bluuebunny/crossref_metadata_2025 huggingface dataset:
Topographical organization of the inferior collicular projection and other connections of the ventral nucleus of the lateral lemniscus in the cat
Authors: Whitley John M. , Henkel Craig K.
Published: January 2005

The topographic distribution of projections from the ventral nucleus of the lateral lemniscus (VNLL) in the cat was investigated with the autoradiographic tracing method. The origin of minor projections was verified by retrograde tracing methods. Small injections of tritiated leucine were placed in restricted zones of VNLL. A major afferent fiber system to the inferior colliculus was labeled in all cases. From the injection site labeled fibers coursed through and around the nuclei of the lateral lemniscus to enter the ipsilateral inferior colliculus. Regardless of the position or small size of the injection, labeled fibers distributed widely in the inferior colliculus. Fibers ended in the central nucleus and deeper layers of the dorsal cortex in most cases. There was also labeling in the ventrolateral nucleus, but very few fibers ended as lateral as the lateral nucleus. A small number of labeled fibers passed from the inferior colliculus into the nucleus of the brachium of the inferior colliculus and adjacent tegmental areas. Some labeled fibers entered the commissure of the inferior colliculus where they were traced into the dorsal cortex and rostral pole of the inferior colliculus on the side contralateral to the injection site.

Though the projections labeled in individual cases were similar in their divergent pattern within the central nucleus of the inferior colliculus, specific variations in the pattern were found. The dorsal zone of VNLL projected more heavily to the deeper layers of the dorsal cortex and an adjacent field in the central nucleus than the other zones. Dorsal injections in the middle zone of VNLL, on the other hand, labeled the medial part of the central nucleus more heavily, whereas ventral injections in the middle zone resulted in heavier lateral labeling. The ventral zone of VNLL projected heavily to a central field in the central nucleus.

In addition to this major afferent system of VNLL to the inferior colliculus, a smaller descending projection was found. The descending projection ended mainly in the dorsomedial periolivary region and ventral nucleus of the trapezoid body. However, in some cases a few fibers were traced to the cochlear nuclei.

Finally, we observed projections to the medial geniculate body from the dorsal and ventral zones of VNLL that ended diffusely in the medial division of the medial geniculate body. Possibly some fibers from the dorsal zone contribute to a broader projection of the lateral tegmentum to the dorsal division of the medial geniculate body.
Projections to the cardioinhibitory region of the nucleus ambiguus of rat
Authors: Stuesse Sherry L. , Fish Stephen E.
Published: January 2005

The nucleus ambiguus is a brainstem structure which sends projections through the vagus nerve to the viscera, primarily heart, lung, and gut. The anatomical relationship between the nucleus ambiguus and other brain structures has not been elucidated nor has the cardiac region been identified physiologically in rats. We have attempted to clarify which areas of the nucleus ambiguus are cardioinhibitory and to determine other regions of the brain which send direct projections to this physiologically identified cardiac region. Stimulating electrodes were positioned stereotaxically in the medulla of anesthetized rats. Small currents were passed through the electrodes to locate regions in the ventrolateral medulla which slowed heart rate. In each rat, the area found was small (less than 200 μm in diameter), very specific, and located in the rostral portion of the nucleus ambiguus. Micro‐quantities of horseradish peroxidase were then iontophoretically ejected into this brainstem area; 24–72 hours following the HRP injection, the rats were processed for HRP reaction product using the tetramethybenzidine method. The major brain area which sent projections to the rostral nucleus ambiguus was the ipsilateral medial subnucleus of the solitary tract. A few labeled cells were found in the ipsilateral ventrolateral subnucleus of the solitary tract, parabrachial complex, the paraventricular nucleus of the hypothalamus, and the contralateral nucleus ambiguus. Control injections in reticular areas surrounding the rostral nucleus ambiguus showed no label in the medial solitary nucleus.
A reevaluation of midbrain and diencephalic projections to the inferior olive in rat with particular reference to the rubro‐olivary pathway
Authors: Rutherford J. G. , Anderson W. A. , Gwyn D. G.
Published: January 2005

Projections from the midbrain and caudal diencephalon to the inferior olivary nucleus (ION) in the rat were investigated by using anterograde and retrograde tracing techniques. Particular attention was directed to studying the projection from the red nucleus (RN.) to the ION.

Tritiated leucine was stereotaxically injected into the RN in six animals. The injection sites and the portion of the medulla containing the ION were processed for autoradiography. In three cases, the injections were largely confined to the RN. In these instances, no terminal labeling was noted in the ION. In the other three animals, the injections spread beyond the RN to include, in one or another of the rats, such areas as the mesencephalic reticular formation (MRF) between the RN and the periaqueductal gray (PAG), the region around the fasciculus retroflexus (FR), the prerubral area, the MRF dorsolateral to the RN, or the region dorsal to the medial geniculate body. In these animals, terminal labeling was observed ipsilaterally in the ION, chiefly in the caudal one‐half of the medial accesssory olive and in the dorsal lamella and lateral bend of the principal olive.

