Alf Brodal

The projection of the superior colliculus onto the reticular formation of the brain stem. An experimental anatomical study in the cat.

SummaryFollowing altogether 18 stereotactically placed lesions of different location and size in the superior colliculus the efferent fibres to the RF and their distribution were traced in silver impregnated, approximately serial sections (Nauta and Fink and Heimer methods), cut in the transverse, horizontal or sagittal plane. The projection to the mesencephalic RF was found to be almost completely ipsilateral, that to the pontomedullary RF largely contralateral. In the mesencephalic RF the fibres end in its dorsal half approximately. In the pons and medulla they supply only the medial 2/3 of the main RF, with two distinct maxima within the total field of termination. One maximum covers the rostral part of the nucleus reticularis gigantocellularis and the adjoining part of the nucleus reticularis pontis caudalis, the other occupies the rostralmost part of the latter and the caudal part of the nucleus reticularis pontis oralis. Of the precerebellar reticular nuclei the contralateral nucleus reticularis tegmenti pontis receives a distinct component of tectal fibres in a small area dorsomedially. Some fibres end in a restricted part of the nucleus reticularis lateralis and in the paramedian reticular nucleus.The tectoreticular projection appears to be organized according to the same principles as other afferents to the RF. In the main RF the areas of termination of the tectoreticular fibres coincide more or less with the areas of termination of corticoreticular, fastigioreticular and vestibuloreticular fibres. These common terminal areas are those which give off the bulk of reticulospinal fibres. Some functional implications of the pattern of organization in the tectoreticular projection are discussed.

THE CEREBELLAR CONNECTIONS OF THE NUCLEUS RETICULARIS LATERALIS (NUCLEUS FUNICULI LATERALIS) IN RABBIT AND CAT. EXPERIMENTAL INVESTIGATIONS

COSTENTS page Aatroductio~i .............................................................................. 171 iiiatel-ial nitd nietAods ............................................................... Sormal anatomy of the nucleus reticularis lateralis .................. The retrograde cellular changes in the nucleus reticularis lateralis Remarks on the evaluation of the retrograde changes found in the nucleus reticularis lateralis after cerebellar injuries ......

Mode of termination of primary vestibular fibres in the lateral vestibular nucleus an experimental electron microscopical study in the cat

SummaryFollowing transection of the vestibular nerve in cats, the electron microscopical changes occurring in the lateral vestibular nucleus were studied after survival periods of 2–11 days. Material for study was taken from the rostroventral part of the nucleus of Deiters since this is known to receive the primary vestibular fibres.Degeneration of terminal boutons is evident two days after the lesion. Degenerating boutons show an increased electron optic density, mitochondrial changes and a loss of synaptic vesicles. They are often surrounded by a pericellular space filled with flocculent (probably protein) material. At three days and later this space is occupied by processes of astrocytes or of a type of phagocytic cells which surround or engulf the degenerating boutons. Nine to eleven days after the lesion almost all degenerating boutons have disappeared. There is evidence of phagocytosis of axons and myelin sheaths by astrocytes but mainly by phagocytes of yet undetermined origin. The “filamentous type” of bouton degeneration has not been observed.Degenerating boutons are found on neuronal perikarya and on proximal as well as on thin distal dendrites and on spines. They are common on small and medium-sized cells, but have also been seen on some giant cells. The degenerating boutons do not form series of synaptic complexes. Degenerating fibres and boutons have so far been found only ipsilateral to the lesion.The findings confirm and extend those made in corresponding experiments with silver impregnation procedures, but emphasize the limitations of the latter methods as regards conclusions concerning synaptic contacts.

The cerebral cortical projection to the lateral reticular nucleus in the cat, with special reference to the sensorimotor cortical areas

Abstract Maturation of evoked cortical responses to visual and auditory stimulation was investigated in normal as well as in acute and chronically starved cats. In normal rats the most prominent changes occur at 14 days of age, i.e., decreased latencies and the appearance of all components of the evoked response. In rats acutely starved (24h) the most marked changes were observed in early periods of postnatal life. Increased latencies and absence of the first positive component were typical modifications of the responses. Chronic starvation (daily for 10–12 h, from 5 to 10 days) was followed by a significant increase in latencies lasting as long as 45 days of age. Some probable mechanisms of these changes are discussed.

