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At least 649 records · Page 36Linked to original sources
PubMed1999

Receptive field properties of single neurons in rat primary visual cortex.

The rat is used widely to study various aspects of vision including developmental events and numerous pathologies, but surprisingly little is known about the functional properties of single neurons in the rat primary visual cortex (V1). These were investigated in the anesthetized (Hypnorm-Hypnovel), paralyzed animal by presenting gratings of different orientations, spatial and temporal frequencies, dimensions, and contrasts. Stimulus presentation and data collection were automated. Most neurons (190/205) showed sharply tuned (</=30 degrees bandwidth at half height) orientation selectivity with a bias for horizontal stimuli (31%). Analysis of response modulation of oriented cells showed a bimodal distribution consistent with the distinction between simple and complex cell types. Orientation specific interactions occurred between the center and the periphery of receptive fields, usually resulting in strong inhibition to center stimulation when both stimuli had the same orientation. There was no evidence for orientation columns nor for orderly change in optimal orientation with tangential tracks through V1. Responses were elicited by spatial frequencies ranging from zero (no grating) to 1.2 cycle/degree (c/ degrees ), peaking at 0.1 c/ degrees, and with a modal cutoff of 0.6 c/ degrees. Half of the neurons responded optimally to drifting gratings rather than flashing uniform field stimuli. Directional preference was seen for 59% of oriented units at all depths in the cortex. Optimal stimuli velocities varied from 10 to 250 degrees /s. Some units, mainly confined to layer 4, responded to velocities as high as 700 degrees /s. Response versus contrast curves (best fit with Naka-Rushton) varied from nearly linear to extremely steep (mean contrast semisaturation 50% and threshold 6%). There was a trend for cells from superficial layers to be more selective to different stimulus parameters than deeper layers cells. We conclude that neurons in rat V1 have complex and diverse visual properties, necessary for precise visual form perception with low spatial resolution.

Animals↗
PubMed1986

Functional characterization of preganglionic neurons projecting in the lumbar splanchnic nerves: neurons regulating motility.

Lumbar preganglionic neurons, which projected in the lumbar splanchnic nerves and were probably involved in regulating motility of colon and pelvic organs (motility-regulating, MR neurons), were analyzed for their discharge patterns. The responses of the neurons to the following stimuli were tested: stimulation of arterial baro- and chemoreceptors and of afferents from the urinary bladder, colon, mucosal skin of the anus and perianal hairy skin. The following findings were made: a total of 131 preganglionic neurons were classified as MR neurons; these reacted to natural stimulation of at least one of the afferent inputs from the urinary bladder, colon and anal and perianal skin. The ongoing activity of these neurons did not correlate with the cardiac cycle or the cycle of the artificial ventilation. Most of them did not respond to an increase of blood pressure produced by i.v. injection of adrenaline or noradrenaline; some showed a weak depression or weak excitation which, in the time course, was untypical for visceral vasoconstrictor neurons. Stimulation of arterial chemoreceptors either did not influence MR neurons or produced only a secondary response owing to contraction of the urinary bladder. Ninety-seven preganglionic MR neurons could be subclassified: MR1 neurons were excited by distension and contraction of the urinary bladder and/or inhibited by distension and contraction of the colon (n = 61), a few were excited from both organs (n = 4); MR2 neurons were inhibited by distension and contraction of the urinary bladder and/or excited by distension and contraction of the colon (n = 32). Ninety-five out of 121 MR neurons (78.5%) were excited, 10 (8%) were inhibited and 16 (13%) not influenced by mechanical shearing stimuli applied to the mucosal skin of the anus. Most neurons which were excited by anal stimulation were not influenced by mechanical stimulation of the perianal (perigenital) skin. Twenty-eight per cent of the MR neurons (18 out of 64) were excited or inhibited upon stimulation of perianal skin. A few of these (7 out of 64 neurons, 11%) were involved in reflex responses which were different from those elicited from anal skin. At present no further consistent subclassification of MR1 and MR2 neurons appears possible on the basis of the excitatory and inhibitory anal and perianal reflexes. The results show that the population of visceral preganglionic neurons, which are probably involved in regulation of motility of colon and pelvic organs, is not homogeneous and probably consists of several subpopulations.

Anal Canal↗
PubMed2006

An fMRI study of somatosensory-implicated acupuncture points in stable somatosensory stroke patients.

