Dynamics of orientational tuning of feling visual cortex neurons under the effects of sombrevine

Dynamics of orientational tuning in 59 primary visual cortex neurons were investigated before and after sombrevine-induced anesthesia during acute experiments on immobilized cats using temporal slice techniques. A dynamic shift in preferred orientation of a flashing light strip, during which peak amplitude of spike discharges was noted (at an angle of between 22 and 157°) occurred as response developed in two-thirds of the cells. We had previously named this effect "scanning the orientational range" [9]. Scanning declined significantly in 45% of the sample, culminating in complete disappearance of this effect in some cells following sombrevine action. Scanning intensified in 30%, while dynamics of tuning remained unchanged in 25% of units. Sombrevine administration induced change in the preferred stimulus orientation of 60% of the neurons (referred to as "unstable" cells) and remained constant in "stable" cells (= 40%). Dynamic changes in preferred stimulus orientation were 2.5 times as high as those of stable cells in the waking state. The scanning effect declined significantly in 60% of "unstable" neurons under the action of anesthesia and remained unchanged in not more than 6%. At the same time, orientational tuning did not alter in the "stable" cell group in 46% of units, either declining (25%) or increasing (29%) in the remaining scanning ranges.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 22, No. 1, pp. 107–113, January–February, 1990.     

Directional tuning of visual cortex neurons in the cat before and after nembutal injection

Directional tuning was investigated in 40 neurons of the primary visual cortex (area 17) before and after Nembutal injection during acute experiments on immobilized cats. Preferred orientation (PO) in 50% of neurons was found to be stable after the drug, while the remainder showed a consistent shift in PO (averaging 53.6±8.0°) for a number of hours. Neurons with consistent PO more frequently showed a preference for horizontal and vertical stimulus orientation; cells with unstable tuning had a wider PO distribution. More refined directional detection (i.e., finer tuning) was noted in "stable" rather than in "unstable" neurons both before and after administering the drug. Under narcosis, directional tuning altered in 50% of cells — an effect more marked in "unstable" than in "stable" cells (68% as against 38%). Mean background discharge rate also fell by an average of 5.5-fold and induced firing rate declined 1.5-fold during narcosis, moreover.Institute of Higher Nervous Activity and Neurophysiology, Russian Academy of Sciences, Moscow. Translated from Neirofiziologiya, Vol. 23, No. 6, pp. 669–676, November–December, 1991.     

Effect of Nembutal narcosis on dynamics of orientation tuning of cat visual cortex neurons

The dynamics of orientation tuning (OT) were investigated in acute experiments on immobilized locally anesthetized cats during response development in 40 neurons of the primary visual cortex before and after Nembutal injection. The range of OT scanning decreased in 53.8% of neurons after Nembutal administration (on the average, by 53.4±5.1°; P<0.001); the phenomenon disappeared completely in some neurons. After Nembutal anesthesia, scanning in 20.5% of units either increased or started up in cases of its absence. The scanning range remained constant in 25.6% of neurons. The mentioned changes in the scanning range were consistently more accentuated in cells for which the preferred orientation, as estimated by standard criteria, was shifted under narcosis than in cells invariant to general anesthesia. In the latter group, units with an unchanged scanning range occurred four times more often at all stages of the experiment as against the group of unstable neurons.Translated from Neirofiziologiya, Vol. 25, No. 2, pp. 141–146, March–April, 1993.     

Double orientation tuning of neurons in the primary cortex of cat at different levels of alertness

