Abstract
The effects of the 5-hydroxytryptamine (5-HT) precursors, 5-hydroxytryptophan (5-HTP) and tryptophan on alpha- and gamma-motoneuron discharges were examined in the spinal cat with a deafferented cord. The injection of 75 mg/kg of dl-5-HTP resulted in a doubling of the spontaneous discharge rate of gamma-motoneurons and the induction of spontaneous alpha-motoneuron activity. These effects of 5-HTP were reversed by the 5-HT antagonists, cinanserin (4 mg/kg) and methysergide (2 mg/kg). Tryptophan alone (100 mg/kg) exhibited minimal effects of motoneuron activity, but in animals pretreated with pargyline it significantly excited alpha- and gamma-motoneurons. Recordings of alpha- and gamma-motoneuron activity in gastrocnemius and semitendinosus nerves revealed that 5-HTP increased alpha- and gamma-motoneuron activity in both flexor and extensor nerves. Reversal of the effects of 5-HTP by 5-HT antagonists suggests that these effects were mediated by 5-HT. The fact that the 5-HTP effects were observed in preparations with an open gamma-loop indicates that the effects on the alpha-motoneurons are not mediated via the gamma-motoneuron facilitation, but results from a central activation.
JPET articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|