bluuebunny/crossref_metadata_2025 huggingface dataset:
A Golgi and ultrastructural analysis of the centromedian nucleus of the cat
Authors: Tseng Guo‐Fang , Royce G. James
Published: January 2005

The morphology of neurons in the centromedian nucleus (CM) was studied in rapid Golgi preparations of the adult cat. The ultrastructure of the nucleus, particularly its synaptic organization, was also studied with electron microscopy.

The CM contains three types of neurons referred to as principal neurons, Golgi type II neurons, and bushy neurons. Principal neurons are the most numerous, have long dendrites, which branch infrequently, and are divided into two subgroups: principal‐A neurons with dendrites that arborize radially, whereas principal‐B neurons display horizontal orientations. Both subgroups show a frontal orientation in their dendritic organization and give rise to myelinated axons. Golgi type II neurons with their characteristic sinuous dendrites and unmyelinated axons are thought to be interneurons. The occurrence of bushy neurons in the cat's CM is a new finding. These bushy neurons resemble those of thalamic specific relay nuclei and give rise to myelinated axons. In addition to these three cell types, neurons with intermediate features between these three neuronal types are also described.

The ultrastructure of CM neurons resembles, in general, typical central nervous system neurons. Presynaptic profiles are classified into four main categories. SR (small round) boutons are small in size, contain clear, round vesicles, and form asymmetrical synaptic contacts with predominantly small‐diameter dendrites. LR (large round) boutons are relatively large and contain both clear and dense‐cored vesicles. They interdigitate and form multiple, moderately asymmetrical synapses with their postsynaptic targets. Pale profiles are identified by their relatively electron‐light appearance. They contain round vesicles and are thought to be dendritic in origin. The last category of presynaptic profiles is pleomorphic boutons. They contain vesicles of different shapes and are further subdivided into two subtypes: pleomorphic‐I ends on soma and dendritic trunks, whereas pleomorphic‐II contacts small‐diameter dendrites. Both subtypes form symmetrical synapses.

The glomeruli of specific thalamic relay nuclei generally contain dendrites, LR boutons, and pale profiles. In addition to these, pleomorphic‐II boutons also participate in the formation of the glomerulus of the cat's CM.
Intracerebral transplants of the rat fascia dentata: A Golgi/electron microscope study of dentate granule cells
Authors: Frotscher Michael , Zimmer Jens
Published: January 2005

In the present study we describe the morphological characteristics of dentate granule cells in intracerebral allografts of the rat fascia dentata. Blocks of hippocampal tissue containing the fascia dentata were taken from late embryonic and newborn rats and transplanted to the hippocampal region of other newborn and young adult rats. After survival periods of several months the recipient brains were fixed by perfusion and serially sectioned on a Vibratome. Some sections were stained with thionin to determine the localization and general histological organization of the transplants, while others were Golgi stained with a modification of the section Golgi technique. Well‐impregnated transplant granule cells were gold‐toned and deimpregnated thus allowing a correlated, light and electron microscopic analysis of identified neurons to be done.

At the light microscopic level the morphology of the dentate granule cells in the transplants was very similar to Golgi‐impregnated, gold‐toned granule cells in the fascia dentata of normal rats (controls). A few irregular, more obliquely curved dendrites occurred, but basal dendrites passing into the hilar region were never observed. Following an initial spine‐free segment granule cell dendrites were densely covered with spines. The axon, the mossy fiber, originated as usual from the basal pole of the cell body.

In the electron microscope, both small and larger complex spines (v and w types) were seen to emerge from the gold‐toned dendrites of the identified granule cells. The thin unmyelinated granule cell axons gave rise to giant mossy fiber boutons in the dentate hilus, but in addition numerous aberrant mossy fiber terminals were found innermost in the dentate molecular layer just above the granule cell layer.

The results demonstrate that dentate granule cells that have gone through the major part of their differentiation‐after transplantation develop characteristic dendritic and axonal elements very similar to those of granule cells in the fascia dentata in situ. The minor changes observed correspond to the redistribution of intrinsic connections that results from the absence of major extrinsic afferents.
Tectal neurons of the frog: Intracellular recording and labeling with cobalt electrodes
Authors: Antal M. , Matsumoto N. , Székely G.
Published: January 2005

