An ipsilateral projection from the red nucleus to the lateral reticular nucleus in the cat

Summary Injections of the wheat germ agglutinin — horse-radish peroxidase complex into the lateral reticular nucleus reveal that in addition to the well known contralateral rubroreticular connection, there is also a small but clear cut ipsilateral projection. Cells of various sizes participate in this ipsilateral pathway, and the retrogradely labelled neurons lie dispersed throughout the entire red nucleus.     

The projection of different retinal ganglion cell classes to the dorsal lateral geniculate nucleus in the hooded rat

Summary The morphology of retinal ganglion cells which project to different parts of the dorsal lateral geniculate nucleus (DLG) in the hooded rat has been investigated. Small amounts of a retrograde tracer (horseradish peroxidase) were injected into the DLG, then labelled retinal ganglion cells were examined in retinal wholemounts. After injections into different parts of the DLG, differences were noted in the size, morphology and retinal distribution of labelled retinal ganglion cells. Specifically, after injections into the antero-ventral part of the DLG labelled retinal ganglion cells were spread sparsely across the retina, had large cell somas, and many were identified with Class I or Class III morphology. After injections into the postero-dorsal part of the DLG, labelled cells were more densely packed, had smaller somas, and more were identified with Class IIa and Class III morphology. The density of labelled cells was estimated to be no more than 37% of the total retinal ganglion cell density at any retinal position examined. These results show that in the rat, as in other species such as the cat or monkey, the terminals of different classes of retinal ganglion cells are segregated within different subdivisions of the DLG. However, unlike these other species, only a minority of the total retinal ganglion cell population projects to the DLG.     

The retinal projection to the ventral part of the lateral geniculate nucleus. An experimental study with silver-impregnation methods and axoplasmic protein tracing

Summary The retinal projection to the ventral part of the lateral geniculate nucleus (LGNv) was studied in 25 adult cats. In 12 cats one or both eyes were enucleated and the terminal degeneration in the LGNv was studied with silver impregnation methods. In 12 cats one or both eyes were injected with ³H-leucine and the terminal labelling in the LGNv was studied with autoradiography. In one animal one eye was enucleated and the other injected. In this case alternate sections were silver impregnated and processed for autoradiography. The series were cut in parasagittal, transverse or horizontal planes. The results revealed by degeneration were in very good agreement with those revealed by axoplasmic protein tracing. Two fields of retinal projection were found in the LGNv. The larger, dorsal one was restricted to subnucleus d (Jordan and Holländer, 1972) and comprised an ipsilateral and a contralateral component which did not overlap each other. The smaller, ventral field of projection was contralateral and extended from subnucleus b into c, e and a. The afferent optic tract fibres to both terminal fields were of small calibers.A preliminary report has already been published (Sanides, 1975)     

Autoshaping in micrencephalic rats

An autoshaping procedure in which the illumination of a lever was predictive of food reinforcement was used to compare learning in rats with micrencephaly induced by irradiation on the 16th day of gestation and in sham-irradiated controls. Both groups showed equivalent levels of lever-directed activity, and the micrencephalic animals differentiated as well as the control animals between the predictive lever and a nonpredictive lever. The micrencephalic animals were able to redistribute their lever-directed activity when the significance of the levers was reversed and did so more readily than the control animals. Results support the claim that association learning survives either traumatic or developmental neocortical damage and have implications for remedial procedures following both head injury and developmental cerebral pathology in humans.     

An anomalous uncrossed retinal input to lamina a of the cats dorsal lateral geniculate nucleus

A small anomalous group of uncrossed retinogeniculate axons has been found terminating in one or two small pericellular terminal nests in the lateral, monocular segment of lamina A of the cat's dorsal lateral geniculate nucleus. Such anomalous islands, demonstrable by fibre degeneration and by autoradiographic methods, have been found in 6 out of 13 normally pigmented cats, and in 2 out of 7 Siamese cats.Thus, in apparently normal cats, the highly ordered geniculate map of the visual field can be interrupted by small islands that do not fit into the overall order.     