PURPOSE: To assess differences in brain responses between stroke patients and controls to tactile and electrical acupuncture stimulation using functional MRI (fMRI). MATERIALS AND METHODS: A total of 12 male, clinically stable stroke patients with left side somatosensory deficits, and 12 age-matched male control subjects were studied. fMRI was performed with two different paradigms; namely, tactile stimuli and electrical stimulation at acupuncture points LI4 and LI11 on the affected side of the body. fMRI data were analyzed using SPM99. RESULTS: Tactile stimulation in both patients and controls produced significant activation in primary and secondary sensory and motor cortical areas and cerebellum. Greater activation was present in patients than controls in the somatosensory cortex with both the tactile task and the acupuncture point (acupoint) stimulation. Activation was greater during the tactile task than the acupuncture stimulation in patients and normal controls. CONCLUSION: Differences observed between patients and controls on both tasks may indicate compensatory over recruitment of neocortical areas involved in somatosensory perception in the stroke patients. The observed differences between patients and controls on the acupoint stimulation task may also indicate that stimulation of acupoints used therapeutically to enhance recovery from stroke, selectively activates areas thought to be involved in mediating recovery from stroke via functional plasticity. fMRI of acupoint stimulation may illustrate the functional substrate of the therapeutically beneficial effect of acupuncture in stroke rehabilitation.

Acupuncture Therapy↗
PubMed1989

Evidence that rat Kupffer cells stimulate and inhibit hepatocyte protein synthesis in vitro by different mechanisms.

Kupffer cell control of hepatocyte protein synthesis may be an important mechanism involved in the regulation of normal liver function and may be one mechanism responsible for the alterations in liver function seen during sepsis. The present series of in vitro experiments compare the response to various inflammatory stimuli of hepatocytes cocultured with Kupffer cells with that of hepatocytes cultured alone. In the absence of inflammatory stimuli, Kupffer cells stimulated hepatocyte protein synthesis. Lipopolysaccharide or gentamicin-killed Escherichia coli triggered Kupffer cell-mediated inhibition of cocultured hepatocyte protein synthesis but had no effect on protein synthesis of hepatocytes cultured alone. Phorbol myristate acetate, muramyl dipeptide, and calcium ionophore had no effect on hepatocytes cultured alone but resulted in a loss of Kupffer cell-mediated stimulation of cocultured hepatocyte protein synthesis without inhibition. Addition of dexamethasone to cocultures prevented the Kupffer cell-mediated inhibition of hepatocyte protein synthesis triggered by lipopolysaccharide, but did not block Kupffer cell-mediated stimulation in the absence of lipopolysaccharide. The data suggest that Kupffer cells can stimulate and inhibit hepatocyte protein synthesis by independent mechanisms. Kupffer cells may be important regulators of hepatocellular function in health and disease.

Acetylmuramyl-Alanyl-Isoglutamine↗
PubMed2000

Comparison of the hemodynamic response to different visual stimuli in single-event and block stimulation fMRI experiments.

Experiments with three different types of basic visual stimulation were performed to compare cortical activation in single-event and block trials. Independent of the stimulation paradigm, the single-event presentation leads to highly consistent signal responses regarding both the activated cortical areas and the dynamics of the signal time course. In contrast, signal time courses during block paradigms depend on the stimulus applied and are a complex and nonlinear function of the single-event responses. Additionally, the initial dip during the first 2 seconds after stimulus onset is consistently observed. However, the small amplitude change (-0.1% to -0.3%) requires signal averaging to establish statistical significance of the effect. Furthermore, different patterns of activation were observed within the primary visual cortex. In an anterior part of the primary visual cortex, activation was only observed at the onset and at the cessation of stimulation involving luminance changes.

Adult↗
PubMed2005

Visual accommodation in vertebrates: mechanisms, physiological response and stimuli.

The mechanism and stimulation of the accommodative reflex in vertebrate eyes are reviewed. Except for lampreys, accommodation is brought about by intraocular muscles that mediate either a displacement or deformation of the lens, a change of the corneal radius of curvature or a combination of these mechanisms. Elasmobranchs have little accommodation and are emmetropic in water rather than hyperopic as commonly stated. Accommodation in teleosts and amphibians is well understood and achieved by lens displacement. The accommodative mechanism of amniotes is of considerable diversity and reflects different lifestyles rather than phylogenetical relationships. In all amniotes, the ciliary muscle never has a direct impact on the lens. It relaxes the tension applied to the lens by zonular fibers and/or ligaments. In birds and reptiles the ciliary muscle is usually split into two parts, of which the anterior portion changes the corneal radius of curvature. The deformation of the lens is generally achieved either by its own elasticity (humans, probably other mammals and sauropsids) or by the force of circular muscle fibers in the iris (reptiles, birds, aquatic mammals). In the second part of the paper, some of the current hypotheses about the accommodative stimulus are reviewed together with physiological response characteristics.

