bluuebunny/crossref_metadata_2025 huggingface dataset:
Transplantation of embryonic occipital cortex to the tectal region of newborn rats: A light microscopic study of organization and connectivity of the transplants
Authors: Jaeger C. B. , Lund R. D.
Published: January 2005

Occipital cortex was taken from fetal rats and transplanted to the tectal region of newborn rats, where it developed a specific structural identity reflecting in part its cortical origin. The implants showed locally distributing intratransplant connections, and the majority formed connections with defined regions of the host cerebral cortex and the brainstem. A sparse afferent projection from the host had its origin in visual, somatosensory, and cingulate areas of the cortex, pretectum, superior colliculus, central gray, hypothalamus, pontine reticular formation, raphe nuclei, and the locus coeruleus. No input was identified from either the retina or the dorsal thalamus. Efferent fibers were observed in normal fiber preparations as compact bundles running through the host brainstem along two main routes, one group of bundles in a dorsal position and a second group more ventral. Efferent fibers traveling rostrally along the first pathway distributed in the ower part of the stratum griseum superficiale and in intermediate laminae of the superior colliculus, and in some cases they reached the pretectum and the lateral posterior thalamic nucleus. Deep efferent fibers ran rostrally and caudally in the central gray, and in some cases laterally directed fibers were seen to distribute in the midbrain tegmentum and reticular formation, in one case reaching the pontine gray.

The finding that most afferent and many efferent connections of cortical transplants are uncharacteristic of normal cortex stands in marked contrast to retina and tectum, which, when transplanted to the same region, make relatively normal connections.
A comparison of thalamocortical and other synaptic inputs to dendrites of two non‐spiny neurons in a single barrel of mouse SmI cortex
Authors: White Edward L. , Rock Michael P.
Published: January 2005

A Golgi impregnated, non‐spiny multipolar cell whose soma occurred in layer V of the region of mouse SmI cortex containing the posteromedial barrel subfield (PMBSF) (Woolsey and Van der Loos, '70) was gold‐toned and deimpregnated (Fairen et al., '77). Two of its dendrites, contained within a single PMBSF barrel, were serial thin‐sectioned and then reconstructed in three dimensions. Dendrites of an unimpregnated, non‐spiny layer IV bitufted cell, present within the same barrel, were also reconstructed in three dimensions from the series of thin sections. This approach permitted a comparison of the distribution of synapses along dendrites of the two non‐spiny neurons. Results showed dendrites of the layer IV bitufted cell formed about twice as many synapses per unit lenght as those of the multipolar cell. Particularly striking was the contrast between the large number of synapses made by degenerating thalamocortical axon terminals with the dendrites of the bitufted cell and the rarity with which such synapses occur on dendrites of the multipolar cell. Furthermore, the proportion of the total number of synapses made by thalamocortical axon terminals onto dendrites of the bitufted cell was six times greater than the proportion of the thalamocortical synapses onto the multipolar cell dendrites.
An ultrastructural and biochemical analysis of norepinephrine‐containing varicosities in the cerebral cortex of the turtle pseudemys
Authors: Ouimet Charles C. , Patrick Robert L. , Ebner Ford F.
Published: January 2005

The fine structure and norepinephrine content of small granular vesicle‐containing profiles were studied in normal and norepinephrine‐depleted cerebral cortex of the turtle, Pseudemys. The cortex was fixed for electron microscopy with the KMnO4 procedure of Koda and Bloom ('77), while the norepinephrine content was assayed with the radioenzymatic method of Coyle and Henry ('73). Green fluorescent fibers have been described by Parent and Poitras ('74) as located almost exclusively in the outer half of the molecular layer in turtle cortex. Small granular vesicle‐containing profiles are found down to 100 μm below the pial surface, but over 50% lie within 20 μm of the surface. Within the outer 100 μm of cortex, the frequency of labeled varicosities is 1.39/1,000 μm2. The average area of the norepinephrine‐containing varicosities is 0.61 μm2, and there is a mean of 18.4 vesicles per single section. The average number of large plus small vesicles in an entire varicosity was estimated to be 72. Synaptic membranes are not well‐preserved with KMnO4 fixation, but good examples were found of small granular vesicle‐containing profiles forming both symmetrical and asymmetrical membrane differentations. Only a small percentage of the small granular vesicle profiles were associated with a synaptic membrane differentiation in single sections. When norepinephrine‐fiber synapses are seen, they usually share a postsynaptic element with another unlabeled vesicle‐containing profile. Normal turtle cortex contains an average norepinephrine concentration of 1.95 μg/gr, which is about eight times higher than in rat cortex. The ratio of norepinephrine to dopamine is about 18 to one, suggesting that dopamine is present predominantly in a precursor pool for norepinephrine. Small granular vesicle‐containing profiles were eliminated after tratment with reserpine and 6‐hydroxydopamine in concentrations that were shown to reducenorepinephrine concentration by 94% and 86%, respectively. The labeled varicosities were partially depleted by midbrain hemisection and by an inhibitor of dopamine‐beta‐hydroxylase (FLA‐63). The norepinephrine‐containing varicosities are remarkably coextensive with the distribution of thalamic fibers, both in the total extent of cortex where they are found and in the depth of cortex where they terminate. The results support the idea that there is a close structural and functional association between locus coeruleus and thalamic fibers in cerebral cortex, and the apparent difference in frequency of synapses suggests that each fiber system exerts its influence on cortical cells in a different way.
Neurogenesis in the 3‐month‐old rat visual cortex
Authors: Kaplan Michael S.
Published: January 2005

