bluuebunny/crossref_metadata_2025 huggingface dataset:
Origin of mammalian thalamocortical projections. I. Telencephalic projections of the medial geniculate body in the opossum (Didelphis virginiana)
Authors: Kudo Motoi , Glendenning K. K. , Frost Shawn B. , Masterton R. B.
Published: January 2005

Telencephalic projections from the medial geniculate nucleus (MG) in opossum were traced with tritiated leucine autoradiography and by horseradish peroxidase and fluorescent dye retrograde labeling techniques. The results show that the opossum's MG contains two separate populations of neurons‐one in the anterior two‐thirds of MG projecting to auditory neocortex, the other occupying the entire caudal one‐third of MG and projecting mostly to lateral amygdala and putamen.

Because the subcortical projection of the MG in opossum is larger than that seen in any other mammal to date, it is reminiscent of the subcortical projections off the MG in reptiles and birds. Furthermore, when the subcortical projections of the MG in reptiles and opossums are compared with % similar‐subcortical projections of the MG in rats, cats, and monkeys, the proportion of the MG neurons projecting to subcortical structures is seen to be inversely related to the recency of each‐Animal's common ancestry with primates. The possibility that the subcortical projection of the MG in mammals is homologous with that seen in reptiles or birds implies that it might be a dwindling vestige of the projection present in the common ancestry of reptiles and mammals.
Optic tectum of the eastern garter snake, Thamnophis sirtalis. IV. Morphology of afferents from the retina
Authors: Dacey Dennis M. , Ulinski Philip S.
Published: January 2005

The morphology of single retinal terminals in the optic tectum of the eastern garter snake was demonstrated by orthograde filling from extracellular injections of horseradish peroxidase (HRP) into the optic tract. HRP‐filled terminals share a characteristic shape and structure. Their parent axons course caudally in the stratum opticum within fascicles of 200‐300 fibers of varying diameters. Single axons exit a fascicle and course into either the stratum fibrosum et griseum superficiale, ventrally, or the stratum zonale, dorsally, where they bifurcate successively two or three times into preterminal branches. Each preterminal branch gives rise to many thin, terminal branchlets laden with boutons. The arbors are ellipsoidal with their long axes oriented mediolaterally and their short axes oriented rostrocaudally. Arbors vary in their overall size (from 45 to 150 μm), in the diameters of their parent axons (from less than 0.5 to 3.0 μm), and in the size of their terminal boutons (from 0.5 to 3.5 μm). Bouton size increased with increasing diameter of the parent axon. The great majority of arbors are confined to one of three retinorecipient sublayers in the superficial tectum. However, the full range of arbor sizes and axon diameters is present in each sublayer.
Glial cells of an insect ganglion
Authors: Hoyle Graham
Published: January 2005

The rapid development of the study of insect neurobiology, which is currently occurring principally because individual neurons can be re‐identifled and because their activities can be recorded in situ and related to behavior, is generating a demand for more knowledge concerning insect glial cells and their functional relationships with neurons. This study examines the ultrastructure of glial cells in locust metathoracic ganglia in relation to general locale within the ganglion and also to specific identified neurons and neuron types. Seven major types of glial cell form are recognized, with subdivisions, requiring a new scheme for classification. Glial invaginations into neurons are of four different kinds: regular, chunky, filigree, and ridge (found only at axon hillocks). They also range from only intrusive to fully reciprocal. In addition, some neurons make projections of various lengths into surrounding glia and between neighboring neuron somata, and some glia make long, branched projections into other glial cells. The differences show that insect glial cells develop highly specific functional specializations; they may not be interchangeable. The complexity and intimacy of relationships of glia with neurons suggest that some glial cells may have roles other than that of nursemaids, possibly in modulation of behaviordetermining neural activity, and in learning and other adaptive acts.
Timing and positioning of reopening of the occluded spinal neurocele in the chick embryo
Authors: Schoenwolf Gary C. , Desmond Mary E.
Published: January 2005

Occlusion and reopening of the spinal neurocele are important morphogenetic events occurring during rapid brain enlargement in amphibians, birds, and mammals. The purpose of the present study, a companion to a previous one on occlusion, is to examine reopening. We determined when reopening occurred and at what frequency, whether it occurred suddenly or gradually, the extents of the neurocele that were patent at particular stages of reopening, and the morphological pattern of reopening. Reopening begins at stages 14 + to 15 and is virtually complete at stages 16–17. Thus, reopening of the spinal neurocele occurs suddenly and occlusion is a relatively short‐lived developmental event. Because rapid brain enlargement still occurs after reopening, occlusion probably functions principally in the initial phases of enlargement prior to closure of the posterior neuropore. Further studies on the mechanisms of occlusion and reopening are under way.
Retrograde transport of fluorescent tracers reveals extensive ipsi‐ and contralateral claustrocortical connections in the rat
Authors: Sloniewski P. , Usunoff K. G. , Pilgrim Ch.
Published: January 2005

The projections from the claustrum to the cerebral cortex in the rat were examined by means of retrogradely transported fluorescent tracers Fast Blue (FB) and Diamidino Yellow dihydrochloride (DY), injected in the prefrontal, motor, somatosensory, auditory, and visual fields. In all cases, substantial numbers of retroo adely labeled neurons were observed in the ipsilateral and moderate to scant numbers in the contralateral claustrum insulare. Symmetrical bilateral injections of FB and DY as well as simultaneous injections of the tracers in the motor and visual cortex of the same hemisphere revealed no double‐labeled neurons in the claustrum.

