bluuebunny/crossref_metadata_2025 huggingface dataset:
The origin of brainstem‐spinal pathways in the north american opossum (didelphis virginiana). Studies using the horseradish peroxidase method
Authors: Crutcher Keith A. , Humbertson Albert O. , Martin George F.
Published: May 2005

Brainstem neurons which project to lumbar, thoracic and cervical spinal levels have been identified in the North American opossum by the horseradish peroxidase (HRP) technique. Neurons which relay to all of the levels studied are located within the medullary and pontine reticular formation as well as within the nucleus cuneatus, the nucleus of the tractus solitarius, the lateral reticular nucleus, the medullary and caudal pontine raphe nuclei, the lateral, medial and inferior vestibular nuclei, the nucleus “F,” the nucleus coeruleus, and the nucleus coeruleus, para α, the red nucleus, and the interstitial nucleus of Cajal. The lateral vestibulospinal and rubrospinal systems are topographically organized, although neurons projecting to different cord levels show considerable intermingling. Our material also provides evidence that raphe‐spinal and reticulospinal connections are organized to some degree. Neurons which backfill after cervical and thoracic placements, but not after lumbar injections, are distributed within the caudal spinal trigeminal nucleus, the nucleus intercalatus, the dorsal vagal nucleus, the cuneiform area of Castaldi, the fields of Forel, and the nucleus of Darkschewitsch. Reactive neurons are present within the lateral, dorsal and posterior hypothalamic areas as well as within the periventricular and paraventricular nuclei after thoracic placements and within the superior colliculus after injections within the cervical cord. Additionally, neurons are reactive in the nucleus ambiguus, the interpolar division of the spinal trigeminal nucleus and the rostral division of the oculomotor nucleus (Oswaldo‐Cruz and Rocha‐Miranda, '68) after HRP placements into the third and fourth cervical segments.
Retinal abnormalities in the Siamese cat
Authors: Stone J. , Rowe M. H. , Campion J. E.
Published: May 2005

Ganglion cell density maps of the retinas of Siamese cats show the same major features of ganglion cell distribution as are found in normally pigmented cats, in particular the area centralis and visual streak. In the retinas of the seven Siamese cats investigated, however, the area centralis was “underdeveloped” when compared with the normally pigmented cat. The beak ganglion cell density was lower and the ganglion cells usually larger than at the area centralis of the normally pigmented cat, and the characteristic blood vessel pattern around the area centralis was less developed. One animal showed a marked blood vessel abnormality, a vessel crossing the area centralis in each retina. In another animal, the distribution of ganglion cells appeared abnormal throughout the retina. Medium‐sized, possibly X‐type ganglion cells were lacking from all retinal areas, overall cell numbers were low and the distribution of ganglion cells showed a prominent visual streak.
Fine structure of reactive cells in injured nervous tissue labeled with 3H‐thymidine injected before injury
Authors: Adrian Erle K. , Williams M. G. , George F. C.
Published: May 2005

To examine the fine structure of blood mononuclear cells in injured nervous tissue, mice were given repeated injections of 3H‐thymidine with the last injection at least 16 hours before injury. Under ether anesthesia the animals either were given a stab wound to the spinal cord or had their left hypoglossal nerve transected. The animals were killed at 2, 4, 8, or 16 days after injury. Tissue sections containing the spinal cord wound or both hypoglossal nuclei were prepared for electron microscopic radioautography, and all labeled cells were photographed. About half the labeled cells in the injured hypoglossal nerves had nuclei with dark staining peripheral heterochromatin, dark cytoplasm with long cisternae of granular endoplasmic reticulum, and other ultrastructural features characteristic of the cells usually identified as microglia. The remaining labeled cells in the injured spinal cords were macrophages, fibroblasts, cells with pale nuclei, some of which contained cytoplasmic filaments, and vascular cells. Since uninjured nervous tissue has extremely few labeled cells and since 3H‐thymidine should be available for only a short time following injection, most of the labeled cells in this experiment should be derived from blood mononuclear cells. However, the possibility is discussed that some or all of the labeled cells proliferating in response to the injury and labeled through reutilization of labeled DNA precursor material.
A stereotaxic atlas of the brain of the three‐day‐old domestic chick
Authors: Youngren Orlan M. , Phillips Richard E.
Published: May 2005

Preparation of a stereotaxic atlas of the brain of the 3‐day‐old domestic chick was prompted by the widespread use of chicks in behavioral and pharmacological research.

The atlas is comprised of 26 frontal plates extending from the frontal pole to the level of the hypoglossal nucleus, and one sagittal plate at lateral 0.4 mm. Marking lesions were used to ascertain coordinates, the brains were embedded in albumin and sections cut at 36 mμ. The brain sections were stained with cresyl violet for nuclei and with hematoxylin for fibers. Unstained brain sections were used as a guide in drawing the plates to correct for shrinkage and distortion.

