SOME PROPERTIES OF INTRINSIC NEURONS OF THE DORSAL LATERAL GENICULATE NUCLEUS OF THE RAT

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Abstract
In urethane anesthetized rats, single unit recordings were made from intrinsic neurons (I-cells) of the dorsal lateral geniculate nucleus (LGN). Among a total of 434 units recorded, 408 (94.0%) were identified as relay neurons (principal cells, P-cells) and 26 (6.0%) as I-cells. There was no particular area of the LGN where the sampling ratio of I to P was relatively high or low. Neurons of the perigeniculate reticular nucleus which previously were taken as the I-cells of the LGN were not encountered in these recordings. The I-cells were fired once by single shock stimulation of the optic tract (OT) at the optic chiasm. The latencies ranged from 1.35-4.60 ms (mean, 2.60 ms). Calculation with an assumption of monosynaptic excitation indicated that among the 3 groups of OT fibers with different conduction velocities, the slowest group constitutes an input to the I-cells almost exclusively. In 15 of 26 I-cells, stimulation of the visual cortex caused orthodromic excitation. The threshold intensity was higher than for antidromic activation of the P-cells. By stimulating the OT with double shocks of suprathreshold intensity, the I-cells recovered responsiveness within 3 ms after the 1st excitation. I-cells (15) were examined for responses to diffuse light stimulation. Only stimulation of the contralateral eye was effective. The responses were of on-off type in 8 units, on-type in 6 units and off-type in 1 unit. Single shock stimulation of the mesencephalic reticular formation suppressed I-cell''s responsiveness to OT stimulation.