bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes in the dorsal lateral geniculate nucleus of the squirrel monkey after unilateral ablation of the visual cortex
Authors: Wong‐Riley Margaret T. T.
Published: December 2004

Young adult squirrel monkeys were subjected to unilateral occipital lobectomies, and were allowed to survive for 3 to 42 days. Both light and electron microscopic techniques were employed to examine orthograde as well as retrograde changes in the ipsilateral dorsal lateral geniculate nucleus. Three stages of degenerative change were described. During the early stage (third to fourth post‐operative day) there were early signs of corticogeniculate terminal degeneration. During the intermediate stage (fifth to eighth day) most of the RS (small axonal terminals with round vesicles) or corticofugal endings were seen to undergo a sequence of degenerative change: swelling or irregularity of the synaptic vesicles; electron dense disintegration; and finally the engulfment by glial elements. The small myelinated axons also become electron dense at this stage, and there were early signs of retrograde degeneration. The late stage was characterized by severe changes and final disappearance of the geniculocortical relay neurons as well as their axons and dendrites. Concurrently, most of the RS terminals were also removed from the LGN, and there was considerable re‐organization of the rest of the synaptic population.
Thalamic projections of the superior colliculus in the rhesus monkey, Macaca mulatta. A light and electron microscopic study
Authors: Partlow G. D. , Colonnier M. , Szabo J.
Published: December 2004

The projections of the superior colliculus to the thalamus have been studied in the monkey, Macaca mulatta, with anterograde degeneration techniques. The superior colliculus has been shown to project to the inferior nucleus of the pulvinar in a topographical manner with the lower visual field represented dorsomedially and the upper field ventrolaterally. The peripheral zone is located along the medial border and the fovea at the dorsolateral angle adjacent to the lateral geniculate nucleus. The superior colliculus also sends a dense projection to the ipsilateral intralaminar complex, i.e., to the parafascicular, central lateral and paracentral nuclei, and a lesser projection to the same contralateral nuclei. Degenerating tectal fibers were also found in the lateral geniculate nuclei. Four types of vesicle containing profiles were observed in the inferior pulvinar and paracentral nucleus. The large RL and small RS terminals contain round vesicles of uniform size and form asymmetric contacts mainly with large and small dendrites respectively. The F terminal contains a mixture of small round and flat vesicles. It forms symmetric contacts with dendrites and cell somata. The P profile is very pale and contains a relatively sparse population of vesicles showing a great variation in size. It forms symmetric contacts with medium to large dendrites. It is frequently found postsynaptic to the other types, especially the RL terminal, and is regularly seen as the intermediate element of serial and triadic synaptic arrangements. The experimental electron microscopic study has shown that many fibers from the superior colliculus terminate as RL profiles, undergoing direct dense degeneration, in both the inferior pulvinar and the paracentral nucleus. Others probably end as smaller RS terminals.
An autoradiographic study of the organization of the efferet connections of the hippocampal formation in the rat
Authors: Swanson L. W. , Cowan W. M.
Published: December 2004

The efferent connections of the hippocampal formation of the rat have been re‐examined autoradiographically following the injection of small quantities of 3H‐amino acids (usually 3H‐proline) into different parts of Ammon's horn and the adjoining structures. The findings indicate quite clearly that each component of the hippocampal formation has a distinctive pattern of efferent connections and that each component of the fornix system arises from a specific subdivision of the hippocampus or the adjoining cortical fields. Thus, the precommissural fornix has been found to originate solely in fields CA1‐3 of the hippocampus proper and from the subiculum; the projection to the anterior nuclear complex of the thalamus arises more posteriorly in the pre‐ and/or parasubiculum and the postsubicular area; the projection to the mammillary complex which comprises a major part of the descending columns of the fornix has its origin in the dorsal subiculum and the pre‐ and/or parasubiculum; and finally, the medial cortico‐hypothalamic tract arises from the ventral subiculum. The lateral septal nuclei (and the adjoining parts of the posterior septal complex) constitute the only subcortical projection field of the pyramidal cells in fields CA1‐3 of Ammon's horn. There is a rostral extension of the pre‐commissural fornix to the bed nucleus of the stria terminalis, the nucleus accumbens, the medial and posterior parts of the anterior olfactory nucleus, the taenia tecta, and the infralimbic area, which appears to arise from the temporal part of field CA, or the adjacent part of the ventral subiculum. The projection of Ammon's horn upon the lateral septal complex shows a high degree of topographic organization (such that different parts of fields CA1 and CA3 project in an ordered manner to different zones within the lateral septal nucleus). The septal projection of “CA2” and field CA3 is bilateral, while that of field CA1 is strictly unilateral. In addition to its subcortical projections, the hippocampus has been found to give rise to a surprisingly extensive series of intracortical association connections. For example, all parts of fields CA1, CA2 and CA3 project to the subiculum, and at least some parts of these fields send fibers to the pre‐ and parasubiculum, and to the entorhinal, perirhinal, retrosplenial and cingulate areas. From the region of the preand parasubiculum there is a projection to the entorhinal cortex and the parasubiculum of both sides. That part of the postsubiculum (= dorsal part of the presubiculum) which we have examined has been found to project to the cingulate and retrosplenial areas ipsilaterally, and to the entorhinal cortex and parasubiculum bilaterally.
Visual cortical areas mediating form discrimination in the cat
Authors: Sprague J. M. , Levy J. , Diberardino A. , Berlucchi G.
Published: December 2004

Cats were trained pre‐ and/or postoperatively on flux and pattern discriminations, and were examined in a series of visuomotor tests which measured attention and orientation to, and following and localization of stationary and moving stimuli, in a free situation and in a perimetry test.

