Adrenergic innervation of cat iris sphincter

Effect of timolol maleate gel-forming solution on intraocular pressure, pupil diameter, and heart rate in normal and glaucomatous cats

OBJECTIVE

To determine the effects of once-daily topical treatment with timolol maleate gel-forming solution (GFS) on intraocular pressure (IOP), pupil diameter (PD), and heart rate (HR) in normal cats and cats with feline primary congenital glaucoma (FCG).

ANIMALS STUDIED AND PROCEDURES

A single drop of timolol maleate 0.5% GFS was administered topically to one randomly assigned eye of 18 adult cats (8 normal, 10 FCG) at 8 am for 8 days; the opposite eye served as the untreated control. IOP was measured in both eyes (OU) every 2 h (PD and HR were measured every 4 h), for 14 h total, 1 day prior to and on days 1 and 8 of treatment. In a second treatment phase, a single drop of timolol was administered at 8 pm for 3 nights and IOP, PD, and HR were measured, as above, beginning at 8 am on day 4. Slit-lamp examinations were conducted prior to and after treatment phases. Comparisons of mean IOP, PD, and HR were made at each time point and between treated and untreated eyes by repeated-measures ANOVA and Tukey-Kramer post hoc test, with P < 0.05 considered significant.

RESULTS

Timolol maleate 0.5% GFS had an inconsistent effect on IOP, with maximum IOP-lowering effect (mean = 5.6 mmHg, 17.4%) observed 6 h post-treatment in FCG. The drug caused significant miosis (from 4 to 8 h post-treatment), but had no effect on HR.

CONCLUSION

Once-daily application of timolol maleate 0.5% GFS may be of limited clinical benefit in the management of feline congenital glaucoma.

Action of biologically active peptides on monkey iris sphincter and dilator muscles

Biologically active peptides modulate pupillary responsiveness in many non-primate mammals. We examined the action of seven different peptides on iris sphincter and dilator muscles of rhesus monkey. Iris sphincter and dilator muscle preparations from rhesus monkeys were mounted in an organ bath, and tension changes were recorded by an isometric transducer. Electrical field stimulation (100Hz, 0.3 msec, 10V) was applied through a pair of platinum plate electrodes. Monkey iris sphincter and dilator muscles produced simple cholinergic and adrenergic excitatory responses respectively to electrical field stimulation. Strong field stimulation did not elicit slow Substance P (SP) mediated contractions like those in rabbit iris sphincter. Exogenously applied pituitary adenylate cyclase-activating peptide (PACAP) enhanced in a concentration-dependent manner (0.3 nM-0.1 microm) the sphincter response to field stimulation, while neuropeptide Y (NPY) and somatostatin (SRIF) attenuated it. These three peptides did not affect sphincter contractions induced by acetylcholine, and therefore were acting at presynaptically. SP, calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP) and galanin (GAL) had no effect (at 0.1 microm) on iris sphincter. None of seven exogenously applied peptides had an effect on monkey iris dilator muscle. The innervation of primate irises may be relatively simple compared to non-primates because each of the peptides in this study can modulate miosis or mydriasis in non-primate mammals. Future studies will be expected on the functional significance of species differences in iridial innervation.

Nonhypotensive autonomic agents in veterinary ophthalmology

The parasympathetic and sympathetic divisions of the autonomic nervous system are involved in homeostatic control of a wide variety of ocular functions, including accommodation, pupillomotor control, lacrimation, eyelid position, and aqueous humor production. Familiarity with the functional anatomy of the autonomic nervous system is paramount to the understanding and application of the large number of autonomic drugs used in veterinary ophthalmology. The cholinergic and adrenergic agents discussed in this article are commonly employed to facilitate routine ophthalmic examination, in the diagnosis of autonomic dysfunction, and in the treatment of a variety of ocular diseases.

Increased firing of neurons in the posterior hypothalamus which precede classically conditioned pupillary dilations

Paralyzed cats were used as subjects in a classical conditioning experiment where each subject was exposed to 40 explicitly unpaired 1-s bursts of white noise and 0.5-s paw shocks. This training was followed by 60 trials of the two stimuli paired, where the white noise immediately preceded the paw shock. Following this training, the subjects were re-exposed to 40 trials of the explicitly unpaired procedure. The pupil was monitored as the behavior and electrodes implanted in the thalamus, the dorsal hypothalamus and the posterior hypothalamus recorded the activity of clusters of cells. Only the cells in the posterior hypothalamus showed robust changes in firing rates that preceded the pupillary behavior, both (a) on any particular trial and (b) as the learned association was being demonstrated behaviorally across trials.

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.

