title: Brain stem reticular influences on lumbar axial muscle activity. II. Temporal aspects.
abstract: Epaxial muscle electromyographic (EMG) responses to electrical stimulation of the pontomedullary reticular formation were analyzed for temporal patterns in the urethan-anesthetized rat. Recordings were obtained from the transversospinalis, medial longissimus, and lateral longissimus groups of back muscles. In response to a series of repetitive stimulus trains, the latency of muscle activation decreased with successive trains. Typically a 10-fold decrease in latency required eight to nine stimulus trains (5 trains/s, 25 pulses/train) with currents of 25-30 microA. Individual pulses within long stimulus trains evoked muscle spike potentials at low probability but with short latencies (population range 4-7 ms). The results suggest that whereas influences on lumbar axial musculature from brain stem reticular formation were not powerful enough to evoke muscle spikes with single-pulse stimulation at currents applied in this study, they can yield short, relatively fixed EMG onset latencies in response to individual pulses within stimulus trains once a potentiation phenomenon has occurred.
mesh_terms: D000818:Animals; D001368:Axis, Cervical Vertebra; D001933:Brain Stem / Q000502:physiology*; D004558:Electric Stimulation; D004576:Electromyography; D005260:Female; D008161:Lumbosacral Region; D009132:Muscles / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time; D012154:Reticular Formation / Q000502:physiology*