The Inferior Olive. Notes on its Comparative Anatomy, Morphology, and Cytology

It is appropriate, before discussing the olivocerebellar connections, to review briefly some features of the normal olive, since these are of relevance for the interpretation of data obtained in studies of the connections of the olive.

Observations on the secondary vestibulocerebellar projections in the macaque monkey

SummaryThe distribution of retrogradely labeled cells in the nuclei of the vestibular nuclear complex following injections of horseradish peroxidase in various parts of the cerebellar cortex (except the nodulus and paraflocculus) has been mapped in the macacus rhesus monkey. In the main the findings correspond to those made in other mammalian species (cf. Table 1). The flocculus receives afferents bilaterally from the superior, medial and descending vestibular nuclus, group y, the interstitial nucleus of the vestibular nerve and also from the abducent nucleus. The projection to the posterior vermis (lobules VIII and IX), expecially to lobule IX, is more abundant than that to lobules VI–VII. The projection to the anterior lobe vermis appears to be modest. Evidence for projections to the cerebellar hemispheres was not obtained. Whether the lateral vestibular nucleus projects to the cerebellum in the macaque is uncertain. The regular occurrence of weakly labeled cells among heavily labeled ones suggests that many of the cerebellar projecting cells may have axonal branches passing to other destinations. The findings lend support to the notion that there are precise topical relations within the entire secondary vestibulocerebellar projection. For example, in the medial nucleus the sites of origin of fibers to the flocculus and uvula are different. Surprisingly, many cells in group z were found to project to the uvula and — to a lesser extent — to lobule VIII. The group z may, therefore, not be a pure relay nucleus in a spinothalamic pathway, as generally assumed. The rather marked cerebellar projection of the abducent nucleus, expecially to the flocculus, is of interest for the analysis of cerebellar control of eye movements in the macaque.

A cerebellar projection onto the pontine nuclei an experimental anatomical study in the cat

SummaryFibres passing from the intracerebellar nuclei to the pontine nuclei proper have been noted only by few students. In the present study this projection is analysed by mapping with the Nauta (1957) and Fink and Heimer (1967) methods the degeneration which occurs in the pontine nuclei following stereotactically placed electrolytic lesions in different parts of the intracerebellar nuclei in the cat. Cerebellopontine fibres come from the lateral cerebellar nucleus (NL) except its ventralmost part, and from the rostral but probably not from the caudal part of the interpositus anterior (NIA) and the interpositus posterior.The fibres end in three fairly well circumscribed regions of the pontine nuclei: a longitudinal column in the paramedian pontine nucleus, a column in the dorsolateral nucleus and one in the dorsal peduncular nucleus. Fibres from the NL as well as the NIA appear to end in all three regions, but the possibility of a more specific distribution cannot be excluded. Parts of the projection areas in the pons appear to be specific to cerebellar afferents, while other parts overlap with terminations of cerebropontine fibres, especially from SmI and SmII.The findings support the conclusions arrived at in recent studies of the cerebral corticopontine projections by P. Brodal (1968a, 1968b, 1971a, 1971 b) that the pontine nuclei are very precisely organized. The general principles in the organization of the corticopontine and cerebellopontine projections appear to be similar.

The organization of the nucleus reticularis tegmenti pontis in the cat in the light of experimental anatomical studies of its cerebral cortical afferents

SummaryThe distribution of degenerating fibres in the nucleus reticularis tegmenti pontis (N.r.t.) has been examined in Nauta (1957) impregnated sections from cats with discrete lesions of various cortical regions. The following cortical regions send fibres to the N.r.t.: Ms I, Sm I, Sm II, the orbital gyrus, the proreate gyrus, the parietal cortex and parts of the medial surface of the frontal lobe. The projection is bilateral, but mainly ipsilateral. The main terminal area of fibres from all cortical regions mentioned is the ventral part of the N.r.t. at middle rostrocaudal levels. Within this territory most cortical regions have their particular terminal sites in the N.r.t., but there is considerable overlapping.The anatomical organization and the role of the N.r.t. as a cerebrocerebellar relay station are discussed. The regions of the N.r.t. not receiving cortical fibres are supplied by fibres from other sources. These fibre groups have their preferential, although overlapping, areas of termination. In its organization the N.r.t. differs markedly from the pontine nuclei proper. Like the two other precerebellar reticular nuclei the N.r.t. appears to provide possibilities for an integration of impulses from the cerebral cortex with those from many other sources before they influence the cerebellum.

