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Eye movements are indispensable for visual image stabilization during self-generated and passive head and body motion and for visual orientation. Eye muscles and neuronal control elements are evolutionarily conserved, with novel behavioral repertoires emerging during the evolution of frontal eyes and foveae. The precise execution of eye movements with different dynamics is ensured by morphologically diverse yet complementary sets of extraocular muscle fibers and associated motoneurons. Singly and multiply innervated muscle fibers are controlled by motoneuronal subpopulations with largely selective premotor inputs from task-specific ocular motor control centers. The morphological duality of the neuromuscular interface is matched by complementary biochemical and molecular features that collectively assign different physiological properties to the motor entities. In contrast, the functionality represents a continuum where most motor elements contribute to any type of eye movement, although within preferential dynamic ranges, suggesting that signal transmission and muscle contractions occur within bands of frequency-selective pathways.

A projection by the superior colliculus to the supraoculomotor area (SOA) located dorsal to the oculomotor complex was first described in 1978. This projection’s targets have yet to be identified, although the initial study suggested that vertical gaze motoneuron dendrites might receive this input. Defining the tectal targets is complicated by the fact the SOA contains a number of different cell populations. In the present study, we used anterograde tracers to characterize collicular axonal arbors and retrograde tracers to label prospective SOA target populations in macaque monkeys. Close associations were not found with either superior or medial rectus motoneurons whose axons supply singly innervated muscle fibers. S-group motoneurons, which supply superior rectus multiply innervated muscle fibers, appeared to receive a very minor input, but C-group motoneurons, which supply medial rectus multiply innervated muscle fibers, received no input. A number of labeled boutons were observed in close association with SOA neurons projecting to the spinal cord, or the reticular formation in the pons and medulla. These descending output neurons are presumed to be peptidergic cells within the centrally projecting Edinger–Westphal population. It is possible the collicular input provides a signaling function for neurons in this population that serve roles in either stress responses, or in eating and drinking behavior. Finally, a number of close associations were observed between tectal terminals and levator palpebrae superioris motoneurons, suggesting the possibility that the superior colliculus provides a modest direct input for raising the eyelids during upward saccades.

During spaceflight and immediately after it, adaptive neuroplastic changes occur in the sensorimotor structures of the central nervous system, which are associated with changes of mainly vestibular and visual signals. It is known that the movement of the eyeball in the vertical direction is carried out by muscles that are innervated by the trochlear nerve (CN IV) and the oculomotor nerve (CN III). To elucidate the cellular processes underlying the atypical vertical nystagmus that occurs under microgravity conditions, it seems necessary to study the state of these nuclei in animals in more detail after prolonged space flights. In this work, we carried out a qualitative and quantitative light-optical and ultrastructural analysis of the nuclei of the trochlear nerve in mice after a 30-day flight on the Bion-M1 biosatellite and followed by a stay for 13-14 hours under the influence of the Earth’s gravity after landing. As a result, it was shown that the motoneurons in the nucleus of the trochlear nerve changed their morphology under the influence of microgravity. Cell nuclei of the motoneurons had a more simplified rounded shape than in the control. In addition, the dendrites of these motoneurons significantly reorganized geometry and orientation under microgravity conditions; the number of dendritic branches has been increased to enhance the reduced signal flow. Apparently, to ensure such plastic changes, the number and size of mitochondria in the soma of motoneurons and in axons coming from the vestibular structures increased. In addition, the experimental animals showed an increase in the size of the cisterns of the rough and smooth endoplasmic reticulum in comparison with the control group of animals left on Earth, for which the environmental conditions in the spacecraft were reproduced. Thus, the main role in the adaptation of the trochlear nucleus to microgravity conditions, apparently, belongs to the dendrites of motoneurons, which rearrange their structure and function to enhance the flow of sensory information. These results are useful for the development of new, more effective means to facilitate the stay and work of space travelers in a long spaceflight.

Marcus Gunn Syndrome (MGS), mostly occurring in congenital ptosis patients, is characterized by jaw movement evoking ptotic eyelid retraction, followed by collapse. Inverted, bilateral and acquired MGS were also reported. Some cases manifest MGS only temporarily in life. These features suggest MGS may be due to multiple pathogeneses, which are still unclear. People also classify MGS as a kind of trigeminal oculomotor synkenesis (TOS), like Duane syndrome (DS), in which ocular adduction prompts eyelid moving or eyeball retraction. The most popular hypothesis for TOS is congenital miswiring, as evidence supporting this hypothesis is found in DS cases: hypoplasia abducens nerve fusing with a branch of oculomotor nerve is observed. Seven mutant genes have been identified associated with TOS and two of them are found among MGS cases. Accordingly, these mutant genes may dominate cranial nerve misconnection and generate TOS. However, unlike in DS case, evidence of miswiring is not encountered in most MGS cases. The fact is that two “MGS genes” are from congenital fibrosis of extraocular muscle (CFEOM) cases presenting with associated MGS. But most of MGS cases do not suffer CFEOM. Thus, mutant genes dominated congenital miswiring may not be the pathogenesis for the majority of MGS. As an alternate pathogenic pathway, a “release hypothesis” proposed that MGS is a primitive physiologic reflex that became suppressed during phylogenetic development but could be released under certain pathologic conditions. This hypothesis was and is overlooked because the hypothesized reflex arc has not been defined. Decades ago, a neural tract tracing study in Xenopus revealed a direct projection from masticator afferent mesencephalic trigeminal nucleus (Vme) neurons to oculomotor and trochlear nucleus (III/IV). In clinical studies, co-firing of pterygoid muscle and levator palpebrae was recorded by electromyography during onset of MGS, and stimulating pterygoid muscle nerve elicited eyelid retraction. Recently, retraction of the ipsilateral eyelid by stimulating the trigeminal motor root was even observed in cases without congenital ptosis and MGS, highlighting the existence of a latent pathway. In rats, recently we demonstrated projections from the Vme neurons to the III/IV, and to their premotor neurons in interstitial nucleus of Cajal by neural tract tracing and electrophysiologic studies. Fos expression in pre-oculomotor neurons was induced by repeated down stretching the lower jaw. Combining previous and our own studies, we assumed the Vme neurons is excited when jaw moves and in turn, some eyelid activity related III motoneurons are activated through projections of Vme to oculomotor system, like in Xenopus. Genetic factors may dominate to what extent this primitive reflex-arc is preserved, which consequently determines phenotype.

The oculomotor (OM) complex is a combination of somatic and parasympatethic neurons. The correct development and wiring of this cranial pair is essential to perform basic functions: eyeball and eyelid movements, pupillary constriction, and lens accommodation. The improper formation or function of this nucleus leads pathologies such as strabismus. We describe the OM organization and function in different vertebrate brains, including chick, mouse, and human. The morphological localization is detailed, as well as the spatial relation with the trochlear nucleus in order to adjust some misleading anatomical topographic descriptions. We detailed the signaling processes needed for the specification of the OM neurons. The transcriptional programs driven the specification and differentiation of these neurons are partially determined. We summarized recent genetic studies that have led to the identification of guidance mechanisms involved in the migration, axon pathfinding, and targeting of the OM neurons. Finally, we overviewed the pathology associated to genetic malformations in the OM development and related clinical alterations. Anat Rec, 302:446-451, 2019. © 2018 Wiley Periodicals, Inc.

There are nine cranial nerves (CNs) that have their nuclei in, and/or enter or exit, the brainstem. These are the oculomotor (CNIII) and trochlear (CNIV) of the midbrain; trigeminal (CNV) of the pons; abducens (CNVI), facial (CNVII), and vestibulocochlear (CNVIII) of the pons-medulla junction; and glossopharyngeal (CNIX), vagus (CNX), and hypoglossal (XII) of the medulla. While correctly regarded as a CN, the accessory nerve (CNXI) arises from motor neurons in cervical levels C1-C5/6, ascends to enter the skull via the foramen magnum, associates with CNs IX and X, and exits the skull via the jugular foramen. CNI (olfactory) and CNII (optic) are CNs of the telencephalon and diencephalon, respectively. With the exception of CNIII, which contains some visceral efferent fibers, the motor nuclei of III, IV, VI, and XII contain somatic efferent cells and fibers. The fibers arising from the trochlear nucleus decussate before they exit to innervate the contralateral superior oblique muscle. The mixed cranial nerves (CNs V, VII, IX, and X) receive somatic and visceral afferent information from appropriate peripheral receptors. Visceral motor nuclei associated with these nerves give rise to preganglionic fibers to peripheral ganglia. Somatomotor nuclei of these CNs project to skeletal muscle that influences eye and tongue movements. The CN of the brainstem regarded as purely sensory is the vestibulocochlear (VIII). It is concerned with balance, equilibrium, and hearing.

