bluuebunny/crossref_metadata_2025 huggingface dataset:
Alterations in receptive field properties of superior colliculus cells produced by visual cortex ablation in infant and adult cats
Authors: Mize R. Ranney , Murphy E. H.
Published: January 2005

To determine if functional alterations in the superior colliculus might account for recovery of visual behaviors following visual cortex removal in infant cats, the receptive field characteristics of single units in the superior colliculus of cats whose visual cortex was removed within the first week of life were compared with those of cats which sustained visual cortex lesions in adulthood and with those of normal cats. In the normal superior colliculus, 90% of all cells responded to moving stimuli irrespective of shape or orientation. Sixty‐four percent of these units were directionally selective, responding well to movement in one direction but poorly or not at all to movement in the opposite direction. Ninety percent of units were binocular, the vast majority of these responding equally to stimulation of either eye or showing only slight preference for stimulation of the contralateral eye. Responses to stationary flashes of light were observed in only 33% of all visually activated cells in the normal superior colliculus. After visual cortex ablation in adult cats, only six percent of movement sensitive cells were directionally selective. Binocular preference was shifted following adult visual cortex lesions such that sixty percent of all cells responded exclusively or predominantly to stimulation of the contralateral eye. Seventy‐one percent of all visually responsive units responded to stationary lights flashed on or off within their receptive field boundaries. Lesions limited primarily to area 17 had the same effect as larger lesions of visual cortex. Infant visual cortex lesions resulted in receptive field alterations similar to those observed after adult ablation. Only fifteen percent of motion sensitive units were directionally selective. Seventy‐one percent responded exclusively or predominantly to stimulation of the contralateral eye. Seventy‐six percent of visually responsive cells were activated by stationary light. Lesions largely confined to area 17 produced the same alterations as more extensive lesions of visual cortex. Thus, no evidence was found that the superior colliculus is involved in the functional reorganization presumed to occur following visual cortex ablation in infant cats. Recovery of visual behaviors following neonatal injury may therefore not involve alterations in the receptive fields of single cells.
Synapse formation in the mouse olfactory bulb. II. Morphogenesis
Authors: Hinds James W. , Hinds Patricia L.
Published: January 2005

Serial thin sections of the mouse olfactory bulb from the fourteenth day of gestation (E14) to postnatal day 44 (P44) have been examined in order to study morphogenesis of individual synaptic junctions. At the initiation of synapse formation structures are found that resemble postsynaptic densities but are facing extracellular space or unmodified processes. Transition forms between these isolated postsynaptic densities and undoubted synapses have been found. These observations as well as quantitative studies support the hypothesis that isolated postsynaptic densities can form independently and be converted to synapses when a presynaptic specialization develops opposite them.

Detailed studies of olfactory axodendritic synaptogenesis throughout the entire developmental period suggests strongly that these asymmetrical synapses pass through an immature symmetrical phase: (1) symmetrical olfactory axodendritic synapses are found in significantly higher concentration on axonal and dendritic growth cones than on more mature processes; (2) the number of symmetrical synapses is correlated with the rate of formation of new synapses determined previously. The time for a recognizable symmetrical synapse to be transformed into a recognizable asymmetrical one has been calculated to be 9–10 hours.

A scheme of synapse formation in the CNS has been proposed in which a postsynaptic structure forms independently followed by aggregation of pre‐existing presynaptic components into a presynaptic specialization. Different morphogenetic sequences of synapse formation from region to region are attributed simply to different relative rates in the development of the postsynaptic density and the presynaptic specialization.
Axonal guidance of developing optic nerves in the frog. I. Anatomy of the projection from transplanted eye primordia
Authors: Constantine‐Paton M. , Capranica Robert R.
Published: January 2005

Right or left eye primordia of Shumway stage 16–18 Rana pipiens embryos were transplanted to the position normally occupied by the ear, where they developed into externally normal eyes.

Ganglion cell density in the retina of the transplanted eye was significantly lower than the ganglion cell density in the animal's normal eyes. No significant difference was observed between normal and transplanted inner and outer nuclear layers.

