The development of synaptic contacts in the cerebellum of Macaca mulatta

Expression of BDNF and TrkB receptor subtypes in the postnatal developing Purkinje cells of monkey cerebellum

In the previous study, we have shown the complementary expression of TrkB subtypes (TK+ and T1) in the adult monkey cerebellar cortex. In this study, to clarify when that expression pattern appeared, we examined the expressions of TrkB subtypes and its ligand brain-derived neurotrophic factor (BDNF) by immunohistochemistry and Western blot analysis. At the newborn stage, both TK+ and T1 were expressed uniformly in the cerebellar cortex. At postnatal month 3.5, the uneven expression of TrkB subtypes was observed, while the BDNF immunoreactivity was strongly detected in all regions of the cerebellar cortex. The expression patterns of TrkB subtypes and BDNF at both postnatal month 6 and year 7 were the same as those at postnatal month 3.5. Western blot analysis demonstrated that TK+ and T1 were expressed at high levels in the synaptic membrane from newborn to adult stages. Furthermore, the dimerization of TrkB subtypes changed at postnatal month 3, which was similar to the adult pattern: at the newborn stage, the TK+ and TK- homodimers; after postnatal month 3.5, the TK+ and TK- homodimers, and the TK+/TK- heterodimer. These findings suggest that the localization of TrkB subtypes in each Purkinje would be changed at postnatal month 3.5, resulting in the uneven expression of TrkB subtypes and the change of TrkB dimerization.

Fetal cerebellum: US appearance with advancing gestational age

PURPOSE

To evaluate the change in ultrasonographic (US) appearance of the fetal cerebellum with advancing gestation.

MATERIALS AND METHODS

A total of 291 normal fetuses of uncomplicated pregnancies were evaluated at gestational ages (GAs) between 15 and 41 weeks with a 3.75-MHz transabdominal curvilinear probe. After the transcerebellar view was obtained, the transverse cerebellar diameter (TCD) was measured and the images were stored. On hard-copy US images, cerebella were assigned three grades of appearance. These grades were analyzed in relation to GA and TCD. Inter- and intraobserver variations were assessed in 91 randomly selected cases.

RESULTS

Cerebella in 137 (47.1%), 71 (24.4%), and 83 (28.5%) of 291 subjects were classified as grade I (hypoechoic, "eyeglass" shape), grade II (intermediate echogenicity, "dumbbell" outline), and grade III (hyperechoic, "fan" shape), respectively. With advancing gestation, the dominant grade changed from I to III gradually and progressively. The median GA and TCD, respectively, were 22 weeks and 22 mm for grade I, 29 weeks and 35 mm for grade II, and 36 weeks and 46 mm for grade III. These differences were statistically significant (P <.001). The agreements within inter- and intraobserver estimations were 96% (87 of 91) and 95% (86 of 91), respectively.

CONCLUSION

A gradual change in US appearance of the fetal cerebellum is seen with advancing gestation.

Compound synapses within the GABAergic innervation of the auditory inner hair cells in the adolescent mouse

Ultrastructural investigation of the gamma-aminobutyric acid (GABA) component of the inner spiral bundle in adolescent mice revealed a pathway of glutamic acid decarboxylase (GAD)-positive and -negative fibers and vesiculated endings that contact inner hair cells and their afferents through a complex of axosomatic and axodendritic synapses. Ultrastructural details were investigated by using conventional electron microscopy. Several synaptic arrangements were observed: Main axosomatic synapses form between vesiculated endings and individual or adjoining inner hair cells (interreceptor synapses). Spinous synapses form on long, spinelike processes that protrude from inner hair cells to reach distant efferent endings. The efferent endings associate with inner hair cells and their synaptic afferents through compound synapses-serial, "converging," and triadic-otherwise characteristic of sensory relay nuclei. Serial synapses form by the sequential presynaptic alignment of the efferent-->receptor-->afferent components. Converging synapses result from the simultaneous apposition of a receptor ribbon synapse and a presynaptic efferent terminal on a recipient afferent dendrite. Triadic synapses comprise a vesiculated efferent ending in contact with an inner hair cell and with its synaptic afferent. Additionally, efferent endings may form simple axodendritic and axoaxonal synapses with GAD-negative vesiculated endings. The combination of different synaptic arrangements leads to short chains of compound synapses. It is assumed that these synaptic patterns seen in the adolescent mouse represent adult synaptology. The patterns of synaptic connectivity suggest an integrative role for the GABA/GAD lateral efferent system, and imply its involvement in the pre- and postsynaptic modulation of auditory signals.