Cortical lesions were placed in areas 17 and 18, or in the middle and posterior suprasylvian gyri and sulci–areas 19, 20, 21, 7 and lateral suprasylvian cortex (LSA), as delineated by cyto‐ and myeloarchitecture, and by electrophysiological mapping.

After removal of all of area 17 and up to 90‐95% of 18, postoperative learning of flux and pattern discriminations is at a high level, although in some cases slowed. Visuomotor behavior is normal. Such lesions result in severe atrophy only of laminae A, AI and C in the lateral geniculate nuclear complex (LGNd).

The neuronal systems for perceiving and discriminating simple, large planime triepat terns and forms, and for mediating visually guided behavior characteristic of this species lie outside of areas 17‐18. The cortices primarily responsible for form discrimination in the cat include those in the suprasylvian gyri and sulci.

After lesions which removed areas 19, 20, 21 and LSA, sparing most of 37‐18, form discriminations based on orientation or shape were prolonged or absent. Although these animals showed slow tracking and poor depth judgment, the visual fields were full and they had good sensory and perceptive capacity as seen in normal flux and near normal pattern (gratings) discrimination. Such lesions result in severe atrophy in lateral and inferior pulvinar complex. Although these nuclei receive visual input primarily from the superficial laminae of the superior colliculus and certain nuclei of the pretectum, both areas 19 and LSA receive a dual input from pulvinar and parts of LGNd.

Whether these marked deficits in form discrimination after suprasylvian lesions are due to involvement of certain crucial areas of this extensive cortex, or whether all are involved in some integrated fashion, is not yet completely clear. Removal of 19, 21 and parts of LSA are followed by similar (but somewhat less marked) deficits of both retention and learning. Lesion in area 20 alone (cortical target of the lateral pulvinar) leaves retention of preoperatively learned discriminations intact but results in prolonged initial learning.

Previous work by the present authors has shown similar deficits in form discrimination in the cat after lesions in the pretectumsuperior colliculus. These data, together with the present findings appear to support the hypothesis that the midbrainpulvinarcortieal pathways provide the first stage in simple, coarse form perception and discrimination in this species.
An autoradiographic study of the development of the entorhinal and commissural afferents to the dentate gyrus of the Rat
Authors: Fricke R. , Cowan W. M.
Published: December 2004

The development of the entorhinal, ipsilateral associational, and commissural afferents to the dentate gyrus have been studied autoradiographically, following the injection of small amounts of tritiated proline into the medial and lateral parts of the entorhinal cortex, and into fields CA3c and CA4 of the hippocampus, ia series of rats, on the third, sixth, and twelfth postnatal days. Clear labeling of the entorhinal afferents was found at the third postnatal day, and from the earliest stage studied the afferents from the two parts of the entorhinal cortex appear to be spatially segregated within the stratum moleculare of the dentate gyrus: the fibers from the lateral entorhinal areà occupying the outermost one‐third, or so, of this stratum, while those from the medial entorhinal cortex occupy its middle zone. The ipsilateral hippocampo‐dentate associational pathway is present at the third postnatal day, but the commissural projection (which shares wiht it the inner part of the stratum moleculare) could not be labeled until the sixth postnatal day. By the twelfth day the characteristic adult pattern of distribution of the terminals of the two hippocampo‐dentate pathways is established. although this pattern is best accounted for on the basis of a temporal competition for the available synaptic sites on the proximal parts of the dendrites of the granule cells, the spatial segregation of these two fiber systems from those arising in the entorhinal cortex, is probably due to the selective fasciculation of fibers in each group of afferents and to their early cytochemical specificity.
An ultrastructural analsis of neurites in the basal lamina of capillaries in the chinchilla cochlear nucleus
Authors: McDonald Donald M. , Rasmussen Grant L.
Published: December 2004

