bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron microscopy of non‐neuronal cellular changes accompanying neural degeneration in thalamic nuclei of the rabbit. II. Reactive elements within the neuropil
Authors: Matthews Murray A. , Kruger Lawrence
Published: January 2005

Surgical destruction of the cortical projections of thalamic neurons results in rapid and profound atrophy of these neurons accompanied by a variety of non‐neuronal reactive changes. During the first post‐operative week, non‐neuronal elements, distinct from astrocytes and normal oligodendrocytes and tentatively designated as “M” cells, become evident in the degenerating thalamic nuclei. Some “M” cells are characterized by heterochromatin nuclei and numerous free ribosomes, and resemble the agranular leukocytes accumulating simultaneously within the perivascular space of small vessels coursing through these regions (Matthews and Kruger, '73). Examples of such cells were sometimes seen bridging the external basal lamina. Other “M” cells display many profiles of granular endoplasmic reticulum and fewer free ribosomes but cannot be precisely classified as to nature and possible source. From the second through fourteenth week, “M” cells increase in prominence and accumulate electronlucent lipid vacuoles and phosphotungstic acid (PTA) positive dense bodies, presumably lysosomes, until these enlarged lipid‐laden cells constitute the predominant non‐neuronal entities in the zone of degeneration, in addition to hypertrophied astrocytes. Thirty‐four weeks post‐operatively “M” cells have decreased in size and apparent numbers, and dense bodies display a lessened affinity for PTA in addition to morphologic patterns suggestive of terminal lysosomes. Normal light and dark oligodendrocytes are encountered within the zone of degeneration throughout the entire survival period.

It is suggested that a significant proportion of “M” cells are of mesodermal (hematogenous; perivascular) origin although “M” cells display sufficient diversity of morphology to warrant consideration of additional sources for the reactive vacuolated forms. The experimental observations are discussed in relation to past and present concepts concerning the nature, origin and pathologic transformation of elements classified as microglia.
The effect of lid suture upon the growth of cells in the dorsal lateral geniculate nucleus of kittens
Authors: Guillery R. W.
Published: January 2005

It has been shown previously that unilateral suture of the eyelids of young kittens produces a reduced growth of cells in the visually deprived geniculate laminae (Wiesel and Hubel, '63). However, this effect is seen only in the parts of the lateral geniculate nucleus in which a binocular competition is possible. That is, where geniculate cells that receive from the deprived eye are aligned with cells that receive from the normal eye, the growth is affected. Where the geniculate cells that receive from the deprived eye are not aligned with any normally innervated cells, either because the deprived cells would normally receive from the monocular crescent of the visual field or because they lie opposite a part of the nucleus that has suffered degenerative changes, the cell growth is not affected (Guillery and Stelzner, '70; Guillery, '72).

The above observations suggest that bilateral lid suture may have relatively little effect upon geniculate cell growth. Eight kittens have been raised with both eyelids sutured and the size of the geniculate cells in layers A and A1 measured. Comparison with measurements obtained from seven normal cats of the same age, shows that binocular lid suture has little, if any, effect upon geniculate cell growth.
Antennal sensory system of the cockroach, Periplaneta americana: Postembryonic development and morphology of the sense organs
Authors: Schafer Rollie , Sanchez Thomas V.
Published: January 2005

Antennal growth in the cockroach, Periplaneta americana, takes place by division of the meriston (third antennal segment) and the meristal segments at the base of the antennal flagellum. Olfactory and contact chemoreceptive sense organs are the most numerous receptor organs on the antenna at all stages of postembryonic development. The sensory complement of male and female antennae is identical during the nymphal period, but a large difference between sexes appears at the adult stage. The adult male has nearly twice as many olfactory sensilla as the female, and more than half of these sensilla appear at the adult stage. These morphological data are consistent with the hypothesis that sensory receptors specific to the female sex attractant appear in the male only at the adult stage.
Congenitally abnormal visual pathways in mink (Mustela vison) with reduced retinal pigment
Authors: Sanderson K. J. , Guillery R. W. , Shackelford R. M.
Published: January 2005

The retinogeniculate pathways of several different genotypes of mink have been studied by the Nauta and Fink‐Heimer methods. An abnormal retinogeniculate pathway has been found in all mink in which the retinal pigment is reduced. Most of the abnormally routed nerve fibers arise in the temporal retina and cross in the chiasm, instead of staying ipsilateral as is normal. Some abnormal fibers in some of the mink also appear to arise in the nasal retina close to the line of decussation, and these pass ipsilaterally instead of following their normal crossed pathway.