Reinnervation of cerebellar Purkinje cells by climbing fibres surviving a subtotal lesion of the inferior olive in the adult rat. II. Synaptic organization on reinnervated Purkinje cells

A salient feature of the cerebellar Purkinje cells is the highly ordered distribution of their excitatory afferents on the dendritic tree. Climbing fibres synapse exclusively on the proximal dendrites, whereas parallel fibres articulate with the distal branches, the so-called spiny branchlets. This input organization is lost following the removal of climbing fibres. Such denervation results in the formation of a large number of new spines on the proximal dendrites, and these become contacted by sprouting parallel fibres, which thereby extend their domain of innervation. We have previously shown that the climbing fibres surviving a subtotal lesion of the inferior olive sprout and reinnervate neighbouring Purkinje cells. In the present ultrastructural study, we have investigated the features of Purkinje cells reinnervated by sprouting climbing fibres. The objectives were to examine the fine morphology of the newly formed synapses and to determine whether the modifications of Purkinje cell morphology and afferent organization are reversed by this reinnervation. Surviving climbing fibres were labelled by the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) and immunohistochemically visualized by means of the gold-substituted silver peroxidase technique, 2 and 6 months after 3-acetylpyridine lesions of the inferior olive in adult rats. Sprouting climbing fibres and newly formed arborizations were identified in the light microscope, isolated, and cut in serial ultrathin sections for electron microscopic analysis. The labelled boutons belonging to newly formed terminal plexuses exhibited the typical morphological features of climbing fibre terminals, i.e., a high number of round synaptic vesicles and a few small mitochondria. Most frequently they formed asymmetric synapses on stubby thorns protruding from the proximal Purkinje cell dendrites. In some instances, however, the postsynaptic element consisted of long slender spines or spines showing an atypical morphology. A number of labelled boutons was also in contact with the perikarya of reinnervated Purkinje cells, either articulating with spines or synapsing directly on the smooth somatic surface. The proximal dendrites of denervated Purkinje cells were characterized by large numbers of spines, which were frequently postsynaptic to parallel fibres. By contrast, Purkinje cells reinnervated by the sprouting climbing fibres generally showed a lower number of spines on their proximal dendrites, indicating a reversal of this morphological change. The aberrant parallel fibre input was also decreased on reinnervated dendrites or had completely disappeared. Nevertheless, some reinnervated Purkinje cells showed the persistence of some parallel fibre synapses on their proximal dendrites. On occasion, climbing fibre and parallel fibre boutons synapsed on the same spine.

Development of spiral ganglion cells in mammalian cochlea

The development of the spiral ganglion in the cat, the rat, and the mouse was studied by electron microscopy, from fetal stages in the cat and from birth in the rodent. In the earliest stages, a single population of ganglion cells is present. Immature spiral ganglion neurons possess small perisomatic processes that seem to disappear with development, before the myelination ganglion cells are surrounded by one or two layers of Schwann cell processes. With maturation, the Schwann process increases in number around the perikaryon and its processes, which leads to the onset of myelination. The onset of myelination of the cell body processes is asynchronous. The perikaryon may be delayed in myelination by several days. Moreover, ganglion neurons from a given region of the cochlea do not myelinate simultaneously. The differentiation of two types of fibers in the intraganglionic spiral bundle and the first appearance of TII neurons occurs around birth in the cat and a few days after birth for the rat and the mouse. The distinction of TII cells is possible due to characteristic accumulation of neurofilamentous structures in the cytoplasm.

Olivocerebellar fiber maturation in normal and lurcher mutant mice: defective development in lurcher

Olivocerebellar fiber maturation was examined in normal and lurcher mutant mice between postnatal day 5 (P5) and P15, using the anterograde transport of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) from the inferior olive. Immunocytochemistry for the Purkinje cell marker PEP-19 was used to demonstrate Purkinje cell development in the same material. In mutant and normal animals, a regional developmental variation is observed such that, when compared at a given age, cortex lining the vermal fissures appears developmentally advanced over cortex in the cerebellar hemispheres. In the primary fissure of the normal animals, the first recognizable Purkinje cell dendrites appear on P6, and the olivocerebellar fibers first enter the climbing stage of their development on P9. In lurcher animals Purkinje cell development proceeds on this schedule, but olivocerebellar fibers are never observed to enter the molecular layer. These afferents maintain dense perisomatic nests around Purkinje cells, even in P13-15 lurchers. Examination of P14 lurchers by transmission electron microscopy indicates that the olivocerebellar fibers form synapses on Purkinje cell somatic spines and that the basket cell axons fail to form their typical perisomal nests around Purkinje cells. In addition, parallel fibers can be observed to synapse on dendritic spines on the Purkinje cell primary dendrites. We interpret these results as indicating a recognition defect between olivocerebellar fibers and Purkinje cell dendrites. An analysis of this defect in lurcher may reveal how the normal transformation of olivocerebellar fibers, from perisomal to dendritic terminals, is achieved.

