bluuebunny/crossref_metadata_2025 huggingface dataset:
Innervation and structure of extraocular muscles in the monkey in comparison to those of the cat
Authors: Spencer Robert F. , Porter John D.
Published: May 2005

Motoneurones that innervate the medial rectus, lateral rectus, and accessory lateral rectus muscles in the monkey have been identified and localized by retrograde transport of horseradish peroxidase. Medial rectus motoneurones were located within both dorsal and ventral regions of the oculomotor nucleus, with a differential distribution along the rostral‐caudal axis of the nucleus. Lateral rectus motoneurones were located predominantly within the abducens nucleus, and were distributed throughout the rostral‐caudal extent of the nucleus. Motoneurones that innervate the accessory lateral rectus muscle comprised a group of large cells located approximately 0.5 mm ventral to the rostral protion of the abducens nucleus, corresponding to the ventral abducens nucleus of Tsuchida ('06). The ventral subgroup of abducens motoneurones, which innervate both the lateral rectus and accessory lateral rectus muscles, thus do not occupy a brain stem location similar to the cat accessory abducens nucleus, whose motoneurones innervate the retractor bulbi muscle, to which the accessory lateral rectus muscle presumably is homologous. A few accessory lateral rectus motoneurones also were located within the abducens nucleus, overlapping the distribution of lateral rectus motoneurones.

Electron microscope examination of the lateral rectus muscle revealed the presence of three morphological types of singly innervated muscle fibers and two morphological types of multiply innervated muscle fibers that exhibited a differential distribution within the orbital, intermediate, and global regions of the muscle. The accessory lateral rectus muscle resembled the global portion of the lateral rectus muscle in containing two morphological types of singly innervated fibers and one type of multiply innervated fiber.

These findings indicate that the central differences in the brainstem locations of motoneurones that innervate the cat retractor bulbi and monkey accessory lateral rectus muscles are correlated with peripheral differences not only in the morphology, but also possibly in the mechanical roles, of the muscles they innervate. The accessory lateral rectus muscle thus appears to have evolved both structurally and functionally towards more of a role in patterned eye movement. Furthermore, with the phylogenetic regression of the retractor bulbi muscle, the various types of eye movement with which this muscle is associated in lower vertebrates may be assumed by the other extraocular muscles in higher mammals, including humans.
The distribution of pontine projection cells in visual and association cortex of the cat: An experimental study with horseradish peroxidase
Authors: Albus K. , Donate‐Oliver F. , Sanides D. , Fries W.
Published: May 2005

The projections from the visual and association areas of the cat's neocortex to the pons were investigated with horseradish peroxidase as retrograde tracer. Small injections were made into the pars basalis of the pons, along its entire rostrocaudal extent. The cortical areas considered were areas 17, 18, 19, 20, 21, and the lateral suprasylvian areas (LSA); the posterior (PMSA), and the anterior middle suprasylvian association area (AMSA), the anterior lateral association area (ALA) and the anterior suprasylvian association area (ASA). A pontine projection was found for all the areas investigated; however, areas differ in the relative strength of their projection, in their intraareal distribution of projection cells, and in the location of their projection zones within the pons.

A low to moderate density of projection cells is seen in the areas 17, 18, 19, 20, 21, and in PMSA. The posterior part of LSA contains only a few projection cells, whereas in more anterior parts of LSA the density of projection cells is moderate to high. A relatively dense distribution of projection cells also appears in AMSA, ALA, and ASA. In those areas which are retinotopically organized (17, 18, 19, LSA) the representation of the center of gaze contains far fewer projection cells than the representation of peripheral vision. In the association areas the distribution of projection cells appears even.

The projection zones from areas 17, 18, and 19 overlap with the zones from LSA in the anterior half of the basal pons. The projection zones from areas 20 and 21 and from ALA and ASA are located in the middle third and the projection zones from PMSA and AMSA spread throughout the entire rostrocaudal extent of the basal pons.

Our findings indicate that efferent impulses from the visual cortical areas and from the association areas on the middle suprasylvian gyrus are relayed to the cerebellum exclusively via the basal pontine nuclei. The findings further suggest that the visual corticopontine projections carry a map of the visual field in which the cortical magnification factor is reduced.
Onset of synapse formation in the human spinal cord
Authors: Okado Nobuo
Published: May 2005

The time of onset of synapse formation was examined in the cervical spinal cord of eight human embryos ranging from 4 (8 mm in crownrump length) to 6 (22 mm) weeks of ovulation age. The first synapses were found in the motor nucleus of a 10‐mm embryo (Streeter's horizon XV). They contained only a small number of synaptic vesicles and had asymmetrical membrane thickenings, with thicker postsynaptic membranes than presynaptic ones. With the exception of an occasional axosomatic synapse, nearly all synapses found in a 10‐mm embryo were axodendritic. In an 11‐mm embryo (Streeter's horizon XVI), synapselike contacts (SLC) were found in the dorsal marginal layer. They contained a small number of synaptic vesicles and had “reversed membrane specalization” with prominent presynaptic membrane densities. The number of SLC decreased in older embryos. Judging from the morphological characteristics of membrane specializations and the temporal decrease in number, SLC are considered to be either transient synapses on the borderline cells or axoglial synapses. Synapses in the regions outside the motor nucleus first appeared in the dorsal marginal layer of a 14‐mm embryo (Streeter's horizon XVII).
The olivocerebellar projection in the monkey. Experimental studies with the method of retrograde tracing of horseradish peroxidase
Authors: Brodal P. , Brodal A.
Published: May 2005

