bluuebunny/crossref_metadata_2025 huggingface dataset:
Anatomy of cultured mouse cerebellum. II. Organotypic migration of granule cells demonstrated by silver impregnation of normal and mutant cultures
Authors: Wolf Merrill K.
Published: December 2004

The architecture of presumptive cortex in whole mount Holmes impregnations of cerebellar cortex was reassessed in order to accomplish accurate identification of the granule cell neurons now known to be present there and to seek evidence concerning possible granule cell migration in vitro. The granule cells, although their processes failed to stain by Holmes' method, were recognized as a layer of naked nuclei of characteristic size, shape, and close packing. The gross foliar and sulcal architecture of cortex remained very immature, as it was when explanted. However, a substantial minority of cultures developed microscopic organotypic lamination characteristic of mature cortex, with molecular, granular, and Purkinje cell layers. All organotypically laminated areas showed anomalous twinning of the granular layer. In the reeler mutation of the mouse, the granule cell migration fails, producing an abnormal laminar pattern in adult cerebellum. Cultures of reeler cerebellum, although well developed in other respects, never showed any trace of cortical lamination, proving that the lamination seen in normal cultures must be produced by the migration which fails in reeler but succeeds in normal mice. This is reinforced by the twinning of the granular layer: any reasonable explanation requires organotypic migration of some of all granule cells. The preferred explanation involves specific geometrical deformation of the developing explant by angular rotation of presumptive cortex.
The organization of mechanoreceptive projections in the ventrobasal thalamus of sheep
Authors: Cabral R. J. , Johnson J. I.
Published: December 2004

To determine the arrangement of projections in the somatic sensory nuclear region in the thalamus of sheep, microelectrodes were used to locate and map neural units and groups of units responding to mechanical stimulation of peripheral receptive fields in nine animals anesthetized with Dialurethane. Most of the sensory nuclear region (70–80%) contains projections from ipsilateral oral and perioral fields, Of this volume 16–25% (10–20% of the total) was responsive to stimulation of tissues inside the mouth. The ipsilateral projections are organized differently than are the meager projections from contralateral fields. The contralateral projections are ordered in the same general pattern seen in other mammalian thalami, with caudal fields represented laterally in the nucleus, rostral fields medially, axial fields and maxillary‐nasal fields dorsally, and limbs and mandibular fields ventrally. In the ipsilateral projections, however, mandibular external fields are represented dorsally, and maxillary and nasal fields more ventrally. Still more ventral are projections from the teeth and palate, and most ventral is the representation of the tongue. In all of the ipsilateral projections, the more ipsilateral fields (fathest from the rostral midline) are represented more medially in the thalamus. The exaggerated relative volume of thalamus responding to stimulation of oral and perioral surfaces may reflect the behavioral specialization of a grazing animal.
The in vitro effect of the nerve growth factor on chick embryo spinal ganglia: An electron microscopic evaluation
Authors: Weis Peddrick
Published: December 2004

Chick embryo spinal ganglia, cultured with and without he nerve growth factor (NGF), were compared by means of electron microscopy with ganglia maintained in vivo for an equal period of time. The results confirm an earlier report that NGF maintains and stimulates only the later‐differentiating mesiodorsal neuroblasts. However, although these cells are stimulated to grow neurites four days prematurely, cytoplasmic maturation does not accompany the outgrowth.

The more‐differentiated ventrolateral neuroblasts all show some signs of degeneration after culturing with or without NGF. Those cells which appear normal in the light microscope failed to continue development like their in vivo counterparts and are seen to have myelin figures, marked indentation of the nuclear membrane, and chromatin clumping. Crystalloid structures originally observed by Crain et al. ('64) are demonstrated to be ribosomal crystals and are found only in hyperchromatic degenerated neuroblasts.

The satellite cells do not continue to develop in vitro. The process of encapsulatin neuroblasts ceases in both the mesiodorsal and ventrolateral areas of the ganglia. The interrelationship of satellite cell and neuroblast develoment is discussed.
An autoradiographic study of cellular proliferation in degenerating rat optic nerve
Authors: Skoff Robert P. , Vaughn James E.
Published: December 2004

Young adult rats were injected with tritiated thymidine, either before or after removal of one eye, to investigate: (1) the possibility of a leukocytic infiltration into degenerating optic nerve during the first six days following the operation, (2) the origin of the increased number of cells seen in degenerating tissue during the first few weeks after operation, and (3) the possibility of a change in the generation pattern of neuroglial cells in degenerating tissue. In order to investigate the possibility of a leukocytic invasion, rats were injected three times before enucleation to label a high percentage of circulating leukocytes while only labeling a few neuroglial cells. On the operated side of these animals, a small increase in the number of labeled cells above control values occurs only on the third day following enucleation. Another experiment shows that this increase can be explained by a change in the genratiion pattern of the neuroglial cells from two to four days postoperative (2–4 d.p.o.). In degenerating optic nerves, the number of labeled neuroglial cells increase almost tenfold in a 28 hour period from 2–3 d.p.o. While a week is required for a similar increase in normal optic nerve. From 1–3 d.p.o., astrocytes and astrocyte‐like cells constitute 30–50% of the labeled cells observed in a pulse label while the remainder of the labeled cells (unclassifiable neuroglia) cannot be categorized as either astrocytes or oligodendrocytes in light micrographs. Our autoradiographic and morphologic studies indicate neuroglial proliferation during the first two weeks of degeneration can account for the numerical increase of cells in optic nerves undergoing Wallerian degeneration. There is no evidence for an important infiltration of leukocytes and/or pericytes into the optic nerve.
Origin and distribution of the amygdalofugal pathways in the rat: An experimental neuronatomical study
Authors: Leonard Christiana M. , Scott John W.
Published: December 2004