The midbrain, most rostral segment of the brainstem, consists of a tectum, a tegmentum, and a large important fiber bundle, the crus cerebri. The cavity of the midbrain, the cerebral aqueduct, is surrounded by cells, the periaqueductal gray (PAG), a structure important in the modulation of pain pathways. Prominent structures of the tectum are the eminences of the superior (related to visual function) and inferior (related to auditory function) colliculi, the nuclei of these elevations, and upper portions of the PAG. The central region of the midbrain, the tegmentum, contains the red nucleus (motor function), important ascending (sensory) and descending (motor) tracts, and a number of smaller tracts that interconnect the various segments of the brainstem with each other and/or with the cerebellum. The substantia nigra and the crus cerebri collectively form the basis pedunculi; the former is the most important source of dopaminergic fibers to the basal nuclei of the telencephalon, and the latter is made up of important descending fibers to the basilar pontine nuclei, the motor nuclei of cranial nerves, and the spinal cord motor neurons. The cranial nerve nuclei associated with the midbrain are the oculomotor (and Edinger-Westphal, level of the superior colliculus), the trochlear (level of the inferior colliculus), and portions of the trigeminal complex. At its position within the tentorial notch, the midbrain is susceptible to a variety of clinical insults, especially those related to increases in intracranial pressure. Caudally the cerebral aqueduct opens into the fourth ventricle.

A solitary cluster of parvalbumin-positive neurons--the PV1 nucleus--has been observed in the lateral hypothalamus of rodents. In the present study, we mapped the efferent connections of the PV1 nucleus using nonspecific antero- and retrograde tracers in rats, and chemoselective, Cre-dependent viral constructs in parvalbumin-Cre mice. In both species, the PV1 nucleus was found to project mainly to the periaqueductal grey matter (PAG), predominantly ipsilaterally. Indirectly in rats and directly in mice, a discrete, longitudinally oriented cylindrical column of terminal fields (PV1-CTF) was identified ventrolateral to the aqueduct on the edge of the PAG. The PV1-CTF is particularly dense in the rostral portion, which is located in the supraoculomotor nucleus (Su3). It is spatially interrupted over a short stretch at the level of the trochlear nucleus and abuts caudally on a second parvalbumin-positive (PV2) nucleus. The rostral and the caudal portions of the PV1-CTF consist of axonal endings, which stem from neurons scattered throughout the PV1 nucleus. Topographically, the longitudinal orientation of the PV1-CTF accords with that of the likewise longitudinally oriented functional modules of the PAG, but overlaps none of them. Minor terminal fields were identified in a crescentic column of the lateral PAG, as well as in the Edinger-Westphal, the lateral habenular, and the laterodorsal tegmental nuclei. So far, no obvious functions have been attributed to this small, circumscribed column ventrolateral to the aqueduct, the prime target of the PV1 nucleus.

Protocadherin 9 (Pcdh9) is a member of the protocadherin family, which includes many members involved in various phenomena, such as cell-cell adhesion, neural projection, and synapse formation. Here, we identified Pcdh9 protein in the mouse brain and examined its distribution during neural development. Pcdh9, with a molecular weight of approximately 180 kDa, was localized at cell-cell contact sites in COS-1 cells transfected with Pcdh9 cDNA. In cultured neurons, it was detected at the growth cone and at adhesion sites along neurites. In the E13.5 brain, prominent Pcdh9 immunoreactivity was detected in the dorsal thalamus along with other regions including the vestibulocochlear nerve. As development proceeded (E15.5-P1), Pcdh9 immunoreactivity became observable in various brain regions but was restricted to certain fiber tracts and brain nuclei. Interestingly, many Pcdh9-positive brain nuclei and fascicles belonged to the vestibular (e.g. vestibulocochlear nerve, vestibular nuclei, and the vestibulocerebellum) and oculomotor systems (medial longitudinal fascicles, oculomotor nucleus, trochlear nucleus, and interstitial nucleus of Cajal). In addition, we examined the distribution of Pcdh9 protein in the olfactory bulb, retina, spinal cord, and dorsal root ganglion. In these regions, Pcdh9 and OL-protocadherin proteins were differentially distributed, with the difference highlighted in the olfactory bulb, where they were enriched in different subsets of glomeruli. In the mature retina, Pcdh9 immunoreactivity was detected in distinct sublaminae of the inner and outer plexiform layers. In the dorsal root ganglion, only certain subsets of neurons showed Pcdh9 immunoreactivity. These results suggest that Pcdh9 might be involved in formation of specific neural circuits during neural development.

The isthmus is recognized as the most rostral segment of the hindbrain in non-mammalian vertebrates. In mammalian embryos, transient Fgf8 expression defines the developing isthmic region, lying between the midbrain and the first rhombomere, but there has been uncertainty about the existence of a distinct isthmic segment in postnatal mammals. We attempted to find if the region of early embryonic Fgf8 expression (which is considered to involve the entire extent of the prospective isthmus initially) might help to identify the boundaries of the isthmus in postnatal animals. By creating an Fgf8-Cre-LacZ lineage in mice, we were able to show that Fgf8-Cre reporter expression in postnatal mice is present in the same nuclei that characterize the isthmic region in birds. The 'signature' isthmic structures in birds include the trochlear nucleus, the dorsal raphe nucleus, the microcellular tegmental nuclei, the pedunculotegmental nucleus, the vermis of the cerebellum, rostral parts of the parabrachial complex and locus coeruleus, and the caudal parts of the substantia nigra and VTA. We found that all of these structures were labeled with the Fgf8-Cre reporter in the mouse brain, and we conclude that the isthmus is a distinct segment of the mammalian brain lying caudal to the midbrain and rostral to rhombomere 1 of the hindbrain.

Background The trochlear (fourth) nerve is the only cranial nerve that decussates before emerging from the posterior aspect of the brainstem. Lesions involving the trochlear nucleus or fascicles mostly give rise to contralesional superior oblique palsy (SOP). Methods We report 2 patients with SOP on the side of intraaxial lesions with a literature review on central trochlear palsy. Results The lesions are more commonly located posterior to the cerebral aqueduct in patients with ipsilesional SOP than in those with contralesional SOP. Conclusions Intraaxial lesions may cause ipsilesional or contralesional SOP depending on the lesion location along the course of trochlear fascicle in the brainstem.

The midbrain represents the uppermost portion of the brainstem, containing numerous important nuclei and white matter tracts, most of which are involved in motor control, as well as the auditory and visual pathways. Notable midbrain nuclei include the superior and inferior colliculus nuclei, red nucleus, substantia nigra, oculomotor nuclear complex, and trochlear nucleus. In addition, white matter tracts include the brachium conjunctivum, medial and lateral lemniscus, spinothalamic tracts, and the fiber tracts within the cerebral peduncles. Although neurologically vital, many of these small midbrain nuclei and white matter tracts are not easily individually identified on neuroimaging. However, given their diverse functions, midbrain pathology often leads to distinct clinical syndromes. A review and understanding of the location and relationships between the different midbrain nuclei and fiber tracts will allow more precise correlation of radiologic findings with patient pathology and symptomatology. Particular syndromes associated with midbrain pathology include the Weber, Claude, Benedikt, Nothnagel, and Parinaud syndromes. The oculomotor and trochlear cranial nerves also reside at this level. An understanding of their functions as well as their projected courses from the midbrain towards the eye allows identification of distinct locations which are particularly vulnerable to pathology.