Following injections of horseradish peroxidase (HRP) in various lobes and lobules of the macaque cerebellum the occurrence of retrogradely labeled cells in the inferior olive was mapped. Only cortical areas showing staining of the molecular layer were considered as sites of uptake of HRP. To facilitate comparisons between cases and presentation of findings, a diagram of the macaque inferior olive as imagined unfolded was constructed (Fig. 1). Attempts were made to compare the findings made with data on the olivocerebellar projection in the cat and the pattern of a longitudinal zonal subdivision of the cerebellum.

In general there appears to be a remarkably close correspondence between the organization of the olivocerebellar projection in the monkey and the cat. The projection is precisely organized and appears to be purely crossed. Within the projections to some of the cerebellar cortical zones a topical pattern can be demonstrated.

Olivary afferents to vermal lobules V, VII, and VIII are derived from the caudal half of the medial accessory olive, projecting to Voogd's zone A. The topical pattern resembles that in the cat (Fig. 8). After injections covering the lateral zone of the anterior lobe vermis (zone B), labeled cells are seen in the caudal part of the dorsal accessory olive. In some cases staining of the intermediate part of the anterior lobe and of the paramedian lobule is followed by labeling of cells in the rostral part of the dorsal accessory olive (zones C1 and C3) or in the rostral half of the medial accessory olive (zone C2). When the injected area covers lateral parts of the cerebellum, there is labeling in the principal olive (projecting to zones D1 and D2). Although not entirely decisive, the findings lend support to the view that the ventral lamella of the principal olive supplies zone D2, whereas the dorsal lamella supplies zone D1. The relatively sparse data in the literature on the afferents to the monkey olive are briefly considered. On many points the projections appear to be as in the cat. However, there is possibly a species difference between cat and monkey as concerns their receipt of afferents from the red nucleus.
The distribution of visceral primary afferents from the pelvic nerve to Lissauer's tract and the spinal gray matter and its relationship to the sacral parasympathetic nucleus
Authors: Morgan Charles , Nadelhaft Irving , de Groat William C.
Published: May 2005

The central distribution of visceral primary afferent fibers from the pelvic nerve of the cat and the relationship of these fibers to preganglionic neurons of the sacral parasympathetic neurons (SPN) have been studied. Horseradish peroxidase (HRP) applied to the cut pelvic nerve was detected ipsilaterally in preganglionic neurons and dorsal root ganglion cells (segments S1–S3), and in central afferent projections to Lissauer's tract (LT), the dorsal columns, the dorsolateral funiculus, and spinal gray matter. The afferent projections were strongest in the region of the SPN (S1–S3) but extended far beyond its limits (e.g., LT was labeled from L4 to Cx7). In the transverse plane, collateral fiber bundles formed a thin shell around the dorsal horn predominantly within lamina I and expanded into terminal fields in the gray matter. The more prominent lateral collateral projection (LCP) extended into laminae V and VI, whereas the medial one (MCP) ended in the dorsal commissure. In longitudinal planes these projections exhibited a periodicity with an interval of approximately 200 μm. The distribution of afferent collateral projections overlaps the regions where many preganglionic neurons and their dendritic extensions are located, and also areas known to contain interneurons involved in visceral pathways. A differential distribution of afferents within the SPN was noted where a higher intensity was observed in proximity to those neurons located in laminae V and VI, which innervate the colon, and a lower intensity near neurons located in lamina VII which innervate the bladder. This is consistent with the known spinal control of colon reflexes and the supraspinal control of bladder reflexes. The widespread rostrocaudal extent of the pelvic primary afferent projection is consistent with the necessity for the integration of somatic and autonomatic elements from various levels of the lumbo‐sacral‐coccygeal spinal cord in the performance of pelvic visceral functions.
Visual topography of V2 in the macaque
Authors: Gattass R. , Gross C. G. , Sandell J. H.
Published: May 2005

The representation of the visual field in the area adjacent to striate cortex was mapped with multiunit electrodes in the macaque. The animals were immobilized and anesthetized and in each animal 30 to 40 electrode penetrations were typically made over several recording sessions.

This area, V2, contains a topographically organized representation of the contralateral visual field up to an eccentricity of at least 80°. The representation of the vertical meridian is adjacent to that in striate cortex (V1) and forms the posterior border of V2. The representation of the horizontal meridian in V2 forms the anterior border of V2 and is split so that the representation of the lower visual field is located dorsally and that of the upper field ventrally. As in V1, the representation of the central visual field is magnified relative to that of the periphery. The area of V2 is slightly smaller than that of V1. At a given eccentricity, receptive field size in V2 is larger than in V1.