The fields of origin of the amygdalofugal pathways in the albino rat were studied by using the Fink‐Heimer technique to stain degenerating fibers and terminals in brains of animals sacrificed four and seven days after small unilateral lesions of the amygdale. A surprisingly restricted field of origin was found for the supracommissural stria terminalis — the component projecting to the ventromedial nucleus of the hypothalamus Only a lesion in the most posterior part of the cortical nucleus produced degeneration in this pathway. The postcommissural stria terminalis which apparently distributes to the bed nucleus of the stria terminalis and preoptic area originates in a more widespread area including parts of both the basolateral and corticomedial complexes. Although intense terminal degeneration could be seen within the amygdala following all lesions, long fibers projecting into the anterior amygdaloid area, lateral preoptic area and lateral hypothalamus were found only after lesions in which fibers of passage from periamygdaloid cortex could have been interrupted. Convincing evidence, therefore, of a long axon ventral amygdalofugal pathway of the rat was not found in this study.
The olfactory connections of the lateral hypothalamus in the rat, mouse and hamster
Authors: Scott John W. , Leonard Christiana M.
Published: December 2004

The afferent olfactory connections of the lateral hypothalamus of the rat were studied by producing lesions of olfactory cortex and staining for degeneration by the method of Fink and Heimer ('67) and by electropysiological recording of responses to olfactory bulb shock and odor stimulation. Direct connections from olfactory areas were found only in a ventrolateral part of the medial forebrain bundle. In the posterior hypothalamus the olfactory fibers turned dorsally and terminated in a more medial area. The region from which strong olfactory responses could be recorded coincided with the path of degenerating axons. Lesions of the olfactory tuercle of hamsters and mice produced a similar restricted pattern of degeneration.
A mid‐aqueductal ependymal organ in the brain of the hyrax (Procavia capensis)
Authors: Quay W. B.
Published: December 2004

Serial sections of the brains of four adult male hyraxes revealed a hitherto undescribed ependymal organ near the middle of the midbrain aqueduct. This structural modification of the dorsal wall of the aqueduct is separate and different from both the subcommissural organ and the posterior collicular recess. It is characterized by: (1) an elaborate system of ridges and crypts, (2) numerous, crowded and distinctive ependymocytes, (3) tissue zonation, and (4) numerous vessels with sleeves of primarily longitudinally arranged glial processes. Comparisons with other ventricular organs and possible functional relations are discussed.
Corticobulbar projections of the marsupial phalanger (Trichosurus vulpecula). I. Projections to the pons and medulla oblongata
Authors: Martin George F. , Megirian David , Roebuck A.
Published: December 2004

A total of 27 adult phalangers was employed to investigate the pattern of neocortical projections to the pontine and medullary portions of the brain stem. Lesions restricted to neocortical areas rostral to the orbital sulcus resulted in fiber degeneration which distributed mainly to midline and medial areas of the pontine and medullary reticular formation. The greatest amount of fiber degeneration was located within the superior central nucleus, the nucleus of the pontine raphe, the nucleus pontis centralis oralis and the nucleus pontis centralis caudalis. However, a few degenerating fibers were present within the nucleus gigantocellularis and the magnocellular portion of the medullary raphe. In contrast, lesions which were located just caudal to the orbital sulcus resulted in fiber degeneration chiefly within the more lateral parvocellular reticular formation and within the subnucleus dorsalis of the nucleus medullae oblongatae centralis. In such cases, additional degenerating fibers were present within the dorsal column nuclei and within more medial areas of the reticular formation. In those brains with ventral parietal ablations, degenerating fibers were present within the chief sensory and spinal nuclei of the trigeminal complex and the closely adjacent reticular formation. All of the above neocortical lesions resulted in fiber degeneration within the basilar pontine gray. In those specimens subjected to caudal (striate and peristriate) or ventrocaudal (temporal) lesions, degenerating fibers were present within the basilar pontine gray, but not within other areas of the pons or the medulla oblongata.
Impulse conduction in the shrimp medullated giant fiber with special reference to the structure of functionally excitable areas
Authors: Kusano Kiyoshi , Lavail Matthew M.
Published: December 2004