Newly formed neurons in the adult mammalian neocortex have been reported by several investigators using light microscopic radioautography, but these reports have not been confirmed by electron microscopy—probably because their rarity precludes any reasonable chance of observing these cells with electron microscopic radioautography. To overcome this problem I have used a recently developed method that allows serial thin sectioning and subsequent electron microscopic examination of plastic‐embedded sections previously prepared for light microscopic radioautography. Ninety‐day‐old rats were injected with 4.3 μCi per gm body weight of [H3] thymidine and allowed to survive for 30 days. In the light radioautographs, labeled cells were found in layer IV of the visual cortex, and analysis of electron micrographs of selected examples of these labeled cells clearly demonstrated their neuronal nature with synapses along their cell bodies and dendrites. In order to quantify the relative frequency of labeled neurons, the number of labeled cells seen in the light microscopic sections was expressed as a percentage of the total number of neurons found in sections through the entire thickness of the visual cortex; the percentage was 0.011%, or about 1 in 10,000. The results of this study are in agreement with evidence of neurogenesis of granular neurons in the adult rat olfactory bulb and dentate gyrus (Kaplan and Hinds, '77). Thus, it has now been confirmed that relatively small labeled neurons and their synapses are found in at least 3 brain regions (olfactory bulb, dentate gyrus, and visual cortex) in a normal adult rodent.
Central distribution of octavolateral afferents and efferents in a teleost (mormyridae)
Authors: Bell Curtis C.
Published: January 2005

The central distribution of afferents from individual eighth nerve branches (N VIII) and mechanical lateral line end organs in mormyrid fish are described. Afferents were labeled with horseradish peroxidase (HRP) placed on the cut ends of the different N VIII branches and the anterior and posterior lateral line nerves.

Descending, tangential, and magnocellular nuclei receive input almost exclusively from the utriculus and canals. Nucleus octavius receives afferents from the lateral line nerves and all N VIII branches, with one part receiving exclusive and bilateral input from the sacculus. Afferents from both lateral line nerves and all N VIII branches, except the sacculus, end in eminentia granularis. Afferents from each of the two lateral line nerves and from each of the three otolith branches of N VIII end in different regions of the anterior lateral line lobe, with some areas of overlap.

Behavioral studies in other families of fish indicate that the utriculus and canals are critical for postural control, whereas the sacculus and possibly the lagena are concerned with hearing. Such findings, together with the results of this study, suggest that mormyrids and perhaps other fish possess separate auditory and vestibular centers within the octavolateral area.

The HRP method also shows the cell bodies and axons of octavolateral efferents. N VIII and lateral line efferents arise from a common nucleus, and the central course of their axons parallels that of facial motoneurons. Axons of efferent cells divide to supply two or more branches of N VIII and some axons supply both lateral line and N VIII end organs.
Abnormal axonal growth in the dorsal lateral geniculate nucleus of the cat
Authors: Robson J. A.
Published: January 2005

Retino‐geniculate axons in the cat were induced to grow abnormally by cutting one optic nerve in kittens. Surviving optic tract axons that had grown into the denervated regions were then filled in the adults with horseradish peroxidase to reveal the terminal arbors of individual axons. Two types of abnormal axonal growth are described—translaminar growth and monocular segment growth. Translaminar growth is the most common and occurs between lamine in the binocular part to the nucleus. Axons giving rise to translaminar growth do not branch as they pass through the denervated regions of the nucleus. Instead, the abnormal branches originate from portions of the terminal arbor within the normal target lamina. These axons look like normal retino‐geniculate axons in terms of their branching patterns, cytological features, and patterns of synaptic contacts except that parts of their terminal arbors have expanded to innervate inappropriate laminae. The distribution of translaminar branches overlaps the distribution of a restricted group of surviving large neurons that have not undergone denervation atrophy.

Monocular segment growth invades the lateral pole of the nucleus directly from the optic tract. These branches arise from axons passing through or near the denervated region and appear to represent the formation of new terminal arbors. The synaptic swellings arising from these branches have cytological features like the synaptic swellings arising from translaminar branches and they from similar patterns of synaptic contacts. However, monocular segment branches degenerate more rapidly when damaged and they are not associated with surviving large neurons.
Anomalous uncrossed retinal projections fail to activate superior colliculus neurons in rabbits unilaterally enucleated by fetal surgery
Authors: Chow Kao Liang , Ostrach Louis H. , Crabtree John W. , Bernegger Otto , Baumbach H. Dale , Lawson Robin
Published: January 2005

Previous studies have shown that unilateral enucleation of rabbit pups produces an aberrant uncrossed retinotectal projection. These fibers failed to drive collicular units when stimulated with either light or electric shock. The present study attempts to assess the possibility that enucleation at earlier stages of development would lead to a greater degree of morphological and physiological reorganization in the uncrossed retinotectal projection.

