摘要:

AbstractThe efferent projections of the nucleus of the lateral descending trigeminal tract (LTTD) in the rattlesnake (Crotalus viridis) were studied by anterograde tracing techniques. The LTTD, a brainstem trigeminal nucleus, is the sole projection site of the infrared‐sensitive trigeminal fibers that innervate the pit organs in these snakes. The efferent fibers exit from the ventromedial edge of the LTTD and course medially and caudally toward the central grey area of the medulla. Upon reaching the central region of the medulla these fibers turn and move laterally and rostrally, eventually forming a tract on the ventrolateral surface of the brainstem. Embedded in this tract and slightly overlapping the LTTD in the rostrocaudal axis, is a population of large (20–45 μm) multipolar neurons that forms the nucleus reticularis caloris. Heavy terminal and preterminal degeneration in this area indicates that many of the efferent fibers of the LTTD terminate in this nucleus. A small bundle of degenerating fibers turn dorsally from the ventrolateral tract and ascend to terminate in a nucleus associated with the cerebellum, the lateral tegmental nucleus. No projection was found to any other nuclei or areas in the brain.This study demonstrates that the infrared‐sensitive snakes, along with developing peripheral specializations (the pit organs), have developed specialized nuclei to handle this additional sensory information. The direct projection from the LTTD to the nucleus reticularis caloris provides a pathway linking the infrared sensitive neurons of the LTTD with neurons of the same modality in the optic tectum. The second LTTD projection, to the lateral tegmental nucleus, suggests a connection between the infrared system and the cerebellum in these a

ISSN:0092-7317    

DOI:10.1002/cne.902010203

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThe projections from the visual and association areas of the cat's neocortex to the pons were investigated with horseradish peroxidase as retrograde tracer. Small injections were made into the pars basalis of the pons, along its entire rostrocaudal extent. The cortical areas considered were areas 17, 18, 19, 20, 21, and the lateral suprasylvian areas (LSA); the posterior (PMSA), and the anterior middle suprasylvian association area (AMSA), the anterior lateral association area (ALA) and the anterior suprasylvian association area (ASA). A pontine projection was found for all the areas investigated; however, areas differ in the relative strength of their projection, in their intraareal distribution of projection cells, and in the location of their projection zones within the pons.A low to moderate density of projection cells is seen in the areas 17, 18, 19, 20, 21, and in PMSA. The posterior part of LSA contains only a few projection cells, whereas in more anterior parts of LSA the density of projection cells is moderate to high. A relatively dense distribution of projection cells also appears in AMSA, ALA, and ASA. In those areas which are retinotopically organized (17, 18, 19, LSA) the representation of the center of gaze contains far fewer projection cells than the representation of peripheral vision. In the association areas the distribution of projection cells appears even.The projection zones from areas 17, 18, and 19 overlap with the zones from LSA in the anterior half of the basal pons. The projection zones from areas 20 and 21 and from ALA and ASA are located in the middle third and the projection zones from PMSA and AMSA spread throughout the entire rostrocaudal extent of the basal pons.Our findings indicate that efferent impulses from the visual cortical areas and from the association areas on the middle suprasylvian gyrus are relayed to the cerebellum exclusively via the basal pontine nuclei. The findings further suggest that the visual corticopontine projections carry a map of the visual field in which the cortical magnification factor is reduced.

ISSN:0092-7317    

DOI:10.1002/cne.902010204

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractWe have examined the maturation of tectal tissue transplanted from fetal rats to the midbrain of newborns and have characterized the distribution of host retinal and cortical afferents within the transplants.The transplants develop characteristic internal order and connections which distinguish them from either embryonic cortex or retina placed in the same region. Host retinal afferents project to clearly circumscribed regions, where they synapase mainly on small dendrites or dendritic spines, and only rarely on vesicle‐containing profiles. The retinorecipient areas contain few stained axons in neurofibrillar preparations and are almost always located at the surface of the transplant. There is very little overlap in the input from the two eyes into a single transplant even though the projections from each eye may lie adjacent to one another. Cortical afferents spread more broadly in the transplants, but are largely absent from areas of optic termination and from other more deeply located regions with sparse fiber staining properties.The observations suggest that when placed close to its normal location, tectal tissue can develop a number of features characteristic of normal superior colliculus. Appreciation of the internal order of the transplants makes it possible to investigate the cortical and retinal afferent pathways using physiological technique

