bluuebunny/crossref_metadata_2025 huggingface dataset:
Ascending pathways from the monkey superior colliculus: An autoradiographic analysis
Authors: Harting John K. , Huerta Michael F. , Frankfurter Anthony J. , Strominger Norman L. , Royce G. James
Published: January 2005

The autoradiographic tracing method has been used to analyze the distribution of ascending tectofugal pathways in the rhesus monkey.

Our findings show that axons which arise from deep collicular neurons terminate within several dorsal thalamic nuclei which in turn project upon the frontal eye fields (area 8) and the inferior parietal lobule (area 7). Both of these cortical areas are functionally quite similar to the deep colliculus, and we suggest that ascending channels from the deep tectum must account, at least in part, for these functional similarities.

The present autoradiographs reveal projections to several nuclear zones previously not identified as deep collicular targets in the monkey. Such targets include the visceral cell columns of the oculomotor complex, the rostral interstitial nucleus of the medial longitudinal fasciculus, and the magnocellular division of the ventral anterior nucleus.

Deep tectal input also has been shown to terminate quite extensively within the paralamellar region of the mediodorsal nucleus and in the parafascicular nucleus; very little input to the central lateral and centromedian nuclei was observed.

Radioisotope injections restricted to the superficial layers reveal dense projections to the parabigeminal nucleus, the pretectum, the inferior and lateral pulvinar nuclei, and to the ventral and dorsal lateral geniculate nuclei. Transported protein within the dorsal lateral geniculate nucleus occupied the “S” layers and the interlaminar zones.
Unmyelinated sensory and preganglionic fibers in rat L6 and S1 ventral spinal roots
Authors: Coggeshall Richard E. , Maynard Christine W. , Langford Lauren A.
Published: January 2005

Approximately 30% of the axons in the L6 and S1 ventral roots in the rat are unmyelinated. Appropriate surgical procedures show that 30% of these unmyelinated axons arise from dorsal root ganglion cells and are therefore presumably sensory. Thus approximately 10% of the total number of axons in these ventral roots are sensory. The other 70% of the unmyelinated axons come from the spinal cord and are therefore presumably preganglionic parasympathetic fibers. Thus approximately 20% of the axons in these ventral roots are unmyelinated preganglionic fibers. The implications of these findings are discussed.
The organization of the lateral posterior nucleus of the golden hamster after neonatal superior colliculus lesions
Authors: Crain Barbara J. , Hall William C.
Published: January 2005

The reorganization of the adult hamster's lateral posterior nucleus after neonatal superior colliculus lesions was studied using primarily light and electron microscopic degeneration techniques. Two types of experiments were conducted.

First, the distributions of the remaining afferents from the contralateral superior colliculus, the contralateral retina, and the ipsilateral posterior neocortex were determined using the Fink‐Heimer ('67) technique. Normally the projections from the contralateral superior colliculus and retina are sparse and restricted to small areas in the rostrolateral subdivision. After neonatal lesions of the ipsilateral colliculus, however, these two minor projections greatly increase in density and expand to share a common border. In contrast, the normal projection from the posterior neocortex is dense throughout the rostrolateral subdivision. After a neonatal colliculus lesion, however, this projection is greatly decreased in the region occupied by the optic tract terminals.

Second, the ultrastructural organization of the rostrolateral subdivision was studied in adult animals which had received neonatal colliculus lesions. Normally, this region is characterized by synaptic clusters in which numerous medium‐sized terminals (M‐terminals), almost all from the ipsilateral colliculus, synapse around the shaft of a large central dendrite. The contralateral colliculus and retina normally contribute only a few M‐terminals. After a neonatal colliculus lesion, typical clusters still form, but now the expanded projections from the contralateral colliculus and retina contribute numerous M‐terminals. The cortex does not contribute M‐terminals in either normal or experimental animals.

These results suggest that the afferents to the rostrolateral subdivision normally compete for synaptic space. The various factors that might be involved in determining the outcome of such competition are discussed.
Organization of the face representation in macaque motor cortex
Authors: McGuinness Evelynn , Sivertsen Dave , Allman John M.
Published: January 2005

We stimulated with microelectrodes the face representation in precentral motor cortex in macaque monkeys. Responses were very discrete; at threshold current levels the usual response was a small focus of movement in part of a muscle. Facial muscles cluster together in the posterior and anterior portions of the precentral gyrus with tongue movements represented in the intervening region and along the lateral extent. Within each cluster there are multiple representations of individual muscle movements. In long penetrations down the anterior wall of the central sulcus we were able to advance the electrode tangentially through cortex. In these penetrations we encountered a series of discrete zones each of which was related to the movement of a particular muscle or part of a muscle in the face. The lowest threshold points were found in the center of each zone, and a the microelectrode progressed toward the edge, thresholds rose until there was a shift to a new muscle movement. Successive stimulation points separated by as little as 50 μm could yield different responses. These zones could be either roughly cylindrical or take the form of narrow curving bands running mediolaterally across cortex. There is a tendency for adjacent muscles to occur together, and the representation may be roughly topographical within the limits set by the morphological structure of the muscles themselves. The most commonly evoked muscle response was in zygomaticus, which retracts the corners of the mouth in expressions of fear and anger.
Development of the brain Stem in the rat. II. Thymidine‐radiographic study of the time of origin of neurons of the upper medulla, excluding the vestibular and auditory nuclei
Authors: Altman Joseph , Bayer Shirley A.
Published: January 2005

