title: The response of alpha-motoneurons of different size to stretch and vibration of extensor muscles after injection of 5-hydroxytryptophan in spinal cats.
abstract: 1. Vibration of the GS muscle at 100/sec, and the peak-to-peak amplitude of about 100 mu, produced slight reflex activity of homonymous and heteronymous alpha-motoneurons in the spinal, unanesthetized cat. 2. Intravenous injection of the 5-HT precursor 5-HTP (25 mg/kg, L-form) performed in the spinal preparation facilitated the responses of single extensor alpha-motoneurons to both vibration and stretch of the corresponding muscle. The 5-HT antagonist methysergide (0-5 mg/kg i. v.) blocked almost completely the facilitation of the vibration and stretch induced motoneuronal discharges produced by 5-HTP in the spinal cat, indicating that the facilitation was 5-HT specific. 4. A comparison of the types of alpha-motoneurons participating in the reflex responses elicited by the different stimuli in the spinal cat following injection of 5-HTP showed that both small-tonic and large-phasic alpha-motoneurons take part in both stretch and vibration reflexes. 5. It is concluded that the alpha-motoneuron pool of the GS muscle represents an homogenous population, no matter what kind of synaptic drive is used for its activation, and that the susceptibility of a motoneuron to discharge depends on the amount of the afferent excitatory input rather than on the modalities of sensory stimulation.
mesh_terms: D006916:5-Hydroxytryptophan / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D002415:Cats; D005260:Female; D008297:Male; D009046:Motor Neurons / Q000502:physiology*; D009119:Muscle Contraction / Q000187:drug effects; D009132:Muscles / Q000187:drug effects* / Q000502:physiology; D012018:Reflex / Q000187:drug effects; D013116:Spinal Cord / Q000502:physiology*; D014732:Vibration
chemical_list: D006916:5-Hydroxytryptophan