Anatomical relationship between mesencephalic trigeminal nucleus and cerebellum in the duck

[Vertical nystagmus]

The review article provides a definition and classification of different nystagmus types, a comparative description of the central and peripheral vestibular nystagmus. The pathogenetic patterns of up-beating and down-beating nystagmus are accurately described. The features of nystagmus formation in various diseases are discussed, such as Wernicke encephalopathy, Arnold-Chiari anomaly, spinocerebellar ataxia and vestibular migraine. The authors provide their own data on oculomotor disorders in 100 patients with vestibular migraine and migraine with a brain stem aura. This article considers approaches to treatment: surgical and conservative. In conclusion, was noted the possibility of differentiating the central and peripheral vestibular nystagmus by means of clinical study. As well, the differences between vertical nystagmus associated with organic lesions of the brain stem or cerebellum and transient nystagmus with vestibular migraine are highlighted. The authors note the need for in-depth studies of nystagmus in vestibular migraine patients and methods of dealing with it.

The mesencephalic trigeminal nucleus of the duck: development and apoptosis

The normal development of the mesencephalic trigeminal nucleus (MesV) of the white Peking duck (Anas platyrhynchos) was studied from the 9th day of incubation until hatching and during adulthood. In the early days of embryonic development, neurons are present in the posterior commissure and in the mesenchymal tissue outside the leptomeninges in addition to those in the tectal commissure (TC) and in the optic tectum. Following the internucleosomal cleavage of DNA, a massive loss of neurons in the MesV starts in the 11-day embryo and continues until the 15th day of incubation. On the 16th day, the nucleus consists of a numerically larger medial division located in the TC and a smaller lateral division within the stratum griseum periventriculare as is found in the adult animal. The programmed cell death occurring in the MesV is discussed herein and correlated with the analogous apoptotic phenomena observed in the trigeminal motor nucleus.

Central connections of the nucleus mesencephalicus nervi trigemini in the mallard (Anas platyrhynchos L.)

BACKGROUND

In the mallard duck, functionally distinct groups of jaw muscles are each innervated by a different subnucleus of the main trigeminal (mV) or facial (mVII) motor nucleus. The other subnuclei of mV and mVII innervate several head muscles, including lingual muscles. The reticular premotor cells of the trigeminal and facial jaw motor subnuclei occupy different areas in the parvocellular reticular formation (RPc). The cell bodies of jaw muscle spindle afferents are situated in the mesencephalic nucleus (MesV). In the present study, the central connections of MesV with jaw motor subnuclei and their premotor areas are investigated.

METHODS

In a first series of experiments, horseradish peroxidase (HRP) injections were made in electrophysiologically identified trigeminal and facial subnuclei. In a second series of experiments, HRP was delivered iontophoretically at different parts of RPc. Anterograde tracing with tritiated leucine was used to confirm the central connections of MesV. Double labeling with fluorescent tracers was used to investigate whether MesV collaterals reach both the rostral and caudal parts of RPc.

RESULTS

MesV projects to only two of the five different subnuclei of the trigeminal motor nucleus. The subnuclei that receive spindle afferents innervate jaw adductor muscles (mV2) or pro- and retractors of the mandible (pterygoid muscles; mV1). The three other subnuclei innervate jaw-opener muscles or other head muscles. MesV fibers also project to the rostral part of the dorsolateral RPc (RPcdl), which serves as a premotor area for the motor subnuclei of adductor and pterygoid muscles. The intermediate part of RPcdl does not contain premotor cells of mV or mVII, and a clear projection of MesV to this area is absent. The caudal part of RPcdl projects to the mV and mVII subnuclei that innervate jaw-opener muscles. This part of RPc receives a projection from the same MesV cells as the rostral RPcdl. The MesV projection to RPc does not include premotor cells of mV and mVII in the ventromedial part of RPc (RPcvm).

CONCLUSIONS

Spindle afferents from jaw-closer muscles project only to mV subnuclei innervating jaw-closer muscles (mV1, mV2) and to a population of premotor cells in the rostral RPcdl that innervates these subnuclei. The mixed population of premotor cells in RPcvm, which innervates both jaw-opener and jaw-closer subnuclei, does not receive a MesV projection. However, a premotor area for jaw-opener subnuclei in the caudal part of RPcdl does receive MesV input and may serve as a relay through which proprioceptive information from jaw closer spindles can reach jaw opener muscles.

Cerebellar connections of the trigeminal system in the pigeon (Columba livia)

Wheat germ-agglutinin conjugated horseradish peroxidase (WGA-HRP) was used to delineate trigeminocerebellar connections in the pigeon. Subnucleus oralis of the nucleus of the descending trigeminal tract (nTTD) is the exclusive origin of trigeminal mossy fibers, which terminate in lobules VIII and IXa. The trigemino-olivary projection originates from subnucleus interpolaris of nTTD, but the existence of an additional pathway relaying in the adjacent lateral reticular formation (i.e. the plexus of Horsley) cannot be excluded. Structures linking the trigeminal cerebellar projections to jaw motoneurons were identified within the cerebellar cortex, the deep cerebellar nuclei and the lateral medullary reticular formation, completing a trigeminocerebellar sensorimotor circuit for the jaw.