Rabbit fetuses were unilaterally enucleated at day 20 or 25 of gestation. Birth is at day 31. After 3 months, the degree of reorganization of the uncrossed retinotectal projection was assessed using the following techniques: (1) autoradiographic demonstration of the projection from the remaining eye, (2) electrophysiological recording of collicular unit activity, and (3) a combination of these methods.

Autoradiographic data indicated a much greater expansion of the anomalous uncrossed projection in fetally enucleated animals than in those enucleated at birth. Labelled terminals were found to occupy more than the anterior third of the ipsilateral colliculus and were distributed to the entire depth of the stratum griseum superficiale and stratum opticum.

Electrode penetrations within the boundaries of the expanded projection failed to locate collicular units which could be driven by either light stimulation of the eye or electric shock of the optic nerve. Only a few cells encountered in the lateral border area, receiving the normal uncrossed retinal projection, could be driven by light stimulation.

These negative findings are in contrast to the data reported for the rat and hamster where anomalous retinal projections are capable of forming functional connections. Further comparative studies of reorganization are needed.
Fate of the hippocampal mossy fiber projection after destruction of its postsynaptic targets with intraventricular kainic acid
Authors: Nadler J. Victor , Perry Bruce W. , Gentry Christine , Cotman Carl W.
Published: January 2005

Intraventricular injections of kainic acid were used to create a model of selective cell death in order to study the fate of afferent projections that are deprived of their postsynaptic targets. This treatment rapidly destroyed hipocampal CA3 pyramidal cells, but not those neurons that give rise to their mossy fiber and entorhinal afferents. Light microscopic studies with the Timm's sulfide silver stain indicated that half or more of the mossy fiber boutons in area CA3b were lost within the first 1–3 days after kainic acid administration. This finding was confirmed by electron microscopy. Electron‐dense, usually vacuolated mossy fiber boutons accounted for about 10–20% of the total population present at a 4‐hour survival time, but were not encountered in control rats nor at survival times longer than 1 day. Other mossy fiber boutons remained electron lucent, but enlarged became more rounded in shape, and suffered and apparent loss of synaptic vesicles. It is suggested that degeneration of some mossy fiber boutons and resorption of others into the axon may have accounted for the precipitous decline in their number. The dendritic excrescences contacted by these boutons were nearly all undergoing electron‐dense degeneration 4 hours after kainic acid administration. In rats that survived 6–8 weeks mossy fiber boutons remained somewhat scarce, individual boutons appeared relatively small, and only one‐third the normal percentage were observed to be engaged in more than one synaptic contact within a single cross section. A qualitative electron microscopic study of the entorhinal projection to area CA3 suggested a response to kainic acid treatment similar to that of the mossy fiber projection, except that no entorhinal boutons were seen to become electron dense.

These findings suggest that presynaptic fibers in the mature hippocampus adjust the size of their terminal arborizations and number of synaptic contacts to accommodate a reduction in the target cell population. The rapid loss of mossy fiber boutons may be attributable to an unsual fragility of these structures when they are deprived of the mechanical support normally provided by the pyramidal cell. Finally, the ability of kainic acid administration to alter the number and distribution of presynaptic elements must be taken into account whenever this toxin is used to make selective lesions of postsynaptic cells.
Fine structure and organization of the infrared receptor relay, The lateral descending nucleus of the trigeminal nerve in pit vipers
Authors: Meszler Richard M. , Auker Charles R. , Carpenter David O.
Published: January 2005

The morphology of the nucleus of the lateral descending tract of V has been studied in species of two genera of pit vipers, cottonmouth moccasin (Agkistrodon piscivorus piscivours), and rattlesnake (Crotalus ruber and Crotalus horridus horridus). The nucleus is the site of termination of primary afferent neurons forming the infrared receptors in the facial pits. It is located on the external surface of the common descending tract of V and contains somata that range in size from 7 to 22 μm in A. A. p. piscivorus and 7 to 27 μm in C. ruber.

Electron microscopy reveals that the lateral descending tract contains both Aδ and C fibers. Degeneration experiments indicate that the Aδ fibers are primary afferents. The source of the C fibers is unknown.

The lateral descending nucleus in both the cottonmouth and rattlesnake is fundamentally similar in organization. Afferent terminals containing clear spherical vesicles make synaptic contact with dendritic processes within the main neuropil. These axon terminals are also postsynaptic to boutons containing pleomorphic vesicles and some large dense‐core vesicles.

The C fibers terminate in a neuropil at the margin of the lateral descending tract on small dendritic processes that appear to come from neurons within the nucleus. This neuropil is found external to the tract in the cottonmouth and internal to the tract in the rattlesnake. The terminals contain clear spherical vesicles and large dense‐core vesicles.

