The accessory nerve nucleus in the baboon

In the savanna baboon, Papio cynocephalus, the accessory nerve nucleus was identified by using a mixture of 20% free horseradish peroxidase (HRP) and 2.5% HRP conjugated to wheat germ agglutinin (WGA) in a 5% aqueous detergent solution (Nonidet P-40). Following surgical exposure of the appropriate nerve branch to the sternocleidomastoid or trapezius muscle, the nerve was transected, placed in an Argyle tubing collar, and bathed in 5-10 microliter of the tracer. After a 48-hour survival time and vascular perfusion-fixation, 40-micron sections of the lower medulla oblongata and the cervical spinal cord were treated according to the tetramethyl benzidine (TMB)-HRP method of Mesulam (J. Histochem. Cytochem. 26: 106-117, 1978). The accessory nucleus extends as a distinct column of neurons from lower medullary levels into the rostral part of C5. One to ten labeled cells were present in each section, and all labeled neurons were located on the side of the bathed nerve. The rostral portion of the accessory nucleus occupies a central position, its intermediate portion occupies a lateral position, and its caudal portion occupies a central position within the ventral horn. All labeled neurons were confined to Rexed's lamina IX, ranged from 15 to 75 micron in diameter, and were either distinctly round (oval) or stellate in shape. Neurons within the baboon accessory nucleus supplying the sternocleidomastoid muscle were located from lower medullary to upper C2 spinal cord levels, while those supplying the trapezius muscle extended from C2 to C5.     

家兔环甲肌运动神经的起核及其性质的实验研究

本文用CT-HRP追踪了环甲肌运动神经的起核及其在脑干中的位置,并用AChE组织化学和ENK免疫组化技术观察了它们的性质。家兔环甲肌运动神经元主要起自同侧疑核,约在闩上0.58—2.73mm处,90％以上的标记细胞位于内侧柱。在舌下神经核尾端(闩下1.18—3.18mm)和面后核中也有较多的HRP标记神经元。应用组织化学和免疫组化技术发现:在疑核和舌下神经核中有HRP-AChE双标神经元,在疑核内有HRP-ENK双阳性神经元。这表明家兔起自疑核和舌下神经核的环甲肌运动神经元有些是胆碱能神经元,起自疑核的神经元有的是ENK样反应阳性神经元。本文首次报告了家兔环甲肌运动神经元起自于舌下神经核和面后核以及起核的性质,并对其机能意义进行了讨论。     

大鼠中脑导水管周围灰质向三叉神经脊束核尾侧亚核的5-羟色胺能投射

大鼠中脑导水管周围灰质(PAG)向三又神经脊束核尾侧亚核(Sp 5 C)投射的起源细胞在其吻、中、尾三个部分的分布不同,且由尾段向吻段有从腹侧向背侧移行的趋势。尾段的HRP逆标细胞主要位于PAG的腹外侧区、内侧区腹侧部;中段的标记细胞较多,主要见于腹外侧区、背侧区和背外侧区腹侧部,尚可见一些顺行标记的终末;吻段的标记细胞主要位于背外侧区,在上丘深层、Cajal氏中介核、Darkschewitsch氏核内,也可见标记细胞。标记细胞和终末均主要位于注射侧的PAG内。PAG向Sp 5 C投射的5-羟色胺(5-HT)样神经元主要位于PAG的中、尾段的腹外侧区和内侧区腹侧部。中段的双标细胞占全部双标细胞数的57％,尾段占41％,吻段占2％。在背中缝核(DR)内,亦可见到一些双标细胞。PAG内的双标细胞占其HRP标记细胞总数的37％,但仅占5-HT样阳性细胞总数的4.5％。标记细胞主要为中型(20—30μm)梭形及三角形,小型(<20μm)梭形和大型(>30μm)多角形细胞较少见。     

A thalamic terminus of the lateral cervical nucleus: the lateral division of the posterior nuclear group

