Ionic bases of action potentials in identified flatworm neurones

Summary The ionic bases for generation of action potentials in three types of identified multimodal neurones of the brain ofNotoplana acticola, a polyclad flatworm, were studied. The action potentials were generated spontaneously, in response to water-borne vibrations, or by intracellularly injected current pulses. At least three components comprise the depolarizing excitable phase of the action potentials: (a) a rapidly inactivating TTXsensitive Na⁺ component (Fig. 2); (b) a Ca⁺⁺ component that is unmasked by intracellular TEA⁺ (Figs. 4, 6, 7); (c) a TTX-resistant Na⁺ component (Fig. 8). Two K⁺ currents appear to account for the repolarization phase of the action potentials: (a) a rapid K⁺ current that is blocked by intracellular TEA⁺ (Figs. 4, 7, 8) and (b) a Ca⁺⁺ -activated K⁺ conductance that is blocked by Ca⁺⁺ and Ba⁺⁺ (Fig. 6). Ionic mechanisms in the generation of action potentials in the central multimodal neurones ofNotoplana pharmacologically resemble those in higher metazoans.Abbreviations TTX tetrodotoxin - TEA ⁺ tetraethylammonium ion - LY lucifer yellow - HRP horseradish peroxidase - BRA bilaterally reciprocally arrayed neurons - SC single contralaterally projecting - SIC single ipsilaterally and contralaterally projecting neurons - HAP hyperpolarizing after potential - AHP after hyperpolarization - EGTA ethyleneglycol-bis-(-amino-ethyl ester) N,N-tetra-acetic acid     

The role of retinula cell types in fixation behaviour of walkingDrosophila melanogaster

Summary Fixation behaviour of free walking wild typeDrosophila and various retinal mutants was tested in a circular arena. Optomotor response was also measured as a test of the function of R1-6.ora andsev,ora do not fixate a narrow stripe (10° or 20°, Fig. 1) but are able to orient towards broad stripes (110° or 180°, Fig. 1). The behaviour ofsev is not different from wild type. Fixation behaviour ofw rdgB is similar toora (Figs. 5, 6). The mutantora has a maximum optomotor response at low contrast frequencies (Fig. 2), but the threshold for this response is at least one log unit higher than in wild type orsev (Fig. 8). The light intensity threshold at 550 nm of fixation to a broad stripe (110°) is 1–2 log units higher inora than in wildtype, and 4 log units higher insev,ora and the structural brain mutantVam (Fig. 7).The conclusions are that retinula cells R1-6 mediate fixation to a narrow stripe at high and low ambient light intensities, and to a broad stripe at low ambient light levels. R8, possibly in conjunction with R1-6, contributes to orientation towards broad stripes at high light intensities. This hypothesis is supported by evidence that blue-adapted white-eyed flies are able to orient towards a broad stripe at high blue light intensities (Figs. 9 and 12). Blue adaptation totally eliminates the optomotor response (Figs. 10, 11) and so the optomotor response observed inora at low contrast frequencies (Figs. 2 and 8) is most likely due to the small remnants of the rhabdomeres of R1-6 that remain.Abbreviations PDA prolonged depolarising afterpotential - ERG electroretinogram     

The neurophysiology of larval firefly luminescence: Direct activation through four bifurcating (DUM) neurons