The use of the atlas for research purposes for one year, plus test lesions targeted for specific brain structures, indicates the atlas is accurate to within 0.5 mm.
Regional differences in pigeon optic tract, chiasm, and retino‐receptive layers of optic tectum
Authors: Duff Thomas A. , Scott Grayson , Mai Regina
Published: May 2005

Electron‐microscopic examination of the pigeon optic chiasm, tract, stratum opticum, and retino‐receptive layers of the optic tectum revealed regional differences at each level. Axonal size in the fiber pathways paralleled that previously reported for pigeon optic nerve, with mean diameter values of 0.96 μm for optic chiasm and 1.06 μm for optic tract. The dorsolateral aspects of these pathways contained a heterogeneous population of fibers (mean diameter ⋍ 1.44 μm) similar to that found in the nasal portion of optic nerve, while the ventromedial regions were occupied by a more homogeneous population of smaller fibers (mean diameter ⋍ 0.82 μm) resembling those observed in the temporal portion of the nerve.

The retino‐receptive layers of anteroventral optic tectum (avT) differed ultrastructurally from those of posterodorsal tectum (pdT) with respect to the thickness of horizontal dendrites in layers 2–3, the size of optic terminals in layers 2–7, and the number of synaptic contacts per terminal. These findings point towards a regional variation in the processing of visual information throughout the retino‐tectal system and suggest that neurons in avT vs. pdT should show differences in the way they modify the neurophysiological characteristics of their respective optic inputs.
Freeze fracture study on three types of synapses in the Xenopus spinal cord
Authors: Watanabe Hiroshi , Yamamoto Toshi Yuki
Published: May 2005

Three types of synapses (S‐, F‐ and C‐types) were identified in the thin‐sectioned Xenopus spinal cord and their structure was analyzed with the freeze‐fracturing technique.

All three types of synapses showed similar specializations of the presynaptic membrane. This finding suggests that the three types of synapses may release their transmitters by a similar mechanism. By contrast, the three types of synapses revealed different specializations of the postsynaptic membrane. The E‐face of the S‐type postsynaptic membrane was characterized by a dense aggregate of large intramembrane particles, 12 to 15 nm in diameter. An aggregate of small particles, 8 to 9 nm, was evident on the E‐face of the postsynaptic membrane of the F‐type synapse. In the C‐type synapse, there was a striking aggregate of intramembrane particles, 10 to 14 nm in diameter, on the P‐face of the postsynaptic membrane. These characteristics features in the distribution of particles in the three types of postsynaptic membranes may reflect differences in the type of transmitter released or transmitter action on the postsynaptic neuron.

The overall size of the area of aggregated particles on the P‐face of the C‐type postsynaptic membrane was coextensive with the underlying subsurface cistern (SSC) which showed partial occulsion of the lumen. This fact supports the view that the SSC is closely related to the C‐type synaptic action which might be distinct from the other synaptic types.
3H‐Thymidine autoradiadiographic analysis of telencephalic histogenesis in the chick embryo: II. Dynamics of neuronal migration, displacement, and aggregation
Authors: Tsai Huei Mei , Garber Beatrice B. , Larramendi Luis M. H.
Published: May 2005

The movements of cells from their sites of origin in the proliferative neuroepithelium to their final positions in the chick telencephalon were traced by autoradiographic analysis of 3H‐thymidine‐labeled brains. A series of chick embryos were labeled on successive days of development between days 5 and 9 and fixed for autoradiography between days 6 and 10. Isochrone maps visualizing neuronal positions on each day of development between days 6 and 10 provided direct information concerning cell migrations, displacements, and aggregations leading to compartmentalization of the telencephalic wall and the generation of the “outside‐in” pattern of histogenesis characteristic of the avian telencephalon. The topological divisions of the telencephalic wall appear to result from two factors: (1) the specification of neuronal precursors within the neuroepithelium and (2) the intrinsic associative and migratory properties of postmitotic neuronal populations expressed within the mantle layers. There was no evidence that glial cell barriers mediated the initial compartmentalization of neuronal populations.
An intracellular electrophysiological study of the ontogeny of functional synapses in the rabbit retina. I. Receptors, horizontal, and bipolar cells
Authors: Dacheux Ramon F. , Miller Robert F.
Published: May 2005

An isolated perfused retina‐eyecup of the rabbit neonate was used to study the functional maturation of synaptic interactions in the outer plexiform layer. Intracellular recordings from receptors, horizontal cells, hyperpolarizing and depolarizing bipolar cells were obtained in the adult and at different stages of maturation. Three types of horizontal cells could be distinguished based on the relative amount of rod and cone input, response wave form, receptive field diameter, and amplitude‐intensity relationships. Two of the horizontal cell types were encountered with sufficient frequency such that maturation of these response characteristics could be followed over the developmental period of this study (8 days–adult). The growth rate of the amplitude‐intensity relationships was different for the two commonly encountered types of horizontal cells; the small diameter receptive field type achieved an adultlike amplitude‐intensity range at an earlier age than the large field type. Immature bipolar cell responses were initially monophasic potentials with transient‐sustained components appearing at a later stage. Center surround antagonism of bipolar cells developed after centermediated responses were first observed. This suggests some secondary modifications during synaptogenesis are responsible for the late maturation of center surround antagonism. The morphological appearance of synaptic contacts during different stages of synaptogenesis is discussed in reference to the different phases of functional, synaptic interactions of this study. It appears that some synapses in the vertebrate retina are functional at a time when synaptic structure is incomplete, based on ultrastructural observation. Maturation of receptive field diameter and amplitude‐intensity function is discussed in relationship to possible presynaptic and postsynaptic mechanisms which may influence this growth.
The development of the oculomotor nuclear complex in the Japanese quail embryo
Authors: Heaton Marieta Barrow
Published: May 2005

