bluuebunny/crossref_metadata_2025 huggingface dataset:
Fine structure of myelinated mechanical nociceptor endings in cat hairy skin
Authors: Kruger L. , Perl E. R. , Sedivec M. J.
Published: January 2005

High‐threshold mechanoreceptors (mechanical nociceptors) with myelinated axons were electrophysiologically identified in hairy skin of the cat as described by Burgess and Perl ('67). Such elements possess receptive fields consisting of a number of punctate areas from which maximal firing can be elicited by intense (skin‐damaging) mechanical stimuli. The spots of the receptive field are separated from each other by unresponsive regions, i.e., by skin areas from which responses cannot be evoked by stimuli effective at the spots.

Fine steel pins were inserted to bracket closely a number of the spotlike responsive areas for each of several units. After aldehyde perfusion of the animal, osmification of the tissue and embedding in plastic, the marked skin zones were examined in semithin and ultrathin sections at the light and electron microscopic level. Near each delineated area, a thinly myelnated axon was fond that could be traced to the papillary layer where it loses its myelin sheath. Unmyelinated axons accompanied by thin Schwann cell processes were then traced and found to penetrate the epidermal basal lamina in one of the papillae.

At the epidermal penetration site, the axons contained both clear round, and large, dense core vesicles; at this level, the surrounding Schwann cell cytoplasm exhibited numerous pinocytotic vesicles. The zone of pentration may constitute the receptive apparatus. Some of these axons have been traced within the basal epidermal layer where they become surrounded by keratinocytes, lose their Schwann sheath, and apparently terminate. This overall morphological pattern was consistently present in the demarked areas of focal responsiveness, and was rare in the surrounding skin; this and its difference from other cutaneous neural endings suggest that the intraepidermal axon‐Schwann cell complex constitutes the receptive structure for myelinated mechanical nociceptors. It is suggested that such complexes are the sense organs responsible for initiating the sensation of pricking pain produced by localized mechanical injury of the skin.
The laminar distribution and ultrastructure of fibers projecting from three thalamic nuclei to the somatic sensory‐motor cortex of the opossum
Authors: Donoghue John P. , Ebner Ford F.
Published: January 2005

The projections of the ventrobasal complex (VB), the ventrolateral complex (VL), and the central intralaminar nucleus (CIN) to the somatic sensory‐motor (SSM) cortex of the Virginia opossum were studied with light and electron microscopic autoradiographic methods. VB, VL, and CIN have overlapping projections to SSM cortex and each one also projects to an additional cortical area. Unit responses to somatic sensory stimulation and the areal and laminar distribution of axons in cortex is different for VB, VL, and CIN, but the axons from each form similar round asymmetrical synapses, predominantly with dendritic spines.

As in other mammals, VB units in the opossum have discrete, contralateral cutaneous receptive fields. VB projects somatotopically to SSM cortex and also projects to the second somatic sensory representation. Within the cortex, VB axons terminate densely in layer IV and the adjacent part of layer III. A few axons also terminate in the outermost part of layer I and the upper part of layer VI. Most VB axon terminate upon dendritic spines (86.6%), but they also contact dendritic shafts (10%) and neuronal cell bodies (3%).

Neurons in VL have no reliable response to somatic stimulation under our recording conditions. VL projects to the SSM cortex and to the posterior parietal area. Throughout this entire projection field VL fibers terminate in layers I, III, and IV most densely, and sparsely in the other cortical layers. The density of termination in the mid‐cortical laminae is quite sparse compared to VB, but the projection to layer I is considerably greater. Nearly all (93%) of VL axons contact dendritic spines, the remainder (7%) end dendritic shafts.

CIN is a thalamic target of ascending medial lemniscal, cerebellar, spinal, and reticular formation axons. Neurons in CIN respond to stimulation restricted to a particular body part, but typically responses may be evoked from larger areas and at longer latencies than neurons in VB that are related to the same body part. CIN neurons require a firm tap or electrical stimulation within their receptive field to elicit a response in the anesthetized preparation. CIN axons terminate throughout the entire parietal cortex, but unlike VB and VL, CIN fibers end almost exclusively in the outer part of layer I. Approximately 21% of CIN fibers contact dendritic shafts in layer I, which is twice the percentage of shafts contacted by VL or VB axons. All of the other CIN synapses are formed with dendritic spines.

These experiments demonstrate three different pathways to SSM cortex. The results suggest that each projection has a unique role in controlling the patterns of activity of neurons within the SSM cortex.
Olfactory bulb projections to the parahippocampal area of the rat
Authors: Kosel Keith C. , Van Hoesen Gary W. , West James R.
Published: January 2005

Recent evidence suggests that the main olfactory bulb projects caudally beyond the prepiriform cortex and the cortical amygdaloid nuclei to the region of the piriform lobe called the parahippocampal area. Included within this area is the entorhinal cortex, which is composed of six major subdivisions. Since question remain as to which of these subdivisions receives centripetal fibers from the bulb, we reexamined these projections using autoradiography and HRP histochemistry and correlated the sites of termination with the cytoarchitecture of the entorhinal cortex.