Neuropeptide-immunoreactive cells and fibers in the developing primate cerebellum

Using the avidin-biotin-peroxide immunohistochemical method, we studied the distributions of somatostatin (SOM)-, cholecystokinin-8 (CCK-8)- and substance P (SP)-like immunoreactivities in the cerebellum of macaque monkeys at embryonic day 120 (E120), E140, newborn, postnatal day 60 (P60) and adults. During the embryonic stages, there were many SOM-, CCK- and SP-immunoreactive structures in the external granular layer, Purkinje cell layer and white matter, SP-immunoreactive mossy fibers and their terminals were distributed in the granular layer and white matter. During these stages, there were SOM-immunoreactive Purkinje cells, Golgi cells and a few cells in the molecular layer, and CCK-immunoreactive Purkinje cells and cells in the molecular layer. At the newborn stage, all of the immunoreactivities in the external granular layer decreased and the number of immunoreactive fibers increased in the white matter. At P60 stage, SOM- and CCK-immunoreactive fibers were observed around Purkinje cells, which seem to be the fiber terminals of basket cells. Many SOM, CCK and SP fibers were distributed in the white matter. In the adult stage, we observed little neuropeptide-immunoreactivity in the cerebellum. The high concentration of the neuropeptide-immunoreactive fibers and cells in the earlier stages suggests that the neuropeptides may be involved in the development of the primate cerebellar cortex.

Ontogeny of glutamic acid decarboxylase, tyrosine hydroxylase, choline acetyltransferase, somatostatin and substance P in monkey cerebellum

The enzyme activities of glutamic acid decarboxylase (GAD), tyrosine hydroxylase (TH) and choline acetyltransferase (ChAT) and concentrations of substance P (SP) and somatostatin were determined in the cerebellum of macaque monkey (Macaca fuscata fuscata) at 3 different ages, embryonic 4 months, embryonic 5.5 months (full-term) and adult. Similar graded increases in the activities of GAD and TH were observed during development. In contrast, ChAT activity was relatively high at embryonic 4 months, increased about twofold between embryonic 4 months and 5.5 months, but did not change between embryonic 5.5 months and adult. These findings suggest that noradrenergic terminals develop synchronously with GABAergic interneurons. On the other hand, the innervation by ChAT-containing fibers is completed during the prenatal period. The concentrations of somatostatin and SP were high at embryonic 4 months, and decreased to, respectively, about 1/18 and 1/4 (expressed per g weight) in adult animals. Several interpretations of the decrease of the two neuropeptides in cerebellar tissue during ontogeny are discussed.

The timing of granule cell differentiation and mossy fiber morphogenesis in the opossum

The timing of developmental events may be important for the orderly formation of neuronal interconnections. In the present study, the timing of granule cell migration is compared with the arrival and maturation of mossy fiber projections. The opossum was chosen as the experimental animal because its protracted postnatal development enables the examination of developmental sequences not as easily recognized in other more commonly used mammalian species. It is shown that all areas that project to the cerebellum as mossy fibers in the adult opossum do so by postnatal day (PD) 30. Their major target, the granule cells begin inward migration from the external germinal layer (EGL) prior to PD 30, but do not form a distinct internal granular layer (IGL) until PD 35. Migrating granule cells penetrate into the IGL deep to granule cells that have begun dendritic differentiation. By PD 50, Golgi impregnations reveal that many granule cells have numerous immature processes, somal spines and dendritic growth cones. After this age these structures are rare and the vast majority of granule cells exhibit short dendrites with digiform endings. Dendritic differentiation subsequent to PD 54 involves an increase in the length of the shaft and the further maturation of terminal digits. Also from Golgi material, immature mossy fiber endings can be identified in the IGL by PD 35 and exhibit mature characteristics at PD 73. Thus, the formation and maturation of granule cell dendrites and their afferents (mossy fibers) occur over an extended period of time (PD 35-73). Moreover, granule cells exhibit a sequence of development similar to that of Purkinje cells: early arrival of their primary afferent projections in the cerebellar anlage; a period of exuberant dendritic growth; and a protracted and overlapping period for dendritic and synaptic maturation.

Neurogenesis of the climbing fibers in the human cerebellum: a Golgi study

The prenatal and early postnatal neurogenesis of the human climbing fibers of the lateral cerebellar hemispheres have been studied, with the rapid Golgi method, and correlated with the developmental stages of Purkinje cells. A transitional phase has been established in the neurogenesis of the human Purkinje cell between the second and third stages of Cajal. This phase coincides with the arrival of the climbing fibers. It is characterized by the reabsorption and subsequent transformation of Purkinje cell's basal dendrites into somatic spines. Following the arrival of the climbing fibers and the establishment of contacts, the Purkinje cell is progressively transformed from an immature stellate and nonoriented cell into a monopolar and spatially oriented one which acquires all of its mature morphological and functional features. The human climbing fibers arrive at the Purkinje cell plate by the 28th week of gestation and establish a transient paraganglionic plexus before contacts with these neurons can be recognized. They start to form pericellular nests by the 29th week, and by the 31st week of gestation all Purkinje cells of the lateral hemispheres have pericellular nests around their bodies. These pericellular nests are progressively and rapidly transformed into supracellular "capuchones" which themselves are also short-lived because the climbing process starts readily in them. Supracellular "capuchones" are recognized by the 34th seek and their fibrils start to climb the dendrites of Purkinje cells (young climbing phase) by the 36th week of gestation. The process of climbing the dendrites of the Purkinje cells will continue through late prenatal and early postnatal life. The human climbing fibers are distributed, in the internal granular layer, within narrow and long vertical territories which are transverse to the long axis of the follium. A single climbing fiber is (1) able to establish contacts with many Purkinje cells located within its narrow territory of distribution; (2) has a tendency to establish contacts with small groups of Purkinje cells rather than with isolate neurons; (3) able to send collaterals to several contiguous cerebellar folia; and (4) able to send collaterals to the internal granular layer and to form pericellular nests in it. The human cerebellum may be considered to be subdivided into a series of parallel, narrow, and transverse structural/functional planes, each one characterized by the distribution of a climbing fiber.(ABSTRACT TRUNCATED AT 400 WORDS)