Orientation tuning (OT) of 225 cat neurons of the primary visual cortex (field 17) to the flashing of a light bar in the discharge centers of their receptive field (RFs) were investigated. It was found that 43% of the cells investigated were monomodally tuned, i.e., were primarily detecting horizontal and vertical orientations. The remaining 57% of the neurons exhibited double OT, i.e, exhibited, in addition to a main preferred orientation (PO), an additional preferred orientation (aPO) at a right or acute angle to the main orientation (the mean angle between the two OT maxima equalled 71.4±2.4°). In bimodal cells, the additional maximum of OT was comparable in magnitude to the main maximum (averaging 0.7±0.03 of the PO) in half the cases. The orientational properties of the main and additional maxima were almost indistinguishable. Under light or moderate anesthesia, approximately half the neurons with double OT became monomodal; at the same time, a small fraction of monomodal cells (12%) manifested double OT. Under anesthesia, the angle between two the preferred orientations decreased, while the ratio of amplitude characteristics remained unchanged. Monomodal neurons frequently exhibited simple RFs and OTs unaffected by anesthesia. Neurons with double OT, on the other hand, exhibited simple and complex types of RFs just as often and their OT changed under the influence of anesthesia. It is suggested that neurons with double OT can function as detectors of angles and angles of intersecting lines; such angles, together with line orientation, are important attributes of images. In contrast, monomodal neurons may provide a benchmark for a stable reference system of orientation coordinates. The interaction of the two neuronal systems mentioned may allow effective analysis of image attributes at the level of the primary visual cortex.Institute of Higher Nervous Activity and Neurophysiology, Russian Academy of Sciences Moscow. Translated from Neirofiziologiya, Vol. 24, No. 3, pp. 260–269, May–June, 1992.     

Bicuculline and orientation tuning of neurons of the visual cortex

Orientation tuning (OT) of 68 visual cortex neurons (field 17) was studied in cats under conditions of a GABA-ergic inhibition blockade by microiontophoretic bicuculline applications; the neuronal responses were evoked by flashing light strips. All characteristics of orientational detection in most neurons got worse after the applications. The OT became wider in 76.3% of cases: its mean value increased from 52.7±2.8° to 85.2±4.6°. In 63.6% of cases OT selectivity decreased by one-third, and in 68.5% of neurons the detection quality decreased by 60%, on average. The threshold dose of bicuculline causing the OT extension was injected by the phoretic current of 31.0±4.5 nA, and the optimum effect was reached at 67.1±6.0 nA. The background activity and the response magnitude increased under the bicuculline influence 3.0 and 4.4 times, respectively, compared with the control. A few minutes after the iontophoresis termination, the frequency of neuronal discharges and OT characteristics returned to their initial values. We conclude that the local blocking of intracortical inhibition, which causes disinhibition of afferent inputs from the neighboring cells with different (compared with the recorded cell) preferred orientations, considerably worsens orientational specificity of visual cortex neurons, or even results in a complete loss of such specificity. These data are consistent with the concept that intracortical inhibition plays a leading role in the formation and sharpening of OT in the visual cortex neurons.Neirofiziologiya/Neurophysiology, Vol. 27, No. 1, pp. 54–62, January–February, 1995.     

Ongoing activity in identified neurons of the rat superior cervical ganglion before and after partial denervation of the submandibular gland

Ongoing activity was investigated in rat superior certical ganglion neurons innervating the submandibular gland using intracellular recording techniques. These cells had previously been labelled by fluorescent marker. Ongoing activity was found in 11% of test cells, with a firing rate of 0.1±0.01 Hz. No ongoing activity occurred in the remainder (89% out of 95). Following an experimentally induced reduction in the number of neurons innervating the gland (which had previously been partially denervated), numbers of cells manifesting ongoing activity rose significantly (from 11 to 42%) and ongoing spike rate rose, at 0.3±0.03 Hz. These changes in neurons innervating the partially denervated gland are thought to result from increased convergence on these neurons of influences from preganglionic fibers.Studies carried out at the Anatomy and Neurobiology Department of Washington University Medical School (St. Louis, USA).A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 6, pp. 826–832, November–December, 1989.     

Different properties of two groups of orientation discriminators in the cat visual cortex

The properties of 149 neurons, divided into two groups, were investigated during acute experiments on immobilized cats. These consisted of "timers" (37%) in which latency of response and time taken for reaction to peak changed in an orientation range of not more than 10 msec. The remaining 63% consisted of "scanners" [2]. "Timers" reliably differed from "scanners" in their shorter latent periods, rising time of discharge rate, duration of response, and higher rate of impulsation at all orientations of the stimulus. "Scanners" display greater orientational tuning and "scan" much more frequently throughout the orientation range. The pattern of acuity of orientational tuning is counterphasic during response in neurons of these two groups, while the distribution of their preferred orientation is complementary in nature. Both timers and scanners were found in the orientation columns of the visual cortex on most occasions, with the latter predominating. Columns consisting of only timers or scanners were met with more seldom. The significance of the differences between the properties of the two groups of neurons in the visual cortex is discussed with a view to orientational discrimination.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 18, No. 1, pp. 85–92, January–February, 1986.     