A note on the method of retrograde transport of horseradish peroxidase as a tool in studies of afferent cerebellar connections, particularly those from the inferior olive; with comments on the orthograde transport in Purkinje cell axons

Summary1.Injections of horseradish peroxidase (HRP) suspension were made in the cerebellar cortex of cats (most often the paramedian lobule). The staining of the cerebellar cortex and the ensuing labeling of neurons in the inferior olive were studied in experiments with variations of concentration of HRP, amounts of fluid injected, survival time and age of the animals. Light microscopical studies were supplemented with electron microscopical observations. The folded cerebellar cortex offers particular difficulties with regard to obtaining a predictable extent of stained tissue, and the spreading of the fluid within the cortex shows great variations even with the same amounts and concentrations of HRP suspension. Diffusion of fluid appears to occur most easily within the molecular layer. Often there are unstained parts of folia between stained parts. Staining of the cortex is barely visible after 7 days, but appreciable shrinking of the stained area does not appear to occur until after 4 days.2.The first signs of labeling of olivary neurons are seen after 5–10 hours, after 7 days there are no labeled cells. The rate of retrograde transport in olivocerebellar fibers is calculated to be between 50 and 100 mm/day. Labeling of cells appears to require staining of the molecular layer of its projection areas in the cerebellum.3.For studies of the olivocerebellar projection survival times of 2–3 days and injections of 0.5 μl of a 50% HRP suspension seem in general to be well suited. Best results are obtained with animals weighing 1–3 kg. There is a clearcut correlation between the site of staining of the cortex of a particular part of the cerebellum and the site(s) and extension of olivary area(s) containing labeled cells.4.Anterograde transport in axons of Purkinje cells has been observed. Electron microscopically the axons of these fibers contain HRP labeled tubules and vesicles as do their terminal boutons in the nuclei.5.In cases where the injected fluid has spread to the cerebellar nuclei, localized parts contain neurons which are labeled as are the cells in the injected cerebellar cortex.

Cerebellar corticonuclear projection in the cat. Crus II. An experimental study with silver methods

Abstract Small differently placed, bilateral lesions were made by transdural coagulation of the cerebellar cortex in the crus II of the cerebellum in 18 cats. In 10 cerebellar halves the lesions were confined to the crus II. The present study is based on these and on 5 halves with some concomitant injury to the dorsal paraflocculus. The ensuing course of the degenerating efferent fibres and the distribution of degeneration in the intracerebellar nuclei were studied with the Nauta31 method and mapped, in most cases in sagittally cut, approximately serial, sections. This facilitated comparisons between cases. The crus II projects onto the nucleus lateralis (NL) as well as the nuclei interpositus anterior (NIA) and posterior (NIP; subdivisions according to Flood and Jansen17). One band of degeneration extends from the dorsocaudal part of the NL, medially and slightly ventrally, through the transition region between NL and NIA into the caudal medial part of the latter. Another band extends from lateral to medial in the rostral part of the lateral half of the NIP. Within both projections there is a topical pattern, less marked in the NIP than in the other band: lateral parts of the crus II project more laterally and ventrally than do medial parts (Fig. 8). The findings demonstrate that the corticonuclear projection of crus II is precisely organized, but there is no strict correlation between lateral and medial parts of the crus II and lateral and medial regions of the lateralis-interpositus complex, respectively, as suggested by Jansen and Brodal21, 22. Even lesions situated most laterally in crus II result in degeneration in the NIP. The pattern of longitudinal subdivisions of the cerebellum which can be recognized during cerebellar corticogenesis24, 25 appears to be considerably distorted during later development. Since there appears to be a somatotopical pattern in the crus II20, 35, it is possible to indicate approximately regions ‘representing’ hindlimb, forelimb and face in the lateralis-interpositus complex.