Summary The paired lanterns of the larval fireflyPhoturis versicolor are bilaterally innervated by four dorsal unpaired median (DUM) neurons the somata of which are found in the terminal abdominal ganglion (A8) and which stain with Neutral Red (Fig. 1A). Both intra- and extracellularly recorded activity in these neurons is always associated with a bilateral glow response, or BGR (Figs. 3 and 4). Luminescence cannot be initiated or maintained in the absence of DUM neuron excitation. Furthermore, there is a linear causative relationship between the frequency of DUM neuron activity and the amplitude of the resultant BGR (Figs. 6 and 7).Due to the intrinsic bilateral morphology, firefly DUM neurons may be antidromically activated through either lantern nerve, resulting in the initiation of luminescence in the contralateral lantern (Figs. 8 and 9). This activation is unaffected by high Mg⁺⁺ saline indicating that the DUM neurons provide a direct pathway for conduction through the ganglion (Fig. 9). The DUM neurons receive synaptic input from axons descending through both anterior connectives, however, stimulation of only one connective results in a BGR since excitation is carried to both sides of the periphery through the bilateral axons.Firefly DUM neurons exhibit physiological qualities typical of neurosecretory cells: spikes are characterized by a slow time course and a long and deep afterhyperpolarization (Fig. 10). This is consistent with the observation that spontaneous firing rates are usually below 3 Hz, but nevertheless elicit a strong BGR (Figs. 3 and 5). The physiological evidence presented in this study correlates well with the morphological, pharmacological and biochemical evidence compiled from previous studies, which indicates that the four DUM neurons represent the sole photomotor output from the central nervous system to the larval lanterns. Evidence is discussed which indicates that these effects are mediated throught the release of octopamine, long presumed to be the lantern neurotransmitter. These results, therefore, describe a novel and unexpected role for DUM neurons in regulating an unusual invertebrate effector tissue and further expands the growing list of functions for octopamine in neural control mechanisms.Abbreviations A1-A7 first through seventh abdominal ganglia - A8 terminal abdominal ganglion - DUM dorsal unpaired median - BGR bilateral glow response     

Changes in the auditory system of locusts (Locusta migratoria and Schistocerca gregaria) after deafferentation

Deafferentation experiments during postembryonic development show morphological and/or physiological changes of receptor fibers and of identified auditory interneurons in the CNS of the locusts Locusta migratoria and Schistocerca gregaria after unilateral ablation of one tympanic organ either in the larva or the adult animal.

The function of auditory neurons in cricket phonotaxis

Summary The activity of auditory receptor cells and prothoracic auditory neurons of the cricket,Gryllus bimaculatus, was recorded intracellularly while the animal walked on a sphere or while passive movement was imposed on a foreleg.During walking the responses to simulated calling song is altered since (i) the auditory sensory cells and interneurons discharged impulses in the absence of sound stimuli (Figs. 1, 3) and (ii) the number of action potentials in response to sound is reduced in interneurons (Figs. 2, 3).These two effects occurred in different phases of the leg movement during walking and therefore masked, suppressed or did not affect the responses to auditory stimuli (Figs. 3, 4). Hence there is a time window within which the calling song can be detected during walking (Fig. 5).The extra excitation of receptors and interneurons is probably produced by vibration of the tympanum because (i) the excitation occurred at the same time as the leg placement (Fig. 4), (ii) during walking on only middle and hindlegs, no extra action potentials were observed (Fig. 6), (iii) in certain phases of passive movements receptor cells and interneurons were excited as long as the ipsilateral ear was not blocked (Figs. 8, 9).Suppression of auditory responses seems to be peripheral as well as central in origin because (i) it occurred at particular phases during active and passive leg movements in receptor cells and interneurons (Figs. 1, 4, 9), (ii) it disappeared if the ear was blocked during passive leg movements (Fig. 9) and (iii) it persisted if the animal walked only on the middle and hind legs (Fig. 6).     

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.     

