Effects of projected cortical epileptiform discharges on unit activity in the cat cuneate nucleus

Recordings of single cells in the cuneate nucleus were made during cortical epileptiform activity. Spontaneous and evoked spiking activity of relay cells was primarily inhibited by the corticofugal epileptiform discharge. Most interneurons were inhibited, but a large proportion also showed an early excitatory corticofugal input. The EPSPs and IPSPs induced by corticofugal discharges were seen in intracellular and quasi-intracellular recordings of cuneate neurons. The observation of IPSPs, and the effectiveness of corticofugal input in inhibiting unit injury discharges and glutamate-induced firing, showed that corticofugal inhibition in cuneate was at least partially postsynaptic. Most cuneate neurons studied during cortical ictal episodes discharged in a fashion consistent with their responses to cortical interictal activity; i.e., units that had been inhibited were inhibited during the ictus and those that had been excited fired during the cortical seizure. Some units were gradually recruited by corticofugal input during seizure, but since most such units were interneurons, cuneate did not provide a positive feedback to the cortical focus. The corticocuneate pathway appeared to provide a negative feedback circuit which may be used to modulate transmission of sensory input.