Michiko Ikeda

Olivary projections to the cerebellar nuclei in the cat

SummaryProjections from the inferior olive to the cerebellar nuclei have been studied in the cat using Nautas silver technique. 1. Numerous degenerating terminals occur after lesions in the inferior olivary complex in the medial nuclei of both sides; the degeneration is considerably less in the subnucl. medialis parvicellularis of both sides. In the interpositus nuclei of both sides degenerating terminals are also abundant, especially in their dorsal and lateral parts. In the lateral nucleus a number of degenerating terminals are seen on both sides restricted to dorsal and lateral parts of the nuclei. Degeneration is scanty in the subnucl. lateralis parvicellularis. 2. Projection of the olivocerebellar fibers to the cerebellar nuclei is always bilateral. The fibers originate in the inferior olive and ascend mainly through the contralateral, however, some also through the ipsilateral restiform body. The olivocerebellar fibers that have crossed in the medulla terminate in the medial and the interpositus nuclei of both sides. It is suggested that the degenerating terminals found in the cerebellar nuclei are derived from collaterals of the olivocerebellar tract fibers.

The cells of origin of the trigeminothalamic, trigeminospinal and trigeminocerebellar projections in the cat.

Using the retrograde horseradish peroxidase technique, we have examined the distribution of labeled thalamic-, spinal- and cerebellar-projecting neurons in the trigeminal sensory nuclei of the cat. Injections into the nucleus ventralis posterior of the thalamus resulted in labeling of neurons in lamina I (subnucleus zonalis), the deeper part of lamina IV (the subnucleus magnocellularis) of the nucleus caudalis and in lamina V (the lateral extension of the nucleus medullae oblongatae centralis) on the contralateral side. A very large number of labeled small neurons were observed mainly in the caudal part of the nucleus interpolaris and in the ventral division of the principal sensory nucleus on the contralateral side and in the dorsal division of the principal sensory nucleus on the ipsilateral side. Injections into the known projection areas of the cerebellar cortex labeled mainly ipsilaterally the trigeminocerebellar neurons in a restricted ventrolateral area of lamina IV of the nucleus caudalis at its rostral level and in lamina V. Many labeled neurons were also observed in the nucleus interpolaris. Although the distribution overlapped with that of the trigeminothalamic neurons, the greatest majority were concentrated in its rostral part where the trigeminothalamic neurons were very small in number. In addition, labeled neurons were observed in the rostral part of the nucleus oralis and the ventralmost part of the ventral division of the principal sensory nucleus. No labeled neurons were observed in the dorsal division of the principal sensory nucleus and the mesencephalic nucleus. The trigeminospinal neurons were labeled mainly ipsilaterally following injections into the upper cervical cord. They were located in laminae I and III, the deeper part of lamina IV of the nucleus caudalis and in lamina V. Only scattered labeled neurons were found in the nucleus interpolaris. The number of labeled neurons increased in the nucleus oralis at the level of the superior olive. They tended to be distributed around or dorsal to the group of the trigeminothalamic neurons at the caudal part of the principal sensory nucleus. No neurons of the principal sensory nucleus appeared to project to the spinal cord. Based on the large size and location, the trigeminospinal neurons could be differentiated from the other projection neurons in the nucleus oralis. The present study demonstrates that the trigeminal sensory nuclei are composed of groups of neurons with different projections, since the main aggregations are localized at different levels. However, it should be examined whether the neuronal groups, which are labeled from the different structures in similar locations, are composed of individual neurons projecting to more than one of these structures.

