bluuebunny/crossref_metadata_2025 huggingface dataset:
Intrinsic connections of the retrohippocampal region in the rat brain. II. The medial entorhinal area
Authors: Köhler Christer
Published: January 2005

The present study describes the efferent projections and terminal distributions within the retrohippocampal region of individual layers of the rat medial entorhinal area (MEA) as studied by the methods of anterograde transport of the lectin Phaseolus vulgaris leucoagglutinin (PHA‐L) and retrograde transport of the fluorescent dye Fast Blue (FB). Analysis of the PHAL injections that were relatively well restricted to single layers of the MEA reveals very sparse projections to the parasubiculum, presubiculum, and subiculum, while numerous projections within the MEA are found. The course and the termination of the intra‐entorhinal projections differ depending upon the particular layer under study, and marked differences are found between the deep and the superficial layers in terms of the divergence of their respective projections. However, the general intra‐entorhinal orientation of these projections is essentially the same for all layers: longitudinal with a slightly oblique course, such that at ventral levels the center of a particular terminal field is always located lateral ‐to the center of the respective PHA‐L injection.

PHA‐L injections into layer II label axons running horizontally within this layer as well as within the deep part of layer I, and PHA‐L injections into the medial sector of layer II reveal horizontal projections that innervate most of the second layer. The horizontal projections of layer III are more restricted than those of layer II but both layer U and III have prominent longitudinal projections directed ventrally. From layers II and III, numerous axons project to the deep layers (IV‐VI) probably en route to extra‐entorhinal structures, since no major terminal fields were detected in the deep layers.

The PHA‐L and the FB experiments show that the deep layers (in particular IV and VI) have far more divergent intra‐entorhinal projections than have layers II and III. PHA‐L injections into layers IV, V, and VI reveal widespread efferent projections to all of the more superficially located layers of the MEA in addition to projections to the Iateral EA. The retrograde transport studies show that layers IV and VI are the major sources of these divergent projections and that cells situated throughout the entire medial to lateral width of these layers project to every sector of the retrohippocampal region.

Taken together, the findings of the present experiments suggest that (1) all layers of the MEA have longitudinal projections, directed primarily toward the ventral (or temporal) part of this cortex, (2) the projections of layers II and III are relatively restricted compared of the deeper layers, and (3) the deep layers (in particular IV and VI) have highly divergent projections such that they reach most parts of layers II and III throughout the longitudinal axis of the MEA, in addition to their innervations of the lateral EA and to some degree the para‐ and presubiculum.
Freeze‐fracture study of the large myelinated club ending synapse on the goldfish Mauthner cell: Special reference to the quantitative analysis of gap junctions
Authors: Tuttle Rebecca , Masuko Sadahiko , Nakajima Yasuko
Published: January 2005

The large myelinated club endings (LMCEs) of primary eighth nerve afferents form mixed synapses on the lateral dendrite of the giant Mauthner cell. The double replica freeze‐fracture technique was employed to examine the intramembrane fine structure of these LMCE synapses. Morphological correlates of both chemical and electrical transmission were found at the LMCE synapses. Electrical synaptic junctions, or gap junctions, were located over much (10‐20%) of the synaptic contact. These were seen in both preand postsynaptic membrane as tightly packed P face particle aggregates and corresponding aggregates of E face pits. Specializations characteristic of chemical synaptic junctions were most prominent at the periphery of the synaptic contact. These specializations consisted of postsynaptic E face particle aggregates which were subjacent to presynaptic active zones. The active zones were distinguishable as regions with an increased density of large particles and vesicle attachment sites represented by P face depressions and E face protuberances.

Quantitative analysis of gap junction particle (connexon) number at five LMCEs revealed 24,000‐106,000 connexons per LMCE. Comparison with data from electrophysiological studies of single LMCEs indicates that only a small fraction of the connexon channels are open at any given time during electrotonic transmission at an LMCE synapse.
Differential effect of visual deprivation on cytochrome oxidase levels in major cell classes of the cat LGN
Authors: Kageyama Glenn H. , Wong‐Riley Margaret
Published: January 2005

Cytochrome oxidase histochemistry was used to examine the effects of visual deprivation on the development of neurons in the lateral geniculate nucleus of the kitten. Early postnatal monocular suture results in a decrease in reactivity within the neuropil of visually deprived binocular laminae A, Al, magnocellular C, and medial interlaminar nucleus. Within these regions, monocular suture has a greater effect on the relative numbers of, and the growth of darkly reactive (normally large), presumed Y‐cells than on other less reactive geniculate neuronal classes. The decreases in the reactivity of the neuropil may be attributed to the decreases in the number of mitochondria, the number of darkly reactive mitochondria, and/or the number of darkly reactive mitochondria localized within dendrites. Although all classes of dendrites appear to be adversely affected, the decrease in C.O. reactivity was most dramatic within the presumed proximal dendrites of class 1 Y‐cells. These dendrites were identified by the type of synaptic contacts they formed with retinal terminals (Rapisardi and Miles, '84, J. Comp. Neurol. 223:515‐534; Wilson et al., '84, Proc. R. Soc. Lond. [Biol.] 221:411‐436). As with Y‐cells, the effects of monocular suture on the large darkly reactive cells were not as dramatic at sites where binocular interactions were either absent or where they had been experimentally eliminated. Based on the present and previously reported findings from several laboratories, it is likely that the selective physiological and morphological effects of monocular suture on Y‐cells are accompanied by metabolic deficits involving both dendrites and perikarya. These effects appear to be due more to binocular interactions than to visual deprivation per se.
Distribution of GABA‐like immunoreactivity in the brain of the honeybee
Authors: Schäfer Sabine , Bicker Gerd
Published: January 2005

