Morphologic basis for cochlear implantation in the cat

The cat cochlear structure has been studied in 20 temporal bones. Owing to the preparations of the osseous cochleae investigated, certain anatomical parameters have been revealed; a detailed anatomo-topographic analysis on relations of the cochlear coils with the cochlear fenestra, the vestibular fenestra is presented. This gives a spatial notion on arrangement of the internal cochlear structures. The data obtained makes it possible to choose a precise place for electrode introduction and direction for their course along the coils. In its turn, this prevents trauma of the functional elements of the cochlea and, thus, contributes to stimulation effect.     

Conditioned food reflexes acquired on the basis of a dominant

By means of daily alimentary deprivation and presentation of acoustic stimuli, a hunger dominant was created in rabbits. After dominant testing by eye stimulation with air puff, when not only winking of one eye but also swallowing or chewing appeared,--the dominant was disrupted by giving food to the animal. Disruption of motivational hunger dominant led to rapid formation of stable temporary connection. At subsequent creation of hunger dominant the animal itself disrupted it by winking reaction with the significant eye. The basis of goal-directed reaction is the activation of feedback temporary connection, established at the dominant summation stage. The conditioned alimentary reflex, elaborated on the basis of dominant disruption is designated as endogenous alimentary conditioned reflex.     

Spinal reflexes and coactivation of ankle muscles during a submaximal fatiguing contraction.

This study examined the involvement of spinal mechanisms in the control of coactivation during a sustained contraction of the ankle dorsiflexors at 50% of maximal voluntary contraction. Changes in the surface electromyogram (EMG) of the tibialis anterior and of two antagonist muscles, the soleus and lateral gastrocnemius, were investigated during and after the fatigue task. Concurrently, the compound action potential (M-wave) and the Hoffmann reflex of the soleus and lateral gastrocnemius were recorded. The results showed that the torque of the ankle dorsiflexors and the average EMG of the tibialis anterior during maximal voluntary contraction declined by 40.9 +/- 17.7% (mean +/- SD; P < 0.01) and 37.0 +/- 19.9% (P < 0.01), respectively, at task failure. During the submaximal fatiguing contraction, the average EMG of both the agonist and antagonist muscles increased, leading to a nearly constant ratio at the end of the contraction when normalized to postfatigue values. In contrast to the monotonic increase in average EMG of the antagonist muscles, the excitability of their spinal reflex pathways exhibited a biphasic modulation. The amplitude of the Hoffman reflexes in the soleus and lateral gastrocnemius increased to 147.5 +/- 52.9% (P < 0.05) and 166.7 +/- 74.9% (P < 0.01), respectively, during the first 20% of the contraction and then subsequently declined to 66.3 +/- 44.8 and 74.4 +/- 44.2% of their initial values. In conclusion, the results show that antagonist coactivation did not contribute to task failure. The different changes in voluntary EMG activity and spinal reflex excitability in the antagonist muscles during the fatiguing contraction support the concept that the level of coactivation is controlled by supraspinal rather than spinal mechanisms. The findings indicate, however, that antagonist coactivation cannot simply be mediated by a central descending "common drive" to the motor neuron pools of the agonist-antagonist muscle pairs. Rather, they suggest a more subtle regulation of the drive, possibly through presynaptic mechanisms, to the motoneurons that innervate the antagonist muscles.     

Spinal reflexes in the long-tailed stingray, Himantura fai

We have exploited the segregation of motor and sensory axons into peripheral nerve sub-compartments to examine spinal reflex interactions in anaesthetized stingrays. Single, supra-maximal electrical stimuli delivered to segmental sensory nerves elicited compound action potentials in the motor nerves of the stimulated segment and in rostral and caudal segmental motor nerves. Compound action potentials elicited in segmental motor nerves by single stimuli delivered to sensory nerves were increased severalfold by prior stimulation of adjacent sensory nerves. This facilitation of the segmental reflex produced by intense conditioning stimuli decreased as it was applied to more remote segments, to approximately the same degree in up to seven segments in the rostral and caudal direction. In contrast, an asymmetric response was revealed when test and conditioning stimuli were delivered to different nerves, neither of which was of the same segment as the recorded motor nerve: in this configuration, conditioning volleys generally inhibited the responses of motoneurons to stimuli delivered to more caudally located sensory nerves. This suggests that circuitry subserving trans-segmental interactions between spinal afferents is present in stingrays and that interneuronal connections attenuate the influence that subsequent activity in caudal primary afferents can have on the motor elements.     