In an ultrastructural study of the chinchilla anteroventral cochlear nucleus (AVCN), we found innervated capillaries in the layer of granule cells that comprises the dorsolateral portion of the AVCN and forms a cap over the principal portion of the nucleus. In 66% of 215 capillaries we examined in the granule cell layer of various levels of the AVCN, we found structures having ultrastructural features of axons that (l) were within the brain parenchyma and were in direct contact with the pericapillary basal lamina, or (2) were separate from the adjacent neuropil and, often in the company of astrocytic processes, were completely enveloped by the pericapillary basal lamina. An analysis of serial sections confirmed that neurites within the pericapillary basal lamina were in continuity with neurites in the brain parenchyma. Most neurites within the basal lamina of capillaries were next to pericytes, but some neurites were next to endothelial cells. None of the neurites adjoining capillaries had the abundance of synaptic vesicles typical of autonomic vasomotor nerve endings and synaptic terminals. Consequently, they may be sensory, responding perhaps to changes in hydrostatic pressure or chemical composition of the blood or cerebrospinal fluid. However, we cannot exclude the possibility that neurites which accompany capillaries in the AVCN terminate elsewhere. In the AVCN the innervation of capillaries is restricted to the superficial layer of granule cells. In none of 177 capillaries of the principal portion of the AVCN did we find an example of a neurite in contact with the pericapillary basal lamina, a pericyte, or an endothelial cell, although it was sometimes necessary to examine specimens at various angles of tilt to confirm that the pericapillary glial sleeve was continuous. Furthermore, we found no innervated blood vessels among 266 capillaries examined in the granular and molecular layers of the cerebellar cortex.
The connections of the trigeminal and facial motor nuclei in the brain of the carp (cyprinus carpio L.) as revealed by anterograde and retrograde transport of horseradish peroxidase
Authors: Luiten P. G. M. , van der Pers J. N. C.
Published: December 2004

The connections of the rostral and caudal parts of the trigeminal and facial motor nuclei in the carp were studied with the horseradish peroxidase technique. Following ionophoretic peroxidase injections in these motor nuclei, retrogradely labeled cells were observed together with anterogradely labeled motor cell processes. Several cellular areas in thalamus, cerebellum and medulla oblongata were shown to project to the V and VII motor nuclei. Labeled cells were found in the inferior lobe and the glomerular complex of the thalamus. In the medulla oblongata, cells in the descending trigeminal nucleus, reticular nuclei and motor nuclei other than those injected were labeled. Besides these conspicuous projections several smaller connections were also found. These findings are discussed on their significance to respiratory function. Anterogradely labeled cellular processes constitute a relatively simple network of fiber connections between the various motor nuclei and the reticular nuclei of the brainstem. This apparently dendritic system of the bulbar motor complex shows a certain degree of similarity to the structure of the motor system in the spinal cord, and might play a role in the coordinated control of the muscular system.
Increased proliferation of neuroglia and endothelial cells in the supraoptic nucleus and hypophysial neural lobe of young rats drinking hypertonic sodium chloride solution
Authors: Paterson Jean A. , Leblond C. P.
Published: December 2004

Male rats aged 30 to 35 days were provided with 1.75% sodium chloride solution as drinking fluid for two weeks, to create a chronic increase in plasma osmolality. During this time, the animals and a control group of water‐drinking rats received two injections per day of 1 μCi of 3H‐thymidine per gram body weight to label dividing cells and their progeny. At the end of this period, the animals were sacrificed by aldehyde perfusion. Sections 1 μm‐thick were saved at intervals from a series cut throughout the length of the supraoptic nucleus; these sections and others taken from the caudate nucleus and the neural lobe of the hypophysis were processed for radioautography.

Neuronal nuclei and nucleoli were enlarged in the supraoptic nucleus of salttreated rats, in accord with previous work indicative of neuronal enlargement associated with increased protein synthesis and probably enhanced vasopressin production. Furthermore, most axon terminals in the neural lobe were depleted of neurosecretory granules in the salt‐treated group, a fact suggesting increased release of vasopressin.

Cell counts in radioautographs of the supraoptic nucleus revealed that 20.6% of the astrocytes were labeled in salt‐treated rats, but only 5.9% in controls, indicating a marked increase in the production of new astrocytes in the treated animals. Also, endothelial cells were more frequently labeled in salt‐treated rats (52.9%) than in controls (17.4%). In the caudate nucleus, by contrast, the labeling percentages of astrocytes or of endothelial cells did not differ between control and treated rats. In the neural lobe, the labelling percentage of pituicytes was 45.8% in treated, but only 3.1% in control animals. The endothelial cell labeling was also greater in treated (46.5%) than controls (23.9%). Thus, in young rats, a period of salt ingestion elicited both an enlargement of supraoptic neurons and an increase in the production of the astrocytes, pituicytes, and endothelial cells associated with these neurons and their processes.
Physiological identification and analysis of dentate granule cell responses to stimulation of the medial and lateral perforant pathways in the rat
Authors: McNaughton B. L. , Barnes C. A.
Published: December 2004

Stimulation of the dorsomedial or ventrolateral perforant pathways resulted in quantitatively different extracellularly recorded EPSPs in the fascia dentata of the rat. The two potential differed in latency to peak and in width at half amplitude in a manner consistent with the different locus of termination of the two pathways on the granule cell dendrites. Both potentials were able to follow brief stimulus trains of 100 Hz, which suggests that they are monosynaptic. Medially elicited responses had their peak negativity approximately 100 to 180 μm deeper in the molecular layer than laterally elicited responses. Stimulation at short intervals along a dorsomedial to ventrolateral track in the angular bundle yielded a step function rather than a continuum of EPSP peak latency and half‐width, in agreement with Hjorth‐Simonsen's ('72) evidence for the separateness of the two pathways. Both pathways were able to induce granule cell discharge. Laterally elicited spikes, however, were delayed. Stimulation at intermediate locations frequently elicited double spikes from granule cell population. Population spikes elicited by either pathway were inhibited for as long as 100 msec after a single discharge. Both pathways showed facilitation with double stimuli at short intervals, and both showed post‐tetanic potentiation lasting at least 30 minutes. Under conditins where it could be shown that the two pathways at least partially converged onto the same granule cells, the response of one pathway did not increase when long lasting potentiation was induced on the other.
Retinal ganglion cells in the crucian carp (Carassius carassius). II. Overlap, shape and tangential orientation of dendritic trees
Authors: Kock Jan‐Henrik , Reuter Tom
Published: December 2004

