Harmaline-induced rhythm in the lateral reticular nucleus.

Extracellular unit recordings were performed in the lateral reticular nucleus of cats under tremogenic doses of harmaline. The 8-12 Hz rhythmic activity induced by the drug in the reticular neurons was suppressed by a total spinal transection and by an ipsilateral injection of xylocaine but not by a contralateral injection of xylocaine. Under harmaline, autoradiographic labelling with 14C-2-deoxyglucose was increased in the lateral reticular nucleus, indicating an increased mean neuronal activity. This labelling was also suppressed by spinal cord transection. A spinal hemisection resulted in the absence of the differential labelling of the ipsilateral lateral reticular nucleus and in a reduction of the labelling of the contralateral lateral reticular nucleus. These data, which indicate that both the rhythmic activity and increased autoradiographic marking under harmaline are elicited through spinoreticular neurons, are discussed in view of the descending olivo-cerebello-spinal pathways.