bluuebunny/crossref_metadata_2025 huggingface dataset:
Morphology of motoneurons in different subdivisions of the rat facial nucleus stained intracellularly with horseradish peroxidase
Authors: Friauf Eckhard
Published: January 2005

Horseradish peroxidase was injected into single facial motoneurons of the rat. Neurons were identified by antidromic stimulation of either the buccal or the marginal mandibular or the posterior auricular nerve branches. Motoneuronal cell bodies supplying the buccal branch were located in the lateral subdivision of the facial nucleus, those supplying the marginal mandibular branch were in the intermediate subdivision, and those supplying the posterior auricular branch were in the medial subdivision. Eleven motoneurons were reconstructed with a computer‐assisted technique. Their soma diameters averaged 20 μm; the average number of primary dendrites was 7.9 and the combined lengths of the dendritic trees averaged 17,650 μm. There was no distinction between the three motoneuron groups in terms of these and other quantitative data. However, on the basis of reconstructed dendritic tree orientation (i.e., dendritic distribution), major differences were observed between motoneurons of the three groups. Dendrites from all groups extended beyond the boundaries of the facial nucleus into the reticular formation. The border between the intermediate and the lateral subdivision was crossed by some dendrites but the overlap was small. In contrast, no dendrite of a motoneuron in the medial subdivision entered the intermediate subdivision and vice versa. The dendritic extent was totally restricted by the borders between these two subdivisions. Outside the Nissl‐defined nuclear border, however, dendrites from cells in adjacent subdivisions overlapped.

It is concluded that the medial subdivision of the facial nucleus can be distinguished from the intermediate and lateral subdivisions not only by its sharp Nissl‐defined border but also by the discrete organization of its dendritic field.
A cholinergic projection to the rat superior colliculus demonstrated by retrograde transport of horseradish peroxidase and choline acetyltransferase immunohistochemistry
Authors: Beninato M. , Spencer R. F.
Published: January 2005

Acetylcholinesterase (AChE) has been localized by histochemistry in the superior colliculus and in the tegmentum of the caudal midbrain and rostral pons of the rat. The pattern of AChE localization in the superior colliculus was characterized by homogeneous staining in the superficial layers and patchlike staining in the intermediate gray layer. In the tegmentum, AChE was localized in the pedunculopontine nucleus (PPN), beginning rostrally at the caudal pole of the substantia nigra and extending caudally to the level of the parabrachial nuclei, and in the lateral dorsal tegmental nucleus (LDTN) of the central gray. The localization of AChE in these nuclei overlapped the distribution of neurons stained by immunohistochemistry using an antibody to choline acetyltransferase (CHAT), the synthesizing enzyme of the neurotransmitter acetylcholine. Other neighboring areas that were stained with AChE, but that did not contain ChAT‐immunoreactive neurons, included the microcellular tegmental nucleus and the ventral tegmental nucleus.

Neurons in the PPN and LDTN were determined to be potential sources of the cholinergic projection to the intermediate gray layer of the rat superior colliculus by double labelling with retrograde transport of horseradish peroxidase (HRP) combined with the immunohistochemical localization of ChAT. Three populations of neurons were identified. A predominantly ipsilateral ChAT‐immunoreactive population was located in the pars compacta subdivision of PPN (PPNpc). Retrograde HRP‐labelled neurons in the pars dissipata subdivison of the PPN (PPNpd), located ventral to the superior cerebellar peduncle (SCP) at the level of the inferior colliculus, composed a second population that was predominantly contralateral but was not ChAT immunoreactive. A third population of retrogradely labelled neurons was predominantly ipsilateral and ChAT immunoreactive and was located in the LDTN. These findings compared favorably with the full extent of the projection from this tegmental region revealed by retrograde transport of HRP from the superior colliculus when more compatible fixation and chromogen procedures were used.

The results suggest that the PPN and the LDTN are two sources of the cholinergic input to the superior colliculus. Since the PPN also has extensive efferent, and afferent, connections with basal‐ganglia‐related structures, this cholinergic excitatory input to the superior colliculus, like the GABAergic inhibitory input from the substantia nigra pars reticulata, may provide the basis for an additional influence of the basal ganglia on visuomotor behavior.
Spatial segregation of synaptic inputs and outputs in a locust auditory interneurone
Authors: Peters Brian H. , Römer Heiner , Marquart Volker
Published: January 2005

Using intracellular injection of cobalt, processing for electron microscopy, and using on‐section silver intensification, we have investigated the distribution of synapses on the metathoracic arborization of the TN1 intersegmental interneurone in the auditory system of the locust. Previous studies have indicated that inputs to this neurone from tympanal afferents are spatially segregated from its outputs to higher‐order inhibitory interneurones. Branches in the area of input are characterised by a smooth appearance in Lucifer Yellow preparations, whereas branches in the main output area appear beaded. Sampling different areas of the TN1 arborization, we have found marked differences in the respective densities of input and output synapses. Labelled profiles in areas of beaded branching have an extremely high density of presynaptic sites, with a much smaller number of synaptic inputs. Smooth branches bear many input synapses, but we have found no output synapses on them. Our results indicate a good correlation between branch beading and presynaptic function and between smooth branches and postsynaptic function. These correlations enable us to predict synapse distribution on other insect neurones with a similar division in brach morphology and also extend our knowledge of the functioning of TN1 itself.
Diencephalic catecholamine neurons (A‐11, A‐12, A‐13, A‐14) show divergent changes in the aged rat
Authors: Selemon Lynn D. , Sladek John R.
Published: January 2005

