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Notizen: This article describes a new, direct way to measure the time evolution of single light pulses in the subnanosecond region using time-of-flight analysis. The light pulse is coupled into a set of 40 optical fibers of increasing length arranged in an array. The output of the fiber array is imaged onto a fast gated optical imager (gatewidth 100 ps) coupled to a CCD camera (12 bit). The intensified part of the pulse of each fiber corresponds to the intensity of the light pulse at a different time due to the different transmission time of each fiber. Additional, two-dimensional (2D) spatial resolution is possible if image guides are used instead of fibers. The temporal resolution is limited by the gatewidth of the detector. The difference in length between the longest and the shortest fiber determines the total period of time displayed by the system (1 ns). The pulse characteristics of a recently developed short-pulse Raman-excimer laser are analyzed as an example of an application. Laser parameters like pulse length, energy stability, and jitter are measured with the fiber array. © 1996 American Institute of Physics.

Notizen: An excitatory connection between an extensor and several flexor tibiae motor neurons that innervate antagonistic muscles in the hind leg of a locust has been characterized using physiological and ultrastructural methods. Simultaneous intracellular recordings from the single fast extensor (FETi) motor neuron and up to three flexor motor neurons show that a spike in FETi is followed by a short latency depolarizing synaptic potential in the flexors that is powerful enough to evoke a burst of flexor spikes. The chemically mediated excitatory postsynaptic potential (EPSP) is caused centrally as it persists when sensory feedback from the leg is removed, and has a latency of 1.6–2.0 ms depending upon the position of the recording electrodes in the somata or neuropilar segments of the pre- and postsynaptic neurons. The amplitude of the EPSP declines gradually in a saline containing no calcium but high magnesium, indicating that no spiking interneuron is interposed in the pathway. With repetitive stimulation, the EPSP decrements markedly so that at intervals of 50 ms the second EPSP of a pair is reduced by 90%. The amplitude of the EPSP is also dependent on the amplitude of the presynaptic spike.The physiological evidence suggesting a monosynaptic connection is directly confirmed by electron microscopy of ganglia in which FETi and a flexor were both labelled with horseradish peroxidase. Direct chemical synapses between the two identified neurons, in which FETi is the presynaptic element, occur in three regions of the neuropil examined. At a synapse, the flexor motor neuron may be the only postsynaptic neuron or it may be one element in a dyad. The synaptic arrangements between the two neurons are complex with serial synapses through unlabelled processes linking FETi to flexor motor neurons and with frequent reciprocal synaptic connections between FETi and unlabelled processes. Unidentified processes also make input synapses on both neurons close to the synapses from FETi.The behavioural significance of the connection lies in the mechanical requirements for kicking and jumping. To prepare for these powerful movements the extensor and flexor tibiae muscles must co-contract. The connection from FETi enhances the depolarization and frequency of spikes in the flexors during the co-contraction.

Notizen: An identified intersegmental interneuron in Locusta and Schistocerca, with its cell body in the fourth abdominal ganglion and an axon which projects to the brain is excited by mechanosensory inputs from receptors on the head and neck. The organization of its receptive field, the types of sensory receptors which contribute to it and the patterns and strengths of the afferent connections were investigated by intracellular recording from the axon of the interneuron close to a spike-initiating site in the prothoracic ganglion. The receptive field of the interneuron consists of a small patch of hairs on the head ipsilateral to the axon, and from hairs on two regions of the prosternum (a cuticular structure on the ventral surface of the prothoracic segment), first an ipsilateral, lateral region and second a medial but contralateral region. Hairs on the pronotum (dorsal neck) also contribute but were not investigated here. Each spike in the afferent from a hair with a filiform appearance and with a pigmented base on the prosternum consistently evokes an EPSP in the interneuron. These have a short and constant latency, indicating that the connection is probably direct. The head hairs also appear to make direct connections with the interneuron in the prothoracic ganglion, so that the spike-initiating site here can integrate signals evoked by wind on the head and on the prosternum. Stiff tactile hairs on the prosternum do not connect with the interneuron. The EPSPs evoked by the long filiform hairs are consistently larger than those produced by the short filiform hairs and a single spike in some of the afferents from the long filiform hairs can evoke a spike in the interneuron. The effectiveness of an afferent is therefore correlated with the length of the filiform hair it innervates. The hairs with the most powerful effects are always the longest and occur in the same position on every locust. The shape of the receptive field and the different strengths of connections are apparent even in early larval instars. The axonal branches of the interneuron are restricted to the same side of the ganglion as the axon itself. Afferents from filiform hairs on the medial region of the prosternum project contralaterally, and those from the lateral region project ipsilaterally. Afferents from some of the head hairs project ipsilaterally directly to the prothoracic ganglion. The terminals of all these afferents overlap with the branches of the interneuron. By contrast, the afferents of tactile hairs which do not connect, project to different regions of neuropile. The connections ensure that the high sensitivity of the filiform hairs is maintained at the first stage in the central processing and suggest a role for this interneuron in supplying information about small changes in air currents that may be of use in controlling steering manoeuvres during flight.

