Types of degenerating geniculocortical axon terminals and their contribution to layer IV of area 17 in the squirrel monkey (Saimiri)

Summary Radiofrequency lesions were made in the lateral geniculate nuclei of six squirrel monkeys. The resulting degenerating terminals and their postsynaptic structures in layer IV of area 17 were quantitatively categorized on photomontages covering large areas of neuropil. Two to five days after the lesion, numerous axon terminals were affected by a variety of degenerative changes, i.e., enlargement and distortion of synaptic vesicles, neurofilamentous hyperplasia, electron-lucent and electron-dense reactions. Based on the aggregation of electron-dense material beneath the postsynaptic membrane, the degenerating terminals were considered to be of the asymmetric type. Among the degenerating boutons were the largest axon endings that occur in layer IV. Three days postoperatively, degenerating boutons contributed an average of 16.2% to the total synapse population; five days postoperatively, the average had increased to 19.3 %. The percentage of degenerating boutons on individual montages, however, amounted to as much as 29%. This amount probably reflects more closely the actual contribution of the geniculocortical fiber system to layer IV of striate cortex. The postsynaptic structure most frequently contacted by degenerating axon endings was the dendritic spine, followed by dendrites of small diameter. To account for the diversity of degenerative changes in the same fiber system, we offer the tentative suggestion that heterogeneously degenerating axon terminals arise from a heterogeneous population of neurons in the lateral geniculate nucleus, i.e., from magnocellular versus parvocellular laminae.     

Neuronal and synaptic organization of the lateral geniculate nucleus of the tree shrew,Tupaia glis

Summary The ultrastructural study of the lateral geniculate nucleus (LGN) of the tree shrew (Tupaia glis) revealed two types of neurons: (1) a large thalamocortical relay cell (TCR), which may bear cilia, and (2) a small Golgi type-II interneuron (IN) with an invaginated nucleus. The narrow rim of pale cytoplasm of the IN contains fewer lysosomes and fewer Nissl bodies than the cytoplasm of the TCR. The IN perikarya, which in some cases establish somatosomatic contacts, frequently contain flattened or pleomorphic synaptic vesicles. The ratio of TCR to IN is 31.Three types of axon terminals were observed in the LGN. Two of them contain round synaptic vesicles but differ in size. The large RL boutons undergo dark degeneration after enucleation; they are the terminals of retino-geniculate fibers. The smaller RS boutons show dark degeneration after ablation of the visual cortex; they are the terminals of the cortico-geniculate fibers. The third type of bouton (F₁ does not degenerate after either intervention. The boutons of this type are filled with flattened vesicles and are believed to be intrageniculate terminals. F₂-profiles were interpreted as presynaptic dendrites of the IN. The characteristic synaptic glomeruli found in the LGN contain in their center an optic terminal. These optic terminals establish synaptic contacts with dendrites or spine-like dendritic protrusions of TCRs as well as with presynaptic dendrites. Synaptic triads were also seen. The distribution of the individual types of synaptic contacts in layers 3 and 4 was determined. Layer 4 contains only one third of the retino-geniculate synapses and of the synaptic contacts of F₁-terminals.     

Glutamate producing aspartate aminotransferase in glutamatergic perforant path terminals of the rat hippocampus

Summary The enzyme aspartate aminotransferase was demonstrated cytochemically in the rat hippocampus 4, 7, and 14 days after unilateral entorhinal cortex lesion. At the light microscopic level the enzyme showed a significant activity decrease in the ipsilateral entorhinal terminal field which was similar at all postlesion times investigated. Non-denervated areas, i.e. the inner one-third of the dentate gyrus molecular layer and the radiatum layer of CA2/3, showed an increase of aminotransferase activities. At the electron microscopic level in the entorhinal terminal field of the control (unoperated) side aspartate aminotransferase was localized preferentially in a great number of boutons, containing the cytoplasmic and mitochondrial isoenzymes. Following entorhinal lesion a significant loss of these positively reacting boutons was seen. Most of the degenerating boutons contained reaction product but a small number was negative for aspartate aminotransferase. From 4 to 14 postlesion days the positively reacting boutons of the non-denervated supragranular zone expanded outward into the denervated area according to the known terminal proliferation of the commissural and associational systems. The remaining denervated entorhinal terminal field was reinnervated predominantly by negatively reacting boutons (probably terminal proliferations of septal afferents) and by a small number of positively reacting boutons (probably terminal proliferations of the crossed temporodentate pathway). The presence of cytoplasmic aspartate aminotransferase in the terminals of a well-known glutamatergic system is discussed in relation to the possible importance of this enzyme for the production of releasable glutamate.     

