bluuebunny/crossref_metadata_2025 huggingface dataset:
Histogenesis of the retina in the killifish, Fundulus heteroclitus
Authors: Hollyfield Joe G.
Published: December 2004

The order of production of retinal cells was studied in embryos of the teleost, Fundulus heteroclitus, using 3H‐thymidine radioautography. Cell division stops first in the fundus of the neuroepithelium and continues longest at the margin. In the fundus, the cells whose nuclei will reside in the inner region of the retina, near the vitreous, stop dividing before the cells whose nuclei will reside near the outer region of the retina. Thus the ganglion cells are produced first and the receptors and horizontal cells last.
Architectonics of the cerebellar nuclei in the rabbit
Authors: O′Leary James L. , Smith Jeanne Marie , Inukai Joseph , Mejia Hugo H.
Published: December 2004

A correlative study utilizing Golgi and Golgi Cox sections from 6–12 day rabbits cut serially, and EM material from rabbits two to three months old.

Notwithstanding differences in myelinated axon content of neuropil which affect shape and dendrite disposition of individual neurones, there were no major disparities in cellular make‐up of the cerebellar nuclei. Large and medium‐sized cells have dendrites which interdigitate in several patterns depending upon the rosette arrangements to which they belong. At the nuclear‐white matter margin dense overlapping between dendritic terminals and edge‐ramified Purkinje axons occurs. Most medium and all large cells possess centrifugal axons showing recurrent collaterals. Small cells overlapping the medium‐sized ones at 20 μ, belong largely to the short axon class, confirming early studies by Saccozzi (1887) and Lugaro (1895). Their fine axons arborize diffusely within a 250 μ perimeter.

Intranuclear arbors of Purkinje axons have funnel or poplar shapes and also contribute to the edge plexus. Besides forming nids about the somata these arbors issue significant extensions along dendrites.

Our EM studies bear similarities to those of Eager (′68) for cerebellar nuclei of cat, and lateral vestibular nucleus of that animal by Mugnaini, Walberg, Hauglie‐Hanssen and Brodal (′67). Terminal and passage boutons arise from myelinated axons, reaching dendrites and somata either directly or through nonmyelinated intermediaries. Terminals reminiscent of mossy and climbing fibers can be identified.

Axon hillocks of large and small cells show a few synapses each.
Ultrastructural alterations in vestibular and cerebellar nuclei of the ataxic rabbit
Authors: O'Leary J. L. , Fox R. R. , Smith J. M. , Inukai J.
Published: December 2004

Using ultrastructural methods degenrative changes were examined in 16 ataxic (ax/ax) rabbits of The Jackson Laboratory strain. These animals were killed between 4 and 53 days after the onset of symptoms using arterial perfusion of a paraformaldehyde‐glutaraldehyde fixative made up in cacodylate buffer. Ten age matched controls were also studied.

Alterations were observed in both neuropil and neurones of the involved nuclei, those in neuropil ordinarily remaining more significant throughout. The neuropil involvement focused upon astrocytes and axon terminals, the astrocytes showing both oedematous swelling and glycogen accumulation, the terminals secondary degeneration of acute and chronic types. Over time the coalescence of swollen glial processes leads to the formation of fluid filled extracellular spaces which appear to result from rupture of astrocytic membranes. That, together with the splitting of the lamellae of myelinated axons to form other lacunae, gives to the neuropil a progressively more spongioform appearance. With the disappearance of degenerating boutons, that vacuolation leads ultimately to loss of the glial investitures of the contained neurones.

Large and medium‐sized nerve cells can become involved in either acute or chronic cell change. Nissl substance may undergo compaction around the nucleus, the cytoplasm becoming quite fibrillar with reduction or loss of organelles. Mitochondrial alteration may be the only marker of an involved element. Cell parts in advanced degeneration are wrapped by processes of scavenger cells and removed.

Lysosomes are found in excess in degenerating nerve cells, in astrocytes and in macrophages.
Postnatal development of the cerebellar cortex in the rat. II. Phases in the maturation of Purkinje cells and of the molecular layer
Authors: Altman Joseph
Published: December 2004

The growth and synaptic maturation of Purkinje cells and of the molecular layer were studied in the cerebellar cortex of rats aged 0, 3, 5, 7, 10, 12, 15, 21 and 30 days with histological (including Golgi), histochemical, autoradiographic and electron microscopic techniques. Five phases were distinguished in the maturation of Purkinje cells. During the first phase, Purkinje cells become dispersed and aligned in a monolayer but as yet few or no synapses are formed. Next, two transient structures appear: a hypertrophied apical cone composed of „reticular”︁ cytoplasm, and lateral perisomatic processes which establish conspicuous asymmetrical synapses with climbing fibers. During the third phase the perisomatic processes disappear; the „reticular”︁ cytoplasm streams upward into the growing dendrites; the soma is invaded by permanent inconspicuous, symmetrical synapses of basket cells; and, finally, it is surrounded by glial processes, which marks the end of the synaptic maturation of the soma. During the fourth phase parallel fibers form synapses with dendritritic spines in the lower half of the molecular layer. During the fifth phase, which occurs after the disappearance of the external germinal layer, parallel fibers establish synapses with dendritic spines in the upper molecular layer. The „march”︁ of synaptogenesis in the molecular layer from the bottom upward is characterized by three successive events: an initial gradient in the appearance and disappearance of coated vesicles, heralding synaptogenesis; a similar subsequent trend in the formation of synapses; and finally, the interposition in the same sequence of glial processes between Purkinje cell dendrities and parallel fibers, marking the cessation of synaptogenesis.
Projection of the lateral part of the entorhinal area to the hippocampus and fascia dentata
Authors: Hjorth‐Simonsen A.
Published: December 2004