An immunohistochemical study of serotonin development in the opossum cerebellum

In the present study we have used the indirect antibody peroxidase anti-peroxidase technique to analyze the development of serotonin in the cerebellum of pouch young opossums ranging in age from birth (postnatal day (PD) 1) - to PD 47. The pathways by which serotoninergic axons enter the cerebellum appear to change during development. Between PD 1 and PD 11 varicose serotoninergic fibers course though the continuity between the tectum and the dorsal medial aspect of the cerebellar plate and distribute primarily to the intermediate zone. By PD 11 serotoninergic fibers enter the cerebellum via a connecting band between the cerebellum and the dorsal lateral aspect of the rostral medulla. Fibers entering the cerebellum via this later route course around the lateral recess of the fourth ventricle and initially distribute to ventral and lateral areas of the cerebellum. At later developmental ages (PD 14-PD 47) serotoninergic fibers are present in: 1) the cellular zone of migration between the Purkinje cell layer and deep nuclei; 2) the Purkinje cell layer; 3) the internal granule cell layer; and 4) the deep cerebellar nuclei. The external granule cell and the molecular layers rarely contain serotoninergic fibers. The present study has shown that serotonin is present in the cerebellar anlage on PD 1 (within 13 days of conception). This is prior to the arrival of other major afferent systems (King et al. 1982; Bishop et al. 1983; Martin et al. 1983; Morgan et al. 1983). Further, serotoninergic axons reach the cerebellum via different routes at different stages of development. The presence of serotonin in the intermediate zone early in development supports the hypothesis that it may influence neuronal migration and differentiation (Lauder and Krebs 1976). Axons containing serotonin and arriving later in development may function in synaptic transmission, a role proposed for this indoleamine in the adult (Strahlendorf et al. 1979).

Purkinje cell maturation in the frog cerebellum during thyroxine-induced metamorphosis

Purkinje cell maturation during thyroxine-induced metamorphosis in premetamorphic bullfrog tadpoles was studied using electron microscopy and Golgi (silver-impregnated) preparations. Cerebella from tadpoles were examined following 1, 2, or 3 weeks of thyroxine treatment. Particular attention was paid to possible differences between the two populations of Purkinje cells previously described, i.e. (i) the smaller population located in the dorsal part of the cerebellum, where the Purkinje cells show dendritic arborization long before the appearance of the external granular layer, and (ii) the larger population located in the middle and ventral regions of the cerebellum, where the Purkinje cells begin to undergo maturation during metamorphosis when the external granular layer is established. Following thyroxine treatment, both populations of Purkinje cells showed rapid maturational change. In the mature (dorsal) group, dendritic growth resumed in the presence of an external granular layer increasing the complexity of their dendritic arbors. Moreover, climbing fiber synapses translocated from contacts on the soma to the thorns of growing dendrites, and somatic processes often disappeared. The immature (ventral) group showed dramatic differentiation of the perikaryon including polarization of cytoplasm with subsequent dendritic outgrowth and formation of somatic processes in the presence of climbing fibers. Stellate cell contacts appeared on the smooth portion of the soma of many Purkinje cells. Dendritic growth during thyroxine-induced metamorphosis was characterized by growth (elongation) with minimal branching, which is initially observed during spontaneous metamorphosis. Typically, these growing dendrites ended in growth cones, some with one or several filopodia. Developing Purkinje cell dendritic spines formed synapses with parallel fibers. The present study has provided an example of the dramatic nature of thyroxine's action in inducing the complex series of detailed maturational changes in the cerebellum 1-2 yr ahead of schedule. In addition, the results show that thyroxine-induced Purkinje cell maturation is more rapid and synchronous than that seen during spontaneous metamorphosis. It is concluded that Purkinje cell maturation during metamorphosis is largely dependent on thyroid hormone.