The following conclusions may be drawn: The claustral projections to the motor, somatosensory, and visual cortex are prominent. The projection to the prefrontal cortex is less substantial and that to the auditory cortex is relatively modest. The claustrocortical connections lack the clear‐cut topographic pattern of the thalamic nuclei but are, to some degree, preferentially arranged, albeit with considerable overlapping of the subpopulations of corticopetal neurons, a coarse anteroposterior topographic distribution appears to exist also in rodents. Neurons contributing to the claustrocortical connection project either ipsilaterally or contralaterally but not bilaterally. Projections to different cortical fields of one hemisphere also originate from separate claustral neurons.
Location and connections of visual cortical areas in the cat's suprasylvian sulcus
Authors: Sherk Helen
Published: January 2005

The initial aim of the experiments described here was to identify and quantify the cortical and thalamic connections of visual cortical areas located in the vicinity of the suprasylvian sulcus. Inputs to various sites in this region were studied by making small injections of wheat germ agglutinin (conjugated to horseradish peroxidase) at physiologically identified locations. Retrogradely labeled cells were counted in each identifiable area of cortex and in thalamic nuclei.

Some injections yielded quantitatively similar distributions of labeled cells, and it is suggested that such evidence provides a useful way of dividing the cortex into areas. By this criterion, a single, relatively large, cortical area was identified that occupied most of the medial bank of the suprasylvian sulcus, all or most of its posterior bank, and a small segment of its lateral bank. It was referred to as the Clare‐Bishop area. Because neighboring visual areas were found to lack input from area 17, while the Clare‐Bishop area received a strong striate input, its boundaries were investigated by labeling afferents from area 17. Together with the results of retrograde tracer injections, these data suggested that the Clare‐Bishop area cuts across several of the visual areas defined physiologically by Tusa et al. ('81). As a consequence, its retinotopic organization must be relatively complex, with duplications of some parts of the visual field.

Three other visual areas were tentatively identified on the basis of their distinctive connections. One was situated on the lateral bank of the suprasylvian sulcus and appeared to border the Clare‐Bishop area laterally. Another, referred to as area 21, lay adjacent to area 19, and, for part of its length, also appeared to bound the Clare‐Bishop area. The third, corresponding approximately to Heath and Jones's ('71) posterior suprasylvian region, lay lateral and anterior to the Clare‐Bishop area' in the depths of the posterior suprasylvian sulcus.
The intercalated cells of the amygdala
Authors: Millhouse O. E.
Published: January 2005

The intercalated cell groups, or massa intercalata, of the amygdala have been studied in rodent brains with Golgi methods. They also have been examined in gallocyanin‐chromalum‐, AChE‐, and Timm‐stained rat brains.

The Golgi data indicate that the intercalated cells are not confined to a series of isolated cell clumps but form a neuronal net that covers the rostral half of the lateral‐basolateral nuclear complex, stretches across a major portion of rostral amygdala, and continues rostrally beneath the anterior commissure. There are two general types of intercalated neuron‐medium and large neurons. The medium intercalated neurons are more common. They have round to elongate somata, 9‐18 μm in diameter, and round to bipolar dendritic tress, depending on their location. Most of the dendrites are spine‐bearing, as are 20% of the somata. Their axons often have locally ramifying collaterals. The parent axons apparently terminate in either the lateral‐basolateral or central nuclei and some of them appear to enter the external capsule. There is a unique medium intercalated neuron that has nearly spine‐free, varicose dendrites and an axon that is typical of short axon (Golgi II) cells. There are two varieties of large intercalated neuron‐spiny and aspiny. Most of them are aspiny, although they usually have a few spines scattered along their dendrites. Both varieties have elongate, sometimes round, somata that can be as much as 60 μm long. Their dendrites are long, thick, and have few branch points. Only the initial part of the large aspiny cell axon has been impregnated. The large spiny cell axons have several local collaterals; the destination of the parent axons is unknown.

The intercalated cells occur along fiber bundles, which are probably afferent to them. The axons that travel among the intercalated cells give off short collaterals and boutons en passant. The sources of these fibers are not known. From the published experimental data, it is likely that they originate in the piriform and entorhinal cortices, the lateral preoptic area, lateral hypothalamus, and ventral pallidum. Axon collaterals of basolateral nucleus pyramidal cells appear to terminate among the intercalated cells. It is suggested that the intercalated cells serve as sites for integration of the output of these various areas and, in turn, communicate it to the lateral basolateral and central amygdaloid nuclei.

