Eliminating afferent impulse activity does not alter the dendritic branching of the amphibian Mauthner cell

In the developing amphibian, the formation of extra vestibular contacts on the Mauthner cell (M-cell) enhances dendritic branching, while deprivation reduces it (Goodman and Model, 1988a). The mechanism underlying the interaction between afferent fibers and developing dendritic branches is not known; neural activity may be an essential component of the stimulating effect. We examined the role of afferent impulse activity in the regulation of M-cell dendritic branching in the axolotl (Ambystoma mexicanum) embryo. M-cells occur as a pair of large, uniquely identifiable neurons in the axolotl medulla. Synapses from the ipsilateral vestibular nerve (nVIII) are restricted to a highly branched region of the M-cell lateral dendrite. We varied the amount of nVIII innervation and eliminated neural activity. First, unilateral transplantation of a vestibular primordium deprived some M-cells of nVIII innervation and superinnervated others. Second, surgical fusion of axolotls to TTX-harboring California newt (Taricha torosa) embryos paralyzed the Ambystoma twin: voltage-sensitive Na+ channel blockade by TTX eliminated action potential propagation. Reconstruction of M-cells in 18 mm larvae revealed that dendritic growth was influenced by in-growing axons even in the absence of incoming impulses: impulse blockade had no effect on the stimulation of dendritic growth by the afferent fibers.     

Electrodiffusion model of a nerve impulse

Electrodiffusion equations are deduced which describe the formation of the action potential in the axone. It is suggested that the membrane dividing internal and external axone electrolytes after being stimulated with an electric impulse returns after some time to the initial "closed" state. It is shown that the overshut of the action potential takes place due to non-linear profile distortion of the shock wave of electrical field tension vector created by the movement of sodium and potassium ions through the membrane of the axone.     

Superposition of modes in a caricature of a model for morphogenesis

In a model proposed for cell pattern formation by Nagorcka et al. (J. Theor. Biol. 1987) linear analysis revealed the possibility of an initially spatially uniform cell density going unstable to perturbations of two distinct spatial modes. Here we examine a simple one-dimensional caricature of their model which exhibits similar linear behaviour and present a nonlinear analysis which shows the possibility of superposition of modes subject to appropriate parameter values and initial conditions.     

Model of the impulse activity of a neuron receiving a stationary impulse imput]

The stationary model of spike activity of a single neuron is considered. This model exponential decay and constant threshold can be described as discontinuous one. The problem of calculation of Laplas' transform the probability density function (PDF) of interspike interval (ISI) can be reduced to the boundary problem for the usual differential equation. For the exponential PDF of the magnitude of the PSP the Laplas' transform of ISI PDF is expressed by special functions. The mean and standard deviation of ISI for different combinations of parameters were plotted with the aid of computer. The experiment without intracellular recoding, allowing to estimate the values of certain physiological parameters of a neuron on the basis of the model is proposed.     

Effect of vestibular,somatic, and autonomic afferent impulsation on vestibular nuclear unit activity in cats

Single unit responses in nuclei of the vestibular complex to stimulation of the labyrinths and of proprioceptive and autonomic afferents were investigated. Different types of unit responses were obtained to stimulation, including evoked activity consisting of a group of action potentials followed by inhibition of the spike discharge. Unit activity in the vestibular nuclei was shown to depend on extralabyrinthine stimulation. In response to adequate stimulation of the labyrinths by tilting the head, the role of receptors of muscles and joints in the neck was distinguished. The question of the somatotopic organization of the vestibular nuclei and convergence of various afferent flows on neurons giving rise to the vestibulospinal tract is discussed.Institute of Medico-Biological Problems, Ministry of Health of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 8, No. 5, pp. 507–513, September–October, 1976.     

Changes in integrated vagal afferent activity induced by model lung diseases in rats.

