Responses of afferent and efferent neurons to auditory inputs in the vestibular nerve of the frog

Summary In the frog, the spontaneous discharges of afferent fibres from the horizontal semicircular canal (HC) and of efferent vestibular units were recorded by means of glass micropipettes filled with 2 mol/l NaCl as well as during acoustic stimulation; pure tones 300–2,000 Hz and clicks 150/s, 80–100 dB re 10^–5 N/m² were used. The activity of 56% of the efferent fibres recorded was increased by such stimulations while the discharge of the others was not modified. In intact preparations the activity of 34.4% of the afferent fibres recorded was either increased or decreased by sound stimulation depending on the unit; the discharge of the others (65.6%) was not modified (Fig. 3). Section of both saccular nerves did not change the percentage of the units modulated by sound showing that the saccules have probably no effect on this modulation (Fig. 4). In preparations where the contralateral auditory papillae were eliminated, 21.1% of the afferent units were facilitated and no unit was inhibited (Fig. 5), while in preparations where the ipsilateral auditory organs were eliminated 21.1% of the afferent units were inhibited and no unit was facilitated (Fig. 6). Therefore, in intact preparations one can assume that decrease and increase of the HC afferent fibre discharges were due to stimulation of the contralateral and the ipsilateral auditory organs, respectively. Such a modulation of canal afferent discharges being mediated by efferent vestibular fibres, it can be postulated that the efferent vestibular system has a double influence upon the hair cells of the vestibular epithelium: one inhibitory and the other facilitatory. Such a double effect is discussed.Abbreviations EVS efferent vestibular system - HC horizontal semicircular canal     

Movement sensitivities of cells in the fly's medulla

Summary Intracellular recordings were made in the medullae of intact, restrained females ofCalliphora vicina that faced a hemispherical, minimum-distortion surface upon which moving patterns and spots were projected from the rear (Fig. 2). In the distal medulla, noisy hyperpolarizations to light, most likely recorded in terminals of laminar (L) cells, had flicker-like oscillations to moving gratings of 15° spatial wavelength but not of 2.5° spatial wavelength (Fig. 3). Medullary (M) cells penetrated distally responded to grating movements with similar but depolarizing oscillations, in one cell 180° out of phase with a nearby laminar response (Figs. 4–6).A characteristic movement response recorded from most medullary cells consisted of abrupt, maintained nondirectional depolarizations in response to movements of gratings, often with directional ripple or spikes superimposed. When directions of movement reversed, there were brief repolarizations, but when movements stopped, depolarizations decayed away more slowly (Figs. 7 and 8). Magnitude of responses increased with increasing speeds of both 15° and 2.5° gratings (Figs. 9–11). In some cells, there were delayed decays of responses after stopping (Fig. 12). Still other cells seemed to receive inhibition from other, characteristically responding cells (Fig. 13).Receptive fields tested were simple and usually large, with only a suggestion of surround inhibition (Fig. 14). In general, intensity and position were interchangeable over a cell's receptive field (Figs. 15 and 16). Moving edges and dark spots elicited responses primarily within receptive field centers (Figs. 18–20).It is argued that waveforms of characteristic movement responses can be explained by multiplicative inputs from L- and M-cells to movement detectors (Figs. 21–26).Abbreviations L cells laminar (monopolar) cells - M cells medullary cells     

Effects of tractotomy on reflex activity in the lumbar segment of the rat spinal cord previously disrupted by severing the sciatic nerve

Evoked electrical discharges in the spinal cord roots and dorsal surface ipsilateral to the previously severed sciatic nerve (as well as on the contralateral side) were investigated in rats one, three, seven, and 14 days after tractotomy. Monosynaptic reflex discharges in the ventral roots were found to return to 20–40% of the level of this parameter as measured on the contralateral side within seven and 14 days after tractotomy. Mean amplitude of antidromic dorsal root discharges, afferent peak, and the N₁ component of potential(s) at the dorsal surface ipsilateral to the severed nerve barely altered, remaining significantly lower than on the contralateral side. Mechanisms are suggested for the increase in monosynaptic reflex ventral root discharges ipsilateral to the severed nerve following tractotomy — thought to be largely due to raised sensitivity to transmitter at the motoneuronal membrane resulting from degeneration of synapses of descending pathways.Medical Institute of the Ukrainian Ministry of Health, Dnepropetrovsk. Translated from Neirofiziologiya, Vol. 21, No. 3, pp. 366–371, May–June, 1989.     

