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At least 127 records · Page 7Linked to original sources
PubMed1991

Inhibition of motoneuron discharge by peripheral nerve stimulation: an F response analysis.

F waves were recorded from the abductor pollicis brevis stimulating the median nerve at the wrist. These data were compared to responses obtained after preceding supramaximal stimulation of digital fibers of the second (II) finger or the median nerve at the wrist. The time between conditioning and test stimuli were 50 msec. Following conditioning stimuli, F wave latencies were significantly increased while F amplitudes, durations, and persistences were all decreased. Chronodispersion was not significantly affected. These changes were associated with increased repetition of individual F responses. The most prominent changes were found after stimulation of fibers of digit II but only at levels of stimulation supramaximal for the sensory nerve action potential. Some, but relatively limited, changes were present after stimulation of digital fibers of the fifth finger. The results are consistent with afferent fiber, probably A delta, inhibition of antidromic motoneuron activation with associated decrease in central motor neuron pool excitability. The study also demonstrates that, except for chronodispersion, changes in F waves found with peripheral nerve injury may also occur due to physiological changes in the central nervous system.

Electric Stimulation↗
PubMed1976

The identification of two inhibitory cells in each segmental ganglion of the leech and studies on the ionic mechanism of the inhibitory junctional potentials produced by these cells.

The present study identifies a pair of inhibitory cells that are located on each anterolateral margin of a leech segmental ganglion. These cells, which we label as cells 119, are electrically interconnected. These cells give rise to inhibitory junctional potentials (ijp's) in contralteral longitudinal body wall muscle cells. The latencies of the ijp's following spikes in cell 119 are variable. The ijp's are caused by transient increases in premeability to the Cl- ion. Previous studies demonstrated that 5-HT causes a hyperpolarization of body wall muscle cells by increasing the permeability of muscle membrane to the Cl- ion. Accordingly, 5-HT was searched for in the 119 cell bodies, but autoradiography, fine structure, and gas chromatography-mass spectrometry gave no indication that 5-HT was present in these cells. However, the variable latencies of the ijp's may indicate that there is a neuron interposed between cell 119 and the muscle cells. If this is the case, then the interposed neuron should be analyzed for 5-HT. Further experiments to locate the terminals of cells 119 and the cell bodies of the presumed interposed neurons are thus desirable.

Action Potentials↗
PubMed1977

Functional development in the Mauthner cell system of embryos and larvae of the zebra fish.

In the embryonic zebra fish as early as 40 hr after fertilization, the Mauthner cells (M-cells) initiate an escape response, elicited by tactile-vibrational stimulation. The initial part of this behavior is similar to the acoustic startle reflex seen during the larval stage which begins at 96 hr. The embryonic response is directional and is followed by a series of strong tail flexures which are more pronounced than those during swimming. In the embryo the M-cell fired at the beginning of the response and rarely fired again during subsequent contractions; in our experiments the M-cell did not mediate iterative movements of the tail. The M-cell system is probably involved in evoked hatching behavior, as the tactile response is sufficient to rupture the egg membrane and allow the animal to escape. The M-cell sometimes fired spontaneously, which suggests that it might function also in spontaneous hatching behavior which occurs in the absence of phasic stimulation. At 48 hr the M-cell has morphologically mature synapses on its soma and dendrites, but its cytoplasm is relatively undifferentiated; it has few oriented neurofilaments and no distinct axon hillock. During these stages the extracellular M-spike is longer in duration and smaller in amplitude than at later times when the cell is more mature morphologically. Our data suggest that long-term inhibitory control of the M-cell system begins to function at about the time of hatching. At this time the cell is morphologically mature and is richly supplied with synaptic endings over its soma and dendrites.

Action Potentials↗
PubMed1994

Isolation of novel and known genes from a human fetal cochlear cDNA library using subtractive hybridization and differential screening.

We used a combination of subtractive hybridization and differential screening strategies to identify genes that may function normally in hearing and, when mutated, result in deafness. A human fetal cochlear (membranous labyrinth) cDNA library was subtracted against total human fetal brain RNAs by an avidin-biotin-based procedure to enrich for cochlear transcripts. Subtracted cochlear clones were differentially screened with 32P-labeled total cochlear and total brain cDNA probes. Sequence analysis of clones that hybridized more intensely with cochlear than with brain cDNA probes revealed some previously characterized genes, including mitochondrial sequences, collagen type I alpha-2 (COL1A2), collagen type II alpha-1 (COL2A1), collagen type III alpha-1 (COL3A1), spermidine/spermine N1-acetyltransferase (SAT), osteonectin (SPARC), and peripheral myelin protein 22 (PMP22). Also identified were clones that are potential novel cochlear genes. Northern blots of cochlear and brain RNAs probed with COL1A2, COL2A1, COL3A1, SAT, SPARC, PMP22, and a novel sequence, designated Coch-5B2, confirm results of the subtractive procedure by showing preferential cochlear expression. A number of these genes serve structural or regulatory functions in extracellular matrix or neural conduction; defects in some of these genes are associated with disorders involving hearing loss. Partial sequence analysis of Coch-5B2 reveals a von Willebrand factor type A-like domain in this cDNA. To assess the cochlear specificity of Coch-5B2, a Northern blot panel of 14 human fetal tissue RNAs was probed with Coch-5B2, showing differential expression of this novel gene in the cochlea.

Avidin↗
PubMed1976

Effects of brain gangliosides on functional recovery in experimental regeneration and reinnervation.