An attempt has been made in the present report to evaluate quantitatively the sensory activity in both vagal nerves of control rats and rats with experimental lung inflammation, by employing the integration technique. We evaluated background vagal nerve activity, resting respiration and activity during inflation at constant pressures of 5 to 20 cm of water. It was found that integrated vagal respiratory activity cannot be assessed in absolute units under our experimental conditions, because of the large scatter of data. However, when the integrated values were related, for example, to resting respiration (in percentage), it was possible to compare some respiratory parameters in control, healthy rats of the Wistar strain and rats with lung inflammation. While background activity in control rats represents 75.9% of resting respiration, this parameter is significantly higher both in rats with 2-day carrageenin lung inflammation and those intoxicated with paraquat. Lung inflation at pressures 5, 10, 15, 20 cm H2O increased vagal activity linearly both in control and the two experimental groups with the degree of lung inflation. However, values in experimental animals corresponding to those of the control group were not reached until higher inflation pressures. From the functional aspect, experimental rats had characteristic tachypnoea which returns to control values after bilateral vagotomy. Since it was found that lung compliance was significantly decreased in both carrageenin and paraquat lung processes, it is being suggested that the diminished activity from lung receptors during inflation is due to mechanical properties of the lung tissue, namely lowered lung compliance.     

A gravitational impulse model predicts collision impulse and mechanical work during a step-to-step transition

The simplest walking model, which assumes an instantaneous collision with negligible gravity effect, is limited in its representation of the collision mechanics of human gaits because the actual step-to-step transition occurs over a finite duration of time with finite impulsive ground reaction forces (GRFs) that have the same order of magnitude as the gravitational force. In this study, we propose a new collision model that includes the contribution of the gravitational impulse to the momentum change of the center of mass (COM) during a step-to-step transition. To validate the model, we measured the GRFs of six subjects' over-ground walking at five different gait speeds and calculated the collision impulses and mechanical work. The data showed a significant contribution of the gravitational impulse to the momentum change during collision. To compensate for the gravity, the magnitudes of collision impulse and COM work were estimated to be much greater than in previous predictions. Consistent with the model prediction, push-off propulsion fully compensated for the collision loss, implying the step-to-step transition occurred in an energetically optimal manner. The new model predicted a moderate change in the collision mechanics with gait speed, which seems to be physiologically achievable. The gravitational collision model enables us to better understand collision dynamics during a step-to-step transition.     

Effect of destruction of afferent inputs on spontaneous unit activity and character of neuronal interconnection in the rat neostriatum

The effect of destruction of afferent inputs on relations between types of spontaneous unit activity, its mean frequency, the distribution of minimal and maximal intervals, and the character of neuronal interconnection in the neostriatum was studied in acute experiments on rats immobilized with D-tubocurarine. In addition, spontaneous activity derived from neurons in slices of rat neostriatum was analyzed. Spontaneous activity of grouped type was not observed, and no positive symmetrical maxima in the zero region were present on graphs of cross-correlation function. The results of the investigation showed that the grouped type of spontaneous activity is determined by activity of the cortical input whereas activity of the thalamic input has a tendency to prevent the development of this type of neostriatal unit activity. Activation of the cortical input also was shown to be probably responsible for the presence of a positive symmetrical peak on the cross-correlation function graph for neurons with the grouped type of spontaneous activity.Institute of Biological Physics, Academy of Sciences of the USSR, Puchchino-on-Oka. Translated from Neirofiziologiya, Vol. 16, No. 1, pp. 110–115, January–February, 1984.     

A model of the mechanisms of formation of unit activity

Dependence of the temporal structure of the spike discharge of a neuron in a weakly interacting network on the characteristics of excitatory and inhibitory input flows and on cell parameters was analyzed by a mathematical model. The intensity of communication between individual neurons corresponded to the intensity of synaptic communication between real spinal neurons. The temporal course of trace and accommodation processes in the model was similar to that of these processes in real spinal neurons. Connection of inhibitory inputs and an increase in the intensity of their influences were shown to be equivalent to a decrease in the intensity of excitatory input flows. Changes in cell parameters had a significant effect on the spike discharge only in the case of weak input influences (the ratio of the amplitude of the combined ESP evoked by the input spike train to the threshold value of membrane potential at rest was about 1.2:1.0 to 1.4:1.0). An increase in the input flow intensity led to considerable reorganization of the firing pattern: Mean values of interspike intervals and their fluctuations were reduced, histograms of interspike intervals became more symmetrical, and periodic waves appeared on the autocorrelation histograms. It is concluded on the basis of these results and of data in the literature that the main factor determining reorganization of the temporal structure of unit activity in a network of weakly interacting cells is the intensity of the input flow.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 2, pp. 199–207, March–April, 1980.     