Groups of pregnant rats were injected with two successive daily doses of 3H‐thymidine from gestational days 12 and 13 (E12 + 13) until the day before birth (E21 + 22). In radiographs from adult progeny of these rats the proportion of neurons generated on specific days was determined in the major nuclei of the upper medulla, with the exception of the vestibular and auditory nuclei. The neurons of the motor nuclei are generated over a brief period. Neurons of the retrofacial nucleus are produced first, with more than 60% of the cells arising on day E11 or earlier. Peak generation time of abducens neurons is day E12 and of the neurons of the facial nucleus is day E13. In contrast, the neurons of the superior salivatory nucleus are produced late, predominantly on day E15 and some on day E16. The generation of the (sensory relay) neurons of the nucleus oralis of the trigeminal complex takes place over an extended period between days E12 and E15; the last generated cells include the largest neurons of this nucleus. Neurons of the raphe magnus are produced between days E11 and E14, the neurons of the rostral medullary reticular formation between days E12 and E15. The latest generated neurons of the upper medulla (excluding the cochlear nuclei) belong to a structure identified as the granular layer of the raphe.

Combining these results with those of the preceding paper (Altman and Bayer, ′80a) and with additional data, it is postulated that the laterally and ventrally situated motor nucleus of the trigeminal, the facial nucleus, and the nucleus ambiguus form a single longitudinal zone of branchial motor neurons with a rostral‐to‐caudal cytogenetic gradient. In contrast, the medially and dorsally situated (juxtaventricular) hypoglossal nucleus and abducens nucleus (together with the other nuclei of the ocular muscles) form a longitudinal somatic motor zone with a caudal‐to‐rostral gradient. The dorsal nucleus of the vagus and the superior salivatory nucleus may constitute a preganglionic motor zone, also with a caudal‐to‐rostral cytogenetic gradient.
A scanning electron microscope study of the in vitro development of dissociated hippocampal cells
Authors: Rothman S. , Cowan W. M.
Published: January 2005

Cultures of dissociated hippocampal neurons from 18‐day‐old rat fetuses were examined by scanning electron microscopy after periods between one hour and 20 days following plating on a poly‐L‐lysine coated substrate. Cell attachment was virtually complete within one hour after plating, and at that stage many cells could be seen which had started to extend processes with broad growth cones. By four hours in culture, process formation was well advanced and some cells had already assumed a pyramidal configuration. After 16 hours in culture, numerous contacts were seen between neighboring growth cones, and this frequently led to fasciculation of the interacting fibers. During the next three weeks the cell bodies enlarged considerably and rounded‐up, and two distinct types of processes became evident: large, rapidly tapering dendrite‐like processes and finer, essentially uniform‐diametered processes that resemble axons. In most of the older cultures a dense plexus of processes was formed, and many of the finer processes appeared to have “bouton‐like” swellings as they traversed the upper surfaces of the neuronal perikarya. Non‐neuronal elements, which comprised only about 5% of the cells initially plated, rapidly proliferated in our cultures and within three to six days formed a confluent monolayer beneath the neurons.
A light and electron microscopic study of the dorsal motor nucleus of the vagus nerve in the cat
Authors: McLean John H. , Hopkins David A.
Published: January 2005

The morphology of the dorsal motor nucleus of the vagus nerve (DMV) in the cat was studied with the aid of light and electron microscopy. In frozen sections stained by the Kluver‐Barrera method or stained to show retrograde labeling in the DMV following injections of horseradish peroxidase (HRP) in the cervical vagus nerve and the stomach wall a range of sizes of DMV neurons was observed but it was not possible to distinguish separate types. In contrast, two distinct types of neurons, one medium‐sized and the other small, were identified with the light microscope in Golgi‐Cox and 1‐μm Epon sections and with the electron microscope in ultrathin sections.

The medium‐sized neurons had a range of sizes but generally measured 18 × 25 μm and possessed three to four proximal dendrites which branched two or three times. Spines were observed occasionally on the soma and on dendrites. These neurons contained a well‐developed cytoplasm and a noninvaginated round to oval nucleus. The small neurons generally measured 9 × 14 μm and were round or slightly elongated in shape. Their dendritic processes were fewer and thinner than those of the medium‐sized neurons and extended for shorter lengths. Their soma contained scanty cytoplasm and an invaginated nucleus. The medium‐sized neurons outnumbered the small neurons by more than three to one but both neuronal types were distributed evenly throughout the nucleus. The medium‐sized neurons seemed to correspond in size to the parasympathetic efferent neurons of the viscera as indicated by the HRP studies.

