Supersensitivity of the rabbit iris sphincter muscle induced by trigeminal denervation: the role of substance P

Ocular Autonomic Nervous System: An Update from Anatomy to Physiological Functions

The autonomic nervous system (ANS) confers neural control of the entire body, mainly through the sympathetic and parasympathetic nerves. Several studies have observed that the physiological functions of the eye (pupil size, lens accommodation, ocular circulation, and intraocular pressure regulation) are precisely regulated by the ANS. Almost all parts of the eye have autonomic innervation for the regulation of local homeostasis through synergy and antagonism. With the advent of new research methods, novel anatomical characteristics and numerous physiological processes have been elucidated. Herein, we summarize the anatomical and physiological functions of the ANS in the eye within the context of its intrinsic connections. This review provides novel insights into ocular studies.

Evidence that central pathways that mediate defecation utilize ghrelin receptors but do not require endogenous ghrelin

In laboratory animals and in human, centrally penetrant ghrelin receptor agonists, given systemically or orally, cause defecation. Animal studies show that the effect is due to activation of ghrelin receptors in the spinal lumbosacral defecation centers. However, it is not known whether there is a physiological role of ghrelin or the ghrelin receptor in the control of defecation. Using immunohistochemistry and immunoassay, we detected and measured ghrelin in the stomach, but were unable to detect ghrelin by either method in the lumbosacral spinal cord, or other regions of the CNS. In rats in which the thoracic spinal cord was transected 5 weeks before, the effects of a ghrelin agonist on colorectal propulsion were significantly enhanced, but defecation caused by water avoidance stress (WAS) was reduced. In knockout rats that expressed no ghrelin and in wild‐type rats, WAS‐induced defecation was reduced by a ghrelin receptor antagonist, to similar extents. We conclude that the ghrelin receptors of the lumbosacral defecation centers have a physiological role in the control of defecation, but that their role is not dependent on ghrelin. This implies that a transmitter other than ghrelin engages the ghrelin receptor or a ghrelin receptor complex.

Morphology and neurochemistry of rabbit iris innervation

The aim of this study was to map the entire nerve architecture and sensory neuropeptide content of the rabbit iris. Irises from New Zealand rabbits were stained with antibodies against neuronal-class βIII-tubulin, calcitonin gene-related peptide (CGRP) and substance P (SP), and whole-mount images were acquired to build a two-dimensional view of the iridal nerve architecture. After taking images in time-lapse mode, we observed thick nerves running in the iris stroma close to the anterior epithelia, forming four to five stromal nerve rings from the iris periphery to the pupillary margin and sub-branches that connected with each other, constituting the stromal nerve plexus. In the anterior side, fine divisions derivated from the stromal nerves, forming a nerve network-like structure to innervate the superficial anterior border layer, with the pupillary margin having the densest innervation. In the posterior side, the nerve bundles ran along with the pupil dilator muscle in a radial pattern. The morphology of the iris nerves on both sides changed with pupil size. To obtain the relative content of the neuropeptides in the iris, the specimens were double stained with βIII-tubulin and CGRP or SP antibodies. Relative nerve fiber densities for each fiber population were assessed quantitatively by computer-assisted analysis. On the anterior side, CGRP-positive nerve fibers constituted about 61%, while SP-positive nerves constitute about 30.5%, of the total nerve content, which was expressed as βIII tubulin-positive fibers. In addition, in the anterior stroma of the collarette region, there were non-neuronal cells that were positive for SP. On the posterior side, CGRP-positive nerve fibers were about 69% of total nerve content, while SP constituted only up to 20%. Similarly, in the trigeminal ganglia (TG), the number of CGRP-positive neurons significantly outnumbered those that were positive for SP. Also, all the SP-positive neurons were labeled with CGRP. This is the first study to provide a two-dimensional whole mount and a cross-sectional view of the entire iris nerve architecture. Considering the anatomical location, the high expression of CGRP and SP suggests that these neuropeptides may play a role in the pathogenesis of anterior uveitis, glaucoma, cataracts and chronic ocular pain.