Glutamate producing aspartate aminotransferase in glutamatergic perforant path terminals of the rat hippocampus. Cytochemical and lesion studies

The enzyme aspartate aminotransferase was demonstrated cytochemically in the rat hippocampus 4, 7, and 14 days after unilateral entorhinal cortex lesion. At the light microscopic level the enzyme showed a significant activity decrease in the ipsilateral entorhinal terminal field which was similar at all postlesion times investigated. Non-denervated areas, i.e. the inner one-third of the dentate gyrus molecular layer and the radiatum layer of CA2/3, showed an increase of aminotransferase activities. At the electron microscopic level in the entorhinal terminal field of the control (unoperated) side aspartate aminotransferase was localized preferentially in a great number of boutons, containing the cytoplasmic and mitochondrial isoenzymes. Following entorhinal lesion a significant loss of these positively reacting boutons was seen. Most of the degenerating boutons contained reaction product but a small number was negative for aspartate aminotransferase. From 4 to 14 postlesion days the positively reacting boutons of the non-denervated supragranular zone expanded outward into the denervated area according to the known terminal proliferation of the commissural and associational systems. The remaining denervated entorhinal terminal field was reinnervated predominantly by negatively reacting boutons (probably terminal proliferations of septal afferents) and by a small number of positively reacting boutons (probably terminal proliferations of the crossed temporo-dentate pathway). The presence of cytoplasmic aspartate aminotransferase in the terminals of a well-known glutamatergic system is discussed in relation to the possible importance of this enzyme for the production of releasable glutamate.     

Terminal degeneration in the mediodorsal cerebral cortex of the lizard Agama agama: Light and electron microscopy

The degeneration of axon terminals in the small-celled part of the mediodorsal cortex (sMDC) of the lizard Agama agama has been studied after lesions in the dorsal cortex at various survival periods. The Fink-Heimer stain was used to map and demonstrate terminal degeneration with the light and electron microscope. Electron microscopy was used to identify and describe degenerating boutons ultrastructurally. One sham-operated and three unoperated animals served as controls. Between 6 and 21 days postsurgically, degenerating terminals can be seen through 80% of the superficial plexiform layer, the zone adjacent to the cellular layer remaining free of degeneration. Swelling of dendrites in the outer part of the superficial plexiform layer and increased numbers of vacuolar invaginations, both present at short (24 hr–6 days; peak at 48–54 hr) survival periods, can be regarded as reaction to the surgical trauma. Degeneration of axon terminals takes three forms, all of the electron-dense type: gray boutons, degenerating bouton-dendritic spine complexes surrounded or engulfed by glia, and degeneration debris inside glial processes. Several forms of terminal degeneration occur concomitantly at any short (3–12 days) survival time. At longer survival times (15–21 days) only debris is present. From 6 days on, considerable numbers of degenerating structures are present, but the majority of degenerating boutons and debris are associated with reactive glia rather than with dendrites. From these observations it is concluded that in this lizard application of the combined degeneration-Golgi-EM technique would probably lead to little success. Electron microscopy of Fink-Heimer-stained sections suggests that degenerating bouton-dendritic spine complexes and degeneration debris accumulate silver particles, whereas gray boutons do not.     

Synchronization of electrical field potentials in neocortex of rat after isolation of a cortex island in the contralateral brain hemisphere

A correlation between the number of boutons and synchronization of electrical activity in two sites of the intact right somatosensory cortex of rats was anakyzed at different stages of axonal sprouting elicited by isolation of a cortex slab in the left cortex. Time delay between the development of epileptiform field potentials in two sites of intact cortex located at a distance of 4 mm from each other was determined as a parameter of synchronization. The analysis was carried out in 30 and 90 days after the complete isolation of the neural island in a symmetrical site of the contralateral cortex. Epileptiform activity was induced by penicillin. A significant increase in the number of boutons in the II and V layers of the intact cortex observed 90 days after the isolation of neural island in a symmetrical site of the cortex corresponded to a significant decrease in the delay of electrical activity development. Similar effects were observed in the V layer of the island 30 days after the isolation. The results suggest that the cortex lesion activates formation of new synaptic boutons in a contralateral site and increases a degree of synchronization of electrical activity, which may affect the epileptogenesis. The data suggest that pyramids of the III and, most probably, V layers form a neuronal network in the rat neocortex thus providing synchronization of epileptiform field potentials.     