Retrograde transport of lectin‐conjugated horseradish peroxidase (WGA‐HRP) or the fluorescent dye fast blue (FB), injected into the ION, was used to localize regions in the midbrain and caudal diencephalon containing neurons which project to the inferior olive. Following WGA‐HRP injections into the ION, retrogradely labeled neurons were found in the ipsilateral ventral PAG, the MRF between the PAG and the RN, the MRF dorsolateral to the RN, and the area dorsal to the medial geniculate body. Large numbers of heavily labeled neurons were found in the area surrounding the FR. No labeled cells were noted in the RN or the nucleus of Darkschewitsch (ND). Subsequent to FB injections into the ION, fluorescent neurons were observed in the same regions which contained HRP‐labeled neurons in the experiments using the enzyme as a tracer. Additionally, very small numbers of FB‐labeled neurons were found in the RN and the ND.

These results indicate that, in the rat, descending input from the midbrain and caudal diencephalon to the ION arises chiefly from a medially located column of neurons extending from the level of the rostral RN to the region of the FR. Little, if any, input to the ION is derived from the ND or RN in this species, unlike the cat, in which a substantial projection to the ION arises from the ND and the RN.
Cell death during differentiation of the retina in the mouse
Authors: Young Richard W.
Published: January 2005

A reproducible pattern of cell death associated with differentiation of the retina in mice was analyzed quantitatively by microscopy. Cell death occurs primarily during the first 2 weeks after birth and is essentially complete by the end of the third week. Death of individual cells involves nuclear condensation and pyknosis (apoptosis), followed by phagocytosis of the cellular remains by adjacent cells or motile phagocytes. From birth through 4 days, an increasing incidence of cell death is observed among ventricular cells. Ganglion cell degeneration is prominent during the first 11 days, peaking on days 2–5. Many presumptive amacrine cells die within the inner plexiform and inner nuclear layers, particularly between 3 and 8 days. Among adjoining bipolar and Müller cells, degeneration reaches a peak at 8–11 days. On day 5, formation of the outer plexiform layer separates the rods into two groups. Rod nuclei situated on the inner side of that layer immediately move across it to enter the outer nuclear layer, but numerous cells die during nuclear migration. Sporadic death of rods continues during the following 2 weeks. Cell death associated with cell differentiation (histogenetic death) is considered to represent a normal developmental process. Possible mechanisms resulting in cell degeneration are discussed. It is suggested that genetically regulated cell death serves to fine‐tune neuronal networks during the terminal stages of development.
Glutamate‐ and GABA‐containing neurons in the mouse and rat brain, as demonstrated with a new immunocytochemical technique
Authors: Ottersen Ole P. , Storm‐Mathisen Jon
Published: January 2005

Antisera were raised against γ‐aminobutyric acid (GABA) or glutamate (Glu) conjugated to bovine serum albumin with glutaraldehyde. After purification, these antisera reacted strongly with fixed GABA or Glu, but not significantly with other amino acids fixed with glutaraldehyde to brain macromolecules. The antisera were used to demonstrate the distributions of Glu‐like and GABA‐like immunoreactivities (Glu‐LI and GABA‐LI) in parts of the perfusion‐fixed mouse and rat brain, including the olfactory bulb, cerebral neocortex, thalamus, basal ganglia, lower brain stem, and cerebellum.

The level of GABA‐LI varied widely among brain regions, thus it was very high in the globus pallidus and substantia nigra and low in the bulk of the thalamus. The GABA antisera labeled nonpyramidal neurons of the neocortex, most cells of the reticular nucleus of the thalamus, medium‐sized cells of the caudatoputamen, and stellate, basket, Golgi, and Purkinje cells of the cerebellum. The distribution of GABA‐LI closely matched that of the GABA‐synthesizing enzyme, glutamic acid decarboxylase (GAD), as revealed in immunocytochemical studies by others. However, the GABA antisera seem to be better suited than GAD antisera for demonstrating putative GABA‐ergic axons. The results suggest that GABA‐LI, as displayed by the present method, is a good marker of neurons thought to use GABA as a transmitter.

Glutamate‐like immunoreactivity was much more evenly distributed among regions than GABA‐LI, but was particularly low in globus pallidus and substantia nigra and high in the cerebral cortex. Mitral cells of the olfactory bulb, pyramidal neocortical cells, and other cells assumed to use Glu or aspartate as transmitter were stained for Glu‐LI, but so also were neurons that are thought to use other transmitters, such as cells in the substantia nigra pars compacta, in the dorsal raphe nucleus, and in the brain stem motor nuclei. The Glu antisera seem to reveal the “transmitter pool” as well as the “metabolic pool” of Glu in perfusion‐fixed material.

