499
J. Anat. (1992) 181, pp. 499-501, with 3 figures Printed in Great Britain
Short Report
The peripheral course of the axons innervating the medial rectus muscle within the subarachnoid portion of the oculomotor nerve ALPER ATASEVER', BARBAROS DURGUN', TULAY KANSU2 AND MESERRET CUMHUR2 Departments of 'Anatomy and 2Neurology, Hacettepe University, Ankara, Turkey (Accepted 25 August 1992)
ABSTRACT
There is clinical evidence of topographic localisation of fibres within the oculomotor nerve. It is generally accepted that the pupillomotor fibres have a localised course within the dorsomedial periphery of the subarachnoid portion. However, the precise course of the individual groups of axons innervating each muscle has not been examined in detail. In this study the course of the axons innervating the medial rectus muscle was investigated in the subarachnoid portion of the oculomotor nerve of the rat. The medial rectus muscle was injected with horseradish peroxidase until it was fully infiltrated. The subarachnoid portion of the oculomotor nerve was removed and sectioned longitudinally in the sagittal plane. Sections were reacted with tetramethylbenzidine as a chromogen. Labelled axons were found to be localised in the ventral part of the subarachnoid portion of the nerve. INTRODUCTION
There are several reports on isolated palsies of the muscles innervated by the oculomotor nerve (Susac & Hoyt, 1977; Guy et al. 1985; Pollard, 1986; Katz & Rimmer, 1989). In such cases, clinicians may encounter problems in locating the site of the lesion. It is generally believed that palsies of this type may be caused by damage to the fascicular, subarachnoid or intracavernous portions of the nerve (Guy et al. 1985; Miller, 1985; Fleet et al. 1988; Katz & Rimmer, 1989). Fibres innervating individual muscles may therefore have a topographic organisation within the oculomotor nerve. Pupil-sparing oculomotor palsy is a common disorder among disturbances affecting the oculomotor nerve. Nadeau & Trobe (1983) proposed that both intrinsic brainstem lesions and peripheral lesions of the oculomotor nerve might cause pupil sparing oculomotor palsies. Clinical findings of Kissel et al. (1983) and Fleet et al. (1988) support this statement. These findings show that the pupillomotor fibres have a topographic organisation throughout their course,
at least within the subarachnoid and precavernous portions of the oculomotor nerve. Sunderland & Hughes (1946) and Kerr & Hollowell (1964) had previously reported this arrangement. However, it is not certain whether such a disposition exists among the fibres comprising the somatic components of the nerve. In this study we have examined the subarachnoid portion of the oculomotor nerve in relation to the course of the fibres innervating the medial rectus muscle of the rat. MATERIALS AND METHODS
Thirty-two adult Sprague-Dawley rats (body weights 240-320 g) of both sexes were anaesthetised with i.p. injections of sodium pentobarbital (30 mg/kg). Under an operating microscope, the right medial rectus muscle was exposed by retracting the eyelids, partially collapsing the eyeball and making a conjunctival incision. 1-2 jl of 30 % horseradish peroxidase (HRP Sigma type VI) were injected into the muscle with a microsyringe. Multiple injections were made to infil-
Correspondence to Dr Alper Atasever, Department of Anatomy, Hacettepe University Faculty of Medicine, Hacettepe 06100, Ankara, Turkey.
500
A. Atasever and others
trate the muscle fully. The muscle was then enveloped with parafilm coated with surgical cement in order to prevent the tracer substance from escaping, following which the eyelids were sutured. After 24-36 h survival time, the rats were deeply anaesthetised and perfused through the ascending aorta with isotonic saline solution followed by 1.25 % glutaraldehyde and 1 % paraformaldehyde in 0.1 M phosphate buffer (pH 7.4) and finally with 500 ml of the same fixative solution containing 5 % sucrose. Following removal of the calvarium, the brain was carefully dissected, exposing the base of the cranium. Under an operating microscope the right oculomotor nerve was identified medial to the trigeminal nerve and proximal to the cavernous sinus. For orientation, the dorsal surface of the distal end of the nerve was marked with red ink. The nerve was then cut between the brainstem and cavernous sinus, postfixed for 2 h in 2% buffered glutaraldehyde containing 5 % sucrose, and stored for 24 h at 4 °C in the phosphate buffer solution containing 30 % sucrose. The nerves were sectioned longitudinally in the sagittal plane on a freezing microtome. Sections were collected in 0.1 M phosphate buffer (pH 7.4) and were reacted with tetramethylbenzidine according to the method of Mesulam (1978). Simultaneously, the noninjected muscles that are innervated by the oculomotor were also sectioned and reacted by the same method in order to ascertain whether or not HRP had escaped from the injected muscle. The medial rectus muscle was treated in the same manner as the other muscles, and HRP injection areas were confirmed on the sections. The course of the labelled axons was examined under a light microscope.