The development of the oculomotor nuclear complex was studied in the Japanese quail. In hatchlings, this complex was found to consist of four subnuclei: The accessory, the dorsolateral, the dorsomedial, and the ventromedial. An arciform subnucleus or central subnucleus was not found in this species. All subnuclei were made up of homogeneous cell populations. The oculomotor primordia can first be recognized at day 3 of incubation, and a clear subdivision within this primordia is apparent on day 5 (total incubation period = 17 days). At this time the accessory subnucleus can be discerned. By day 6, a horizontally oriented dorsal cell mass, the anlagen of the dorsolateral and dorsomedial subnuclei, is seen, as is a vertically oriented ventral cell mass, the anlagen of the ventromedial subnucleus. The boundaries between the subnuclei are not yet distinct at this age, however. By day 7 of incubation, all four subnuclei can be detected as separate entities. Migrating cells, apparently moving primarily between the ventromedial subnuclei, are first seen on day 5, at which time the oculomotor commissure begins to appear. Migratory traffic is extensive during days the 6 and 7 of incubation, with wide bands of migrating cells typically seen, spanning the entire dorsal‐ventral extent of the oculomotor complex. These cells do not appear to be associated exclusively with the ventromedial subnuclei. In many instances, migratory cells appear to be affiliated with the dorsomedial cell group. By day 10 of incubation, migration has ceased and the oculomotor complex has attained its definitive configuration. These observations are discussed with comparative reference to earlier studies of chick and duck embryos and hatchlings.
The ascending projection of the nucleus of the lateral descending trigeminal tract: A nucleus in the infrared system of the rattlesnake, Crotalus viridis
Authors: Stanford L. R. , Schroeder Dolores M. , Hartline Peter H.
Published: May 2005

The efferent projections of the nucleus of the lateral descending trigeminal tract (LTTD) in the rattlesnake (Crotalus viridis) were studied by anterograde tracing techniques. The LTTD, a brainstem trigeminal nucleus, is the sole projection site of the infrared‐sensitive trigeminal fibers that innervate the pit organs in these snakes. The efferent fibers exit from the ventromedial edge of the LTTD and course medially and caudally toward the central grey area of the medulla. Upon reaching the central region of the medulla these fibers turn and move laterally and rostrally, eventually forming a tract on the ventrolateral surface of the brainstem. Embedded in this tract and slightly overlapping the LTTD in the rostrocaudal axis, is a population of large (20–45 μm) multipolar neurons that forms the nucleus reticularis caloris. Heavy terminal and preterminal degeneration in this area indicates that many of the efferent fibers of the LTTD terminate in this nucleus. A small bundle of degenerating fibers turn dorsally from the ventrolateral tract and ascend to terminate in a nucleus associated with the cerebellum, the lateral tegmental nucleus. No projection was found to any other nuclei or areas in the brain.

This study demonstrates that the infrared‐sensitive snakes, along with developing peripheral specializations (the pit organs), have developed specialized nuclei to handle this additional sensory information. The direct projection from the LTTD to the nucleus reticularis caloris provides a pathway linking the infrared sensitive neurons of the LTTD with neurons of the same modality in the optic tectum. The second LTTD projection, to the lateral tegmental nucleus, suggests a connection between the infrared system and the cerebellum in these animals.
Synaptic termination of thalamic and callosal afferents in cingulate cortex of the rat
Authors: Vogt Brent A. , Rosene Douglas L. , Peters Alan
Published: May 2005

The distribution of degenerating thalamic and callosal afferents to cingulate cortex in the rat is analyzed. Both light microscopic silver impregnation and quantitative electron microscopic techniques demonstrate differences in the form, number, and laminar distribution of these two afferents in anterior and posterior cingulate cortices.

Afferents from the mediodorsal thalamic nucleus terminate in area 24. Most terminals are in layer IIIb, fewer in layer Ia–b, and least in layers V and VI. In contrast, callosal afferents terminate mainly in layers Ib–c, II, IIIa, V, and VI. Thus, thalamic and callosal afferents terminate in a complementary pattern except in layers Ib and IIIb where they overlap. Quantitative analysis of degenerating axon terminals in area 24 indicates that there may be as many as seven times more callosal than mediodorsal thalamic terminals in this cortex.

Projections of the anterior thalamic nuclei terminate in areas 29b and 29c, primarily in layer Ia, with fewer in layers Ib–IV and least in layers V and VI. Callosal afferents end mainly in layers V and VI and less densely in layers I–IV, which results in some overlap of thalamic and callosal afferents in layers Ic, IV, and V. In addition, patterns of termination of callosal afferents in posterior cingulate cortex change at borders between previously defined cytoarchitectural areas.