The submodality and receptive field properties of single units in the lateral cervical nucleus (LCN) of barbiturate anesthetized cats were studied with glass microelectrodes. In other experiments, a region of the posterior thalamus containing neurons with properties comparable to those seen in the LCN was examined with tungsten microelectrodes. The responses of most units in the LCN reflected a major input from large myelinated afferent fibers innervating guard hairs but no input from Pacinian afferent fibers. The large size of the receptive fields indicated that excitatory input converged selectively from afferent fibers serving hairs over large areas of the body. In the posterior thalamus rapidly adapting neurons characterized by very large receptive fields and driven by the movement of guard hairs were observed to a region identified histologically as the rostral extension of the lateral division of the posterior nuclear group (POl). Caudally this region was located immediately adjacent to the dorsolateral part of the ventroposterior inferior nucleus (VPI). In more rostral parts of the thalamus it was located more dorsally and the ventroposterior lateral nucleus intervened between it and the VPI. This region was less than 1 mm wide in the frontal plane but extended rostrocaudally for several millimeters. Horseradish peroxidase injected into the region of the VPI and the POl labeled many cells in the LCN and the caudal pole of the dorsal column nuclei demonstrating that neurons in the LCN relay information to this part of the thalamus. These data, plus previous experiments showing that the VPI receives a major projection from the caudal poles of the dorsal column nuclei, suggest that the rostral portion of the POl receives an important afferent supply from the LCN. The responses of neurons in the POl appear to arise from specific classes of sensory receptors and cannot be considered less precise or more primitive than responses observed in the ventroposterior nucleus of the thalamus.     

The B?tzinger complex as the pattern generator for retching and vomiting in the dog.

To clarify the location of the pattern generator for the emetic act, the bulb was systematically stimulated and partially cut in decerebrate, paralyzed dogs. Stimulation of the following bulbar structures elicited the activities which could be recognized as retching and vomiting in the following muscle nerves. The bulbar structures were: the intra-bulbar bundle of the vagal afferents, the solitary tract and the medial subdivision of its nucleus (NTS), the area postrema, the commissural nucleus, the raphe area at the obex level, and the longitudinal reticular column which consists of 3 areas--the area between the caudal parts of the solitary complex (SC) and the nucleus ambiguus, the area ventromedial to the rostral part of the nucleus and the area dorsomedial to the retrofacial nucleus (RFN) which may correspond to the B?tzinger complex (BOT). The muscle nerves were: the phrenic branches to the dome and hiatal parts of the diaphragm, the abdominal muscle nerve, the pharyngo-esophageal branch of the vagus nerve, the mylohyoid muscle nerve, and the recurrent nerve branches to the adductors and abductor of the glottis. Emetic responses to stimulation of the vagal ventral trunk and the rostral SC still remained after cutting of the bilateral SCs at about 1 mm rostral to the obex, but disappeared after cutting at about 3.5 mm rostral to the obex. After the rostral cuts, stimulation of the SC part caudal to the cuts and the reticular column still induced the emetic act. Emetic responses to stimulation of the caudal SC remained after transection of the bulb at the rostral end of the RFN, but disappeared after transection at its caudal end or after partial cutting of the caudal BOT. The following hypothesis was proposed from these results. Emetic vagal afferents enter the rostral bulb, then descend through the SC to the area subpostrema. Subpostrema neurons project through the reticular column to the pattern generator of the emetic act in the BOT and activate it.     

Motor neurons of the laryngeal nerves

The present study was undertaken to determine the relationship between the motor neurons of the superior and recurrent laryngeal nerves within the nucleus ambiguus. The retrograde transport of horseradish peroxidase was utilized to identify the motor neurons subsequent to its application to the proximal transected end of the superior and recurrent laryngeal nerves. Labeled superior laryngeal motor neurons were distributed ventrolaterally in the rostral portion of the nucleus. The recurrent laryngeal motor neurons were distributed throughout the nucleus with two distinct populations: a rostral group and a caudal group. The rostral group overlaps the motor neurons of the superior laryngeal nerve. The caudal group occupies that portion of the nucleus that is classically described for the recurrent laryngeal nerve. Additional superior laryngeal nerve labeled perikarya were found in the dorsal motor nucleus of the vagus. This study defines the rostral distribution of the recurrent laryngeal nerve motor neurons and suggests that this rostral group is a component of the neuroanatomical substrate that is involved in the co-activation of the laryngeal abductors controlling the laryngeal aperture.     