Accommodation, Ocular↗
PubMed1987

Contribution of glia and neurons to the surface-negative potentials of the cerebral cortex during its electrical stimulation.

In 20 cats anaesthetized with pentobarbital the suprasylvian gyrus was stimulated by single stimuli or by trains of 50 s stimuli and the potentials from the cortical surface and the intracellular potentials from glial and nerve cells were recorded. Glial cells were identified according to conventional electrophysiological criteria: the absence of action potentials and postsynaptic potentials; slow depolarization in response to electrical stimulation. The slow negativity of direct response to a single stimulus is similar in shape and time course to the depolarization of the cortical glial cells and is unlike the hyperpolarization of the cortical neurons. Quantitative analysis showed that the basic part of the slow negativity is the glial component, whereas the neuronal component--inhibitory postsynaptic potential--plays a much lesser role. The negative shift of the potential on the cortical surface evoked by its high-frequency stimulation is similar in shape and time course to the depolarization shift of the membrane potential of the cortical glial cells (the mean value and standard error of time to peak for glial depolarization were 567.6 +/- 26.8 ms and 427 +/- 24 ms for negative shift of potential). (The results are based on recordings from 37 cells.) The negative shift decays much quicker; it is not similar in shape and time course to the hyperpolarization shift of the neuronal membrane potentials (the mean value and standard error of time to peak for inhibitory postsynaptic potential was 44.9 +/- 4.5 ms). According to the quantitative analysis, the negative shift of the potential reflects mainly the depolarization of the cortical glial cells. The contribution of the hyperpolarization of neurons to the surface-negative shift can be distinctly observed during the first 0.2-0.3 s of stimulation. It is supposed that accumulation of K+ ions in intercellular clefts results in depolarization of glial syncytium, which is reflected on the cortical surface as a slow negativity and a negative shift of the potential.

Animals↗
PubMed1994

Discharge pattern in the auditory nerve evoked by vowel stimuli: a comparison between acoustical and electrical stimulation.

Single channel cochlear implants only transmit the time structure of the electrically coded input signal. All nerve fibres show similar thresholds for monopolar round window stimulation, i.e., activation does not depend on their site of origin. To investigate the fine structure of the firing pattern elicited by stimulation with an analogue coded speech processing system (VIENNA 1-channel implant), cats were electrically stimulated with German steady-state vowels at the round window. Single fibre activity was recorded from primary auditory fibres and period histograms were calculated. The electrically evoked impulse patterns were compared with those from acoustic stimulation with the same vowels. With acoustic stimulation, the response of a fibre depends on the individual characteristic frequency (CF) with regard to the fundamental F0 and the formants F1, F2 and F3 of the vowels, the spontaneous activity of the fibre and the sound level. The evoked firing pattern was used to calculate period histograms, the frequency content of which was analysed by Fourier transformation. With electrical stimulation in the threshold range, an action potential is strongly synchronized to a cathodic peak of the current within one period of F0. With increasing current level 3-5 impulses can be locked to the same period. The timing of the short intervals is determined by the relative refractory period and current peaks (negative or positive) caused by the dominant higher formant F2 or F3. The acoustically evoked patterns are specific for the CF of the neuron and represent the spectral information of the different vowels.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed2004

cDNA cloning and functional characterization of a novel splice variant of c-Cbl-associated protein from mouse skeletal muscle.