Mechanisms of interaction between central neurons and abdominal stretch receptors in the crayfish

Mechanisms of interaction between central and receptor neurons of the crayfish (the principal inhibitory neuron — PIN — and the slow-adapting stretch receptor — SAR) when functioning under different conditions were investigated: during regular spontaneous activity of SAR, grouped discharges of PIN, and regular spontaneous activity of PIN. A close connection was found between the various parameters of the PIN and SAR responses. Adaptation of SAR to the action of adequate, regular repetitive stimulation takes place faster in the presence of stationary background activity of PIN. The appearance and disappearance of SAR spike activity are determined by the ratio between the firing rates of SAR and PIN: at the moment of changeover the neuron with the higher firing rate is predominant.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Institute of Zoology, Academy of Sciences of the Moldavian SSR, Kishinev. Translated from Neirofiziologiya, Vol. 4, No. 4, pp. 429–438, July–August, 1972.     

SPONTANEOUS AND STIMULATED BIOLUMINESCENCE OF THE DINOFLAGELLATE CERATOCORYS HORRZDA (PERIDINIALES)1

This is the first report of spontaneous bioluminescence in the autotrophic dinoflagellate Ceratocorys horrida von Stein. Bioluminescence was measured, using an automated data acquisition system, in a strain of cultured cells isolated from the Sargasso Sea. Ceratocorys horrida is only the second dinoflagellate species to exhibit rhythmicity in the rate of spontaneous flashing, flash quantum flux (intensity), and level of spontaneous glowing. The rate of spontaneous flashing was maximal during hours 2–4 of the dark phase [i.e. circadian time (CT)16–18 for a 14:10 h LD cycle (LD14:10)], with approximately 2% of the population flashing-min^?1, a rate approximately one order of magnitude greater than that of the dinoflagellate Gonyaulax polyedra. Flash quantum flux was also maximal during this period. Spontaneous flashes were 134 ms in duration with a maximum flux (intensity) of 3.1×10⁹ quanta-s^?1. Light emission presumably originated from blue fluorescent microsources distributed in the cell periphery and not from the spines. Values of both spontaneous flash rate and maximum flux were independent of cell concentration. Isolated cells also produced spontaneous flashes. Spontaneous glowing was dim except for a peak of 6.4× 10⁴quanta-s^?1 cell^?1, which occurred at CT22.9 for LD14:10 and at CT22.8 for LD12:12. The total integrated emission of spontaneous flashing and glowing during the dark phase was 4×10⁹ quantacell^?1, equivalent to the total stimulable luminescence. The rhythms for C. horrida flash and glow behavior were similar to those of Gonyaulax polyedra, although flash rate and quantum flux were greater. Spontaneous bioluminescence in C. horrida may be a circadian rhythm because it persisted for at least three cycles in constant dark conditions. This is also the first detailed study of the stimulated bioluminescence of C. horrida, which also displayed a diurnal rhythm. Cultures exhibited >200 times more mechanically stimulated bioluminescence during the dark phase than during the light phase. Mechanical stimulation during the dark phase resulted in 6.7 flashes. cell^?1; flashes were brighter and longer in duration than spontaneous flashes. Cruise-collected cells exhibited variability in quantum flux with few differences in flash kinetics. The role of dinoflagellate spontaneous bioluminescence in the dynamics of near-surface oceanic communities is unknown, but it may be an important source of natural in situ bioluminescence.     

