Biomedical subjects

F Walberg

Publications and source records attributed to F Walberg.

At least 19 recordsLinked to original sources

PubMed1992

Neuroactive amino acids in the area postrema. An immunocytochemical investigation in rat with some observations in cat and monkey (Macaca fascicularis).

The localization of five neuroactive amino acids in the rat area postrema was studied by postembedding immunocytochemistry in semithin and ultrathin sections. Antisera to GABA, glycine, glutamate and aspartate produced labelling of cells that were identified as neurons in the electron microscope. GABA-like and glycine-like immunoreactivities occurred in about 20% and 60% of the neurons, respectively, and a minor proportion of the cells displayed both immunoreactivities, suggesting a cellular colocalization of GABA and glycine. Immunoreactivities for glutamate and aspartate were found in a large majority of the neurons, including most of the cells that were positive for GABA and/or glycine. Taurine immunoreactivity was highly concentrated in a few small cells with ultrastructural features typical of microglial cells, and in processes that were probably derived from these. Taurine also appeared to be abundant in cells confined to the perivascular space. The electron microscopic, immunogold analysis of the neuropil revealed numerous nerve terminals that were enriched in GABA or glutamate immunoreactivity, compatible with a transmitter role of these amino acids. Glycine immunolabelling was found preferentially in postsynaptic elements, suggesting that the glycine-containing cells lack locally ramifying axon collaterals, and that they mainly project outside the area postrema. Aspartate immunolabelling was also generally low in axon terminals. This is similar to the situation in several other brain areas and could indicate that the latter amino acid primarily serves metabolic functions in the area postrema.

Animals↗

PubMed1992

Metabolic compartmentation of glutamate and glutamine: morphological evidence obtained by quantitative immunocytochemistry in rat cerebellum.

An electron microscopic, double-labelling immunocytochemical procedure was used to assess the level of fixed glutamate and glutamine in different cell profiles in ultrathin sections of rat cerebellar cortex. The procedure was based on sequential immunolabelling with two rabbit antisera, using gold particles of different sizes as markers and formaldehyde vapour as a means to avoid interference between the two incubations. Model sections containing a series of known concentrations of the respective amino acids (aldehyde--fixed to rat brain protein) were incubated together with the tissue material. These revealed a close to linear relationship between gold particle density and antigen concentration throughout the range of biological relevance. The ratio between the density of the two categories of gold particles was calculated for the individual profile types. This ratio showed a 20-fold variation, with the highest glutamate/glutamine ratios obtained for putative excitatory terminals (terminals of parallel fibres in the outer part of the molecular layer, followed by mossy and climbing fibre boutons) and the lowest for glial cells (Bergmann glia, astrocytes in the granule cell layer, and oligodendrocytes). Granule cell bodies and dendrites, and cell bodies and processes of putative GABAergic cells (Purkinje, basket and Golgi cells) displayed intermediate ratios. The ratios corresponded to millimolar ratios (mM fixed glutamate/mM fixed glutamine) ranging from 4.5 to 0.2, tentatively assessed by adjusting for differences in labelling efficiency of the two antigens. Our results show that the compartmentation of glutamate and glutamine, an issue previously addressed mainly in the test tube, can be studied in morphologically intact preparations at a resolution that matches the complexity of CNS tissue. The data indicate that glutamate is effectively converted to glutamine in all categories of glial cells, and that glutamate synthesis prevails in each of the three types of excitatory terminals in the cerebellar cortex. Terminals of putative GABAergic cells form a distinct low glutamate/low glutamine compartment.

Animals↗

PubMed1991

An electron microscopic, immunogold analysis of glutamate and glutamine in terminals of rat spinocerebellar fibers.

A semiquantitative, electron microscopic immunocytochemical procedure based on the use of colloidal gold particles as markers was employed to analyze the subcellular distribution of glutamate and glutamine, a major glutamate precursor, in a subpopulation of spinocerebellar mossy fiber terminals. These terminals were identified by anterograde transport of a horseradish peroxidase-wheat germ agglutinin conjugate, injected in the thoracic spinal cord. Gold particles signalling glutamate-like immunoreactivity were enriched over clusters of synaptic vesicles relative to organelle-free cytoplasmic matrix, and there was a strong positive correlation between gold particle and synaptic vesicle densities (correlation coefficient 0.94). Gold particles indicating glutamine-like immunoreactivity showed a much weaker correlation with vesicle density (correlation coefficient 0.36) and were about equally concentrated over cytoplasmic matrix as over clusters of synaptic vesicles. Compared with the mossy fibers, the putative GABAergic Golgi cell terminals exhibited a lower level of glutamate-like immunoreactivity, which was very weakly correlated with the vesicle density (correlation coefficient 0.27). The level of glutamine-like immunoreactivity in the Golgi cell terminals was similar to that in mossy fibers, but much lower than that in glial cells. The anterogradely labelled mossy fiber terminals were not enriched in immunoreactivities for aspartate or GABA. These results suggest that the level and subcellular distribution of glutamate in presumed glutamatergic terminals differs from that in terminals in which glutamate only serves metabolic or precursor roles, and that these differences can be exploited in immunocytochemical studies aimed at identifying glutamate-using neurons. In contrast, glutamine immunocytochemistry does not seem to be generally useful in this regard.