ISSN:0092-7317    

DOI:10.1002/cne.902010205

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThe time of onset of synapse formation was examined in the cervical spinal cord of eight human embryos ranging from 4 (8 mm in crownrump length) to 6 (22 mm) weeks of ovulation age. The first synapses were found in the motor nucleus of a 10‐mm embryo (Streeter's horizon XV). They contained only a small number of synaptic vesicles and had asymmetrical membrane thickenings, with thicker postsynaptic membranes than presynaptic ones. With the exception of an occasional axosomatic synapse, nearly all synapses found in a 10‐mm embryo were axodendritic. In an 11‐mm embryo (Streeter's horizon XVI), synapselike contacts (SLC) were found in the dorsal marginal layer. They contained a small number of synaptic vesicles and had “reversed membrane specalization” with prominent presynaptic membrane densities. The number of SLC decreased in older embryos. Judging from the morphological characteristics of membrane specializations and the temporal decrease in number, SLC are considered to be either transient synapses on the borderline cells or axoglial synapses. Synapses in the regions outside the motor nucleus first appeared in the dorsal marginal layer of a 14‐mm embryo (Streeter's ho

ISSN:0092-7317    

DOI:10.1002/cne.902010206

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThe deep layers of the rodent superior colliculus contain a vibrissae‐related organization that is in “spatial register” with the overlying visuotopic organization (Dräger and Hubel, '76). The distribution of vibrissae‐related afferents and their cells of origin were determined with a number of anatomical techniques. The brainstem trigeminal complex afferents to the superior colliculus terminate in the lateral portions of the strata album intermediale and griseum profundum and, to a lesser degree, in deep portions of the stratum griseum intermediale. The cells giving rise to these afferents are located mainly in the ventral portions of the contralateral principal sensory nucleus, subnucleus oralis, and subnucleus interpolaris. The majority of tectal projection cells are found in subnucleus interpolaris, and the fewest in the principal sensory nucleus. Further, the density of projection cells in the three components of the brainstem trigeminal complex can be correlated with the density of their projections to the superior colliculus.The afferents from the somatosensory cortex terminate in a continuous band in the strata album intermediale and griseum intermediale. The cells of origin of this projection are located in layer Vb of the agranular zones of the ipsilateral somatosensory cortex.The present results suggest that the organization of trigeminal afferents to the deep portion of the superior colliculus is similar to that of the visual afferents to the superficial laminae. Further, the results suggest that observations on the nature of afferent termination patterns should be made with care, considering both the techniques employed and the idiosyncrasies of the local

ISSN:0092-7317    

DOI:10.1002/cne.902010207

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractWith the indirect immunofluorescence technique of Coons, the overall distribution of the substance P (SP)‐positive neuron system in the frog brain and spinal cord was explored. SP‐positive cells were observed in more than ten areas, such as olfactory bulb, amygdaloid complex, septal area, bed nucleus of hippocampal commissure, hypothalamic periventricular zone, dorsal and ventral thalamus, infundibulum, torus semicircularis, optic tectum, the area dorsal to the interpeduncular nucleus, central gray matter of the mesorhombencephalon, and raphe region, etc. A dense network of SP‐positive fibers was also widely distributed in the frog brain and spinal cord. SP‐positive fibers were roughly divided into two types. One consisted of very fine SP‐positive fibers and gave the region a diffuse appearance. The area medial to n. Bellonci, interpeduncular nucleus, n. isthmi, and optic tectum contained this type of SP‐positive fibers. The other one consisted of clearly distinguishable varicose fibers. A number of SP‐positive fibers located in the amygdaloid complex, striatal complex, hypothalamus, central gray matter of the mesorhombencephalon, trigeminal spinal nucleus, and posterior horn of the spinal cord belonged to this category. The functional role of the SP‐positive neuron system in the central nervous system is also br

ISSN:0092-7317    

DOI:10.1002/cne.902010208

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractStudies using axonal transport techniques on the North American opossum show that rubral neurons innervating the cervical cord are not distinctly separated from those which project to lumbar levels. This absence of clear rubrospinal somatotopy contrasts with that described for the placental mammals studied to date. Use of fluorescent markers in double‐labelling experiments shows that most rubral neurons in the opossum still innervate either the cervical or lumbar enlargement alone, but that some supply collaterals to both level

ISSN:0092-7317    

DOI:10.1002/cne.902010209

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThe distribution of degenerating thalamic and callosal afferents to cingulate cortex in the rat is analyzed. Both light microscopic silver impregnation and quantitative electron microscopic techniques demonstrate differences in the form, number, and laminar distribution of these two afferents in anterior and posterior cingulate cortices.Afferents from the mediodorsal thalamic nucleus terminate in area 24. Most terminals are in layer IIIb, fewer in layer Ia–b, and least in layers V and VI. In contrast, callosal afferents terminate mainly in layers Ib–c, II, IIIa, V, and VI. Thus, thalamic and callosal afferents terminate in a complementary pattern except in layers Ib and IIIb where they overlap. Quantitative analysis of degenerating axon terminals in area 24 indicates that there may be as many as seven times more callosal than mediodorsal thalamic terminals in this cortex.Projections of the anterior thalamic nuclei terminate in areas 29b and 29c, primarily in layer Ia, with fewer in layers Ib–IV and least in layers V and VI. Callosal afferents end mainly in layers V and VI and less densely in layers I–IV, which results in some overlap of thalamic and callosal afferents in layers Ic, IV, and V. In addition, patterns of termination of callosal afferents in posterior cingulate cortex change at borders between previously defined cytoarchitectural areas.Anterior thalamic terminals in area 29c differ from other thalamocortical afferents described previously in that they form two types of terminals. One is large (2–4 μm in diameter) and occurs mainly in layer Ia, whereas the second type is smaller and is present in layers Ib–V. Both types of terminals form asymmetric synapses mainly with dend