The results indicate that olfactory bulb axons reach all parts of the parahippocampal area, including the cortex which forms the medial and lateral banks of the amygdaloid sulcus (area TR), and both subdivisions of the laterally located entorhinal cortex (28L' and 28L). Also, label is observed over the more medially located fields of the entorhinal cortex, including the cortex posterior to the cortical amygdaloid nucleus (28M'), as well as the ventrolateral parts of medial entorhinal cortex (28M). In addition, evidence of label occurs over the full extent of the trasition zone (28i) which separates areas 28L and 28M. These results suggest that the olfactory bulb has a more extensive projection to the parahippocampal area in the rat than previously thought, and may provide at least some input to all of the parahippocampal areas which project to the hippocampal formation.
Pontocerebellar projections to the pyramis and copula pyramidis in the rat: Evidence for a mediolateral topography
Authors: Eisenman Leonard M.
Published: January 2005

In this study, using the horseradish peroxidase (HRP) retrograde tracing technique, the pontocerebellar projection to the pyramis and copula pyramidis in the rat has been analyzed in a series of experiments which had been performed to study the olivocerebellar projection (Eisenman, '81). Microinjections of HRP were made in different mediolateral positions along the width of the pyramis and copula pyramidis. Injections situated within the pyramis but in different loci resulted in the retrograde labeling of primarily two bilateral (much heavier contralaterally) groups of pontine cells: a medial and a ventrolateral group, both situated in the caudal pontine nuclei. With injections in the intermediate region, i.e., the border between the pyramis and copula pyramidis, a different pattern of labeled cells is seen. In these cases the intermediate part of the caudal pontine nuclei contains labeled cells. Injections placed in the lateral parts of the copula pyramidis resulted in still another pattern of retrograde labeling. Injections in this region resulted in the presence of labeled cells in four pontine areas, three caudal groups, and one group in the rostral pontine nuclei. Two of the caudal groups overlap with, but extend more rostrally than, the regions containing labeled cells after pyramis injections. These data suggest the presence in the pyramis and copula pyramidis of three parasagittal zones of differing widths, each of which receives a mainly differential projection from the pontine nuclei.
Time of cell origin and cell death in the avian dorsal motor nucleus of the vagus
Authors: Wright Linda L.
Published: January 2005

Cessation of cell proliferation and cell death were studied in the dorsal motor nucleus of the vagus of the chick embryo, hatchling, and adult. Most of the cells comprising the nucleus (94%) complete their final DNA synthesis on days 2 and 3 of incubation. There is a caudo‐rostral gradient in the cessation of proliferation, with the caudalmost cells withdrawing from the cell cycle slightly in advance of the middle and rostral cells. Cell death in the dorsal motor nucleus results in a 21% loss of cells between days 8 and 12, and 37% loss by hatching. A caudo‐rostral gradient was also present with respect to cell death, with more delayed and gradual cell loss occurring in the rostral region. The timing and spatial pattern of cell death may be related to the asynchronous innervation of the several targets of the nucleus.
Light‐microscopic immunocytochemical localization of tyrosine hydroxylase in prenatal rat brain. II. Late ontogeny
Authors: Specht Linda A. , Pickel Virginia M. , Joh Tong H. , Reis Donald J.
Published: January 2005

The immunocytochemical localization of tyrosine hydroxylase is examined at embryonic (E) days 18 and 21 in rat brain in order to determine changes in the distribution and cytology of neurons showing immunoreactivity for the enzyme during late prenatal developmnt. As compared with earlier stages of development, the distribution and morphology of the tyrosine hydroxylasecontaining neurons at E18 and E21 more closely resemble catecholaminergic neurons in the adult brain. The changes occuring from the early to the late prenatal stages of development appear to be the result of an increase in number of cells and continued aggregation and migration of the labeled neurons.

The major differences in the distribution of labeled perikarya between E18 and E21 are in the olfactory bulb and cerebral cortex. In the olfactory bulb, tyrosine hydroxylase‐containing neurons are not detected until E21. In contrast in the cerebral cortex, a few neurons are transiently labeled for the enzyme at E18, but are not detected at E21 and have not been reported in the adult brain.

The most striking change in the tyrosine‐hydroxylase labeled structures in the late prenatal period is the increase in detectable immunoreactivity in bundles of axons and in terminal aborizations. The orderly appearance of tyrosine hydroxylase‐labeled axons in the neostriatum and cortex are discussed in relation to the formation of these two contrasting regions innervated by catecholaminergic neurons.
An ultrastructural examination of early ventral root formation in amphibia
Authors: Nordlander Ruth H. , Singer Jon F. , Beck Ruth , Singer Marcus
Published: January 2005

The morphology of early interactions between neural tube and myotome in the amphibian embryo and tail regenerate was examined using the electron microscope. Two types of contacts were observed. At the most primitive level where the myotome was yet unsegmented, multiple adhesive‐type contacts linked neural tube and myotome. In newly segmented areas early ventral roots were recognizable as small bundles of one to five axons extending the short distance to the myotome. There was only one bundle per segment and in addition to axons, each bundle always contained one or more primitive glial cell processes which accompanied axons as they left the cord. At points of root exit primitive glial processes appeared to funnel axons into the root. The cytoarchitecture of the cord and the new roots suggested that the primitive glia may play a role in pathfinding for motor axons as they leave the cord and extend toward their targets.
Organization of thalamic afferents to anterior dorsal ventricular ridge in turtles. II. Properties of the rotundo‐dorsal map
Authors: Balaban Carey D. , Ulinski Philip S.
Published: January 2005