The distribution of afferent neurones in the mesencephalic nucleus of the fifth nerve in the cat

The objective of this study was to examine anatomically the distribution of afferent neurones in the mesencephalic nucleus of the fifth nerve (Mes V). HRP was applied, in separate experiments, to the inferior alveolar, infraorbital, and masseter nerves, and injected into the masseter muscle and periodontal ligament. Following application of HRP to the masseter muscle and masseter nerve, labelled cells were found in the ipsilateral motor nucleus of the fifth nerve and in the ipsilateral Mes V. Labelled cells in Mes V, identified as belonging to proprioceptor afferents from jaw-closing muscles, were distributed throughout the full extent of the nucleus. Following application of HRP to the inferior alveolar nerve, infraorbital nerve, and periodontal ligament, labelled cells were found in the ipsilateral trigeminal ganglion and Mes V, and the latter identified as belonging to periodontal receptor afferents. In contrast to the distribution of spindle afferent somata, they were restricted to the caudal region of Mes V. The differential distribution of afferent neurones within Mes V demonstrated in this study confirms previous electrophysiological findings, and its significance is considered.

Exteroceptive and proprioceptive afferents of the trigeminal and facial motor nuclei in the mallard (Anas platyrhynchos L.)

Central pathways converging upon the trigeminofacial motor nuclei of the mallard were studied in order to elucidate neuroanatomically the presumed influence of primary sensory trigeminal afferents upon jaw muscle activity. The techniques used included the Fink-Heimer I method after lesions, and axonal transport labeling following injections of 3H-leucine or of HRP for retrograde identification of the neurons of origin. A general description is given of the trigeminofacial motor complex. Jaw closer muscles are innervated by trigeminal motor neurons, and facial motor neurons innervate the jaw depressor muscles. Two afferents premotor systems, one including the mesencephalic trigeminal nucleus (MesV) and the other the rhombencephalic reticular formation, are distinguished. The proprioceptive neurons of the mesencephalic trigeminal nucleus project upon the ipsilateral trigeminal motor nucleus and upon the nucleus supratrigeminalis. The latter cell group bilaterally projects upon the dorsal and intermediate parts of the facial motor nucleus and upon the dorsal and intermediate parts of the facial motor nucleus and upon part of the trigeminal motor nucleus. Exteroceptive information, relayed through the primary sensory trigeminal column (PrV and nTTD), ultimately reaches the motor nuclei via the reticular formation. The reticular formation forms the final link of three separate circuits: a telencephalic one entered through the principal trigeminal sensory nucleus, a cerebellar one via subnucleus oralis of the descending trigeminal system, and a direct one via subnucleus interpolaris. No direct connections between the principal trigeminal sensory nucleus or subnuclei of the descending trigeminal system and the motor nuclei of the trigeminal (NV) and facial (NVII) nerves have been observed, nor are such direct projections present in the outflow of the presumed telencephalic and cerebellar circuits, viz. of the archistriatum and the central cerebellar nuclei, respectively. The archistriatum projects via the occipitomesencephalic tract upon the lateral rhombencephalic reticular formation as far down as the rostral cervical cord, as well as upon the subnucleus interpolaris of the descending trigeminal system. Similarly, efferents from the central cerebellar nuclei reach the reticular formation, which in turn projects bilaterally upon the motor nuclei. Finally, commissural intermotor connections apparently are mediated by reticular cells surrounding the motor nuclei of NV or NVII, rather than emanating from these nuclei directly.

Reevaluation of projections from the mesencephalic trigeminal nucleus to the medulla and spinal cord: new projections. a combined retrograde and anterograde horseradish peroxidase study

Microinjection of horseradish peroxidase (HRP) into the medullary parvocellular reticular formation (NPvc) resulted in retrograde labeling of neurons throughout the mesencephalic trigeminal nucleus (Mes V). Labeled cells were large and ovoid and were distributed primarily in the expanded pontine part of the nucleus. However, none of the small neurons in Mes V were labeled. Injections of HRP made into adjacent brainstem structures including the nucleus gigantocellularis, ventrolateral reticular formation, vestibular complex, and the spinal trigeminal nucleus failed to label neurons in Mes V. Injections made into the medullary raphe and into regions reported to receive inputs from Mes V--spinal cord, nucleus tractus solitarius, hypoglossal nucleus, and facial nucleus--were also not followed by transport to Mes V. Anterograde axonal transport of HRP from the region of reticular formation innervated by Mes V also labeled axons projecting to Mes V and to visceral and somatic sensorimotor nuclei in the lower brainstem. Recent reports of afferents from the amygdala to Mes V suggest that reflexes involving the mesencephalic trigeminal nucleus might be modulated by signals from limbic and autonomic as well as somatic centers in the brain.