The width of the nerve was approximately 310-330 gm and we obtained 3 longitudinal sections 80-100 gm thick from each nerve. The course of the HRP labelled axons showed the same distribution throughout the entire length of the intracranial portion of the nerve. The localisation of the labelled axons was virtually the same in each of the 3 sections. Labelled axons showed a ventral curve at the level at which the nerve emerged from the brainstem, and they were found to be densely accumulated within the ventral part of the nerve (Fig. 1). These axons kept their localised course throughout the subarachnoid portion, invading the ventral fifth of the nerve (Figs 2, 3).
d
-
~
~~~
~~~~~~~
*b
.5
V
1
Fig. 1. Sagittal section of the oculomotor nerve showing its point of emergence from the midbrain. Labelled axons (arrows) curve ventrally as they leave the brainstem. d, dorsal; v, ventral. Bar, 100 gim.
RESULTS
Despite careful injection of HRP, in 5 cases examination of the noninjected muscles revealed contamination of HRP into the other extraocular muscles. In 2 of these cases there was HRP contamination to the inferior rectus. Three other cases showed contamination of HRP both to the inferior rectus and inferior oblique muscles. In these cases HRP injection into the medial rectus muscle was inadequate. There were 2 other cases in which the HRP injection was found to be insufficient although there was no contamination to the other extraocular muscles. In 6 cases HRP labelling of the nerve was either insufficient or lacking, even though HRP injection into the muscle was adequate in all and there was no contamination to the other extraocular muscles. These 13 cases were discarded during the evaluation of the results.
d ..N
Fig. 2. Saita
Fig. 2. Sagittal section of the oculomotor nerve showing the intermediate part of the subarachnoid portion. Labelled axons (arrows) exhibit a localised course through the ventral periphery of the nerve. d, dorsal; c, connective tissue; v, ventral. Bar, 100 gim.
Axons innervating medial rectus muscle
z
d
z
\7.
501
topographic organisation of fibres with superior and inferior components before they separate anatomically. Clinical evidence supports the existence of a topographic organisation in man that is comparable to what we observed in rats. Although isolated palsies of the medial rectus muscle are extremely rare, in such cases the causative lesion may be an aneurysm or a tumour that compresses the subarachnoid portion of the nerve ventrally, or an ischaemic lesion that affects the ventral portion of the nerve in its subarachnoid portion. We believe that this should be taken into consideration in patients with isolated medial rectus muscle palsies. REFERENCES
Fig. 3. Sagittal section of the oculomotor nerve showing the precavernous portion. Labelled axons (arrows) keep their localised course within the ventral periphery. d, dorsal; c, connective tissue; v, ventral. Bar, 100 pm. DISCUSSION
In this study we found that the nerve fibres innervating the medial rectus muscle showed a distinct localisation within the ventral periphery of the subarachnoid portion which has not been noted previously. This finding is inconsistent with the results of Miyazaki (1985) who reported that the fibres joining the inferior ramus intermingle with each other in the brainstem of the cat and do not show any organisation within the oculomotor nerve. This difference may be attributable to species differences. Ksiazek et al. (1989) reported 3 clinical cases, 1 having an isolated inferior ramus and the other 2 having isolated superior ramus paralysis. In these cases the causative lesions were located in the midbrain. These authors concluded that the separation of superior and inferior divisions also exists within the fascicular portion of the oculomotor nerve. Hriso et al. (1991) reported a case of superior ramus palsy associated with a brainstem lesion involving the lateral fascicles of the oculomotor nerve. They also concluded that the fibres contributing to the superior ramus have a fascicular organisation. All these data support the existence of a fascicular organisation of the oculomotor nerve fibres in man. Recently a model for the oculomotor fascicular organisation in the human was proposed by Castro et al. (1990). Such an organisation was also found in some animals (Gomez & Labandeira, 1980). It is likely that the oculomotor nerve has a