The intercalated cells closely resemble neurons in the corpus striatum. Thus the question is raised and discussed of whether the intercalated cells are a ventral extension of the corpus striatum.
Anatomical and electrophysiological study of multitransmitter neuron r14 of aplysia
Authors: Rittenhouse Ann R. , Price Christopher H.
Published: January 2005

This study provides detailed information on the Aplysia neuron R14, including its endogenous electrical activity and extensive axonal projections to a variety of vascular and vascular‐related tissues. With the aid of intracellular recording techniques, R14 was found to display in vitro variable spontaneous patterns of silent, beating, or bursting activity. Electrophysiological tracing and intracellular cobalt staining revealed the peripheral processes and target tissues of R14. The white‐colored axons of R14 exit the parietovisceral ganglion in the genito‐pericardial, spermathecal, branchial, and vulvar nerves. These processes extended 20 mm or more into peripheral tissues: the pericardial wall and lumen, digestive gland sheath, aortae, arteries, and veins. R14 axons also project to the right bag cell cluster. Its extensive axonal projections to tissues associated with the cardiovascular system verify physiological studies that show that R14 plays a role in cardiovascular regulation. This neuron appears to have a wide influence over several aspects of circulation in contrast to individual neurons of the R3‐13 group, each of which projects to limited numbers of vascular and vascular‐related tissues. R14 also uniquely innervates digestive tissues, thus suggesting that it may act as a nexus between influences on digestive and renal physiology such as ion/water regulation, in addition to modulating cardiovascular homeostasis.
Projections from the anteroventral cochlear nucleus to the lateral and medial superior olivary nuclei
Authors: Cant Nell Beatty , Casseday J. H.
Published: January 2005

The projections from the cochlear nucleus to the lateral and medial superior olivary nuclei were studied in the cat by use of retrograde transport of horseradish peroxidase to demonstrate the connections. The medial superior olivary nucleus receives input only from the anterior and posterodorsal subdivisions of the anterior division of the anteroventral cochlear nucleus (AA and APD, respectively; Brawer, Morest, and Kane: J. Comp. Neurol 155: 251‐300, 1974). These two subdivisions are populated almost exclusively by spherical bushy cells. Like the medial superior olivary nucleus, the lateral, superior olivary nucleus receives inputs from AA and APD, In addition, the lateral superior olivary nucleus receives projections from the posterior subdivision (AP) of the anterior division and also from the posterior division of the anteroventral cochlear nucleus. The projections to the medial superior olivary nucleus are bilateral, whereas the projections to the lateral superior olivary nucleus are almost entirely ipsilateral. One implication of the results is that the medial superior olivary nucleus receives inputs from only one cell type‐the spherical bushy cell‐but that, at the least, two cell types project to the lateral superior olivary nucleus. Both the olivary nuclei receive input from most, if not all, of the dorsoventral extent of the anteroventral cochlear nucleus, implying that both receive input from neurons arrayed across the entire frequency representation of the anteroventral cochlear nucleus. All of the projections appear to be organized topographically such that frequency representation is preserved.
A quantitative study of neuronal and glial numerical density in the visual cortex of the bottlenose dolphin: Evidence for a specialized subarea and changes with age
Authors: Garey L. J. , Leuba G.
Published: January 2005

Neuronal and glial numerical densities were measured in the lateral gyrus of the cerebral hemisphere of dolphins (Tursiops truncatus) from the neonatal period to adulthood. The cortex studied is the area known to be visually excitable in evoked potential studies. Two distinct parts of the adult lateral gyrus are identifiable, one relatively anterior, in which neuronal density is 23,000/mm3, the other more posterior, with' almost double this density. In a neonate, the neuronal density in the anterior lateral gyrus was found to be more than double that of the adult. No samples from the immature posterior area were available.

Glial density varies much less than neuronal density, both with age and between areas. Soon after birth the glia/neuron ratio is 1.6 in anterior lateral gyrus, rising to around 3 in the adult anterior lateral area, and rather less in the posterior region, where neuronal density is high.

We speculate that the existence of a high numerical density of neurons in the posterior part of the dolphin visual cortex could perhaps indicate a specialized area corresponding to the primate primary visual cortex, also known to have high neuronal density.
Somatosensory cortical representation in the Australian ghost bat, Macroderma gigas
Authors: Wise Lisa Z. , Pettigrew John D. , Calford Michael B.
Published: January 2005

Bats of the two suborders Microchiroptera and Megachiroptera have a modified hand in which the digits of the forelimb are caudally oriented to form the wing. In a previous study of a megachiropteran species, this modification of body plan was found to be reflected in the somatosensory cortical representation such that the orientation of the digit representation was reversed compared with walking mammals. This finding suggests that the precisedetails of arrangement of topographical maps are functionally significant and do not merely reflect an order imposed by peripheral innervation. Recentevidence for separate origins of Microchiroptera and Megachiroptera raises the question of whether the cortical somatosensory representation in Microchiroptera will also have a reversal of digit orientation compared with walking mammals. We recorded multiunit activity from the somatosensory cortex of a microchiropteran bat, Macroderma gigas. We found two orderly representations of the body surface, SI and SII, in both of which the digit orientation was opposite to the head orientation in accordance with adaptation for flight, and reversed with respect to equivalent maps in other mammals. We also found minor variations in body surface representation compared with Megachiroptera, in line with their proposed independent evolution.
Myelination of the corpus callosum in the cat: Time course, topography, and functional implications
Authors: Looney Greg A. , Elberger Andrea J.
Published: January 2005

