Kaeko Hoshino

Chapter 17 Extrinsic and intrinsic connections of the cat's lateral suprasylvian visual area

The lateral suprasylvian visual area (LS) is known to have numerous interconnections with visual cortical areas as well as with subcortical structures implicated in visually-guided behaviors. In contrast, little data is available regarding connections within the LS itself. In order to obtain information about intra-areal connections and to re-investigate LS connectivity with various cortical and subcortical areas, the traces (biocytin or WGA-HRP) was injected into various loci along the medial and lateral banks of the LS. The anterograde tracer, biocytin injections into both medial and lateral bank produced label contained within the respective bank that extended rostrally and caudally from the infection site. In addition, following medical bank injections, considerable label was distributed throughout the fundus and, to a lesser extent, in the lateral bank. In contrast, no label could be detected in the medial bank after lateral bank injections, and, although label was observed in the fundus, it was restricted to the most lateral aspects. Moderate labeling could be observed in the medial bank following the tracer injection into the most rostral aspect of the lateral bank. It is likely that input derived from various visual cortical areas which project to the medial bank of the LS has access to this intra-areal circuitry. This may provide a route by which visual cortical information can be relayed to other cortical and subcortical structures involved in visually-guided behaviors such as the anterior ectosylvian visual cortex, striatum, and the deep layers of the superior colliculus, despite the fact that these structures themselves do not receive substantial direct projections from the visual cortical areas that are associated with the medial bank. Examination of the laminar location of the cells-of-origin of striate and extrastriate projections to LS using retrograde trace, WGA-HRP, revealed that the supragranular laminae of areas 17, 18 and 19 were the source of LS afferents whereas afferents from the other cortical areas (e.g., 20a, 20b, 21a, 21b, 7 and anterior ectosylvian visual area) were from both supra- and infragranular laminae. In addition, all LS subregions received intra-areal afferent projections from all LS cortical laminae. Thus, although rather clear hierarchical relationship between LS and visual cortical areas appears to exist, the interconnections among LS subregions provide no clear evidence of simple hierarchical relationships between regions LS or may have feed-forward and feed-back pathways.

Anisotropic functional connections between the auditory cortex and area 18a in rat cerebral slices

We developed a new method to visualize the myeloarchitecture in fresh slices, and investigated the properties of the functional neural connections around the boundary between the primary auditory cortex (area 41) and area 18a in rat cerebral slices. A fresh slice illuminated by near-vertical light was observed with a CCD camera. The translucent images of the slice showed contrast patterns very similar to myeloarchitecture. The boundary between these areas was identified by the well-developed layer IV/V in area 41 but not in area 18a. Antidromic/presynaptic components of the field potentials stimulated and recorded across the areal boundary showed symmetric distribution, while the postsynaptic field potentials in the direction from area 41 to 18a were more prominent than those in the opposite direction in layer II/III. In contrast, the dominant direction of propagation of postsynaptic potentials was from area 18a to 41 in layer V. In the presence of 1 microM bicuculline, an inhibitor of GABA(A) receptors, the polysynaptic activities propagating from area 18a into 41 via layer V were elicited by stimulation of area 18a. The propagation measured by Ca(2+) imaging or field potential recordings was potentiated after both areas 18a and 41 were alternately stimulated several times.

Metabotropic glutamate receptor 2/3 immunoreactivity in the developing rat cerebellar cortex.