The myeloarchitecture of V2 is distinguishable from that of the surrounding cortex. The location of V2 corresponds, at least approximately, to that of cytoarchitectonic Area OB. V2 is bordered anteriorly by several other areas containing representations of the visual field.
Hypothalamic, other diencephalic, and telencephalic neurons that project to the dorsal midbrain
Authors: Morrell J. I. , Greenberger L. M. , Pfaff D. W.
Published: May 2005

Neurons in the hypothalamus, other diencephalic regions, and the telencephalon which project to the mesencephalic central gray (CG) and the region lateral to it were demonstrated, in the rat, by the horseradish peroxidase retrograde neuroanatomical tracing method with diaminobenzidine and tetramethyl benzidine visualization reactions. The greatest concentrations of neurons that project to the dorsal mesencephalon were found in the ventromedial nucleus, particularly the anterior and ventrolateral subdivisions, in the dorsal premammillary nucleus, and in the zona incerta. Neurons that project to or lateral to the CG were also found in the laterocaudal hypothalamus, the dorsomedial hypothalamus, regions of the anterior hypothalamic area, specific areas of the cerebral cortex (32, 29, 8, 8A, 13, 14), and the central nucleus of the amygdala. Some neurons that project were also found in the preoptic area, septum, bed nucleus of the stria terminals, and the habenula.

More neurons in the mediocaudal quadrant of the hypothalamus project to the mesencephalon than do those in laterocaudal, mediorostral, or laterorostral quadrants. More neurons in the medial than the lateral half, and more in the caudal than the rostral half of the hypothalamus project to the mesencephalon. More neurons project to the central gray, or the region lateral to it, at the inferior colliculus.

These descending connections to the midbrain, particularly from the hypothalamus and zona incerta, are probably components of neural networks that regulate nociception, certain neuroendocrine functions, sexual and other behaviors, and certain autonomic functions.
Anatomical organization of primate visual cortex area VII
Authors: Lund J. S. , Hendrickson A. E. , Ogren M. P. , Tobin E. A.
Published: May 2005

The Golgi Rapid and Kopsch techniques have been used to provide material for an examination of the internal neuronal organization of cortical area VII of the Macaca monkey. The afferent and efferent relationships of area VII, as shown by axoplasmic transport tracing techniques in our own material and in previous studies in other laboratories, are reviewed. Comparison is made between the internal organisation of VI and VII cortex in terms of (1) the marked difference in spiny and nonspiny neuron populations of granular layer 4, (2) the difference in relationship of lamina 6 pyramidal neurons to the overlying layers with a shift away from any relationship to granular layer 4 in VII, and (3) differences in the organization of VI lamina 4B and VII lamina 3B—both similarly placed, fiber‐rich bands in the two cortical areas. The extrinsic relationships of VI and VII with the lateral geniculate nucleus, superior colliculus, pulvinar, peristriate cortex, cortical area STS, and with each other are compared in terms of laminar locations of efferent neurons and afferent axon terminal fields. It is hoped that this anatomical survey will provide a better foundation for physiological explorations of the region.
Changes in the length and organization of nucleus laminaris dendrites after unilateral otocyst ablation in chick embryos
Authors: Parks Thomas N.
Published: May 2005

To evaluate the contributions of the ear and acoustic stimulation to the structural development of central auditory neurons, the right otocyst was surgically destroyed in chick embryos on the third day of incubation. This pro‐cedure prevents the formation of the inner ear and acousticovestibular nerve and thus removes the dominant afferent synaptic input to nucleus magnocellularis (NM). Subsequently, nucleus laminaris (NL), which receives afferent synaptic input to its dorsal dendrites from the ipsilateral NM and afferents to its ventral dendrites from the contralateral NM, was studied on both sides of the brain in Golgi preparations. By embryonic day 17, the total lengths of the individual NL dendritic fields connected to the right NM (i.e., the manipulated dendrites) were decreased by an average of 44% as compared to those NL dendrites connected to the left NM (i.e., the unmanipulated dendrites). The mean length of the unman‐ipulated dendrites in experimental animals, however, did not differ from average dendritic length in normal control embryos. The amount of dendritic length lost by a NL neuron was strongly correlated with the length of the unmanipulated dendrites on the opposite side of the same neuron and with that neuron's position within NL. The lengths of dorsal and ventral dendrites on individual neurons were at least as highly correlated in experimental as in normal control animals. Correlation of dendrite length with the position of measured neurons within NL indicated that the large rostromedial‐to‐caudolateral gradient of increasing den‐drite length present in the normal NL is also found in the manipulated dendrites in experimental animals. Regression and correlation analyses relating the length of dendrites to their longitudinal cross‐sectional area revealed that there was no difference in mean dendritic diameter between the manipulated and unmani‐pulated dendrites in experimental animals. The findings of a high dorsal‐ventral length correlation in experimental animals and a normal spatial gradient of dendritic length among the manipulated dendrites suggests two explanations. Either (1) acoustically evoked synaptic activity is not essential for the develop‐ment of these two aspects of dendritic organization, or (2) the normal NM afferents to the unmanipulated dendrites of each NL neuron in an animal with one ablated otocyst can, under the influence of acoustically driven activity, control develop‐ment of the manipulated dendrites. These alternate hypotheses can be tested experimentally.
Sensory representation in reptilian optic tectum: Some comparisons with mammals
Authors: Stein Barry E. , Gaither Neal S.
Published: May 2005