The parameters of myelin development were ascertained in two specific regions of the corpus callosum in a series of cats aged 12 postnatal days through adult. The posteriormost portion of the splenium and the anterior‐most portion of the genu were examined in cross section by using the electron microscope. Measurements were made to determine the age at which myelin first appeared, the number and distribution of myelinated fibers, the number and distribution of myelin lamellae, and cross‐sectional area of ensheathed axons during development. The results indicate that myelination begins and ends earlier in the anterior region of the callosum. Measurements of myelin lamellae indicate similarities between anterior and posterior regions of the callosum, although development occurs earlier in the genu than in the splenium. No evidence was found for a sequence in the size of axons acquiring myelin sheaths, except that extremely small fibers are the last to begin myelinating. Myelination of the splenium of the corpus callosum begins at the very end of the behaviorial and physiological critical period for the corpus callosum's role in visual functional development (Elberger: Behav. Brain Res. 11:223–231, '84; Elberger and Smith: Exp. Brain Res. 57:213–223,'85). Since myelination of a pathway is used as an index of functional reliability, this indicates that the basis for the callosal role in developing visual functions is probably not based on its physiological input to visual cortex.
Regeneration of normal afferent input does not eliminate aberrant synaptic connections of an identified auditory interneuron in the cricket, Teleogryllus oceanicus
Authors: Pallas Sarah L. , Hoy Ronald R.
Published: January 2005

In the cricket, Teleogryllus oceanicus, the dendritic arborizations of an identified auditory interneuron (Int‐1) are normally restricted to the ipsilateral auditory neuropile; unilateral deafferentation causes the medial portion of the dendritic field to sprout across the midline and make functional connections with the contralateral auditory neuropile (Hoy et al., '78: Soc. Neurosci. Abstr. 4:115, '85: Proc. Natl Acad Sci. USA 82:7772–7786; Hoy and Moiseff, '79: Soc. Neurosci. Abstr. 5:163). We have found that regeneration of the auditory afferents also results in an aberrant pattern of innervation of Int‐1.

Crickets were unilaterally deafferented during postembryonic development by crushing or cutting the auditory nerve. Regeneration of afferent‐to‐Int‐1 connections was tested behaviorally. Of 86 nerve‐crushed crickets tested as adults in the behavioral assay, 66% showed functional regeneration of the afferents. Similar results were obtained from the nerve‐cut group. However, morphological investigations demonstrated that most of the regenerates still retained the aberrant contralateral dendritic projection. Electrophysiological recordings from these Int‐1s showed that not only are some of them driven by their regenerated auditory afferents (the normal pathway) but that they retain their excitability via their contralateral dendrites (the aberrant pathway). This demonstrates that reinnervation of Int1 by its normal afferent pool neither causes retraction nor prevents the formation of connections made with foreign, contralateral afferents.

When the contralateral afferent pool was removed after Int‐1 had sprouted, the sprouts remained present, but preliminary results suggest that if the contralateral afferents are removed before Int‐1 is deafferented, sprouts are not formed.

The results are discussed in relation to the roles of competition and conservation of membrane area in controlling synapse formation.
Distribution of neurons and axons immunoreactive with antisera against neuropeptide Y in the normal human hippocampus
Authors: Chan‐Palay V. , Köhler C. , Haesler U. , Lang W. , Yasargil G.
Published: January 2005

The detailed distribution of neuropeptide tyrosine (neuropeptide Y; NPY) immunoreactive neurons and fibers is given for the normal human hippocampus. These neuronal elements are detected by a polyclonal antibody raised against the unconjugated peptide and controls were obtained by using liquid phase absorption immunocytochemistry. The description covers the distribution in the area dentata, the hippocampal subfields CA3 and CA1, the subicular complex, and the entorhinal area. Each region is distinct in its NPY content. In general, the hippocampal NPY immunoreactive neurons fall into distinct classes—large hilar neurons; cortical small bipolar or bitufted neurons; medium‐sized multipolar neurons in the deep cortical layers; and finally the distinct, small bipolar NPY neurons of the white matter bundles. None of the NPY neurons are pyramidal; many are likely to be local circuit neurons, but some appear to have extrinsic connections. The NPY immunoreactive axonal innervation is dense throughout the hippocampus but shows distinct regional differences in the hippocampal subdivisions. The area dentata has hilar NPY immunoreactive neurons and radial varicose fibers scattered throughout without a clear laminar preference. Subfield CA3 is comparatively the weakest NPY‐containing region and contrasts with CA1, which is well endowed with reactive neurons and a rich and unusual axonal innervation, with distinct laminar axonal specializations. The subicular complex is well endowed with cells and fibers and the parasubiculum consistently displays unusually heavy NPY innervation. The entorhinal area exhibits a rich cortical distribution pattern, like that previously described for the human cerebral cortex (Chan‐Palay et al.; J. Comp. Neurol 238:382–390, '85a, b). The fimbria, alveus, and angular bundle have NPY neuron embedded within the white matter. Like the NPY immunoreactive innervation of the hippocampal regions of laboratory animals, the human NPY innervation seems to follow a common fundamental pattern with respect to cell locations, cell morphology, and axonal innervation. The difference, however, is the greater complexity and profusion of the NPY‐immunoreactive axonal plexuses in the human hippocampus. This rich peptide network within the hippocampus with likely extrahippocampal interconnections raises questions concerning coexistence with other neuroactive substances, the functions of such substantial networks, and how they are altered in human neurological disease.
A quantitative analysis of the spinal motor pool and its target muscle during growth in the dogfish, Scyliorhinus canicula
Authors: Mos W. , Williamson R.
Published: January 2005