Anterior thalamic terminals in area 29c differ from other thalamocortical afferents described previously in that they form two types of terminals. One is large (2–4 μm in diameter) and occurs mainly in layer Ia, whereas the second type is smaller and is present in layers Ib–V. Both types of terminals form asymmetric synapses mainly with dendritic spines.
Afferent connections of the rostral medulla of the cat: A neural substrate for midbrain‐medullary interactions in the modulation of pain
Authors: Abols I. A. , Basbaum A. I.
Published: May 2005

In order to study the organization of the rostral medulla of the cat and its contribution to pain control mechanisms, we have examined the afferent connections of the midline nucleus raphe magnus (NRM), the laterally located nucleus reticularis magnocellularis (Rmc), and the nucleus reticularis gigantocellularis (Rgc) located dorsal to Rmc. Iontophoretic injections of HRP were made into the three regions; the distribution of retrogradely labeled neurons in brainstem and spinal cord was then mapped. While significant differences characterize the source of afferents to Rgc and NRM/Rmc, there is little to distinguish that between NRM and Rmc.

The predominant spinal projection is to Rgc; fewer labeled neurons were recorded after injections into Rmc. In contrast, no significant direct spinal projection to NRM was found. All three regions receive input from widespread areas within the medullary and pontine reticular formation. The most pronounced differences in the distribution of retrogradely labeled neurons were found in the midbrain. The major projection to both NRM and Rmc derives from the periaqueductal gray (PAG) and from the adjacent nucleus cuneiformis. Labeled cells are concentrated in the dorsal and lateral PAG; few are found in the ventrolateral PAG. In contrast, Rgc receives few afferents from the PAG; however, after Rgc injections, many cells were recorded in the deep layers of the contralateral tectum. None of the injection sites produced significant labeling of the catecholamine‐rich dorsolateral pontine tegmentum or of the nucleus raphe dorsalis.

The demonstration of significant PAG projections to NRM/Rmc provides anatomical evidence for the hypothesis that opiate and stimulation‐produced analgesia involves connections from PAG to neurons of NRM and Rmc which, in turn, inhibit spinal nociceptors.
The vestibular nuclei in the domestic hen (Gallus domesticus): VI. Afferents from the cerebellum
Authors: Wold Jan Egil
Published: May 2005

Following horseradish peroxidase (HRP) injections in the superior, in the Deiters', in the medial, and in the descending vestibular nuclei in the hen, labeled cells are found in lateral longitudinal zones in the ipsilateral cerebellar cortex, most numerously in the anterior lobe, the nodulus, the uvula, and the auricle. Furthermore, labeled cells are found bilaterally in the ventral parts of the medial and intermediate cerebellar nuclei. Lesions in the cerebellar cortex of the anterior lobe and in anterior parts of the posterior lobe result in terminal degeneration, mainly in the nucleus Deiters dorsalis, but also scantily, in peripheral regions of the superior nucleus, the nucleus Deiters ventralis, the ventrolateral part of the medial nucleus and, mainly medially, in the descending nucleus. Lesions in the posterior part of the uvula, in the nodulus, and in the auricle result in much denser degeneration, most heavily affecting the nucleus Deiters dorsalis, but also affecting peripheral regions of the superior nucleus, the nucleus Deiters ventralis, the entire descending and medial nuclei, and the tangential nucleus. Lesions in the medial cerebellar nucleus result in degeneration bilaterally in the vestibular complex, most heavily affecting the nucleus Deiters ventralis and cell group B, but also affecting peripheral regions of the superior nucleus, the medial nucleus—mainly in dorsomedial regions, lateral and caudal parts of the descending nucleus and, very scantily, in the nucleus Deiters dorsalis. The findings are discussed in the light of the data concerning the organization of the cerebellovestibular projections in mammals and the known connections of the vestibular nuclei in birds.
The neural pathway involved in “efferent inhibition” of chemoreceptors in the cat carotid body
Authors: McDonald Donald M. , Mitchell Robert A.
Published: May 2005

This study was done to determine whether a pathway of efferent axons in the carotid sinus nerve is necessary for the phenomenon of “efferent inhibition” (inhibition induced in carotid body chemoreceptors by electrical stimulation of the carotid sinus nerve). Our approach was to eliminate efferent axons in the carotid sinus nerve of cats without destroying the sensory axons. This was achieved by cutting the ipsilateral glossopharyngeal and vagus nerves central to their sensory ganglia and/or by removing the nodose and superior cervical ganglia. In neurophysiological studies we found that the response of chemoreceptors in cats 10 days after surgery was the same as that in controls. Chemoreceptor activity was decreased by electrical stimulation of the carotid sinus nerve and was increased by hypoxia and cyanide. In operated cats as in control animals, “efferent inhibition” was abolished by haloperidol and dihydroergotamine, drugs that block the inhibitory action of dopamine. Electron microscopic studies disclosed that the number of nerve endings in glomus cell/sheath cell complexes was not measurably different in control and experimental carotid bodies. By contrast, 10 days after the carotid sinus nerve was cut the number of nerve endings next to such cells was reduced by more than 99%. Cutting the nerve roots and excising the ganglia eliminated most nerve endings on blood vessels: The number of noradrenergictype nerve endings was reduced by 99% and other types of nerve endings (presumptive cholinergic and peptidergic types) were reduced by more than 90%. Our experiments indicate that “efferent inhibition” is not abolished by operations that destroy inputs to blood vessels and to carotid body glomus cells from (1) the nodose ganglion, (2) superior cervical ganglion, or from (3) neurons in the brain stem whose axons run in the glossopharyngeal or vagus nerves. We conclude that “efferent inhibition” may be caused by antidromic stimulation of sensory axons.
Postembryonic production and aging of inner ear hair cells in sharks
Authors: Corwin Jeffrey T.
Published: May 2005