Neuronal architecture of the central complex in Drosophila melanogaster

Summary On the basis of 1200 Golgi-impregnated brains the structure of the central complex of Drosophila melanogaster was analyzed at the cellular level. The four substructures of the central complex — the ellipsoid body, the fanshaped body, the noduli, and the protocerebral bridge — are composed of (a) columnar small-field elements linking different substructures or regions in the same substructure and (b) tangential large-field neurons forming strata perpendicular to the columns. At least some small-field neurons belong to isomorphic sets, which follow various regular projection patterns. Assuming that the blebs of a neuron are presynaptic and the spines are postsynaptic, the Golgi preparations indicate that small-field neurons projecting to the ventral bodies (accessory area) are the main output from the central complex and that its main input is through the large-field neurons. These in turn are presumed to receive input in various neuropils of the brain including the ventral bodies. Transmitters can be attributed immunocytochemically to some neuron types. For example, GABA is confined to the R1–R4 neurons of the ellipsoid body, whereas these cells are devoid of choline acetyltransferase-like immunore-activity. It is proposed that the central complex is an elaboration of the interhemispheric commissure serving the fast exchange of data between the two brain hemispheres in the control of behavioral activity.     

Peculiarities of summation processes in visual-sensitive neurons in the pretectal area of cat

Summation processes occurring in single neurons of the pretectal area in response to either moving or stationary light stimuli were studied in acute experiments on cats. In most neurons studied (85%), gradual increase of the angular size of stimulus resulted in clearly defined summation. In neurons lacking directional sensitivity (nondirectional neurons) the stimulus movement in two opposite directions caused, as a rule, similar and symmetrical changes in the number of spikes, whereas under the same conditions direction-sensitive neurons, in addition to symmetrical development of summation processes, could exhibit substantial differences in the summation curves. The responses to a preferred movement direction could be significantly inhibited or facilitated, while the responses to a non-preferred direction remained stable or changed reciprocally. Neuronal responses to different directions of the movement of stimulus might change independently of each other. This was also the case whenon andoff responses of theon—off neurons to stationary stimuli were compared. It is concluded that neurons of the pretectal area have a complex infrastructure of receptive fields that significantly influences the integration of incoming information.Neirofiziologiya/Neurophysiology, Vol. 25, No. 5, pp. 376–382, September–October, 1993.     

Direct high-performance liquid chromatographic resolution of the enantiomers of tiaprofenic acid using immobilized human serum albumin

Resolution of racemic tiaprofenic acid (TA) has been performed using immobilized human serum albumin as the stationary phase. The eluent was phosphate buffer—acetonitrile—n-octanoic acid (90:10:0.015, v/v). Detection was achieved at 305 nm. The pharmacokinetics of the enantiomers were studied following oral administration into humans and after subcutaneous injection in rats. Plasma concentrations of (+)-TA were much greater than those of (−)-TA. For the rat, the pharmacokinetic parameters between (−)-TA and (+)-TA were all statistically different (p < 0.005).     

Proprioceptors and sensory nerves in the legs of a spider,Cupiennius salei (Arachnida,Araneida)

Summary Retrograde CoS-impregnation was used to trace and map the course of sensory nerves and the distribution and innervation of the various proprioceptor types in all leg segments of Cupiennius salei, a Ctenid spider.1. Sensory nerve branches. In both the tibia and femur, axons of all proprioceptor types ascend in just two lateral nerves which do not merge with the main leg nerve until they reach the next proximal joint region. In the short segments — coxa, trochanter, patella, and tarsus — axons of the internal joint receptors often run separately from those of the other sensilla. Axons of the large lyriform slit sense organ at the dorsal metatarsus and of the trichobothria join with only a few hair axons and form their own nerve branches (Figs. 1, 2, 3).2. Proprioceptors. Each of the seven leg joints is supplied with at least one set of the well-known internal joint receptors, slit sensilla (single slits and lyriform organs), and long cuticular hairs. In addition, we found previously unnoticed hair plates on both sides of the coxa, near the prosoma/coxa joint; they are deflected by the articular membrane during joint movements (Fig. 4).3. Sensory cells and innervation. CoS-impregnation shows that each slit of the slit sense organs — be it a single slit or several slits in a lyriform organ — is innervated by two bipolar sensory cells (Fig. 6). We also confirm previous reports of multiple innervation in the internal joint receptors and in the long joint hairs and cuticular spines.Most of the ascending nerve branches run just beneath the cuticle for at least a short distance (Fig. 5); hence they are convenient sites for electrophysiological recordings of sensory activity even in freely walking spiders.     