The distribution of GABA‐like immunoreactivity in the brain of the honeybee was investigated with antisera generated against GABA protein conjugates. The binding of the antisera in paraffin serial sections was studied with the peroxidase‐antiperoxidase method. GABA‐like immunoreactive fibers appeared in all main neuropile areas. The staining of the optic lobes showed pronounced stratification. The receptor cells of compound eyes, ocelli, and antennae were not labelled. Several prominent fiber tracts showed GABA‐like immunoreactivity, whereas other tracts were devoid of staining. There are no major immunoreactive commissures linking the two brain hemispheres with the exception of small commissures that bridge short distances between the β‐lobes and the antennal lobes. Several fibers in the cervical connective were also labelled; some of those may descend from the suboesophageal ganglion to the thoracic ganglia. The dense reactivity seen in the optic and antennal neuropiles implies that GABA is more important in mediating local rather than more distant neural interactions.
The architecture of nerves and ganglia of the ferret trachea as revealed by acetylcholinesterase histochemistry
Authors: Baker David G. , McDonald Donald M. , Basbaum Carol B. , Mitchell Robert A.
Published: January 2005

The goal of this study was to determine the architecture of the nerves and ganglia of the ferret trachea. Tracheas from four newborn ferrets and three adult ferrets were stained histochemically for acetylcholinesterase activity and analyzed in their entirety as whole mounts. The architecture consisted of one or two longitudinal nerve trunks overlying the posterior surface of the trachealis muscle, a dense plexus of nerves superficial to the trachealis muscle that interconnected these longitudinal nerve trunks, and, on the anterior surface, a plexus superficial to the submucosal glands and located between the cartilaginous rings. In addition, deep neural plexuses were associated with the trachealis muscle and with the submucosal glands. Ganglion cell bodies along the longitudinal nerve trunks were large (mean diameter ± S.E. = 34.3 ± 0.3 μm), were usually attached to the nerve trunk by a stalk, and were loosely clustered in groups of as many 38 cell bodies. By contrast, those cell bodies of the superficial muscle and gland plexuses were significantly smaller (mean diameter ± S.E. = 24.2 ± 0.3 μm), were never attached by a stalk, and were tightly clustered in ganglia of one to four cell bodies. We conclude that nerves and ganglia of the ferret trachea constitute one or two longitudinal nerve trunks containing ganglia with large cell bodies, two superficial nerve plexuses containing ganglia with small cell bodies overlying the smooth muscle and submucosal glands, respectively, and two deep nerve plexuses providing the terminal innervation to the muscle and glands.
Cell generation, death, and retinal growth in the development of the hamster retinal ganglion cell layer
Authors: Sengelaub D. R. , Dolan R. P. , Finlay B. L.
Published: January 2005

During the early postnatal period in the hamster, the retinal ganglion cell layer grows, establishes its central connections, and undergoes substantial cell loss. In this study, we describe the development of the retinal ganglion cell layer with particular attention to the creation of local specializations in cell density. Changes in the number and spatial distribution of cells identified by a single 3H thymidine injection were examined through the period of maximal cell loss (postnatal days 4–10) and at adulthood.

The cells of the retinal ganglion cell layer are generated from embryonic day 10 to postnatal day 3. Overall, cell number in the ganglion cell layer increases by approximately 108,000 cells (223%) from postnatal day 1 to 5, because of continued migration of cells generated prenatally. Cell number decreases from postnatal day 5 to 10 (25%), coincident with the presence of degenerating cells. Cell type is correlated with day of generation: the largest cells, all having retinal ganglion cell morphology, are generated on embryonic days 10 and 11; intermediate‐sized cells predominantly of ganglion cell morphology on embryonic day 12; and smaller cells of displaced amacrine or glial cell morphology thereafter.

At adulthood, the hamster retina shows a streaklike elevation of cell density through central retina. However, at the time of maximal cell number (postnatal day 5), cell density is uniform across the retina. During the period of cell degeneration, cells are lost in greater relative numbers from the retinal periphery. This cell loss occurs principally from the first‐generated cells (embryonic days 10 and 11), as shown by both changes in the distribution of labeled cells and by the spatial pattern of labeled degenerating cells. From postnatal day 10 to adulthood, relative cell density continues to decline in the periphery of the retina, thus suggesting that differential growth completes the production of the adult cell density distribution.
Origins of afferents to visual suprageniculate nucleus of the cat
Authors: Hicks T. P. , Stark C. A. , Fletcher W. A.
Published: January 2005

