摘要:

Size and distribution of ganglion cells surviving unilateral visual cortical removal at 5–7 days of age were examined in domestic cats. Such lesions were expected to result in a substantial loss of X cells in ipsilateral temporal and contralateral nasal retina, leaving ipsilateral nasal and contralateral temporal retina to serve as intact controls. A computer model of normal retinal ganglion cell topography was used to make qualitative predictions of the distribution of surviving ganglion cells. Contrary to expectations, a visual streak was no more prominent in the distribution of surviving cells than in the distribution of the normal ganglion cell population. The magnitude of ganglion cell loss, furthermore, was at least twice as great in nasal retina as in temporal retina. In nasal retina, the cell loss extended well into the small-medium size range, while in temporal retina, cell loss was restricted to the large-medium size range. Taken together, the differential magnitude of cell loss in nasal and temporal retina and the greater loss of small-medium cells in nasal retina cannot be explained by the exclusive degeneration of X cells and suggest that many of the degenerated ganglion cells were medium-sized W or gamma cells. These cells, therefore, share the susceptibility of retinal X cells to early cortical ablation. Surviving gamma cells in both nasal and temporal retina appeared to increase in soma size which may explain why their decreased numbers were not detected in previous physiological studies. Alpha cells, at least in nasal retina, decreased in some siz

ISSN:0006-8977    

DOI:10.1159/000115872

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

Three species of synodontid catfish can produce weak biphasic electric discharges in either continuous or burst-like fashion. The peak-power frequency of these electric organ discharges is around 100 Hz. The electric organ appears to have originated from a sonic muscle: the organ lies dorsal to the swim bladder, contains modified muscle tissue, and is innervated from a motor nucleus located in the caudal medulla. It is possible that synodontid catfish use electric signals in communication and/or object detection.

ISSN:0006-8977    

DOI:10.1159/000115873

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

The responses of cerebellar units following electrical stimulation applied to the area dorsalis centralis (Dc) of the telencephalon were studied in the siluroid teleost Ictalurus nebulosus. Two kinds of units are distinguished on physiological criteria, identified as Purkinje and eurydendroid cells (the efferent neurons of the cerebellum in teleosts equivalent to cells of the deep nuclei in other vertebrates). A high proportion of both kinds of units in the corpus cerebelli are sensitive to such stimulation. Each kind of unit shows several consistent response types. Purkinje cells fire simple spikes spontaneously at the rate of 8–50 spikes/s and respond to a single shock to Dc with an initial latency of 34–64 ms. The response can be one of the following types: (1) inhibition alone, with a duration of 0.3–1.5 s; (2) initial inhibition for 0.04–0.2 s, followed by postinhibitory rebound, or (3) initial excitation followed by inhibition which may or may not be followed by a late excitation. It is suggested that the initial excitation and initial inhibition reflect the activation of mossy fiber-granule cell-Purkinje cell circuitry and mossy fiber-granule cell-inhibitory interneuron-Purkinje cell circuitry, respectively. Indirect evidence suggests the involvement of climbing fibers, but their characteristic complex spikes are rarely seen. Changing the stimulation sites within Dc does not appear to change the response pattern but may alter the threshold intensities, latencies and amplitudes. Changing stimulation frequency has complex effects depending on the response type. Purkinje cells responding with initial excitation are located along the lateral edges and along the midline of the corpus cerebelli; units responding with initial inhibition are more often found in an intermediate zone. This suggests three sagittal bands on each side. The contralateral cerebellum has a relative excess of Purkinje cells with initially inhibitory response. Putative eurydendroid cells show either initial excitation or a pattern of inhibition, excitation, inhibition. The initial latency is longer than in Purkinje cells. The contralateral cerebellum has a relative excess of eurydendroid cells with initially excitatory responseThe high proportion of units that respond to Dc stimulation, their complex dynamics, diverse response types and compartmentalization point to the importance of the cerebrocerebellar influence in teleosts. Principal differences from mammals are the much longer latencies and less differentiation according to place stimulation in the c

ISSN:0006-8977    

DOI:10.1159/000115874

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

Extracellular spikes from Purkinje and eurydendroid cells as well as evoked field potentials were recorded from the cerebellum in a catfish following trains of 50–100 stimuli at 2–10 Hz delivered to the area dorsalis centralis (Dc) of the telencephalon. Forty out of 48 Purkinje cells tested showed some response, either an increase or a decrease in the level of ongoing spike discharge following the 10- to 25-second tetanic pulse trains. The altered level lasted for > 3 min. Four out of 16 eurydendroid cells showed an increase in posttrain ongoing discharge; none showed a decrease. In those Purkinje cells responding to single pulse stimulation with early excitation, that response was converted to early inhibition during the later cycles of a tetanic pulse train. When tested with posttrain stimulation, they resumed the pretrain early excitation about 100 s after the train; before that, the recovery stages are complex, neither a simple continuation of, nor a simple rebound from, the later cycles of the stimulus train. Bursting discharge of Purkinje cells is often induced or, if already present, enhanced and regularized, typically at approximately 3/s, by train stimulation of Dc. This pattern begins during the train but continues for tens of seconds after its end. The effects of a stimulus train on the mean frequency and on the pattern of ongoing discharge depend on the train parameters: intensity, duration and stimulus rate within the train; 4–5 Hz is most effective. Higher rates or repeated trains produce a more intense but shorter-lasting effect. Evoked field potentials change during a train, and posttrain test stimuli show a slow recovery, especially after longer pulse trains. The cerebrocerebellar influence in a teleost is nontrivial, widespread, differentiated and shows long-lasting posttetanic plast

ISSN:0006-8977    

DOI:10.1159/000115875

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

This study compared the patterns of retinal projections and oxidative metabolism in the hypothalamus of squirrel monkeys, Bonnet macaques, and tree shrews. Intraocular injections of horseradish peroxidase in primates demonstrated that retinal terminals were present from the anterior to posterior poles of the suprachiasmatic nucleus (SCN). The terminals were primarily located in the ventral and ventrolateral regions of the SCN. In addition, there was a relatively even density and distribution of retinal terminals between the ipsilateral and contralateral projections. The pattern of oxidative metabolism in the hypothalamus of the primates examined demonstrated that the SCN is highly metabolic relative to the surrounding area, and distinct regions of the SCN exhibit clear differences in metabolism. These distinct metabolic regions may reflect functional subdivisions within the SCN. In addition, elevated metabolism is found along the hypothalamo-optic chiasm border. The retinal projection to the hypothalamus in tree shrews was very different from that of the primates examined. The contralateral retinal projection was very dense, but the ipsilateral retinal projection was very sparse. Retinal terminals were primarily distributed along the lateral border of the SCN. Both the SCN and the region lateral to the SCN exhibited elevated oxidative metabolism relative to the surrounding hypothalamus.

ISSN:0006-8977    

DOI:10.1159/000115876

出版商:S. Karger AG    

年代:1990

数据来源: Karger