A projection from the periaqueductal grey to the lateral reticular nucleus in the cat

Summary A projection from the periaqueductal grey (PAG) to the lateral reticular nucleus (NRL) in the cat was demonstrated by means of retrograde transport of the wheat germ agglutinin-horseradish peroxidase complex. The connection has its main origin ipsilaterally in the ventral part of the caudal PAG, but scanty projections from other parts of the PAG were also found. The neurons projecting to the NRL are of varying shapes and sizes, but most cells have a maximum diameter of less than 20 m. The findings are discussed in relation to the other afferent and efferent connections of the NRL.     

A direct projection from the nucleus oculomotorius to the retina in rats

The centrifugal projection to the eye has been studied in rats with anterograde and retrograde tracing techniques. As a retrograde tracer Nuclear Yellow (NY) was used. Following NY injections into the vitreous body of the eye, labeled neurons were exclusively found bilaterally in nucleus oculomotorius. The course and termination site of the retinopetal fibers were studied with the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHA-L). Iontophoretic injections of PHA-L in nucleus oculomotorius resulted in labeling of retinopetal fibers which reach the eye via the optic tract and optic nerve. Preterminal arborizations were found in the inner nuclear layer of the retina. In addition, labeled fibers have been observed which seem to terminate within the optic tract and optic nerve. It is suggested that the projection from the nucleus oculomotorius to the retina constitutes a link in the multisynaptic efferent pathway from the visual cortex to the eye, by which the visual cortex can influence the functioning of the retina.     

A GABAergic projection from the pretectum to the dorsal lateral geniculate nucleus in the cat.

To study the projection from the pretectum to the lateral geniculate nucleus, we placed wheat-germ agglutinin conjugated to horseradish peroxidase into the lateral geniculate nuclei of six cats, allowed this marker to be retrogradely transported by afferent axons to their parent somata in the pretectum, and revealed the label in these cells with stabilized tetramethylbenzidine histochemistry. In three cases we made large pressure injections that completely infiltrated the lateral geniculate nucleus and extended into neighboring thalamic nuclei; in the other three we made smaller iontophoretic injections largely confined to the A- and C-laminae of the lateral geniculate nucleus. In both types of injection we found labeled pretectal cells mainly in the nucleus of the optic tract but also found some cells labeled in the olivary pretectal nucleus and the posterior pretectal nucleus. After one of the larger injections we analysed both sides of the pretectum and found that 11% of the labeled cells were located contralaterally and were distributed in the same three nuclei. We analysed only the ipsilateral side in the remaining five cats. In those five experiments we also immunohistochemically stained the pretectal sections with an antibody directed against the neurotransmitter, GABA. Of the retrogradely labeled pretectal cells, 40% were also labeled for GABA, and those were similar in soma size (350 microns 2 in cross-sectional area) to those labeled only with the retrograde marker (331 microns 2). GABA-positive cells not labeled by retrograde transport were smaller (246 microns 2) than either of these other cells populations. These results indicate that at least 40% of the cells involved in the projection from the pretectum to the lateral geniculate nucleus are GABAergic. We suggest that this extrathalamic projection may serve to inhibit thalamic GABAergic cells. This, in turn, would disinhibit geniculate relay cells, thereby facilitating the geniculate relay of retinal information to cortex.     

A ventral lateral geniculate nucleus projection to the dorsal thalamus and the midbrain in the cat

