bluuebunny/crossref_metadata_2025 huggingface dataset:
Subcortical projections, cortical associations, and some intrinsic interlaminar connections of the striate cortex in the squirrel monkey (Saimiri)
Authors: Spatz W. B. , Tigges J. , Tigges Margarete
Published: December 2004

Laminar lesions made by the thermocoagulation in the lateral striate cortex of Saimiri reveal details of three distinct groups of descending fibers: interlaminar, cortico‐cortical, and cortico‐subcortical. The two most massive connections originate mainly from layer III. These are the interlaminar fibers terminating in the underlying layer V, and the systematically arranged projection upon area 18. Another cortical projection upon a narrow region in the superior temporal sulcus originates mainly from the infragranular layers, from which originate also the fibers passing to three subcortical structures, viz. the colliculus superior, the medial pulvinar and the griseum pontis. These subcortical projections are sparse compared to the interlaminar and cortico‐cortical connections. In particular, no evidence was obtained that the lateral geniculate nucleus receives fibers from the lateral striate cortex. Lesions injuring the white matter, however, produced, in addition, anterograde degeneration in the nucleus praetectalis, three pulvinar nuclei, the lateral geniculate nucleus and the pregeniculate nucleus. This degeneration must have resulted from the interruption of fibers originating in areas other than the lateral striate cortex, and passing beneath the site of the lesion.

The origin of the interlaminar fibers and of the association fibers upon area 18 provided strong evidence that, in Saimiri's striate cortex, the two sublayers traditionally referred to as sublayers IVa and IVb, actually form part of the conspicuously enlarged layer III which thus is subdivided into three distinct sublayers.
Electron microscopic studies of Wallerian degeneration in rat optic nerves. II. Astrocytes, oligodendrocytes and adventitial cells
Authors: Vaughn James E. , Pease Daniel C.
Published: December 2004

Fibrous astrocytes, oligodendrocytes and adventitial cells have been studied in rat optic nerves undergoing Wallerian degeneration. Postoperative survival times ranged from five hours to 250 days. Fibrous astrocytes fill the spaces made available by the removal of degenerating nerve fibers. In addition, some astrocytes apparently become phagocytic and engulf degenerating myelin fragments. This reaction is small in comparison to that of multipotential glia (Vaughn), Hinds and Skoff, '70, and it appears to be secondary to the role of astrocytes in scar formation. There is no evidence from this study suggesting that oligodendrocytes engulf degenerating nerve fibers. Indeed, they do not exhibit dramatic changes during fiber degeneration beyond forming aberrant myelin sheaths during the late postoperative stage. Similarly, adventitial cells generally remain unaltered although a few adventitial cells containing numerous inclusions are encountered in degenerating tissue. Adventitial cells are always located within the perivascular space and neither they nor leukocytes have been observed in transit from blood vessels into the neural parenchyma. Finally, an attempt is made to reconcile some of the diverse results concerning the origin of CNS phagocytes. It is suggested that in most pathological situations there is contribution of phagocytes from several different sources and the relative importance of each source is determined by the extent of degeneration and the degreed of inflammation.
Cells of origin of sympathetic pre‐ and postganglionic cardioacceleratory fibers in the pigeon
Authors: Macdonald Robert L. , Cohen David H.
Published: December 2004

The pre‐ and postganglionic cardioacceleratory innervation is described in the pigeon. The peripheral course of the postganglionic cardiac nerves has been determined using microdissection and electrical stimulation. Using these techniques and retrograde degeneration methods, the distribution within the sympathetic ganglia of the cells of origin of these fibers has been localized to the three right caudal cervical ganglia (12, 13 and 14). It has also been shown on the basis of electrical stimulation combined with selective ablation of the right sympathetic chain that cardioaccelerator preganglionic fibers probably arise from the most caudal cervical segment of the spinal cord (14), always arise from the upper two thoracic segments (15 and 16), and occasionally arise from a mid‐thoracic segment (17). The left sympathetic chain was shown to have an inconsistent influence on heart rate. On the basis of retrograde degeneration, the cells of origin of sympathetic preganglionic fibers have been localized to a welldefined cell column dorsal to the central canal (column of Terni).
Symmetry in a receptor mosaic demonstrated in the chick from the frequencies, spacing and arrangement of the types of retinal receptor
Authors: Morris Valerie B.
Published: December 2004

The mean percentages of receptors in the central retina were 14% rods, 32% double cones and 54% single cones. The mean percentages in the periphery were 33% rods, 30% double cones and 37% single cones. Single cones were classified into type I, type II and type III and the ratio of these types was about 5:2:1, respectively, in both central and peripheral retina. A statistical analysis showed that each type of receptor was evenly spaced in the receptor mosaic, but single cone type I tended to occur in pairs. The types of receptor were arranged in a pattern which was in the form of a hexagonal lattice. The pattern in the mosaic is regarded as the outcome of an evenly spaced distribution of the types of receptor. Perhaps pattern in the receptor mosaics of other vertebrate retinae should be interpreted as evenly spaced distributions of the types of receptor present. A method for detecting pattern in receptor mosaics, in which pattern is obscure, is described. A scheme accounting for the formation of the pattern in the chick retina during development is proposed.
Fine structural localization of acetylcholinesterase in sensory and motor neurons of the muscle receptor organ in Homarus
Authors: Nadol Joseph B. , Brzin Miro , de Lorenzo A. J. Darin
Published: December 2004