The Inhibitory Effects of Local Anesthetics on Primary Sensory Nerve and Parasympathetic Nerve in Rabbit Eye

Primary sensory nerves transmit information to both the periphery and central nervous systems, and they mediate neurogenic inflammation by release of neurotransmitters, such as tachykinins, in the periphery. Because the effect of local anesthetics on neurogenic inflammation is a subject of controversy, we investigated the direct effect of local anesthetics on tachykininergic neurotransmission, comparing it with cholinergic neurotransmission in the rabbit iris sphincter muscle. Rabbit iris sphincter muscle is innervated by trigeminal tachykininergic and parasympathetic cholinergic nerves, and the electrical transmural stimulation produces tachykininergic and cholinergic contractions. Cocaine and lidocaine (1-300 microM) attenuated tachykininergic and cholinergic contractions induced by electrical transmural stimulation in concentration- and stimulus frequency-dependent manner. However, the sensitivity to both local anesthetics was slightly, but significantly, higher in tachykininergic than in cholinergic responses. Exogenous neurokinin A and carbachol produced contractions that were not inhibited by 100 microM of cocaine and lidocaine. These results show that local anesthetics have a direct inhibitory effect on tachykininergic neurotransmission of the trigeminal sensory nerve, and the effect on this nerve is more potent than on the parasympathetic nerve and suggests that local anesthetics may have antineurogenic inflammatory effects via the inhibitory effects on the peripheral transmission of primary sensory nerve.

Peptidergic nerves in the eye, their source and potential pathophysiological relevance

Over the last five decades, several neuropeptides have been discovered which subsequently have been found to be highly conserved during evolution, to be widely distributed both in the central and peripheral nervous system and which act as neurotransmitters and/or neuromodulators. In the eye, the first peptide to be explored was substance P which was reported to be present in the retina but also in peripherally innervated tissues of the eye. Substance P is certainly the best characterized peptide which has been found in sensory neurons innervating the eye. Functionally, it has been shown to act trophically on corneal wound healing and to participate in the irritative response in lower mammals, a model for neurogenic inflammation, where it mediates the noncholinergic nonadrenergic contraction of the sphincter muscle. Over the last three decades, the interest has extended to investigate the presence and distribution of other neuropeptides including calcitonin gene-related peptide, vasoactive intestinal polypeptide, neuropeptide Y, pituitary adenylate cyclase-activating polypeptides, cholecystokinin, somatostatin, neuronal nitric oxide, galanin, neurokinin A or secretoneurin and important functional results have been obtained for these peptides. This review focuses on summarizing the current knowledge about neuropeptides in the eye excluding the retina and retinal pigment epithelium and to elucidate their potential functional significance.

Effect of chronic sciatic nerve lesion on the neurogenic inflammatory response in intact and acutely injured denervated rat skin

A supersensitivity to the neuropeptide substance P (SP) has been shown to develop in post-terminal membranes of many denervated tissues. This study examined changes in the sensitivity of post-terminal vascular receptors to SP and calcitonin gene-related peptide (CGRP) in rat skin microvasculature following sciatic nerve section. In anaesthetised rats, 0.5 cm of sciatic nerve in the right mid-thigh region was removed. Two weeks later, SP (100 microM) and sodium nitroprusside (SNP, 1 mM), a direct smooth muscle vasodilator, were introduced into denervated intact footpad skin, via the electrophoresis technique. Laser doppler flowmeter was used to record changes in relative blood flow in the rat hind footpad. The results showed a significant increase in SP response over controls and slight increase in smooth muscle reactivity as determined by an increase in the vascular response to SNP. In another set of experiments, the sensitivity of post-terminal receptors was examined over a 4 weeks period in an acutely injured footpad skin of sciatic nerve lesioned rats. A vacuum-induced blister was raised on the hind footpad and SP, CGRP (each at 1 microM) or SNP (100 microM) were superfused over the blister base. In nerve lesioned rats, using the acutely injured footpad skin model, the results showed a reduction in the vascular responses to SP, CGRP and SNP. The response to SP continued to decrease over time reaching 22% of control values by 4 weeks. Responses to SNP and CGRP were reduced to 53% and 45% respectively by 2 weeks and then improved to 75% of control values by 4 weeks. Possible contributions of sympathetic efferents and the saphenous nerve to these reduced responses in acutely injured skin of nerve lesioned rats were examined using guanethidine (50 mg/kg i.p.) or sectioned saphenous nerve respectively. These procedures did not significantly modify the reduced vascular responses in the blister base of lesioned rats. Possible activation of endogenous opioids and/or the release of endothelin due to blister induction in nerve lesioned rats was examined using naloxone and the endothelin receptor antagonist, BQ-123, respectively. Treatment with naloxone increased SP response in lesioned rats to 41% of control value with no change in smooth muscle reactivity. BQ-123 significantly increased the responses to SP and SNP to 51% and 100% of their own control values respectively. It is concluded that supersensitivity of post-terminal vascular receptors develops in intact skin following chronic nerve lesion. On the other hand, acute injury of the denervated skin area induces activation of endogenous inhibitory modulatory mechanisms that masks this supersensitivity.