ISSN:0092-7317    

DOI:10.1002/cne.902010210

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractIn order to study the organization of the rostral medulla of the cat and its contribution to pain control mechanisms, we have examined the afferent connections of the midline nucleus raphe magnus (NRM), the laterally located nucleus reticularis magnocellularis (Rmc), and the nucleus reticularis gigantocellularis (Rgc) located dorsal to Rmc. Iontophoretic injections of HRP were made into the three regions; the distribution of retrogradely labeled neurons in brainstem and spinal cord was then mapped. While significant differences characterize the source of afferents to Rgc and NRM/Rmc, there is little to distinguish that between NRM and Rmc.The predominant spinal projection is to Rgc; fewer labeled neurons were recorded after injections into Rmc. In contrast, no significant direct spinal projection to NRM was found. All three regions receive input from widespread areas within the medullary and pontine reticular formation. The most pronounced differences in the distribution of retrogradely labeled neurons were found in the midbrain. The major projection to both NRM and Rmc derives from the periaqueductal gray (PAG) and from the adjacent nucleus cuneiformis. Labeled cells are concentrated in the dorsal and lateral PAG; few are found in the ventrolateral PAG. In contrast, Rgc receives few afferents from the PAG; however, after Rgc injections, many cells were recorded in the deep layers of the contralateral tectum. None of the injection sites produced significant labeling of the catecholamine‐rich dorsolateral pontine tegmentum or of the nucleus raphe dorsalis.The demonstration of significant PAG projections to NRM/Rmc provides anatomical evidence for the hypothesis that opiate and stimulation‐produced analgesia involves connections from PAG to neurons of NRM and Rmc which, in turn, inhibit spinal nocicept

ISSN:0092-7317    

DOI:10.1002/cne.902010211

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThe sequential reinnervation and distribution of optics axons in diencephalic and mesencephalic targets was studied after crushing the optic nerve in 37 adultRana pipiens.Following intravitreal injection of3H‐proline at various times after nerve crush the distribution of regenerating optic axons was traced using autoradiographic methods. The maximal distribution of regenerating axons was reached between 6 and 8 weeks after optic nerve crush. On the contralateral side of the brain, the distribution of fibers was similar to the normal projection. Ipsilaterally, silver grain density was greater than normal in the optic tract and projections were expanded to all optic targets on this side of the brain. These abnormal projections were sustained for a least 6 months after nerve crush.The sequence of reinnervation of targets on both sides of the brain differed from normal development. Unlike development, regenerating optic axons were found in the ipsilateral optic tract prior to the time they were found on the contralateral side of the brain. Also unlike development, regenerating axons did not begin to reinnervate targets in the anterior thalamus until several weeks after reinnervation of the posterior thalamus and tectum had begun. The expanded distribution of regenerating axons within optic targets on the ipsilateral side of the brain became evident at the time optic axons first invaded each area.Most optic axons appeared to regenerate from the point of nerve crush. The retinal stump of the crushed nerve was filled with labeled axons in all six frogs given intravitreal3H‐proline injections between 1 and 7 days after nerve crush. In addition, using a modified Fink‐Heimer method, few degenerating axons were found in the retinal stump of four frogs sacrificed between 2 and 8 days after optic nerve crush.In ten frogs studied between 3 and 6 months after nerve crush, horseradish peroxidase (HRP) was placed on different portions of the tectum ipsilateral to the crush. In each case HRP was retrogradely transported to ganglion cells in both retinae. The cells labeled in the ipsilateral retina corresponded in position to the same region of the contralateral retina although many fewer cells were labeled ipsilaterally. Cutting the optic tract on the side opposite the HRP placement did not affect the results. No ganglion cells were labeled in the ipsilateral retina of two frogs not receiving optic nerve crush.These results show that axons from all parts of the retina regenerate to the ipsilateral side of the brain during optic nerve regeneration and the distribution of these misrouted axons, at least to the tectum, overlaps the intact distribution from the other eye. Differences between development and regeneration in the patterns of growth of optic axons may be related to this an

ISSN:0092-7317    

DOI:10.1002/cne.902010212

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY