Ultrastructural observations on beaded alpha-motoneuron dendrites

Beaded dendrites of alpha-motoneurons intracellularly labelled with horseradish peroxidase (HRP) were studied ultrastructurally in eight adult cats. For comparison, adjacent unlabelled beaded dendrites of unknown origin were also included in the study. Electron microscopy revealed no signs of degeneration or poor fixation according to common criteria. With the exception of the HRP-reaction product no difference in structure was observed between labelled and unlabelled beaded dendrites. Both the beads and their interconnecting segments were postsynaptic to boutons of normal appearance containing spherical (S-type boutons) or flattened vesicles (F-type boutons). The values for synaptic covering and synaptic packing density of the beaded dendritic regions, which usually were located in the periphery of the dendritic trees, were clearly lower than values obtained previously for cell bodies and proximal dendrites of alpha-motoneurons.     

Quantitative analysis of the ultrastructural distribution of GABA-like immunoreactivity in the intermediate and medial part of hyperstriatum ventrale of chick

Summary The intermediate and medial part of the hyperstriatum ventrale of the chick telencephalon plays a crucial role in the learning processes of imprinting. The distribution within the intermediate and medial part of the hyperstriatum ventrale of the neurotransmitter -amino butyric acid was studied with light and electron microscopy using an antibody against this amino acid. The antibody labelled 18.4% of neuronal somata. GABA-labelled terminals made symmetrical synapses onto somata and dendrites of labelled and unlabelled neurons. Labelled somata received about three times as many synaptic boutons as unlabelled somata. Approximately 21% of synaptic terminals on labelled somata were themselves labelled; unlabelled somata received a higher proportion (37.6%) of such terminals. Most labelled terminals synapsing with dendrites were confined to the shafts; very few labelled terminals contributed to axospinous synapses. Synaptic contacts made on dendritic shafts by labelled boutons were intermingled with symmetrical and asymmetrical contacts from non-immunoreactive terminals. The proportion of labelled terminals received by labelled dendrites (33.1%) was approximately twice that received by unlabelled dendrites (15.9%). Labelled neurons therefore received a higher proportion of labelled terminals on their dendrites and a lower proportion on their somata compared with unlabelled neurons. No immunoreactivity was seen in glial cells or ependyma.     

The dendrites of single brain-stem motoneurons intracellularly labelled with horseradish peroxidase in the cat. An ultrastructural analysis of the synaptic covering and the microenvironment

Two laryngeal motoneurons intracellularly stained with horseradish peroxidase were studied ultrastructurally. The precise position of the ultrastructural observations made along the dendrites was obtained from the computer-reconstruction of the motoneurons in three dimensions. The shape and the size of the synaptic boutons, the percentage of membrane covered by bouton appositions and active zones, the number of boutons per 100 microns2 (packing density) were analysed on the soma and on the labelled dendrites at different distances from the soma up to 1000 microns. The results revealed no important regional differences in the mean length of synaptic apposition. The packing density was in the range of 9.3-14.9 boutons per 100 microns2 and was not correlated with the distance from the soma. The percentage apposition covering was higher on the soma and the proximal part of the dendrites than on the remaining part of the dendritic arborization. Close appositions between labelled dendrite and unlabelled somata and/or dendrites together with dendro-dendritic synapses suggested the possibility that the dendrites may be involved in local cell-to-cell communication. Microdendrites emerging from the soma or the proximal dendrites were contacted by synaptic boutons which may be more efficient as revealed by computation.     

The striatonigral projection and nigrotectal neurons in the rat. A correlated light and electron microscopic study demonstrating a monosynaptic striatal input to identified nigrotectal neurons using a combined degeneration and horseradish peroxidase procedure

In a light and electron microscopic study of the substantia nigra of the rat, the distribution and morphology of nigrotectal neurons and the pattern of termination of striatonigral fibres have been examined following the placement of horseradish peroxidase injections in the superior colliculus and kainic acid lesions in the dorsal striatum. In confirmation of previous findings, nigrotectal neurons which had been identified by the retrograde transport of horseradish peroxidase from the superior colliculus had mainly medium sized somata, varied from fusiform to stellate in shape and were found in mainly ventral regions of the rostral two-thirds of the substantia nigra pars reticulata. On electron microscopic examination, single and multiple (from two to six) degenerating striatonigral boutons were found in synaptic contact with the soma, proximal mainstem dendrites and small dendrites (but mainly on small dendrites) of labelled nigrotectal and unlabelled nigral neurons in the ventral region of the pars reticulata. In addition, a small number of degenerating striatonigral boutons formed axoaxonic synapses with degenerating or normal boutons which were presynaptic to nigral dendrites. Almost all of the identified striatonigral synapses were of the symmetrical type, although a few degenerating boutons established asymmetrical synaptic contacts on unlabelled dendrites. These findings provide evidence of a monosynaptic input from the dorsal striatum to nigrotectal projection neurons in the substantia nigra and thus demonstrate the existence of a bineuronal pathway from the striatum through the substantia nigra to the superior colliculus. The possible significance of the pattern of termination of striatonigral fibres in the substantia nigra is discussed with reference to the known dendritic arborization of nigral neurons.     