In order to relate the phenomenon of continuous growth in fishes to the development of the neuromuscular system, we established the numbers and sizes of spinal motoneurons and red and white axial muscle fibers in late‐and post‐embryonic dogfish within the size range 6–71 cm. We found that (1) motoneuron somata, ventral root axons, and red and white muscle fibers increase their size throughout the life of the animal; (2) there is an initial increase in the number of motoneurons that ceases as the fish reaches a length of about 40 cm; (3) white muscle fibers initially decrease in number during post‐embryonic life; and (4) red muscle fibers increase in number, but this increase levels off at a fish length of about 40 cm.

Spinal motoneurons innervating red myotomal muscle fibers or centrally located white muscle fibers were identified after retrograde labeling with horseradish peroxidase, which was injected in small amounts into the respective muscle areas. The motoneurons supplying the red muscle are smaller and occupy a more lateral position in the ventral horn than the white muscle motoneurons. The number of motoneurons in the ventral horn per unit area increases from medial to lateral and this is associated with a reduction in the sizes of the somata.

Values for the ratio of number of muscle fibers to number of supplying motoneurons in the various muscle areas were based on axon counts within the peripheral nerves. This ratio was higher for the centrally located white muscle fibers than for the ventral or dorsal white fibers, but was highest for the red fibers.
Ventral root nonmedullated fibers: Proportion, calibers, and microtubular content
Authors: Vergara Ismael , Oberpaur Bernd , Alvarez Jaime
Published: January 2005

Proportion, caliber, and microtubular content of the L7 ventral root nonmedullated fibers were studied in the cat. Nonmedullated fibers constituted 28% of the axonal population at the far end of the root. The number of myelinated profiles at the far end of the root and in the vicinity of the ventral surface of the cord (1–2‐mm distance) was the same whereas the number of nonmedullated fibers decreased toward the proximal site of the root by 42%. Caliber and microtubular content of nonmedullated fibers were assessed only at the far end of the ventral root. Nearly 90% of the axons were smaller than 0.3 μm2. The average cross‐sectional area was 0.15 μm2, a value 35% below that of the L7 dorsal root fibers. The microtubular density was highest in the finest fibers (116 microtubules/μm2 in fibers smaller than 0.1 μm2) and decreased with the increase in cross‐sectional area (25 microtubules/μm2 for 0.7–0.8‐μm2 axons). The number of microtubules per axon in axons of both roots was similar in fibers smaller than 0.3 μm2; in larger axons, composing about 10% of the population, ventral root fibers had more microtubules than dorsal root fibers.

The ventral and dorsal nonmedullated fibers differ slightly but significantly in caliber and microtubule content. However, they are similar in contrast to peripheral nonmedullated fibers, which are three to four times as big and contain two to three times as many microtubules as radicular fibers.

Our results confirm the presence of a large admixture of nonmedullated profiles in the L7 ventral root of the cat, support the notion that a number of these fibers make a U turn in the ventral root, and suggest that these arise from the central process of the primary sensory axon.
Telodendrites of cone photoreceptors: Structure and probable function
Authors: Kraft Timothy W. , Burkhardt Dwight A.
Published: January 2005

Intracellular dye injection and compartmental modeling were used to analyze the structure and function of telodendrites of cones in the retina of the walleye. After identifying the spectral type of an impaled cone on the basis of its response to red and green light, horseradish peroxidase and/or Lucifer Yellow were injected for 1 to 25 minutes. In 38 of 58 recovered cells, dye spread into the telodendrites; so in many cases, the detailed pattern of the telodendritic arbor could be reconstructed from serial sections. Typically, five telodendritic processes, about 1 μm in diameter and 18 gm in length, radiated from the cone pedicle. A majority of the processes terminated at pedicles of neighboring cones. Some of the Lucifer Yellow injections provided evidence for electrical coupling between cones via telodendrites. Calculations from a compartmental model, based on the measured dimensions of cones and telodendrites, indicate that the signal arising in the inner segment spreads with little loss to the end of a telodendrite, whereas about half of the signal is lost in transmission from telodendrite to inner segment. Assuming that each contact point within the telodendritic network is an electrical synapse of 2,500 MΩ, the model shows spatial interaction over a field of some 80 μm, which is comparable to that measured experimentally. Although our anatomical data indicate that orange‐ and green‐sensitive cones may be interconnected via telodendrites, model calculations indicate that such connections do not appreciably distort the intrinsic spectral sensitivity of walleye cones. This outcome agrees with previous experimental results.
The distribution and morphology of parasympathetic preganglionic neurons in the cat sacral spinal cord as revealed by horseradish peroxidase applied to the sacral ventral roots
Authors: Nadelhaft Irving , de Groat William C. , Morgan Charles
Published: January 2005