Ascending and descending internuclear connections of the trigeminal sensory nuclei in the cat. A study with the retrograde and anterograde horseradish peroxidase technique

The distribution of cells of origin of ascending and descending internuclear connections in the trigeminal sensory nuclei was studied by the retrograde horseradish peroxidase technique in the cat. The termination of collaterals of these ascending axons was also studied by the anterograde transport of horseradish peroxidase. Following injections of horseradish peroxidase into the ventral part of the principal sensory nucleus and the adjacent reticular formation many small neurons were labeled ipsilaterally in the whole area of the caudal portion of the nucleus interpolaris and in laminae III and IV of the nucleus caudalis. Labeled neurons were also found in laminae I and V. Injections limited to either nucleus oralis, the ventral part of the principal sensory nucleus and the medial parabrachial nucleus labeled similar types of neurons in the above regions with a topographic relationship; neurons in the dorsal part of the nuclei caudalis and interpolaris project, dorsally, to rostral portions of the trigeminal sensory nuclei while those in the ventral part of the nuclei caudalis and interpolaris project ventrally. Anterograde labeling of axons arising from the nucleus caudalis demonstrates that the axons ascend in the intranuclear bundles and the adjacent reticular formation, and give off collaterals to the nuclei interpolaris and oralis, and the ventral part of the principal sensory nucleus. Injections limited to the nucleus caudalis labeled small neurons in the rostral portion of the nucleus oralis and the caudal portion of the nucleus interpolaris. The present study suggests that these ascending and descending internuclear connections of the trigeminal sensory nuclei may modulate transmission of afferent inputs to various projection sites, such as thalamus, superior colliculus, cerebellum and spinal cord.

Spinocerebellar projections from the upper lumbar segments in the cat, as studied by anterograde transport of wheat germ agglutinin-horseradish peroxidase.

The projection fields of spinocerebellar tracts arising from the cervical enlargement were studied by the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA‐HRP) in the cat.

Identification of Rat Brainstem Sites with Neuronal Fos Protein Induced by Acoustic Stimulation with Pure Tones

Induction of Fos, a proto-oncogene c-fos protein product, was immunohistochemically examined in the rat brainstem by using pure tone stimuli (0.25 kHz, 4kHz and 8 kHz) at 60 and 80 dB sound pressure levels for 30 min. In comparison with non-stimulated control rats, the brainstem of sound-stimulated rats exhibited distinct Fos-labeled neuronal cell nuclei in i) the ascending auditory nuclei, ii) the brainstem sites which receive afferents from the auditory nuclei, i.e. the pretectum and rostroventrolateral reticular nucleus, iii) the parvocellular part of the ventral lateral geniculate nucleus, lateral reticular nucleus, ventral border region of the spinal trigeminal nucleus, and the medial vestibular and spinal vestibular nuclei, all of which lack established auditory projections, and iv) the brainstem sites where some Fos-labeled neurons were present in controls. Sound stimulation at 80 dB led to widespread Fos-labeling in all these sites. Sound stimulation at 60 dB caused a decrease in number of positive cells in the brainstem sites and yielded a tone-dependent subregional distribution pattern in the dorsal cochlear nucleus and central nucleus of the inferior colliculus.

A brain-specific transcript from the 3'-terminal region of the skeletal muscle ryanodine receptor gene.

We have shown previously that the skeletal muscle ryanodine receptor mRNA of ∼16,000 nucleotides codes 5,037 amino acid residues constituting the calcium release channel in skeletal muscle. In this study, RNA blot hybridization analysis shows that the brain contains an RNA species with an estimated size of ∼2,400 nucleotides hybridizable with the 3′‐terminal region of the skeletal muscle ryanodine receptor cDNA. cDNA cloning and genome analysis indicated that two transcripts differing in their start sites are produced from the skeletal muscle ryanodine receptor gene in a tissue‐specific fashion, and that the mRNA in brain may code the carboxyl‐terminal region of the ryanodine receptor molecule. cDNA expression experiments suggested that the ATG triplet encoding Met4382 of the skeletal muscle ryanodine receptor can function as a translation initiation codon, and that the expressed protein composed of the carboxy terminal 656 amino acid residues of the receptor is located on the endoplasmic reticulum membrane.