In many animals the sensory hair cells of the inner ear are ultrastructurally variable within individual epithelia. This variation has been hypothetically related to both the function and the age of the individual cells. In this study, growth‐related changes in hair cell populations were examined in the macula neglecta sensory epithelia of juvenile and adult sharks. Scanning electron microscopy demonstrated that more than 80% of the 200,000 hair cells in the adult's macula neglecta are produced postembryonically. Tritiated thymidine autoradiography and histological descriptions of the hair cells in this sound detector indicate that new sensory cells are produced in growth zones at the edges of the epithelia. The hair cells in those zones have small cell bodies, small and heterogeneous cilia complexes, and associations with small numbers of particularly thin nerve terminals. Their cytological features and their sparse innervation contrast with the features of the more numerous central cells in each epithelium, but appear to resemble the published descriptions of embryonically developing hair cells. Thus, a germinal zone at the leading edge of sensory epithelium growth appears to persist into adult life in sharks. Published reports reinterpreted in light of this evidence suggest that such hair cell population growth may be expected in other anamniotes and that latent growth zones might persist in the ears of amniotes.
Brainstem afferents to the torus semicircularis of the Queensland cane toad (Bufo marinus)
Authors: Pettigrew A. G.
Published: May 2005

The ascending projections to the major midbrain auditory center of anura, the torus semicircularis, have been examined using the technique of retrograde labeling with horseradish peroxidase (HRP). Localized iontophoretic injections of HRP were made in one torus semicircularis of Queensland cane toads (Bufo marinus). Visualization of HRP‐labeled neurons with tetramethyl benzidine revealed that the torus semicircularis receives its major afferent input from the ipsilateral superior olive. Other prominent projections arise in the contralateral dorsal nucleus of the eighth nerve and the contralateral torus semicircularis. HRP‐labeled neurons were also associated with the lateral lemniscus at a level ventral and lateral to the nucleus isthmi on both sides. It is suggested that these neurons constitute diffuse nuclei of the lateral lemnisci. Relatively minor projections to the torus semicircularis arise in the contralateral superior olive, ipsilateral dorsal nucleus of the eighth nerve, and the ventral division of both the ipsilateral and contralateral eighth nerve nuclei.
Topographic atlas of somatostatin‐containing neuron system in the avian brain in relation to catecholamine‐containing neuron system. I. Telencephalon and diencephalon
Authors: Takatsuki Kenichi , Shiosaka Sadao , Inagaki Shinobu , Sakanaka Masahiro , Takagi Hiroshi , Senba Emiko , Matsuzaki Takashi , Tohyama Masaya
Published: May 2005

The morphological organization of the somatostatin (SRIF)‐positive neurons in the forebrain (telencephalon and diencephalon) of the warbling grass parakeet (Melopsittacus undulatus) was studied using the indirect immunohistochemical technique of Coons and co‐workers ('58). In the telencephalon, a number of SRIF‐positive neurons was detected in the lobus paraolfactorius, hippocampus, and paleostriatum. Furthermore, scattered SRIF‐labeled cells were noticed in the area corticoidea dorsolateralis and area temporoparieto‐occipitalis. A moderate density of immunoreactive fibers was found in the above areas. In addition, although the septal area was devoid of SRIF‐positive neurons, this area contained a moderate number of SRIF‐positive fibers. A large number of SRIF‐positive neurons occurred in the following hypothalamic areas: (1) nucleus medialis hypothalami posterior, (2) lateral hypothalamus, and (3) mammillary nucleus. The bird hypothalamus also received a strikingly massive SRIF innervation. The heaviest concentration of SRIF‐labeled fibers was detected in the median eminence. Many SRIF‐labeled fibers were also observed in other hypothalamic regions. Their locations roughly corresponded in many cases to the areas in which SRIF‐positive neurons were disclosed.

The overall distribution of the catecholamine system (CA) of the avian forebrain is also presented by means of histofluorescent technique. A possible interaction between SRIF and CA neuron systems is briefly discussed.
Topographic atlas of somatostatin‐containing neuron system in the avian brain in relation to catecholamine‐containing neuron system. II. Mesencephalon, rhombencephalon, and spinal cord
Authors: Shiosaka Sadao , Takatsuki Kenichi , Inagaki Shinobu , Sakanaka Masahiro , Takagi Hiroshi , Senba Emiko , Matsuzaki Takashi , Tohyama Masaya
Published: May 2005

With the indirect immunofluorescence technique of Coon's and collaborators, overall distribution of the somatostatin (SRIF)‐positive neuron system in the avian lower brain stem was explored. Numerous cell somata containing SRIF were identified in the interpeduncular nucleus and substantia grisea centralis (GCT) at the level of the nucleus nervi trochlearis. Furthermore, a moderate number of SRIF‐positive neurons were seen in the tectum opticum, nucleus tractus solitarii, and spinal cord. Scattered labeled cells were noticed in the rhombencephalon. A dense network of SRIF‐positive fibers was distributed widely in the lower brain stem of birds. Their locations corresponded in many cases to the areas where SRIF‐positive neurons were found.