Development of a functional innervation of the iris dilator muscle by sympathetic nerve fibres in the rat

These studies using both in situ and in vitro preparations were designed to determine the time of onset of a functional sympathetic innervation to the dilator muscle of the rat iris during postnatal development. The preganglionic nerve trunk to the superior cervical ganglion was stimulated and measurements made of pupil diameter. Alternatively, intracellular recordings were made from the dilator muscle cells and the response to stimulation of the intramural nerves was measured. During the second postnatal week, a decrease in the resting pupil diameter under low lighting conditions was observed, reflecting the normal developmental increase in size of the iris. On account of the small size of the iris in rats up to 10 days postnatal, the in vivo experiments were a reliable test of a functional innervation only in older animals. In all cases, stimulation of the preganglionic nerve trunk in situ caused dilatation of the pupil. Stimulation of the sympathetic nerves in vitro, in preparations of iris taken from rats of various ages, evoked a slow depolarisation mediated via alpha adrenoceptors. Such responses could be recorded in irides from rats as young as 3 days postnatal. Spontaneous activity was recorded in irides towards the end of the second postnatal week just prior to the time of normal eye opening, and may reflect the onset of photomechanical coupling. We conclude that the sympathetic nerves within the iris are capable of evoking membrane potential changes in the dilator muscle cells in the early postnatal period, well before the nerve plexus in the iris is fully differentiated.

The midbrain reticular formation as an integration center for the 'near reflex' in the cat

This report describes an experimental study on the localization of converging organization of the near-reflex triad in the chloralose-anesthetized encéphale-isolé cat, in which electromyographic (EMG) recordings were used to elicit responses from the intrinsic and extrinsic eye muscles. Electrical stimulation to several subdivisional areas in the oculomotor nuclear complex evoked EMGs in both the iris sphincter and ciliary muscles. Conduction time from the caudal Edinger-Westphal nucleus to the postganglionic ciliary nerve was about 1.8 ms, whereas that to the iris sphincter muscle was about 6.5 ms. Conduction time from the anteromedian nucleus to the muscle was about 4.5 ms; however, that from the postganglionic short ciliary nerve to the muscle was about 6.7 ms. A direct pathway without synapse in the ciliary ganglion is suggested. Excitatory responses were elicited in the effectors of the near-reflex triad by electrical stimulation of the midbrain reticular formation of the dorsomedial division adjacent to the magnocellular red nucleus (MRFdmMRN). Converging movements in electro-oculography (EOG) were also observed. Conduction time from the MRF to the iris sphincter muscle was about 5.6 ms, whereas that to the postganglionic short ciliary nerve was 5.1 ms. The neural connection between the MRF and the muscle is thought to be mediated by the anteromedian subnucleus. Electrical stimulation of the posteromedial division of the Clare-Bishop (C-B) area evoked a discharge on the MRF and EMGs of all effectors of the triad. The sum of the conduction time from the C-B area to the MRF and that from the MRF to EMGs corresponds well to the latency of EMGs evoked by C-B area stimulation. We conclude that the MRFdmMRN is the supranuclear organization which converges the sensory-motor cortical activities on the precise linkage of the near-reflex triad and becomes an integration center for each nucleus in the oculomotor nuclear complex.

Functional innervation and contractile properties of the human iris sphincter muscle

To investigate the pattern of innervation and the contractile properties of human iris sphincter muscle, we have observed the effects of field stimulation, various drugs and excess-K+ solutions on isometric tension development in strips of the iris sphincter from five humans. Spontaneous mechanical responses were not observed in these tissues. Electrical field stimulation (50 V, 0.8 msec, 20 Hz) evoked a contraction which was abolished by 10(-7) M tetrodotoxin (TTX) or by 10(-6) M atropine, thereby indicating that the response was cholinergically mediated. In the presence of atropine, electrical field stimulation did not affect muscle tone, even when this was elevated by histamine. The effect of exogenously applied noradrenaline (NA) varied among the specimens, i.e. in three out of four cases a contraction was evoked while a relaxation occurred in one preparation. The contraction evoked by NA was blocked by phentolamine (10(-6) M) and the relaxation was blocked by timolol (10(-6) M). Excess-K+ solutions, dose dependently contracted the muscle strips and application of 10(-6) M atropine decreased the amplitude of these contractions. The results indicate that the human iris sphincter is innervated by excitatory cholinergic nerve fibres and that the adrenergic innervation is sparse. In addition, this muscle possesses both alpha and beta adrenoceptors. Activation of alpha receptors produces a contraction whilst activation of the beta adrenoceptors causes relaxation.

