CONVERGENCE OF CENTRAL RESPIRATORY AND LOCOMOTOR RHYTHMS ONTO SINGLE NEURONS OF THE LATERAL RETICULAR NUCLEUS

We have analyzed the behavior of neurons of the lateral reticular nucl eus (LRN) during fictive respiration and locomotion and found that som e LRN neurons have both central respiratory and locomotor rhythms. Exp eriments were conducted on decerebrate, decerebellate, immobilized, an d artificially ventilated cats, with the spinal cord transected at the lower thoracic cord. Fictive respiration and fictive forelimb locomot ion were ascertained by monitoring activities from the phrenic nerve a nd forelimb extensor and flexor nerves, respectively. Fictive locomoti on was evoked by electrical stimulation of the mesencephalic locomotor region (MLR) or sometimes occurred spontaneously. During fictive loco motion many LRN neurons fired in certain phases of the locomotion cycl e; i.e., with respect to the nerve discharge of the ipsilateral foreli mb they fired in either the extensor, flexor, extensor-flexor, or flex or-extensor phase. Firing of some LRN neurons was modulated synchronou sly with central respiratory rhythm. Neurons with inspiratory activity and those with expiratory activity were both found. More than half of these respiration-related LRN neurons had locomotor rhythm as well. T he majority of the three types of LRN neurons, i.e., neurons with only locomotor rhythm, those with only respiratory rhythm, and those with both respiratory and locomotor rhythms, were antidromically activated by electrical stimulation of the ipsilateral inferior cerebellar pedun cle. Electrical stimulation of the upper cervical cord showed that the se LRN neurons, not only locomotion-related but also respiration-relat ed neurons, received short latency inputs from the spinal cord. The LR N neurons studied were distributed widely in the LRN, relatively dense ly in the caudal two-thirds of the nucleus. No particular differences were detected between the three types of LRN neurons with respect to t heir location in the nucleus. These results indicate that the informat ion about central respiratory and locomotor rhythms that is necessary for cerebellar control of the coordination between respiration and loc omotion converges, at least partly, at the level of the LRN.