Respiratory response to somatic stimulation in fetal lambs during sleep and wakefulness

1. The respiratory response to electrical stimulation of the nose, tail, gum and fibular nerve (nonspecific somatic stimulation) was tested in chronically instrumented fetal lambs during sleep and wakefulness. 2. The respiratory response to somatic stimulation was greatest during REM sleep, lowest during NREM sleep, and intermediate during the awake state (AW). 3. Respiratory responses could follow electrical somatic stimulation up to 2 Hz in any sleep state without changing sleep state. 4. The fetal breathing (FB) response to repetitive stimulation depended on the initial sleep state and whether or not the sleep state was affected by the stimulation. Five patterns of response were seen: a) NREM leads to NREM (initial sleep state and sleep state at end of stimulation)--FB was initiated and did not continue beyond the duration of the stimulation. b) NREM leads to REM sleep--FB was initiated and continued beyond the time of stimulation. c) REM leads to REM sleep--spontaneous FB was enhanced and continued beyond the time of stimulation. d) REM leads to NREM sleep--spontaneous FB was enhanced but did not continue beyond the time of stimulation. e) NREM, REM sleep, Awake leads to Awake--FB was initiated or enhanced and continued beyond the time of stimulation until the onset of NREM sleep.