Protein- und RNS-Gehalt des Hypokotyls beim stationären Wachstum im Dunkeln und unter dem Einfluß von Phytochrom (Keimlinge von Sinapis alba L.)

Zusammenfassung Das Wachstum des Hypokotyls wurde an Restkeimlingen ohne Kotyledonen (Abb. 1) untersucht. Die Wachstumsgeschwindigkeit ist in dem von uns untersuchten Zeitraum sowohl im Dunkeln als auch unter dem Einfluß von P₇₃₀ (Dauer-Dunkelrot) praktisch konstant. Obgleich sich die Wachstumsgeschwindigkeiten im Dunkeln und im Dauer-Dunkelrot um den Faktor 4 unterscheiden, hat das Dunkelrot keinen signifikanten Einfluß auf den Gesamt-Proteingehalt des Hypokotyls (bzw. der durchschnittlichen Hypokotylzelle). Der Proteingehalt nimmt im Dunkeln und im Licht kontinuierlich ab. Auch der Gesamt-RNS-Gehalt zeigt innerhalb des Versuchszeitraums eine Abnahme, die unter dem Einfluß von Dunkelrot früher einsetzt als im Dunkeln. — Man kann aus den Daten der vorliegenden Arbeit schließen, daß nur ein kleiner Teil des Gesamt-Proteins und der Gesamt-RNS einer Zelle mit dem Zellwachstum unmittelbar in Verbindung gebracht werden kann.

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Protein and RNA contents of the hypocotyl during steady state growth lengthening in the dark and under the influence of phytochrome (seedlings of sinapis alba L.)

Summary Inhibition of hypocotyl lengthening by phytochrome can be regarded as a prototype of a negative photoresponse. The hypothesis has been advanced (Schopfer, 1967) that negative photoresponses are the consequence of a differential gene repression which is exerted by P₇₃₀, the active phytochrome. This hypothesis is mainly based on experiments with specific inhibitors of RNA- and protein synthesis. —The present paper is part of an experimental program which has been designed to check this hypothesis.—Continuous irradiation with standard far-red has been used to establish a virtually stationary concentration of P₇₃₀ over the whole period of experimentation (36–60 hours after sowing). To correlate more strictly the growth response of the hypocotyl with molecular changes in this organ the axis system without cotyledons has been used (Fig. 1). Even under these conditions the growth rate of the hypocotyl is nearly constant in light (continuous far-red) and dark during the whole period of experimentation (36–60 hours after sowing) (Fig. 2, 3). It is known from earlier experiments that cell division in the hypocotyl are very rare during this period and that there is virtually no increase in the DNA contents of the organ during the period of our experimentation (Weidner, 1967). Obviously the number of cells per hypocotyl is virtually constant between 36 and 60 hours after sowing. Organ (i.e. hypocotyl) lengthening is nearly exclusively due to cellular lengthening.—If we follow the protein contents of the hypocotyl we find (Fig. 4) that the total protein of the organ decreases steadily in spite of the fact that the organ grows at a constant rate. There is no significant difference in protein contents between dark-grown and far-red grown systems although the growth rates differ by a factor of 4 (Fig. 2, 3).—The situation is some-what different with respect to total RNA (Fig. 5). The RNA contents eventually decrease in far-red as well as in dark-grown systems but the decrease is significantly faster in the far-red treated systems than in the dark controls.—It is concluded that only a very small part of the total RNA and total protein of a cell can be related to the control of cellular growth. Changes in bulk RNA and bulk protein obviously do not necessarily reflect changes in the growth rate or growth capacity of an organ or a cell.