A lack of pigment in the coat is not by itself associated with a pathway abnormality. In general, the size of the abnormal fiber component is related to the severity of the retinal pigment deficit. The abnormality is not related specifically to one gene or gene combination. We have found eight different gene combinations which produce a reduction of retinal pigment associated with a pathway abnormality.
Topographical localization in the olivo‐cerebellar projection: An electrophysiological study in the cat
Authors: Armstrong D. M. , Harvey R. J. , Schild Renée F.
Published: January 2005

Micro‐electrodes have been used to record the antidromic responses generated in olivary neurones by electrical stimulation of their axon terminations in the cerebellar cortex. This electrophysiological technique, in combination with precise histological methods for locating postions of the micro‐electrode tip, has been used to reinvestigate the topography of much of the olivo‐cerebellar projection. The results are partly in accord and partly in conflict with those of earlier investigations in which purely anatomical techniques were employed. In general, the terminations of a circumscribed group of olivary neurones have been found to be located within a longitudinal strip of the cerebellar cortex. Such strips frequently ignore the anatomical landmarks which divide the cerebellar cortex into lobules. The axons of a number of individual olivary neurones have been found to branch to provide a termination in both the anterior and the posterior lobe of the cerebellum. It was also found that olivary neurones projecting to a particular area of cerebellar cortex were in some cases situated in neighbouring regions of more than one of the main anatomical subdivisions of the olive (principal olive and medial and dorsal accessory olives). The discrepancies between the present findings and those made earlier are discussed.
The adrenergic innervation of the rat thalamus as revealed by the glyoxylic acid fluorescence method
Authors: Lindvall Olle , Björklund Anders , Nobin Anders , Stenevi Ulf
Published: January 2005

The adrenergic innervation of the thalamus, epithalamus, metathalamus, and subthalamus in the rat has been investigated by means of the recently introduced glyoxylic acid fluorescence method. Many areas of the thalamus and adjoining regions, that appear sparsely innervated by catecholamine (CA) fibers in specimens processed according to the standard Falck‐Hillarp formaldehyde method, were found to be richly supplied with such fibres in the glyoxylic acid‐treated specimens. Moreover, the glyoxylic acid method allows the tracing of the CA axons from the cell bodies up to the terminals, and in combination with stereotaxic lesions the following CA systems to the thalamus could be established:

The locus coeruleus system. Most of these axons ascend in the so‐called dorsal tegmental bundle through the mesencephalon and the zona incerta into the medial forebrain bundle. From this bundle branches were traced along several routes, giving rise to extensive terminal systems in many thalamic, metathalamic and pretectal areas, most notably the anterior, ventral and lateral nuclear complexes, and the medial and lateral geniculate bodies.

The dorsal periventricular bundle, which constitutes a previously not described adrenergic component of the dorsal longitudinal fasciculus. This system originates in cell bodies (defined as the A11 cell group) in the dorsal raphe region, the central gray of the mesencephalon, and in the periventricular gray of the caudal thalamus. The axons ascend within the dorsal longitudinal fasciculus and give rise to a thalamic and hypothalamic periventricular system, projecting to medial and midline thalamic, epithalamic and pretectal regions.

Part of the terminals in the paraventricular thalamic nucleus was identified with a non‐locus projection from cell bodies in the pontine or medullary reticular formation.

A system of delicate, probably dopamine‐containing axons was revealed in the caudal thalamus, the zona incerta and the dorsal and anterior hypothalamus. This system probably originates in the dopamine cell bodies of the diencephalic A11 and A13 cell groups, forming a hitherto unknown intradiencephalic dopaminergic system.

The adrenergic afferent systems to the thalamus can, to a large extent, be regarded as adrenergic components of known ascending reticular projections. The information on the adrenergic systems obtained with the glyoxylic acid method revealed new features of the organization of the thalamic projections from the brain stem reticular formation.
Retrograde axonal transport and the demonstration of non‐specific projections to the cerebral cortex and striatum from thalamic intralaminar nuclei in the rat, cat and monkey
Authors: Jones E. G. , Leavitt Randi Y.
Published: January 2005

The intralaminar nuclei of the thalamus have been examined particularly in the rat but with additional observations in the cat and squirrel monkey, with a view to determining the extent of their connections with the cerebral cortex and/or striatum. Cells in the intralaminar and other thalamic nuclei were labeled by retrograde axonal transport of the enzyme, horseradish peroxidase, from injection sites of varying size in the cerebral cortex and striatum.

This system provides a useful means of determining certain parameters of the horseradish peroxidase technique. It is concluded that the degree of retrograde labeling of a cell is primarily dependent upon the number and concentration of its axon terminals in the vicinity of the injection site. Injections of the striatum in the rat and monkey cause intense labeling of many cells in the intralaminar nuclei. Conversely, injections in the medial, frontal and parietal cortex of all three species, though leading to heavy labeling of many cells in the appropriate thalamic relay nuclei, result in only light labeling of relatively few cells in the intralaminar nuclei. Cells in a single intralaminar nucleus, however, though showing a broad topographical relationship, can be labeled from quite wide areas of the cerebral cortex. These results are consistent with the view that the intralaminar nuclei (including the parafascicular and centre médian) project densely to the striatum and sparsely and diffusely upon the cerebral cortex.
Differences in membrane structure between excitatory and inhibitory synapses in the cerebellar cortex
Authors: Landis Dennis M. D. , Reese T. S.
Published: January 2005

