bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental reorganization of the cerebellar cortex. IV. Parallel fiber reorientation following regeneration of the external germinal layer
Authors: Altman Joseph
Published: January 2005

The heads of Long‐Evans hooded rats were irradiated with a schedule of low‐level x‐ray which allowed regeneration of the external germinal layer. In the subsequently regenerated molecular layer, parallel fibers were often reoriented. In some cerebella this was restricted to a single lobule, frequently several lobules were affected, rarely almost the entire vermis. It was postulated that the reorientation of parallel fibers was determined by the invasion route of multiplying cells from spared foci of the external germinal layer. Where parallel fibers were rotated transversely, the axons of basket cells and the arborizing dendrites of Purkinje cells became oriented longitudinally. This, and other considerations indicated that parallel fibers exert a guiding influence on the pattern of growth of the spiny branchlets of Purkinje cells.
Projections of individual axons in lamprey spinal cord determined by tracings through serial sections
Authors: Rovainen C. M. , Johnson Patricia A. , Roach Eileen A. , Mankovsky J. A.
Published: January 2005

The brain and spinal cord of one adult sea lamprey, Petromyzon marinus, 12 cm in length, were fixed in glutaraldehyde and osmium, stained in toluidine blue, embedded in Araldite, and sectioned serially at 5 μ. Over 50 large axons were traced through the spinal cord to their probable cells of origin.

The axon of one giant interneuron was followed from the posterior spinal cord rostrally into the lateral medulla of the brain.

A formerly unrecognized pair of Müller axons was found to originate from the reticular cells I2.

An unusual feature of some Müller axons was their migration out of the ventral columns and their subsequent branching.
Autoradiographic studies of the commissural and ipsilateral association connections of the hippocampus and dentate gyrus. I. The commissural connections
Authors: Gottlieb D. I. , Cowan W. M.
Published: January 2005

The commissural connections of the two major cytoarchitectonic fields of the hippocampus (fields CA1 and CA3) and of the dentate gyrus of the rat have been studied autoradiographically following injections of 3H‐leucine into the contralateral hippocampal formation.

The commissural projection to the dentate gyrus has its origin in the hilar region of the gyrus of the opposite side (probably from the pyramidal cells of subfield CA3c) and the majority of its fibers terminate upon a restricted segment of the granule cell dendrites (about 30 μ wide) in the inner one‐third of the molecular layer. Like the ipsilateral association pathway to this region, the commissural projection has an extensive distribution along the septo‐temporal axis of the gyrus. The commissural connections of field CA3 appear to be organized homotopically in the sense that each of its subfields seems to be related principally (if not exclusively) to the corresponding subfield on the opposite side. However, along the septo‐temporal axis of the hippocampal formation the commissural projection seems to be much more widespread, so that isotope injections into this field at any one level always give rise to transported label over a considerable rostro‐caudal extent on the opposite side. Within field CA3 the commissural terminals are confined to the region of the basal dendrites in the stratum oriens, and the middle portion of the apical dendrites in the stratum radiatum. Field CA1 does not appear to contribute to the commissural system: this is certainly true of its anterior portion which projects into the dorsal fornix rather than the fimbria, and may also hold for the posterior part of the field. Most, if not all, of the commissural fibers to field CA1 have their origin in field CA3 of the opposite side. After crossing the midline in the ventral hippocampal commissure, these fibers follow an intrahippocampal course which appears to parallel that of the Schaffer collateral system. Within field CA1 the crossed fibers terminate in relation to the basal dendrites and the proximal three‐fourths of the apical dendrites in the stratum oriens and the stratum radiatum.
Quantitative studies of transneuronal atrophy in the dorsal lateral geniculate nucleus of cats and kittens
Authors: Guillery R. W.
Published: January 2005

The transneuronal cell atrophy that occurs in the dorsal lateral geniculate nucleus after removal of one eye is more rapid in young than in adult cats. The change in the rate of the atrophic change continues well beyond the time at which geniculate cell growth has stopped.

In a three and a half month old kitten transneuronal cell shrinkage is clearly evident within three days on the side contralateral to an enucleation, but it does not appear clearly on the ipsilateral side until the twelfth post‐operative day. On both sides of the brain there is some apparent recovery and then a later, slower cell shrinkage. In a seven month old cat the cell changes are slower, and the two stages of the atrophy are less clearly distinguishable.

