Hideshi Shibata

Organization of projections of rat retrosplenial cortex to the anterior thalamic nuclei

The organization of the projections from the retrosplenial cortex (Brodmanns area 29) to the anterior thalamic nuclei was examined in the rat with retrograde transport of the cholera toxin B subunit and anterograde transport of biotinylated dextran amine. Areas 29a and 29b project mainly ipsilaterally to the rostral two‐thirds of the anteroventral nucleus, with area 29a projecting more rostrodorsally than area 29b. Area 29c projects bilaterally to the ventromedial part of the anteroventral nucleus. The projections from area 29c are organized in a topographic pattern such that the rostral area 29c projects to the caudoventral part of the anteroventral nucleus, whereas the caudal area 29c projects to the more rostrodorsal parts. Caudal area 29d projects mainly ipsilaterally to the rostrodorsal part of the anteromedial nucleus, and the rostral and dorsal parts of the anteroventral nucleus, whereas rostral area 29d projects bilaterally to the caudodorsal part of the anteromedial nucleus and the caudolateral part of the anteroventral nucleus. All the areas of the retrosplenial cortex provide sparse projections, mainly ipsilateral, to the anterodorsal nucleus, with a crude topographic pattern such that the rostrocaudal axis of the retrosplenial cortex corresponds to the caudorostral axis of the anterodorsal nucleus. The results indicate that each area of the retrosplenial cortex has a distinct projection field within the anterior thalamic nuclei. This suggests that each of these projections transmits distinct information that is important for complex memory and learning functions, e.g. discriminative avoidance learning and spatial memory.

Somatotopic Representation of Facial Muscles within the Facial Nucleus of the Mouse

The somatotopic representation of facial muscles within the facial nucleus was investigated by means of the retrograde horseradish peroxidase and cell degeneration techniques in the mouse. The nasolabial muscle is represented in the dorsolateral, lateral, and dorsal intermediate subnucleus; the mentalis muscle, in the ventral intermediate subnucleus; the platysma, in the dorsomedial part of the dorsal intermediate subnucleus and along the lateral border of the dorsomedial and ventromedial subnucleus; the orbicularis oculi and frontalis muscle, in the dorsal portions of the dorsolateral, dorsal intermediate, and dorsomedial subnucleus; the rostral and caudal auricular muscles, in the dorsomedial and ventromedial subnucleus, respectively; and the caudal belly of the digastric muscle, in the suprafacial nucleus. The present study shows that the facial muscles are represented in an orderly fashion in seven subnuclei of the facial nucleus, as in other animal species.

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.

Efferent projections of the interpeduncular complex in the rat, with special reference to its subnuclei: a retrograde horseradish peroxidase study

Projections of the subnuclei of the interpeduncular complex were studied by the retrograde horseradish peroxidase technique in the rat. The pars caudalis and pars dorsalis magnocellularis project to the septum, hippocampus and entorhinal cortex; a part of the pars medialis and the pars paramediana, to the dorsal thalamus; all subnuclei, to the midbrain raphe; and the pars lateralis, to the dorsal tegmental nucleus.

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.

A correlative quantitative study comparing the nerve fibers in the cervical sympathetic trunk and the locus of the somata from which they originate in the rat

Correlative quantitative analyses were performed on the rat comparing the number of fibers in the cervical sympathetic trunk (CST) and the horseradish peroxidase (HRP)-labeled neurons in the superior cervical sympathetic ganglion (SCG), stellate ganglion, as well as in the spinal cord. The total number of nerve fibers in the left CST was 4180 +/- 169 (mean +/- S.E.M.) among which 92 +/- 3 (mean +/- S.E.M.) were myelinated. The diameter of unmyelinated fibers was 0.68 +/- 0.22 (mean +/- S.D.) microns and showed single-peaked distribution. After the application of HRP to the proximal cut end of the CST, labeled neurons were found in the stellate ganglion as well as in the ipsilateral spinal cord from C7 to T4 segments. The total number of HRP-labeled neurons in the spinal cord was 1334 +/- 45 (mean +/- S.E.M.) with the range between 844 and 1808. Ninety-nine percent of labeled neurons were located in the intermediolateral column and in the lateral funiculus while 1% were in the intercalated region and central autonomic area. Labeled neurons were encountered only sporadically in the dorsal root ganglia (DRG) from C8 to T3 level. After the application of HRP to the distal cut end of the CST, about 200 labeled neurons were observed in the caudal part of the SCG. The present results were discussed with special reference to the organization of the CST of the rat.