Axosomatic synapses on both types of neurons and axodendritic synapses were observed in the DMV. Terminals containing mainly small clear round vesicles and making asymmetrical contact with the postsynaptic membrane were involved in the majority of synapses on both the soma and dendrites. Terminals containing predominantly pleomorphic vesicles and making symmetrical contact with the postsynaptic membrane were also common, comprising up to one‐third of all synapses observed. Serial sections revealed that most synaptic terminals contained varying numbers of large (75–110 nm) dense‐cored vesicles. Smaller dense‐cored vesicles (45–55 nm) were sometimes observed, often close to the area of synaptic contact. Terminals 1–2 μm in diameter which contacted dendrites 1–3 μm in diameter formed the most common synaptic combination throughout the rostral to caudal extent of the DMV. No distinct regional differences were observed with respect to distribution of synaptic types.
The cytoarchitecture, cytology, and synaptic organization of the basilar pontine nuclei in the rat. I. Nissl and golgi studies
Authors: Mihailoff Gregory A. , McArdle Craig B. , Adams Catherine E.
Published: January 2005

Studies of the rat basilar pontine gray in Nissl‐stained frozen sections revealed the presence of four major subdivisions referred to as medial, ventral, lateral, and peduncular nuclei with respect to their position relative to the cerebral peduncle. Neurons located adjacent to the surface of, or within the cerebral peduncle were considered collectively as the peduncular nucleus. It should be emphasized that the above subdivisions are useful only for descriptive purposes and do not necessarily reflect distinct cytological similarities or differences within the identified cell groups. The dorsal peduncular (pontine) region was continuous around the lateral and medial boundaries of the peduncle with more ventral pontine areas. A distinct cluster of neurons was consistently observed near the ventromedial surface of the basilar pons, seemingly walled‐off by fascicles of pontocerebellar axons. In addition, in most animals, a cleft appeared in the peduncle and allowed direct communication between dorsal and ventral peduncular regions, while the medial lemniscus formed a partial boundary separating dorsal pontine neurons from the nucleus reticularis tegmenti pontis.

Golgi studies indicated that four general varieties of pontine neurons could be distinguished, and in order of relative frequency were described as spine‐laden, pauci‐spined, pauci‐spined with long, thin dendrites, and small bipolar or unipolar cells whose axon sometimes collateralized within the pons. A wide variety of spinous processes and finger‐like dendritic protrusions, some of which formed a terminal tuft‐like arrangement, characterized pontine neuron dendrites. In addition, some dendrites of small neurons gave rise to rather long, thin, beaded processes which in certain instances emanated from an unusual triangulated branch point enlargement. Dendritic orientation (neuron shape) was sometimes determined by location, with cells in the peduncular nucleus oriented parallel to the nearest peduncular surface, while cells near the ventral pontine surface were arranged parallel to transversely directed pontocerebellar axons. Cells of medial pontine regions did not project dendrites across the midline, while neurons near the peduncular cleft sent dendrites into that space. Based on the locations of various pontine afferent termination zones as determined in previous as well as ongoing studies, it appears that some pontine neurons exhibit dendritic systems reaching into more than one afferent projection area, thereby affording them an opportunity to receive inputs from several afferent systems.
Organization of spinothalamic tract axons within the rat spinal cord
Authors: Giesler G. J. , Spiel H. R. , Willis W. D.
Published: January 2005

Two techniques have been used to examine the organization of spinothalamic tract axons within the spinal cord of the rat. In the initial experiments, the thalamus was filled on one side with horseradish peroxidase (HRP) using a series of small injections. The injections were preceded by lesions of various areas of the ventral quadrant. These studies indicated that the cells of origin of STT axons ascending within the ventral funiculus (VF) are located primarily in the ventral‐most areas of the dorsal horn and the intermediate gray zone. The cells of origin of STT axons projecting within the ventrolateral funiculus (VLF) are located not only deep within the gray matter but in addition within the dorsal‐most two thirds of the dorsal horn, the area of the spinal cord gray matter shown in previous studies to contain the vast majority of cells with cutaneous tactile and nociceptive input. To examine these projections directly, rats received either a series of HRP injections that filled the thalamus on one side or a small injection into either medial or lateral thalamus. Examination of the labeled axons in horizontal sections through the cervical cord indicated that STT axons ascending to lateral thalamus do so in the VLF. In contrast, axons terminating in medial thalamus ascend in the VF. Additional experiments have shown that axons ascending to the lateral thalamus are distributed throughout the VLF at lumbar levels. Within the thoracic cord, lateral projecting STT axons are distributed throughout much of the VLF but are not found in close proximity to the ventral horn. At cervical levels all lateral‐projecting STT axons have assumed a position on the lateral rim of the VLF. These and previously published data have demonstrated that the rat spinothalamic tract is composed of two components that differ in the distribution of their cells of origin, the area of the cord in which they ascend, and the thalamic nuclei in which they terminate.
Thalamic connections with limbic cortex. II. Corticothalamic projections
Authors: Kaitz Suzan S. , Robertson Richard T.
Published: January 2005

The corticothalamic projections from the cat limbic cortex have been investigated with anterograde and retrograde axonal transport techniques. Five limbic cortical areas—the anterior limbic area, the cingular area, the granular and dysgranular retrosplenial areas, and the presubiculum—were identified on the basis of their cytoarchitecture. Emphasis was placed on determining the laminar distribution of the cells of origin of the efferent projections, the projection pathways, and the sites of termination within the thalamus.

