bluuebunny/crossref_metadata_2025 huggingface dataset:
Rohon‐Beard cells in frog development: A study of temporal and spatial changes in a transient cell population
Authors: Eichler Victor B. , Porter Richard A.
Published: May 2005

The spatial distribution and temporal disappearance of Rohon‐Beard cells in the spinal cords of larval and newly metamorphosed Rana pipiens were studied histologically to provide a basis for further research dealing with this particular cell type. It was found that a maximum number of approximately 250 Rohon‐Beard neurons have differentiated within the spinal cord of Rana pipiens by larval stage I. The majority of these cells are located in the cephalic end of the spinal cord, with a large number found near the boundary of the anterior quarter and the second quarter of the spinal cord. Fewer cells are found in the third and fourth quarters.

There is a gradual degeneration of these cells during larval life so that by stage XXV, which is the completion of the metamorphic climax, there are no normally appearing Rohn‐Beard cells present. Degeneration of the Rohon‐Beard cells does not progress cephalocaudally with development, but rather there appears to be a nearly equal proportional loss of Rohon‐Beard cells in each quarter of the spinal cord at each of the stages studied. All Rohon‐Beard cells present during larval development of Rana pipiens are located in a dorsal position, close to the midline. At all ages and in each quarter of the spinal cord there are no significant bilateral differences in number of these cells.
Target dependency of developing motoneurons in Xenopus laevis
Authors: Lamb Alan H.
Published: May 2005

The effect of complete and partial limb bud removal on motoneuron survival was studied in Xenopus laevis tadpoles. Amputation of both hind limb buds at stage 49 before limb innervation begins caused the subsequent death of all motoneurons. This result confirms that there are no exceptions to the rule that developing motoneurons must contact the limb to survive. Partial removals of the limb at early stages of innervation caused the subsequent death of motoneurons that normally project to the deleted segments while motoneurons for the remaining segments survived. Before dying, the motoneurons deprived of their normal targets invaded the remaining limb segments thereby forming erroneous projections. Since the motoneurons died despite contacting limb tissue, it is concluded that they must be dependent on contact with specific limb regions and that errors of projection lead to death. Since large‐scale errors of the type induced by this experiment affect only a minority of developing motoneurons in normal embryos, the possibility of small‐scale errors is discussed in an attempt to equate all naturally occurring motoneuron death with error correction.
The afferent and efferent organization of the lateral geniculo‐prestriate pathways in the macaque monkey
Authors: Benevento L. A. , Yoshida K.
Published: May 2005

Both anterograde (autoradiographic) and retrograde (horseradish peroxidase) tracing techniques were used to identify and characterize projections from the dorsal lateral geniculate nucleus (DLG) of the thalamus to the subdivisions of occipital prestriate cortex (generally defined by areas 18 and 19) in macaque monkeys. It was found that the DLG projects to area 19 and the anterior portion of area 18 located on the lateral, ventral, and ventromedial surfaces of the hemisphere. There is a general topographical organization such that the medial portion of the DLG projects to dorsal prestriate located between the lunate and superior temporal sulci, while the lateral portion of the DLG projects to ventral prestriate extending from the inferior occipitotemporal sulcus. In contrast DLG inputs to the lunate, superior temporal, and inferior occipital sulci are limited in extent, and involve only a portion of the bank or shoulder of each sulcus which is continuous with the cortex located on the surfaces of the surrounding preoccipital gyri. The projection to the inferior occipital sulcus is more extensive than the ones to the lunate and superior temporal sulci and involves the floor as well as the ventral bank. This means that there are certain functional subdivisions, such as those located within the lunate (eg, visual area 2) and superior temporal sulici which do not receive DLG input. Regardless of the location of these projections the terminal pattern was the same and occurred in horizontally segregated “patches” which were restricted to layer V and the lower, adjacent portion of layer IV. In contrast, the projections from the nearby pulvinar to cortical layers IV, III, and I of the same prestriate areas do not overlap with those from the DLG. An attempt was made to identify possible afferent inputs to these DLG‐prestriate paths. The HRP experiments reveal that the DL‐Gprestriate cells are concentrated in the DLG interlaminar zones and that their distribution overlaps the distribution of terminals from the superior colliculus and, as shown previously, prestriate cortex. Intraocular injections of radioactive precursors demonstrated transsynaptic transport to a number of structures except prestriate cortex. While the latter result does not prove that the DLG‐prestriate cells do not receive retinal input, one conclusion is that the DLG‐prestriate projection could be organized like pulvino‐prestriate systems which receive their inputs from the midbrain and cortex.
Cholinergic and catecholaminergic afferents to the olfactory bulb in the Hamster: A neuroanatomical, biochemical, and histochemical investigation
Authors: Macrides Foteos , Davis Barry J. , Youngs William M. , Nadi N. Suzan , Margolis Frank L.
Published: May 2005

