Orientation sensitive properties of visually driven neurons in extrastriate area 21a of cat cortex.

Orientation sensitive properties of extrastriate area 21a neurons were investigated. Special attention was paid to the qualitative characteristics of neuron responses to the different orientations of visual stimulus motion across neuron classical receptive fields (CRF). The results of experiments have shown that a group of neurons (31%) in area 21a with specialized responses to moving visual stimuli changed their direction selective (DS) characteristics depending on the orientation of the stimulus movement. Some neurons reveal an abrupt drop of the direction sensitivity index (DI) to certain orientation (58%), and some show significant increase of DI at one of applied orientations of stimulus motion (22%). Detailed investigation of response patterns of non-directional neurons to different orientations of stimulus motion have revealed clear-cut qualitative differences, such as different regularities in the distribution of inter-peak inhibitory intervals in the response pattern in dependence of the orientation of stimulus motion. The investigation of neuron CRF stationary functional organization did not reveal correlations between RF's spatial functional organization, and that of qualitative modulations of neuron response patterns. A suggestion was put forward, that visual information central processing of orientation discrimination is a complex integrative process that includes quantitative as well as qualitative transformations of neuron activity.

Spatial summation processes in the receptive fields of visually driven neurons of the cat's cortical area 21a.

The spatial summation in receptive fields (RF) of single neurons in cat's extrastriate area 21a was investigated as a basic neurophysiological substrate for central integration processing of visual information. The results showed that the majority of investigated neurons changed their response patterns with gradual increase of applied stimulus size. In approximately 82% of cases the suppression of neuron discharges was observed when the length of the moving strip exceeded that of the RF. In some neurons the increased size of the moving stimulus leads to the changes in the RF substructure. Receptive fields of neurons recorded at the same microelectrode penetration depth showed a great variety of RF superpositions distributed in a spatially asymmetric manner. As a result, every single RF consists of multiple sub-regions within the RF, differing from each other by the number of superimposed RF-s (density factor). We suggest that such complex spatial organization of the RF provides the neurophysiological basis for central integration processing of the visual information.

Simplified method for polarization-sensitive optical coherence tomography.

We report a method for extracting the birefringence properties of biological samples with micrometer-scale resolution in three dimensions, using a new form of polarization-sensitive optical coherence tomography. The method measures net retardance, net fast axis, and total reflectivity as a function of depth into the sample. Polarization sensing is accomplished by illumination of the sample with at least three separate polarization states during consecutive acquisitions of the same pixel, A scan, or B scan. The method can be implemented by use of non-polarization-maintaining fiber and a single detector. In a calibration test of the system, net retardance was measured with an average error of 7.5 degrees (standard deviation 2.2 degrees ) over the retardance range 0 degrees to 180 degrees , and a fast axis with average error of 4.8 degrees over the range 0 degrees to 180 degrees .

Single channel properties and regulated expression of Ca(2+) release-activated Ca(2+) (CRAC) channels in human T cells.

Although the crucial role of Ca(2+) influx in lymphocyte activation has been well documented, little is known about the properties or expression levels of Ca(2+) channels in normal human T lymphocytes. The use of Na(+) as the permeant ion in divalent-free solution permitted Ca(2+) release-activated Ca(2+) (CRAC) channel activation, kinetic properties, and functional expression levels to be investigated with single channel resolution in resting and phytohemagglutinin (PHA)-activated human T cells. Passive Ca(2+) store depletion resulted in the opening of 41-pS CRAC channels characterized by high open probabilities, voltage-dependent block by extracellular Ca(2+) in the micromolar range, selective Ca(2+) permeation in the millimolar range, and inactivation that depended upon intracellular Mg(2+) ions. The number of CRAC channels per cell increased greatly from approximately 15 in resting T cells to approximately 140 in activated T cells. Treatment with the phorbol ester PMA also increased CRAC channel expression to approximately 60 channels per cell, whereas the immunosuppressive drug cyclosporin A (1 microM) suppressed the PHA-induced increase in functional channel expression. Capacitative Ca(2+) influx induced by thapsigargin was also significantly enhanced in activated T cells. We conclude that a surprisingly low number of CRAC channels are sufficient to mediate Ca(2+) influx in human resting T cells, and that the expression of CRAC channels increases approximately 10-fold during activation, resulting in enhanced Ca(2+) signaling.