Small iontophoretic ejections of horseradish peroxidase (HRP) were made from recording‐multibarrel micropipette assemblies in areas of the cat's suprageniculate nucleus (SGn) that contained visually responsive neurones. The sources of afferents of the SGn were determined by locating the labeled cell bodies of neurones that were presumed to send their axons to the area of the SGn containing the light‐sensitive cells. The greatest concentration of labeled cell bodies was found in the granular insular cortex and the adjacent area of agranular insula. Most cells projecting to SGn from these areas were distributed in the middle and lower laminae. A second intensely labeled region was found in stratum opticum and stratum griseum intermediate of the superior colliculus. Other areas containing labeled cells that were distributed with intermediate density included the ventral thalamic nuclear complex (basal, medial, and lateral divisions), periaqueductal gray (PAG), zona incerta, and pretectal nuclei (posterior, medial, and anterior divisions). Sparsely labeled sites included the fields of Forel, substantia nigra (pars reticulata), peri‐insular cortex, superior colliculus (profundum), lateral suprasylvian cortex (posterolateral lateral suprasylvian, PLLS and posteromedial lateral suprasylvian, PMLS), anterior ectosylvian cortex, thalamic reticular complex, nucleus of the optic tract, basal part of the ventromedial hypothalamic nucleus, and the pontine reticular nucleus (oralis) and adjacent reticular formation. Together with previous electrophysiological and neuroanatomical studies, the findings suggest that the SGn provides an integrating link between limbic structures and certain modalities of sensory information.
Thalamostriatal projections from the ventral anterior nucleus in the dog
Authors: Tanaka Duke , Isaacson Lori G. , Trosko Beverly K.
Published: January 2005

Thalamostriatal projections from the ventral anterior nucleus (VA) were mapped by using autoradiographic and horseradish peroxidase techniques in the dog. Injections of tritiated leucine and proline into the lateral, central, and medial parts of VA resulted in anterograde label over the dorsolateral, midlateral, and dorsal parts of the head of the caudate nucleus, respectively. The dorsolateral and midlateral parts of the caudate contained the heaviest label. No silver grains were located over the medial or ventral parts of the caudate. Light to moderate label was located over the most dorsal part of the putamen. After injections of lectin‐conjugated horseradish peroxidase (WGA‐HRP) into the dorsolateral or intermediate areas of the head of the caudate, retrogradely labeled cells were present in the lateral and central parts of VA, respectively. In cases with dorsolateral caudate injections, labeled cells formed a narrow dorsoventrally oriented band located in the lateral part of VA whereas in the case with a larger injection into midcaudate, large numbers of labeled neurons were scattered throughout the central area of VA. Retrogradely labeled cells were also found in the rostral part of the ventral lateral nucleus (VL). Injections of WGA‐HRP into the medial part of the caudate resulted in only a few labeled cells located in the dorsomedial part of VA.

Combining these data with those from other studies mapping neostriatal afferents from the cerebral cortex in the dog, it is apparent that the midlateral part of the caudate receiving input from VA also receives afferents from cortical area 6. Furthermore, the dorsolateral part of the caudate that receives input from the lateral part of VA also receives afferents from cortical area 4. These results indicate that the dorsal and lateral parts of the canine caudate nucleus may constitute important links in the transmission and integration of information related to complex motor activities.
Simple and complex retinal ganglion cell axonal rearrangements at the optic chiasm
Authors: Springer Alan D. , Mednick Adam S.
Published: January 2005

The rearrangements that retinal ganglion cell (RGC) axons undergo near the optic chiasm were determined by ablating either the nasal, temporal, dorsal, ventral, or peripheral retina. The axons of the remaining intact RGCs were then labelled with cobaltous lysine. RGC axons change their relationship with respect to the axes of the brain and with respect to one another. Toward the caudal end of the optic chiasm, the optic tract begins to rotate axially such that its rostral edge ultimately becomes located medially. Thereby, the column of ventronasal RGC axons shifts from a rostral to a medial position. In addition, columns of axons from other retinal sectors move with respect to one another. Ventrotemporal RGC axons, located initially at the caudal edge of the tract, move toward and come to be positioned laterally to, the column of ventronasal RGC axons. The column of dorsonasal RGC axons moves from the rostral to the lateral side of the column of dorsotemporal RGC axons. Concurrently, the axons within each column reorganize internally. Each chronological lamina of axons within a column twists such that the nasal and temporal axons within each column invert their positions with respect to the edges of the column. All of these reorganizations take place between the caudal end of the optic chiasm and the division of the main optic tract into the optic brachia. Furthermore, the rearrangements that occur do not involve any alterations in the positions of central and peripheral RGC axons with respect to the surface of the diencephalon. The results are discussed with respects to mechanisms that might influence the organization of the visual pathways.
Patterns of afferent synaptic contacts in the alligator lizard's cochlea
Authors: Mulroy Michael J.
Published: January 2005

Afferent synapses on both free‐standing and tectorial hair cells in the alligator lizard's cochlea are described quantitatively. Semiserial sections were photographed with a transmission electron microscope. Hair cells together with their afferent nerves were reconstructed and morphometrically analyzed with the aid of a computer. Each afferent nerve forms many synapses with its hair cell. Tectorial afferents make more than twice the number of synapses with their hair cells as do free‐standing afferents. This suggests a possible neuroanatomical basis for the physiological difference in synchrony reported in these two types of auditory nerve fibers; namely, the greater the number of synapses the better a fiber is able to follow faithfully the response of its hair cell.
The organization of the pudendal nerve in the male and female rat
Authors: McKenna Kevin E. , Nadelhaft Irving
Published: January 2005