A series of neuroanatomical, biochemical, and histochemical studies have been conducted to determine the sources of cholinergic afferents to the main olfactory bulb (MOB) in the hamster. Following horseradish peroxidase (HRP) injections that are restricted to the MOB, retrograde neuronal labeling is observed bilaterally in the anterior olfactory nucleus, locus coeruleus, and raphe nuclei, and ipsilaterally in the ventral hippocampal rudiment, dorsal peduncular cortex, piriform cortex, nucleus of the lateral olfactory tract, anterior pole of the medial septal area and vertical limb of the diagonal band, nucleus of the horizontal limb of the diagonal band (HDB), and hypothalamus. Spread of HRP into the accessory olfactory bulb results in additional neuronal labeling ipsilaterally in the bed nucleus of the accessory olfactory tract, medial amygdaloid nucleus, and bed nucleus of the stria terminalis, and bilaterally in the posteromedial cortical amygdaloid nucleus. Retrograde tracing studies also have been conducted in cases with lesions in the basal forebrain or hypothalamus to assess the extent to which such lesions interrupt fibers of passage from other sources of centrifugal afferents, and the effects of such lesions on choline acetyltransferase (CAT) activity and catecholamine content in the MOB and on acetylcholinesterase (AChE) activity in the forebrain have been evaluated. Lesions in the basal forebrain reduce or eliminate CAT and AChE activity in the MOB in direct relationship to the extent of damage to the HDB. Norepinephrine (NE) content in the MOB also is reduced by basal forebrain lesions, but in relationship to damage of the medial forebrain bundle (MFB). The hypothalamic lesions have no effect on AChE activity in the forebrain or on CAT activity in the MOB, but they eliminate retrograde labeling in the locus coeruleus and raphe nuclei and reduce the NE content of the MOB to undetectable levels. The dopamine content of the MOB is not reduced by any of the lesions. Anterograde tracing studies have been conducted to compare the rostral projection patterns of the HDB with the distribution of AChE activity. Most of the rostrally directed axons travel in association with the MFB. A small component of axons travels in association with the lateral olfactory tract. Within the MOB, the axons terminate predominantly in the glomerular layer and in the vicinity of the internal plexiform layer. The projection and termination patterns of the HDB correspond well with the distribution of AChE activity. These various results indicate that the HDB is the major source of cholinergic afferents to the MOB.
Plasticity in a central nervous pathway in Xenopus: Anatomical changes in the isthmotectal projection after larval eye rotation
Authors: Udin Susan B. , Keating Michael J.
Published: May 2005

In this paper we present evidence that early eye rotation in Xenopus leads to anatomical rearrangements in a portion of the binocular visual system. In the past, electrophysiological mapping had shown that the topography of the ipsilateral visuotectal projection is changed by such eye rotation and that this change requires visual experience. However, knowledge of the anatomical basis for this electrophysiological change was lacking. The identification of the nucleus isthmi as a link in the projection has allowed us to study the topography of the ipsilateral system by use of horseradish peroxidase. We present data showing that early eye rotation alters the topography of the crossed isthmotectal projection. These results demonstrate that the orientation of a topographically organized projection can be changed by procedures which do not involve direct manipulation of the source, pathway, or target of the projection.
The accessory optic system of Rana pipiens: Neuroanatomical connections and intrinsic organization
Authors: Montgomery Neil , Fite Katherine V. , Bengston Lynn
Published: May 2005

The accessory optic system of Rana pipiens was investigated by autoradiographic, horseradish peroxidase, and Golgi techniques, revealing a complexity of neuroanatomical organization previously unrecognized. Retinal afferents project to the nucleus of the basal optic root (nBOR) via a primary bundle and more diffuse, medial bundle of optic axons, both of which contain large‐ and small‐diameter fibers. At least six types of retinal ganglion cell contribute to the basal optic root (BOR), including giant ganglion cells, two intermediate‐sized ganglion cell types, small ganglion cells, and two types of displaced ganglion cell. The major retinal projection is contralateral, but a small, ipsilateral component also exists. Afferents from neurons which are postsynaptic to the thalamic retinal terminal fields also reach nBOR.

Four distinct cell types were identified within the terminal field of nBOR: stellate neurons (63%), amacrine cells (19%), elongate neurons (14%), and large ganglionic neurons (4%). Both stellate and amacrine cells appear to be intrinsic neurons, while elongate and ganglionic neurons constitute the efferent neuron population of nBOR. In addition, cells which lie medial to the terminal field, pyriform and commissural neurons, send dendrites into nBOR. Pyriform neurons project to the nucleus of the medial longitudinal fasciculus (nMLF) and cranial nerve nuclei III and IV, while commissural neurons project to the contralateral nBOR. Large reticular neurons of the nMLF also send dendrites into nBOR.

Efferent projections from nBOR were observed in the large‐celled pretectal nucleus and in nucleus lateralis profundus. A second major projection originates from the peri‐nBOR region and is associated with the oculomotor system and with the nMLF. Efferent projections from the nMLF to the vestibular nuclei and to the rostral spinal cord were also observed, as well as projections which reach the brainstem from the large‐celled pretectal nucleus, the posterior thalamic and anterior mesencephalic central gray.
The central projections of trigeminal primary afferent neurons in the cat as determined by the tranganglionic transport of horseradish peroxidase
Authors: Marfurt Carl F.
Published: May 2005