The external potential field along the functionally isolated medullated giant fiber of the shrimp (Penaeus setiferus) was recorded during impulse conduction using 1 M NaCl‐filled glass capillary electrodes. The giant fiber displays no nodes of Ranvier, yet shows a conduction velocity greater than 90m/second at 20°C. Recordings from most parts of the myelin‐covered giant fiber surface showed only small monophasic positive potentials. However, at the areas of giant fiber‐motor giant fiber synapses and where giant fiber axons branch into abdominal ganglia, a small positivity was followed by a negativity (sink of the action current). The local application of action potential depressants to these areas abolished the negativity and converted it into positivity, and consequently impulse conduction was blocked. Application of the action potential depressants to other areas of the giant fiber did not block impulse conduction. The sink of the action current was not found from the axolemma in the myelin cylinder; this part of the axolemma together with the low resistance gap fluid simply serves as a passive current conductor. Light and electron microscopic studies of the two functionally excitable areas revealed the absence of a myelin sheath in some small areas of both regions. Thus, impulse conduction appears to be saltatory, and these excitable areas function as nodes of Ranvier.
The effects of chronic denervation on spindle discharge patterns and morphology in isolated costocutaneous muscles of garter snakes
Authors: Fukami Y. , Ridge R. M. A. P.
Published: December 2004

Experiments on spindles in normal and chronically denervated lateral costocutaneous muscles of snakes are described. The discharge patterns in response to stretch of tonic and phasic spindles are compared between normal spindles and those denervated for various periods of time. The main findings are that spindle function is lost after denervation periods of about 150 hours (the animal being kept at 30°C during the denervation period), and that prior to this (130–140 hours) both tonic and phasic spindles lose their ability to discharges; i.e., they become totally adapting.

Electronmicrographs, prepared mainly from material used in the physiological experiments, reveal certain structural changes occurring in parallel with the physiological changes. These consist of increase of neurofilaments, swelling and increasing electron density of mitochondria and appearance of electron‐dense bodies in the sensory ending; these changes occur at times when the spindles are still functioning, though in a modified way. Later the gap between nerve ending and underlying intrafusal fiber is invaded by satellite cell processes. Eventually the nerve endings totally disappear.
Synaptic development in long‐term organized cultures of murine hypothalamus
Authors: Masurovsky Edmund B. , Benitez Helena H. , Murray Margaret R.
Published: December 2004

Synapse formation and development were studied in organized cultures of mouse hypothalamic tissues from perinatal stages through a high degree of maturation during several months in vitro. Original explants from fetal and newborn animals were found to contain few definitive primordial synapses (ca. 4 per 10 grid‐squares); newly‐formed synaptic configurations began to appear with regularity in explanted tissues after the third day in vitro. These “immature” synapses contain small clusters of ∼ 300–600 Å agranular vesicles adjoining the presynaptic membrane, are usually devoid of mitochondria, and display diminutive junctional areas as yet little specialized. They are principally axodendritic, and may occur in the company of short, symmetrical, avesicular membrane‐junctions which link neuritic extensions.

By about one month in vitro a substantial increase in number of synapses (up to 25/grid square) as well as advances in degree of maturity are evident in the outgrown neuropil; axosomatic synapses are relatively less numerous, as in vivo. Synaptic junction complexes henceforth appear well developed, and the presynaptic portions of boutons terminaux and boutons en passant now contain mitochondria and numerous agranular vesicles (sometimes packed in crystalloid arrays). Glomerulus‐like profiles, synaptic spines displaying typical spine apparatuses, and multifarious synaptic complexes containing a variety of ∼ 500–1,400 Å granular vesicles are also in evidence. The impressive amount of synapse formation and degree of specialization observed here suggests the utility of such cultures as a model system for further hypothalamic investigations.
Topography and numerical distribution of neurons of the thoraco‐lumbar intermediolateral nucleus in the cat
Authors: Henry James L. , Calaresu Franco R.
Published: December 2004

Serial transverse sections of the spinal cord of eight adult cats were stained with thionin and examined to determine the topography of the thoraco‐lumbar intermediolateral nucleus (ILN) and the numerical segmental distribution of its neurons. The ILN was found to extend from C8—T1 to L4 and to be located within the lateral horn of the grey matter except in segments C8—T1 and L1—L2 where neurons were observed scattered throughout finger‐like projections of the grey matter. The total number of neurons ranged from 32,790 to 53,340. The mean counts of neurons on the left and right sides were not significantly different. A statistically significant (p < 0.02) difference, however, was demonstrated between the mean counts in four female cats (35,543 ± 1,411) and those in four males (45,765 ± 2,556). The number of ILN neurons was found to vary considerably from segment to segment, with the highest counts occurring in segments T1—T2 and L3—L4. Quantitative estimates of cell sizes were also obtained from one male cat. The modal cross‐sectional area was found to be 290 μ2. The data reported provide a useful map for neurophysiological studies of this nucleus. In addition, the demonstration of a sex difference in the number of ILN neurons suggests that the number of neurons in the mammalian central nervous system may be different in the two sexes.
Control of myelin formation by axon caliber. (With a model of the control mechanism)
Authors: Friede Reinhard L.
Published: December 2004

