The Involvement of Bulbospinal Serotonergic Neurons in the Effect of 5-Hydroxytryptophan on Alpha and Gamma Motoneurons
As indicated by the work of other investigators, there exists a system of serotonin (5-HT)-containing neurons which originate in the nucleus raphe and terminate near motoneurons in the spinal cord (Carlsson et al., 1964; Dahlström and Fuxe, 1965; Anderson and Holgerson, 1966). It has also been shown that the i.v. administration of the 5-HT precursor, 5-hydroxytryptophan (5-HTP), leads to the facilitation of both alpha and gamma motoneurons (Myslinski and Anderson, 1978). The general belief is that 5-HTP produces this effect via the bulbospinal 5-HT pathway which converts it to 5-HT and subsequently releases it to activate the postsynaptic receptor sites (Anderson, 1972). If 5-HTP does produce this effect via the 5-HT neurons, the concurrent use of a 5-HT reuptake inhibitor should potentiate its effects; pre-treatment with a 5-HT synthesis inhibitor should depress its effects; and the electrical stimulation of the bulbospinal 5-HT system should produce effects similar to that of 5-HTP. We found all three cases to be true, which argues that 5-HTP works via the 5-HT pathway to facilitate alpha and gamma motoneurons.
KeywordsNucleus Raphe Gamma Activity Spinal Cord Dorsal Horn Gallamine Triethiodide Gamma Motoneuron
Unable to display preview. Download preview PDF.
- Koe, B.K., and Weissman, A., 1968, p-Chlorophenylalanine: a specific depletor of brain 5-HT, Adv. Pharmacol., 6B: 27–29.Google Scholar
- Myslinski, N.R., and Anderson, E.G., 1978, The effect of precursors on alpha and gamma motoneuron activity. J. Pharmacol. Exp. Therap., 204: 19–26.Google Scholar
- Taber, C.A., and Anderson, E.G., 1973, Paradoxical blockade by p-chloro-phenylalanine of 5-hydroxytryptophan facilitatory actions on spinal reflexes, J. Pharmacol. Exp. Therap., 187: 229–238.Google Scholar