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1.
Recent evidence suggests that the amygdaloid central nucleus (ACE) may contribute significantly to Pavlovian fear-conditioned bradycardic responses during the presentation of conditioned emotional stimuli. Because the medial component of the medial geniculate nucleus (MGm) is a major source of input to the region of the ACE, the extracellular single-unit responses of MGm neurons were examined during Pavlovian differentially conditioned bradycardic responding in rabbits. Conditioning involved pairing one tone (CS+) with paraorbital shock and presenting another tone (CS-) in the absence of shock. Two general classes of MGm neurons were identified based on their conditioned-response characteristics. Both groups responded differentially to the CSs. One group responded with greater increases in activity and at a shorter latency to the CS+ compared with the CS-, whereas the other group responded with greater increases in activity and at a shorter latency to the CS- compared with the CS+. Recordings from MGm neurons in naive rabbits prior to conditioning provided evidence that the acoustic stimuli used subsequently as the CS+ and CS- did not evoke differential responses. These results suggest that the MGm along with the ACE may be forebrain components of a neural circuit involved in the acquisition and/or expression of Pavlovian fear-conditioned bradycardic responses.  相似文献   

2.
We measured response properties of X- and Y-cells from laminae A and A1 of the dorsal lateral geniculate nucleus of monocularly lid-sutured cats at 8, 12, 16, 24, and 52-60 wk of age. Visual stimuli consisted of small spots of light and vertically oriented sine-wave gratings counterphased at a rate of 2 cycles/s. In cats as young as 8 wk of age, nondeprived and deprived neurons could be clearly identified as X-cells or Y-cells with criteria previously established for adult animals. Nonlinear responses of Y-cells from 8- and 12-wk-old cats were often temporally labile; that is, the amplitude of the nonlinear response of nondeprived and deprived cells increased or decreased suddenly. A similar lability was not noted for the linear response component. This phenomenon rarely occurred in older cats. At 8 wk of age, Y-cell proportions (number of Y-cells/total number of cells) in nondeprived and deprived A-laminae were approximately equal. By 12 wk of age and thereafter, the proportion of Y-cells in deprived laminae was significantly lower than that in nondeprived laminae. At no age was there a systematic difference in response properties (spatial resolution, latency to optic chiasm stimulation, etc.) for Y-cells between deprived and nondeprived laminae. Spatial resolution, defined as the highest spatial frequency to which a cell would respond at a contrast of 0.6, was similar for nondeprived and deprived X-cells until 24 wk of age. In these and older cats, the mean spatial resolution of deprived X-cells was lower than that of nondeprived X-cells. This difference was noted first for lamina A1 at 24 wk of age and later for lamina A at 52-60 wk of age. The average latency of X-cells to optic chiasm stimulation was slightly greater in deprived laminae than in nondeprived laminae. No such difference was seen for Y-cells. Cells with poor and inconsistent responses were encountered infrequently but were observed far more often in deprived laminae than in nondeprived laminae. Lid suture appears to affect the development of geniculate X- and Y-cells in very different ways. Not only is the final pattern of abnormalities quite different between these cell groups, but the developmental dynamics of these abnormalities also differ.  相似文献   

3.
An ultrastructural and quantitative study of the age-related changes occurring in the relay neurons of the dorsal lateral geniculate nucleus (dLGN) was carried out using male Wistar rats aged 3, 18, 24, and 28 months. Morphometric techniques were used to obtain data regarding cellular activity including soma, nuclear, and nucleolar size. Volume fractions for rough endoplasmic reticulum (RER), mitochondria, and lipofuscin, as well as numbers and sizes of mitochondria and dense bodies (DB) was also calculated. Among the few alterations found in the perikaryon, we can highlight the redistribution and fragmentation of RER and an increase and progressive aggregation of lipofuscin. Quantitative data show a significant decrease in the volume of the soma (-42.77%) and the nucleus (-33.66%), and in the volume fraction of the RER (-18.81%) and mitochondria (-10.16%). A significant increase in lipofuscin (+213.29%), and variations in size and number of mitochondria and dense bodies were also found. Some histophysiological considerations about the findings are discussed. The findings lead to the conclusion that a relative degree of morphological stability is exhibited by relay neurons, although the quantitative data show evident intracellular changes, especially from 24 to 28 months. These changes suggest that accompanying physiological alterations may occur, with putative effects on visual function during ageing.  相似文献   