Summary Retrograde tracing experiments using horseradish peroxidase (HRP) have been utilized for demonstrating the origin of efferent projections of the ventral lateral geniculate nucleus (LGNv) in the cat. HRP-positive cells identifiable as origins of thalamic projections were found in LGNv after injections of HRP into the lateral central intralaminar nucleus. The labeled cells appeared concentrated in the medial part of the internal division of LGNv, consisting of medium-sized multipolar cells. Contralaterally, fewer labeled cells were present in the corresponding part of LGNv. In the case of injections of HRP into the midbrain (pretectum and superior colliculus), labeled cells in LGNv were distributed almost exclusively in its external division, composed of mainly small cells. Little overlap of the distribution of HRP-positive cells was seen in LGNv between the thalamic and midbrain injection cases.Abbreviations Ad Dorsal anterior nucleus - Am Medial anterior nucleus - Av Ventral anterior nucleus - BSC Brachium of superior colliculus - Cg Central gray - Cl Lateral central nucleus - Ld Dorsal lateral nucleus - LGNd Dorsal lateral geniculate nucleus - LGNv Ventral lateral geniculate nucleus - Lp Posterior lateral nucleus - Md Dorsal medial nucleus - NIII Oculomotor complex - NOT Nucleus of the optio tract - NPC Nucleus of posterior commissure - OT Optic tract - P Posterior nucleus (Rioch 1929) - Pc Paracentral nucleus - Po Posterior group of thalamic nuclei - Pt Parataenial nucleus - PTa Anterior pretectal nucleus - PTm Medial pretectal nucleus - PTp Posterior pretectal nucleus - Pul Pulvinar - R Red nucleus - Rt Thalamic reticular nucleus - Sg Suprageniculate nucleus - Va Anterior ventral nucleus - VI Lateral ventral nucleus - Vm Medial ventral nucleus - Vpl Posterolateral ventral nucleus - Vpm Posteromedial ventral nucleus - Zi Zona incerta - II Layer of superior colliculus - III Layer of superior colliculus - IV (Kanaseki and Sprague, 1974)     

The crossed projection from the temporal retina to the dorsal lateral geniculate nucleus in the rat

The crossed projection from the temporal crescent in the rat's retina was studied by producing a discrete retinal lesion in one eye and examining the dorsal lateral geniculate nucleus and superior colliculus contralateral to the lesion for anterograde degeneration products. The position of this crossed degeneration was described in relation to the uncrossed retinal termination in the same structures by injecting the opposite eye with [³H]proline and processing the tissue for autoradiography. The location of the retinal lesion in relation to the temporal cresent was identified by injecting the dorsal lateral geniculate nucleus ipsilateral to the lesioned eye with a fluorescent tracer, to retrogradely label the ipsilaterally projecting retinal ganglion cells in the lesioned eye.

Retinal lesions that were histologically verified to be restricted to the temporal crescent produced crossed degeneration in the superior colliculus at its rostral border, in accord with this projection's published visual topography. These same lesions consistently yielded a very circumscribed and sparse amount of degeneration in the contralateral dorsal lateral geniculate nucleus at its dorsomedial border, abutting the optic tract dorsally and the lateroposterior nucleus medially. The degeneration bore no consistent relationship to the position of the uncrossed retinal terminal field, which is situated further 9ventrally in the dorsal lateral geniculate nucleus; rather, this crossed temporal projection terminated in the outer shell of the nucleus along its medial border.

This crossed temporal retinogeniculate projection, together with the crossed projection from nasal retina, forms a continuous map of the complete contralateral retina in the outer shell of the dorsal lateral geniculate nucleus, likely to arise from a population of retinal ganglion cells possessing small soma sizes. This dorsomedial part of the rat's dorsal lateral geniculate nucleus, receiving a crossed projection from the temporal retina, may by similar to the cat's lamina 3 in the medial interlaminar nucleus of its retinogeniculate pathway. This result clarifies the homologous subdivisions of the dorsal lateral geniculate nucleus in the rodent and feline thalamus.     

大鼠前庭核向迷走神经背侧复合体的间接投射

目的：研究大鼠前庭核向迷走神经背侧复合体的间接投射,探索前庭信息向脑干呕吐区传递的神经通路。方法：向前庭神经下核和前庭神经内侧核注入顺行追踪剂菜豆凝集素（PHA-L）,向迷走神经背侧复合体注入逆行追踪剂荧光金（FG）,用免疫荧光组织化学方法显示PHA-L顺行标记纤维和终末,在荧光显微镜下观察顺行标记PHA-L的纤维和终末与FG逆行标记的细胞重叠区域。结果：在延髓外侧巨细胞旁核和腹外侧区有顺行纤维和终末与逆行标记细胞的重叠。结论：前庭核团可能经外侧巨细胞旁核和腹外侧区向迷走神经背侧复合体有间接投射,为进一步揭示前庭核团与呕吐相关的内脏反应区之间的功能关系提供了形态学基础。     

