Shigeyoshi Higo

The cerebellar projections to the superior colliculus and pretectum in the cat: An autoradiographic and horseradish peroxidase study

Efferent projections from the cerebellar nuclei to the superior colliculus and the pretectum have been studied using both retrograde and orthograde labeling techniques in the cat. In order to identify what parts of the cerebellar nuclei project to the superior colliculus and the pretectum, the retrograde horseradish labeling technique was employed. In another set of experiments, tritiated amino acids were injected into each of the cerebellar regions from which the cerebello-tectal and cerebello-pretectal projections arise, and the laminar and spatial distributions of orthograde labeling in the superior colliculus and the pretectum were compared. The results showed that the cerebello-tectal projections arise from two different regions of the cerebellar nuclei: the caudal half of the medial nucleus and the ventrolateral part of the posterior interposed nucleus. Fibers arising from the medial nucleus distribute bilaterally in the superficial zone of the intermediate gray layer in the superior colliculus, while those originating from the posterior interposed nucleus terminate contralaterally in the deeper aspect of the intermediate gray layer and in the deep gray and white layers. Although the lateral nucleus does not contribute to the cerebello-tectal projection, it projects profusely to the pretectum contralaterally. The origin of the cerebello-pretectal projection lies in the parvicellular part of the lateral nucleus. Among several pretectal nuclei, the posterior pretectal, the medial pretectal nucleus and the reticular part of the anterior pretectal nucleus receive the cerebellar afferents. The findings of the differential projections from the cerebellum to the superior colliculus and the pretectum suggest that the cerebellum exerts a regulatory influence on visuo-motor and somato-motor transfer in these midbrain structures by differential circuits.

Ascending projections from the nucleus of the brachium of the inferior colliculus in the cat.

SummaryAscending projections from the nucleus of the brachium of the inferior colliculus (NBIC) in the cat were studied by the autoradiographic tracing method. Many fibers from the NBIC ascend ipsilaterally in the lateral tegmentum along the medial border of the brachium of the inferior colliculus. At midbrain levels, fibers from the NBIC end in the superior colliculus, the pretectum, the central gray and the peripeduncular tegmental region bilaterally with ipsilateral predominance. NBIC fibers to the superior colliculus are distributed densely to laminae VI an III throughout the whole rostrocaudal extent of the colliculus. In the pretectum, NBIC fibers terminate in the anterior and medial nuclei and the nucleus of the posterior commissure. NBIC fibers to the dorsal thalamus are distributed largely ipsilaterally. Many NBIC fibers end in the dorsal and medial divisions of the medial geniculate body, but few in the ventral division. The NBIC also sends fibers to the suprageniculate, limitans and lateralis posterior nuclei and the lateral portion of the posterior nuclear complex; these regions of termination of NBIC fibers constitute, as a whole, a single NBIC recipient sector. Additionally, the NBIC sends fibers to the centralis lateralis, medialis dorsalis, paraventricular and subparafascicular nuclei of the thalamus.

Long-range GABAergic projection neurons in the cat neocortex

Neocortical γ‐aminobutyric acid (GABA)ergic neurons have been previously described as largely involved in local intracortical circuitry. However, our recent findings in the murine model described select neocortical GABAergic neurons that project to both neighboring and more distant neocortical regions. Here, we investigated whether such GABAergic projection neurons are also found in the cat neocortex. Wheat germ agglutinin‐conjugated horseradish peroxidase (WGA‐HRP) was injected into the visual, auditory, or somatosensory cortex, in order to label efferent cortical neurons retrogradely and to label axons and terminals orthogradely. Staining for nicotinamide adenine dinucleotide phosphate diaphorase (NADPH‐d), an enzyme involved in nitric oxide synthesis, was employed, and co‐localization with WGA‐HRP was determined by means of both polarizing and brightfield microscopy. We concluded that neurons double‐labeled with WGA‐HRP and NADPH‐d in a distant region from the WGA‐HRP‐injection site are GABAergic neurons with long‐range projection axons. All double‐labeled neurons were found in cortical layers VIa and VIb and in the white matter. Neurons with intense NADPH‐d reactivity (type I) were determined to be neuronal nitric oxide synthase (nNOS) positive in all cases. However, weakly NADPH‐d‐reactive neurons (type II) lacked nNOS immunoreactivity. Moreover, nNOS often co‐localized with GABA, neuropeptide‐Y, and somatostatin in the cat neocortex. In summary, the GABAergic neurons described here projected in a manner similar to that previously described for neocortical principal neurons, although some unique GABAergic long‐range projections were also demonstrated. J. Comp. Neurol. 503:421–431, 2007.

Parvalbumin neurons in the forebrain as revealed by parvalbumin-Cre transgenic mice

Neurons expressing the calcium-binding protein parvalbumin (PV) constitute an abundant subpopulation of GABAergic neurons in the cerebral cortex. However, PV is not unique to the GABAergic neurons of the forebrain, but is also expressed in a small number of pyramidal neurons and in a large number of thalamic neurons. In order to summarize the PV neurons in the forebrain, we employed the PV-Cre transgenic mice in the present study. In the progeny of crossbreed between PV-Cre mice and GFP-Cre reporter mice, we found that the GFP-positive neurons include many excitatory neurons in the neocortex and the thalamus as well as GABAergic neurons in the cerebral cortex and basal ganglia. All the reported PV-positive GABAergic neurons in the cerebral cortex and the basal ganglia seemed to be included in the GFP-positive cells. We found GFP-positive layer V pyramidal neurons inhabit a broader neocortical area than was previously reported. They were located in the primary somatosensory, motor, and visual areas. The somatosensory area of the neocortex contained the greatest number of PV-positive pyramidal neurons. A large number of thalamic relay neurons and virtually all the reticular thalamic neurons appeared as GFP-positive. Thalamic relay nucleus and a neocortical area for the same modality corresponded and seemed to contain a characteristic amount of PV-positive excitatory neurons.