Sequential alterations of neuronal architecture in nucleus magnocellularis of the developing chicken: an electron microscope study

The development of the auditory nerve endings and their target cells in nucleus magnocellularis was studied by electron microscopy of perfusion-fixed brains from embryonic day 12 to hatching. Embryonic days 12-13: somatic processes extend from the perikaryon. The cytoplasm of the soma and processes contains free ribosomes, mitochondria, lysosomes, rough endoplasmic reticulum, Golgi apparatus and an eccentric, heterochromatic nucleus. Small profiles of auditory nerve fibers containing round, clear vesicles make specialized contacts, including some synapses, on distal somatic processes but rarely on proximal somatic processes or on the soma. The postsynaptic zones contain a flocculent matrix. Days 15-17: somatic processes disappear and occasional attachment plaques are seen between cell bodies. The nucleus appears euchromatic. Cytoplasmic organelles form a dense matrix indicative of intense metabolic activity. Somatic spines are evident. The afferent axons form large, vesiculated profiles located, increasingly, on the cell body and somatic spines, with many points of synaptic contact. Opposite each ending a band of amorphous, flocculent material fills the postsynaptic cytoplasm. Embryonic day 18-hatching: the somatic cytoplasm becomes less dense; stacks of rough endoplasmic reticulum start to condense. Afferent axon terminals mature, especially the synaptic membrane complex and associated densities. The postsynaptic flocculent material diminishes in extent until it is found associated only with somatic spines. The ultrastructural observations on the maturation of nucleus magnocellularis closely corroborate and extend previous results with the Golgi methods. Developing auditory nerve fibers initially synapse on the distal parts of the somatic processes of the immature cells. As the somatic processes disappear or retract, axonal endings move to the soma and develop into large axosomatic end-bulbs. Possibly, the somatic processes as they retract drag the auditory nerve endings to the cell body. The findings also suggest a role of the transiently appearing, flocculent material of the postsynaptic regions in the formation of synapses.

Golgi studies on Purkinje cell development in the frog during spontaneous metamorphosis. II. Details of dendritic development

The development of Purkinje cell dendrites was studied in the bullfrog from premetamorphic tadpoles to 10-week-old postmetamorphic frog-lets by the Golgi-Kopsch method. In this species two distinct patterns of arbor formation may be seen, which appear to be related to differences in the timing of initial dendritic development. In Purkinje cells that begin development in early tadpole stages, the dendritic tree is elaborated by continuous and concomitant growth and branching, a process by which the developing arbor expands in both height and width. Arbor formation in Purkinje cells that begin development in metamorphosing tadpoles proceeds in two separate steps. Initially, dendrites of such cells elongate, but form only a few poorly developed branches; only when the arbor reaches near-adult height does branching become extensive. Additional differences present in Purkinje cells are reflected in the paucity of growth cones and filopodia in the tadpole, and numerous filopodia and growth cones in the metamorphic period. An interesting feature of dendritic development in this species is a tendency to alter the arboreal domain by the formation of extra-arboreal dendrites, and possibly by the occasional resorbtion of other partially formed dendrites. The pattern of dendritic development in the frog is different than in mammals and is difficult to interpret. Such unusual development may be due to disturbances in the timing of the formation of Purkinje cell dendrites and of the establishment of the external granular layer (EGL).

Synaptogenesis in the cervical cord of the human embryo: sequence of synapse formation in a spinal reflex pathway

Synaptogenesis in the cervical cord was studied by light and electron microscopy in human embryos ranging from four to seven weeks of ovulation age. The stage of embryonic development was estimated on the basis of external morphology of embryos and histology of the eye ball with reference to Streeter's horizon. No synapses were found in the cervical cord of the embryo at Streeter's horizon XIV (8 mm; estimated ovulation age, 28-30 days). A small number of axodendritic synapses appear in the motor neuropil of the cervical cord at Streeter's horizon XVII (14 mm; estimated ovulation age, 34-36 days). Since no primary afferents are demonstrated to reach the motor neuropil at this stage (the premotile period), these synapses are considered to be formed between interneurons and motor neurons. On the other hand, the formation of synapses outside the motor neuropil of the cervical cord was recognized at Streeter's horizon XX (22 mm; estimated ovulation age, 40-42 days), which corresponded to the period of onset of the precocious reflex, but not by horizon XIX (18 mm; estimated ovulation age, 38-40 days). The first axosomatic synapses were found in the motor neuropil at Streeter's horizon XVII (estimated ovulation age, 34-36 days). The present study suggests that the formation of synapses between interneurons and dendrites of spinal motor neurons precedes that of synapses between interneurons and collaterals of primary afferents. This sequence of synaptogenesis is in agreement with that reported in earlier studies with silver stain methods.

