Evidence for the presence of substance P in cat nasal receptor afferents.

The afferents of the nasal receptors responsible for many upper airway protective reflexes are carried in the ethmoidal branch of the ophthalmic division of the trigeminal nerve. Previous electrophysiological studies indicate that a significant number of ethmoidal afferents respond to noxious stimuli applied to the nose. The objective of the present study was to identify ethmoidal nerve cell bodies within the trigeminal ganglion which demonstrated the presence of the neurotransmitter substance P (SP). SP is believed to be involved in the relay of nociceptive information. A double-labelling technique was employed and involved tracing the afferents to their cell bodies using horseradish peroxidase (HRP) and subsequent identification of SP-immunoreactivity within HRP-filled cells using monoclonal antibody immunohistochemistry. SP-immunoreactive cell bodies constituted 43 per cent-50 per cent of the total number of labelled ethmoidal cell bodies within the trigeminal ganglion. Although ethmoidal cell bodies were much smaller than the overall population of trigeminal ganglion cells, the size of SP-immunoreactive ethmoidal cell bodies was not significantly different from that of ethmoidal cell bodies not exhibiting SP-immunoreactivity.