The central projections of five peripheral branches of the trigeminal nerve were investigated by the method of transganglionic transport of horseradish peroxidase (HRP). In separate animals, the corneal, supraorbital, infraorbital, mental, or inferior alveolar branches were transected and soaked in concentrated solutions of HRP. Forty‐eight to 72 hours after surgery, the brainstem, upper cervical spinal cord, and trigeminal ganglia were perfusion‐fixed and processed according to the tetramethylbenzidine technique. The results show that trigeminal primary afferent neurons which innervate the cornea project mainly to the levels of caudal pars interpolaris and caudal pars caudalis. In contrast, trigeminal primary afferent neurons whose peripheral processes course through the supraorbital, infraorbital, or mental nerves project most heavily to the trigeminal main sensory nucleus, pars interpolaris, and the rostrocaudal middle three‐fifths of pars caudalis. Trigeminal primary afferent neurons which give origin to the inferior alveolar nerve project heavily and in approximately equal numbers of all rostrocaudal levels of the trigeminal brainstem nuclear complex (TBNC). A small number of fibers from each of the latter four cell populations project directly to the contralateral C1‐C2 dorsal horn. A small number of fibers from each cell population studied end in the reticular formation immediately adjacent to the spinal nucleus of V. It is concluded that the cornea and facial skin regions of the cat are represented nonuniformly along the rostrocaudal length of the TBNC.
Efferent systems of the rabbit visual cortex: Laminar distribution of the cells of origin, axonal conduction velocities, and identification of axonal branches
Authors: Swadlow Harvey A. , Weyand Theodore G.
Published: May 2005

Several efferent systems of visual area I in Dutch rabbits were studied with anatomical (horseradish peroxidase) and physiological (antidromic) methods. Anatomical studies provided information regarding the laminar origin of the projections to the contralateral hemisphere, visual area II, the dorsal lateral geniculate nucleus, and the superior colliculus. Physiological studies provided information regarding conduction velocities and multiple destinations of efferent axons. Both the callosal projection and the projection to V‐II were shown to originate primarily in layer II‐III. However, approximately 10‐20% of the callosal projection and 20–40% of the projection to V‐II originated in layers IV and V. In contrast, the projection to the dorsal lateral geniculate nucleus originated nearly exclusively in layer VI, while corticotectal neurons occurred primarily in layer V. A significant number of corticotectal neurons were, however, found in layer IV. Thus, the above efferent systems were found to differ in their principal laminar origin and in the diffuseness of that origin. The origins of corticocortical projections were considerably more diffuse than those of corticofugal projections.

In addition to differences in laminar origin, efferent systems also differed significantly in the conduction velocities of their axons. The projection to visual area II and to the lateral geniculate nucleus consisted primarily of very slowly conducting axons, while the projection to the superior colliculus was fast conducting. The callosal projection consisted of both slow and fast conducting axons. Finally, the question of branching of V‐I efferent axons was addressed. Although the laminar origin of the projections to the contralateral hemisphere and to visual area II overlapped considerably, none of these corticocortical axons could be shown to project to both locations or to a subcortical destination. In contrast, approximately one‐third of corticotectal axons were shown to project a collateral into the thalamus. Although the destination of this collateral is unclear, it is medial to the lateral geniculate nucleus and may be the pulvinar.
Uptake and localization of 3H‐2 deoxy‐D‐glucose by retinal photoreceptors
Authors: Witkovsky Paul , Yang Chen‐Yu
Published: May 2005

Following dark incubation of isolated retinas of Xenopus laevis in Ringer solution supplemented with 3H‐2 Deoxy‐D‐glucose (2DG), virtually all of the uptake of the label was by the inner segments and synaptic bases of the photoreceptor cells. Autoradiographs prepared from conventionally fixed tissue showed the same cellular distribution of label as those prepared from identically incubated, unfixed, freeze‐dried retinas. However, fixation removed about 77% of the total counts. This fixation‐labile, soluble fraction was identified as being primarily 2DG‐6 phosphate by thin‐layer chromatography. The remaining insoluble fraction corresponded in distribution to glycogen grains. In cones, glycogen is stored primarily in the paraboloid, whereas in rods it is distributed throughout the inner segment and synaptic base. EM autoradiographs illustrated that these were the sites over which fixationresistant 2DG label was localized. Measurements of radioactivity associated with extracts of retinal glycogen following 2DG incubation demonstrated that a disproportionately high fraction of total counts were associated with the glycogen fraction. We conclude that in the amphibian retina 2DG may be incorporated into glycogen.
The organization of binocular cortex in the primary visual area of the rabbit
Authors: Hughes A. , Vaney David I.
Published: May 2005

A conscious rabbit which crouches in the ‘freeze’ position has an unequivocal 24° wide binocular field formed by the overlap of the two 12° sectors of uniocular optical field which extend nasal of its midline. Although this investigation reveals that the horizontal representation of the uniocular visual field in cortical visual area I extends more nasal than in earlier reports, it is found to terminate at the midline when the eyes are set in the standard freeze position. The 12° sectors of uniocular field nasal of the midline were not represented in spite of being served by retina. The binocular field of the rabbit in the freeze posture thus appears to have no binocular representation in visual area I.

Nevertheless, the presence of a binocular region was confirmed in rabbit visual area I but the projections to it, via the contralateral and ipsilateral eyes, deal with the nonoverlapping sectors of monocular field when the eyes are in the freeze position. The maps of the visual field obtained in one hemisphere via the contralateral and ipsilateral projections were subject to a horizontal divergent disparity of some 18°. The presence of binocular single units in these regions was also confirmed but their two receptive fields were necessarily located in different visual hemispheres and again subject to an 18° mean horizontal divergent disparity. They could not be simultaneously stimulated by any localized feature of an object and are thus precluded from involvement in binocular single vision during the freeze position.