The singularity of input to this nucleus is apparently reflected in the morphology. This is discussed in relation to the subnucleus caudalis of the mammalian brainstem.
Hematogenous cells in the central nervous system of developing human embryos and fetuses
Authors: Choi Ben H.
Published: January 2005

Examination of large blocks of Epon‐embedded, 1.0‐μm sections of human embryos and fetuses reveal the presence of hematogenous cells in various stages of differentiation in neural tissue. In every embryo and fetus of 10 weeks ovulation age and younger, hematogenous cells are found randomly scattered in the cerebrum, cerebellum, and spinal cord. Many of these cells appear to undergo spontaneous degeneration in neural tissue and become rarer in older fetuses. Also identified in the neuropil of normal embryos and fetuses are cells with the typical morphological appearance of macrophage containing numerous inclusions of various kinds, both inside and outside the blood vessels. In addition, scattered in the subpial, perivascular, and perineuronal regions of the neural parenchyma are small cells with fusiform nuclei and a small amount of cytoplasm as well as cells with a moderate amount of elongated cytoplasm containing various inclusions and oblong nuclei. All of these cells have clumped heterochromatin along the nuclear membrane which differs from other neuroectodermal cells of the developing human CNS.

Although there is no direct evidence to indicate transformation of macrophages to “microglia” or vice versa, the presence of cells having similar nuclear morphology and chromatin pattern while appearing to tbe transitional forms of macrophage, varying from undifferentiated to fully developed, suggest a common lineage of these latter types. It is concluded that migration of hematogenous cells into neural tissue is a ubiquitous developmental phenomenon in young human embryos and fetuses.
GABAergic amacrine cells in rat retina: Immunocytochemical identification and synaptic connectivity
Authors: Vaughn James E. , Famiglietti Edward V. , Barber Robert P. , Saito Kihachi , Roberts Eugene , Ribak Charles E.
Published: January 2005

GABAergic neurons have been identified in light and electron microscopic preparations of rat retina by an immunocytochemical localization of the GABA‐synthesizing enzyme, glutamic acid decarboxylase (GAD). GAD‐positive neuronal somata are found only in the inner and middle parts of the inner nuclear layer, and GAD‐positive neuronal terminals are observed exclusively within the inner plexiform layer (IPL) and the outermost part of the ganglion cell layer. Dense aggregations of GAD‐positive terminals alternate with less dense zones to form a lamination of the IPL. GAD‐positive terminals contain pleomorphic synaptic vesicles and are the presynaptic elements of conventional synapses onto bipolar and amacrine cell processes, as well as onto the somata and dendrites of ganglion cells. In addition, GAD‐positive terminals are postsynaptic to unstained bipolar terminals and are components of synaptic dyads where they occasionally appear to form reciprocal synapses with the bipolar terminals, and serial synapses with unstained amacrine processes. Probable synaptic contacts between adjacent GAD‐positive terminals also have been observed. Most of the synaptic input to GAD‐positive terminals comes from bipolar cells, while the small remaining input mainly comes from other GAD‐positive terminals. The synaptic output of GAD‐positive terminals is greatest to bipolar cells, followed in decreasing order by GAD‐negative amacrine cells, ganglion cells, and other GAD‐positive cells. The total synaptic output of GAD‐positive cells appears to be more than twice as great as the total input to these cells.

The location of GAD‐positive somata, the distribution of GAD‐positive terminals, and the synaptic relationships formed by these terminals all indicate that amacrine cells are the only GABAergic neurons in rat retina. Our observations also indicate that not all amacrines are GABAergic and suggest that GABAergic neurons may be limited to a narrow field subclass of amacrine cell. The findings concerning the synaptic connections of GABAergic amacrines suggest that such cells are the first link in several divergent pathways from bipolar to ganglion cells and that they probably serve more than one function since they feed synaptic activity forward directly upon ganglion cells as well as back upon bipolar cells.
Population magnitudes and distribution of the major modal classes of cat retinal ganglion cell as estimated from HRP filling and a systematic survey of the soma diameter spectra for classical neurones
Authors: Hughes A.
Published: January 2005

A survey of diameter spectra in presented for classic neurones of the cat retinal ganglion cell layer. From these, with the aid of retrograde HRP filling for central retina, a set of density distribution maps has been prepared for each of the major modes of the neuronal diameter spectrum. The total population of classical neurones, the presumed ganglion cells of Hughes ('75), confirms published values with a minimum of some 207,000 comprised 5,600 cells in the γ mode, 80,700 cells in the β mode, and 120,700 cells in the γ mode.

A proportion of classical neurones in the γ mode do not fill by retrograde transport of HRP from either optic nerve or superior colliculus. Their morphology is characteristic and includes a conspicuous basophilic nuclear bar or fold; they remain subsequent to ganglion cell retrograde degeneration and resemble some prifles of the amacrine layer. It is presumed that they represent a class of displaced amacrine cells.

Estimates based on ganglion cell identification by HRP filling indicate populations of about 80,000 cells in both the γ and the β modes and a total count of about 170,000 ganglion cells; a good agreement with Hughes and Wässle's ('76) optic nerve fibre count, but lower than the classic neurone count.