Mature male and female Sprague‐Dawley rats were used in this study to compare the organization of the pudendal nerve in the two sexes. Experiments included (1) incubating the cut pudendal nerve in diamidino‐2‐phenylindole HCl (DAPI), fast blue (FB), or horseradish peroxidase (HRP) and (2) injecting individual perineal muscles with these substances. In both sexes, incubation of the pudendal nerve labelled two motoneuron nuclei in the L5‐L6 segments of the spinal cord. These nuclei are the dorsomedial (DM) and dorsolateral (DL) cell columns described by Schrϕder (J. Comp. Neurol. 192:567–587, 1980). In agreement with previous studies, there were significantly more neurons in both nuclei in the male than in the female and the neurons were larger in the male. In both sexes, the DL and DM nuclei were characterized by a longitudinal dendritic structure. The DM nucleus also had numerous dendritic bundles extending across the midline, linking the DM nuclei bilaterally.

Pudendal nerve afferent neurons were located in the L6 and S1 dorsal root ganglia. In the male, the afferent neurons were larger and more numerous. In both sexes, labelled pudendal afferent fibers in the spinal cord were located in the dorsal columns, the medial half of Lissauer's tract, the extreme medial edge of the dorsal horn, both ipsilaterally and contralaterally, and in a large terminal field in the dorsal gray commissure. No labelled afferents were seen in the intermediate or ventral gray.

Perineal muscle injections established that there was no difference between males and females in the number of motoneurons innervating the external anal or urethral sphincters. In the female, urethral sphincter motoneurons accounted for almost all the DL motoneurons, and anal sphincter motoneurons accounted for almost all the DM motoneurons. The ischiocavernosus and bulbospongiosus muscles are vestigial in the female rat. In the male, neurons innervating the anal sphincter and bulbospongiosus muscles were intermingled in the DM nucleus. In contrast, in the DL nucleus, the urethral sphincter neurons were located in the lateral portion of the nucleus and the ischiocavernosus neurons were located in the medial portion.
Immunohistochemical localization of urotensin I/corticotropin‐releasing factor, urotensin II, and serotonin immunoreactivities in the caudal spinal cord of nonteleost fishes
Authors: Onstott Donna , Elde Robert
Published: January 2005

Neurosecretory cells in the caudal spinal cord of fishes were first discovered in elasmobranches. However, most of the subsequent work on the caudal neurosecretory system has emphasized its morphology and function in teleosts. Two major peptides, urotensins I and II (UI and UII), have been isolated from this system in teleosts and their amino acid sequences have been determined. We have used immunohistochemical techniques to confirm and expand previous morphological and pharmacological findings regarding the phylogenetic occurrence and the anatomical organization of the caudal neurosecretory system and to localize putative neurohormonal products within its structural elements. UII‐immunoreactive neuronal structures were found in the holocephalan, Hydrolagus collei; the elasmobranches, Squalus acanthias, Dasyatis sabina, and Raja binoculata; the dipnoan, Protopterus annectens; the brachiopterygian, Erpetoichthys calabaricus; the chondrostean, Polyodon spathula; and the holosteans Lepisosteus platyrhinchus and Amia calva. UI/corticotropin‐releasing‐factor immunoreactive elements were detected in the caudal spinal cords of Petromyzon marinus, Raja binoculata, Polydon spathula, Lepisosteus platyrhinchus, L. osseus, L. platostomus, and Amia calva. In addition, in several of these species, immunohistochemical techniques have provided evidence for serotoninergic input to the caudal neurosecretory system.
Accurate reinnervation of motor end plates after disruption of sheath cells and muscle fibers
Authors: Kuffler D. P.
Published: January 2005

After injury, regenerating motor axons grow back to form neuromuscular junctions at the original synaptic sites on muscle fibers. The pathways they grow along consist of basement membrane, Schwann cells, and perineurium that remained after degeneration of the original axons. All the factors necessary for directing axons to the original synaptic sites persist in muscles even after disruption of myofibers. The aim of the present experiments was to determine whether structural integrity of nerve sheath cells is required for precise reinnervation in the presence and absence of muscle fiber targets.

The region of innervation of the cutaneous pectoris muscle of the frog was briefly frozen to eliminate all living cells from neuromuscular junctions, intramuscular nerve bundles, and from a 1–3‐mm length of the nerve trunk. Only extracellular matrices persisted within the frozen region of muscle and nerve. These consisted of the basement membrane sheaths of myofibers, of Schwann cells, and of perineurial cells and the small fragments of disrupted cells that were bound to them. In some preparations new muscle fibers developed within the basement membrane sheaths. Regenerating axons grew through the naked basement membrane sheaths of original Schwann cells, formed numerous branches, and contacted the myofibers precisely at the original synaptic sites. By 5 weeks 75% of the original synaptic sites became reinnervated; the terminals were indistinguishable from those at normal neuromuscular junctions. In contrast, preparations in which all muscle fibers were prevented from regenerating far fewer synaptic sites became reinnervated. Five weeks after cell damage axon terminals were at only 6% of these naked synaptic sites.