Secondary trigeminocerebellar projections in sheep studied with the horseradish peroxidase tracing method

Secondary trigeminocerebellar connections have been studied with HRP histochemistry in 25 sheep. The results indicate that almost all of the cerebellar cortex except flocculus, ventral paraflocculus and lobules I-IV receives bilateral (mostly ipsilateral) fibers from the trigeminal nuclei. A topographical organization of trigeminocerebellar fibers is present. The mesencephalic tract nucleus projects to the anterior lobe, the simple lobule (HVI), lobules VI, VIII, and the dorsal paraflocculus. The ventral group of the princeps and spinal tract (mainly IDV) nuclei projects to all lobules studied in vermis and hemispheres. More dorsal parts of these nuclei have a more restricted projection field including the vermal lobules VI, VII, and IX and the hemisphere. Cells within and ventral to the motor nucleus of the trigeminal nerve were found labeled after injections into the anterior lobe, the simple lobule, and lobule IX. Labeled cells in the region of the nucleus ovalis and close to the solitary tract project to the simple and paramedian lobule and lobule IX.

The absence of proprioceptive nerve endings in the human periodontal ligament: the role of periodontal mechanoreceptors in the reflex control of mastication

A review of the literature was conducted to determine the presence or absence of proprioceptive nerve endings in the human periodontal ligament. A histologic review of the periodontal ligament innervation concluded that nerve endings found were those mediating pain, pressure, or touch and that there is no histologic evidence of any "classic" proprioceptive nerve ending in the periodontal ligament. A summary is given concerning the precise role of nerve endings in the periodontal membrane, their afferent pathways, and the role of masticatory muscle proprioception, jaw reflexes, and the temporomandibular joint in the coordinated control of mastication and mandibular proprioception.

The trigeminal system in the pigeon (Columba livia). I. Projections of the gasserian ganglion

The central projections of the Gasserian ganglion were investigated in the pigeon, Columba livia. Lesions were placed in the ganglion either by direct surgical exposure or stereotaxically, and following survival times of one to four days, the brains stained with the Fink-Heimer method. The main group of central axons bifurcate to form distinct ascending and descending branches, the tractus trigemini ascendens (TTA) and the tractus trigemini descendens (TTD). A smaller tract also courses caudally (ITTD) separate of TTD proper to terminate in the nucleus cuneatus externus. The TTA projects topographically upon the principal sensory nucleus of the trigeminus, ending in both the pars dorsalis and a smaller pars ventralis. The neurons at the point of bifurcation of the entering radix have been designated as the pars oralis of nTTD. The TTD distributes caudally to several distinct subnuclei at each level, and extends into the cervical spinal cord. Relatively discrete regions corresponding to the pars interpolaris and caudalis were recognized. The projections to the cervical cord terminate in laminae I-IV. There was no evidence of projections to the cerebellum, or contralateral PrV or TTD. There was a small projection to the contralateral cervical spinal cord. No clear evidence of a projection to the nucleus solitarius was found. The distribution of primary trigeminal axons is compared to that described in other vertebrates.

Some visual and other connections to the cerebellum of the pigeon

By anatomical techniques it has been shown that folia VIc-IXc of the pigeon cerebellum receive inputs from the following groups of neurons: the medial and lateral pontine nuclei, the superficial synencephalic nucleus, the medial spiriform nucleus, the inferior olive, and the deep cerebellar nuclei. From all but the last of these, the projection is mainly crossed, though the uncrossed component from the lateral pontine nucleus is not insubstantial. The input from the superficial synencephalic nucleus provides a direct pathway from the retina to the cerebellum (folia VIc, VII, VIII and IXc). Less direct visual pathways reach the cerebellum via the following routes: (i) the superficial synencephalic nucleus projects ipsilaterally to the lateral pontine nucleus and sparsely to the inferior olive; (ii) the tectum projects ipsilaterally to the lateral and medial pontine nuclei, though the latter connection is sparse. In electrophysiological experiments, the importance of the tecto-pontine component of the projection has been demonstrated by cooling the tectum while recording visual responses from the cerebellum. The visual receptive fields of pontine cells have been analysed. They vary in extent from 10 degrees to the whole monocular field. They respond best to moving targets, preferring speeds of 20 to 60 degrees/second, and are usually direction-selective.

Electron microscopic observations of the mesencephalic nucleus of the fifth nerve in the Selachian brain

The mesencephalic nucleus of the trigeminal nerve (mes V) in the brain of the skate (Raja oscellata) was studied by electron microscopy. Mes V neurons are large (40-80 mum diameter) and are located in the periventricular grey matter. Their perikaryal cytoplasm is rich in Golgi apparatus, small mitochondria, rough endoplasmic reticulum, polysomes and bundles of neurofilaments. A striking feature is the presence of masses of glycogen granules, at times surrounded by membrane wrappings and lysosomal bodies. Two types of conventional synaptic contacts were made onto mes V perikarya and dendrites. One had round, agranular vesicles and usually also contained dense-cored vesicles, the other had flattened, pleomorphic, agranular vesicles and usually lacked dense-cored vesicles. Additional membrane complexes consisting of a region of gap junction flanked by sites of desmosomal attachment were observed to link neighbouring mes V neurons. Somato-somatic, dendro-somatic, axo-somatic, and dendro-dendritic junctions were noted. Except for the somato-somatic union, one or more chemical synapses were located close to the sites of gap junctions.