Projections to the thalamus originate in layers V and VI of limbic cortex. In the cingular region the cells of origin are predominantly in layer V and to a lesser extent in layer VI, while the majority of cells projecting from the more caudal retrosplenial areas and presubiculum are in layer VI. There are two fiber pathways from each cortical area to the thalamus. One system of fibers passes through the internal capsule and lateral thalamic peduncle, and a second system travels in the cingulate fasciculus before piercing the corpus callosum to join the postcommissural fornix.

The lateral dorsal nucleus and the anterior nuclear group, including the anterior dorsal, anterior ventral, and anterior medial nuclei, are the major thalamic recipients of projections from limbic cortex. Corticothalamic projections also terminate sparsely in the midline and intralaminar nuclear complex, including the central lateral, central dorsal, paracentral, central medial, rhomboid, and reuniens nuclei. Projections from the anterior limbic area project predominantly to the anterior medial, centrall lateral, and paracentral nuclei. The anterior ventral nucleus, anterior medial nucleus, and lateral dorsal nucleus are the major thalamic recipients of projections from the cingular area, the granular and dysgranular retro‐splenial areas, and the presubiculum. It appears that the anterior dorsal nucleus receives afferents only from the dysgranular retrosplenial area. Bilateral corticothalamic projections were found in the anterior medial, dorsal medial, central lateral, central medial, paracentral, and reuniens nuclei.
Cytoarchitecture of primitive brains: Golgi studies in flatworms
Authors: Keenan C. Larry , Coss Richard , Koopowitz Harold
Published: January 2005

Notoplana acticola, a free‐living polyclad flatworm, has a small but well‐defined brain that controls behavior of peripherally based motoneurones. This is the most primitive brain currently being studied electrophysiologically, but little is known of its cytoarchitecture. Using a modified rapid Golgi method, we have investigated neurone configurations within this brain. Superficially the brain resembles those of other invertebrates, but its cells also possess many vertebrate features. There is a surprising diversity of cell types with complicated branching patterns. Multipolar neurones appear to be the most common type. A few typical invertebrate monopolar cells were also stained. Bipolar cells occur in the rind. Processes resembling dendritic spines were observed. Measurements of these indicate that they fall within the range found in other vertebrates and invertebrates. Small multipolar cells that could either be glial or interneurones were found scattered through the brain.
Reciprocity of receptive field images and point images in the superior colliculus of the cat
Authors: Capuano Umberto , McIlwain James T.
Published: January 2005

The largest receptive fields mapped during microelectrode penetrations through the upper strata of the cat's superior colliculus vary substantially in size and shape in different collicular regions. Previous work has shown that when these large fields are plotted in the retinotopic map of the colliculus, their profiles become elliptical and vary little in size and orientation over the central regions of the map. Such profiles are called the receptive field images (RFIs) in the visual coordinate system of the colliculus. Of particular interest here is the relationship of these RFIs to the region of the colliculus occupied by cells whose receptive fields include a common visual point. We call this region the point image in the colliculus. A straightforward geometric argument indicates that the point image in the upper collicular strata should have the same size, shape, and orientation as the RFIs of the large‐field cells recorded here, if, indeed, these RFIs are translationally invariant as suggested by the earlier studies.

The experiments reported here directly assessed the translational invariance of large‐field RFIs in the superior colliculi of individual cats. The results support the previous inference that the profiles are oval with their long axes oriented mediolaterally. The mediolateral and anteroposterior dimensions of the profiles were about 2.7 and 2.0 mm, respectively, wherever they were measured in the central regions of the colliculus. Since the boundaries of the point images in the superficial strata must have similar shape and dimensions, these data indicate that a visual point is “seen” by collicular cells spread through a substantial fraction of the tissue recieving the projection of the contralateral visual field.
The representation of the auditory and somatosensory systems in the external nucleus of the cat inferior colliculus
Authors: Aitkin L. M. , Kenyon C. E. , Philpott P.
Published: January 2005

Parallel single unit and retrograde tracing experiments were carried out in the anesthetized cat to elucidate the representation of the auditory and somatosensory systems in the external nucleus of the inferior colliculus (ICX).

Units responding to tonal stimuli were more commonly encountered in ICX and the adjacent intercollicular area (ICA) than were units with identified tactile receptive fields. Concomitantly, a larger number of retrogradely labeled cells were identified in midbrain auditory structures, following injections of horseradish peroxidase (HRP) into ICX, than were found in the combined dorsal column nuclei.

Microelectrode recording revealed that the entire accessible body surface was represented in ICX, and receptive fields of individual units were usually large and mostly located on the contralateral side. HRP‐labeled cells were scattered throughout the contralateral cuneate, gracile, and spinal trigeminal nuclei. tations of tone pips. Responses to complex sound were commonly observed. Binaural stimuli influenced the firing of the majority of auditory units. Labeled auditory neurons following ICX injections were found mainly in the inferior colliculus of both sides. Spread of tracer into the central and pericentral nuclei was associated with labeling of many neurons in hind brain auditory structures.