Dynamics of orientational tuning of cat visual cortical neurons

Orientational tuning of primary visual cortical unit activity was investigated in acute experiments on cats immobilized by a muscle relaxant, by the time slices method. Poststimulus histograms of responses of a neuron to presentation of a flashing bar of light in the center of its receptive field, with different orientations, were plotted; graphs of orientational tuning with respect to mean discharge frequency in consecutive time cuts of the responses with a 10 or 20 msec step were then plotted. Orientational tuning in all cortical neurons studied exhibited considerable dynamic changes in sharpness and preferred orientation. In two thirds of cells an effect of scanning a certain part of the range of orientations was observed, in the form of a successive shift of the maximum of the orientational tuning curve from some preferred orientations to others was discovered. The possible functional significance of spike discharges of visual cortical neurons is discussed.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 13, No. 5, pp. 451–459, September–October, 1981.     

Response in tonic type neurons of the cat auditory cortex to tones of different frequencies and intensities

In experiments on immobilized cats, intra- and extracellular response in tonic type neurons to tones of differing frequencies and intensities were investigated, as well as the organizational pattern of receptive fields in these units. Tonic type neurons were encountered at different cortical layers, but mostly (93% of the total) were located at a depth of 1.0–2.2 mm. Minimum thresholds required for response in these neurons were on average 7.7 dB below that found in neurons generating a phasic reaction in response to a tone. "Tonic" differed from "phasic" neurons in their inferior frequency-discriminative ability, with a Q₁₀ value averaging 4.1±0.4 as against 9.1±0.7 in phasic neurons. Size of receptive fields in tonic neurons (as revealed by occurrence of spike response in these units) was 3.5 times that observed in phasic cells. Length of action potentials in the majority (80%) of tonic neurons was about one and a half times to twice that found in phasic units. Tonic neurons also displayed a high degree of sensitivity to changes in the duration and intensity of acoustic stimulation.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 4, July–August, pp. 498–506, 1969.     

"Timers" and "scanners" among orientation detectors in cat visual cortex

Experiments were carried out on immobilized cats to determine whether, among visual cortical neurons, besides the "scanners" described by the writers previously, which are responsible for a dynamic shift of preferred orientation, there exist also "timer" cells, which do not change the temporal parameters of their responses during rotation of a flashing stimulus. The existence of such cells is postulated on the basis of the previous hypothesis on the spatiotemporal principle of orientational coding. Of 76 neurons tested 27, i.e., 36%, were classed as "timers." They differed significantly from the "scanners" (64%) by the following properties: shorter latent periods, shorter time to the peak and duration of responses, more rapid rise of discharge frequently in the volley. The "timers" had less sharp orientational tuning and a low ratio between values of responses to presentation of preferred and worst stimuli (on account of a considerable increase in responses to unpreferred orientations). The set of preferred orientations of the "timers" was found to be highly selective and additional relative to the corresponding distribution for "scanners."The difference in frequency-temporal properties of responses and orientational tuning of the "timers" and "scanners" and their possible mutually complementary role in orientational coding at the visual cortical level are discussed.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 17, No. 1, pp. 35–43, January–February, 1985.     