Ganglion cells were studied in methylene blue stained flatmounted retinas. Three categories of cells are described: small (S) and large (L) ganglion cells in the main ganglion cell layer, and large ganglion cells (LD) with somata more or less displaced into the inner plexiform layer. These LD cells have two to four very thick primary dendrites and are identifiable as ganglion cells by their axons.

An analysis of published data reveals that the large genglion cells of the crucian carp (types L and LD) have several striking characteristics in common with the large ganglion cells of the dogfish, the frog and the cat: (1) they are selectively stained by methylene blue; (2) they comprise only 2–5% of all the ganglion cells; (3) the large cells can be divided into two or three subtypes, and within each subtype the dendritic trees usually cover the retinal surface with a two‐ or threefold overlap.

New ganglion cells are formed from neuroblasts at the retinal margin and most dendrites first grow along this neuroblastic zone. Thus the main dendrites of the L and LD cells tend to be oriented parallel to the margin all around the periphery of a crucian carp retina. Independent of the size of the eye this parallel orientation disappears at the same relative distance from the margin (about one‐third of the distance from the margin to the optic disc). If all L and LD cells are formed at the retinal margin and first develop oriented dendrites, we have to assume that the more randomly oriented dendritic trees in the central retina have undergone a reorganization.
The synaptic organization of the motor nucleus of the trigeminal nerve in the opossum
Authors: Hamos James E. , King James S.
Published: December 2004

The motor nucleus of the opossum trigeminal nerve consists of a main body and a small dorsomedial cell cluster. The cell bodies form a unimodal population with areas that range from 150–2700 μm2. Golgi impregnations reveal that each neuron has three to six primary dendrites which radiate in all planes from the cell body. Within 300 μm from the soma, the primary dendrites divide into secondary branches and these, in turn, bifurcate into thinner distal dendrites. The overall diameter of the dendritic tree often extends as much as 1 mm, with a rare branch leaving the confines of the nucleus to enter the neighboring reticular formation. Somatic and dendritic spines are often present and are either sessile or complex appendage forms.

The perikarya and initial dendritic trunks of trigeminal neurons are contacted by four types of presynaptic terminals which cover more than 40% of the membrane. Most endings are 1–3 μm long and contain either spherical (S) or pleomorphic (P) synaptic vesicles. Another, less common, type of bouton is marked by large dense‐core (DC) vesicles. Approximately 8% of the terminals on trigeminal cell bodies are large (2–5 μm) with spherical synaptic vesicles and are always associated with a subsynaptic cistern (C‐boutons). These terminals very often interdigitate with adjacent synaptic endings. S‐, P‐, and C‐boutons synapse on the dendritic tree of trigeminal neurons in the following characteristic pattern: proximal dendrites (greater than 5 μm in diameter) are contacted by all three types of terminals; intermediate‐sized dendrites (between 2.5 and 5.0 μm in diameter) are most often contacted by S‐boutons although P‐boutons are also present; and small, distal dendrites (less than 2.5 μm in diameter) are almost always contacted by S‐ boutons. Both S‐ and P‐boutons contact spines.

In order to determine the ultrastructural identity of some of the major afferent systems to the trigeminal motor nucleus, adult opossums were subjected to two different types of lesions. Three and 5 days subsequent to lesions which destroyed most of the trigeminal mesencephalic nucleus, degenerating terminals containing spherical vesicles were found. These endings were S‐boutons on more distal parts of the dendritic tree while on the cell body and proximal dendrites they were C‐boutons. Seven days after a mesencephalic lesion, expanded glial processes approximated the trigeminal cell membrane. Two days subsequent to lesions which transected commissural fibers from the contralateral trigeminal complex, degenerating S‐ and P‐boutons were found in contact with intermediate and distal parts of the trigeminal dendritic tree.
Ultrastructure of normal and degenerating glomerular terminals of dorsal root axons in the substantia gelatinosa of the rhesus monkey
Authors: Knyihar‐Csillik E. , Csillik B. , Rakic Pasko
Published: December 2004

The fine structure of primary sensory terminals within glomerular complexes of lamina II of Rexed (substantia gelatinosa Rolandi) in the spinal cord was investigated in normal adult rhesus monkeys and in monkeys subjected to thoracic or lumbosacral dorsal root transection. Three types “scalloped” primary sensory terminals were distinguished on the basis of their ultrastructural characteristics, size, and distribution of synaptic vesicle population: (1) dense sinusoid axon (DSA) terminals contain mediumsized (42–46 nm and 58–62 nm) and large (80 nm) clear synaptic vesicles; (2) large dense‐core vesicles (LDCV) terminals are equipped with empty synaptic vesicles ranging from 30 to 106 nm, large, (80 nm) and very large, (100 nm) dense‐core vesicles; and (3) regular synaptic vesicles (RSV) terminals contain a homogeneous population of 45–50 nm clear synaptic vesicles.