The periaqueductal gray (PAG), especially in a region between the levels the oculomotor nucleus and the trochlear nucleus, was suggested to be the essential relay center that conveys information of bladder fullness to the pontine micturition center (Barrington's nucleus). The present study examined this hypothesis by transecting the brainstem in anesthetized cats. In eight cases of the midbrain transection, all (n=3) or most (n=5) of the PAG between the levels the oculomotor nucleus and the trochlear nucleus was separated from the intact side of the brain. Furthermore, in the former three cases, the PAG at the level caudal to the trochlear nucleus was separated from the intact brain by more than half (n=2) or completely (n=1). In all these cases, there were no remarkable differences in the amplitude of the micturition contraction (80-98% of that before transection), irrespective of the levels of the transection. In the cases of the pontine transection, micturition contraction disappeared after transecting through the caudal part of Barrington's nucleus (n=1) or through regions caudal to this nucleus (n=5). In the one case that received a transection through the rostral part of Barrington's nucleus, the amplitude of the micturition contraction was 43% of that before transection. This study demonstrates that Barrington's nucleus is essential, but the PAG is not essential, for evoking micturition. Our results suggest that the information of bladder fullness in the cat is conveyed to Barrington's nucleus either directly from the lumbosacral neurons or indirectly via relay neurons located below the midbrain.

Little is known about the cues controlling the generation of motoneuron populations in the mammalian ventral midbrain. We show that Otx2 provides the crucial anterior-posterior positional information for the generation of red nucleus neurons in the murine midbrain. Moreover, the homeodomain transcription factor Nkx6-1 controls the proper development of the red nucleus and of the oculomotor and trochlear nucleus neurons. Nkx6-1 is expressed in ventral midbrain progenitors and acts as a fate determinant of the Brn3a+ (also known as Pou4f1) red nucleus neurons. These progenitors are partially dorsalized in the absence of Nkx6-1, and a fraction of their postmitotic offspring adopts an alternative cell fate, as revealed by the activation of Dbx1 and Otx2 in these cells. Nkx6-1 is also expressed in postmitotic Isl1+ oculomotor and trochlear neurons. Similar to hindbrain visceral (branchio-) motoneurons, Nkx6-1 controls the proper migration and axon outgrowth of these neurons by regulating the expression of at least three axon guidance/neuronal migration molecules. Based on these findings, we provide additional evidence that the developmental mechanism of the oculomotor and trochlear neurons exhibits more similarity with that of special visceral motoneurons than with that controlling the generation of somatic motoneurons located in the murine caudal hindbrain and spinal cord., This work was supported by the ‘Ramón y Cajal’ Program and Micinn (BFU2008-03708) to E.P.; a CIRM postdoctoral fellowship (Training Grant No T1-00008) to K.F.; NIH/NIDDK-1R01-DK68471-01 and NIH/NIDDK-1U19-DK072495-01 grants to M.S.; the Italian Association for Cancer Research (AIRC); the FP6 EuTRACC Integrated Project (LSHG-CT-2007-037445) and ‘Fondazione Cassa di Risparmio’ of Rome to A.S.; and by the Initiative and Networking Fund in the framework of the Helmholtz Alliance on Systems Biology, Bayerischer Forschungsverbund ‘ForNeuroCell’ (F2-F2410-10c/20697), the European Union (EuTRACC LSHG-CT-2006-037445) and the Deutsche Forschungsgemeinschaft (DFG) WU 164/3-2 and WU 164/4-1 to W.W.

In all vertebrates the eyes are moved by six pairs of extraocular muscles enabling horizontal, vertical and rotatory movements. Recent work showed that each extraocular muscle is controlled by two motoneuronal groups: 1. Motoneurons of singly-innervated muscle fibers (SIF) that lie within the boundaries of motonuclei mediating a fast muscle contraction and 2. motoneurons of multiply-innervated muscle fibers (MIF) in the periphery of motonuclei mediating a tonic muscle contraction. Currently only limited data about the transmitter inputs to the SIF and MIF motoneurons are available. Here we performed a quantitative study on the transmitter inputs to SIF and MIF motoneurons of individual muscles in the oculomotor and trochlear nucleus in monkey. Pre-labeled motoneurons were immunostained for GABA, glutamate decarboxylase, GABA-A receptor, glycine transporter 2, glycine receptor 1, and vesicular glutamate transporters (vGlut) 1 and 2. The main findings were: 1. the inhibitory control of SIF motoneurons for horizontal and vertical eye movements differs. Unlike in previous primate studies a considerable GABAergic input was found to all SIF motoneuronal groups, whereas a glycinergic input was confined to motoneurons of the medial rectus muscle mediating horizontal eye movements and to those of the levator palpebrae muscle elevating the upper eyelid. Whereas SIF and MIF motoneurons of individual eye muscles do not differ numerically in their GABAergic, glycinergic and vGlut2 input, vGlut1 containing terminals densely covered the supraoculomotor area targeting medial rectus MIF motoneurons. It is reasonable to assume that the vGlut1 input affects the near response system in the supraoculomotor area, which houses the preganglionic neurons mediating pupillary constriction and accommodation and the medial rectus MIF motoneurones involved in vergence.

Primary and secondary sensory trigeminal projections were studied by means of tract-tracing methods in a cyprinid teleost, the carp. Tracer injections into the trigeminal nerve root labeled terminals in the ipsilateral principal sensory trigeminal nucleus, descending trigeminal nucleus, medial funicular nucleus, facial lobe, and medial part of posterior lateral valvular nucleus. The principal sensory trigeminal nucleus is considered a major origin of the secondary sensory trigeminal projections in teleosts. To investigate the secondary sensory trigeminal projections, tracer injections were performed into the principal sensory trigeminal nucleus. The present study suggests that the principal sensory trigeminal nucleus projects to the bilateral ventromedial thalamic nucleus, periventricular pretectal nucleus, stratum album centrale of the optic tectum, caudomedial region of lateral preglomerular nucleus, ventrolateral nucleus of semicircular torus, medial part of rostral and posterior lateral valvular nucleus, oculomotor nucleus, trochlear nucleus, trigeminal motor nucleus, facial motor nucleus, superior and inferior reticular formation, descending trigeminal nucleus, medial funicular nucleus, inferior olive, and to the contralateral sensory trigeminal nucleus. These observations indicate that the primary and secondary trigeminal sensory projections of a cyprinid teleost, the carp, are similar to those in percomorph teleosts. J. Comp. Neurol. 499:626–644, 2006. © 2006 Wiley-Liss, Inc.

The sensory trigeminal nucleus of teleosts is the rostralmost nucleus among the trigeminal sensory nuclear group in the rhombencephalon. The sensory trigeminal nucleus is known to receive the somatosensory afferents of the ophthalmic, maxillar, and mandibular nerves. However, the central connections of the sensory trigeminal nucleus remain unclear. Efferents of the sensory trigeminal nucleus were examined by means of tract-tracing methods, in a percomorph teleost, tilapia. After tracer injections to the sensory trigeminal nucleus, labeled terminals were seen bilaterally in the ventromedial thalamic nucleus, periventricular pretectal nucleus, medial part of preglomerular nucleus, stratum album centrale of the optic tectum, ventrolateral nucleus of the semicircular torus, lateral valvular nucleus, prethalamic nucleus, tegmentoterminal nucleus, and superior and inferior reticular formation, with preference for the contralateral side. Labeled terminals were also found bilaterally in the oculomotor nucleus, trochlear nucleus, trigeminal motor nucleus, facial motor nucleus, facial lobe, descending trigeminal nucleus, medial funicular nucleus, and contralateral sensory trigeminal nucleus and inferior olive. Labeled terminals in the oculomotor nucleus and trochlear nucleus showed similar densities on both sides of the brain. However, labelings in the trigeminal motor nucleus, facial motor nucleus, facial lobe, descending trigeminal nucleus, and medial funicular nucleus showed a clear ipsilateral dominance. Reciprocal tracer injection experiments to the ventromedial thalamic nucleus, optic tectum, and semicircular torus resulted in labeled cell bodies in the sensory trigeminal nucleus, with a few also in the descending trigeminal nucleus.

Galectin-1 is a member of the animal lectin family that displays conserved consensus sequences and similar carbohydrate binding specificities. Recent analyses revealed that galectin-1 plays an important role in the process of nerve regeneration. We analyzed the topological expression of galectin-1 mRNA in adult rat nervous system. Galectin-1 mRNA was predominantly observed in the cell bodies of neurons such as oculomotor nucleus (III), trochlear nucleus (IV), trigeminal motor nucleus (V), abducens nucleus (VI), facial nucleus (VII), hypoglossal nucleus (XII), red nucleus, and locus ceruleus. Neurons in pineal gland and dorsal root ganglia expressed galectin-1 mRNA. We next tested whether the axotomy of facial nerve altered the expression of galectin-1 mRNA in motor neurons. In the adult rats, the axotomy of facial nerve induced transient upregulation of galectin-1 mRNA around 6 h after axotomy. These results indicate that galectin-1 may play roles in the early event of the nerve injury and regeneration through the transient change of its expression level.

