Katsuma Nakano

Topographical projections from the thalamus, subthalamic nucleus and pedunculopontine tegmental nucleus to the striatum in the Japanese monkey, Macaca fuscata

Topographical projections from the thalamus, subthalamic nucleus (STN) and pedunculopontine tegmental nucleus (PPN) to the striatum were examined in the Japanese monkey (Macaca fuscata) by using the retrograde axonal transport technique of WGA-HRP (wheat germ agglutinin-conjugated horseradish peroxidase). After WGA-HRP injection in the head of the caudate nucleus (CN) or putamen (Put), labeled neuronal cell bodies in the thalamus were distributed mainly in the nucleus ventralis anterior (VA)-nucleus ventralis lateralis (VL) complex and the nucleus centrum medianum (CM)-nucleus parafascicularis (Pf) complex, and additionally in the paraventricular, parataenial, rhomboid, reuniens, centrodorsal, centrolateral, paracentral, and centromedial nuclei. The data indicated that the pars principalis of VA (VApc) projected mainly to CN and additionally to Put, and that the pars magnocellularis of VA (VAmc) or pars oralis of VL (VLo) projected selectively to CN or Put, respectively. It was also indicated that CM projected to the middle and caudal parts of Put, while Pf projected to CN and the rostral part of the Put. The data further indicated that the dorsomedial, ventromedial, or lateral part of CM projected respectively to the dorsolateral, ventromedial, or intermediate part of Put, and that the medial or lateral part of Pf projected respectively to the medial or lateral part of the head of CN. Direct projections from STN and PPN to the striatum were confirmed. The subthalamostriatal projections showed a mediolateral topography. The PPN was shown to project bilaterally to the striatum with an ipsilateral predominance.

Projections of the vestibular nuclei to the thalamus in the rat: A Phaseolus vulgaris leucoagglutinin study

Injections of the anterograde axonal tracer Phaseolus vulgaris leucoagglutinin were made into individual nuclei of the vestibular nuclear complex of the rat to identify specific projections to the thalamus. The results showed that the superior vestibular nucleus and the medial vestibular nucleus, especially its rostral‐to‐middle parts, project to the lateral part of the parafascicular thalamic nucleus (corresponding to the centromedian nucleus in primates), the transitional zone between the ventrolateral thalamic nucleus (VL) and the ventral posterolateral thalamic nucleus (VPL) (the region considered to be the nucleus ventralis intermedius of Vogt [Vogt C. 1909. La myeloarchitecture du thalamus du cercopitheque. J Psychol Neurol 12:285–324.]), the lateral part of the centrolateral thalamic nucleus and the dorsal part of the caudal VL; the spinal vestibular nucleus projects to the lateral part of the parafascicular thalamic nucleus, the transitional zone between the VL and the VPL, the caudal part of the ventrobasal complex, and the suprageniculate thalamic nucleus. These results suggest that vestibular information is transmitted not only to the cerebral cortex (mainly area 2V and area 3a) but also to the striatum. They also suggest that vestibular activity may affect gaze control by means of vestibulothalamocortical pathway in addition to vestibulo‐ocular and vestibulopremotoneuronal routes. J. Comp. Neurol. 407:318–332, 1999.

Long-Term Stress Degenerates, But Imipramine Regenerates, Noradrenergic Axons in the Rat Cerebral Cortex

Exposed to a forced walking stress for 2 weeks, some rats became persistently inactive (depression-model rats), whereas others gradually recovered from exhaustion (spontaneous recovery rats). We also studied rats exposed to short-term stress, rats without stress, and the model rats treated with imipramine or saline. We examined the density of noradrenergic axons in the frontal cortex using retrograde labeling of the locus coeruleus with horseradish peroxidase injected into the cortex and immunohistochemical staining of cortical axons with dopamine beta-hydroxylase antiserum. The density was significantly lower in the depression-model rats, but tended to be higher in the recovery rats and short-term stressed rats. Chronic treatment with imipramine significantly increased the density in the model rats. There was also a correlation between the density of noradrenergic axons and the recovery rate of activity. Our results suggest that cortical noradrenergic degeneration is involved in the pathogenesis of depression.