In adult rat cerebellar cortex, the metabotropic glutamate receptors (mGluRs) 2 and 3 (mGluR2/3) are present in somata, dendrites, and terminals of Golgi cells as well as in presumed glial processes (Ohishi et al. [1994], Neuron 13:55–66). In the present study, spatiotemporal changes in immunostaining for mGluR2/3 were examined in postnatal rat cerebellar cortex. mGluR2/3‐immunoreactive Golgi cell somata appeared first in the internal granular layer at postnatal day 3 (P3) and were restricted to lobules IX and X; however, by P5, they were present in all lobules. Immunoreactive Golgi cell axons were adult‐like, appearing as tortuous fibers with clusters of varicosities. They were observed first in the internal granular layer at P7 and increased in number and complexity with time. It was confirmed that mGluR2/3‐immunoreactive Golgi cell axon terminals belong to the synaptic glomerulus by P10. Immunoreactive Golgi cell dendrites extending into the molecular layer became prominent after P15. By that time, the immunostaining pattern was characteristic of Golgi cells, as seen typically in adults. Many intensely immunoreactive radial processes existed at birth (P0). These traversed the molecular and external granular layers, reaching the pial surface in every cerebellar lobule. Because they showed coimmunoreactivity for glial fibrillary acidic protein, they were confirmed to be Bergmann glial fibers. After P9, they began to lose immunoreactivity at the portion corresponding to the molecular layer, while an immunostained granular pattern appeared in that layer. Immunoreactive radial processes, however, remained in the external granular layer, and finally, at P21, they disappeared together along with the external granular layer. Granular staining in the molecular layer reached background levels at this time. These spatiotemporal changes in mGluR2/3 distribution suggested that there may be distinct roles for mGluR2/3 in Golgi cells and Bergmann glial cells during the early postnatal period. mGluR2/3 in Golgi cells might be associated closely with systemic maturation, whereas mGluR2/3 in Bergmann glia might be needed for neuron‐glia interactions related to granule cell development. J. Comp. Neurol. 410:243–255, 1999.

Normal ontogenic observations on the expression of Eph receptor tyrosine kinase, Cek8, in chick embryos

Abstract The spatio-temporal pattern of expression for the Eph receptor tyrosine kinase, Cek8, was observed in normal chick embryos from H–H stage 6 to 23 by immunohistochemical techniques. Expression of Cek8 was already present in embryos at H–H stage 6, where it was located in the neural plate of the brain region, paraxial mesoderm, and the primitive streak. Regions expressing Cek8 subsequently increased during development to include the neural folds of the brain, rhombomeres 3 and 5, the caudal part of the neural plate, neural creast cells related to the formation of glossopharyngeal nerve ganglia, invaginated cells throughout the primitive groove and the epithelium of the rudiment of the gall bladder. Cek8 was also expressed in the mesenchymal cells of the pharyngeal arches, allantoic stalk and limb buds as well as in the areas surrounding the eye vesicles and nasal pits. Furthermore, cells in the tail bud progressing to the secondary neurulation expressed Cek8. Thus, the spatio-temporal patterns of Cek8 expression appears to have intimate relationships with tissue rebuilding, the maturation of differentiated cells, and the spatial organization of tissues. Consequently, it appears that Cek8 plays an integral role in the developmental events leading to the formation of a wide – though not inclusive – variety of tissues and organ systems.

Distribution of terminals from pedunculopontine tegmental nucleus and synaptic organization in lateralis medialis-suprageniculate nucleus of cat's thalamus : Anterograde tracing, immunohistochemical studies, and quantitative analysis

The cats lateralis medialis-suprageniculate nuclear complex (LM-Sg) in the thalamus receives input from various brain regions such as the superior colliculus, brain stem, and spinal cord, as well as from visual association cortex. In a previous study, we demonstrated that LM-Sg receives cholinergic fibers from the pedunculopontine tegmental nucleus (PPT) and that cholinergic terminals make synaptic contacts with the dendrites of glutamatergic projection neurons and of GABAergic interneurons (Hoshino et al., 1997). In this study, we investigate the distribution and the organization of PPT terminals by means of a combined anterograde tracer (biotinylated dextran amine, BDA) and immunohistochemical methods. When stained by acetylcholinesterase (AChE), the LM-Sg is not uniformly immunoreactive, but rather is patchily labeled and shows a streaming type of reactivity. The tissue content appears high in enzyme activity in AChE-positive zones and is much lighter in activity in AChE-negative zones. We compared the synaptic organization between AChE-positive and AChE-negative portions of the LM-Sg in separate groups of electron-microscopic material: four types of vesicle containing profiles (RS, RL, F1, and PSD) as well as synaptic glomeruli were observed in this nucleus. Among these, the PSD profiles were observed more frequently in AChE-positive portions than in AChE-negative zones. Furthermore, the number of glomeruli was significantly higher in AChE-positive than in AChE-negative zones. Following the injection of BDA into PPT, labeled terminals within LM-Sg were rather more concentrated in the AChE-positive portion. Although the majority of PPT terminals made synaptic contacts with dendrites in the neuropil, a few terminals were involved in the synaptic glomeruli. The present results show that the synaptic organization is distinctly different between the AChE-positive and AChE-negative portions of LM-Sg. These results suggest that the AChE-positive portions of LM-Sg are relatively more involved in integrating information arising from a diverse set of inputs and processing that information within glomeruli in a complex manner than occurs in the AChE-negative portion of LM-Sg.

