bluuebunny/crossref_metadata_2025 huggingface dataset:
Involvement of the avian amygdalar homologue (archistriatum posterior and mediale) in defensively conditioned heart rate change
Authors: Cohen David H.
Published: January 2005

Archistriatal involvement in visually conditioned heart rate change (established by pairing light and foot‐shock) was studied in 198 pigeons by evaluating conditioning performance following lesions of different archistriatal subdivisions or interruption of their subtelencephalic projections. Lesions of the anterior‐intermedium archistriatum or interruption of its descending projection (tractus occipitomesencephalicus) had no effect on conditioned response development. In contrast, destruction of the posterior‐mediale region or interruption of its descending projection (tractus occipitomesencephalicus, pars hypothalami) produced profound conditioning deficits. The findings are entirely consistent with a recent anatomical analysis (Zeier and Karten, 1971) suggesting that only the posterior‐mediale archistriatum constitutes the avian amygdalar homologue. It is concluded that the integrity of the posterior‐mediale region and its projection to the hypothalamus via the tractus occipitomesencephalicus, pars hypothalami are essential for establishing visually conditioned heart rate change in a defensive conditioning paradigm, and these findings are discussed in the context of structures previously implicated in mediating this conditioned autonomic response.
The number, size and spatial distribution of neurons in Lamina IV of the mouse SmI neocortex
Authors: Pasternak Joseph F. , Woolsey Thomas A.
Published: January 2005

We located the corresponding barrel in Layer IV of the mouse Sml cortex in eleven cerebral hemispheres sectioned in a plane tangential to the pia overlying Sml and in one sectioned in a plane normal to the pia. All of the brains were serially sectioned and prepared by a combined Golgi‐Nissl method. In the section in which barrel C‐1 could be optimally visualized each neuronal soma was outlined with a camera lucida and the cross‐sectional area measured with the aid of a small computer.

In all, nearly 7,000 neurons were measured. We estimate that on average barrel C‐1 contains about 2,000 neurons. The mean cross‐sectional area of the perikarya is 62.51 μ2 (S.D. ± 14.51 μ2) and the size distribution of the neurons is unimodal and positively skewed. There is no segregation of cells within the barrel on the basis of size. The spatial distribution of cells in the barrel is fairly constant, from specimen to specimen, and the characteristic cytoarchitectonic appearance of the barrel can be related to regional neuronal packing density sicne there are at least 1.6 as many neurons in the sides of the barrel as the hollow.

The constancy of the cellular composition of the barrels indicates that the mechanisms responsible for the development of the mouse SmI cortex are fairly rigidly determined, and that the barrel field should lend itself well to further quantitative, developmental and physiological analysis.
The ascending projections of the superior colliculus in the rhesus monkey (Macaca mulatta)
Authors: Benevento L. A. , Fallon James H.
Published: January 2005

We studied and compared the ipsilateral afferents of the superficial and deep layers of the superior colliculus of the rhesus monkey. Using a stereptaxic method, microelectrodes were inserted through the contralateral hemisphere in order to make electrolytic lesions of the superior colliculus. Large lesions involved all layers of the superior colliculus, while smaler lesions involved either the superficial or the deep layers of the superior colliculus. Following various survival times, the brains were prepared with the Fink‐Heimer technique (1967). Following lesions of the superficial layers of the superior colliculus, definite degenerated axonal endings were found in the dorsal and ventral lateral genuculate nuclei, inferior pulvinar, centrontermediate nucleus, magnocellular dorsomedial nucleus, anterior pretectal nucleus and pretectal refion. Sparse degenerated axonal endings were found in the limitans nucleus, lateral posterior nucleus and some intralaminar nuclei following lesions of the superficial layers in the rostral portion of the superior colliculus. Following lesions of the deep layers of the superior colliculus, degenerated axonal endings were found in the central gray, magnocellular medial geniculate nucleus, suprageniculatre nucleus, limations nucleus, lateral posterior nulceus, medial and oral pulvinarm nucleus of athe accessory optic tract, zona incerta, subdivisions of the ventral lateral and ventral posterior lateral nuclei, ventral posterior inferior nulceus, densocellular and mulriform dorsomedial nuclei, all intralaminar nucleim inferior coliculus, parabigeminal nucleus, olivary nucleus, reunions nucleus, Forel's Field H and an undefined midbrain nucleus. In general the projections were topographically organized in that the caudal portions of thalamic nuclei. All the degeneration patterns seen after lesions of the superficial and dep layers were accoundted for by large lesions which involved all layers of the superior colliculus. It is conclude that the superficial and deep layers of the rhesus monkey superior colliculus have different ascending projections. The findings are related to the organization of visual and multimodal thalamocortical system in primates and other mammals.
Cerebellar corticovestibular fibers of the posterior lobe in a prosimian primate, the lesser Bushbaby (Galago senegalensis)
Authors: Haines Duane E.
Published: January 2005

The organization of cerebellar corticovestibular fibers was studied in a prosimian primate (Galago senegalensis) using the Fink and Heimer (1967) method. The vestibular complex of Galago is larger than in other mammals and some higher primates. Vermis lobule IX contributes the largest number of fibers to the ipsilateral vestibular complex. Lobules VI and VIII give rise to lesser, but similar, numbers of fibers which also pass into the ipsilateral vestibular nuclei. Vermis lobule VII and the paravermal and lateral cortices contribute extremely sparse numbers of fibers to the dorsal area of the ipsilateral vestibular complex. All degenerated fibers enter the vestibular nuclei through a large diffusely organized juxtarestiform body.