Histochemical techniques with the electron microscope for the localization of specific acetylcholinesterase and non‐specific cholinesterases have been applied to preparations of the abdominal muscle receptor organ, or stretch receptor, of the lobster. Reaction product specific for AChE was found to be localized in a discrete but interrupted fashion on the external surface of the cell membranes of both the fast and slow sensory neurons at the levels of axon, cell body, large and small dendritic processes, and fine dendritic terminations. Reaction product specific for AChE was also found on the external surface of the limiting membranes of motor axons, but not at neuromuscular endings. Non‐specific ChE was limited to cytoplasmic vacuoles and cisternae of the Schwann cells of the neural sheaths. These findings lend support to the hypothesis that in the lobster the ACh system may mediate membrane excitability of nerve fibers. Furthermore, at the level of dendritic terminations this system may mediate the transduction of mechanical into electrical energy via reversible permeability changes.
Fiber spectrum and functional properties of pyramidal tract neurons in the american opossum
Authors: Biedenbach M. A. , Towe A. L.
Published: December 2004

The number and size of pyramidal tract (PT) axons and the functional properties of cerebral PT neurons were examined in the American opossum. The pyramidal tract contains 30,000–40,000 axons, none greater than 5 μ in diameter and 99% of 3 μ or less in diameter. Cerebral neurons were isolated and classified as PT or non‐PT according to standard antidromic spike criteria in response to stimulation of the medullary pyramid. Response to natural stimulation and to electrical stimulation of the four paws was tested. PT neurons displayed a wider convergence than non‐PT neurons, but the more superficially isolated PT neurons showed only weak or nonexistent excitation from the skin. Response to stimulation of one paw could be blocked by prior stimulation of another paw, whether or not the conditioning stimulus evoked a discharge. At least some of the blocking may be due to intracortical inhibitory synapses, for weak conditioning shocks applied to the pyramidal tract could block the peripherally evoked response in half of the neurons tested, both PT and non‐PT. During high‐frequency stimulation of the pyramidal tract, antidromic spikes readily separated into distinct A and B components, the B spike frequently failing altogether. The slow antidromic conduction speeds, 4–14 m/sec, agreed well with the small axon diameters found by histological methods.
A quantitative ultrastructural study of the inner plexiform layer of the rat retina
Authors: Sosula Leo , Glow Peter H.
Published: December 2004

The inner plexiform layer (IPL) and adjacent regions of the rat retina were studied by electron microscopy. The IPL contains neural processes of amacrine, bipolar, and ganglion cells, and glial (Müller) processes. Type 1 amacrine processes (maximum diameter 3.1 μ) traced from their somata structurally resemble amacrine perikarya. These processes rarely form synapses. Type 2 amacrine processes (maximum diameter 0. 7 μ) are radially oriented, forming synaptic expansions en passant, giving origin to collaterals, also with expansions. The type 2 amacrine processes form conventional synapses onto bipolar, ganglionic and other amacrin processes, onto amacrine and ganglionic somata, and onto dendritic spines. Amacrine perikarya in rare cases contain synaptic vesicles and form somatic synapses onto surrounding processes.

Bipolar processes traverse the IPL, forming terminal expansions up to 6 μ in diameter near the ganglion somata, which they contact without synaptic vesicle clustering. Bipolar processes form synapses onto dyads. In 73% of dyads, both processes are vesiculated. One process of the dyad pair could usually be identified as an amacrine by its reciprocal synapse back onto the presynaptic bipolar process. The other dyad process, when vesiculated, contains vesicles which are significantly larger and less concentrated than in the adjacent amacrine, and is presumably a ganglion cell dendrite.

The ratio of the incidence of amacrine synapses: bipolar synapses is about 8:1. A subdivision of the IPL into thirds shows that the highest incidence of amacrine synapses is in the middle third. Amacrine somata are significantly larger than bipolar somata. Synaptic vesicles in receptor terminals of the outer plexiform layer are significantly larger and more concentrated than those in axonal processes of the IPL. The functional aspects of these findings are discussed in relation to physiological investigations and interspecies differences described in the literature.
Neuromuscular junctions on the muscle cells in the central nervous system of the leech, Hirudo medicinalis
Authors: Tulsi Ram S. , Coggeshall Richard E.
Published: December 2004

The central nervous system of the leech is surrounded by fibrous tissue in which are contained muscle cells whose presumed function is to accommodate the length of the nervous system to coincide with changes in the length of the animal. In this paper a three‐dimensional reconstruction of these muscles was described. Each neuromuscular junction consists of 5–50 neural terminals closely applied to the muscle. Furthermore, some morphologic evidence for synaptic interaction between terminals was obtained. We believe that this complex morphology of the terminals indicates that there is a relatively complex integrative mechanism for neuromuscular transmission at the periphery.
Somatotopic organization of spider monkey somatic sensory cerebral cortex
Authors: Pubols Benjamin H. , Pubols Lillian M.
Published: December 2004

