Thalamo-tectal projections in the frog (original) (raw)
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Visual neurons in frog anterior thalamus
Brain Research, 1977
The amphibian visual system has become an increasingly valuable model for many aspects of the neurobiology of vertebrate visionS, 6. Recent evidence indicates that frogs possess the major components of two major visual pathways that are welldeveloped in more complex vertebrates; the retino-thalamo-telencephalic and the retino-tecto-thalamo-telencephalic systems11,19. These findings have stimulated further interest in the coding of visual information within each of the major target and relay structures comprising these pathways in anuran amphibians. The retinotopic organization of optic projections to the frog diencephalon is now relatively wellunderstood and there appear to be 4 complete maps of the retina in the thalamus13, 20. Two of these highly organized retinal projections occur in the anterior thalamus, in the neuropil of Bellonci and the corpus geniculatum neuropil, respectively. The majority of thalamic perikarya are located more medially in cell groups bordering the third ventricle (see ) and send lengthy dendrites into these laterally placed terminal fields of optic axons~L Relatively little information is currently available concerning the response properties of thalamic visual neurons. Muntz 16 recorded from the dorsal thalamus (exact sites unspecified) and described two major types of units responding to visual stimuli: (1) "on" units with small retinal receptive fields and exceptional sensitivity to blue light, and (2) units similar to those previously described for the deep layers of the optic tectum 14, which he believed to be tectal efferents. Subsequent studies have also reported thalamic "on" units, some of which were binocular, and a few with "on-off" responses to transient illumination9,12,15. However, none of these studies specified recording sites in relation to thalamic neuroanatomical organization.
Neuroscience, 1987
Abatraet-The nucleus isthmi is a prominent part of the frog's visual system. Bach nucleus isthmi receives input from the ipsilateral tectum and sends output to both tecta. Until now, no non-tectal inputs to the nucleus isthmi of amphibians have been demonstrated. Anterograde and retrograde tracing with horseradish peroxidase in Rana pipiens and Acris crepitans now reveal that a diffuse group of cells in the mesencephalic tegmentum projects to the caudal region of the contralateral nucleus isthmi. These cells are primarily within the nucleus anterodorsalis tegmenti. This same group of tegmental cells may also project to the caudal region of the ipsilateral nucleus isthmi. A similar investigation of the brain of another frog, Xenopus laevis, has not revealed any evidence of this tegmento-isthmic projection.
Unilateral removal of the telencephalon in the leopard frog, Rana pipiens, produces a contralateral deficit in visual prey orienting behavior [Patton and Grobstein, 1997]. In mammals, such deficits are most commonly associated with damage to the isocortex, a pallial derived structure. In contrast, we here report that in leopard frogs, lesions that remove substantial areas of one telencephalic lobe, including virtually the entire pallium, have no discernible effect on visual orienting behavior. Restricted lesions to the ventrocaudal telencephalon, however, produce an effect that closely resembles that produced by the complete removal of one telencephalic lobe. The ‘critical area’ that is both included in all lesions that are effective in producing a severe deficit and excluded from all ineffective lesions includes a portion of the caudal striatum. The striatum is known to play a significant role in anuran vision. It thus seems likely that the deficit produced by unilateral removal of the telencephalon in the leopard frog is due specifically to the removal of the caudal striatum. Unilateral lesions to the striatum have previously been shown to produce a contralateral deficit in visual orienting behavior in cats, and a role for the striatonigral pathway in the production of the visual orienting deficit that follows visual cortex lesions has been proposed. The current findings call attention to the possible general importance of the striatum in the control of vertebrate visual orienting behaviors.