Parasympathetic preganglionic neurons in the sacral parasympathetic nucleus (SPN) of the cat were studied by applying horseradish peroxidase (HRP) to the sacral ventral roots. The results were compared to data from earlier experiments in which these same neurons were labelled by HRP applied to the pelvic nerve at a point much further from the spinal cord. The present experiments have shown (1) The total number of neurons in the SPN determined by ventral root labelling is equal to the number obtained by pelvic nerve labelling. This indicates that virtually all SPN neurons send their axons into the pelvic nerve. (2) More extensive dendritic projections from SPN neurons were revealed than in the pelvic nerve experiments. In particular, a strong dendritic projection extended within the lateral marginal zone of the dorsal horn close to Lissauer's tract and horizontal dendrites projected well into the contralateral gray matter, some reaching the contralateral sacral parasympathetic nucleus. (3) The neurons labelled via any one ventral root were all contained within a region equal in length to one spinal segment but shifted rostrally by a small amount. Thus, no evidence was obtained for a long intraspinal pathway in which axons of spinal cord neurons entered ventral roots many segments away from their somata.
Neuromuscular relationships in a muscle having segregated motor endplate zones. II. The response to partial denervation
Authors: Wines Melvin M. , Hall‐Craggs E. C. B.
Published: January 2005

The cranial belly of the anterior gracilis muscle of the rat has two discrete motor endplate zones. A promixal zone is innervated by short branches of the obturator nerve, and a distal zone is innervated by (usually) two longer branches. Each muscle fiber is innervated at a single motor endplate although a substantial number lie within both endplate zones. In addition, motor units are divided between the two zones. In order to dissociate the role of the denervated endplate from that of the denervated muscle fiber in the promotion of motoneuron sprouting, the distal endplate zone in this model was denervated and the response at the proximal zone was studied. Comparisons were made with partial denervation of the muscle by division of the L4 ventral ramus and with partial denervation of the distal endplate zone. Denervation of the distal endplate zone produced profuse terminal sprouting at the proximal zone whereas division of L4 predominantly produced nodal sprouting at both zones. Partial denervation of the distal zone resulted in nodal sprouts in that zone and again mainly terminal sprouts at the proximal zone. The repeated association of terminal sprouting with division of the motor axons supplying the distal zone together with the knowledge that motor units are distributed between the two zones led to the conclusion that the terminal sprouting was stimulated by the reduction in size of motor units rather than by the presence of denervated muscle fibers in the vicinity of the endplates.
Microtubules and calibers in normal and regenerating axons of the sural nerve of the rat
Authors: Espejo Francisco , Alvarez Jaime
Published: January 2005

The calibers and microtubular content of axons were studied in normal and regenerating fibers of the sural nerve from 17 to 122 days after a lesion of the sciatic nerve of young adult rats. During this period (70–175 days of age), the cross‐sectional area of control myelinated axons almost doubled but that of nonmedullated axons did not change. In regenerating nerves, after 122 days of recovery, the cross‐sectional area of myelinated fibers was still 38% below that of the normal side. In contrast, the regenerating nonmedullated population was richer in fine (< 0.2 μm2) and in coarse (> 0.9 μm2) fibers than on the control side; the cross‐sectional area averages were 0.50 and 0.54–0.70 μm2 for the normal and regenerating populations, respectively.

The microtubular density of normal 3‐μm myelinated fibers averaged 24.0 microtubules/μm2. In regenerating fibers of the same size the density varied between 19.2 and 23.2 microtubules/μm2. Microtubular density values of normal and regenerating fibers were not statistically different. In nonmedullated fibers, the microtubular content (expressed as microtubular density or number of microtubules per axon) correlated with the caliber of the fiber. In these correlations, only minor differences were observed between regenerating and uninjured fibers.

Our results indicate that nonmedullated fibers terminate their radial growth well before myelinated fibers do, and that axonal microtubular content correlates with the local size of the fiber and is largely insensitive to regeneration.
Microtubules and calibers in developing axons
Authors: Faundez Victor , Alvarez Jaime
Published: January 2005

The caliber and microtubular content of growing axons were assessed with the electron microscope in the sural nerve of the rat from birth until the age of 63 days (young adult). The caliber of both nonmedullated and myelinated fibers increased throughout the period of observation. At birth, nonmedullated fibers smaller than 0.2 μm2 represented 69% of the population; at day 63 less than 7% were that small. Irrespective of the age of the rat, the number of microtubule profiles of nonmedullated fibers increased with the cross‐sectional area of the axon although their packing decreased. In myelinated fibers of a given caliber, the packing of microtubules increased with time, and by day 63 the density had reached its final value. In nonmedullated fibers of a given caliber, a similar trend was observed after day 31; i.e., fibers showed a small but consistent increase in density. However, before that, and in contrast to myelinated fibers, nonmedullated fibers of defined calibers exhibited a transient increase in the microl ubular density. Notwithstanding, during the history of an individual fiber the packing of its microtubules may decrease continuously until stabilizing, because the developing fiber is increasing its caliber and hence decreasing its microtubular density. In the 5‐day‐old rats, the caliber spectra of myelinated and nonmedullated axons overlapped in the 0.49–0.83 μm2 range and their microtubular densities were similar.