The effects of aging on diencephalic (A‐11, A‐12, A‐13, A‐14) Catecholamine neurons in the F334 male rat were examined with Falck‐Hillärp histofluorescence. In contrast to the age‐related increase in A‐12 perikaryal fluorescence intensity previously reported (Hoffman and Sladek: Neurobiol, Aging 1:27–37, '80), incertohypothalamic perikarya showed decreased (A‐13) or unchanged (A‐11, A‐14) fluorescence intensity with age. Cell counts of fluorescent A‐12 perikarya disclosed a 47% increase in the number of fluorescent A‐12 neurons in 30‐month‐old F344 rats relative to the 3‐month‐old controls; numbers of A‐11 and A‐13 fluorescent perikarya decreased with age, but the declines were not statistically significant. It is unlikely that the age‐related increase in number of fluorescent A‐12 perikarya is the result of proliferation of neurons in the aged F344 rat. Rather, the greater number of fluorescent A‐12 perikarya in 30‐month‐old F344 rats indicates that some A‐12 neurons in 3‐month‐old F344 rats contain levels of dopamine that are subthreshold for detection with the Falck‐Hillärp fluorescence technique, whereas virtually all A‐12 perikarya in 30‐month‐old F344 rats contain detectable quantities of dopamine. These findings suggest that diencephalic catecholamine neurons exhibit divergent changes in transmitter content and cell number that may reflect varying degrees of functional integrity during brain aging.
Pallidal neurons in the rat
Authors: Millhouse O. E.
Published: January 2005

The globus pallidus has been examined in rat brains with Golgi methods. Most of the impregnated cells, the typical pallidal neurons, have relatively large cell bodies and thick, infrequently branched dendrites that are several hundred microns long. Most dendrites have one or two spines, some of them are moderately spiny, and a few are quite spiny. Although the dendrites generally end by simply becoming thinner and beaded, they occasionally form special dendritic ramifications, which are similar to the complicated dendritic endings reported in primate brains. The variability in the size of the somata and in the structure of the dendrites is not sufficiently consistent to permit dividing the neurons into distinctive subsets. However, two forms of dendritic trees can be defined. The neurons in the center of the pallidum have radiate dendritic trees, whereas the cells along the borders have compressed dendritic trees. Two axonal patterns have been seen: ones with and ones without collaterals. All of the axons are beaded.

Two other cell types were found. The special border cells along the external medullary lamina in caudal pallidum have dendrites that extend for some distance into the caudate‐putamen. They otherwise resemble typical pallidal neurons. Small neurons that were infrequently impregnated may be interneurons, but their axons were not visualized. Their dendrites are short, varicose, and have a few spines. The spherical dendritic trees have a radius of 150–170 μm.

Two sorts of axons that are probably afferent fibers were observed. The more common ones are nonbeaded, thin axons that have several boutons en passant and collaterals spaced along their length. In comparison, the other afferent fiber has numerous swellings, boutons en passant, and collaterals that are crowded together. They appear to invest the dendrites closely.
The ipsilateral retinocollicular projection in the rabbit: An autoradiographic study of postnatal development and effects of unilateral enucleation
Authors: Ostrach Louis H. , Crabtree John W. , Chow Kao Liang
Published: January 2005

The postnatal development of the ipsilateral retinocollicular projection in the rabbit and the effects of unilateral enucleation (performed on the day of birth, day 0) on that development were studied by using the anterograde axonal transport of tritiated proline injected introcularly. Material from 1‐, 6‐, and 10‐day‐old (i.e., at days 1, 6, and 10) and adult animals was examined. On day 1, autoradiographically labelled optic fibers from the ipsilateral eye formed distinct patches and bands within the superior colliculus (SC), which were restricted primarily to the lateral one‐half and anterior one‐third to one‐half of the nucleus. At subsequent ages no major changes in the location of this projection were found for normal animals or animals enucleated on day 0 (0‐DE animals). From dorsal‐view reconstructions, the pattern of the ipsilateral projection appeared wedge‐shaped with a broad base aligned with the lateral SC border for all normal and 0‐DE animals at the various postnatal ages examined. In normal animals the surface area of this projection increased with age and maintained a constant proportion of the increasing surface area of the total SC. In 0‐De animals the surface area of the projection initially increased more rapidly than in normal animals. Thus, by day 6 the area was already within the normal adult range but did not exceed this range at later postnatal ages. The only obvious difference in the appearance of the ipsilateral retinocollicular projection between normal and 0‐DE animals at corresponding ages was an enhanced radial distribution of the projection across laminae in the 0‐De animals. Taken together these findings suggest that, in the rabbit, once topographically appropriate connections are established between the SC and the ipsilateral retinal projection, they are maintained regardless of substantial postnatal growth of the SC and removal of the contralateral retinal projection to the SC.
Pre‐ and postsynaptic correlates of interocular competition and segregation in the frog
Authors: Constantine‐Paton Martha , Ferrari‐Eastman P.
Published: January 2005

Segregated zones of termination between converging inputs that arise from different presynaptic populations are a common property of topographically organized zones within the vertebrate central nervous system. Increasing evidence suggests that such segregation is at least in part established on the basis of competitive interactions that depend upon the activity patterns within each afferent population. However, the cellular mechanisms of these interactions are poorly understood.

