Jumpei Naito

Organization of anterior cingulate and frontal cortical projections to the anterior and laterodorsal thalamic nuclei in the rat

The anterior and laterodorsal thalamic nuclei provide massive projections to the anterior cingulate and frontal cortices in the rat. However, the organization of reciprocal corticothalamic projections has not yet been studied comprehensively. In the present study, we clarified the organization of anterior cingulate and frontal cortical projections to the anterior and laterodorsal thalamic nuclei, using retrograde and anterograde axonal transport methods. The anteromedial nucleus (AM) receives mainly ipsilateral projections from the prelimbic and medial orbital cortices and bilateral projections from the anterior cingulate and secondary motor cortices. The projections from the anterior cingulate cortex are organized such that the rostrocaudal axis of the AM corresponds to the rostrocaudal axis of the cortex, whereas those from the secondary motor cortex are organized such that the rostrocaudal axis of the AM corresponds to the caudorostral axis of the cortex. The ventromedial part of the anteroventral nucleus receives ipsilateral projections from the anterior cingulate cortex and bilateral projections from the secondary motor cortex, in a topographic manner similar to the projections to the AM. The ventromedial part of the laterodorsal nucleus (LD) receives ipsilateral projections from the anterior cingulate and secondary motor cortices. The projections are roughly organized such that more dorsal and ventral regions within the ventromedial LD receive projections preferentially from the anterior cingulate cortex. The difference in anterior cingulate and frontal cortical projections to the anterior and laterodorsal nuclei may suggest that each thalamic nucleus plays a different functional role in spatial memory processing.

Organization of retrosplenial cortical projections to the anterior cingulate, motor, and prefrontal cortices in the rat

The retrosplenial cortex (areas 29a-29d) has been implicated in spatial memory, which is essential for performing spatial behavior. Despite this link with behavior, neural connections between areas 29a-29d and frontal association and motor cortices--areas also essential for spatial behavior--have been analyzed only to a limited extent. Here, we report an analysis of the anatomical organization of projections from areas 29a-29d to area 24 and motor and prefrontal cortices in the rat, using the axonal transport of biotinylated dextran amine (BDA) and cholera toxin B subunit (CTb). Area 29a projects to rostral area 24a, whereas area 29b projects to caudodorsal area 24a and ventral area 24b. Caudal area 29c projects to mid-rostrocaudal area 24b, whereas rostral area 29c projects to caudal areas 24a and 24b and caudal parts of primary and secondary motor areas. Caudal area 29d projects to mid-rostrocaudal areas 24a and 24b, whereas rostral area 29d projects to the caudalmost parts of areas 24a and 24b and the secondary motor area and to the mid-rostrocaudal part of the primary motor area. Area 29d also projects weakly to the prefrontal cortex. These differential corticocortical projections may constitute important pathways that transmit spatial information to particular frontal cortical regions, enabling an animal to accomplish spatial behavior.

Organization of anterior cingulate and frontal cortical projections to the retrosplenial cortex in the rat.

The retrosplenial cortex (areas 29a–d), which plays an important role in spatial memory and navigation, is known to provide massive projections to frontal association and motor cortices, which are also essential for spatial behavior. The reciprocal projections originating from these frontal cortices to areas 29a–d, however, have been analyzed to only a limited extent. Here, we report an analysis of the anatomical organization of projections from anterior cingulate area 24 and motor and prefrontal cortices to areas 29a–d in the rat, using the axonal transport of cholera toxin B subunit and biotinylated dextran amine. Area 29a receives projections from rostral area 24a, area 24b, the ventral orbital area, and the caudal secondary motor area. Rostral area 29b receives projections from caudal area 24a, whereas caudal area 29b receives projections from rostral area 24a. Area 29b also receives projections from area 24b and the ventral orbital area. Areas 29c and 29d receive projections from areas 24a and 24b and the secondary motor area in a topographic manner such that the rostrocaudal axis of areas 29c and 29d corresponds to the caudorostral axis of areas 24a and 24b and the secondary motor area. Rostral areas 29c and 29d also receive projections from the caudal primary motor area, and area 29d receives projections from the ventral, lateral, and medial orbital areas. These differential frontal cortical projections to each area of the retrosplenial cortex suggest that each area may contribute to different aspects of retrosplenial cortical function such as spatial memory and behavior. J. Comp. Neurol. 506:30–45, 2008.