The hippocampus and fascia dentata receive their major extrinsic input from the entorhinal area through the so‐called perforant path. This pathway is now shown to be composed of at least two distinct fiber systems: (1) A medial perforant path coming from the medial part of the entorhinal area and terminating in the middle of the dentate molecular layer and in the deep half of the stratum lacunosum‐moleculare of the hippocampal subfield CA3. (2) A lateral perforant path from the lateral part of the entorhinal area to a superficial zone in the dentate molecular layer and to the superfcial part of the stratum lacunosum‐moleculare of CA3. This paper deals specifically with the lateral perforant path. A third group of perforant fibers, bing intermediate to the others with regard to both origin and termination has been noticed in one animal.

The fiber‐course of the lateral perforant path is found to be identical to that previously described for the medial path. The terminal field is present along the whole axial extent of the hippocampus and fascia dentata, i.e., from the temporal tip to the subsplenial portion.

No sings of degeneration corresponding to the so‐called alvear path were observed following lesions of either the medial or the lateral part of the entorhinal cortex.

Terminal degeneration appeared in the molecular layer of the subiculum and CA1 and in the anterior continuation of the hippocampal formation subsequent to lesions including the prepyriform cortex.
Experiments to determine whether retinogeniculate axons can form translaminar collateral sprouts in the dorsal lateral geniculate nucleus of the cat
Authors: Guillery R. W.
Published: December 2004

An earlier study has shown that in young kittens, but not in adult cats, section of one optic nerve produces a curious pattern of cell survival in the denervated geniculate laminae. Most of the cells in these laminae are shrunken, but a few large cells remain close to the borders of the adjacent, normally innervated laminae, giving the impression that these cells are sustained by collaterals arising from the normal retinogeniculate axons.

Adult cats and kittens aged 7, 9 and 20 days have been used to determine the extent to which normal retinogeniculate axons can invade a denervated geniculate lamina. One eye was removed and the animals were kept for periods varying from four months to four years. The fiber degeneration produced by removal of the second eye was then studied. There is no evidence for any collateral sprouting in the adults. If the first operation is done at seven or nine days a limited number of axons grow across laminar borders and invade a small border zone of the denervated laminae. These axons do not appear in all of the regions that show surviving large border cells.

It is concluded that new sprouts are probably not formed, but that growing axons can invade an inappropriate lamina if this is denervated during the normal period of axonal growth.
Experimental‐anatomical studies on the “middle temporal visual area (MT)” in primates. I. Efferent cortico‐cortical connections in the marmoset Callithrix jacchus
Authors: Spatz W. B. , Tigges J.
Published: December 2004

The efferent cortico‐cortical fiber connections of the middle temporal visual area (MT) have been studied. The primate area MT was shown by various authors to receive a fiber projection from area 17; physiologically it shows a retinotopical organization. Lesions placed in area MT of Callithrix revealed a surprising variety of cortico‐cortical connections. Termination sites of degenerating axons were found ipsilaterally in the frontal eye field and in eight regions of the temporal, parietal and occipital lobes all known to be photically responsive.

Callosal fibers terminated in the contralateral area MT and in two adjoining areas. The termination site in area MT suggested a homotopic point to point connection meaning that in area MT the entire retinal representation is connected transcallosally, whereas in the classical visual areas only the regions of midline representation are connected.

The projection of intrinsic interlaminar fibers from the supragranular layers upon layer V was weakly developed in area MT.
Observations on complex vesicles, neurofilamentous hyperplasia and increased electron density during terminal degeneration in the inferior colliculus
Authors: Jones E. G. , Rockel A. J.
Published: December 2004

The central nucleus of the inferior colliculus has been examined electron microscopically two, four and five days after section of the lateral lemniscus and four and five days after ablation of the auditory cortex. The findings confirm the differential distribution of lateral lemniscal and corticofugal fibers to the two divisions of the central nucleus and, in the case of the lateral lemniscal fibers, to the two cell types of the ventro‐lateral division.

The material from brains in which the lateral lemniscus was divided contains examples of every type of terminal degeneration which has been described: swelling and glycogen deposition, swelling (often with flattening) of synaptic vesicles, neurofilamentous hyperplasia, greatly increased electron density. At two days, only the first three of these are seen; at four days, all occur together; at five days, only the electron dense type is present. In addition, at two days, a proportion of the early degenerating terminals show almost complete loss of synaptic vesicles and their replacement by the empty “shells” of complex vesicles (of Gray). Aggregations of shell fragments can be discerned at this and later survival periods clustered about presynaptic membranes left devoid of synaptic vesicles.

