothesis, which shows that the depletion model and quantal hypothesis describe different synaptic mechanisms.
Involvement of the cells of pedal ganglia in the regulation of heart activity and their connections with visceral neurons was studied in the central nervous system of Helix pomatia L. It was found that (1) numerous cells of pedal ganglia receive inputs from the heart. The reaction of the pedal cells to heart afferents was characteristic: initial high frequency increase of firing followed by inhibition, then a secondary tonic increase occurred in activity. Some of the pedal cells were activated after a brief delay; (2) many of the cells of the visceral and right parietal ganglia were activated simultaneously with pedal neurons during tactile stimulation of the heart. In different ganglia the answer to heart afferents can be observed to the same or opposite directions but its duration was identical in every cell; (3) one cell of the left pedal ganglion (LP3) formed monosynaptic connections with several cells of the visceral ganglion. The axons of the visceral cells, connected monosynaptically to the neurons LP3, runs into the intestinal nerve. LP3 caused EPSPs on the visceral cells; (4) the heart excitatory motoneuron V41, simultaneously with a number of pedal cells, receives excitatory inputs from the heart. The heart excitatory motoneuron is involved in the afferent and efferent pathways of heart regulatory network; (5) a motoneuron (V43) was identified to cause relaxation of the heart, giving branches into the intestinal nerve and similarly to other motoneurons activated by heart afferents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Application of desglycine-arginine-vasopressin to spontaneously nonactive command neurones of the snail's defensive reflex in the process of low-frequency (2-4 min intervals) intracellular stimulation led under certain conditions to an increase of excitability that was expressed in the shortening of latency of action potential generation, increase of the number of action potentials in response to a stimulus of fixed value, increase of membrane resistance, lowering of critical level of membrane depolarization and amplifying of pacemaker activity. However in spite of unidirectional changes of all the recorded parameters, the increases of values, opposite to the latency, did not correlate with the increases of membrane resistance and correlated well with the changes of depolarization critical level. If desglycine arginine-vasopressin was added to the medium during worsening of the neurones' excitability was probably caused by the influence of desglycine-arginine-vasopressin on the membrane active properties.
Explore the source record for details and available documents.