The reflection of the operations of comparing afferent flow with internal pretuning in the neuronal impulse activity of the frontal cortex in the dog

From 192 neurons, recorded in the frontal cortex of dogs trained for differential classical conditioning of salivary reflex, 24 cells were identified related to the detection of matching-mismatching conditioned and unconditioned stimuli (CS and US) to internal set. Impulse reactions of the 1-st group of neurones (11 cells) to US disappeared, when any deviation from standard pattern of CS-US pairing occurred or when US characteristics were suddenly changed. These reactions developed again at the 3-5th repeated presentation of the stimuli delivered in "new" regime. Neurones of the 2-nd group (13 cells) were activated in response to CS only when two sequential CSs had different meaning. The 1-st group of neurones is considered as detectors of matching, and the 2-nd group--as detectors of mismatching the stimulus to its neural model, formed by mechanism of reinforcement.     

Evoked impulse activity in neuronally isolated cortex

The reactions of neurons of the isolated cortex of one hemisphere to direct cortical stimulation were investigated in cats under Nembutal anesthesia. Isolation of the cortex was carried out by Khananashvili's method [10]. It is shown that phasic reactions develop in the isolated cortex in response to such stimulation: initial discharge, initial pause, first after-discharge, first after-pause, late after-discharges and pauses, as well as reactions of presumably inhibitory neurons. A majority of the cells (85%) which manifest background activity respond to direct electrical stimulation, and the frequency of the late after-reactions is twice as great as in the intact cortex. It is concluded that cortical elements of the isolated cortex retain their principal neurophysiological properties.Institute of Experimental Medicine, Academy of Medical Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 3, No. 3, pp. 236–244, May–June, 1971.     

Pharmacology of airway afferent nerve activity

Afferent nerves in the airways serve to regulate breathing pattern, cough, and airway autonomic neural tone. Pharmacologic agents that influence afferent nerve activity can be subclassified into compounds that modulate activity by indirect means (e.g. bronchial smooth muscle spasmogens) and those that act directly on the nerves. Directly acting agents affect afferent nerve activity by interacting with various ion channels and receptors within the membrane of the afferent terminals. Whether by direct or indirect means, most compounds that enter the airspace will modify afferent nerve activity, and through this action alter airway physiology.     

Somatosensory cortical unit responses in the waking cat to afferent stimuli

Extracellular and intracellular responses of 183 neurons in the primary projection area of the somatosensory cortex to electrical and tactile stimulation of the skin on the contralateral fore limb and to stimulation of the ventro-posterolateral thalamic nucleus of the ipsilateral hemisphere were studied in chronic experiments on cats. Spike responses to afferent stimuli are subdivided into three types: initial with a latent period of under 60 msec; initial followed by late responses with a latent period of over 60 msec; late with a latent period of over 60 msec. In addition another group of neurons responding to peripheral stimuli in the interval between the initial and the late response was identified. In nearly all cases the initial responses to peripheral stimulation had the form of a series of spikes, unlike responses to thalamic stimulation. It is concluded from the durations of the latent periods of these responses that about 70% of neurons in the primary projection area are activated mono- and disynaptically in response to peripheral stimulation; consequently, the intracortical spread of excitation in this zone is restricted.     

Abnormal impulse discharge in primary afferent axons injured in the peripheral versus the central nervous system

Chronic injury to sensory axons in the rat peripheral nerve induces pathophysiologic changes in the axolemma at the cut nerve end, which are reflected in spontaneous ectopic impulse discharge and hyperexcitability to a range of depolarizing stimuli. We asked whether sensory axons injured in the central nervous system (CNS) also respond in this way. Primary afferent axons were severed in the sciatic nerve and, alternatively, in the midcervical or upper lumbar dorsal column (DC). Measurements of abnormal discharge from myelinated afferents showed high levels of spontaneous activity generated at the nerve injury site, especially during the period 3-16 days postoperatively, but comparatively little activity generated at the DC lesion site at any postoperative time. There was a corresponding difference in ectopic hyperexcitability to mechanical and adrenergic stimulation, and to depolarization with topical K+. DC lesion sites were not made more excitable by concurrent transection of the sciatic nerve, or by placing an autologous graft of excised sciatic nerve tissue into the DC defect at the time of initial surgery. Transection sites on dorsal roots L4 and L5 yielded abnormal discharge similar to that of sciatic nerve neuromas, indicating that the relative silence of DC transection sites was related to the CNS environment and not to position with respect to the sensory cell body.