Sensory nerves play an efferent role in the function of the arterioles, but not the dilator muscle, of the rat iris

We have studied the expression, distribution and function of receptors for the sensory neurotransmitters, substance P (SP) and calcitonin gene-related peptide (CGRP) in the dilator muscle and arterioles of the rat iris. Immunohistochemical studies showed that the sensory fibres containing these peptides are distributed throughout the connective tissue stroma of the iris and in association with the larger arterioles, but do not come into close association with the dilator muscle cells. Using reverse-transcription polymerase chain reaction, we have shown that both NK1 and NK3 receptor message is expressed by iris tissue, comprising both dilator muscle and stromal tissue. Binding sites for the NK1 agonist, [Sar9, Met(O2)11]-substance P (SarSP), and for CGRP are confined to the stromal layer and to the larger arterioles within that layer and do not appear to be associated with the dilator muscle itself. Application of either SarSP or CGRP produced both a vasodilatation and an inhibition of sympathetic nerve-induced vasoconstriction of the larger arterioles. Neither SarSP nor CGRP altered the resting tone of the dilator nor were they capable of modulating the contractions due to sympathetic nervous activity. These results suggest that the sensory fibres perform an efferent role in the larger irideal arterioles while their presence in the irideal stroma appears not to modulate the activity of the dilator muscle.

Investigation of the specificity of FK 888 as a tachykinin NK1 receptor antagonist

1. A recently described peptide tachykinin (NK1) receptor antagonist, FK 888, was found to inhibit the electrically-evoked, tachykinin-mediated contractile responses of the rabbit iris sphincter in a concentration-dependent manner; the pIC50 value was 6.6 +/- 0.08. 2. Contractions induced by a selective NK1 receptor agonist, [Sar9,Met(O2)11]substance P, were inhibited competitively by FK 888; the pKB value was 7.1. 3. FK 888 (1 nM-100 microM) was without effect on the electrically-evoked, cholinergic response of the rabbit iris sphincter and the electrically-evoked, sympathetic response of the guinea-pig vas deferens. The contractions of the rabbit iris sphincter, induced by either carbachol (10 nM-30 microM) or noradrenaline (0.1-100 microM), were not affected by 10 microM FK 888. 4. FK 888 (1-30 microM) did not induce histamine release from rat peritoneal mast cells. 5. FK 888 (33 and 333 microM) was without effect on the electrically-evoked action potentials of the frog sciatic nerve. Thus, FK 888 is a moderately high affinity and selective tachykinin (NK1) receptor antagonist.

Non-specific actions of the non-peptide tachykinin receptor antagonists, CP-96,345, RP 67580 and SR 48968, on neurotransmission

1. Three non-peptide tachykinin receptor antagonists, CP-96,345, RP 67580 and SR 48968, were found to inhibit the electrically-evoked, tachykinin-mediated contractile responses of the rabbit iris sphincter in a concentration-dependent fashion; the pIC50 values were 5.6 +/- 0.01, 5.4 +/- 0.07 and 4.8 +/- 0.03, respectively. 2. These antagonists also inhibited the electrically-evoked, parasympathetic response of the rabbit iris sphincter and the sympathetic response of the guinea-pig vas deferens in a concentration-dependent manner; the pIC50 values were 0.3-1.2 log units lower than those recorded for the tachykinin-mediated responses. 3. Two local anaesthetics, bupivacaine and oxybuprocaine, were also found to inhibit the tachykinin-mediated, cholinergic and sympathetic contractile responses in these tissues in a concentration-dependent manner; the concentration ranges for producing the inhibition were similar to those of the non-peptide tachykinin receptor antagonists. 4. On the sciatic nerves of frogs, the tachykinin receptor antagonists inhibited action potentials in a concentration-dependent manner; the potency of the three drugs was similar to that of bupivacaine. 5. Our results suggest that, in addition to blocking tachykinin receptors, the non-peptide tachykinin receptor antagonists, CP-96,345, RP 67580 and SR 48968, may exert non-specific inhibitory effects on neurotransmission.