Characterization of a Ca2+-activated K+ current in insulin-secreting murine betaTC-3 cells.

1. The whole-cell perforated-patch recording mode was used to record a Ca2+-dependent K+ current (IK(Ca)) in mouse betaTC-3 insulin-secreting cells. 2. Depolarizing voltage steps (to potentials where Ca2+ currents are activated) evoked a slowly activating, outward current, which exhibited a slow deactivation (in seconds) upon subsequent hyperpolarization. 3. This current was shown to increase with progressively longer depolarizing voltage steps. It could be reversibly abolished by the removal of Ca2+ from the external medium or by application of Ca2+ channel blockers, such as Cd2+ and nifedipine. It was concluded that the depolarization-evoked current was activated by Ca2+. 4. Variations in external K+ concentration led to shifts in the reversal potential of the Ca2+-dependent current as predicted by the Nernst equation for a K+-selective current. 5. The Ca2+-activated K+ current was insensitive to external TEA (10 mM), a concentration sufficient to block the large-conductance Ca2+-dependent (maxi-KCa) channel in beta-cells. It was also insensitive to apamin, tubocurarine and scyllatoxin (leiurotoxin I), specific blockers of small-conductance KCa channels. 6. The current was blocked by quinine, a non-specific KCa channel blocker and, surprisingly, by charybdotoxin (ChTX; 100 nM) but not iberiotoxin, a charybdotoxin analogue, which blocks the maxi-KCa channel. It was sensitive to block by clotrimazole and could be potently and reversibly potentiated by micromolar concentrations of niflumic acid. Thus, the current exhibited unique pharmacological characteristics, not conforming to the known KCa channel classes. 7. The ChTX-sensitive KCa channel was permeable to Tl+, K+, Rb+ and NH4+ but not Cs+ ions. 8. The ChTX-sensitive IK(Ca) could be activated by the muscarinic agonists in the presence or absence of external Ca2+, presumably by releasing Ca2+ from internal stores. 9. Acutely isolated porcine islet cells also exhibited a slow IK(Ca) resembling that described in betaTC-3 cells in kinetic properties, insensitivity to TEA (5 mM) and sensitivity to quinidine, an analogue of quinine. The porcine IK(Ca), however, was not sensitive to block by 100-200 nM ChTX. It is likely, that species differences account for pharmacological differences between the mouse and porcine slow IK(Ca).

A calcium-dependent chloride current in insulin-secreting beta TC-3 cells.

Ca(2+)-dependent conductances have been hypothesized to play a role in the bursting pattern of electrical activity of insulin-secreting beta cells in response to high plasma glucose. A Maxi K+ channel has received the most attention, while a low-conductance Ca(2+)-activated K+ current has also been identified. We used an increasingly popular beta cell model system, the beta TC-3 cell line, and the perforated-patch technique to describe the properties of a novel Ca(2+)-dependent Cl- current [ICl(Ca)] in insulin-secreting pancreatic beta cells. The reported ICl(Ca) could be activated under physiological Ca2+ concentrations and is the first of its kind to be described in pancreatic insulin-secreting cells. We found that long depolarizing steps above -20 mV elicited an outward current which showed slow inward relaxation upon repolarization to negative membrane potentials. Both the outward currents and the inward tails showed dependence on Ca2+ influx: their current/voltage (I/V) relations followed that of the "L-like" Ca2+ current (ICa) present in these cells; they were blocked completely by the removal of external Ca2+ or application of Cd2+ at concentrations sufficient for complete block of ICa; and their magnitude increased with the depolarizing step duration. Moreover, the inward tail decayed monoexponentially with a time constant which at voltages negative to activation of ICa showed a weak linear voltage dependence, while at voltages positive to activation of ICa it followed the voltage dependence of ICa. This Ca(2+)-dependent current reversed at -21.5 mV and when the external Cl- concentration was reduced from 159 mM to 62 mM the reversal potential shifted by approximately +20 mV as predicted by the Nernst relation for a Cl(-)-selective current. Cl- channel blockers such as DIDS (100 microM) and niflumic acid (100 microM) blocked this current. We concluded that this current was a Ca(2+)-dependent Cl- current [ICl(Ca)]. From substitution of the external Cl- with various monovalent anions and from the reversal potentials we obtained the following permeability sequence for ICl(Ca): I- > NO3- > Br- > Cl- > Acetate.