These results show that the original nerve sheath cells need not be intact for restoration of the normal pattern of innervation and that the naked basal lamina has associated with it factors that direct the regenerating axons to the original synaptic sites. However, myofibers also play a role by contributing cues that significantly increase the rate of innervation of synaptic sites.
Cholinergic innervation of the cat striate cortex: A choline acetyltransferase immunocytochemical analysis
Authors: De Lima Ana Dolabela , Singer Wolf
Published: January 2005

In area 17 of adult cats the morphology, distribution, and synaptology of cholinergic elements were examined by immunocytochemical methods with a monoclonal antibody against choline acetyltransferase (ChAT). ChAT(+) fibers are present throughout the entire depth of the cortex but are particularly dense in layer I. Typically these fibers are very thin and possess numerous irregularly spaced varicosities. Except in layer I and deep layer VI, where the fibers tend to run parallel to the pial surface, they appear to be randomly oriented.

At the electron microscope level, immunolabeling was present in unmyelinated fibers of irregular contour and diameter. Most of the ChAT(+) varicose profiles contained mitochondria and round vesicles; Synaptic complexes were relatively infrequent and tended to be of the symmetrical type. They were located mostly on dendritic shafts and only rarely on cell bodies and dendritic spines. Both pyramidal and nonpyramidal cells were found to be innervated by cholinergic afferents.

These anatomical data are consistent with the known physiology of acetylcholine in the visual cortex, which indicates that it acts as a modulator of cortical excitability.
Optic fibers follow aberrant pathways from rotated eyes in Xenopus laevis
Authors: Grant Philip , Ma Pokay M.
Published: January 2005

The rotated eye paradigm has been a major experimental test of the neuronal specificity model for the development of ordered retinotectal connections in amphibians. In most studies, however, no optic fiber pathways were traced from rotated eyes and correlated with visuotectal projections. As an initial approach to this question, optic fibers from eyes rotated at different embryonic stages were traced with 3H‐proline autoradiography. Three experimental series were prepared: (1) in situ eye rotations, (2) isochronic transplants of eyes rotated between embryos at the same stage, and (3) heterochronic transplants of eyes rotated between embryos at different stages. Single or multiple optic fiber pathways developing from rotated eyes are identified by their sites of entry and trajectory in the brain. These include a normal chiasmatic (CH) pathway, and three aberrant pathways, identified as trigeminal (TR), diencephalic (DI), and oculomotor (OC). The latter three enter the brain ipsilaterally, some crossing contralaterally via commissural pathways. Depending on stage and type of operation, TR pathways develop in 50–100% of the animals, while CH pathways are more common after rotation at stage 21/22. The surgical procedure affects the initial trajectory of fibers from the retina, perturbs guidance cues in the surrounding orbit, and determines the patterns of optic pathways that develop. In most cases, optic fibers follow motor (oculomotor) or sensory (trigeminal) nerves, usually the first fibers encountered near the orbit by axonal pioneers exiting the retina. Evidently, optic fibers exhibit no pathway selectivity; any axon serves as a guidance cue. Tecta are innervated in about 50% of the cases, usually by fibers following abnormal trajectories from CH and OC pathways. The results suggest that the development of ordered visuotectal projections from rotated eyes is a complex process that may be independent of the trajectory of fiber arrival. Unless pathways and visuotectal maps are directly compared in each animal, however, the question remains open because we still do not know which anomalous pathways, if any, correlate with ordered projections.
The motor trigeminal nucleus of the rat: Analysis of neuronal structure and the synaptic organization of noradrenergic afferents
Authors: Card J. Patrick , Riley Joseph N. , Moore Robert Y.
Published: January 2005

The organization of the rat motor trigeminal nucleus (MTN) and the morphology of noradrenergic afferents terminating in this cranial motor nucleus were analyzed with light and transmission electron microscopy. Two morphologically distinct types of neurons are present in the MTN. Large multipolar neurons are the most prevalent cell type and are distributedd uniformly throughout the nucleus. The morphology of these cells is identical to that of motor neurons described previously in both the brainstem and spinal cord. The neurons are characterized ultrastructurally by a light, organelle‐rich cytoplasmic matrix containing numerous cisternal arrays of rough endoplasmic reticulum (RER) and a centrally placed spherical nucleus containing a single prominent nucleolus. Approximately 80% of the surface of these cells is contacted by axon terminals. The second major class of neuron consists of small spherical and fusiform cells that are located predominantly at the peripheral borders of the MTN. These cells are significantly smaller than motor neurons and exhibit only scattered axosomatic contacts. This small cell population appears to be composed of two distinct subclasses of neurons that probably represent interneurons and gamma motor neurons.