Organization of the tactile receiving area of the postcentral gyrus of the spider‐monkey (Ateles) has been investigated using microelectrode recording procedures. The neocortical region in which single units or unit clusters respond to light mechanical region in skin (SmI) is smaller than the tactile receiving area as defined by earlier evoked potentials studies, failing to extend into sylvian sulcus or to the posterior margin of the postcentral gyrus. It forms a precise, detailed, and somatotopically organized pattern of representation of the complete contralateral body surface. The sensory sequence is orderly and continuous from tail to tongue with one exception, each body region in represented by a band of cortical tissue extending anteroposteriorly across SmI. The ratio, area of glabrous surface of the hand as it is for the glabrous tail pad, which correlates with the greater tactile acuity of the former.
The interpeduncular nuclear complex of selected rodents
Authors: Ives W. R.
Published: December 2004

The internal differentiation of the interpeduncular nuclear complex was determined by quantitative cytoarchitectonic analysis in specimens from each of the suborders of Rodentia: rat (Rattus) of the Myomorpha; guinea pig (Cavia), chinchilla (Chinchilla), and capybara (Hadrochoerus) of the Caviamorpha; and the mountain beaver (Aplodonia) from the Sciuromorpha. In each of these rodents the constituent cells of the complex ae grouped into four spatially distinct subnuclei: pars lateralis (PL), pars medialis (PM), pars dorsalis magnocellularis (PDM), and pars dorsalis parvocellularis (PDP). There is a fifth subnucleus, the paramedian, in Chinchilla. Sample distributions, and means, of cell sixes were measured in each of these subdivisions in each species; and cell densities of each subdivision were determined in Rrattus. In all these animals PD had the smallest cells. PDM had the largest cells, except that in Hydrochoerus cells of PL, and in Cavia cells of PM, were as large as those of PDM. In Rattus and Aplodontia PL and PM were not different in cell size, and in Rattus their cells were of the same density. These findings cast doubt upon criteria previously used to subdivide this nuclear complex, and provide a consistent and replicable classification of its components.
Hypothalamo‐hypophyseal neurosecretory and vascular systems in the catfish, Heteropneustes fossilis (Bloch)
Authors: Sundararaj Bangalore I. , Viswanathan N.
Published: December 2004

The hypothalamo‐neurohypophyseal system of the catfish, as revealed by in situ techniques, consists of the prominent nucleus preopticus, the axonal tracts, and the neurohypophysis. The preoptic nucleus, which is composed of the pars magnocellularis and the parvocellularis, is situated on either side of the optic recess slightly anterior to the optic decussation. Axons arising from the nucleus preopticus form two ventro‐lateral tracts; bundles of axons separate out from these tracts at 10 to 12 points and extend medially to form two ventro‐medial tracts lying on either side of the optic recess. The ventro‐lateral and ventro‐medial tracts eventually merge slightly anterior tc the hypophysis to form the infundibular stalk which penetrates the pituitary and ramifies. The nucleus lateralis tuberis is situated rostral and antero‐ventral to the third ventricle and their axons join the ventro‐medial tracts.

The arterial supply to the hypophysis is through a median hyophyseal vessel whose branches penetrate the pituitary along with the infundibular stalk and follow the ramifications of the neurohypophysis. A portal circulation between the hypothalamus and the hypothalamus is discussed.
The cat coeliac and hypogastric ganglia following post‐ganglionic nerve ligation. A study by electron autoradiography and formol fluorescence techniques for noradrenaline distribution
Authors: McQuiston R. W. , Ivens Caroline , Lever J. D. , Spriggs T. L. B. , Graham J. D. P.
Published: December 2004

Noradrenaline uptake is a property not only of sympathetic axons but also of their ganglion cells. This has been shown by electronautoradiography which indicates higher than background levels of 3H‐noradrenaline in ganglion cells (incubated in isotope solution) following post‐ganglionic nerve ligation. Under these circumstances noradrenaline concentrations have been found specifically related to the Golgi complex and granular endoplasmic reticulum in hypogastric ganglion cells.
Stellate cells of the rat parietal cortex
Authors: Peters Alan
Published: December 2004

Stellate cells have rounded or oval cell bodies which contain nuclei bounded by a ruffled, and frequently indented, nuclear envelope. Te cytoplasm of these neurons is usually darker than that of pyramidal neurons because it contains a greater concetration of ribosomes. Where the perikaryal cytoplasm is thick, the granular endoplasmic reticulum is often arranged in parallel arrays. On the surface of the perikarya are three types of synapses: (1) ones with a wide cleft and a prominent postsynaptic density, (2) ones with a wide and straight synaptic cleft that lack a prominent postsynaptic density, and (3) ones with a narrow synaptic cleft and short synaptic complexes. The dendrites of stellate cells lack spines and frequently bear many synapses. On the thinner dendritic branches the type of synapse with a side cleft and a prominent postsynaptic density is most common. The cytoplasm of the dendrites is characterized by closely arranged microtubules.
Neurogenesis in the optic tectum of larval Rana pipiens following unilateral enucleation
Authors: Eichler Victor B.
Published: December 2004