This study describes some properties of the map of nucleus rotundus onto dorsal area of anterior dorsal ventricular ridge (ADVR) in emydid turtles by correlating results of anterograde and retrograde tracing experiments with observations from Golgi‐ and myelin‐stained brains. An earlier paper (Balaban and Ulinski, '81) demonstrated that this projection is restricted to zone 4 of dorsal area of ADVR. This paper indicates that the rotundal pathway is organized such that longitudinally aligned groups of neurons in nucleus rotundus project to longitudinal regions in zone 4 of dorsal area. The projection field spans the dorsoventral (or concentric) dimension of zone 4 at each transverse level. Comparisons of experimental and Golgi preparations suggest that each rotundal neuron projects, via collaterals, to the entire rostrocaudal extent of rotundorecipient zone 4. Individual terminal branches span the dorsoventral dimension of zone 4 and are confined within both sagittal and transvere planes. Lesion experiments suggest that collaterals of a single rotundal axon are also distributed over at least one‐third to one‐half of the superficial‐deep dimension of zone 4. This is also reflected in the observation that neurons from disjoint dorsal, dorsolateral and medial rotundal loci project to overlapping, concentric regions of dorsal area. Both this prominent concentric component of terminal branches and the extensive overlap of projections of neurons at distinct rotundal loci preclude the possibility of a topographic representation of either dorsoventral or mediolateral rotundal axes in zone 4 of dorsal area.
The central cholinergic system studied by choline acetyltransferase immunohistochemistry in the cat
Authors: Kimura H. , McGeer P. L. , Peng J. H. , McGeer E. G.
Published: January 2005

An atlas of the distribution of cholinergic cell bodies, fibers, and terminals, as well as cholinoceptive cells, in the central nervous system of the cat (excluding the cerebellum) is presented from results obtained in immunohistochemical work on choline acetyltransferase. Cholinergic cell bodies are observed in more than forty areas, and cholinoceptive cells in sixty discrete areas of brain sections from the spinal cord to the olfactory bulb. The atlas is presented in seventy cross‐sectional drawings of cat brain extending from the olfactory bulb to the upper cervical spinal cord.
Transplantation of embryonic occipital cortex to the brain of newborn rats: A golgi study of mature and developing transplants
Authors: Jaeger C. B. , Lund R. D.
Published: January 2005

Segments of the occipital cortex were taken from rat embryos (E16–E19) and transplanted to the cerebral cortex or the tectal region ofa new‐born rat host. With the aid of Golgi impregnation techniques, neuron morphology was studied in cortical transplants which had survived for 1 week or more in the host brain. In mature transplants (> 4 weeks) three main groups of neurons, termed groups I–III, were identified. Group II neurons resembled pyramidal neurons of the intact cerebral cortex. No preferential orientation of either soma or dendrites of group I neurons was observed in the transplants, and some group I neurons was observed in the transplants, and some group I neurons had curved spical dendrites. Group II neurons had predominantly stellate form and their dendrites were densely covered with spines. Paucity or absence ofdendritic spines characterized group III neurons which exhibited various dendritic topologies.

Different neuron types were also recognized in immature transplants growing for 1 and 2 weeks in the host brain. The sequence of dendritic maturation of transplanted cortical neurons is similar to that seen in intact cortex, although the stage reached related more to the actual age of the transplant than to that of the host. Thus, group I neurons in the 1‐week‐old transplants taken from E16 embryos had not attained the same complexity of branching as pyramidal neurons in the surrounding host cortex, but rather resembled slightly younger cells more like those found in the cerebral cortex of the newborn rat.

These results show, therefore, that at least the basic cell classes identified in intact visual cortex can also be recognized in the cortical transplants. This will provide a foundation for studies defining which cells project to the host brain and which are involved in particular intrinsic connections.
Identification of early neurons in the brainstem and spinal cord. II. An autoradiographic study in the mouse
Authors: McConnell Jo Ann
Published: January 2005

Early neurogenesis was studied in two series of mouse embryos with tritiated thymidine (3H‐Tdr) autoradiography to determine (1) the time of origin and (2) the identity of the first postmitotic neurons. Time of origin was studied in embryos cumulatively labeled on the 9th–11th day of gestation (E8, E9, or E10, since the day of finding the vaginal plug is EO) and terminated after one cell cycle (8 hours). Autoradiographs were examined for unlabeled neurons, those which had undergone final DNA synthesis and which were usually also postmitotic. A 16‐somite embryo, cumulatively labeled from the 6‐somite stage, demonstrated 234 such cells in both alar and basal plates from the caudal diencephalon to the cervical spinal cord. Some of these young neurons, therefore, arose prior to neural tube closure, which begins at the 7‐somite stage. Data from other embryos in this series suggests that the first neurons arise at the 1–2 somite stage.

