Substance P sensitizes group III but not group IV afferent units from cat knee joint to noxious movement

Effect of substance P on mechanosensitive units of tissues around and in the lumbar facet joint

The purpose of this study was to examine how substance P affects the mechanosensitive afferent units identified in the tissues around and in the lumbar facet joint of the rabbit. Substance P was applied to the receptive fields of the units by microinjection, and the afferent activity of the units was recorded from dorsal root filaments. Changes in afferent discharge rates and von Frey thresholds were measured sequentially after the application of substance P. Most of the units (83.3%) had an increase in the ongoing discharge rates after the application of substance P: 54.2% of the units had immediate excitation and 29.2% had delayed excitation. One-third of the units had a decreased von Frey threshold after the application of substance P. Substance P had an excitatory effect on 81.8% of the units with a threshold of > 5.0 g and a conduction velocity of < 30 m/s, which may serve as nociceptors, and on 84.6% of the units with a threshold of < 2.0 g, which may serve as proprioceptors. These results suggest that substance P has an excitatory effect on both nociceptive and proprioceptive units in the tissues around and in the lumbar facet joint.

The localization and release of substance P and calcitonin gene-related peptide at nerve fibre endings in rat cutaneous nerve neuroma

This study uses radiological and immunocytochemical techniques to investigate the localization, content, transport and release of substance P- and calcitonin gene-related peptide-like immunoreactivity (SP-LI and CGRP-LI, respectively) in nerve fibre endings in 1-, 3- and 5-week-old cutaneous nerve neuromas. Neuromas were induced by ligating and transecting the saphenous nerve in anaesthetized Sprague-Dawley rats. The content of both neuropeptides in 3-week-old saphenous nerve neuroma was significantly reduced compared to that in normal saphenous nerve. At 5 weeks the levels of the peptides in the neuromas had returned to normal but remained reduced in the nerve just proximal to the neuroma. Following a 24-h ligation of the nerve proximal to 3-week-old neuromas there was a diminished immunocytochemical staining for SP-LI and CGRP-LI both proximal and distal to the ligature when compared to that seen at ligations of normal nerves. This indicates a decreased transport of the neuropeptides both to and from the 3-week-old neuromas. The density of neuropeptide staining at ligatures of nerves with 5 week or older neuromas had increased, but still remained less than that seen at ligations of normal nerve. Both a basal and a bradykinin-induced release of SP-LI and CGRP-LI from nerve fibre endings in the neuroma was demonstrated. The basal release was demonstrated by exposing the neuromas, in situ, to solutions containing 50 microM morphine plus 2 mM CoCl2 for 24 h.(ABSTRACT TRUNCATED AT 250 WORDS)