DNA synthesis and interlayer migrations of cells in the optic tectum of larval Rana pipiens were investigated, using several series of larvae which had been subjected to unilateral enucleation at stage 25, the last embryonic stage. It has been found that DNA synthesis occurs in all cellular layers of the tectum with least activity in peripheral layers. The location of the most active DNA synthesis during the larval period is the same as the location of cell division in the larval tectum, namely, in the layers bordering the ventricle of the optic lobe

Unilateral enucleation of stage 25 embryos results in a decrease in DNA synthesis in all cellular layers of the optic tectum contralateral to the operation when compared to the corresponding layers in the ipsilateral tectum. The differences in rate of incorporation of 3H‐thymidine between the control and affected lobes become greater during development. Fewer cells are found in each layer of the affected larval tectum than in the corresponding layer of the control tectum. The decrease is greatest in more peripheral layers, whose cells are more intimately associated with the visual circuit than are cells of the deeper layers. Peripheral to layers 1 and 2, the percentages of labeled cells found in each layer are very similar on the two sides, suggesting common factors which control migration. Differences in cell number, therefore, reflect differential cell production rather than differential cell migrations.

The distribution of label resulting from 3H‐thymidine incorporation at stage III indicates that the distribution of mitotic activity is not uniform in the cephalocaudal axis of the tectum. Greater cell proliferation occurs in the posterior portion of the tectum than in the anterior region throughout larval development.

The peripheral control of mitotic divisions in the frog optic tectum remains unknown. The data in the present study, however, support the hypothesis that influences from afferent fibers of the optic tract modify the rates or timing of DNA synthesis in the optic tectum. The data support the notion that the deepest tectal cells respond earliest to the stimulus and these may be ependymal cells which have processes extending to the outer surface of the tectum.
An experimental study of ascending connections from the posterior group of thalamic nuclei in the cat
Authors: Heath C. J. , Jones E. G.
Published: December 2004

The cortical projections of the posterior group of thalamic nuclei have been studied in the cat by means of the Nauta technique. Small stereotaxic lesions introduced in such a manner as to cause no direct damage to the main thalamic nuclei adjoining the posterior group or to the overlying cortex, indicate the following pattern of projections: Only that part of the posterior group consisting of the suprageniculate and magnocellular medial geniculate nuclei, and particularly the region of transitions between the two, projects to the cortex. The cortical region of fibers is a band comprising the third auditory area (AIII) of Tunturi, the insular cortex, the banks of the anterior ectosylvian sulcus, zones A and B of Carreras and Andersson ('63) in the upper part of the anterior ectosylvian gyrus, the vestibular projection area, the suprasylvian fringe of Woolsey ('61). It is possible that different parts of the suprageniculate‐magnocellular complex project to different parts of this cortical band. The suprageniculate‐magnocellular complex and certain parts of the band of cortex to which it projects are regions of multi‐sensory convergence. Although all parts of the posterior group as presently defined, have been damaged, no part seems to project to the first (SI) or second (SII) somatic sensory areas (other than AIII and zone B, which overlap SII). The main efferent connections of these parts of the poeterior group appear to be with the striatum. The results can be correlated to some extent with previous studies carried out with the method of retrograde cellular degeneration, but there are certain problems in relation to electrophysiological studies.
Median and caudal apertues in the roof of the fourth ventricle in rodents and primates
Authors: Cammermeyer Jan
Published: December 2004

In serial paraffin sections of brainstems fixed by perfusion, ventriculo‐cisternal communications in the caudal part of the fourth ventricle are demonstrable in seven species of a total of 27 species, representing Marsupialia, Edentata, Lagomorpha, Rodentia, Ungulata, Carnivora, and Primates, in all of which the lateral apertures of Luschka are well developed. Caudal apertures appear as irregular defects in the taenia of the fourth ventricle with flattening of the roof against the surrounding leptomeninges over the crebello‐medullary cistern in the guinea pig, the mulatta monkey, the squirrel monkey and the cynomolgus monkey. In addition, the one capuchin monkey and the one vervet monkey studied have a midline defect in the roof. In the capybara, a circular midline opening through the roof is closed off dorsally by the cerebellar vermis. These caudal and median defects are thought to be ruptures developed late in fetal life due to accumulation of cerebrospinal fluid before egress through lateral apertures of Luschka is established; although they seem to have served their purpose in the fetus and are no longer needed in the adult, they are kept open by continued flow. Study of fetuses from these selected species could prove useful to determine factors concerned with the development of cerebrospinal fluid circulation.
The red nucleus in the monkey (Macaca mulatta): A Golgi and an electron microscopic study
Authors: King James S. , Schwyn Robert C. , Fox Clement A.
Published: December 2004

This study of the ultrastructure of the red nucleus of the monkey (Macaca mulatta) also includes light microscopic observations made with Golgi, Nissl and one micron plastic section techniques.

Sagittal Nissl sections reveal the abrupt transition between the magnocellular and parvicellular division of the nucleus; therefore, it is advantageous to study the red nucleus in this monkey because small tissue blocks from each of its subdivisions can be prepared for electron microscopy.

The characteristic neurons of the magnocellular division have well formed, evenly distributed Nissl bodies. The multipolar cell bodies (50–70 μ) and elongated cell bodies (80–90 μ in length) are the large or giant neurons; those 30 to nearly 50 μ are the medium‐size neurons of some descriptions.

