Influence of l-DOPA on transmission in long ascending propriospinal pathways in the cat

Abstract

In high spinal cats the influence of an intravenous injection of l-3,4,-dihydroxyphenylalanine (DOPA) has been investigated on the transmission of long ascending propriospinal pathways to certain groups of forelimb motoneurones. The early discharge evoked in pectoralis major and deep radial motoneurones on electrical stimulation of hindlimb afferents, which may be obtained in some high spinal preparations, is facilitated after DOPA. A late discharge (30–80 msec) appears after DOPA in the same forelimb motoneurones and may often last up to 600 msec or more. Facilitation by hindlimb nerves of forelimb mono- and polysynaptic reflexes is similarly prolonged. Ipsilateral hindlimb nerves are more effective than contralateral. Late discharges have also been evoked in forelimb motoneurones on stimulation of forelimb afferents after DOPA and it is concluded that a somewhat similar organization of late reflexes exists in brachial segments as previously reported by Jankowska et al. in the lumbar cord. The influence of DOPA on long ascending propriospinal and forelimb reflexes is ascribed to excitation of the terminals of noradrenergic reticulospinal fibres. The reflex changes are considered to reflect activity in neuronal systems involved in the control of stepping in the cat. A further system modifying long ascending propriospinal transmission could be excited by stimulation of the ventral quadrant of the spinal cord at C 1. The effects on propriospinal transmission could outlast the stimulus by several tens of minutes.