Inflammatory peptide in spinal cord: evidence that the mediator of antidromic vasodilatation is not substance P

Behavioural effects of substance P through dopaminergic pathways in the brain

Some of the highest concentrations of substance P in forebrain are found in areas where dopaminergic neurons arise or terminate. In the rat, native substance P has been injected directly into brain areas where interactions between substance P and dopamine are suspected. In the ventral tegmental area (A10 dopamine neurons), bilateral infusions of substance P induce locomotor activity and exploration. It is concluded that substance P activates A10 dopamine neurons innervating the limbic system because (i) the behavioural effects resemble those seen after systemic treatment with low doses of d-amphetamine, a drug response known to depend on the integrity of the A10 dopamine neurons; (ii) lesions to the A10 dopamine neurons abolish the behavioural response to intracerebrally infused substance P; and (iii) dopamine antagonist drugs abolish the response to substance P. In parallel experiments substance P was injected into the origins of the nigrostriatal (A9 dopamine neurons) system and found to produce stereotyped behaviour. Substance P analogues protected from enzymic degradation have been studied in these model systems. The prolongation of the behavioural effects is correlated with the presence of undegraded substance P in the ventral tegmental area. Unrelated behavioural responses are also observed, which appear not to be mediated by dopamine neurons, and probably reflect the spread of stable substance P from the ventral tegmental area to other brain sites.

The contribution of sensory nerves to xylene-induced cystitis in rats

The role of capsaicin-sensitive sensory nerves of the rat urinary bladder in xylene-induced cystitis was investigated. Instillation of xylene into the urinary bladder of female rats induced cystitis, e.g. detrusor hyperreflexia and increased vascular permeability. Detrusor hyperreflexia was also observed in rats desensitized to capsaicin as adults (50-125 mg/kg s.c., 4 days before) but only for a short period (1 h) after instillation. When a longer time lag (24 h) was allowed to elapse following instillation, reflex micturition was almost abolished. In rats desensitized to capsaicin as newborns (50 mg/kg s.c. on second day of life) reflex micturition was almost abolished and xylene (given 1 h before measurement) was ineffective. The xylene-induced plasma extravasation was greater in the bladder neck than in the dome. In the bladder neck the "early" response to xylene was reduced but not abolished in rats densensitized to capsaicin as adults or pretreated with compound 48/80 and was abolished in rats desensitized to capsaicin as newborns. The bladder content of substance P-like immunoreactivity decreased at various times following xylene instillation but this change occurred in parallel to the increase in bladder weight. These findings indicate that xylene-induced cystitis involves, at least in part, an irritation of capsaicin-sensitive sensory nerves in the bladder wall. The present results further suggest that xylene acts by stimulating at least two populations of sensory nerves which differ in their sensitivity towards capsaicin.

A substance P-like peptide in bullfrog autonomic nerve terminals: anatomy biochemistry and physiology

Substance P immunoreactivity was localized to dense-cored vesicles in parasympathetic preganglionic nerve terminals in the bullfrog cardiac ganglion. Analysis with radioimmunoassay and high pressure liquid chromatography indicated that the immunoreactive substance was more similar to substance P than to substance K but was not identical to either. The bullfrog substance P was also shown to be different than kassinin, eledoisin, ranatensin, bombesin, neuromedin K and physalaemin. Although the peptide was present in most of the terminals in the ganglion and appeared to be releasable in a calcium-dependent manner, intracellular recordings from ganglion neurons during stimulation revealed no electrophysiological events that might be mediated by an endogenous peptide. In addition, the direct application of substance P to ganglion neurons generally produced no changes in membrane potential, membrane conductance, somal calcium spikes or nerve-evoked release of acetylcholine. High concentrations of substance P did cause an apparent increase in the rate of desensitization of the nicotinic receptors but there was little indication that this phenomenon would occur under physiological conditions. It is suggested that bullfrog substance P is released as a neurotransmitter but is involved in electrically silent events in the postsynaptic neurons or is acting on non-neuronal cells near the terminals. The possible implications of these results for peptidergic systems in general are discussed.

The spinal cord contains multiple factors causing plasma protein extravasation in the skin

Nervous tissue was analyzed for possible mediators of neurogenic inflammation. Acid extracts of spinal cord or spinal roots contained activity causing plasma protein extravasation when injected into the rat abdominal skin. The activity was more than 1000-fold higher than could be attributed to the content of substance P (SP). It was not depleted from spinal cord after destruction of afferent C fibers by capsaicin and was resistant to proteolytic enzymes. The activity was clearly separated from SP or neurokinins by HPLC or gel filtration and was due to compounds of high polarity and low molecular weight. Further HPLC separated at least 6 peaks, two of which were found to contain adenosine and AMP, respectively, as active substances. The activity of these compounds and of the peaks was reduced by antihistaminics. A further compound identified was 5-HT. Thus, while several active non-peptidergic compounds were found, no clear evidence for a new mediator of neurogenic inflammation was obtained.