Several synapses of known physiological action are antomically segregated in the cerebellar cortex and are readily identified in freeze‐fracture preparations. Excitatory synapses, such as the parallel fiber‐to‐Purkinje spine synapse, climbing fiber‐to‐Purkinje spine synapse, and mossy or climbing fiber‐to‐granule cell dendrite synapse, were characterized by small aggregates of large particles on the cytoplasmic half of the presynaptic membrane, by a distinctly widened synaptic cleft, and by a large aggregate of particles on the external half of the postsynaptic membrane. Inhibitory synapses, such as the stellate cell axon‐to‐Purkinje dendrite synapse and the basket cell axon‐to‐Purkinje soma synapse, had no comparable specialization of either the pre‐ and postsynaptic membrane. The striking contrast in membrane structure at excitatory and inhibitory synaptic contacts presumably reflects differences in either the composition or organization of membrane proteins integral to synaptic function. Puncta adhaerentia between granule cell dendrites in cerebellar glomeruli were characterized by particles aggregated on the external half of both apposed membranes and were further differentiated from synaptic contacts by the smaller size of the particles. Protuberances on the external half of the presynaptic membrane were either small and coextensive with the synaptic contact or were larger and surrounded it; it is suggested that the small protuberances are synaptic vesicle sites whereas the large ones are coated vesicle sites.
Arachnoid villi in the spinal cord of dasyurid marsupials
Authors: Attwood H. D. , Wooley Patricia A.
Published: January 2005

During a routine histopathological study of dasyurid marsupials a high incidence of meningo‐encephalo‐myelitis due to Toxoplasma gondii was found. Decalcified blocks of the vertebral columns contained nodules closely related to the nerve roots and projecting into the venous sinuses. At first, these nodules were considered to be granulomata, but further studies revealed a constant relationship to the anterior nerve roots, a frequency of bilateral symmetry and an organoid structure which were more in keeping with a physiological rather than a pathological structure. These structures were morphologically similar to arachnoid villi in the head of dasyurid marsupials and were confined to the lumbo‐sacral cord. It is suggested that they are spinal arachnoid villi and that their varying cellularity results from the associated Toxoplasma infection.
Specification of retinal central connections in Rana pipiens before the appearance of the first post‐mitotic ganglion cells
Authors: Sharma S. C. , Hollyfield Joe G.
Published: January 2005

The order of production of retinal cells and the time when retinal cells become post‐mitotic was studied in Rana pipiens embryos using 3H‐thymidine autoradiography. Cell division stops first in the fundus of the retinal rudiment between embryonic stages 17 and 18 and gradually becomes restricted to the retinal margin. The ganglion cells in the fundus are among the first cells to become post‐mitotic.

The specification of the central connections of ganglion cells was studied by rotating the eye primordium at embryonic stages 16–21. After metamorphosis, the visual projection from the rotated eye to the contralateral optic tectum was mapped electrophysiologically and compared with the normal retinotectal map. In all cases, the visual projection map was rotated through the same angle as was indicated by the position of the choroidal fissure. It appears that ganglion cell connections with the tectum were specified by stage 17. These results indicate that ganglion cell central connections are specified before the first ganglion cells become post‐mitotic.
Synaptogenesis in the photoreceptor terminal of the mouse retina
Authors: Blanks Janet C. , Adinolfi Anthony M. , Lolley Richard N.
Published: January 2005

Observations are presented of a combined light and electron microscopic study of synaptogenesis in the photoreceptor terminal of visuallycompetent mice. Our study suggests that photoreceptor synaptogenesis in these retina progresses through a sequence of postnatal changes which leads to the ordered arrangement of processes within the adult photoreceptor terminal. On the 5th postnatal day, neuronal processes from synaptic contacts with a photoreceptor terminal, usually in the vicinity of a synaptic ribbon. Following the formation of synaptic contacts, the processes invaginate into the photoreceptor terminal, maintaining their position, lateral to a synaptic ribbon. Beginning on about the 10th day, a central process enters the terminal to yield a triad configuration which is a characteristic of a mature photoreceptor terminal. The formation of triads is essentially complete by the 14th postnatal day.

Our observations suggest that horizontal cell processes form synaptic contacts with the photoreceptor terminal before bipolar cell dendrites, implying that the horizontal cells mature in advance of the bipolar cells. This possibility is discussed in terms of the appearance of the electroretinogram (ERG) in the developing mouse retina.
Some observations on the early development of the optic tectum in the frog (Rana pipiens), with special reference to the effects of early eye removal on mitotic activity in the larval tectum
Authors: Currie Julia , Cowan W. M.
Published: January 2005