Amino Acids↗

PubMed1991

Afferent connections to the abducent nucleus in the cat.

The afferent connections to the abducent nucleus in the cat were studied by means of retrograde transport of WGA-HRP after implantations of the tracer in crystalline form. Retrogradely labelled cells were found bilaterally in the medial and descending vestibular nuclei, mainly in their ventral and medial portions, in the rostral part of the ipsilateral gigantocellular reticular nucleus, in the medial part of the contralateral caudal pontine reticular nucleus and bilaterally in the oculomotor nucleus, mainly in its dorsolateral division. Some labelled cells were also found bilaterally in the mesencephalic reticular formation, the periaqueductal grey and the nucleus of the trapezoid body.

Abducens Nerve↗

PubMed1990

GABA, glycine, aspartate, glutamate and taurine in the vestibular nuclei: an immunocytochemical investigation in the cat.

The distributions of five amino acids with well-established neuroexcitatory or neuroinhibitory properties were investigated in the feline vestibular complex. Consecutive semithin sections of plastic-embedded tissue were incubated with antisera raised against protein-glutaraldehyde conjugates of GABA, glycine, aspartate, glutamate and taurine. This approach allowed us to study the relative densities of the different immunoreactivities at the level of individual cell profiles. The results indicate that in the vestibular nuclei, neuronal colocalization of two or more neuroactive amino acids is the rule rather than an exception. Colocalization was found of immunoreactivities for GABA and glycine; glycine, aspartate and glutamate; glycine and aspartate, and glutamate and aspartate. GABA immunoreactive neurons were generally small and were found scattered throughout the vestibular complex. Glycine immunoreactive neurons were similarly distributed, except in the superior nucleus where the latter type of neuron could not be detected. Neuronal profiles colocalizing immunoreactivities for GABA and glycine occurred in all nuclei, but were most numerous in the lateral nucleus. The vast majority of the neurons showed noteworthy staining for glutamate and aspartate, although the level of immunoreactivities varied (e.g., the large neurons in the lateral and descending nuclei were more intensely aspartate immunoreactive than the smaller ones). Taurine-like immunoreactivity did not occur in neuronal cell bodies but appeared in Purkinje cell axons and in glial cell profiles. The functional significance of the complex pattern of amino acid colocalization remains to be clarified. In particular it needs to be distinguished between metabolic and transmitter pools of the different amino acids. The present results call for caution when attempts are made to conclude about transmitter identity on the basis of amino acid contents alone.

Amino Acids↗

PubMed1990

Aspartate-like and glutamate-like immunoreactivities in the inferior olive and climbing fibre system: a light microscopic and semiquantitative electron microscopic study in rat and baboon (Papio anubis).

A post-embedding immunogold procedure was used to analyse, in a semiquantitative manner, the distributions of aspartate-like and glutamate-like immunoreactivities in the inferior olive and climbing fibre system in rats and baboons. The neurons in the inferior olive were uniformly labelled for aspartate as well as glutamate, indicating a 100% co-localization of these two amino acids in the cell bodies. The level of glutamate-like immunoreactivity in the climbing fibre terminals was similar to that in the parent cell bodies, as judged by a computer-assisted calculation of gold particle densities. In contrast, the level of aspartate-like immunoreactivity in the climbing fibre terminals was only one-seventh of that of the olivary neurons. No differences were found between the hemispheres and vermis. Nerve terminals in the inferior olive were generally moderately labelled with the aspartate antiserum, as were cell bodies of astrocytes. With a few exceptions, the results obtained in baboons were similar to those in rats. Notably, no evidence was found of an enrichment of aspartate-like immunoreactivity in climbing fibres. The present results do not support previous data suggesting that aspartate is the transmitter of the climbing fibres but indicate that glutamate or another excitatory compound should be considered as candidate for this role. Our findings show that the presence of aspartate-like immunoreactivity in cell bodies is an unreliable indicator of transmitter identity.

