The role of the autonomic nervous system in extraocular muscle function

Transcription

1 The role of the autonomic nervous system in extraocular muscle function Kenneth E. Eakins and Ronald L. Katz The purpose of this study was to determine the possible role of the autonomic nervous system in the function of mammalian extraocular muscle. Experiments were carried out on the cat anesthetized with pentobarbital. Stimulation of the cervical sympathetic nerve and the injection of epinephrine increased the tension of the superior rectus muscle. These responses were unaffected by sympathetic ^-receptor blocking agents, potentiated by cocaine, and antagonized by sympathetic a-receptor blocking agents. Similar results were observed with the nictitating membrane. The superior rectus muscle and nictitating membrane differed in that atropine blocked the response of the nictitating membrane to epinephrine, but not that of the superior rectus muscle. The implications of these remits are discussed..he histological observations of Boeke 1 and Wolter 2 indicating that the striated muscle fibers of extraocular muscles have a double innervation, motor and autonomic, led Alpern and Wolter 3 to advance the view that the slow vergence movements of the eye were under autonomic control. This aspect of the control of extraocular muscle activity has since received little scientific attention. For this presentation, I would like to deal exclusively with some results we have obtained in our laboratory concerning the effect of cervical From the Departments of Ophthalmology Research and Anesthesiology, College of Physicians and Surgeons, Columbia University, New York, N. Y. Supported by Fight-for-Sight Grant-in-Aid G 303- C-2-C3 of the National Council to Combat Blindness, Inc., New York, and United States Public Health Service National Institutes of Health Grant GM Figs. 1, 2, 5, 6, and 7 are reprinted from and with the permission of The Journal of Pharmacology and Experimental Therapeutics. In press. 253 sympathetic stimulation and systemically administered epinephrine on extraocular muscle tension. No attempt will be made to assess the relative importance of the role of the parasympathetic nervous system in extraocular muscle function at this stage, except to point out that we have repeatedly observed in our laboratory that the contracture of the extraocular muscle produced by acetylcholine is unaffected by atropine, which would seem to preclude the involvement of parasympathetic muscarinic receptors in the response. In an earlier study, 4 we observed that the intravenous injection of epinephrine in the cat resulted in a small but fairly wellmaintained contracture of the superior and lateral rectus muscles. This observation was of interest to us in that, as long ago as 1930, Duke-Elder and Duke-Elder 1 had drawn attention to the fact that mammalian extraocular muscles behave in many respects like denervated mammalian'skeletal muscle; for example, both the external muscles of the eye and chronically denervated leg muscles respond to acetylcholine with

2 254 Eakins and Katz Investigative Ophthalmology June 1967 a contracture, and, in contrast to the lack of effect of sympathetic amines on normal peripheral skeletal muscle, these compounds will produce a slowly developing reversible increase in resting tension several weeks after section of the motor nerve. Bowman and Raper in 1965 reported that the response of the chronically denervated tibialis anterior and soleus muscles of the cat to epinephrine corresponded on AhlquistV 1948 classification to a sympathetic /3-receptor effect since it was selectively blocked by sympathetic /3-receptor, but not by a-receptor antagonists. In this presentation, we will describe some experiments that we have carried out to determine whether the increased tension of extraocular muscles observed after systemic administration of epinephrine represents yet another similarity between extraocular and chronically denervated skeletal muscle. We have examined the response of the superior rectus muscle of the cat to epinephrine and sympathetic stimulation and its modification by a variety of agents. In addition, we determined the response of the nictitating membrane under these conditions to monitor the behavior of the orbital smooth muscle. Methods Cats of either sex, weighing between 2.5 and 3.5 kilograms, were used in these experiments. The animals were anesthetized with sodium pentabarbital (36 mg. per kilogram) given by intraperitoneal injection. The trachea was cannulated and artificial respiration employed. Arterial blood pressure was recorded from the right femoral arteiy with a Statham (P23Db) pressure transducer coupled to a Grass Model 5 ink-writing polygraph. The superior rectus of one eye was separated from the globe and a suture placed through the tendon, the thread then being connected to a Grass force displacement transducer (FT-03). Contractions of the ipsilateral nictitating membrane were recorded by a similar force displacement transducer. The animal's head was immobilized in a stereotaxic apparatus. The cornea of the test eye was incised and the eyeball eviscerated and ligatured. Intra-arterial injections were made via a polyethylene cannula inserted into the ipsilateral common carotid artery. Intravenous injections were made via a cannula inserted into the left femoral vein. Nerve stimulation. For preganglionic stimulation, the sympathetic trunk was cut just above the sternum and laid on a pair of silver electrodes. For postganglionic stimulation, the superior cervical ganglion was exposed, and postganglionic nerve isolated and laid on a pair of silver electrodes. The preparation was prevented from drying with warm liquid paraffin. Rectangular pulses with parameters determined in each experiment were delivered by a Grass S4 stimulator in conjunction with a stimulus isolation unit. Drugs used in this study were 1-epinephrine chloride (Parke, Davis & Co.), phenoxybenzamine hydrochloride (Dibenzyline, Smith, Kline & French Labs.), phentolamine (Regitine, Ciba Pharmaceutical Products, Inc.), pronethalol (Alderlin, Ayerst Labs.), propanolol (Inderal, Ayerst Labs.), atropine sulfate (Burroughs Wellcome & Co.), and cocaine hydrochloride. The drugs were diluted in 0.9 per cent weight per volume saline. All doses refer to the. salts. EPINEPHRINE t 16 C D kg 2OO r B.P. mm Hg tl t t8 t 16 Fig. 1. Cat anesthetized with pentobarbital. Effect of increasing intravenous doses of epinephrine on the superior rectus muscle (). Calibrations 2 g tension and 1 minute.

