Plasticity of GABAergic terminals in Deiters' nucleus of weaver mutant and normal mice: a quantitative light microscopic study.

This study reports on the developmental changes in size and the average density of GABAergic axonal boutons bordering on the somata of large neurons in the dorsal part of the lateral vestibular nucleus (Deiters' nucleus) in normal and mutant mice. Weaver mutants, PCD mutants and the corresponding wild types were used to test for size alterations and differences in the number of GABA-immunopositive terminals. Hemicerebellectomized animals were examined in addition. Quantification of bouton profile size was performed from 30-microns-thick vibratome and 0.5-micron Araldite-embedded semi-thin sections immunoreacted for GABA from 7 days postnatally up to an age of 9 months. Terminal density was determined at the 5-6 month stage from semi-thin sections only. Morphometric analysis over the lifetime of normal animals (B6CBA) revealed a progressive increase in the size of bouton profiles, which peaked at 5-6 months and reached sizes of 2-3 microns2. In weaver mutants a parallel development in terminal size was found to be present, but the size of the largest terminals exceeded those of the controls by 75-100%, reaching 3-6 microns2 with the same time course. PCD mutants, with an almost total absence of Purkinje cells had, on the contrary, small bouton profiles that reached a maximum of only 2 microns2. The hemicerebellectomized animals responded with decreased bouton profile size ipsilaterally. The terminal numbers per unit membrane length were surprisingly similar in wild types and weaver mutants, despite a reduction in Purkinje cells of almost 50% in the weaver anterior lobe.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebellar afferents in normal and Weaver mutant mice.

Cerebellar afferents in 3-week-old normal and homozygous Weaver mutant mice were investigated using retrograde transport of horseradish peroxidase. Almost all afferents found in other mammals were demonstrated in both normal and mutant mice of this age. Labelling in the trigeminal nuclei in both mutants and normals was found only in cases in which the ansoparamedian or uvular lobules were included in the injection site, indicating that the projection domains of mossy fiber afferent systems retain their normal boundaries in the mutants despite a lack of normal synaptic partners. Thus the neurological signs which the Weaver exhibits from about the 10th postnatal day are unlikely to depend on primary or secondary losses of cerebellar afferents or on a breakdown of the gross topographic organization of these afferents.

Cerebellar afferents in the frogs, Rana esculenta and Rana temporaria.

Afferents to the cerebellum in frogs (Rana esculenta, Rana temporaria) were studied by use of retrograde transport of horseradish peroxidase. Following injections restricted to the molecular layer of the cerebellum cell labelling was found in the contralateral inferior olive and the ventral portion of the caudal medullary raphe. Injections involving the granular layer resulted in labelling in the ventral horn of the cervical spinal cord, the caudal spinal trigeminal nucleus, the nucleus caudalis and the medial portion of the nucleus ventralis of the vestibular nerve, the inferior reticular nucleus and the nucleus of the fasciculus longitudinalis medialis. Following larger injections, which may have spread significantly into the cerebellar, secondary gustatory, trigeminal or vestibular nuclei, labelled cell bodies were also found in the nucleus ruber, nucleus solitarius, the rostral spinal trigeminal nucleus and the rostral rhombencephalic reticular formation. It is unclear whether the fibers from these latter areas innervate the cerebellum of the frog, as they do in mammals, or only reach the underlying areas. This situation emphasizes a limitation of the HRP technique when applied to small structures as is often the case in lower vertebrates.

Organization of extrinsic tectal connections in Goldfish (Caraccius auratus).

Nonretinal sources of tectal afferents, the laminar and regional organization of the inputs, and the relation of the tectum with primary and secondary visual and motor centers in goldfish were studied following HRP injections in the optic tectum, orbit of the eye, cerebellum, pretectal area, and dorsolateral mesencephalic tegmentum. Ipsilateral tectal afferents include the area dorsalis centralis of the forebrain, the nucleus dorsalis lateralis of the thalamus, the area pretectalis, the nucleus pretectalis, a nucleus in the rostral mesencephalic tegmentum, the torus longitudinales, the torus semicircularis, a dorsolateral tegmental nucleus, the nucleus isthmi, and a rostral cell group of the nucleus motorius tegmenti. Comparison of results in a series of tectal HRP injections which differed in depth, tangential extent, and location indicated that projections from the area pretectalis, nucleus pretectalis, and nucleus isthmi terminate in the stratum fibrosum et griseum superficiale of the tectum. Terminals of the forebrain and nucleus dorsolateralis and contralateral tectum are sparse and widely branching. Projections from the area and nucleus pretectalis tend to terminate in the rostral tectum, and those from the contralateral tectum, torus semicircularis, dorsolateral tegmental nucleus, and nucleus motorius tegmenti terminate preferentially in the caudal tectum. Cells of origin of extrinsic tectal efferents were also identified following HRP injections in the pretectal area and mesencephalic tegmentum. Proximal dendrites and axons of these cells were labeled sufficiently to allow comparison with morphological types characterized in Golgi studies. HRP injections in the cerebellum labeled cells bodies in the area pretectalis, nucleus pretectalis, and the nucleus of the posterior commissure. Double label experiments with intraocular injection of tritiated proline demonstrated direct retinal input to these three areas. No indications of direct connections between the tectum and cerebellum were found following tectal or cerebellar HRP injections.

Tectal projections in the goldfish (Carassius auratus): a degeneration study.

Efferents revealed by degeneration staining following tectal lesions in goldfish are presented. Four major projections were found. Ascending ipsilateral projections to pretectal-diencephalic areas exit the tectum rostrally and laterally and terminate in the area pretectalis (AP), lateral geniculate (LGN), nucleus pretectalis (NP), and nucleus rotundus (NR). Ascending contralateral projections exit rostrally and possibly laterally, enter the posterior and postoptic commissures and terminate in the contralateral AP, LGN, NP, NR, and rostral tectum. A medially directed projection enters the intertectal commissure, and some of these fibers may terminate sparsely in an area of the contralateral tectum homotopic to the lesion. A descending projection exits the tectum laterally and projects ipsilaterally to a dorsolateral tegmental nucleus (DLT) and the lateral reticular formation of the tegmentum and pons, and contralaterally to the medial reticular formation of the tegmentum and pons.

Visual function in goldfish with unilateral and bilateral tectal ablation.

Following complete bilateral tectal ablation, the ability to detect light recovers in about three weeks. The non-tectal retinal connections which may mediate detection are about one log unit less sensitive than the retinotectal connections. At moderate illumination levels, tectumless fish do not react visually to objects. Tectumless fish integrate luminous flux over a very wide area (at least 25 degrees diameter) while the critical diameter for the normal in this experiment is smaller. Subcortical structures may mediate the interocular transfer of a brightness discrimination. The ipsilateral retinotectal projection following unilateral tectal removal is functional, with normal sensitivity to detection of light.

Temporal summation of light by a vertebrate visual receptor.

Using aspartate to isolate mass receptor-activity, we have investigated the reciprocity of flash intensity and flash duration in determining the response of the frog's cone receptor. The duration over which reciprocity holds decrease with increases in either flash energy of ambient light intensity. These findings parallel those of human psychophysical experiments.