CASTRO 0, JOHNSON LN, MAMOURIAN AC (1990) Isolated inferior oblique paresis from brain-stem infarction. Archives of Neurology 47, 235-237. FLEET WS, RAPCSAK SZ, HUNTLEY WW, WATSON RT (1988) Pupilsparing oculomotor palsy from midbrain hemorrhage. Annals of Ophthalmology 20, 345-346. GoMEz SLA, LABANDEIRA GJL (1980) The central course of the axons of motoneurons innervating the superior rectus muscle in the mammalian eye. Trabajos del Instituto Cajal 71, 169-178. Guy J, SAVINO PJ, SCHATZ NJ (1985) Superior division paresis of the oculomotor nerve. Ophthalmology 92, 777-782. HRiso E, MASDEU JC, MILLER A (1991) Monocular elevation weakness and ptosis: an oculomotor fascicular syndrome? Journal of Clinical Neuro-Ophthalmology 11, 111-113. KATZ B, RIMMER S (1989) Ophthalmoplegic migraine with superior ramus oculomotor paresis. Journal of Clinical Neuro-Ophthalmology 9, 181-183. KERR F, HOLLOWELL OW (1964) Location of pupillomotor and accommodation fibres in the oculomotor nerve: experimental observations on paralytic mydriasis. Journal of Neurology, Neurosurgery and Psychiatry 27, 473-481. KISSEL JT, BURDE RM, KLINGELE TG (1983) Pupil-sparing oculomotor palsies with internal carotid-posterior communicating artery aneurysms. Annals of Neurology 13, 149-154. KSIAZEK SM, REPKA MX, MAGUIRE A (1989) Divisional oculomotor nerve paresis caused by intrinsic brainstem disease. Annals of Neurology 26, 714-718. MESULAM MM (1978) Tetramethylbenzidine for horseradish peroxidase neurochemistry. A non-carcinogenic blue reactionproduct with superior sensitivity for visualizing neural afferents. Journal of Histochemistry and Cytochemistry 26, 106-117. MILLER NR (1985) Oculomotor nerve (Discussion). Ophthalmology 92, 783-784. MrYAZAKI S (1985) Location of motoneurons in the oculomotor nucleus and the course of their axons in the oculomotor nerve. Brain Research 348, 57-63. NADEAu SE, TROBE JD (1983) Pupil sparing in oculomotor palsy: a brief review. Annals of Neurology 13, 143-148. POLLARD ZF (1986) Inferior oblique paresis: a benign entity. Annals of Ophthalmology 18, 178-180. SUNDERLAND S, HUGHES ESR (1946) The pupillo-constrictor pathway and the nerves to the ocular muscles in man. Brain 69, 301-309. SUSAC JO, HOYT WF (1977) Inferior branch palsy of the oculomotor nerve. Annals of Neurology 2, 336-339.
J. Anat. (1992) 181, pp. 499-501, with 3 figures Printed in Great Britain
Short Report
The peripheral course of the axons innervating the medial rectus muscle within the subarachnoid portion of the oculomotor nerve ALPER ATASEVER', BARBAROS DURGUN', TULAY KANSU2 AND MESERRET CUMHUR2 Departments of 'Anatomy and 2Neurology, Hacettepe University, Ankara, Turkey (Accepted 25 August 1992)
ABSTRACT
There is clinical evidence of topographic localisation of fibres within the oculomotor nerve. It is generally accepted that the pupillomotor fibres have a localised course within the dorsomedial periphery of the subarachnoid portion. However, the precise course of the individual groups of axons innervating each muscle has not been examined in detail. In this study the course of the axons innervating the medial rectus muscle was investigated in the subarachnoid portion of the oculomotor nerve of the rat. The medial rectus muscle was injected with horseradish peroxidase until it was fully infiltrated. The subarachnoid portion of the oculomotor nerve was removed and sectioned longitudinally in the sagittal plane. Sections were reacted with tetramethylbenzidine as a chromogen. Labelled axons were found to be localised in the ventral part of the subarachnoid portion of the nerve. INTRODUCTION
There are several reports on isolated palsies of the muscles innervated by the oculomotor nerve (Susac & Hoyt, 1977; Guy et al. 1985; Pollard, 1986; Katz & Rimmer, 1989). In such cases, clinicians may encounter problems in locating the site of the lesion. It is generally believed that palsies of this type may be caused by damage to the fascicular, subarachnoid or intracavernous portions of the nerve (Guy et al. 1985; Miller, 1985; Fleet et al. 1988; Katz & Rimmer, 1989). Fibres innervating individual muscles may therefore have a topographic organisation within the oculomotor nerve. Pupil-sparing oculomotor palsy is a common disorder among disturbances affecting the oculomotor nerve. Nadeau & Trobe (1983) proposed that both intrinsic brainstem lesions and peripheral lesions of the oculomotor nerve might cause pupil sparing oculomotor palsies. Clinical findings of Kissel et al. (1983) and Fleet et al. (1988) support this statement. These findings show that the pupillomotor fibres have a topographic organisation throughout their course,
at least within the subarachnoid and precavernous portions of the oculomotor nerve. Sunderland & Hughes (1946) and Kerr & Hollowell (1964) had previously reported this arrangement. However, it is not certain whether such a disposition exists among the fibres comprising the somatic components of the nerve. In this study we have examined the subarachnoid portion of the oculomotor nerve in relation to the course of the fibres innervating the medial rectus muscle of the rat. MATERIALS AND METHODS
Thirty-two adult Sprague-Dawley rats (body weights 240-320 g) of both sexes were anaesthetised with i.p. injections of sodium pentobarbital (30 mg/kg). Under an operating microscope, the right medial rectus muscle was exposed by retracting the eyelids, partially collapsing the eyeball and making a conjunctival incision. 1-2 jl of 30 % horseradish peroxidase (HRP Sigma type VI) were injected into the muscle with a microsyringe. Multiple injections were made to infil-
Correspondence to Dr Alper Atasever, Department of Anatomy, Hacettepe University Faculty of Medicine, Hacettepe 06100, Ankara, Turkey.