The characteristic neurons (20–30 μ) of the parvicellular division, referred to here as medium‐size neurons, have no distinct Nissl granules and their Nissl substance usually occupies the peripheral rim of their cell bodies. In both subdivisions of the nucleus there are small (10–15 μ), achromatic, Golgi type II neurons.

The cell bodies of the large neurons have prominent somatic spines and their dendrites and the dendrites of the medium‐size neurons have scattered spines. There are large (4–5 × 10–12 μ) and small (1–2 μ) synaptic endings on the dendrites. Some of the former are formed at nodes of Ranvier. It is suggested that the large endings are terminals of the superior cerebellar peduncle.
Changes in the hypothalamus associated with regeneration of the hypothalamo‐neurohypophysial tract after pituitary stalk section in the ferret
Authors: Adams James Hume , Daniel Peter Maxwell , Prichard Marjorie Mabel Lucy
Published: December 2004

Anatomical features of the hypothalamus of the normal ferret are described. Transection of the pituitary stalk, with or without the insertion of a barrier to prevent reunion, caused consistent changes in the neural tissue of the median eminence. The rostral part of the median eminence was relatively unaffected but the caudal part, near the site of the lesion, showed marked changes. In the early post‐operative stage there was a large mass, containing few cells but much neurosecretory material (NSM), projecting up from the neural tissue of the median eminence into the infundibular recess of the third ventricle. After a few weeks this seemingly structureless mass had disappeared and the neural tissue had become reorganised and enlarged, and contained large numbers of newly grown nerve fibers and heavy concentrations of NSM. The appearances suggested that an ectopic infundibular process had formed at this level, even in animals in which the original infundibular process had also been re‐innervated. Changes in the supraoptic and paraventricular nuclei were surprisingly slight.

In the ferret the hypothalamo‐neurohypophysial tract runs through an unusually long median eminence. Thus many of its nerve fibers (or their collaterals) may terminate well above the level of stalk section, and this may account for the minimal changes seen both in the rostral part of the median eminence and in the supraoptic and paraventricular nuclei.

An explanation is suggested for the persistent but diminishing diabetes insipidus that occurred in the stalk‐sectioned animals.
Somatotopic organization and response properties of neurons of the ventrobasal complex in the opossum
Authors: Sousa Aglai P. B. , Oswaldo‐Cruz E. , Gattass R.
Published: December 2004

Thalamic responses to somatic stimulation were studied in 47 specimens of the South American opossum, D. marsupialis aurita. Topographic representation of the body surface in the ventrobasal complex was determined by recording unit cluster responses to natural stimulation in sodium pentobarbital anesthetised animals. The pattern of representation observed was similar to that reported in the North American subspecies and comparable to the findings in eutherian mammals.

The analysis of single units recorded with extra‐cellular microelectrodes showed that the great majority of neurons are place and modality specific. A predominance of skin (vs. deep) sensibility was observed. Units activated by displacement of hairs and vibrissae displayed receptive fields similar to those reported in higher mammals. Of the units isolated within the anatomical boundaries of the ventrobasal complex only 1% showed wide receptive fields, or bilateral representation. None of the units could be activated by auditory stimulation. Neurons displaying wide, discontinuous or bilateral receptive fields showing auditory‐somatic convergence were isolated in nucleus parafascicularis, subparafascicularis and in the Posterior group.
Methods of fixation and the morphology of synaptic vesicles
Authors: Valdivia Oswaldo
Published: December 2004

Cerebellar mossy, parallel, basket and Golgi axons were used to study the variables contributing to vesicle shape.

It has been found that, when aldehydes are used as a primary fixative, synaptic vesicles can be either small round vesicles (less than 400 Å in diameter), large round vesicles (400–500 Å in diameter) or flat, with a ratio of large to small diameters of 2 or greater (500–600 Å × 250 Å). The proportion of round vesicles as well as the presence and the number of flat vesicles in each axon depend basically upon the osmotic pressure of the buffer. Concentration of aldehydes, duration of the fixation and dehydration, temperature of the fixative, etc. do not affect the synaptic vesicle shape. With buffers (phosphate and sodium cacodylate) of low osmolarity, mossy and parallel axons exhibit a round synaptic vesicle population and no flat vesicles are seen at all. With the same low osmolarity buffers, basket and Golgi axons have a synaptic vesicle population that is mainly round with a low proportion of flat vesicles. As the osmolarity of the buffers is increased, the number of flat vesicles in basket and Golgi axons increases. In mossy and parallel axons the flat vesicles are present with highest osmolarities but always in a lower proportion than in basket and Golgi axons.

Quantitative observations indicate that each axon type, under given conditions of fixation, exhibits a mixed vesicle population with a characteristic vesicle ratio. Although this vesicle ratio is modified significantly with changes in the osmotic pressure of the buffer, each axon type exhibits a different and characteristic modification of its vesicle ratio. These observations show that the vesicle ratio and its changes in different conditions of fixation are useful parameters for classifying axon.
The relations of ependyma to neurons and capillaries in the hypothalamus: A Golgi‐Cox study
Authors: Bleier Ruth
Published: December 2004

Numerous basal processes of ependymal cells extend peripherally into every cell group and area of the hypothalamus of the four species of mammals examined: mouse, rat, rabbit and cat. With Golgi‐Cox impregnation and Nissl counterstaining, ependymal cell processes appear to have a variety of forms and of intricate structural relationships with neurons and capillaries within the hypothalamus. It is proposed that hypothalamic ependymal cells and their processes function as a communication system between the cerebrospinal fluid of the third ventricle and neurons and capillaries within the hypothalamus. The role that such a system may play in the regulation of adenohypophysial function is discussed.