The relation between the growth of axons and the development of their myelin sheaths was determined in rats for normal, myelinating sciatic nerves, and for an experimental model allowing to retard or accelerate axon growth. Axon caliber was measured, and sheath development was determined from measurements of thickness (light microscopy), from counts of the number of turns of myelin lamellae (electron micrographs), and from the rate of the incorporation of acetate‐H3 into ether‐ethanol extractable lipids. An excellent correlation between changes in sheath thickness and acetate‐H3 incorporation was obtained for all experiments. For the myelinating nerves the changes in the rate of acetate‐H3 incorporation were related specifically to the rate with which new length of myelin leaflet was added to the existing turns of sheath.

The rate of axonal growth was manipulated by applying a snug ligature around the nerve by the fourteenth day, allowing the nerve to compress itself by its own growth. Most axons passed the constriction without interruption, but they were markedly hypoplastic distal to the constriction. After removal of the ligature these axons regrew to their normal caliber ranges. Examination of myelin sheath development in this model showed that retardation of axon growth retarded sheath growth, while acceleration of axon growth accelerated sheath growth. Thus, the rate of axon growth appeared to be the factor controlling the rate of myelin formation by the sheath cells.

An appendix describes a model consisting of two interrelated feedback mechanisms by which expansion of the axon may directly control the number of turns of myelin lamellae formed by the sheath cell. The model correspons on all points to established features in the fine structure of fibers.
The synaptic glomerulus and the intrinsic neuron in the dorsal lateral geniculate nucleus of the cat
Authors: Famiglietti Edward V. , Peters Alan
Published: December 2004

The morphological characteristics of Class III, Golgi Type II neurons are analyzed in Golgi impregnations of the lateral geniculate nucleus (LGN) in the cat with special attention given to the complex dendritic appendages of these cells, the multilobed dendritic terminals. In addition, electron microscopic studies demonstrate the presence of presynaptic dendritic (ID) terminals as major components of synaptic glomeruli. Electron microscopic analysis of serial thin sections confirm the dendritic origin and the complex, multilobed nature of these terminals. An hypothesis is proposed identifying the ID terminal with the multilobed dendritic terminals of light microscopically identified Class III cells and the IA terminal, the “peripheral axon” of the glomerulus, with the axonal endings of all Golgi Type II cells.

The Class III neuron has a short axon ramifying near the cell of origin. The axon terminates in boutons en passant and boutons terminaux: single, bilobed or “claw‐like” endings. Optic axons terminate not in “claw‐like” fashion, as previously thought, but in club‐shaped endings with scalloped silhouettes. The principal dendrites of Class III cells are characterized by long‐stalked appendages, often multilobed and occurring at the end of preterminal stalks 5 to 100 μ in length. One impregnated multilobed terminal studied in the electron microscope was found to innervate two adjacent glomeruli.

The relationship of ID terminals to optic axon terminals and to other processes in synaptic glomeruli is analysed with the aid of the electron microscope. The ID terminal contains vesicles of the same size as those in presynaptic dendrites and makes small, macular synaptic contacts with other pre‐ and postsynaptic dendrites. ID terminals are the only elements in the LGN which synapse on others of their own kind, and are postsynaptic to all types of axon identified. As the only postsynaptic processes containing synaptic vesicles in the dorsal layers of the LGN, they support the conclusion that there are no axo‐axonic synapses in these layers. The ID terminal, the optic terminal and spinous dendrites originating presumably from geniculo‐cortical relay (GCR) cells, are seen to enter into a triadic relationship characteristic of the synaptic glomerulus in which the presynaptic dendrite synapses on the spinous dendrites and the optic terminal synapses on both dendrites. ID terminals reconstructed from serial sections communicate as “internuncial” presynaptic dendrites between optic central axons in adjacent synaptic glomeruli. IA terminals, which like ID terminals contain flattened vesicles, are presynaptic to ID terminals, as well as to postsynaptic dendrites, cell somata and axon initial segments.

A model for the internuncial character of multilobed dendritic terminals and the potential for inhibition of Golgi Type II axon terminals is proposed, and theories about the function of Golgi Type II cells in lateral geniculate transmission are briefly considered.
Projection of the cochlear nuclei on the inferior colliculus in the cat
Authors: Osen Kirsten Kjelsberg
Published: December 2004

The present study was carried out in order to define the topographical organization and the cells of origin of the second order auditory fibers terminating in the inferior colliculus. The findings are based on anterograde fiber degeneration studies in Nauta preparations of adult cats following stereotactical lesions of the cochlear nuclei, and on retrograde cell degeneration studies in Nissl sections of kittens following transection of the ascending auditory fiber tracts. Both the dorsal and ventral cochlear nuclei were found to contribute fibers to the central nucleus of the contralateral inferior colliculus in a definite topographical order supporting the tonotopical organization of the inferior colliculus revealed physiologically by Rose, Greenwood, Goldberg and Hind (′63). The fibers leading to the inferior colliculus from the dorsal cochlear nucleus, undoubtedly originate in the pyramidal cells, while no definite conclusions could be drawn regarding the cells of origin of fibers derived from the ventral cochlear nucleus.
The effects of dorsal root lesions on Clarke neurons in cats of different ages
Authors: Loewy Arthur D.
Published: December 2004