The sensory representations in the tectum of Iguana iguana were studied with electrophysiological recording techniques, and visual, somatic, and auditory cells were found to be represented here. These cells were not equally distributed throughout the tectal laminae. Upper tectal laminae were populated exclusively by visual cells, and deeper laminae were primarily nonvisual. The intermediate laminae had nonvisual, as well as visual, cells.

Maps of the visual and somatic representations were constructed, and both representations were topographic and in register with one another. When electrical stimulation was presented via implanted electrodes, orientation responses were evoked that were predictable on the basis of the visuotopic and somatotopic maps.

These organizational features of the iguana tectum are strikingly similar to those described in various mammalian species. It is suggested that the pattern of sensory and motor representation used in the midbrain of mammals is an ancient scheme that was retained during the transition from reptilian to mammalian forms more than 180 million years ago.
Distribution of somatostatin in the frog brain, Rana catesbiana, in relation to location of catecholamine‐containing neuron system
Authors: Inagaki Shinobu , Shiosaka Sadao , Takatsuki Kenichi , Sakanaka Masahiro , Takagi Hiroshi , Senba Emiko , Matsuzaki Takashi , Tohyama Masaya
Published: May 2005

The distribution of somatostatin (SRIF)‐immunoreactive structures in the central nervous system of the bull frog (both with and without treatment of colchicine) was studied, using the indirect immunofluorescence technique of Coons and co‐workers (Coons, '58). SRIF‐containing cells were observed in more than ten areas including the spinal cord. These SRIF‐positive cells showed segmental distribution, in that SRIF‐positive neurons were identified in various areas at various brain levels. An extensive network of SRIF‐positive fibers was found in most parts of the central nervous system. The distribution of a catecholamine (CA)‐containing neuron system in the frog brain is also presented in this study. The possible interactions between SRIF and CA neuron systems are briefly discussed.
Comparative anatomy of the distribution of catecholamines within the inferior olivary complex from teleosts to primates
Authors: Kamei Ichiro , Shiosaka Sadao , Senba Emiko , Takagi Hiroshi , Sakanaka Masahiro , Inagaki Shinobu , Takatsuki Kenichi , Nakai Kunio , Imai Harumichi , Itakura Toru , Komai Norihiko , Tohyama Masaya
Published: May 2005

The distribution of catecholamine (CA) in the inferior olivary complex (IO) of various vertebrate (from fish to monkey) was investigated by means of the histofluorescence technique. In addition, using rats, a further attempt was made to elucidate the origins of CA in the IO.

The IO of the lower vertebrates (from fish to birds) was in general poorly innervated by the CA neuron system. IO in the lower mammals, such as insectivora and bats, contained only a few CA nerve terminals, while that in the higher mammals such as rat, guinea pig, rabbit, cat, and monkey revealed quite a number. In these animals, species‐specific patterns of CA nerve terminals were found. In the rat, the highest concentration was observed in the dorsal lamella of the principal nucleus and in the guinea pig ventral lamella. In the rabbit and cat, maximum CA nerve terminals were detected in the dorsal accessory nucleus, while in the monkey, they were detected in the medial accessory nucleus.

The retrograde tracer technique of horseradish peroxidase (HRP) suggested that the main source of the abundant CA terminals in IO of the rat might be A1, A2, and A3 noradrenaline neurons, though not locus coeruleus and not dopaminergic ones.
Structural diversity of marginal (Lamina l) neurons in the adult monkey (Macaca mulatta) lumbosacral spinal cord: A Golgi study
Authors: Beal John A. , Penny Joseph E. , Bicknell H. Ryan
Published: May 2005

Utilizing the Golgi technique, the present study provides a structural analysis of primate marginal (lamina I) neurons in the lumbosacral spinal cord. Marginal neurons are classified on the basis of major structural differences in dendritic conformation, distribution, and specialization. Cell size and shape alone were not found to be reliable criteria. Marginal cells can be divided into four major groups. Group I (Aspiny Neurons with Thick, Blunt Dendrites) consists of neurons with relatively thick dendrites which have an abrupt, blunt termination and few spines. This heterogeneous group includes large, medium, and small neurons of various shapes. Group II cells (Large to Medium Spiny Neurons) can be subdivided into two distinct groups: Group IIA neurons, which have longitudinal spiny dendritic arbors, and Group IIB cells, which have a moderately spiny, fan‐shaped dendritic arbor which spreads across the lateral portion of the dorsal marginal zone. Both Groups A and B exhibit several types of spines. Group III (Aspiny Neurons with Thin, Tapering Dendrites) consists of small to medium size neurons which can be further divided into two groups: Group IIIA, which is characterized by oval‐ to fusiform‐shaped neurons with tortuous, fine, tapered dendrites which ramify in the dorsolateral fasciculus and the lateral funiculus, and Group IIIB, which is composed of fusiform‐, pyramidal‐ and polygonal‐shaped neurons with fine, tapering dendrites confined to lamina I. Group IV (Small Spiny Neurons) are characterized by a small fusiform‐to pyramidal‐shaped cell body and delicate longitudinal dendrites with small, short‐necked pedunculated spines. This group is subdivided into Group IVA cells, which are found within lamina I proper and Group IVB cells, which are located in the dorsolateral fasciculus and have unmyelinated axons.