Neurokinin A-stimulated phosphoinositide breakdown in rabbit iris sphincter muscle

Specific [3H]-substance P binding was saturable and of high affinity (KD = 2.5 nM) with a Bmax of 725 fmol/mg protein in the isolated rabbit iris sphincter muscle. The competition for [3H]-substance P binding was in the order of eledoisin greater than substance P greater than kassinin greater than neurokinin B greater than neurokinin A greater than physalaemin. In the same preparation, neurokinin A, as well as substance P induced a concentration-related accumulation of [3H]-inositol phosphates (IPs), and the maximum increase was about 200% of the control at 10(-4) M. [D-Arg1, D-Trp7,9, Leu11]-substance P (SP) and [D-Pro2, D-Trp7,9]-SP (10(-3) M) inhibited substance P or neurokinin A (10(-4) M)-induced phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis significantly. [D-Arg1, D-Pro2, D-Trp7,9, Leu11]-SP (10(-3) M) also inhibited neurokinin A (10(-4) M)-induced PIP2 hydrolysis significantly. Neurokinin A and substance P produced concentration-related contractions in normal Ca(2+)-containing medium. The contractile response was weaker in Ca(2+)-free medium, and there was no response in 0.2 mM EGTA medium. In Ca(2+)-free medium, the basal level of [3H]-IPs accumulation was smaller than that in normal medium, and neurokinin A and substance P significantly increased PIP2 hydrolysis. In the 0.2 mM EGTA containing medium, neurokinin A and substance P did not stimulate the PIP2 hydrolysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Elevated levels of substance P in intraocular fluid in proliferative vitreoretinopathy

Proliferative vitreoretinopathy is the most common reason for failure in retinal reattachment surgery. Since both substance P (SP) and SP receptors were found to be present in the human eye, and as pharmacological studies suggest an importance of SP for ocular functions, we investigated intraocular fluids for the presence of SP in eyes elected for cataract surgery, retinal detachment surgery and retina surgery for severe proliferative vitreoretinopathy (PVR) as well as in eyes with proliferative diabetic retinopathy (PDR). High performance liquid chromatography and radioimmunoassay (RIA) for SP immunoreactivities were performed. The SP mean concentration in intraocular fluid (IOF) of patients for cataract surgery (CS) was 2.2 fmol/ml, for retinal detachment (RD) was 2.7 fmol/ml and for PDR was 1.9 fmol/ml; significantly higher levels (mean concentration of 26.9 fmol/ml) were measured in eyes with PVR. HPLC analysis revealed two immunoreactive peaks coeluting with synthetic SP and SP-sulfoxide, indicating that RIA values represent authentic SP. We conclude that SP may play an important role in PVR. Since SP antagonists are known to inhibit a variety of SP effects in the eye, there might be a useful tool to reveal the importance of SP in this disease and, in this instance, a new possible treatment.

Serotonin and migraine

Migraine has long been considered as a "vascular headache" but clearly neurological mechanisms are involved. The pathophysiology appears to somehow involve serotonin, both peripherally and centrally, but its involvement may be just epiphenomenal. Adding to the enigma it is apparent that many of the presently available drugs for the treatment of migraine interact in one way or another with serotonin receptors. However, they tend to have a number of other unrelated actions and they are only of limited clinical value. Interestingly a promising new drug for the treatment of the acute attack, sumatriptan, has a very selective action as an agonist at a specific 5-HT1-like receptor sub-type, mediating vasoconstriction, which is localized on cranial blood vessels. Its action may, or may not, be independent of any involvement of serotonin in the genesis of migraine. Hopefully though, current attempts to determine sumatriptan's mechanism of action will shed further light on the pathology of migraine itself and the putative involvement of serotonin.

