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J Physiol Volume 516, Number 2, 571-582, April 15, 1999
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The Journal of Physiology (1999), 516.2, pp. 571-582
© Copyright 1999 The Physiological Society

Inspiration-promoting vagal reflex under NMDA receptor blockade in anaesthetized rabbits

Kazuo Takano and Fusao Kato

Department of Pharmacology II, Jikei University School of Medicine, Tokyo 105-8461, Japan


This study describes a novel vagal respiratory reflex in anaesthetized rabbits. In contrast to the well-known inspiratory (I) off-switching by vagal afferent excitation, this vagal reflex initiates and maintains the central I activity of phrenic nerve discharges in rabbits pre-treated with antagonists of N-methyl-D-aspartate-type excitatory amino acid receptors (NMDA-Rs).


Under NMDA-R blockade with either dizocilpine (0·025-0·3 mg kg-1), D-2-amino-5-phosphonopentanoic acid (AP5, 0·5-1 mg, i.c.v.) or ketamine (10 mg kg-1), vagal stimulation at low frequencies (5-40 Hz) during the I phase prevented or markedly delayed the spontaneous I termination. In contrast, stimulation of the same vagal afferent at the same intensity but at a higher frequency (100-160 Hz) during the I phase immediately terminated the I phase.


In non-vagotomized rabbits, maintaining the tidal volume at end-expiratory levels during the I phase prevented spontaneous I termination and maintained apneusis after NMDA-R blockade with dizocilpine.


Brief stimulation of vagal afferents at low frequency (5-40 Hz) during the expiratory (E) phase constantly initiated phrenic I discharge after NMDA-R block.


We conclude that low-frequency discharge of vagal pulmonary stretch receptor afferents, as when lung volume is near functional residual capacity, promotes central I activity under NMDA-R blockade.




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