Abstract
In urethane-anesthetized rats, single unit recordings were made from intrinsic neurons (I-cells) of the dorsal lateral geniculatenucleus (LGN).
1. 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 found 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 had previously been taken as the I-cells of the LGN were not encountered in these recordings.
2. The I-cells were fired once by single shock stimulation of the optictract (OT) at the optic chiasm. The latencies ranged from 1.35 to 4.60 msec (mean, 2.60 msec). Calculation with an assumption of monosynaptic excitation indicates that among the three groups of OT fibers with different conduction velocities, the slowest group constitutes an input to the I-cells almost exclusively.
3. In 15 out 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.
4. By stimulating the OT with double shocks of suprathreshold intensity, the I-cells were found to recover responsiveness within 3 msec after the first excitation.
5. Fifteen I-cells were examined of responses to diffuse light stimulation. Only stimulation of the contralateral eye was effective. The responses were of on-off-type in 8 units, of on-type in 6 units and of off-type in 1 unit.
6. Single shock stimulation of the mesencephalic reticular formation suppressed I-cell's responsiveness to OT stimulation.