Following unilateral eye removal in Rana pipiens at embryonic stages 21–24 there is a statistically significant reduction in the numbers of mitoses found in the contralateral optic tectum at larval stage XIV amounting to approximately 16 per cent. Most of the reduction in mitotic activity occurs in the rostral third of the tectum and does not appear to involve its caudal pole, where cell proliferation is most vigorous. Since thymidine autoradiography indicates that the majority (if not all) of the cells being generated in the rostral third of the tectum at stage XIV are either glial or ependymal cells, it is suggested that the primary effect of eye removal on cell proliferation in the tectum is upon gliogenesis. Using the autoradiographic method for tracing axonal connections, it has been found that the axons of the retinal ganglion cells reach the tectum by embryonic stage 22, and by larval stage XIV have spread to all but its caudomedial region.
Connections of the median and dorsal raphe nuclei in the rat: An autoradiographic and degeneration study
Authors: Conrad Lily C. A. , Leonard Christiana M. , Pfaff Donald W.
Published: January 2005

Ascending and descending projections from the median and dorsal raphe nuclei of the midbrain were mapped in the albino rat, using reduced‐silver stains after lesions or the autoradiographic technique following injections of tritiated proline. In all major respects the two techniques gave the same results. The majority of the ascending projections sweep ventrally from the raphe nuclei, then curve rostrally to course through the ventral tegmentum and into the medial forebrain bundle (MFB). Others radiate through the mesencephalic reticular formation (RF) and central grey, turning ventrally at the posterior thalamic border to enter the subthalamus. From the MFB, fibers branch into the hypothalamus, preoptic areas, anterior amygdala and olfactory tubercle, while some fibers enter the fornix or the stria terminalis. Many fibers continue rostrally in the MFB, joining the diagonal bands of Broca to reach the septal nuclei or, further rostrally, the cingulum bundle. Fibers in the cingulum bundle turn caudally around the genu of the corpus callosum, some branching into the cell‐free layers of the pregenual cortex. Runing caudally, then curving around the splenium, the cingulum bundle projection sprays out into the subiculum and in some cases a projection into the hippocampus is seen.

Other ascending projections include one to the habenular nuclei through the fasciculus retroflexus. Projections to the mediodorsal, parafascicular and reuniens nuclei of the thalamus were also noted.

Descending projections were observed to the dorsal tegmental nucleus and locus coeruleus and diffusely to the pontine reticular formation and caudal central grey. No projections were seen below the level of the facial nerve nucleus and none were observed to the cerebellum, caudal raphe nuclei or cranial nerve nuclei.
The localization of 5‐hydroxytryptamine in chromaffin cells of the leech body wall
Authors: Coggeshall Richard E. , Yaksta‐Sauerland Barbara A.
Published: January 2005

The present study is an analysis of the sites of uptake of radioactive 5‐HT into the leech body wall. Two sites of uptake are noted: (1) the axons and nerve terminals containing large dense core vesicles and (2) the type I cells of the vasofibrous tissue. Both of these cell types are chromaffin cells in that they contain vesicles or granules with cores that reduce dichromate salts. Chemicla analysis indicates that most of the radioactivity in the body wall at the time of sacrifice is 5‐HT. Thus, these two cell types acquire 5‐HT when it is present in the extracellular environment and presumably store it in the cores of the vesicles of granules that characterize these cells. This acquisition of 5‐HT may be an impotrant method of inactivation for 5‐HT.

In addition, the fine structure of the vasofibrous tissues is described here for the first time. There are two types of cells in the vasofibrous tissue, rather than one as previously thought, and the electorn microscope clearly shows that the fibrils of vasofibrous tissue are not pigmented capillaries.
Time of neuron origin in preoptic and septal areas of the mouse: An autoradiographic study
Authors: Creps Elaine S.
Published: January 2005

Times of neuron origin were determined for septal and preoptic nuclei of adult mice given a single injection of H3‐thymidine at some stage of development. In the septal area, the sequence of neuron origin for its constituent nuclei roughly follows phylogenetic trends. Mediolateral and lateromedial gradients in septal and preoptic areas, respectively, seem to be opposites but are both “outside‐in,” as is a rostrocaudal septal gradient when viewed sagittally. An “inside‐out” gradient characterizes the olfactory tubercle and possibly the periventricular proptic region. These findings strengthen the impression that cells of nuclear areas undergo final division in an “outside‐in” sequence; those of layered structures arise “inside‐out.” A dorsoventral gradient in periventricular preoptic region parallels that in hypothalamus. The significance of these gradients is unknown, but they often presage corresponding gradients in nuclear differentiation, as in the preoptic area.

Cell birthdates for nucleus accumbens resemble those in the striatum more than in the septum, where the nucleus is usually catalogued. To help resolve the issue of whether the preoptic area is telencephalic or diencephalic, it was compared with neighboring regions. No conclusions were reached, since similarities exist in both directions. The validity of a telodiencephalic boundary based on cytoarchitectonics. circuitry, or function is considered; such separation of the forebrain, except for topographical convenience, appears unwarranted.
Restitution of function and collateral sprouting in the cat spinal cord: The partially hemisected animal
Authors: Murray Marion , Goldberger Michael E.
Published: January 2005