Follwing transection of the dorsal roots, all three types of primary afferents degenerate and become engulfed and phagocytosed by glial cells. However, each type of terminal displays a different mode and tempo of degeneration as seen in monkeys sacrificed 36, 48, and 72 hours following rhizotomy. DSAs follow the osmiophilic degeneration pattern; LDCVs are characterized by a gradual increase in the number of “electron‐dense bodies” and, less frequently, by a progressive osmiophilic process; RSVs exhibit signs of a filamentous degeneration, accompanied by clusters of synaptic vesicles.

The three types of terminals are distributed in an overlapping but distinct pattern within posterior horn. Thus DSAs are present in highest numbers in lamina II where they constitute the most frequent terminal type. LDCVs also occur in lamina II in its outer half but are most concentrated in lamina I. RSVs predominate in the deepeer layers of the dorsal horn (lamina III) but are also found in the internal half of lamina II. On the basis of these ultrastructural data and a comparison with afferent profiles impregnated according to the Golgi method, it appears that DSAs and LDCVs correspond respectively to superficial and marginal collaterals of small, thin dorsal root fibers whereas RSVs represnt terminals of deep collaterals from large, thick dorsal root axons.
Differentiation of cerebellar anlage heterotopically transplanted to adult rat brain: A light and electron microscopic study
Authors: Alvarado‐Mallart Rosa Magda , Sotelo Constantino
Published: December 2004

Pieces of cerebellar primordia from (days 14 or 15 of gestation) E14 or E15 rat embryos were dissected out and transplanted into a cavity of the occipital cortex and underlying hippocampus, over the superior colliculus of 2‐month‐old rats. The host animals were allowed to survive for 2 to 3 months. The cytoarchitectonic and the synaptic organizations were analyzed in 16 of such transplants. Only 4 of the implants established connections with the host brain through several thin peduncles composed of myelinated fibers. The remaining 12 implants survived in an extraparenchymal situation. Independently of its partial linking to the host brain, the graft grew and developed a cerebellar structure composed of nuclear and cortical regions. The latter exhibited normal lamination and foliation, and contained the five categories of neurons which characterize normal cerebellar cortex.

Electron microscopic examination disclosed that the synaptic connections normally present in the cerebellar cortex were also formed in the implants with the exception of climbing fibers, which were absent. The cerebellar interneurons kept their normal topographic distribution and gave origin to numerous synapses which maintained their own specificity. Some mossy fibers were present in the granule cell layer at the center of typical glomeruli. However, abnormal synaptic arrangements were also observed within the neuropil of this granule cell layer. They consisted of pseudo‐glomerular formations composed of clusters of tightly packed small axon terminals covered by granule cell dendrites. The origin of these boutons was not established. Since they did not correspond to the classes of presynaptic elements normally synapsing on these dendrites, they constitute a new example of cerebellar heterologous synapses. Their presence could be related to changes in the cellular environment due to the rarity of mossy afferents.

HRP tracing experiments, carried out in extraparenchymal transplants, have allowed us to determine that the corticonucleocortical loop of normal cerebellum is also developed in the implants. Nuclear neurons are at the origin of the mossy fibers involved in glomerular formations, whereas Purkinje cells project to the nuclear region. The establishment of these reciprocal connections could determine the functional stabilization of both kinds of cerebellar neurons and thus the long survival of extraparenchymal grafts.

These results allow the conclusion that the presence of extracerebellar afferents is not necessary for the organotypic and synaptotypic differentiation of cerebellar anlage.
Inhibitory and excitatory synapses in crayfish stretch receptor organs studied with direct rapid‐freezing and freeze‐substitution
Authors: Nakajima Yasuko , Reese Thomas S.
Published: December 2004

Crayfish abdominal stretch receptor organs are innervated by inhibitory (GABA) and excitatory (glutamate) synapses. Previous studies with aldehyde fixation showed that synaptic vesicles in the inhibitory synapse are flat and small, whereas those in the excitatory synapse are rounder and larger. We have reexamined these inhibitory and excitatory synapses by using direct rapid‐freezing and freeze‐substitution in order to preserve synaptic structure closer to its living state. Fine details of synaptic structure appear to be better preserved by this method. Synaptic vesicles in inhibitory as well as excitatory synapses are round, so the conventional flattened shape of vesicles in the inhibitory synapse must depend on some aspect of aldehyde processing. However, the average size of vesicles in the inhibitory synapse is significantly smaller than that of vesicles in the excitatory synapse, so synaptic vesicle size is regarded as having functional significance.
Retinal ganglion cell size groups projecting to the superior colliculus and the dorsal lateral geniculate nucleus in the North American opossum
Authors: Rapaport David H. , Wilson Paul D.
Published: December 2004