It is concluded that the distribution maps for ganglion cells in each of the three modes of the soma diameter spectra are similar in from and resemble that of the total neurone density map. The ganglion cell population of the γ mode in the visual streak is not found to increase in proportion relative to that of the β mode, as has been reported elsewhere.
A light microscopic investigation of the afferent connections of the lateral reticular nucleus in the cat
Authors: Hrycyshyn A. W. , Flumerfelt B. A.
Published: January 2005

The topographical organization of the projections to the lateral reticular nucleus (LRN) of the cat was investigated using the horseradish peroxidase (HRP), silver‐impregnation and autoradiographic tracing methods. Following injection of HRP into the LRN, labelled cells were found mainly within Rexed's laminae VII and VIII of the spinal cord, the contralateral red nucleus, the ventrorostral aspect of the contralateral fastigial nucleus and the contralateral anterior sigmoid and coronal gyri of the cerebral cortex. Animals with injections of tritiated amino acids placed within the pericruciate cortex, red nucleus or fastigial nucleus were processed for autoradiography. In a corresponding series of animals, electrolytic lesions were placed selectively into the above sources of reticular afferents, and terminal degeneration within the LRN was studied by light microscopy. An extensive input from the spinal cord was found to terminate predominantly on the ipsilateral side throughout the rostrocaudal extent of the LRN, except for a small ventromedial area of the rostral parvocellular division and a small rostromedial area of the magnocellular division. The cortical projection terminated diffusely within the middle one‐half of the contralateral magnocellular division, while the rubral projection terminated extensively within the contralateral subtrigeminal division and the dorsolateral region of the rostral magnocellular and neighbouring parvocellular divisions. The rubral projection did not overlap the cortical projection. The fastigial nucleus projected sparsely to the contralateral LRN, mainly to the medial aspect of the rostral two‐thirds of the magnocellular division, with less to the parvocellular and subtrigeminal divisions.

The LRN therefore receives spinal and supraspinal projections within at least its rostral one‐half, and these terminate within specific areas in a partially overlapping fashion, whereas the caudal one‐half is primarily a spinal receiving region. No convergence of the rubral and sensorimotor cortical projections was evident.
Habenular asymmetry and the central connections of the parietal eye of the lizard
Authors: Engbretson Gustav A. , Reiner Anton , Brecha Nicholas
Published: January 2005

Histochemical and autoradiographic analyses of the axonal transport of horseradish peroxidase and tritiated amino acids were employed to study the central connectivity of the lizard parietal eye. Somata and processes of centrifugal fibers to the parietal eye were localized in tissue of the dorsal sac and in the leptomeningeal sheath of the pineal gland. Analyses of series of transverse sections of the brain showed the left medial habenular nucleus to be subdivided into pars dorsolateralis and pars ventromedialis, and the right medial habenular nucleus not to be so subdivided. Centripetal fibers of parietal eye ganglion cells project to only the pars dorsolateralis of the left medial habenular nucleus and terminate there in two distinct fields. The asymmetry of the lizard habenula may be a specialization associated with the unilateral projection from the parietal eye.
Thalamocortical synapses of pyramidal cells which project from SmI to MsI cortex in the mouse
Authors: White Edward L. , Hersch Steven M.
Published: January 2005

Electrolytic lesions were made of the nucleus ventralis posterior pars lateralis thalami and of the nucleus posterior thalami in male CD/1 mice to label thalamocortical axon terminals in mouse SmI cortex. Pyramidal cells in layers II through V of SmI cortex were labeled by the retrograde transport of horseradis peroxidase injected into ipsilateral MsI. Numerous pyramidal cells, particularly in the more superficial layers of SmI cortex, were filled with reaction product so that even their dendritic spines and local axon collaterals were clearly visible. Six well‐filled pyramidal cells with somata in layers III and IV were serial thin‐sectioned, and portions of their dendrites in layer IV were examined with the electron microscope to determine the distribution of their thalamocortical and other synapses. It was found that, in general, different dendrites of a single pyramidal cell formed similar proportions of thalamocortical synapses and that the six pyramidal cells, as a group, also formed similar proportions of thalamocortical synapses with their dendrites in layer IV. In contrast, when the thalamocortical connectivity of the six cells was considered as a function of their depths within the cortex, a clear trend was seen for the proportion of thalamocortical synapses to increase with increasing proximity of the cell body to layer IV. A hypothesis based on the timing of developmental events is proposed to account for this observation.
Locations of androgen‐concentrating cells in the brain of Xenopus laevis: Autoradiography with 3H‐dihydrotestosterone
Authors: Kelley Darcy B.
Published: January 2005

The distribution of hormone‐concentrating cells in the brains of South African clawed frogs, Xenopus laevis, was examined autoradiographically after the administration of 3H‐dihydrotestosterone. Hormone‐accumulating cells were found in cranial nerve nucleus IX‐X and adjacent smaller cells, a presumed medullary vestibular nucleus, a presumed sensory nucleus of cranial nerve V, dorsal tegmental area of the medulla, laminar nucleus of the torus semicircularis, ventral thalamus, and anterior pituitary.