Overlap of nigrothalamic terminals and thalamostriatal neurons in the feline lateralis medialis-suprageniculate nucleus.

The lateralis medialis-suprageniculate nucleus (LM-Sg) of the feline posterior thalamus is a relay nucleus with a clear visuomotor function. In this study, we examined the distribution of axon terminals of the nigral afferent to the LM-Sg following injection of an anterograde tracer, biocytin, into the substantia nigra pars reticulata, and the distribution of the thalamostriatal projection neurons in the LM-Sg following the injection of wheat germ agglutinin conjugated with horseradish peroxidase (WGA-HRP) as a retrograde tracer into the caudate nucleus. The biocytin-labeled terminal-like puncta were located in the ventromedial portion of this nucleus in such a way that most of the labeled elements took the form of swellings having boutons in places, while a minority appeared in clusters of 3-5 large terminal-like puncta. The retrograde WGA-HRP-labeled neurons were also found in the ventromedial part of the LM-Sg, and the distributions of labeled nigrothalamic axon terminals and labeled thalamostriatal projection neurons therefore overlapped in this region. The present results indicate that the nigral afferent may make synaptic contacts directly with the thalamostriatal projection neurons within the LM-Sg.

Direct synaptic connections between superior colliculus afferents and thalamo-insular projection neurons in the feline suprageniculate nucleus: A double-labeling study with WGA-HRP and kainic acid

The suprageniculate nucleus (Sg) of the feline thalamus, which subserves largely unimodal sensory and orientation behavior, receives input from the deep layers of the superior colliculus (SC), and projects to the suprasylvian cortical areas, such as the anterior ectosylvian visual area and the insular visual area (IVA), which contain visually responsive neurons. Through a double tract-tracing procedure involving the injection of wheat germ agglutinin conjugated with horseradish peroxidase (WGA-HRP) into the IVA and the injection of kainic acid into the SC, this study sought to determine the nature of the synaptic relationship between the SC afferents and the thalamo-cortical projection neurons. WGA-HRP injections labeled numerous neurons in the Sg, while kainic acid injections destroyed many tectothalamic terminals in the Sg. The distributions of the WGA-HRP-labeled neurons and the degenerated axon terminals overlapped in the dorsal part of the Sg. Electron microscopic observations demonstrated that the degenerated axon terminals made synaptic contacts with the dendrites of the WGA-HRP-labeled neurons in this overlapping region of the Sg. These results provide the first anatomical evidence that the Sg may play a role in the key relay of visual information from the SC to the IVA, within an identified extrageniculo-cortical pathway.

Ultrastructural organization of transmitters in the cat lateralis medialis-suprageniculate nucleus of the thalamus: an immunohistochemical study.