The hypothesis that collateral sprouting might be correlated with recovery of function was tested by a combination of behavioral and anatomical studies. Partial hemisections, sparing the dorsal columns, were made between T12 and L1 of cat spinal cord. Initially, all reflex and locomotor hindlimb activity was depressed ipsilaterally. During two postoperative weeks behavioral and electromyographic responses increased in response to intrinsic reflex elicitation but not to descending or crossed reflex elicitation. Marked improvement in use of the limb occurred as intrinsic reflex activity increased and became, in some cases, hyperactive. The status then remained stable for ten months. Since intrinsic reflexes are mediated by ipsilateral dorsal roots, the intraspinal distribution of L5 or L6 dorsal roots was determined by degeneration methods ten months after hemisection or by quantitative radioautography 20 days after hemisection. By both methods, the dorsal root distribution was found to be asymmetrical in the spinal gray. It was greater on the experimental side and the distribution was altered, having a greater distribution medially in Rexed's lamina VI and laterally in lamina VII. These anatomical changes are considered as signs of collateral sprouting from dorsal roots in response to degeneration of descending tracts on the same side. Dorsal root distribution to dorsal horn (laminae I–IV), motor nuclei, and nucleus gracilis is symmetrical. Regions of increased and of expanded dorsal root input can be correlated with electrophysiologically determined location of interneurons in the path of cutaneous reflexes and of stretch reflex facilitation. Behavioral and anatomical changes were selective; intrinsic reflexes recovered or became hyperactive and ipsilateral dorsal roots showed evidence of collateral sprouting during the recovery period, although a causal relationship between the two cannot be proven, by the present experiments.
Restitution of function and collateral sprouting in the cat spinal cord: The deafferented animal
Authors: Goldberger Michael E. , Murray Marion
Published: January 2005

Unilateral hindlimb deafferentation is followed initially by generalized loss of all reflex and useful function. As useful movement returns, certain descending reflexes recover and become hyperactive: crossed reflexes do not. Recovery of movement and reflex hyperactivity are then abolished by subsequent destruction of the ipsilateral descending systems. Although there is no sprouting from contralateral dorsal roots, bilateral degeneration of descending systems is asymmetrical, being greater in density and distribution on the previously deafferented side. Collateral sprouting to certain spinal laminae apparently took place during the recovery period from the same source which mediated reflex hyperactivity; the ipsilateral descending systems. A substantial descending projection to Clarke's nucleus was found only on the experimental side, however, suggesting that a central feedback system replaced the abolished peripheral feedback. If functional, this might subserve recovery of the ability to maintain a limb position.

Chronically deafferented cats which are then transected show, for the first time, hyperreflexia of crossed responses, which develops gradually during the first week post‐transection. It may be related to sprouting of contralateral dorsal roots for contralateral ganglion injection with 3H‐proline gives a larger than normal ipsilateral distribution of grain density over the commissural nuclei.

It is suggested that recovery and hyperactivity of reflex responses underlie the recovery of useful movement and that reflex recovery may be related to collateral sprouting. It is also suggested that both the reflex and the anatomical response to a given lesion is restricted to only one of the remaining systems and is therefore a specific rather than a generalized response.
Hippocampal development in the rat: Cytogenesis and morphogenesis examined with autoradiography and low‐level X‐irradiation
Authors: Bayer Shirley A. , Altman Joseph
Published: January 2005

The cytogenesis and morphogenesis of the rat hippocampus was examined with the techniques of 3H‐thymidine autoradiography, cell pyknosis produced by low‐level X‐irradiation, and quantitative histology.

The procedure of progressively delayed cumulative labelling was used for autoradiography. Groups of rats were injected with four successive daily doses of 3H‐thymidine during non‐overlapping periods ranging from birth to day 19. They were killed at 60 days of age, and the percentage of labelled cells was determined. The pyramidal cells of Ammon's horn and the polymorph cells of the dentate gyrus are not labelled postnatally, confirming earlier conclusions of their prenatal origin. In the dentate gyrus, 85% of the granule cells are formed postnatally, with 45% forming during the first week. The majority of the small cells of the dentate molecular layer and of the Ammonic strata oriens, radiatum, and lacunosum‐moleculare are formed during the second week.

As an aid to locating the proliferative compartments of the hippocampus during development and to characterize the time course of both cell differentiation and morphological development, rats ranging in age from gestation day 17 to postnatal day 103 were killed six hours after one exposure to 200r X‐rays, and the pyknotic cells were counted. Cell pyknosis in Ammon's horn reaches a maximal level prenatally and declines rapidly during the early postnatal period. Cell pyknosis in the dentate gyrus reaches its highest level during the second postnatal week and declines gradually with some radiosensitive cells still present in the adult. Immature granule cells are also at their highest level during the second postnatal week, while mature granule cells gradually accumulate to attain asymptotic levels at around two months of age. The alignment of the pyramidal cells to form the characteristic curvature of Ammon's horn occurs shortly after pyramidal cell cytogenesis is completed. Conversely, the sharp fold in the dentate gyrus is apparent from the day of birth onward, before the completion of granule cell cytogenesis. Possible mechanisms for the morphological development of the dentate gyrus along with a consideration of the possible migratory route of granule cell precursors is also discussed.
Fiber projections from trigeminal nucleus caudalis in primate (squirrel monkey and baboon)
Authors: Tiwari Rajendra K. , King Robert B.
Published: January 2005