Le contrôle automatique du flux lumineux dans l'oeil composé des Diptères

In the compound eye of the fly Musca, tiny pigment granules move within the cytoplasm of receptor cells Nos. 1–6 and cluster along the wall of the rhabdomeres under light adaptation, thus attenuating the light flux to which the visual pigment is exposed (Kirschfeld and Franceschini, 1969). Two recently developed optical methods (the neutralization of the cornea and the deep pseudopupil) combined with antidromic and orthodromic illumination of the eye (Fig. 1) make it possible to analyse the properties of the mechanism at the level of the single cell, in live and intact insects (Drosophila and Musca). The mechanism is shown to be an efficient attenuator in the spectral range (blue-green) where cells Nos. 1–6 have been reported to be maximally sensitive (Figs. 4c and d, 5b and 11b). In spite of the fact that the granules do not penetrate into the rhabdomere, the attenuation spectrum they bring about closely matches the absorption spectrum of the substance of which they are composed (ommochrome pigment, dotted curve in Fig. 11b). The dramatic increase in reflectance of the receptors after light adaptation (Figs. 3, 4b, 5a and 11a) can be explained as a mere by-product of the high absorption index of the ommochrome pigment, especially if one takes into account the phenomenon of anomalous dispersion (Chapter 8). The vivid green or yellow colour of the rhabdomeres would thus have a physical origin comparable to a metallic glint. Contrasting with the lens eye in which the pupillary mechanism is a common attenuator for both receptor types (rods and cones), the compound eye of higher Diptera is equiped with two types of pupils adapted respectively to both visual subsystems. A scotopic pupil is present in each of the six cells (Nos. 1–6) whose signals are gathered in a common cartridge of the first optic ganglion. This pupil comes into play at a moderate luminance (0,3 cd/m² in Drosophila; 3 to 10 cd/m² in Musca. Figs 13, 14, 15, 16). A photopic pupil is present in the central cell No. 7 whose signal reaches one column of the second optic ganglion. Attenuating the light flux for both central cells 7 and 8, the photopic pupil has its threshold about two decades higher than the scotopic pupil, just at the point where the latter reaches saturation (Fig. 3b, e-State II of Figs. 6b and 15). The photopic pupil itself saturates at a luminance one to two decades higher still (Fig. 3c, f=State III of Figs. 6c and 15). The two-decades-shift in threshold of these pupil-mechanisms supports the view that receptors 1–6 are a scotopic subsystem, receptors 7 and 8 a photopic subsystem of the dipteran eye. The luminance-threshold of the scotopic pupil (as determined with the apparatus described in Fig. 2) appears to be located at least 3.5 decades (Drosophila) or even 5 decades (Musca) higher than the absolute threshold of movement perception (Fig. 16). After a long period (1 hr) of darkness a light step of high intensity can close the scotopic pupil within about 10 sec (time constant 2 sec as in Fig. 9) and the photopic pupil within no less than 30–60 sec. Some mutants of Drosophila possess only a scotopic pupil (w , Figs. 4 and 5) whereas ommochrome deficient mutants lack both types of pupil (v, cn, see Fig. 7c, d). Comparable reflectance changes, accomplished within about 60 sec of light adaptation, are described for two insects having fused rhabdomes: the bee and the locust (Fig. 17).     

Bradycardial response inAplysia exposed to air

Summary Heart rate was chronically monitored (Figs. 1, 3) in two species of the marine gastropodAplysia. The warm waterA. brasiliana have an average basal heart rate in water of 33 min^–1, whereas the cold waterA. californica's heart rate is 20.6 min^–1. The heart rate in both species shows a strong temperature dependence and the difference in basal heart rate is negligible when measured at the same temperature (Fig. 2). Both species show a consistent bradycardia when exposed to air (Fig. 4):A. brasiliana showed a 43% average decrease in air, whereasA. californica showed only a 16.5% decrease. Removal of the abdominal ganglion produced no significant decrease in heart rate in either species, nor did it reduce the bradycardial response to air exposure inA. californica (Fig. 8). However, it significantly reduced, but did not abolish, the bradycardia inA. brasiliana (Figs. 5, 6, 7). We conclude that the bradycardia has a significant central component inA. brasiliana, but is peripherally mediated inA. californica. The bradycardial response to air exposure may be analogous to the diving response in air breathing vertebrates.     