This report shows that it is possible by means of immunocytochemistry to display reliably the tissue contents of GABA and Glu in material that has been fixed by perfusion with glutaraldehyde.
The non‐pyramidal cells in layer III of cat primary auditory cortex (AI)
Authors: Winer Jeffery A.
Published: January 2005

The form and location of non‐pyramidal neurons in layer III of the primary auditory cortex (AI) of adult cats is described in Golgi, Nissl, and other material. The cells were compared to the profiles of retrogradely labeled, commissurally interconnected cells. A principal finding is that certain non‐pyramidal and pyramidal cells project interhemispherically to AI; a second conclusion is that the retrogradely labeled commissural cells form small clusters or narrow strips separated by unlabeled patches even after massive injections in the opposite AI. The non‐pyramidal cells of origin have not yet been conclusively identified, but they must include one (or more) of the following six types of cells observed in Golgi‐impregnated material: (1) tufted or bitufted cells with a radially elongated dendritic arbor; (2) sparsely spinous stellate neurons with thin, smooth dendrites and vertically disposed axonal branches; (3) small stellate cells with varicose dendrites, a restricted dendritic field, and a profusely branched local axon; (4) bipolar neurons with long, thin dendrites; (5) medium‐sized multipolar cells with radiating, sparsely branched dendrites; and (6) small stellate neurons with smooth dendrites and a tiny dendritic field. These non‐pyramidal cells are found throughout layer III but are more numerous in the upper part, layer IIIa, where they mingle with the small pyramidal neurons. As a rule the axonal branches of non‐pyramidal cells are more numerous than those arising from layer III pyramidal neurons, and although they have many axonal collaterals, most project locally and vertically in narrow radial strips. In contrast, pyramidal cell axons have ascending and descending components which invade large, lateral territories in many cortical layers. Layer III non‐pyramidal neurons are similar to those in layer IV in certain respects, although their dendritic fields are more spherical and less tufted than those of layer IV cells, and their axons have more local, limited targets. These axons appear to contribute but little to the conspicuous, lateral fiber striae in layer III. The primary intrinsic targets of non‐pyramidal cell axons appear to be the apical dendrites of medium‐sized and large layer III pyramidal cells, and recurrent branches to the parent cell; their fine, distal branches fortify the vertical plexus in layer III, and certain axons may descend into layer IV. Since layer III in AI receives both commissural and thalamic input, it is possible that these parallel, afferent channels are to some degree segregated, and to some degree convergent, onto particular types of cells. Whether any single cell receives both kinds of input is unknown, but the evidence suggests that not all non‐pyramidal cells project only locally, nor may all project interhemispherically or from AI to AI. This implies that there may be connectionally and perhaps functionally distinct subsets among layer III non‐pyramidal neurons which remain to be identified by experimental methods.
An HRP study of hypothalamo‐cerebellar and cerebello‐hypothalamic connections in squirrel monkey (saimiri sciureus)
Authors: Haines D. E. , Dietrichs E.
Published: January 2005

This study describes the distribution of labeled hypothalamic neurons in squirrel monkey following pressure injections of horseradish peroxidase (HRP) into cerebellar cortex and the pattern of labeling in the cerebellar nuclei subsequent to iontophoretic injections localized in the hypothalamus. Two types of HRP (HRP and a wheat germ agglutinin conjugate, HRP‐WGA) were used as tracers; tetramethylbenzidine was the chromogen.

Retrogradely filled neurons were found in lateral (LHAr) and posterior (PHAr) hypothalamic areas, and in the lateral mammillary (LMNu) and supramammillary (SMNu) nuclei following injections into ansiform and paramedian lobules and into the paraflocculus. Labeled cells were occasionally seen in the medial mammillary nucleus (parafloccular cases) and among fascicles of the mammillothalamic tract (all posterior lobe cases) immediately above the medial nucleus. After injections into the anterior lobe, labelling was again found in the LHAr, PHAr, LMNu, and SMNu. In addition, retrogradely filled cells were present in ventromedial, dorsomedial, and dorsal hypothalamic nuclei and in the dorsal hypothalamic area. Labeled cells were occasionally found among fascicles of the fornix along its intrahypothalamic course. In general, labeling extends into slightly more rostral hypothalamic levels in anterior lobe cases when compared to posterior lobe experiments. We interpret these data as indicating that some hypothalamic neurons project directly to the cerebellar cortex (i.e., hypo‐thalamo‐cerebellar fibers); this projection is bilateral with an ipsilateral preponderance.

In experiments with injections of HRP‐WGA into the cerebellar nuclei, anterogradely filled axons were traced into the contralateral PHAr and LHAr; this was suggestive of a direct cerebello‐hypothalamic projection. Following iontophoretic injections localized in the LHAr and the medial mammillary nucleus, labeling was seen in the medial (NM), posterior interposed (NIP), and lateral (NL) cerebellar nuclei; this is essentially a contralateral projection. Retrogradely labeled cells were found in the rostral and ventral NM, the ventral and dorsocaudal NL, and diffusely throughout the NIP. On the basis of the known distribution of cerebello‐thalamic fibers and other criteria, these labeled cells are representative of a true cerebello‐hypothalamic projection. It is suggested that the cerebellum, through these pathways, may have a relatively direct influence on visceral centers in the brainstem and spinal cord.
Telencephalic connections in lizards. I. Projections to cortex
Authors: Bruce Laura L. , Butler Ann B.
Published: January 2005

The afferent connections to five cortical regions in two distantly related species of lizards (Gekko gecko and Iguana iguana) were studied by means of retrograde transport of horseradish peroxidase conjugated to wheat germ agglutinin. Each of the five cortical regions is characterized by a specific pattern of projections from telencephalic, thalamic, hypothalamic, and brainstem regions. Subdivisions within the five cortical regions also receive different patterns of projections. The thalamo‐cortical projections are as follows: The small‐celled mediodorsal cortex receives a projection from nucleus dorsolateralis anterior pars magnocellularis. The large‐celled mediodorsal cortex receives projections from nucleus dorsolateralis anterior pars parvicellularis and pars magnocellularis. The dorsal cortex receives a projection from nucleus dorsolateralis anterior pars parvicellularis. The lateral cortex receives a projection from nucleus dorsolateralis anterior pars magnocellularis. The pallial thickening receives projections from nucleus dorsomedialis and nucleus intercalatus. The latter nucleus receives a direct retinal projection. Thus, the pallial thickening is the recipient of a retino‐thalamo‐cortical projection.