As a step towards the identification of the neuronal populations responsive to glial cell line-derived neurotrophic factor (GDNF) in the human nervous system and their changes with age, this study reports on the immunohistochemical localization of the protein GDNF in the autoptic normal human brain stem of pre- and full-term newborns and adult subjects. Two different anti-GDNF polyclonal antibodies were used. Western blot analysis on homogenates of human and rat brain and recombinant human GDNF resulted in differential detection of monomeric and dimeric forms of the proteins. The ABC immunohistochemical technique on cryostat tissue sections showed an uneven distribution of GDNF-like immunoreactive nerve fibers and terminals and neuronal cell bodies. Immunoreactive elements were mainly localized to the spinal trigeminal, cuneate, solitary, vestibular, and cochlear sensory nuclei, dorsal motor nucleus of the vagus nerve, ventral grey column, hypoglossal nucleus, dorsal and ventrolateral medullary reticular formation, pontine subventricular grey and locus coeruleus, lateral regions of the rostral pontine tegmentum, tectal plate, trochlear nucleus, dorsal and median raphe nuclei, caudal and rostral linear nuclei, cuneiform nucleus, and substantia nigra. Comparison between pre- and full-term newborns and adult subjects revealed changes with age in density of positive innervation and frequency of immunoreactive perikarya. The results obtained provide detailed information on the occurrence of GDNF-like immunoreactive neurons in the human brain stem and suggest that the protein is present in a variety of neuronal systems, which subserve different functional activities, at developmental ages and in adult brains.

The trochlear nerve is the fourth cranial nerve and supplies one muscle of the orbit—the superior oblique. After exiting from the trochlear nucleus in the midbrain, it enters the orbit through the superior orbital fissure. With its long course and size, it is the longest yet smallest of all the cranial nerves. The muscle it supplies (superior oblique) results in intorsion of the eyeball, with a little abduction and depression too. Due to its long intracranial course, it is very susceptible to any changes of intracranial pressure, for whatever reason. Diplopia is one symptom the patient will experience, classically when looking down, as in walking down a flight of stairs.

Eye muscle fibers can be divided into two categories: nontwitch, multiply innervated muscle fibers (MIFs), and twitch, singly innervated muscle fibers (SIFs). We investigated the location of motoneurons supplying SIFs and MIFs in the six extraocular muscles of monkeys. Injections of retrograde tracers into eye muscles were placed either centrally, within the central SIF endplate zone; in an intermediate zone, outside the SIF endplate zone, targeting MIF endplates along the length of muscle fiber; or distally, into the myotendinous junction containing palisade endings. Central injections labeled large motoneurons within the abducens, trochlear or oculomotor nucleus, and smaller motoneurons lying mainly around the periphery of the motor nuclei. Intermediate injections labeled some large motoneurons within the motor nuclei but also labeled many peripheral motoneurons. Distal injections labeled small and medium-large peripheral neurons strongly and almost exclusively. The peripheral neurons labeled from the lateral rectus muscle surround the medial half of the abducens nucleus: from superior oblique, they form a cap over the dorsal trochlear nucleus; from inferior oblique and superior rectus, they are scattered bilaterally around the midline, between the oculomotor nucleus; from both medial and inferior rectus, they lie mainly in the C-group, on the dorsomedial border of oculomotor nucleus. In the medial rectus distal injections, a “C-group extension” extended up to the Edinger-Westphal nucleus and labeled dendrites within the supraoculomotor area. We conclude that large motoneurons within the motor nuclei innervate twitch fibers, whereas smaller motoneurons around the periphery innervate nontwitch, MIF fibers. The peripheral subgroups also contain medium-large neurons which may be associated with the palisade endings of global MIFs. The role of MIFs in eye movements is unclear, but the concept of a final common pathway must now be recon

Detection of changes in numbers of neurons is essential for an understanding of neuronal development, function, and death. Optical disector counting is claimed to be the most efficient technique to estimate accurate numbers of neurons in microscopic sections. We calibrated the optical disector by comparison with three-dimensional reconstructions from serial sections and determined how accurate this technique is relative to conventional profile counting methods. The calibration was performed on the trochlear nucleus in developing chicks. Optical disector estimates, when obtained as generally recommended, were about 25% lower than the actual number of neurons. This underestimate was caused by a nonuniform (bimodal) distribution of neuronal nuclei in paraffin and plastic (glycolmethacrylate) sections, but not in cryosections. The density of neurons in the core of the paraffin and plastic sections was substantially lower than in the upper and lower margins of these sections. Accurate estimates of neuronal numbers were obtained with a modified optical disector method that sampled the entire extent of tissue sections. Previous estimates of numbers of trochlear neurons in the developing chick have been controversial. The modified (calibrated) optical disector method revealed that the number of trochlear neurons decreased from about 1,600 at day 8.5 of incubation (embryonic day, [E]8.5) to about 900 at the time of hatching. Numbers of pyknotic nuclei peaked at E6 and at E9, revealing an additional early, but postproliferative, period of cell death. Taken together, these data emphasize the need for calibration of stereological counting techniques and the need to examine sampling strategies for potential bias. J. Comp. Neurol. 409:169–186, 1999. © 1999 Wiley-Liss, Inc.

Serine proteases are considered to play several important roles in the brain. In an attempt to find novel brain-specific serine proteases (BSSPs), motopsin (PRSS-12) was cloned from a mouse brain cDNA library by polymerase chain reaction (PCR). Northern blot analysis demonstrated that the postnatal 10-day mouse brain contained the most amount of motopsin mRNA. At this developmental stage, in situ hybridization histochemistry showed that motopsin mRNA was specifically expressed in the following regions: cerebral cortical layers II/III, V and VIb, endopiriform cortex and the limbic system, particularly in the CA1 region of the hippocampal formation. In addition, in the brainstem, the oculomotor nucleus, trochlear nucleus, mecencephalic and motor nuclei of trigeminal nerve (N), abducens nucleus, facial nucleus, nucleus of the raphe pontis, dorsoral motor nucleus of vagal N, hypoglossal nucleus and ambiguus nucleus showed motopsin mRNA expression. Expression was also found in the anterior horn of the spinal cord. The above findings strongly suggest that neurons in almost all motor nuclei, particularly in the brainstem and spinal cord, express motopsin mRNA, and that motopsin seems to have a close relation to the functional role of efferent neurons.

Spinal and cranial motoneurons express alpha- and beta-calcitonin gene-related peptide (CGRP) mRNAs constitutively at variable ratios, and these two mRNAs are differentially regulated following axotomy in spinal, facial, and hypoglossal motoneurons. The purpose of this study was to investigate the change in CGRP mRNA expression following nerve injury in oculomotor, trochlear, abducens, and trigeminal motor nuclei in which beta-CGRP mRNA is predominantly expressed under normal conditions. Using male Sprague-Dawley rats, either the left eyeball and the orbital contents including the bulbar muscles were removed, or the left masseter nerve was ligated and transected. The rats were allowed to survive for 1, 3, 7, 14, 28, 56 days following these procedures. The levels of mRNAs for alpha- and beta-CGRP and growth-associated protein (GAP)-43 were analyzed by in situ hybridization histochemistry using 35S-labeled oligonucleotide probes. Following nerve injury, the expression of alpha-CGRP mRNA rapidly increased on the directly-injured side in all of these nuclei. Thereafter, it gradually decreased and returned to about the control level at postoperative day 56 within oculomotor, trochlear, and abducens motoneurons, but it sustained at a high level within trigeminal motoneurons. The expression of beta-CGRP was quite variable among these nuclei, and significant changes were also seen on the side contralateral to the directly-injured side. These data indicate that the up-regulation of alpha-CGRP mRNA may be a common response of cranial motor neurons following axotomy even if the constitutive expression of beta-CGRP mRNA exceeds that of alpha-CGRP mRNA in these neurons.