The transneuronal effects of dorsal root lesions on Clarke neurons in cats of varying ages were studied. Chromatolytic and degenerative lumbar Clarke neurons were observed 5 to 15 days following dorsal rhizotomy from the lower thoracic to the coccygeal levels in the adult cat. Fiber degeneration was seen in the ipsilateral dorsal and dorsolateral columns in the cervical spinal cord. The finding of fiber degeneration in dorsolateral columns is supportive evidence for the hypothesis that the chromatolytic and neurofibrillar hypertrophic neurons are the result of ischemic myelopathy or direct surgical trauma to the lateral columns during the dorsal root surgery. Within 15 days post‐operatively, degenerative changes were not seen in lumber Clarke neurons when the dorsal root lesions were begun at the L 4 level.

The effects of dorsal root lesions at different ages with an increased postoperative survival period were studied. Unilateral dorsal rhizotomies were done beginning at the L 4 level in kittens of two, four, and six weeks of age and adult cats. The degree of mean perikaryal and nuclear shrinkage in Clarke neurons was determined from Nissl preparations after these cells were partially denervated. The kittens of each age group showed approximately the same area reduction, and the adult cats did not show this shrinkage. It is deduced that the differentiation of Clarke neurons is almost completed by two weeks of age and that partial dorsal root denervation causes an arrest of growth rather than a transneuronal atrophy.
Blood supply to primitive mammalian brains
Authors: Gillilan Lois A.
Published: December 2004

Brains of mammals are supplied by paired internal carotid arteries and also by paired vertebral arteries. The internal carotids distribute to the forebrain with its developing neopallium. The hindbrain with the expanding cerebellum and newly acquired middle cerebellar peduncle are supplied by the vertebral‐basilar system. In the opossum and armadillo the caudal rami of the internal carotid arteries resemble the patterns seen in submammals. The major source of blood to the posterior cerebral arteries is variable, coming from the basilar, the internal carotids or both. The ventral arterial circle (circulus arteriosus) is open as there is no anterior communicating artery in the two forms described. With the increase in size of the lateral lobes, the cerebellum of lower mammals is sufficiently larger and better developed to require a pair of inferior cerebellar arteries in addition to the phylogenetically older superior cerebellar arteries which originate from the basilar trunks. The latter are formed by the bifurcation of the basilar artery. The tectum in these forms is supplied by branches from the posterior cerebral and superior cerebellar arteries as well as tectal rami arising from the basilar trunks. Branches of the basilar artery going to the brainstem have a branching pattern similar to that seen in the submammals.

The intrinsic patterns in both the opssum and armadillo are essentially like those observed in all vertebrates. They are remarkably constant and are easily recognized from one form to another. The arterioles penetrating the armadillo brain terminate in a continuous capillary plexus like the intrinsic plexuses observed in most of the submammals as well as in all mammals except marsupials. Arterioles penetrating the brain of the American opossum, as well as of all other marsupials, do not form a capillary plexus but terminate in capillary loops. Every penetrating arteriole is accompanied by a venule; each pair of vessels terminates in one or more capillary loops, thus constituting a true end‐system. However, as in the rest of its body, capillaries in the infundibular process and stalk, choroid plexuses, area postrema, supraoptic crest and subfornical organ are not paired but form freely anastomosing plexuses.

The major developmental advance, i.e., the “mammalian shift,” in the blood supply to brains of primitive mammals is the addition of the vertebral arteries to supply the brainstem and an inferior cerebellar branch going to the cerebellum. The implications of these phylogenetic changes are discussed and related to the functional development.
Postnatal development of the cerebellar cortex in the rat. I. The external germinal layer and the transitional molecular layer
Authors: Altman Joseph
Published: December 2004

The multiplication of cells in the proliferative zone of the external germinal layer and the early steps in the differentiation of basket, stellate and granule cells were studied in the cerebellar cortex of rats aged 0, 3, 5, 7, 10, 12, 15, 21 and 30 days with histological, histochemical, autoradiographic and electron microscopic techniques. Between 0–9 days the proliferative zone has a constant depth of four to five cells; the bipolar cells in the underlying premigratory zone increase in depth during this period from 0–6 cells. Thereafter, there is a decline in the cell depth of both zones. In the premigratory zone there is a gradient in the length of the extruded processes of the bipolar cells (concentration of such profiles), the future parallel fibers. Presumably when the latter reach their final length, the cell body migrates downward and the parallel fiber becomes part of the upper zone of the molecular layer.