The retinal ganglion cells projecting to the superior colliculus (SC) and dorsal lateral geniculate nucleus (LGNd) of the North American opossum (Didelphis virginiana) were studied by using the horseradish peroxidase (HRP). The four ganglion cell size groups recognized previously were found to project in systenatically different ways. After injections of HRP into the superior colliculus, labeled cells were seen in nasal retina contralateral to the injection and in temporal retina both ipsilateral anc contralateral to the injection. In contralateral nasal retina cells of all size classes were labeled, while in contralateeral temporal retina small (8–14 μm diameter), small‐medium small‐medium (15–19 μm diameter), and large (>24 μm diameter)cells were labeled but few, if any, large‐medium (20–24 μm diameter)cells were labeled. In ipsilateral temporal retina, soma size groups labeled included small‐medium, large‐medium, and large cells, but very few small cells. A nasal–temporal difference in the soma size of ganglion cells projecting to the SC was found: Labeled cells in temporal retina were 1.7–4.2 μm larger than their counterpats in nasal retina.

Following injection of HRP into the LGNd, label was seen in contralateral nasal and ipsilateral temporal retina witn no label seen in contralateral temporal retina. The labeled cells were small‐medium, large‐medium, and large. No small ganglion cells were labeled from the LGNd. A small nasal‐temporal soma size difference in retinal ganglion cells projecting to the LGNd was seen: labeled cells in temporal retina were 1.0–2.1 μm larger than in nasal. It is concluded that all four ganglion cell size groups in the opossum project to the SC, but that only the three largest project to the LGNd.
A cobalt study of medullary sensory projections from lateral line nerves, associated cutaneous nerves, and the VIIIth nerve in adult Xenopus
Authors: Altman J. S. , Dawes E. A.
Published: December 2004

The medullary projections of the anterior lateral line nerve, dorsal branch (Alln.d), the posterior lateral line nerve, dorsal branch (PLLn.d), associated cutaneous nerves, and the VIIIth nerve in Xenopus laevis have been delineated by axonal infusion of cobalt chloride and silver intensification. The peripheral innervation of the posterior lateral line sense organs has also been traced. From wholemount and sectioned preparations, we describe three central projections, extending the length of the ipsilateral medulla but occupying distinct zones: lateral line afferents dorsomedially, stato‐acoustic dorsolaterally, and cutaneous ventrolaterally.

Arborizations of ALLn.d and PLLn.d afferents are morphologically similar, intermingling throughout the lateral line lobe. Each divides into ascending and descending limbs bearing collaterals, which terminate in the lateral line neuropile and nucleus. Evidence is presented for directional and positional mapping in the branching of individual PLLn.d afferents and for topography in the ALLn.d projection. Second‐order neurones have been identified by transneuronal staining and their axons traced into the contralateral torus semicircularis. The morphology of efferent neurones is also described.

Rostral branches of PLLn.d also contain cutaneous afferents which run through the medulla into the spinal cord, similar to the nerve V (cutaneous) projection. In nerve VIII preparations, the projection to the compact cochlear nucleus and the massive vestibular projection are identified. Cutaneous and vestibular but not lateral line afferents extend into the cerebellum.

The separation of VIIIth nerve and lateral line afferents in Xenopus medulla is considered as evidence against the validity of the acousticolateralis concept. Information processing in the lateral line lobe is discussed in relation to connectivity patterns between first‐ and second‐order neurones.
Developmental relationships between trigeminal ganglia and trigeminal motoneurons in chick embryos. III. Ganglion perikarya direct motor axon growth in the periphery
Authors: Moody Sally A. , Heaton Marieta B.
Published: December 2004

The previous study in this series demonstrated that the ingrowth of the central axons of the trigeminal (V) ganglion is prerequisite to V motor axon outgrowth and somatic translocation. In the present experiment we determined whether further interactions with V ganglion cell bodies were required by V motoneurons after the V ganglion innervates the brainstem. Soon after the ganglion axons had penetrated the brainstem they were severed, and a barner, either permeable or impermeable, was placed between the ganglion cell bodies and the metencephalon. V motor axons grew along aberrant pathways to circumvent the impermeable barriers, many rerouting to reach the V ganglion. Only those V motor nerves which contacted the V ganglion distal to the barrier reached their target musculature in the mandible. The pattern of migration of V motoneurons was normal regardless of the V motor nerve trajectory, but the cell bodies of those axons which did not reach a muscle were not fully differentiated.

When permeable barriers (Millipore filters) were implanted, the nerves followed two types of trajectories. If the pore size of the filter was small (0.45 and 0.025 μm), the V motor nerves grew identically to those observed in embryos in which impermeable barriers had been implanted. If the pore size of the filter was large (8.0 and 0.08 μm), the V motor nerve grew along its normal path directly to the barrier. Small axonal bundles from these nerves frequently grew into the filter toward the distal V ganglion.