We examined the distribution of choline acetyltransferase (ChAT) mRNA in the brain of six autopsied individuals by in situ hybridization with 35S-labeled human ChAT riboprobes. Neurons containing hybridization signal for ChAT mRNA were observed in the nucleus of the diagonal band of Broca, the basal nucleus of Meynert, the caudate nucleus, the putamen, the pedunculopontine tegmental nucleus, the laterodorsal tegmental nucleus, the parabigeminal nucleus, the oculomotor nucleus and the trochlear nucleus. These findings were in good agreement with previous ChAT-immunohistochemical data. In contrast, labeled neurons were not observed in the medial septal and medial habenular nuclei, in which previously ChAT-immunoreactive neurons have been identified in many mammalian species, including the human. An unexpected result of the present study was the demonstration of neurons with ChAT mRNA signal in restricted areas of the human cerebral cortex.

We have recently shown that spinal muscular atrophy (SMA), an autosomal recessive disorder characterized by motor neuron loss, is associated with deletion of a gene that encodes the neuronal apoptosis inhibitory protein (NAIP). In the present study, we have examined the distribution of NAIP-like immunoreactivity (NAIP-LI) in the rat central nervous system (CNS) by using an affinity-purified polyclonal antibody against NAIP. In the forebrain, immunoreactive neurons were detected in the cortex, the hippocampus (pyramidal cells, dentate granule cells, and interneurons), the striatum (cholinergic interneurons), the basal forebrain (ventral pallidum, medial septal nucleus, and diagonal band), the thalamus (lateral and ventral nuclei), the habenula, the globus pallidus, and the entopenduncular nucleus. In the midbrain, NAIP-LI was located primarily within neurons of the red nucleus, the substantia nigra pars compacta, the oculomotor nucleus, and the trochlear nucleus. In the brainstem, neurons containing NAIP-LI were observed in cranial nerve nuclei (trigeminal, facial, vestibular, cochlear, vagus, and hypoglossal nerves) and in relay nuclei (pontine, olivary, lateral reticular, cuneate, gracile nucleus, and locus coeruleus). In the cerebellum, NAIP-LI was found within both Purkinje and nuclear cells (interposed and lateral nuclei). Finally, within the spinal cord, NAIP-LI was detected in Clarke's column and in motor neurons. Taken together, these results indicate that NAIP-LI is distributed broadly in the CNS. However, high levels of NAIP-LI were restricted to those neuronal populations that have been reported to degenerate in SMA. This anatomical correspondence provides additional evidence for NAIP involvement in the neurodegeneration observed in acute SMA.

Immunocytochemical studies and fiber-tracing studies were performed in adult cats to analyze the input-output organization of the interstitial nucleus of Cajal.Glutamate and aspartate immunoreactivity produced intense labelling of many cell bodies and terminals in the interstitial nucleus of Cajal and its adjacent reticular formation (Nint-RF). GABA immunoreactivity in the Nint-RF showed no labelling in cell bodies and strong labelling in the terminals. Some choline acetyltransferase-positive neurons and terminals, and a few substance P-positive fine fibers were also observed in the Nint-RF.Following WGA-HRP injection in the Nint-RF, many labelled neurons were found in the zona incerta (ZI), the Forel's field H (FF), the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF), the Nint, the nucleus of the posterior commissure (NPC), the pretectum, the superior colliculus, the dorsal tegmental nucleus, the locus coeruleus, all cerebellar nuclei, the superior and medial vestibular nuclei, the dorsal group y, the nucleus prepositus hypoglossi (PH), and the pontomedullary reticular formation (PMRF). Many labelled terminals were observed in the thalamic central lateral and parafascicular nuclei, the ZI, the FF, the riMLF, the Nint, the NPC, the magnocellular red nucleus, the oculomotor nucleus, the trochlear nucleus, the facial nucleus, the medial and desending vestibular nuclei, the ventral group y, the PH, the PMRF, the medial part of the vetrolateral outgrowth, the rostral part of the dorsal cap, the caudal parts of the medial and dorsal accessory olive, and the spinal cord.The nomenclature of the cat mesodiencephalic structure was also described: the nucleus of Darkschewitsch, the nucleus accessorius medialis of Bechterew, the FF, the riMLF, the Nint, the suprarubral reticulal formation, and the subnucleus dorsomedialis and ventrolateralis of the parvicellular red nucleus. All of these nuclei fuse with each other, and the borders do not always remain apparent.

Neurons in the interstitial nucleus of Cajal (INC) that are known to be involved in eye and head movements are excitatory. We investigated the input-output organization of inhibitory INC neurons involved in controlling vertical saccades. Intracellular recordings were made in INC neurons activated antidromically by stimulation of the contralateral trochlear or oculomotor nucleus, and their synaptic input properties from the superior colliculi (SCs) and the contralateral INC were analyzed in anesthetized cats. Many INC neurons projected to the contralateral trochlear nucleus, Forel's field H, INC, and oculomotor nucleus, and mainly received monosynaptic excitation followed by disynaptic inhibition from the ipsi- and contralateral SCs. After sectioning the commissural connections between the SCs, these neurons received monosynaptic excitation from the ipsilateral medial SC and disynaptic inhibition via the INC from the contralateral lateral SC. Another group of INC neurons were antidromically activated from the contralateral oculomotor nucleus, INC and Forel's field H, but not from the trochlear nucleus, and received monosynaptic excitation from the ipsilateral lateral SC and disynaptic inhibition from the contralateral medial SC. The former group was considered to inhibit contralateral trochlear and inferior rectus motoneurons in upward saccades, whereas the latter was considered to inhibit contralateral superior rectus and inferior oblique motoneurons in downward saccades. The mutual inhibition existed between these two groups of INC neurons for upward saccades on one side and downward saccades on the other. This pattern of input-output organization of inhibitory INC neurons suggests that the basic neural circuits for horizontal and vertical saccades are similar.

The rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) contains premotor neurons that are related to the control of vertical and torsional saccadic eye movements. In the present study, complimentary light microscopic anterograde biocytin and retrograde horseradish peroxidase experiments have been performed to determine the organization of premotor neurons in the riMLF in the cat that are related intimately to the vertical motoneuron populations in the oculomotor and trochlear nuclei. The results indicate a rostral-caudal topographic arrangement of neurons in the riMLF that is related to the target projections to vertical downward (inferior rectus and superior oblique) and vertical upward (superior rectus and inferior oblique) motoneurons, respectively, in the oculomotor and trochlear nuclei. Both the anterograde and the retrograde studies are consistent, in that they demonstrate the tendency for downward and upward riMLF neurons to be separated spatially by a distance of approximately 0.5 mm in the rostral-caudal axis of the nucleus. The riMLF projections to inferior oblique and superior oblique motoneurons are predominantly ipsilateral. Projections to inferior rectus and superior rectus motoneurons, however, are bilateral, and, presumably, they provide one means for assuring the conjugacy of vertical saccadic eye movements. Because premotor burst neurons that encode parameters for upward or downward saccades are intermingled within the riMLF, and excitatory and inhibitory premotor neurons also coexist in this region, the findings from this study suggest that subregions of the riMLF contain coexistent populations of excitatory and inhibitory neurons that are related to opposite directions of vertical eye movements. The spatial segregation of excitatory premotor neurons in the riMLF that are related to vertical upward vs. downward movements, furthermore, provides a basis for the interpretation of vertical upward and/or downward gaze palsies that might result from discrete lesions at the mesodiencephalic junction in humans.

1. The efferent projections of the interstitial nucleus of Cajal (NIC) were studied in the squirrel monkey after iontophoretic injections of biocytin and Phaseolus Vulgaris leucoagglutinin into the NIC. To ensure the proper placement of the tracer, the same pipettes were used to extracellularly record the discharge pattern of NIC neurons. 2. Three projection systems of the NIC were distinguished: commissural (through the posterior commissure), descending, and ascending. 3. The posterior commissure system gave rise to dense terminal fields in the contralateral NIC, the oculomotor nucleus, and the trochlear nucleus. 4. The descending system of NIC projections deployed dense terminal fields in the ipsilateral gigantocellular reticular formation and the paramedian reticular formation of the pons, as well as in the ventromedial and commissural nuclei of the first two spinal cervical segments. It also gave rise to moderate or weak terminal fields in the vestibular complex, the nucleus prepositus hypoglossi, the inferior olive, and the magnocellular reticular formation, as well as cell groups scattered along the paramedian tracts in the pons and the pontine and medullary raphe. 5. The ascending system of NIC projections gave rise to dense terminal fields in the ipsilateral mesencephalic reticular formation and the zona incerta as well as moderate or weak terminal fields in the ipsilateral centromedian and parafascicular thalamic nuclei. It also provided dense bilateral labeling of the rostral interstitial nucleus of the medial longitudinal fasciculus and the fields of Forel, and moderate or weak bilateral labeling of the mediodorsal, central medial, and central lateral nuclei of the thalamus. 6. Models of saccade generation that rely on feedback from the velocity-to-position integrators and include the superior colliculus in their local feedback loop are contradicted because no fibers originating from the NIC traveled to the superior colliculus to deploy terminal fields. 7. Consistent with its morphological and functional diversity, these data indicate that the primate NIC sends signals to a multitude of targets implicated in the control of eye and head movements.