A recombinant inwardly rectifying potassium channel coupled to GTP-binding proteins.

GTP-binding (G) proteins have been shown to mediate activation of inwardly rectifying potassium (K+) channels in cardiac, neuronal and neuroendocrine cells. Here, we report functional expression of a recombinant inwardly rectifying channel which we call KGP (or hpKir3.4), to signify that it is K+ selective, G-protein-gated and isolated from human pancreas. KGP expression in Xenopus oocytes resulted in sizeable basal (or agonist-independent) currents while coexpression with a G-protein-linked receptor, yielded additional agonist-induced currents. Coexpression of KGP and hGIRK1 (a human brain homolog of GIRK1/Kir3.1) produced much larger basal currents than those observed with KGP or hGIRK1 alone, and upon coexpression with receptor, similarly large agonist-induced currents could be obtained. Pertussis toxin treatment significantly diminished agonist-dependent currents due to either KGP or KGP/hGIRK1 expression. Interestingly, PTX also significantly reduced basal KGP or KGP/hGIRK1 currents, suggesting that basal activity is largely the result of G-protein gating as well. When the two channels were coexpressed with receptor, the relative increase in current elicited by agonist was similar whether KGP and hGIRK1 were expressed alone or together. When in vitro translated or when expressed in Xenopus oocytes or CHO mammalian cells, KGP gave rise to a nonglycosylated 45-kD protein. Antibodies directed against either KGP or hGIRK1 coprecipitated both proteins coexpressed in oocytes, providing evidence for the heteromeric assembly of the two channels and suggesting that the current potentiation seen with coexpression of the two channel subunits is due to specific interactions between them. An endogenous oocyte protein similar in size to KGP was also coprecipitated with hGIRK1.

Two ion currents activated by acetylcholine in the ARC muscle of Aplysia.

1. This work continues our examination of the electrophysiology and contractions of single fibers dissociated from a widely studied molluscan muscle, the accessory radula closer (ARC) muscle of Aplysia californica, aimed at understanding its excitation-contraction mechanisms and their modulation. 2. Extensive previous work has characterized a number of basal ion currents present in the fibers and effects of transmitters and peptide cotransmitters that modulate ARC-muscle contractions in vivo. Here we use current clamp, voltage clamp, and contraction measurements to examine the actions of acetylcholine (ACh), the transmitter that induces the contractions. 3. As in the whole ARC muscle, ACh depolarizes unclamped fibers maximally to about -25 mV where, no matter how much ACh is applied, the depolarization saturates. 4. The underlying ACh-activated current is in fact the sum of two quite distinct components, IACh,cat and IACh,Cl. 5. IACh,cat is itself a mixed current carried by cations (physiologically mainly by Na+, but to a significant degree also by Ca2+), reverses near +20 mV, rectifies inwardly, exhibits prominent voltage-dependent kinetics of activation with hyperpolarization, and is selectively blocked by hexamethonium. 6. In contrast, IACh,Cl is carried by Cl-, reverses near -60 mV, exhibits little rectification or voltage-dependent kinetics, is activated selectively by suberyldicholine, and is blocked by alpha-bungarotoxin. 7. Both currents activate fast when ACh is applied, desensitize relatively slowly in its presence, then deactivate fast. Both currents are activated at similar ACh concentrations, half-maximally at approximately 10 microM. Both currents also are activated by carbachol and propionylcholine and blocked by d-tubocurarine, bicuculline and paraoxon. Picrotoxin and atropine block IACh,cat better, 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid (SITS), 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), and anthracene 9-carboxylic acid IACh,Cl better. 8. The two currents are virtually identical to ACh-activated cationic (Na) and Cl currents that are ubiquitous in molluscan neurons. As has been proposed for the neuronal currents, IACh,cat resembles vertebrate neuronal nicotinic ACh-receptor (nAChR) currents, whereas IACh,Cl resembles vertebrate skeletal muscle nAChR currents. 9. Functionally, we believe that IACh,cat serves primarily to depolarize the ARC muscle to open voltage-activated L-type Ca channels, allow Ca2+ influx, and initiate contraction. Physiologically significant Ca2+ may also enter through the ACh,cat channels themselves. 10. By superimposing on IACh,cat, IACh,Cl brings the reversal potential of the combined current to around -25 mV and thereby sets a relatively negative upper limit to the ACh-induced depolarization. We propose that this is its physiological role. By limiting the depolarization, IACh,Cl limits the degree of activation of the Ca current and Ca2+ influx, and so prevents excessive contraction. More importantly, it moderates the voltage during contraction to a range where small voltage changes can finely grade contraction amplitude in this nonspiking muscle. 11. Indeed, in contraction experiments on the single fibers, there is an inverse correlation between the IACh,Cl/IACh,cat ratio and the magnitude of the ACh-induced depolarization and contraction. Furthermore, increased pharmacological activation of IACh,Cl depresses, and block of IACh,Cl enhances, both the depolarization and contraction. 12. Obligatory simultaneous coactivation of IACh,cat and IACh,Cl in the ARC muscle may be part of a peripheral control mechanism that automatically keeps the size of its contractions within behaviorally optimal limits.