Fibers from vermis lobule VII and the paravermal and lateral cortices terminate in dorsal areas of the ipsilateral vestibular nuclei. Vermis lobule VI projects into dorsal and lateral regions of the ipsilateral SVN, LVN and SpVN. Vermis lobules VIII and IX project into the dorsal and into progressively more central and medial regions of the ipsilateral SVN, LVN and SpVN. This gives the clear impression of a rostro‐caudal origin of fibers from the posterior lobe vermis which terminate in an overlapping lateral to medial sequence in the vestibular nuclei, lesions of vermis lobule IX also elicit degeneration in dorsal areas of the ipsilateral medullary reticular formation and in the ipsilateral parabrachial nuclei.
Relations between auditory nerve endings and cell types in the cat's anteroventral cochlear nucleus seen with the Golgi method and nomarski optics
Authors: Brawer James R. , Morest D. Kent
Published: January 2005

Rapid Golgi impregnations of the ascending branches of the auditory nerve fibers and of the types of neurons in the anteroventral cochlear nucleus (AVCN) were studied. Entire ascending branches could be observed; some of these branches project to each subdivision, others do not. There are two main types of large neurons: the bushy and stellate cells. Criteria were established for identifying unimpregnated bushy and stellate perikarya by means of Nomarski optics, and these criteria were checked by Nomarski observations on neurons which had either impregnated dendrites and unimpregnated cell bodies or impregnated portions of perikarya. In this way, the relations of unimpregnated cell bodies to auditory nerve endings were observed. Furthermore, with Nomarski optics, the cytoarchitectonic subdivisions of AVCN could be determined. Differences in the end‐bulbs and collateral endings formed by the auditory nerve fibers were distringuished in three of the cytoarchitectonic subdivisions of the AVCN. End‐bulbs in the anterior division were much larger than those in the dorsa and ventral parts of the posterior division. The large end‐bulbs of held in the anterior division of the AVCN were consistently associated with the perikarya of bushy cells and not with those of stellate cells. The large end‐bulbs are not observed in the posterior division. Thus, bushy cells in the posterior division, although morphologically similar to those in the anterior division, must have a different synaptic organization. This difference may correspond to electrophysiological distinctions in the time‐patterns of response recorded in these regions following acoustic stimulation.
The inferior olivary nucleus of the opossum (Didelphis marsupialis virginiana), its organization and connections
Authors: Martin George F. , Dom R. , King J. S. , Robards M. , Watson C. R. R.
Published: January 2005

Although the inferior olivary nucleus of the opossum is small, sections stained either for Nissl substance, normal axons or cholinesterase activity reveal distinct medial, dorsal and principal nuclei. The medial nucleus contains three major subdivisions (labelled a, b, c after Bowman and Sladek, 1973) and a group of neurons which is comparable to the cap of Kooy. In contrast to the cat and monkey, the major portion of the “medial” nucleus (subgroup a) lies lateral to the principal nucleus in rostral sections. The dorsal nucleus can also be subdivided, as can the principal nucleus which contains distinct dorsal and ventral lamellae. A small area is identified which based on position and connections may conform to the dorsal medial cell group.

The experimental portion of the study provides evidence for an olivary projection from the motor‐sensory cortex and a massive input from the midbrain (red nucleus, pretectum, midbrain tegmentum). In addition, the opossum inferior olive receives fibers from the deep cerebellar nuclei (cerebellar feedback loops), the spinal cord and the dorsal column nuclei. Of particular interest is the finding that fibers from the nucleus cuneatus and nucleus gracilis have distinctly different olivary targets and that those from the nucleus gracilis, but not the cuneate nucleus, overlap (in part, at least) with the direct spinal fibers. Other examples of overlapping fields of terminal degeneration are present and are discussed. In general our results reveal that although certain relationships between the nuclear divisions are different, the opossum olive conforms well to that of placental mammals and provides a basic mammalian model for future experimental electron microscopic and physiological studies.
Cell death in the development of the lateral motor column of the chick embryo
Authors: Hamburger Viktor
Published: January 2005