Characteristics of background unit activity in the nucleus reticularis of the human thalamus

Background firing activity was examined in 240 neurons belonging to the thalamic nucleus reticularis (Rt) in the unanesthetized human brain by extracellular microelectrode recording techniques during stereotaxic surgery for dyskinesia. The cellular organization of Rt was shown to be nonuniform, and distinguished by the presence of three types of neuron: one with arrhythmic single discharge (A-type, 40%), another with rhythmic (2–5 Hz) generation of short high-frequency (of up to 500/sec) burster discharges (B-type, 49%) and a third with aperiodic protracted high-frequency (of up to 500/sec) bursting discharges separated by "silent" intervals of a constant duration of 80–150 msec (i.e., C-type, 11%). Differences between the background activity pattern of these cell types during loss of consciousness under anesthesia are described. Tonic regulation of neuronal type was not pronounced but a tendency was noticed in the cells towards a consistent rise in firing rate, rhythmic frequency and variability, etc. in both A and B units, especially in the latter. Findings pointing to the absence of a direct relationship between rhythmic activity in the Rt and parkinsonian tremor were confirmed. Background activity in B-type cells was found to increase and then stabilize with a rise in the degree of tremor. The nature of regular bursting activity patterns in B and C neurons is discussed in the light of our findings.Institute of Chemical Physics, Academy of Sciences of the USSR, Moscow. Institute of Neurosurgery, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 19, No. 4, pp. 456–466, July–August, 1987.     

Effect of somatostatin on neurons of the partially deafferented rabbit amygdala

Changes in spontaneous activity of 291 neurons in the rabbit amygdala were analyzed during microelectrophoretic application of somatostatin under pentobarbital anesthesia. Somatostatin was found both to enhance and to inhibit the spontaneous activity of these cells, by contrast with the exclusively inhibitory effect on spontaneous activity of hypothalamic neurons described previously. After partial chronic deafferentiation of the amygdala, 76% of 103 neurons responded to somatostatin application; 90% of the responding cells, in which the initial spontaneous firing rate was 6–20 spikes/sec, responded by more rapid firing, and only 10% of neurons (with an initial spontaneous discharge frequency of over 20 spikes/sec) showed a decrease in firing rate. Neuronal responses in the amygdala to somatostatin, glutamate, and noradrenalin are compared. Preliminary application of noradrenalin caused an increase in the number of inhibitory responses on subsequent application of somatostatin to the same cell.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 14, No. 6, pp. 601–607, November–December, 1982.     

Cerebral impedance with different kinds of anesthesia

Values of specific impedance of the cat's cerebral cortex were measured in the awake state and under various kinds of anesthesia (epontol, sodium thiopental, and ether). Measurements were taken at a frequency of 1 kHz using Ranck's four-electrode method. It was found that the development of general anesthesia was not accompanied by definite changes in impedance (±4%). The fact that substantial functional changes in cortical neurons such as these do not lead to changes in impedance can be explained by the relative independence of total cortical impedance from the membrane resistance of nerve cells. The quite small phase difference (5°) between the measuring current and the potential difference recorded in the cortex proves that the current passes virtually through the intercellular space only. The impedance of the cerebral cortex was assumed to be an entity essentially unrelated to the functional state of the cortex; the impedance cannot therefore determine the amplitude changes of the electrocorticogram (ECoG) recorded. The magnitude of cortical specific impedance was found to be 258 ±10·cm.A. V. Vishnevskii Institute of Surgery, Academy of Medical Sciences of the USSR. Moscow Physicotechnical Institute. Translated from Neirofiziologiya, Vol. 3, No. 3, pp. 260–265, May–June, 1971.     

Effects of temperature on the properties of primary auditory fibres of the spectacled caiman,Caiman crocodilus (L.)

Summary The effect of temperature on the response properties of primary auditory fibres in caiman was studied. The head temperature was varied over the range of 10–35 ° C while the body was kept at a standard temperature of 27 °C (T_s). The temperature effects observed on auditory afferents were fully reversible. Below 11 °C the neural firing ceased.The mean spontaneous firing rate increased nearly linearly with temperature. The slopes in different fibres ranged from 0.2–3.5 imp s^–1 °C^–1. A bimodal distribution of mean spontaneous firing rate was found (<20 imp s^–1 and >20 imp s^–1 at T_s) at all temperatures.The frequency-intensity response area of the primary fibres shifted uniformly with temperature. The characteristic frequency (CF) increased nearly linearly with temperature. The slopes in different fibres ranged from 3–90 Hz °C^–1. Expressed in octaves the CF-change varied in each fibre from about O.14oct °C^–1 at 15 °C to about 0.06 oct °C^–1 at 30 °C, irrespective of the fibre's CF at T_s. Thresholds were lowest near T_s. Below T_s the thresholds decreased on average by 2dB°C^–1, above T_s the thresholds rose rapidly with temperature. The sharpness of tuning (Q_10db) showed no major change in the temperature range tested.Comparison of these findings with those from other lower vertebrates and from mammals shows that only mammalian auditory afferents do not shift their CF with temperature, suggesting that a fundamental difference in mammalian and submammalian tuning mechanisms exists. This does not necessarily imply that there is a single unifying tuning mechanism for all mammals and another one for non-mammals.Abbreviations BF best frequency: frequency of maximal response at an intensity 10 dB above the CF-threshold - CF characteristic frequency - FTC frequency threshold curve, tuning curve - T _s standard temperature of 27 °C     

