Visual wulst influences on flash evoked responses in the ectostriatum of the zebra finch.

Anatomical data suggest that visual information from the thalamofugal pathway contributes to visual processing in the tectofugal pathway. We addressed the question of the functionality of anatomically described connections to the visual system of a laterally eyed bird, the zebra finch. The study shows the contribution of visual wulst efferents, to visual processing in the ectostriatum by recordings of visually evoked slow field potentials. Suppression of visual wulst activity resulted in a selective reduction of distinct potential components in contralaterally evoked slow field potentials. A clear reduction was observed in the maximum amplitude of short latency components in the negative wave. Long latency components of the negative wave and the entire positive wave of the contralaterally flash evoked potentials were almost abolished. Ipsilateral visual evoked potentials (VEPs) were not significantly affected. Cooling and spreading depression of the optic tectum resulted in a uniform amplitude reduction of the negative wave. The positive wave was almost abolished. Ipsilateral VEPs disappeared completely during suppression of optic tectum activity. The results showed that the visual wulst has a significant, most likely facilitatory, influence on the processing of contralateral visual information in the ectostriatum. Ipsilateral stimulus processing was partly independent from visual wulst activity. A model for thalamo- and tectofugal connectivity in the ectostriatum is suggested.

Flash evoked responses in a song control nucleus of the zebra finch (Taeniopygia guttata castanotis).

The song of the zebra finch is facilitated and altered by the presence of a female. Thus, visual information should affect the song system of the bird. Visually evoked potentials can be recorded from n. hyperstriatum ventrale pars caudale (HVc). The long latency of this potential and its variability indicate several processing steps between primary sensory areas of the telencephalon and HVC. Within HVc, under these experimental conditions no interaction between acoustic and visual input could be demonstrated. However, at the dorsal border and within the shelf below HVc, visual information seems to enhance acoustically evoked potentials.

A program to measure new energetic particle nuclear interaction cross sections.

The Transport Collaboration, consisting of researchers from institutions in France, Germany, Italy and the USA, has established a program to make new measurements of nuclear interaction cross sections for heavy projectiles (Z > or = 2) in targets of liquid H2, He and heavier materials. Such cross sections directly affect calculations of galactic and solar cosmic ray transport through matter and are needed for accurate radiation hazard assessment. To date, the collaboration has obtained data using the LBL Bevalac HISS facility with 20 projectiles from 4He to 58Ni in the energy range 393-910 MeV/nucleon. Preliminary results from the analysis of these data are presented here and compared to other measurements and to cross section prediction formulae.

Enucleation enhances ipsilateral flash evoked responses in the ectostriatum of the zebra finch (Taeniopygia guttata castanotis Gould).

The tectofugal pathway in birds has been reported to process primarily information from the contralateral eye. Although this pathway has access to the contralateral hemisphere by various connections, electrophysiological recordings up to now have failed to demonstrate any excitatory influence of visual stimulation in the higher stations of this pathway. This study is the first to demonstrate an excitatory projection from the ipsilateral eye to the telencephalic projection area of the tectofugal pathway by recordings of visually evoked potentials in the ectostriatum. The excitatory projection probably leads from the eye to the contralateral tectum opticum, then recrosses back to the nucleus rotundus of the ipsilateral side where it reaches the ectostriatum. In normal birds, the ipsilateral stimulus responses in the ectostriatum are smaller in amplitude and have a longer latency than responses to contralateral stimuli. In unilaterally enucleated birds, the ipsilateral response is enhanced in the ectostriatum and can be detected in the nucleus rotundus, too. The results suggest that in normal birds the ipsilateral response is inhibited to a high degree by spontaneous activity of the contralateral eye. Possibly, this counterbalanced inhibition provides a mechanism for weighting information from the left and right eye field in order to ensure adequate processing of stimuli.

Flash evoked potentials in the ectostriatum of the zebra finch: a current source-density analysis.