Autoradiographic analysis of binding sites for 125I-Bolton-Hunter-substance P in the human eye

Substance P is known to exert potent effects in peripheral tissues, and is thought to be important for ocular function. The mechanism of action of substance P in the human eye is not known. As a basis for biochemical characterization specific binding of 125I-Bolton-Hunter-substance P was demonstrated in the human eye using autoradiographic methods. Biochemical characterization on slide-mounted tissue preparations showed that binding was saturable with a KD of 0.27 +/- 0.1 nmol/l. Specific binding occurred at comparable autoradiographic densities to both human retina and choroid. Substance P and its carboxyterminal fragment, substance P(3-11), were shown to be highly potent in binding competition experiments against 125I-Bolton-Hunter-substance P. Similar concentrations of substance P(1-9), neurokinin A and neurokinin B failed to significantly alter specific binding of 125I-Bolton-Hunter-substance P. The results indicate expression of high affinity substance P binding sites in human retina and choroid.

Muscarine receptor types mediating autoinhibition of acetylcholine release and sphincter contraction in the guinea-pig iris

The potencies of several muscarine receptor antagonists in blocking either the autoinhibition of acetylcholine release or the muscarinic contraction of the sphincter muscle upon acetylcholine release were investigated in the guinea-pig iris. The agonist at pre- or postjunctional muscarine receptors was acetylcholine released upon field stimulation (5.5 Hz, 2 min) of the irides preloaded with 14C-choline. The stimulation-evoked 14C-overflow was doubled in the presence of atropine 0.1 mumol/l but unaffected by the agonist (+/-)-methacholine (50 mumol/l). Thus, under the present stimulation conditions, the autoinhibition of acetylcholine release on the guinea-pig iris cholinergic nerves was nearly maximally activated. Isotonic contractions of the irides upon field stimulation consisted of a rapid, atropine (0.1 mumol/l)-sensitive peak phase followed by a sustained contraction which involved a cholinergic and a non-cholinergic stimulation of the sphincter muscle. The M2-selective antagonists methoctramine (10 mumol/l) and gallamine (100 mumol/l) increased both the 14C-overflow and the peak contractions evoked by field stimulation. In contrast, the M3-selective antagonist hexahydrosiladifenidol (0.1-10 mumol/l) failed to affect the evoked 14C-release but concentration-dependently (1-10 mumol/l) reduced the iris contractions. Pirenzepine (10 mumol/l) enhanced the evoked 14C-overflow and inhibited the peak contractions (0.1-10 mumol/l; maximal effect at 10 mumol/l). The low potency of the antagonist at both receptor sites indicates that an M1 muscarine receptor is not involved. The results are consistent with the idea of M2 muscarine receptors mediating autoinhibition of acetylcholine release in the guinea-pig iris and M3-like receptors inducing the contraction of the sphincter muscle.

Blockade of sensory nerve mediated contraction of the rabbit iris sphincter by a series of novel tachykinin antagonists

Electrical stimulation of the isolated rabbit iris sphincter muscle in the presence of atropine gives rise to a contraction that can be blocked by tachykinin antagonists. The ability of a series of novel tachykinin antagonists to inhibit the contractile effect of SP on the guinea-pig taenia coli and to suppress the electrically evoked contraction of the atropinized rabbit iris sphincter was tested. Several of the novel antagonists were found to be more potent in terms of pA2 and pIC50 values than the two previously described analogs, [D-Pro2, D-Trp7,9]SP9(1-11) and [D-Arg1, D-Trp7,9, Leu11]SP-(1-11) (Spantide). Apart from D-Trp in positions 7 and 9 the characteristic features of the potent novel antagonists were D-Cl2Phe (or D-Cys(Bzl] in position 5, Asn in position 6 and Nle in position 11. In addition Pal in position 3 seemed to offer an enhanced potency.

Capsaicin-induced inhibition of motility of the rat isolated vas deferens: do multiple neuropeptides mediate the visceromotor effects of capsaicin?

