Nasonasal reflex mechanisms in anaesthetized dogs

In dogs anaesthetized with pentobarbitone, we recorded bilateral vascular a nd secretory responses to unilateral stimulation of intranasal afferent ner ves. Nasonasal reflexes evoked by intranasal light mechanical stimulation, intranasal application of cold saline (2 ml at 3 degrees C), capsaicin (0.0 03-0.3 mmol) and antidromic electrical stimulation (15 V, 0.2 ms) of the tr igeminal nerve at 10 Hz for 45 s were recorded. Vascular and secretory resp onses were studied before and after atropine pre-treatment, after ipsilater al section of the post-ganglionic parasympathetic fibres and the trigeminal nerve, and after administration of the ganglionic nicotinic receptor antag onist chlorisondamine. All stimuli studied induced bilateral increases in n asal arterial blood flow and secretion, although the contralateral response s were smaller under control conditions (p < 0.05). Bilateral vasodilatatio n evoked by mechanical stimulation, capsaicin and antidromic trigeminal ner ve stimulation was resistant to atropine. The ipsilateral non-cholinergic v asodilatation evoked by mechanical stimulation or capsaicin was reduced by 50% (p < 0.05) after section of both trigeminal and post-ganglionic parasym pathetic fibres. The remaining ipsilateral vasodilatation induced by these two stimuli was significantly reduced after chlorisondamine. The ipsilatera l secretory responses to all stimuli studied were significantly reduced (p < 0.05), but not abolished by atropine. Contralateral secretory responses t o all stimuli studied were not affected by atropine, the section of either the parasympathetic or trigeminal nerves, or chlorisondamine, suggesting th e activation of local axon reflexes only. We conclude that unilateral intra nasal stimulation of primary afferent neurons with light pressure, cold sal ine and capsaicin induces bilateral vascular and secretory responses via ax on reflex mechanisms, as well as the activation of local and central sensor y-parasympathetic reflex arcs.