Morphology and location of tectal projection neurons in frogs: A study with hrp and cobalt-filling
Journal of comparative neurology, 1983
Tectal projection neurons were labeled by retrograde transport of horseradish peroxidase (HRP) or cobaltic-lysine. The tracer substances were delivered iontophoretically or by pressure injection or diffusion into various regions of the brain or spinal cord. Histochemical procedures allowed identification of labeled cells projecting to the injected regions. Many neurons were filled with cobaltic-lysine, resulting in a Golgi-like staining. After cobalt injections in the diencephalon most of the labeled cells, identified as small piriform neurons, were located in layer 8 of the tectum. Two types of small piriform neurons were distinguished. Type 1 neurons have flat dendritic arborizations confined to lamina D, while the dendrites of type 2 cells may span all of the superficial tectal strata. In smaller numbers large piriform, pyramidal, and ganglionic cells of the periventricular tectal layers were labeled after diencephalic injections. Rhombencephalic cobalt and HRP injections labeled cells whose axons form the tectobulbospinal tract. The neurons most frequently labeled were large ganglionic cells. Ipsilaterally, the majority of their somata were located in layer 7, and their dendrites arborized mainly in lamina F. Contralaterally, labeled ganglionic cell somata occupied the top of layer 6, and most of their dendritic end-branches entered lamina B. The possible functional significance of this anatomical arrangement is discussed. After tectal cobalt injections the topography of the tectoisthmic projection and the terminals of tectal efferent fibers in the diencephalon and brainstem were observed. It is concluded that the organization of frog tectofugal pathways is very similar to that of mammals.
Thalamo-telencephalic connections: new insights on the cortical organization in reptiles
Brain Research Bulletin, 2002
Tracer injections into the dorsal tier of the lacertilian dorsal thalamus revealed an extensive innervation of the cerebral cortex. The medial cortex, the dorsomedial cortex, and the medial part of the dorsal cortex received a bilateral projection, whereas the lateral part of dorsal cortex and the dorsal part of the lateral cortex received only an ipsilateral thalamic projection. Thalamocortical fibers were found superficially in all cortical regions, but in the dorsal part of the lateral cortex, varicose axons within the cellular layer were also observed. The bilateral thalamocortical projection originates from a cell population located throughout the dorsolateral anterior nucleus, whereas the ipsilateral input originates mainly from a rostral neuronal subpopulation of the nucleus. This feature suggests that the dorsolateral anterior nucleus consists of various parts with different projections. The dorsal subdivision of the lateral cortex displayed hodological and topological (radial glia processes) features of a dorsal pallium derivative. After tracer injections into the dorsal cortex of lizards, we found long descending projections that reached the striatum, the diencephalic basal plate, and the mesencephalic tegmentum, which suggests that it may represent a sensorimotor cortex.
Brain Research, 1978
The origin of medial lemniscus fibres from the round cells of the 'cell nest" region m the dorsal column nuclei (DCN) has long been suspected 17 but not until recently proven :~,4,s. On the other hand, the overlapping thalamic termination ofefferents from the DCN and the lateral cervical nucleus (LCN) are anatomically well establishedS,~L DCN projections to structures other than the ventrobasal thalamus have been described, and recently interest has been particularly centred on somatosensory projections to the mesencephalic tectum, which, for example, have been described as a result of anterograde degeneration studies ~a,la on the DCN but not the LCN. The present investigation, using the technique of retrograde transport of horseradish peroxidase (HRP), has been designed to answer the following questions: (a) Does the LCN, as well as the DCN, project upon the mesencephalic tectum? (b) Do tectal and thalamic terminations represent collateral projections, or do they come from different ceils within their nuclei of origin? (c) What is the relative quantitative importance of these projections'? Stereotaxic injection of 20'~ or 33",' 'o (w/w) HRP in NaCI was performed hydraulically into the brains of 14 cats under anaesthetic. In 4 cases 0.5 #l of 33 '!; H R P was injected into the thalamus, and the animals perfused after 24 and 48 h. In the other I0 animals, 0.1 or 0.2 #l of 20 °/ ' .!/o ¢o or 33 HRP was injected into the tectum, with sacrifice by perfusion with 2 ~ glutaraldehyde and I °/,,, formaldehyde in 0.05 M sodium cacodylate buffer after 24 or 48 h (Table i). After fixation, serial frozen sections were cut from the injected areas and the region containing DCN and LCN. Every tenth section was processed for the peroxidase reaction and counterstained with I °/oo thionin. In all 4 cases subjected to thalamic injections, all the diencephalic regions to which DCN and LCN are known to project were filled with peroxidase reaction products. If anything, the injection site was less widespread in the animals sacrified after 48 h than in animals perfused at 24 h.