Cell counts were made in the lumbar lateral motor column (l.m.c.) of chick embryos of 5.5, 6, 7, 8, 9, 12, 18 days of incubation and five days posthatching (n = equals; 68). Only nuclei with nucleoli were counted and corrections were made for double counting (Abercrombie, 1946). The population attains a peak value of over 20,000 cells (corrected figure: over 17,000) at 5.5–6.5 days = stages 28 and 29 (Hamburger and Hamilton, 1951). The l.m.c. loses between 7,000 and 8,000 cells between days 6.5 and 9.5, (between stages 29 and 36). In other words, 60% of the population survive. A plateau of approximately 12,300 cells (corrected figure: 10,300) is maintained throug five days posthatching. Massive cell degeneration was observed in 7‐ and 8‐day embryos. Counts of distinctly pyknotic cells indicate that at least 5–6% of the total population is in the process of degeneration at any particular time. This figure is probably an underestimation; hence it is virtually certain that the depletion of the l.m.c. is due entirely to cell death. Arguments are presented in support of the hypothesis that the naturally occurring cell death in the l.m.c. is due to the failure of their axons to survive in a competion process at the periphery. Observations of the time pattern of muscle differentiation and their neurotization in the leg further endorse this hypothesis. However, it is not clear whether the axons compete for contact sites on muscle fibers or for a “trophic” agent.
Locus ceruleus in rhesus monkey (Macaca mulatta): A combined histochemical fluorescence, Nissl and silver study
Authors: German Dwight C. , Bowden Douglas M.
Published: January 2005

The locus ceruleus (LC) of the rhesus monkey (Macaca mulatta) was investigated using the histochemical fluorescence method and Nissl and ammoniacal silver stains. Caudally, a few fluorescent cells were observed in the lateral wall of the ventriculus quartus near the velum medullaris superior. Rostrally, the fluorescent cells were compactly clustered and reached their greatest density medial and, to a lesser extent, lateral to the tractus mesencephalicus n. trigemini at the level of the decussation of the nervus trochlearis. In the most rostral plane, fluorescent cells were more diffusely scattered ventral and medial to the pedunculus cerebellaris superior with a few cells situated near the nervus trochlearis. Nissl staining of tissue previously used for histochemical fluorescence showed that fluorescent cells were largely found in a region labelled LC in two rhesus monkey brain atlases and erroneously labelled nucleus tractus mesencephalicus n. trigemini in one brain atlas. Ammoniacal silver staining resulted in a dense accumulation of silver granules in the cells found to display a positive reaction for monoamines. The silver stains therefore offer an alternative to the histochemical fluorescence method for identifying the monoamine‐containing LC neurons.
Olivocochlear and vestibular efferent neurons of the feline brain stem: Their location, morphology and number determined by retrograde axonal transport and acetylcholinesterase histochemistry
Authors: Warr W. Bruce
Published: January 2005

Anterograde degeneration studies have shown that the cochlear and vestibular receptor organs receive an efferent innervation from neurons in the brain stem. This pathway may provide a mechanism by which the CNS could modulate its own afferent input. The neurons which provide this innervation have so far escaped positive identification with methods which depend on retrograde cell changes after axotomy. In the present study, horseradish peroxidase (HRP) was injected into the labryinths of kittens and after allowing 24 hours for the retrograde axonal transport of this tracer, its presence in neurons of the brain stem was demonstrated histochemically. Because there is evidence that the efferent innervation of the labyrinth is cholinergic, acetylcholinesterase (AChE) was also demonstrated histochemically in the same or in adjacent tissue sections. Neurons labelled with HRP were found bilaterally in most periolivary cell groups of the superior olivary complex (cochlear efferents) and in the parvocellular reticular nucleus lateral to the abducens nucleus (vestibular efferents). Counts of labelled neurons yielded estimated totals of 1,700–1,800 cochlear and 400–500 vestibular efferent neurons. Approximately 60% of the neurons in each total were located on the side ipsilateral to the injection. The distribution of HRP‐labelled neurons was virtually identical to that of AChE‐positive neurons found in adjacent sections, and in those regions with predominantly ipsilateral or contralateral projections, there was an approximate correspondence in number of HRP‐ and AChE‐positive neurons. In tissue sections processed successively for demonstration of HRP and AChE, virtually all HRP‐labelled neurons were found to be AChE‐positive. These findings suggest that a number of current conceptions regarding labyrinthine efferent systems may need revision.
Behavioral and morphological evidence for binocular competition in the postnatal development of the dog's visual system
Authors: Sherman S. Murray , Wilson James R.
Published: January 2005

Two normally‐reared dogs and five dogs reared with monocular eyelid closure were studied. The two normal dogs and three of the deprived dogs were tested with a perimetry technique for the extent of behavioral visual field, and all of the dogs were studied histologically to determine the size of cell somata in the lateral geniculate nucleus.

Behaviorally, the normal dogs saw with each eye approximately from 120° ipsilateral to 30° contralateral. The deprived dogs had a normal field of view for the non‐deprived eye, but with the deprived eye they saw only in the monocular segment (i.e., approximately 120° to 30° ipsilateral).

Histologically, geniculate cells in the monocular segment of deprived dogs were of normal size. In the deprived laminae of the binocular segment, however, cells averaged about two‐thirds normal size, and in non‐deprived laminae of this segment, neurons were hypertrophied. The hypertrophy was greater for cells in lamina A (40%) than for those in lamina A1 (17%).

These data indicate that in monocularly deprived dogs, the monocular segment of the visual system develops normally, but the binocular segment does not. Therefore, we conclude that binocular competition operates in the developing dog's visual system much as it does in the cat's.
Projections of the dorsal column nuclei and the spinal cord on the inferior olive in the cat
Authors: Boesten A. J. P. , Voogd J.
Published: January 2005

This study demonstrates partially overlapping fiber termination areas in the inferior olive originating from the dorsal column nuclei and the spinal cord.