Only vague suggestions of somatotopy or tonotopy were observed in the electrophysiological experiments; similarly, no topographical relationship between HRP injection site and locus of retrograde label in a given projecting nucleus could be discerned.

Speculations were made, in the light of the dual convergent sensory representation in ICX, about the role of this structure in acoustico‐motor mechanisms.
The time of origin of neurons in the hippocampal region of the rhesus monkey
Authors: Rakic P. , Nowakowski R. S.
Published: January 2005

The time of origin of neurons in the hippocampal region was determined in a series of rhesus monkeys, each of which had been exposed to a pulse of tritiated thymidine (3H‐TdR) at a different time during ontogeny and sacrificed between the second and fifth month after birth. No heavily labeled cells were found in the hippocampal region of animals exposed to 3H‐TdR before embryonic day 33 (E33). Exposure to 3H‐TdR given at E36 labels a few neurons in the deepest layers of the entorhinal area, and 3H‐TdR given at E38 labels a small number of neurons in all hippocampal subdivisions. Although the first neurons are generated almost simultaneously throughout the hippocampal region, the proliferation ceases at a different time in each subdivision. The last neurons destined for the entorhinal area and presubiculum are generated between E70 and E75, whereas the last parasubicular neurons are generated between E75 and E80. The production of neurons that form the subiculum ends about two weeks earlier, between E56 and E65. Within the hippocampus, genesis of pyramidal cells ends between E70 and E80 in area CA1, between E56 and E65 in area CA2, between E65 and E70 in area CA3, and between E75 and E80 in area CA4. In contrast, the genesis of granule cells of the fascia dentata is considerably prolonged. It continues throughout the second half of gestation, declines steadily in the course of the first postnatal month, and tapers off during the next 2 months.

There is a distinct inside‐to‐outside spatiotemporal gradient in the parahippocampal formation and in the stratum pyramidale of both the subiculum and hippocampus. In contrast, the spatiotemporal pattern of granule cell origin in the dentate gyrus is outside‐to‐inside. Furthermore, granule cells generated between E36 and E80 are distributed in a distinct suprapyramidal‐to‐infrapyramidal gradient, whereas those generated at later ages are distributed evenly throughout the fascia dentata. Correlation of the present findings with histological data on hippocampal neurogenesis in the human brain demonstrates that the timing and sequence of developmental events as well as spatiotemporal gradients are similar in both primate species.
The site of origin and route and rate of migration of neurons to the hippocampal region of the rhesus monkey
Authors: Nowakowski R. S. , Rakic P.
Published: January 2005

The site of origin and route and rate of migration of neurons in the developing hippocampal region of the rhesus monkey were studied with tritiated thymidine (3H‐TdR) autoratiography. Analysis of specimens sacrificed approximately 1 hour after exposure to 3H‐TdR shows that the neurons destined for the hippocampus and subiculum are generated exclusively in the ventricular zone lining the medial wall of the lateral cerebral ventricle. In contrast, neurons of the parahippocampal formation are generated in two proliferative zones: The majority of neurons destined for the lamina principalis interna arise from the ventricular zone, whereas most of those destined for the lamina principalis externa originate from the subventricular zone. The neurons of the dentate gyrus are also generated in two locations: in the ventricular zone (between E38 and E85) and within the prospective hilus of the dentate gyrus (from E58 up to approximately 3 months after birth).

Analysis of specimens sacrificed at progressively longer intervals after exposure to 3H‐TdR indicates that neurons destined for all of the subdivisions of the hippocampal region (except those cells generated in the hilus of the dentate gyrus) migrate through the intermediate zone, bypassing previously generated neurons on their way to the superficial limits of the developing cortical plate. Estimated migration rates are approximately 15 μm/day in the sector of the hippocampal formation, about 100 μm/day in the parahippocampal formation, and about 115 μm/day in the region of adjacent neocortex. Thus simultaneously generated neurons destined for three distinct cytoarchitectonic areas have significantly different rates of cell migration. These differences are unrelated to the length of cell trajectories and may depend on the mechanism of cell translocation and/or the timing of signals that initiate cell movement. The differential rate of migration indicates that the fate of postmitotic cells may be determined before they have reached their final destination.
The topography of primate retina: A study of the human, bushbaby, and new‐ and old‐world monkeys
Authors: Stone Jonathan , Johnston Elizabeth
Published: January 2005

The distribution of ganglion cells has been studied in the retinas of four primates: the prosimian bushbaby, the New‐World squirrel monkey, the Old‐World crab‐eating cynamolgous monkey, and the human. The sizes of ganglion cell somas were also measured at a number of retinal locations and compared with similar measurements in the cat retina to test for the presence in primates of retinal specializations such as the visual streak, and for gradients in retinal structure, such as that between temporal and nasal retina.