The present study demonstrates considerably more structural diversity within the marginal zone than has been previously reported, and offers sufficient variation to correlate with functional differences described for lamina I neurons.
Rules of motor innervation in chick embryos with supernumerary limbs
Authors: Hollyday Margaret
Published: May 2005

The positions of motoneurons supplying individual muscles in chick embryos with grafted supernumerary limbs have been identified using retrograde transport of horseradish peroxidase. For a given muscle, motor pool location varied depending on the embryonic origin of the muscle, the position of the limb along the rostrocaudal axis of the body, and the limb's orientation with respect to the body wall. Limb muscles derived from the ventral part of the embryonic premuscle mass were always innervated by medially located motoneurons. Muscles derived from the dorsal portion were consistently innervated by motoneurons in either intermediate or far lateral positions. These relationships were invariant with changes in limb position and orientation. These findings indicate that motor axons can recognize and selectively innervate muscles derived from either dorsal or ventral muscle mass.

In addition, the spinal nerves innervating each limb were identified. The type of limb plexus (e.g., crural, sciatic, or wing) and the peripheral branching patterns of the nerves within the limbs were also studied and found to be controlled by the limbs. The rostrocaudal variation in motor pool position similarly depended on the position and orientation of the limb. This rostrocaudal variation in motor pool position can be explained by the limb's ability to determine axonal outgrowth pathways and hence to constrain the possible target choices of outgrowing axons.

The process of limb innervation involves interactions between motoneuron axons having intrinsic differences or specificities, and the character of the local environment of the limb into which they grow.
Neuronal and neuroglial responses following retinal lesions in the neonatal rats
Authors: Miller Nancy Muchnick , Oberdorfer Michael
Published: May 2005

Lesions were produced in the nasal‐superior quadrant of rat retinas at 1 day postnatal. Both the optic fiber and ganglion cell layers were destroyed at the lesion site. Retrograde changes in the more peripherally located ganglion cell bodies, their optic fibers, and neuroglia were monitored by light and electron microscopy. No optic fibers remained in the region peripheral to the lesion site after 2 days postoperative (DPO). Neither regenerative sprouting nor axonal ingrowth from late‐maturing ganglion cells in the retinal periphery was observed. Cell death of the large and the majority of medium ganglion cell bodies was very rapid, as was clearing of the degeneration products. These processes peaked at 1 DPO and were complete by 2 DPO. Microglia and Mueller cell cytoplasm actively phagocytized degenerating ganglion cell bodies and their optic fibers.

A stable population of cell bodies in the ganglion cell layer peripheral to the lesion remained intact from 2 DPO to 21 DPO. The surviving somata were consistently 65% of the control ganglion cell population, and they remained after their axons had degenerated. The cell bodies measured 6–12.1 m̈m in diameter, a range which included the small cell population and a few of the medium cells. Dendritic patterning, used to designate ganglion cell types, corroborated their classification as small and medium ganglion cells. Morphological changes in these perikarya due to axotomy were limited to a mild chromatolytic response.
Axonal guidance during development of the optic nerve: The role of pigmented epithelia and other extrinsic factors
Authors: Silver Jerry , Sapiro Jacob
Published: May 2005

It is well established that a congenital lack of ocular melanin (albinism) can lead to developmental abnormalities of the central visual pathways. However, it is yet unknown how the pigmentation per se acts to influence formation of the optic projection. In order to study the possible interaction between eye pigment and optic axons during development, we have examined, with the use of serial section techniques, a series of timed embryos at stages when the ocular pigment and outgrowing axons first become apparent. Our results have demonstrated that, in mice and rats, the upper wall of the distal half of the primitive eye stalk (a region which lies along the potential route to be taken by the earliest developing nerve fibers) is transiently pigmented prior to and during the migration of the pioneer optic axons. All outgrowing neurites avoid this stretch of melanotic tissue and instead grow preferentially through a system of extracellular tunnels in the ventral, pigment‐free zones of the distal eye stalk. The stalk remains unpigmented from about its midpoint and continuing toward the brain. At the pigment/pigment‐free interface many of the axons shift upward from their ventral positions, forming a marginal annulus. In the chick, on the contrary, pigmentation of the stalk does not occur and as the optic axons exit the globe they grow immediately in an annulus configuration. In Xenopus, the entire stalk becomes pigmented and the optic fibers congregate in one discrete bundle of fascicles along the length of the stalk's most ventral margin. These observations suggest that melanin‐producing stalk cells may play a role in controlling the topographic patterning of optic fibers within the developing nerve by inhibiting the lateral spread of axonal growth cones into or within their territory. To test this hypothesis we have charted the distribution of optic fibers in the developing optic stalks of timed albino rat embryos. Indeed, as fibers leave the mutant eye, it was found that a small but consistent number of pioneering axons (day E15) become ectopic and immediataely invade nonpigmented regions (those normally pigmented and axon‐free) in the distal optic stalk. Thus, the usual topographic arrangement of the collection of pioneer optic fibers is altered in the albino.
Ipsilateral corticocortical projections related to binaural columns in cat primary auditory cortex
Authors: Imig Thomas J. , Reale Richard A.
Published: May 2005