To date, comparisons of data from experimental studies have suggested that the cortical regions in lizards and turtles may be organized differently. However, the results of the present study suggest that the organization of cortical regions among reptiles is more similar than previously realized.
Telencephalic connections in lizards. II. Projections to anterior dorsal ventricular ridge
Authors: Bruce Laura L. , Butler Ann B.
Published: January 2005

Three distinct cytoarchitectonic regions were identified within the anterior dorsal ventricular ridge (ADVR) of two species of lizards, Gekko gecko and Iguana iguana. These regions have been named according to their general topographical positions: medial area, caudolateral area, and rostrolateral area.

Injections of horseradish peroxidase throughout the ADVR demonstrated that each of the three areas of the ADVR receives projections from specific thalamic nuclei which are associated with specific sensory modalities. The medial area receives an auditory thalamic projection from nucleus medialis. The caudolateral area receives thalamic projections from nucleus medialis posterior and nucleus posterocentralis. The latter two nuclei were shown to receive projections from the spinal cord and, therefore, are presumed to be associated with body somatosensory information. The rostrolateral area receives a thalamic projection from nucleus rotundus, which receives visual information. In addition, the mesencephalic tegmentum and the thalamic nucleus dorsomedialis project to the entire ADVR. The latter projection is similar to the diffuse cortical projections of the intralaminar thalamic nuclei in mammals.

These findings support previous suggestions that the ADVR is comparable to sensory regions of the mammalian neocortex.
On the location and size of laryngeal motoneurons in the cat and rabbit
Authors: Davis P. J. , Nail B. S.
Published: January 2005

Motoneurons supplying the posterior crico‐arytenoid (PCA), thyro‐arytenoid (TA), lateral crico‐arytenoid (LCA), and crico‐thyroid (CT) laryngeal muscles were localized in the cat, the rabbit, and the 6‐week‐old kitten by using the technique of intramuscular injection of horseradish peroxidase. Each muscle was found to be innervated by a single, ipsilateral pool of motoneurons, a result which was reliably established only after controlling adventitious spread of the label to nontarget muscles by prior denervation of adjacent musculature. The laryngeal motoneuron column extended in the nucleus ambiguus for a distance of 5–6 mm caudally from the facial nucleus. CT motoneurons were located in the rostral third of this column while the PCA, TA, and LCA motoneurons were located more caudally. These results are in general agreement with earlier degeneration studies (Lawn, '66a; Szentágothai, '43).

Although labelled cells were widely dispersed in the nucleus, particularly in the adult cat, a limited amount of topographical structure could still be discerned in the arrangement of recurrent laryngeal nerve motoneurons. In the cat, the PCA pool was located in the ventral part of the recurrent laryngeal nerve representation and did not extend as far caudally as the TA or LCA pools; the LCA pool was located in the caudal and dorsomedial part of the recurrent laryngeal nerve pool; TA motoneurons appeared to overlap the PCA and LCA pools on all three anatomical planes. TA motoneurons were more numerous than PCA or LCA motoneurons, the numbers of cells in the three pools being estimated at 170, 111, and 112, respectively.

In the cat bilateral labelling of different pools pointed to certain differences in morphology between cells from these pools and also suggested a functional basis for such differences. The mean soma diameter for the PCA and CT motoneurons was each significantly smaller than that for the TA and LCA motoneurons. The rabbit data were similar. The findings on motoneuron morphology are considered in relation to anatomical and physiological characteristics known to have been established for individual laryngeal muscles and with which they appear to be consistent.
The cytoarchitectonic organization of the spinal cord in the rat. I. The lower thoracic and lumbosacral cord
Authors: Molander C. , Xu Q. , Grant G.
Published: January 2005

A laminar Cytoarchitectonic scheme of the lower thoracic and lumbosacral segments of the rat spinal cord is presented in which Rexed's principles for the cat are applied. The material consists of 80‐μm‐thick sections stained with toluidine blue or according to van Gieson and 2‐μm‐thick sections stained with p‐phenylenediamine or toluidine blue. The Cytoarchitectonic organization of the rat spinal cord was found to be basically similar to that of the cat, although certain differences exist—for example, in the extension of the laminae. In addition to the laminar scheme, the distribution of certain cell groups, Lissauer's tract, and the pyramidal tract were investigated.
Interhemispheric connections of visual cortex of owl monkeys (Aotus trivirgatus), marmosets (Callithrix jacchus), and galagos (Galago crassicaudatus)
Authors: Cusick C. G. , Gould H. J. , Kaas J. H.
Published: January 2005

Interhemispheric connections of visual cortex were studied in owl monkeys, marmosets, and galagos after multiple injections of horseradish peroxidase into one cerebral hemisphere. Areal patterns of connections were revealed in sections of cortex that was flattened and cut parallel to the surface. Results were related to the locations of known visual areas, especially in owl monkeys, in which more visual areas have been established.