Based on the distribution of the terminations the dorsal accessory olive can be divided into a rostral and a caudal part. In the caudal part terminations are found of fibers originating in the contralateral gracile nucleus and in the lumbar and cervical spinal cord. Terminations in the rostro‐medial part of the dorsal accessory olive arise from the contralateral internal cuneate nucleus and from the opposite intermediate grey at C.1. Fibers from more caudal regions of the internal cuneate nucleus terminate in the dorsal accessory olive caudal to those originating from more rostral regions of this nucleus. The gracile nucleus and the lumbar spinal cord project to the rostro‐lateral portion of the dorsal accessory olive.

The terminations in the medial accessory olive from the lumbar spino‐olivary fibers are found in a laterally located zone in the caudal one‐third of the nucleus. This spino‐olivary termination area extends more rostrally and medially after interruption of the cervical spino‐olivary fibers. Fibers from the contralateral gracile nucleus terminate in a medial zone in the caudal half of the medial accessory olive, while terminations of the contralateral internal cuneate nucleus are found at a more rostral level in the medial part of the medial accessory olive.

Connections between the inferior olive and the caudal part of the spinal trigeminal nucleus, the lateral cervical nucleus and the cervical dorsal horn could not be demonstrated.
Translaminar growth of axons in the kitten dorsal lateral geniculate nucleus following removal of one eye
Authors: Hickey T. L.
Published: January 2005

The distribution of retinal afferents to the dorsal lateral geniculate nucleus of the cat following the early removal of one eye has been studied using autoradiographic as well as degeneration techniques. The degeneration techniques have confirmed earlier observations that axons from the remaining, normal eye grow across laminar borders into the deafferented lamina A. Autoradiographic techniques, however, have shown further examples of translaminar growth between lamina A and lamina A1 as well as between lamina A1 and lamina C. Although the possibility exists that such growth also occurs between the other C laminae (C1, C2 and C3) such growth is harder to demonstrate since no well defined interlaminar regions exist in this part of the nucleus.

In the monocular segment of the nucleus degeneration techniques have shown some translaminar invasion of the deafferented lamina A. Autoradiographic techniques have demonstrated similar growth as well as an abnormal invasion of the most lateral parts of the monocular segment. This latter growth originates in the optic tract as it curves around the nucleus on the way to the superior colliculus.
The development of half‐eyes in Xenopus tadpoles
Authors: Feldman Joan D. , Gaze R. M. , MacDonald Neil
Published: January 2005

When the nasal or temporal half of a developing eye in Xenopus larvae between stages 32 and 38 was removed, the remaining fragment became rounded up and subsequently developed into a normal eye by mid‐larval stages. The contralateral retinotectal projection was normal in approximately two‐thirds of the animals, when mapped in later tadpole life. The remaining animals showed either some form of mirror reduplication in the visual map or else some degree of lack of order, as compared with a map taken from a normal tadpole of equivalent age. We conclude that the regulative powers of the larval Xenopus eye extend to much later stages (stage 38) than was previously thought; and a possible mechanism for the production of reduplicated maps from half‐eyes is considered.
A cytoarchitectonic and Golgi stody of the red nucleus in the rat
Authors: Reid J. M. , Gwym D. G. , Flumerfelt B. A.
Published: January 2005

The cytology of rubral neurons was investigated using both paraffin and 1 μ thick Epon sections. The neurons were divided into four size categories which form a continuum with regard to cellular characteristics. Giant neurons ( >40 μ) and large neurons (26–40 μ) predominate in the caudal one‐third of the nucleus. Large neurons extend up the ventral, medial and lateral borders of the nucleus into its middle one‐third. The caudal one‐third of the nucleus together with this extension of large cells is designated as the magnocellular part of the nucleus. The more rostral part of the nucleus con tains predominantly small (<20μ) and medium size (20–25 μ) neurons, and this constitutes the parvocellular part or the nucleus. The characteristics of each cell type are described. Camera lucida drawings of the rubral neurons were made in three different planes of section, and the extent of the magnocellular and parvocellular portions of the nucleus was determined. Dorsomedial and ventrolateral subgroups of the manocellular part of the nucleus are found 300–400 μ from the caudal pole. A lateral horn of small and medium size neurons with the addition of a few large neuraons extends from the lateral part of the nucleus 500–700 μ from the caudal pole.

Golgi preparations of the red nucleus were examined in three planes of section. Giant and large neurons display short spines on the soma and also, along the entire length of the dendrites. In addition, more elongate spinous processes are seen on these dendrites and are frequently aggregated into tufts at loci on the dendrites or at their terminations. The dendrites of these neurons radiate in all directions from the soma but remain within the confines of the nucleus. Medium size neurons demonstrate radially arranged dendrites. Sparsely positioned spines are seen along the length of the dendrites but are absent on the soma. A number of such neurons demonstrate tufts of elongate spines on their dendrites. The dendrites. The dendrotes of such neurons branch infrequently and remain within the confines of the nucleus. A few dendritic but no somatic spines are seen in association with these neurons.
Golgi studies of the substantia gelationsa neurons in the spinal trigeminal nucleus
Authors: Gobel Stephen
Published: January 2005

This Golgi study identifies three neuronal cell types in the substantia gelatinosa (SG) layer of the spinal trigeminal nucleus. The SG neurons are distinguished from each other based on: (1) dendritic branching pattern, (2) dendritic spine distribution, (3) geometric shape of the dendritic tree, (4) laminar distribution of the dendrites, (5) axonal branching pattern and (6) laminar distribution of the axonal arbor.