Corticopontine projection in the guinea pig. Electron microscopic study

Guinea pigs were subjected to unilateral thermocoagulation of the frontal, parietal, temporal and occipital cortex, and were allowed to survive 4 and 7 days. Routine electron microscopic technique was employed to examine orthograde degenerative changes in the ipsilateral pontine nuclei. Following four days survival the degenerating corticofugal synaptic boutons (d.s.b.) exhibited features attributed to all three basic degeneration types: dark, filamentous, and light. Most of the synaptic boutons arising in the frontal, parietal and occipital cortex display filamentous degenerative changes, and measure approximately 3 micrometers. The temporopontine axons terminate as dark d.s.b. Also, some d.s.b. following frontal ablation (collaterals of the corticospinal tract?), and a small number of occipitopontine d.s.b. (visual associative cortex?), develop dark degenerative changes. Most of the dark d.s.b. measure less than 2 micrometer. The light d.s.b., with mean diameter 2 micrometer, are rarely found following frontal and occipital lesions. Following 7 days survival almost exclusively dark d.s.b. are to be observed--a great part of them, apparently, representing the late stage of the evolution of the filamentous and light degeneration. No d.s.b. were encountered in the pontine nuclei contralateral to the cortical lesion. In good agreement with preceding studies in other animal species, the present study provides a morphological evidence for a complex, multichannel relationships between the various regions of the cerebral cortex and the pontine nuclei.     

Effect of reduced impulse activity on the development of identified motor terminals in Drosophila larvae

In Drosophila larvae, motoneurons show distinctive differences in the size of their synaptic boutons; that is, axon 1 has type Ib ("big" boutons) terminals and axon 2 has type Is ("small" boutons) terminals on muscle fibers 6 and 7. To determine whether axon 1 develops large boutons due to its high impulse activity, we reduced impulse activity and examined the motor terminals formed by axon 1. The number of functional Na(+) channels was reduced either with the nap(ts) mutation or by adding tetrodotoxin (TTX) to the media (0.1 microg/g). In both cases, the rate of locomotion was decreased by approximately 40%, presumably reflecting a decrease in impulse activity. Locomotor activity was restored to above wild-type (Canton-S) levels when nap(ts) was combined with a duplication of para, the Na(+)-channel gene. Lucifer yellow was injected into the axon 1 motor terminals, and we measured motor terminal area, length, the number of branches, and the number and width of synaptic boutons. Although all parameters were smaller in nap(ts) and TTX-treated larvae compared to wild-type, most of these differences were not significant when the differences in muscle fiber size were factored out. Only bouton width was significantly smaller in both different nap(ts) and TTX-treated larvae: boutons were about 20% smaller in nap(ts) and TTX-treated larvae, and 20% larger in nap(ts); Dp para(+) compared to wild-type. In addition, terminal area was significantly smaller in nap(ts) compared to wild-type. Bouton size at Ib terminals with reduced impulse activity was similar to that normally seen at Is terminals. Thus, differences in impulse activity play a major role in the differentiation of bouton size at Drosophila motor terminals.     

Long‐term stability of axonal boutons in the mouse barrel cortex

Many lines of evidence indicate that postsynaptic dendritic spines are plastic during development and largely stable in adulthood. It remains unclear to what degree presynaptic axonal terminals undergo changes in the developing and mature cortex. In this study, we examined the formation and elimination of fluorescently‐labeled axonal boutons in the living mouse barrel cortex with transcranial two‐photon microscopy. We found that the turnover of axonal boutons was significantly higher in 3‐week‐old young mice than in adult mice (older than 3 months). There was a slight but significant net loss of axonal boutons in mice from 1 to 2 months of age. In both young and adult barrel cortex, axonal boutons existed for at least 1 week were less likely to be eliminated than those recently‐formed boutons. In adulthood, 80% of axonal boutons persisted over 12 months and enriched sensory experience caused a slight but not significant increase in the turnover of axonal boutons over 2–4 weeks. Thus, similar to postsynaptic dendritic spines, presynaptic axonal boutons show remarkable stability after development ends. This long‐term stability of synaptic connections is likely important for reliable sensory processing in the mature somatosensory cortex. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 252–261, 2016     