Motor neurons of the laryngeal nerves.

The present study was undertaken to determine the relationship between the motor neurons of the superior and recurrent laryngeal nerves within the nucleus ambiguus. The retrograde transport of horseradish peroxidase was utilized to identify the motor neurons subsequent to its application to the proximal transected end of the superior and recurrent laryngeal nerves. Labeled superior laryngeal motor neurons were distributed ventrolaterally in the rostral portion the nucleus. The recurrent laryngeal motor neurons were distributed throughout the nucleus with two distinct populations: a rostral group and a caudal group. The rostral group overlaps the motor neurons of the superior laryngeal nerve. The caudal group occupies that portion of the nucleus that is classically described for the recurrent laryngeal nerve. Additional superior laryngeal nerve labeled perikarya were found in the dorsal motor nucleus of the vagus. This study defines the rostral distribution of the recurrent laryngeal nerve motor neurons and suggests that this rostral group is a component of the neuroanatomical substrate that is involved in the co-activation of the laryngeal abductors controlling the laryngeal aperture.     

兔腭肌运动神经元的定位

目的：探讨腭肌的运动神经元在脑干内的分布。方法：辣根过氧化物酶逆行追踪技术。结果：腭帆张肌的运动神经元位于三叉神经运动核的腹内侧群。腭帆提肌和咽腭肌的运动神经元位同侧疑核的吻侧部。悬雍垂肌的运动元位于双侧疑核的吻侧部。舌腭肌的运动神经元位于同侧疑核吻侧部和下舌神经核尾侧端的腹外侧部。结论：腭肌的运动神经元位于不同的脑神经核中,在各脑神经核中的分布有其特殊性。     

The cells of origin of the trigeminothalamic,trigeminospinal and trigeminocerebellar projections in the cat

Using the retrograde horseradish peroxidase technique, we have examined the distribution of labeled thalamic-, spinal- and cerebellar-projecting neurons in the trigeminal sensory nuclei of the cat.Injections into the nucleus ventralis posterior of the thalamus resulted in labeling of neurons in lamina I (subnucleus zonalis), the deeper part of lamina IV (the subhucleus magnocellularis) of the nucleus caudalis and in lamina V (the lateral extension of the nucleus medullae oblongatae centralis) on the contralateral side. A very large number of labeled small neurons were observed mainly in the caudal part of the nucleus interpolaris and in the ventral division of the principal sensory nucleus on the contralateral side and in the dorsal division of the principal sensory nucleus on the ipsilateral side.Injections into the known projection areas of the cerebellar cortex labeled mainly ipsilaterally the trigeminocerebellar neurons in a restricted ventrolateral area of lamina IV of the nucleus caudalis at its rostral level and in lamina V. Many labeled neurons were also observed in the nucleus interpolaris. Although the distribution overlapped with that of the trigeminothalamic neurons, the greatest majority were concentrated in its rostral part where the trigeminothalamic neurons were very small in number. In addition, labeled neurons were observed in the rostral part of the nucleus oralis and the ventralmost part of the ventral division of the principal sensory nucleus. No labeled neurons were observed in the dorsal division of the principal sensory nucleus and the mesencephalic nucleus.The trigeminospinal neurons were labeled mainly ipsilaterally following injections into the upper cervical cord. They were located in laminae I and III, the deeper part of lamina IV of the nucleus caudalis and in lamina V. Only scattered labeled neurons were found in the nucleus interpolaris. The number of labeled neurons increased in the nucleus oralis at the level of the superior olive. They tended to be distributed around or dorsal to the groups of the trigeminothalamic neurons at the caudal part of the principal sensory nucleus. No neurons of the principal sensory nucleus appeared to project to the spinal cord. Based on the large size and location, the trigeminospinal neurons could be differentiated from the other projection neurons in the nucleus oralis.The present study demonstrates that the trigeminal sensory nuclei are composed of groups of neurons with different projections, since the main aggregations are localized at different levels. However, it should be examined whether the neuronal groups, which are labeled from the different structures in similar locations, are composed of individual neurons projecting to more than one of these structures.     