These results indicate that V motor axons preferentially grow to the V ganglion perikarya after exiting from the brainstem. Contact with the V ganglion always results in V motor nerve growth to the mandible while growth of the V motor axons to aberrant target sites only occurs when the axons fail to contact the V ganglion cells distal to the barrier.
Substance P, somatostatin, and methionine enkephalin immunoreactive elements in the spinal cord of the domestic fowl, Gallus domesticus
Authors: Lavalley A. L. , Ho R. H.
Published: December 2004

The occurrence and distribution of substance P (SP), somatostatin (SOM), and enkephalin (ENK) immunoreactive elements were examined in the spinal cord of the domestic fowl, Gallus domesticus. SP immunoreactive fibers and their varicosities were densest in laminae I and II, although they were also found within deeper regions of the dorsal horn. In contrast, the intermediate gray area, the area around the central canal, and the ventral horn, contained fewer SP immunoreactive fibers. The distribution of ENK immunoreactivity in the gray matter was similar to that described for SP although immunoreactive fibers were denser around the central canal and in the intermediate zone. Few SOM immunoreactive fibers were present in the dorsal horn the area around the central canal, and the ventral horn. All three peptidergic immunoreactive elements were found in and around the nucleus of Terni, an autonomic area. Throughout the lumbosacral enlargement SP, SOM, and ENK immunoreactive varicosities were found adjacent to the lumbosacral sinus and in fibers traversing the glycogen body. In addition, at caudal lumbar and rostral sacral levels a plexus of SP and SOM immunoreactive fibers was observed to be in close relationship with presumed motoneurons.
Immunohistochemical studies on the distribution and origin of candidate peptidergic primary afferent neurotransmitters in the spinal cord of an elasmobranch fish, the atlantic stingray (Dasyatis sabina)
Authors: Ritchie T. C. , Leonard R. B.
Published: December 2004

The distribution and origin of four peptide neurotransmitter candidates of primary afferents (substance P, SP; somatostatin, SS; cholecystokinin, CCK; and vasoactive intestinal polypeptide, VIP) were studied in the stingray with peroxidase‐antiperoxidase (PAP) immunohistochemistry. This elasmobranch has virtually no unmyelinated primary afferents, having instead only large and small myelinated afferents. SP‐like immunoreactivity was distributed densely in the superficial aspect of the substantia gelatinosa (SG), particularly laterally, and was scattered in the nucleus proprius, the intermediate zone, and the ventral horn. The distributions of SS‐, CCK‐, and VIP‐like immunoreactivities were similar to each other, but different from that of SP. Stained fibers appeared to issue from a prominent tract in the dorsolateral funiculus to form a plexus at the lateral margin of the nucleus proprius. The fibers spread dorsally and medially through the SG to terminate in a thin band at the superifical margin of the SG. Both SS and CCK were more dense in the lateral third of the SG, while VIP was more diffusely distributed within this structure. The remaining regions of the spinal gray matter contained immunoreactive fibers and terminals in variable densities. Many SS‐positive cell bodies were observed in the ventral horn, in the deep dorsal horn, and in the ependymal layer. CCK‐positive cells were observed in the medial ventral horn, and VIP‐positive cells were observed subjacent to the SG and within the dorsolateral funiculus. After unilateral dorsal rhizotomies, SP‐like immunoreactivity in the SG was depleted, while SP staining elsewhere and all SS, CCK, and VIP staining was indistinguishable from control. Thus all four peptides are present in the stingray spinal cord, although only SP appears to be a candidate primary afferent transmitter.
Physiological response properties of cells labeled intracellularly with horseradish peroxidase in cat ventral cochlear nucleus
Authors: Rhode W. S. , Oertel D. , Smith P. H.
Published: December 2004

To determine the correspondence between anatomical and physiological cell types in the ventral cochlear nucleus of the cat, intracellular injections of horseradish peroxidase were made into cells whose extracellular and intracellular responses to sound had been studied.

Three identified cells responded to a short tone burst at their characteristic frequencies with an onset pattern. This pattern is characterized by a strong response to the onset of the stimulus. One was an octopus cell. The second cell, located in the octopus‐cell area, was a giant cell with a few somatic spines and thin tapering dendrites; the intracellular record revealed that even in the absence of sound it received continuous synaptic input, while tones at characteristic frequency produced a sustained depolarization. A third cell, which had an onset response at low intensities and a chopper response at high intensities, was a stellate cell located in the intermediate acoustic stria with dendrites oriented parallel to the fiber tract. This cell had an unusually broad dynamic range in response to changes in intensity.

Two cells with transient chopper response patterns were stellate cells in the posteroventral cochlear nucleus with many branched and beaded dendrites. Three cells with more sustained chopper response patterns were stellate cells in the anteroventral cochlear nucleus with fewer, less‐branched, smooth dendrites.

Two cells with primarylike responses to tones were bushy cells with numerous short, thin, highly branched dendrites in the posterior division of the anteroventral cochlear nucleus. Intracellular responses to tones at the characteristic frequency consisted of large brief depolarizations, which were not sustained.

Another cell, which responded to tones in a phase‐locked fashion, was also located in the anteroventral cochlear nucleus. It was a small, stellate cell with relatively few, smooth dendrites.