3 Volume 6 Number 3 Role of autonomic nervous system 255 Results and discussion Intravenous injections of epinephrine (1 to 16 /xg per kilogram) were repeatedly found to produce an increase in the resting tension of the superior rectus muscle. A typical result is illustrated in Fig. 1. In these experiments, injections were made every 5 to 10 minutes; with more frequent administration a marked decrease in the response was observed. The response of the extraocular muscle to epinephrine did not appear to be associated with cardiovascular changes, since an increase in muscle tension was always noted, irrespective of whether the dose of epinephrine resulted in a rise or fall in the arterial blood pressure. Fig. 2 illustrates the voltage-dependent increase in tension of the superior rectus muscle to electrical stimulation of the ascending cervical sympathetic nerve carried out at a frequency of 20 cycles per second. It was of importance to determine whether these responses of the superior rectus muscle were the result of a direct action of sympathetic stimulation and epinephrine on this striated muscle or if the changes in extraocular muscle tension were secondary to an effect on intraorbital smooth muscle. Consequently, we compared the responses of both the superior rectus muscle and the nictitating membrane to these procedures in the presence of various compounds known to modify the response of smooth muscle. First of all, we studied the sympathetic a- and /^-receptor blocking agents. The ^-receptor blocking agents, pronethalol (5 mg. per kilogram intravenously) and propanolol (1 mg. per kilogram intravenously), did not antagonize the response of either muscle to sympathetic stimulation or epinephrine. Examples of these results are seen in Figs. 3 and 4. The doses of the blocking agents used in these experiments are well known to produce substantial sympathetic /3-receptor blockade elsewhere. The increased pressor response to epinephrine after the dose of propanolol in Fig. 4 indicates a high degree of /^-receptor blockade in the animal. Substantial antagonism of the responses of both muscles to epinephrine and sympathetic stimulation was observed after treatment with the sympathetic a-receptor blocking agents, phenoxybenzamine (1 to 2 mg. per kilogram intravenously) and phentolamine (2 to 3 mg. per kilogram intravenously). Fig. 5 illustrates the effect of an intravenous injection of 1 mg. per kilogram of phenoxybenzamine on the response of the nictitating membrane and superior rectus muscle to postganglionic sympathetic stimulation and intra-arterial injection of 3 [xg of epinephrine. It can be seen that all the responses were markedly depressed by this sympathetic a-receptor blocking agent. Epinephrine is well known to modify skeletal neuromuscular transmission in the cat (see Bowman and Raper s for references); it has not previously been demonstrated to alter resting tension in normally innervated mammalian striated muscles, although chronically denervated mammali- 2V 2.5 V 3V 4V Fig. 2. Cat anesthetized with pentobarbital. Effect of electrical stimulation of the cervical sympathetic nerve on the superior rectus muscle () 20 per second, 3 msec, duration, Calibrations 2 g tension and 1 minute.

4 256 Eakins and Katz Investigative Ophthalmology June V t 15V Pronethalol 5mg/kg 10 g ig I min Imin Fig. 3. Cat anesthetized with pentobarbital. Lack of eflect of pronethalol on the response of the superior rectus () and nictitating membrane () to sympathetic stimulation. Calibrations in g tension and minutes as indicated. an striated muscle will respond to epinephrine with a slowly developing reversible increase in resting tension." 19 > 10 ~ 13 It has been reported that the response of the chronically denervated tibialis anterior and soleus muscles corresponds on Ahlquist's 7 classification of catecholamine receptive mechanisms to a sympathetic /?- receptor effect, since the response was most effectively produced by Levisoprenaline and was selectively blocked by the sympathetic /3-receptor blocking agents, dichlorisoproterenol and pronethalol. 0 The results obtained after systemic administration of epinephrine in these experiments indicate that the response of the striated superior rectus muscle to the catecholamine differs from the response obtained from chronically denervated mammalian skeletal muscles, since the response was unaffected by the sympathetic /3-receptor blocking agents, but was abolished by the sympathetic a- receptor blocking agents. A B BP mm Hg 200r L t t Propanalol I mg/kg Fig. 4. Cat anesthetized with pentobarbital. Response of the superior rectus () and nictitating membrane () to epinephrine () before (A) and after (B) 1 mg. per kilogram of propanolol. All drugs given intravenously. Note increase in effect of epinephrine on arterial blood pressure (B.P.) after the propanolol. Calibrations in g tension and minutes as indicated.