The pattern of dihydrotestosterone‐labelled cells differs from previously reported results following testosterone or estradiol administration. Unlike these latter hormones, dihydrotestosterone does not accumulate in anterior preoptic or ventral infundibular nuclei. Both androgens but not estradiol label medullary motor neurons; limbic telencephalic nuclei appear to concentrate only estradiol. Hormone‐concentrating brain nuclei in X. laevis have been implicated in neuroendocrine regulation and the control of male and female reproductive behaviors.
A study of Golgi preparations from the human lateral geniculate nucleus
Authors: Hickey T. L. , Guillery R. W.
Published: January 2005

The Golgi method was used to study nerve cells and their processes in the human lateral geniculate nucleus. Only a few axons were successfully impregnated. These enter the nucleus from the optic radiations and were tentatively indentified as corticogeniculate axons. In one brain from a 2‐week‐old infant these axons showed unusually dense terminal arbors, suggesting that significant developmental changes occur in this fiber system postnatally.

Neurons in the magnocellular layers show a great variety of dendritic patterns, and are not readily grouped into well‐defined morphological classes. At one extreme are cells with a restricted dendritic arbor, having dendrites that run a sinuous course close to the perikaryon. At the other extreme, cells have a more extended dendritic arbor; their dendrites are long, relatively straight in some cells, markedly tortuous in others. There is a continuous range of intermediate cell types between the “restricted” and the “extended” cells. Many magnocellular dendrites cross freely into adjacent layers; whereas the short dendrites of restricted cells rarely cross from one layer to another, the dendrites of extended cells may either be confined to a single layer (intralaminar) or may have a translaminar distribution across two or even three layers. Small cells, with dendrites entirely confined to an interlaminar region, have been seen in the magnocellular division of the nucleus on either side of layer 2.

Parvocellular elements also show a wide range of dendritic patterns, but the extreme forms of restricted and extended cells are not seen. Parvocellular dendrites commonly are oriented perpendicular to the layers and generally show an intralaminar distribution; translaminar dendrites are extremely rare. A minority of parvocellular neurons have most of their dendrites confined to an interlaminar zone. These “interlaminar” cells have large perikarya close to or in the interlaminar zones, and show a predominant dendritic orientation parallel to the layers. A few parvocellular elements with complex axoniform dendrites were seen, and these dendrites, too, tend to run parallel rather than perpendicular to the layers.
Brainstem innervation of prefrontal and anterior cingulate cortex in the rhesus monkey revealed by retrograde transport of HRP
Authors: Porrino Linda J. , Goldman‐Rakic Patricia S.
Published: January 2005

The cells of origin of projections from the brainstem to the dorsolateral and orbital prefrontal granular cortex and to the anterior cingulate cortex of the rhesus monkey were analyzed by means of retrograde axonal transport of the enzyme horseradish peroxidase (HRP). Following injections in various portions of the dorsolateral prefrontal and in the cingulate cortex, HRP‐positive neurons were found in three main locations: (1) the ventral midbrain including the anterior ventral tegmental area, the medial one‐third of the substantia nigra pars compacta, and the retrorubral nucleus; (2) the central superior nucleus and the dorsal raphe nucleus, primarily in its caudal subdivision; and (3) the locus coeruleus and adjacent medial parabrachial nucleus. Labeled neurons in the raphe nuclei and locus coeruleus were distributed bilaterally. A basically similar pattern of labeled somata was found in the brainstem with HRP injections in the orbital prefrontal cortex. Scattered HRP‐positive cells were found throughout the ipsilateral ventral tegmental area and in ventromedial portions of the retrorubral nucleus, and a large number of HRP‐positive cells were distributed bilaterally in the dorsal raphe and central superior nuclei as well as the dorsolateral pontine tegmentum. However, in contrast to the results obtained with injections on the dorsolateral and medial aspects of the hemisphere, labeled neurons were not found in any portion of the substantia nigra. The neurons labeled retrogradely after injection of HRP in these various regions of the frontal lobe in rhesus monkey correspond both in location and morphology to the monoamine‐containing neurons of the brainstem and are thus very likely the source of dopamine, norepinephrine, and serotonin found in the frontal cortex of the same species (Brown, R. M., A. M. Crane and P. S. Goldman (1979) Brain Res. 168:133–150).
Early development of the circumferential axonal pathway in mouse and chick spinal cord
Authors: Holley John A.
Published: January 2005