Gait acts as a gate for reflexes from the foot

During human gait, electrical stimulation of the foot elicits facilitatory P2 (medium latency) responses in TA (tibialis anterior) at the onset of the swing phase, while the same stimuli cause suppressive responses at the end of swing phase, along with facilitatory responses in antagonists. This phenomenon is called phase-dependent reflex reversal. The suppressive responses can be evoked from a variety of skin sites in the leg and from stimulation of some muscles such as rectus femoris (RF). This paper reviews the data on reflex reversal and adds new data on this topic, using a split-belt paradigm. So far, the reflex reversal in TA could only be studied for the onset and end phases of the step cycle, simply because suppression can only be demonstrated when there is background activity. Normally there are only 2 TA bursts in the step cycle, whereas TA is normally silent during most of the stance phase. To know what happens in the stance phase, one needs to have a means to evoke some background activity during the stance phase. For this purpose, new experiments were carried out in which subjects were asked to walk on a treadmill with a split-belt. When the subject was walking with unequal leg speeds, the walking pattern was adapted to a gait pattern resembling limping. The TA then remained active throughout most of the stance phase of the slow-moving leg, which was used as the primary support. This activity was a result of coactivation of agonistic and antagonistic leg muscles in the supporting leg, and represented one of the ways to stabilize the body. Electrical stimulation was given to a cutaneous nerve (sural) at the ankle at twice the perception threshold. Nine of the 12 subjects showed increased TA activity during stance phase while walking on split-belts, and 5 of them showed pronounced suppressions during the first part of stance when stimuli were given on the slow side. It was concluded that a TA suppressive pathway remains open throughout most of the stance phase in the majority of subjects. The suggestion was made that the TA suppression increases loading of the ankle plantar flexors during the loading phase of stance.     

DNA structural changes as the basis for a nanomolecular device.

There is currently great interest in the design of nanodevices that are capable of performing movements. Protein molecular machines are abundant in biology but it has recently been proposed that nucleic acids could also act as nanomolecular machines in model systems. Several types of movements have been described with DNA machines: rotation, extension-contraction and "scissor-like" opening and closing. Here we analyze the properties of a simple and robust device composed of a single 21-base-long oligonucleotide which relies on a duplex/quadruplex equilibrium fueled by the sequential addition of DNA single-strands, generating a DNA duplex as a by-product. The interconversion between two well-defined topological states induces a five nanometer two-stroke, linear motor type movement, which is detected by FRET spectroscopy.     

Conditioned reflexes before and after lesioning the substantia innominata in the cat

It has been shown that bilateral lesion of the substantia innominata has caused temporary depression of unconditioned and conditioned alimentary reflexes, disturbances of the elaboration and performance of conditioned reflexes. It is suggested that the latter produced by the operative memory disturbances.     

Spinal control of afferent temperature information in the cat

The effect of picrotoxin (at sub-convulsant doses, i.v.) on the background and invoked spike activity of cat dorsal horn internerons was investigated while thermal and mechanical influences were at work on the skin receptor areas. It was found that information on skin temperature is modulated at the presynaptic level and largely mediated by competitive interaction between large and small diameter fibers.Institute of Physiology, Academy of Sciences of the Kazakh SSR, Alma Ata. Translated from Neirofiziologiya, Vol. 18, No. 6, pp. 773–779, November–December, 1986.     

Spinal dysplasia with stump tail and hind limb paralysis in a laboratory bred cat.

A case is presented of a specified pathogen free bred cat which was apparently tail-less at birth and at three weeks of age revealed hind limb paralysis. The animal was euthanized at 4 weeks and X-radiography revealed an abnormal spinal curvature, greatly reduced caudal vertebrae and abnormal pelvic development. A small tail was dissected at post-mortem, but other abnormalities were not seen.