The islet cell is found in small clusters and its dendrites and axonal arbor are confined within the SG layer. Its dendrites span the full width of the SG layer and extend up to 500 μm in the layer. Dendritic spines are generally sparse with small clustrs of spines found on the higher order dendritic branches. The islet cell axon extends for at least 1 mm in the long axis of the layer. Each of its collaterals divide every 50–100 μm with one branch doubling back in the direction of the cell body and the other branch continuing on in the direction of its parent. In this manner each islet cell generates a profuse axonal plexus in the SG layer.

The stalked cell is found individually within the SG layer. Its cell body is usually found in the inner half of the SG layer and its sinuous dendrites cross the SG layer and enter the marginal layer. The stalked cell dendrites emit numerous fine stalk‐like branches and dendritic spines. Its axon emits branches in the SG and marginal layers.

The spiny cell is found singly between groups of islet cells. Its extensive dendritic tree spans up to 500 μ rostrocaudally and mediolaterally crossing into both the marginal and magnocellular layers. Spiny cells have evenly distributed dendritic spines along their dendrites in the SG layer. The spiny cell axon sends branches into all three layers of nucleus caudalis. Numerous branches enter the outer 300 μm of the magnocellular layer where they undergo further branching with some branches returing in recurrent fashion toward the SG layer.

The three neuronal cell types of the SG layer satisfy all of the morphological criteria for Golgi type II interneurons. Their dendrites are confined within small foci in nucleus caudalis. Their highly branched axone generate many collaterals within the confines of their dendritic trees and do not project out of nucleus caudalis. The SG neurons are considered to be inhibitory interneurons interposed between V nerve primary afferent axons which arborize in the SG layer and second order projection neurons of nucleus caudalis.
Olfactory relationships of the telencephlaon and diencephalon in the rabbit. 1. An autoradiographic study of the efferent connections of the main and accessory olfactory bulbs
Authors: Broadwell Richard D.
Published: January 2005

The efferent connections of the main and accessory olfactory bulbs in the female albino rabbit have been studied using the autoradiographic method for tracing axonal pathways. Following unilateral injections of 3H‐leucine into the main olfactory bulb, radioactively labeled material transported intraaxonally by axoplasmic flow in an anterograde direction from soma to axon terminal is present ipsilaterally in the superficial half of the plexiform layer (IA) of: the entire circumference of the olfactory peduncle, the tenia tecta, the full mediolateral extent of the olfactory tubercle, the entire length of the prepyriform cortex, a transition area between the prepyriform cortex and the horizontal limb of the nucleus of the diagonal band, the nucleus of the lateral olfactory tract, the anterior cortical and posterolateral cortical amygdaloid nuclei (periamygdaloid areas 1, rostral half of 2, 5 of Rose, '31), and the ventrolateral entorhinal cortex (entorhinal areas 1, 2, 4, 5, 7 of Rose, '31). No subcortical or contralateral projection of main bulb efferents was found.

After a unilateral injection of 3H‐leucine into the accessory olfactory bulb, transported material could be followed caudally along the dorsal surface of the ipsilateral lateral olfactory tract. This heavily labeled projection is distinct from the unlabeled lateral olfactory tract and has been termed the accessory olfactory tract. Beginning at the level of the caudal third of the olfactory tubercle and extending caudally to the nucleus of the lateral olfactory tract is a group of small neurons intimately associated with the accessory olfactory tract. This cell group is referred to as the bed nucleus of the accessory olfactory tract. Projection sites of the accessory bulb include the bed nucleus of the accessory olfactory tract and layer IA of the medial nucleus and the posteromedial cortical nucleus of the amygdala (periamygdaloid areas 3, 4, PAM, caudal half of 2, 6 of Rose, '31). An additional accessory bulb efferent projection was found to enter the stria terminalis at the level of the medial amygdaloid nucleus and could be traced to a posterior segment of the bed nucleus of the stria terminalis.