These observations are considered in terms of recent concepts of the mode of formation and release of synaptic vesicles. It is postulated that terminals showing replacement of synaptic vesicles by shell fragments may have been excessively stimulated during or after the operation and have, thus, had a higher turn‐over of synaptic vesicles. It is suggested that, in this and other sites, accumulation of large numbers of shell fragments may be a necessary pre‐requisite for neurofilamentous hyperplasia, the protein of the shells being reorganized into neurofilaments.
Spreading of uncrossed retinal projection in superior colliculus of neonatally enucleated rabbits
Authors: Chow Kao Liang , Mathers Lawrence H. , Spear Peter D.
Published: December 2004

Dutch‐belted rabbits were enucleated shortly after birth and allowed to survive 14–26 weeks. In some animals, the second eye was then removed and the distribution of retinal axons studied. It was found that while there was no evidence of axonal sprouting in the lateral geniculate body, uncrossed retinofugal axons had spread throughout the lateral half of the superior colliculus, in areas normally innervated only by the contralateral eye.

Other animals were prepared for electrophysiological recording, to see if neurons in the area of new axonal growth could be activated by light or electric shock to the optic nerve. Only four of 70 neurons tested could be driven by light, and only two of 26 tested could be driven by shock. All responsive neurons were judged to be located within the limits of the normal ipsilateral projection. It is concluded that while anatomical evidence of spreading of the uncrossed retinal input has been shown, the functional significance of this new growth is yet to be demonstrated.
Transneuronal cell atrophy in the congenitally deaf white cat
Authors: West Christopher D. , Harrison J. M.
Published: December 2004

Deaf white cats with congenitally determined lesions of the organ of Corti were found to have transneuronal degeneration in the form of reduced cell size in the ventral cochlear nucleus and the superior olivary complex. A young deaf white cat with a normal spiral ganglion cell population showed no evidence of acoustic nerve fiber or ending loss despite the presence of atrophied cells in the ventrical cochlear nucleus. Spiral ganglion cell depopulation as found in an adult deaf white cat was evident only in the lower cochlear turns. Graphic reconstructions of the cochleas showed that deaf white cats fell within the normal range of cochlear length and spiral development. A non‐deaf white cat with overdeveloped convolutions of the lateral superior olivary nucleus had the most extensively coiled cochlea of the cats examined.
A comparison of visual pathways in Boston and Midwestern Siamese cats
Authors: Shatz Carla
Published: December 2004

A genetic mutation in Siamese cats causes retinogeniculate fibers representing roughly the first 20 degrees of ipsilateral visual field in each eye to cross aberrantly in the optic chiasm and terminate in the wrong lateral geniculate nucleus (LGN). Previous investigations have shown that in the visual cortex this extra representation of ipsilateral visual field can be organized into one pattern in Boston Siamese cats, another in Midwestern. This finding was confirmed here.

The possibility that the organization of the LGN might account for these two patterns was studied using combined anatomical and physiological methods. On the basis of microelectrode recordings from the visual cortex, 11 out of the 12 Siamese cats included here were Boston cats; one was Midwestern. The distribution of retinogeniculate terminals was examined in each cat using autoradiographic techniques following an eye‐injection of 3H‐proline. Overall, the LGN organization in Boston cats was similar to that of Midwestern: both lateral and medial normal segments of lamina A1 (mnA1) were present. In Boston cats, however, the mnA1 was remarkably small and shifted ventromedially in the nucleus to allow for the fusion between the medial borders of lamina A and the abnormal segment of A1. In the Midwestern cat this fusion was not apparent and the medial normal segment of A1 was significantly larger.

These differences in organization of the LGN are consistent with those seen at the level of the visual cortex in Midwestern and Boston Siamese cats. It was not possible, however, to relate them clearly to the characteristic strabismus of these animals.
Cortical projections of posterior parietal cortex in owl monkeys
Authors: Kaas J. H. , Lin C. S. , Wagor E.
Published: December 2004

Efferent cortical projections of posterior parietal cortex were determined by degeneration and autoradiographic methods in owl monkeys. Intraregional connections were to the immediate surround of the injection or lesion site, and to distinct foci within the posterior parietal region. The extraregional ipsilateral connections were with (1) previously established subdivisions of visual association cortex (the Dorsomedial Area, the Medial Area, the Dorsolateral Area, and the Middle Temporal Area), (2) other locations in caudal neocortex, and (3) frontal cortex. The callosal projections were to separate foci in posterior parietal cortex of the contralateral cerebral hemisphere. The separate foci of both ipsilateral and contralateral terminations in posterior parietal cortex raise the possibility that this region contains more than one functional subdivision. The connections with visual association cortex suggest a role for parietal cortex in visual behavior. Other foci in caudal neocortex indicate the possible locations of additional subdivisions of association cortex.
Development of the barrels and barrel field in the somatosensory cortex of the mouse
Authors: Rice Frank Lambert , Van Der Loos Hendrik
Published: December 2004