     

Body movements and retinal pattern displacements while approaching a stationary object in the walking fly,Calliphora erythrocephala

When a walking fly approaches a stationary object two types of body movements are distinguishable. Type I body movements are characterized by low frequencies (0.4–1.3 Hz) and large amplitudes (28–65°). Superimposed on these movements are type II body movements which are characterized by high frequencies (7.3–10.6 Hz) and small amplitudes (5.9–8.2°) (Figs. 3–6; Table 1). Type II movements occur no matter whether the fly is fixating a pattern or orientating itself in homogeneous surroundings without any pattern. In contrast, only 72% of the flies with immobilized heads and 62% of the flies with movable heads make type I body movements. The amplitude of type I and type II body movements increases slightly after immobilization of the head. Binocular as well as monocular pattern projection occurs for the whole walking trajectory (Fig. 7–9). Monocular pattern projection seems to be more frequent in flies with immobilized heads than in those with movable heads. The degree of pattern fluctuations in the visual field of the flies increases slightly along the walking trajectory. Near the starting point in the centre of the arena it amounts to 5–7°, while at the end of the walking trajectory it amounts to 8–10° (Table 2). The following conclusions and hypothesis can be drawn from these experiments. 1. The graph BT for the direction of the fly's logitudinal axis can be approximated by the first derivative of the walking trajectory WT, that means, dWT(x)/dxBT(x) (Fig. 11). 2. The amplitudes of type II body movements are caused by the alternating movements of the legs during forward motion, while type I body movements are classified as exploring movements. During evolution of visually guided behaviour it is possible that blowflies have adapted their elementary movement detector system to type II body movements. 3. The types of pattern projection into the visual field of the fly while approaching an object can be explained by a simple neuronal network characterized by either inhibitory and/or excitatory influences of the visually activated neurones on the motor neurones generating the propulsive forces, that means the forward motion. In addition it is postulated that the large frontal and antero-lateral receptive fields of these neurones are not coupled with the motor centres on the same side of the body (Fig. 12).     

Directionality of antennal sweeps elicited by water jet stimulation of the tailfan in the crayfish Procambarus clarkii

Summary Directionality and intensity dependence of antennal sweeps elicited by water jet stimulation of the tailfan in tethered, reversibly blinded adult and juvenile crayfish (Procambarus clarkii) were analyzed.Resting crayfish keep their antennae at about 50° symmetrically to the longitudinal body axis (Figs. 2 bottom, and 3).In adults, tailfan stimulation elicits synchronous backward sweeps of both antennae, which increase for more caudal stimulus directions (Figs. 2–4 and 5A). Directions differing by 30°–60° are significantly distinguished (Fig. 4). The mean sweep of the ipsilateral antenna significantly overrides that of the contralateral antenna for rostrolateral stimulation at 40–200 mm/s stimulus velocity and lateral to caudolateral stimulation at 40 mm/s and thus lateralization of the stimulus is revealed (Figs. 2 top, 4 and 5A). Mean antennal sweeps at a given stimulus direction and distance increase with increasing stimulus velocity (40–250 mm/s, Fig. 5A).In juveniles, the directional dependence of antennal sweeps is reduced compared to that of adults, while a similar intensity dependence is found (Fig. 5B).The pronounced directionality of the antennal response in adult crayfish vanishes and response latencies increase after reversibly covering the tailfan with a small bag or the telson with waterproof paste (Figs. 6 and 7). Thus, tailfan and especially telson mechanoreceptors play an important role in the localization of water movements elicited by predators or prey behind the crayfish.     

In vivo recordings of neuroendocrine cells (caudo-dorsal cells) in the pond snail

Summary Ovulation and egg-laying behavior in the pond snailLymnaea stagnalis are controlled by the neuroendocrine caudodorsal cells (CDCs), constituting two clusters — one in each cerebral ganglion — totaling about 100 cells. In vitro studies have shown that the CDCs release their products, including the ovulation hormone, during a burst of spiking activity lasting for about 30 min (CDC discharge). This burst can be initiated by repeated intracellular stimulation with depolarizing current pulses, in which case the firing pattern is termed afterdischarge.Using cuff electrodes we recorded extracellularly from the intercerebral commissure, (the neurohaemal area of the CDCs) to study the activity of these cells during spontaneous egg-laying of freely behaving snails.The cuff-implanted snails showed long-lasting spiking activity prior to every bout of egg-laying. These spontaneous long-lasting discharges had several features in common with the intracellularly recorded activity of the CDCs in vitro: the time courses of spike broadening and of firing rates in the cuff-implanted animals were very similar to the characteristic patterns found in the isolated brain. Firing rates were higher and durations were longer in the cuff-implanted animals, however. In vitro, the duration of the discharge could be prolonged appreciably by recording in blood instead of normal saline, indicating that the bathing fluid normally used causes shortening of the CDC discharge. The way in which CDC discharges are triggered is discussed as a possible explanation for the differences in firing rates.The pattern of locomotion during spontaneous egg-laying was largely similar in cuff-implanted and unoperated animals. The level of locomotion was lower in the experimental animals. In addition, the rate of locomotion only partially returned to pre-oviposition levels. This is ascribed to the effect of the operation.It is concluded that the afterdischarge is the natural firing pattern of the caudodorsal cells ofLymnaea, and that this firing pattern constitutes the central event in the egg-laying behavior of this animal.Abbreviations CDC caudodorsal cells - CDCH caudodorsal cell hormone - CDCA caudodorsal cell autotransmitter     