Golgi studies on Purkinje cell development in the frog during spontaneous metamorphosis. I. General pattern of development

The development of Purkinje cells was studied in the bullfrog from prometamorphic tadpoles to 10-week-old postmetamorphic froglets by the Golgi-Kopsch method. In this species, the rate of Purkinje cell development is unusually slow and proceeds in two waves. The first wave of development begins prior to the establishment of the external granular layer (EGL), and proceeds slowly for two to three months during the formation of the EGL; then accelerating as metamorphosis is being completed, the cells reach near-adult dimensions a month later. Even prior to the formation of the EGL these cells are already present in the stage of dendritic orientation and flattening which, however, varies from the norm. The second wave of Purkinje cell development begins during metamorphosis and proceeds at a more rapid pace until two months after metamorphosis, at which time they appear to have reached adult dimensions. In these cells the development of the apical dendrite does not always coincide with the stellate stage but may proceed directly to the stage of dendritic orientation and flattening which, in accordance with the norm, is towards the pia and in the sagittal plane. Many variations are present in the dendritic trees and orientation of the dendritic branches of Purkinje cells throughout their development. These variations are similar to those seen in mammals, however, since the frog cerebellum consists of a simple plate, they cannot be attributed to a Cartesian transformation of dendrites to accomodate the curvatures of a folial pattern. Similarly, since these morphological variations occur in the course of normal development they cannot be attributed to a reaction to, or recovery from, injury during development.

Electron microscopic analysis of postnatal histogenesis in the cerebellar cortex of staggerer mutant mice

Postnatal development of the cerebellar cortex has been compared in staggerer mutant and unaffected littermate mice. From postnatal day 3 to about day 21 the external granular layer in staggerer mice is decreased in thickness and area, and the number of postmitotic granule cell neurons is reduced. Those granule cells that are generated seem to differentiate normally, with the remarkable exception that they form only primitive junctions with Purkinje cell dendritic shafts. These specialized junctions are not superseded by the normal parallel fiber:Purkinje spine synapses and disappear by the third week. Purkinje cell somata and dendrites are smaller than normal at all stages examined. The dendrites are not confined to the sagittal plane as in the normal and, unique among mutant or other animals described to date, they exhibit virtually no branchlet spines. All other cortical synaptic relations of granule and Purkinje cells, including climbing fiber:Purkinje spine synapses, appear qualitatively normal. However, by 28 days virtually all staggerer granule cells have degenerated. While the primary genetic defect remains unknown, we postulate that the morphological abnormalities may be attributable to a block in the normal developmental relationship between granule cells and Purkinje cells. The small cell size and failure to form branchlet spines suggest that the Purkinje cell abnormality may be closer to the primary effect of the mutant gene than the more flagrant hypoplasia and degeneration of granule cell neurons.

The prenatal development of some of the visual pathways in the cat

Lesions were made in the visual system in a series of cat fetuses of known gestational age, and fiber and terminal degeneration were stained by the Eager method. The times of development of the retinal projection, of the thalamcortical and corticothalamic projections of area 17 of the visual cortex, and of the intrinsic fibers in the visual cortex were examined. Enucleation of one eye resulted in degeneration being detected bilaterally in the lateral geniculate nuclei (LGN), superior colliculi (SC) and optic tracts. The optic nerves reached the optic chiasm by the thirtieth embryonic day (E30) and the optic tract connections with the LGN and SC were made by E37. The projection always appeared stronger in the contralateral LGN and SC, and the amount of degeneration increased in both sides with increasing age. A parasagittal knife cut was made in the dorsomedial crest of the visual cortex. Where the lesion passed through the cellular layers of the cortex, intrinsic fibers were cut when these were present. The deeper part of the incision through the white matter undercut the medial wall of the visual cortex, interrupting thalamocortical and corticothalamic fibers when these were present. The longer horizontal fibers that were intrinsic to the visual cortex began to develop during the last two weeks of gestation but were not fully developed at birth. In the undercut visual cortex distant from the place of entry of the lesion, and before the intrinsic fibers of the cortex had developed, degeneration was found in layers 1 and 4, demonstrating the presence of a thalamocortical pathway. The youngest fetus to show this degeneration was operated at E48. This degeneration was not present three days earlier at E45. Fiber plexuses that have been described earlier in development (Marin-Padilla, '71; Cragg, '75) do not appear to degenerate after undercutting the cortex. The corticothalamic pathway to the lateral posterior nucleus medial to the LGN was developed at E45. The descending pathways to the ipsilateral LGN and SC were developed by E48, but it is not known whether they are present before this. Thus degeneration has been used to detect the development of axonal pathways in the fetus for the first time; the major afferent and efferent pathways are developed at an earlier stage than has previously been described.

The growth of the dendritic trees of Purkinje cells in irradiated agranular cerebellar cortex