We have used a preparation in which a stereotyped interdigitating pattern of retina‐specific termination stripes are produced in frog tecta innervated by two retinas as a result of embryonic implantation of a third eye primordia. In these animals it has been possible to examine the relationship between the number of retinal ganglion cells in each of the retinas innervating a striped tectum, the volumetric changes in the tectum as a result of this double innervation, and the pattern of eye‐specific segregation that is produced. Counts of retinal ganglion cells in the retinas of the three‐eyed frogs with one completely striped tectal lobe revealed no significant differences between cell numbers in the doubly innervating retinas and the normal retinas of the same animals. The average increase in retinal ganglion cell innervation to the striped tecta of these animals was 100%. However the tecta only increased in total volume by 26%. This later increase consisted of a 25% increase in the volume of the deep lying and predominately cellular tectal laminae and a 37% increase in the superficial retinotectal synaptic zone.

In many of these same animals HRP and 3H‐proline were used to differentially label the set of stripes from each retina and measurements of the extent of each projection were performed. We found that the volume of tectal neuropil occupied by a striped projection is relatively unrelated to the number of ganglion cells making up that projection.

Observations of the striping pattern after HRP processing to visualize stripes in whole unsectioned tecta indicate that the periodicities and rostrocaudal orientation of stripes are robust over a wide range of relative innervation densities. When one projection is much smaller than the other, stripes appear to break down into a series of “puffs” or islands of retina‐specific termination zones. Nevertheless, these puffs still have a rostrocaudal alignment and the spacing of fully formed stripes.

These observations suggest that the formation of exclusive termination zones may be a threshold phenomenon: so after a certain innervation density is reached one input can take over a unit of target neuropil in an all‐or‐none manner. The data are discussed in the context of how activity and functional circuits in the tectum may control the segregation pattern.
Postembryonic differentiation of serotonin‐immunoreactive neurons in fleshfly optic lobes developing in situ or cultured in vivo without eye discs
Authors: Näussel Dick R. , Ohlsson Lennart , Sivasubramanian Pakkirisamy
Published: January 2005

The differentiation of serotonin‐immunoreactive (5‐HTi) neurons in the optic lobes of fleshflies was studied during in situ development and in in vivo cultures. All 5‐HTi neurons with cell bodies in the imaginal optic lobes differentiate during postembryonic (pupal) development. These are local anaxonal neurons. In addition there are two large 5‐HTi bilateral neurons that connect all optic lobe neuropil regions on both sides of the brain and have their cell bodies in the midbrain proper.

Deafferentation of optic lobes cultured in vivo leads to drastic reduction in optic lobe volume and increased cell death. All the 5‐HTi neurons differentiate after deafferentation but their morphology changes. The neuropil receiving the photoreceptor inputs, the lamina, degenerates but a disorganized “pseudolamina” is formed by the processes of the two large 5‐HTi neurons. The layering of the optic lobe neuropils cannot be distinguished and 5‐HTi processes form novel projectional patterns. Hence, the 5‐HTi neurons do not require afferent inputs from the retina for their differentiation and survival, but the effect on other optic lobe interneurons is reflected in the morphological plasticity of the 5‐HTi neurons.
Spinal and trigeminal projections to the nucleus of the solitary tract: A possible substrate for somatovisceral and viscerovisceral reflex activation
Authors: Menétrey D. , Basbaum A. I.
Published: January 2005

This study used the retrograde transport of a protein‐gold complex to examine the distribution of spinal cord and trigeminal nucleus caudalis neurons that project to the nucleus of the solitary tract (NST) in the rat.

In the spinal grey matter, retrogradely labeled cells were common in the marginal zone (lamina I), in the lateral spinal nucleus of the dorsolateral funiculus, in the reticular part of the neck of the dorsal horn (lamina V), around the central canal (lamina X), and in the region of the thoracic and sacral autonomic cell columns. The pattern of labeling closely resembled that seen for the cells at the origin of the spinomesencephalic tract and shared some features with that of the spinoreticular and spinothalamic tracts. Labeled cells in lamina IV of the dorsal horn were only observed when injections spread dorsally, into the dorsal column nuclei, and are thus not considered to be at the origin of the spinosolitary tract. They are probably neurons of the postsynaptic fibers of the dorsal column.

Retrogradely labeled cells were also numerous in the superficial laminae of the trigeminal nucleus caudalis, through its rostrocaudal extent. The pattern of marginal cell labeling appeared to be continuous with that of labeled neurons in the paratrigeminal nucleus, located in the descending tract of trigeminal nerve.