With the aid of cobalt‐filled intracellular electrodes, responses evoked by electrical and visual stimulation were recorded from tectal neurons. Diffuse light and “edge” and “spot” stimuli were used for visual stimulation; electrical stimuli were delivered by means of bipolar electrodes to the optic tract. The cells were subsequently filled with cobalt for a correlative histological study. The following types of neurons were distinguished: (1) Pear‐shaped neurons with restricted and broad dendritic fields occurring in tectal layers 8, 6, 4, and 2. In one group, the dendrites bore beads and small protrusions and the short axon arborized within, or close to, the dendritic arbor. They responded mostly with inhibitory postsynaptic potentials to the various stimulations. This type of neuron was interpreted to be a tectal interneuron. In the second group the dendrites were smooth, the dendritic arbor was large, and the axon could be followed to layer 7 in a few cases. Excitatory activities with frequent spike discharges prevailed in their responses. They were regarded as efferent neurons of the tectum. (2) Large ganglionic neurons showed a greater variation in form than has been described in previous Golgi studies. Their responses to the different stimulations were also very variable. The axons of five neurons could be followed to the dorsal part of the thalamus, to the postoptic commissural system, and to the direct and crossed tectobulbar tract. These axons emitted several collaterals to tectal, pretectal, and tegmental structures. (3) A single stellate neuron was impaled in layer 9. It responded only to electrical stimulation with excitation. (4) Deep bipolar neurons were not mentioned in earlier works. Their somata were found in layer 6; the vertically oriented dendrites arborized in plexiform layers 7, 5, and 3, over a distance of more than 1 mm. These cells were sensitive only to electrical stimulation.
Studies on the evolution of multiple somatosensory representations in primates: The organization of anterior parietal cortex in the new world callitrichid, Saguinus
Authors: Carlson Mary , Huerta M. F. , Cusick C. G. , Kaas J. H.
Published: January 2005

Because members of the New World family, Callitrichidae, are generally regarded as the most primitive of monkeys, we studied the organization of somatosensory cortex in the tamarin (Saguinus) in hopes of better understanding differences in the organization of anterior parietal cortex in primates and how these differences relate to phylogeny. In most prosimian primates only one complete representation of cutaneous receptors has been found in the region of primary cortex, S‐I, while in all Old and New World monkeys studied to date, two cutaneous representations exist in distinct architectonic fields, areas 3b and 1. In detailed microelectrode mapping studies in anesthetized tamarins, only one complete representation responsive to low‐threshold cutaneous stimulation was evident in the S‐I region. This topographic representation was in a parietal koniocortical field that architectonically resembles area 3b of other monkeys, and the general somatotopic organization of the field was similar to that of area 3b of other monkeys. Cortex rostral to the single representation was generally unresponsive to somatosensory stimuli, or required more intense stimulation for neural activation. Cortex caudal to the representation, in the region of area 1 of other monkeys, was generally either unresponsive or responded to only high‐threshold stimulation, although some recording sites were activated by low‐threshold tactile stimulation.

The present evidence, together with that from previous studies, suggests that the single, complete body surface representation in Saguinus is homologous to the S‐I representation found in some prosimians (Galago, Perodicticus) and the area 3b cutaneous representation found in New World Cebidae (Aotus, Saimiri, and Cebus) and Old World Macaca. Cortex rostral to S‐I in Saguinus has the appearance of areas 3a and 4 of other primates. The cortex caudal to S‐I in Saguinus, while resembling area 1 in some ways, does not have all of the features of area 1 of other monkeys. In particular, the field was not easily activated by low‐threshold cutaneous stimuli, as area 1 is in other monkeys, and therefore a second cutaneous representation of all body parts was not demonstrated. Thus, cortex in the expected location of area 1 of Saguinus was not as responsive as area 1 of other monkeys, and it somewhat resembled the high‐threshold fringe zones found caudal to S‐I in anesthetized prosimians and some nonprimates. The results raise the possibility that the area 1 cutaneous representation that is characteristic of other New World monkeys and Old World monkeys evolved from a less responsive precursor along the caudal border of S‐I in early monkeys.
Organization of spinal inputs to the perihypoglossal complex in the cat
Authors: Stechison Michael T. , Saint‐Cyr Jean A.
Published: January 2005

First‐ and second‐order spinal afferents to the perihypoglossal complex were sought by using axonal transport of WGA‐HRP. Injections in C1, 2, and 3 dorsal root ganglia resulted in axonal labeling in the nucleus intercalatus and the external cuneate nucleus, with a number of retrogradely labeled cells seen as well in the latter. A similar pattern of axonal labeling in the nucleus intercalatus as well as several retrogradely labeled cells were found after spinal cord injections at levels C1, 2, and 3. A prominent field of labeled axons was also present in the rostral main cuneate nucleus. No labeling was seen in the perihypoglossal nuclei after injections in the spinal cord or dorsal root ganglia at levels caudal to C3. After injections of HRP into the perihypoglossal nucleus we were able to identify labeled neurons within Rexed, s laminae V‐VIII and the central cervical nucleus. Anterograde labeling in the main cuneate nucleus was observed after C1 to C5 ganglion and C1 to C6 cord injections. The pattern and extent of labeling in the perihypoglossal nuclei and adjacent structures seen after cerebellar injections into lobules V and VI were comparable to those previously reported and permitted evaluation of the relay from dorsal root ganglia through the intercalatus to the vermis.