It was also noted that in all hypothalamic cell groups, dendrites of some neurons extend to the ependymal layer.

An unusual cell, resembling microglia forms, within the infundibular nucleus appears to be selectively impregnated by the Golgi‐Cox technique employed. The cell is characteristic of the infundibular nucleus and, with rare exceptions, is confined to that cell group. Some of these spider‐cells lie on the ependymal layer and also have endfeet extending to the ventricular surface of the ependyma.
The optic nerve of the Mallard duck: Fiber‐diameter frequency distribution and physiological properties
Authors: O'Flaherty Juan J.
Published: December 2004

A correlative study of the anatomy and physiology of the axons of the optic nerve of the Mallard duck was carried out. The principal findings were:

Electronmicroscopy used in conjunction with phase contrast microscopy showed the nerve to have a fiber spectrum ranging from 0.3 μ to 6.0 μ with a mode at 1.15 μ.

No unmyelinated axons were found.

The cross‐sectional area of the nerve was estimated to be 4.38 mm2; assuming a mean fiber density of 350,000 fibers/mm2, the total number of axons in the nerve was estimated to be about 1,500,000.

The conduction velocities of the fibers were found to range from 21 m/sec to about 3 m/sec.

Different recovery cycles were found for each of the different compound action potentials.

Using a graphical method, a good correlation could be established between the fiber‐size spectrum and the configuration of the compound action potential.
Comparisons in the strucure of avian muscle spindes
Authors: Maier Alfred , Eldred Earl
Published: December 2004

A study of muscle spindles in several species of birds was made to determine if avian intrafusal (IF) fibes are separable into the nuclear bag and chain fiber types found in mammals, and whether prominent differences in spindle structure might exist among species. Van Gieson‐stained serial sections of the sartorius, a flexor muscle, and the antigravity adductor profundus muscle were examined in the chicken, quail, pigeon and canary. Avian IF fibers did not exhibit the pronounced “bag” of nuclei characteristic of mammalian nuclear‐bag fibers, although the non‐striated region at mid‐length was marked by a moderate excess of eccentric, vesicular nuclei. No consistent differentiation in pattern of nuclear aggregation or manner of fiber termination among fibers of a spindle was detected, nor was there unequivocal bimodality in cross‐sectional areas. These characteristics in bird spindles, therefore, do not afford trustworthy criteria for separation of types of IF fibers. The number of spindles per unit volume was particularly high in the canary and lowest in the chicken muscles. Spindles in the chicken were larger and more complex than canary spindles in respect to numbers of fibes per spindle, spindle length, and cross‐sectional area of intrafusal fibers at the equator. Values for the quail and pigeon ocupied an intermediate position. Relation of the differences in spindle structure to the size of the bird and to other factor is discussed, and some contrast between avian and mammalian spindles are pointed out.
Primary optic pathways in the echidna, Tachyglossus aculeatus: An experimental degeneration study
Authors: Campbell C. B. G. , Hayhow W. R.
Published: December 2004

The retinofugal axons of Tachyglossus aculeatus were found to project to two diencephalic nuclei, disparate in size and location and designated provisionally as LGNa and b, and to the pretectum and superior colliculus. The primary optic pathways of the echidna are crossed except for a few fibers which pass to the ipsilateral large diencephalic nucleus (LGNa). Further work is required before the homologies of the two diencephalic nuclei can be determined. In addition, entirely crossed projections were also found to a large number of optic nuclei including a medial terminal nucleus, four cell groups interstitial to the optic tract, and a nucleus located within the brachium of the superior colliculus which may represent a dorsal terminal nucleus. The latter nucleus may, however, actually be the nucleus of the optic tract which is displaced from its usual close association with the pretectal area. Only an inferior fasciculus of the accessory optic tract was found.
The contribution of the dorsal lateral geniculate nucleus to the total pattern of thalamic terminations in striate cortex of the virginia opossum
Authors: Benevento L. A. , Ebner Ford F.
Published: December 2004

