Plastic changes in the spontaneous activity of pond snail neurons during rhythmic and associated intracellular electrostimulation

In experiments on spontaneously active neurones of the isolated CNS of pond snail, under contingent stimulation with selective auto-reinforcement of interpulse intervals longer than their mean background value, 70 per cent of neurones were capable of adaptive rearrangements of the initial firing frequency, leading to frequency minimization or maximization of influences applied to them. After control rhythmic stimulation, usually no substantial changes of spontaneous activity were observed. The detected phenomena of initial transformation of the spontaneous impulse activity are considered as a cellular analogue of the instrumental conditioned reflex.     

The comparative roles of acetylcholine and noradrenaline in regulation of spontaneous spike activity of cortical neurons

The effects of acetylcholine and noradrenaline applications on neuronal sponta-neous activity were investigated in slices of guinea-pig parietal cortex. Iontophoretic ejections of both neurotransmitters to the cortical neurons evoked the same-type slowly-developing and long-lasting increase in the rate of spike activity. The different temperature sensitivity of cholinergic and noradrenergic reactions were revealed. During the temperature shift from 32-34 degrees C to 35-36 degrees C the cholinergic effect on neuronal spike activity became extremely strong, that is why even silent at t = 32-32 degrees C neurons became to acetylcholine responsive. Temperature-dependent changes in spike reaction to acetylcholine were accompanied by stable increase in spontaneous spike activity. The noradrenergic reactions did not change with temperature in limits from 32-34 to 35-36 degrees C. In this temperature range spike reactions to glutamate, the main excitation transmitter in the cortex, remained constant. The results obtained suggest that acetylcholine is the main neurotransmitter regulating spontaneous spike activity in cortical neurons.     

Correlations of neuronal spike discharges of VL neurons during spontaneous firing and during the activity evoked by peripheral stimulation

The temporal relations between simultaneously recorded neurons of the nucleus ventralis lateralis (VL) of cat thalamus were studied. The interaction and the functional connections between individual VL neurons are described. This was achieved with an application of cross correlation techniques. The response patterns of different individual neurons to somatic sensory and photic stimuli were also analyzed. For the purpose of classifying neurons as thalamocortical relay cells (T-C) and non relay cells (N-C) which do not project to the motor sensory cortex antidromic cortical stimulation was used. This stimulation was also used as conditioning one when proceeded peripheral stimuli. To analyze the nonspecific specific interactions upon single neurons conditioning photic stimuli were applied. The results show that T-C neurons are antidromically excited from a wide cortical areas and that the functional interaction between T-C neurons is mediated by a shared input from common sources. It is further postulated that N-C cells interposed between relay neurons subserve the functions of gating units modifying the neuronal network of lateral ventral nucleus of the thalamus.     

Background spike activity of cerebellar nucleus interpositus neurons in rats

Using computer analysis of the background spike activity recorded from cell units of the cerebellar nucleus interpositus, it was possible to distinguish several dynamic types and regularity gradings that specifically characterize these neurons, and to correlate these characteristics with the statistical parameters of their activity.Translated from Neirofiziologiya, Vol. 25, No. 2, pp. 98–100, March–April, 1993.     

Regression analysis of an instrumental conditioned tentacular reflex in the edible snail

Regression analysis revealed the opportunity of approximation with exponential mathematical model of the learning curves of conditioned tentacle reflex. Retention of the reflex persisted for more than three weeks. There were some quantitative differences between conditioning of the right and the left tentacle. There was formation of the reflex in every session during spring period, but there was no retention between sessions. The conditioned tentacle reflex may be employed in neuropharmacological studies.     

Activity-dependent suppression of spontaneous spike generation in the Retzius neurons of the leech Hirudo medicinalis L.

We report on factors affecting the spontaneous firing pattern of the identified serotonin-containing Retzius neurons of the medicinal leech. Increased firing activity induced by intracellular current injection is followed by a ‘post-stimulus-depression’ (PSD) without spiking for up to 23 s. PSD duration depends both on the duration and the amplitude of the injected current and correlates inversely with the spontaneous spiking activity. In contrast to serotonin-containing neurons in mammals, serotonin release from the Retzius cells presumably does not mediate the observed spike suppression in a self-inhibitory manner since robust PSD persists after synaptic isolation. Moreover, single additional spikes elicited at specific delays after spontaneously occurring action potentials are sufficient to significantly alter the firing pattern. Since sub-threshold current injections do not affect the ongoing spiking pattern and PSD persists in synaptically isolated preparations our data suggest that PSD reflects an endogenous and ‘spike-dependent’ mechanism controlling the spiking activity of Retzius cells in a use-dependent way.     

Somatic polyploidy in neurons from gastropod mollusks. I. Morphological characteristics of ganglia and neurons in the CNS of the snail Succinea lauta

A study was made of general anatomy and histological organization of the central nervous system in Succinea lauta, a gastropod pulmonate snail. Neurons grow by means of polyploidy during the postnatal succineid ontogeny. In the adult individuals diameters of perikaria of large neurons increase 2.5 to 5 times, in comparison with young individuals. As a whole, in adult snails sizes of ganglian cells vary from 3 to 380 mkm. Most of giant neurons are in parietal, abdominal and pallial ganglia. The chromatin structure has been described in neurons of young and adult snails. The endomitotic mechanism of polyploidization in the succineid ganglioneurons is proposed.     