Early arising neurons were identified in embryos pulse labeled with 3H‐Tdr during E8–11 and killed after postnatal day (P) 30, when neuronal types could be determined. Autoradiographs were examined for heavily labeled cells, those in final DNA synthesis at the time of treatment. Heavily labeled cells in the youngest mouse in this series (injected at E8½; ca. 8‐somite stage) were primarily small‐to medium‐sized neurons of the brainstem reticular formation, but also some small neurons of the superior olivary nucleus and large primary sensory neurons of the mesencephalic nucleus of the trigeminal nerve. The earliest neurons in the spinal cord appeared early on E9, were medium sized, and were located in the ventral horn and the intermediate zone.

Comparisons between the results of this study and those of McConnell and Sechrist ('80) in the chick suggest that the youngest stages of neurogenesis are similar. The first chick nerve cells arise just before formation of the first somites; a slightly later time is indicated in the mouse. Reticular neurons are the earliestarising cells in the chick and make up the majority of the population in each of the youngest chick and mouse stages obtained. Motor and sensory neurons do not begin to originate in large numbers until later, during E3 in the chick and E9 in the mouse.
Astrocyte cell lineage. I. Astrocyte progenitor cells in mouse neopallium
Authors: Juurlink B. H. J. , Fedoroff S. , Hall C. , Nathaniel E. J. H.
Published: January 2005

The astrocyte cell lineage during postnatal development of the neopallium of Swiss mice was studied, using a colony culture assay method in which dissociated neopallial cells form discrete colonies in culture.

It was found that immature epithelial‐like cells that form type A colonies in culture come primarily from the subventricular zone but also from other regions of the neopallium. In culture, cells oftype A colonies form type C colonies consisting of cells, which although still epithelial like, differ morphologically from the type A colony‐forming cells. In the presence of dibutyryl cyclic adenosine monophosphate (dBcAMP) the type C colonies form cells rich in glial fibrillary acidic protein (GFAP) and stainable with Cajal's gold chloride sublimate, a stain specific for astrocytes. Therefore, it is proposed that type A colony‐forming cells are astrocyte progenitor cells resembling the “pale” cells found in the subventricular zone (Blakemore and Jolly, '72), the “largeglioblasts” (Sturrock, '76) and the free subependymal cells (Privat, '70; Paterson et al., '73) in the corpus callosum.

The sequence of the lineage, i.e., cells forming type A colonies give rise to cells forming type C colonies which eventually differentiate into astrocytes, takes place in situ as well as in culture. As postnatal development of the neopallium progresses the number of colony‐forming cells decreases in the subventricular zone and in other parts of the neopallium. The astrocyte progenitor cells migrate from the subventricular zone to other parts of the neopallium and progress through the lineage of differentiation in all regions of the neopallium.
Lesion‐induced sprouting of hippocampal mossy fiber collaterals to the fascia dentata in developing and adult rats
Authors: Laurberg Søren , Zimmer Jens
Published: January 2005

A lesion‐induced formation of an abnormal projection of hippo‐ campal mossy fiber collaterals to the molecular layer of the fascia dentata was studied in rats. Both immature (1–30 days old) and adult rats were subjected to hippocampal and entorhinal lesions which alone or in combination removed one or more of the major afferents to the dentate molecular layer (commissural, associational, and perforant path). Some lesions in addition transected the main part of the mossy fibers en route from the dentate granule cells to the hippocampal pyramidal cells in regio inferior (CA3). The formation of aberrant mossy fiber terminals in fascia dentata (supragranular mossy fibers) was monitored by the histochemical Timm sulphide silver method, but the presence of aberrant terminals was also observed in the electron microscope. Abnormal amounts of supragranular mossy fiber terminals were found following entorhinal lesions of both immature and adult rats, but not following commissural lesions. Even larger amounts of aberrant terminals were, however, found in immature and adult rats subjected to lesions which removed most of the associational hippocampodentate projection by isolating columns of fascia dentata from major parts of the hilus (CA4). Pure transections of the fascia dentata perpendicular to its longitudinal septotemporal axis did not in itself cause aberrant supragranular terminals, although such lesions partially damaged the associational afferents. When the transections were combined with commissural lesions or entorhinal lesions or both, large amounts of supragranular terminals did, however, form at the denervated levels septal to the transection.

After comparison of the amounts and distributions of the aberrant terminals found after the different lesions and in transplants of dentate tissue with different amounts of afferent input, we conclude that it is deafferentation of the dentate molecular layer, and not axotomy of the mossy fibers in the hilus or CA3 (pruning), that causes the aberrant growth of mossy fiber collaterals. Moreover, simultaneous removal of more than one afferent system seems to have a potentiating rather than a simple additive effect on the formation of supragranular mossy fibers.
The distal limb motor neurons in the thoracic ganglion of the spiny lobster
Authors: Silvey Gerald E.
Published: January 2005