Projections from the high‐frequency representations of auditory cortical fields A and P were autoradiographically labeled using anterograde transport of a mixture of tritiated proline and leucine. A single injection of isotope into either cortical field resulted in multiple regions of dense labeling within ipsilateral AI. As the result of an injection of radioactive label into field A in one experiment, densely labeled regions were found to be systematically related to the binaural map throughout the high‐frequency representation of AI. Contralateral dominant suppression responses were located in regions of dense labeling while summation responses were located in regions of less dense labeling. In contrast, it was previously found that callosal axon terminations were more densely concentrated in summation columns than in contralateral dominant suppression columns (Imig and Brugge, '78). Thus, the two classes of binaural columns differ with respect to the density of innervation they receive from these ipsilateral and contralateral populations of neurons.

In other experiments in which isotope was injected into field A, a systematic relationship between density of ipsilateral labeling and binaural response class was only seen in a portion of AI; in other regions no relationship was evident. A simple interpretation of these data follows. Within a contiguous territory in field A is a population of neurons whose axons provide more dense innervation to contralateral dominant suppression columns than to summation columns in ipsilateral AI. Injections of radioactivity confined to this territory result in a systematic relationship between the density of labeling and the binaural map throughout AI. Outside this territory is a population of neurons whose axonterminations are not systematically related to the binaural map in AI. Isotope injections which engage both territories may result in a systematic relation between density of labeling and the binaural map in one portion of AI, while in another, no relationship may be evident.

There is some indication that projections from field P may also be related to binaural columns in AI in the same manner as are the projections from field A.
Pulpal axons in developing, mature, and aging feline permanent incisors. A study by electron microscopy
Authors: Fried K. , Hildebrand C.
Published: May 2005

The ingrowth, maturation, and aging of pulpal axons was followed by electron microscopy in permanent mandibular incisors of 44 cats aged 35 days–11 years. The first axons entered the incisor pulps about 2 months after birth. Cells resembling Schwann cells, but lacking an axonal relation, were also observed at this time. Axonal ingrowth and maturation continued until 7 months, when the pulps contained 92–394 axons, 81–88% of which were unmyelinated. Between month 7 and 20 months the character of the incisor pulpal axons remained largely unchanged. In adult cats the myelinated pulpal axons had diameters of 1–6 μm. The relation between the number of myelin lamellae and the axon size correlated better with linear + logarithmic than linear functions. The g‐ratios were higher than in most peripheral nerves, and tended to increase with axon diameter. In the old adult this tendency was more evident and the g‐ratios were generally lower. From 3 years on the incisors displayed various age‐related or pathological alterations. These were accompanied by axonal changes and axon loss. In contrast to earlier stages perineriumlike sheaths were frequent in old teeth. The findings are discussed in relation to axon development in the inferior alveolar nerve and in primary incisor pulps.
Developmental growth and degeneration of pulpal axons in feline primary incisors
Authors: Fried K. , Hildebrand C.
Published: May 2005

The life history of pulpal axons in primary mandibular incisors was examined by light and electron microscopy in 56 kittens aged from 25 days postconception to 120 days after birth. Cells resembling Schwann cells preceded the first arrival of pulpal axons, 1 week postnatally. Myelination was initiated during the second week. Two months after birth the incisors were fully grown and each pulp contained about 100 axons. Between 10 and 20% of these were myelinated and ranged in size from 1 to 5 μ. The relation between number of myelin lamellae and axon size appeared nonlinear and differed markedly from that in similarly sized inferior alveolar nerve axons. During the third month many unmyelinated axons showed signs of degeneration. With progress of root resorption an increasing proportion of both unmyelinated and myelinated axons degenerated. In highly resorbed incisors necrotic Schwann cells were associated with degenerating axons and there was a generalized pulpal tissue reaction. In some teeth with advanced root resorption pulpal axons were lacking. A progressive derangement of all pulpal tissue elements continued until shedding during the second half of the fourth month. In incisor nerve branches below the incisor teeth axon degeneration was very limited.
Superior colliculus neurons which project to the cat lateral posterior nucleus have varying morphologies
Authors: Caldwell Ruth B. , Mize R. Ranney
Published: May 2005