Since the NST is an important relay for visceral afferents from both the glossopharyngeal and vagus nerves, we suggest that the spinal and trigeminal neurons that project to the NST may be part of a larger system that integrates somatic and visceral afferent inputs from wide areas of the body. The projections may underlie somatovisceral and/or viscerovisceral reflexes, perhaps with a significant afferent nociceptive component.
Ultrastructural studies of physiologically identified electrosensory afferent synapses in the gymnotiform fish, Eigenmannia
Authors: Mathieson William B. , Heiligenberg Walter , Maler Leonard
Published: January 2005

Eigenmannia is a weakly electric fish that emits a constant‐frequency electric organ discharge (EOD). Probability coder (P unit) and phase coder (T unit) electroreceptive afferents differentially encode changes in EOD amplitude and phase, respectively. physiologically identified T and P units were intracellularly labelled with HRP and their terminals were examined with electron microscopy to determine their postsynaptic targets. This technique reveals that phase and amplitude are relayed to first‐order electrosensory neurons by two parallel but not independent pathways. P‐type afferents terminate on granular interneurons, basilar pyramidals, and polymorphic cells, electrosensory lateral line lobe targets that monitor amplitude modulations, but P‐type afferents do not contact spherical cells. T‐type afferents relay phase information to spherical cells and thus form a separate afferent pathway. T unit terminals do not synapse directly on basilar pyramidal cells. Collateral branches from T‐type afferents, however, were also found to terminate on granule and polymorphic cells, thereby adding phase information into the amplitude channel. P‐ and T‐type afferents exhibit cellular specificity by forming synaptic junctions with different subsets of post synaptic targets in the deep neuropil. The afferent terminals make either asymmetric chemical or gap junction synapses depending on the identity of the post synaptic target.

T units contacting granule cells or polymorphic cells had not been previously described. Two possible roles of adding phase to amplitude information are discussed in terms of electrolocation.
Development of synaptic connections between muscle sensory and motor neurons: Anatomical evidence that postsynaptic dendrites grow into a preformed sensory neuropil
Authors: Jackson Patrick C. , Frank Eric
Published: January 2005

The anatomical development of muscle sensory arbors and dendrites of brachial motoneurons in the spinal cord of the bullfrog was studied by labeling both types of cells with horseradish peroxidase. Sensory and motoneurons were labeled in tadpoles (stages XV‐XVIII) by backfilling the triceps nerve in vivo with HRP throughout the stages in development when functional monosynaptic connections between these cells are first being formed. Individual triceps motoneurons were injected with HRP in other tadpoles at the same developmental stages. By stage XV, triceps sensory afferents already projected to and arborized in the ventral sensory neuropil region of the spinal cord where sensory‐motor connections are made. In contrast, the dendrites of triceps motoneurons rarely were present in this region until stage XVI. By stage XVII, triceps dendrites in this region were common and they intermingled with the collaterals of muscle sensory axons. Thus, sensory axons supplying limb muscles grow into the future neuropil region well in advance of the arrival of motoneuronal dendrites.

Electrophysiological studies have shown that the connections between triceps sensory and motor neurons are already specific at stage XVII, as soon as monosynaptic potentials between these cells can be detected (Frank and Westerfield: J. Physiol (Lond.) 343:593–610, '83). The present anatomical results demonstrate that the processes of sensory and motor cells are not in close anatomical proximity before this time; thus the selection of appropriate synaptic partners must occur from the outset.
Synapses of cone horizontal cell axons in goldfish retina
Authors: Marshak David W. , Dowling John E.
Published: January 2005

The axon terminals of cone horizontal cells in the goldfish retina form typical chemical synaptic contacts in the middle of the inner nuclear layer. Approximately 60% of the identified postsynaptic elements were perikarya, axons and dendrites of bipolar cells. The other identified postsynaptic elements were perikarya and processes of interplexiform cells. We propose that the horizontal cell axon terminals contribute to the antagonistic surround responses of the bipolar cells and that they modulate inputs to the outer plexiform layer conveyed by interplexiform cells. Output synapses from horizontal cell axons to unidentified neuronal processes as well as occasional input synapses to the axons from interplexiform cell processes and unidentified perikarya were also observed in the same region of the inner nuclear layer.
Ultrastructural organisation of the projection from the superior colliculus to the ventral lateral geniculate nucleus of the rat
Authors: Taylor Alison M. , Lieberman A. R.
Published: January 2005

Retinorecipient regions of the ventral lateral geniculate nucleus of the thalamus and the superior colliculus of the midbrain are linked by reciprocal axonal projections. In this study we have investigated the ultrastructural characteristics, the distribution, and the postsynaptic targets of the terminals of axons projecting to the ventral lateral geniculate nucleus from the superior colliculus. Horseradish peroxidase was injected into the superior colliculi of adult albino rats, and the Hanker‐Yates method was used to visualize anterogradely and retrogradely transported peroxidase in the ventral lateral geniculate nuclei 24 hours following the injection.

Labelled terminals were found in the lateral and ventrolateral parts of the external division of the ipsilateral ventral lateral geniculate nucleus. The labelled terminals were confined to areas of simple, nonglomerular neuropil. They were 0.45–1.5 m̈m in diameter; contained small, dark mitochondria and spherical synaptic vesicles; and established Gray type I (asymmetrical) synaptic contacts with the dendritic shafts, dendritic spines, and occasionally cell bodies of cells with the ultrastructural characteristics of projection cells. A few labelled terminals established synaptic contact with retrogradely labelled cells.