Perinatal development of mammillotegmental connections in rats

Development of direct axonal connections of the hypothalamic mammillary bodies with ventral and dorsal tegmental nuclei of Gudden was studied on fixed rat brains from day 14 of embryonic development until day 10 of postnatal development using the method of diffusion of the lipophilic fluorescent carbocyanine tracer 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate along the neuronal membranes. The tracer was inserted into the mammillary bodies or into the tegmentum and, after incubation in a fixative, fluorescent nerve cells and nerve fibers were visualized in the brain tissue. The mammillotegmental tract was found to start developing earlier than other projection systems of the mammillary bodies. On days 14–15 of embryonic development, it was visualized as a bundle of axons running from the mammillary bodies caudally to the midbrain. A group of neurons in the midbrain tegmentum and their axons going to the mammillary bodies via the mammillary peduncle were first visualized on day 19 of embryonic development. The mammillotegmental tract and mammillary peduncle developed progressively from the moment of birth. Ventral and dorsal tegmental nuclei were formed in the midbrain by day 10 of the postnatal development. Thus, the formation of reciprocal connections of the mammillary bodies with midbrain tegmental nuclei was first described during perinatal development in rats.     

Effects of frontal motor cortex ablation on the ultrastructure of cat substantia nigra

3,4 and 5 days after the removal by suction of the left motor and premotor cortex in cats, the presence of ultrastructural changes in the substantia nigra was investigated. Whereas after 3 days dark bouton degeneration was rare, after 4- and 5-day survival it was regularly found for a distinct type of synapse containing in its bouton densely packed small round vesicles and possessing an asymmetric synaptic junction with a dendrite. Often these darkly degenerated boutons contained dense bodies which were also observed in the same type of synapse not yet exhibiting a dark axoplasm. Various inclusions, especially glycogen depots, were present in these boutons suggesting that they were in the process of degeneration. The glial reaction was comparatively severe. In addition, darkly shrunken dendrites contacted both, by intact and by altered boutons were frequently encountered as well as single degenerated neuronal perikarya. The nature of this effect, i.e. whether transneuronal or retrograde, could not be clarified. All these alterations were found bilaterally after the unilateral cortex ablation, and were confined to the substantia nigra pars compacta along its whole anterior-posterior extent. In the pars reticulata, solely traversing myelinated axons in the process of degeneration were observed. Thus, the results are in agreement with the older studies and with evidence from primates demonstrating that the substantia nigra receives a bilateral projection from the motor and premotor cortex.     

Intracortical synchronization of the epileptiform field potentials at different stages of ultrastructural reorganizations in neuronally isolates island in rats

A temporal delay (parameter of synchronization) between the incidence of epileptiform discharges in cortical sited located at a distance of 4 mm from each other was studied in rat intact cortex and neuronally isolated cortical slab using the cross-correlation function. Experiments were carried out at different stages of axonal sprouting. By 30 days of isolation, a significant increase in the number of boutons in the V cortical layer coincided with a significant decrease in the delay, whereas a reduction of the number of boutons by 90 days corresponded to its increase. These findings convincingly testify that the newly formed boutons form a basis for increase in synchronization and thus affect the epileptogenesis. The results obtained in this work and literature data suggest that under pathological conditions large pyramids of the V layer form a neuronal network which provides exclusively cortical synchronization of epileptiform field potentials.     