Barrels of the PMBSF of the mouse somatosensory cortex become apparent in Nissl‐stained tangential sections simultaneously, on the fourth postnatal day. At this time they are miniatures of those in the adult and are situated in the deepest sublamina of the trilaminar cortical plate. An early barrel appears as a patch of decreased cell density: the prospective hollow of the barrel. Septa become noticeable during the sixth postnatal day. From that period to adulthood, the relative contribution of the PMBSF to the total cortical surface area increases — an increase that goes against one's expectation: the barrel related periphery matures very early and so does the central, lateral region of the cortex. Barrel growth parallel to the pial surface is greater along the major axes than along the minor axes. By using the barrels to identify prospective layer IV in immature cortex, we could determine that layers V and VI attain their adult height during the sixth postnatal day — an age when prospective layers I‐IV are only half their adult height. The onset of barrel formation coincides with the moment after which injury to the pertinent somatosensory periphery (the vibrissal papillae) no longer causes profound alterations in barrel morphology.
Brain stem afferents to the festigial nucleus in the cat demonstrated by transport of horseradish peroxidase
Authors: Ruggiero David , Batton Robert R. , Jayaraman A. , Carpenter Malcolm B.
Published: December 2004

Although retrograde and anterograde degeneration studies have provided important information concerning brain stem afferents to the fastigial nuclues (FN), these data may be incomplete and should be confirmed by axonal transport methods. Attempts were made to inject horseradish peroxidase (HRP) unilaterally into the FN in a series of adult cats. Animals were perfused with dextran and a fixative solution of paraformaldehyde and glutaraldehyde in 0.1 M phospate buffer. Representataive sections were treated by the Graham and Karnovsky (1966) method.

Selective HRp injections in one FN resulted in retrograde transport of the marker of Purkinje cells of the ipsilateral vermis and distinctive appendages of the contralateral medial accessory olivary (MAO) nucleus (nucleus β and the dorso‐medial cell column). Retrograde transport of the label was found bilaterally in cells of the medial (MVN) and inferior (IVN) vestibular nuclei, in cell group x and in the nucleus prepositus (PP). Labeled vestibular neurons, most numerous in MVN, were identified in dorsal, caudal and lateral regions, with a slight ipsilateral preponderance. Only a few neurons in caudal, dorsal and lateral regions of th IVN were labeled and none of these included cells of group f. Labeled cells in the caudal third of PP were greatest ipsilaterally. Rostral and caudal injections of FN labeled smaller numbers of cells in MVN, IVN, cell group x and PP.

HRP injections of FN and portions of lobules VIII and IX resulted in bilateral retrograde lableing of larger numbers of cells in MVN, IVN and cell group x, and ipsilateral labeling of cells in group y and the interstitial nucleus of the vestibular nerve. Injections of HRP into basal folia of lobules V and VI resulted in retrograde transport of the marker to cells of the medial and dorsal accessory olivary nuclei contralaterally, and to cells of the ipsilateral accessory cuneate nucleus. Transport of label injected into portions of the pyramis was detected in parts of the contralateral MAO and bilaterally in parts of the pontine and reticulotegmental nuclei

This study suggests that the principal afferents of the fastigial nucleus arise from: (1) Purkinje cells of the ipsilateral vermis, (2) restricted portions of the contralateral MAO (nucleus ß and dorsomedial cell column), (3) portions of the MVN and IVN (bilaterally) and (4) caudala parts of the PP. Secondary vestibular inputs to the fastigial nucleus probably are relayed mainly by cells in the cerebellar cortex.
Hair cell distribution and orientation in goldfish otolith organs
Authors: Platt Christopher
Published: December 2004

Structurally diverse sensory regions occur in the otolith organs of the goldfish inner ear. Scanning electron microscopy reveals regional distinctions based on thre criteria. (1) Hair cells have difference sizes of apical bundles, based on thickness. In all three maculae, two central regions have hair cells with bundles significantly thicker than those in surrounding regions. (2) Hair cell population density varies, with regional aggregations present. The central regions with thick bundles have two to three times the density of surrounding regions with thin bundles, and contain 40‐80% of the total hair cell number in each macula. (3) Hair cell orientation maps show that each macula has two oppositely oriented cell populations that can be separated completely, not by a zone of interspersion, but apparently by a single unbroken line

The lagena is like the utricle in having hair cells with the kinocilium on the side of the cell toward the opposition line, but in the saccule the kinocilia face away from the line, and the small macula neglecta consists of two completely separate, oppositely oriented patches. The opposition line does not divide each macula simply down its midline; instead, the line divides the regions with thick bundles into narly equal opposing aras, except for a remarkably abrupt large loop in the line in the anterior part of the saccule

The regional structural diversity in these organs may relate to localized functional diversity of responses to tilt, vibration and sound.
Scanning electron microscopy of the subarachnoid space in the dog. V. Macrophages challenged by bacillus calmette‐GUERIN
Authors: Merchant Randall E. , Low Frank N.
Published: December 2004

Mongrel dogs were anesthetized intraperitoneally with pentobar‐bitol. One cc of cerebrospinal fluid was drawn through a needle inserted into the cisterna magna and mixed with 1 cc (4–9 million viable BCG organisms) of freeze‐dried bacillus Calmette‐Guerin. One minute later this mixture was injected by the same needle into the cisterna magna. At 1 and 12 days postinjection, experimental animals were perfused with buffered aldehydes. Samples of the leptomeninges were post‐fixed in OsO4 and routinely prepared for scanning and transmission electron microscopy. Leptomeningeal samples of untreated, control animals were similarly prepared.