Thus, in the rat, the projection from the superior colliculus gives rise to a uniform population of axon terminals in the nonglomerular neuropil of the lateral portion of the ventral lateral geniculate nucleus, which synapse with, and are probably excitatory to, geniculocollicular and other projection cells.
Structural features of the terminal loop region of frog retinal rod outer segment disk membranes: II. Organization of the terminal loop complex
Authors: Corless Joseph M. , Fetter Richard D. , Zampighi Olga B. , Costello M. Joseph , Wall‐Buford Deena L.
Published: January 2005

In addition to a lipid bilayer component (Corless, Fetter, and Costello:J. Comp. Neurol. 257:1–8, '87), the terminal loop region of frog rod outer segment (ROS) disks displays a clustering of discrete elements referred to as theterminal loop complex.It consists of (1) semicircular or crescentic densities within the terminal loop, (2) linear interdisk densities spanning the cytoplasm near terminal loops, and (3) distinctive freeze‐fracture particles associated with the terminal loop, located between 1 and 2.

The linear interdisk densities are organized on a two‐dimensional lattice that appears to ensheath completely the lamellar domains of all ROS disks. Indirect evidence is presented for a net axial alignment of intraloop densities. We interpret the large freeze‐fracture particles of the terminal loop region to reflect transmembrane components that connect the interdisk and intraloop densities. Thus, we propose that the entire terminal loop (TL) complex is organized on a two‐dimensional net. We further infer that each TL complex is organized as a dimeric unit and that such dimers interact axially and laterally to generate the observed lattice structure. It is suggested that one component of the terminal loop complex is the high molecular weight protein localized along the disk perimeter by Papermaster, Schneider, Zorn, and Kraehenbuhl (J. Cell Biol 78:415–425, '78).
The gonadotropin‐releasing hormone containing ventral hypothalamic tract in the fetal rhesus monkey (Macaca mulatto)
Authors: Goldsmith Paul C. , Song Tianbao
Published: January 2005

A well‐defined, gonadotropin‐releasing hormone (GnRH)‐containing fiber pathway, the ventral hypothalamic tract (VHT), is described by immunostaining in fetal rhesus macaques (109–156 days gestation). The VHT arises above the lateral aspects of the optic chiasm near the supraoptic nucleus, and courses ventromedially close to the ventral hypothalamic surface to terminate in the infundibulum and zona externa of the median eminence. It is formed by the confluence of GnRH‐immunopositive (GnRH +) axons from local neurons, from a few GnRH+ cells in the inferior thalamic peduncle, and probably from more anterior neurons in the septum and preoptic area. Bipolar GnRH 4‐ neurons contributing directly to the VHT are grouped at its origin dorsolateral to the optic chiasm, dorsal and medial to the optic tracts, at the infundibular lip, and within the pathway between. At the infundibular lip, GnRH+ perikarya are generally lateral or ventral to the infundibular (arcuate) nucleus, and are rarely within the nucleus itself. Cell bodies here are sometimes tripolar, but GnRH+ intercellular contacts are seldom seen. A few VHT fibers extend to the ventral surface of the brain just beneath the pia mater. Abundant capillaries in the subarachnoid space suggest a possible route for delivery of GnRH to the adenohypophysis in early gestation, before maturation of the hypophysial portal system occurs. Posterior to the infundibulum, a few VHT fibers are joined by descending periventricular fibers forming a dense fiber band beneath the premammillary recess of the third ventricle.

Totals of GnRH+ cell bodies in the prosencephalon of the fetal rhesus macaque are estimated to be 5,600 in females (n=2) and 2,600 in males (n=3). More than 60% of VHT neurons are located in the medial basal hypothalamus, and the majority of basal hypothalamic GnRH+ neurons (86%) are associated with the VHT. Furthermore, reports of the autonomy of the medial basal hypothalamic‐hypophysial unit in control of gonadotropin secretion suggest that the VHT may be the most important GnRH system involved in primate reproduction. It is clear that fetal material may offer the best model to study the GnRH neuronal system in primates.
Thalamocortical and thalamo‐amygdaloid projections from the parvicellular division of the posteromedial ventral nucleus in the cat
Authors: Yasui Yukihiko , Itoh Kazuo , Sugimoto Tetsuo , Kaneko Takeshi , Mizuno Noboru
Published: January 2005

Projections from the parvicellular division of the posteromedial ventral thalamic nucleus (VPMpc) of the cat were examined. After injection of horseradish peroxidase conjugated with wheat germ agglutinin (WGA‐HRP) into the VPMpc, both anterogradely labeled axon terminals and retrogradely labeled neuronal cell bodies were found ipsilaterally in three discrete regions of the cerebral cortex, i.e., in the orbital cortex, caudoventral part of the infralimbic cortex, and medial part of the fundus of the posterior rhinal sulcus (perirhinal area); in the subcortical regions, anterogradely labeled axon terminals were seen ipsilaterally in the rostrodorsal part of the lateral amygdaloid nucleus. Neuronal connections between these VPMpc‐recipient regions were further verified by injecting WGA‐HRP into each of the three cortical and the lateral amygdaloid regions. After injection of WGA‐HRP into each of the three cortical regions, labeled neuronal cell bodies and axon terminals were seen ipsilaterally in the VPMpc, especially in its medial part, and in the other two of the three VPMpc‐recipient cortical regions. In the rostrodorsal part of the lateral amygdaloid nucleus, both axon terminals and neuronal cell bodies were labeled after WGA‐HRP injection into the perirhinal area, and only axon terminals were labeled after WGA‐HRP injection into the orbital cortex, but no labeling was observed after WGA‐HRP injection into the infralimbic cortex. After injection of WGA‐HRP into the rostrodorsal portion of the lateral amygdaloid nucleus, both axon terminals and neuronal cell bodies were labeled ipsilaterally in the perirhinal area and the ectorhinal area, and only neuronal cell bodies were labeled ipsilaterally in the VPMpc (especially in its medial part) and orbital cortical region; no labeling was observed in the infralimbic cortex.

