Nerve fiber composition of the intracranial portion of the oculomotor, trochlear, and abducens nerves in the sheep

Abstract

In the present investigation, the fiber content and the diameter spectra of the intracranial portion of the three oculomotor nerves (oculomotor, trochlear, and abducens nerves) were analysed in sheep by light and electron microscopy. It was determined that up to 14.98% of fibers in the oculomotor nerve, 17.01% in the trochlear nerve, and 11.87% in the abducens nerve were unmyelinated. The myelinated fibers showed a bimodal distribution in their size spectrum in all three nerves, with a majority of large myelinated axons, but a considerable proportion of small myelinated fibers, as well. The sensory function of the unmyelinated fibers present in the three oculomotor nerves is discussed also on the basis of our previous morphofunctional investigations. Anat Rec 260:294–298, 2000. © 2000 Wiley‐Liss, Inc.

Morphometric Changes in the Dog Trochlear Nerve with Growth

“…In sheep, Berardinelli et al. () examined the composition of the intracranial portion of nerves III, IV and VI, determining the number, size and percentage of myelinated and unmyelinated fibres, as did Hildebrand et al. () for nerves IV and VI in the cat.…”

“…As was previously carried out by Berardinelli et al. () from the total ultrathin cross sections, 25% was analysed in randomly chosen squares, and the number of unmyelinated fibres was counted. Their cross‐sectional area and maximum and minimum diameter were calculated.…”

“…Distinct fibre types have been found in the extraocular muscle nerves, which can be classified in several different ways according to either their morphological characteristic myelinated and unmyelinated fibres, or their conduction velocity (Manni et al., , ). The discovery of unmyelinated fibres in these somatomotor nerves and in certain species is currently the subject of widespread scientific discussion (Batíni et al., ; Fraher, ,b; Berardinelli et al., ).…”

“…The trochlear nerve has been studied in a large variety of species: rat (Kerns, ; Nojyo et al., ; Fraher, ,b), sheep (Berardinelli et al., ), sheep and humans (Abo‐El‐Enene, ), and the cat (Batíni et al., ; Hildebrand et al., ). Morphometrical characteristics of the extraocular muscle nerves in dogs have been scarcely investigated.…”

Cluster headache and intracranial aneurysm

“…Compression of pain sensory afferent fibres of the ophthalmic division of the f f trigeminal nerve present in the third cranial nerve by the aneurysm is alleged by some as the cause of the orbital headache [25]. In this regard, Berardinelli et al [26] identified unmyelinated fibres in the oculomotor, trochlear and abducens nerves, and suggested that they are sensory in nature and are involved in the transport of pain signals arising from the trigeminal territory. Bortolami et al [27] demonstrated that trigeminal neurons send their process centrally through the oculomotor nerve, which supplies the extra-ocular muscles, the cornea, and the superior eyelid, and contains neuropeptides (substance P, calcitonin gene-related peptide and cholecystokinin) that are usually associated with pain sensation.…”