Scanning and transmission microscopy confirm that free cells resting on the sub‐arachnoid linings and within the subpial connective tissue space of control animals possess the morphology of macrophages (Malloy and Low, 1976). Viable BCG in the subarachnoid space produces a 3‐fold increase in the free cell population of the leptomeninges in 24 hours and a 10‐fold increase in 12 days. These cells tend to form associations varying from loose aggregates to tight clusters. Approximately 80% of these free cells express macrophage morphology, with abundant plasma‐lemmal microappendages and cytoplasmic vacuoles. Transmission electron microscopy of the free cell population of BCG‐stimulated animals reveals at least two other members of the leukocyte series on the leptomeningeal linings.
Afferents to the optic tectum of the leopard frog: An HRP study
Authors: Wilczynski Walt , Northcutt R. Glenn
Published: December 2004

Folowing unilateral HRP injections in the optic tectum of Ran pipiens, HRP ‐ positive cells were seen in three pretectal nuclei: bilaterally in the dorsal posterior nucleus; in the dorsal half of the ipsilateral posterior nucleus; and ipsilaterally in the large‐celled pretectal nucleus. HRP ‐positive cells were also seen ipsilaterally in the anterodorsal, posterodorsal and posteroventral tegmental fields, the nucleus isthmi, and the dorsal gray columns of the cervical spinal cord; bilaterally in the suprapeduncular nucleus, a paramedian cell group dorsal to the interpeduncular nucleus; and in the deep layers of the contralateral tectum. In addition, evidence for a bilateral ventral preopto‐tectal projection was seen in half the experimental animals. No tectal afferents from telencephalic or rostral thalamic areas were seen. Both the ascending and descending tectal efferent fibers were also filled with reaction product. The pale reaction indicative of terminating tectal efferents was seen in the dorsal pretectum, partially overlapping the lateral nucleus and uncinate neuropil; in the core of nucleus isthmi; and in the superior olive.
Rearrangements of the retinotectal projection in Rana pipiens after unilateral caudal half‐tectum ablation
Authors: Udin Susan H.
Published: December 2004

When the caudal half‐tectum is ablated aid the optic nerve is cut in adult Rana pipiens, recordings from optic nerve terminals show that the entire visual field comes to be represented in retinotopic ordcr on the reinairring rostral half‐tecturn (compression). In contrast, if the caudal half‐tectum is ablated but the optic nerve is left intact, no compression of the retinotectal projection results. Instead, the terminals displaced from the ablatcd tissue form apermanently disorganized projection to the rostral half‐tectum superimposed on the unaltered representation of those parts of the retinawhich normally project there. The receptive field locations of tectal ncurons in both groups of animals show that the altered retinotectal projections make functional synapses. This conclusion is further supported by hehavioral data. which show that the accuracy of prey‐catching movements is altered in both groups of frogs.

The anomalous retinotectal maps can be interpreted by menas of amodel which includes polarity cues derived from the tectum and ordering cues derived from repelling interactions among fiber terminals.
Fastigial efferent projections in the monkey: An autoradiographic study
Authors: Batton Robert R. , Jayaraman A. , Ruggiero David , Carpenter Malcolm B.
Published: December 2004

Because fastigial efferent fibers partially decussate within the cerebellum and cerebellar corticovestibular projections pass near, or through, the fastigial nucleus (FN), degeneration studies based on lesions in the nucleus leave unresolved questions concerning fastigial projections. Attempts were made to determine fastigial projections in the monkey using autoradiographic tracing technics. Cells in rostral, caudal and all parts of the FN were labeled with [3H] amino acids.

Selective labeling of neurons in either rostral or caudal parts of the FN results in transport of isotope primarily via fibers of the contralateral uncinate fasciculus (UF) and the ipsilateral juxtarestiform body (JRB). Fastigial projections to the vestibular nuclei are mainly to ventral portions of the lateral (LVN) and inferior (IVN) vestibular nuclei, are nearly symmetrical and are quantitatively similar on each side.

Fastigiovestibular projections to cell groups f and x arise from all parts of the FN and are mainly crossed; modest projections to the medial vestibular nucleus are uncrossed. No fastigial efferent fibers end in the superior vestibular nucleus on either side, or in dorsal regions of the LVN. Crossed fibers descending in IVN terminate in the nucleus parasolitarius. Fastigioreticular fibers arise predominately from rostral regions of the FN, are entirely crossed and project mainly to: (1) medial regions of the nucleus reticularis gigantocellularis, (2) the dorsal paramedian reticular nucleus and (3) the magnocellular part of the lateral reticular nucleus. Fastigiopontine fibers, emerge with the UF, bypass the vestibular nuclei and terminate upon the contralateral dorsolateral pontine nuclei. Crossed fastigiospinal fibers separate from fastigiopontine fibers and descend in the ventrolateral tegmentum beneath the spinal trigeminal tract; in the medulla and upper cervical spinal cord these fibers are intermingled with those of the vestibulospinal tract. Fastigiospinal fibers terminate in the anterior gray horn at C‐1 and probably descend further.

Ascending fastigial projections arise from caudal parts of the FN, are entirely crossed and ascend in dorsal parts of the midbrain tegmentum. Label is transported bilaterally to the superior colliculi and the nuclei of the posterior commissure. Contralateral fastigiothalamic projections terminate in the ventral posterolateral (VPLc and VPLo) and in parts of the ventral lateral (VLo) thalamic nuclei. The major region of termination of fastigiothalamic fibers is in VPLo.