Directionality of phase locking in auditory nerve fibers of the leopard frog Rana pipiens pipiens

Summary A dorsal approach to the eighth nerve and free-field stimulation were used to investigate the effect of sound direction and intensity on phase locking in auditory nerve fibers of the leopard frog Rana pipiens pipiens.Tuning curves of 75 auditory neurons were analyzed (Fig. 2). Amphibian papillar neurons, but not basilar papillar neurons, exhibit significant phase locking to short tone bursts at the characteristic frequency (CF), the degree of phase locking (vector strength) decreasing with the neuron's CF (Figs. 3, 4 and 10E). Vector strength increases with sound pressure level to saturate about 20 dB above threshold, while the preferred firing phase is only slightly affected (Figs. 5 and 6).In contrast, sound direction hardly affects vector strength (Figs. 7, 8, 9A and 10A and C), but has a strong influence on the preferred firing phase (Figs. 7, 8, 9B and C, 10B and D): With respect to anterior tone presentation there are phase lags for ipsilateral and phase leads for posterior and contralateral presentation. Phase differences between both ears show a sinusoidal or cardioid/ovoidal directional characteristic; maximum differences are found with antero-lateral tone presentation (Fig. 11). The directionality of phase locking decreases with the neuron's CF (Fig. 10F) and only slightly changes with sound pressure level (Fig. 12). Thus, phase locking of amphibian papilla neurons can potentially provide intensity-independent information for sound localization.Abbreviations SPL sound pressure level - FTC frequency threshold curve - CF characteristic frequency - TF test frequency - VS vector strength - AP amphibian papilla - BP basilar papilla     

Characteristics of a circadian pacemaker in the suprachiasmatic nucleus

Summary The nature of the circadian rhythms of the SCN in a hypothalamic island was examined in male rats by recording multiple unit activity from the SCN for longer durations. Successful continuous recording lasted up to 35 days. Neural activity of the SCN inside the island showed free-running rhythms whose periods were slightly longer than 24 h (Figs. 2, 3, Table 1). When the retino-hypothalamic pathway was spared, re-entrainment to a displaced light and dark cycle was attained following a transition period of a few days (Fig. 4). Phases of the rhythms shifted in a phase-dependent manner in response to single light pulses interrupting constant darkness (Fig. 5 and Fig. 6). These results suggest an endogenous nature of the circadian rhythm of the SCN within the hypothalamic island. Thus, neurons or neuronal networks in the SCN may have not only an inherent ability to generate a circadian rhythm, but also an intricate machinery to regulate its phase. Simultaneous recordings from the left and right SCN showed a slight but visible discrepancy in their phases between the two rhythms in 3 out of 12 cases (Fig. 7).Abbreviations LL constant light - LD light-dark - DD constant darkness - SCN Suprachiasmatic nucleus     

Calcium and action potentials in primary afferent terminals.

Group I afferents were antidromically activated with twin pulses and the action potentials were recorded with a micropipette located in the axon, in decerebrated spinal cats. Absolute refractory periods (ARPs) were determined from the duration of refractoriness of the terminals to suprathreshold stimulations with the second pulse. The actions of iontophoretically applied tetraethylammonium (TEA), 4-aminopyridine (4-AP), Ba⁺⁺, Mn⁺⁺, Co⁺⁺ and verapamil were examined on the ARP. While TEA, 4-AP and Ba⁺⁺ prolonged the ARP, calcium antagonists, Mn⁺⁺, Co⁺⁺ and verapamil decreased the ARP in the terminal regions. The ARP was longer in the terminal regions than in non-terminal regions of the afferents. The terminal-, but not non-terminal-, refractory period was decreased by Mn⁺⁺. These results indicate that calcium influx occurs during the primary afferent terminal-action potential.     

A defective conditioned behavior and a defective adenylate cyclase in theDrosophila mutantrutabaga

Summary TheDrosophila X-linked mutantrutabaga (Duerr and Quinn 1982) fails to perform normally in olfactory conditioning paradigms, in spite of being able to sense odorants and shock (Figs. 1–3).rut is capable of forming an association between shock and odorant, but memory decays rapidly; the memory of the mutant following intensive training resembles that of normal flies following very brief training (Fig. 4).rut flies also display in vitro a defective adenylate cyclase activity (Fig. 6). The enzyme in the mutant is responsive to stimulation by a putative neurotransmitter and by a guanyl nucleotide (Fig. 8) but the activity is lower than normal even in the presence of forskolin (Fig. 8) and MnATP (Fig. 9), suggesting that the lesion is closely associated with the function of the catalytic subunit.rut/ + heterozygotes are semi-recessive with regard to both the behavioral defect and the biochemical defect (Figs. 5, 7). The behavioral and the biochemical lesions detected inrut flies are discussed in light of current molecular models of learning.     

