Electrophysiological investigation of central neurons of the electroreceptor system of the skate

Bioelectrical responses of acoustico-lateral neurons to electrical stimulation of the ampullae of Lorenzini were investigated in acute experiments on the anesthetized Black Sea skateTrigon pastinaca. Three types of responses were found: a primary composite response, prolonged activity, and single unit activity. Excitation of the neurons corresponded to a more marked negative phase, and inhibition to a more marked positive phase of the primary response. The thresholds of the unit responses to adequate electrical stimulation were 10^–9–10^–10 A/mm² and the minimal latent period 20 msec. The spontaneous activity of some neurons clearly depended on the animal's respiration. The character of the response depended on stimulus polarity, as reflected in the appearance of on- and off-responses. A tonic type of response with features of adaptation was predominant. The dependence of some response parameters (latent period of on- and off-responses, firing rate, duration of the contrast interval, response thresholds) on those of the stimulus is analyzed. The mechanisms of these bioelectrical responses are discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol.6, No.1, pp.59–67, January–February, 1974.     

The response of generalized motor activation in man

The effect of short acoustic and photic stimuli on the magnitude of the T- and H-reflexes was investigated in man. Two periods of increase in the amplitude and dispersion of the two test reflexes, disappearing during repetition of the stimulation, were found. Its first component differs from the second in the greater change in the T-reflex and the smaller extinction. The pattern of changes after photic and acoustic stimulation was the same but acoustic evoked a stronger response. The changes discovered are a subthreshold manifestation of the generalized response of motor activation evoked by a wide range of stimuli. It is postulated that its first component is determined by interaction between pyramidal impulses and the motor cortex and the second is due to the efferent volley from the primary cortical projection zones through the reticulo-spinal tract.     

Flow through a Collapsible Tube: Experimental Analysis and Mathematical Model

Flow through thin-wall axisymmetric tubes has long been of interest to physiologists. Analysis is complicated by the fact that such tubes will collapse when the transmural pressure (internal minus external pressure) is near zero. Because of the absence of any body of related knowledge in other sciences or engineering, previous workers have directed their efforts towards experimental studies of flow in collapsible tubes. More recently, some attention has been given towards analytical studies. Results of an extensive series of experiments show that the significant system parameter is transmural pressure. The cross-sectional area of the tube depends upon the transmural pressure, and changes in cross-section in turn affect the flow geometry. Based on experimental studies, a lumped parameter system model is proposed for the collapsible tube. The mathematical model is simulated on a hybrid computer. Experimental data were used to define the functional relationship between cross-sectional area and transmural pressure as well as the relation between the energy loss coefficient and cross-sectional area. Computer results confirm the validity of the model for both steady and transient flow conditions.     

Potentials of spinal motoneurons in cats with experimental tetanus

Potentials of motoneurons of the lower segments of the spinal cord were recorded with the aid of intracellular microelectrodes in experiments on cats with induced tetanus produced by injection of tetanus toxin (1500–2000 mouse LD₅₀) into the extensor muscles of the left shin. Neither afferent volleys of impulses in cutaneous and muscle nerves, nor antidromic volleys in the corresponding ventral roots, produced IPSPs in motoneurons of the extremity into which toxin was injected. The form both of antidromic peak potentials and of monosynaptic EPSPs in motoneurons in which IPSPs were blocked by tetanus toxin did not differ from the form of corresponding potentials of motoneurons in normal cats. The values of threshold depolarization for peak discharges during synaptic and direct stimulation were equal in tetanus and control motoneurons. Resistance and time constant values of the membrane in "tetanus" motoneurons did not differ from the corresponding values for "control" motoneurons.N. I. Pirogov Second Medical Institute, Moscow. Translated from Neirofiziologiya, Vol. 1, No. 1, pp. 25–34, July–August, 1969.     

Corticofugal influences on neurons of the main trigeminal sensory nucleus

The effects of stimulation of the ipsilateral sensomotor cortex were studied on 88 neurons in the region of the main trigeminal sensory nucleus of a cat. The cortex was stimulated via a coaxial electrode by single impulses. Stimulation of the cortex caused the appearance of EPSPs and action potentials in these neurons; a small number of these responses were monosynaptic. The polarity of the impulse applied to the cortex had a significant effect on the magnitude of the latent period of the response and the postsynaptic reaction, which is apparently caused by the stimulation of different types of cortex neurons. Apparently, corticofugal pulsation regulates the level of sensitivity of the trigeminal sensory neurons.A. A. Bogomolets' Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 1, pp. 47–53, July–August, 1969.