Projections from the nucleus of the solitary tract in the rat

The axonal projections of neurons in and near the nucleus of the solitary tract have been visualized using titrated amino acid autoradiography. Axons of neurons of this nucleus ramify extensively within the nucleus itself, but much less so in the nucleus commissuralis. They also enter cranial motor nuclei within the medulla. Axons originating in the anterior part of the nucleus of the solitary tract extend to the hypoglossal, facial and probably trigeminal motor nuclei, but not to the dorsal motor nucleus of the vagus or the nucleus ambiguus. The posterior part of the nucleus of the solitary tract projects to all these motor nuclei. In the spinal cord solitary nucleus axons remain in the medial gray directly caudal to the solitary nucleus itself. The distribution becomes very weak by C₃ after some fibers spread laterally into the caudal trigeminal nucleus. Fibers are labeled in the contralateral ventral columns, but they could not be unequivocably attributed to solitary neurons. Axons ascending from the nucleus of the solitary tract extend no further rostrally than the pons, where they terminate in the caudal end of the parabrachial nuclei.Although often treated as entirely separate systems, the present results indicate that secondary gustatory neurons in the anterior solitary nucleus and secondary visceral afferent neurons in the posterior solitary nucleus have very similar rostral and caudal projections. The pontine parabrachial nuclei, the rostral termination of solitary nucleus neurons, have extensive direct connections to the thalamus, the hypothalamus and the limbic forebrain. Assuming similar connections occur in other mammals, these findings establish the existence of di-synaptic visceral afferent access to the highest autonomic integrative centers in the brain.     

Collateralized projections from neurons in the rostral medulla to the nucleus locus coeruleus, the nucleus of the solitary tract and the periaqueductal gray.

We have examined collateral projections of locus coeruleus afferent neurons in the rostral medulla to the caudal nucleus of the solitary tract or to the periaqueductal gray using double retrograde labeling techniques in the rat. The present findings confirm previously reported connections to the locus coeruleus, the nucleus of the solitary tract and the lateral periaqueductal gray from the nucleus paragigantocellularis in the rostral ventral medulla. Our results also reveal previously unreported projections from the rostral dorsomedial medulla (in a similar region as locus coeruleus-projecting neurons) to the lateral periaqueductal gray. Following retrograde tracer injections into the nucleus of the solitary tract and the locus coeruleus, doubly labeled neurons were seen in both the nucleus paragigantocellularis and in the rostral dorsomedial medulla. Cell counts revealed that approximately 25% of locus coeruleus-projecting neurons in the nucleus paragigantocellularis, and 12% in the dorsomedial medulla, also innervate the caudal nucleus of the solitary tract. In contrast, no doubly labeled neurons within the rostral ventral medulla were found following injections into the lateral periaqueductal gray and the locus coeruleus, although singly labeled neurons for the two tracers were interdigitated in some regions. Following these injections, numerous neurons were also retrogradely labeled in the dorsomedial medulla in the region of the medial prepositus hypoglossi and the perifascicular reticular formation. A small percentage of locus coeruleus afferents in the dorsal medulla (approximately 10%) also projected to the lateral periaqueductal gray. These results indicate that neurons in both the ventrolateral and dorsomedial rostral medulla frequently send collaterals to both the locus coeruleus and the caudal nucleus of the solitary tract. A small number of neurons in the dorsomedial medulla project to both the locus coeruleus and the lateral periaqueductal gray, but separate populations of neurons project to the locus coeruleus and the lateral periaqueductal gray from the ventrolateral medulla. These results functionally link the locus coeruleus and the nucleus of the solitary tract by virtue of common afferents, and support other studies indicating the importance of central autonomic circuitry in the afferent control of locus coeruleus neurons.     