1 The effects of capsaicin have been investigated in the field-stimulated (0.1 Hz) or unstimulated rat isolated vas deferens and compared with those of some neuropeptides (neurokinins, calcitonin gene-related peptide (CGRP) putatively stored in capsaicin-sensitive sensory fibres. 2 Capsaicin (0.01-3 microM) produced a concentration-related transient inhibition of the field-stimulation-induced twitches. This effect was characterized by marked desensitization and could not be elicited in preparations excised from capsaicin-pretreated rats (50 mg/kg s.c., 4 days before). The amplitude of the nerve-mediated twitches was unaffected by capsaicin-desensitization. 3 Neurokinins (substance P, Kassinin) produced a potentiation of the nerve-mediated contractions while CGRP had a potent inhibitory effect. In the presence of Kassinin, CGRP still inhibited twitches although the time course of this inhibitory effect was delayed as compared to controls. 4 In the unstimulated rat vas deferens neither capsaicin (3 microM) nor CGRP (0.1 microM) had any significant motor effect. However, when phasic contractions were initiated by previous exposure to Kassinin (0.2 microM), both capsaicin (3 microM) or CGRP (10-100 nM) had a prompt inhibitory effect. Capsaicin inhibition exhibited a marked desensitization while the effect of CGRP was still evident after capsaicin-desensitization. 5 The inhibitory effect of capsaicin or CGRP on the Kassinin-stimulated rhythmic contractions of the rat isolated vas deferens was unaffected by a previous exposure to tetrodotoxin (0.5 microM). 6 Storage at 4 degrees C for 24 h produced a 65% reduction of the response of the rat isolated vas deferens to nerve-stimulation. The residual response was tetrodotoxin-sensitive and could be potentiated by Kassinin (0.2 microM) or inhibited by CGRP (10-100 nM) as observed in controls. In these preparations the inhibitory effect of capsaicin (3 microM) was significantly reduced (approximately equal to 50%) and in some preparations abolished, as compared to controls. 7 These findings indicate the existence, in the rat isolated vas deferens, of capsaicin-sensitive sensory innervation which, upon chemical stimulation, releases, through a tetrodotoxin-insensitive mechanism, a substance(s) which inhibits motility at postjunctional level. CGRP is a possible candidate for the role of inhibitory sensory transmitter released from capsaicin-sensitive nerve endings in this preparation.

Comparison of the responses to the sensory neuropeptides, substance P, neurokinin A, neurokinin B and calcitonin gene-related peptide and to trigeminal nerve stimulation in the iris sphincter muscle of the rabbit

Three mammalian tachykinins (substance P, neurokinin A and B) and two non-mammalian ones (eledoisin and physalaemin) produced potent contractions of the isolated rabbit iris sphincter muscle. The rank order of potencies was eledoisin greater than neurokinin B = physalaemin greater than substance P greater than neurokinin A. The maximum efficacy was much the same. The contractile responses to neurokinin A and eledoisin developed more rapidly than did those to the other tachykinins used and were selectively attenuated by [D-Arg1, D-Pro2, D-Trp7,9, Leu11]-SP. Electrical transmural stimulation produced a contraction consisting of cholinergic and tachykininergic components. The tachykininergic component was abolished by pretreatment with capsaicin or by trigeminal denervation (Fujiwara et al., 1984). [D-Arg1, D-Pro2, D-Trp7,9, Leu11]-SP attenuated the tachykininergic component, but not the cholinergic one. KCl and capsaicin also produced a tachykininergic contraction which was inhibited by [D-Arg1, D-Pro2, D-Trp7,9, Leu11]-SP. Calcitonin gene-related peptide affected neither the iris sphincter muscle nor the response to electrical transmural stimulation. These results suggest that the tachykininergic responses induced by electrical transmural stimulation, KCl and capsaicin are predominantly mediated by neurokinin A, probably released from the peripheral endings of trigeminal nerves.

Improved photographic assessment of the pupils in the syndromes of Horner and Holmes-Adie