In all four primates, ganglion cell somas in peripheral retina ranged considerably in diameter (6–16 μm in the bushbaby, 8–22 μm in the squirrel monkey, 8–23 μm in the cynamolgous monkey, 8–26 μm in the human). It seems likely that the strong physiological correlates of soma size which have been described among cat retinal ganglion cells and among the relay cells of the macaque lateral geniculate nucleus are generally present in primates. In all four primates, evidence was also obtained of a visual streak specialization; the isodensity lines in ganglion cell density maps were horizontally elongated, and small‐bodied ganglion cells were relatively more common in the region of the proposed streak than in other areas of peripheral retina. However, the visual streak seems less well developed than in the cat; among the four primate species examined it was best developed in the bushbaby, at least as assessed by the shape of the isodensity lines.

All four primates showed a clear foveal specialization, but this feature seemed least developed in the bushbaby. At the fovea, ganglion cells are smaller in soma size than in peripheral retina; they also seemed more uniform in size, although some distinctly larger cells persist in the human and bushbaby. Soma size measurements also provided evidence of a difference between nasal and temporal areas of peripheral retina comparable to that reported for the cat and other species.

Thus the primate retinas examined show features, such as the foveal specialization, which seem unique to them among mammals. They also show features, such as nasal‐temporal differences in ganglion cell size, and (though weakly developed) a visual streak, which they have in common with other mammals with widely different phylogenetic histories.
Collateral sprouting of insect motorneurons
Authors: Donaldson P. Lynn , Josephson Robert K.
Published: January 2005

The metathoracic extensor tibiae muscle of the cricket, Teleogryllus oceanicus, is innervated by two excitatory axons: a fast axon, which initiates large twitches to single stimuli, and a slow axon, which evokes minute twitches to single stimuli, but which, through facilitation and summation, evokes readily measurable tension to repetitive stimulation. The fast axon and the slow axon leave the metathoracic ganglia in different nerve roots, the fast axon through nerve 5 and the slow axon through nerve 3. The fast axon innervates muscle fibers in the middle of the extensor tibiae, and the slow axon innervates muscle fibers at the proximal and distal ends of the muscle. A central region of muscle fibers is innervated by only the fast axon. This region is flanked on either side by dually innervated fibers, fibers that receive both the fast and the slow axons. Fibers with only slow axon innervation are restricted to a wedge‐shaped patch in the proximal extensor tibiae and a larger region in the most distal portion of the muscle. Sectioning nerve 5 containing the fast axon, or nerve 3 containing the slow axon, partially denervates the extensor tibiae. Functional transmission by the fast axon fails 7–10 days after nerve section. The innervation field of the intact motorneuron expands in a partially denervated muscle. The linear expansion rate of the slow axon field is about 20–40 μm per day. The enlarged slow field does not regress when axons regenerate to the muscle through nerve 5. The progressive expansion of the slow innervation field suggests that the expansion is due to collateral sprouting of slow axon terminals.
Studies on the somatotopy of the trigeminal system in the mallard, Anas platyrhynchos L. III. Afferents and organization of the nucleus basalis
Authors: Dubbeldam Jacob L. , Brauch Christiane S. M. , Don Anneke
Published: January 2005

The ascending projections from the principal sensory nuclues V (PrV) have been studied by tracing degeneration after lesions in the PrV and by injections of HRP into the projection zone of PrV. The quintofrontal tract arises from PrV, ascends into the forebrain, and terminates in the ipsilateral and the contralateral nucleus basalis (NB). The contralateral fibers decussate in the the tegmentum at the level of the trochlear‐oculomotor nuclei. NB is a laminar nucleus lying over the rostral part of the paleostriatal complex. Dorsally NB is bounded by the neostratum. NB consists of small neurons. In the dorsal part of NB, these neurons are arranged in vertical columns; the afferents ascend through these columns, and clusters of degenerated boutons are found around the cells. It is possible to distinguish regions in NB receiving ophthalmic, maxillary, mandibular, or glossopharyngeal afferents. The rostral part of NB receives an exclusive ipsilateral projection; the intermediate part, a bilateral projection; and the caudal part, a contralateral projection, with the exception of the most caudal area, which also receives a bilateral projection. It is not clear whether NB should be considered a thalamic, a telencephalic, or even a pallial structure. The hypothesis that the columnar organization of the NB is a prerequisite to preserve a precise somatotopy of the tactile system of the oral region is discussed. In this respect the organization of NB can be compared to that of layer IV of the somatosensory (SI) cortex of mammals. Knowledge of the structure and functions of the peripheral tactile sense system opens the possibility of subdividing the NB into functional units.
Primary afferent axons in the tract of lissauer in the monkey
Authors: Coggeshall Richard E. , Chung Kyungsoon , Chung Jin Mo , Langford Lauren A.
Published: January 2005

The main thrust of the present study was to determine the numbers of primary afferent fibers in the tract of Lissauer in the monkey. The findings are that approximately 40% of the axons in the tract of Lissauer are primary afferent axons from a single segment, and approximately another 40% are primary afferents from segments cranial and caudal to the segment under consideration. Presumably, the remaining 20% are propriospinal axons. There is relatively little difference in the proportions of primary afferents in medial as opposed to lateral parts of the tract, and in this respect the monkey differs somewhat from the rat and cat. Thus in the monkey the tract of Lissauer should probably be regarded as a primary afferent pathway with the propriospinal fibers forming a distinct but relatively minor component of the tract.
Organization of extrinsic tectal connections in goldfish (Carassius auratus)
Authors: Grover B. G. , Sharma S. C.
Published: January 2005

Nonretinal sources of tectal afferents, the laminar and regional organization of the inputs, and the relation of the tectum with primary and secondary visual and motor centers in goldfish were studied following HRP injections in the optic tectum, orbit of the eye, cerebellum, pretectal area, and dorsolateral mesencephalic tegmentum.