The 16 motor neurons which innervate the muscles in the limb distal to the autotomy plane have been found in the third thoracic ganglion of the southern rock lobster, Jasus novaehollandiae. They were traced from the autotomy plane to the ganglion by stripping them from the small and large leg nerves to the edge of the ganglion where they were filled with cobalt dye. Cell bodies of 11 of these neurons lie in an anterior cluster of somata, and the remainder lie in a ventral rind of somata. The neurites from these somata expand into enlarged central segments, 400 μm long and 10–30 μm in diameter. These segments run parallel and in apposition to each other as they course through the neuropile a few cell layers beneath the dorsal surface of the ganglion. Near their origin some central segments send branches both medially between fibers of the interganglionic connectives, and anteroventrally into the connective. Distally the segments give rise to side branches which project around the anterior and posterolateral borders of the neuropile. The central segments constrict near the lateral edge of the neuropile, rise to its surface, and form axons. Eight axons, including those which innervate the flexor muscle of the carpus, enter an anterior motor tract which exists the side of the ganglion in a first root, the source of the small leg nerve. The remaining eight axons, which include those that innervate the extensor muscle of the carpus, enter a posterior motor tract which exits the side of the ganglion in a second root, the source of the large leg nerve. All the motor fibers which innervate the muscles of the limb, with the exception of the retractor of the coxa, run in these two tracts within the ganglion. Fibers which innervate the retractor of the coxa and the muscles of the thorax leave the ganglion in a third root at the posterodorsal border of the ganglion. The central segment, as the common structure of confluence of neuropilar branches, is the likely candidate for the integrating region of each neuron.
Differences in binocular interactions between cortical areas 17 and 18 and superior colliculus of siamese cats
Authors: Antonini A. , Berlucchi G. , Di Stefano M. , Marzi C. A.
Published: January 2005

In Siamese cats most retinal projections are crossed and almost all neurons in cortical areas 17 and 18 respond exclusively to the contralateral eye. However, neurons in visual areas in the suprasylvian sulci (LSA) can be activated from both eyes, since the input from the ipsilateral eye is relayed to them by the corpus callosum (Marzi et al., '80). This study shows that the superior colliculus (SC) is also the site of binocular interactions in Siamese cats with a predominantly monocular organization of areas 17 and 18. In 8 unanesthetized, brainstem‐sectioned Siamese cats, identified as “Boston” on the basis of the pattern of visual field representation in areas 17 and 18 (Hubel and Wiesel, '71; Shatz, '77a), only 25 out of 140 neurons in these areas could be driven from both eyes, whereas as many as 124 out of 143 SC neurons showed a clear binocular input.

The input from each eye to the ipsilateral SC and the resulting binocular interactions in our Siamese cats might have depended on corticotectal projections from LSA. If so, since a posterior callosal section abolishes the input from each eye to ipsilateral LSA, the SC should similarly be affected by callosotomy. The posterior half of the corpus callosum was sectioned acutely in three Siamese cats after recording from SC; the input from the ipsilateral eye to SC was suppressed by this operation in one cat (which, however, also had an unintended interruption of the posterior, habenular, and anterior intertectal commissures), and drastically reduced in the other two. In a fourth cat, in which callosotomy was performed three weeks before recording from SC, the number of SC neurons responsive to the ipsilateral eye was significantly inferior to that of Siamese cats with an intact corpus callosum. These findings indicate the importance of the corpus callosum for ipsilateral eye‐SC relations, as well as for SC binocularity, in Siamese cats. At the same time they imply that noncallosal routes can also transmit information from each eye to the ipsilateral SC in callosotomized Siamese cats.
Glial fibrillary acidic protein in the optic nerve of the developing albino rat: An immunoperoxidase study of paraffin‐embedded tissue
Authors: Dixon Richard G. , Eng Lawrence F.
Published: January 2005

The unlabeled peroxidase‐anti‐peroxidase method was used to stain glial fibrillary acidic (GFA) protein in the optic nerve of the developing albino rat. Optic nerves from animals ranging in age from the day of birth to adulthood were embedded in paraffin following fixation with various agents for times ranging from 30 minutes to 48 hours. GFA protein activity was demonstrable at birth in large astrocytic processes following fixation with alcohols or with Perfix for short intervals, but not with 4% or 2% buffered paraformaldehyde solutions. With increasing age, GFA protein could be demonstrated using higher aldehyde concentrations, longer fixation times, and longer paraffin embedding schedules. At all ages GFA protein activity was greater following treatment with nonaldehyde fixatives rather than those containing formaldehyde or glutaraldehyde. At birth the majority of GFA protein‐containing processes were confined to planes which were perpendicular to the axons of the optic nerve. With increasing age, tangential and longitudinal processes became more numerous until, in the mature optic nerve, astrocytic processes were best characterized as being multidirectional.
The connections of the inferior colliculus and the organization of the brainstem auditory system in the greater horseshoe bat (Rhinolophus ferrumequinum)
Authors: Schweizer Hermann
Published: January 2005

The connections of the inferior colliculus, the mammalian midbrain auditory center, were determined in the greater horseshoe bat (Rhinolophus ferrumequinum), using the horseradish peroxidase method. In order to localize the auditory centers of this bat, brains were investigated with the aid of cell and fiber‐stained material.