The labeled cells largely support previous attempts at physiological‐morphological correlations: (1) bushy cells exhibit primarylike pattern; (2) stellate cells exhibit chopper patterns; and (3) octopus cells exhibit an onset pattern. It was also demonstrated that more than one cell type can exhibit a particular response pattern.
Afferent and efferent pathways of the vibrissal region of primary motor cortex in the mouse
Authors: Porter Linda L. , White Edward L.
Published: December 2004

The afferent and efferent connections of the vibrissal representation within the mouse primary motor cortex (Msl) were identified by using the retrograde transport of horseradish peroxidase (HRP) and the anterograde transport of tritiated amino acids injected into Msl. Following aldehyde perfusion brains were frozen‐sectioned at 40 μm and reacted for HRP using the 3‐3′ diaminobenzidine‐cobalt chloride technique of Adams (77). Alternate HRP reacted sections were processed for autoradiography.

HRP‐filled pyramidal cell somata and concentrations of developed silver grains above background levels were observed in both the vibrissal area of primary somatosensory cortex (SmI) cortex (i.e., the posteromedial barrel subfield; PMBSF cortex) and in the face region of Smll (area 40). In both regions labeled somata occurred predominantly in cortical layers II‐III and V. Autoradiographic label was superimposed over the regions containing labeled soinata but exhibited a less distinct laminar organization.

A dense reciprocal projection connected the injection site with the hom‐otopic area in contralateral Msl; somata occurred for the most part in layers III and V. Developed silver grains were uniformly dispersed over the area containing labeled cell bodies. HRP‐labeled pyramidal somata were noted in contralateral PMBSF cortex, but no silver grains occurred in this region.

Reciprocal projections linked Msl cortex with the ipsilateral thalamic nuclei: ventralis pars lateralis (VL) and centralis pars lateralis (CL) and with the zona incerta (ZI). Labeled cell bodies and developed silver grains were more dense in VL than in CL. The ipsilateral striatum and thalamic reticular nucleus (NRT) received afferents from the motor cortex but did not project to it.

Thus, the vibrissal area of primary motor cortex is connected with a number of cortical and subcortical structures, each of which has been shown to play a role in motor performance. Identification of the afferent and efferent pathways of Msl cortex will now enable further investigation of the ultrastructural and synaptic organization of the vibrissal area of MsI.
The visual cells of the skate retina: Structure, histochemistry, and disc‐shedding properties
Authors: Szamier R. Bruce , Ripps Harris
Published: December 2004

Earlier studies have shown that visual function in skate is subserved solely by the rod mechanism and that the retina of this elasmobranch contains only rod photoreceptors. Nevertheless, the skate retina is capable of responding to levels of illumination that extend well into the photopic range, and we have detected in histological sections (usually from younger animals) small, proximally displaced, conelike photoreceptors which possibly represent another class of visual cell. However, ultrastructural and histochem‐ical studies showed that the membranous discs of the outer segments of these cells were isolated from the plasma membrane, and that their synaptic terminals appeared immature and unlike those usually associated with cone receptors. In addition, the pattern of incorporation of 3H‐fucose, as revealed by radioautography, was similar for both the rods and the smaller visual cells; i.e., the label was concentrated along the basal discs of the outer segment. When we examined the disc‐shedding behavior of the visual cells in skates entrained for 2 weeks or longer to a 12‐hour light: 12‐hour dark cycle, enhanced phagocytic activity was seen only following light onset; there was no significant increase following light offset. On the available evidence, it seems reasonable to conclude that the small visual cells are rods that have recently differentiated, and are growing and being incorporated into the photoreceptor layer of the retina.
The neurotrophic analogue of ACTH(4–9) reduces the perineuronal microglial reaction after rat facial nerve crush
Authors: Ulenkate Herman J. L. M. , Verhagen Marc A. M. T. , Gispen Willem‐Hendrik , Jennekens Frans G. I.
Published: December 2004

Following peripheral nerve cursh, microglial cells proliferate and migrate to motoneuron cell bodies of the injured nerves. Newly formed glial processes displace nerve terminals from the cell bodies. This process is known as synaptic stripping. In animal models of peripheral nerve diseases, the ACTH(4–9) analogue, ORG2766, was shown to facilitate axonal regeneration and to protect against experimental neuropathy. In the present study we examined the effect of ORG2766 on the microglial reaction. After facial nerve crush, rats were treated with either ORG2766 on the microglial reaction. After facial nerve crush, rats were treated with either ORG2766 (75 μg/kg/48 h) or saline and were killed on day 2–6 after operation. Blind counting of the number of perineuronal glial cells in the facial nucleus was used to assess the effect of ORG2766 treatment on the microglial reaction. In the saline‐treated animals the number of perineuronal glial cells per motoneuron cell body on the curshed side increased significantly. This number increased up to day 5 after operation and decreased significantly from day 5 to 6. After initial increase in the peptide‐treated animals, however, the number of perineuronal glial cells remained constant form day 3 onwards. Hece, on post‐operation days 4 and 5, this number was significantly less than that seen in saline‐treated animals. Microglial cells proliferate, presumably through signalling by injured motoneurons. It is suggested that the decrease in the number of perineuronal glial cells in the ORG2766‐treated animals is the result of a peptide‐induced reduction in the release of mediating signals/cytokines or, alternatively, increased protection of motoneurons by stress proteins. Further research should address the mechanism of action of ORG2766 in animal models of motoneuron disease. © 1993 Wiley‐Liss, Inc.