To glue or not to glue? Reassembling broken otoliths for population discrimination.

Twenty-five Atlantic cod Gadus morhua otoliths were examined using eight shape measurements along with Fourier analysis of their outlines to test whether discrimination using otolith shape is affected by gluing broken otoliths. Small differences in seven of the eight shape measurements were found between unbroken otoliths and the same otoliths after breaking and subsequently gluing together; however, none of the Fourier descriptors differed. Cluster analyses indicated that resultant morphological differences will have no impact when applying discriminant analysis.

Social anxiety and depression in adolescents in relation to perceived competence and situational appraisal.

The Social Anxiety and Phobia Inventory for Children (SPAI-C), the Children's Depression Inventory (CDI), Harter's (1982) Perceived Competence Scale for Children (PCSC), as well as an inventory of cost and likelihood appraisal of negative social and non-social events, were filled in by 184 adolescents (14-15 years old). It was expected that social anxiety would be specifically related to low perceived competence in the social domain and threat appraisal in the same domain, whereas depression would be related to more general perceived competence deficits. The relationships of social anxiety and depression to perceived competence and appraisal were largely supported. Social anxiety was most strongly related to perceived social competence as well as to both social cost and likelihood appraisals, whereas depression was more generally related to perceived competence, and appraisal of negative events did not improve the prediction of depression any more than the prediction based on perceived competence.

Regional specificity of developing reticulospinal, vestibulospinal, and vestibulo-ocular projections in the chicken embryo.

The regional mapping of reticulospinal, vestibulospinal, and vestibulo-ocular neuron groups onto specific axonal pathways was determined in the chicken embryo by retrograde axonal tracing. Experiments were performed on in vitro preparations of the brain stem to allow for precisely localized tracer injections combined with selective lesions of axon tracts. Brain-stem neuron groups were labelled from 3 days of embryonic development, when the first reticulospinal axons reached the cervical spinal cord, to 9 days of embryonic development, when each of the three systems studied had acquired a relatively mature organization. A striking feature at all stages was the spatial segregation of many neuron groups that projected along different trajectories. Examples of such segregation were found for neuron groups projecting in the same tract on different sides of the brain stem, in different tracts on the same side of the brain stem, and rostrally versus caudally. The occurrence of this segregation from early stages suggests that the choice of projection pathway by many brain-stem neurons is in some way linked to cell position. In some regions of the brain stem, neuron groups projecting along different pathways are intermingled. At least some of this intermingling, however, appears to occur subsequent to the initial establishment of axon projection patterns. Comparison of the mapping patterns at progressively older stages, and with previous mapping in the 11-day-old embryo (Glover and Petursdottir, 1988; Petursdottir, 1990) suggests that these projections are established with little error. The one obvious example of remodelling involved the pontine reticulospinal projection, in which an early contralateral axon population appeared to retract from spinal to medullary levels over the course of a few days. A similar phenomenon may be involved in the elimination of part of the contralateral reticulospinal projection from the midmedulla.

Vestibulo-ocular projections in the 11-day chicken embryo: pathway specificity.

The organization of vestibulo-ocular projections and their spatial relationship to vestibulo-spinal projections were ascertained in the 11-day chicken embryo through retrograde tracing experiments. An in vitro preparation of the brainstem facilitated precisely localized application of tracers. Unilateral labelling of the ascending medial longitudinal fascicle (MLF), just caudal to the trochlear nucleus, labelled coherent groups of vestibular neurons that had an asymmetrical distribution on the two sides of the brainstem. Axons originating from either side followed one of four trajectories, and the groups of neurons could therefore be identified on the basis of their position and their projection pathway. Labelling each side of the MLF with a different tracer showed that although neurons projecting in the ipsi- and contralateral MLF were intermingled in some areas, individual neurons projected on one side only. Labelling the ascending MLF and the high cervical spinal cord with different tracers showed that vestibulo-ocular neurons had a wider rostro-caudal distribution than vestibulospinal neurons. Some vestibulospinal and vestibulo-ocular groups were spatially segregated, others were intermingled. Very few (in most preparations no) neurons were found to project to both targets. Together with our previous study on vestibulospinal projections in the 11-day chicken embryo (Glover and Pétursdóttir, J. Comp. Neurol. 270:25-38, '88) the results show that vestibular neurons in different regions project in characteristic subsets of the available pathways.

Pathway specificity of reticulospinal and vestibulospinal projections in the 11-day chicken embryo.

The organization of the axonal pathways of reticulospinal and vestibulospinal projections in the 11-day chicken embryo was ascertained through retrograde tracing experiments. An in vitro preparation of the brainstem and cervical spinal cord facilitated precisely localized tracer applications. Single- and double-labelling experiments involving high cervical injections of tracers in combination with selective lesions defined the specific pathways by which different brainstem neurons project to the spinal cord. Coherent, and in many cases distinct, groups of reticulospinal and vestibulospinal neurons could thus be identified on the basis of their position and projection pathway. The organization of these groups and their projections in the 11-day chicken embryo is similar to that in avian and other vertebrate adults and therefore serves as a reference point for studies of pathfinding by bulbospinal axons during early development.

Fluorescent dextran-amines used as axonal tracers in the nervous system of the chicken embryo.

We have used recently developed fluorescein- and rhodamine-conjugated dextran-amines as axonal tracers in in vitro preparations of the nervous system of the chicken embryo. These substances are efficiently taken up by injured axons and transported rapidly to the cell bodies. They are also, albeit to a lesser degree, taken up by intact nerve terminals in skeletal muscle. They reveal the dendritic and axonal structure of labelled neurons, and are well suited for use in double-labelling experiments.