We have studied the laminar position, morphology, and synaptic relationships of neurons in the cat superior colliculus which project to the interadjacent division of the lateral posterior nucleus (LPi), using the retrograde transport of horseradish peroxidase. The neurons which project to LPi are remarkably varied in depth, size, morphology, and synaptic density and appear to consist of at least four cell types. Labeled cells were found in four laminae. Forty‐seven percent were found in the superficial gray layer (50–550μm), all but a few within its deep subdivision. Forty‐seven percent were located in the optic layer (550–1,200μm), the majority of these being within the upper one‐half of the layer. Seven percent were found in the intermediate and deep gray layers (below 1,200μm). Cell body area varied widely, ranging from 37 to 768 μm2 (mean of 243μm2). Based on cell size, shape, and dendritic field orientation, we identified four distinct cell morphologies which were labeled. Thirty‐five percent were stellate, 32% were vertical fusiform, 19% were granule, and 12% were horizontal cells. Electron microscope analysis confirmed that neurons projecting to the lateral posterior nucleus are a morphologically diverse group. A sample of 71 labeled cells varied significantly in density of synaptic input as well as in size, shape, depth, dendritic distribution, and cytology.
Quantitative study of synapse formation in the duck olfactory bulb
Authors: Rebiere A. , Dainat J.
Published: May 2005

Synaptic emergence and development in the duck olfactory bulb was quantiatively studied by electron microscopy from the 14th day of incubation (E 14) to the adult stage. Overall synaptic density in this bulb grew considerably during the last weeks of embryonic life and the first postnatal week.

The pattern of synatpic density development was similar in the four main architectonic layers of the bulb. However, lower density values were observed in the mitral and inner granule cell layers.

In the glomerular layer (GL), axodendritic synapse density was always higher than dendrodentritic synapse density. In the external plexiform layer, most synapses were dendrodendritic and were established between the gemmules of the granule cells (GC) and the dendrites of the mitral cells (MC) or tufted cells (TC). Synapses established by MC and TC on GC gemmules, or by GC on MC and TC dendrites had densities very similar to each other at all the stages studied. Reciprocal synapses already appeared at E 14; their density grew until a week after birth (P7) and thereafter remained stable. In the internal granular layer, the density of asymmetrical synapses was always higher than that of symmetrical synapses.

Excitatory synapses formed earlier on MC and TC than inhibitory synapses. The ratio of inhibitory‐to‐excitatory synapses rose rapidly after birth, reaching 2.5 in the adult duck. The density of excitatory synapses received by granule cells was as high in the external plexiform layer as in the inner granule layer, at all stages of GC development. However, the ratio of received‐to‐formed synapses fell in these cells from 8.42 at E 14 to 2 after birth. These results are discussed as a function of the evolution of the different synaptic balances during olfactory bulb development.

Synaptic development in the duck olfactory bulb at birth is relatively close to the adult state. It appears sufficiently advanced to enable the olfactory system to function in a way compatible with the relatively independent behavior displayed by the duckling.
Afferent sources of a lateral midbrain tegmental zone associated with the pinnae in the cat as mapped by retrograde transport of horseradish peroxidase
Authors: Henkel Craig K.
Published: May 2005

A paralemniscal zone in the lateral midbrain tegmentum of the cat has been identified in a possible pathway from the superior colliculus to the facial nucleus that may control pinna movements (Henkel and Edwards, '78). Other brainstem afferent projections to this paralemniscal zone have been mapped in the present study using the retrograde horseradish peroxidase tracing method and are discussed in three groups. First, potential sources of auditory afferents were limited mainly to the external nucleus of the inferior colliculus, the nucleus sagulum, and the dorsomedial periolivary cell group. Labeled cells in other superior olivary regions and the dorsal cochlear nucleus were apparently related to uptake of horseradish peroxidase from the axons of the lateral lemniscus. Second, afferents from several premotor regions involved in aspects of gaze control were identified. These were mainly from the nucleus prepositus hypoglossi and adjacent pontine reticular formation, butalso included projections from the medial vestibular and abducens nuclei and possibly subthalamic regions such as the zona incerta and fields of Forel. Third, a relatively large group of midbrain afferents was closely related to the origin of the collicular projection to the paralemniscal zone. This group consisted of labeled cells in the periaqueductal gray matter, nucleus cuneiformis, and pretectum. The relatively sparse labeling in auditory regions that projected to the paralemniscal zone seems to indicate that the sensorimotor integration necessary to guide pinna movements does not take place primarily in the lateral midbrain tegmentum. The interaction of gaze‐related sources with the pinna‐related pathway is also discussed.
Cholecystokinin in hippocampal pathways
Authors: Greenwood Robert S. , Godar Steve E. , Reaves Troy Albert , Hayward James N.
Published: May 2005

The distribution of cholecystokininlike (CCK‐L) immunoreactive cells and fibers in the rat hippocampal formation and its afferent and efferent connections was studied using the immunoperoxidase technique. In the hippocampal formation CCK‐L immunoreactive perikarya were located in the polymorphic zone of the dentate hilus, all layers of Ammon's horn, the subiculum, the presubiculum, and the entorhinal cortex. Cholecystokininlike immunoreactive fibers extended from cell bodies or were located around the cell bodies in the entorhinal cortex, subiculum and stratum pyramidale of Ammon's horn, and among the granule cells and inner molecular layer of the dentate gyrus. The immunoreactive cells in the stratum oriens may be a type of basket cell, since processes from these cells extend into stratum pyramidale and collections of CCK‐L immunoreactive fibers are seen around cell bodies in stratum pyramidale.