Comparison of cardiovascular and bronchoconstrictor effects of substance P, substance K and other tachykinins

The effects of substance P (SP), substance K (SK), physalaemin, eledoisin, kassinin, neuromedin K and bombesin on blood pressure, heart rate, respiratory insufflation pressure and plasma extravasation were studied in the guinea-pig. All tachykinins except neuromedin K caused a fall in blood pressure with rather similar potency. The hypotensive response after physalaemin was comparatively more long-lasting. SK and eledoisin (2.5 nmol X kg-1 i.v.) caused an initial bradycardia which then changed into tachycardia. The other tachykinins induced a slowly developing tachycardia. Neuromedin K (up to 40 nmol X kg-1) did not influence heart rate. SK, kassinin and eledoisin were more potent than SP and physalaemin in increasing respiratory insufflation pressure. The effect of SK had a particularly long duration. Neuromedin K only induced a weak increase in insufflation pressure at a very high dose. All tachykinins except neuromedin K induced an increase in vascular permeability to plasma proteins in many visceral organs, as indicated by Evans blue extravasation. The trachea and ureter were the most sensitive organs with regard to this effect. Physalaemin and eledoisin were generally more potent in increasing vascular permeability in various organs than SP and SK. The maximal permeability-increasing effect of SK was smaller than that of SP, although the potency was similar. Bombesin increased insufflation pressure with no clearcut effects on vascular permeability. It is concluded that in the same species, i.e. guinea-pig, several tachykinins have rather similar hypotensive action, while the vascular permeability increase to plasma proteins is especially pronounced after physalaemin and eledoisin. SK, kassinin and eledoisin have prominent bronchoconstrictor effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Topical capsaicin pretreatment inhibits axon reflex vasodilatation caused by somatostatin and vasoactive intestinal polypeptide in human skin

1 Wheal and flare reactions are described following intradermal injections of somatostatin, vasoactive intestinal polypeptide, substance P and histamine in normal human forearm skin. Bombesin failed to produce a significant wheal and flare.2 Pretreatment of skin with capsaicin in all cases dramatically inhibited the flare but not the wheal. This result is in accord with the hypothesis that capsaicin blocks the effector side of the axon reflex, perhaps by depleting nerve terminals of vasodilatory peptide(s).

Vascular and sensory responses of human skin to mild injury after topical treatment with capsaicin

1 Immediately after several topical applications of capsaicin at 2-hourly intervals, human forearm skin would no longer develop flare (vasodilation) around a small injury. At the same time heat pain thresholds were reduced on average by 3.5 degrees C. These results are consistent with block by capsaicin of the effector side of the axon reflex, perhaps by depleting nerve terminals of substance P. 2 Over a period from several days to several weeks after treatment, flare was diminished and heat pain thresholds were slightly elevated. These changes may be due to long-lasting damage of cutaneous nerve terminals by capsaicin.

Postocclusive cutaneous vasodilatation mediated by substance P

1. The cutaneous vasodilatation following arterial occlusion ("reactive hyperemia") was studied in the rat hind paw. A peak increase in venous outflow of 200-250% was observed within 1 min after a 3 min occlusion period. 2. Chronic denervation as well as capsaicin pretreatment reduced the postocclusive cutaneous vasodilatation by more than 60% (P less than 0.01). This demonstrates that the reactive vasodilatation is of neurogenic origin and mediated by small diameter afferent fibres. 3. Reduction of the postocclusive cutaneous vasodilatation after histamine depletion by compound 48/80 indicates the involvement of histamine. 4. Among all neuropeptides known to occur in primary sensory neurones only substance P and vasoactive intestinal polypeptide cause vasodilatation when infused i.a. into the rat paw. In contrast to antidromic sensory nerve stimulation or i.a. substance P infusion, vasoactive intestinal polypeptide does not cause plasma extravasation. The vasodilator potency of vasoactive intestinal polypeptide is about 1/500 of substance P in the rat paw. Therefore only substance P is able to mimic the reactive vasodilatation. 5. It is concluded that the postocclusive cutaneous vasodilatation is caused mainly by the release of substance P from peripheral endings of small diameter nerve fibres. The "axon reflex", also involving neurogenic vasodilatation, is assumed to be exerted by the same mechanism.