The use of photographic methods to assess pupillary abnormalities has usually been restricted to the measurement of anisocoria in light and darkness. An improved, accurate and relatively inexpensive photographic technique of recording pupillary movement was described, and tested in normal individuals and in the Horner and Holmes-Adie syndromes. A modern SLR camera, preprogrammable for exposure frequency and interval, was used for serial flash-lit photographs of the eyes during the course of darkness and near vision/accommodation reflexes. Measurement of pupillary diameter from these photographs permitted graphs of pupillary reflexes to be drawn that resemble traces obtained by other authors, who used less readily available and cumbersome cinematographic and electronic infra-red pupillometric methods. In Horner's syndrome, the affected pupil was invariably smaller, and the anisocoria was more marked in bright light or darkness, depending on the individual. The rate of dark mydriasis was abnormally slow, and most effectively quantified by measuring the pupillary 'half opening time', which was the interval required for the initial 50% of dark-induced pupillary dilatation. Constriction of tonic pupils during near vision/accommodation in subjects with the Holmes-Adie syndrome was consistently slow, and these pupils also failed to dilate fully in darkness. The amplitude of the darkness and near vision accommodation reflexes correlated significantly. The diverse pathophysiological mechanisms implicated by these changes were discussed.

Levels of neurokinin A, neurokinin B and substance P in rabbit iris sphincter muscle

We investigated the contents of neurokinin A, neurokinin B and substance P in the rabbit iris sphincter muscle, combining HPLC and radioimmunoassay, as our previous reports indicated that a slow component of neurogenic contractions of this muscle is most probably mediated by such tachykinins. The concentrations of these tachykinins were 44.3 +/- 8.7 fmol/mg protein, 35.3 +/- 10.2 fmol/mg protein and 186.8 +/- 29.8 fmol/mg protein (N = 4), respectively. These results demonstrated that neurokinin A, neurokinin B and substance P are all present in the rabbit iris sphincter muscle.

Trigeminal antidromic vasodilatation and plasma extravasation in the rat: effects of sensory, autonomic and motor denervation

The cutaneous vasodilatation and plasma extravasation observed following antidromic stimulation of trigeminal sensory branches in the rat are reduced by atropine. The atropine-sensitive component does not originate from the seventh cranial nerve (facial nerve) or from the mental nerve, because after chronic section of these nerves an atropine-sensitive component persists. The cholinergic component of the plasma extravasation is abolished by chronic bilateral extirpation of the superior cervical ganglia but this is not the case for the vasodilatation. Our data suggest that trigeminal sensory fibres are not the only fibres involved in these vascular responses seen in the lower lip of the rat after electrical stimulation of the mental nerve.

Effects of the substance P antagonist [D-Arg1,D-Pro2,D-Trp7,9,Leu11]SP on miosis caused by echothiophate iodide or pilocarpine hydrochloride

The anticholinesterase agent echothiophate iodide (EI) and the cholinergic agent pilocarpine hydrochloride (pilocarpine), drugs commonly used in glaucoma therapy, cause miosis in rabbits as well as in man. In rabbits the miotic effect decreases after a few days of treatment, a phenomenon possibly due to a drug-induced decrease in the number of muscarinic receptors. However, the muscarinic pupillary contraction caused by stimulation of the retina with light is intact. In this investigation the miosis caused by the doses of EI was found to be very resistant to muscarinic or nerve blockade but inhibited by the substance P (SP) analog [D-Arg1,D-Pro2,D-Trp7,9, Leu11]SP, which seems to be a SP/SPLI blocker in the rabbit pupillary sphincter. Miosis caused by pilocarpine was partly inhibited by muscarinic blockade and partly by the SP blocker. In eyes treated with EI topically twice daily for three weeks, SP or the red pepper extract capsaicin, a releaser of SP-like immunoreactivity (SPLI), had less miotic effect than in control eyes. Capsaicin caused more pronounced miosis in eyes treated with topical pilocarpine for three weeks than in controls. The radioimmunoassay technique did not reveal a significant change in the amount of SPLI in the retinas or iris-ciliary bodies from EI-treated eyes as compared with the controls. It is concluded that, besides cholinergic miosis, EI causes non-muscarinic miosis, probably by release of SP or a related substance and that pilocarpine may have similar effects.

Prostaglandins enhance trigeminal substance P-ergic responses in the rabbit iris sphincter muscles

Contractile responses due to substance P released from the trigeminal nerve were observed after electrical transmural stimulation or exogenous application of bradykinin in the isolated rabbit iris sphincter muscle. Prostaglandins, particulary prostaglandin E1, enhanced and indomethacin inhibited these substance P-ergic responses. Since the responses to exogenously applied substance P were neither affected by prostaglandins nor indomethacin, it was suggested that prostaglandins acted presynaptically to enhance the release of substance P from the trigeminal nerve terminals.