Ipsilateral tectal afferents include the area dorsalis centralis of the forebrain, the nucleus dorsalis lateralis of the thalamus, the area pretectalis, the nucleus pretectalis, a nucleus in the rostral mesencephalic tegmentum, the torus longitudinales, the torus semicircularis, a dorsolateral tegmental nucleus, the nucleus isthmi, and a rostral cell group of the nucleus motorius tegmenti.

Comparison of results in a series of tectal HRP injections which differed in depth, tangential extent, and location indicated that projections from the area pretectalis, nucleus pretectalis, and nucleus isthmi terminate in the stratum fibrosum et griseum superficiale of the tectum. Terminals of the forebrain and nucleus dorsolateralis and contralateral tectum are sparse and widely branching. Projections from the area and nucleus pretectalis tend to terminate in the rostral tectum, and those from the contralateral tectum, torus semicircularis, dorsolateral tegmental nucleus, and nucleus motorius tegmenti terminate preferentially in the caudal tectum.

Cells of origin of extrinsic tectal efferents were also identified following HRP injections in the pretectal area and mesencephalic tegmentum. Proximal dendrites and axons of these cells were labeled sufficiently to allow comparison with morphological types characterized in Golgi studies.

HRP injections in the cerebellum labeled cells bodies in the area pretectalis, nucleus pretectalis, and the nucleus of the posterior commissure. Double label experiments with intraocular injection of tritiated proline demonstrated direct retinal input to these three areas. No indications of direct connections between the tectum and cerebellum were found following tectal or cerebellar HRP injections.
The aberrant retino‐retinal projection during optic nerve regeneration in the frog. I. Time course of formation and cells of origin
Authors: Bohn Ronald C. , Stelzner Dennis J.
Published: January 2005

We have reported previously that during optic nerve regeneration in Rana pipiens, axons are misrouted into the opposite nerve and retina. In the present investigation we have examined the time course of formation of these “misrouted” axons and their cells of origin. The right eye of 31 frogs was injected with 3H‐proline at various times after right optic nerve crush. In every frog examined 2 weeks and later after nerve crush, the distribution of autoradiographic label indicated that axons from the right eye had grown into the left optic nerve at the chiasm. The amount of label increased from 2 weeks to reach a maximum at 6 weeks where the entire left nerve was filled with silver grains. At 5 to 6 weeks after crush, laboled axons were found within the ganglion cell fiber layer (GCFL) of the retina of the opposite eye for a maximum distance of 2.3 mm from the optic disc. In frogs examined at intervals later than 6 weeks after crush, the amount of label within the left eye and nerve progressively decreased, indicating a gradual disappearance of the misrouted axons. Studies using anterograde transport of horseradish peroxidase (HRP) after nerve injection confirmed these autoradiographic findings. The position of ganglion cells in the right eye whose axons were misrouted to the left eye was determined by retrograde transport of HRP. Five or 6 weeks after crushing the right optic nerve, the left eye was injected with HRP and labled ganglion cells were found throughout the right eye retina. The largest percentage of labeled cells was found within the ventral half of the retina, particularly within the temporal quadrant, and nearly all of the labeled cells were found in more peripheral portions of the retina. Since few retino‐retinal axons are found during normal development, the present results show that the factors guiding regenerating axons in the adult frog differ substantially from those present during development.
Central projections of the lateral line and eighth nerves in the bowfin, Amia calva
Authors: McCormick Catherine A.
Published: January 2005

The first‐order connections of the anterior and posterior lateral line nerves and of the eighth nerve were determined in the bowfin, Amia calva, using experimental degeneration and anterograde HRP transport techniques. The termination sites of these nerves define a dorsal lateralis cell column and a ventral octavus cell column.

The anterior and posterior lateralis nerves distribute ipsilaterally to two medullary nuclei—nucleus medialis and nucleus caudalis. Nucleus medialis comprises the rostral two‐thirds of the lateralis column and contains large, Purkinje‐like cells dorsally and polygonal, granule, and fusiform cells ventrally. Nucleus caudalis is located posterior to nucleus medialis and consists of small, granule cells. Anterior lateralis fibers terminate ventrally to ventromedially in both nucleus medialis and nucleus caudalis. Posterior lateralis fibers terminate dorsally to dorsolaterally within these two nuclei. A sparse anterior lateralis input may also be present on the dendrites of one of the nuclei within the octavus cell column, nucleus magnocellularis. In contrast, the anterior and posterior rami of the eighth nerve each terminate within four medullary nuclei which comprise the octavus cell column: the anterior, magnocellular, descending, and posterior octavus nuclei. An eighth nerve projection to the medial reticular formation is also present.

