Development in neonatal rats of the sensory resetting of the locomotor rhythm induced by NMDA and 5-HT.
Developmental changes in the effects of quadriceps (Q) nerve stimulation on the locomotor rhythm induced by a mixture of N-methyl-D-aspartic acid and 5-hydroxytryptamine were examined using in vitro preparations from neonatal rats at postnatal days (P) 1-6. The effects of such stimulation on the rhythm were dependent both on stimulus strength and on the age of the animal. Low-intensity stimulation (< or =3.0 x T, where T=threshold for the monosynaptic reflex) during the flexor phase reset the rhythm via a prolongation of the flexor burst in most rats at P1-3, but via flexor burst truncation at P4-6. At any age, low-intensity stimulation during the extensor phase had no consistent effect on the ongoing rhythm. Activation of muscle afferents evoked via isometric contraction of the Q muscle caused effects similar to those obtained on low-intensity electrical stimulation in all age groups. In all age groups, high-intensity stimulation (> or =5.0 x T) caused resetting when delivered during the flexor phase via a prolongation of the flexor burst and during the extensor phase via a truncation of the extensor burst. These results suggest that the type of resetting evoked from low-threshold muscle afferents changes drastically during postnatal weekl, while effects evoked from high-threshold afferents remain unchanged.
Iizuka
M
M
Center for Medical Sciences, Ibaraki Prefectural University of Health Sciences, Japan. iizukam@ipu.ac.jp
Kiehn
O
O
Kudo
N
N
D000375:Aging / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn; D004558:Electric Stimulation; D004576:Electromyography; D008959:Models, Neurological; D009043:Motor Activity / Q000187:drug effects* / Q000502:physiology; D009119:Muscle Contraction; D024510:Muscle Development; D018482:Muscle, Skeletal / Q000254:growth & development / Q000294:innervation* / Q000502:physiology; D016202:N-Methylaspartate / Q000494:pharmacology*; D009412:Nerve Fibers / Q000187:drug effects / Q000502:physiology; D009475:Neurons, Afferent / Q000187:drug effects / Q000502:physiology*; D010525:Peripheral Nerves / Q000254:growth & development / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012018:Reflex; D012701:Serotonin / Q000494:pharmacology*; D013569:Synapses / Q000502:physiology
D012701:Serotonin; D016202:N-Methylaspartate