The systematic, rather than reportedly random, topography of the ipsilateral projection to visual area I ensured that it could be well fused with the similarly organized contralateral projection by means of an 18° vergence of the eyes from the freeze position. The horizontal receptive field disparity of binocular single units is then brought to a zero mean value which enables their receptive fields through each eye to be simultaneously stimulated by the same part of an image. Tested units then evinced response summation; a minimum requirement for binocular vision. In this equivalent primary position of the eyes, the entire binocular visual field is completely represented in visual area one of both hemispheres.

The rabbit thus appears to employ a two‐state cortical system for forward vision. In the freeze position the visual field attains a cyclopean extent of 360° but the receptive fields of cortical binocular units are widely divergent. The classic binocular optical field may then project to some other region of brain which subserves binocular vision. Upon examination of a frontal object the animal must verge its eyes in order to obtain binocular single vision in visual area I; it then temporarily surrenders part of its rear visual field. An explanation in terms of ocular image quality is suggested.
Axon morphology of mesencephalic trigeminal neurons in a snake, Thamnophis sirtalis
Authors: Dacey Dennis M.
Published: May 2005

The morphology of single axons of mesencephalic trigeminal neurons (Mes V) was studied in the eastern garter snake (Thamnophis sirtalis) by solid filling them with an extracellular horseradish peroxidase technique. Each Mes V axon can be divided into central, peripheral, and descending branches. The central branch descends from its soma of origin in the midbrain to the dorsal aspect of the motor nucleus of the trigeminal (Motor V) and the motor root, where it splits into peripheral and descending branches. The descending branch travels caudally from Motor V to the brainstemspinal cord junction. The peripheral branch passes dorsal to motor V and joins the motor root of V to exit the brainstem. All three branches issue a massive collateral system that distributes terminal swellings within the nuclear boundaries of Motor V. Single Mes V axons diverge to sparsely contact a large number of motoneurons throughout the nucleus, suggesting that single motoneurons receive a convergent input from many Mes V neurons. Since Motor V contains multiple, highly overlapping motor pools, single afferents are positioned to contact different motor pools. The descending branch is situated medial and adjacent to the spinal sensory nucleus of the trigeminal (Sensory V). It issues a collateral field to the entire length of Sensory V. The terminal swellings of these collaterals form rostrocaudally aligned sheets, flattened in the horizontal plane. Single terminal sheets have a divergent projection to a large field of sensory cells and single, fusiform sensory cells are positioned to receive a convergent projection from many terminal sheets.

The results provide the first detailed description of Mes V axon morphology. The overall pattern of these axons closely resembles that recently described for spinal Ia afferent fibers in cat. There is evidence in both cases for divergence of single afferent terminal fields to a set of spatially overlapping motor pools and a convergence of input to single motoneurons from a large population of afferents. This anatomical pattern is consistent with the recently proposed role of sensory feedback in the activity of single motoneurons.
Topography, cytoarchitecture, and sulcal patterns in primary somatic sensory cortex (SmI) of the prosimian primate, Perodicticus potto
Authors: Fitzpatrick Kathleen A. , Carlson Mary , Charlton John
Published: May 2005

The topographic organization of the primary somatic sensory projection area (SmI) in relation to cytoarchitectural fields and sulcal patterns was examined in the prosimian primate Perodicticus potto. The area of cortex responding to low threshold (LT) cutaneous stimulation of the glabrous and hairy surfaces of the hand was determined by microelectrode mapping techniques, with standardized threshold stimuli for defining receptive fields. A single somatotopic projection of the two hand surfaces was found; the glabrous projection area is rostral to that of the hairy hand. Within both the glabrous and hairy areas, receptive fields on the distal digits are found anterior to those on the proximal hand. The glabrous hand projection area is coextensive with a dense granular area typical of koniocortex. The hairy hand area corresponds to a cytoarchitectural field which is less granular than the glabrous field. While koniocortex occupies the crown of the gyrus caudal to the coronally oriented sulcus, a large more rostral field, which contains both granule and large pyramidal cells, occupies the whole of the caudal bank of the sulcus. Force thresholds of many receptive fields (RFs) in Perodicticus were high both on the borders and within the LT area (perhaps because of the advanced age of these animals). However, the receptive field sizes for both the glabrous and hairy hand areas were of the same magnitude as those of Nycticebus (Carlson and FitzPatrick, '82). From the combined studies of three species of Lorisidae, Perodicticus, Galago (Carlson and Welt, '80), and Nycticebus (Carlson and FitzPatrick, '81), using similar mapping and stimulation techniques, both general and specific features of SmI hand area organization can be illustrated. A single projection of the glabrous and hairy hand is common to Perodicticus and Galago, but two glabrous projection areas are seen in Nycticebus. The projection area for the hand in Perodicticus is twice as large (relative to brain size) as in Galago and Perodicticus. The possible behavioral significance of increased differentiation of the hand area in Nycticebus and elaboration of the area in Perodicticus could be examined by study of hand use and tactile capacity in these same spcies.
Localization of neurons afferent to the optic tectum in longnose gars
Authors: Northcutt R. Glenn
Published: May 2005