Topography of the cervical projections to the nucleus intercalatus is considered with respect to that of the perihypoglossal‐collicular projection. A discussion is offered of the apparent importance of nucleus intercalatus as a relay of cervical and vestibular afferent information to premotor structures involved in neck motor control. The perihypoglossal complex is viewed as being organized in such a fashion as to allow the nuclei intercalatus and prepositus hypoglossi to function as key structures in the integration of inputs related to neck and ocular motor control, respectively.
The synaptic ultrastructure in the outer plexiform layer of the catfish retina: A three‐dimensional study with hvem and conventional em of golgi‐impregnated bipolar and horizontal cells
Authors: Hidaka Soh , Christensen Burgess N. , Naka Ken‐Ichi
Published: January 2005

Synaptic structures between receptors and horizontal and bipolar cells in the outer plexiform layer (OPL) of Golgi‐impregnated catfish retina were examined by conventional electron microscopy of serial ultrathin sections and by high‐voltage electron microscopy (HVEM) off thick sections. Cone terminals contained multiple synaptic ribbons and rod terminals contained single synaptic ribbons. This observation was used to identify these two types of photoreceptors. The cone horizontal cell, located in the most distal part of the inner nuclear layer (INL), invaginated only cone terminals, whereas the rod horizontal cell, located in the proximal part of the INL, invaginated only rod terminals. Both lateral elements of the triad in the rod terminal originated from a single rod horizontal cell whereas the same structures in the cone terminal were often derived from several cone horizontal cells. Golgi‐impregnated catfish bipolar cells were classified into two types based on the differences in their axonal arborization as described by Famiglietti et al. ('77). Axonal endings of type a bipolar cells were located in the distal part, sublamina a, of the inner plexiform layer (IPL), and axonal endings of type b cells were located in the proximal part, sublamina b, of the IPL. Dendrites from type a bipolar cells made direct contact with the synaptic ribbons in both rod and cone terminals whereas those from type b cells made indirect contact with the ribbons in both rod and cone terminals, but rare direct contact with the ribbon in rod terminals were also seen. In addition, bipolar cells made basal junctions or superficial contact in both rod and cone terminals. The “lateral” processes of bipolar cells invaginating rods penetrated between the rod terminal and rod horizontal cell processes, and made basal junctions with both rod terminals and rod horizontal cells. There was no definitive morphological feature that could be associated with signconserving and sign‐inverting signal transmission.
Identification of medial preoptic neurons that concentrate estradiol and project to the midbrain in the rat
Authors: Fahrbach Susan E. , Morrell Joan I. , Pfaff Donald W.
Published: January 2005

Fluorescent dye retrograde tracing was combined with steroid hormone autoradiography to study the midbrain projections of the estrogen‐concentrating neurons in the preoptic region of the rat brain. Microinjections of the dyes DAPI, true blue, or a mixture of DAPI and primuline were made into the ventral tegmental area and into the midbrain central gray of ovariectomized, adrenalectomized 2‐3‐month‐old female rats; 3 or 4 days later these animals were injected with [3H]estradiol; the brains were then processed for autoradiography. After exposures of from 3 to 12 months, the autoradiograms were developed and examined for reduced silver grains under cell nuclei (indicating binding of [3H]estradiol) and retrogradely transported fluorescent dye in the cytoplasm (indicating an efferent projection to the midbrain).

Numerous [3H]estradiol‐concentrating neurons in the medial preoptic region were found to send their axons to the medial midbrain. The largest numbers of estrogen target neurons that were afferent to the ventral tegmental area and to the midbrain central gray were found in the medial preoptic nucleus, in the surrounding medial preoptic area, and in the ventral bed nucleus of the stria terminalis. Double‐labeled neurons were also identified in the preoptic suprachiasmatic area, in the lateral preoptic area, and in the rostral anterior hypothalamic area. Thus, a subset of the gonadal steroid target cells of the preoptic region have long projections to the medial midbrain, and a subset of the medial preoptic neurons that project to the ventral tegmental area and to the midbrain central gray concentrate estrogen. Behaviors (for example, maternal behavior, male copulatory behavior, and wheel‐running) that are regulated by estrogen action in the medial preoptic region may be controlled by the direct estrogen‐sensitive pathway to the medial midbrain revealed in this study.
Cell surface changes in the developing optic nerve of mice
Authors: Lund R. D. , Perry V. H. , Lagenaur C. F.
Published: January 2005

A recently defined antibody to a cell surface protein, M6, inhibits neurite outgrowth in culture (Lagenaur, Fushiki, and Schachner: Soc Neurosci. Abstr. 10:739, '84). In the developing mouse, the antibody stains all parts of the primary optic pathway at birth. Over the next week, staining is lost from the proximal segment of the optic nerve and a week later from the more central part of the nerve. By contrast staining persists through adulthood in the optic fiber layer of the retina. This means that single axons in the mature optic nerve express the antigen over only the proximal few millimeters of their course and over their terminal region.

The results are discussed in relation to the overall maturation of the optic pathway and to the processes of membrane maturation and myelination.
Development of the crossed retinocollicular projection in the mouse
Authors: Edwards M. A. , Schneider G. E. , Caviness V. S.
Published: January 2005

