Gabrielle Pinganaud

Trigeminal Projections to Hypoglossal and Facial Motor Nuclei in the Rat

This study was undertaken to identify the trigeminal nuclear regions connected to the hypoglossal (XII) and facial (VII) motor nuclei in rats. Anterogradely transported tracers (biotinylated dextran amine, biocytin) were injected into the various subdivisions of the sensory trigeminal complex, and labeled fibers and terminals were searched for in the XII and VII. In a second series of experiments, injections of retrogradely transported tracers (biotinylated dextran amine, gold‐horseradish peroxidase complex, fluoro‐red, fluoro‐green) were made into the XII and the VII, and labeled cells were searched for in the principal sensory trigeminal nucleus, and in the pars oralis, interpolaris, and caudalis of the spinal trigeminal nucleus. Trigeminohypoglossal projections were distributed throughout the ventral and dorsal region of the XII. Neurons projecting to the XII were found in all subdivisions of the sensory trigeminal complex with the greatest concentration in the dorsal part of each spinal subnucleus and exclusively in the dorsal part of the principal nucleus. Trigeminofacial projections reached all subdivisions of the VII, with a gradual decreasing density from lateral to medial cell groups. They mainly originated from the ventral part of the principal nucleus. In the spinal nucleus, most of the neurons projecting to the VII were in the dorsal part of the nucleus, but some were also found in its central and ventral parts. By using retrograde double labeling after injections of different tracers in the XII and VII on the same side, we examined whether neurons in the trigeminal complex project to both motor nuclei. These experiments demonstrate that in the spinal trigeminal nucleus, neurons located in the pars caudalis and pars interpolaris project by axon collaterals to XII and VII. J. Comp. Neurol. 415:91–104, 1999.

Trigemino‐reticulo‐facial and trigemino‐reticulo‐hypoglossal pathways in the rat

This study was undertaken to identify premotor neurons in the pontomedullary reticular formation serving as relay neurons between the sensory trigeminal complex and the motor nuclei of the VIIth and XIIth nerves. Trigeminoreticular projections were first investigated after injections of anterogradely transported tracers (biotinylated dextran amine, biocytin) into single subdivisions of the sensory trigeminal complex. The results show that the trigeminoreticular projections were abundant from the pars interpolaris (5i) and caudalis (5c) and moderate from pars oralis (5o) of the spinal trigeminal nucleus. Injections into the 5i and 5c produce dense anterograde labeling (1) in the dorsal medullary reticular field; (2) in the parvocellular reticular field, medially adjacent to the 5i; and (3) more rostral in the region dorsal and lateral to the superior olivary nucleus. Some labeled terminals were also found in the intermediate reticular field, whereas only light anterograde labeling was observed in the gigantocellular and oral pontine reticular formation. The 5o sends fibers and terminals throughout the whole reticular formation, with no clear preferential projections within a particular field. Only light projections originated from the principal nucleus (5P). In a second series of experiments, we examined whether premotor neurons in the reticular formation are afferented by trigeminal fibers. Double labeling was performed by injection of an anterograde tracer in the 5i and 5c and retrograde tracer (gold–horseradish peroxidase complex) into the VII or the XII motor nucleus on the same side. Retrogradely labeled neurons in contact with anterogradely labeled boutons were found throughout the reticular formation with predominance in the parvocellular and intermediate reticular fields. These experiments demonstrate the existence of trigeminal disynaptic influences, via reticular neurons of the pontomedullary reticular formation, in the control of orofacial motor behaviors. J. Comp. Neurol. 429:80–93, 2001.

Primary trigeminal afferents to the vestibular nuclei in the rat: existence of a collateral projection to the vestibulo-cerebellum.

Projections from the mesencephalic trigeminal nucleus to the vestibular nuclei were analyzed using retrograde and anterograde tracing methods. The results show that neurons in the caudal part of the trigeminal mesencephalic nucleus project mainly to the medial, inferior and lateral vestibular nuclei and moderately to the peripheral part of the superior vestibular nucleus. Using the double-labeling technique we demonstrate that individual neurons of the mesencephalic nucleus send collaterals to the vestibular nuclei and the vestibulo-cerebellum. These results suggest that these anatomical connections are involved in mechanisms of eye-head coordination.