The effects of yohimbine on presynaptic and postsynaptic events during sympathetic nerve activation in cattle iris: a critique of presynaptic receptor theory

1 The effects of presynaptic alpha-adrenoceptor blockade on both the efflux of 3H-transmitter and on the magnitude of the effector response were measured simultaneously in a smooth muscle preparation which responds to field stimulation with noradrenergic beta-receptor-mediated relaxation. 2 In the presence of atropine, the circular muscle of cattle iris relaxes in response to noradrenaline and to field stimulation at 2 Hz with 10, 20, 50 and 100 pulses. 3 Yohimbine (3 x 10(-6) M), a potent presynaptic alpha-adrenoceptor antagonist, increased the stimulation-induced efflux of tritium to about 2.0 times control values and, contrary to theory, did so to a similar extent regardless of pulse number and with apparent indifference to the synaptic concentration of transmitter, as confirmed by the varying size of the postsynaptic response. 4 In most cases, yohimbine had no significant effect on the magnitude of the relaxations to nerve stimulation. 5 It is concluded that negative feedback regulation of transmitter release, if it functions at all, and this itself seems doubtful, would not have a substantial impact on the size of the effector response.

Substance P-like immunoreactive nerves in the anterior segment of the rabbit, cat and monkey eye

The indirect immunofluorescence technique demonstrates a substance P-like immunoreactive innervation to the anterior segment of the rabbit, cat and monkey eye. In all three species there is a sparse, but definite, corneal innervation. For the rabbit, substance P-like immunoreactive nerves to the aqueous outflow apparatus are found chiefly in the pectinate ligament. In the cat, this innervation is somewhat more extensive, being seen in the septae of the ciliary cleft as well. The monkey has a more plentiful innervation to the outflow apparatus than either the cat or the rabbit. Substance P-like immunoreactive nerves are visible in the trabecular meshwork and at the inner and outer walls of Schlemm's canal. For all three animals, the iris contains immunoreactive nerve fibers to the sphincter muscle, to the large blood vessels and to the anterior stromal melanocytes. In the ciliary body, the ciliary processes receive a constant innervation; it is somewhat more dense in the rabbit. Some of the large ciliary body blood vessels also are innervated. Ciliary body melanocytes are innervated; it was not possible to determine whether or not immunoreactive fibers innervate the ciliary muscle cells as well. The present study extends prior knowledge of the innervation of the eye. Taken with the known physiologic effects of substance P, it indicates a series of potential roles for this peptide in the vegetative processes of the eye.

Histochemical study of the postnatal development of autonomic nerves in the mouse iris, using a whole-mount preparation method

Postnatal development of autonomic nerves in the mouse iris was studied histochemically from one day to five months of age. For the demonstration of aminergic nerves the glyoxylic acid method was used, while for cholinergic nerves, Karnovsky and Roots' method was utilized on the whole-mount preparations of irises. The results obtained were as follows. In one-day-old mice, many aminergic nerves could already be seen, while cholinergic nerves were scarcely observable. Both types of nerve increased rapidly in the first 2 weeks. Both completed development between 3 and 4 weeks, although aminergic nerves were observed to develop earlier than the cholinergic.

Differentiation of alpha-adrenergic responsiveness in the neonatal rat iris after decentralization or extirpation of the superior cervical ganglion

The effects of stimulating alpha-adrenergic receptors in the iris of neonatal rats (up to 30 days of age) whose superior cervical ganglion (SCG) has been decentralized or extirpated 3 days after birth were investigated by measuring changes in pupil diameter. The responses of these experimental animals were compared with those of normal animals of similar age. Alpha-adrenergic stimulation was effected by topical application of noradrenaline (NA) after blockade of beta-adrenoceptors with dichlorisoproterenol and cholinoceptors with atropine. The results reveal that although decentralization of the SCG depletes the NA content of the ipsilateral iris as demonstrated by radio-chemical assay and formaldehyde-induced fluorescence, it does not affect the development of alpha-adrenoceptor responsiveness. Even the more severe disruption of the innervation caused by extirpation of the SCG did not affect the responsiveness of the ipsilateral iris.

