Sensorimotor cortical influences on cuneate nucleus rhythmic activity in the anesthetized cat

This work aimed to study whether the sensorimotor cerebral cortex spreads d own its rhythmic patterns of activity to the dorsal column nuclei. Extracel lular and intracellular recordings were obtained from the cuneate nucleus o f chloralose-anesthetized cats. From a total of 140 neurons tested (106 cun eolemniscal), 72 showed spontaneous rhythmic activity within the slow (<1 H z), delta (1-4 Hz), spindle (5-15 Hz) and higher frequencies, with seven ce lls having the delta rhythm coupled to slow oscillations. The spindle activ ity recorded in the cuneate was tightly coupled to the thalamo-cortico-thal amic spindle rhythmicity. Bilateral or contralateral removal of the frontop arietal cortex abolished the cuneate slow and spindle oscillations. Oscilla tory paroxysmal activity generated by fast electrical stimulation (50-100 H z/1-2 s) of the sensorimotor cortex induced burst firing synchronized with the paroxysmal cortical "spike" on all the non-lemniscal neurons, and inhib itory responses also coincident with the cortical paroxysmal "spike" in the majority (71%) of the cuneolemniscal cells. The remaining lemniscal-projec ting neurons showed bursting activity (11%) or sequences of excitation-inhi bition (18%) also time-locked to the cortical paroxysmal "spike". Additiona lly, the cerebral cortex induced coherent oscillatory activity between thal amic ventroposterolateral and cuneate neurons. Electrolytic lesion of the p yramidal tract abolished the cortically induced effects on the contralatera l cuneate nucleus, as well as on the ipsilateral medial lemniscus. The results demonstrate that the sensorimotor cortex imposes its rhythmic p atterns on the cuneate nucleus through the pyramidal tract, and that the co rticocuneate network can generate normal and abnormal patterns of synchroni zed activity, such as delta waves, spindles and spike-and-wave complexes. T he cuneate neurons, however, are able to generate oscillatory activity abov e 1 Hz in the absence of cortical input, which implies that the cerebral co rtex probably imposes its rhythmicity on the cuneate by matching the intrin sic preferred oscillatory frequency of cuneate neurons. (C) 1999 IBRO. Publ ished by Elsevier Science Ltd.