Afferent Pathways↗

PubMed1990

The olivocerebellar projection to lobules I and II.

The olivocerebellar projection to lobules I and II was studied by means of retrograde transport from implants of the crystalline WGA-HRP complex. Retrogradely labelled neurons were found in the medial and dorsal accessory olives. Judged from the distribution of labelled cells, we conclude that parasagittally the olivocerebellar terminal zones A and B (i.e., the cerebellar cortical strips receiving axons from the olivary A and B regions) extend anteriorly into lobule Ia, whereas the fused olivocerebellar terminal C1/C3 zones reach lobule IIa. The olivocerebellar terminal C2 zone extends into lobule IIIa but not into lobule IIa. In lobule I the medial border of the B zone lies about 1 mm from the midline, in lobule II the B zone extends somewhat more medially. The lateral border of this zone is 1.9-2 mm from the midline. Compared to previous results, it appears that most of the Purkinje cells in lobule I projecting to the vestibular nuclei lie medially to the olivocerebellar terminal B zone.

Animals↗

PubMed1989

Demonstration of GABA immunoreactive cells in the inferior olive of baboons (Papio papio and Papio anubis).

The distribution of gamma-aminobutyric acid (GABA)-like immunoreactivity was studied in semithin sections through the inferior olivary complex in two baboon species. About 5% of the olivary neurons were GABA-immunoreactive. The GABA-immunoreactive neurons differed from the large majority of olivary neurons by their smaller size and their lower contents of aspartate, as judged by analysis of alternate sections labelled with an aspartate antiserum. The present observations raise the possibility that in primates the GABAergic modulation of the activity of the climbing fibre system is effected not only by the previously described input from the cerebellar nuclei and other extrinsic sources, but that intrinsic neurons also participate.

Animals↗

PubMed1988

The interconnection between the vestibular nuclei and the nodulus: a study of reciprocity.

The reciprocal connections between the nodulus and the vestibular and perihypoglossal nuclei in the cat have been studied by anterograde and retrograde transport after implants of crystalline wheatgerm agglutinin-horseradish peroxidase complex (WGA-HRP) restricted to one or two nodular folia. The findings supplement the previous study by Epema et al. (Neurosci. Lett., 1985, 57: 273-278), who injected WGA-HRP into the vestibular nuclei. In that study, details concerning the nodular origin and termination of the fibres within the reciprocal connections were given; in the present study, details are given concerning the origin and termination of the fibres within the vestibular and perihypoglossal nuclei. Our observations give evidence that the nodulovestibular fibres are distributed to a somewhat larger area than that projecting back to the nodulus. The distribution of the labelled cells and fibres is shown in Fig. 2. Of the 4 main nuclei, it is only the lateral vestibular nucleus which is devoid of a reciprocal connection with the nodulus, while only groups x and z of the minor cell groups are found to have such projections. Of the perihypoglossal nuclei, it is only the nucleus praepositus hypoglossi which appears to be interconnected with the nodulus.

Afferent Pathways↗

PubMed1987

The olivonodular projection: a re-examination based on folial cerebellar implants.

In 5 cats implants of crystalline wheat germ agglutinin-horseradish peroxidase complex were placed in one or two folia of the nodulus with no contamination of adjacent cerebellar lobules. In the inferior olive only the dorsal cap with the adjacent ventrolateral outgrowth and the caudalmost part of nucleus beta were found to project to the nodulus. Negative findings were consistently made in all other parts of the inferior olive, some of which have previously been described to contribute to the olivonodular projection.

Animals↗

PubMed1987

Cerebellar nuclear afferents--where do they originate? A re-evaluation of the projections from some lower brain stem nuclei.

Cerebellar nuclear afferents from some caudal brain stem nuclei in the cat were studied by means of retrograde transport after implantation of the wheat germ agglutinin-horseradish peroxidase complex in crystalline form in the cerebellar nuclei. The findings give evidence that projections to the cerebellar nuclei from certain nuclei of the reticular formation proper (e.g., from the gigantocellular reticular nucleus) are very modest, while there appears to be no or extremely few cerebellar nuclear afferents from the paramedian reticular, spinal trigeminal, gracile, cuneate and external cuneate nuclei. Previous tracer studies have given evidence that also the pontine and red nuclei send very few, if any, fibres to the cerebellar nuclei. All these brain stem regions are known to project to the cerebellar cortex. This relative lack of mossy fibre collaterals to the cerebellar nuclei is discussed with references to previous literature on the distribution of cerebellar nuclear afferents, and the problem of how the cerebellar nuclei are facilitated is considered.

