Lateral funiculus

Abstract: This study examined the hypothesis that descending inhibitory pathways from brain stem to spinal cord mediate the analgesic effect of both electrical brain stimulation and morphine. In the first set of experiments, the effect of subtotal midthoracic spinal cord lesions on the analgesic effect of electrical stimulation in the periaqueductal gray matter of the rat was examined. In the second, the effect of similar cord lesions on the analgesic effect of intraperitoneal morphine was studied. In both cases, a lesion of the dorsal part of the lateral funiculus (DLF) reduced or abolished the analgesia of the hindlimbs. Analgesia of the forelimbs was unaffected. Lesions of the dorsal columns, which include the corticospinal tract, or lesions of the ventral part of the lateral funiculus had no effect on analgesia. It is concluded that an inhibitory pathway, which descends in the dorsal part of the lateral funiculus and which probably originates in the nucleus raphe magnus of the medulla, mediates the descending control found in both morphine and stimulus-produced analgesia.

Abstract: 1 The activation of neurones in the mLRN (major portion of lateral reticular nucleus comprising its parvi- and magnocellular parts) by two spinal tracts ascending through the ventral part of the lateral funiculus has been studied by recording from 277 neurones of which 187 could be antidromically activated by stimulation of the cerebellar surface Forty-eight % of the neurones were activated by the bVFRT and described in a previous paper (Clendenin et al, 1975b) and 12% were activated by a previously unknown tract denoted the ipsilateral forelimb (iF) tract and described in the present paper 2 The iF-tract is activated by stimulation of nerves in the ipsilateral forelimb only The response consists of a train of impulses with a high initial frequency and an almost constant latency Cutaneous afferents and high threshold muscle afferents contribute to the excitation which is mediated by interneurones 3 The responses to stimulation of peripheral receptors were weak and difficult to classify 4 The iF-tract activates neurones in the dorsolateral portion of the magnocellular part of the mLRN which projects to the ipsilateral pars intermedia of the anterior lobe and the ipsilateral paramedian lobule 5 The possible information carried by the iF-tract is discussed

Abstract: Following stereotaxically placed lesions in the magnocellular and parvicellular portions of the red nucleus in a series of young adult albino rats, the site of termination of the rubrospinal fibers in the cervical cord has been studied using the Nauta-Gygax and Fink-Heimer silver methods and electron microscopy. Following three days survival the degenerating rubrospinal tract could be identified in the dorsal aspect of the lateral funiculus, principally contralateral to the lesion. Degenerating axons could be seen projecting to the base of the dorsal horn and intermediate regions of the ventral horn. Degenerating synaptic terminals were electron dense, contained remnants of synaptic vesicles and mitochondria, and usually made synaptic contact with small to medium size dendrites. This study finds that the rubrospinal tract in the rat projects chiefly to the base of the dorsal horn and intermediate regions of the ventral horn. The system forms axodendritic synapses with spinal neurons. This projection is in contrast to the dorsomedial projection of corticospinal terminals seen in this species. The significance of these apparently diverging pathways is discussed.