Organization of intrinsic connections of the retrosplenial cortex in the rat

The retrosplenial cortex consists of areas 29a–d, each of which has different connections with other cortical and subcortical regions. Although these areas also make complex interconnections that constitute part of a neural circuit subserving various functions, such as spatial memory and navigation, the details of such interconnections have not been studied comprehensively. In the study reported here, we investigated the organization of associational and commissural connections of areas 29a–d within the retrosplenial cortex in the rat, using the retrograde tracer cholera toxin B subunit and anterograde tracer biotinylated dextran amine. The results demonstrated that each of these areas has a distinct set of interconnections within the retrosplenial cortex. Each area interconnects strongly along the transverse axis of the retrosplenial cortex: area 29a, area 29b, caudal area 29c, and caudal area 29d connect with each other, and rostral area 29c and rostral area 29d connect with each other. In the longitudinal direction, rostral-to-caudal projections from rostral areas 29c and 29d to areas 29a and 29b and caudal areas 29c and 29d are strong, whereas reciprocal caudal-to-rostral projections are relatively weak. Although most of the intrinsic connections are homotopical, contralateral connections are weaker and less extensive than ipsilateral connections. These findings suggest that each retrosplenial area may not only process specific information somewhat independently but that it may also integrate and transmit such information through intrinsic connections to other areas in order to achieve retrosplenial cortical functions, such as spatial memory and learning.

Morphological properties of chick retinal ganglion cells in relation to their central projections

Morphological properties of chick retinal ganglion cells (RGCs) were studied in relation to their central projections in 23 chicks. A total of 217 RGCs were retrogradely labeled by applying a carbocyanine dye (DiI) to the thalamus and optic tectum. The labeled RGCs were classified into six groups on the basis of their somal areas, dendritic fields, and branching patterns. The dendrites of these RGCs extended horizontally in the inner plexiform layer (IPL) forming eight dendritic strata. The RGCs in each group showed certain specificities in their central projections. Group Ic predominantly projected to the tectum. Groups IIs and IIIs showed a high thalamic dominance. Groups Is and IIc were nonspecific with regard to their tectal and thalamic projections. Group IVc showed tectal‐specific projections. Occurrence rates of the dendritic strata increased progressively toward the inner part of the IPL, i.e., DSs (dendritic strata) 1–4 were scantily distributed, DSs 5 and 6 were moderately distributed, and DSs 7 and 8 were the most frequently distributed. A total of 42 dendritic stratification patterns were identified, and of these, 18 patterns were common to the tectal RGCs (tec‐RGCs) and thalamic RGCs (tha‐RGCs). The common patterns were detected very frequently in the tec‐ and tha‐RGCs (≈85%), and the dendritic strata were largely distributed in the inner part of the IPL (DSs 5–8). In contrast, the remaining 24 noncommon stratification patterns showed low occurrence rates (≈15%); however, these dendritic strata were widely distributed in both the outer (DSs 1–4) and inner (DSs 5–8) IPL. J. Comp. Neurol. 514:117–130, 2009.

Afferent and Efferent Connections of the Nucleus Rotundus Demonstrated by WGA‐HRP in the Chick

Organization of the fibre connections in the chick nucleus rotundus (Rt) was investigated by an axonal tracing method using wheat germ agglutinin conjugated to horseradish peroxidase (WGA‐HRP). After an injection of WGA‐HRP into the Rt, labelled neurones were observed in the striatum griseum centrale (SGC) in both sides of the tectum (TO) and in the ipsilateral nucleus subpretectalis/nucleus interstito‐pretecto‐subpretectalis (SP/IPS). Labelled fibres and terminals were also found in the ipsilateral ectostriatum (Ect). These fibre connections were topographically organized rostrocaudally. In the TO‐Rt projection, the rostral and the dorsocaudal parts of the Rt received afferents from the superficial part of the SGC, the middle part of the Rt received afferents from the intermediate part of the SGC, and the ventrocaudal part of the Rt received mainly fibres from the deep part of the SGC. These topographic projections were accompanied by a considerable number of diffuse projections to the thalamic regions surrounding the Rt. In addition, the rostral and middle caudal parts of the Rt received afferents from the lateral and medial parts of the SP/IPS, respectively, and respective parts of the Rt sent efferents to the lateral and medial parts of the Ect.