Afferent pathways to the optic tectum in the longnose gar were determined by unilateral tectal injections of HRP. Retrogradely labeled cells were observed in the ipsilateral caudal portion of the rostral entopeduncular nucleus and bilaterally in the rostral half of the lateral zone of area dorsalis of the telencephalon. The following diencephalic cell groups were also labeled following tectal injections: the ipsilateral anterior, ventrolateral, and ventromedial thalamic nuclei, the periventricular pretectal nucleus, and the central pretectal nucleus (bilaterally); the ventromedial thalamic and central pretectal nuclei revealed the largest number of labeled cells. At midbrain levels, retrogradely labeled cells were seen in the ipsilateral torus longitudinalis, nucleus isthmi, and accessory optic nucleus; cells were labeled bilaterally in the torus semicircularis and a rostral tegmental nucleus. Only a few cells were labeled in the contralateral optic tectum, suggesting that few of the fibers of the intertectal commissure are actually commissural to the tectum. At hindbrain levels, retrogradely labeled cells were seen bilaterally in the locus coeruleus, the superior, medial, and inferior reticular formations, the eurydendroid cells of the cerebellum, and the nucleus of the descending trigeminal tract; the contralateral dorsal funicular nucleus also exhibited labeling. Clearly, the tectum in gars receives a substantial number of nonvisual afferents from all major brain areas, most of which have been reported in other vertebrates. The functional significance of these afferent sources and their probable homologues in other vertebrate groups are discussed.
The location of cerebellar‐projecting neurons within the lumbosacral spinal cord in the cat. An anatomical study with HRP and retrograde chromatolysis
Authors: Grant G. , Wiksten B. , Berkley K. J. , Aldskogius H.
Published: May 2005

The locations of lumbosacral spinocerebellar neurons were examined by two anatomical methods in kittens. In one group of animals chromatolytic changes were provoked by cerebellar lesions. In another group horseradish peroxidase (HRP) was injected into the cerebellum. Projection laterality was investigated by making unilateral spinal lesions prior to the cerebellar HRP injections. Diaminobenzidine (DAB) or tetramethylbenzidine (TMB) was used as substrate for HRP. The morphological characteristics of HRP‐labeled neurons in the TMB‐processed material were examined.

Neurons marked by the two methods were located within the same regions. A greater number of cells were marked with the HRP method, however, than with the retrograde chromatolysis method. Spinocerebellar neurons were found in laminae IV–IX with large differences with regard to specific locations depending on segmental level. Numerous marked neurons were found in the following areas: laminae IV–VI in L3–L7, the column of Clarke in L3–L4, the medial part of lamina VII in L6–L7, the lateral part of lamina VII in L3–L4, the dorsolateral nucleus of lamina IX in L3–L6, the ventrolateral nucleus of lamina IX in L4–L5, and the ventromedial nucleus of lamina IX in S3 (and Ca1). Dorsally located neurons were in general more likely to project ipsilaterally than ventrally located neurons. Marked structural differences were frequently observed between spinocerebellar neurons in different locations.

These results provide additional information on the anatomical complexity of the spinocerebellar pathways from the lumbosacral region in the cat. Together with results from some other recent anatomical studies on spinocerebellar tracts, they also form a basis for further anatomical and physiological investigations which could contribute to a better understanding of the organization of the spinocerebellar tracts.
The midbrain periaqueductal gray in the rat, cat, and monkey: A Nissl, Weil, and Golgi analysis
Authors: Mantyh Patrick W.
Published: May 2005

Anatomical staining methods including Nissl, Weil, Golgi, and horseradish peroxidase stain have been used to elucidate the cyto‐ and myeloarchitectural organization of the periaqueductal gray in monkey, cat, and rat. From these various staining methods it appears that the periaqueductal gray is composed of a tightly packed group of cells, which show a slight increase in soma size, dendritic diameter, and degree of myelinization from central to peripheral borders. This central gray region contains a wide variety of cell types including multipolar, fusiform, stellate, and pyramidal neurons. Clearly delineated subnuclei, distinguished on the basis of soma size, dendritic arborizations, pigmentation, or evidence of cytological individuality could not be discerned in this study. Together with the immunohistochemical and connectivity studies the present data suggest that the neuronal organization of the PAG could be described as a mosaic of clusters of functional related neurons rather than as three distinct subnuclei, each with its own unique cytoarchitecture and connectivity.
Synaptogenesis and its relation to growth of the postsynaptic cell: A quantitative study of the developing mauthner neuron of the axolotl
Authors: Jacoby Jean , Kimmel Charles B.
Published: May 2005