5 Volume 6 Number 3 Role of autonomic nervous system 257 I min Imin Postgang.stim. Phenoxybenzamine Img/kg Postgong.stim. Fig. 5. Cat anesthetized with pentobarbitone. Inhibition of the responses of both muscles to sympathetic stimulation and intravenous epinephrine () by phenoxybenzamine. (A) Control responses of superior rectus () and nictitating membrane (); (B) responses after phenoxybenzamine. Calibrations in g tension and minutes as indicated. A B D Pregang stim. t t Pregang stim. COCAINE 5mg/kg Fig. 6. Cat anesthetized with pentobarbital. Effect of cocaine on the responses of the superior rectus () and nictitating membrane () to preganglionic' sympathetic stimulation and epinephrine () (A) and (B) control responses; (C) and (D) responses after cocaine. All drugs injected intravenously. Calibrations in g tension and minutes as indicated. t The effect of cocaine (5 mg. per kilogram intravenously) on these responses is seen in Fig. 6. Notice that the responses of both muscles to preganglionic sympathetic stimulation were slightly depressed, but that the epinephrine responses were definitely enhanced. Further studies showed that these doses of cocaine always potentiated the effects of postganglionic sympathetic stimulation on both muscle systems. This difference between the effect of cocaine on the responses to pre- and postganglionic sympathetic stimulation has been reported by other workers, the im-

6 258 Eakins and Katz Investigative Ophthalmology June 1967 portant point here being that both muscles responded in the same way. Lastly, we examined the effect of atropine (1 to 2 mg. per kilogram intravenously) on these responses. A typical result is seen in Fig. 7. It can be observed that the injection of 1 mg. per kilogram of atropine differentiated the responses to some extent. The response of the superior rectus muscle and nictitating membrane to sympathetic stimulation and the response of the nictitating membrane to epinephrine were depressed by atropine, whereas the response of the superior rectus muscle to epinephrine was unaffected. The identical behavior of the nictitating membrane and superior rectus muscle to sympathetic stimulation through all the procedures reported here raises the possibility that a part of the response of the superior rectus muscle produced by stimulation may be a pseudocontracture secondary to contraction of intraorbital smooth muscle. However, it is possible that the sympathetic nervous system may be involved with something other than the control of the vasculature in the extraocular muscles. We hope that studies now in progress (in collaboration with Dr. R. Barrett of Columbia University), utilizing the fluorescence technique developed by Hillarp and Falck for the histological localization of catecholamines in tissues, will yield more precise information on this problem. In addition, we also have to rule out the possibility that the extraocular muscles, already rather unusual in terms of their structure as compared with other skeletal muscles, 14 ' 15 may possess smooth muscle elements which may be responsible for the present observations. It is also difficult to explain the response of the superior rectus muscle to epinephrine entirely in terms of an effect on orbital smooth muscle in view of the differential action of atropine. It has been demonstrated before that atropine is capable of antagonizing the response of the smooth muscle cells of the nictitating membrane to both epinephrine and sympathetic stimulation. 10 ' 17 Thus, the observation that atropine did not reduce the response of the superior rectus muscle to epinephrine argues against the total extraocular muscle response being secondary to changes in tone of the intraorbital smooth muscle. This effect of epinephrine on the superior rectus muscle may be related to its anti- B 5g Imin t Postgang stim. Postgang stim. Atropine I mg/kg Fig. 7. Cat anesthetized with pentobarbital. Differential action of atropine. (A) Control responses of the superior rectus () and nictitating membrane () to sympathetic stimulation and intra-arterial epinephrine (1 Hg); (B) responses after intravenous atropine. Note all responses depressed except the response of to epinephrine. Calibrations in g tension and minutes as indicated.