The present results indicate that the VPMpc of the cat is connected reciprocally with the orbital, infralimbic, and perirhinal cortical regions on the ipsilateral side, that the three VPMpc‐recipient cortical regions are reciprocally connected with each other, that the VPMpc sends fibers ipsilaterally to the rostrodorsal part of the lateral amygdaloid nucleus, which may relay information from the VPMpc to the perirhinal cortical area, and that the VPMpc‐recipient area in the lateral amygdaloid nucleus receives cortical fibers from the orbital and perirhinal cortical regions.
Crossed corticothalamic and thalamocortical connections of macaque prefrontal cortex
Authors: Preuss Todd M. , Goldman‐Rakic Patricia S.
Published: January 2005

We have conducted a systematic comparison of the ipsilateral (uncrossed) and contralateral (crossed) thalamic connections of prefrontal cortex in macaque monkeys, using cortical implants of horseradish peroxidase pellets and tetramethyl benzidine histochemistry to demonstrate anterograde and retrograde thalamic labeling. Contrary to the prevailing belief that thalamocortical projections are entirely uncrossed, our findings indicate that a modest crossed projection to prefrontal cortex arises from the mesial thalamus, principally the anteromedial and midline nuclei. Also, while confirming that corticothalamic projections are bilateral, we found that the pattern of crossed projections differs from that of uncrossed projections. Projections to mesial thalamic nuclei, specifically to the anteromedial nucleus, the midline nuclei, and the magnocellular part of the mediodorsal nucleus are bilateral, the contralateral projection being nearly as dense as the ipsilateral projection. Projections to the parvicellular part of the mediodorsal and ventral anterior nuclei are also bilateral, but the contralateral projection is much weaker than the ipsilateral projection. Prefrontal projections to the reticular nucleus, medial pulvinar, suprageniculate nucleus, and limitans nucleus appear to be exclusively ipsilateral.

These results indicate that prefrontal cortex has prominent bilateral and reciprocal connections with the nuclei of the mesial thalamic region. As this region of the diencephalon has been implicated by anatomical and behavioral studies in memory functions, our findings suggest that prefrontal cortex, through its connections with this region, may be involved in the bilateral integration of mnemonic systems.
Neurotensin in projection neurons of the striatum and nucleus accumbens, with reference to coexistence with enkephalin and GABA: An immunohistochemical study in the cat
Authors: Sugimoto Tetsuo , Mizuno Noboru
Published: January 2005

Neurotensin‐like immunoreactivity (NT‐LI) was demonstrated in projection neurons of the striatum and nucleus accumbens in the cat by combining immunohistochemistry and the fluorescent retrograde neuronal labeling method. In colchicine‐treated cats, many neurons with NT‐LI were found in the caudate nucleus, nucleus accumbens, and putamen. Most of these neurons were medium‐sized neurons with spiny dendrites. NT‐LI of neuronal elements in the caudate nucleus and nucleus accumbens formed dense aggregates with irregular figures, which appeared to correspond to the striosomes of Graybiel et al. (Proc. Natl. Acad. Sci. USA 75: 5723–5726, '78; Exp. Brain Res. 34: 189–195, '79; Neuroscience 6: 377–397, '81). Fibers with NT‐LI were distributed massively to the globus pallidus and ventral midbrain regions, but not to the entopeduncular nucleus. In the ventral midbrain regions, many fine varicose fibers with NT‐LI were distributed to the pars compacta and pars lateralis of the substantia nigra, ventral tegmental area, and retrorubral area. In the pars reticulata of the substantia nigra, however, fibers with NT‐LI were rather sparse.

Examination of consecutive sections immunostained for NT, enkephalin (Enk), GABA, and substance P (SP) revealed that 50% of neurons with NT‐LI in the caudate nucleus and nucleus accumbens exhibited Enk‐LI, 15% showed GABA‐LI, and 5% manifested both Enk‐LI and GABA‐LI; no NT‐positive neurons in the striatum and nucleus accumbens showed SP‐LI. No morphological differences were found between NT‐positive neurons with Enk‐LI and/or GABA‐LI and those without Enk‐LI and GABA‐LI.

Most neurons with NT‐LI in the striatum and nucleus accumbens were retrogradely labeled with True Blue injected into the globus pallidus, pars compacta and pars lateralis of the substantia nigra, and ventral tegmental area. After hemitransection severing neuronal connections between the ventral midbrain regions and the forebrain structures, fibers with NT‐LI and those with Enk‐LI in the ventral midbrain regions were markedly reduced in number.