The autoradiographic findings indicate that the accessory olfactory bulb connects with portions of the amygdala that do not receive afferent input from the main olfactory bulb and provide evidence for the existence of two distinct and separate olfactory systems.
Fiber trajectories of olfactory bulb efferents in the hamster
Authors: Devor Marshall
Published: January 2005

Olfactory bulb efferents sweep caudally over the surface of the piriform lobe in a broad fiber sheet. The internal organization of this axon population was analysed by topologically transforming the cortical surface from its in situ cylindrical form into an unrolled (flattened) map. The distribution of degeneration elicited by restricted bulb lesions and fiber transections was then reconstructed onto this map. Most of the projection cortex of the main olfactory bulb is innervated in a widespread, non‐topographic manner by axons that collect in the compact bundle of the lateral olfactory tract (LOT). LOT collateral branches bound for the prepiriform cortex veer laterally off the main trajectory of the tract at an angle of 50° or less. Thus, transection of discrete fiber populations leaves only a small wedge‐shaped pocket of totally denervated cortex distal to the cut. The medial half of the olfactory tubercle and the hippocampal rudiment receive their bulbar input along medially disposed fibers that do not join the LOT proper. The lateral half of the olfactory tubercle, however, receives an input from LOT fiber collaterals as well as these medial bulb efferents. Finally, much of the corticomedial amygdaloid complex receives fibers from the accessory olfactory bulb along a specialized subdivision of the LOT, the accessory olfactory tract. These observations are expressed in a schematic summary of the trajectories of olfactory bulb efferents as they appear in the unrolled map and in the more standard ventral view of the hamster brain.
An experimental inquiry into the central source of preganglionic fibers to the chick ciliary ganglion
Authors: Narayanan C. H. , Narayanan Y.
Published: January 2005

Degenerative changes in the entire third nerve nucleus were studied following selective removal of the ciliary ganglion, usually of the right side, in day‐old chicks. The operated animals were allowed to survive three, six, nine, and twelve days after ciliary ganglionectomy. Retrograde degenerative changes proceed rapidly between three and nine days post‐operatively, and are strictly limited to the ipsilateral accessory oculomotor nucleus. The changes are at first observed in the medial division of the accessory oculomotor nucleus, followed by the lateral divisions of the accessory oculomotor nucleus. By nine days following the operation, both the divisions of the accessory oculomotor nucleus are virtually depleted of almost all neurons. The other components of the oculomotor complex were not affected at any stage by ciliary ganglionectomy. These observations provide conclusive evidence that the accessory oculomotor nucleus is indeed the avian homologue of the Edinger‐Westphal nucleus.
Pyramidal cell abnormalities in the motor cortex of a child with Down's syndrome. A Golgi study
Authors: Marin‐Padilla Miguel
Published: January 2005

The neuronal organization of the motor cortex of a 19‐month old child with Down's syndrome (mongolism) has been studied with the rapid Golgi method. This congenital syndrome, also known as 21 Trisomy is caused by a chromosomal abnormality consisting of the presence of an extra chromosome in the group 21. Various structural abnormalities have been found in the dendritic spines (postsynaptic structures) of the pyramidal neurons of the motor cortex of this child. The axo‐spinous synapses of these neurons are considered to be altered by these spine abnormalities. In addition, a peculiar form of intrinsic vacuolar change affecting the dendrites and scattered neuronal fragmentation and necrosis have also been found. At least three different types of abnormality involving the spines — (the unusually long spine, the very short spine and a reduction in the number of spines) — are recognized among the pyramidal cells of the motor cortex. It is postulated herein: that a basic anomaly, possibly related to the genetic disorder affects primarily some cortical neurons which undergo progressive degenerative changes terminating in cell fragmentation and death. The different spine abnormalities are considered to represent various developmental stages of the common genetic anomaly. These changes might be structural correlates of the motor incoordination and mental retardation which are characteristic of this genetic disorder, but, final conclusions should await the investigation of other cases with this or similar methods capable of demonstrating the normal as well as the abnormal structural organization of the human cerebral cortex.
A cytoarchitectonic atlas of the mouse hypothalamus
Authors: Broadwell Richard D. , Bleier Ruth
Published: January 2005

A description of the organization, areas, and cell groups within the hypothalamus of the mouse is presented in detail. Photomicrographs of cellstained serial sections through the hypothalamus in frontal, sagittal and horizontal planes are included. The hypothalamus has been divided basically into medial and lateral parts with most well‐defined cell groups or nuclei lying within the medial subdivision and surrounded by diffuse collections of cells referred to as areas.

The heterogeneity of cell types within most hypothalamic nuclei and areas has been emphasized with the consequent implications for heterogeneity of neuronal connections and of functions. Recently introduced neuroanatomical techniques permitting increased attention to the cellular level of organization have demonstrated precise connections and functional localization of cells within the hypothalamus. While cytoarchitectonic distinctions imply functional distinctions, morphological and experimental evidence suggest the existence also of systems of cells which transcend conventional cytoarchitectonic boundaries, the cells within each system being interconnected functionally or neuronally.
The neurons in the primate subthalamic nucleus: A Golgi and electron microscopic study
Authors: Rafols José A. , Fox Clement A.
Published: January 2005

In Golgi preparations of the adult monkey(Macaca mulatta) local interneurons and two varieties of principal neurons, radiating and elongated fusiform, are found in the subthalamic nucleus. The cell bodies of the radiating neurons have a few delicate, somatic spines some of which are occasionally bilobed and trilobed. Five to eight dendritic trunks give rise to branching, tapering dendrites, which may extend for over 400 microns. These dendrites are much thinner than the dendrites in the globus pallidus and the substantia nigra. Some neurons have many and some neurons have few dendritic spines. When numerous the dendritic spines are concentrated on the dendritic trunks and proximal dendrites. The relatively few elongated fusiform neurons are found not only in the capsule but also in the center of the nucleus. Most dendrites emerge from the opposite poles of their smooth surfaced cell bodies. They have a few dendritic spines. Some of these dendrites extend for more than 750 microns.