Kinetic analysis of acetylcholine-induced chloride current in isolated snail neurons

1. Kinetics of activation and desensitization phases of the acetylcholine (ACh)-induced chloride current (ICI) were studied using isolated single neurons of Japanese land snail and the "concentration clamp" technique. 2. The dose-response curve for the peak ICI gave a dissociation constant of 7.1 x 10(-6) M and a Hill coefficient of 1.8. 3. The current-voltage relationship was linear in the voltage range examined (-60 to +10 mV) and the reversal potential (EACh) was -7.2 +/- 1.5 mV (N = 10). The value was close to the calculated equilibrium potential for chloride ions (ECI). 4. Both activation and desensitization phases of the ACh-induced ICI consisted of a single exponential at concentrations less than 3 x 10(-6) M and a double exponential at higher concentrations. The time constants of both phases decreased with increasing ACh concentrations but showed no potential dependency. 5. The recovery from desensitization of the ICI induced by 5 x 10(-6) M ACh proceeded double exponentially, with time constants of 11 and 114 sec at a holding potential of -30 mV. 6. Noise analysis was performed on a steady-state current induced by 3 x 10(-7) to 2 x 10(-6) M ACh. The mean open time was about 60 msec at 10(-6) M ACh and the single-channel conductance was 14 PS. 7. These results suggest that the ACh receptor-Cl channel complex in snail neurons has two binding sites with the dissociation constant of 7.1 x 10(-6) M and is rapidly activated and desensitized to a steady level in the presence of the agonist.     

Wiener analysis of spike transmission by identified molluscan neurons

A mathematical model of spike train transmission by identified molluscan neurons was obtained by Wiener analysis. Poisson-distributed sequences of near-threshold stimuli were used as input trains for model construction and testing. Assuming that the error of describing responses of the synapse-neuron system purely by mean outflow frequency is 100%, addition of a linear component to the equation of the model reduces this error to 25%, and addition of a term allowing for nonlinear properties of the system reduces it to 16%. Comparison of the standard error of predicted responses of the model to testing stimulus trains and of responses of a real neuron to these same trains showed that the prediction error with allowance for nonlinear properties does not exceed 21%. Choice of adequate criteria for comparing model and experimental results is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 1, pp. 49–54, January–February, 1984.     

NADPH-diaphorase activity in the nociceptive pathways of land snail Megalobulimus abbreviatus: the involvement of pedal ganglia

NADPH-diaphorase (NADPH-d) is a histochemical marker for nitric oxide synthase (NOS), widely used to identify nitric oxide (NO) producing cells in the nervous system of both vertebrates and invertebrates. Using NADPH-d histochemistry and semi-quantitative optical densitometry, we characterized the NO-producing neurons in the pedal ganglia of young and adult Megalobulimus abbreviatus, subjected to aversive thermal stimulus. The animals were killed at different times (3, 6, 12 and 24 h) following stimulus. The enzymatic activity was detected in different cellular subsets and neuronal processes. In all the studied pedal ganglia subregions, the optical density of positive neurons (P < 0.05) and neuropilar area 1 (P < 0.01) was significantly different in treated animals when compared to controls. The increase in nitrergic activity induced by nociceptive stimulus suggests the involvement of NO in the nociceptive circuit of M. abbreviatus, which is well maintained throughout evolution, and could be helpful in drawing cellular homologies with other gastropods.     

Functional activity of ganglion neurons from the pond snail upon temperature variations

Changes in the functional state of the synthetic apparatus of neurons of the peripharyngeal ring of the mollusk Lymnaea stagnalis upon elevating the temperature of the habitat from 4 to 18-22 degrees C were studied. In the first series of experiments, it was found that the synthetic activity of neurons of the great and small parietal, visceral, and pleural ganglia increases on the average by 70%. In the second series of experiments, changes in the average synthetic activity for all ganglia at 4.0, 6.5, 13.0, 16.8, 20.5, 21.5, 21.9, and 22.0 degrees C were studied. The increase in the synthetic activity of neuron cytoplasm (35% higher than the control values at 4.0 degrees C) was maximal at 13.0 degrees C; then the synthetic activity decreased to reach the level 20% higher than the control. The physiological range of temperature-dependent changes in the functional state of neurons was determined.     

Randomness of spontaneous activity and information transfer in neurons

The analysis of information coding in neurons requires methods that measure different properties of neuronal signals. In this paper we review the recently proposed measure of randomness and compare it to the coefficient of variation, which is the frequently employed measure of variability of spiking neuronal activity. We focus on the problem of the spontaneous activity of neurons, and we hypothesize that under defined conditions, spontaneous activity is more random than evoked activity. This hypothesis is supported by contrasting variability and randomness obtained from experimental recordings of olfactory receptor neurons in rats.     

Periodic components in integral spontaneous activity of sympathetic neurons

In experiments on rabbits anesthetized with urethane, we made multichannel coherent recordings of spontaneous activity and evoked activity of preganglionic sympathetic fibers in peripheral nerves of a leg and unmyelinated preganglionic fibers of the cervical sympathetic nerve trunk (CSNT). The results of a spectral analysis of the activity recorded and a correlational analysis of the activity and changes in arterial pressure allow us to conclude that preganglionic unmyelinated fibers of the CSNT are primarily vasoconstrictive and are under stronger baroreceptor control than vasoconstrictive fibers going to the skin and limb muscles. This is possibly due to differences in the functions of the innvervated organs. The latent period of the change in arterial pressure evoked by a change in the activity of vasoconstrictor fibers equals 4–10 sec.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 3, pp. 266–273, May–June, 1991.