The present study also presents the distribution of the catecholamine (CA) neuron system in the avian lower brain stem.

Possible interactions between SRIF and CA neuron systems are briefly discussed.
Structural and histochemical features of the avian blood‐brain barrier
Authors: Stewart P. A. , Wiley M. J.
Published: May 2005

We have investigated the structural and histochemical features of the blood‐brain barrier (b‐bb) in both adults and embryos of chicken (Gallus domesticus, White Leghorn) and quail (Corturnix coturnix japonica). We found that brain endothelial cells of both species are characterized structurally by tight junctions, a low density of pinocytotic vesicles, and a moderately elevated density of mitochondria. Both alkaline phosphatase and butyryl cholinesterase were found in adult quail brain capillaries, but only alkaline phosphatase was found in adult chick brain capillaries. Aromatic amino acid decarboxylase was not found in brain capillaries of either species.

In the chick embryo alkaline phsophatase appeared during the time when b‐bb matures functionally; i.e., during the third week of development. However, an elevation in mitochondrial density was not apparent until after hatching.

In the quail, alkaline phosphatase and butyrl cholinesterase appeared during the last week of embryonic development. By 2 days posthatching the structural characteristics of the brain capillaries were similar to those in the adult.
Localization of sympathetic postganglionic neurons of physiologically identified cardiac nerves in the dog
Authors: Armour J. Andrew , Hopkins David A.
Published: May 2005

Cardiac nerves were identified physiologically and injected with horseradish peroxidase in 38 dogs. Retrogradely labeled neurons were present in the greatest number in the middle cervical ganglion, whereas fewer labeled neurons were present in the stellate ganglion. Only occasional neurons in the superior cervical ganglion were labeled, and no labeled cells were found in the T3 to T6 paravertebral ganglia or in the ganglia contralateral to the nerve injected. Following injections into specific cardiac nerves, retrograde labeling was widespread within the middle cervical ganglion, and the distributions of labeled neurons from different nerves overlapped considerably. In the middle cervical ganglion there was little or no regional grouping of cells projecting to specific cardiac nerves. Within the stellate ganglion, however, the cardiac‐sympathetic cells were clustered primarily at the cranial pole near the origin of the ventral and dorsal ansae. Mediastinal ganglia and ganglia located in cardiac nerves were frequently as heavily labeled as the ipsilateral stellate ganglion. The occurrence of heavy labeling in mediastinal and cardiac nerve ganglia indicates that these hitherto unreported ganglia play a significant role in cardiac neural regulation. These data imply that the organization of sympathetic neurons controlling the heart is much more complex than has previously been considered.
Origin of the parallel fibers in the cerebellar crest overlying the intermediate nucleus of the elasmobranch hindbrain
Authors: Montgomery John C.
Published: May 2005

This study utilizes anterograde transport of horseradish peroxidase (HRP), Golgi staining, and electrophysiological techniques to demonstrate the origin of the parallel fibers which constitute the molecular layer overlying the intermediate nucleus of the dogfish hindbrain. The parallel fibers are shown to arise from granule cells of the auricle. The majority come from the granular area of the lower leaf of the auricles, which is termed the lateral granule cell area of the auricle. A band of parallel fibers at the ventrolateral extent of the molecular layer arises from the ipsilateral and contralateral granule cell layers of the upper leaf of the auricle. The functional continuity of the molecular layer between vestibular and lateral‐line areas may provide an additional basis for interactions between these two sense modalities.
Changing retinal ganglion cell distribution in the frog Heleioporus eyrei
Authors: Dunlop S. A. , Beazley L. D.
Published: May 2005

The number and distribution of retinal ganglion cells were examined in the burrowing frog Heleioporus eyrei. Retinae of midlarval tadpoles, animals at metamorphic climax, 2‐month postmetamorphic juveniles, and adults were flat‐mounted and stained with cresyl violet.

The identity of retinal ganglion cells was established in the adult using retrograde transport of horseradish peroxidase applied to the optic nerve. Horseradish peroxidase‐filled cells, identified as neurons, had an axon hillock and contained Nissl substance within a pale‐staining cytoplasm. Glial cells, which never filled with horseradish peroxidase, had very dark nuclei and a thin film of cytoplasm lacking Nissl. The diameter of horseradish peroxidase‐filled neurons ranged from 7 to 16 m̈m. Cells identified as glia, which represented less than 1% of cells in the ganglion layer, were 3–8 m̈m in diameter. There were, however, a proportion (14%) of cells which did not fill with horseradish peroxidase. These small cells (5–7 m̈m diameter) had a similar appearance to the horseradish peroxidase‐filled cells and may be neuronal.