Morphology of electrophysiologically identified baroreceptor afferents and second order neurones in the brainstem of the cat

Baroreceptor afferent fibres and second order baroreceptor neurones were identified by their discharge pattern and were intracellularly injected with horseradish peroxidase. Three afferent fibres and three second order neurones were reconstructed by camera lucida drawings from serial sections of the brainstem. The afferent fibres were classified as A delta-fibres and had terminal arborizations with synaptic boutons in the dorsomedial region of the nuclei of the solitary tract (TS). The afferent fibres had additional collaterals with a medial projection to the commissural nucleus and in a direction lateral to the TS. The terminals of these collaterals could not be demonstrated. The second order neurones were located in the same dorsomedial region as the synaptic boutons of the afferent fibres. Neurones were small and spindle-shaped with two primary dendrites: one dendrite projected cranially along the medial border of the TS, and the second one projected caudally and medially into the commissural nucleus. The unmyalinated axons of these neurones could be traced over a distance of 1 mm. In only one neurone could an axon collateral be detected. The axons projected dorsally around the TS in a ventrolateral direction beyond the boundaries of the nuclei of the TS. The axon collateral projected in the medial direction into the commissural nucleus. In no case were axon terminals demonstrated.     

Perinatal development of mammillotegmental connections in rats

Development of direct axonal connections of the hypothalamic mammillary bodies with ventral and dorsal tegmental nuclei of Gudden was studied on fixed rat brains from day 14 of embryonic development until day 10 of postnatal development using the method of diffusion of the lipophilic fluorescent carbocyanine tracer 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate along the neuronal membranes. The tracer was inserted into the mammillary bodies or into the tegmentum and after incubation in a fixative fluorescent nerve cells and nerve fibers were visualized in the brain tissue. The mammillotegmental tract was found to start developing earlier than other conducting systems of the mammillary bodies. On days 14-15 of embryonic development, it was visualized as a bundle of axons running from the mammillary bodies caudally to the midbrain. A group of neurons in the midbrain tegmentum and their axons going to the mammillary bodies via the mammillary peduncle were first visualized on day 19 of embryonic development. The mammillotegmental tract and mammillary peduncle developed progressively from the moment of birth. Ventral and dorsal tegmental nuclei were formed in the midbrain by day 10 of the postnatal development. Thus, the formation of reciprocal connections of the mammillary bodies with midbrain tegmental nuclei was first described during perinatal development in rats.     

Trace changes in the quantity of RNA in neurons and neuroglia of the hypothalamic nuclei of the brain following short-term intermittent exposure to cold]

Adult albino rats were kept for 2 minutes at --20 degrees C, then for 5 minutes at 25 degrees C, this intermittent cooling being repeated 15 times. One hour after the end of the cooling, the RNA quantity per cell was determined by means of visible cytospectrophotometry to find the increase in the cytoplasm of medial preoptic area neurons and in the nuclei of their glial satellite cells as well as in the nuclei of the perineuronal glial cells of mammillary bodies. Two days after the rats had stayed at the room temperature, these RNA changey bodies the RNA content decreased. 3 days later, the RNA content in the whole neuron--neuroglia unit of the preoptic area returned to normal, while in the neurons and neuroglia of mammillary bodies augmented markedly: this augmentation was found as late as 15 days after the cessation of the cooling. 30 days after the end of the cooling, the RNA quantity in the mammillary body neurons returned to normal, whiel in the neuroglia of this hypothalamic nucleus decreased even lower than the normal level. The authors discuss the problem of a so-called "vegetative memory" and of the involvement of hypothalamic neuron--neuroglia units in the metabolism tranformation dealing with a consolidation of this memory.     

Ultrastructure of the serotoninergic system of the motor area of the cerebral cortex

Owing to the microscopical investigation, using selective neurotoxin 5,7-dihydroxytryptamine, it has been possible to reveal the serotoninergic system and targets of its innervation in the rat cerebral cortex motor area. The serotoninergic axonal varicosities and synaptic boutons are present in all layers of the neocortex. Their large amount is revealed in the I and II layers. The terminals form contacts with dendrites of small size, sometimes they terminate on the head of the spines, as well as on bodies of neurons in different layers. According to their position and ultrastructural organization these neurons are, perhaps, pyramidal, that is glutamatergic, and those less in their size--refer to interneurons and can be GABAergic ones. Basing on own data and those of the literature, concerning the existence of nonsynaptic link for transmission of serotoninergic effects, a conclusion is made that a coordinating functioning of the synaptic and non-synaptic intercellular integrative mechanisms ensure a wide range of functions of the serotoninergic system in the cerebral cortex.     