The distribution and morphological characterization of nicotinamide adenine dinucleotide phosphate-diaphorase (ND)–positive cells and fibers in the tench central nervous system was mapped by using a direct histochemical method. This enzyme was observed in specific cell populations throughout all main divisions of the tench brain. In the telencephalon, we found strongly labeled olfactory fibers, as well as positive cells and fibers in the area ventralis of the telencephalic lobes. Positive staining was observed in the following diencephalic nuclei: nucleus preopticus magnocellularis pars magnocellularis, nucleus recessus lateralis, nucleus recessus posterioris, nucleus posterior tuberis, and nucleus diffusus torus lateralis, as well as small cells with a diffuse distribution surrounding the diencephalic ventricle. In the mesencephalon, heavily stained ND-positive neurons were observed in the nucleus fasciculi longitudinalis medialis, nucleus nervi oculomotorius, and nucleus nervi trochlearis. In the hindbrain the most evident staining was observed as large neurons located in the nuclei of the cranial nerves, scattered positive cells located between the negative fibers of the cranial nerves, and in the nucleus fasciculi solitari. Finally, in the spinal cord, ND-positive cells and fibers were mainly located in the ventral horn. This distribution of ND labeling in the brain of the tench is significantly different from previous data on ND activity in the brain of terrestrial vertebrates and does not correlate with the presence and distribution patterns of several neurotransmitters and neuroactive substances in the teleost brain. © 1995 Wiley-Liss, Inc.

The distribution of neurons projecting to the trochlear nucleus of goldfish (Carassius auratus) was studied by the electrophoretic injection of horseradish peroxidase into the nucleus. The location of

This article provides a basic scheme of sequential anatomic and some physiologic events occurring during the course of embryonic development of motor neurons and muscles, leading to the establishment of mature nerve-muscle relationships. Motor neurons and muscles begin their development independently and during embryogenesis they become dependent on each other for further development and survival. Aspects of development which occur independently and those requiring mutual interactions are identified. The development of motor neurons is discussed with respect to their production, projection, neuromuscular transmission, myelination, sprouting, survival, and death. The development of muscles is discussed with respect to the origin, differentiation, and muscle fiber types. Discussion on the development of neuromascular junction includes differentiation of presynaptic nerve terrninal, postsynaptic components, and elimination of multiple axons.© 1995 John Wiley &Sons, Inc.

Background: Myokymia of the obliquus superior muscle is a rare episodic microtremor caused by uncontrolled activities of the trochlearis nerve fibres. Epilepsy is also caused by spontaneous discharges of neurons. In our report we present an associated epilepsy which to the best of our knowledge is described for the first time. Patient: An 61-year old man with twitches of the right eye for 6 weeks and a subjective feeling of eye movement was investigated at our hospital. His history was void of any ophthalmologic diseases. However, he suffered from cryptogenetic epilepsy known since childhood. The morphological and orthoptical findings of his eyes were normal. During the slit-lamp investigation a unilateral rotating microtremor of the right eye induced by looking downward was seen. The neurologic investigation, magnetic resonance imaging and assessment of the thyreoid function did not show further pathological results. The patient underwent treatment with carbamazepine. Under this therapy he did not show any symptoms of myokymia during follow-up. Summary: To the best of our knowledge this is the first case of myokymia of the obliquus superior muscle associated to epilepsy. To our opinion, any case of this syndrome should be investigated for epilepsy. A causal relation is unlikely since the most probable etiologies are either spontaneous discharges of trochlear nucleus neurons or a close contact between vessel and nerve analogously to trigeminal neuralgia.

The midbrain periaqueductal grey matter (PAG) has numerous functional roles that include mediating nociceptive inhibition and integrating behavioural and physiological responses to potentially threatening or stressful stimuli. Underlying these behaviours is the diverse interconnectivity of this region, and it is possible that neurochemical subdivisions within the PAG reflect the functional properties of the different PAG regions. In this study, using in situ hybridization, we have investigated the distribution in the rat PAG of the messenger ribonucleic acids (mRNAs) encoding seven neuropeptides: enkephalin (ENK), substance P (SP), somatostatin (SST), galanin (GAL), vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY), and calcitonin gene-related peptide (CGRP). Each peptide mRNA had a distinct topographical distribution in the PAG. Preproenkephalin A (ENK) mRNA-expressing cells were found at all levels of the PAG in three distinct longitudinal columns. Preprotachykinin A (SP)-expressing cells were found at all levels of the PAG, principally in the Edinger-Westphal nucleus and the lateral and dorsal PAG. There was a column of neurons producing mRNA-encoding somatostatin that extended along the rostrocaudal extent of the ventrolateral PAG; there were also labelled cells in the dorsal and dorsolateral subdivisions at some levels of the PAG. Galanin mRNA-producing neurones were limited to the dorsal raphe nucleus and to a second population in the ventral border of the aqueduct. VIP mRNA-producing neurones were found in very localized regions of the PAG, including the cell-sparse region immediately ventral to the aqueduct and the ventral part of the dorsal raphe nucleus. NPY mRNA-producing neurones were localized mainly in some cells of the Edinger-Westphal nucleus and dorsal raphe nucleus. CGRP mRNA-expressing neurons were limited to the oculomotor and trochlear nucleus. The results showed a topographical distribution of neuropeptides over the rostrocaudal extent of the PAG that is compatible with the emerging theory that the anatomical and functional specificity of the PAG is expressed in the form of longitudinally arranged neuronal columns that extend for varying distances along the rostrocaudal axis of the midbrain PAG.

Based on enzymatic activity, the localization and the identification of d -amino-acid oxidase-containing cells in rat whole brain was systematically studied in serial fixed sections. The oxidase activity was absent or scarce in the forebrain, was confined to the brain stem (midbrain, pons and medulla oblongata) and cerebellum, and its localization was extended to the spinal cord. In the brain stem the oxidase was mainly localized in the tegmentum, particularly in the reticular formation. The intense oxidase reactions were present in the red nucleus, oculomotor nucleus, trochlear nucleus, ventral nucleus of the lateral lemniscus, dorsal and ventral cochlear nuclei, vestibular nuclei, nuclei of posterior funiculus, nucleus of the spinal tract of the trigeminal nerve, lateral reticular nucleus, inferior olivary nucleus, and hypoglossal nucleus. In the cerebellum the activity in the cortex was much more intense than that in the medulla. In all the fields described above, the oxidase-containing cells were exclusively astrocytes including Bergmann glial cells, and neither neuronal components, endothelial cells, oligodendrocytes nor ependymal cells showed oxidase activity. These results indicated that the astrocytes regionally differentiated into two distinct types, one of which expressed oxidase in the midbrain, rhombencephalon and spinal cord, and the other which did not in the forebrain. The localization of the oxidase was inversely correlated with the distribution of free d -serine in mammalian brains (Nagata, Y., Horiike, K. and Maeda, T., Brain Res. , 634 (1994) 291–295). Based on the characteristic localization of the oxidase-containing astrocytes, we discussed the physiological role of the oxidase.

Introduction. Nuclei of oculogyric nerves (principal oculomotor nucleus, trochlear nucleus and abducens nucleus) are densely vascularized brain­stem structures. The aim of this study was to determine quantitative characteristics of the vascular network of these nuclei. Material and methods. The study was done on 30 adult brainstems, both male and female, without diagnosed neurological disturbances. Three-millimetrethick stratums were taken in transversal plane and cut in 0.3 micrometer semi-serial sections stained with Mallory method. The images of studied nuclei were taken with „Leica” DM 1000 microscope and „Leica” EC3 digital camera under 400x magnification, and analyzed by ImageJ software with A 100 grid. The statistical analysis was performed by Statistical Package for the Social Sciences software with 5% level of significance. Results. A statistically significant difference was found in the volume and surface density between principal oculomotor nucleus and trochlear nucleus, and between trochlear nucleus and abducens nucleus. No difference was found in the length density. Discussion. The results of this research match the results of studies on characteristics of vascular network of oculogyric nerve nuclei, while the comparison of vascular networks of these nuclei, substantia nigra, vestibulocochlear nuclei and precentral gyrus illustrates differences in quantitative characteristics of blood vessels in these structures. Conclusion. Blood vessels of principal oculomotor nucleus and abducens nucleus have similar dimensions and approximately the same arborization pattern, while vessels of trochlear nucleus have significantly smaller dimensions and density.