Changes in the distribution of axons of the crossed retinal projection within the superior colliculus of the developing mouse were studied by means of normal fiber and Golgi impregnations and by anterograde horseradish peroxidase labelling. Retinal axons advance along the optic tract from gestational days E12 to E14 and first invade the superior colliculus on E15. Over the subsequent days until birth (E19), the retinal axons extend within rostrocaudally oriented fascicles that distribute through the full thickness of the uppermost collicular layer, the stratum superficiale (SS). A dramatic transformation of this fiber stratification pattern into the mature pattern occurs over the first postnatal week. The fiber bundles are progressively cleared from the upper half of SS, identified as the future stratum griseum superficiale (SGS). Concurrently, the fiber bundles in the deep SS, identified as the stratum opticum (SO), give rise to individual, nonfasciculated fibers, which arborize within SGS. The contralateral retinal origin of the transient population of axons in SGS as well as the majority of axons that persist in SO is evident from the observation that they degenerate following neonatal enucleation. The number of fiber bundles lost is estimated to be 40–50% of the total population present in the superficial layers at birth. The combined set of observations indicates that axon elimination plays a major role in shaping the laminar pattern of retinal innervation of the colliculus. Retinal ganglion cell death, and not axon pruning, is proposed as the most probable mechanism by which axon fascicles are eliminated from SGS.
Central afferent connections and origin of efferent projections of the facial nerve in the chicken (Gallus gallus domesticus)
Authors: Ganchrow Donald , Ganchrow Judith R. , Gentle Michael J.
Published: January 2005

The central afferent connections and origin of efferent projections of the facial nerve in the adult domestic chicken were studied by anterograde and retrograde transport of horseradish peroxidase from the geniculate ganglion. Ipsilateral afferent projections were traced caudal to the level of entrance of the facial nerve and into tractus solitarius (TS), located dorsomedial to the spinal trigeminal nuclear complex. At several rostrocaudal levels in the medulla, fibers exited from TS and terminated in n. sensorius N. facialis (SVII), and nn. ventrolateralis anterior (Vla) and intermedius anterior (Ia) solitarii. Some axons were followed to n. presulcalis anterior (Pas) solitarii. A separate component terminated in subnucleus interpolaris (ip) of n. descendens nervi trigemini or its medially adjacent reticular formation either by exiting from TS or coursing caudally through the trigeminal complex from entering facial rootlets. Another diffuse component of facial axons ascended dorsally and rostrally from the level of entrance of the facial nerve; these projections dissipated in the pons–some on the dorsomedial border of n. principalis N. trigemini (PrV).

Ipsilateral efferent projections were traced through the main genu of the facial nerve to retrogradely labelled somata of pars dorsalis (FMd), pars intermedia (FMi), and pars ventralis (FMv) of n. motorius nervi facialis. A separate group of smaller, multipolar, and spindle‐shaped cells (8–25 μm) wedged between n. olivarius superioris (OS) and the caudal end of FMv, rostrally, and extending caudally in ventrolateral medulla were labelled. These small cells contrast with the larger (21–45 μm), oval, round, and multipolar somata of FMv and may correspond, in part, to a parasympathetic n. salivatorius (Sal).
Dorsal funicular projections to the dorsal column nucleus in a reptile, Caiman crocodilus
Authors: Pritz Michael B. , Stritzel Mark E.
Published: January 2005

Projections to the dorsal column nucleus were investigated in the reptile Caiman crocodilus following application of horseradish peroxidase (HRP) crystals to the cervical spinal cord after dorsal myelotomy. Brains were processed for HRP histochemistry by use of tetramethylbenzidine as the chromogen. Injection of the dorsal funiculus alone labelled axons that terminated solely in the ipsilateral dorsal column nucleus. Application of HRP that extended beyond the dorsal funiculus labelled axons that terminated in brainstem areas in addition to the dorsal column nucleus depending upon the injection site. Retrogradely labelled neurons in the brainstem were seen only after HRP injections that extended beyond the dorsal funiculus and varied depending upon the injection site.

Dorsal funiculus fibers travel rostrally and turn laterally to reach more anterior portions of the dorsal column nucleus. Fibers peel off in an oblique ventrolateral fashion to terminate in the posterior part of the nucleus where boutons are intermixed with fibers. The anterior portion of the nucleus contains a greater proportion of axon terminals as compared to fibers than does the posterior part. A graphic reconstruction of the dorsal column nucleus was made by superimposing serial sections to view the nucleus in transverse, sagittal, and horizontal planes.
Isolated satellite cells of a peripheral nerve direct the growth of regenerating frog axons
Authors: Kuffler Damien P.
Published: January 2005

Frog motor axons regenerate and grow back to reinnervate their targets, the original motor end plates, after a lesion. When the cutaneous pectoris muscle is cut away and a segment of peripheral nerve is placed in the vicinity of regenerating axons they turn and grow toward it. This is in marked contrast to the random pattern of axonal outgrowth seen in the absence of a target. The influence on the direction of axonal growth of motor neurons can be produced by a 1‐mm segment of nerve satellite cells over a distance of more than 8 mm.

The nerve satellite cells have no influence on the direction of growth of the regenerating axons after all the cells in the nerve segment have been killed, leaving only the Schwann cell basal lamina tubes intact. These results show that the cells in the segment of the nerve trunk contain cues that actively direct the growth of motor neurons. Two possible explanations for this effect might be (1) that the cells act indirectly by influencing the organization of the substructure over which axons regenerate or (2) that the nerve satellite cells release a diffusible substance that acts directly on the regenerating axons.
Ultrastructural characterization of identified cholinergic neurons transplanted to the hippocampal formation of the rat
Authors: Anderson Kevin J. , Gibbs Robert B. , Salvaterra Paul M. , Cotman Carl W.
Published: January 2005

The ultrastructural features of cholinergic neurons transplanted to the rat hippocampal formation were studied by using a monoclonal antibody to choline acetyltransferase (ChAT). Septal cell suspensions were prepared from E‐18 rat embryos and injected into the hippocampus of host rats that had been previously subjected to a bilateral transection of the fimbria‐fornix. Rats with fimbria‐fornix lesions alone and unoperated rats served as controls and were examined to characterize the native hippocampal cholinergic system.