Location of motoneurons and internuclear neurons within the rat abducens nucleus by means of horseradish peroxidase and fluorescent double labeling

The distribution of abducens motoneurons and internuclear neurons was determined in the rat by injections of horseradish peroxidase or fluorochromes into the ipsilateral lateral rectus muscle and the contralateral oculomotor nucleus either separately or simultaneously. The labeled somata of abducens internuclear neurons were intermingled with the labeled motoneurons at the medial third of the nucleus, but they were more segregated at the rostral third, where the labeled interneurons were more numerous. Internuclear neurons were preferentially located around and ventral to the central part of the facial genu, while motoneurons were located more dorsomedially, closer to the midline than in other species of mammals. The evolutionary trend of the location of both populations of neurons is also discussed.     

Localization of the spinal nucleus of accessory nerve in rat: a horseradish peroxidase study

The spinal nucleus of the accessory nerve (SNA) comprises the group of somata (perikarya) of motor neurons that supply the sternocleidomastoid and trapezius muscles. There are many conflicting views regarding the longitudinal extent and topography of the SNA, even in the same species, and these disagreements prompted the present investigation. Thirty Sprague-Dawley rats (15 males, 15 females) were used. The SNA was localized by retrograde axonal transport of horseradish peroxidase. Longitudinally, the SNA was found to be located in the caudal part (caudal 0.9-1.2 mm) of the medulla oblongata, the whole lengths of cervical spinal cord segments C1, C2, C3, C4, C5 and rostral fourth of C6. In the caudal part of the medulla oblongata, the SNA was represented by a group of perikarya of motor neurons lying immediately ventrolateral to the pyramidal fibres that were passing dorsolaterally after their decussation. In the spinal cord, the motor neuronal somata of the SNA were located in the dorsomedial and central columns at C1, in the dorsomedial, central and ventrolateral columns at C2 and in the ventrolateral column only at C3, C4, C5 and rostral quarter of C6. The perikarya of motor neurons supplying the sternocleidomastoid were located in the caudal part (caudal 0.9-1.2 mm) of the medulla oblongata ventrolateral to the pyramidal fibres that were passing dorsolaterally after their decussation. They were also located in the dorsomedial and central columns at C1, in the dorsomedial, central and ventrolateral columns at C2 and only in the ventrolateral column at the rostral three-quarters of C3. The perikarya of motor neurons supplying the trapezius muscle were located in the ventrolateral column only in the caudal three-quarters of C2, the whole lengths of C3, C4 and C5, and in the rostral quarter of C6.     

The afferent connections of the inferior olivary complex in rats: A study using the retrograde transport of horseradish peroxidase

Retrograde transport of horseradish peroxidase (HRP) was used to define the origin of afferents to the inferior olivary complex (IOC) in rats. Using both ventral and dorsal surgical approaches to the brainstem, HRP was injected into the IOC through a micropipette affixed to the tip of a 1-μl Hamilton syringe. After a 2-day postoperative survival, animals were sacrificed by transcardiac perfusion with a 1% paraformaldehyde-1.25% gluteraldehyde solution, and brains were processed according to the DeOlmos protocol (1977), using o-dianisidine as the chromogen. Labeled cells were found at many levels of the nervous system extending from lumbar spinal cord to cerebral cortex. This wide-ranging input from numerous regions clearly underscores the complexity of the IOC and its apparent involvement in several functions. Within the spinal cord, labeled neurons were identified from cervical to lumbar but not at sacral levels. These neurons were found contralaterally in the neck region of the dorsal horn and in the medial portions of the intermediate gray. In the caudal brainstem, reactive cells in the dorsal column nuclei, the spinal trigeminal nucleus, and the subnucleus y of the vestibular complex were observed primarily contralateral to the injection sites. Labeling within the gigantocellular, magnocellular, ventral, and lateral reticular nuclei and the nucleus prepositus hypoglossi was primarily ipsilateral. Reactive neurons in the medial and inferior vestibular nuclei were predominantly ipsilateral or contralateral to HRP injections into the caudal or rostral IOC, respectively. The dentate and interposed nuclei of the cerebellum contained small, lightly labeled neurons primarily contralateral to the injection site, while the fastigial nuclei contained a few relatively large, heavily labeled cells bilateral to caudal olivary injections. Ipsilaterally labeled mesencephalic regions included the periaqueductal gray, interstitial nucleus of Cajal, rostromedial red nucleus, ventral tegmental area, medial terminal nucleus of the accessory optic tract, nucleus of the optic tract, and the lateral deep mesencephalic nucleus. The caudal part of the pretectum and small cells of the stratum profundum of the superior colliculus were labeled predominantly contralateral to the injection. In the caudal diencephalon labeled neurons were most numerous within the nucleus of Darkschewitsch and the subparafascicular nucleus, primarily ipsilateral to olivary injections. Scattered reactive neurons were also found within the ipsilateral zone incerta. With the exception of the zona incerta, all labeled mesencephalic and diencephalic nuclei had some bilateral representation of labeled cells. No labeled neurons were identified within the basal ganglia, while numerous reactive cells were found bilaterally within layer V of the frontal and parietal cerebral cortex.     