Synaptic connections of GABA-containing boutons in the lateral cervical nucleus of the cat: an ultrastructural study employing pre- and post-embedding immunocytochemical methods

The lateral cervical nucleus receives input from the spinocervical tract and projects to the thalamus and mesencephalon. The organization of this nucleus was examined using two immunocytochemical methods. Pre-embedding immunolabelling was performed using an antibody against glutamate decarboxylase, and post-embedding immunogold-reaction was performed with an antibody to glutaraldehyde-fixed GABA. Light microscopic analysis of material reacted for glutamate decarboxylase revealed that punctate structures were present throughout the nucleus and were associated with large cells in the dorsolateral region of the nucleus. Electron microscopy demonstrated that the punctate structures were synaptic boutons which formed symmetrical synaptic junctions with dendrites and somata of cells in the nucleus. The ultrastructural preservation of material prepared for the post-embedding immunogold technique was superior to that prepared for pre-embedding immunostaining. Positively labelled synaptic boutons exhibited high colloidal gold density and, like those prepared for the pre-embedding method, formed symmetrical synaptic junctions with dendrites and somata of neurons. Labelled boutons were densely packed with irregularly-shaped synaptic vesicles. They displayed characteristics which were distinct from those unlabelled boutons. Boutons, revealed by both immunolabelling methods, were not observed to form synaptic associations with other axon terminals and were presynaptic to dendrites and somata only. Therefore, it is probable that such boutons are responsible for postsynaptic inhibition of cells in the nucleus. In view of this evidence, it is concluded that the lateral cervical nucleus is not simply a relay but is actively involved in processing sensory information.     

Enkephalin-, thyrotropin-releasing hormone- and substance P-immunoreactive axonal innervation of the ventrolateral dendritic bundle in the cat sacral spinal cord: An ultrastructural study

The distribution and synaptic arrangement of thyrotropin-releasing hormone-, substance P- and enkephalin-immunoreactive axonal boutons have been studied in the ventrolateral nucleus (Onuf's nucleus) of the upper sacral spinal cord segments in the cat. For this purpose, the peroxidase-antiperoxidase immunohistochemical technique was used. Immunoreactive axonal boutons were traced in complete series of sections in order to reveal synaptic contacts with the bundled dendrites of the ventrolateral nucleus. As judged from the cross-sectional diameter of the postsynaptic dendrites, the distribution of immunoreactive boutons was non-random. Enkephalin-immunoreactive axonal boutons, presumed to be mostly of segmental origin, displayed a rather restricted distribution to mainly (> 80%) medium-to-large dendrites. Thyrotropin-releasing hormone-immunoreactive boutons, that derive from supraspinal levels, were also found to impinge on medium-to-large dendrites (> 80%), indicating a proximal location within the dendritic trees. The skewness toward large postsynaptic dendrites was even more marked for thyrotropin-releasing hormone- than for enkephalin-immunoreactive boutons. Substance P-immunoreactive boutons, that are of either supraspinal or spinal origin, showed a more even distribution throughout the dendritic trees, including both thin distal branches and thick proximal dendrites. In view of the well-known fact that virtually all thyrotropin-releasing hormone-immunoreactive boutons in the ventral horn cocontain substance P (and serotonin) it was assumed that substance P-immunoreactive boutons in synaptic contact with the finest-calibre dendrites as well as most of those with a very proximal juxtasomatic location on the dendritic trees were of segmental origin, while those impinging on medium-to-large dendrites could be of either spinal or supraspinal origin. Fine-calibre dendrites (< 1 μm) represent about 25% of the dendritic branches in the ventrolateral nucleus, but receive, with the exception of substance P (8%), very little (< 3%) peptidergic or GABAergic (Ramírez-León and Ulfhake, 1993) input, although the degree of dendritic membrane covering by bouton profiles in the ventrolateral nucleus does not seem to vary much with the calibre of the postsynaptic dendrite (Ramírez-León and Ulfhake, 1993). Both substance P- and enkephalin-immunoreactive axonal boutons established synaptic contact with more than one dendrite. Furthermore, one and the same bouton could be found in contact with two dendrites that were coupled to each other by a dendro-dendritic contact of desmosomal or puncta adherentia type. This synaptic arrangement was, however, not seen among thyrotropin-releasing hormone-immunoreactive boutons, indicating that these axonal boutons act on a single postsynaptic element, while inputs intrinsic to the spinal cord can show a divergence also at the terminal level.     