Reticular premotor neurons projecting to both facial and hypoglossal nuclei receive trigeminal afferents in rats

The distribution of premotor neurons projecting to motor nuclei of both the VIIth (VII) and XIIth (XII) nerves was examined in the pontomedullary reticular formation (RF) of the rat by using retrograde double labeling. After injection of two different tracers in the VII and the XII, most of the double labeled neurons were found caudally in the dorsal RF whereas rostrally they were located in the ventral RF. In some experiments, additional injections of an anterograde tracer were made in the sensory trigeminal nuclei. Anterogradely labeled trigeminal boutons were found in contact with retrogradely double labeled neurons throughout the pontomedullary RF. These neurons were mainly encountered ventral to the trigeminal motor nucleus and dorsal to the VII. Functionally, this region is known to be involved in eye protection mechanisms.

Projections from the Superior Colliculus to the Trigeminal System and Facial Nucleus in the Rat

To determine the influence of the superior colliculus (SC) in orienting behaviors, we examined SC projections to the sensory trigeminal complex, the juxtatrigeminal region, and the facial motor nucleus in rats. Anterograde tracer experiments in the SC demonstrated predominantly contralateral colliculotrigeminal projections. Microinjections in the deep layers of the lateral portion showed labeled nerve fibers and terminals in the ventromedial parts of the caudal principal nucleus and of the rostral oral subnucleus and in the medial part of the interpolar subnucleus. Some terminals were also observed in the juxtatrigeminal region and in the dorsolateral part of the facial motor nucleus contralaterally, overlying the orbicularis oculi motoneuronal region. Verification by retrograde tracer injections into the trigeminal target regions showed labeled SC neurons mostly in lateral portions of layers 4–7. When the juxtatrigeminal region was involved, a remarkable increase of labeled neurons was observed, having a patch‐like arrangement with a decreasing gradient from lateral to medial SC portions. Retrograde tracer injections in the dorsolateral VII nucleus showed bilateral labeled neurons mainly in the deep lateral SC portion. Retrograde BDA microinjections into the same trigeminal or juxtatrigeminal regions, followed by gold‐HRP into the dorsolateral VII nucleus, demonstrated a significant number of SC neurons in deep layers 6–7 projecting to both structures by axon collaterals. These neurons are mediolaterally grouped in patches along the rostrocaudal SC extent; a subset of them are immunoreactive for glutamic acid decarboxylase (GAD). They could be involved in the coordination of facial movements. Simultaneous anterograde and retrograde tracer injections into the lateral SC portion and the VII nucleus respectively localized trigeminofacial neurons receiving collicular input in the trigeminal principal nucleus and pars oralis. Therefore the SC should play a crucial role in regulating motor programs of both eye and eyelid movements. J. Comp. Neurol. 478:233–247, 2004.

Organization of trigeminocollicular connections and their relations to the sensory innervation of the eyelids in the rat

Relationships between the trigeminal component of blinking and the superior colliculus (SC) were studied in rats. To localize primary afferent eyelid projections in the sensory trigeminal complex, neuronal tracing experiments were performed as well as analysis of c‐Fos protein expression after supraorbital (SO) nerve stimulation. Labelled nerve fibers were found to enter ventrally within the ipsilateral sensory trigeminal complex. Labelled boutons were observed at the junction of the principal nucleus (5P) and the pars oralis (5o) and in the pars caudalis (5c). The c‐Fos immunoreactivity was observed in neurons located in the ipsilateral ventral parts of 5P, 5o, and the pars interpolaris (5i) and bilaterally in 5c. Injections in 5P, 5o, 5i, and 5c resulted in anterogradely labelled fibers, with a contralateral preponderance, within the intermediate and deeper SC layers. Injections in 5P or 5o showed anterogradely labelled nerve fibers, profusely terminating in small patches in the medial and central portions of SC layer 4. Subsequently, dense labelling was found in the lateral portion of SC layers 4–7, without patch‐like organization. Injections in SC showed retrogradely labelled neurons predominantly within the contralateral part of the sensory trigeminal complex (28% in 5P, 20% in 5o, 50% in 5i, and 2% in 5c). Colocalization of the retrograde tracer after SC injections and c‐Fos immunoreactivity in neurons demonstrated that some 5P, 5o, and 5i neurons receive SO nerve inputs and project to SC. This implies that intermediate and deeper SC layers receive sensory information from the eyelids and may be directly involved in the regulation of eye–eyelid coordination. J. Comp. Neurol. 448:373–387, 2002.