The MTN neuropil contains four morphologically distinct classes of axon terminals that are characterized by either spherical or pleomorphic vesicles within cytoplasm that is lucent or dense. Quantitative morphometric analysis demonstrated differential distribution of each of the four terminal types upon motor neuron somata and dendrites. Intracerebral injection of 5‐hydroxydopamine into the brainstem tegmentum immediately adjacent to the MTN labeled axon terminals containing spherical vesicles and a lucent axoplasmic matrix. Intracerebral injection of the neurotoxin 6‐hydroxydopamine resulted in degeneration of the same terminal population and thus confirmed that noradrenaline‐containing axons innervating the MTN exhibit a distinctive terminal morphology. The number of synaptic complexes exhibited by noradrenergic terminals did not differ significantly from other terminal populations in the MTN.
Laminar organization of ON and OFF regions and ocular dominance in the striate cortex of the tree shrew (Tupaia belangeri)
Authors: Kretz R. , Rager G. , Norton T. T.
Published: January 2005

The organization of ON and OFF responses and ocular dominance in the striate cortex of the tree shrew was electrophysiologically investigated by using flashed, stationary visual stimuli presented monocularly to either the ipsilateral or contralateral eye. We measured cortical multi‐unit activity at 25‐μm intervals with glass‐insulated platinum‐plated tungsten microelectrodes. Penetrations were made perpendicular to the cortical layers and the responses were quantitatively analyzed in layers IIIc to V. In sublayers IIIb, IIIc, and upper V, phasic responses of approximately equal magnitude occurred to both light ON and light OFF (ON‐OFF regions). In layer IV, tonic as well as phasic responses were often evoked by the flashed spot of light. In sublayer IVa stronger responses occurred to light ON than to light OFF (ON region) while in sublayer IVb stronger responses occurred to light OFF than to light ON (OFF region). In an ON region, the increased neural activity that occurred at light ON was often accompanied by a decrease in activity below baseline level at light OFF. A similar decrease often occurred in an OFF region at light ON. Recordings from the region of the cell‐sparse cleft in layer IV were characterized by ON‐OFF responses, signalling a transition zone between sublayers IVa and IVb. In addition, the responses to stimulation of the ipsilateral eye typically were very weak in the cleft region. In the other regions examined, the multi‐unit activity generally was driven binocularly with slightly greater responses being elicited by the contralateral eye. We conclude that the ON‐center and OFF‐center afferent pathways that are organized at the retinal level remain generally segregated in the tree shrew through the first synapse in the striate cortex. In addition, our recordings confirm that a horizontal organization of ocular dominance occurs in layer IV of the striate cortex in tree shrews.
Avenues for entry of peripherally administered protein to the central nervous system in mouse, rat, and squirrel monkey
Authors: Balin Brian J. , Broadwell Richard D. , Salcman Michael , El‐Kalliny Magdy
Published: January 2005

Pathways traversed by peripherally administered protein tracers for entry to the mammalian brain were investigated by light and electron microscopy. Native horseradish peroxidase (HRP) and wheat germ agglutinin (WGA) conjugated to peroxidase were administered intranasally, intravenously, or intraventricularly to mice; native HRP was delivered intranasally or intravenously to rats and squirrel monkeys. Unlike WGA‐HRP, native HRP administered intranasally passed freely through intercellular junctions of the olfactory epithelia to reach the olfactory bulbs of the CNS extracelluarly within 45–90 minutes in all species. The olfactory epithelium labeled with intravenously delivered HRP, which readily escaped vasculature supplying this epithelium. Blood‐borne peroxidase also exited fenestrated vessels of the dura mater and circumventricular organs. This HRP in the mouse, but not in the other species, passed from the dura mater through patent intercellular junctions within the arachnoid mater; in time, peroxidase reaction product in the mouse brain was associated with the pial surface, the Virchow‐Robin spaces of vessels penetrating the pial surface, perivascular clefts, and with phagocytic pericytes located on the abluminal surface of superficial and deep cerebral microvasculature. Blood‐borne HRP was endocytosed avidly at the luminal face of the cerebral endothelium in all species. WGA‐HRP and native HRP delivered intraventricularly to the mouse were not endocytosed appreciably at the abluminal surface of the endothelium; hence, the endocytosis of protein and internalization of cell surface membrane within the cerebral endothelium are vectorial. The low to non‐existent endocytic activity and internalization of membrane from the abluminal endothelial surface suggests that vesicular transport through the cerebral endothelium from blood to brain and from brain to blood does not occur. The extracellular pathways through which probe molecules enter the mammalian brain offer potential routes of passage for blood‐borne and airborne toxic, carcinogenic, infectious, and neurotoxic agents and addictive drugs, and for the delivery of chemotherapeutic agents to combat CNS infections and deficiency states. Methodological considerations are discussed for the interpretation of data derived from application of peroxidase to study the blood brain barrier.
Connections of the parahippocampal cortex in the cat. IV. Subcortical efferents
Authors: Witter Menno P. , Groenewegen Henk J.
Published: January 2005

The present report deals with the projections from the entorhinal and perirhinal cortices to subcortical forebrain structures and the brainstem in the cat. By using anterograde and retrograde tracing techniques, it could be demonstrated that the entire mediolateral extent of the parahippocampal cortex issues prominent projections to the dorsal and ventral striatum, the amygdala, and the claustrum. In addition, the entorhinal cortex sends projections to the septum and the diagonal band of Broca. Only the perirhinal cortex gives rise to a weak projection to the dorsolateral periaquaductal gray and the ventral pontine region. The major proportion of the subcortical projections originates in the perirhinal cortex and the lateral entorhinal cortex, whereas the medial entorhinal cortex has a much sparser output and sends no fibers to the amygdala. The subcortical projections from both the entorhinal cortex and the perirhinal cortex arise mostly from their deep layers. It was further found that these projections are topographically organized along the mediolateral axis of the parahippocampal cortex. This mediolateral axis is related to a ventrolateral to dorsomedial axis in the septum, a mediolateral axis in the amygdala and the ventral striatum, and a ventrodorsal coordinate in the dorsal striatum and the claustrum.