The connection patterns in owl monkeys and marmosets are very similar, suggesting that the organization of visual cortex differs little in these two New World simians. Galagos have a basically similar pattern, but the connections are more widespread. In all three primates, connections are not restricted to cortex representing the line of decussation of the retina, and even striate cortex has connections displaced from the border. These connections extend up to 2 mm into area 17 in owl monkeys, and they arc most extensive in galagos, where they form foci that are coextensive with regions of high cytochrome oxidase activity. Connections are concentrated in the caudal half of area 18, but protrusions of connections cross the width of the field. The middle temporal visual area (MT) has unevenly distributed connections throughout, with some increase in density along the border. The dorsomedial visual area (DM) of owl monkeys has connections restricted in the rostral border, and a similar region of sparse connections identifies the probable location of DM in marmosets and galngos. Caudal parts of the dorsolateral visual area (DL) of owl monkeys have dense interhemispheric connections. Other visual areas are characterized by unevenly distributed clumps of connections, suggesting that functions are not uniformly distributed, and that semiregular processing modules exist. The results indicate that most extrastriate visual neurons are subject in interhemispheric influences and support the conclusion that callosal connections are functionally heterogeneous.
Brainstem afferents to the omnipause region in the cat: A horseradish peroxidase study
Authors: Langer Thomas P. , Kaneko Chris R. S.
Published: January 2005

“Omnipause” neurons (OPNs), located in the nucleus raphe pontis and the reticular formation, actively suppress saccadic eye movements during intersaccadic intervals. To determine the brainstem afferents that may inhibit the OPNs and thereby allow a saccade to occur, we injected horseradish peroxidase into the raphe pontis of four cats at the site of physiologically identified OPNs. Labeled neurons were found in a number of brainstem nuclei. The greatest concentrations, composed of small to medium‐sized neurons, were located in a group of nuclei around the habenulopeduncular tract, in the rostral mesencephalic reticular formation, in the deep layers of the superior colliculus, and in parts of the subjacent cuneiform and subcuneiform reticular nuclei. Smaller numbers were found in the nucleus reticularis pontis oralis. Caudal to the injection site, labeled neurons were scattered in parts of the nuclei reticularis gigantocellularis, paragigantocellularis dorsalis, and paragigantocellularis lateralis. A few neurons were labeled in a restricted region of the caudal part of the nucleus prepositus hyppglossi and in the nucleus reticularis medullaris ventralis. Larger numbers of neurons were labeled in the dorsal column nuclei and in parts of the cochlear nuclei. Smaller numbers were found in the spinal trigeminal nucleus, the lateral nucleus of the superior olive, and the fastigial nucleus of the cerebellum. The nonreticular brainstem projections may contribute sensory information in a number of modalities since OPNs respond to visual, somesthetic, and auditory stimuli.

Our findings indicate a number of regions that may contain neural elements impinging on the OPNs. The best prospects for a saccade initiation signal from one of the labeled populations appear to be the meso‐diencephalic reticular formation and/or the superior colliculus.
Amygdalo‐cortical projections in the monkey (Macaca fascicularis)
Authors: Amaral D. G. , Price J. L.
Published: January 2005

Amygdalo‐cortical projections were analyzed in the macaque monkey (Macaca fascicularis) in a series of experiments in which 3H‐amino acids were injected into each of the major divisions of the amygdaloid complex and the anterogradely transported label was demonstrated autoradiographically. Projections to widespread regions of frontal, insular, temporal, and occipital cortices have been observed. The heaviest projections to frontal cortex terminated in medial and orbital regions which included areas 24, 25, and 32 on the medial surface and areas 14, 13a, and 12 on the orbital surface. Lighter projections were also seen in areas 45, 46, 6, 9, and 10. The heaviest projection to the insula terminated in the agranular insular cortex with a decreasing gradient of innervation to the more caudally placed dysgranular and granular insular areas. The projection to this region continues around the dorsal limiting sulcus to terminate in the somatosensory fields 3, 1–2, and SII. Essentially all major divisions of the temporal neocortex receive a projection from the amygdaloid complex with the most prominent projections ending in the cortex of the temporal pole (area TG) and the perirhinal cortex. The entire rostrocaudal extent of the inferotemporal cortex (areas TE and TEO) is also in receipt of an amygdaloid projection. While the rostral superior temporal gyrus (area TA) is heavily labeled in several of the experiments (with light labeling continuing into AI and adjacent auditory association regions) there was little indication of labeling in the caudal reaches of area TA. There was a surprisingly strong projection to prestriate regions of the occipital lobe and, in at least one case, clear‐cut labeling in areas OB and 17. Labeling in the parietal cortex was primarily observed in the depths of the intraparietal sulcus. In all cortical fields, label was heaviest at the border between layers I and II and in some regions layers V and VI also had above background levels of silver grains.
Axonal growth and target selection during development: retinal projections to the ventrobasal complex and other “nonvisual” structures in neonatal Syrian hamsters
Authors: Frost Douglas O.
Published: January 2005