Cholecystokininlike immunoreactive fibers were also observed in the alveus, ventral and lateral fimbria, and ventrolateral lateral septal nucleus. Some of these immunoreactive fibers, therefore, belong to either an efferent or afferent hippocampal formation and/or from the hippocampal subcortical nuclei, the supramammillary nucleus, and the dorsomedial hypothalamic nucleus which contain CCK‐L immunoreactive perikarya. The distribution of these immunoreactive fibers in the fimbria and lateral septal nucleus is most consistent with an anteriorly directed efferent hippocampal pathway.
Efferent projections of the medial preoptic nucleus and medial hypothalamus in the pigeon
Authors: Berk Mitchell L. , Butler Ann B.
Published: May 2005

The efferent projections of the medial preoptic nucleus (POM), anterior‐medial hypothalamic area (AM), and the posteromedial hypothalamic nucleus (PMH) in the pigeon were traced by the autoradiographic technique. Similar and differential connections were noted from these regions. Projections from POM and AM‐PMH were traced to nucleus septalis lateralis, nucleus dorsomedialis thalami, nucleus dorsolateralis anterior thalami (pars ventralis), posterior hypothalamic and medial mammillary areas, area ventralis tegmenti (Tsai), central gray of midbrain and nucleus intercollicularis and substantia grisea periventricularis of the midbrain. The density of silver grains in these regions differed with POM and AM‐PMH injections. Other projections were observed exclusively from only one or two of the nuclear regions injected. Connections from POM and the rostral part of AM were seen to the median eminence, neurohypophysis, and the nucleus of anterior pallial commissure. Only cells of the anterior part of AM project fibers to nucleus septalis medialis. In the hypothalamus, projections from POM are concentrated in the periventricular region and in the preoptic‐hypophyseal tract in the extreme lateral hypothalamus, while AM‐PMH projections are heaviest in the medial hypothalamus and lateral preoptic area. A major difference in the connections of PMH from POM is the more substantial PMH projection to the midbrain. A prominent projection courses dorsolaterally and posteriorly from PMH toward nucleus ovoidalis and splits into two pathways: a lateral pathway which heavily innervates n. intercollicularis and the periventricular gray and a ventrolateral projection to the midbrain tegmentum. The projections described above provide anatomical substrates for neuroendocrine, autonomic, and behavioral functions.
Morphology of axosomatic endings in an avian cochlear nucleus: Nucleus magnocellularis of the chicken
Authors: Parks Thomas N.
Published: May 2005

The axonal endings formed on the somata of neurons in the brainstem auditory nucleus magnocellularis (NM) were measured and classified in thin‐sectioned material from adult chickens. Degeneration of primary endings after destruction of the basilar papilla and labeling of cochlear nerve fibers by injection of horseradish peroxidase (HRP) into the inner ear were used to determine which ending types arise from the cochlear ganglion. About 60% of the perikaryal surface is apposed by primary type terminals. These primary endbulbs are characterized by round clear synaptic vesicles distributed at an average density of 63 vesicles/μm2 and a number of small, punctate, highly asymmetrical synaptic contacts. The primary type is the only class of endings which disappears after destruction of the basilar papilla and which is consistently labeled after HRP injections into the ear. These endings probably account for the “fast” EPSP seen in NM during stimulation of the cochlear nerve. NM neurons receive two types of nonprimary ending. About 13% of the perikaryal surface is apposed by a morphologically homogeneous class of small “symmetrical” endings; these are characterized by a flattened rhomboidal shape, numerous mitochondria, frequent coated vesicles, and small round or ovoid synaptic vesicles at an average density of 165 vesicles/μm2. Most of the length of the apposition between ending and cell body is occupied by a synaptic complex with thin symmetrical presynaptic and postsynaptic densities. These endings were frequently found on short somatic processes. The second nonprimary axosomatic ending type in NM is most easily identified in experimental material; these endings occupy about 5% of the cell surface area and have a distinctly rounded profile in cross section. These endings typically exhibit clear round synaptic vesicles at a density of 111 vesicles/μm2 arrayed before synaptic contacts which occupy a substantially larger fraction of the total appostion length than in the endbulbs. Many of these synaptic contacts show well‐defined presynaptic grids and have postsynaptic densities intermediate in width between the endbulbs and the symmetrical endings. This second type of nonprimary ending may be responsible for the long‐latency excitatory postsynaptic potentials seen in intracellular recordings from NM during electrical stimulation of the cochlear nerve. The morphology and distribution of the three ending types does not differ significantly along the posterior‐to‐anterior axis of NM.