Fastigiothalamic projections, probably conveying impulses concerned with equilibrium and somatic proprioception, appear to impinge upon thalamic neurons receiving inputs from less specialized receptors that signal information concerning position sense and body movement. More modest fastigial projections to VLo could directly influence activity of neurons in the primary motor cortex.
An autoradiographic analysis of postnatal cell proliferation in the normal and degenerative mouse retina
Authors: Blanks Janet C. , Bok Dean
Published: December 2004

Light microscopic autoradiography, following injection of tritiated thymidine, was used to study the postnatal development of cells in the inner nuclear layer (INL) of the normal and rd (C57BL/6J‐rd le) mouse retina. Specific attempts were made to determine whether some bipolar cell degeneration occurs in conjunction with previously noted photoreceptor cell degeneration in the retina of the mutant (rd) mouse. A differential count of cell types in the INL of both the central and peripheral retina indicates that the same ratio of bipolar cells to Müller cells (3:1) exists in the normal and the rd retina during postnatal development. The density of cells in the INL was similar in both groups during development and similar decreases in width of the INL occurred in the normal and rd mouse during maturation. In addition, autoradiographic analysis of the proliferation of postnatally forming bipolar cells suggested that the rd gene is not lethal to the bipolar cell population which forms after birth. The labeling index (percent labeled cells) in the INL, determined as a function of the date of 3H‐thymidine injection and assessed in the mature retina (day 41), was similar in both mice. Analysis of the number of silver grains/nucleus presented a more complete picture of how the progenitor pool of cells contributes to the cell types formed postnatally in the retinas of both mice.

The conclusion that bipolar cell death does not occur to any significant degree in the retina of the rd also suggests that transneuronal degeneration does not occur in the retina of the mutant mouse during the period (up to day 41) when most of the photoreceptor cells die. The observation in both groups of mice that cell density remains constant between postnatal day 14 and day 41, while the width of the INL changes tremendously, suggests that there is a significant redistribution of cells during growth of the eyeball and/or cell death which occurs in all cell types found in the INL in both the normal and mutant mouse.
Some visual and other connections to the cerebellum of the pigeon
Authors: Clarke P. G. H.
Published: December 2004

By anatomical techniques it has been shown that folia VIc‐IXc of the pigeon cerebellum receive inputs from the following groups of neurons: the medial and lateral pontine nuclei, the superficial synencephalic nucleus, the medial spiriform nucleus, the inferior olive, and the deep cerebellar nuclei. From all but the last of these, the projection is mainly crossed, though the uncrossed component from the lateral pontine nucleus is not insubstantial. The input from the superficial synencephalic nucleus provides a direct pathway from the retina to the cerebellum (folia VIc, VII, VIII and IXc). Less direct visual pathways reach the cerebellum via the following routes: (i) the superficial synencephalic nucleus projects ipsilaterally to the lateral pontine nucleus and sparsely to the inferior olive; (ii) the tectum projects ipsilaterally to the lateral and medial pontine nuclei, though the latter connection is sparse.

In electrophysiological experiments, the importance of the tecto‐pontine component of the projection has been demonstrated by cooling the tectum while recording visual responses from the cerebellum. The visual receptive fields of pontine cells have been analysed. They vary in extent from 10° to the whole monocular field. They respond best to moving targets, preferring speeds of 20 to 60°/second, and are usually direction‐selective.
Localization of sensory neurons traversing the stellate ganglion of the cat
Authors: Oldfield B. J. , McLachlan Elspeth M.
Published: December 2004

The distribution of sensory cells whose axons traverse the stellate ganglion and project via sympathetic cardiac nerves to the heart of the cat has been examined quantitatively. Horseradish peroxidase (HRP) injected at multiple sites in the right stellate ganglion, or applied to the middle cardiac nerve, labelled small numbers of cells in the thoracic dorsal root ganglia (DRG) from T1 to T8. These cells were most numerous between T2 and T5 and were consistently small (< 40 μm) relative to other cells in the DRG. When HRP was applied to middle cardiac nerves, the numbers of labelled sensory cells always exceeded the numbers of myelinated axons counted in the same nerves from other cats. It is concluded that the distribution of the cells of cardiac sensory fibres is more extensive within thoracic DRG than has been previously reported, and it is suggested that such fibres travelling in the sympathetic cardiac nerves may be either myelinated or unmyelinated.
Development of the diencephalon in the rat. I. Autoradiographic study of the time of origin and settling patterns of neurons of the hypothalamus
Authors: Altman Joseph , Bayer Shirley A.
Published: December 2004