In the three and a half month kittens there is no significant differences between the atrophy that occurs in the binocular and the monocular parts of the nucleus and it is concluded that a binocular, or translaminar competition plays no part in producing the atrophic changes in these kittens. However, in a seven day old kitten removal of one eye appears to produce more severe atrophy in the binocular than in the monocular parts of the nucleus. Thus, a binocular competition, similar to that seen after a lid suture in seven day old kittens, may play a part in the transneuronal atrophy in these very young animals but not in older kittens.
The sensura neglecta in the pigeon: A scanning electron and light microscope study
Authors: Correia Manning J. , Landolt Jack P. , Young Eric R.
Published: January 2005

Both scanning electron and light microscopy have been used to observe the tiny sensura neglecta which is located in the inferior utricular sinus of the vestibular labyrinth in the pigeon. The following new observations were made. The end organ, which occupies one‐third of the floor of the inferior utricular sinus, is ovoid, measuring 200 μm in length × 80 μm in width and 30 μm in height. The neuroepithelium of the neglecta is uniformly innervated by the neglectar nerve which contains about 60 to 90 myelinated nerve fibers that fasciculate from the posterior ampullary nerve. The fiber spectrum is unimodal with a mode diameter of 1–2 μm. From 150 to 200 Type I and Type II hair cells are found on the surface of the neglecta. The surface features of the hair cells, i.e., the pipe organ patterns of the stereocilia are identical to that of the other vestibular sensory regions. No hair cells are found on the sides of the neglecta and all hair cells project their tufts upward from the top surface. The sensory region of the neglecta is covered by a gelatinous membrane. In no instance are statoconia observed on this covering. The non‐sensory epithelium contiguous to the sensura neglecta is comprised only of “light cells” (Dohlman, '67).

The above observations indicate that the sensura neglecta in the pigeon has both crista‐ and macula‐like features. It is hypothesized that this is reasonable from an evolutionary and teleological point of view. It is further suggested that regardless of its similarities to the statolithic and canalicular organs, the mode of stimulation of the neglecta can best be described by analogy to the culmen type of system associated with the auditory papilla of the lizard (Wever, '71).
A radioautographic study of the efferent pathways of the nucleus locus coeruleus
Authors: Pickel Virginia M. , Segal Menahem , Bloom Floyd E.
Published: January 2005

The projections of neurons in the nucleus locus coeruleus (LC) of the rat were traced by radioautography following stereotaxic injections of 3H‐proline. An ascending bundle consisting of a dense cluster of labeled axons accompanied the medial forebrain bundle (MFB) into the lateral hypothalamus. Rostral to the anterior commissure, the labeled fibers contributed to other major pathways: the stria terminalis to the amygdala, and the cingulum bundle and the supracallosal stria to the cingulate cortex, subiculum, and hippocampus. The rest of the ascending fibers terminated diffusely in the pyriform cortex and frontal neocortex. In addition, a lateral group of labeled fibers entered the cerebellum through the superior cerebellar peduncle and terminated around the Purkinje cell somata and in the molecular layer. Descending fibers which entered the medulla either terminated around brainstem nuclei or passed into the ventral portion of the spinal cord. In all areas except the brainstem, the labeling was unilateral with respect to the injection site. This distribution of label from LC provides direct confirmation for connections which have been difficult to visualize in their entirety by any other histological or cytochemical method.
Axonal proliferation following lesions of cerebellar peduncles. A combined fluorescence microscopic and radioautographic study
Authors: Pickel Virginia M. , Segal Menahem , Bloom Floyd E.
Published: January 2005

The hippocampus and the cerebellar cortex, two terminal fields of N. locus coeruleus (LC), contain increased adrenergic innervation 30 days after partial lesions of the superior cerebellar peduncle (SP). The qualitative observation of enhanced terminal fluorescence after lesioning was confirmed by counting terminals in the hippocampus and cerebellum labeled by radioautography after injection of 3H‐proline into LC of the rat. Use of the Vibratome method for catecholamine‐fluorescence permitted the observation of both fluorescence and labeled terminals in sections from the same animal. The increased terminal density in the hippocampus following partial SP lesions suggests that this growth may be initiated by retrograde changes within LC neurons or collaterals of the cut axons and does not require a prior denervation of the post synaptic cells.
Differences in membrane structure between excitatory and inhibitory components of the reciprocal synapse in the olfactory bulb
Authors: Landis Dennis M. D. , Reese T. S. , Raviola Elio
Published: January 2005

The reciprocal dendro‐dendritic synapse between granule and mitral or tufted dendrites in the external plexiform layer of the olfactory bulb consists of an excitatory mitral‐to‐granule synaptic contact and an adjacent inhibitory granule‐to‐mitral synaptic contact. The pre‐ and postsynaptic membranes of both synaptic contacts were identified in replicas of freeze‐fractured external plexiform layer in rabbits, mice, and chinchillas. At the excitatory synaptic contact there is a prominent specialization in the postsynaptic memberane, represented by an aggregate of homogeneous particles associated with the external half of the membrane. In contrast, the postsynaptic membrane at the inhibitory granule‐to‐mitral synaptic contact lacks evident internal specializations, and the distribution of particles on both fracture faces resembles that at non‐synaptic regions. Less marked differences in particle distribution characterized the cytoplasmic half of the presynaptic membranes. These differences probably reflect diversity in the nature or distribution of membrane proteins at excitatory and inhibitory synapses. Protuberances on the external half of the presynaptic membrane, possibly sites of vesicle interaction with the plasma membrane, surrounded but were not coextensive with both types of synaptic contact. A few gap junctions connected proximal dendrites of mitral or tufted cells with granule cell dendrites.
The specification of the retino‐tectal projection in the chick
Authors: Crossland W. J. , Cowan W. M. , Rogers Lynn A. , Kelly James P.
Published: January 2005