The development of the ocular motor system was studied in 3- to 6-year old larval lampreys with two different retrograde tracers. Motor neurons of the oculomotor and trochlear nuclei are situated closely to one another in younger larvae. Cases in which only trochlear neurons were labelled revealed trochlear motor neurons scattered from the midbrain tegmentum through the anterior medullary velum. We believe this distribution reflects the place of final mitosis (midbrain tegmentum) and subsequent migration (anterior medullary velum) of lamprey trochlear motor neurons. Evidence is also presented for contralateral migration of oculomotor motor neurons and for ventrolateral migration of abducent motor neurons. The distances covered by migrating ocular motor neurons range from 100 to 150 μm in small larvae; these are distances that could be covered easily during the several years duration of larval development in lampreys.

Accompanying neurological symptoms and signs are diagnostic hallmarks of fourth nerve palsy (4NP) from an intra-axial lesion. Due to the proximity of the trochlear nucleus and fascicles to the inferior colliculus (IC), auditory symptoms including tinnitus may occur with an intra-axial 4NP. A 53-year-old man with hypertension and diabetes developed right 4NP with a sudden worsening of tinnitus. MRI disclosed an infarction involving the trochlear fascicle and IC in the left dorsal midbrain. Tinnitus may be a symptom indicating an intra-axial lesion causing a 4NP.

Summary Background The trochlear nucleus, the smallest of the extraoculomotor nuclei, is unique or even curious, because the nerve roots emerge dorsally from the superior medullary velum after decussation. Little information is available on the developmental anatomy of this nucleus in humans. Design/subjects We examined serial brain sections from 10 premature infants aged 20–39 weeks of gestation to document the histology and morphometry. Results The trochlear nucleus was composed of three parts: the rostral tip, the main body, and the caudal division. The rostral tip was a rostral continuation of the main body, being closely related to the oculomotor nucleus; the main body was enveloped by a fibrous capsule; the caudal division was a small separate cluster of neurons in the medial longitudinal fasciculus or the root fibers with individual variations. Tigroid Nissl bodies first appeared at 28 weeks in presumed motoneurons. Various sizes of motoneurons were recognized; medium-sized to small motoneurons were preferentially accumulated in the rostral tip. Among the motoneurons, presumed non-motor neurons were infrequently scattered. Morphometric analysis showed that the nuclear volume exponentially increased with age, about 15 fold over 20–39 weeks, while the average profile area of the neurons linearly increased. Statistical analysis confirmed that cell area was smallest in the rostral tip among the three parts. Conclusion Although the sample number is small in this study, it suggests that the human trochlear nucleus can be divided into three parts, and that the overall growth may be accelerated at about 30 weeks of gestation.

Three cases of superior oblique myokymia (SOM) were analyzed neuro-ophthal-mologically using single neuromuscular unit (NMU)-electromyography (EMG), single fiber EMG, and a two-dimensional eye movement analyzing system.The action potentials of the superior oblique muscle had high amplitude, long duration and many turns, and single NMU-EMG of the inferior oblique muscle showed no decrease of discharge synchronized with the burst discharges of the superior oblique muscle. Moreover, the jitter value calculated from single fiber EMG of the superior oblique muscle was relatively small and essentially the same as in normal controls and muscles completely recovered from oculomotor nerve palsy.Two-dimensional eye movement analysis showed unilateral rotary eye movements with a lower frequency than had been previously reported.These studies suggested that the lesion responsible for SOM was in either the ipsilateral trochlear nucleus or its infranuclear tract and that SOM might be associated with the recovery stage ...

Biocytin was injected into the oculomotor, trochlear, or abducens nucleus on one side using isolated chicken brainstem preparations or brain slices to identify the medial vestibular nucleus (MVN) neurons projecting to these targets. Oculomotor nucleus injections produced retrogradely labeled neurons in the contralateral ventrolateral MVN (MVNVL), with few labeled neurons in the ipsilateral MVNVL and rarely in the dorsomedial MVN on either side. Labeled MVNVL neurons were identified as stellate (95%) and elongate (5%) cells. Trochlear nucleus injections produced a similar pattern of MVN neuron labeling. Abducens nucleus injections resulted in retrogradely labeled stellate (87%) and elongate (13%) neurons in the MVNVL, which had smaller cell bodies than those projecting to the oculomotor nucleus. Anteroposteriorly, labeled MVNVL neurons were coextensive with the tangential nucleus, with neurons projecting to the oculomotor nucleus distributed lateral to and intermixed with the more medially situated neurons projecting to the abducens nucleus. The fundamental pattern of vestibuloocular projecting neurons was similar at both embryonic ages studied, E16 and E13. In contrast to the case in mammals, where most vestibuloocular projection neurons reside within the MVN, most retrogradely labeled neurons in these chicken preparations were found within the ventrolateral vestibular, descending vestibular, and tangential nuclei. The morphological identification and mapping of vestibuloocular projection neurons in the chicken MVN described here represents the first step in a systematic evaluation of the relationship between avian vestibuloocular neuron structure and function. © 2009 Wiley-Liss, Inc.

Trochlear palsy from intra-axial lesions usually accompanies other neurological deficits, and isolated trochlear palsy due to midbrain stroke is extremely rare. We report two patients with isolated trochlear nerve palsy due to circumscribed dorsal midbrain strokes, one from infarction and the other from hemorrhage, which are located in the region of the trochlear nucleus or adjacent fascicle. Focal brain stem stroke should be considered as a rare cause of trochlear palsy even though there are no associated neurological deficits.

About half of the motor neurons produced by some neural centers die during the course of normal development. It is thought that the size of the target muscle determines the number of surviving motor neurons. Previously, we tested the role of target size in limiting the number of survivors by forcing neurons to innervate a larger target (Sohal et al., '86). Results did not support the size-matching hypothesis because quail trochlear motor neurons innervating duck superior oblique muscle were not rescued. We have now performed the opposite experiment, i.e., forcing neurons to innervate a smaller target. By substituting the embryonic forebrain region of the duck with the same region of the quail before cell death begins, chimera embryos were produced that had a smaller quail superior oblique muscle successfully innervated by the trochlear motor neurons of the duck. The number of surviving trochlear motor neurons in chimeras was significantly higher than in the normal quail but less than in the normal duck. The smaller target resulted in some additional loss of neurons, suggesting that the target size may regulate neuron survival to a limited extent. Failure to achieve neuron loss corresponding to the reduction in target size suggests that there must be other factors that regulate neuron numbers during development.

In order to study the morphological characteristics and terminating patterns of the neurons of the trigeminal mesencephalic nucleus (Vme), 55 masseteric neurons in Vme in the rat were stained by intracellular injection of horseradish peroxidase (HRP). Labeled cells were distributed throughout the nucleus. These neurons were divided into three types: uni- or pseudounipolar (type A, n = 43), bipolar (type B, n = 5), and multipolar cells (type C, n = 7). Each type was further divided into two subtypes according to the largest diameter of the perikarya (type a greater than or equal to 30 microns, type b less than 30 microns). The central processes of type Aa neurons projected to the following three groups of target nuclei: 1) nuclei functioning as interneurons, including supratrigeminal nucleus (Vsup), intertrigeminal nucleus (Vint), juxta-trigeminal region (Vjux), and parvicellular nucleus of the pontomedullary reticular formation (PcRF); 2) motor nuclei, including the trigeminal motor nucleus (Vmo), accessory facial nucleus (NVIIacs), accessory abducens nucleus (NVIacs), and a small number of labeled axons in the oculomotor nucleus and trochlear nucleus; 3) sensory nuclei, including the dorsomedial part of the principal trigeminal sensory nucleus (Vpdm) and the dorsomedial part of subnucleus oralis of the trigeminal spinal nucleus (Vodm). Labeled processes were dense in the Vsup, Vmo, and Vpdm. The proprioceptive pathway of the fifth nerve is discussed. Direct projections from type Aa neurons of Vme to the Vpdm and dorsolateral part of the Vsup contribute to conduction of the proprioceptive information from spindles of masticatory muscle to the contralateral thalamus in the rat. Different axon morphology, distribution, terminal branch density, and terminating patterns of type Aa neurons were noted in different functional groups of the projecting nuclei, especially in the Vsup, Vmo, and Vpdm. The highest terminal branching density, the most extensive distribution, and two different types of branching patterns (claw-like and comb-like) were observed in Vsup. Selective distribution and single-beaded or "Y"-shaped terminal branches were observed in Vmo. In the Vppdm the axonal branches were sparser than in the Vsup or Vmo, and had an arrangement like the branches of a weeping willow tree. These characteristics of anatomical organization might be related to the function of each projecting nucleus.