Groups of pregnant rats were injected with two successive daily doses of 3H‐thymidine from gestational day 13 (E13+14) until the day before birth (E21+22). This double labelling procedure was combined with an injection schedule of a single day delay between groups (E13+14; E14+15; E1516.). The two injections assured the comprehensive labelling of practically all neurons of a given structure prior to the onset of their differentiation (comprehensive labelling), whereas the progressive daily delay in injections made it possible to estimate the proportion of neurons formed in various regions of the hypothalamus on a single day. Hypothalamic areas or nuclei were assigned into four classes on the basis of their cytogenetic isochronicity. Structures composed of the earliest arising (class 1) neurons constitute a lateral tier that includes the lateral preoptic and lateral hypothalamic areas, and the lateral mammillary nucleus. Structures composed of early arising (class 2) neurons form a heterogeneous collection of nuclear systems, including the Para ventricular, intern clear and supraoptic magnocellular neurons, and several intermediate tier nuclei of the anterior and posterior hypothalamus. The late arising (class 3) and latest arising (class 4) nuclei constitute a periventricular system anteriorly and a more extensive region posteriorly. The latter two nuclear systems may constitute the hypophysiotropic area of the hypothalamus. The nuclei of the mammillary system, which are produced sequentially, are distinguished from other hypothalamic structures by their more rapid generation time. Internuclear labelling gradients were used to infer the neuroepithelial site of origin and setting pattern of neurons. common sites of origin were indicated for the following structures: the magnocellular neurohypophysial neurons; the neurons of the dorsomedial and ventromedial nuclei; and the neurons of the tuberomammillary and arcuate nuclei. The sites of origin of these groups of nuclei were related to specialized ventricular linings in the mature hypothalamus.
Radial organization of thalamic projections to the neocortex in the mouse
Authors: Frost Douglas O. , Caviness Verne S.
Published: December 2004

The intracortical distributions of the thalamic projections to a large number of neocortical fields are studied by the anterograde degeneration method in the mouse. The basic radial distribution of terminating thalamofugal axons is uniform throughout the mouse cortex and is essentially the same as that encountered in other mammalian species. Terminating axons are concentrated in three tiers: an outer tier in layer I, a middle tier in layers IV and/or III, and an inner tier in layer VI. In most fields, terminating axons also extend, to some extent, into layer V. Variations are encountered from field to field, particularly in the density and degree of divergence of projections and in the radial extent of individual tiers with respect to cytoarchitectonic layers.

In accord with other studies, the thalamic projections to each field appear to be composed of two general axon classes. Class I axons terminate densely in the middle tier, seem to be of large caliber, and often have collaterals to the other tiers. Class II axons do not terminate densely in the middle tier and seem to be of small caliber. Terminating class II axons may be distributed to one or more tiers and may be concentrated in the inner and/or outer tiers. The thalamic projection to each field has its origin in multiple nuclei. All thalamic nuclei projecting to the neocortex appear to have class II projections and many also have class I projections.

Patterns of degeneration in the cortex associated with lesions in different positions in many nuclei suggest that thalamic relay neurons are organized along “lines of projection”–neurons in the same line projecting to the same tangentially restricted cortical region. The neurons of origin of class I and class II axons are intermixed along the lines of projection.
Neurotensin: Topographical distribution in rat brain by immunohistochemistry
Authors: Jennes Lothar , Stumpf Walter E. , Kalivas Peter W.
Published: December 2004

The anatomical distribution of neurotensin perikarya and fibers in rat brain, spinal cord, and pituitary has been studied by immunohistochemistry. Neurotensin immunoreactivity is widely distributed throughout the brain, especially in forebrain and midbrain limbic structures, but also in the pons, medulla, and spinal cord.

Areas with low immunoreactivity, or lack of it, stand out and include most of the hippocampus, isocortex, ventromedial and dorsomedial hypothalamic nuclei, somatomotor nuclei, cerebellum, and dorsal column nuclei.

Strong neurotensin immunoreactivity is found in accumbens‐caudateputamen, central and medial amygdaloid nuclei, ventrolateral septum, pars lateralis of the nucleus of the stria terminalis, paraventricular, periventricular, and lateral hypothalamus, median eminence, thalamic intralaminar and periventricular nuclei, ventral tegmentum, central gray, certain raphe nuclei, locus ceruleus, necleus parabrachialis medialis and lateralis, nucleus of the solitary tract and area postrema, spinal and trigeminal substantia gelatinosa, as well as certain cells in the anterior pituitary.

The anatomical data suggest the existence of neurotensin circuits for (1) the control of autonomic‐endocrine functions, involving the nucleus tractus solitarii, area postrema, nucleus ambiguus, nucleus parabrachialis, nucleus paraventricularis, nucleus centralis amygdalae, and pars lateralis of the bed nucleus of the stria terminalis; and (2) for the transmission and modulation of certain somatosensory qualities, involving the spinal substantia gelatinosa, trigeminal sensory nuclei, and thalamic intralaminar nuclei.
Reissner's fiber in the sacral cord and filum terminale of the possum Trichosurus vulpecula: A light, scanning, and electron microscopic study
Authors: Tulsi R. S.
Published: December 2004

The ending of Reissner's fiber (RF) and structural features associated with gaps or fissures in the rostral part of the filum were investigated using light, scanning, and transmission microscopic techniques in young and mature possums of both sexes. To the best of the author's knowledge the report contains results of the first successful application of the SEM for a study of RF in the spinal cord. Some new observations suggest that while the bulk of RF is formed by the subcommissural organ and moved caudally, additional secretory products may be added by ependymal cells in the sacral and possibly other regions of the spinal cord. Evidence is provided in support of the view that RF may pass through gaps in the ependymal lining in the rostral part of the dorsal wall of the filum terminale and caudal end of the sacral cord to reach the periependymal loose tissue and possibly the subarachnoid space.