The results show that most auditory centers are highly developed in this echolocating bat. However, the organization of the central auditory system does not generally differ from the mammalian scheme. This holds also for the organization of the superior olivary complex where a well‐developed medial superior olivary nucleus was found. In addition to the ventral and dorsal nuclei of the lateral lemniscus a third well‐developed nucleus has been defined which projects ipsilaterally to the inferior colliculus and which was called the intermediate nucleus of the lateral leminiscus.

All nuclei of the central auditory pathway project ipsi‐, contra‐, or bilaterally to the central nucleus of the inferior colliculus with the exception of the medial nucleus of the trapezoid body and the medial geniculate body. The tonotopic organization of these projections and their possible functions are discussed in context with neurophysiological investigations.
Efferent connections of the olfactory bulb in the opossum (Didelphis marsupialis aurita): A Fink‐Heimer study
Authors: Shammah‐Lagnado Sara J. , Negrão Núbio
Published: January 2005

The efferent connections of the olfactory bulb (OB) in the opossum (Didelphis marsupialis aurita) were studied by the aid of the Fink‐Heimer technique.

Following lesions restricted to the OB, ipsilateral degenerating fibers entered the lateral olfactory tract and were traced to terminal fields essentially limited to the outer portion of the plexiform layer (sublamina IA) of the following structures: all the subdivisions of the anterior olfactory nucleus, the rostroventral tenia tecta, the full extent of the olfactory tubercle, the nucleus of the lateral olfactory tract, the anterior portion of the medial amygdaloid nucleus, the whole cortical amygdaloid nucleus (in the posteromedial subdivision of this structure the degeneration was very scanty), and the sulcal, piriform, and lateral entorhinal cortices. Some degree of topographical organization in the OB projections was noticed in the rostral portion of the lateral olfactory tract and within the external and lateral subdivisions of the anterior olfactory nucleus.

In another series of experiments, when the lesion also involved the accessory olfactory bulb, heavy terminal degeneration occurred along the whole extent of the medial amygdaloid nucleus and in the posteromedial subdivision of the cortical amygdaloid nucleus.

These findings indicate that, although very similar to those described in other mammals, the OB efferent connections in the opossum present some peculiarities; namely, the existence of dense terminal fields in the sulcal cortex and in the rostral district of the medial amygdaloid nucleus.
Cerebellar corticonuclear fibers of the paramedian lobule of tree shrew (Tupaia glis) with comments on zones
Authors: Haines D. E. , Patrick G. W.
Published: January 2005

Following a series of lesions in dorsal (DPML) and ventral (VPML) divisions of tree shrew (Tupaia) paramedian lobule (PML), the distribution of degenerated axons within the deep cerebellar nuclei was determined using the Fink and Heimer ('67) method. Damage to PML produced axonal degeneration in lateral (NL), anterior interposed (NIA), and posterior interposed (NIP) cerebellar nuclei. No degenerated fibers could be traced to either the medial cerebellar nucleus or vestibular complex, via juxtarestiform body, from lesions in PML. Corticonuclear fibers to NL, NIA, and NIP from PML cortex are topographically organized. Subsequent to lesions of lateral DPML, axonal debris is found in rostral and medial NL, while the lateral edge of VPML projects primarily into medial NL. According to the terminology of Voogd ('69) these lateral regions of PML represent the D zone. The NIP receives corticonuclear input from a relatively wide middle area of both portions of PML, interpreted as the C2 zone. There is some evidence which suggests that medial portions of the C2 area of DPML project into more lateral areas of NIP, while lateral regions of this zone in DPML are related to more medial NIP. This projection pattern is inverted for the C2 area of VPML; medial C2 to medial NIP, lateral C2 to lateral NIP. Corticonuclear fibers of PML which enter NIA appear to arise from a narrow, irregular, partially discontinuous strip of cortex located at the interface of the D and C2 areas in lateral PML and from a wider, more regular region in the most medial areas of this lobule. These represent, respectively, the C3 and C1 zones.

Although an overall pattern of zones is present, there is evidence to suggest that their spatial organization differs from DPML to VPML. The zonal pattern appears to be more obvious in VPML, while this pattern for DPML is less distinct. This is interpreted as indicating that either (1) zones C1−C3 overlap to a greater degree in DPML than in VPML, or (2) zones C1 and C3 may converge in rostral DPML, partially obliterating the intervening zone C2. The different ways in which zonal terminology is applied to both corticonuclear and certain of the afferent cerebellar systems are discussed.
Photoreceptor degeneration preceding clinical scrapie encephalopathy in hamsters
Authors: Buyukmihci Ned , Goehring‐Harmon Faye , Marsh Richard F.
Published: January 2005

Hamsters experimentally inoculated with scrapie had histologic and ultrastructural changes in their retinas before clinical signs of central nervous system disease became evident at 50 days postinoculation. The retinal changes were limited to the photoreceptors and began with degenerative changes in the inner segments as early as 8 days postinoculation. As the inner segment lesions became more prominent, associated degenerative changes within outer segments were seen (38 days postinoculation). An influx of macrophages was associated with increasing degenerative changes; these cells engulfed cellular debris but did not appear to contribute directly to the degenerative process. Retinas having the greatest damage to the inner segment area also had moderate reduction in outer nuclear layer density and outer segment length, and in numbers of outer segments. All of the retinal changes described occurred almost exclusively in the central to mid‐region of retina with relative sparing of peripheral retina.
Ultrastructural evidence for compensatory sprouting of climbing and mossy afferents to the cerebellar hemisphere after ipsilateral pedunculotomy in the newborn rat
Authors: Angaut P. , Alvarado‐Mallart R. M. , Sotelo C.
Published: January 2005

