[Facilitating effects of axotomy of the glossopharyngeal nerve on the motor reflex response of the frog medulla oblongata].

In the previous papers we have reported that the innervation of the frog lingual mucosa exercises a presynaptic inhibition at the bulbar region in order to integrate the mechanoreceptive information coming from the tongue. The present investigation was undertaken to establish if also the complementary tactile innervation of fungiform papillae has a similar ability. First of all it has been assayed the evocation of PAD tests by papillary innervation; then the facilitating effects, induced by the glossopharyngeal axotomy, on the afferents mass discharges recorded from hypoglossal nerve have been examined. Electrical stimulation of mechanical neurons at the root of IX produced DRP and DRR both at glossopharyngeal and hypoglossal nerves. After 5 and 10 days from glossopharyngeal axotomy becomes evident a considerable enhancement of efferent responses in many diastaltic arches of bulb. These effects strongly suggest a very evident inhibitory activity at the bulbar projection of papillary innervation. From all these observations it follows that presynaptic inhibition is joint to all the lingual mechanoreceptive afferences.