Subtypes of GABAergic neurons project axons in the neocortex.

γ-aminobutyric acid (GABA)ergic neurons in the neocortex have been regarded as interneurons and speculated to modulate the activity of neurons locally. Recently, however, several experiments revealed that neuronal nitric oxide synthase (nNOS)-positive GABAergic neurons project cortico-cortically with long axons. In this study, we illustrate Golgi-like images of the nNOS-positive GABAergic neurons using a nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) reaction and follow the emanating axon branches in cat brain sections. These axon branches projected cortico-cortically with other non-labeled arcuate fibers, contra-laterally via the corpus callosum and anterior commissure. The labeled fibers were not limited to the neocortex but found also in the fimbria of the hippocampus. In order to have additional information on these GABAergic neuron projections, we investigated green fluorescent protein (GFP)-labeled GABAergic neurons in GAD67-Cre knock-in/GFP Cre-reporter mice. GFP-labeled axons emanate densely, especially in the fimbria, a small number in the anterior commissure, and very sparsely in the corpus callosum. These two different approaches confirm that not only nNOS-positive GABAergic neurons but also other subtypes of GABAergic neurons project long axons in the cerebral cortex and are in a position to be involved in information processing.

Soma size comparison of the trigeminal ganglion cells giving rise to the ascending and descending tracts: A horseradish peroxidase study in the cat

Soma size was compared between the trigeminal ganglion cells projecting to the main sensory trigeminal nucleus (Vs) and those projecting to the nucleus caudalis (Vc) of the spinal trigeminal nucleus in the cat after injection of horseradish peroxidase (HRP) into each nucleus. The results showed that the cells projecting to the Vc (Vc cells) contained by far a greater percentage of small cells than do those projecting to the Vs (Vs cells). In the Vc case, about one-half the total number of measured labeled cells were the smallest with a diameter less than 36 microns, whereas in the Vs cases, only a small proportion of the total number of measured labeled cells were that small. In addition, the results also made it clear that the Vs cells in the ophthalmic and maxillary divisions contained a higher percentage of larger cells than those in the mandibular division.

Topographical linkage of tecto-thalamo-anterior ectosylvian sulcal cortex in the cat: An125I-WGA autoradiographic study

Following injection of 125I-WGA into various parts of the caudal thalamus in the cat, the distribution of orthograde and retrograde labels in the cortex around the anterior ectosylvian sulcus (AESS) and the superior colliculus (SC) was examined autoradiographically. When 125I-WGA injections involved the medial part of nucleus lateralis posterior (Lp) of the thalamus, both orthograde and retrograde labels consistently appeared in the cortex around AESS, and retrograde labels in the SC. The topographical organization of the cortical connections with the medial part of Lp can be well correlated with that of the tecto-thalamic projections, in such a way that the dorsal portion of the medial part of Lp which receives fibers from the rostromedial part of SC is connected reciprocally with the lateral lip of AESS and the crown of the anterior sylvian gyrus; whereas, the most ventral portion of the medial part of Lp which receives tectal afferents from the caudolateral part of SC is connected with the dorsal bank and fundus of AESS. These results suggest the existence of retinotopically ordered linkage between the tecto-Lp and the Lp-AESS connections in the cat.

Direct projections from the pedunculopontine and laterodorsal tegmental nuclei to area 17 of the visual cortex in the cat

Direct projections from the pedunculopontine tegmental nucleus (PPT) and the laterodorsal tegmental nucleus (LDT) in the brainstem to area 17 of the visual cortex were investigated in the cat by the tract-tracing method with WGA-HRP. Neurochemical nature of neurons which were labeled retrogradely with WGA-HRP injected into area 17 was also examined immunohistochemically with antibodies against choline acetyltransferase (ChAT), tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH), and serotonin (5-HT). After injections of WGA-HRP into area 17, neurons in the caudal half of the PPT and the LDT were retrogradely labeled bilaterally with marked ipsilateral predominance. In the LDT, about 20% of the labeled neurons showed ChAT immunoreactivity (ChAT+); the vast majority (about 80%) of the labeled cells showed TH(+) and DBH(+). In the PPT, all retrogradely labeled cells exhibited TH(+) and DBH(+), but not ChAT(+). No retrogradely labeled cells with WGA-HRP showed 5-HT(+) in the PPT or LDT. The results indicate that the caudal part of the PPT and LDT sends projection fibers to area 17, and that PPT-neurons projecting to area 17 are noradrenergic, whereas LDT-neurons projecting to area 17 are cholinergic (20%) and noradrenergic (80%).

Distribution of cells of origin of the corticotrigeminal projections to the nucleus caudalis of the spinal trigeminal complex in the cat. A horseradish peroxidase (HRP) study.

The cortical distribution of cells of origin of the corticotrigeminal projections to the nucleus caudalis of the cat was examined using the method of retrograde axonal transport of horseradish peroxidase (HRP). After injections of HRP into the nucleus caudalis, labeled cells were distributed densely in the anterior suprasylvian gyrus, the coronal gyrus, and the ventral part of the anterior sigmoid gyrus, and moderately in the rostral part of the anterior ectosylvian gyrus on the contralateral side. In the anterior suprasylvian gyrus, the distribution extended rostrocaudally from the lateral ansate sulcal level to about 4.0 mm caudal to this level and mediolaterally throughout the convex of the anterior suprasylvian gyrus. All cortical labeled cells were pyramidal cells of various sizes in layer V.