Spread of fast thermowaves through the cerebral cortex produced by visual stimulation

Thermowaves spreading through the cerebral cortex were observed and investigated during acute experiments on white rats using a new technique — that of thermoencephaloscopy (TES) through the intact skull. These waves were induced by regular visual stimulation (at intervals of 1.5–3 min) or by initiating one of the flashes and spread through the cortex along trajectories of five basic types; amplitude of thermowaves: 0.005–0.1°C; length: 10–15 mm; duration 1.2–11.4 sec; velocity: 1–33 mm/sec; extent of pathway: 2–56 mm. They appeared with a high degree of probability (of 0.92) during the interval between 15 sec before and 26 sec after the flash. Numbers of moving waves declined by the point of stimulus application and rose by 7–8 sec after the flash. Waves arose in 50% of cases in the contralateral visual cortex (areas 17 and 18a), spreading to the midline and crossing to the ipsilateral hemisphere (areas 17, 18a, and 7). Local waves moving along a circular trajectory were also discovered in the contralateral visual cortex. Several types of wave, differing in trajectory, also arose in the ipsilateral visual cortex. Mechanisms and possible significance of this effect are examined.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 21, No. 4, pp. 467–475, July–August, 1989.     

Die experimentelle Beeinflussung des Puffmusters von Riesenchromosomen

By treating larvae and prepupae of Ch. thummi with 2 mg/ml oxytetracycline (OTC) about 30 puffs not present in normal development are induced in the salivary gland chromosomes. Already existing puffs become enlarged (cf. Fig. 4). A considerable number of induced puffs appeared in heterozygous condition (cf. Fig. 1a-c). The species Ch. strenzkei does not react in any way to the same treatment. Other inhibitors of protein synthesis such as cycloheximide and chloramphenicole do not influence the puffing pattern in both species. — Animals which had been treated with OTC for 2 hrs show the first signs of puffing. Fully developed OTC-induced puffs are detectable 20 hrs after treatment. At this time the Balbiani rings and the nucleolus are mostly regressed. — Both the induced puffing pattern and the number of heterozygous puffs depend on the genetic constitution of the animals. Animals derived from different locations can be shown to possess different specific spectra of induced puffs. The induced puffing pattern of animals bred from single egg masses is reduced, and heterozygous puffs are rare or absent. — OTC-induced puffs show a strong uptake of tritiated uridine (cf. Fig. 2). Heterozygous puffs are labelled only in the puffed half of the band (cf. Fig. 3).     

Die Wirkung von „Störlicht” auf die Blütenbildung von Sinapis alba L.

Summary The induction of flowering in mustard (Sinapis alba L.) was studied by means of night-breaks (Störlicht). The plants were cultivated under fully controlled conditions: 8000 Lux white light (mixed fluorescent and incandescent) 18°C, 80% relative humidity. Raised under our conditions in short days (8 hours of white light) mustard behaved as a quantitative long-day plant (Fig. 2). Flowering can be promoted by long-day treatment (Fig. 3). The long day (16 hours of white light) can be replaced by a short day plus a night-break. The highest effectiveness of the night-break is found near the middle of the dark period (Figs. 4, 5). —The spectral dependence of flower induction was studied with blue, green, yellow, red (Fig. 1) and far-red light using a 2-hour break near the middle of the dark period. The dose response curves (Fig. 6) and the action spectrum (Fig. 7) indicate a very strong effectiveness in the blue part of the spectrum, a small response in red and yellow light and no response at all in green and far-red light. The participation of phytochrome is indicated (Table 1), but no far-red reversibility could be detected (Table 2). Simultaneous irradiation with red and far-red light yielded significant enhancement effects (Fig. 8). In view of the strong shadowing in the leaves (Figs. 9, 10) these data are interpretable on the basis of phytochrome.     