These studies were carried out to show the manner of projection of the dorsal lateral geniculate nucleus and other thalamic nuclei to striate cortex in the Virginia opossum. In order to demonstrate these projections, lesions were made in the dorsal lateral geniculate nucleus, in the ventral lateral geniculate nucleus, in most of the thalamus on one side except for the dorsal lateral geniculate nucleus, and in the entire unilateral thalamus. Following various survival times, usually seven days, the brains were appropriately prepared and stained with procedure I of the Fink‐Heimer technique. Dorsal lateral geniculate neurons project in a topographical manner only to certain layers of striate cortex. These projections from the lateral geniculate are compared with the same system in other mammals, and it is concluded that it is similar in all mammals studied, except for the cat. In the cat the lateral geniculate projects beyond the border of striate cortex, but even in the cat the layers of termination within striate cortex are apparently similar. The ventral lateral geniculate nucleus does not project to visual cortex. Dorsal thalamic nuclei other dian the lateral geniculate project to peristriate cortex and to layers VI and I of striate cortex. The finding that thalamic nuclei, other than the lateral geniculate nucleus, project to striate cortex has never been described as part of the visual pathways in other mammals. It is suggested that these additional projections arise mainly from the lateral nuclear group of the thalamus in the opossum, and must be considered in relation to any response characteristics and organization of striate cells determined from physiological studies. These multiple thalamic projections can provide the substrate for more than one representation or “map” of sensory information in striate cortex.
Behavioral encephalization in the bullhead embryo and its neuroanatomical correlates
Authors: Armstrong Philip B. , Higgins Don C.
Published: December 2004

Three physiological phases can be recognized in the encephali‐zation of motor control in the developing bullhead. These are in succession 1. the spinal phase, 2. the hindbrain phase and 3. the optic‐midbrain phase. During the spinal phase motility is limited to lateral flexions of the trunk and tail by the contractions of the somitic muscle. The flexions become amplified as additional somites participate in this activity. There is no evidence of any encephalic control. Random undulatory swimming characterizes the hindbrain phase. It emerges with the maturation of the Mauthner cell and its labyrinthine afferents. In the optic‐midbrain phase there is a superposition of a visual control on swimming, a control which comes on with the differentiation of the rods and cones of the eye and their projection by way of the optic tectum and the tecto‐bulbar tracts to the Mauthner cells. The response in this phase is directed, a negative phototaxis for a major share of this phase. However, toward the end of this phase the photomechanical properties of the retina come into play providing an adaptive mechanism in which the response, negative or positive, is determined by the photomechanical state of the retina. Thus the retina, an exteroceptor, serves as an analyzer. The photic response in the advanced embryos can be predicted if the adaptive state of the photomechanical apparatus is known.

It is suggested that the spinal and hindbrain activities result from endogenous neural activating mechanisms. Spontaneous firing in the labyrinth transmitted to the Mauthner cells may spark the random swimming characteristic of the hindbrain phase. This provides an activity base for the directed optic responses. The Mauthner cells thus receive input from both the labyrinth and the retina, a case of heterogenous summation. The random motor activities in the spinal and hindbrain phases do not appear to have survival value. The optic midbrain responses are reactions to an environmental situation and appear to have survival value or “purpose.”
Quantitative cytoarchitectonic distribution of neurons, glia, and DNA in rat cerebral cortex
Authors: Bass Norman H. , Hess Helen H. , Pope Alfred , Thalheimer Caroline
Published: December 2004

A new technique combining microfluorometric DNA assays with differential cell counts was used to quantitate the intralaminar distribution of neuronal and non‐neuronal cells (chiefly glial) in rat somatosensory cortex (Charles River 250 gm males, C D® strain). The intracortical amounts of DNA per unit fresh volume were calculated from the DNA contents of serial frozen slices of known volume sampled serially from the pial surface to white matter in frozen cortical cylinders; respective amounts per unit solids were calculated from predetermined dry weights of the slices. Cell counts were performed on serial horizontal sections from formalin‐fixed cylinders stained by Nissl's method. Neuronal DNA and glial DNA were calculated based on the percentages of the respective cells counted.

Total DNA averaged 5.43 μg/mg dry weight (1.19 μg mm3 fresh volume). Values were highest in layers II and IV. Neuronal DNA paralleled total DNA in its intracortical distribution and showed distinct peaks in layers II and IV. Glial DNA showed an even distribution. Glia exceeded neurons only in layers I and VIc. The mean neuron/glia ratio was 2.5. This method gives a more precise estimate of the absolute numbers of neurons and glia than can be obtained by histological methods alone, since DNA assays eliminate the need to correct the histological counts for volume changes during fixation and staining.
Neuronal and synaptic organization of the normal dorsal lateral geniculate nucleus of the squirrel monkey, Saimiri sciureus
Authors: Wong‐Riley Margaret T. T.
Published: December 2004