The specificity of the connections between the retina and the optic tectum has been studied in the chick by ablating between 15% and 75% of the optic cup (usually during the third day of incubation) and subsequently determining the distribution, within the tectum, of the synapses formed by the axons of the surviving ganglion cells. This was done towards the end of the incubation period, or shortly after hatching, either autoradiographically following the injection of a tritiated amino acid into the eye, or using a variant of the Nauta‐Gygax method after sectioning the optic nerve. In every case in which the initial retinal lesion was placed after Stage 12/13 (i.e., late on the second day of incubation) the surviving ganglion cells could be shown to have formed synapses in only a limited region of the contralateral optic tectum; and as far as could be determined from an examination of the cell loss in the isthmo‐optic nucleus (in which the centrifugal fibers to the retina have their origin) the remaining portion of the neural retina consistently projected only to the homotopic region of the tectum (i.e., the region to which it would normally have been expected to project). In several cases it was found that the axons had passed over a heterotopic region of the tectum in order to reach a more distant region in which they had formed synapses. After a lesion of the optic vesicle before Stage 11 the surviving ganglion cells appeared to innervate all parts of the tectum; since the earliest retinal ganglion cells are formed at Stage 11/12 it would seem that in the chick, as in Xenopus, there is a clear temporal co‐incidence between the withdrawal of the first ganglion cells from the cell‐cycle and the establishment of the topographic specification of the retino‐tectal projection.

Preliminary studies of the projection of the retina upon the optic tectum, and of the tectum upon the isthmo‐optic nucleus, in four to five week old chicks, indicates that the organization of these connections (and hence, presumably, that of the centrifugal fibers from the isthmo‐optic nucleus to the retina) is essentially the same as that in the pigeon. However, there is a significant difference in the overall morphology of the isthmo‐optic nucleus in the two species: as can best be seen in parasagittal sections, the isthmo‐optic nucleus of the chick lacks a well‐developed “anterior limb,” so that the representation of the horizontal meridian lies close to the junction of the “body” of the nucleus and its “posterior limb”.
Cell survival and architectonic differentiation of the hypothalamic mamillary region of the newborn mouse in culture,
Authors: Sobkowicz Hanna M. , Bleier Ruth , Monzain Rachel
Published: January 2005

The development of the hypothalamic mamillary region of the newborn mouse has been studied in 519 cultures. The nuclear groups of the mamillary configuration as well as the infundibular nucleus may survive for at least 50 days. The surviving neuronal groups undergo in culture a further cytological and structural organization. The presence of ependymal tissue at the surface of the substrate enhances ependymal‐glial proliferation and this in turn supports the survival and new growth of the nerve cells in the adjacent areas. On the other hand, degeneration of white matter, especially if it occurs between the substrate and the overlying neuronal groups, has a highly detrimental effect leading to a profound regional neuronal loss. The survival of neuronal groups, the new axonal growth and the preservation of the cellular architectonics, which make possible their identification in culture, indicate that the mamillary complex has a capacity for regeneration during its development in isolation. The mamillary region and the infundibular nucleus display different developmental patterns and different structural organizations of their cells and axons. As a result, the culture seems to be divided morphologically into two distinctly separate regions.
The distribution of the sensory input in the dorsal spinal cord of the tortoise
Authors: Rosenberg M. E.
Published: January 2005

The functional distribution of dorsal horn structures in the lumbo‐sacral spinal cord of the tortoise (T. graeca, T. hermanni) was determined by surface mapping of the cord dorsum potential in the decerebrate animal. Electrical stimuli were applied to either skin, peripheral nerve, dorsal roots or dorsal tracts. It was shown that the cord dorsum potential in this reptile could be interpreted in the same way as that in the mammal; this permitted identification of the primary volley separately from the consequent activity of post‐synaptic structures within the dorsal horn. The longitudinal distribution of post‐synaptic activity suggested that the associated structures are not distributed uniformly along the cord but rather have concentration maxima within segments in regions just rostral to the root entry zones. Combined transverse and longitudinal mapping revealed streaming of postsynaptic activity, traced over two or three segments, towards the mid line, when proceeding rostrally from a given root entry zone. The fact that this occurred for successive roots suggests that somatotopic representation exists in the transverse plane within the dorsal horn.

The longitudinal distribution of post‐synaptic activity suggested that the associated structures are not distributed uniformly along the cord but rather have concentration maxima within segments in regions just rostral to the root entry zones.