Das Belichtungspotential der isolierten Retina des Einsiedlerkrebses (Eupagurus bernhardus L.) in Abhängigkeit von den extrazellulären Ionenkonzentrationen

Summary 1.The action potential of the isolated retina of the hermit crab Eupagurus bernhardus L. resulting from exposure to light has been measured with external electrodes under constant stimulus conditions.Three measurements of the retinal action potentials (RAP's) were taken to observe the changes of the RAP's quantitatively: a) The amplitude h _max of the maximum; b) the amplitude h _e of the plateau, measured at the end of the stimulus, for taking the shape quotient h _max /h _e ; c) the peak-amplitude-time t _max. 2.The RAP's of the retina in a standard physiological saline are compared with those of the retina in salines of different ionic composition while osmotic pressure and p _h were kept constant. 3.Increasing K⁺-concentration reduces the amplitude h _max of the RAP's gradually, which is zero at 500 mM K⁺/l. The peak-time t _max decreases with increasing K⁺-concentration up to 50 mM K⁺/l, whereas at higher concentrations it increases. In contrast to this fact h _max/h _e increases up to 50 mM K⁺/l and decreases above this concentration (Fig. 3). 4.Increasing Ca⁺⁺-concentration reduces h _max (zero above 350 mM Ca⁺⁺/l) and t _max. h _max/h _e rises up to a Ca⁺⁺-concentration of about 30 mM Ca⁺⁺/l; whereas at a higher Ca⁺⁺-concentration it decreases again (Fig. 6). When the Ca⁺⁺-concentration is very low the fall of the RAP is much slowed down and the plateau h _e extremly rises. In a Ca⁺⁺-free saline which contained 1 mM/l Ethylendiamintetraacetic acid (EDTA) the retina lost its irritability reversibly (Fig. 8). 5.The amplitude of the RAP's is augmented with increasing Mg⁺⁺-concentration up to 10–30 mM Mg⁺⁺/l and decreases above this concentration (Fig. 11). When the saline contains virtually no other cations but Mg⁺⁺ (367 mM/l) the amplitude of the RAP is small (20%) but not zero. 6.In a buffered isotonic NaCl-solution as well as in a saline in which all the Cl^--ions are substituted by SO₄ ^---ions the amplitude of the RAP's is higher but the shape of the RAP's is changed in the same way as in other solutions with very low concentrations of Ca⁺⁺. 7.All the changes of the RAP's described so far are reversible. 8.Even when the retina is kept in a salt solution containing sodium in a very low concentration (ca. 3–5 mM/l, the sodium substituted by choline⁺-ions) for 5 hours the amplitude h _max of the RAP does not change significantly but the shape: the peaktime t _max is longer, h _max/ h _e is much greater. Afterwards when the retina is brought into standard saline again, the amplitude h _max increases, t _max remains almost unchanged and h _max/h _e , decreases strongly (Fig. 17). 9.Substitution of all the Na⁺-, Ca⁺⁺- and Mg⁺⁺-ions by choline⁺-ions results in a decrease of the amplitude h _max, a lengthening of t _max and a small increase of h _max/h _e . 10.Substitution of all the NaCl by glucose decreases the amplitude h _max, lengthens t _max very much and decreases the value of h _max/h _e but little. Afterwards, when the retina is brought into standard saline again the effect of the glucose solution on the amplitude h _max is only little reversible: h _max increases very little, t _max decreases strongly and h _max/h _e increases (Fig. 21). 11.With increasing external K⁺-concentration the resting potential decreases. The changes of the resting potential cause the changes in the shape of the RAP's. 12.The presence of a small concentration of Ca⁺⁺-ions outside of the cell membrane is obviously necessary for the ability of the cell membrane of the photoreceptor to increase its ionic permeability consequent to stimulation by light. Above a Ca⁺⁺-concentration of about 1 mM/l the raise of permeability of the cell membrane during illumination is smaller with increasing Ca⁺⁺-concentration. The velocity of the changes in permeability is augmented, especially of those changes concerned with the fall of the RAP. The effect of Mg⁺⁺-ions is somewhat similar to that of Ca⁺⁺-ions, but much weaker. 13.The changes of the RAP are mainly determined by the low Ca⁺⁺-content when the retina stays in the NaCl- or sulfate saline. 14.Choline⁺-ions probably greatly increase the raise of permeability of the cell membrane for the divalent cations Ca⁺⁺ and Mg⁺⁺ during excitation. 15.It is suggested that under normal conditions in Eupagurus the amplitude of the RAP is determined primarily by the Na⁺-concentration gradient over the receptor cell membrane. But also the divalent cations Ca⁺⁺ and Mg⁺⁺ contribute to the amplitude of the RAP, especially after the retina has been treated with choline chloride.