Both unoperated controls and rats with fimbria‐fornix lesions showed a sparse population of intrinsic ChAT‐immunoreactive neurons that were most numerous in the subgranular zone, the hilus fascia dentata, and near the hippocampal fissure. ChAT‐positive terminals from controls formed synapses on dendritic structures that were primarily symmetrical. ChAT‐positive dendrites in controls received synaptic input from nonimmunoreactive axon terminals.

In rats with septal transplants, ChAT‐immunoreactive transplant neurons were found that were either bipolar or multipolar. Axons of transplanted neurons were unmyelinated and arose either from the cell body or a primary dendritic process where they gave off numerous collaterals. Terminals from transplant neurons formed synapses with many nonimmunoreactive neurons. In transplant animals, two main targets of ChAT‐immunoreactive terminals were identified: (1) The great majority of synapses were symmetrical junctions with dendritic spines and shafts. (2) A number of terminals were found that appeared to be juxtaposed to nonimmunoreactive axon terminals, possibly forming symmetrical axo‐axonic connections. In contrast, such axo‐axonic contacts were not observed in the controls.

It is concluded that transplanted cholinergic neurons may reinnervate the host hippocampus; however, this reinnervation is different from what is seen in the intact hippocampal formation.
Immunocytochemical studies on astroglia of the cat retina under normal and pathological conditions
Authors: Karschin Andreas , Wässle Heinz , Schnitzer Jutta
Published: January 2005

The cell density and morphology of astrocytes in whole‐mounted adult cat retinae have been studied by immunocytochemical localization of glial fibrillary acidic protein (GFAP). There was a peak density at the optic nerve head of about 2,000 astrocytes/mm2 dropping to approximately 200 astrocytes/mm2 in the far periphery. In the central area there was a local minimum of astrocyte density. Whereas the processes of astroglia in the outermost retinal periphery were radially arranged, thus giving the cells a characteristic star‐shaped appearance, the majority of astroglial processes in the central region of the retina were aligned in parallel with the ganglion cell axon bundles. To study the correlation between optic nerve fibres and astrocytes, ganglion cell axons were caused to degenerate following photocoagulation lesions close to the optic disc. Postlesion the processes of astrocytes in the central retina lost their directional preference and linearity, thus appearing to develop a star‐shaped morphology typical of astroglia in the far periphery of normal retinae. The density of astrocytes decreased by approximately 50% on the optic disc side of the lesions and by up to 80% on the peripheral side of the lesions. The results show that the morphology and number of astrocytes vary as a function of their proximity to optic nerve fibres and to the density of these fibres.
A second ascending visual pathway from the optic tectum to the telencephalon in the pigeon (Columba livia)
Authors: Gamlin Paul D. R. , Cohen David H.
Published: January 2005

Previous studies in the pigeon (Karten and Revzin: Brain Res. 2:368–377, '66; Karten and Hodos: J. Comp. Neurol. 140:35–52,'70) have described an ascending tectofugal visual pathway from the optic tectum to the ectostriatum by way of the nucleus rotundus of the thalamus. This present study used anterograde autoradiographic and retrograde horseradish peroxidase pathway‐tracing techniques to investigate another ascending tectofugal pathway in the pigeon. Injections of 3H‐proline/leucine confirmed a previous report that the optic tectum projects to the nucleus dorsolateralis posterior of the thalamus (DLP). This projection is predominantly ipsilateral and is confined to a large‐celled caudal region of the nucleus (DLPc); the rostral region of the nucleus (DLPr) is not tectorecipient. Injections of horseradish peroxidase in DLPc labeled cells predominantly ipsilaterally in layers 8–15 of the optic tectum. Injections of 3H‐proline/leucine placed in the DLPc labeled a discrete region of the ipsilateral telencephalon. Similar injections of DLPr labeled a contiguous, but more rostral, region of the neostriatum intermedium. Nissl‐ and silver‐stained material indicated that the region in which DLP terminates is cytoarchitecturally distinct from ventromedial ectostriatal core and belt. Injections of horseradish peroxidase at various locations in the neostriatal DLP terminal field demonstrated a rostrocaudal ordering of the DLP projection upon the neostriatum intermedium. Singleunit recording demonstrated that cells in DLPc respond to whole‐field illumination at the same latency as cells in the nucleus rotundus, indicating that the tecto‐DLPc‐neostriatal pathway transmits visual information to the telencephalon. We suggest that comparable pathways may exist in both reptiles and mammals.
Histochemical and architectonic differentiation of zones of pretectal and collicular inputs to the pulvinar and dorsal lateral geniculate nuclei in the macaque
Authors: Lysakowski Anna , Standage Gregg P. , Benevento Louis A.
Published: January 2005