4.
Quantitative methods were used to compare the changes taking place in the volume of the dorsal lateral geniculate nucleus (dLGN) and corresponding neurons of young, adult and old rats. The study was carried out on male albino rats aged 3, 18, 24 and 28 months. In order to estimate the volume of the dLGN, neuronal volume density, numerical density and total number of neurons, we used serial sections stained according to the Klüver-Barrera technique and stereological methods. We found that dorsal lateral geniculate nucleus volume increases between 3 and 28 months, with a larger increase between 24 and 28 months. Neuronal volume density and numerical density of neurons are greater at 3 months and undergo a significant decrease between 24 and 28 months. Finally, the total number of neurons is shown to be smaller in adult and old animals than in younger ones, even though no significant variations are found between 18 and 28 months. Furthermore, this study confirms the need to analyze the total number of neurons and not just neuronal density if we want to correctly evaluate some of the microscopic changes occurring during senescence.  相似文献   

5.
Summary The morphology of neurons in the dorsal lateral geniculate nucleus (dLGN) of rats made micrencephalic by prenatal exposure (E13 or E15) to the cytotoxic agent, methylazoxymethanol acetate, has been examined in Golgi impregnations. Type B neurons were unaffected by exposure on either day while type A neurons showed significant reductions in both soma diameter and dendritic field area following exposure on E15, but not E13. These results indicate that target deprivation of type A neurons (by destruction of neurons in the granular and supragranular layers of the occipital cortex with exposure on E15) has a more significant effect on development of type A neurons than the direct cytotoxic action of the agent on precursors of dorsal lateral geniculate nucleus neurons in the fetal thalamus (seen with exposure on E13 in a previous study). The findings are significant because they indicate that the indirect effects of cytotoxic teratogens on the developing brain (acting via the target dependence of some neuronal classes) may cause structural und functional alterations in the brain which differ from those predicted on the basis of the direct action above. This study also shows that the percentage of relay neurons in the dorsal lateral geniculate nucleus is unaffected in animals exposed to the agent on E15, despite pronounced reductions in neuronal numbers and changes in relay neuron morphology.  相似文献   

6.
7.
We present a quantitative analysis of the visual response properties of single neurons in the dorsal lateral geniculate nucleus (dLGN) of wild-type C57Bl/6J mice. Extracellular recordings were made from single dLGN cells in mice under halothane and nitrous oxide anesthesia. After mapping the receptive fields (RFs) of these cells using reverse correlation of responses to flashed square stimuli, we used sinusoidal gratings to describe their linearity of spatial summation, spatial frequency tuning, temporal frequency tuning, and contrast response characteristics. All cells in our sample had RFs dominated by a single, roughly circular "center" mechanism that responded to either increases (ON-center) or decreases (OFF-center) in stimulus luminance, and almost all cells passed a modified null test for linearity of spatial summation. A difference of Gaussians model was used to relate spatial frequency tuning to the spatial properties of cells' RFs, revealing that mouse dLGN cells have large RFs (center diameter approximately 11 degrees) and correspondingly poor spatial resolution (approximately 0.2c/degree). Temporally, most cells in the mouse dLGN respond best to stimuli of approximately 4 Hz. We looked for evidence of parallel processing in the mouse dLGN and found it only in a functional difference between ON- and OFF-center cells: ON-center cells were more sensitive to stimulus contrast than their OFF-center neighbors.  相似文献   

8.
Laminar organization of tree shrew dorsal lateral geniculate nucleus   总被引:4,自引:0,他引:4  
This study investigated the organization of the dorsal lateral geniculate nucleus (LGN) of the tree shrew (Tupaia glis) using both microelectrode recording and anatomical techniques. The tree shrew LGN contains approximately 100,000 cells, of which 20% are in layers 2 and 6. These two layers receive input from the ipsilateral eye. The topography of the tree shrew LGN was delineated by taking systematic penetrations through the structure. Examination of the organization of the LGN laminae showed the following: in layer 1 (the lamina next to the optic tract) a mixture of on-center, off-center and on-off center cells was found; the majority of these cells responded transiently to visual stimuli and they had slightly longer conduction latencies than did cells in the other laminae. On-center and off-center cells in laminae 2-6 were sharply segregated: layers 2, 3, and 4 contained off-center cells and layers 5 and 6 contained on-center cells. Most of the cells in laminae 2-6 responded in a sustained manner to visual stimuli. These results suggest that one function of the LGN lamina is to group cells into various classes. Such grouping has now been shown to occur partially or completely for 1) eye of origin, 2) cell types characterized as on-center and off-center, and 3) cell types characterized as producing transient and sustained responses. The nature and degree of laminar specificity, however, varies considerably from species to species.  相似文献   

9.
Monkeys whose left striate cortex had been removed in infancy received bilateral injections of horseradish peroxidase (HRP) into the prelunate gyrus (PLG) prestriate cortex. Scattered large neurons in the dorsal lateral geniculate nucleus were retrogradely labeled in both hemispheres. On the lesioned side, the HRP-labeled cell bodies were 58% larger in area, showing an overall increase in soma size and complexity of dendritic field, suggesting a hypertrophy of the geniculate-PLG pathway following a neonatal striate cortex lesion.  相似文献   