Bilateral projections of neurons in the lateral geniculate nucleus and nucleus lateralis posterior to the visual cortex in the neonatal rat

The projection from the lateral geniculate nucleus (LGN) and nucleus lateralis posterior (LP) to the visual cortex was examined in rat pups 3-7 days of age using the fluorescent tracers True Blue, Fast Blue and Nuclear Yellow. Our data provide the first evidence that (1) these projections are bilateral, (2) the ipsilateral projection from these nuclei to the visual cortex in the neonatal rat is well localized and is similar in distribution and organization to that reported by others in the adult and (3) bilaterally projecting geniculocortical cells are morphologically heterogeneous; bilaterally projecting cells in LP are morphologically homogeneous.     

Organization of the projection from the superior colliculus to the dorsal lateral geniculate nucleus of the cat

The projection from the superior colliculus to the dorsal lateral geniculate nucleus has been studied in the cat, with special emphasis on its relation to the retino-geniculate pathway. The central visual pathways through the colliculus come into close relation with the retino-geniculate pathways in the parvocellular layers of the dorsal lateral geniculate nucleus. To define this relation in detail, one of the pathways was labelled with radioactive proline and the other by silver techniques for degenerating axons. The collicular axons terminate primarily in geniculate layer C₃, which has no demonstrable retinal afferents, but they also overlap to some extent with contralateral retinal terminals in geniculate layer C₂. The tecto-geniculate pathway is retinotopically organized, contains a complete representation of the contralateral visual hemifield and the retinotopic pattern is in register with the direct retinal input. In addition, the synaptic relationships established by the tecto-geniculate axons were studied light- and electron-microscopically. The axons were identified by anterograde filling with horseradish peroxidase and this was complemented by the electron-microscopical study of degeneration of these axons after tectal lesions. Tecto-geniculate axons are fine calibered and have multiple, small en passant and terminal synaptic swellings. They contain round synaptic vesicles and make asymmetric junctions, generally with dendritic stems. Some of the axons, perhaps a distinct and small subset, also are presynaptic to vesicle-containing profiles and are involved in the formation of triads similar to those made by retinal afferents. These findings provide an anatomical basis for possible interactions between tecto-geniculate and retinogeniculate pathways.     

大鼠三叉神经中脑核到三叉神经运动核的间接投射通路研究

目的:搞清大鼠三叉神经中脑核(mesencephalic trigeminal nucleus,Vme)与三叉神经运动核(trigeminal motor nucleus,Vmo)神经元之间的间接投射通路。方法:将束路追踪剂霍乱毒素b亚单位(cholera toxin b subunit,CTb)注入一侧咬肌神经跨节标记Vme神经元及其中枢突,同时将四甲基罗达明(tetramethyl rhodamine,TMR)注入对侧Vmo逆行标记运动前神经元,激光共聚焦显微镜下观察二者之间的重叠分布和接触情况。结果:CTb跨节标记终末(Vme神经元的中枢突)与TMR逆标神经元(Vmo的运动前神经元)的胞体或树突重叠分布区域包括:(1)三叉上核(supratrigeminal nucleus,Vsup)尾端,该区域范围小,其内CTb跨节标记终末极密集;(2)Vmo周边区域,以Vmo与Vsup之间的区域为主,其内CTb跨节标记终末呈中等密度分布;(3)小细胞网状结构(parvicellular reticular formation,PCRt),该区域范围最广,CTb跨节标记终末在该区域呈松散分布。激光共聚焦显微镜下可见上述区域内一些CTb标记终末与其中的部分TMR逆标神经元的胞体或树突形成密切接触。结论:大鼠Vme神经元的中枢突经分布在Vsup,Vmo周边区域及PCRt内广泛的运动前神经元向Vmo发出间接投射。     