三叉神经本体觉中枢通路二级传入神经元所在地(三叉神经脊束核吻侧亚核背内侧区,Vodm)的核团形态、细胞构筑及纤维联系——光镜观察

本文用HRP顺行、逆行标记技术,在光学显微镜下探索了王百忍等发现的三叉神经本体觉中枢通路二级神经元所在地-三叉神经脊束核吻侧亚核背内侧区(Vodm)的核团形态及纤维联系,证实了此区存在着一个独立存在于三叉神经脊束核之内的中继核团,它既接受三叉神经中脑核神经元的投射,又向王百忍等所发现的此通路第三级神经元所在地的所谓“带状区”的腹侧部和背侧部都有投射。本研究的结果既证实了王百忍等发现的三叉神经本体党中枢通路在形态学上的可靠性,又对Vodm区的核团位置、形态、细胞构筑及传出联系做了全面的观察,证明它是此通路中的二级传入神经元所组成的核团。     

Morphology of the decrementing expiratory neurons in the brainstem of the rat

In anesthetized and artificially-ventilated rats, the morphological properties of decrementing expiratory (E-DEC) neurons were studied using intracellular recording and labeling with Neurobiotin. Sixteen E-DEC neurons were successfully labeled; ten of which were cranial motoneurons located in the facial (FN) and ambiguus (NA) nuclei. Two interneurons were labeled in the B?tzinger complex (BOT) and the ventral respiratory group (VRG) rostral to the obex, and the remaining four in the VRG caudal to the obex. All the interneurons had extensive intramedullary collaterals within the ventrolateral medulla. Terminal-like boutons were distributed ventral to the NA at the level of the BOT, both ventral to and within the NA at the level rostral to the obex and largely within the cell column tentatively designed as the ambiguous-retroambiguus complex (NA/NRA) caudal to the obex. The four interneurons in the NA/NRA had axons projecting to the spinal cord as well. The extensive intramedullary projections suggest that these E-DEC interneurons of the BOT and the VRG play a significant role in respiration. The simultaneous projections from the caudal E-DEC neurons to both the spinal cord and the NA suggest that these neurons also play integrative roles in non-respiratory behaviors including vocalization, swallowing and defecation.     

The cerebellar projection from the reticular formation of the brain stem in the rabbit

Summary By retrograde transport of horseradish peroxidase the reticulocerebellar projections were examined in twenty-six rabbits.After injections in the cerebellum retrogradely labeled neurons were more numerous in the caudal reticular formation (ventral and gigantocellular reticular nuclei) than in its rostral part (caudal and oral pontine reticular nuclei). The labeled cells were of all sizes, large, medium-sized and small. Giant cells were labeled only after injections in the posterior lobe vermis.After injections in the anterior lobe, the posterior vermis, the fastigial nucleus and the flocculus, retrogradely labeled neurons were found bilaterally in the ventral reticular nucleus, the gigantocellular reticular nucleus and the caudal pontine reticular nucleus. Some cases with posterior vermal and fastigial injections in addition showed labeled neurons bilaterally in the oral pontine reticular nucleus. There were no major side differences. The cases with injections in the anterior part of the paramedian lobule gave rise to only a few labeled cells in the gigantocellular reticular nucleus.Negative findings were consistently made in the mesencephalic reticular formation.     