We describe the relation between growth and branching of an identified dendrite and the formation of synapses on its surface during a 3 1/2‐day period early in development. We studied the lateral dendrite and the adjacent lateral perikaryon of the Mauthner cell (M‐cell) during embryonic stages 39–43 in the axolotl Ambystoma mexicanum. Reconstructions from light micrographs of serial sections through the cell revealed that during this interval the dendrite elongates rapidly, and large numbers of ventrally directed branches are formed. Samples of the same material by electron microscopy showed that large numbers of synaptic contacts appear during the same interval. We quantitatively estimated changes in local synapse densities (the number of contacts/100 μm2 of M‐cell surface) and local surface areas of the M‐cell and found that synapses were most densely clustered, and accumulated most rapidly, on regions of the cell that were rapidly expanding. These data are in accord with previous evidence from work in this and in other systems that synaptic contacts induce local growth of dendrites. Furthermore, the data are consistent with a proposal that outgrowth of new dendritic branches is induced or stabilized by synapses in a concentration‐dependent fashion.
Localization of methionine‐enkephalin, substance P, and somatostatin immunoreactivities in the main olfactory bulb of the hamster
Authors: Davis Barry J. , Burd Gail D. , Macrides Foteos
Published: May 2005

Methionine‐enkephalin, substance P, and somatostatin immunoreactivities are associated with different classes of neurons in the main olfactory bulb of the hamster. In the glomerular layer, methionine‐enkephalin immunoreactivity is observed in the somata and dendrites of periglomerular cells whereas substance P immunoreactivity is present in the somata and dendrites of external tufted cells. Substance P immunoreactivity may also be present in the superficial short axon cells. In the deeper layers, methionine‐enkephalin immunoreactivity is observed in a mixed population of neurons which appear to be primarily granule cells, whereas somatostatin immunoreactivity is present only in deep short axon cells. Methionine‐enkephalin‐, substance P‐, and somatostatin‐positive fibers of central origin are also observed in the main olfactory bulb.
Relation of medullary motor nuclei to nerves supplying the vocal tract of the budgerigar (Melopsittacus undulatus)
Authors: Manogue Kirk R. , Nottebohm Fernando
Published: May 2005

The locations of brainstem motor nuclei supplying efferents to organs of the vocal tract of the budgerigar (Melopsittacus undulatus) were determined as a first step in describing brain pathways for vocal control in this species. We identified four major nerves supplying the muscles of the syrinx, larynx, and tongue, and separately treated each of these with horseradish peroxidase. Nerves supplying efferents to the larynx and tongue arise from ipsilateral cells in the nucleus ambiguus and hypoglossal nucleus, respectively. Each right and left half of the syrinx is supplied by both right and left halves of the hypoglossal nucleus, via axons crossing in the common anastomosis of the tracheosyringeal nerves. This bilateral innervation of the syrinx will allow testing for central asymmetries of dominance for vocal control in the absence of any underlying anatomical laterality in the periphery.
Studies on cell migration and axon guidance in the developing distal auditory system of the mouse
Authors: Carney Paul R. , Silver Jerry
Published: May 2005

The events that take place along the potential route of distal auditory axons (future vestibular component) prior to and during their outgrowth were examined morphologically using timed mouse embryos. During embry‐onic (E) day 9.5 a discrete zone of cell death appears in the rostrolateral wall of the otic cup. Necrosis is accompanied by outward migration of epitheloid cells from the same region of the otic wall. Temporally and spatially corre‐lated with these two events is the widening of extracellular spaces between otic neuroepithelial cells and the breakdown of basement membrane. During E 10.5 migrating epitheloid cells condense to form a funnel‐shaped configu‐ration. This cellular “funnel” begins narrowly at the dorsorostrolateral wall of the otocyst and broadens as it reaches the auditory ganglion. During E 11.5 through E 12.5, “pioneer” distal auditory axons take a circuitous route and ascend from the auditory ganglion to enter the otocyst. Axons extend toward the otocyst moving along cells of the “funnel,” maintaining an orien‐tation similar to that of the cells that compose it. Axon growth cones enter the otocyst at sites devoid of basement membrane and invade the wall of the otocyst moving tangentially along radially arranged cells that bridge the otocyst and the “funnel.”

These observations demonstrate that a preformed, funnel‐shaped tissue exists along the future route of the auditory fibers. We suggest that the “fun‐nel” may influence the growth and directionality of distal auditory axons as they extend from the auditory ganglion to the wall of the otocyst. At the otic wall, the transition provided by “bridge” epitheloid cells, together with the absence of basement membrane at specific sites of the otic wall, provide the auditory axons with a route into the otocyst.
Atlas of catecholamine perikarya, varicosities and pathways in the brainstem of the cat
Authors: Jones Barbara E. , Friedman Lee
Published: May 2005