On the basis of the present results, combined with those reported previously, it was assumed that most of the NT‐containing neurons in the striatum and nucleus accumbens sent projection fibers massively to the globus pallidus, pars compacta and pars lateralis of the substantia nigra, and retrorubral area, and sparsely to the pars reticulata of the substantia nigra; NT‐containing striatal neurons with Enk‐LI sent projection fibers mainly to the globus pallidus, pars compacta and pars lateralis of the substantia nigra.
Development of the precerebellar nuclei in the rat: I. The precerebellar neuroepithelium of the rhombencephalon
Authors: Altman Joseph , Bayer Shirley A.
Published: January 2005

Short‐survival thymidine radiograms from rat embryos aged 13–19 days were analyzed to delineate the precerebellar neuroepithelium of the rhombencephalon. The original definition of the term “rhombencephalon” was modified to refer only to the unique dorsal portion (surface plate) of the medulla and pons where the neural groove fails to fuse and, instead, the medullary velum covers the rhomboid lumen of the fourth ventricle. Initially, the neuroepithelial tissue of the rhombencephalon consists of a pair of rostral and caudal bridgeheads: the former the primary neuroepithelium of the cerebellum and the latter the primary neuroepithelium of the octavo‐precerebellar system. The spatial relationship between the cerebellar and precerebellar neuroepithelia soon changes as a result of ongoing morphogenetic events, such that the cerebellar primordium assumes a dorsal position and the precerebellar primordium a ventral position, and the distance between the two decreases. Concurrently the tela choroidea invaginates into the fourth ventricle and a secondary precerebellar neuroepithelium develops. The rostral portion of the secondary precerebellar neuroepithelium grows forward along the choroid plexus and forms the medial recess of the anterior fourth ventricle, while its caudal portion grows in the opposite direction beneath the medullary velum and forms the rostral wall of the posterior fourth ventricle. Evidence will be presented in the succeeding papers that the primary precerebellar neuroepithelium first generates the neurons of the inferior olive that migrate by a circumferential intramural (parenchymal) route to their destination. Next, the neurons of the lateral reticular and external cuneate nuclei are generated. These migrate by a posterior extramural (superficial) route and settle contralaterally. Subsequently, the primary precerebellar neuroepithelium produces the neurons of the nucleus reticularis tegmenti pontis and these form the anterior extramural migratory stream and settle ipsilaterally. Finally, the secondary precerebellar neuroepithelium produces the latest generated neurons of the basal pontine gray that follow the anterior extramural stream and settle ipsilaterally.
Development of the precerebellar nuclei in the rat: IV. The anterior precerebellar extramural migratory stream and the nucleus reticularis tegmenti pontis and the basal pontine gray
Authors: Altman Joseph , Bayer Shirley A.
Published: January 2005

Sequential thymidine radiograms from rats injected on days E16, E17, E18, and E19 and killed 2 hours after injection and at daily intervals up to day E22 were used to establish the site of origin, migratory route, and settling patterns of neurons of the nucleus reticularis tegmenti pontis and basal pontine gray. The nucleus reticularis tegmenti pontis neurons, which are produced predominantly on days E15 and E16, derive from the primary precerebellar neuroepithelium. These cells, unlike those of the lateral reticular and external cuneate nuclei, take an anteroventral subpial route, forming the anterior precerebellar extramural migratory stream. This migratory stream reaches the anterior pole of the pons by day E18. In rats injected on day E16 and killed on day E18 some of the cells that reach the pons are unlabeled, indicating that they represent the early component of neurons generated on day E15. The cells labeled on day E16 begin to settle in the pons on day E19, 3 days after their production. These cells, migrating in an orderly temporal sequence, form a posterodorsal‐to‐anteroventral gradient in the nucleus reticularis tegmenti pontis.

Unlike the neurons of all the other precerebellar nuclei, the basal pontine gray neurons derive from the secondary precerebellar neuroepithelium. The secondary precerebellar neuroepithelium forms on day E16 as an outgrowth of the primary precerebellar neuroepithelium, and it remains mitotically active through day E19, spanning the entire period of basal pontine gray neurogenesis. The secondary precerebellar neuroepithelium is surrounded by a horizontal layer of postmitotic cells, representing the headwaters of the anterior precerebellar extramural migratory stream. In rats injected on day E18 and killed on day E19 the cells are labeled in the proximal half of the stream around the medulla but those closer to the pons are unlabeled, indicating an orderly sequence of migration. In rats injected on day E18 and killed on day E20 the labeled cells reach the pole of the pons. In the basal pontine gray the sequentially generated neurons settle in a precise order. The neurons generated on day E16 form a small core posteriorly and the neurons generated on days E17, E18, and E19 form regular concentric rings around the core in an inside‐out sequence.
The projection of the nucleus reticularis tegmenti pontis and adjacent regions of the pontine nuclei to the central cerebellar nuclei in the cat
Authors: Gerrits N. M. , Voogd J.
Published: January 2005

The projection of the nucleus reticularis tegmenti pontis (NRTP) and the pontine nuclei (NP) to the central cerebellar nuclei (CCN) was investigated by means of anterograde transport of tritiated leucine. Although termination was found in all the CCN, it was most pronounced in the lateral nucleus and the lateral aspect of the posterior interposed nucleus. The extreme lateral aspect of the anterior interposed nucleus and the caudal part of the fastigial nucleus received a projection of modest intensity. Termination in the infracerebellar nucleus and group Y is likely to be present but could not be confirmed with certainty from the light microscopical material. The contribution from the NP was small and originated from the dorsolateral and dorsal paramedian subdivisions of the NP. Within the NRTP the total area giving rise to projections to the CCN was extensive, and the origin of the projections to the individual CCN overlapped considerably.