The effect of brain cortex gangliosides has been tested in two different experimental models of peripheral sympathetic regeneration and reinnervation: a) the preganglionic trunks of the cervical sympathetic nerve were joined in an end-to-end anastomosis after severing the preganglionic trunk, caudally to the superior cervical ganglion; this reinnervation is mainly of cholinergic type. b) the postganglionic trunks of the superior cervical ganglion were joined in an end-to-end anastomosis after severing the postganglionic trunk; this reinnervation is mainly of adrenergic type. Functional recovery following the regeneration and reinnervation has been evaluated by measuring tha contraction of the nictitating membrane, evoked by electrical stimulation of the sympathetic trunk caudally to the point of anastomosis. Some of the operated animals were daily treated with 50mg/kg i.p. of brain cortex gangliosides during the entire post-operative period. Forty-five, sixty days after the operation we observed in the treated animals of both experimental sets a relevant increase in the functional recovery (between 30 and 100%) compared to the operated but untreated controls. In the case of postganglionic anastomosis the physio-pharmacological studies were substantiated by the histochemical fluorescence observations of the distributions of catecholamines in the smooth muscle of the nictitating membranes. These results strongly suggest that the treatment with gangliosides greatly influences the regeneration and reinnervation process of both cholinergic and adrenergic nerve fibers.

Animals↗
PubMed1992

Universality in neural networks: the importance of the 'mean firing rate'.

We present a general analysis of highly connected recurrent neural networks which are able to learn and retrieve a finite number of static patterns. The arguments are based on spike trains and their interval distribution and require no specific model of a neuron. In particular, they apply to formal two-state neurons as well as to more refined models like the integrate-and-fire neuron or the Hodgkin-Huxley equations. We show that the mean firing rate defined as the inverse of the mean interval length is the only relevant parameter (apart from the synaptic weights) that determines the existence of retrieval solutions with a large overlap with one of the learnt patterns. The statistics of the spiking noise (Gaussian, Poisson or other) and hence the shape of the interval distribution does not matter. Thus our unifying approach explains why, and when, all the different associative networks which treat static patterns yield basically the same results, i.e., belong to the same universality class.

Mathematics↗
PubMed1991

Reorganisation of descending motor pathways in patients after hemispherectomy and severe hemispheric lesions demonstrated by magnetic brain stimulation.

Numerous clinical studies on patients after hemispherectomy (HS) have provided clear evidence that two distinct groups can be recognized on the basis of the quality of their motor functions after operation. One of these consists of cases where HS was performed after normal brain maturation, the other of patients where the removed hemisphere was damaged early in life. The postoperative motor function has been found to be much better in the latter group. In the present paper it is demonstrated that in contrast to normal subjects ipsilateral compound muscle action potentials (CMAPs) induced by magnetic stimulation of the one intact motor cortex are present in patients after HS. The amplitudes of ipsilateral CMAPs in the muscles roughly correlate with their individual residual motor capacities and show a proximo-distal gradient. In patients with early brain damage prior to HS, CMAPs had short latencies and large amplitudes, whereas in patients with later acquired brain damage prior to HS, CMAPs had long latencies and small amplitudes. It is suggested that reinforcement of the ipsilateral corticospinal pathway may be responsible for residual motor functions in patients with early brain damage, whereas in patients with later acquired brain damage cortico-reticulospinal pathways may play a dominant role in ipsilateral motor control.

Action Potentials↗
PubMed1976

Spinal branching of corticospinal axons in the cat.

Branching patterns of single corticospinal (CS) neurons were studied in the cat by activating these neurons antidromically from various regions of the spinal cord. 1. One hundred and ninety-three neurons were activated antidromically by microstimulation in the gray substance of the cervical cord and the majority of them were found in the forelimb area of the pericruciate cortex. 2. Branches to the lower levels of the spinal cord were found for 30% of the neurons projecting to the cervical gray matter. 3. The remaining 70% sent axons only to the cervical gray matter and some of them sent multiple branches to several segments in the cervical cord. 4. Only a few CS neurons located outside of the forelimb area could be activated from the cervical cord, but all of them also sent branches to the lower levels of the spinal cord. Neurons projecting to both the cervical cord and the lower levels were intermingled in the cortex with those projecting only to the cervical cord. 5. CS neurons activated from a given area of the cervical cord were often clustered together in a small area of the cortex, although some of these CS neurons sent their other branches to other parts of the spinal cord and neurons projecting to other parts were also intermingled among them. 6. The functional significance of multiple axonal branching of CS neurons is discussed in relation to cortical motor functions.

Animals↗
PubMed1976

The effect of morphine on the activity evoked in ventrolateral tract axons of the cat spinal cord.

The effect of morphine on the activity in ventrolateral tract axons was studied in intercollicularly decerebrate cats with and without spinal section. Activity was elicited by electrical stimulation of Adelta- and C-fibres in the sural nerves. In spinal animals, morphine injected intravenously in a dose as low as 0.5 mg/kg reduced the post-stimulus discharge of impulses recorded in ventrolateral tract axons below the site of transection. The depression was not only abolished but reversed by levallorphan and naloxone. Pretreatment with reserpine did not diminish the effect of morphine. The effect of morphine was considerably weaker in decerebrate cats. Reversible block of the spinal cord produced by cold revealed that morphine reduced inhibition from the brain stem controlling the impulse transmission to ventrolateral tract axons. It is concluded that a spinal effect contributes to the analgesic action of morphine.

Afferent Pathways↗