500
A. Atasever and others
trate the muscle fully. The muscle was then enveloped with parafilm coated with surgical cement in order to prevent the tracer substance from escaping, following which the eyelids were sutured. After 24-36 h survival time, the rats were deeply anaesthetised and perfused through the ascending aorta with isotonic saline solution followed by 1.25 % glutaraldehyde and 1 % paraformaldehyde in 0.1 M phosphate buffer (pH 7.4) and finally with 500 ml of the same fixative solution containing 5 % sucrose. Following removal of the calvarium, the brain was carefully dissected, exposing the base of the cranium. Under an operating microscope the right oculomotor nerve was identified medial to the trigeminal nerve and proximal to the cavernous sinus. For orientation, the dorsal surface of the distal end of the nerve was marked with red ink. The nerve was then cut between the brainstem and cavernous sinus, postfixed for 2 h in 2% buffered glutaraldehyde containing 5 % sucrose, and stored for 24 h at 4 °C in the phosphate buffer solution containing 30 % sucrose. The nerves were sectioned longitudinally in the sagittal plane on a freezing microtome. Sections were collected in 0.1 M phosphate buffer (pH 7.4) and were reacted with tetramethylbenzidine according to the method of Mesulam (1978). Simultaneously, the noninjected muscles that are innervated by the oculomotor were also sectioned and reacted by the same method in order to ascertain whether or not HRP had escaped from the injected muscle. The medial rectus muscle was treated in the same manner as the other muscles, and HRP injection areas were confirmed on the sections. The course of the labelled axons was examined under a light microscope.
The width of the nerve was approximately 310-330 gm and we obtained 3 longitudinal sections 80-100 gm thick from each nerve. The course of the HRP labelled axons showed the same distribution throughout the entire length of the intracranial portion of the nerve. The localisation of the labelled axons was virtually the same in each of the 3 sections. Labelled axons showed a ventral curve at the level at which the nerve emerged from the brainstem, and they were found to be densely accumulated within the ventral part of the nerve (Fig. 1). These axons kept their localised course throughout the subarachnoid portion, invading the ventral fifth of the nerve (Figs 2, 3).
d
-
~
~~~
~~~~~~~
*b
.5
V
1
Fig. 1. Sagittal section of the oculomotor nerve showing its point of emergence from the midbrain. Labelled axons (arrows) curve ventrally as they leave the brainstem. d, dorsal; v, ventral. Bar, 100 gim.
RESULTS
Despite careful injection of HRP, in 5 cases examination of the noninjected muscles revealed contamination of HRP into the other extraocular muscles. In 2 of these cases there was HRP contamination to the inferior rectus. Three other cases showed contamination of HRP both to the inferior rectus and inferior oblique muscles. In these cases HRP injection into the medial rectus muscle was inadequate. There were 2 other cases in which the HRP injection was found to be insufficient although there was no contamination to the other extraocular muscles. In 6 cases HRP labelling of the nerve was either insufficient or lacking, even though HRP injection into the muscle was adequate in all and there was no contamination to the other extraocular muscles. These 13 cases were discarded during the evaluation of the results.
d ..N
Fig. 2. Saita
Fig. 2. Sagittal section of the oculomotor nerve showing the intermediate part of the subarachnoid portion. Labelled axons (arrows) exhibit a localised course through the ventral periphery of the nerve. d, dorsal; c, connective tissue; v, ventral. Bar, 100 gim.
Axons innervating medial rectus muscle
z
d
z
\7.