In newborn hamsters, there is a direct retinal projection to the ventrobasal complex, the principal thalamic somatosensory nucleus. The projection decreases precipitously between the second and third postnatal days. A few retinofugal axons remain dorsally along the lateral border of the nucleus on day 4, and none are present thereafter. In neonatal hamsters, retinofugal axons project to additional “nonvisual” nuclei including the periventricular and anterior nuclei of the hypothalamus, zona incerta, substantia nigra, inferior colliculus, pons, and mesencephalic tegmentum. Some of these connections remain in adult hamsters, although in apparently reduced density or relative volume, while others disappear. The contribution of transient connections to the normal morphological or functional development of the brain remains to be clarified. The combined results of this and other studies show that the normally transient retino‐ventrobasal projection is a substrate for abnormal connections in that it can be permanently stabilized by appropriate neurosurgery on the day of birth.
Ultrastructure of the dorsal motor nucleus of the vagus nerve in monkey with a comparison of synaptology in monkey and cat
Authors: McLean John H. , Hopkins David A.
Published: January 2005

Neurons of the dorsal motor nucleus of the vagus nerve were studied following injections of horseradish peroxidase into the vagus nerve in a monkey (Macaca fascicularis). In frozen sections, the dorsal motor nucleus appeared to be completely filled by labeled medium‐sized (20–30 μm in long axis) neurons. Labeled dendrites from these neurons often extended outside the borders of the nucleus into the nucleus of the tractus solitarius. In 1 μm thick plastic sections and ultrathin sections of the dorsal motor nucleus, two distinct types of neurons were observed with the light and electron microscope. Medium‐sized neurons with abundant cytoplasm and an oval nucleus were retrogradely labeled with HRP, while small (10–15 μm in long axis) neurons with a paucity of organelles and an invaginated nucleus remained unlabeled. Medium‐sized neurons outnumbered the small neurons by approximately five to one.

The synaptic organization of the dorsal motor nucleus in monkey was studied and compared with that in cat. The porportions of different types of axosomatic synapses were similar in both species. Terminals containing round vesicles and making symmetrical or asymmetrical contact with the postsynaptic structure were more common than synaptic terminals containing pleomorphic vesicles. In both species, there was a slightly greater synaptic density on the medium‐sized neurons than on the small neurons. The synaptic density in the monkey dorsal nucleus was greatest on the smallest dendrites in the neuropil and least on the somata.
Effect of a conditioning lesion on axonal sprout formation at nodes of ranvier
Authors: McQuarrie Irvine G.
Published: January 2005

The effect of a conditioning lesion on the time‐course of axonal sprout formation after a subsequent testing lesion was evaluated in myelinated axons of the rat sciatic nerve. Transmission electron microscopy of longitudinal nerve sections was used to examine nodes of Ranvier located 200–500 μm proximal to the testing lesion. The conditioning lesion was a cut of the tibial nerve at the ankle; the testing lesion, made 2 weeks later, was a crush of the sciatic nerve at the hip. Sprouts were defined as unmyelinated evaginations of the nodal axolemma that (1) had reached the basement membrane of the Schwann cell, and (2) were located between the myelin sheath of the distal paranode and the basement membrane. Photomicrographs of the nodes at 9, 18, and 27 hours after the testing lesion were assigned to one of seven categories: normal, retracted, myelin degeneration, axonal degeneration, type A sprout formation (cytoskeleton absent), type B sprout formation (cytoskeleton present), and type B sprout degeneration. By 9 hours after the testing lesion, type B sprout formation was found in 9% of the nodes in control nerves (testing lesion alone) and 33% of those in conditioned nerves (P <.01). A 33% incidence of type B sprout formation was not reached in control nerves until 27 hours after the testing lesion. Since the conditioning lesion was located 50 mm distal to the testing lesion and did not induce neuronal death, earlier sprout formation can be attributed to a neuronal response to the conditioning lesion rather than to a putative factor that arises from pre‐degenerated fibers and acts on newly formed sprouts.
The organization of the lateral thalamus of the hooded rat
Authors: Takahashi Terry
Published: January 2005