In 1‐micron thick plastic sections lipofuscin granules are present in some but not all principal neuron cell bodies of the pig‐tail monkey(Macaca mulatta); but these granules are present in all principal neuron cell bodies of the pig‐tail monkey(Macaca nemestrina) and of the squirrel monkey (Saimiri sciureus).

The local interneurons have small cell bodies and a few relatively long undulating dendrites. The dendrites have bulbous dendritic appendages of varying complexity and beaded axon‐ like processes. The dendritic appendages and axon‐like processes are more numerous distally and on the distal ends of the dendrites they form complex entanglements. Axons coming from the cell body have not been observed. The cell bodies of the local interneurons are identified in cresyl violet stained sections of the monkey (Macaca mulatta), in 1‐micron thick plastic sections and electron micrographs of the squirrel monkey(Saimiri sciureus). They have relatively large nuclei surrounded by a thin rim of cytoplasm rich in polyribosomes.
Impulse conduction in the myelinated giant fibers of the earthworm. Structure and function of the dorsal nodes in the median giant fiber
Authors: Günther Jorge
Published: January 2005

The dorsal openings in the myelin sheath of the median giant fiber (MGF) of the earthworm (Lumbricus terrestris L.) have been studied with electronmicroscopical and electrophysiological methods. The fine structure of the dorsal nodes (DN) resembles in many aspects the Ranvier nodes in vertebrate and crustacean nerve fibers. The nodal membrane directly faces the extracellular collagenous capsule of the ventral cord and displays a conspicuous electrondense undercoat. The myelin sheath of the paranode shows a characteristic differentiation into large desmosomal contacts.

Recordings of the transmembrane and longitudinal surface currents along the dorsal side of the MGF during spike propagation support the view that an active inward current is restricted there to the DN. The inward current density in the DN reaches outstandingly high values similar to those measured in vertebrate nodes of Ranvier. The nodal activity can be blocked by application of tetrodotoxin and local anaesthetics. Local electrical stimulation of only one DN may suffice to elicit propagated actions potentials up and down the MGF. It is concluded that the dorsal nodes of the median giant fiber of the earthworm are highly specialized excitable structures mediating saltatory impulse conduction in these fibers.
Plasticity in the developing visual system: The effects of retinal lesions made in young rats
Authors: Lund Raymond D. , Lund Jennifer S.
Published: January 2005

The central visual pathways of the rat have been used as a model for investigating the significance of axonal interactions in mammalian neural development. Attention is restricted largely to the aberrant distribution of optic axons to the ipsilateral side of the brain and their distribution in the superior colliculus after early unilateral eye damage.

The normal ipsilateral retinotectal pathway in pigmented rats appears as a series of patches located anteriorly and laterally in the stratum opticum, whereas in albino animals it is a small area lying anteromedially. In both, a few axons are often found at the extreme posterior border of the superior colliculus.

After unilateral eye enucleation at birth, an aberrant ipsilateral pathway from the remaining eye arises at the optic chiasm. It originates from all parts of the retina and terminates in the ipsilateral superior colliculus in a topographic fashion such that the upper retina projects laterally and the lower retina, medially. The pathway is heaviest anteromedially (from lower temporal retina) and lightest posterolaterally (from upper nasal retina). There is always a heavy projection to the extreme posterior border of the superior colliculus. In only two animals of a large series was direct intertectal sprouting found.

After partial retinal lesions, there is again an ipsilateral pathway from the unlesioned eye which fills the projection area of the lesion. As after total enucleation, the pathway arises from most of the ipsilateral retina, not just that region homotypic to the lesion site, being heaviest from the lower temporal and lightest (or deficient) from the upper retina. There is suggestion of ordering of the projection into the deafferented region in that the ipsilateral degeneration after lesions in the intact eye is compact but does not fill the gap in the crossed projection completely. There is also indication that some intact parts of the retina lesioned at birth may also project in an inappropriate retinotopic fashion to the deafferented region. The corticotectal pathway shows a normal map. Study of the ipsilateral retinotectal pathway indicates that the axons terminating at the extreme posterior border of the superior colliculus arise from the lower temporal retina.

The results are interpreted as indicating that the aberrant uncrossed pathways after complete or local retinal lesions, compare very closely in most features. Both distribute to the deafferented area of the superior colliculus – in one, this is the whole surface, while in the other it is a small area. The fact that in the latter case axons are ending in quite inappropriate parts of the tectal map, may be explained more simply in terms of interactions between adjacent axons in the optic pathway rather than by an hypothesis involving a change in the cell labels across the tectal map.
Electron microscopic autoradiographic studies of gliogenesis in rat optic nerve I. Cell proliferation
Authors: Skoff Robert P. , Price Donald L. , Stocks Adelaine
Published: January 2005

Electron microscopy and 3H‐thymidine autoradiographic techniques were used to study the fine structure of proliferating cells in developing rat optic nerve. Before the closure of the optic canal almost all of the cells incorporating radioactive thymidine are ventricular cells, but after closure (16 days of gestation) the vast majority are differentiating astroblasts or oligodendroblasts. Labeled astroblasts show a range in their degree of differentiation; some cells lack 90 Å cytoplasmic filaments while others have glial filaments and abundant cytoplasmic organelles. In contrast to astroblasts, all of the labeled oligodendroblasts are in the early stages of differentiation. The proliferation of oligodendroblasts starts at five days postnatal, approximately a day or two before the onset of myelination. During myelinogenesis a few of the labeled oligodendroblasts show presumptive connections to myelin sheaths. Microglial cells do not appear to play a major role in gliogenesis since they form less than 2% of all the labeled cells.