Thus, parallel fibers are progessively formed on the surface of others from the bottom upward by a stacking process and the external germinal layer, as a consequence, is continually pushed upward. This design makes possible the assembly of a matrix of very long, thin and straight beams of horizontally oriented parallel fibers which pile up vertically according to their age. When synaptogenesis starts during the second week in the molecular layer the enlarging junctional processes produce a spurt in the growth of this layer.

Basket cells which are formed in the pyramis on days 6–7 are arrested in the formative molecular layer because their processes are oriented at a right angle to the underlying bed of parallel fibers. Therefore, there is also a stacking of the cells of the molecular layer from the bottom upward as a function of time of onset of their differentiation. Parallel fiber synapses may be seen on differentiating basket cells as early as the seventh day, forming connections with these inhibitory interneurons before they synapse with spines of Purkinje cells.
The fine structure of glial cells in the chicken
Authors: Lyser Katherine M.
Published: December 2004

The glial cells of the chicken spinal cord and optic nerve, studied after aldehyde fixation, are comparable in fine structure to those of mammals and other vertebrates. Most astrocytes are characterized by an overall low density and cytoplasmic filaments, which vary in quantity and may occur in prominent bundles or may be scattered. Particular features in the chicken include the observations that the lumbar level of the spinal cord seems to be the only region, of those studied, in which astrocytes contain glycogen particles. Astrocyte processes with very dense cytoplasm, in addition to typical light ones, were observed, particularly in the glia limitans. Oligodendrocytes are characterized by a greater overall density, more extensive granular endoplasmic reticulum, more numerous microtubules, and absence of cytoplasmic filaments. The variations in cell type involve mainly the granular endoplasmic reticulum, ranging from short, scattered to long, stacked cisternae, and the texture of the nuclei.
Development of the cetacean spinal cord
Authors: Sinclair John G.
Published: December 2004

Embryos of dolphins and whales have been studied in sectional series ranging from 4.2 mm to 95 mm crown rump (CR) in length. The species include Stenella ceruleoalbus, Prodelphinius ceruleoalbus, Escherichtius robustus, Physeter catodon. Development of the spinal cord is similar in all these forms and differs from that of the seals and primates largely in the much slower expansion of the brain and eyes. By a 26 mm CR stage the lumbar swelling is relatively suppressed, but is still evident at the 95 mm CR length. This retention is based on the development of the tail muscles and the profuse autonomic system. The dorsal horn also is repressed, probably because of the relatively insensitive trunk skin. Paired intravertebral vessels form a blood reservoir, particularly in the thoracic region, but still large to lumbar levels.
Experimental reorganization of the cerebellar cortex. I. Morphological effects of elimination of all microneurons with prolonged x‐irradiation started at birth
Authors: Altman Joseph , Anderson William J.
Published: December 2004

The heads of Long‐Evans rats were irradiated from birth with a schedule of repeated doses of low‐level x‐ray which prevented the acquisition of the postnatally‐forming basket, stellate and granule cells. The absence of these microneurons led to several changes in the organization of the cerebellar cortex, studied at 30 days of age with light and electron microscopy. The somata of Purkinje cells were not strung out in a monolayer. Their primary dendrites were randomly oriented and arborized differently depending on the position of their somata in the depth of the cortex. Many Purkinje cell perisomatic processes, normally seen only in infants, were retained. Climbing and mossy fibers formed inconspicuous, symmetrical synapses with the somata and conspicuous, asymmetrical synapses with the perisomatic processes and dendritic thorns of Purkinje cells. Massive Purkinje cell dendrites with innumerable thorns made up much of the neuropil of the cortex. The dendritic thorns, in addition to forming true synapses, also established pseudosynapses with glial processes and synapses devoid of vesicles with the surface or the interior of Purkinje cell dendrites. The latter type of contact apparently led to autolysis of part of the dendrite, which was the only clear pathological phenomenon observed. These results indicated considerable autonomy in the growth of Purkinje cell dendrites, which arborized richly and sprouted innumerable small processes in the absence of parallel fibers, and formed postsynaptic dense membranes in contiguity with inappropriate processes, such as those of Purkinje cells or astrocytes.
Relationship between the septum and the cingulate gyrus in Macaca mulatta
Authors: Kemper Thomas L. , Wright Sanford J. , Locke Simeon
Published: December 2004

The relation between the lateral septal nucleus and the cingulate cortex of the monkey was investigated by the technique of retrograde cell degeneration. One hemidecorticate animal in which the gyrus cinguli was relatively preserved showed no cell loss in the lateral septal nucleus. Three animals, two with bilateral anterior cingulate gyrus lesions and one with a posterior cingulate gyrus lesion, showed cell loss in the lateral septal nucleus. These findings suggest that in the monkey there is a projection from the lateral septal nucleus to the gyrus cinguli.
The nucleus basalis of the pigeon: A single‐unit analysis
Authors: Witkovsky Paul , Zeigler H. Philip , Silver Rae
Published: December 2004

