Anesthesia effect on rabbit hypothalamic neuron impulse activity

Neuronal impulse activity in the thermoregulation center in the anterior and posterior sections of the rabbit hypothalamus was studied in chronic experiments and in intravenously injected anesthetics (urethane and chloralose). Anesthesia decreased the neuronal firing rate, changed the impulse activity pattern, and decreased the number of neurons responding to skin thermal stimulation. These changes were most pronounced in the posterior hypothalamic section.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 23, No. 5, pp. 574–579, September–October, 1991.     

A perturbation method for the analysis of impulse propagation in a mathematical neuron model

A perturbation method is presented for the calculation of signal propagation velocities in a mathematical neuron model. Impulse frequencies and waveforms are also determined. The method uses a non-linear conduction model containing a small parameter, such that analytical solutions are possible, yet the inherently non-linear physiological phenomena involved, can be explained. A simple two-variable membrane equation is used, but the method is generally applicable to various more complete systems.     

Interferometric study of a single living neuron in relation to its electrical activity]

Interferometric microscopic study of living neurons of the isolated brain of Limnaea stagnalis has revealed some fluctuation of dry weight of the cytoplasm and the nucleolus in the absence of electrical activity of the neuron. The character of these changes was different for different neurons. During the neuron-induced generation of action potentials in response to the intracellular electrical stimulation, the changes in dry weight became similar for all neurons: the dry weight of the cytoplasm increased and the dry weight of the nucleolus decreased. This effect grew with the time of stimulation.     

Evaluation of synaptic potential dynamics from evoked impulse activity of neurons]

To evaluate intracellular potentials in the region of spike initiation of function lambda (t) is suggested which describes the dependence on time of the density of conditional probability of generation by the neuron of the first impulse in response to the stimulus. Qualitative correspondence of the dynamics of membrane potentials and function lambda (t) is demonstrated on the analog model. The application of the function lambda (t) to the classification of the neurons of auditory system is shown to be promising. The difference between the function lambda (t) and normalized poststimulus histogram allows to evaluate the refracteriness of the neuron.     

Classification of cortical neurons according to the character of their background impulse activity]

The method of basic components and cluster analysis was used to classify 75 units in the visual cortex of alert rabbits, proceeding from the empiric form of distribution of interspike intervals (DII), the mean frequency of impulsation and the relative number of intervals up to 500 msec. They were classified into nine groups containing from two to twelve units. Besides the cues, used as a basis for classification, the groups of units also differed in the structure of burst activity, the correlation of adjacent intervals and the ratio between the short (up to 20 to 60 msec) and long intervals. The latter served to make suggestions on the genetic affinity of bimodal DII to those with a bend on the waning after the maximum, and on the nature of formation of high frequency bursts and intervals exceeding 20 to 60 msec.     

Discrete wave mechanism of integral activity in heterogenic neuron synapses]

On the basis of the conception of the discrete wave mechanism for the integration of heterogeneous neuron elements, a hypothesis was put forward that neuron excitation propagates as waves of changes in the conformational states of neuron membrane lipids. A mathematical model was constructed, which confirms the wave mode of excitation propagation. The model enables one to consider the integration of postsynaptic potentials as a process of wave interference. It was assumed that the training of neuron elements can be considered as a process of nonuniform distribution of lipids.     

Superposition of impulse activity in a rapidly-adapting afferent unit model

Mechanosensory afferent units consist of a parent axon, the peripheral axonal arborization, and the branch terminal mechanoreceptors. The present work uses a mathematical model to describe the contribution of a given number of rapidly-adapting mechanoreceptors to the impulse pattern of their parent axon. In the model impulses initiated by any driven mechanoreceptor instantaneously propagate orthodromically and antidromically. The model also incorporates the axonal absolute refractory period as well as ortho-and antidromically elicited recovery cycles. In separate computations, periodic or random (Poisson process) trains of short-duration stimuli at constant amplitude are delivered to a given number (N=2–30) of co-innervated mechanoreceptors. The superposition of component impulse trains always departs from the theoretical ideal (Poisson process). Such departures are attributable to: (i) the number of driven mechanoreceptors, when N is small, (ii) axonal absolute refractory period, during maximal amplitude stimulation, and (iii) antidromic recovery cycles as well as absolute refractoriness, during submaximal-amplitude stimulation. Computations reveal that this instantaneous reset model results in the elimination of information extracted by driven mechanoreceptors. Model predictions with Poisson stimulation at varied amplitudes are compared to G-hair afferent unit responses to analogous stimulation. Qualitatively opposite results with respect to parent axonal impulse patterns imply that the axonal arborization is not simply a substrate for impulse propagation from branch terminals to parent axon.