10.
11.
Summary Quantitative changes in cell number during development of the dorsal lateral geniculate nucleus were determined using semithin serial sections of tissue obtained from 28 rats on postnatal day 0, 5, 8, 10, 20, 30, 90 or 165. Our results show three phases of postnatal development in the rat dorsal lateral geniculate nucleus: phase 1 from birth until eye opening, which occurs around the 12th day in these litters; phase 2 from eye opening through stabilization of neuron number on the 30th postnatal day, and phase 3 from that event until adulthood. During the first period increases in neuron number and in glial cell number are found accompanying a nearly seven-fold increase in dorsal lateral geniculate nucleus volume. Phase 2 includes a high incidence of neuronal cell death and a continuous increase in the number of glial cells. The third phase is characterized by a stabilization in the number of neurons, although the glial cell number continues to increase. Neuronal density decreases exponentially throughout the postnatal life of the rat, while the density of glial cells remains relatively stable over the period of study. The postnatal phenomenon of an initial increase in neuron number followed by a period of neuron death may be related to modulating and plastic functions which occur in the rat dorsal lateral geniculate nucleus before a stable neuronal population is achieved on the 30th postnatal day.  相似文献   

12.
Summary The responses of rabbit dorsal lateral geniculate neurons to light or optic nerve shock were tested for 415 units in 43 rabbit pups 2–20 days of age. Units were driven by optic nerve shock at the youngest ages tested, but could not be driven by light until postnatal day six. Examples of each of the three prominent categories of receptive fields found in the adult were first observed at 8 days of age. Cells with receptive field properties not characteristic of the dorsal lateral geniculate nucleus of the adult were encountered until 17 days of age. The percentage of neurons with uniform and motion sensitive receptive fields approached adult levels soon after eye opening (11–12 days) but the percentage of cells with concentric receptive fields showed a steady increase throughout the neonatal period studied. The relevance of our data to the development of the visual response in the dorsal lateral geniculate nucleus and striate cortex is discussed.  相似文献   

13.
Summary Synapse formation and maturation were examined in the rat dorsal lateral geniculate nucleus (dLGN) from birth to adulthood. Examination of animals, whose ages were closely spaced in time, showed that the maturation of the synaptic organization of the nucleus takes place chiefly during the first 3 weeks of postnatal life. This period of maturation may be divided into 3 broad stages. During the first stage, which spans the first 4 days of life, there are only a few immature synapses scattered throughout the nucleus; occasionally aggregates of 3 or 4 synapses are encountered. Dendrodendritic synapses first appear at the end of this stage. The second stage, which lasts from the end of the first stage through day 8, is characterized by intensive synaptogenesis as well as extensive growth and degeneration. For the first time, large boutons resembling retinal terminals form multiple synaptic contacts with dendrites and dendritic protrusions; these synaptic arrangements are partially covered by glial processes.A feature characteristic of the developing dLGN during the first 2 postnatal weeks, and particularly during the second stage, is the presence of membrane specializations that resemble vacant postsynaptic densities. These specializations, which may be unapposed or opposite another neuronal process, decrease in frequency as the number of synapses increases. It is not known whether these densities are converted to synapses or whether they result from loss of presynaptic elements.The third stage in the process of synaptogenesis, which spans a period between days 10 and 20, is characterized by myelination and by the diminution of growth cones, degenerating profiles and vacant postsynaptic densities. There is also a very significant increase in the number and maturation of synapses including synaptic glomeruli. However, it is not until the end of this stage that synapses appear qualitatively indistinguishable from synaptic arrangements identified in adult animals.  相似文献   

14.
Light and electron microscopy were used to investigate the morphology of neuropil and neuronal cell bodies of the dorsal lateral geniculate nucleus (LGNd) of aged rats. Light microscopic examination reveals that, despite the optic tract showing signs of degeneration, the LGNd is scarcely affected. Thus, a slight but significant reduction in the diameters of both soma and nuclei is observed in aged neurons of the LGNd. Ultrastructural analysis demonstrates a few degenerating profiles of the neuropil. Neurons resembling relay cells exhibit typical features of aged neurons. Cells showing a very infolded nucleus, most of the ER cisternae connected with the nuclear envelope, abundant free polyribosomes and subsurface cisterns associated with mitochondria are similar to interneurons of adult rats. Therefore, aging and partial loss of visual input appear to induce small changes in the morphology of most of LGNd neurons.  相似文献   