Combined transverse and longitudinal mapping revealed streaming of post‐synaptic activity, traced over two or three segments, towards the mid line, when proceeding rostrally from a given root entry zone. The fact that this occurred for successive roots suggests that somatotopic representation exists in the transverse plane within the dorsal horn.
An autoradiographic study of the efferent connections of the ventral lateral geniculate nucleus in the albino rat and the cat
Authors: Swanson L. W. , Cowan W. M. , Jones E. G.
Published: January 2005

The efferent connections of the ventral lateral geniculate nucleus (LGNv) of the albino rat and the cat have been studied using the autoradiographic method for tracing axonal pathways. Following the injection of 3H‐proline or 3H‐leucine into the LGNv of the rat, label transported in the rapid phase of axonal flow was found bilaterally in the olivary pretectal nuclei, the lateral terminal nuclei of the accessory optic system, and the ventral portion of the suprachiasmatic nuclei of the hypothalamus, and ipsilaterally in the rostrolateral portion of the superior colliculus. Since these regions are known to receive a direct projection from the retina, comparisons have been made of the distribution of silver grains in autoradiographs of each region following injections of 3H‐proline into the eye and into the LGNv; in every nuclear region except the superior colliculus the grain distributions were found to overlap precisely and, in the suprachiasmatic nuclei there also appears to be a similarity in the relative intensity of the input to the nuclei on the two sides. In the superior colliculus, the retinal fibers end mainly within the more superficial laminae, whereas those from the LGNv are distributed mainly to the deeper layers where they overlap the projection from the striate and peristriate cortex. The LGNv has also been found to project to the zona incerta on the same side and to the contralateral LGNv, In the cat a similar set of projections to the lateral terminal nuclei of the accessory optic tract, the suprachiasmatic nuclei, and the pretectal areas of both sides has been found, together with a projection to the ipsilateral superior colliculus and the zona incerta of both sides. No evidence could be found in either species for a projection from the LGNv to the visual cortex.
Topological analysis of the brain stem: A general introduction
Authors: Nieuwenhuys Rudolf
Published: January 2005

This paper introduces a research project within the framework of which the brain stems of twelve representative vertebrates will be analysed according to a new procedure termed topological analysis. The first part reviews the development of the concept that the brain stem essentially consists of a number of longitudinal zones or columns. From this review it appears that, although during the past 80 years a considerable amount of evidence favoring this concept has been accumulated, a number of important questions pertaining to number, delimitation and content of the zones in the brain stem are still awaiting a definitive answer. The second part of this paper is devoted to a detailed description and a critical evaluation of the topological procedure. This procedure, which has been especially designed to facilitate the study of the zonal pattern of the brain stem, essentially involves two steps. First the cell masses are projected back to their site of origin at the ventricular surface, and next the ventricular surface, with its sulci and the projections of the cell masses marked upon it, is flattened out, i.e., is subjected to a one‐to‐one topological transformation. In the third part of this paper the choice of the species which will be studied within the framework of our program is discussed. The species selected are: the lamprey Lampetra fluviatilis, the shark Squalus acanthias, the actinopterygians Acipenser fulvescens, Lepisosteus osseus and Salmo irideus, the brachiopterygian Polypterus ornatipinnis, the lungfish Lepidosiren paradoxa, the crossopterygian Latimeria chalumnae, the amphibians Ambystoma mexicanum and Rana esculenta, the turtle Testudo hermanni, and the opossum Didelphis virginiana. In the final part the objectives of the project are discussed. Most important among these are: (1) furnishing clear and succinct analyses of the brain stems of representatives of all groups of vertebrates, (2) specification of the fundamental plan of the brain stem, (3) facilitation of the establishment of homologies and simplification of the nomenclature and (4) presentation of a sound basis for experimental hodological work.
Catecholamine‐containing neurons of the nucleus locus coeruleus in the cat
Authors: Jones Barbara E. , Moore Robert Y.
Published: January 2005

The nucleus locus coeruleus of the cat brain was studied using the Falck‐Hillarp fluorescent histochemical method for the demonstration of cellular monoamines. In the cat, as in other mammals, the locus coeruleus is made up of catecholamine‐containing neurons. The cell bodies of these neurons are diffusely distributed in the dorsolateral pontine tegmentum, occupying a portion of the lateral central gray and extending laterally across the paralemniscal tegmental field to surround the brachium conjunctivum in its marginal nucleus. The neurons of the locus coeruleus are readily distinguished from others in the area in Nissl‐stained material as well as in that prepared by the Falck‐Hillarp method. No subdivisions of the nucleus are evident in either Falck‐Hillarp or Nissl stained material. The locus coeruleus nucleus appears to include those neurons previously identified as the magnocellular component of the marginal nucleus of the brachium conjunctivum and the Kölliker‐Fuse nucleus.
Postembryonic growth of the optic lobe of Octopus vulgaris, lam
Authors: Giuditta Antonio , Prozzo Nicola
Published: January 2005

The pattern of growth of the optic lobe of Octopus vulgaris has been investigated from 0.1 to 6.0 gms body weight by measuring the weight of the lobe and the number of nuclei present in the tissue homogenate. In the normal habitat, the rate of increase in nulcear number relative to increase in body weight is 1.32 up to 1.5–1.8 gms, but undergoes a three‐fold decrease above this size. On the other hand, the rate of increase in tissue weight remains essetially constant throughout the same period of development, with the exception of the interval between 1.0 g and 1.5 gms during which it rises markedly. Nuclear density increases steadily up to approximately 1.2 gms and approaches a constant value above this size.