The development of the oculomotor and trochlear nuclei (nIII and nIV) was studied with the horseradish peroxidase (HRP) and the cobalt labelling techniques in Xenopus laevis tadpoles. The earliest labelling of the oculomotor neuroblasts was observed at stage 32. The ipsi- and contralateral nuclei were found in two distinct groups on either side of the brainstem and the oculomotor commissure formed by crossing axons was present at this early stage. The fusion of the two nuclei began at the late larval stage when the axonal outgrowth had been presumably completed. The trochlear neuroblasts could be first labelled at stage 39 when the position of the nucleus and axonal pathway was similar to the adult form.

The organization of vestibulo-ocular projections and their spatial relationship to vestibulo-spinal projections were ascertained in the 11-day chicken embryo through retrograde tracing experiments. An in vitro preparation of the brainstem facilitated precisely localized application of tracers. Unilateral labelling of the ascending medial longitudinal fascicle (MLF), just caudal to the trochlear nucleus, labelled coherent groups of vestibular neurons that had an asymmetrical distribution on the two sides of the brainstem. Axons originating from either side followed one of four trajectories, and the groups of neurons could therefore be identified on the basis of their position and their projection pathway. Labelling each side of the MLF with a different tracer showed that although neurons projecting in the ipsi- and contralateral MLF were intermingled in some areas, individual neurons projected on one side only. Labelling the ascending MLF and the high cervical spinal cord with different tracers showed that vestibulo-ocular neurons had a wider rostro-caudal distribution than vestibulospinal neurons. Some vestibulospinal and vestibulo-ocular groups were spatially segregated, others were intermingled. Very few (in most preparations no) neurons were found to project to both targets. Together with our previous study on vestibulospinal projections in the 11-day chicken embryo (Glover and Petursdottir, J. Comp. Neurol. 270:25-38, '88) the results show that vestibular neurons in different regions project in characteristic subsets of the available pathways.

1. The preceding study in the alert cat has shown that many secondary vestibular axons that ascend in the medial longitudinal fasciculus (MLF) increase their firing rate in proportion to downward eye position. In the present study, projection and termination of these downward-position-vestibular (DPV) neurons within extraocular motoneuron pools were studied electrophysiologically by spike-triggered averaging techniques and morphologically be reconstructing their axonal trajectory after intra-axonal injection of horseradish peroxidase (HRP). 2. Extracellular field potentials recorded within the trochlear nucleus and/or the inferior rectus subdivision of the oculomotor nucleus were averaged by the use of spike potentials of single DPV neurons as triggers. All the crossed-DPV axons tested induced negative unitary field potentials in the trochlear nucleus (n = 9) and in the inferior rectus subdivision of the oculomotor nucleus (n = 5), suggesting that they made monosynaptic excitatory connection with motoneurons in these nuclei. The four crossed-DPV axons tested in the two motoneuron pools induced unitary field potentials in both. The majority of crossed-DPV axons terminated in these nuclei were directly activated from the caudal MLF, indicating that they had descending collaterals projecting to the spinal cord as well. The uncrossed-DPV axons did not induce such unitary field potentials either in the trochlear nucleus (n = 4) or in the inferior rectus subdivision (n = 3). 3. All the uncrossed-DPV axons examined (n = 14) induced positive unitary field potentials in the superior rectus subdivision of the oculomotor nucleus, suggesting that they made monosynaptic inhibitory connections with motoneurons innervating the superior rectus muscle. These uncrossed-DPV axons displayed regular firing patterns and were not activated from the caudal MLF. None of the crossed-DPV axons tested (n = 4) induced unitary field potentials in the superior rectus subdivision. 4. Five crossed-DPV axons were injected with HRP. All these axons ascended in the MLF contralateral to their soma, gave off many collaterals to the trochlear nucleus, and projected more rostrally. For three well-stained axons, numerous terminal branches were also found in the rostroventral part of the contralateral oculomotor nucleus, the area corresponding to the inferior rectus subdivision. Some collaterals in the oculomotor nucleus recrossed the midline to terminate in the medial part of the ipsilateral oculomotor nucleus. Other terminations were observed in the interstitial nucleus of Cajal and in the periaqueductal gray adjacent to the oculomotor nucleus. The crossed axons injected included both regular and irregular types, and three of the four examined were activated from the caudal MLF.(ABSTRACT TRUNCATED AT 400 WORDS)

The responses to injury of myelinated central axons in neonatal (5-day) and weanling (30-day) rats were compared, using the trochlear nerve fibres in the anterior medullary velum (AMV) as an experimental system. In intact animals, fibres of the trochlear nerve decussate completely in the AMV, to enter the contralateral nerve. Sprouting from proximal axon stumps was seen within 36 h after injury in silver-stained, whole mounts of mid-sagittally lesioned AMVs from weanlings. Subsequent growth produced a tangled axon mass which persisted until 15-20 days post-lesion (d.p.l.) but then began to degenerate. By 50 d.p.l., the majority of surviving axons looped within the AMV to enter the ipsilateral trochlear nerve; few axons remained growing randomly within the AMV. Axonal debris persisted within the velum 50 d.p.l. In neonatal rats, lesioned trochlear axons initially developed axon sprouts, but then degenerated with rapid clearance of debris, leaving the AMV devoid of both axons and degeneration products by 6 d.p.l. From 8 d.p.l., the velum became repopulated by axons which either grew randomly or looped to enter the ipsilateral peripheral nerve. Both patterns of axon growth were still observed 50 d.p.l. In both experimental groups, horseradish peroxidase injection to the right superior oblique muscle 40 d.p.l. indicated that at least some of the looping fibres observed within the lesioned AMVs originated in the ipsilateral trochlear nucleus. The origin of those axons growing randomly within the AMVs of neonatally-lesioned animals is unknown. The results are discussed with reference to current ideas concerning regeneration-inhibiting elements in the CNS, and regeneration-promoting factors in the PNS.

The natriuretic peptide receptor type C (NPR-C) binds all natriuretic peptides. It is thought to be involved in the clearance of natriuretic peptides and more recently has been defined as essential for the neuromodulatory effects of natriuretic peptides. Although the distribution of NPR-C mRNA has been reported in the rat forebrain, there are no data on the distribution of NPR-C in the brainstem. We report an immunofluorescence study on the distribution of NPR-C immunoreactivity in the rat brainstem, and its presence in cholinergic and catecholaminergic neurons. NPR-C immunoreactivity was detected in several regions, including the periaqueductal gray, oculomotor nucleus, red nucleus and trochlear nucleus of the midbrain; the pontine nucleus, dorsal tegmental nucleus, vestibular nucleus, locus coeruleus, trigeminal motor nucleus, nucleus of the trapezoid body, abducens nucleus and facial nucleus of the pons; and the dorsal motor nucleus of the vagus, hypoglossal nucleus, lateral reticular nucleus, nucleus ambiguus and inferior olivary nucleus of the medulla oblongata. Interestingly, NPR-C immunoreactivity was detected in the cholinergic neurons of the oculomotor nucleus, trochlear nucleus, dorsal tegmental nucleus, motor trigeminal nucleus, facial nucleus, dorsal motor nucleus of the vagus, nucleus ambiguus and hypoglossal nucleus. Furthermore, NPR-C immunoreactivity was detected in several catecholaminergic neuronal groups including the A6, A5, A1, C3 and C1 cell groups. These results are consistent with an important role for natriuretic peptides in neuroendocrine regulation and central cardiovascular integration. The extensive distribution of NPR-C in the brainstem supports the hypothesis that NPR-C is involved in the neuromodulatory effect of natriuretic peptides.