Responses of cat's dorsal hippocampal neurones to moving visual stimuli.

Response properties of visually driven neurones in the cat's hippocampal region were investigated. Out of 688 single cells observed 181 (26%) were visually driven. Ocular dominance was determined for 147 of those cells, 90 of which were driven only by the contralateral eye, 20 were driven exclusively by ipsilateral eye and 37 neurones could be activated by both eyes. Receptive field boundaries were outlined for 157; 152 of those neurones were movement-sensitive, and 125 neurones were sensitive to stationary stimuli. A small group of neurones (13%) showed more pronounced reactions to the vertical direction of motion. Some neurones (22%) revealed sensitivity to the shape and size of the applied visual stimuli. These results confirmed earlier data indicating that visually driven neurones in hippocampal region possess complex properties. They are probably involved in a higher level of visual information processing.

Anterior lumbar fusion options. Technique and graft materials.

The biomechanical requirements of the ideal lumbar interbody fusion are important in the surgical treatment of the vertebral endplates and graft selection. A series of 45 patients with anterior lumbar fusion were reviewed retrospectively. The fusion was performed with a composite construct consisting of femoral allograft cross-sections and allograft cancellous bone. Preparation of vertebral endplates consisted of scraping the endplate until punctate bleeding appeared. The major part of the endplate was preserved to withstand interspace distraction and stability. A 97% fusion rate was achieved based on flexion and extension analysis with a six- to 12-month follow-up period. A final average interspace distraction of 2.39 mm was reported. The graft should consist of a rigid structure that exceeds physiologic loads anticipated in the postoperative period, and the composition to promote arthrodesis. Anterior lumbar fusion with femoral allograft is an excellent procedure, but long-term further follow-up studies and statistical data are essential.

Effect of operative position on sagittal alignment of the lumbar spine.

A variety of techniques and frames are used for positioning patients during posterior lumbar spinal instrumentation and fusion. Little information is available on the relationship of lumbar lordosis and the various positioning options, so it was felt that further investigation was warranted. Ten volunteers with no history of back pain were positioned and radiographed in the standing position followed by four lateral radiographs with the patient positioned on chest rolls, Andrew's frame, the Hasting's frame, and a four-poster spinal frame. Total lumbar lordosis from L1 to S1 as well as intervertebral body angles at each of the lumbar interspaces using standardized techniques were computed. No significant difference was found in lumbar lordosis between the standing and chest roll position. However, there was approximately a 50% reduction in lumbar lordosis when using the Hasting's, Andrew's, and four-poster frame as compared to the standing and chest roll configuration. The clinical implications are discussed.

Spatial summation processes in visually driven neurones of cat's pretectal region.