Single unit responses were recorded from neurons in the nucleus basalis of the pigeon. Two hundred and twelve basalis cells, from 23 birds, were characterized in terms of modality, receptive area and adaptive properties. Most basalis units (97%) fired spontaneously in bursts of a few spikes separated by one to two seconds of silence. All units were activated by light mechanical stimulation of the beak or buccal cavity. The units adapted rapidly to a maintained stimulus, but fired vigorously when the stimulating probe moved back and forth across the surface of the receptive area. Receptive fields fell into two clearly separable groups with respect to size: small fields, less than 15 mm2, generally clustered near the beak tips, and large fields occupying from one‐third to the entire beak surface. Both unilateral (ipsilateral or contralateral) and bilateral receptive areas were encountered. Nucleus basalis units could be driven electrically by stimulation of the beak surface or the main sensory trigeminal nucleus (PrV). The data suggest that n. basalis cells are particularly responsive to movement of food (grains) within the mouth and that this information is relayed by trigeminal afferents to the PrV, thence to the n. basalis via a partially decussating quinto‐rontal tract. The results are discussed in relation to the role of the n. basalis in the control of feeding behavior in the pigeon.
The mode of innervation of the dorsal lateral geniculate nucleus and the pulvinar of the rabbit by axons arising from the visual cortex
Authors: Giolli Roland A. , Pope James E.
Published: December 2004

Sections prepared by the Nauta method were used to study the fiber degeneration in the dorsal lateral geniculate nucleus and the pulvinar of the rabbit after lesions in the visual cortex, and sections processed by the Golgi and the Cajal methods provided the material needed to study the normal fiber architecture of these nuclei.

Two distinct systems of fibers are recognizable in the dorsal lateral geniculate nucleus and in the pulvinar. One is a transverse system formed by the fiber bundles which run within these nuclei oriented in parallel with the optic tract; some of these bundles mingle with the fibers of the optic tract. The other is a longitudinal system whose fibers course perpendicularly to those of the transverse system. Lesions in the visual cortex produce degeneration within both of these fiber systems, in the geniculate nucleus as well as in the pulvinar. The degenerating transverse fibers are corticopretectal and corticotectal axons, and these send collateral branches into the longitudinal systems of these nuclei.

The degenerating longitudinal fibers are of two types. One type consists of fibers which are fine in caliber, give rise to numerous short terminal branches, and degenerate early (undegenerated fibers showing this same morphology are identified in the Golgi preparations). These longitudinal fibers are the collateral branches of the degenerating transverse fibers and at the same time they represent the terminal portions of the fibers which provide the visual cortical input to the geniculate nucleus and the pulvinar. It is noteworthy that within the geniculate nucleus these terminal fibers run along the lines of projection for individual points on the visual field.

The second type of degenerating longitudinal fibers is found in the dorsal lateral geniculate nucleus but not in the pulvinar. Its fibers are coarser and degenerate later than the longitudinal fibers described above, and they are probably geniculocortical axons undergoing retrograde degeneration.
The connective tissue coverings of leech peripheral nerves: Anatomical evidence for the absence of cerebrospinal fluid in the leech
Authors: Wilkinson Joyce M. , Coggeshall Richard E.
Published: December 2004

The central nervous system of Hirudo medicinalis is contained within a blood vessel, the ventral longitudinal sinus, but the nervous system is separated from the blood by the visceral endothelium. The visceral endothelium possesses many pinocytotic vesicles and basal infoldings and thus appears active whereas the parietal endothelium appears inactive. The junction between the visceral and parietal endothelia is abrupt. Peripheral nerves in this animal, as in vertebrates, are covered by endoneurium, perineurium, and epineurium. The endoneurium is continuous with the fibrous tissue of the segmental ganglia. The perineurium, consisting of a single layer of flattened cells that surrounds the peripheral nerve like a sleeve, is not continuous with the endothelium of the ventral sinus, but is separated from it by 5–10 microns. Therefore, at the point where the peripheral nerve joins the segmental ganglion, the extracellular spaces of the central nervous system, the peripheral nervous system, and the body wall are all confluent. Thus, there are only two compartments of the extracellular space in the leech: the blood, which is enclosed by the endothelia of the coelomic sinuses, and the extracellular fluid of the body, which includes the extracellular fluid of the nervous system. There seems to be no equivalent of cerebrospinal fluid in the gnathobdellid leech.
Effects of low‐level X‐irradiation on cat cerebella at different postnatal intervals: I. Quantitative evaluation of morphological changes
Authors: Anderson William J. , Stromberg Melvin W.
Published: December 2004