The pattern of acetylcholinesterase (AChE) reactivity was studied in the pulvinar and dorsal lateral geniculate nucleus (DLG) of the adult macaque monkey. Discrete islands of AChE reactivity were found that correlated precisely in location with the pattern of projections from the superior colliculus and pretectum. Specifically, AChE overlies terminal fields of superior colliculus projections in the DLG, in four foci in the medial and lateral pulvinar, and in several foci in the inferior pulvinar. All of these tectal projection areas have very high AChE reactivity such that they are easily distinguished. In addition, the pretectum projects to a specific focus in the lateral pulvinar that also has a very dense AChE histochemical reaction. A number of these AChE foci could be further distinguished from other areas in the pulvinar by myeloarchitectonic characteristics. Some of the foci in the lateral and inferior pulvinars could also be distinguished by unique cytoarchitectonic features (as seen with both Nissl and Golgi stains). In an attempt to determine the possible origin of a cholinergic input to the pulvinar, horseradish peroxidase (HRP) injections and choline acetyltransferase immunohistochemistry were also done. The results of this experiment indicate that the AChE reactivity seen in the midbrain projection zones to the thalamus may be due to the precise overlap of terminal projections from the brainstem cholinergic cell groups, Ch5, Ch6, and Ch8. These results, taken together, imply that there are several anatomically and histochemically distinct zones related to extre ageniculate pathways located within classically defined thalamic boundaries.
Organization of immature intrahemispheric connections
Authors: Clarke Stephanie , Innocenti Giorgio M.
Published: January 2005

In the adult cat injections of retrograde fluorescent tracers near the border between areas 17 and 18 and extending to the underlying white matter label neurons in restricted parts of nine other ipsilateral visual areas. A very similar, restricted distribution of retrograde labeling is found in newborn kittens when injections near the 17/18 border are confined to the cortical gray matter. When, however, the neonatal 17/18 border injection reaches the underlying white matter, more visual areas and numerous nonvisual areas become labeled, each of them over nearly its whole tangential extent. Labeled nonvisual areas include the primary and secondary auditory areas, the auditory areas of the posterior ectosylvian gyrus, areas 7 and 5, the cingulate gyrus, and the primary and secondary somatosensory areas. The widespread labeling in kittens was not due to larger or differently placed injections, since the distribution and extent of retrograde labeling in the ipsilateral lateral geniculate nucleus were similar at all ages. The transitory projections from the auditory and somatosensory areas are not reciprocated by a projection from areas 17 or 18.

In kittens injected around the end of the first postnatal month the distribution of labeled association neurons is similar to that found in the adult; i.e., many of the juvenile projections have been eliminated.

Only a few of the transitory axons to areas 17 and 18 enter the gray matter; the others remain confined to the white matter. Some of these axons were anterogradely labeled with rhodamine‐B‐iso‐thiocyanate from the auditory cortex; they show bulbous endings, some of which are probably growth cones.

Retrograde double‐labeling experiments showed that, in the newborn, some neurons on the lateral sulcus have at least two long collaterals, one running rostrally, the other caudally; such branching is not observed in adults.

In conclusion, areas 17/18 receive at birth from a large, continuous territory including areas, or parts of areas, which will later eliminate these projections. Most of the transitory projections do not appear to enter the cortex to any great extent. The major reshaping of association projections occurs before end of the first postnatal month. The development of association projections resembles that of callosal projections.
Segmental homologies among reticulospinal neurons in the hindbrain of the zebrafish larva
Authors: Metcalfe Walter K. , Mendelson Bruce , Kimmel Charles B.
Published: January 2005

We have examined the morphology of identified reticulospinal neurons in larval zebrafish by retrogradely labeling them with horseradish peroxidase. We describe the morphology of 27 different types of reticulospinal neurons found in the hindbrain 5 days after fertilization. Nineteen of these types are present as single identified neurons on each side of the brain; the other are present as pairs or small groups of cells.

The hindbrain reticulospinal neurons are present in seven bilateral clusters that are spaced periodically along the neuraxis. Each cluster contains two to five different types of reticulospinal neurons. Cells with similar morphological features are found in adjacent clusters. By considering cell position within the cluster and axon pathway, nearly all of the cells can be assigned to one of about seven serially repeated classes. Independent morphological features of the cells support the same classification.

We propose that the clusters represent hindbrain segments and that the neurons of the same class that are present in the different clusters are segmental homologues. Assuming that this series evolved by successive duplications and divergence of the primitive segments, we have analyzed the changes that may have occurred during the evolution of each new segment. Changes between ipsilaterally and contralaterally projecting axons may have occurred several times during the evolution of the series. In addition, cells may have been added or deleted.
Light‐evoked and kainic‐acid‐induced disc shedding by rod photoreceptors: Differential sensitivity to extracellular calcium
Authors: Besharse Joseph C. , Spratt Gwendolyn , Forestner Donna M.
Published: January 2005