In octopuses reared in transparent containers or under an opaque cover the rates of increment in number of nuclei and in tissue weight are generally lower than normal between 0.2 g and 1.5 gms. In both experimental conditions the wave of acceleration in the rate of increase of tissue weight occurring between 1.0 g and 1.5 gms in normal animals appears earlier particularly in octopuses reared under an opaque cover. At body weights larger than 1.5–2.0 gms the rates of increment in number of nuclei and tissue weight become higher than normal in octopuses reared in transparent boxes, but change in the opposite direction when rearing takes place in opaque containers. In the former condition, the nuclear density of newly added tissue starts decreasing earlier than normal but reaches a higher level at body weights above 2 gms, while in octopuses reared under an opaque cover the decrease occurs at approximately normal timing but attains lower values at higher body weights.
Age differences in the morphology of posterior tibial nerves of mice
Authors: Samorajski T.
Published: January 2005

Light microscopic examination of posterior tibial nerves of C57BL/10 female mice at 3, 8 and 26 months of age revealed an age‐related decrease in the total number of myelinated fibers per nerve with a fairly uniform loss across all caliber of fibers present. However, the size of the individual nerves increased with age as did also mean axon diameter of individual fibers and the proportion of connective tissue between fibers in the older nerves. Ultrastructural comparisons revealed an increase in mean axone circumference of myelinated fibers between 3 and 8 months and, of unmyelinated fibers between 8 and 26 months. Also, there was a significant decrease in mitochondrial concentration in myelinated fibers between 8 and 26 months of age. There was no change in blood vessels, myelin sheath thickness, concentration of unmyelinated fibers per nerve, and in the concentration of filaments and tubules in myelinated and unmyelinated axons in relation to increasing age.
Behavioral, electrophysiological and morphological studies of binocular competition in the development of the geniculo–corticalpathways of cats
Authors: Sherman S. Murray , Guillery R. W. , Kaas J. H. , Sanderson K. J.
Published: January 2005

Cats were raised with one eye sutured and with a lesion in the retina of the other eye. In these cats the competitive interaction between the pathways that go to the cortex from each eye was tested by studying the behavioral capacities, the electrophysiological responses and the morphological appearance of the geniculo‐cortical pathways.

Two parts of the visual system in which no binocular competition was possible were defined. One is the segment that receives inputs from the monocular crescent of the visual field, which has been called the monocular segment. The other is the artificial monocular segment created by the limited lesion of the non‐deprived retina, and this has been called the critical segment.

In the binocular segments of the visual pathways we found, as have others, that: (1) behaviorally, cats do not respond to objects viewed by the deprived eye; (2) cortical cells tend not to respond to stimulation of the deprived eye; and (3) geniculate cells innervated by the deprived eye grow less than the normally innervated cells. However, we found that the deprived eye is more effective in driving neurons in contralateral than in ipsilateral cortex.

Within the monocular and the critical segments of the visual pathways we found: (1) that cats orient appropriately to visual stimulation of the deprived eye, (2) that cortical cells respond to visual stimulation of the deprived eye, and (3) that geniculate cells grow more than the deprived cells in the binocular segment of the nucleus. Thus, the deleterious effects of visual deprivation of one eye can, to some extent, be prevented by damage to the other.
A multisomatic axon in the central nervous system of the leech
Authors: Frank Eric , Jansen Jan K. S. , Rinvik Eric
Published: January 2005

There is one particularly large axon in the medial bundle of the nerve cord of the leech. It extends along the entire length of the cord and is connected to a single cell body in each ganglion. The cell bodies in adjacent ganglia are tightly electrically coupled, and dye injected into one cell body can diffuse along the axon and into the cell body of the next ganglion. If the nerve cord is cut between two ganglia, neither end of the axon degenerates. Repair of the axon appears to occur by end‐to‐end fusion.
Deafferentation slows the growth of specific dendrites of identified giant interneurons
Authors: Murphey R. K. , Mendenhall Barbara , Palka J. , Edwards J. S.
Published: January 2005

The effect deafferentation has on the morphology of giant interneurons was studied in the abdominal nervous system of crickets (Acheta domesticus). The morphology of four uniquely identified giant interneurons was examined by iontophoresing cobalt chloride into the neurons of interest. A major source of afferents for these interneurons consists of mechanoreceptors located on paired abdominal sensory appendages—the cerci. Partial deafferentation of the giant interneurons was obtained by pinching off the cercus at hatching and maintaining the specimen in this deprived condition until adulthood.