猫丘脑腹后外侧核内皮质投射神经元超微结构及其突触联系——HRP法电镜研究

本文应用HRP逆行追踪法在电镜水平上对猫丘脑腹后外侧核内皮质投射神经元的超微结构及其突触联系进行了研究。该核内投射神经元超微结构特点为胞核较大,核仁清晰,核膜常有凹陷,常染色质较多,异染色质较少,胞浆丰富,含有大量的游离核糖体、粗面内质网及线粒体。标记的皮质投射神经元胞体和树突与非标记轴突形成轴-体突触和轴-树突触;标记树突还可以和突触前树突形成树-树突触,并做为中央树突参与形成汇聚型突触复合体。此外在标记的胞体与非标记的树突之间,标记的树突与非标记的树突之间,两标记的树突之间还存在着非突触丝状连接。     

Immunocytochemical study of GABAergic neurons containing the calcium-binding protein parvalbumin in the rat hippocampus

Summary The structural features of PV-immunoreactive (PV-I) neurons, a particular subpopulation of GABAergic neurons, in the hippocampus were studied by immunocytochemistry. The PV-I cell bodies were concentrated within the stratum pyramidale (SP) and stratum oriens (SO) in the hippocampus. PV-I puncta were frequent in SP, while they were rarely seen in other layers. The dendritic arborization of PV-I neurons resembled that of some of the nonpyramidal cells observed after Golgi-impregnation. The most commonly observed PV-I neurons had their perikarya located in SP with dendrites extending into SO and the stratum radiatum (SR). Most of the dendrites in SR had typical beaded or varicose segments. The dendrites extending into SO had few beaded parts. There were many bipolar and multipolar neurons with smooth dendrites in SO, but only a small number of such multipolar neurons in SR. An electron microscopic analysis revealed that PV-I products were located to perikarya, dendrites, myelinated axons and synaptic boutons. The perikarya of PV-I neurons exhibited several ultrastructural features of nonpyramidal cells, e.g., abundant cisternae of endoplasmic reticulum, mitochondria and other perikaryal organelles, an infolded nuclear envelope and intranuclear inclusions. They received many asymmetric synapses with round presynaptic vesicles. There were numerous PV-I boutons, presumably axonal endings, covering the pyramidal cell bodies. The PV-I boutons also contacted the axon initial segments and proximal dendrites of the pyramidal cells. In addition PV-I terminals were found on somata and dendrites of both PV-I or PV-negative nonpyramidal cells. The results suggest that PV-containing neurons include basket and axo-axonic cells.     

Demonstration of serotoninergic axons terminating on luteinizing hormone-releasing hormone neurons in the preoptic area of the rat using a combination of immunocytochemistry and high resolution autoradiography

The synaptic relationship between serotoninergic terminals and luteinizing hormone-releasing hormone-containing neurons was investigated in the medial preoptic area using a combined technique. Axon terminals selectively taking up 5-[3H]hydroxytryptamine were labelled autoradiographically and luteinizing hormone-releasing hormone-containing neuronal elements were identified by means of immunocytochemistry. Synaptic contacts were observed between tritiated 5-hydroxytryptamine-labelled boutons and luteinizing hormone-releasing hormone-immunoreactive dendrites. About 5% of the boutons which formed synapses with luteinizing hormone-releasing hormone-immunoreactive dendrites were found to be labelled by the tritiated indolamine. Luteinizing hormone-releasing hormone-immunoreactive axon terminals occurred as presynaptic elements in contact with unidentified dendritic spines, shafts or perikarya. These observations provide morphological basis for the idea that 5-hydroxytryptamine-containing neurons can act directly on luteinizing hormone-releasing hormone release. Further, they support the assumption that luteinizing hormone-releasing hormone is not only a neurohormone but may also function as a neurotransmitter or neuromodulator.     