Unilateral section of the inferior and middle cerebellar peduncles was performed in rats at postnatal days 1 or 2. The ultrastructure of the cerebellar hemispheric cortex ipsilateral to the lesion was examined 3 months later. The absence of contralateral inferior olive and of ipsilateral middle peduncle, together with a marked regression of the contralateral pontine gray, were indicative of successful pedunculotomy.

In spite of a relative atrophy of the hemisphere, its cytological structure was qualitatively normal. Mossy and climbing fibers were present and their terminal varicosities disclosed normal features. The density of climbing fiber terminals was reduced compared to control cerebellum, whereas the density of mossy terminals seemed unchanged. Subsequent to the reduction of climbing afferents two subclasses, or types, of Purkinje cells were present: A “normal” type characterized by its climbing fiber innervation and a “hyperspiny” type devoid of climbing fiber.

In some of the adult rats pedunculotomized at birth, section of the contralateral peduncles was performed 24 hours before fixation. Terminal degeneration of climbing and mossy fibers was observed in the neonatally deprived hemisphere, providing the proof that these fibers result from a compensatory transcommissural sprouting of afferents destined to the contralateral hemicerebellum.

These results demonstrate that the cerebellar cortex neonatally deprived of its main afferents can be innervated by climbing and mossy fibers through a process of transcommissural sprouting. Although the newly formed synapses maintain their target specificity, a functional reorganization must occur because of the altered distribution of both systems of afferents.
Ganglion cells of the cat accessory optic system: Morphology and retinal topography
Authors: Farmer Samuel G. , Rodieck R. W.
Published: January 2005

The ganglion cells of the cat's retina form classes that are distinct in their cell morphology, retinal distribution, central projections, and functional properties. By means of the retrograde transport of horseradish peroxidase injected into the accessory optic nuclei of the cat midbrain, we have characterized the retinal ganglion cells projecting to these nuclei.

The retinal projection is virtually completely crossed to the medial terminal nucleus and to the lateral terminal nucleus. This appears to be true for the dorsal terminal nucleus as well, although difficulties of the technique limit our findings for this region. No differences were found in either the spatial distribution, or the somal size distribution, or the morphological characteristics of the ganglion cells projecting to these three nuclei. In spatial distribution, these cells are concentrated in the area centralis and visual streak and show no evidence of a nasotemporal divison. Morphologically, they have small to medium‐sized somas and delicate, sparsely branching dendrites. They do not appear to belong to any of the morphological cell types thus far identified.
Cytoarchitecture, fiber connections, and ultrastructure of nucleus isthmi in a teleost (Navodon modestus) with a special reference to degenerating isthmic afferents from optic tectum and nucleus pretectalis
Authors: Ito Hironobu , Sakamoto Noboru , Takatsuji Koichi
Published: January 2005

Cytoarchitecture and fiber connections of the nucleus isthmi in a teleost (Navodon modestus) were studied by means of Nissl, Bodian, toluidine blue, Golgi, and Fink‐Heimer methods. Synaptic terminals were classified by the ultrastructural characteristics, and their origins were determined by electron microscopic degeneration experiments.

The nucleus isthmi is composed of an outer cellular area or shell and an inner noncellular area or core. The shell covers anterior, dorsal, and ventral aspects of the core. The cell bodies in the shell are oval (15 × 20 μm) with an anteroposterior long axis, and have many somatic spines. Spines are also seen on the initial segment of the axon. Primary dendrites extend postermedially and branch out in the core. The core contains thin and thick myelinated fibers, which originate in the optic tectun and in the nucleus pretectalis, respectively.

At least two types of axons terminal were distinguished in the nucleus isthmi: S type, containing spherical vesciles, and F type, containing flattened vesicles. S terminals are derived from thin myelinated fibers and are only seen in the core where they form asymmetric synapses with dendrites. Frequently a portion of the S terminal membrane near the usual synaptic cleft is in close apposition with the membrane of an adjacent small dendrite or spine. F terminals, which derived from thick myelinated fibers, make symmetric synaptic contacts with both cell bodies in the shell and dendrites in the core. S terminals degenerate after ipsilateral ablation of the optic tectum, whereas F terminals degenerate after destruction of the nucleus pretectalis.
Reorganization of raccoon somatosensory cortex following removal of the fifth digit
Authors: Rasmusson Douglas D.
Published: January 2005