Mapping of the cochlear nucleus subregions in the rat with neuronal Fos protein induced by acoustic stimulation with low tones

To explore the mode of appearance of Fos, a gene product of proto-oncogene c-fos, in the cochlear nucleus, a pure tone was given to rats and Fos was detected by immunohistochemistry. Following low-tone stimuli applied with moderate ranges of sound intensity, neurons with Fos-label occurred band-like in the ventral subregions of the dorsal cochlear nucleus. Organization of low-to-high tones in the ventral-to-dorsal orientation became visible at the caudal level. Several other subnuclei consistently exhibited Fos with no topographic pattern. Neurons interspersed in the adjoining vestibulocochlear nerve were also found to elicit Fos. Low-tone stimuli with very high sound intensity led to a rather widespread distribution of Fos, making the tone-specific distribution less visible.

Termination and cells of origin of the ascending intranuclear fibers in the spinal trigeminal nucleus of the cat. A study with the horseradish peroxidase technique

Termination and cells of origin of the ascending intranuclear fibers in the spinal trigeminal nucleus were studied with the anterograde and retrograde horseradish peroxidase (HRP) techniques in the cat. HRP injections into the nucleus caudalis labeled many axons ascending ipsilaterally within the trigeminal spinal nucleus. These fibers gave off collaterals to the nucleus interpolaris and oralis, and the ventral part of the principal sensory nucleus. HRP injections into the principal sensory nucleus labeled ipsilaterally many small neurons in the caudal portion of the nucleus interpolaris and in laminae III and IV of the nucleus caudalis. A few neurons were labeled in laminae I and V.

Choline acetyltransferase immunoreactivity in the cat cerebellum.

Choline acetyltransferase immunoreactivity was demonstrated in particular projection systems in cat cerebellum by combining immunohistochemistry, retrograde tracing and lesioning paradigms. The monoclonal antibody used in this study recognized a 68,000 mol. wt protein on immunoblots of cat cerebellum and striatum. Choline acetyltransferase immunoreactivity was localized to some neurons and varicose fibers in the cerebellar nuclei, and also to some mossy fibers and endings (rosettes), fiber plexuses around Purkinje cells, granule cells and parallel fibers in the cerebellar cortex. In addition, the presence of choline acetyltransferase-immunoreactive large cells, presumptive Golgi cells, in the granular layer was confirmed. In each cerebellar nucleus, choline acetyltransferase-immunoreactive neurons contained either large, medium-sized or small cell bodies and were distributed evenly in the entire nuclear domain. Large and medium-sized ones were frequently encountered. Choline acetyltransferase-immunoreactive mossy fibers and rosettes were most abundant in the vermal lobules I-III, VIII, IX and the simple lobule, moderately accumulated in the vermal lobules IV-VII, X, crus I and crus II, and less abundant in the paramedian lobule, paraflocculus and flocculus. Some granule cells with prominent dendritic claws and bifurcating parallel axons were immunolabeled in the entire vermis with infrequent occurrence in the remaining cortices. Following unilateral lesioning of the cerebellar nuclei with electrocoagulation or kainate injections, a reduction in number of choline acetyltransferase-immunoreactive fibers occurred ipsilaterally in the cerebellar cortex and contralaterally in the red nucleus, ventrolateral thalamic nucleus and ventroanterior thalamic nucleus. In addition, perikarya of some cerebellothalamic neurons were shown to contain choline acetyltransferase immunoreactivity. The results indicate that some nucleocortical, cerebellorubral and cerebellothalamic projections are cholinergic and that a subpopulation of cholinergic granule cell-parallel fibers exists.

The vermal projection of spinocerebellar tracts arising from lower cervical segments in the cat: an anterograde WGA-HRP study

Following injections of WGA-HRP into lower cervical segments, the distribution of anterograde labeled terminals of spinocerebellar fibers was examined in the vermal cortex of the cat. The labeled terminals were seen in sublobules Ib to VIc, VIIb, VIIIa and VIIIb, and lobule IX. They were present mainly in the medial part of the vermis, at most within 2.0 mm from the midline, and in the apical to middle parts of these lobules in the apicobasal extent. The present study demonstrates that the neuronal groups in the medial part of lamina VI and the central part of lamina VII of lower cervical segments project to the vermis of the caudal lobules of the anterior lobe and the rostral lobules of the posterior lobe.