Small radiofrequency lesions were produced in the trigeminal nucleus caudalis and adjacent lateral reticular formation (LRF) in seven squirrel monkeys and four baboons. Frozen brain sections were stained for cellular morphology and for axonal and terminal degeneration. The lesions in pars marginalis and gelatinosa produced terminal degeneration in pars magnocellularis and LRF. Pars magnocellularis lesions produced degeneration into the ascending trigeminal intranuclear tract and the adjacent lateral reticular formation. Ascending thalamic and reticular projections emanated from LRF lesions. These observations suggest that elements of the LRF adjacent to the nucleus caudalis are an integral part of the trigeminal somesthetic fiber projection system and may subserve the perception of noxious stimuli.
Cycle times of the neural epithelial cells of various types of neuron in the rat. An autoradiographic study
Authors: Schultze Brigitte , Nowak Bogdan , Maurer Werner
Published: January 2005

Cell kinetic studies of the proliferation of the neural epithelium during the embryonic development of the rat brain are described.

Pregnant rats received a single injection of 3H‐thymidine (3H‐TdR) between the tenth and twenty‐first day of pregnancy. Autoradiographs of the brains of the 25‐day‐old offspring were prepared. For a number of different cell types (table 1, II) the percentage of labeled neurons as a function of time of prenatal 3H‐TdR injection was determined.

The end of the proliferating period of the neural epithelial cells of certain cell types can be derived from these percentages of labeled cells (table 1, V). Further‐more, it can be demonstrated that the percentage of labeled neurons is equal to the labeling index of the neural epithelial cells of these cell types at the time of prenatal 3H‐TdR injection.

Based on the labeling index of the neural epithelial cells and their S phase, cycle times can be calculated. This way it is possible for the first time to determine the cycle times of those neural epithelial cells that later on differentiate into a certain type of neuron (table 1, IV).

The calculated cycle times show that up to the sixteenth prenatal day the neural epithelial cells behave like a homogeneous cell population which proliferates with an approximately constant cycle time of about half a day. The cycle time seems to increase with increasing fetal age.

From the total number of a certain type of neuron the number of mitotic divisions or cycle times respectively can be derived which is necessary to produce the number of neural epithelial cells providing these neurons. With regard to the mean cycle time of the neural epithelial cells it can be concluded that the beginning of proliferation of the neural epithelial cells coincides with the formation of the neural plate on the ninth day of embryonic development or starts even shortly before this time.
Retinogeniculate projections in the rabbits of the albino allelomorphic series
Authors: Sanderson K. J.
Published: January 2005

Retinogeniculate pathways have been studied by fiber degeneration and autoradiographic methods in rabbits that are homozygous for alleles of the albino series of genes. It has been found that albino and Himalayan rabbits, which both lack all melanin pigment in the eye, have a similar abnormality of the retinogeniculate pathway. The number of ipsilateral optic fibers going to the lateral geniculate nucleus is reduced in these rabbits, the ipsilateral projection forms a discontinuous terminal zone instead of the normal continuous zone, and some of the ipsilateral axons terminate in an inappropriate part of the nucleus, so that regions receiving a crossed input in normal rabbits receive an uncrossed input in the abnormal rabbits. Chinchilla rabbits show a slightly reduced fur pigmentation but have a normal distribution of pigment in the retinal pigment epithelium and these rabbits have normal retinogeniculate pathways.

In addition, the normal retinogeniculate pathway was studied. Autoradiographic methods show that the β segment of the lateral geniculate nucleus receives a contralateral input. Hence, earlier views that this segment projects to the visual cortex but receives no retinal input, are untenable. Further, in the autoradiographic material it was not possible to identify separate ipsilateral laminae and it was concluded that in the normally pigmented rabbit the ipsilateral retinogeniculate projection forms one relatively continuous group.
The distribution of acetylcholinesterase in buds of the rat vallate papilla as determined by electron microscope histochemistry
Authors: Paran Nava , Mattern Carl F. T.
Published: January 2005

The distribution of acetylcholinesterase (AChE) in the rat vallate papillary bud was investigated by histochemical electron microscopy. Previous reports of specific AChE activity around subgemmal and intragemmal nerves and between some taste bud cells have been confirmed. In addition we have consistently observed dense precipitation between microvilli in the taste pore. The studies suggest that the neurotransmitter, acetylcholine, may be involved in early events in the taste process which are believed to occur in the pore.
The radial fibers in the globus pallidus
Authors: Fox C. A. , Rafols J. A.
Published: January 2005

In our Golgi collection of adult monkey brains the striatal efferents, i.e., the radial fibers in the globus pallidus and the “comb” bundle fibers in the internal capsule and in the cerebral peduncle, are well impregnated in the horizontally sectioned brain and in a sagittal sectioned brain. Since collaterals emerging from radial fibers are seen only in the horizontal series and not in the sagittal series, the interpretation is that they proceed anteriorly and posteriorly only, following the curvature of the pallidal segments, and do not run superiorly or inferiorly as they emerge.