Field potential analysis of the cortical projection of the central lateral nucleus in the cat

A previous field potential study has indicated a monosynaptic projection of fibres from the central lateral nucleus (CL) to the mid-suprasylvian gyrus (MSSG). The present study, which is based on an analysis of current source density (CSD), aims to investigate further the sites of major localized synaptic activities in different layers of the MSSG after electrical stimulation in the CL. An initial positive surface potential was evoked in the MSSG with a latency of 3-5 ms and followed by a large negative potential with a peak latency of 8-15 ms. The initial positivity was only found in the rostral part of the MSSG, which corresponds to area 5. The positivity reversed in deeper layers. The CSD analysis showed a sink at a depth from 650 to 1050 microns. A corresponding source was found more superficially at 400-600 microns. This indicates that CL fibres have an excitatory synaptic termination on the soma or proximal dendrites of neurons in layers III and IV. The surface negative potential reversed at the border between layers II and III, suggesting a superficial CL projection. The CSD analysis of potentials in superficial layers showed a sink appearing between the pial surface and a depth of 350 microns, and a source lying in layers below. This indicates a depolarization of apical dendrites of cells in layers II and III. The superficial sink appeared in a large part of the MSSG. Application of a solution of 0.5% gamma-aminobutyric acid (GABA) on the surface of the cortex blocked the superficial sink and source and revealed a prominent sink current in layers III and IV in agreement with a deep termination of CL fibres. Application of a solution of 25 mM DL-2-amino-5-phosphono-valeric acid (APV) abolished CL-evoked cortical responses indicating that N-methyl-D-aspartate (NMDA) receptors are involved in the cortical activation. The CSD analysis confirms that CL has a wide superficial projection to the MSSG. It also confirms a deeper monosynaptic projection from CL to area 5.     

The posterior pretectal nucleus: evidence for a direct projection to the inferior olive of the cat

In our horseradish peroxidase (HRP) study of the afferents to the medullary raphe nuclei in the cat, HRP uptake by damaged axons en route to the inferior olive (IO) was thought to be responsible for retrograde labelling of specific midbrain nuclei. To control for such indirect labelling, HRP was injected iontophoretically into the inferior olive. The location of retrogradely labelled neurons was related to the specific locus of HRP injection within the IO. Injection of HRP into the caudal dorsal accessory olive resulted in dense neuronal labelling in the ipsilateral caudal pole of the posterior pretectal nucleus (PPN). There was no labelling of the nucleus of Darkschevitch (Dk), interstitial nucleus of Cajal (ICA) or Edinger-Westphal nucleus (EW). In contrast, an injection focussed more rostrally, into the rostral, dorsal accessory, the medial accessory and the principal olive, produced dense labelling of Dk, ICA and EW; there was much less PPN labelling. It is concluded that labelling of Dk and PPN after HRP injections rostral to the IO, is due, at least in part, to uptake of HRP by damaged medial longitudinal fasciculus axons en route to the inferior olive. The direct PPN-inferior olivary projection provides a potential disynaptic retino-cerebellar connection, which may be involved in rapidly timed eye-body coordinate movements.     

GABAergic projection from the arcuate nucleus to the supraoptic nucleus in the rat

Electrical stimulation of the neurones in the hypothalamic arcuate nucleus results in a transient inhibition followed by a marked post-stimulus excitation of magnocellular neurones of the supraoptic nucleus. Microdialysis administration of the gamma-aminobutyric acid agonist (GABA(A)), muscimol, directly into the supraoptic nucleus inhibited both oxytocin and vasopressin neurones and these actions were fully reversed by the GABA(A) antagonist bicuculline. In addition, bicuculline administration blocked the inhibition induced by arcuate stimulation, but had no effect on the post-stimulus excitation. Thus, part of the inhibitory pathway arising from or passing through the arcuate nucleus to the supraoptic nucleus is mediated by the neurotransmitter GABA. However, the post-inhibitory excitation induced by arcuate stimulation is not a rebound response, but appears to involve an independent excitatory pathway.