Whole head fractionated doses of 200 r and 150 r were initiated postnatally in five experimental age groups (birth, 1‐week, 2‐week, 3‐week and 4‐week) and continued over a period of 14 or 20 days to prevent reconstitution of the external granular layer. Animals irradiated at birth displayed minor deficits in behavior, which included ataxia, tremor, hypertonus and dysmetria, while animals irradiated at 1‐week showed only mild symptoms of hypermetria. All other animals displayed no motor deficits. Animals irradiated at birth had smaller eyes and ears, a reduction in the size of the entire head and were susceptible to seizures. All animals were sacrified at 70 days of age. The cerebellum was found to be reduced in size and weight, the greatest deficit being seen in animals x‐irradiated at the very early ages. Newborn condition animals were found to have large compliments of interneurons in the molecular layer, an established internal granular layer, and Purkinje cells were found to have a normal orientation, position, and to be unreduced in number or size. Total granule cell deficits were found to range from 83% at birth to 29% at four weeks. Quantitative changes for the molecular layer, internal granular layer, medullary layer, Purkinje cell to granule cell ratio, and granule cell density, all depicted the greatest changes in the newborn, 1‐week and 2‐week conditions. This experiment confirmed that the critical period in the development at which damage would result in behavioral abnormalities was from birth to five days, while for neuroanatomical abnormalities, this critical period was from birth to 18 days.
Anatomical studies of a temporal visual area in the rabbit
Authors: Mathers Lawrence H. , Douville Arthur , Chow Kao Liang
Published: December 2004

Using Fink‐Heimer, autoradiographic and horseradish peroxidase techniques, the connections of a temporal visual cortical region of the rabbit were explored. The temporal visual area covers portions of areas T1 and T2, and is reciprocally connected with the posterior nucleus and suprageniculate nuclei of the thalamus. It was also shown that the temporal visual area projects to a similar region in the opposite hemisphere, and to intermediate laminae of the superior colliculus.

The temporal visual area is discussed in comparison to other similar regions in the cortex of primate species. It is pointed out that recent evidence indicates visual areas in the occipital cortex of non‐primate species may be no less numerous and complex than those in primate species.
The cortical projections of the mediodorsal nucleus and adjacent thalamic nuclei in the rat
Authors: Krettek J. E. , Price J. L.
Published: December 2004

The mediodorsal nucleus of the rat thalamus has been divided into medial, central and lateral segments on the basis of its structure and axonal connections, and these segments have been shown by experiments using the autoradiographic method of demonstrating axonal connections to project to seven distinct cortical areas covering most of the frontal pole of the hemisphere. The position and cytoarchitectonic characteristics of these areas are described. The medial segment of the nucleus projects to the prelimbic area (32) on the medial surface of the hemisphere, and to the dorsal agranular insular area, dorsal to the rhinal sulcus on the lateral surface. The lateral segment projects to the anterior cingulate area (area 24) and the medial precentral area on the dorsomedial shoulder of the hemisphere, while the central segment projects to the ventral agranular insular area in the dorsal bank of the rhinal sulcus, and to a lateral part of the orbital cortex further rostrally. (The term “orbital” is used to refer to the cortex on the ventral surface of the frontal pole of the hemisphere.) A ventral part of this orbital cortex also receives fibers from the mediodorsal nucleus, possibly its lateral segment, but the medial part of the orbital cortex, and the ventrolateral orbital area in the fundus of the rhinal sulcus receive projections from the paratenial nucleus and the submedial nucleus, respectively. All of these thalamocortical projections end in layer III, and in the outer part of layer I. The basal nucleus of the ventromedial complex (the thalamic taste relay) has been shown to have a similar laminar projection (layer I and layers III/IV) to the granular insular area immediately dorsal to, but not overlapping, the mediodorsal projection field. However, the principal nucleus of the ventromedial complex appears to project to layer I, and possibly layer VI, of the entire frontal pole of the hemisphere. The anteromedial nucleus does not appear to project to layer III of the projection field of the mediodorsal nucleus, although it may project to layers I and VI, especially in the anterior cingulate and medial precentral areas.

A thalamoamygdaloid projection from the medial segment of the mediodorsal nucleus to the basolateral nucleus of the amygdala has also been demonstrated, which reciprocates an amygdalothalamic projection from the basolateral nucleus to the medial segment. The habenular nuclei also appear to project to the central nucleus of the amygdala.

These results are discussed in relation to the delineation and subdivision of the prefrontal cortex in the rat, and to amygdalothalamic and amygdalocortical projections which are described in a subsequent paper (Krettek and Price, '77).
The specificity of re‐innervation by identified sensory and motor neurons in the leech
Authors: Van Essen D. C. , Jansen J. K. S.
Published: December 2004

Re‐innervation of skin and muscle by identified sensory and motor neurons in segmental ganglia of the leech was studied using physiological techniques. After lesions of peripheral nerves, sensory axons which re‐innervated the skin always regained sensitivity to their original stimulus modality (touch, pressure or noxious stimuli). Motor neurons invariably re‐innervated the appropriate type of body wall muscle, such as longitudinal or circular muscle layers. Both sensory and motor axons usually returned to the appropriate region of the body wall (dorsal, lateral, or ventral) when regenerating after a nerve crush or cut. This capacity was lost, however, when growth along old nerve branches was prevented by evulsing long segments of the nerve. Re‐innervation usually occurred by way of growth of new axons all the way the periphery, but in a few cases reconnection with the surviving distal segment of the original axon had taken place. The specificity of reinnervation can be accounted for by a combination of selective growth along appropriate nerve branches and specific interactions with target tissues.