The spatial summation processes of single neurones of cat's pretectal region were investigated with moving and stationary visual stimuli. The results indicate that the majority of the investigated neurones changed their responses essentially at the gradual increase of size of the applied stimuli (i.e. showed negative or positive summation). Particularly, direction non-sensitive neurones showed symmetrical changes of spatial summation curves in response to two opposite directions of movement. By contrast, in some direction sensitive neurones different characteristics of responses for the two opposite directions of movement were observed. Thus the number of discharges in the responses to the preferred direction could increase or decrease at the gradual increase of the moving stimulus size, while the responses to the null direction could remain stable or vice versa. The same was observed for the "ON" and "OFF" responses in the ON-OFF neurones. Thus, it appears that the pattern of responses of a given neurone to different directions of movement and to the "on" and "off" periods of stationary stimulation are shaped by independent mechanisms.

Interspace distraction and graft subsidence after anterior lumbar fusion with femoral strut allograft.

The authors performed a retrospective review of 32 patients who had undergone a single-level anterior lumbar fusion with femoral strut allograft as an isolated procedure. The goal of the study was to use clinical radiographs to measure interspace distraction, graft subsidence, interspace collapse, the nature of allograft incorporation, and to correlate these results with successful arthrodesis. Results were categorized according to plain radiographic appearance and flexion/extension stability. Sixty-six percent of the group exhibited radiographic union with flexion/extension stability. Twenty-two percent exhibited stability on the flexion-extension analysis but less than complete arthrodesis was present. Twelve percent exhibited radiographic non-union and flexion-extension instability. Interspace distraction of 11 mm was obtained initially with a follow-up distraction of 5.5 mm. Graft subsidence was noted posteriorly in 27 patients with an average subsidence of 4 mm. The authors' conclusions were: 1) Interspace distraction can be achieved with anterior lumbar fusion if appropriate interbody grafts are used. 2) Despite a solid arthrodesis rate of only 66%, "functional arthrodesis" was achieved in 88%. In a retrospective review of patients who underwent anterior lumbar fusion with femoral strut allograft, interspace distraction, graft subsidence, and incorporation and arthrodesis status were measured. A solid arthrodesis was achieved in 66% of the patients, and functional arthrodesis in another 22%. Interspace distraction was maintained in 59% of cases.

The limitations of magnetic resonance imaging in the diagnosis of pathologic vertebral fractures.

Magnetic resonance imaging has been increasingly used in recent years to screen patients with suspected spinal metastases. The authors present four cases, all of whom were elderly patients with vertebral compression fractures, who were diagnosed with magnetic resonance imaging to have probable neoplastic involvement. In each case, vertebral body biopsies indicated a benign pathology. The authors discuss the diagnostic criteria of magnetic resonance imaging of spinal metastases and the limitations of magnetic resonance imaging in the diagnosis of pathologic vertebral fractures.

Simultaneous combined anterior and posterior fusion. An independent analysis of a treatment for the disabled low-back pain patient.

Sixty-nine patients were treated by a simultaneous combined anterior and posterior fusion for disabling low-back pain as directed by discographic pain provocation. They were evaluated independently, with an average follow-up of 2 1/2 years (range, 1.6 to 4.1 years). Fusion rates in excess of 90% were noted in patients who had undergone one- and two-level fusions, whereas the fusion rate for three-level procedures dropped to 77.8%. Acceptable clinical results were seen in approximately 80% of the primary low-back pain and the postlaminectomy patients. Results within the group of patients who had undergone previous fusion procedures were less favorable: two thirds good or fair. The available evidence suggests that this procedure is a valid surgical technique, especially applicable to multilevel lumbar fusions and the postlaminectomy patient. Despite its seemingly radical nature, it can be performed quickly and safely with adequate surgical training.

Anterior discectomy, microscopic decompression, and fusion: a treatment for cervical spondylotic radiculopathy.

A consecutive series of 47 patients with cervical radiculopathy secondary to spondylosis were treated with complete discectomy, root decompression accomplished by microscopic foraminotomy on the affected side(s), and iliac graft fusion at the involved interspace(s). Forty of the 47 patients were contacted with an average follow-up of 15 months. Eighty-three percent of the patients were judged as having good results. Fusion of the involved interspace(s) occurred in 87% of cases, although this did not appear to correlate with the clinical results.