Although radial fibers emitting collaterals in the lateral segment and in the medial segment of the globus pallidus have been observed, it has not been possible to observe the same radial fiber emitting collaterals in both pallidal segments and the prospects of ever doing so are not good. The radial fibers converging in the globus pallidus pursue many radii and there is little coincidence between the plane of section and the planes in which they travel. At most only severed radial fiber segments 100–150 microns in length can be found in the horizontal sections needed to observe the collaterals. Moreover, sagittal sections show that radial fibers are deflected in their course, either dorsoventrally or ventrodorsally, as they pass through the internal medullary lamina to enter the medial segment of the globus pallidus.

The radial fibers in the medial segment of the globus pallidus are continuous with the “comb” bundle fibers and appear to be thinner than the radial fibers in the lateral segment of the globus pallidus. It is not proved; nonetheless, the view expressed here is that the radial fibers are thinner in the medial segment of the globus pallidus because they may be the same fibers that gave off collaterals in the lateral segment of the globus pallidus. This is discussed in the light of the electrophysiological disclosure of Yoshida et al. ('71, '72) that caudatopallidal fibers are collaterals off caudatonigral fibers.

The afferent plexuses of fine, “bouton en passage” fibers, which completely ensheath the long radiating dendrites in the globus pallidus (Fox et al., '66) are well impregnated in the horizontal series. Obviously, they are formed by a number of ultimate branches converging from the collateral branches of a number of different radial fibers. The divergence, too, in this system must be considerable; however, its true extent can only be surmised from the severed radial fibers and radial fiber collaterals seen in the incompletely impregnated Golgi section. One severed segment of a radial fiber displays three collaterals and one of these collaterals has five branches, one of which can be traced to a point where it gives off an ultimate branch in an afferent, dendrite‐ensheathing plexus.
Computer measurements of axis cylinder diameters of radial fibers and “comb” bundle fibers
Authors: Fox C. A. , Rafols J. A. , Cowan W. M.
Published: January 2005

In electron micrographs of the squirrel monkey (Saimiri sciureus) brain the striatal efferents were observed at two different levels in their course: (1) in cross‐sectioned radial fiber bundles just before they enter the globus pallidus; (2) in cross‐sectioned “comb” bundle fibers just before they enter the substantia nigra. In the radial bundles nearly all of the fibers are myelinated; in the “comb” bundle most are unmyelinated. The polarity of all the “comb” bundle fibers is descending. None of them degenerate following a large lesion in the substantia nigra but they do degenerate following a large lesion in the striatum. Also following this latter lesion the endings with large synaptic vesicles, which make up most of the endings in the globus pallidus and the substantia nigra, degenerate.

For computer measurements, electron micrographs of the radial bundle were enlarged photographically to a final magnification of 20,000; those of the “comb” bundle to × 50,000. Measurements of 1309 radial fibers revealed a mean axis‐cylinder diameter of 0.68 microns, and measurements of 749 unmyelinated “comb” bundle fibers gave a mean axis‐cylinder diameter of 0.21 microns. Myelinated fibers were not included in the “comb” bundle measurements because it contains myelinated fibers of pallidal origin in addition to myelinated fibers of striatal origin.

The results here indicate that the striatal efferents undergo a decided decrease in axis‐cylinder diameter during their transit through the globus pallidus. It is suggested that the large non‐spine bearing neurons in the striatum are the source of the striatal efferents and that they send their axons into the substantia nigra and enroute spend a great quantity of their axoplasm by extending extensive collaterals in both segments of the globus pallidus. This could account for the decreased caliber of the striatal efferents in the “comb” bundle and other findings in the striatum, globus pallidus and substantia nigra.
Demonstration of terminalis, olfactory, trigeminal and perivascular nerves in the rat nasal septum
Authors: Bojsen‐Møller Finn
Published: January 2005

The innervation of the nasal septum and around the olfactory bulb has been investigated in rats by means of whole‐mount preparations and histological sections. Silver staining, OsO4 staining, PAS staining, cholinesterase reaction and fluorescence for catecholamine‐containing nerves were used. The nervus terminalis forms on the medial side of the olfactory bulb a ganglionated plexus, from which branches are given off which course peripherally with the vomeronasal nerves. From a dorsal part of the terminalis nerve plexus an anterior branch is given off which runs along the anterior ethmoidal nerve to the nasal vestibule where it connects with a group of ganglia. The peripheral branches of the nerve run from here along two epithelial cristae formed histologically like dermal papillae. Ventrally in the respiratory region at the junction of the nasal cavity and the nasopharynx is a 1 × 2 mm area with olfactory epithelium, glands of Bowman and an independent innervation from the olfactory bulb. This is the so‐called septal olfactory organ. Trigeminal nerves form a plexus in the respiratory region and in the vestibule, but do not supply the olfactory region. Catecholamine‐containing and cholinesterase‐positive nerves run along the meningeal arteries on the cribriform plate and accompany their branches to the vascular plexus in the olfactory and respiratory regions. Double innervation is found not only of this vascular plexus but of the venous sinuses in the swell bodies of the vestibule. The glands of the nose are not surrounded by catecholamine‐containing nerves.
A scanning electron microscopic study of the morphology and geometry of neural surfaces and structures associated with the vestibular apparatus of the pigeon
Authors: Landolt Jack P. , Correia Manning J. , Young Eric R. , Cardin Ronald P. S. , Sweet Robert C.
Published: January 2005

