We previously showed that propriospinal pathways in the cervicothoracic region contribute to the descending activation of locomotor-like activity in the in vitro neonatal rat spinal cord (SFN 27:297.11,2001); these experiments involved chemical activation of the brainstem using a combination of 5-HT, NMDA and bicuculline. The present series attempts to further characterize bulbospinal pathways activating locomotor-like rhythms, using a combination of bath partitions, selected spinal cord lesions, and neurochemical manipulation of propriospinal transmission. Brain stem-spinal cord preparations were isolated from rats (days 1-6) and subjected to either chemical or electrical stimulation of the brainstem. Lumbar ventral root locomotor-like rhythms induced by chemical, but not electrical, stimulation of the brainstem were abolished by bilateral ventral white matter lesions of the thoracic cord, or by application of calcium-free bath solutions or an NMDA receptor antagonist (AP5) to the cervicothoracic region. ...