Abstract
In the first series of experiments we determined the distribution of cells in the medial reticular formation (MRF) and the pontomedullary locomotor strip (PLS) which, when activated, can induce locomotion. Experiments were performed on precollicular-postmamillary decerebrate cats walking on a treadmill. Controlled microinjections of neuroactive substances into the MRF or PLS demonstrated that these areas contained cell bodies capable of producing locomotion. Furthermore, the PLS was demonstrated to be closely related to or synonymous with the spinal nucleus of the trigeminal nerve and is related to the sensory activation of locomotion. In a second series of treadmill locomotion experiments, the descending pathways from the brainstem locomotor areas were investigated by utilizing reversible (cooling to block synaptic or fiber transmission) and irreversible subtotal lesions of the brainstem or spinal cord. The results demonstrate that the mesencephalic locomotor region (MLR) projects through the MRF and through the spinal cord in the ventrolateral funiculus (VLF). Furthermore, the PLS can produce locomotion by activation of this pathway or by another pathway which descends through the dorsal half of the spinal cord. In a third series of experiments, we examined the characteristics of short-latency MLR-evoked postsynaptic potentials (PSPs) observed in lumbar spinal motoneurons and their relationship to the production of motoneuron locomotor drive potentials (LDPs) and locomotion. Experiments were performed on paralyzed, precollicular-postmamillary decerebrate cats during intracellular recording from lumbar motoneurons. Evidence is presented that MLR-evoked PSPs are highly related to the process of locomotion and that LDPs and PSPs observed in motoneurons with stimulation of the MLR are produced by a common pathway which relays in the MRF and descends bilaterally through the spinal cord in the VLF. Spinal interneurons that may be related to the production of MLR-evoked PSPs are described.