Musculotopic innervation of the primary flight muscles, the pectoralis (Pars thoracicus) and supracoracoideus, of the pigeon (Columba livia): a WGA-HRP Study

The distribution of motoneurons innervating the primary depressor and elevator muscles of the wing of the domestic pigeon (Columba livia) was studied by using the retrograde axonal tracer lectin-conjugated horseradish peroxidase (WGA-HRP). Injection of WGA-HRP into the pectoralis (pars thoracicus) labeled neurons in the ventromedial corner of the lateral motor column of the spinal cord. These neurons were arranged in a column extending from spinal segment X or XI to spinal segment XII or XIII. The pectoralis, the primary depressor muscle of the wing, consists of two parts which are anatomically and functionally distinct, the sternobrachialis (SB) and thoracobrachialis (TB). Injection into the SB labeled neurons in the rostral and middle regions of the pectoralis motoneuron column. In contrast, injection into the TB labeled neurons in the middle and caudal regions of the pectoralis motoneuron column. Injection into the primary elevator muscle of the wing, the supracoracoideus, labeled neurons in the lateral motor column in spinal segments X and XI. These motoneurons were located dorsolateral to motoneurons labeled following pectoralis injection. These data demonstrate musculotopic segregation of the motoneurons innervating the primary flight muscles in the pigeon and, further, illustrate that the SB and TB subregions of the pectoralis are innervated by discrete aggregations of motoneurons.     

An anatomical study of brainstem projections to the trigeminal motor nucleus of lampreys.

This study was undertaken to identify and describe populations of brainstem neurons that project to the area of the nucleus motorius nervi trigemini in lampreys as a first step in the study of neurons that control feeding behavior in this species. To identify these neurons, the retrograde tracer cobalt-lysine was injected into the nucleus motorius nervi trigemini on one side of the in vitro isolated brainstem preparation of seven spawning adult lampreys (Petromyzon marinus). Transport times ranged from 42 to 48 h. Retrogradely labeled neurons were found within the rostral spinal cord, the rhombencephalon, the mesencephalon and the caudal diencephalon. This study concentrates on the labeled neurons in the rhombencephalon, since the essential circuits for mastication and swallowing are confined to this region in higher vertebrates. Within the rhombencephalon, labeled cells were in the nucleus sensibilis nervi trigemini on both sides. A densely packed column of labeled neurons was found medial to the nucleus motorius nervi trigemini on the ipsilateral side, extending further rostrally in the isthmic region. Continuous columns of labeled cells were observed in the lateral reticular formation on each side in the basal plate ventral to rhombencephalic cranial motor nuclei. They extended from the rostral trigeminal region down into the rostral spinal cord. A comparison with data from cats and rats shows that the distribution of neurons that project to the nucleus motorius nervi trigemini is very similar in mammals and in agnathes. We conclude that the organization of the motor command network of the trigeminal system is well preserved throughout phylogeny and that the in vitro isolated brainstem of lampreys should be a useful model for the study of vertebrate feeding behavior.     

Brain stem afferents to the periabducens reticular formations (PARF) in the cat

Summary Six injections of HRP were placed in the periabducens reticular formation (PARF). Two were placed ventromedial to the caudal half of the abducend nucleus (VIn), two were placed further laterally and ventral to the rostral half of the nucleus, and two were placed rostral to the nucleus. Most injections in PARF produced cell labeling in the vestibular and perihypoglossal nuclei bilaterally and labeled cells in the reticularis gigantocellularis (Rgc) and reticularis pontis caudalis (Rpc) nuclei contralateral to the injection site. Few labeled neurons were found in the caudal part of the paramedian pontine reticular formation (PPRF). In the mesencephalon, bilateral but more numerous ipsilateral labeled cells were found in the medial mesodiencephalic region including the nuclei of Cajal, Darkschewitsch and the posterior commissure. Injections placed caudomedial to VIn resulted in a characteristic concentration of labeled cells in the ipsilateral nucleus cuneiformis and rostral half of the contralateral superior colliculus (SC). Injections placed rostral to VIn in PARF produced cell labeling in the nucleus campi Foreli. The results are related to physiological evidence which suggests that PARF is an important premotor center for coordination of oculomotor, head and body movements.