Notizen: Juvenile plaice Pleuronectes platessa are particularly useful for studying forager search behaviour because their search paths are essentially two dimensional, and punctuated by natural stops. Their prey occur in a range of natural distributions from highly aggregated to over-dispersed. Juvenile plaice use area-restricted search near aggregated prey and extensive search, consisting of longer moves and fewer turns, between aggregations and when searching for dispersed prey. They search for less conspicuous prey items mainly in the pauses between movements. This saltatory search behaviour contrasts with the continuous search that is usually assumed in search models. A simulation model of saltatory search behaviour showed that a strategy combining extensive and intensive search allows the efficient exploitation of a range of natural prey distribution patterns, and that it is particularly effective when the search behaviour is controlled by perceived prey density. This allows the predator to respond to the localized aggregations which often occur in nature. The selective use of intensive search was more efficient than the continuous use of extensive search even in prey distribution patterns that were statistically over-dispersed.

Notizen: During searching, discovery of a prey patch by juvenile plaice Pleuronectes platessa was associated with a change from extensive to intensive search behaviour several moves before an attack on a prey. Intensive search behaviour was characterized by reduced distance of moves, a greater rate of turning per unit distance and shorter pauses between moves. The increase in turn rate was associated with area-restricted seaching, while a decrease in distances moved suggests that plaice search more efficiently for prey when stationary than while moving. The klinokinetic mechanism that appears to regulate search behaviour in juvenile plaice should allow efficient exploitation of a range of prey distribution patterns based on localized cues alone. Such a mechanism is especially useful to a migratory predator, like plaice, whose foraging is subject to time constraints imposed by tidally available feeding areas.

Notizen: Juvenile plaice Pleuronectes platessa in a laboratory arena used intensive search behaviour, characterized by short movements and frequent turning, in the five movements before and after attacking a prey in an aggregated distribution. They used extensive search behaviour with, on average, longer movements and less turning at all other times. Intensive search was, apparently, triggered by a high local density of prey but not by isolated prey. This response to local prey density resulted in area-restricted search when prey were aggregated and win-shift behaviour when prey were dispersed. There was no evidence that the use of intensive search increased with experience of aggregated prey. It therefore appears that the fish were able to exploit encountered prey distribution patterns using their immediate perceptions rather than prior experience.

Notizen: Juvenile plaice Pleuronectes platessa on a sand slope in a laboratory tank showed depthselection behaviour consistent with offshore migration by day and onshore by night, as seen in natural conditions. Plaice stayed deep (0·5 m) and avoided the shallowest water (〈10 cm depth) during light periods, but ventured up the slope and into the shallows in darkness. The freshly caught fish showed circatidal cycles of activity, but showed no change in depth selection between periods of high (time of expected high water) and low activity (expected low water). This suggests that changing direction of movements in tidal migration is controlled by responses to changing environmental conditions. Further analysis showed movements of fish up the slope to be slower, covering less distance and with shorter pauses in between than moves down the slope. Frequency, distance travelled and speed of moves up and down the slope did not change with tidal or light-dark cycles, and so such modulation could be ruled out as a mechanism for migration.