The lateralis medialis‐suprageniculate nuclear (LM‐Sg) complex of the cats posterior thalamus receives a rather wide variety of inputs from diverse cortical and subcortical areas. Previous ultrastructural studies of this nucleus demonstrated the presence of four types of vesicle‐containing profiles and characterized some of these as γ‐aminobutyric acid (GABA)–containing terminals (Norita and Katoh [ 1987 ] J. Comp. Neurol. 263:54–67; Norita and Katoh [ 1988 ] Prog. Brain Res. 75:109–118). The present study has extended these observations by examining the immunoreactivity (ir) of LM‐Sg, with antibodies raised against aspartate (Asp), glutamate (Glu), GABA, the acetylcholine (ACh) marker, choline acetyltransferase (ChAT), and substance P (SP), by using light and electron microscopy. Neuronal somata immunopositive for the excitatory amino acids (EAAs) Asp and Glu, were of medium size. EAA‐ir terminals also were of medium size and contained round synaptic vesicles; they made asymmetrical synaptic contacts with dendritic profiles. Neuronal somata immunopositive for GABA were small. GABA‐positive terminals also were small and contained pleomorphic synaptic vesicles; they formed symmetrical synaptic contacts with dendritic profiles. No neurons immunolabeled for ChAT were found. Terminals immunopositive for ChAT were small and contained round synaptic vesicles; these made symmetrical synaptic contacts, asymmetrical synaptic contacts, or both, of the en passant type with dendritic profiles. SP‐immunolabeled neuronal somata were not found. Immunolabeled terminals were small, contained round synaptic vesicles, and made asymmetrical synaptic contacts with dendritic profiles. ChAT‐ir and SP‐ir axon terminals were not expressed evenly within LM‐Sg. This difference in distribution suggests that within the LM‐Sg, there may be a difference in specific sensory processing functions which correlate with transmitter type. J. Comp. Neurol. 419:257–270, 2000.

Neuroanatomical study on the tecto-suprageniculate-dorsal auditory cortex pathway in the rat

Previous anatomical and physiological studies suggest that the superior colliculus sends integrated sensory information to the multimodal cortical areas via the thalamic suprageniculate nucleus (SG). However, the detailed distribution of rat tecto-SG axon terminals and SG neurons projecting to the multimodal cortex, as well as synaptic connections between these tectal axons and SG neurons, remains unclear. In this study, the organization of the tecto-thalamo-cortical pathway was investigated via combined injections of anterograde and retrograde tracers followed by light and electron microscopic observations. Injections of a retrograde tracer, cholera toxin B subunit (CTB), into the temporal cortex, area 2, dorsal part (Te2D), and injections of an anterograde tracer, biotinylated dextran amine (BDA), into the deep layers of the superior colliculus produced the following results: (1) Retrogradely CTB-labeled neurons were found throughout SG, predominantly in its rostral part. CTB-labeled neurons were also found in other cortical areas such as the visual cortex, the auditory cortex, the parietal association cortex, and the perirhinal cortex. (2) Anterogradely BDA-labeled axons and their terminals were also observed throughout SG. Dual visualization of BDA and CTB showed that retrogradely labeled SG neurons and anterogradely labeled tectal axon terminal boutons overlapped considerably in the rostral part of SG, and their direct synaptic contacts were also confirmed via electron microscopy. These findings suggest that multimodal information from the superior colliculus can be processed directly in SG neurons projecting to Te2D.

Cholinergic innervation of the lateralis medialis-suprageniculate nuclear complex (LM-Sg) of the cat's thalamus: a double labeling immunohistochemical study

The purpose of this study was to investigate morphological characteristics of the synaptic relations of choline acetyltransferase (ChAT)-positive terminals that are made with a variety of post-synaptic profiles in the lateralis medialis-suprageniculate nuclear complex (LM-Sg) using ChAT, gamma-aminobutyric acid (GABA) and glutamate immunohistochemistry in combination with electron microscopical observations. The ChAT immunopositive profiles make asymmetrical synaptic contacts with glutamate immunopositive dendrites that are presumably derived from projection neurons, and/or GABA immunopositive interneurons. The present results indicate that ascending cholinergic mechanisms may be important for modifying information in both the extrinsic and intrinsic circuitries of LM-Sg.