The total number of ganglion cells rose almost 6‐fold, being approximately 61,000–83,000 for the tadpole, 100,000–118,000 at metamorphic climax, 170,000–184,000 in juveniles, and 454,000–495,000 in adults. Estimates for left and right sides in the same animal were within 1.9% for the tadpole, 1.6% at metamorphic climax, and 7.5% in the juvenile. Fiber counts were made by electron microscopy and were within 11% of ganglion cell estimates for the adult and within 5% for the remaining stages. Overall ganglion cell densities dropped from tadpoles to adults as retinal area increased 20‐fold.

The topography of retinal ganglion cells changed at each stage. In the tadpole there was a radial anisotropy, the lowest density being in central retina. Anisotropy was still characteristically radial in animals at metamorphic climax but was less extreme since cell densities had dropped, particularly at the periphery. In contrast, the juvenile was beginning to form a visual streak with higher density patches appearing in nasal and temporal retina. The adult topography was similar, the highest densities still being in the nasal and temporal retina, but now a complete band of intermediate density extended across the horizontal axis of the eye. The transition of retinal ganglion cell topography to produce a visual streak after metamorphosis presumably reflects a change in life‐style from an aquatic, browsing tadpole to an animal which actively seeks its prey.

The striking changes in retinal ganglion cell number and distribution provide an experimental model to study the continual development of the amphibian eye. The implications of this finding in terms of neuronal plasticity of connections formed within the visual centers are discussed.
Primary afferent distribution pattern in the marginal zone (Lamina I) of adult monkey and cat lumbosacral spinal cord
Authors: Beal John A. , Bicknell H. Ryan
Published: May 2005

Using Golgi preparations from adult cat and monkey, the present study describes the general arborization pattern of primary afferent collaterals to the marginal layer (lamina I) of the dorsal horn. The dorsal root origin of the Golgi‐impregnated afferents was verified in the cat by matching the structural properties of these fibers with horseradish peroxidase (HRP)‐stained primary afferents which were filled with HRP via anterograde transport through dorsal rootlets. The marginal afferents, in both the cat and the monkey, are relatively fine‐caliber fibers which emanate from the dorsolateral fasciculus of Lissauer. Superficially they form a transverse plexus of fibers which runs across the surface of the dorsal horn and is especially dense in the lateral portion of the dorsal aspect of the marginal layer where lamina I is thickest. In deeper regions of the marginal layer, marginal afferents are longitudinally oriented and have collaterals within the outer zone of lamina II. In both superficial and deep regions of the marginal layer the afferents run parallel with large numbers of marginal cell dendrites. Most marginal afferents give rise to collaterals with widely spaced, round to oval “boutons en passant” and “boutons terminaux” which are 1.5–2.0 m̈m in diameter. Structural correlation with previous physiological and anatomical studies suggests that most of these fibers are finely myelinated, A‐delta, high‐threshold mechanoreceptive fibers.
The tectopontine projection in the rat with comments on visual pathways to the basilar pons
Authors: Burne R. A. , Azizi S. A. , Mihailoff G. A. , Woodward D. J.
Published: May 2005

The projection from the superior and inferior colliculi to the basilar pons in the rat was studied with the technique of orthograde transport of labeled amino acids and autoradiography. Injections restricted to the medial or lateral regions of the superior colliculus gave rise to grain labeling representing terminal fields over the ipsilateral peduncular, dorsolateral, and ventrolateral regions of the caudal basilar pons and over the dorsomedial area of the contralateral nucleus reticularis tegmenti pontis (NRTP). The pontine projection from the superior colliculus to the lateral basilar pons is topographically organized; the medial superior colliculus projects primarily to the peduncular region, wheras the lateral superior colliculus terminates chiefly in ventrolateral pontine areas. A projection from the superior colliculus to the contralateral dorsomedial pontine and medial peduncular pontine regions, a previously undescribed finding, has also been shown. Descending fibers from the inferior colliculus do not appear to terminate extensively within the basilar pons but rather course adjacent to pontine cells of the dorsolateral region in the caudal pons. Pretectal nuclei project ipsilaterally to medial and lateral nuclei in the rostral and middle basilar pons, respectively. A rostrocaudal topography exists in the tectopontine projection; the pretectum projects to rostromiddle basilar pons, the superior colliculus to more caudal pontine regions, and the inferior colliculus (although sparsely) to further caudal areas.

The pontine projection pattern from the colliculi and pretectum differs from the pontine afferents from the visual cortices. The findings of this study, when compared to our results from previous investigations on the pontocerebellar projection system, suggest that the tectal inputs to certain lateral cerebellar lobules are relayed primarily through NRTP rather than the basilar pons. The collicular projections to midvermal lobules of the cerebellum appear to be mediated in part by both NRTP and lateral pontine nuclei.
Neurogenetic gradients in the superior and inferior colliculi of the rhesus monkey
Authors: Lee Cooper Michael , Rakic Pasko
Published: May 2005