Changes in synaptology of adult cat spinal α-motoneurons after axotomy

The aim of this electron-microscopic study was to analyze the distribution of synaptic contacts on the cell bodies and dendrites of permanently axotomized adult cat spinal α-motoneurons. Following transection and ligation of the medial gastrocnemius nerve, the synaptic covering of the cell bodies and three different dendritic compartments of homonymous α-motoneurons was analyzed quantitatively at 3, 6, and 12 weeks postoperatively. The synaptic boutons were classified according to their size and the shape of their synaptic vesicles. On the soma, a transient increase in the number of boutons was noted at 3 weeks and 6 weeks postoperatively, while after 12 weeks the bouton number had decreased to half of its normal value. The transient increase was mainly due to an increase in the number of F-type boutons. At 12 weeks postoperatively, the synaptic covering was reduced by 83% on the soma and by 57% on the proximal dendrites. In the distal dendritic regions, the values for synaptic covering remained largely unchanged. In summary, axotomized motoneurons exhibit a reduction in synaptic covering which is maximal on the cell body and becomes less pronounced centrifugally along the dendrites. However, if also taking into account the loss of distal dendritic branches that occurs in axotomized motoneurons, the total loss of boutons is several times larger in the dendrites than on the soma. Received: 18 October 1996 / Accepted: 13 June 1997     

The distribution of inhibitory and excitatory synapses on single, reconstructed jaw-opening motoneurons in the cat

In a previous study, we reported that the distribution of inhibitory input, in contrast to excitatory input, decreased somatofugally along dendrites of cat jaw-closing alpha-motoneurons [J Comp Neurol 414 (1999) 454]. The present study examined the distribution of GABA, glycine, and glutamate immunopositive boutons covering horseradish peroxidase-labeled cat jaw-opening motoneurons. The motoneurons were divided into four compartments: the soma, and primary, intermediate, and distal dendrites. Ninety-seven percent of the total number of studied boutons had immunoreactivity for at least one of the three amino acids. The proportion of boutons immunoreactive for GABA and/or glycine was lower than the proportion of boutons immunoreactive for glutamate. Boutons immunoreactive to glycine alone were more numerous than boutons double-labeled for GABA and glycine, which, in turn, occurred more frequently than boutons immunoreactive to GABA alone. The percentage synaptic covering (proportion of membrane covered by synaptic boutons) of the putatively excitatory (glutamate containing) and putatively inhibitory (GABA and/or glycine containing) boutons decreased somatofugally along the dendrites. Such systematic variations were not seen in the packing density (number of boutons per 100 microm(2)); the packing density showed a distinct drop between the soma and primary dendrites but did not differ significantly among the three dendritic compartments. Overall, the packing density was slightly higher for the putatively excitatory boutons than for the inhibitory ones. When taken together with previous analyses of jaw-closing alpha-motoneurons the present data on jaw-opening alpha-motoneurons indicate that the two types of neuron differ in regard to the nature of synaptic integration in the dendritic tree.     

猫后索核—丘脑—皮质通路在丘脑水平的突触联系

应用顺行溃变和ＨＲＰ逆行追踪相结合的方法对猫内侧丘系与丘脑皮质投射神经元在丘脑腹后外侧核内的突触联系组合型式进行了研究。电损毁一侧后索核后将ＨＲＰ注射于对侧皮质躯体感觉颈、躯干、四肢代表区，电镜下在注射区同侧的丘脑腹后外侧核内可见到下列七种突触形式；（１）溃变的内侧丘系轴突终末与ＨＲＰ标记树突形成的轴－树突触，较多；（２）溃变的内侧丘系轴突终末与ＨＲＰ标记的神经元体形成的轴－体突触较少；（３）溃变     