Dynamics of axonal degeneration in the neuronally isolated cerebral cortex]

The brains of 11 cats were studied after unilateral isolation of the cortex after M. M. Khananashvily (1961) by means of resection of the projection fibres connecting the cortex with subcortical formations. The character and peculiarities of axonal degeneration in the large hemisphere cortex, were investigated after Nauta and Fink--Heimer. It was found that distribution of degenerating terminals in every layer depended on the time when the material was taken for investigation. Maximal concentration of the degenerating fibres was observed 3--5--10 days after the operation, then a gradual decrease in density of degeneration in every cortical layer was observed. By the 9th month after the operation, the processes of axonal degeneration completely came to their end. The problem of retrograde and anterograde nature of the axonal degeneration in the cortex of the large hemispheres was discussed in the article and it was demonstrated that in the field 4 of the neuronally isolated cortex it is of mixed nature.     

The rat olivocerebellar system visualized in detail with anterograde PHA-L tracing technique, and sprouting of climbing fibers demonstrated after subtotal olivary lesions

The rat olivocerebellar climbing fiber system has been investigated at the light and electron microscopic level with anterograde Phaseolus vulgaris leucoagglutinin (PHA-L) tracing. From PHA-L Injections in different parts of the inferior olive labelled axons could be traced to the contralateral cerebellum. Arriving in the deep cerebellar white matter, the olivocerebellar axons ran around and through the cerebellar nuclei. Plexuses of labelled terminal fibers appeared in the cerebellar nuclei, and the density of this innervation was estimated to 1-4 million varicosities per mm3. Ultrastructurally, these boutons engaged in asymmetric synapses with small dendrites. Bundles of labelled fibers continued into the folial white matter, and terminated as climbing fibers in sagittal zones of the cerebellar cortex. Both the cortical and nuclear terminations of the olivocerebellar system are strictly topographically organized. The plasticity of climbing fibers was studied after partial lesions of the inferior olive induced by 3-acetylpyridine. One to 6 months after the lesion, surviving climbing fibers demonstrated extensive sprouting. The newly formed axons originated from parent climbing fiber plexuses, grew in the direction of parallel fibers, and formed terminal plexuses around several neighbouring Purkinje cells. As normal climbing fiber terminals, these terminals formed asymmetric synapses with spines of proximal Purkinje cell dendrites, and evidence by Benedetti et al. (1983) shows that the regenerated innervation is electrophysiologically functional. It is suggested that denervated Purkinje cells release a trophic substance, which stimulate surviving climbing fibers to sprouting, axonal growth and synapse formation.     

Distribution of afferents from the association nuclei of the thalamus in the projection and association cortex in cats

Patterns of distribution of terminal degeneration in the parietal cortex (field 7) and in the occipital cortex (field 17) were studied after ultrasonic destruction of the pulvinar by the Fink-Heimer and electron microscopy methods. Degenerating fibers and their terminals were observed in the parietal cortex within all the layers; the greatest amount of degeneration was found in the III--V layers. In the occipital cortex the fibers from the pulvinar end predominantly in the IV layer. Degenerating axons end on the dendritic spines and thin dendritic branches both in the parietal and occipital cortex.     

Immunocytochemistry of glycine in small neurons of the granule cell areas of the guinea pig dorsal cochlear nucleus: a post-embedding ultrastructural study

The axon terminals of the acoustic nerve contact different part of the cochlear nucleus including granule cell areas. Little is known of the cell composition and neural circuits of granule cell areas present in the fusiform and upper polymorphic layers of the dorsal cochlear nucleus in the guinea pig. The present ultrastructural immunocytochemical study exploits the technique of post-embedding immunogold and silver intensification to reveal the characteristics of small neurons in granule cell areas. Few neurons (Golgi-stellate cells) use glycine as inhibitory neurotransmitter which is present in symmetric synaptic boutons with pleomorphic and flat vesicles. In contrast, most neurons (granule and unipolar brush cells) are not glycine-positive, and presumably not excitatory. Most of the large axons (mossy fibres) in granule areas are probably excitatory (glycine-negative and storing round synaptic vesicles) and contact unipolar brush cells forming large synapses or granule cell dendrites by small synapses. A few large glycinergic boutons (inhibitory) also contact unipolar brush cells. The excitatory circuit of mossy fibre-unipolar brush and granule cells may be inhibited by the glycinergic terminals from the few glycinergic cells (Golgi-stellate neurons) present within the granule cell areas. The latter are not contacted by large mossy-like glycine terminals.