The spatiotemporal patterns of neurogenesis in the superior colliculus (SC) and inferior colliculus (IC) were analyzed by plotting the positions of heavily labeled neurons in autoradiograms from a series of rhesus monkeys that had been exposed to 3H‐thymidine at various embryonic (E) days and killed either shortly thereafter or at 2–3 months postnatally. Tectal neurons in this species are generated in the ventricular and subventricular zones surrounding the mesocoele (future Sylvian aqueduct) within the first third of the 165‐day gestation period. Cells destined for the SC undergo final mitosis from E30 to E56, with peak proliferation from E38 to E43. These cells exhibit only a weak ventrodorsal gradient of neurogenesis and virtually no mediolateral or rostrocaudal gradients. Genesis of the neurons of the central nucleus (CN) of the IC also occurs between E30 and E56 and peaks around E43; but in contrast to cells of the SC, CN cells exhibit distinct rostrocaudal, lateromedial, and ventrodorsal gradients of genesis. Quantitative analysis revealed that whereas neurogenesis of the SC proceeds with about equal strength along the three cardinal axes, in the CN the lateral‐medial gradient is significantly stronger than the anterior‐posterior gradient. In addition, both the lateral‐medial and ventral‐dorsal IC gradients are significantly stronger than any SC gradients. Analysis of embryos sacrified at short intervals following 3H‐thymidine injection shows that the gradients are not caused by secondary lateral cell movement or by selective cell death. Thus, these findings suggest that within the generative zone of the midbrain tectum significant regional differences exist which result in distinctive spatiotemporal patterns of proliferation for the neurons of the primate superior and inferior colliculi.
Neurons and glia in cat superior colliculus accumulate [3H] gamma‐aminobutyric acid (GABA)
Authors: Mize R. Ranney , Spencer Robert F. , Sterling Peter
Published: May 2005

We have examined by autoradiography the labeling pattern in the cat superior colliculus following injection of tritiated gamma‐aminobutyric acid (GABA). Silver grains were heavily distributed within the zonal layer and the upper 200 m̈m of the superficial gray. Fewer grains were observed deeper within the superficial gray, and still fewer were found within the optic and in‐termediate gray layers. The accumulation of label was restricted to certain classes of neuron and glia. Densely labeled neurons were small (8—12 m̈m in diameter) and located primarily within the upper 200 m̈m. Dark oligodendrocytes and as‐trocytes showed a moderate accumulation of label while pale oligodendrocytes and microglia were unlabeled. Label was also selectively accumulated over sev‐eral other types of profile within the neuropil, including presynaptic dendrites, axons, and axon terminals.
Sprouting in the avian brainstem auditory pathway: Dependence on dendritic integrity
Authors: Rubel Edwin W. , Smith Zaid D. J. , Steward Oswald
Published: May 2005

The brainstem auditory pathways of the chicken were used to examine the relationship between the maintenance of dendrites following de‐nervation and the successful reinnervation (sprouting) by surviving afferents. In the system the third‐order cells in n. laminaris receive spatially segregated bi‐naural innervation from n. magnocellularis. Afferents from the ipsilateral n. magnocellularis innervate the dendrites on the dorsal aspect of n. laminaris cells, while afferents from contralateral magnocellular neurons innervate ventral den‐drites via the crossed dorsal cochlear tract. Denervation of the ventral dendrites of n. laminaris cells by transection at the midline results in rapid and severe atrophy of the denervated dendrite. Unilateral cochlea removal induces tran‐sneuronal degeneration of 30–45% of the ipsilateral magnocellular cells, thereby partially denervating one dendrite of the n. laminaris cells on each side of the brain.

In animals with long‐standing transections of the crossed dorsal cochlear tract there is no evidence of sprouting of fibers from the ipsilateral n. magnocellularis when the projections of the surviving magnocellular neurons are traced with degeneration methods after a secondary cochlea removal. However, when den‐drites of n. laminaris are partially denervated dendrites do not disappear. Fur‐thermore, secondary lesions of the crossed dorsal cochlear tract or secondary cochlea removal reveal that these denervated dendrites are reinnervated by the afferents from the opposite n. magnocellularis which are normally restricted to the opposite dendrite of the n. laminaris cells.
Comparative study of the posterior red nucleus in baboons and gibbons
Authors: Padel Y. , Angaut P. , Massion J. , Sedan R.
Published: May 2005

The posterior red nucleus (PRN) was studied in two species of primates by the technique of retrograde degeneration of rubrospinal cells following transection of the spinal cord at different levels. The form of the PRN was reconstructed for both a quadruped monkey (baboon) and an anthropoid with erect posture (gibbon). The PRN contains polymorphic cells characterized by their very chromophilic and granular NIssl substance. These neurons vary in diameter from 25 μm to 70 μm. Some of them give rise to the rubrospinal tract.

Baboon: The approximately 1,300 rubrospinal cells in this species are divided into two equal groups, one related to the contralateral forelimb, with axons ending between the second cervical and third thoracic segment, and the otehr related to the contralateral hindlimb, projecting caudally beyond T3. Following a high cervical lesion, nondegenerated cells of similar description remain throughout the nucleus. A significantly large group of these cells occurs medially and may be the source of fibers ending in the brain stem or cerebellum.

Gibbon: In this species, the number of rubrospinal cells controlling the hindlimb is less than half that found in the baboon. This reduction in the gibbon is much greater for medium‐sized cells, but is also significant for the giant cells.

These results obtained from primates are compared with those reported for the cat. A possible function for the PRN in the control of limb movements is discussed from the viewpoint of phylogeny.