Glutamatergic components of the retrosplenial granular cortex in the rat

The ultrastructural characteristics, distribution and synaptic relationships of identified, glutamate-enriched thalamocortical axon terminals and cell bodies in the retrosplenial granular cortex of adult rats is described and compared with GABA-containing terminals and cell bodies, using postembedding immunogold immunohistochemistry and transmission electron microscopy in animals with injections of cholera toxin- horseradish peroxidase (CT-HRP) into the anterior thalamic nuclei. Anterogradely labelled terminals, identified by semi-crystalline deposits of HRP reaction product, were approximately 1 microm in diameter, contained round, clear synaptic vesicles, and established asymmetric (Gray type I) synaptic contacts with dendritic spines and small dendrites, some containing HRP reaction product, identifying them as dendrites of corticothalamic projection neurons. The highest densities of immunogold particles following glutamate immunostaining were found over such axon terminals and over similar axon terminals devoid of HRP reaction product. In serial sections immunoreacted for GABA, these axon terminals were unlabelled, whereas other axon terminals, establishing symmetric (Gray type II) synapses were heavily labelled. Cell bodies of putative pyramidal neurons, containing retrograde HRP label, were numerous in layers V-VI; some were also present in layers I-III. Most were overlain by high densities of gold particles in glutamate but not in GABA immunoreacted sections. These findings provide evidence that the terminals of projection neurons make synaptic contact with dendrites and dendritic spines in the ipsilateral retrosplenial granular cortex and that their targets include the dendrites of presumptive glutamatergic corticothalamic projection neurons.     

Ultrastructure of degenerating cerebellothalamic terminals in the ventral medial nucleus of the cat

Summary Terminal degeneration of cerebellar afferents in the ventral medial thalamic nucleus (VM) was studied in cats at the ultrastructural level after uni- or bilateral lesions in the brachium conjunctivum (BC). To achieve discrete lesions within the BC, a new very accurate stereotaxic technique was used. Numerous large terminals belonging to a population of so-called LR boutons were observed degenerating in the VM. The boutons displayed a wide variety of degenerative changes. Some revealed the features of the classical neurofilamentous type of degeneration. Others, although containing a slightly increased number of neurofilaments, featured much more prominently large numbers of coated vesicle shells and heavy accumulations of a flocculent electrondense material. Degeneration in a third group of boutons similar to some extent to the light type of degeneration was characterized by tight clumping of enormously swollen or distorted synaptic vesicles within a light matrix. At later stages, however, all these boutons were believed to become shrunken and electron-dense since intermediate stages between the light- and dark-appearing boutons were observed. The degenerating cerebellar boutons formed asymmetrical synaptic contacts. Groups of 3 or 4 boutons terminated upon dendrites of projection neurons synapsing more frequently on spines than on dendritic stems. The synaptic contacts between cerebellar boutons and the vesicle-containing dendrites of local circuit neurons were encountered as often if not more than the contacts on projection neuron dendrites. Triads consisting of cerebellar boutons and dendrites of both types of neurons were observed very regularly. This synaptic arrangement provides the anatomical basis for the modification of cerebellar input in the VM by interneurons.     

Electron microscopic observations on recurrent axon collateral boutons of a triceps surae gamma-motoneuron in the cat

Boutons from the recurrent axon collaterals of an adult cat gastrocnemius gamma-motoneuron were studied after intracellular labelling with horseradish peroxidase (HRP). Light and electron microscopic observations revealed that the studied gamma-motoneuron possessed 6 dendrites with 39 dendritic end branches totally and that its axon gave off two axon collaterals with together 8 synaptic boutons of either en passant or terminal type. Both collateral trees were confined to the ventral part of lamina VII. Four of the synaptic boutons were studied electron microscopically. They were all found to be S-type boutons containing spherical vesicles. In two cases the bouton could be further subclassified as a type T bouton. All of the studied boutons made synaptic contact with thin dendrites of unknown origin.     

猫丘脑中央外侧核内脊丘系终末与丘脑-皮质投射神经元之间的突触联系

本实验应用顺行溃变和HRP逆行追踪相结合的方法，首次在电镜水平对猫丘脑中央外侧核内脊丘系终末与丘脑-皮质投射神经元之间的突触联系进行了研究．在脊髓第4颈段刀切损毁一侧侧索和前索后，将HRP注射于同侧大脑前上薛氏回和中上薛氏回前端。在电镜下于损毁同侧中央外侧核内可见下列突触连结：（1）溃变的脊丘系轴突终末与标记树突形成的轴-树突触；（2）溃变的脊丘系轴突终末与非标记树突形成的轴-树突触，个别非标记树突含有突触小泡；（3）正常的轴突终末与HRP标记树突和胞体形成的轴-树突触和轮一体突触；（4）正常的两个轴突终末与HRP标记树突形成的轴-轴-树连续性突触；（5）非标记的含突触小泡的突触前树突与HRP标记树突形成的树-树突触。同时可见大量汇聚型突触复合体。本文首次报道在丘脑中央外侧核内，脊丘系终末与丘脑-皮质投射神经元之间存在着直接的突触联系。     