The heads of noenatal Wistar rats were irradiated with 200 rads daily from birth to the 10th day post-partum. Ten litters each containing 5 animals were killed at 30 days post-partum and their brains treated by the Golgi-Cox technique. The dendritic trees of 24 Purkinje cells were analysed using the quantitative technique of network analysis, and comparisons made between parameters obtained from 20 normal Purkinje cells. All dendritic trees in agranular irradiated cortex were markedly reduced in size (as indicated by total dendritic length and total number of segments) although mean path lengths were normal. Segment lengths were normal over proximal branches, but uniformly increased over distal branches. Abnormal appendages, called 'giant spines' were observed on many dendrites. They were often some 10 mum in length and their presence effectively reduced segment lengths, increased the frequency of trichotomy and deviated growth from the normal random terminal pattern so that long collateral branching topologies were formed. Nevertheless, trichotomy was uniformly reduced in those trees without 'giant spines' and the distribution of branching patterns suggested that growth had proceeded by random terminal dichotomy. These results demonstrate that the development of dendritic trees is retarded in the agranular irradiated cerebellum, where synaptogenesis is very greatly reduced below normal. The quantitative changes in segment lengths, size of trees, and trichotomy accord with those predicted by the filopodial synaptogenic hypothesis of dendritic growth formulated by Vaughn et al. 99, whilst the results of the topological analysis suggest that branching is established by a degree of non-random interaction between growing dendrites and their substrate. 'Claw-like' dendritic complexes within some Purkinje cell trees may have been induced by aberrent fibre bundles of few surviving granule cells.

The development of the cerebellar cortex of the Syrian hamster, Mesocricetus auratus. Foliation, cytoarchitectonic, Golgi, and electron microscopic studies

Although a number of investigations of abnormalities of cerebellar development have been carried out in the hamster, no detailed Golgi or ultrastructural studies of cerebellar development in this species have been reported. This report describes the development of the hamster cerebellar cortex from birth (day 0) through postnatal day 78, as studied by light, Golgi, and electron microscopic methods. Foliation patterns correlate with the expansion of the cerebellar layers and of total cerebellar area. Cytologic and morphologic development of the major cerebellar cell types--Purkinje, Golgi, basket, stellate, granule, and Bergmann glial cells--correlate with those of other species, such as the rat and mouse. Electron microscopic observations at selected developmental ages allow identification and classification of synapses in the early postnatal hamster. Parallel fiber and climbing fiber synapses are already present at birth. Although synaptogenesis probably continues through the first two postnatal months, all major cell types have developed initial synapses by postnatal day 6, at a time when little cellular maturation has occurred. By using gestational rather than natal age, close developmental correlations between hamsters and rat and mouse are possible. Since the gestational period of the hamster is only 16 days, the hamster cerebellum is less mature at birth than that of either the rat or mouse. Thus, the hamster is a convenient animal in which to investigate the effects of various procedures on early cerebellar development.

The growth of the dendritic trees of Purkinje cells in the cerebellum of the rat

The growth of Purkinje cell dendritic trees in the cerebellum of the rat was studied over the first 50 days of life, using the technique of network analysis and the Golgi-Cox impregnation method. Our findings showed that a growth spurt occurred from the 10th to 30th day post partum (pp) and involved the production of a massive number of branches of fairly constant length. Growth of the tree occurred firstly in the lateral domain, so that by 15 days pp most trees were of adult width. Thereafter, increases in height occurred until 30 days pp. Associated with this change in direction of growth, from the mainly transverse to the vertical plane, was a deviation from the normal random pattern of branching of the tree, but this was reestablished when reorientation was complete, and growth in the vertical plane underway. The lengths of proximal segments increased once they had become established, but distal branches probably maintained a constant length. The above results, together with changes in segment length, trichotomy, branching probability, and growth cone morphology during development have been discussed in relation to current concepts of dendritic growth.

Electrophysiological study on the postnatal development of neuronal mechanisms in the rat cerebellar cortex

(1) Functional commencements of the neuronal elements in the cerebellar cortex of young rats were studied electrophysiologically by means of laminar field potential analyses in the cortex on stimulation of the cerebellar surface (Loc) and the white matter (WM). (2) The antidromic action potential of Purkinje cells on the WM stimulation was observed at one day after birth. The climbing fiber excitation of Purkinje cells on the stimulation was noted at 3 days after birth. (3) The mossy fiber-granule cell synapses were found to function at 10 days after birth and the Golgi cell inhibition of granule cells could be proved at the same time. The excitatory action of parallel fibers and the inhibitory action of basket-stellate cells on Purkinje cells appeared simultaneously at about 12 days after birth. The transverse distribution across the cerebellar folium of the basket-stellate cell inhibitory action on Purkinje cells was found to be narrow up to 60 days after birth. (4) These results concerning the dates of commencement of excitatory and inhibitory synaptic actions in the cerebellar cortex were compared with those of synaptogenesis studied morphologically, and some implications of the dates in the functional development of the cerebellar cortex were discussed.