Analysis of cytoarchitecture and connectivity showed that the lateral thalamus of the hooded rat is composed of eight nuclei. An examination of the cytoarchitecture permitted the identification of seven cellular fields: nucleus suprageniculatus (sg), nucleus lateralis posterior pars caudomedialis (lpcm), nucleus lateralis posterior pars lateralis (lpl), nucleus lateralis posterior pars rostromedialis (lprm), intramedullary area (ima), nucleus lateralis dorsale pars ventrolateralis (ldvl), and nucleus lateralis dorsale pars dorsomedialis (lddm). An analysis of the connectivity showed that lpl is further divisible into a rostral (lplr) and a caudal (lplc) sector, bringing the total number of nuclei to eight. Nucleus suprageniculatus, the most caudal element of the lateral thalamus, is composed of medium to large, fusiform, and multipolar neurons. It contains a terminal field of the projection of the superficial layers of the ipsilateral superior colliculus. Nucleus lpcm, found rostrolateral to sg, is loosely packed with large multipolar neurons. A terminal field of the superficial layers of the superior colliculus of both sides fits precisely within its cytoarchitectural boundaries. Nucleus lpl, a long cellular territory found lateral to lpcm, extends from the caudal pole of the dorsal lateral geniculate nucleus to the caudal pole of ldvl and contains round cells which are smaller and more densely packed than those of lpcm. Its caudal portion (lplc) contains another terminal field of the ipsilateral superior colliculus while its rostral portion (lplr) contains a terminal field of the projection of Area 17. Area 18 also projects to lplr, whereas Area 18a projects to both lplr and lplc. The intramedullary area, which occupies the fibrous zone between lpl and the dorsal lateral geniculate nucleus, contains round and fusiform neurons and is innervated by Area 18a. Nucleus lprm, situated medial to lpl, is characterized by round neurons which are frequently found in clusters. It is innervated by Areas 17, 18, and 18a. Nucleus ldvl is evenly packed with moderately large, polygonal cells and contains the complete terminal fields of both Areas 17 and 18. It also receives inputs from Area 18a. Finally, lddm, tightly packed with small, round cells and lying medial to ldvl, receives inputs from Area 4.
Afferent influences on brain stem auditory nuclei of the chicken: Changes in succinate dehydrogenase activity following cochlea removal
Authors: Durham Dianne , Rubel Edwin W.
Published: January 2005

We have examined one of the metabolic consequences of unilateral cochlea (basilar papilla) removal in the chick brain stem auditory system. We assessed changes in succinate dehydrogenase (SDH), a mitochondrial enzyme involved in energy metabolism, in neurons of second‐order n. magnocellularis (NM) and third‐order n. laminaris (NL). Chickens undergoing surgery at 10 days of age were perfused 4 hours to 35 days postlesion. Chickens 6 or 66 weeks of age at cochlea removal were examined 1 or 8 days after surgery. In all groups, cryostat sections were prepared for SDH histochemistry or Nissl staining.

In normal chickens, NM cell bodies and NL neuropil contain SDH reaction product. In young birds, the density of SDH reaction product in NM shows a rapid biphasic response to cochlea removal. From 8 to 60 hours postlesion, density increases ipsilateral to cochlea removal; for survival times of 3–35 days, SDH density decreases in ipsilateral NM. In NL, no changes were observed until 3 days after cochlea removal. Then we observed a long‐lasting decrease in density of SDH reaction product in the neuropil regions receiving input from the deafferented NM. All of these changes are age‐dependent in that they were observed only following cochlea removal on or before 6 weeks of age.
An electron microscopic study of terminals of rapidly adapting mechanoreceptive afferent fibers in the cat spinal cord
Authors: Semba K. , Masarachia P. , Malamed S. , Jacquin M. , Harris S. , Yang G. , Egger M. D.
Published: January 2005

The intra‐axonal horseradish peroxidase technique was used to examine the central terminals of 7 Aβ primary afferent fibers from rapidly adapting (RA) mechanoreceptors in the glabrous skin of the cat's hindpaw.

At the light microscopic level, labelled collaterals were seen to bear occasional boutonlike swellings, mostly (75–82%) of the en passant type. These swellings were distributed more or less uniformly from lamina III to a dorsal part of lamina VI in the dorsal horn, over a maximum longitudinal extent of about 4 mm.

At the electron microscopic level, we observed that labelled boutons of RA afferent fibers were 1.0 to 3.3 μm in longest sectional dimension, and contained clear, round synaptic vesicles. They frequently formed asymmetric axospinous and axodendritic synapses and commonly appeared to receive contacts from unlabelled structures containing flattened or pleomorphic vesicles plus occasional large dense‐cored vesicles. The examination of synaptic connectivity over the entire surface of individual boutons indicated that RA afferent boutons each made contacts with an average of one spine and one dendrite and, in addition, appeared to be postsynaptic to an average of two unlabelled vesicle‐containing structures. This synaptic organization was, in general, more complex than that we had seen previously in Pacinian corpuscle (PC) and slowly adapting (SA) type I mechanoreceptive afferent fibers.

Our findings indicate that RA, SA, and PC afferent terminals, while displaying some differential synaptic organizations, have many morphological and synaptological characteristics in common. These afferent terminals, in turn, seem to be generally distinguishable from the terminals of muscle spindle Ia afferents or unmyelinated primary afferents.
(3H) glycine‐accumulating neurons of the human retina
Authors: Marc Robert E. , Liu Wei‐Ley S.
Published: January 2005