Topographic relationship between anteromedial thalamic nucleus neurons and their cortical terminal fields in the rat

The present study has examined the topographic relationship between cells in the anteromedial thalamic nucleus (AM) and their cortical terminal fields, with retrograde transport of Fluoro Gold in the rat. Projections to the frontal area 2 originate from the ventrolateral part of the AM and the entire interanteromedial nucleus (IAM). Projections to the anterior cingulate area originate from the peripheral part of the rostral AM and the entire IAM. Fibers to the rostral retrosplenial area arise from the caudodorsal part of the AM, whereas those to the caudal retrosplenial area arise from the rostralmost and the rostrodorsomedial parts. Fibers to the rostral area 29D originate from the rostrocentral part of the AM, whereas those to the caudal area 29D originate from the rostroventrolateral and the ventromedial parts. Projections to the medial half of the entorhinal area originate from the rostrodorsomedial part of the AM. In contrast, projections to the lateral half of the entorhinal area originate from the IAM and the central part of the AM. The results show a complex topographic relationship between cells of origin of the AM and their cortical terminal fields, suggesting complex functional roles played by the AM in learning behavior such as discriminative avoidance behavior.

Organization of retrosplenial cortical projections to the laterodorsal thalamic nucleus in the rat

The organization of the projections from the retrosplenial cortex (areas 29a--d) to the laterodorsal thalamic nucleus (LD) was examined in the rat with axonal transport of the cholera toxin B subunit and biotinylated dextran amine. The results showed that an area of the retrosplenial cortex provides ipsilateral projections to a distinct part of the LD at the level of its rostral two-thirds. The projections originate from layer VI and, to a lesser extent, layer V cells of the retrosplenial cortex. Area 29a and area 29b project, respectively, to the dorsolateral and the dorsomedial part of the LD. Area 29c projects to the ventromedial two-thirds of the LD, in a topographic pattern such that the rostral part of area 29c projects more ventromedially within the projection field than the caudal part of area 29c. Area 29d projects to the ventrolateral two-thirds of the LD in a topographic pattern similar to area 29c; the rostral part of area 29d projects more ventromedially within the projection field than the caudal part. These precise topographic projections from the retrosplenial cortex to the LD may constitute part of the circuitry underlying spatial navigation and various memory and emotional functions.

Differential thalamic connections of the posteroventral and dorsal posterior cingulate gyrus in the monkey

Previous functional studies suggest that the posterior cingulate gyrus is involved in spatial memory and its posteroventral part, in particular, is also involved in auditory memory. However, it is not clear whether the neural connections of the posteroventral part differ from those of the rest of the posterior cingulate gyrus. Here, we describe the thalamic connections of the posteroventral part of monkey area 23b (pv‐area 23b), the main component of the posteroventral posterior cingulate gyrus. We compare these thalamic connections with those of the more dorsal area 23b (d‐area 23b) and of adjoining retrosplenial areas 29 and 30. Thalamocortical projections to pv‐area 23b originate mainly from the anterior nuclei, nucleus lateralis posterior and medial pulvinar. In contrast, projections to d‐area 23b originate from the nucleus lateralis posterior, medial pulvinar, nucleus centralis latocellularis, mediodorsal nucleus and nucleus ventralis anterior and lateralis and weakly from the anterior nuclei. Projections to retrosplenial areas 29 and 30 originate from the anterior nuclei. Corticothalamic projections from pv‐area 23b terminate in the anterior and laterodorsal nuclei, nucleus lateralis posterior and medial pulvinar. Projections from d‐area 23b terminate in these nuclei as well as the nucleus ventralis anterior and lateralis. Projections from area 30 terminate mainly in the anterior nuclei and, to a lesser extent, in the medial pulvinar. These results show that the connections of pv‐area 23b differ from those of d‐area 23b or areas 29 and 30. This suggests that pv‐area 23b may play distinct functional roles in memory processes, such as spatial and auditory memory.

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.