Vestibulotrigeminal and vestibulospinal projections in rats: retrograde tracing coupled to glutamic acid decarboxylase immunoreactivity.

Immunohistochemical experiments were performed using glutamic acid decarboxylase (GAD) to identify gamma-aminobutyric acid (GABA)ergic neurons in the vestibular nuclei (VN). VN neurons projecting to the sensory trigeminal complex (STC) or to the C1-C2 segments of the spinal cord were identified by injection of wheat germ agglutinin-apo-horseradish peroxidase coupled to colloidal gold (gold-HRP), a retrogradely transported tracer, in these structures. The experiments combining injection of gold-HRP in spinal cord and GAD immunohistochemistry revealed the existence in the medial, inferior and lateral VN of GAD immunoreactive neurons projecting to the spinal C1-C2 level. Experiments combining injection of gold-HRP in the STC and GAD immunohistochemistry demonstrated that, at least, 30-50% of the vestibulo-trigeminal neurons also contained GAD. Injections of two different retrograde tracers (gold-HRP and Biotinylated dextran amine) in the STC and the spinal cord demonstrated that some VN neurons project by axon collaterals to both structures. Because of the GABAergic spinal and STC vestibular projections we assume that these VN neurons with collateral projection are GABAergic. Therefore primary afferents from the face, neck or hindlimb could be modulated by inhibitory influences from GABAergic vestibular neurons.

Projection from trigeminal nuclei to neurons of the mesencephalic trigeminal nucleus in rat

The mesencephalic trigeminal nucleus contains cell bodies of primary somatic sensory neurons that innervate the head region. The neurons resemble dorsal root ganglion cells but a striking difference is the presence of synaptic boutons in the nucleus. The present report demonstrates with anterograde tracers, the existence of a direct trigeminal projection from secondary sensory neurons of the principal and spinal nuclei to the mesencephalic nucleus. Our observations strongly suggest that synaptic contact may be established on the cell bodies as well as on the neurites of the mesencephalic neurons. These pathways could play a modulatory role in the processing of sensory afferent information and in the control of orofacial and/or oculomotor functions.

The sensory trigeminal complex projects contralaterally to the facial motor and the accessory abducens nuclei in the rat

Anterograde tracer injections in the rat sensory trigeminal complex are shown here to demonstrate projections to the contralateral facial motor (VII) and accessory abducens (VIacc) nuclei. Most of the trigeminal fibres originated within the pars oralis (5o) and contacted neurones in the medial and intermediate VII. Moderate projections from the pars caudalis (5c) and interpolaris (5i) reached the lateral and dorsolateral VII. Rare projections from the principal nucleus (5P) were found. Trigeminal projections to the contralateral VIacc originated mainly from the 5P and 5o. Few projections from the 5i and 5c to the contralateral VIacc were found. Retrograde tracer injections in the VII showed premotor neurones to the contralateral VII scattered throughout the 5o and in the ventromedial portion of the caudal 5i and the 5c. Double retrograde tracing experiments provide evidence that neurones in the 5o and 5c project to both the ipsi- and contralateral VII. Such collateralization would play a significant role in the co-ordination of the musculature of the face.

Are locus coeruleus neurons involved in blinking

To investigate the involvement of the noradrenergic locus coeruleus (LC) in the reflex blink circuit, c-Fos and neuronal tracer experiments were performed in the rat. LC neurons involved in reflex blink were localized by analyzing c-Fos protein expression after electrical stimulation of the supraorbital nerve. Subsequently, neuronal tracers were injected in two different nuclei which are part of the reflex blink circuit. Anterograde tracer experiments in the sensory trigeminal complex (STC) explored the trigemino-coerulear connection; retrograde tracer experiments in the latero-caudal portion of the superior colliculus (SC) established coerulear-collicular connections. The combination of retrograde tracer injections into the latero-caudal SC portion combined with electrical stimulation of the supraorbital nerve identified c-Fos positive LC neurons that project to the latero-caudal SC. Our results revealed the existence of a STC-LC-SC loop.