Recent research has demonstrated that ipsilaterally visually evoked potentials (VEPs) can be measured within the ectostriatum, the telencephalic target area of the tectofugal visual pathway in birds. In this paper we systematically measured contra- and ipsilateral VEPs within the ectostriatal complex to obtain more detailed information on the processing of contra- and ipsilateral stimuli. The similarity of neighbouring VEPs at equal depth and a comparison of a one dimensional and a three dimensional analysis of current source-densities (CSDs) for identical coordinates suggested that a one dimensional current source-density analysis might be applicable. The one dimensional current source-density analysis demonstrated largely corresponding patterns in the sink-source sequences of the current source-density depth profiles for the contra- and ipsilateral stimulus responses. The occurrence of a large sink in the centre of the ectostriatal core, together with the results of multiunit recordings, shows that the ectostriatal core is the location of the generators for both the contra- and the ipsilaterally evoked responses. The occurrence of macroscopic sinks and sources and the fact that VEPs can be recorded from the ectostriatum shows that there is a higher degree of order in the ectostriatum than has been previously demonstrated by anatomical methods. The time coincidence between the maximum spike rate of multiunit responses, the negative peak of the evoked potential, and the large central sink demonstrates that the influence of ipsi- as well as of contralateral stimuli is predominantly excitatory.

Development of flash-evoked responses in the ectostriatum of the zebra finch: an evoked potential and current-source-density analysis.

The morphological development of the tectofugal pathway in the zebra finch has recently been described in a series of studies from our laboratory. No data are currently available on the development of visual responsiveness in this pathway. We therefore investigated the development of visually evoked potentials (VEPs) in the ectostriatum, the telencephalic target area of the tectofugal pathway. Contralateral VEPs could already be recorded in 20-day-old birds, whereas ipsilateral VEPs could first be recorded in 40-day-old birds. The latencies of contralateral VEPs decrease to adult values between 20 and 40 days of age, probably due to an increase in the myelination of afferent fibers. The amplitudes of the contralateral VEPs increase continuously from day 20 to day 60; however, between 60 and 80 days of age the responses diminish substantially (-60%). Thus, contralateral VEPs in 80-day-old birds are not significantly different from those in 20-day-old birds. Thereafter the responses recover and reach their final amplitude values at about 150 days of age. The relationship of these results to morphological studies and possible mechanisms which may cause the double-peaked development of visual-evoked potentials in the ectostriatum are discussed.

Visual system alterations in White Zebra Finches.

Visual system anomalies in albino mammals are generally seen to be caused by a lack of retinal pigment and misrouting of retinofugal optic fibers. This study shows that the central visual system of white zebra finches is physiologically different from normally colored (wild type) birds, although the eye pigmentation and the retinofugal projection appear to be normal. Ipsilaterally evoked potentials in our white birds are enhanced in comparison to wild type birds, whereas in albino mammals the ipsilateral component of visually evoked potentials is reduced. Picrotoxin-induced blockade of inhibitory synapses in the ectostriatum reveals remarkable differences between wild type and white zebra finches. In wild type zebra finches, a significant shift of ipsilateral to contralateral stimulus response ratios is observed. However, there is no detectable shift in the white morph. The data suggest that inhibition of ipsilateral stimulus processing, as observed in wild type zebra finches, is significantly reduced in the white morph. Our results indicate that the effects observed in white zebra finches cannot be explained by the theories that have been developed for albinotic animals. We assume that in white zebra finches a genetic defect, which causes the white plumage, is coupled with the demonstrated deviations of inhibitory mechanisms in the central visual system.

Lambda spectra in 11.6A GeV/c Au-Au collisions.

E896 has measured Lambda production in 11.6A GeV/c Au-Au collisions over virtually the whole rapidity phase space. The midrapidity p(t) distributions have been measured for the first time at this energy and appear to indicate that the Lambda hyperons have different freeze-out conditions than protons. A comparison with the relativistic quantum molecular dynamics model shows that while there is good shape agreement at high rapidity the model predicts significantly different slopes of the m(t) spectra at midrapidity. The data, where overlap occurs, are consistent with previously reported measurements.