Some fibers of the lateralis and eighth nerves terminate within the ipsilateral eminentia granularis of the cerebellum. Lateralis fibers distribute to approximately the lateral half of this structure with posterior lateral line fibers terminating laterally and anterior lateral line fibers terminating medially. Eighth nerve fibers distribute to the medial half of the eminentia granularis.
Morphology of the cochlear nucleus of the normal and reeler mutant mouse
Authors: Martin Michael R.
Published: January 2005

The morphology of the cochlear nuclei of normal and reeler mutant mice were studied in Nissl‐stained sections. The cochlear nucleus in both mice is divisible into three parts: the anteroventral, posteroventral, and dorsal nuclei. Nine cell types can be recognized in the normal mouse. In the anteroventral nucleus spherical cells occupy the rostral pole. Globular cells are located caudally and extend to the interstitial region of the anteroventral nucleus. In the posteroventral nucleus multipolar cells are located rostrally and dark‐staining cells occupy the caudal pole. Multipolar cells are also present in the anteroventral nucleus and in the deep region and molecular layer of the dorsal cochlear nucleus. The dorsal and lateral aspects of the ventral nuclei are covered by a granule cell layer. The dorsal nucleus consists of superficial molecular and pyramidal layers and a deep region. The deep region contains small and giant cells as well as multipolar cells. The pyramidal layer is made up of pyramidal cells, horizontal cells, and granule cells. Small cells are also present in the molecular layer and throughout the ventral nuclei.

The dorsal cochlear nucleus of the reeler mutant mouse is disorganized and the molecular layer is reduced in thickness. The organization of the pyramidal layer is disrupted with granule cells superficial to pyramidal and horizontal cells. Cells which appear to be homologous to pyramidal cells are also present in the deep region of the dorsal nucleus. The total number of granule cells is reduced by an average of 42% over the whole nucleus and the reduction in granule cells is greatest in the granule cell cap covering the dorsal and lateral surface of the ventral cochlear nuclei. The cytoarchitecture of the ventral cochlear nucleus appears normal.
The organization of indoleamine neurons in the brain of the rhesus monkey (Macaca mulatta)
Authors: Schofield Susan P. M. , Everitt Barry J.
Published: January 2005

The organization of indoleamine‐containing neurons throughout the CNS of Macaca mulatta was examined with Falck‐Hillarp histofluorescnce and radioenzymatic biochemical techniques. Indoleamine‐containing cell bodies, corresponding to the serotonin‐containing groups B1 to B9, were observed within the brain stem. The pontine cell populations, however, were far more numerous than in the rat and represented caudal subpopulations of cells within the nucleus raphe dorsalis (B7) and nucleus centralis superior (B8). Additionally, the pontine indoleamine‐containing cells in M. mulatta extended laterally through the tegmentum such that they were often adjacent to catecholamine‐containing neurons of the locus coeruleus complex. Ascending indolaemine‐containing fiber bundles, similar to those defined in nonprimate mammals, were also observed within the pons and mesencephalon.

Regional differences in the distribution of serotonin within hypothalamic nuclei and other forebrain regions of M. mulatta were revealed through a highly sensitive radioenzymatic assay in conjunction with microdissection. Significant concentrations of serotonin were evident in most areas, although the levels of this neurotransmitter were much lower in the median eminence region and nucleus suprachiasmaticus than in the rat. These differences may reflect variations in the control of neuroendocrine events in the two species.
Homotopic and heterotopic callosal afferents of caudal inferior parietal lobule in Macaca mulatta
Authors: Hedreen John C. , Yin Tom C. T.
Published: January 2005

We have examined callosal‐axon neurons giving rise to homotopic and heterotopic callosal projections to caudal inferior parietal lobule (area PG) in Macaca mulatta, identifying these neurons by means of retrograde axonal transport of horseradish peroxidase. The labeled neurons in the homotopic region occur predominantly in layers IIIB and V. A moderate number are seen also in layer VI, a smaller number in layer IV, and rare cells occur in layer II. These neurons occupy a region very similar in outline to the injection area, and though variable in density in the horizontal plane are continuously distributed in this plane.

The heterotopic neurons are seen in the contralateral cingulate gyrus, continuing caudally into medial parietal cortex, in the cortex of the superior temporal and occipitotemporal sulci, in the caudal superior temporal gyrus, and in the caudal inferior parietal lobule, behind the homotopic area. These same regions on the ipsilateral side contain labeled neurons of origin of ipsilateral association projections to area PG. For other ipsilateral association regions (e.g., frontal lobe), no corresponding contralateral heterotopic labeling was found. A review of the literature on heterotopic callosal connections allows tentative generalization of this conclusion: The callosal heterotopic connections of a particular cortical area are made with regions which on the ipsilateral side have association connections with that area, though usually not with all of such regions.