The region of the gap shows the surface of the ependyma facing the lumen of the filum to be covered with microvilli and cilia, and to be in direct continuity with the external surface of the ependyma covered with basement membrane with glial processes and collagen fibers in close proximity. The present results confirm and extend observations reported by Wislocki et al. ('56).
Quantitative analysis of the optic nerve of the north american opossum (Didelphis Virginiana): An electron microscopic study
Authors: Kirby Michael A. , Clift‐Forsberg Lori , Wilson Paul D. , Rapisardi Salvatore C.
Published: December 2004

On the basis of an electron microscopic examination of the optic nerve of the North American opossum it was estimated that the nerve has approximately 100,000 axons, of which 98% are myelinated, The myelinated axons ranged from 0.3 to 6.7 μm in diameter (mean 1.6 μm), while unmyelinated axons were 0.2 to 1.6 μm in diameter (mean 0.6 μm). Axoplasm and axon (axoplasm plus myelin) diameter spectrums were unimodal and positively skewed. The mean of the ratio of axoplasm to axon diameter was 0.69. However, this ratio varied widely across axons and was nonlinearly distributed, decreasing with axon diameter. An inverse relationship between axon density and the proportion of large‐diameter axons was noted. A region having a low axon density and a high proportion of large‐caliber axons was located dorsally in a cross section obtained near the eye. However, in sections obtained near the optic chiasm, regions having the highest proportion of large‐diameter axons were in the ventral periphery of the nerve. It is suggested that within the 40‐mm length of the nerve, there may be a change from a retinotopic organization to an organization of axons according to their diamerer and central targets.
The developmental morphology of Torpedo marmorata: The electric lobes
Authors: Richardson Guy P. , Fox Geoffrey Q.
Published: December 2004

The development of the electric lobes of Torpedo marmorata has been investigated using light and electron microscopical techniques. The lobe Anlagen become visible in the rhombencephalon along the floor of the 4th ventricle at the 10‐mm stage. Many of the neuroepithelial cells in the Anlagen differentiate, becoming postmitotic and axonic by the 24 mm stage. Proliferative zones of neuroepithelial cells disappear from the electric lobes by the 30‐mm stage. After their initial, early differentiation the electromotor neurons remain monopolar until the 40‐mm stage when dendrite formation begins. The differentiation of the electromotor neuron from a mono‐ to an immature multi polar form occurs between the 40‐ and 55‐mm stages and involves, in addition to dendrite formation, a change from a pear‐shaped to a spherical cell body, a dramatic increase in cytoplasmic volume, a centralization of the nucleus, an enlargement of the nucleolus and its migration away from the nuclear membrane, and differentiation of the axon hillock. The electric lobes are invaded by sinusoids at the 24‐mm stage but formation of the capillary network by sprouting cords of endothelial cells begins later at the 40‐mm stage. Neuronal cell death (26–74‐mm stages) appears to be mainly an autolytic process and the debris is removed by immature glial cells. Afferent fiber growth cones are first recognized in the lobes at the 60‐mm stage but synapses are not observed until the 78‐mm stage. Myelination begins in the electric lobes concomitantly with the onset of synaptogenesis. A twofold increase in dendrite length occurs over the period when synapses begin to form in the lobes but dendritic maturation is not complete until the neonatal (120‐mm) stage. The results are discussed in relation to the development of the electric organs.
A Golgi and ultrastructural study of the monkey globus pallidus
Authors: Difiglia Marian , Pasik Pedro , Pasik Tauba
Published: December 2004

Golgi preparations reveal that the most frequent type of pallidal neuron (principal cell), which has been recognized in all previous reports, is large (20–50 (Am)), fusiform, with dendrites up to 700 μm long. Large neurons of globular shape are less frequently impregnated. The morphology of dendrites varies considerably within the same neuron. Some exhibit numerous spines and protrusions and are seen to terminate in elaborate arborizations. A small interneuron (12 (μm)), with relatively short dendrites, up to 150 μm, and a short sparsely branching axon is observed less frequently. At least two types of afferent axons are present. A small‐diameter fiber from the neostriatum enters the pallidum in bundles and gives rise to numerous thin branching processes with varicosit es about 1 μm in size. The axon collaterals are oriented orthogonal to the main axon and parallel to the dendrites of principal cells. A large‐caliber fiber with clusters of 2–3‐μm swellings can also be seen in close proximity to large pallidal dendrites.

Ultrastructurally, principal cell dendrites (trunks, spines, and protrusions) are totally covered by synapsing axon terminals. In contrast, some small dentrites, presumed to belong to interneurons, form very few synapses. At least six categories of profiles containing vesicles are observed. One group has cytologic features of dendrites and participates in serial and triadic synapses with other profiles in the pallidal neuropil.

Results suggest that the synaptic organization of the globus pallidus may be viewed as a repetitive, geometric arrangement of striatal and other afferent axons ensheathing and synapsing with the dendrites of principal cells. This pattern is interrupted by the presence of presynaptic dendrites, probably belonging to interneurons, which participate in complex synaptic arrangements.