The organization of part of the primary somatosensory cortex was examined in anesthetized raccoons at 2, 8, or 16 weeks after the normal peripheral input to this region of cortex had been removed by amputation of the fifth digit. Electrophysiological recordings were made in and around the cortical area representing the fifth digit. Eight intact animals were used to verify that this specific area could be accurately localized on the basis of the sulci and to determine the normal response characteristics of this area. The results from nine animals with the fifth digit removed provided evidence for a gradual reorganization of the cortical area which had been functionally denervated. At 2 weeks postamputation the field was almost totally unresponsive to sensory input. At 8 weeks many sites were responsive to high intensity stimulation of rather extensive regions of the hand. At 16 weeks the cells fired more readily to peripheral stimulation than at 8 weeks and tended to have smaller, more restricted receptive fields. The location of receptive fields in this latter group suggested that the fifth digit area was taken over primarily by input from the fourth digit. The time course of this reorganization is suggestive of extensive anatomical changes either within the cortex itself or at subcortical levels.
The medial forebrain bundle of the rat. I. General introduction
Authors: Nieuwenhuys Rudolf , Geeraedts Leo M. G. , Veening Jan G.
Published: January 2005

This paper is the first of a projected series of studies on the strcture and composition of the medial forebrain bundle (MFB) of the rat and the relations of this fiber system to its bed nucleus, the lateral hypothalamic area. The first part of the paper comprises an extensive review of literature on the MFB from its discovery by Ganser in 1882 to the present. This review serves as the basis for an evalution of our present‐day knowledge of the organization of the MFB, which is presented in the second part of this paper. Despite the wealth of information available on the origins and sites of termination of the axons that constitute the MFB, surprisingly little attention has been given to the bundle itself, to its topographic boundaries, its fiber composition, or to the spatial arrangement of its constituent components. These features of the MFB as it extends through the lateral preoptic and lateral hypothalamic areas have been analyzed in normal Klüver‐Barrera‐ and Bodian‐stained material. From this analysis, a detailed atlas of the MFB and some of the surrounding structures has been prepared. This atlas, which forms the third section of this paper, illustrates the appearance and organization of the MFB at ten equidistant levels through the lateral preoptic and lateral hypothalamic continuum.
The medial forebrain bundle of the rat. II. An autoradiographic study of the topography of the major descending and ascending components
Authors: Veening Jan G. , Swanson Larry W. , Cowan W. Maxwell , Nieuwenhuys Rudolf , Geeraedts Leo M. G.
Published: January 2005

The medial forebrain bundle (MFB) is a complex fiber system that courses through and partly arises and partly terminates within the lateral preoptic and lateral hypothalamic areas. It consists mainly of thin fibers and may be comprised of as many as 50 descending and ascending components of varying lengths and of different origins and/or destinations (Nieuwenhuys et al., 1982). With the aid of an an atlas of the MFB and the surrounding brain areas in the rat presented in the preceding paper (Nieuwenhuys et al.,1982), the position and topographic relationships of some 21 components of the bundle have been analyzed in detail, in brains that had been prepared for autoradiography following injections of tritiated amino acids into a number of structures that are known to contribute fibers to the MFB. From this analysis it is clear that most of the labeled components occupy specific and rather constant positions within the MFB. For example, the ascending components are largely confined to the dorsal half of the bundle; those arising from the medial preoptic area and the various hypothalamic nuclei are distributed rather diffusely over much of the MFB; and the descending components that arise from the olfactory tubercle and the magnocellular preoptic nucleus are confined to restricted parts of the bundle. These findings indicate that the neurons which occupy different parts of the lateral hypothalamic area probably receive distinctive inputs, and to a first approximation these are likely to be determined principally by their position within the MFB.
The ultrastructure of the subnucleus gelatinosus of the nucleus of the tractus solitarius in the cat
Authors: Leslie R. A. , Gwyn D. G. , Hopkins D. A.
Published: January 2005

The dorsomedial region of the nucleus of the tractus solitarius termed the subnucleus gelatinosus (SNG) was studied at the light and electron microscopic level in the cat. In cresyl violet and luxol fast blue stained sections the SNG contained small neuronal somata that were scattered throughout a pale‐staining neuropil containing few myelinated fibers. These neurons were difficult to impregnate with Golgi staining techniques, but in successful impregnations the somata were observed to be 10–19 μm in diameter and bore few sparsely branching primary dendrites. Spines were present on the dendrites of some neurons and were more numerous on distal portions of the dendritic tree.

Ultrastructural examination of the SNG revealed that the neuronal complement consisted of round, oval, or spindle shaped neurons with little or no organized Nissl substance. Rare myelin‐like ensheathments of neuronal perikarya were also observed. Bundles of fine unmyelinated axons that coursed mainly longitudinally were a prominent feature of the area. The most common type of axon terminal observed contained mainly round clear vesicles, approximately 31 nm in diameter, and made asymmetrical synaptic contact with a dendritic profile. Pleomorphic vesicle‐containing terminals involved in symmetrical synaptic contact were also commonly seen. Axodendritic and axosomatic synapses were associated with terminals containing either round clear vesicles or pleomorphic vesicles. Less commonly, dendrodendritic and dendrosomatic synapses were seen, the presynaptic elements of which contained pleomorphic vesicles.

Following removal of a nodose ganglion, degenerating terminals of vagal afferent fibers were observed throughout the neuropil. Such terminals contained round, clear vesicles with an occasional large, dense‐cored vesicle, and made axodendritic and axosomatic synaptic contacts.