Afferent and Efferent Connections of the Nucleus Geniculatus Lateralis Ventralis Demonstrated by WGA-HRP in the Chick

Fibre connections of the chick nucleus geniculatus lateralis ventralis (GLv) were investigated using the axonal tracing method with wheat germ agglutinin conjugated to horseradish peroxidase (WGA‐HRP). After an injection of WGA‐HRP into the GLv, many labelled neurons were observed in layer i of the stratum griseum et fibrosum superficiale (SGFS) in the ipsilateral tectum opticum (TO) and in the nucleus lentiformis mesencephali (LM). In the TO‐GLv projection, cells of origin were located in the deeper part of layer i of the TO and were topographically distributed along the direction from the rostrodorsal part to the caudoventral part of the TO relating to a rostrocaudal axis of the GLv. In the LM‐GLv connection, the dorsal and ventral parts of the LM connected reciprocally with the rostral and caudal halves of the GLv, respectively. In contrast, in the GLv efferent connection, labelled axon terminals spread widely in the ipsilateral area pretectalis without any clear topographical arrangement.

Quantitative Analysis of Cells in the Ganglion Cell Layer of the Chick Retina: Developmental Changes in Cell Density and Cell Size

Changes in cell density and size in the ganglion cell layer (GCL) of the retina were studied in chick embryos and post‐hatching chicks. The total number of cells in the GCL increased from 3.64u2003million at embryonic day 8 (E8) to the maximal 7.85u2003million at E14. After E14, the number of cells decreased to 6.08u2003million at post‐hatching day 1 (P1) and 4.87u2003million at P8. Cell density in the GCL decreased unevenly according to retinal regions; cell density in the presumptive central area (pCA) of P8‐chicks decreased to approximately 45% of that in E8‐embryos. Densities of the nasal peripheral retina (NP) and temporal peripheral retina (TP) of P8‐chicks decreased to 23 and 18% of E8‐embryos, respectively. Differentiation of the central (44u2003000u2003cells/mm2 in pCA) – peripheral (28u2003000u2003cells/mm2 in TP) gradient in cell density was formed by E8. The presumptive dorsal area (pDA) was shaped by E11, but became obscure with age. Although ganglion cell sizes were basically uniform at E8, differentiation occurred with the appearance of larger ganglion cells after E14. Mean size of retinal ganglion cells increased 2.8‐fold in the pCA and 3.8‐fold in the TP between E8 and P8, accompanying a similar scale of decreases in cell densities.

Role of sympathetic nerves on early embryonic development and immune modulation of uterus in pregnant mice

To determine the role of sympathetic nerves in the early embryonic development and the immune modulation of maternal uterus during pregnancy, a model of chemical sympathectomy in mice was established by intraperitoneal injection of 6-hydroxydopamine (6-OHDA). The embryonic development and the distribution of maternal uterine immunocytes were investigated during early pregnancy (E1-E9) with methods of histology, immunohistochemistry and ELISA. Our data showed that in the 6-OHDA-treated group, the number of implanted embryos was only 64.4% of that in the control group at E7, and the development of uterine glands and vessels was poor in pregnant mice. In addition, in uterine tissues of 6-OHDA-treated mice, the number of CD8+ T cells increased ten-fold and the concentration of IL-2 increased 3.6-fold at E5. However, no obvious changes to the number of CD4+ T cells and IL-4 were observed. Thus, the CD4+/CD8+ T cells ratio significantly decreased, while the IL-2/IL-4 ratio significantly increased. These findings indicated that the activation of sympathetic nerves might be favorable to fetal survival and development during early pregnancy through influencing on immune function and decidua formation of uterus.

Retrograde Tracing with Fluorescent Microspheres Reveals Bifurcating Projections from Central Retina to Tectum and Thalamus in Chicks

The goal of this study is to demonstrate the dual‐projection pattern of retinal ganglion cells (RGCs) projecting to the tectum and visual thalamus in chick using retrograde fluorescent tracers and also to define the morphological properties of these RGCs with dual projections by intracellular injection of Lucifer Yellow (LY) combined with immunohistochemistry. Thirty‐two chicks received double injections of green and red fluorescent microspheres into their thalamus and tectum in the same side. In the central retina, most of the labelled RGCs were tec‐RGCs (RGCs projecting to the tectum), a quarter was tha‐RGCs (RGCs projecting to the thalamus), and almost all of the tha‐RGCs were double‐labelled RGCs. An intracellular injection of LY into the double‐labelled RGCs showed all six groups of RGCs without specific populations in each group (J. Comp. Neurol., 2004, 469: 360). These dendritic patterns were mostly mono‐ and bistrata, which extended horizontally in the deeper part of the inner plexiform layer.