The interneurons of three groups of animals were examined; control specimeans which were not treated surgically, unilaterally treated specimens which has single cercus removed and bilaterlly treated specimens which had both cerci removed. Two types of morphological changes were detected. (1) Chronic removal of a cercus was correlated with a reduction in length of dendrites ipsilateral to the ablated cercus; however the general form of the dendritic branching pattern remained constant and recognizable. Two dendrites of a single neuron could be influenced independently if they were innervated by separate cerci. Thus deprivation did not have a generalized effect on growth of a neuron, rather it specifically influenced the dendrites deprived of afferents. (2) it was also observed that the projection of cercal sensory fibers in specimens reared with a single cercus differed from normal in that scattered fibers cross the midline in regions of the ganglion where none usually exist. It is suggested that modifications in the response properties of these deprived neurons are based on these two changes in morphology.
The basilar pontine gray of the opossum: A correlated light and electron microscopic analysis
Authors: Mihailoff Gregory A. , King James S.
Published: January 2005

Neurons within the basilar pontine gray (BPG) of the American opossum can be subdivided into four major nuclei which are named medial, lateral, ventral and peripeduncular in accordance with previous studies. In addition, several smaller subnuclei, such as the median and dorsolateral cell groups, are present, as well as two longitudinal columns of neurons within the ventral nucleus. Neurons in the BPG range in size from 9 to 35 μ and appear randomly distributed so that none of the subdivisions contains exclusively nerve cells of the same perikaryal dimension. Projection neurons as shown in Golgi impregnations have a variable dendritic pattern; those in peripeduncular zones exhibit dendrites closely applied to the surface of the cerebral peduncle, whereas those in other regions generally have a radial type of arrangement. Certain projection neurons can be distinguished on the basis of their dendritic surface, which bears either claw‐like protrusions or stalked appendages. Smaller nerve cells measuring less than 18 μ may be intrinsic neurons, since axon‐like processes arise from their dendrites and course for some distance near the parent cell before becoming thin and beaded. Ultrastructural observations show profiles of neurons comparable in size to those seen in Golgi impregnations and suggest at least four classes of presynaptic profiles. One category ranges in size from 2 to 8 μ, contains round vesicles (average diameter 450 Å) and characteristically forms multiple asymmetric syaptic contacts with several small postsyaptic profiles, some of which appear to be the dendritic claws mentioned above. The other three types of axon terminals measure less that 2 μ in their greatest dimension and are distinguished by their synaptic vesicles; one group containing round vesicles with an average diameter of 380 Å, a second group exhibiting larger round vesicles with an average diameter of 500 Å and a third group containing flattened or eliptical vesicles. Transection of the superior cerebellar peduncle produces early filamentous and later electron dense degenerative chages in some, but not all, of the larger types of presynaptic profiles. Subsequent to large motor‐sensory cortex ablations both filamentous and dark degenerating profiles are simultaneously observed at all survival times. In one case with a cortical lesion restricted to the motor‐sensory cortex, mainly dark degenerating terminals are apparent in the ipsilateral pontine gray, whereas in a lesion confined to the visual cortex only filamentous degeneration was observed. It is suggested, therefore, that some of the dark degenerating profiles represent the terminals of collaterals of corticospinal axons and the filamentous boutons are terminal expansions of direct corticopontine fibers.
The role of supraspinal input in embryonic motility: A re‐examination in the chick
Authors: Oppenheim Ronald W.
Published: January 2005

The present experiments represent an attempt to further clarify the role of the brain in embryonic motility and behavior. By making high chronic cervical transections (“gaps”) at early prefuntional stages of incubation (i.e., 40–50 hours) and studying the subsequent emergence of motility in the chick it has been possible to determine that supraspinal input is not functional until about the tenth day of incubation. Acute cervical transections done at either 4–5 or 8–9 days lead to the same conclusion.

At ten days and thereafter chronic cervical transection results in a modification of the temporal pattern (rhythm) of motility without affecting the frequency of activity. Qualitatively the movements of spinal embryos are indistinguishable from controls up to 16–17 days. At that time there are detectable differences in the character of spontaneous movements, in reflex responsivity and in hatching behavior; spinal embroyos are not able to initiate the coordinated Type III movements necessary for escape from the shell.

Injection of strychinine into chronic cervical and control embryos at 10 days and at 16–17 days indicates that certain aspects of the typical strychnine response are lost following removal of brain input to the spinal cord.

Finally, chronic thoracic gaps result in a clear modification of cyclic motility at 7‐days of incubation, whereas chronic cervical gaps have no effect at this age. These data suggest that propriospinal integration is present at least several days prior to the onset of supraspinal input in the chick spinal cord.
Projections from the nucleus and tractus solitarius in the cat
Authors: Cottle Merva K. Warren , Calaresu Franco R.
Published: January 2005

After lesions in the nucleus of the tractus solitarius (NTS) in cats and kittens, the termination of degenerating fibers was localized using the Nauta and the Fink‐Heimer techniques. The distribution of degenerating fibers was compared with that seen after lesions of the dorsal nucleus of the vagus (DNV) and after section of the ninth and tenth cranial nerves. The projection from the NTS is to the nucleus ambiguus (A), the other divisions of the NTS including the medial NTS and the ventrolateral NTS, the DNV, the medial reticular formation ventral to the NTS (probably the paramedian reticular nucleus), the nucleus intercalatus (INC), and the intermediate nucleus (INT). The probable functional significance of projections from the NTS to these medullary nuclei is discussed in relation to pathways of cardiovascular reflexes. Of particular note is the projection to the INT which may be part of a descending pathway to spinal cardiovascular neurons in the intermediolateral horn.
Ascending projections from marginal zone (Lamina I) neurons of the spinal dorsal horn
Authors: Kumazawa T. , Perl E. R. , Burgess P. R. , Whitehorn D.
Published: January 2005