c-Cbl-associated protein (CAP) is an SH3-containing adapter protein that binds to the proto-oncogene c-Cbl. Recent work suggests that signaling through these molecules is involved in the regulation of insulin-stimulated glucose uptake in 3T3-L1 adipocytes. Skeletal muscle is the major site of insulin-stimulated glucose disposal but there have been no reports of CAP function in this tissue. Using RT-PCR of mouse skeletal muscle RNA, we discovered a novel splice variant of CAP (CAPSM; GenBank Accession No. AF521593) that is different from the adipocyte form by inclusion of a novel 168 bp fragment. This fragment encodes a peptide sequence that shows very high similarity with exon 25 of the human homologue of CAP (SORBS1). To understand the function of CAPSM in glucose uptake regulation, L6 myotubes were transfected with either CAPSM or a truncated CAPSM devoid of all three SH3-binding domains (CAPDeltaSH3), which prevents CAP association with c-Cbl. Transfection with CAPDeltaSH3 decreased insulin-stimulated 2-deoxyglucose (2-DG) uptake and reduced c-Cbl phosphorylation. In contrast, transfection of L6 myotubes with CAPDeltaSH3 had no effect on dinitrophenol (DNP)- or hypoxia-stimulated glucose uptake, stimuli that work through insulin-independent mechanisms for the regulation of glucose uptake. These data demonstrate the existence of a novel CAP isoform expressed in skeletal muscle, and suggest the involvement of the CAP/Cbl pathway in the regulation of insulin-stimulated glucose uptake in L6 myotubes.

Alternative Splicing↗
PubMed1999

Dynamic properties of corticothalamic excitatory postsynaptic potentials and thalamic reticular inhibitory postsynaptic potentials in thalamocortical neurons of the guinea-pig dorsal lateral geniculate nucleus.

The properties of postsynaptic potentials evoked by stimulation of cortical, retinal and GABAergic thalamic afferents were examined in vitro in thalamocortical neurons of the guinea-pig dorsal lateral geniculate nucleus. Brief trains of stimulation (2-10 stimuli) delivered to corticothalamic fibers led to a frequency-dependent increase in excitatory postsynaptic potential amplitude associated with an increase in activation of both N-methyl-D-aspartate and non-N-methyl-D-aspartate glutamate receptors. In addition, repetitive stimulation of corticothalamic fibers also gave rise to a slow excitatory postsynaptic potential that was blocked by local application of the glutamate metabotropic receptor antagonist alpha-methyl-4-carboxyphenylglycine. In contrast, repetitive stimulation of optic tract fibers resulted in monosynaptic excitatory postsynaptic potentials that did not potentiate and were not followed by the generation of a slow excitatory postsynaptic potential. Repetitive activation of the optic radiation also evoked both GABA(A) and GABA(B) receptor-mediated inhibitory postsynaptic potentials. These inhibitory postsynaptic potentials exhibited frequency-dependent depression during repetitive activation. The presence of frequency-dependent facilitation of corticothalamic excitatory postsynaptic potentials and frequency-dependent decrement of inhibitory postsynaptic potentials, as well as the ability of corticothalamic fibers to activate glutamate metabotropic receptors, suggests that sustained activation of corticothalamic afferents in vivo may result in postsynaptic responses in thalamocortical cells that are initially dominated by GABAergic inhibitory postsynaptic potentials followed by prominent monosynaptic excitatory postsynaptic potentials as well as a slow depolarization of the membrane potential.Therefore, the corticothalamic system may inhibit or enhance the excitability and responsiveness of thalamocortical neurons, based both on the spatial and temporal features of thalamocortical interactions.

Animals↗
PubMed2006

Multihormonal resistance to parathyroid hormone, thyroid stimulating hormone, and other hormonal and neurosensory stimuli in patients with pseudohypoparathyroidism.

In patients with pseudohypoparathyroidism, hormonal resistance first affects parathyroid hormone (PTH), which leads to calcipenia, a decrease in renal vitamin D activation, and a tendency to bone receptor remodeling. However, because G proteins are ubiquitously distributed, multiple hormonal resistance occurs in pseudohypoparathyroidism type Ia and type Ic, impairing responses to other calciotropic hormones (PTHrP, calcitonin), TSH, and also pituitary and hypothalamic hormones, and to neurosensory stimuli. The diversity of multihormonal resistance contributes to the various phenotypes of the disease. Some clinical discomfort and medical consequences of the disease can be treated or prevented with hormone supplementation or modulation.

Hearing↗
PubMed2004

Synergistic action of GABA-A and NMDA receptors in the induction of long-term depression in glutamatergic synapses in the newborn rat hippocampus.