By application of a modified glyoxylic acid‐paraformaldehyde histoflu‐orescence technique, catecholamine perikarya, varicosities, and pathways were delineated within the brainstem of kittens that were either untreated, pretreated pharmacologically, or injected intracerebrally with 6‐OHDA. Three principal catecholamine cell groups were identified within the medulla and pons: the dorsomedial medullary cell group, the dorsolateral pontine cell group, and a ventrolateral cell group extending from the medulla into the pons. Induced axonal accumulation of catecholamines with intracerebral 6‐6‐OHDA injections revealed a major longitudinal catecholamine bundle which courses in a dorsolateral position through the entire brainstem tegmentum. The dorsomedial medullary and dorsolateral pontine cell groups contribute ascending and descending fibers to this bundle. Axons of the ventrolateral pontomedullary cells also feed into the bundle at successive levels through radially coursing transverse fibers. Via this major dorsolateral conduit and its ventrally and medially coursing tributaries, catecholamine fibers and terminals are distributed to multiple nuclei through the brainstem. The regions of the catecholamine cell groups and the serotonin raphe nuclei all receive a dense catecholamine innervation. Varicosities are also dense in the visceral cranial nerve nuclei, moderately dense in most somatic spinal and cranial nerve motor nuclei, and moderate to light in sensory cranial nerve and relay nuclei. The lateral and ventromedial reticular formation are moderately innervated by varicose catecholamine fibers that traverse these regions. The longitudinal catecholamine bundle continues caudally into the lateral funiculus to descend into and innervate the spinal cord. Rostrally it continues into the tegmental fascicles of the midbrain to ascend into and innervate the diencephalon and there join the medial forebrain bundle to ascend into the telencephalon. Thus, the catecholamine neurons utilize this dorsolateral longitudinal bundle to distribute collaterals to mul‐tiple bulbar nuclei and to travel beyond the brainstem to innervate the spinal cord and forebrain.
Four types of amacrine in the cat retina that accumulate GABA
Authors: Freed Michael A. , Nakamura Yasuhisa , Sterling Peter
Published: May 2005

Roughly one‐quarter of neurons in the amacrine cell layer accumulate exogenous γ‐aminobutyric acid (GABA). Some of these (8%) are interplexiform cells; the remainder are true amacrine cells. We partially reconstructed, from serial electron microscope autoradiograms, 25 GABA‐accumulating amacrines and distinguished four types based on cytoplasmic appearance, soma size and shape, and the form of primary and secondary processes. Type 1 had a large (609 ± 60 μm3), dark soma, and multiple, medium‐diameter (0.6 μm) processes splayed from the soma margins like the appendages from a crab. Type 2 had a medium (360 ± 40 μm3), helmet‐shaped, pale soma, and medium‐diameter (0.8 μm) processes that branched in sublamina α. Type 3 had a small (267 ± 44 μm3), dark, pyriform soma. The latter formed a single stout (3.0 μm) process that bifurcated in the middle of sublamina α. Type 4 had a very large, pale soma (860 μm3). This was pyriform, tapering into a stout (2.0 μm) process that descended into the middle of sublamina α where it emitted smaller tangential processes. It is to be expected that each of these amacrine cell types will have distinct functions in neurotransmitter retinal circuitry.
The relation of corpus callosum connections to architectonic fields and body surface maps in sensorimotor cortex of new and old world monkeys
Authors: Killackey H. P. , Gould H. J. , Cusick C. G. , Pons T. P. , Kaas J. H.
Published: May 2005

Corpus callosum connections of parietal and motor cortex were studied in New World owl monkeys (Aotus trivirgatus)and Old World macaque monkeys (Macaca fascicnlaris) after multiple injections of 3H‐proline and horseradish peroxidase, HRP, into one cerebral hemisphere, and extensive microelectrode mapping of architectonic Areas 3b, 1, and 2 of the other hemisphere. Results were obtained both from parasagittal brain sections cut orthogonal to the brain surface and from sections from flattened brains cut parallel to the brain surface. Cortical fields varied in density of callosal connections, and the density of connections varied according to body part within sensory representations. Thus, Area 3b had few, Area 1 had more, and Area 2 had relatively dense callosal connections. Within each of these fields, connections were much less dense for the representations of the glabrous hand and foot and much more dense for the representations of the face and trunk. For the representation of the hand, retrogradely labeled cells were extremely sparse in Area 3b, moderately sparse in Area 1, and moderate in Area 2. There were less dense callosal connections in the hand representations of Areas 3b, 1, and 2 in macaque as compared to owl monkeys. Label in posterior parietal cortex was uneven with zones of extremely dense connections. A large region of very dense callosal connections was noted in motor cortex just medial to the probable location of the hand representation. In all regions, callosally projecting cells appeared to be more broadly distributed than callosal terminations. In no region was the discontinuous arrangement of callosal connections obviously organized into an extensive pattern of mediolateral or rostrocaudal bands or strips.
Investigations on the development and topographic order of retinotectal axons: Anterograde and retrograde staining of axons and perikarya with rhodamine in vivo
Authors: Thanos Solon , Bonhoeffer Friedrich
Published: May 2005

Rhodamine‐B‐isothiocyanate (RITC) is shown to be a convenient and advantageous fluorescence tracer both for anterograde staining of retinal ganglion cell axons on the tectum and for retrograde staining of ganglion cell bodies in the retina of chick embryos. After intravitreal injection the dye is taken up by ganglion cells of the retina from the extracellular space and is transported anterogradely at about 10 mm/day up to the axonal growth cones on the tectum. RITC can be taken up by growing axons on the tectum and it is transported retrogradely at about 5 mm/day to the cell bodies in the retina. Local staining can be achieved if RITC is applied in its crystalline form. RITC is nontoxic for the cells and their axons, is resistant to histologi‐cal fixation procedures, and allows quick observation in vivo and on dissected stained tissue.

Local application of RITC to distinct retinal areas allows examination of the position of the corresponding stained fibers along the retinotectal pathway. Fibers which arise from the central temporal retina occupy deeper layers, whereas fibers from the peripheral temporal retina occupy more superficial layers in the optic tract and in the stratum opticum on the anterior tectum.