A search for postsynaptic elements, excited only by slowly‐conducting afferent fibers (Aδ and C), was made by recording from the dorsal horn of cats and monkeys with dye‐filled microelectrodes. Units identified by afferent responsiveness were tested for antidromic invasion by electrical stimulation of the opposite ventrolateral funiculus at the midcervical level. Recording points were marked by iontophoretically passing dye from the recording electrode and subsequently located in histologically‐prepared material. Evidence for antidromic excitation from spinal cord stimulation was found for five of 21 units in cat and 13 of 31 neurons in monkey. Antidromically excited cells were located within the distribution of the large posteromarginal neurons of the dorsal marginal zone (Lamina I). Although recording loci for a number of the elements studied were unequivocally located within Laminae II (substantia gelatinosa) or III, none could be antidromically excited. All antidromically driven units received a powerful input from Aδ primary afferent units and upon testing with natural stimuli responded specifically to stimuli of the type initiating activity either for high threshold mechanoreceptors or for low threshold thermoreceptors. It is concluded that some Lamina I neurons form part of an ascending projection which follows the spinal pathway of the spinothalamic tract and thereby contribute to the mechanical nociceptive and thermoreceptive features of this pathway. The absence of antidromic response is argued to be uncertain and evidence for a lack of projection is open to alternative explanation.
Mode of distribution of aminergic fibers in the cerebellar cortex of the chicken
Authors: Mugnaini Enrico , Dahl Anne‐Lise
Published: January 2005

The cerebellar cortex of adult hens contains a dense plexus of thin varicose nerve fibers which display a formaldehyde‐induced green fluorescence. This plexus is not distributed at random in the cortical layers. Within the granular layer the plexus forms a netlike pattern. The fiber branches, which have numerous varicosities, are predominantly oriented in the traverse plane of the folium. In the molecular layer the fluorescent plexus shows some variations in the convex, flat and concave portions of the folia. Many of the fluorescent branches are oriented parallel to the course of the folium. They arise from a T‐division of radially oriented axons resembling parallel fibers in Golgi sections.

The meshes of the fluorescent plexus in the granular layer measure 10–60 μ. In the molecular layer (top of the folia) there are about 30 fluorescent fibers per 100 μ2.

The fluorescent fibers originate from the locus coeruleus and form a rostral and a caudal bundle in the cerebellar peduncle.

The mode of distribution of the fluorescent fibers in the cortical layers seems to depend on the organization of the innervated tissue. Light microscopy suggests that the aminergic fibers innervate more than one class of cerebellar neurons.
An electron microscope study of the retino‐receptive layers of the pigeon optic tectum
Authors: Hayes B. P. , Webster K. E.
Published: January 2005

The fine structure of the superficial layer of the optic tectum of the pigeon, Columba livia, has been examined both in normal animals and after unilateral eye removal. Optic afferent terminals distributed throughout sublaminae IIa‐f, are principally concentrated at three depths in the retinoreceptive zone. At first, degeneration of optic afferent terminals occurs as swelling of synaptic vesicles and accumulation of neurofilaments and later as dense degeneration. There appear to be several classes of optic afferent terminals in the retino‐receptive zone, as would be expected from most previous studies of the avian tectum. The non‐optic components of the neuropil, which include glomerular and pleomorphic vesicle terminals, and the synaptic interrelationships between optic and non‐optic components are described. Optic afferent terminals mainly make synaptic contact with the branches of radial dendrites but also, in sublaminae IIb and IIc, with the dendrites of non‐radial cells. In sublamina IIc afferent terminals synapse onto the horizontal presynaptic dendrites of spindle cells and triplet synaptic arrays including optic afferent terminals, horizontal dendrites and radial dendrite profiles and radial dendrite profiles are found. This optic projection to non‐radial elements in IIb, c is discussed in relation to light microscope and electrophysiological studies.
The projections of different morphological types of ganglion cells in the cat retina
Authors: Kelly James P. , Gilbert Charles D.
Published: January 2005

The central projections of the retinal ganglion cells of the cat were examined using the method of retrograde transport of horseradish peroxidase. Peroxidase was injected into the lateral geniculate nucleus and into the superior colliculus by means of a recording micropipette. After injections at retinotopically homologous points in these two structures in separate animals, the patterns of retinal ganglion cell labeling were compared. We found that there were three populations of ganglion cells: small cells, that projected predominantly to the superior colliculus; medium‐sized cells, that projected predominantly to the lateral geniculate nucleus; and large cells, some of which projected to both structures, and some of which projected to the lateral geniculate nucleus alone. Quantitative studies showed that the average size of the cells in each population was smaller at the area centralis than in the periphery. These results could be directly related to physiological classifications of retinal ganglion cells proposed by other authors.
The effects of early tectal lesions on development in the retinal ganglion cell layer of chick embryos
Authors: Hughes W. Franklin , Lavelle A.
Published: January 2005