Optimized protocol for the pilot-scale preparation of fungal cellulase

Summary A 25-l scale protocol is devised for the optimal secretion and recovery of fungal cellulase. Using a selected higher yieldingTrichoderma viride SMC strain, a protocol consisted of: a) an optimized production medium rich in microcrystalline cellulose (MCC), fortified with 1% (w/v) ammonium sulphate, 0.5% (w/v) soybean flour, 0.1% (v/v) Tween-80 and other trace nutrients; b) optimized physical parameters of production, such as an inoculum containing a homogeneous suspension of 6×10⁷ conidia per 1,28±1°C, pH 4.0±0.5, 300±20 rpm, 11000±1000 l/h aeration, and 170–220 h duration; c) optimal recovery through a filter press (450 l/h rate of filtration) followed by precipitation with 2.5–3.0 volumes of acetone (15°C and basket centrifugation (27°C, 1700 rpm)); and d) vacuum drying (35°C, 4–6 h). This afforded 70% recovery of cellulase in the form of white fluffy powder containing 20000±2000 carboxy methyl cellulase and 1000±50 units filter paperase per g activities, with raw material cost of US$ 8–10 per million carboxy methyl cellulase units. During storage for 18 months at 4°C, ambient temperature and 37°C, the cellulase preparation was found to retain 100, 75 and 60% of its initial activity, respectively.     

Structure of spike activity of cold thermoreceptors at its various levels

In acute experiments on anesthetized rabbits we investigated the spike activity of cold fibers of the infraorbital nerve during a steady decrease in skin temperature from 39 to 7°C at a rate of 0.8 ± 0.05°/min. Analysis of interspike intervals (ISI) in the firing of receptors demonstrated that in the investigated range of skin temperatures the ISI histograms changed significantly several times, reflecting a shift in the pattern of firing. In addition, the reactions of each cold thermoreceptor had individual aspects, which lays the foundation for discussion of the perception of various characteristics of the temperature stimulus of the set of thermoreceptors.I. P. Pavlov Physiology Institute, Russian Academy of Sciences, Saint Petersburg. Translated from Neirofiziologiya, Vol. 24, No. 5, pp. 559–566, September–October, 1992.     

Spatio-temporal convergence (STC) in otolith neurons

It has been recently demonstrated that some primary otolith afferents and most otolith-related vestibular nuclei neurons encode two spatial dimensions that can be described by two vectors in temporal and spatial quadrature. These cells are called broadly-tuned neurons. They are characterized by a non-zero tuning ratio which is defined as the ratio of the minimum over the maximum sensitivity of the neuron. Broadly-tuned neurons exhibit response gains that do not vary according to the cosine of the angle between the stimulus direction and the cell's maximum sensitivity vector and response phase values that depend on stimulus orientation. These responses were observed during stimulation with pure linear acceleration and can be explained by spatio-temporal convergence (STC) of primary otolith afferents and/or otolith hair cells. Simulations of STC of the inputs to primary otolith afferents and vestibular nuclei neurons have revealed interesting characteristics: First, in the case of two narrowly-tuned input signals, the largest tuning ratio is achieved when the input signals are of equal gain. The smaller the phase difference between the input vectors, the larger the orientation differences that are required to produce a certain tuning ratio. Orientation and temporal phase differences of 30–40° create tuning ratios of approximately 0.10–0.15 in target neurons. Second, in the case of multiple input signals, the larger the number of converging inputs, the smaller the tuning ratio of the target neuron. The tuning ratio depends on the number of input units, as long as there are not more than about 10. For more than 10–20 input vectors, the tuning ratio becomes almost independent of the number of inputs. Further, if the inputs comprise two populations (with different gain and phase values at a given stimulus frequency), the largest tuning ratio is obtained when the larger population has a smaller gain. These findings are discussed in the context of known anatomical and physiological characteristics of innervation patterns of primary otolith afferents and their possible convergence onto vestibular nuclei neurons.     