In order to study the light and Ca2+ dependence of disc shedding by rod photoreceptors, we have used eyecups prepared from adult Rana pipiens frogs that had been kept in constant light for 4 days. Disc shedding was initiated by a treatment involving 1 hour of darkness followed by exposure to light or by treatment with kainic acid. Maximal L‐evoked disc shedding occurred quickly (within 30–60 minutes) after light onset and could be triggered by brief (15 minutes) exposure to light. L‐evoked disc shedding was completely blocked by omission of Ca2+ from culture medium or by treatment with 3mM Co2+ or 12 mM Mg2+ in the presence of Ca2+ (2 mM). The response was also blocked by the organic Ca2+ antagonist nifedipine. Experiments designed to distinguish between Ca2+ dependence of the dark or light‐dependent processes necessary for shedding suggest that volage‐sensitive channels mediate a Ca2+‐dependent process involved in light‐triggering. Kainic acid caused a dose‐dependent stimulation of disc shedding under lighting conditions (continuous culture in light or darkness) that did not normally result in a significant response in the absence of the drug. Disc shedding induced by kainic acid was similar in time course and magnitude to that induced by light. However, kainic‐acid‐induced disc shedding was not inhibited by medium Ca2+ reduction or by the presence of Co2+. The latter observation suggests that kainic acid activates disc shedding directly, bypassing the Ca2+‐dependent process involved in the L‐evoked response. The Ca2+‐dependent process may involve release of an effector of disc shedding that is mimicked by kainic acid.
Morphology of retinogeniculate X and Y axon arbors in monocularly enucleated cats
Authors: Garraghty P. E. , Sur M. , Weller R. E. , Sherman S. M.
Published: January 2005

We examined the terminal arbors of single, physiologically identified retinogeniculate X and Y axons from the remaining retinas of adult cats raised from birth with monocular enucleation. These were compared with arbors of X and Y axons in normally reared cats. We used intra‐axonal injections of horseradish peroxidase to label each axon after recording its response properties. While the axons in monocularly enucleated cats exhibited normal response properties, both X and Y axons in these cats had abnormally large terminal arbors. Each of the hypertrophied X arbors appeared to be completely confined to the single geniculate lamina A or A1 appropriate to its eye of origin (i.e., lamina A for the contralateral retina and lamina A1 for the ipsilateral retina). In contrast, in addition to their normal terminations, most of the Y arbors seemed to extend well into laminae normally innervated only by the retina that was removed. Thus most or all of the translaminar sprouting previously reported for monocularly enucleated cats appears to reflect extensions of Y axon arbors. These data, in addition to earlier, analogous data from young kittens and cats reared with monocular lid suture, suggest the following sequelae during postnatal development: the retinogeniculate X arbors mature first and develop exuberant arbors that are later competitively pruned as the Y axons expand their innervation of the lateral geniculate nucleus; monocular lid suture prevents the Y axons from succeeding in this competition, so they fail to establish normal arbors and cannot reduce the exuberant X arbors; monocular enucleation offers a less resistant path in the denervated laminae for the rapidly growing Y arbors from the remaining eye, and the expansion of these arbors there reduces the competitive pressure on the exuberant X arbors. Thus, in monocularly enucleated cats, sprouting is limited to Y axons, either because only they possess the capacity to sprout or because they are in the midst of a period of relatively rapid growth at the time of the neonatal enucleation. The X axon arbors are also abnormally large within their appropriate laminae. This occurs presumably because they are able to maintain their immature exuberance, although we cannot rule out the possibility that they are pruned and later regrow to the final size seen in our experiments.
Callosal projections from area SII to SI in monkeys: Anatomical organization and comparison with association projections
Authors: Manzoni Tullio , Conti Fiorenzo , Fabri Mara
Published: January 2005

The present research was aimed at ascertaining in the macaque monkey the reciprocity of the heterotopical callosal connections between SI and SII, with particular regard to the connectivity of the hand representation, and at comparing the topographical and laminar pattern of these callosal connections with those of association connections entertained by these areas. Horseradish peroxidase (HRP) was unilaterally injected into area SI in five monkeys. The sites of HRP delivery included the trunk and the hand zones preliminarily identified by recording multi‐unit responses to peripheral stimulation by means of microelectrodes. Anterograde and retrograde labelling was studied in SII of both sides.

The results showed the complete reciprocity of the heterotopical callosal connections between SI and SII. In the latter area both callosal axon terminals and neurones were found, which were labelled from either the trunk or the hand zone of contralateral SI. Labelling of callosal axon terminals occurred mainly in layer IV and in the lowermost part of layer III. Labelled callosal neurones were mainly in the lower half of layer III, whereas few occurred in infragranular layers. Topographically, the distribution of callosal terminals and cell bodies duplicated the distribution of association terminals and cell bodies labelled in SII on the side ipsilateral to HRP injection. The laminar pattern of termination of association fibres from SI was similar to that of callosal fibres. However, the distribution of association‐projecting neurones in SII showed a striking difference from that of callosal‐projecting neurones. Unlike the latter neurones, which were mainly located in supragranular layers, association cell bodies overwhelmingly dwelt in layers V and VI and were less numerous in layers II and III. This laminar pattern of association SII‐SI cells corresponds to the “feed‐backward” model and fits the laminar pattern of their axon terminations (Friedman: Brain Res. 273: 147–151, '83).