DEGENERATION OF LOCUS COERULEUS AXONS IN STRESS-INDUCED DEPRESSION MODEL

Antidepressants such as desipramine induce axonal regeneration of brain noradrenergic neurons. This novel action of antidepressants suggests the involvement of degeneration or retraction of brain noradrenergic axons in the pathophysiology of clinical depression. The present study was designed to further confirm this view in an animal model of stress-induced depression. The depression model was produced by exposing rats to prolonged forced walking stress. To see if axonal degeneration of noradrenergic neurons occurred in the depression model, the density of noradrenergic axons in the cerebral cortex was assessed by three different methods, antidromic stimulation technique, retrograde tracing with horseradish peroxidase and immunohistochemical staining with dopamine-beta-hydroxylase antiserum. These methods all assured of degenerative changes of noradrenergic axon terminals in the depression model. Furthermore, it was found that repeated treatments of the depression-model rats with imipramine could cause regeneration of cortical noradrenergic axons. These findings support the view that degeneration or retraction of noradrenergic axons is involved in the pathophysiology of depression.

Descending projections from the superior colliculus to the reticular formation around the motor trigeminal nucleus and the parvicellular reticular formation of the medulla oblongata in the rat

We observed by the anterograde and retrograde tracing techniques in the rat that the lateral part of the superior colliculus (SC), where the nigrotectal fibers from the dorsolateral part of the substantia nigra pars reticulata (SNr) terminated, sent projection fibers to the reticular region around the motor trigeminal nucleus (RFmt) and parvicellular reticular formation (RFp) of the medulla oblongata, where many premotor neurons for the orofacial motor nuclei were known to be distributed. The SC neurons sending their axons to the RFmt and RFp were mainly located in the stratum griseum intermedium, and additionally in the stratum griseum profundum. Our results suggest that neuronal signals conveyed through the nigro-tecto-bulbar pathway to the RFmt and RFp may exert control influences upon oral behavior.

Non-dopaminergic projections from the substantia nigra pars lateralis to the inferior colliculus in the rat

The substantia nigra pars lateralis (SNI) of the rat was found, by the anterograde and retrograde tracing methods, to send projection fibers to the peripheral shell region surrounding the central nucleus of the inferior colliculus (IC), bilaterally with a clear-cut ipsilateral dominance. SNI neurons sending their axons to the IC were distributed throughout the entire rostrocaudal extent of the SNI. None of these SNI neurons showed tyrosine hydroxylase-like immunoreactivity.

The vestibular nuclei of the rat project to the lateral part of the thalamic parafascicular nucleus (centromedian nucleus in primates).

To clarify the vestibular projections to the centromedian-parafascicular nuclear complex, the Phaseolus vulgaris leucoagglutinin (PHA-L) and horseradish peroxidase conjugated to wheat germ agglutinin (WGA-HRP), tracing studies have been done in rats. The data demonstrated that the lateral parafasicular nucleus received vestibular afferents mainly from the ventral part of medial vestibular nucleus, and the superior and inferior vestibular nuclei, with an ipsilateral predominance. These findings suggest the vestibular influence to the motor loop of the basal ganglia thalamocortical projections.

The subparafascicular thalamic nucleus of the rat receives projection fibers from the inferior colliculus and auditory cortex

The sources of afferent fibers to the subparafascicular thalamic nucleus (SPF) of the rat were investigated by the retrograde WGA-HRP and anterograde PHA-L methods. Layer V of the areas 3, 1 and 2 of the temporal cortex as well as the dorsal and external cortices of the inferior colliculus were found to send projection fibers to the whole rostrocaudal extent of the SPF bilaterally with a clear-cut ipsilateral dominance. The results indicate that the SPF of the rat may constitute a relay nucleus in the central auditory pathways.

Pallido-thalamo-motor cortical connections: an electron microscopic study in the macaque monkey

We combined the retrograde transport of horseradish peroxidase conjugated to wheat germ agglutinin (WGA-HRP) technique and degenerating electron microscopic investigations to confirm the motor cortical area projection from the medial pallidal segment (GPm) via the thalamic nucleus ventralis lateralis pars oralis (VLo). We found first degenerated boutons arising from the GPm make synaptic contact with the somata and proximal dendrites of VLo neurons containing WGA-HRP reaction products transported retrogradely from motor area.

Direct projections from the globus pallidus to the inferior colliculus in the rat.

A retrograde and anterograde wheat germ agglutinin-horseradish peroxidase (WGA-HRP) study in the rat indicated that some neurons in the globus pallidus (GP) sent their axons ipsilaterally to the inferior colliculus (IC). These neuronal cell bodies were located in the ventrolateral portions of the caudal part of the GP, and their axons were distributed mainly in the peripheral region of the external cortex of the IC.