Role of muscle receptors connected to nonmedullated fibres in reflex hyperventilation.

Experiments using electrical stimulation of different groups of muscle afferent nerve fibres have shown that most of the known medullated fibres in muscle nerves are involved in reflexly stimulatihg ventilation (Bessou et al. 1959, Koizumi et al. 1961, Senapati 1966). Investigations using natural stimulation of muscle receptors and pmsive limb movements (Kao et al. 1963, Senapati 1966, Kalia et al. 1972) have confirmed these results. From available histological evidence it is (known that one-third of the total number of fibres in m w l e afferent nerves are non-medullated fibres (Ranson and Davenport 1931). The role of this component of muscle nerves in the reflex hyperventilation of muscular exercise remains to be established. Accordingly, an attempt was made to study the reflex ventilatory effects of stimulating the receptors connected to non-medullated fibres when the activity in the endings of all medullated fibres had been blocked by repetitive antidrornic stimulation (Paintal 1959, 1961). These experiments were carried out on dogs anaesthetized with sodium pentobarbitone (30-35 mgkg, intraperitoneally). The experimental arrangements for recording ventilation (v ~) , stimulating the lateral gastrocnemius nerve, preparing the muscle for natural <stimulation and fixing the limbs were similar to those described earlier (Senapati 1966, Kalia et al. 1972). The sensory muscle receptors were blocked by stimulating electrically 'the fibres d the lateral gastrocnemius nerve repetitively as described by