A further topography was observed in the projections from the perirhinal cortex to the lateral amygdaloid nucleus. A rostrocaudal axis in the perirhinal cortex corresponds to a mediolateral axis in the lateral amygdaloid nucleus. The present observations are compared with data concerning the connectivity of the parahippocampal cortex with the hippocampal formation and other cortical structures. It is suggested that the parahippocampal cortex in the cat may be conceptualized as an interface between the hippocampal formation and several subcortical structures in the realm of the limbic and motor systems.
Frequency representation in auditory cortex of the common marmoset (Callithrix jacchus jacchus)
Authors: Aitkin Lindsay M. , Merzenich Michael M. , Irvine Dexter R. F. , Clarey Janine C. , Nelson John E.
Published: January 2005

The location and characteristics of the primary auditory cortex of the common marmoset, Callithrix jacchus jacchus, were determined in five anesthetized male adult animals by mapping the responses of cortical units and unit clusters to pure tone stimuli presented to the contralateral ear. The primary auditory cortex lies largely ventral to the lateral sulcus, the only major fissure on the lateral cortex of this smooth‐brained primate, but in some animals it may extend significantly down the ventral bank of this sulcus. Responses are distributed such that low best frequencies are found rostroventrally whereas high best frequencies occur caudally. The disposition of frequency‐band contours is fan‐shaped, with contours separating low‐frequency octaves nearly parallel to the lateral sulcus and high‐frequency (>8 kHz) contours perpendicular to that sulcus. Best frequencies range from 0.6 to 30 kHz across the primary field, but there is a disproportionate representation of the three octaves between 2 and 16 kHz. The most sensitive thresholds (as low as −2 dB SPL) are found between 7 and 9 kHz. The primary auditory cortex is similar in cytoarchitecture to that reported for the cat, showing a blurring of lamination in the middle layers (II–IV) and a preponderance of small cells in these merged layers, giving a highly granular appearance. The accessiblity of the cochlear representation on the gyral surface makes the marmoset an attractive animal for studies of primate auditory cortex.
Intracephalic transplants of freeze‐Stored rat hippocampal tissue
Authors: Sørensen Torben , Jensen Steen , Møller Anders , Zimmer Jens
Published: January 2005

The survival and cellular and connective organization of intracephalic transplants of developing, freeze‐stored rat hippocampal tissue were examined. Blocks of tissue containing the hippocampus and fascia dentata were obtained from late embryonic (E16‐‐E22) and early postnatal rats (P0‐‐P4) and immersed in a tissue culture medium with 10% of the cryoprotective agent DMSO, frozen at a cooling rate of approximately 1°C/minute, and stored for 1‐‐226 days in liquid nitrogen. After quick thawing and washing out of the DMSO the tissue blocks were transplanted to the brain of adult rats. From 2 weeks to 3 months later the recipient brains were processed histologically. The cellular and connective organization of the transplants and their interaction with the host brains were analyzed after thionin cell staining, Timm's staining for hippocampal and dentate afferents, immunohistochemical staining for enkephalin‐, CCK‐, and somatostatin‐reactive neurons and afferents, AChE staining for cholinergic afferents, and silver stains for fiber architectonics and tracing of connections by anterograde axonal degeneration.

Freeze‐storage narrowed the range of donor ages with good transplant survival. The best surviving hippocampal and dentate transplants thus came from 17‐‐21‐day‐old embryos. There was no correlation between the length of storage and survival. Structurally the transplants of stored tissue were more frequently fragmented than the transplants of fresh tissue when located outside the brain parenchyma in the brain ventricles. This was in accordance with the results of a previous study of grafts of freeze‐stored and fresh hippocampal tissue placed in the anterior eye chamber. Despite the decrease in survival and the tendency for fragmentation many well‐structured and organotypically organized hippocampal and dentate transplants were recovered corresponding to the donor ages E19‐‐E21. In addition to the main cell types (granule cells and pyramidal cells) the freeze‐stored transplants also contained peptidergic nerve cells reacting for CCK, somatostatin, and enkephalin. The organization of the intrinsic nerve connections and the exchange of connections with the host brain were similar for transplants of stored and fresh tissue. Besides the consistent innervation of the hippocampal and dentate transplants by host cholinergic afferents monitored by AChE staining, several appropriately located dentate transplants thus sent mossy fibers to the host CA3. Others received host perforant path projection. A CA3‐associated transplant projection to the denervated perforant path zones in the host fascia dentata was also observed.