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Herrn Professor Dr. C. Kosswig zum 60. Geburtstag überreicht.Der Deutschen Forschungsgemeinschaft danke ich für großzügige Unterstützung, Herrn Peter Thomsen und meiner Frau für technische Hilfe.     

Learning and discrimination of coloured papers in the walking blowfly,Lucilia cuprina

Summary A new training and testing paradigm for walking sheep blowflies, Lucilia cuprina, is described. A fly is trained by presenting it with a droplet of sugar solution on a patch of coloured paper. After having consumed the sugar droplet, the fly starts a systematic search. While searching, it is confronted with an array of colour marks consisting of four colours displayed on the test cardboard (Fig. 1). Colours used for training and test include blue, green, yellow, orange, red, white and black.Before training, naive flies are tested for their spontaneous colour preferences on the test array. Yellow is visited most frequently, green least frequently (Table 2). Spontaneous colour preferences do not simply depend on subjective brightness (Table 1).The flies trained to one of the colours prefer this colour significantly (Figs. 5 and 9–11). This behaviour reflects true learning rather than sensitisation (Figs. 6–7). The blue and yellow marks are learned easily and discriminated well (Figs. 5, 9, 11). White is also discriminated well, although the response frequencies are lower than to blue and yellow (Fig. 11). Green is discriminated from blue but weakly from yellow and orange (Figs. 5, 9, 10). Red is a stimulus as weak as black (Figs. 8, 9). These features of colour discrimination reflect the spectral loci of colours in the colour triangle (Fig. 14).The coloured papers seem to be discriminated mainly by the hue of colours (Fig. 12), but brightness may also be used to discriminate colour stimuli (Fig. 13).     

Simulations of a model for transmitter kinetics

The influence of the internal water balance on the phototactic behaviour in the walking female fly (Calliphora erythrocephala Meig.) was investigated. The phototactic reaction depends on the age of the flies and the duration of water withdrawal. In young blowflies with progressive dehydration, the strength of the light reaction varies considerably from fly to fly. From the 4th. day of life onwards up to day 21 the flies respond much more homogeneously and elicit a reproduceable temporal pattern of reaction (Figs. 2 and 3). All the following statements refer to the behaviour of 10-day-old, virgin females, which, under optimal humidity conditions, have been shown to be spontancously photonegative (Meyer, 1978). The phototactic reaction of progressively dehydrated flies depends in a characteristic manner on the illumination conditions during the intervals between tests. If the flies are kept in darkness during these intervals, the light reaction varies rhythmically, with a period of almost exactly 12 h (Figs. 4a and 5). Under the test conditions this rhythm is found not to vary with the time of day (Fig.4a), or with the length of the between-test intervals, for intervals up to 4h long (Fig. 6). If the flies are kept under illumination during the intervals between tests, the light reaction becomes arhythmical. After an initial maximum after 2–4h of dehydration, further photopositive responses are severely suppressed (Fig. 4b). When the ocelli are covered, the between-test illumination no longer influences the mean response to light. The arhythmic dehydrationtime vs. light-reaction curve in this case is characterised by a strong sustained enhancement of runs towards the light after 10h of dehydration (Fig. 7). A preliminary model of a possible control system for this moisture-dependent phototactic switching is presented, from which all essential results can be deduced. This system determines the phototactic turning direction from the ocelli afferences. These afferences act upon the central nervous system in two ways: directly and also indirectly via the internal water regulation.This work was supported by the DFG-(Me417/4)     