501
topographic organisation of fibres with superior and inferior components before they separate anatomically. Clinical evidence supports the existence of a topographic organisation in man that is comparable to what we observed in rats. Although isolated palsies of the medial rectus muscle are extremely rare, in such cases the causative lesion may be an aneurysm or a tumour that compresses the subarachnoid portion of the nerve ventrally, or an ischaemic lesion that affects the ventral portion of the nerve in its subarachnoid portion. We believe that this should be taken into consideration in patients with isolated medial rectus muscle palsies. REFERENCES
Fig. 3. Sagittal section of the oculomotor nerve showing the precavernous portion. Labelled axons (arrows) keep their localised course within the ventral periphery. d, dorsal; c, connective tissue; v, ventral. Bar, 100 pm. DISCUSSION
In this study we found that the nerve fibres innervating the medial rectus muscle showed a distinct localisation within the ventral periphery of the subarachnoid portion which has not been noted previously. This finding is inconsistent with the results of Miyazaki (1985) who reported that the fibres joining the inferior ramus intermingle with each other in the brainstem of the cat and do not show any organisation within the oculomotor nerve. This difference may be attributable to species differences. Ksiazek et al. (1989) reported 3 clinical cases, 1 having an isolated inferior ramus and the other 2 having isolated superior ramus paralysis. In these cases the causative lesions were located in the midbrain. These authors concluded that the separation of superior and inferior divisions also exists within the fascicular portion of the oculomotor nerve. Hriso et al. (1991) reported a case of superior ramus palsy associated with a brainstem lesion involving the lateral fascicles of the oculomotor nerve. They also concluded that the fibres contributing to the superior ramus have a fascicular organisation. All these data support the existence of a fascicular organisation of the oculomotor nerve fibres in man. Recently a model for the oculomotor fascicular organisation in the human was proposed by Castro et al. (1990). Such an organisation was also found in some animals (Gomez & Labandeira, 1980). It is likely that the oculomotor nerve has a
CASTRO 0, JOHNSON LN, MAMOURIAN AC (1990) Isolated inferior oblique paresis from brain-stem infarction. Archives of Neurology 47, 235-237. FLEET WS, RAPCSAK SZ, HUNTLEY WW, WATSON RT (1988) Pupilsparing oculomotor palsy from midbrain hemorrhage. Annals of Ophthalmology 20, 345-346. GoMEz SLA, LABANDEIRA GJL (1980) The central course of the axons of motoneurons innervating the superior rectus muscle in the mammalian eye. Trabajos del Instituto Cajal 71, 169-178. Guy J, SAVINO PJ, SCHATZ NJ (1985) Superior division paresis of the oculomotor nerve. Ophthalmology 92, 777-782. HRiso E, MASDEU JC, MILLER A (1991) Monocular elevation weakness and ptosis: an oculomotor fascicular syndrome? Journal of Clinical Neuro-Ophthalmology 11, 111-113. KATZ B, RIMMER S (1989) Ophthalmoplegic migraine with superior ramus oculomotor paresis. Journal of Clinical Neuro-Ophthalmology 9, 181-183. KERR F, HOLLOWELL OW (1964) Location of pupillomotor and accommodation fibres in the oculomotor nerve: experimental observations on paralytic mydriasis. Journal of Neurology, Neurosurgery and Psychiatry 27, 473-481. KISSEL JT, BURDE RM, KLINGELE TG (1983) Pupil-sparing oculomotor palsies with internal carotid-posterior communicating artery aneurysms. Annals of Neurology 13, 149-154. KSIAZEK SM, REPKA MX, MAGUIRE A (1989) Divisional oculomotor nerve paresis caused by intrinsic brainstem disease. Annals of Neurology 26, 714-718. MESULAM MM (1978) Tetramethylbenzidine for horseradish peroxidase neurochemistry. A non-carcinogenic blue reactionproduct with superior sensitivity for visualizing neural afferents. Journal of Histochemistry and Cytochemistry 26, 106-117. MILLER NR (1985) Oculomotor nerve (Discussion). Ophthalmology 92, 783-784. MrYAZAKI S (1985) Location of motoneurons in the oculomotor nucleus and the course of their axons in the oculomotor nerve. Brain Research 348, 57-63. NADEAu SE, TROBE JD (1983) Pupil sparing in oculomotor palsy: a brief review. Annals of Neurology 13, 143-148. POLLARD ZF (1986) Inferior oblique paresis: a benign entity. Annals of Ophthalmology 18, 178-180. SUNDERLAND S, HUGHES ESR (1946) The pupillo-constrictor pathway and the nerves to the ocular muscles in man. Brain 69, 301-309. SUSAC JO, HOYT WF (1977) Inferior branch palsy of the oculomotor nerve. Annals of Neurology 2, 336-339.