Mechanisms of inactivation of noradrenaline in the iris sphincter, tracheal muscle and facial artery of cattle: implications for beta-adrenoceptor-mediated responses

1 The role of neuronal and extraneuronal pathways of amine inactivation in regulating the inhibitory actions of noradrenaline was investigated in three bovine smooth muscle preparations in which the primary adrenoceptor is of the beta-type.2 The extraneuronal uptake inhibitor, 17beta-oestradiol, sensitized the inhibitory responses to noradrenaline in the facial artery, the iris sphincter and in tracheal muscle preparations, indicating a major role for non-neuronal processes in agonist-inactivation in all three preparations. Cocaine also increased responses to noradrenaline, pointing to a role for neuronal uptake either as a terminating mechanism or as a process limiting access of exogenous agonist molecules to their site of action.3 Cocaine did not enhance significantly responses to isoprenaline, a potent beta-adrenoceptor agonist which is not taken up neuronally. Further, relaxations to metaraminol, a sympathomimetic amine which is taken up extraneuronally, but much less so than noradrenaline, were also less enhanced by 17beta-oestradiol in the three preparations tested. These findings support the specificity of action of cocaine and 17beta-oestradiol as neuronal and extraneuronal uptake inhibitors in the present experiments.4 Studies of the uptake of [(3)H]-noradrenaline revealed that 17beta-oestradiol reduced the uptake of amine in the presence of cocaine, confirming a cocaine-resistant site of action for the steroid in all three preparations.5 It is concluded that extraneuronal uptake sites are located sufficiently close to the beta-adrenoceptors to modulate the concentration and duration of action of noradrenaline at these sites of action. It is proposed that in smooth muscles which contain a preponderance of beta-receptors, extraneuronal metabolism is a key event in terminating the inhibitory effects produced.

Specificity of innervation of iris musculature by sympathetic nerve fibres in tissue culture

Irides from 3-5 day old rats have been grown 1-3 mm from superior cervical or lumbar paravertebral sympathetic ganglia in modified Rose chambers. The two muscles of the iris received distinctly different innervation patterns in vitro, and these were similar to those seen in vivo. Varicose, adrenergic fibres were consistently associated with the dilator pupillae rather than with the sphincter pupillae while excitatory, cholinergic junctions developed between the nerve fibres and the muscle cells of the spincter but not the dilator. There was a lack of specificity shown by the sympathetic neurons during this innervation. Fibres from lumbar ganglia formed plexuses within the dilator similar to those formed by superior cervical fibres, and sympathetic, cholinergic fibres were able to substitute for the normal parasympathetic, cholinergic fibres in the sphincter.

Potentiation by prostaglandins e1, e2, and f2alpha of the contraction response to transmural stimulation in the bovine iris sphincter muscle

The contraction response to transmural stimulation in the bovine iris sphincter muscle was abolished by atropine but was left virtually unchanged by hexamethonium, and by adrenergic neuron and receptor blockers, indicating activation of postganglionic cholinergic nerve fibres. Low doses of prostaglandins e1, e2 and F2alpha (0.1-5.3 ng/ml) consistently and apparently in a dose-dependent manner enhanced the contraction response to transmural stimulation. Prostaglandins E1 and E2 were equipotent while F2alpha was at least 10 times less active. Within the same dose range the prostaglandins also enhanced the contraction response to exogenous acetylcholine, indicating that part of the enhancing effect of the prostaglandins on neuromuscular transmission was due to a postjunctional action. A spontaneous increase in tone of the preparation commonly occurred about 1 h after the beginning of the experiment. SC 19220, a potent antagonist of prostaglandin action, reduced the tone and the contraction responses as well as the enhancing effect of the prostaglandins. It is concluded that prostaglandins might serve the function of controlling neuroeffector transmission and muscular tone in the sphincter muscle of the bovine iris.

Changes in the physiology and fine structure of the taenia of the guinea-pig caecum following transplantation into the anterior eye chamber

1. The taenia of the guinea-pig caecum has been used as a model to study the re-establishment of autonomic innervation following transplantation into the anterior eye chamber. The ultrastructure, the histochemical localization of noradrenaline and acetylcholinesterase and the pharmacology of transmission to the taenia have been examined 1 day to 16 weeks following transplantation. Both ganglion-free strips of the taenia and caecal wall segments including the underlying Auerbach's plexus were used.2. Caecal wall preparations: nerve fibres from intramural ganglion cells retracted during the first 2 days following transplantation, but reappeared in the muscle soon afterwards. Adrenergic nerves from the iris formed terminals about ganglion cells at about 2-4 weeks. Both cholinergic excitatory and non-adrenergic (;purinergic') inhibitory transmission to the muscle was re-established by 2-4 days following transplantation.3. Taenia strip preparations: both adrenergic and cholinergic nerve fibres were demonstrated histochemically in muscle bundles by 2-4 weeks. Non-adrenergic inhibitory and cholinergic transmission was not re-established until 2-4 weeks following transplantation. There was an abnormally dense re-innervation of the muscle by adrenergic nerve fibres by about 8 weeks which is compared with the innervation of aganglionic bowel in Hirschsprung's disease.4. The origin of non-adrenergic inhibitory responses in the transplanted taenia is discussed and the results considered in relation to the re-innervation of transplants of the vas deferens and of intestine during early development.