We show that activation of GABA(A) receptors (GABA(A)Rs) promotes induction of N-methyl-D-aspartate (NMDA) receptor (NMDAR)-dependent long-term depression (LTD) of glutamatergic synapses in the newborn rat hippocampal area CA1 in a developmentally restricted manner. In the newborn rat hippocampus two mechanistically different types of LTD of glutamatergic synapses could be induced under similar experimental conditions. The form of the LTD induced depended on the stimulation protocol and on the age of the animal. Low-frequency stimulation (1 Hz) with 100 stimuli induced a robust homosynaptic, reversible LTD at postnatal days 2-8 (P2-P8) but not at P14. This LTD was blocked by the NMDAR antagonist AP5 or by the GABA(A)R antagonist picrotoxin. Use of a low-chloride solution in the patch pipette resulting in E(GABA-A) < -70 mV blocked the NMDAR-dependent LTD, whereas clamping the cell to -40 mV during induction rescued it. In addition, it was possible to induce LTD at P14 with 100 stimuli if the cells were clamped to -40 mV during induction. Low-frequency stimulation with 900 stimuli induced a robust homosynaptic, reversible LTD both at P2-P8 and at P14. However, neither AP5 nor picrotoxin affected the LTD induced by 900 pulses at P2-P8. Instead, the 900 stimuli-induced LTD was blocked by the metabotropic glutamate receptor antagonists when co-applied with AP5. We suggest that during the first postnatal week postsynaptic depolarization provided by the activation of GABA(A)Rs shifts the threshold for the LTD induction, making the synapses more prone to activity-induced plasticity. From the second postnatal week onwards, when the GABA(A) responses are already hyperpolarizing, different mechanisms for LTD induction prevail.

Age Factors↗
PubMed2003

Formation of hydroxyapatite-mediated three-dimensional structures by mouse fibroblasts in response to physical stimulation.

Hydroxyapatite (HAP) ceramics are widely used as implant materials for periodontal bone defects because of their excellent biocompatibility. We demonstrated that physical stimulation, that is, (1). mechanical stimuli or (2). laser irradiation, causes HAP-mediated C3H10T1/2 mouse fibroblasts to form three-dimensional tissue-like structures. Trypsinized 10T1/2 cells were cultured simultaneously with 200 HAP granules on a rotator for 7 days in mechanical stimulation experiments. The cells were later transferred to a regular incubator. Cell reactions were observed by phase-contrast microscopy. The formation of three-dimensional structures around the HAP granules was observed in the third week of cultivation after stimulation. In laser irradiation experiments, trypsinized cells were irradiated with 1, 5, and 16 J/cm(2) at a wavelength of 1000 nm and cultured with 200 HAP granules for 10 weeks. The formation of three-dimensional structures, like those observed in the mechanical stimulation experiments, was observed in the third week after irradiation. The formation of these structures was most frequent at 1 J/cm(2), and the frequency of formation of these structures gradually decreased as the irradiation dose was increased. These results indicate that physical stimuli may stimulate cell proliferation, leading to the repair of damaged tissue. These results also indicate that mouse fibroblasts do not form these three-dimensional structures without HAP and that HAP alone is not sufficient to stimulate the formation of three-dimensional structures.

Animals↗
PubMed1979

Frequency sweep analysis of neuromuscular junction continuity.

A new technique for measuring neuromuscular junction continuity is described. Junctional transmission is evaluated by integration of the electromyographic (EMG) response induced by intramuscular electrical stimulation. The unique characteristics of this monitoring technique are the use of intramuscular stimulation and a varying stimulation rate. The stimulus frequency is made to increase exponentially from 1 to 100 pulses per second over a period of 10 or 15 seconds. Thin coiled wire electrodes are used for stimulation and recording of the EMG response. The frequency sweep electromyogram (FS-EMB) response was measured in uncurarized and curarized tibialis anterior muscle of cat. In the uncurarized preparation, the FS-EMG response was only slightly decreased with an increasing stimulus frequency. During neuromuscular blockade with d-tubocurarine the FS-EMG response diminished with increasing frequency. The response failed at successively lower frequencies during deeper levels of neuromuscular block. Recovery proceeded in the reverse order. The frequency sweep technique provides quantitative assessment of neuromuscular junction continuity over a broad spectrum of driving frequencies without inducing fatigue. This method does not require force measurements nor voluntary effort. Intramuscular stimulation minimises painful stimuli thus making the frequency sweep technique suitable for evaluating neuromuscular transmission in either conscious or unconscious individuals.

Action Potentials↗