The projection of the NRTP to the ventrocaudal part of the lateral nucleus was found in conjunction with a projection to the ventrolateral part of the posterior interposed nucleus. Both projections seemed to branch off the fiber bundle terminating in the ventral paraflocculus. Similar correlations could be established in the projection of the NRTP to the dorsal paraflocculus and crus II of the ansiform lobule with other parts of the lateral and posterior interposed nuclei.

It was concluded that the transverse, lobular organization of mossy fibers, which differs fundamentally from the longitudinal, modular organization of climbing fibers, is maintained in the collateral projection to the CCN. The results are further discussed in relation to the corticonuclear projection and the engagement of the NRTP and different parts of the CCN in pontocerebellar circuits.
Structural alteration and possible growth of afferents after kainate lesion in the adult rat thalamus
Authors: Peschanski Marc , Besson Jean‐Marie
Published: January 2005

Afferents to the thalamic ventrobasal complex (VB) originating from the spinal cord, the dorsal column nuclei, and the somatosensory cortex were anterogradely labeled by WGA‐HRP 30 days after an injection of kainic acid (KA), which produced a complete unilateral neuronal loss in the VB, the opposite side being used as a control.

At the light microscopic level, there was no obvious rerouting of spinal afferents away from the lesioned areas towards unlesioned parts of VB. There was an apparent decrease in the number of lemniscal afferents to the lesioned side, which may indicate a progressive retrograde degeneration. At higher magnification, all three afferent systems studied demonstrated morphological changes, predominantly manifested by terminal swellings that reached up to 25 μm in diameter. Control experiments suggested that these morphological alterations were related neither to a direct action of the excitotoxin nor to the absence of a different afferent system but to the loss of neuronal postsynaptic targets.

At the electron microscopic level, the normal ultrastructural features of VB were not observed after a KA lesion. No neuronal somata, dendrites, or normal presynaptic elements were observed. Neural elements, some of which were labeled from the somatosensory cortex or the dorsal column nuclei, were essentially of two types: varicosities and unmyelinated axonal profiles. Varicosities could be separated into two broad classes: (1) The majority were large structures derived from large, sometimes myelinated, axons and containing a wealth of organelles. Since they were not completely surrounded by glial elements, we have denoted them unensheathed varicosities. Among the organelles, the most obvious features were vesicles and tubules of smooth endoplasmic reticulum, microtubules, mitochondria, and various lysosome‐like inclusions. These unensheathed varicosities gave rise to large, mound‐like protrusions containing large vacuoles and thin long protrusions either filled with neurofilaments or resembling unmyelinated axonal profiles. (2) Others were completely surrounded by a glial sheet and were therefore called ensheathed varicosities. These ensheathed varicosities presented several characteristics typical of degenerating profiles, including neurofilamentous proliferation and morphological alterations of the mitochondria. Unmyelinated axonal profiles occupied a substantial territory in the lesioned area. They were most often grouped in bundles sometimes wrapped by glial processes.

The proliferation of unmyelinated fibers and the appearance of axonal varicosities are compared to the regeneration phenomena described in the literature after a lesion in the central nervous system. The hypothesis that the varicosities are growth‐cone‐like structures in the adult CNS is discussed.
Distribution of laminin and fibronectin along peripheral trigeminal axon pathways in the developing chick
Authors: Riggott Marcia J. , Moody Sally A.
Published: January 2005

The trigeminal region of the chick was studied with indirect immunofluorescence in order to determine whether extracellular matrix components might be distributed in such a way as to guide trigeminal axons to their peripheral targets in the mandibular arch. Tissue sections from stages 13–15 and 21/22 were immunolabeled indirectly with affinity‐purified antibodies raised against fibronectin and laminin, two extracellular matrix glycoproteins that support axon growth in vitro. Fibronectin was distributed ubiquitously throughout the head mesenchyme prior to and during initial axon growth from the brainstem (stages 13–15). Shortly after trigeminal axons reached their target tissues (stage 21/22), fibronectin immunolabeling was distributed throughout the head mesenchyme, but was present only at low levels in the trigeminal ganglion and motor nerve. Laminin immunolabeling was distributed in the lateral head mesenchyme at stage 13 as small specks and patches. At stage 14, when the motor axons first exit from the brainstem, short, linear arrays of laminin immunostaining were present from the basement membrane of the neural tube to the core of the mandibular arch, and many were parallel to the direction of axon growth. By stage 21/22 the trigeminal ganglion and motor root showed intense antilaminin immunofluorescence as did the central core of the mandibular arch. These studies suggest that the distribution of fibronectin within the head mesenchyme cannot give directional information to the growing trigeminal axons because of its homogeneous distribution. However, the initial distribution of laminin during the earliest stages of axon outgrowth may provide an extracellular matrix pathway that permits trigeminal axons to reach their targets.