A discussion of light scattering in the Squilla rhabdom

The fine structure of the Squilla ommatidium suggests that elastic scattering of light may occur in the rhabdom. A detailed study of this phenomenon allows us to interpret the movement of the pigment granules of the retinula cells and the corresponding change of the rhabdom shape in light — and dark — adaptation.     

The effect of nitrogen refeeding on the carbohydrate content into nitrogen-starved cells of Platymonas striata Butcher

Studies on the mean cellular carbohydrate contents of Platymonas striata Butcher under conditions of nitrogen-starvation, and after refeeding these starved cultures with either nitrate or ammonium ions (growing under continuous illumination or with an alternating light/dark regime) have shown that nitrogen-starved cells accumulated abnormal amounts of cellular carbohydrate and that nitrogen refeeding produced a marked drop in the cellular carbohydrate. Cells grown in a light/dark regime accumulated less carbohydrates than those grown in continuous light. The mean cellular carbohydrate levels 16 h after nitrogen refeeding were still much in excess of those of cells grown with normal nutrition. It was therefore suggested that the differences in nitrogen uptakes in this period — when comparing either the uptake of cells grown in continuous light with that of cells grown in a light/dark regime; or when comparing the uptakes of cells presented with either nitrate or ammonium ions and grown in a light/dark regime —cannot be directly due to shortages of carbohydrate for the provision of carbon skeletons for nitrogen assimilation.     

High-performance liquid chromatographic method for the determination of cefpodoxime levels in plasma and sinus mucosa

A selective HPLC method is described for the determination of cefpodoxime levels in plasma and sinus mucosa. Sample preparation included solid-phase extraction with a C₈ cartridge. Cefpodoxime and cefaclor (internal standard) were eluted with methanol and analyzed on an optimised system consisting of a C₁₈ stationary phase and a ternary mobile phase (0.05 M acetate buffer pH 3.8—methanol—acetonitrile, 87:10:3, v/v) monitored at 235 nm. Linearity and both between- and within-day reproducibility were assessed for plasma and sinus mucosa samples. Inter-assay coefficients of variation were lower than 13.6% (n = 10) for plasma (0.2 μg/ml) and lower than 12.4% (n = 5) for sinus mucosa (0.25 μg/g). The quantification limit was 0.05 μg/ml for plasma and 0.13 μg/g for tissue. The method was used to study the diffusion of cefpodoxime in sinus mucosa.     

Relationship between functional characteristics of cat visual cortex neurons,their response to novelty,and short-term memory

In the visual cortex of unanesthetized cats, the number and frequency of discharges in response to a new stimulus differed from the subsequent responses: the first response was more intensive in 34% of the neurons, but in 30% it was inhibited. The phenomenon of short-term memory was detected in 19% of the cells: it was expressed in regeneration of the configuration of response discharges after the cessation of rhythmic stimulation. These peculiarities can be linked with functional organization of the neurons. We divided them into two groups according to their response to photic stimuli. The first group includes short-latent neurons that respond with discharges of the phasic type and that virtually or totally lack spontaneous activity. The second group consists of long-latent neurons with the tonic type of discharges and distinct spontaneous activity. In the overwhelming majority of cases, response to novelty and short-term memory were discovered in neurons of the second group. It is hypothesized that the population of neurons of the first group — having narrower afferent connections — takes part mainly in analysis of properties of a photic stimulus; the population of neurons of the second group participates in information processing at the final and highest level, on which mechanisms of memory and attention are implicated.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 2, No. 6, pp. 611–617, November–December, 1970.