Differentiation of Purkinje cells and their relationship to other components of developing cerebellar cortex in man

The differentiation of Purkinje cells and their relationship to other components of the developing cerebellar cortex were analyzed by the Golgi impregnation method and by electron microscopy in human specimens of various pre- and postnatal ages. The three stages of Purkinje cell maturation that have been previously recognized in other species are also evident in man: the first stage occupies primarily the fourth fetal month (12-16 weeks); the second stage lasts through the fifth, sixth and seventh feta months (16-28 weeks); the third stage extends throughout the remaining period of intrauterine life and the first postnatal year and continues at a slow rate thereafter. During the first stage, Purkinje cells are distributed in a layer, several rows deep. Their bipolar somas are relatively smooth and have only a few processes at the apical and basal cell poles. In the 3-month period of the second stage, Purkinje cells become gradually organized into a single row. Their somas become invested with additional randomly oriented dendritic processes and numerous somatic spines (pseudopodia). The first morphologically well-defined synapses appear on the Purkinje cell somatic spines and on their immature dendritic shafts at the beginning of the second stage and become more prominent during the period from 18 to 24 weeks. In the third stage, the dendritic arbor becomes flattened in the plane transverse to the folium and somatic spines disappear. Spines appear on the secondary and tertiary dendrites between the twenty-fourth and twenty-eighth fetal weeks and continue to increase in number during the entire third stage as new dendritic branches develop. These observations indicate that cellular maturation and synaptogenesis in the primate cerebellum differ from these events in non-primate species, with respect to time of birth, in the relative duration of each phase and in the total time necessary for neuronal differentiation. The protracted time of differentiation and the slow growth of Purkinje cell dendrites in man may be due to the numerically complex relationships existing between granule and Purkinje cells. It is probably not simply a reflection of the larger size of human Purkinje cells and their dendrites.

The fine structural localization of glutamate decarboxylase in developing axonal processes and presynaptic terminals of rodent cerebellum

The immunocytochemical localization of L-glutamate decarboxylase (GAD), the enzyme which which forms gamma-aminobutyric acid (GABA), has been studied in developing rodent cerebellum. During the first 3-4 postnatal days, GAD is distributed along non-terminal portions of axonal processes in close association with small vesicles. Some of the axonal processes emanate from profiles which resemble growth cone varicosities, and are presumed to be foliopodia which extend distally from axonal growth regions. At the end of the first postnatal week the GAD-containing axonal processes are seen to form protosynaptic contacts, and GAD is localized around synaptic vesicles and at presynaptic junctional membranes. During the second and third postnatal weeks GAD gradually becomes localized to mature synaptic terminals in association with synaptic vesicle, mitochondrial, and presynaptic junctional membranes. The results suggest that GAD is present in growing neurites in close association with small vesicles prior to the time the neurites make protosynaptic contacts, and that differentiation of these contacts results in a sequestering of GAD into synaptic terminals.

The radial fibers in the globus pallidus

In our Golgi collection of adult monkey brains the striatal efferents, i.e., the radial fibers in the globus pallidus and the "comb" bundle fibers in the internal capsule and in the cerebral peduncle, are well impregnated in the horizontally sectioned brain and in a sagittal sectioned brain. Since collaterals emerging from radial fibers are seen only in the horizontal series and not in the saggittal series, the interpretation is that they proceed anteriorly and posteriorly only, following the curvature of the pallidal segments, and do not run superiorly or inferiorly as they emerge. Although radial fibers emitting collaterals in the lateral segment and in the medial segment of the globus pallidus have been observed, it has not been possible to observe the same radial fiber emitting collaterals in both pallidal segments and the prospects of ever doing so are not good. The radial fibers converging in the globus pallidus pursue many radii and there is little coincidence between the plane of section and the planes in which they travel. At most only severed radial fiber segments 100-150 microns in length can be found in the horizontal sections needed to observe the collaterals. Moreover, sagittal sections trodorsally, as they pass through the internal medullary lamina to enter the medial segment of the globus pallidus. The radial fibers in the medial segment of the globus pallidus are continuous with the "comb" bundle fibers and appear to be thinner than the radial fibers in the lateral segment of the globus pallidus. It is not proved; nonetheless, the view expressed here is that the radial fibers are thinner in the medial segment of the globus pallidus because they may be the same fibers that gave off collaterals in the lateral segment of the globus pallidus. This is discussed in the light of the electrophysiological disclosure of Yoshida et al. ('71, '72) that caudatopallidal fibers are collaterals off caudatonigral fibers. The afferent plexuses of fine, "bouton en passage" fibers, which completely ensheath the long radiating dendrites in the globus pallidus (Fox et al., '66) are well impregnated in the horizontal series. Obviously, they are formed by a number of ultimate branches converging from the collateral brances of a number of different radial fibers. The divergence, too, in this system must be considerable; however, its true extent can only be surmised from the several radial fibers and radial fiber collaterals seen in the incompletely impregnanted Golgi section. Continued.

Human fetal cerebellar cortex: organization and maturation of cells in vitro

Human fetal cerebellar cortex was maintained up to 5 months in vitro. Important features included early migration of granule neurons followed by maturation of Purkinje and granule neurons. Unique areas of organization developed in which a rim of leptomeningeal cells surrounded an explant and its outgrowth zone; these areas subsequently grew as well-defined units.

Neurogenesis and morphogenesis in the cerebellar cortex

The cerebellum presents the best site in the central nervous system for defining fundamental problems concerning the origin and differentiation of neurones, and their growth and development. The many recent experimental investigations of these problems are reviewed, and hypotheses based upon them are developed in relation to neurogenesis, morphogenesis, and synaptogenesis.