Ultrastructural immunocytochemistry of gamma-aminobutyrate in the cerebral and cerebellar cortex of the rat

gamma-Aminobutyrate containing structures in the cerebral and cerebellar cortex of the rat were visualized by an immunocytochemical method using glutaraldehyde fixation and an antiserum developed against a gamma-aminobutyrate-glutaraldehyde-protein conjugate. Labelled elements (perikarya and cell processes) were observed to be distributed throughout the layers of the cerebral cortex in a pattern similar to that described using glutamate decarboxylase immunocytochemistry. The morphological features of many immunoreactive cell bodies were typical of stellate neurons. In the cerebellar cortex, Purkinje, basket, Golgi and stellate, cell bodies were found to be immunoreactive along with numerous labelled neuronal processes. At the ultrastructural level, the labelled processes in both areas corresponded to immunoreactive dendrites and fibres. Labelled synaptic boutons, generally of the symmetrical type, could also be seen in contact with positive or negative cell bodies and dendrites. In the cerebellum, glomeruli could be clearly identified including mossy fibres surrounded by unlabelled dendrites in contact with immunoreactive terminals. At the subcellular level in both brain regions, the areas occupied by the Golgi apparatus were never labelled, although the nuclei had varied reactions. The strong glutaraldehyde fixation that limits the diffusion of gamma-aminobutyrate limits also antibody diffusion. However, this fixation is compatible with a good morphological preservation and should enable immunocytochemistry studies to be compared to other methods such as autoradiography.     

Fine structure of granule cells and related interneurons (termed Golgi cells) in the cochlear nuclear complex of cat, rat and mouse

Summary This paper describes the fine structure of granule cells and granule-associated interneurons (termed Golgi cells) in the cochlear nuclei of cat, rat and mouse. Granule cells and Golgi cells are present in defined regions of ventral and dorsal cochlear nuclei collectively termed cochlear granule cell domain.The granule cells are small neurons with two or three short dendrites that give rise to a few branches with terminal expansions. These participate in glomerular synaptic arrays similar to those of the cerebellar cortex. In the glomeruli the dendrites form short type 1 synapses with a large, centrally-located mossy bouton containing round synaptic vesicles and type 2 synapses with peripherally located, smaller boutons containing pleomorphic vesicles. The granule cell axon is thin and beaded and, on its way to the molecular layer of the DCN, takes a straight course, which in the ventral nucleus is parallel to the pial surface.Neurons of the second category resemble cerebellar Golgi cells and occur everywhere interspersed among the granule cells. They are usually larger than the granule cells and give rise to dendrites which may branch close to and curve around the cell body. The dendrites contain numerous mitochondria and are laden with thin appendages, giving them a hairy appearance. Both the cell body and the stem dendrites participate in glomerular synaptic arrays. Golgi cell glomeruli are distinguishable from the granule cell glomeruli by unique features of the dendritic profiles and by longer, type 1 synaptic junctions with the central mossy bouton. The Golgi cell axon forms a beaded plexus close to the parent cell body.The synaptic vesicle population of the mossy boutons suggests that they are a heterogeneous group and may have multiple origins. Apparently, each of the various classes participates in both granule and Golgi cell glomeruli. The smaller peripheral boutons with pleomorphic vesicles in the two types of glomeruli may represent Golgi cell axons which make synaptic contacts with both granule and Golgi cells. The Golgi cell dendrites, on the other hand, are also contacted by small boutonsen passant with round synaptic vesicles, which may represent granule cell axons. A tentative scheme of the circuitry in the cochlear granule cell domain is presented. The similarity with the cerebellar granule cell layer is striking.     

The projection of the visual cortex on the Clare-Bishop area in the cat

Summary Following large lesions of the cat visual cortex, the distribution of degenerating terminal boutons in the Clare-Bishop area was studied electron microscopically. Degenerating boutons were found throughout the cortical layers but mostly in layer III (51% of the total number of degenerating boutons) and layer V (24%). A smaller number of boutons were found in layers II (12%) and IV (9%), and very few in layers VI (3%) and I (1%). No degenerating terminals were observed in the upper two-thirds of layer I. Seventy-six per cent of the total degenerating boutons terminated on dendritic spines, 22% on dendritic shafts, and 2% on somata. Some degenerating boutons made synaptic contacts with somata and dendrites of nonpyramidal neurons. For example, one degenerating bouton was observed in contact with an apical dendrite of a fusiform cell. Three examples of dendritic spines, with which degenerating boutons made synaptic contacts, were found to belong to spinous stellate cells. No degenerating boutons were observed making synaptic contacts with profiles that could conclusively be traced to pyramidal cell somata.