The results of this study indicate that astroblasts and oligodendroblasts, rather than undifferentiated glioblasts, are the major source of macroglia. The finding that proliferating glia are in the process of differentiation agrees with recent studies which show that differentiated cells can divide.
Cells of origin of entorhinal cortical afferents to the hippocampus and fascia dentata of the rat
Authors: Steward Oswald , Scoville Sheila A.
Published: January 2005

The pathway from the entorhinal cortical region to the hippocampal formation has previously been shown to be comprised of two sub‐systems, one of which projects predominantly to the ipsilateral fascia dentata and regio inferior of the hippocampus proper, and a second which projects bilaterally to regio superior. The goal of the present investigation was to determine if these two pathways might originate from different cell populations within the entorhinal area. The cells of origin of these entorhinal pathways were identified by retrograde labeling with horseradish peroxidase (HRP).

Injections which labeled the entorhinal terminal fields in both the fascia dentata and regio superior resulted in the retrograde labeling of two populations of cells in the entorhinal area. Ipsilateral to the injection, HRP reaction product was found in the cells of layer II (predominantly stellate cells) and the cells of layer III (predominantly pyramidal cells). Contralateral to the injections, however, the reaction product was found almost exclusively in the cells of layer III.

With selective injections of the entorhinal terminal field in regio superior, only the cells of layer III were labeled, but these were labeled bilaterally. Selective injection of the entorhinal terminal field in the fascia dentata, however, resulted in the labeling of cells of layer II, but not of layer III, and these cells of layer II were labeled almost exclusively ipsilaterally. A very small number of labeled cells in layer II were, however, found contralateral to the injection as well.

No labeled cells were found either in the presubiculum or parasubiculum following injections of the hippocampal formation. These cell populations were found capable of retrograde transport of HRP, however, since cells in both presubiculum and parasubiculum were labeled following HRP injections into the contralateral entorhinal area.

These results suggest that the projections to the fascia dentata originate from the cells of layer II, while the projections to regio superior originate from the cells of layer III of the entorhinal region proper. The very slight crossed projection from the entorhinal area to the contralateral area dentata probably originates from the small population of cells in layer II which are labeled following HRP injections in the contralateral area dentata.
Neuroglial reactions secondary to wallerian degeneration in the optic nerve of the postnatal rat: Ultrastructural and quantitative study
Authors: Fulcrand J. , Privat A.
Published: January 2005

Wallerian degeneration has been studied in the optic nerve of the rat after unilateral enucleation. The operation was performed at the key stages 2, 5, 8, 20 days post natal (DPN), in order to compare the reactions of immature cells with those of their adult counterpart. Post operation delay (DPO) was staged from 1 to 204 days. The electron microscope study provided qualitative data relative to the function and the fate of the different cell lines, neuroglial and exogenous, in the reactive processes. Semi‐thin 1–μm sections stained with toluidine blue were used for the quantification of the different cell types at the various stages. Criteria of identification were those set‐up by Ling et al. ('73) for the corpus callosum and neighboring structures. In the three first key stages (2, 5, 8 DPN) the proliferation of glioblasts is reduced in amount and shortened in time when compared to the control. In the last one (20 DPO) a small peak over control value of glioblastic gliosis corresponds to a reactive gliosis already shown by other in the adult. Glioblasts are closely dependent upon the surrounding tissue for their ultimate fate. Microglia are exclusively involved in the phagocytosis of axonal and cellular debris, in the form of loaded macrophages. The comparison of the different percentage curves reflects the intensity and the timing of their reactions which are dependent upon the surrounding tissue. Reactive astrocytes, whose essential function is the formation of a scar, may participate in phagocytosis, especially in young animals, whose glial cells are not fully differentiated. They progressively constitute up to 90% of the glial population. Oligodendrocytes which are normally responsible for myelination, are only rarely involved in active phagocytosis; the oligodendrocyte line is either inhibited (key stages 2,5 DPN) or interrupted in its differentiation (key stage 20). It appears then that the presence of healthy axons is essential for the differentiation and even to a lesser degree the survival of the oligodendrocyte line. For the latter, the more differentiated the cell is the better it survives. Finally, hematogenous cells occur only in youngest animals, and in the close vicinity of the lesion. The influence of the enucleation upon gliogenesis and maturation of the optic nerve illustrates the interference between genetic and epigenetic factors and the interdependence of neurons and glia in the ontogenesis of the central nervous system. It exemplifies the great plasticity of the central nervous system in the youngest animals, thus validating our experimental onto‐pathologic approach.