15.
The intrinsic stability of the rabbit eye was exploited to enable receptive-field analysis of LGNd neurons and optic tract axons in the awake, unparalyzed state. We found eye position to remain within a range of less than 1.0 degrees for periods of 4-5 min, and in some cases for periods in excess of 10 min. Such stability is comparable to that seen in awake monkeys that have been trained to fixate. Receptive fields of dorsal lateral geniculate nucleus (LGNd) neurons were analyzed, and approximately 84% were concentrically organized. This is a higher value than previously reported in this species. In addition, the receptive-field centers of concentric cells were much smaller than those previously reported (mean diameter = 2.5 degrees). Most remaining neurons in the LGNd were either directionally selective (6.5%) or motion/uniform (6.5%). Concentric cells were classified as sustained or transient based on response duration to standing contrast. In the LGNd the receptive fields of sustained concentric cells were predominantly near the horizontal meridian, within the representation of the visual streak, while the receptive-field positions of transient concentric cells were more prevalent in the upper visual field. In the optic tract the receptive-field positions of both sustained and transient cells were more evenly distributed than was seen in the LGNd. Sustained and transient concentric cells in LGNd showed primarily nonlinear spatial summation. The receptive-field properties of LGNd neurons were related to geniculocortical antidromic latency. Most LGNd neurons of all receptive-field classes projected axons to the visual cortex. Thus, any intrinsic interneurons in the rabbit LGNd may have receptive-field properties similar to those of some principal neurons. There was significant overlap in the distribution of antidromic latencies in neurons of different receptive-field classes. Concentric sustained neurons, however, did conduct somewhat more slowly than did concentric transient neurons. Nonvisual sensory stimuli that resulted in EEG arousal (hippocampal theta activity) had a profound effect on the response duration of most (28/32) sustained concentric neurons. For these cells, the sustained response to standing contrast began to diminish and sometimes disappeared after 2-15 s. However, arousing stimuli that resulted in hippocampal theta activity reestablished the sustained response. Such arousing stimuli usually had little or no effect on the discharge of the cell in the absence of visual stimuli. Arousing stimuli had no effect on optic tract axons with sustained concentric receptive-field properties.(ABSTRACT TRUNCATED AT 400 WORDS)  相似文献   

16.
Dendrites of relay neurons in the subcortical visual center (lateral geniculate nucleus) of adult cats develop presynaptic sites following chronic disconnection from the visual cortex. The capability of otherwise exclusively postsynaptic dendrites to be transformed into presynaptic dendrites indicates a remarkable plasticity of the relay cells. It is suggested that the ‘axonization’ of relay neuronal dendrites which enables the neuron to establish new synaptic connections in replacement of those lost in the cortex is a main factor in the survival of the axotomized nerve cell.  相似文献   

17.
18.
Thalamic relay cells fire action potentials in two modes: burst and tonic. Previous studies in cats have shown that these two modes are associated with significant differences in the visual information carried by spikes in the dorsal lateral geniculate nucleus (dLGN). Here we describe the visual response properties of burst and tonic firing in the mouse dLGN. Extracellular recordings of activity in single geniculate cells were performed under halothane and nitrous oxide anesthesia in vivo. After confirming that the criteria used to isolate burst spikes from these recordings identify firing events with properties described for burst firing in other species and preparations, we show that burst firing in the mouse dLGN occurs during visual stimulation. We then compare burst and tonic firing across a wide range of visual response characteristics. While the two firing modes do not differ with respect to spatial summation or spatial frequency tuning, they show significant differences in the temporal domain. Burst spikes are phase advanced relative to their tonic counterparts. Burst firing is also more rectified, possesses sharper temporal frequency tuning, and prefers lower temporal frequencies than tonic firing. In addition, contrast-response curves are more step-like for burst responses. Finally, we present analyses that describe the stimulus detection abilities and spike timing reliability of burst and tonic firing.  相似文献   

19.
20.
Summary The postnatal growth of the dorsal part of the lateral geniculate nucleus (LGNd) is studied in paraffin sections through the brains of 32 cats of known age. The changes in shape and position of the LGNd are described and it is shown that its volume increases from about 3.4 mm3 at birth to about 26.4 mm3 in the adult cat. When this value is corrected for shrinkage, the volume of the LGNd in the adult cat turns out to be about 44 mm3. The detailed measurements reveal that during the second and third week of postnatal life there is a particularly steep increase in volume and that the final values are already reached at around the 40th day. Concomitant with the increase in volume there is a decrease of the number of cells per unit volume of grey matter. In the binocular segment of lamina A the number of cells decreases from about 470 per (0.1 mm)3 at birth to between 95 and 130 per (0.1 mm)3 in the adult cat. Separate measurements of nerve cells and neuroglial cells indicate that the absolute number of nerve cells remains fairly constant during postnatal life, whereas between the second and sixth week a great number of neuroglial cells are newly formed.Dedicated to Professor W. Bargmann, Kiel, on the occasion of his seventieth birthday  相似文献   

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