Response of trigeminal ganglion neurons to thermal stimulation of the beak in pigeons

Summary The activity of neurons from the trigeminal ganglion of pigeons have been recorded while cooling or warming the beak. Thermosensitive neurons were seldom compared with mechanosensitive units. From a total of 16 thermosensitive neurons, 13 were excited by cooling and 3 by warming. The impulse frequency strongly depended on temperature. At constant temperatures, constant firing rates were established. The static curves of cold-sensitive units showed, that with decreasing temperature a nearly linear rise in firing rate occurred between about 36 °C and 20 °C. One quantified, warm-sensitive neuron showed, with increasing temperature, a nearly linear rise between about 35 °C and 44 °C. Sudden cooling or warming caused no pronounced overshoot as in mammals. Six cold-sensitive neurons were totally inhibited by rewarming as were 2 warm-sensitive units by cooling. No comparable influence of temperature on the discharge rate of some slowly-adapting mechanoreceptors (pressure stimulus) was exhibited.Supported by the Deutsche Forschungsgemeinschaft (SFB Bionach).     

Interaction between central and peripheral temperature signals on temperature-sensitive hypothalamic neurons

Changes in the mean firing rate of posterior hypothalamic neurons were studied in experiments on unanesthetized cats in response to elevation of the brain temperature by 0.7–1.5°C and the skin temperature by 3–5°C separately or simultaneously. Altogether 85 neurons were studied in 14 animals: 11 responded to only one form of temperature stimulation, whereas in 16 neurons changes in the firing pattern (in most cases in the same direction) were observed in response to both forms of temperature stimulation. Different types of responses of these neurons were established. Sensitivity to the central temperature stimulus was increased in some neurons of this group when skin temperature stimulation was intensified.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 8, No. 6, pp. 613–619, November–December, 1976.     

Lack of effect of thrombin on fibrin(ogen)-endothelial cell interaction

In the present study we investigate the fibrin(ogen)-endothelial cell binding and the effect of thrombin on the endothelial cells in relation to fibrin(ogen) binding capacity. Endothelial cell fibrinogen binding was concentration and time-dependent, reaching saturation at 1.4 M of added ligand. At equilibrium, the number of fibrinogen molecules bound per endothelial cell in the monolayer was 5.8±0.7×10⁶. When endothelial cells were activated by different concentrations of thrombin (0–0.1 NIH units ml^–1), no increase in fibrinogen binding capacity was observed at all the thrombin concentration tested. Whereas disruption of endothelial cell monolayers was observed at thrombin concentrations higher than 0.05 NIH units ml^–1, no increase in the amount of fibrinogen bound was observed. Therefore, resting and thrombin-activated endothelial cells show the same fibrinogen binding capacity.The adhesion of endothelial cells in suspension on immobilized fibrinogen or fibrin was studied to ascertain whether the behavior of fibrin is similar to that of fibrinogen. The extent of endothelial cell attachment to immobilized fibrinogen and fibrin was similar (4275±130 cells cm^–2 for fibrinogen and 4350±235 cells cm^–2 for fibrin) and represent approximately 40% of the added endothelial cells. However, endothelial cell adhesion to immobilized fibrin was significantly faster than endothelial cell adhesion to immobilized fibrinogen. The maximum binding rate was 66±9 and 46±8 cells cm^–2 min^–1 for fibrin and fibrinogen, respectively. Therefore, the fibrinopeptides released by thrombin from fibrinogen induce qualitative changes which enhance the fibrin interaction with the endothelial cells.