The association and callosal inputs and outputs of area SII are discussed in relation to the function of the forward and backward type of reciprocal connections entertained with SI in the ipsilateral hemisphere and to the function of SII in the interhemispheric exchange of somatosensory information.
Cytoarchitecture and saccular innervation of nucleus Y in the mouse
Authors: Frederickson Christopher J. , Trune Dennis R.
Published: January 2005

The cytoarchitecture and saccular innervation of the mouse nucleus y were investigated by using Golgi, Nissl, and myelin stains and anterograde axonal transport of horseradish peroxidase. Nucleus y was found to be a compact group of cells in a small fiber‐free region dorsal to the restiform body. Qualitative and morphometric analyses showed that most (75%) of the nucleus y neurons could not be reliably subdivided into morphologic subgroups, but varied continuously in soma size (15–25 μm), shape (fusiform to stellate), and number of dendrites (two to four), and had sparsely branched dendrites with an average of 3 to 4 spines per 10 μm of length. Three groups of cells that were identified morphometrically accounted for 10% (type I: large stellate cells), 9% (type II: long‐dendrite cells), and 6% (type III: elongated soma cells) of the y neurons. Vestibular nerve axons transporting horseradish peroxidase after injury at their origin in the saccular neuroepithelium were found to form a dense terminal meshwork that was virtually co‐extensive with the cytoarchitectonic boundaries of nucleus y. Nucleus y was distinguished from the overlying infracerebellar nucleus on the basis of anatomical, cytoarchitectural, and hodological features.
Thalamic connectivity of the second somatosensory area and neighboring somatosensory fields of the lateral sulcus of the macaque
Authors: Friedman David P. , Murray Elisabeth A.
Published: January 2005

The thalamocortical relations of the somatic fields in and around the lateral sulcus of the macaque were studied following cortical injections of tritated amino acids and horseradish peroxidase (HRP). Special attention was paid to the second somatosensory area (S2), the connections of which were also studied by means of thalamic isotope injections and retrograde degeneration. S2 was shown to receive its major thalamic input from the ventroposterior inferior thalamic nucleus (VPI) and not, as previously reported, from the caudal division of the ventroposterior lateral nucleus (VPLc). Following small injections of isotope or HRP into the hand representation of S2, only VPI was labeled. Larger injections, which included the representations of more body parts, led to heavy label in VPI, with scattered label in VPLc, the central lateral nucleus (CL), and the posterior nucleus (Po). In addition, small isotope injections into VPLc did not result in label in S2 unless VPI was also involved in the injection site, and ablations of S2 led to cell loss in VPI. Comparison of injections involving different body parts in S2 suggested a somatotopic arrangement within VPI such that the trunk and lower limb representations are located posterolaterally and the hand and arm representations anteromedially. The location of the thalamic representations of the head, face, and intraoral structures that project to S2 may be in the ventroposterior medial nucleus (VPM).

The granular (Ig) and dysgranular (Id) fields of the insula and the retroinsular field (Ri) each receive inputs from a variety of nuclei located at the posteroventral border of the thalamus. Ig receives its heaviest input from the suprageniculate‐limitans complex (SG‐Li), with additional inputs from Po, the magnocellular division of the medial geniculate n. (MGmc), VPI, and the medial pulvinar (Pulm). Id receives its heaviest input from the basal ventromedial n. (VMb), with additional inputs from VPI, Po, SG‐Li, MGmc, and Pulm. Ri receives its heaviest input from Po, with additional input from SG‐Li, MGmc, Pulm, and perhaps VPI. Area 7b receives its input from Pulm, the oral division of the pulvinar, the lateral posterior n., the medial dorsal n., and the caudal division of the ventrolateral n.

These results indicate that the somatic cortical fields, except for those comprising the first somatosensory area, each receive inputs from an array of thalamic nuclei, rather than just one, and that individual thalamic somatosensory relay nuclei each project to more than one cortical field.
Projection of septal organ receptor neurons to the main olfactory bulb in rats
Authors: Pedersen Patricia E. , Benson Thane E.
Published: January 2005

The septal organ of Masera is a distinct patch of olfactory epithelium on the septal wall of the nasal cavity. It lies ventral to the main olfactory receptor sheet. Central projections of the septal organ to the main and/or accessory olfactory bulb were studies with puncate HRP injections into the posterior dorsomedial olfactory bulb of rat pups. Injection sites encompassed 2‐‐8% of the main olfactory bulb glomeruli and some injection sites were confined to the accessory olfactory bulb glomeruli. The distribution of receptor neurons in the septal organ that were labeled as a result of retrograde transport from the injection sites was determined.

Olfactory receptor neurons were labeled in septal organs of those animals with injection sites confined to the main olfactory bulb. Subsequent to the posterior dorsomedial bulbar injections of this study, labeled receptor neurons were preferentially located in the posterior portion of the septal organ and were clustered about a plane dorsal to the plane bisecting the organ. Injections confined to the accessory olfactory bulb only labeled vomeronsal organ receptor neurons. Thus it is likely that the main olfactory bulb and not the accessory olfactory bulb is the bulbar terminus of septal organ receptor neurons. To date, experimental evidence suggests that the septal organ system may comprise an anatomically and functionally unique chemosensory pathway for odor detection.