From this and the previous study of intraocular grafting of freeze‐stored immature brain tissue we conclude that cryopreservation is a feasible method that increases both the practical and the experimental potentials of transplantation of CNS tissue.
Adrenaline‐synthesizing neurons in the medulla of the cat
Authors: Ruggiero David A. , Gatti Philip J. , Gillis Richard A. , Norman Wesley P. , Anwar Muhammad , Reis Donald J.
Published: January 2005

In this study, the distribution of neruons containing the adrenaline‐synthesizing enzyme phenylethanolamine‐N‐methyltransferase (PNMT) was mapped in the medulla of the cat. Data from recent studies in the rat suggest that the anatomical structure responsible for cardiorespiratory changes that occur following application of neurotransmitters and drugs to Schlaefke's area on the ventral medullary surface is the nucleus reticularis rostroventrolateralis (RVL), which is distinguished from adjacent regions of the reticular formation, in part, by the presence of adrenaline‐synthesizing neurons. To determine whether an equivalent adrenergic population is present in the RVL of the cat, we used antibodies raised against bovine adrenal PNMT to map the distribution of adrenaline‐synthesizing neurons in the reticular formation. In the ventrolateral medulla, we found that labeled cells extended from the level of the retrofacial nucleus to the calamus scriptorius. The majority of labeled cells were seen in a nucleus designated RVL at the level of the rostral one‐third of the inferior olive. In the dorsomedial medulla, cells were labeled in the caudal aspect of the nucleus tractus solitarii (NTS) and were especially dense in the subnucleus gelatinosus and commissural nucleus of the vagus. A few lightly labeled cells were also present in the rostral pole of the area postrema (AP). In contrast to the rat, few or no immunoreactive cells were found in the rostral NTS, medial longitudinal fasciculus, nucleus paragigantocellularis dorsalis, or periventricular gray. Our results are consistent with the notion that an area of the RVL containing adrenergic perikarya is the anatomical structure responsible for cardiovascular changes that occur when chemicals are applied to Schlafke's area.
Transient midline raphe glial structure in the developing rat
Authors: Van Hartesveldt Carol , Moore Blake , Hartman Boyd K.
Published: January 2005

A major glial structure is present during development within the midline raphe of the midbrain, hindbrain, and cervical spinal cord of the rat. It is composed of great numbers of glial cell bodies lying immediately ventral to the cerebral ventricular system and the large radial processes extending from these cells toward the ventral surface of the brain roughly within the midsagittal plane. There is also a smaller group of glial cells on the dorsal surface of the aqueduct and the central canal whose processes extend to the dorsal surface of the brain. The entire structure exhibits an intensely positive immunoreactivity with the antibody to the S‐100 protein, a nervous‐system‐specific protein found primarily in the cytoplasm of astrocytes. This immunoreactivity makes possible a clear visualization of the extent, magnitude, and continuity of this structure from at least embryonic day 15, the first age examined, until postnatal days 7–8, when it is no longer visible by this technique.

This glial structure has several prominent morphological characteristics. During prenatal and early postnatal development the fibers forming the ventral aspect of the structure in the midbrain and hindbrain are formed into two parallel plates on either side of the midline with S‐100‐negative tissue between the plates. As development progresses, S‐100‐positive fibers are continually added so that the plates become thicker at the expense of the nonstaining intervening area. By postnatal day 4 only a single midline plate of fibers is visible, occupying the entire midline raphe. In the region of the pontine flexure the entire structure takes on a distinctly pleated configuration. This fact produces a curious “sine wave” appearance when the plane of section crosses these vertical pleats. At postnatal day 5 the structure begins to disappear, and it is no longer visible by 7–8 days postnatal. This glial structure does not stain with antisera to glial fibrillary acidic protein, a protein associated with fibrous astrocytes, or routine cell stains such as cresyl violet. With these techniques the raphe area appears essentially devoid of identifiable cellular elements.
Granule cell development in the frog cerebellum during spontaneous and thyroxine‐induced metamorphosis
Authors: Hauser Kurt F. , Uray Nándor J. , Gona Amos G.
Published: January 2005

Granule cell maturation in the cerebellum of bullfrog tadpoles was studied during both spontaneous and thyroxine‐induced metamorphosis by using electron microscopy and Golgi‐impregnated preparations. The production of cerebellar microneurons, a majority of which are granule cell precursors, was quantitatively compared during spontaneous and thyroxineinduced metamorphosis by using stereological methods and biochemical measurements of DNA.

Granule cell migration and differentiation appeared morphologically similar during spontaneous and thyroxine‐induced metamorphosis. In both instances, granule cells (1) migrated tangentially along the pial surface, (2) migrated into the internal granular layer, (3) developed dendritic arbors, and (4) formed synaptic contacts with the processes of Golgi cells and with mossy fibers. These events are similar to developmental processes that have been described in detail in other animals. Quantitative stereological measurements demonstrated similar overall patterns of change during spontaneous and thyroxine‐induced metamorphosis. Most notably, increases in the volume of the external granule layer correlated with increases in the relative and total amounts of DNA. However, measurements of total DNA were consistently reduced during the period of accelerated change that occurs in thyroxine‐induced metamorphosis, although external granular layer volume was greater in these tadpoles after 2 and 3 weeks of thyroxine treatment than in spontaneously metamorphosing tadpoles. While granule cell development in the frog is largely dependent on thyroid hormone, differences between thyroid‐hormone‐induced and spontaneously metamorphosing tadpoles suggest that normal patterns of cerebellar development are also dependent on events that occur in premetamorphic tadpoles in the absence of thyroid hormone.