Cells In Cat Lateral Geniculate Nucleus Research Articles

Effects of short-term IOP elevation on receptive field properties of cat LGN cells

To investigate the effects of short-term intraocular pressure (IOP) elevation on the receptive field properties of lateral geniculate nucleus (LGN) cells, responses of the LGN cells to annulus, disc and drifting gratings with high or low spatial frequencies have been recorded extracellularly in the cat with the retinal perfusion pressure kept stable (30 mmHg). Our results indicated that the responses of the X and Y type LGN cells were significantly weakened during IOP elevation. And the responses varied with the different mechanisms of receptive fields. Specifically, while using annulus and disc as stimuli, the responses of Y cells were more tolerant than X cells to IOP elevation. The surround area of the receptive field was more sensitive to IOP elevation than the center. The mean responses during IOP elevation decreased more than the peak responses did. IOP elevation has more influence on the responses of X cells than on the response of Y cells to the drifting gratings with high spatial frequency. These results may reflect different degrees of ischemia on corresponding retinal structures caused by IOP elevation.

A model of cortically induced synchronization in the lateral geniculate nucleus of the cat: a role for low-threshold calcium channels.

Recently Sillito et al. (Nature 1994;369:479-82) discovered correlations in the spike trains of a relatively distant pair of cat lateral geniculate nucleus cells when simultaneously stimulated by a drifting grating; no such correlation occurs when the visual cortex is removed. In a further analysis of the data, we have found that short, high-frequency bursts contribute substantially to the synchronization and we hypothesize that the origin of the bursts is the low-threshold calcium spike. Guided by this hypothesis, our model of the corticogeniculate pathway and early visual system reproduces the experimental data in nearly every detail, as well as making predictions about cortical activity during the synchronizing process. We also discuss the possible behavioral relevance of correlations in the geniculo-cortical loop as well as other neural systems.

The effect of contrast on the visual response of lagged and nonlagged cells in the cat lateral geniculate nucleus: Erratum

Hartveit, E. & Heggelund, P. (1992). The effect of contrast on the visual response of lagged and nonlagged cells in the cat lateral geniculate nucleus. Visual Neuroscience9, 515–525.

A T‐type Ca2+ current underlies low‐threshold Ca2+ potentials in cells of the cat and rat lateral geniculate nucleus.

1. The characteristics of a transient inward Ca2+ current (IT) underlying low-threshold Ca2+ potentials were studied in projection cells of the cat and rat dorsal lateral geniculate nucleus (LGN) in vitro using the single-electrode voltage-clamp technique. 2. In cat LGN slices perfused at 25 degrees C with a solution which included 1 mM-Ca2+ and 3 mM-Mg2+, IT could be evoked by depolarizing voltage steps to -55 mV from a holding potential (Vh) of -95 mV and was abolished by reducing [Ca2+]o from 1 to 0.1 mM. IT was also blocked by 8 mM-Mg2+ and 500 microM-Ni2+, but 500 microM-Cd2+ was a significantly less effective antagonist. 3. The inactivation of IT, which occurred at Vh positive to -65 mV, was removed as Vh approached -100 mV. The process of inactivation removal was also time dependent, with 800-1000 ms needed for total removal. Activation curves for IT showed a threshold of -70 mV and illustrated that IT was extremely voltage sensitive over the voltage range from -65 to -55 mV. 4. The decay phase of IT followed a single-exponential time course with a time constant of decay which was voltage sensitive and ranged from 20 to 100 ms. The mean peak conductance increase associated with IT was 8.4 nS (+/-0.9, S.E.M.). 5. In more 'physiological' conditions (35 degrees C and 1.5 mM-Ca2+, 1 mM-Mg2+) the voltage dependence of activation and inactivation were unaffected. However, the development and decay of IT proceeded more rapidly and only 500-600 ms were needed for total removal of inactivation. Under these conditions, the use of voltage ramps showed that depolarization rates of greater than 30 mV/s were necessary for IT activation. 6. The use of multiple voltage-step protocols illustrated that the process of inactivation removal was rapidly reversed by brief returns to a Vh of -50 mV. Furthermore, any delay in IT activation, once the LGN cell membrane potential was in the IT activation range, resulted in a current of reduced amplitude. 7. Although IT in rat LGN cells was briefer and had a shorter latency to peak, it was otherwise similar to that seen in cat LGN cells. 8. The characteristics of IT are very similar to those of the T-type Ca2+ currents of other excitable membranes. The properties of IT are discussed with respect to its role in generating the low-threshold Ca2+ potentials which are central to the oscillatory behaviour of thalamic projection cells.

Localization of gamma-aminobutyric acid (GABA) in type 3 cells and demonstration of their source to F2 terminals in the cat lateral geniculate nucleus: a Golgi-electron-microscopic GABA-immunocytochemical study.

Postembedding immunocytochemistry with a gamma-aminobutyric acid (GABA) antiserum was done on semithin sections of cat lateral geniculate nucleus (LGN) previously processed with the rapid-Golgi and gold-toning procedures, to determine which of the three main morphological types (1, 2,3) of neurons in the A-laminae show immunoreactivity and are, therefore, presumably GABAergic. Only type 3 cells were found to be GABA positive. These cells were characterized by small somata and few, scarcely branched dendrites bearing almost exclusively appendages with long slender stalks. Some of these cells have extensive filiform "axonlike" processes originating from different regions of dendrites and having appendages similar to those originating directly from dendrites. Many of these Golgi gold-toned impregnated dendritic appendages of type 3 cells were analyzed in the electron microscope and were identified as typical F2 terminals by their content of pleomorphic synaptic vesicles; by being postsynaptic to retinal (RLP), cortical (RSD), and perigeniculate (F1) terminals; and by being presynaptic to dendrites. In addition, since it was previously demonstrated that glutamic acid decarboxylase (GAD) and GABA-positive cells are not retrogradely labeled with horseradish peroxidase (HRP) from the visual cortex, the present results, by showing that GABA-positive cells have type 3 morphology, provide supporting evidence for the interneuronal nature of type 3 cells in cat LGN.