The scanning electron microscope (SEM) was used to investigate the morphology of the neuroepithelial regions of the vestibular ampullary structures in 47 White King pigeons. The specific neural surfaces studied were (1) the cristae ampullares of the vertical and lateral membranous ampullae, (2) the hair cells lining the cristae, (3) the ampullary nerve fibers, and (4) the bipolar cells of the vestibular (Scarpa's) ganglion. Additionally, some observations of the gross anatomical structures of the bony labyrinth are given. Arguments are advanced which show that if the surface area of a given semicircular canal can be projected onto one of the three normal head planes, then that canal can be made to respond to motion in the appropriate plane, provided that the projected area is sufficiently large to achieve a threshold pressure as determined by a generalized form of Groen's equation ('57). With regard to the cristae ampullares, it is hypothesized that their surface areas can be described by means of a revolved catenary, i.e., a catenoid of revolution. (The catenary is found in nature as the approximate shape taken by a flexible cable when it is suspended at two points). The surface area of a catenoid provides a minimum surface of revolution. In the context of a crista, this implies that the given number of hair cells could not be fitted onto a smaller surface area. One advantage of this is that nature is able to utilize a thinner cupula than would be possible with other configurations and therefore an increased sensitivity to cupular motion can be realized. A second important factor is that all hair cells must revolve (by way of cupular motion) about the same centre of rotation in response to angular acceleration. Thus, all of the orthogonally‐positioned hair cell tufts on the cristae surface may be stimulated simultaneously by way of a tangential shear. Other arguments show that the classical “swinging door” type of cupular motion is not consistent with SEM and other recent observations. Two alternate modes of cupular motion are presented, each of which requires far less energy expenditure than does the “swinging door” cupula. The suggestion is then made that, during normal head movements, the cupula behaves as a drum much like the tympanic membrane and that only for large, non‐physiological motions does the “swinging door” mode of cupular motion take place. It must be remembered, however, that cupular motions during normal physiological head movements are infinitesimally small (Oman and Young, '72).
The distribution of the alpha type of ganglion cells in the cat's retina
Authors: Wässle H. , Levick W. R. , Cleland B. G.
Published: January 2005

There is a distince class of large ganglion cell bodies observable in whole‐mount preparations of the cat's retina stained with cresyl violet. Measurements of perikaryal size and its variation with eccentricity from the central area support the indetification of the large cells with the class of alpha cells previously defined in Golgi‐stained preparations. A complete enumeration of alpha cell sin one retina yielded a total of 6212. They were encountered in all parts of the retina and had a peak density within the central area (200/mm2). The retinal distribution was displayed as a contour map of alpha‐cell density. Away from the central area, the lines of iso‐density had the form of a 4‐pointed star with rather blunt points corresponding to horizontal and vertical ridges of augmented density. Along horizontal, vertical and oblique strips through the central area, alpha‐cell density was an approximately constant fraction of total ganglion cell‐density. The averag; value of the fraction was 3.3% from which it has been calculated that the cat's retina may contain as many as 190,000 ganglion cells.
Color‐specific interconnections of cones and horizontal cells in the retina of the goldfish
Authors: Stell William K. , Lightfoot David O.
Published: January 2005

In Golgi preparations of goldfish retina we have observed three types of horizontal cell which receive exclusively from cones and one which receives exclusively from rods. The cone horizontal cells were designated H1, H2 and H3, in order of increasing dendritic spread, increasing separation from the outer synaptic layer, decreasing size of perikaryon, and decreasing density of cone contacts. Slender appendages with knobby terminal enlargements project horizontally from the perikarya and larger dendrites of both rod and cone horizontal cells.

We determined patterns of cone inputs to Golgi‐impregnated horizontal cells by analyzing serial 1 μm sections with the light microscope. The probable inputs, in terms of visual pigments in the cones which contact them, are: H1, red + green + blue; H2, green + blue; H3, blue. Analysis of previously published work suggests (1) that H1 cells generate monophasic or L‐type responses, H2 cells generate biphasic or C1‐type responses, and H3 cells generate triphasic or C2‐type responses; (2) that H1 cells receive direct functional input at least from red‐sensitive cones, H2 cells from green‐sensitive cones, and H3 cells from blue‐sensitive cones; and (3) that H1 cells constitute pathways from cones to H2 cells, and H2 cells constitute pathways from cones and H1 cells to H3 cells. The precise location and route of the transfers, from H1 to H2 and from H2 to H3, are not yet known.