The growth cones of early retinal fibers growing directly on the tectal surface show a different morphology to later growth cones growing on top of the stratum opticum on the tectum.
The length of cerebellar parallel fibers in chicken and rhesus monkey
Authors: Mugnaini Enrico
Published: May 2005

The cerebellar parallel fibers, which course through the molecular layer parallel to the long axes of the cortical folds known as folia, originate from ascending granule cell axons and relay the mossy fiber input to dendrites of Purkinje cells. Purkinje cell axons in the cerebellar white matter collect into sheets or zones oriented at right angles to the folia. Each of these zones, which are approximately 0.5‐1 mm wide, innervates a different portion of the deep cerebellar and the vestibular nuclei. An experimental light microscopic study was carried out to determine the maximal length of parallel fibers in long folia of avian and primate cerebellar cortex. With a fine surgical knife, vermal folia were cut perpendicular to their long axes in four adult White Leghorn hens and in three adult rhesus monkeys deeply anesthetized with sodium pentobarbital. The animals were killed 3‐5 days after the operation. Sections of the transected folia were stained with the Fink‐Heimer or the DeOlmos‐Ir.gram methods, which revealed the anterogradely degenerated parallel fibers as darkly stained dots. In both species, the pattern of parallel fiber regeneration in the molecular layer had a trapezoidal configuration with the shorter base bordering the Purkinje cell layer and the longer base bordering the pia mater. In both species, the length of parallel fibers averaged approximately 6 mm, although the range was 4‐8 mm in chickens and 4.8‐6.6 mm in monkeys. The same trapezoidal pattern of degeneration and average parallel fiber lengths of 6 mm were obtained previously from long folia of cat and rabbit cerebella. Thus, parallel fibers show only small variation in their maximal length in relation to cerebellar size. In all the species studied, parallel fibers are consistently longer than the width of single efferent cortical zones, and they modulate the activity of Purkinje cells projecting to different groups of neurons in the deep nuclei.
Axons connecting somata and axon terminals of luminosity‐type horizontal cells in the turtle retina: Receptive field studies and intracellular injections of HRP
Authors: Ohtsuka Teruya
Published: May 2005

Luminosity (L)‐type horizontal cell responses to small and large spots of light in the turtle (Geoclemys) retina were recorded intracellularly, and each cell so studied was filled with horseradish peroxidase (HRP) by ionophoretic injection. Following histochemical reaction of the HRP with diaminobenzi‐dine (DAB), light microscopic inspection demonstrated that this type of horizontal cell has a cell body connected to a tuberous axon terminal by a fine axon. By examining the location of the cell in relation to the linear array of electrode penetrations in each preparation, it was possible to determine whether a given recording was made in the cell body or in the axon terminal. The size of the receptive field of the cell body was significantly smaller than that of the axon terminals. Although the center‐to‐center distances between the cell body and the axon terminal of some L‐type horizontal cells were as short as 50 μm, the length of the intervening axon was invariably longer and was at least 250 μm. Unless signals are amplified by some active mechanisms during their propagation along the axon, it is unlikely that current generated in the cell body spreads to the axon terminal through the thin axon, or in the opposite direction. The difference in receptive field sizes of cell body and of axon terminal may therefore indicate that these two structural subunits are electrically isolated.
The posteromedial ventral nucleus of the thalamus (VPM) of the cat: Direct ascending projections to the cytoarchitectonic subdivisions
Authors: Yasui Yukihiko , Itoh Kazuo , Mizuno Noboru , Nomura Sakashi , Takada Masahiko , Konishi Akika , Kudo Motoi
Published: May 2005

The post eromedial ventral nucleus (VPM) of the cat is divided cytoar‐chitectonically into the magnocellular (VPMmc), lateral parvocellular (VPMpcl), and medial parvocellular (VPMpcm) divisions. Cell bodies of neurons in the VPMpcm are small, while those in the VPMpcl are small to medium‐sized. The VPMmc contains large neurons.

Direct projections from the lower brain stem structures to each of the three divisions of the VPM were examined by the retrograde horseradish peroxidase (HRP) method. When HRP injection was done into the VPMmc, labeled neurons were mainly located conlralaterally in the ventral division of the principal sensory trigeminal nucleus (Vp), in the rostral part of the oral subnucleus in the spinal trigeminal nucleus (Vsp), and in the interpolar sub‐nucleus of the Vsp; a few labeled neurons were also found contralaterally in lamina I of the caudal subnucleus of the Vsp. When HRP injection was restricted to the VPMpcl or VPMpcm, HRP‐labeled neurons were mainly observed ipsilaterally, respectively, in the dorsal division of the Vp, or in the parabrachiaJ nucleus (PBN) regions dorsomedial and ventromedial to the brachium conjunctivum. After HRP injection into the parvocellular part of the VPM (VPMpc), labeled neurons were also seen contralaterally in the Vsp, but these were far less numerous than those seen after HRP injections into the VPMmc.

Thus, each of the three divisions of the VPM receives main ascending afferent fibers from different brain stem structures; the VPMpcm, VPMpcl, or VPMmc receives afferent fibers, respectively, from the PEN ipsilaterally, from the dorsal division of Vp ipsilaterally, or from the ventral division of the Vp and the Vsp contralaterally.