Simulation of mechanisms responsible for initiation and modulation of bursting activity in RPa1 neuron of theHelix snail

A mathematical model of bursting activity in the RPa1 neuron of theHelix snail has been developed. The model allowed us to describe the processes of initiation and augmentation of the bursting activity related to transient secretion of a modulatory factor. Based on the analysis of computer simulations of various mechanisms underlying the effect of a modulating factor on the ionic membrane conductances in the bursting neuron, we suggested that modulating factor evokes a transition of non-voltage-dependent sodium channels and hyperpolarization-activated outward current channels to an active state and influences the gating of voltage-dependent sodium channels.Neirofiziologiya/Neurophysiology, Vol. 27, No. 1, pp. 11–17, January–February, 1995.     

Antagonists of NMDA glutamate receptors selectively affect synaptic mechanisms of the nociceptive sensitization in the snail

The effects of N-methyl-D-aspartate (NMDA) glutamate receptor antagonists on the mechanisms of nociceptive sensitization were studied in LPl1 and RPl1 neurons of the semiintact preparation of a Helix lucorum snail. Application of sensitizing stimuli on the head part of the control preparation led to a depolarization of the membrane and increase in its excitability. A depression of responses of neurons evoked by tactile or chemical sensory stimulation during the short-term period and significant facilitation of responses during the long-term period of sensitization were observed. Sensitization performed under conditions of application of NMDA antagonists (AP5 or MK801) produced similar changes in membrane potential, membrane excitability, and neuronal responses evoked by tactile stimulation of the head or foot. However, the chemical stimulation of the head under these conditions evoked a significant depression of responses during the short- and long-term sensitization periods. The results suggest that the NMDA glutamate receptor antagonists selectively affect the plasticity induction mechanisms of the command neuron synaptic inputs, which mediate the chemical sensory stimulation from the snail's head.     

Neurophysiological mechanisms of the reflex lacrimation

Neurophysiological mechanisms of the reflex lacrimation were analyzed in anesthetized rabbits. The secretory pattern of the lacrimation elicited by stimulation of the cornea consisted of two phases, that is, a rapid flow phase during stimulation and the subsequent slow flow phase in post-stimulus time. Parasympathetic nerve activities are closely related to the secretory volume in the rapid flow phase of the reflex lacrimation. On the other hand, excitation of the sympathetic nerve depressed the secretion in the rapid flow phase, while it facilitated slightly the secretion in the slow flow phase. The postganglionic parasympathetic fibers innervating the lacrimal gland showed two responses, i.e., the early and late discharges, when a single electrical shock was applied to the cornea. Their latencies were 68.7 +/- 8.7 msec and 173.3 +/- 14.2 msec, respectively. The threshold of the late response was about 10 times greater than that of the early one. With moderate anesthesia by pentobarbital or with transection of lateral 1/3 of medulla oblongata at the rostral level of the subnucleus caudalis of the spinal trigeminal nucleus, the late response was abolished whereas the early one was left almost unaffected. It is assumed that the early response is elicited by afferent impulses transmitted via the rostral part of the trigeminal sensory nuclear complex and the late one via the caudal part of the complex and also possibly the reticular formation.     

Neurophysiological mechanisms in the genetics of ethanol sensitivity

Abstract

Cerebellar Purkinje neurons of long‐sleep (LS) mice express a higher sensitivity than do those of short‐sleep (SS) mice to the depressant effects of ethanol in situ, in vitro, and in intraocular cerebellar brain grafts. The ethanol sensitivity of Purkinje neurons is intrinsic to the cerebellum, may be associated with only certain brain areas, and shows a high genetic correlation with the behavioral sensitivity of mice to ethanol‐induced ataxia. Tolerance develops to the depressant effects of ethanol on cerebellar neurons in both lines of mice. However, ethanol‐tolerant LS mice are more sensitive to the electrophysiological effects of ethanol on Purkinje neurons than are ethanol‐tolerant SS mice. In addition, the behavioral sensitivity to this drug probably also involves noncerebellar neurons since neonatally cerebellectomized LS and SS mice retain a different sensitivity to the ataxic effects of ethanol.     

Neurophysiological mechanisms involved in language learning in adults

Little is known about the brain mechanisms involved in word learning during infancy and in second language acquisition and about the way these new words become stable representations that sustain language processing. In several studies we have adopted the human simulation perspective, studying the effects of brain-lesions and combining different neuroimaging techniques such as event-related potentials and functional magnetic resonance imaging in order to examine the language learning (LL) process. In the present article, we review this evidence focusing on how different brain signatures relate to (i) the extraction of words from speech, (ii) the discovery of their embedded grammatical structure, and (iii) how meaning derived from verbal contexts can inform us about the cognitive mechanisms underlying the learning process. We compile these findings and frame them into an integrative neurophysiological model that tries to delineate the major neural networks that might be involved in the initial stages of LL. Finally, we propose that LL simulations can help us to understand natural language processing and how the recovery from language disorders in infants and adults can be accomplished.     