7 Volume 6 Number 3 Role of autonomic nervous system 259 curare action in partially curarized striated muscles. 18 ' 21 In common with the present response of the superior rectus muscle, the anticurare action is blocked by sympathetic a-receptor blocking agents. 21 " 23 This anticurare effect of epinephrine is thought to be due to an increase in acetylcholine release resulting from a hyperpolarizing action of epinephrine on motor nerve endings.-' 1-25 Thus, mobilization of acetylcholine from prejunctional storage sites in the superior rectus muscle by epinephrine would result in an increase in tension in the muscle, the acetylcholine most probably affecting the "slow" or multiply innervated muscle fibers. Since the contracture of the superior rectus muscle produced by acetylcholine is unaffected by atropine this would also explain the lack of effect of atropine on the response to epinephrine described in this paper. However, these experiments do not rule out two further possibilities which could also explain the response of the extraocular muscle to epinephrine: (1) the presence of smooth muscle elements within the extraocular muscle, as suggested above, and (2) that epinephrine may be acting directly on the neuromuscular junctions, most probably the multiple endplates of the "slow" fibers. We hope that work currently in progress in our laboratory will yield answers to some of these problems. REFERENCES.1. Boeke, J.: Die Beziehungen cler Nervenfasern zu den Bindegewebselementen und Tastzellen, Ztschr. mikr.-anat. Forsch. 4: 448, Wolter, J. R.: Morphology of the sensory nerve apparatus in the striated muscle of the human eye, Arch. Ophth. 53: 201, Alpern, M., and Wolter, J. R.: The relation of horizontal saccadic and vergence movements, Arch. Ophth. 56: 685, Eakins, K. E., and Katz, R. L.: The action of succinylcholine on the tension of extraocular muscle, Brit. J. Pharmacol. 26: 205, Duke-Elder, W. S., and Duke-Elder, P. M.: The contraction of the extrinsic muscles of the eye by choline and nicotine, Proc. Roy. Soc. (B). 107: 232, Bowman, W. C, and Raper, C.: The effects of sympathomimetic amines on chronically denervated skeletal muscles, Brit. J. Pharmacol. 24: 98, Ahlquist, R. P.: A study of the adrenotropic receptors, Am. J. Physiol. 153: 586, Bowman, W. C, and Raper, C: Effects of sympathomimetic amines on neuromuscular transmission, Brit. J. Pharmacol. 27: 313, Euler, U. S. von, and Gaddum, J. H.: Pseudomotor contractures after degeneration of the facial nerve, J. Physiol. (Lond) 73: 54, Biilbring, E., and Bum, J. H.: The Sherrington phenomenon, J. Physiol. (Lond) 86: 61, Luco, J. V., and Sanchez, P.: Spontaneous activity and contractile responses to adrenaline of denervated auricular muscles, Acta physiol. latinoam. 6: 171, Luco, J. V., and Sanchez, P.: The effect of adrenaline and noradrenaline on the activity of denervated skeletal muscles. Antagonism between curare and adrenaline-like substances, in Curare and curare-like agents, Amsterdam, 1959, Elsevier Publishing Company, pp Bowman, W. C, and Zaimis, E.: The action of adrenaline, noradrenaline and isoprenaline on the denervated mammalian muscle, ]. Physiol. (Lond.) 158: 24, Hess, A., and Pilar, C: Slow fibres in the extraocular muscles of the cat, J. Physiol. (Lond.) 169: 780, Dietert, S. E.: The demonstration of different types of muscle fibres in human extraocular muscle by electron microscopy and cholinesterase staining, INVEST. OPHTH. 4: 51, Cervoni, P., West, T. C, and Fink, L. D.: Autonomic postganglionic innervation of the nictitating membrane of the cat, J. Pharmacol. & Exper. Therap. 116: 90, D'Alena, P., and Featherstone, R. M.: Effects of atropine and related alkaloids on epinephrine induced contractions of the cat nictitating membrane, J. Pharmacol. & Exper. Therap. 149: 351, Panella, A.: Action due principe actif surrenal sur la fatigue musculaire, Arch. ital. biol. 48: 430, Rosenblueth, A., Lindsley, D. B., and Morison, R. S.: A study of some decurarizing substances, Am. J. Physiol. 115: 53, Wilson, A. T., and Wright, S.: Anticurare effect of potassium and some other substances, Quart. J. Exper. Physiol. 26: 127, Brown, G. L., Goffart, M., and Dias, M. V.: The effects of adrenaline and of sympathetic stimulation on the demarcation potential of

8 260 Eakins and Katz Investigative Ophthalmology June 1967 mammalian skeletal muscle, J. Physiol. (Lond.) Ill: 184, Maddock, W. O., Rankin, V. M., and Youmans, W. B.: Prevention of the anticurare action of epinephrine by dibenamine, Proc. Soc. Exper. Biol. & Med. 67: 151, Bowman, W. C, Goldberg, A. A. J., and Raper, C: A comparison between the effects of a tetanus and the effects of sympathomimetric amines on fast- and slow-contracting mammalian muscles, Brit. J. Pharmacol. 19: 464, Krnjevic, K., and Miledi, R.: Some effects produced by adrenaline upon neuromuscular propagation, J. Physiol. (Lond.) 141: 291, Krnjevic, K., and Miledi, R.: Presynaptic failure of neuromuscular propagation in rats, J. Physiol. (Lond.) 149: 1, 1959.