The normal cellular architecture and synaptic organization of the dorsal lateral geniculate nucleus (LGN) of Saimiri sciureus has been studied with light and electron microscopic techniques. Golgi preparations reveal at least four types of neurons: type I and II are large and medium‐sized cells; type II cells have grape‐like dendritic protrusions, while type I cells do not. Type III small neurons have very long dendrites that cross laminar borders freely; and type IV very small neurons resemble glial cells. The last type may correspond to small, spindle‐shaped or round, neurons which show somato‐dendritic synapses under the electron microscope. Types I and II neurons are regarded as geniculocortical relay cells. Types III and IV are good candidates for interneurons. A serial dorsal to ventral interlaminar dendritic overlap is noted throughout the LGN. With the electron microscope, several types of axonal profiles can be seen: large axons with round vesicles (RL's), small axons with round vesicles (RS's), and intermediate axons with flattened or pleomorphic vesicles (F's). The RL's are retinal terminals; some of the RS's are corticogeniculate fibers; while the F's are believed to be intrageniculate in origin. The F type is then subdivided into F1 and F2; F1 being darker and containing more evenly dispersed synaptic vesicles than F2. There is also a distinct class of presynaptic dendrites, Fd, which contains pleomorphic vesicles and has a light cytoplasmic density similar to that of the F2 profiles. It is possible that some or all of the F2 processes may prove to be dendritic. Somato‐dendritic synapses arise from very small neurons and form a part of the normal synaptic organization in the LGN. The RL and RS axons form asymmetrical synaptic contacts, whereas the F (F1, F2 and Fd) processes mainly form symmetrical ones. Non‐synaptic filamentous contacts are also found. The rules of synaptic connectivity are such that the RL and RS terminals are never synaptic to either the RL or the RS terminals, and presynaptic to other dendrites. If the F profiles contact each other, the F1 axon is never the post‐synaptic element. The RL and F processes synapse upon any part of the perikaryal and dendritic surfaces, whereas the RS terminals do not contact the soma.
Central projections of the spiral ganglion of the squirrel monkey
Authors: Moskowitz Norman , Liu Jung‐Ching
Published: December 2004

For establishing the relationships of the central projections of the spiral ganglion with the cytoarchitectural regions of the cochlear nuclear complex in a primate species, 23 squirrel monkeys, Saimiri sciureus were utilized. Restricted lesions of the cochlea were confirmed histologically and the resulting degeneration was traced to the cochlear nuclei in sections prepared with Nauta (′57) and Fink‐Heimer (′67) technics. By following the course of degeneration, the cochlear root fibers can be seen to bifurcate into ascending and descending branches. The ascending branches from the apical through basal turns of the spiral ganglion terminate in a rostro‐lateral to caudo‐medial gradient in the anteroventral cochlear nucleus. The descending branches from the apical through basal segments of the spiral ganglion terminate in a ventral to dorsal pattern in the posteroventral and dorsal cochlear nuclei. Ascending branches terminate chiefly on large and small spherical cells and globular cells in the anteroventral region. Terminals of descending branches are associated with globular, multipolar and octopus cells of the posteroventral nucleus and cells of the central and granular layers of the dorsal cochlear region.
Electron microscopic distribution of axoplasmic transport
Authors: Hendrickson Anita E.
Published: December 2004

Light and electron microscopic radioautography have been used to localize the rapid and slow components of axoplasmic flow within the monkey lateral geniculate nucleus (LGN). Three days after an intravitreal injection of H3 leucine, 53% of the silver grains found in the LGN were localized to retinal synaptic terminals and 27% were over retinal axons. By 30 days post‐injection, 66% of the grains were localized to retinal axons while retinal synaptic terminals now contained 21% of the grains. At both 3 and 30 days LGN neurons postsynaptic to the radioactive retinal axons showed higher levels of labeling than LGN neurons in the layers not receiving afferents from the injected eye. These data indicate that the rapid phase is mainly confined to the synaptic terminal while the slow phase is mainly localized in the axon. This differing distribution of radioactivity may now be utilized as the basis of a neuroanatomical tracing method.
Mode of cell migration to the superficial layers of fetal monkey neocortex
Authors: Rakic Pasko
Published: December 2004

Golgi and electronmicroscopic methods were used to define the shapes and intercellular relationships of cells migrating from their sites of origin near the ventricular surface across the intermediate zone to the superficial neocortical layers of the parietooccipital region in the brains of 75‐ to 97‐day monkey fetuses. After mitotic division in either ventricular or subventricular zones, the cells enter the intermediate zone and assume an elongated bipolar form oriented toward the cortical plate. The leading processes, 50 to 70 μ long, are irregular cytoplasmic cylinders containing prominent Golgi apparatus, mitochondria, microtubules, ribosomal rosettes, immature endoplasmic reticulum and occasional centrioles. They usually terminate in several attenuated expansions, the longest one oriented toward the cortical plate. The trailing processes are more slender, relatively uniform in caliber and display few organelles.

Throughout the 3500 μ pathway across the intermediate zone the migrating cells are apposed to elongated, radially oriented, immature glial processes which span the full thickness of the cerebral wall. Most of the perikarya of these glial cells in the younger specimens lie in the ventricular or subventricular zones, but in older fetuses of this series many are found in the intermediate zone. The main characteristics of these fibers are: elongated cylindrical form contaiing numerous microtubules; electronlucent cytoplasmic matrix; short lamellate expansions protruding at right angles from the segment of the fiber which runs through the intermediate zone; and terminal endfeet joined at the pial surface to form a continuous sheet coated externally with basement membrane. It is suggested that glial radial fibers provide guidelines for cell migration through the complex mixture of closely packed cell processes and cell bodies that compose the developing cerebral wall. Strong surface affinity between radial fiber and migrating cell is suggested in regions where both follow precisely the same curving course from subventricular to intermediate zones and also in areas where large extracellular spaces separate other cells and processes but in which migrating cells and radial fibers remain closely paired nonetheless. Specific affinity between them is implied in the failure of migrating cells to follow any of the myriad differently‐oriented processes they encounter. Several generations of postmitotic cells appear to migrate along the same radial fiber, a developmental mechanism that would allow for the vertical cell columns of adult neocortex.