We conclude that the microtubular content of developing axons correlates with caliber, an architectural feature, and is largely independent of growth and of its myelinated condition. We propose that the cytoskeletal rather than the transport function commands the organization of axonal microtubules.
Ultrastructural characterization of choline acetyltransferase‐containing neurons in the basal forebrain of rat: Evidence for a cholinergic innervation of intracerebral blood vessels
Authors: Armstrong David M.
Published: January 2005

The ultrastructural morphology and vascular associations of cholinergic neurons in the horizontal limb of the nucleus of the diagonal band of Broca (nDBBh1) and amygdala of rat were determined by the immunocytochemical localization of choline acetyltransferase (ChAT), the acetylcholine biosynthetic enzyme. Within the nDBBh1 peroxidase reaction product was distributed throughout the cytoplasm of selectively labeled neuronal perikarya and dendrites. Labeled perikarya were characterized by an oval cell body (7–10, μm × 17–26 μm in diameter) in which was located a large nucleus and often a prominent nucleolus. Dendrites were by far the most numerous immunolabeled profiles in the nDBBh1. The labeled dendrites had a cross‐sectional diameter of 0.4–4.6 μm and contained numerous mitochondria and microtubules. Approximately 10% of all immunolabeled dendrites received synaptic contacts from unlabeled presynaptic boutons. In contrast to the relatively large number of ChAT‐labeled dendrites within the nDBBh1, ChAT‐positive axons were less frequently observed and immunolabeled axon terminals were never detected. The labeled axons had an outside diameter of 0.4–1.4 μm and were myelinated. The absence or relative paucity of immunolabeled terminals in the nDBBh1 indicates that most if not all of the cholinergic perikarya within this nucleus are efferent projection neurons. The nDBB is known to have widespread projections to many areas of the neocortex, hippocampus, and amygdala. In the present study we examined the amygdala and observed many ChAT‐labeled axon boutons. The immunolabeled varicosities contained numerous agranular vesicles and although ChAT‐positive termirs als were in direct contact with unlabeled neuronal elements within the amygdala, few if any synaptic densities were detected in a single plane of section. With respect to the vasculature, immunolabeled perikarya and dendrites within the nDBBh1 and axon terminals in the amygdala were often in direct apposition to blood vessels. In many instances the labeled profile was observed lying directly on the basal lamina of a capillary endothelial cell. In no instance, however, were membrane densities observed. The presence of cholinergic neuronal elements contacting the vessel wall provides morphologic evidence suggesting that the neurogenic control of cerebral vasculature is in part, mediated via a cholinergic mechanism.
Anatomical organization of the visual system of the mink, Mustela vison
Authors: McConnell Susan K. , LeVay Simon
Published: January 2005

The organization of the retinogeniculocortical visual system of the mink was studied by anterograde and retrograde tracer techniques, by physiological mapping, and by direct recordings from axonal terminals after injection of kainic acid.

In the lateral geniculate nucleus, retinogeniculate afferents are segregated according to eye of origin between the two principal layers, A and Al. Within each of these layers there is a further parcellation according to functional type: on‐center afferents terminate in the anterior leaflets of A and Al, and off‐center afferents in the posterior leaflets. This separation is preserved in area 17: geniculocortical afferents terminate in ocular dominance patches in layer IV, and these patches coexist with an alternating, partially overlapping set of patches for on‐center and off‐center inputs that we have demonstrated previously (McConnell and LeVay: Proc. Natl. Acad. Sci. USA 81:1590–1593. '84). In both the lateral geniculate nucleus and in area 17, the contralateral eye predominates to a much greater extent than in the cat.

Visual cortical areas corresponding to the cat's areas 17, 18, and 19 can be identified in the mink, but they are shifted posterolaterally in the hemisphere, and they show less emphasis on the representation of central retina. Mapping studies also revealed the existence of a fourth visual area in the splenial sulcus (area SV) adjacent to the representation of the far periphery in area 17. This area differs from the corresponding region in the cat in that it receives direct projections from the lateral geniculate nucleus and from areas 17 and 18.

The lateral geniculate nucleus projects to each of the four cortical areas that were mapped. The bulk of the projection to area 17 is derived from the principal layers, A and Al, while most cells projecting to areas 18 and SV are found in the C‐layer complex. The recurrent projection from area 17 to the lateral geniculate nucleus arises from pyramidal neurons in layer VI, and terminates through all layers of the lateral geniculate nucleus, but most densely in the interlaminar zones. Areas 18 and SV projectt predominantly to the C layers.