Afferent Pathways↗

PubMed1986

Is there a reciprocal connection between the red nucleus and the interposed cerebellar nuclei? Conclusions based on observations of anterograde and retrograde transport of peroxidase-labelled lectin in the same animal.

The rubrointerposital projection was studied in cats where wheat germ agglutinin-horseradish peroxidase (WGA-HRP) was implanted in various parts of the interposed nuclei. No retrogradely labelled rubral cells were observed following implantations in the posterior interposed nucleus, and only very few such cells were identified in the contralateral red nucleus after implantations restricted to the anterior interposed nucleus with no contamination of cerebellar white matter or cortex. However, when WGA-HRP was delivered by a pressure injection, which in addition to the anterior interposed nucleus included the adjacent white cerebellar matter along the needle track and the overlying cortex, many retrogradely labelled cells were present contralaterally in the magnocellular red nucleus, with some also found in its rostral parvicellular part. The same observation was made when injection of free HRP exceeded the boundaries of the anterior interposed nucleus. These observations indicate that there is a negligible projection from the red nucleus to the contralateral interposed cerebellar nuclei. What has been considered to be rubrointerposital cerebellar fibres probably is the projection to the cerebellar cortex (Exp. Brain Res., 50 (1983) 353-358). Anterogradely labelled fibres could be followed from the implantations in the posterior interposed nucleus to a medial crescent of the entire contralateral red nucleus. Caudal as well as rostral parts of the posterior interposed nucleus project into the same area of the red nucleus. Implantations restricted to the anterior interposed nucleus label a projection to the contralateral magnocellular red nucleus which is topographically organized. The caudal part of the anterior interposed nucleus projects to the dorsomedial portion of the magnocellular red nucleus, the rostral part to its ventrolateral portion. In addition, a mediolateral organization in the anterior interposed nucleus coincides with a caudorostral arrangement in the red nucleus. This topical arrangement corresponds to what has previously been observed in cat and monkey, but due to the small implantation sites used in the present study a more precise mapping of the projection has been obtained. Furthermore, our implantations of WGA-HRP into the red nucleus show especially well the latter topical arrangement in the projection. The observations mentioned above are discussed and related to previous studies of the rubrocerebellar and cerebellorubral projections.

Animals↗

PubMed1986

The cerebellar nucleo-olivary and olivocerebellar nuclear projections in the cat as studied with anterograde and retrograde transport in the same animal after implantation of crystalline WGA-HRP. III. The interposed nuclei.

The bidirectional connections between the inferior olive and the cerebellar nuclei were investigated by means of anterograde and retrograde transport after implantation of crystalline wheat germ agglutinin-horseradish peroxidase complex in the interposed nuclei. The projections from the interposed nuclei to the inferior olive show a detailed topical arrangement. The main projection from the anterior interposed nucleus reaches the rostral two thirds of the dorsal accessory olive, while the main projection from the posterior interposed nucleus reaches the rostral half of the medial accessory olive. The projections from the inferior olive to the interposed nuclei show a more widespread distribution and appear to be less precisely organized. Both interposed nuclei receive afferents from the medial and dorsal accessory olives, the dorsomedial cell column, nucleus beta and the dorsal cap. Our findings give evidence that the olivo-interposed and interposito-olivary projections are in part reciprocally organized. Our observations are discussed and related to previous investigations on the cerebello-olivary and olivocerebellar pathways. Some methodological comments are made. It appears from our results that anterograde transport in some of our cases has occurred only from a restricted part of the stained area at the implantation site.

Animals↗

PubMed1986

Ultrastructure of spinal efferents to the lateral reticular nucleus: an EM study using anterograde transport of WGA-HRP complex.

Anterograde transport of lectin-conjugated horseradish peroxidase and subsequent incubation with tetramethylbenzidine were employed to label the spinal terminals within the feline lateral reticular nucleus (NRL) for ultrastructural identification. Quantitative studies demonstrated that compared to the unlabelled terminals the spinal boutons were more than twice as large and contained fewer synaptic vesicles. Most of the synaptic contacts of the labelled terminals were located on dendritic shafts but contacts on dendritic spines as well as perikarya were also present. In four cases (all with cervical injections), the postsynaptic cells could be studied in the transversal sections of the medulla in the nuclear plane. The neurons were large and elongated with longest and shortest diameters of about 60 X 30 microns, belonging to the largest category of cells within the NRL. The observations were discussed and related to the findings made in other studies of the NRL.