The large monopolar cells L1 and L2 are responsible for ERG transients inDrosophila

Summary The mutantVam (Vacuolar medulla ^KS74) has age specific degeneration of the large monopolar cells L1 and L2 (LMC) in the lamina and reduced ERG transients. The size of the on- and off-transients in the ERG is negatively correlated with degeneration of the LMCs (Figs. 1 and 2) as assessed by examination of ultrastructure. The retinula cells function normally as indicated by the induction of a prolonged depolarizing after potential inw Vam flies (Fig. 7) and genetic mosaic analysis (Figs. 5, 6). This indicates that the LMCs are probably the major contributers to ERG transients inDrosophila. Independent evidence in support of this hypothesis comes from the triple mutantrol mnb sol. This mutant has an abnormal lamina with some cartridges with no LMC and others with a single LMC (Fig. 8). The ERG ofrol mnb sol shows reduced on- and off-transients (Fig. 9) which is as expected if the LMCs are principally responsible for ERG transients.Abbreviations ERG electroretinogram - PDA prolonged depolarizing afterpotential - LMC large monopolar cell - EM electron microscope - LED light emitting diode     

Acoustic orientation in adult, female crickets (Gryllus bimaculatus de Geer) after unilateral foreleg amputation in the larva

Summary InGryllus bimaculatus females one foreleg was amputated at the coxa-trochanter joint in the 2nd, 4th or 8th/9th larval instar. A leg of up to normal length is regenerated (Fig. 1) but it lacks a functional ear. In spite of the, usually shorter, regenerated foreleg, the adult one-eared crickets show no impairments in walking when tested on a locomotion compensator. Without sound they walk erratically and most of them weakly circle towards the intact side (Fig. 2).With calling song presentation three response types can be distinguished:tracking (Fig. 3A), hanging on (Fig. 3B) or continuouscircling towards the intact side (Fig. 3C, D). Turning tendencies in monaurals increase with song intensity and exceed those of intact and bilaterally operated animals (Fig. 4). Course deviations towards the intact side also slightly increase with intensity (Fig. 5). Course stability is reduced compared to that of intact animals but exceeds that of bilaterally operated crickets (Figs. 5, 6). It is best at 60 dB and deteriorates at higher sound intensities (Fig. 6). The percentage of monaurals tracking or hanging on decreases with increasing intensity (Fig. 7B). Tracking is established in most animals but it is limited to a narrow intensity range (Fig. 7A, C). Apart from an increased percentage of tracking after early operations (Fig. 7D), there are no prominent changes in orientational parameters with the date of foreleg amputation.Reamputation of the regenerated leg in the adult monaurals does not significantly impair acoustic orientation (Figs. 8, 9), but occlusion of the ipsilateral prothoracic spiracle does (Figs. 10, 11).An attempt is made to correlate the behavioral performance with the activity of auditory interneurons which have undergone morphological and physiological changes (Fig. 12).     

The duration of recovery and DNA repair in excision deficient derivatives of Escherichia coli K-12 after ultraviolet irradiation

Summary Our results indicate that cells of excision deficient (uvr) mutants of Escherichia coli K-12 which survive exposure to ultraviolet radiation may require several hours to complete their recovery. For example, the duration of the recovery period for cells exposed to 63 ergs mm^-2 at 254 nm was about 5 hours, the equivalent of slightly more than 4 generations of the unirradiated controls. During the recovery period the rate of cell division was reduced (Figs. 3 and 4), the cells gradually regained resistance to complex medium (Figs. 1 and 3), and they became refractory to photoreactivation (Fig. 1). Over the same period of time their pattern of DNA synthesis changed. More intact molecules, similar to those found in unirradiated controls, and relatively fewer discontinuous molecules were synthesized (Figs. 6 and 7).