Areas 17, 18, and SV are reciprocally connected with tiie claustrum and the LP‐pulvinar complex, and project to the superior colliculus: All four visual cortical areas are mutually interconnected; these associational projections arise from both the supragranular and infragranular layers.
Electron microscopic study of synaptic contacts between photoreceptors and HRP‐filled horizontal cells in the turtle retina
Authors: Ohtsuka Teruya , Kouyama Nobuo
Published: January 2005

The synaptic contacts between photoreceptors and horizontal cells in the retina of the turtle (Geoclemys) were studied. Horizontal cells were classified into three types according to their intracellularly recorded spectral responses: Luminosity, biphasic chromaticity, and triphasic chromaticity horizontal cells (LHC, BHC, and THC). These cells were then iontophoretically filled with horseradish peroxidase (HRP). The various types of photoreceptors located within the dendritic field of the HRP‐filled horizontal cells were identified either as rods or as one of the three chromatic types of cones; the latter were identified by the presence and colors of their oil droplets in the inner segments. The synaptic contacts between photoreceptors and labeled horizontal cells were then investigated by light and election microscopy of serial sections on three LHCs, two BHCs, and one THC. LHCs made synaptic contacts with about 100 photoreceptors, including rods and three chromatic types of cones; two‐thirds of these photoreceptors contacted the cell body and the remaining its axon terminal. BHCs contacted about 30 cones; red‐, green‐, and blue‐sensitive cones in the ratio of 3:4:1. THC contacted 20 cones; red‐ and blue‐sensitive cones in the ratio of 2:1. The dendritic processes of HRP‐filled horizontal cells were found as the lateral element of the ribbon synaptic complexes. The present finding suggests that the responses of BHC and THC to red flashes are fed directly from red‐sensitive cones in addition to the feedback pathway of cone‐horizontal cell connections in the previous studies.
Topography of corticopontine remodelling after cortical lesions in newborn rats
Authors: Kartje‐Tillotson Gwendolyn , Neafsey E. J. , Castro Anthony J.
Published: January 2005

Autoradiographic and axonal degeneration staining techniques were combined in individual animals to study the distribution of corticopontine fibers. In normal animals, forelimb and hindlimb motor cortical projections terminated somatotopically within the ipsilateral pontine nuclei. Sparse crossed projections also displayed a somatotopic pattern. After unilateral sensorimotor cortical lesions in newborn rats, an increase in the crossed corticopontine fibers arising from the opposite unablated motor cortex was observed at maturity. These fibers distributed in a topographic pattern similar to the normal ipsilateral corticopontine pattern; forelimb motor cortical projections terminated rostral to hindlimb motor cortical fibers. The specific distribution of the anomalous fibers suggests that they constitute a functional pathway.
Pathway of acetylcholinesterase containing nerves to the major cerebral arteries in rats
Authors: Hara Hideaki , Weir Bryce
Published: January 2005

The pathway of nerves containing acetylcholinesterase (AChE) to the major cerebral arteries was investigated in the rat. In this species, the internal ethmoidal artery (IEA) arises from the anterior cerebral artery (ACA) and anastomoses with the external ethmoidal artery (EEA), forming the ethmoidal rete on the cribriform plate. The ethmoidal nerve (EN) and EEA enter the cranial cavity through the ethmoidal foramen. Densely distributed adventitial nerve plexi were present around the IEA, ethmoidal rete, and EEA. Many thick nerve bundles were found in the periadventitial layers in association with these vessels. Around the EN, just before it enters the ethmoid foramen, intensely staining nerve bundles were present that entered the cranial cavity with the EN.

After unilateral. section of the EN and EEA, a marked decrease of the nerve fibers was observed around the arteries of the anterior part of the circle of Willis on the operated side, whereas the basilar artery (BA) showed a moderate decrease in the AChE activity. After bilateral section of the EN and EEA, nerves disappeared from around all the major cerebral vessels including the BA. Section of the EEA alone did not produce any visible change of the cerebral perivascular innervation.

The present study suggests that (1) AChE‐containing nerves on the cerebral arteries arise from the AChE‐positive nerve bundles, which enter the cranial cavity with the EN through the ethmoid foramen; (2) The anterior part of the circle of Willis is innervated unilaterally by the AChE‐positive nerve bundles from the ethmoidal foramen, whereas the BA receives bilateral innervation.
Neurofilament proteins in fish: A study with monoclonal antibodies reacting with mammalian NF 150K and NF 200K
Authors: Dahl D. , Crosby C. J. , Bignami A.
Published: January 2005

Monoclonal antibodies were obtained upon immunization of mice with chicken brain antigen and with the two high molecular weight neurofilament proteins (NF 150K and NF 200K) isolated from bovine spinal cord by anion exchange chromatography. By the immunoblotting procedure, the antibodies selected for this study reacted with bovine NF 150K and NF 200K. By the same procedure the antibodies reacted with sea raven, goldfish, sea bass, shark, and trout spinal cord extracts. In goldfish and sea raven the antibodies stained a single band at approximately 150 kDa and 200 kDa, respectively. Two bands were stained in the shark, sea bass, and trout. In the shark and sea bass these bands were in the molecular weight range of mammalian NF 150K and NF 200K. In the trout the upper band was approximately 150 kDa and the lower band 130 kDa. Our findings suggest an early origin of NF 150K and NF 200K in vertebrate phylogeny as well as considerable divergence in several species.