Isolated human retinas were incubated in physiological saline containing micromolar (3H) glycine. The types, distributions, and synaptologies of glycine‐accumulating neurons were determined by light and electron microscope autoradiography. Two types of amacrine cells were discriminated on the bases of number of processes descending into the inner plexiform layer, density of label in light‐microscope autoradiographs, size, and synaptic features: (1) Gly1 amacrine cells have moderate labeling, several oblique dendrites arising from the soma, and electron lucent synaptic terminals containing large presynaptic specializations, and (2) Gly2 amacrine cells have dense labeling, a single proximal dendrite, and moderately electron‐dense terminals with small presynaptic specializations. Gly1 amacrine cells constitute ∼ 15% and Gly2 amacrine cells ∼ 38% of all cells in the amacrine cell layer. The laminar distribution of label in the inner plexiform layer was measured by scanning microdensitometry, which provided a format for categorizing types of synaptic contacts. Many features of glycine‐accumulating amacrine cell contacts were similar to those of cat AII/Gly2 amacrine cells: a diffuse yet bisublaminar distribution of label, concentration of synaptic output in sublamina a, rod bipolar cell input in sublamina b and gap junctions in mid‐inner plexiform layer involving labeled cells. The evidence seems to indicate that human Gly2 amacrine cells and cat AII/Gly2 amacrine cells are homologous cell types. Finally, some cone bipolar cells were labeled with (3H) glycine.
Regulation of neuron numbers in Xenopus laevis: Effects of hormonal manipulation altering size at metamorphosis
Authors: Sperry David G. , Grobstein Paul
Published: January 2005

Xenopus laevis tadpoles reared in a 0.01% solution of 6‐n‐propyl‐2‐thiouracil (PTU) are blocked in their development at larval stage 54 out continue to increase in size. When released from the effects of PTU they metamorphose into frogs of sizes significantly larger than those of their untreated siblings. Using this size difference to examine the hypothesis that neuron numbers are matched to the size of their postsynaptic targets during neuronal cell death, we measured the following on stage 66 frogs metamorphosing from PTU‐treated and untreated tadpoles: lumbar lateral motor column (L‐LMC) motoneuron number and mean nuclear cross‐sectional area; thoracic and lumbar dorsal root ganglion (DRG) cell number and mean nuclear cross‐sectional area; and muscle fiber number in two representative thigh muscles. A few measurements of neuron number and cell size were also made on untreated and PTU‐treated stage 54 tadpoles.

The most striking correlations observed were not between peripheral size and neuron numbers but between peripheral size and neuron size. Motoneuron numbers were not increased in the PTU‐treated animals, perhaps because the increase in peripheral size involved an increase in muscle fiber diameter rather than an increase in muscle fiber number. Thoracic DRG cell number, but not the sum of thoracic and lumbar DRG cell numbers, was increased. In general, our findings do not support the hypothesis that neuron numbers are matched to peripheral size by a process regulating the amount of cell death that occurs during metamorphic stages in Xenopus laevis.
Neuronal death and synapse elimination in the olivocerebellar system. I. Cell counts in the inferior olive of developing rats
Authors: Delhaye‐Bouchaud Nicole , Geoffroy Brigitte , Mariani Jean
Published: January 2005

A transient multiple innervation of cerebellar Purkinje cells by climbing fibers has been described during postnatal development of the rat. The aim of the present study was to determine if the regression of redundant synapses is related to the loss of presynaptic cells in the inferior olivary nucleus (ION), which is the sole source of climbing fibers in rodents. To this end, the population size of the ION was evaluated by counting healthy cells of the four main subnuclei in rats from birth to adulthood. The cell population at birth was found to be very similar to that of the adult animal (27,655 versus 28,385), but a loss of 25% of the cells occurred in the first five days, presumably through their death since degenerating cells were observed over the same period. Although cell loss was found throughout the whole nucleus, it was more pronounced in the medial accessory olive. A subsequent apparent increase of the cell population was observed so that the adult value was again reached at 15 days. The evolution of the ION population is then characterized by a period of moderate cell death which takes place before the peak of polyneuronal innervation of Purkinje cells by olivary axons is attained. This strongly suggests that the removal of the redundant synaptic contacts established by climbing fibers onto Purkinje cells during development is caused by a progressive reduction of the branching of olivary axons rather than by degeneration of the presynaptic cells.
Ascending somatosensory projections to the medial accessory portion of the inferior olive: A retrograde study in cats
Authors: Molinari Helen H.
Published: January 2005

The cells in the dorsal column nuclei, lumbosacral spinal cord, lateral cervical nucleus, and nucleus z that project to the medial accessory portion of the inferior olive of cats were identified with retrograde tracing techniques. Injections of wheat germ agglutinin complexed to horseradish peroxidase were made in the caudal portion of the medial accessory olive, either (1) involving no portion of the dorsal accessory olive or (2) involving in addition the caudal tip of the dorsal accessory olive. The tissue was processed with tetramethyl benzidine. The locations of all relay neurons were compared with those of dorsal accessory olive projection neurons, as described in a previous study (Molinari, 1984a).

Localized populations of neurons gave rise to most of the projection to the medial accessory olive. These neurons were found in the peripheral portions of the dorsal column nuclei caudal to the obex and in the ventromedial ventral horn of the entire lumbosacral enlargement. Few projection neurons were found in the lateral cervical nucleus and none in the nucleus z.

Neurons in the peripheral dorsal column nuclei and ventromedial ventral horn were labeled by injections in either the medial or dorsal accessory olives. Following medial accessory olive injections, however, they constituted the only labeled somatosensory neurons, while following dorsal accessory olive injections they represented only a small fraction of the labeled neurons. Based on their locations, it is proposed that these neurons might be the source for both the medial and dorsal accessory olives of information signalling movement of the proximal limb. Such a proposal is consistent with functional descriptions of the medial and dorsal accessory olives and the cerebellar anterior lobe.