The early development of the circumferential axonal pathway in the brachial and lumbar spinal cord of mouse and chick embryos was studied by scanning and transmission electron microscopy. The cellular processes which comprise this pathway grow in the transverse plane and along the lateral margin of the marginal zone (i.e., circumferentially oriented), as typified by the early embryonic commissural axons. The first formative event observed was in the ventrolateral margin of the primitive spinal cord ventricular zone. Cellular processes were found near the external limiting membrane that appeared to grow a variable distance either dorsally or ventrally. Later in development, presumptive motor column neurons migrated into the ventrolateral region, distal to these early circumferentially oriented processes. Concurrently, other circumferentially oriented perikarya and processes appeared along the dorsolateral margin. Due to their aligned sites of origin and parallel growth, the circumferential processes formed a more or less continuous line or pathway, which in about 10% of the scanned specimens could be followed along the entire lateral margin of the embryonic spinal cord. Several specimens later in development had two sets of aligned circumferential processes in the ventral region. Large numbers of circumferential axons were then found to follow the preformed pathway by fasciculation, after the primitive motor column had become established. Since the earliest circumferential processes appeared to differentiate into axons and were found nearly 24 hours prior to growth of most circumferential axons, their role in guidance as pioneering axons was suggested.
Brain cells of the male rhesus monkey accumulate 3H‐testosterone or its metabolites
Authors: Rees Howard D. , Michael Richard P.
Published: January 2005

Autoradiography was used to localize target cells for 3H‐testosterone or its labeled metabolites in the brain of the rhesus monkey. Two castrated males were injected intravenously with 3H‐testosterone (2 mCi/monkey) and were killed 1 hour later. In both animals, neurons that concentrated radioactivity in their nuclei were located in a well‐circumscribed system that included the bed nucleus (n.) of the stria terminalis, medial preoptic n., suprachiasmatic preoptic n., anterior hypothalamic area, ventromedial hypothalamic n., cortical, medial, and basal accessory amygdaloid n., mesencephalic reticular n., and periaqueductal gray matter. In contrast to reports in some nonprimate mammalian species, little or no cellular labeling was observed in the lateral septum, arcuate n.‐median eminence, motor nuclei of cranial nerves, or spinal cord.
Connections of vocal control nuclei in the canary telencephalon
Authors: Nottebohm Fernando , Paton John A. , Kelley Darcy B.
Published: January 2005

Connections of two telencephalic vocal control nuclei, the hyperstriatum ventrale, pars caudale (HVc), and robust nucleus of the archistriatum (RA), were investigated in adult canaries. Methods used were transport of horseradish peroxidase and 3H‐adenosine and silver staining of degenerating axons. Three nuclei project to HVc: medial nucleus magnocellularis ofthe anterior neostriatum (MAN), nucleus interfacialis (NIf) of midneostriatum, and nucleus uvaeformis (Uva) of the diecephalon. Uva also projects to NIf. NIf and Uva have not been described previously. HVc projects to area X of lobus parolfactorius, to RA, and to field Avalanche of hyperstriatum ventrale. Nucleus RA receives projections from HVc and from lateral MAN. All these projections are ipsilateral. No gross male/female differences were apparent in the projections to and from HVc. Uptake of HRP by cell somata in HVc following localized injections of this substance into RA or HVc suggests that HVc is composed of rostrocaudally organized clusters of cells, with little lateral communication between them.
Ontogeny of the peptidergic system in the rat spinal cord: Immunohistochemical analysis
Authors: Senba Emiko , Shiosaka Sadao , Hara Yoshinobu , Inagaki Shinobu , Sakanka Masahiro , Takatsuki Kenichi , Kawai Yuriko , Tohyama Masaya
Published: January 2005

The ontogeny of neuropeptides, such as somatostatin (SRIF), substance P (SP), leucine‐enkephalin (LE), and neurotensin (NT) in the spinal cord (including the spinal ganglion) of the rat, was examined by means of the indirect immunofluorescence method. SRIF and SP appear in the early fetal period before the establishment of the spinal synaptic transmission system, and their appearance precedes that of LE and NT, thus suggesting that SRIF and SP might have some important role in the development of the spinal cord. Furthermore, a number of SRIF‐positive structures are found during the fetal period in the spinal cord; however, SRIF‐positive fibers in the ventral horn, lamina V, VI, and X tend to decrease remarkably in number after birth, while those found in the dorsal horn maintain their immunoreactivity even in the adult rats. These facts suggest that SRIF in the latter area might function as a neurotransmitter, whereas in the former areas, SRIF might have another role in the development of the spinal cord. SP‐positive structures also made their appearance during the fetal period. SP‐positive fibers continue to increase in number after birth, and they can be seen throughout the entire spinal cord even in the adult rats. It becomes difficult to identify SP‐positive neurons as the rats grow. Numerous SP‐positive cells are demonstrated, however, by colchicine pretreatment, thus suggesting that this system is functioning actively in the adult rats. LE‐and NT‐positive structures appear at perinatal stages and they continue to increase in number after birth. These facts suggest that these peptides (SP, LE and NT) might act as neurotransmitters.
The organization of the thoracic spinal nerve projection in the rat dorsal horn demonstrated with transganglionic transport of horseradish peroxidase
Authors: Ygge J. , Grant G.
Published: January 2005

Transganglionic transport of horseradish peroxidase (HRP) was used to study the organization of the thoracic spinal nerve projection to the dorsal horn in rats. Labeling was found in the superficial dorsal horn 16–20 hours after application of HRP to the cut ends of various spinal nerve rami. Labeling was restricted to the outer part of the substantia gelatinosa at these stages. Longer survivals (25–48 hours) gave rise to labeling of the deep part of substantia gelatinosa and deeper parts of the dorsal horn as well. The dorsal ramus projected to the lateral third of the horn from half a segment rostral to half a segment caudal to the entry segment. The ventral ramus projected to the medial two‐thirds of the horn from 1 1/2 segments rostral to half a segment caudal to the entry segment. The two branches of the ventral ramus that were examined projected to separate medial and lateral compartments for the entire ventral ramus. There was a distinct laterp‐medial shift of the projection found from rostral through caudal levels within the projection compartment for each nerve.

