Phase-linked modulation of excitability of presynaptic terminals of low-threshold afferent fibers in the inferior alveolar nerve during cortically induced fictive mastication in the guinea pig.
Excitability of presynaptic terminals of low-threshold primary afferent fibers in the inferior alveolar nerve was tested in the trigeminal spinal nucleus of the ketamine-anesthetized, paralyzed guinea pig, by Wall's method. Fictive mastication was induced by repetitive stimulation of the cortical masticatory area, and was monitored by rhythmical burst activity in the jaw-opening anterior digastric motoneuron pool. The excitability was rhythmically modulated in a phase-linked manner during the masticatory cycle: it was decreased coincidentally with the digastric burst activity (jaw-opening phase) and increased during the middle and late periods of the interburst phase (jaw-closing phase) of the masticatory cycle. The results imply that presynaptic modulation of synaptic transmission of peripheral inputs from primary afferents to interneurons in the jaw-opening reflex pathway may contribute to the rhythmical modulation of the jaw-opening reflex evoked by innocuous stimulation of the intraoral structures during mastication; presynaptic inhibition contributing to the depression of the jaw-opening reflex during the jaw-closing phase and presynaptic facilitation to its enhancement during the jaw-opening phase.
Kurasawa
I
I
Department of Physiology, Faculty of Dentistry, Tokyo Medical and Dental University, Japan.
Hirose
Y
Y
Sunada
T
T
Nakamura
Y
Y
D000344:Afferent Pathways / Q000502:physiology*; D000818:Animals; D002540:Cerebral Cortex / Q000502:physiology*; D004558:Electric Stimulation; D006168:Guinea Pigs; D008340:Mandibular Nerve / Q000502:physiology*; D008409:Mastication; D008839:Microelectrodes; D009412:Nerve Fibers / Q000502:physiology; D012018:Reflex; D013569:Synapses / Q000502:physiology*