Animals↗

PubMed1986

The origin and termination of the dentatorubral fibres in the cat as studied with retrograde and anterograde transport of peroxidase labelled lectin.

The dentatorubral projection in the cat was studied by means of retrograde and anterograde transport after implantations of crystalline wheat germ agglutinin-horseradish peroxidase (WGA-HRP) in the red and dentate nuclei, respectively. Our retrograde transport findings give evidence that rubral afferents originate in the contralateral dentate nucleus, mainly dorsally in its central part. The dentate implantations (with no contamination of the adjacent interposed nuclei) show that in the cat the great majority of the dentatofugal fibres leave the ipsilateral brachium conjunctivum to decussate below the red nucleus. Scattered crossing fibres also penetrate the contralateral red nucleus at all caudorostral levels on their way to the contralateral thalamus. Terminal fibres were found only in the rostral part of the red nucleus, but no retrogradely labelled rubral cells were observed. The findings are discussed in relation to previous studies on the dentatorubral projection.

Animals↗

PubMed1986

Do pontocerebellar mossy fibres give off collaterals to the cerebellar nuclei? An experimental study in the cat with implantation of crystalline HRP-WGA.

In 15 cats with implantations of crystalline HRP-WGA in the cerebellar nuclei and tetramethylbenzidine histochemistry, the pontine nuclei were carefully examined for presence of retrogradely labelled cells. Findings in the nucleus reticularis tegmenti pontis and the inferior olive, both known to project to the cerebellar nuclei, served as controls for effectiveness of uptake and transport. After implantations restricted to the lateral cerebellar nucleus in 5 cats altogether two labelled cells were found in the contralateral pontine nuclei in regions receiving afferents from the lateral nucleus. In contrast, many labelled cells occurred in the nucleus reticularis tegmenti pontis and the inferior olive. After implantations in 5 cats restricted to the posterior or anterior interposed nuclei, altogether only one labelled cell was found in the pontine nuclei, while many labelled cells occurred in the inferior olive. The nucleus reticularis tegmenti pontis contained a small number of retrogradely labelled cells after implantations in the anterior interposed nucleus, but none after implantations restricted to the posterior interposed nucleus. After implantations restricted to the medial (fastigial) nucleus, no retrogradely labelled cells were found in the pontine nuclei and nucleus reticularis tegmenti pontis (although many were present in the inferior olive). The present findings support earlier conclusions based on anterograde tracing methods that the cerebellar nuclei receive very few, if any, afferents from the pontine nuclei.

Animals↗

PubMed1985

On the projections from the vestibular and perihypoglossal nuclei to the spinal trigeminal and lateral reticular nuclei in the cat.

The projection from the vestibular and perihypoglossal nuclei to the spinal trigeminal and lateral reticular nuclei has been studied in cats where the wheat germ agglutinin-horseradish peroxidase complex has been used as a retrograde tracer. All injections were made at the level of the caudal pole of the inferior olive. The medial and descending vestibular, and the perihypoglossal nuclei were found to project to the spinal trigeminal nucleus. The projection to the lateral reticular nucleus reaches its medial-most part only, and originates in the lateral vestibular nucleus. The lateral part of the reticular formation also appears to be the target for some vestibular efferent fibres, mainly from the descending vestibular nucleus. The retrogradely labelled cells within the medial and descending vestibular nuclei are of all sizes and distributed throughout their entire territory. Certain observations furthermore indicate that the fibres reaching the lateral reticular nucleus are collaterals only from the vestibulospinal tract. The projections are bilateral. The observations confirm and extend previous observations on the afferent projections to the spinal trigeminal and lateral reticular nuclei.

Animals↗

PubMed1985

Cerebellar nuclear afferents from feline hypothalamus demonstrated by retrograde transport after implantation of crystalline wheat germ agglutinin-horseradish peroxidase complex.

A hypothalamo-cerebellar projection has recently been discovered in the cat, and its presence has been verified in other mammalian species. Due to methodological limitations only hypothalamic projections to cerebellar cortex had been demonstrated. By means of modification of the new implantation technique described by Mori et al. [10], hypothalamic projections to the cerebellar nuclei have been revealed using retrograde transport of a wheat germ agglutinin-horseradish peroxidase complex (WGA-HRP). This method permits identification of afferents to restricted nuclear regions without uptake of the tracer into passing fibers. The projection from hypothalamus has an ipsilateral predominance and has its main terminal area in the fastigial nucleus. These findings were verified in anterograde transport experiments after hypothalamic injections of WGA-HRP.

Animals↗