The results indicate that the dorsal horn projection of thoracic spinal nerve branches is organized in longitudinal compartments which are arranged in a strictly somatotopic fashion.
The evolution of an area and visual streak in the marsupial Setonix brachyurus
Authors: Beazley L. D. , Dunlop S. A.
Published: January 2005

The distribution, morphology, size, and number of cells in the retinal ganglion layer of the marsupial Setonix brachyurus, “quokka,” was studied from 25 days postnatal to adulthood using Nissl‐stained wholemounts

The total cell population was evenly distributed up to 50 days, but by 75 days highest densities were generally observed in a broad band extending across the nasotemporal axis. At 87 days, a temporally situated area centralis was seen for the first time. This was embedded in a horizontally aligned visual streak, the nasal arm of which contained areas of high density. By 106 days, densities in the area centralis had stabilized while peripheral values were higher than adult levels even at 180 days. In the adult, the area centralis was surrounded by a weak visual streak Retinal area increased steadily during development to reach 168 mm2 180 days, the adult range being 225–250 mm2

All cells in the ganglion layer appeared undifferentiated and rounded at 33 days with soma diameters of 3‐6 μm; by 70 days diameters had increased to 4‐12 μm and some cells had axon hillocks containing Nissl substance. From 87 days we distinguished ganglion cells, which constituted 54‐63% of the total. These were identified by deeply stained Nissl substance and had diameters of 7‐18 μm, compared to 7–23 μm at 143 days and 7‐24 μm in the adult; the remaining cells, termed glia/interneurons, were 5–8 μm throughout. Only ganglion cells were organized into an area centralis and visual streak. Glia/interneurons were evenly distributed except at the extreme periphery, where their density increased. In sectioned material, the ganglion layer was distinct from 25 days while the neuroblastic layer separated only between 48 and 85 days

From 25 to 250 days the total number of cells in the ganglion layer remained similar to the adult range of 336, 000‐393, 000. At both 87 days and in adults optic axon counts fell between 180, 000 and 224, 000, close to ganglion cell estimates. At 25 and 34 days, respectively, optic axon numbers were 75, 000 and 172, 000. Myelination was absent at 25 and 34 days, 3% at 87 days, and almost 100% in adults

Mechanisms are discussed whereby the area centralis and visual streak may evolve from an even distribution of cells while their number remains constant; migration is considered likely to be important.
The ultrastructure of rat rod synaptic terminals: Effects of dark‐adaptation
Authors: Brandon Christopher , Lam Dominic M.‐K.
Published: January 2005

The ultrastructure of synaptic terminals of rat rod photoreceptors was studied in light‐adapted and dark‐adapted states. In the light‐adapted state, horizontal cell processes embedded in the photoreceptor terminal show smooth surface contours and are ovoid in cross section. In the dark‐adapted state, fingerlike protrusions of photoreceptor cytoplasm extend into the horizontal cell processes on either side of the synaptic ribbon. An electron‐dense structure lies under the horizontal cell membrane that surrounds these fingerlike protrusions. This submembrane specialization is generally associated with areas of concavity of the horizontal cell membrane; it occurs in goldfish rods as well as rat rods. The protrusions and the horizontal cell specialization may be involved in membrane dynamics during synaptic activity.
The number of neurons in the different laminae of the binocular and monocular regions of area 17 in the cat
Authors: Beaulieu Clermont , Colonnier Marc
Published: January 2005

The number of neurons in individual laminae of area 17 was determined separately for both the binocular and the monocular, regions in the left hemi‐sphere of six cats. The number of neurons/mm3 of tissue was obtained for each lamina by using the method of size‐frequency distribution applied to neuronal nuclei. The number of neurons per unit of cortical surface could then be calculated from measurements of layer, thickness. The number of neurons/mm3 of tissue for trie total cortical thickness is on the order of 48,000 to 50,000 neurons, with no statistically significant differences be‐tween binocular and monocular regions. There are no significant differences for any of the layers except layer IV, in which the numerical density is 20% higher in the monocular region. The thickness of the cortex and of many of its layers, however, do vary between the two regions. Consequently there are significant differences in the number of neurons under 1 mm2 the total cortical thickness there are significantly more (27%) neurons in the binocular (78,440) than in the monocular region (61,900). This overall difference is due to significant changes in layers II, IIIA, IVA, and especially in layers V and VIA where neurons are 40% more numerous in the binocular region. These findings could signify either that the binocular region contains additional interneurons specifically related to binocular interactions or that it has a greater number of neurons projecting to other cortical and subcortical areas, or both.