Neurophysiological and behavioral responses to olfactory stimuli in the snail Helix pomatia L

Some aspects of olfactory sensitivity in the pulmonate Helix pomatia L. were studied by means of neurophysiological and behavioral methods. Single fiber recordings were carried out in the olfactory nerve of the posterior tentacles. Olfactory stimulations with different odors were performed by means of a continuous air stream. The order of neuronal sensitivity to different odors was as follows: ethanol > or = ethyl acetate > pentanol > hexanol > octanol > or = diethyl malonate > vanillin. Furthermore, the results revealed a relative specificity for some substances. A comparison between neurophysiological and behavioral data shows that those substances, which cause the highest increases in impulse frequency, also evoke a behavioral avoidance reaction.     

Neurophysiological mechanisms of voluntary attention: a review

The review is focused on attention as behavior-controlling process. Neurophysiological, electrophysiological and neuropsychological studies of different brain structures during voluntary attention are analyzed. These data show that selective voluntary attention modulates activity of sensory specific cortical zones involved in relevant signal processing. Fronto-thalamic system consisting of prefrontal cortex and thalamic mediodorsal nuclei is shown to be main source of top-down selective modulation of voluntary attention. The review proposed the hypothetical model of selective cortical activity modulation during voluntary attention based upon the available data and evidence of own electroencephalographic studies.     

Neurophysiological and neurotransmitter mechanisms of behavior inhibition in normal and pathological conditions

The data concerning neurophysiological and neurotransmitter mechanisms of two principal kinds of inhibition of behavior is carried out: the inborn genetically determined inhibition and that developed in the course of training. On the basis of the experiments performed by the author and the literature on general neurophysiology the conclusion is made that development of inhibition of behavior during training (i.e. internal inhibition, including "latent inhibition") is determined by the relative strengthening of inhibitory hyperpolarization processes either locally (in a conditioned stimulus analyzer) or globally in the brain cortex and other brain structures during intensification of the inhibitory state (profound inhibition of a reflex and sleep). The main neurotransmitter in development of internal inhibition is gamma-aminobutyric acid. Inhibition of behavior without preliminary training arises either during the action of superstrong stimuli, (exceeding the maximum value inhibition) or during interaction of two and more active systems. A stronger one of these two systems suppresses another one (external inhibition, dominant inhibition, "freezing", "prepulse inhibition", etc.). These kinds of inhibition develop on the background of EEG activation, which suggests participation in their realization of reticular structures and corresponding neurotransmitters (acetylcholine, noradrenalin, dopamine and serotonin). Behavior pathology causes a break of the balanced interaction between the excitation and inhibition in the central nervous system. This affects both genetically determined forms of behavior inhibition and the learned internal inhibition.     

Gravity mechanisms in tonic motor system. Neurophysiological and muscle aspects

Nowadays it is widely believed that the animal motor system historically evolved under the powerful pressure of gravity forces. By the late 1970s, many manifestations of the microgravity effects on the motor system had already been known. At the same time, the basic sensorimotor relationships during exposure to zero-gravity remained unexplored. The article considers the main results of the studies of the scientific school of I.B. Kozlovskaya regarding the roles of the gravitational forces in the functioning of the tonic motor system in humans and other mammals. In these studies, it was demonstrated that the muscle tonic system is relatively independent and possesses its own structures and mechanisms at every level—from receptors to effectors. The support afferent input plays the main role in the regulation of the postural tonic system. The withdrawal of the support afferentation leads to the decline of the tonic motor units activity in extensor muscles and the alteration of the motor units recruitment patterns in the spinal cord. The decline of the tonic activity of the extensor motoneurons triggers on the development of the sensorimotor effects of microgravity including atony and muscle atrophy.     

Electrophysiological and neurochemical study of long-term sensitization in the snail

The long-term sensitization of avoidance reflex was produced in snail Helix pomatia, which led to the remarkable increase in the pneumostome closures period. The formation of long-term sensitization is also accompanied by increase in excitability of command neurons of this reflex. One of the possible mechanisms of this phenomenon is the depolarization of these cells. The quantitative redistribution of water-soluble proteins with relative mobility 0.54 0.42 0.40 was also observed in the identified neurons, both included in the avoidance reflex (command neurons) and non-included (bursting neurons, nerve cells of pool D). The protein with the relative mobility of 0.75 was unique for the nerve cells of neurosecretory pool D in sensitized snails, and was never found in control animals.