The possibility that the arrival of retinal ganglion cell axons in their efferent target field could influence the subsequent progress of cytomorphogenesis in the ganglion cells was tested by destroying all or portions of the primordial optic tectum at four or five days of incubation. The lesions were made essentially prior to the outgrowth of axons from the eye. Complete bilateral or unilateral destruction of the primordial tectal field did not detectably alter the morphogenesis of the inner retina or of the ganglion cells until 11 days of incubation. After this time, extensive loss of ganglion cells occurred within the retinas contralateral to the projection field that were destroyed. The cytology of this degeneration is described as seen with the light and electron microscope. After smaller lesions involving the anterior or posterior half‐tectum on one side, however, variable results occurred both in tectal development and in the retinal locus of ganglion cell degeneration observed in flat mount preparations. Many partial or punctate lesions, in fact, resulted in no detectable loss of cells from the ganglion cell layer. These results are discussed in regard to specification and possible regulatory capabilities of the tectum. Cell death in normal retinas, not previously reported in the chick, is also considered in relation to the experimental results.
Cell growth in the lateral geniculate nucleus of kittens following the opening or closing of one eye
Authors: Wan Yoke Kum , Cragg Brian
Published: January 2005

Closing one eye of kittens at 23 days after birth resulted in paler Nissl staining of the deprived cells in the lateral geniculate nucleus (LGN) that was detectable two days later. Differences between the two sides of the brain in mean cell area increased to a peak in binocular lamina A at 4–6 days after eyelid suture, and then fell to a trough at eight days before rising progressively to a higher level at 31 days. In lamina A1 the peak and trough were later.

Opening one eye of kittens after 23 days of binocular closure from birth resulted in more intense Nissl staining of the stimulated cells in the LGN that was detectable four days later. The stimulated cells grew faster than the cells connected to the eye that remained closed, and this differential growth reached a peak at 17 days in binocular lamina A and at 21 days in lamina A1 before falling to a trough at 26–31 days. These results are compared with the time course of anabolic changes that have been measured in other neurons during stimulation.

The coefficient of variation of cell size was computed and found to be slightly decreased for deprived cells and increased for stimulated cells. This suggests that larger cells change their sizes proportionately more than smaller cells. The cells were measured in frozen sections without shrinkage, and the areas are at least 25% larger than those reported previously after paraffin or celloidin embedding.
Auditory cortex in the grey squirrel: Tonotopic organization and architectonic fields
Authors: Merzenich Michael M. , Kaas Jon H. , Roth G. Linn
Published: January 2005

The representation of sound frequency within auditory cortex has been investigated with microelectrode mapping techniques in grey squirrels. The cyto‐ and myeloarchitecture of mapped cortical surfaces was examined and related to recording data. Among the results were the following: (1) A primary field can be defined on the basis of both physiological and anatomical criteria. It occupies nearly half of the auditory responsive area in the squirrel. (2) The best frequency of neurons is relatively constant within vertical penetrations across the active middle cortical layer(s) of the primary field. (3) Best frequencies ranging from 190 Hz to 33 kHz were defined within the primary field. There is an orderly representation of sound frequency (and of the cochlear partition) within the field, with lowest frequencies represented rostrally and highest frequencies represented caudally. A given frequency band (sector of the basilar partition) is represented across a roughly straight belt of cortex of approximately constant width that crosses the mediol‐lateral dimension of the primary field. There is a proportionately greater surface area of representation of higher frequency octaves within the field. (4) In different squirrels, there is significant variation in the location of the primary field and in the orientation of the frequency representation within it. (5) Auditory responses were recorded within at least two secondary auditory fields. The total region responsive to tonal stimulation approximately corresponded with the anterior temporal field, as defined by Kaas et al. ('72).
The olivocerebellar projection in the cat as studied with the method of retrograde axonal transport of horseradish peroxidase. II. The projection to the uvula
Authors: Brodal A.
Published: January 2005

Following injections of small quantities of horseradish peroxidase (HRP) suspension in the uvula of the cat, the distribution of labeled cells in the inferior olive has been mapped. The findings confirm the conclusion made on the basis of studies of retrograde cell loss in the olive following ablations of the uvula (Brodal, '40b) that two small olivary subdivisions, the nucleus β and the dorsomedial cell column project heavily to the uvula. In addition the HRP‐study shows that the uvula receives a smaller number of fibers from two circumscribed areas of the contralateral medial accessory olive. These areas appear to project to the lateralmost parts of the uvula (fig. 4). The findings thus support the presence of a longitudinal zonal subdivision in the uvula. Labeled cells are found in the nucleus β and the dorsomedial cell column also following injections of the fastigial nucleus and to a lesser degree of lobulus VII of the vermis (Hoddevik et al., '76). This may be due to collateral branching of olivary efferents. There is some evidence for a topographical correlation between dorsal and ventral parts of the uvula and rostral and caudal parts, respectively, of the nucleus β and the dorsomedial cell column. This may be related to functional differences between the two parts of the uvula.