In several preparations a large piece of embryonic forebrain was included in the initial eye graft. Optic nerves from the transplanted eyes penetrated this transplanted forebrain and established a dorsocaudal growth trajectory relative to the ectopic tissue's original anterior‐posterior and dorsal‐ventral axes. After traversing the forebrain, the transplanted optic nerve fibers penetrated the medulla where they invariably grew dorsocaudally to take up and maintain a dorsolateral position in the white matter of the spinal cord.

The consistent dorsocaudal trajectory established by the translocated optic tract in the ectopic forebrain and in the hindbrain and spinal cord is very similar to the growth trajectory in the normal diencephalon, suggesting that dorsocaudal growth relative to the three major axes of the neural tube is an inherent property of optic nerve fibers. These results also suggest that the polarity cues which guide normal optic tract growth are not unique to the diencephalic regions of the neural tube.
Origins of axons in the cat's acoustic striae determined by injection of horseradish peroxidase into severed tracts
Authors: Adams Joe C. , Warr W. Bruce
Published: January 2005

Origins and terminations of fibers of the dorsal and intermediate acoustic striae were studied by surgically severing these tracts and injecting HRP into the incision. This procedure results in filling the severed axons with HRP. Filled axons were traced to cell groups of origin and to some terminations of the acoustic striae. HRP‐labeled terminals were found in the cochlear nuclei as well as in periolivary cell groups. Filling of cells with HRP ranged from being complete, resulting in Golgi‐like images, to being barely detectable. Labeled cells were abundant in the dorsal and posteroventral cochlear nucleus adjacent to the injection as well as scatered throughout the periolivary cell groups of both sides, being highest in concentration around the ipsilateral lateral superior olive. On the side contralateral to the injection, labeled cells were found along the medial border of the dorsal cochlear nucleus, in the interstitial nucleus of the stria of Held, and sparsely throughout the ventral cochlear nucleus. The distribution of labeled cells was similar following HRP injections of the dorsal cochlear nucleus, except that these injections revealed additional descending projections from the inferior colliculi and from the ventral nucleus of the trapezoid body of both sides. These additional projections were interpreted as entering the CN by a ventral route. Findings of this study are in accord with physiological recordings made from fibers of the acoustic striae.
Recovery from the effects of monocular deprivation in kittens
Authors: Mitchell Donald E. , Cynader Max , Anthony Movshon J.
Published: January 2005

Significant recovery from the effects of early unilateral eye closure has been found following a period of reversed deprivation involving forced usage of the deprived eye. A simple period of binocular vision, however, has been reported to be ineffective. We have compared these two recovery conditions (reversed deprivation and binocular vision) in kittens initially deprived to the age of 45 or 60 days, and given seven to eight weeks of recovery. We estimated behavioral recovery by measuring visual acuity through the deprived eye. Kittens deprived to day 45 attained nearly normal grating resolution in their deprived eyes (5–6 cycles/degree), while those deprived to day 60 showed enduring partial acuity deficits (4–5 cycles/degree). Surprisingly, the deprived eye's acuity in kittens given binocular vision during recovery was nearly the same as that possessed by the deprived eyes of reverse‐deprived kittens. We estimated physiological recovery from the visual response properties and eye dominance of 359 cortical neurons; all kittens showed shifts in eye dominance from the situation that obtains after a period of deprivation. Reverse‐deprived kittens, in agreement with previous reports, showed more pronounced shifts of cortical eye dominance than did binocularly recovered kittens. Nevertheless, significant recovery of both the deprived eye's influence and of the selectivity of its receptive fields was seen in kittens given binocular vision. In no case was there significant recovery of cortical binocular interaction: most neurons were monocularly driven, and were aggregated into ocular dominance columns strongly dominated by one eye or the other. Since both behavioral and electrophysiological measurements suggest considerable recovery of function even in cases where kittens were merely given binocular vision during recovery, we conclude that the two eyes'effectiveness is not solely determined by competitive interaction – significant changes can occur when neither eye has a competitive advantage over the other.
Cytoarchitectonic analysis of the bullfrog (Rana catesbeiana) spinal cord by means of electron microscopy with special reference to distribution of microneurons
Authors: Sasaki Hiroshi
Published: January 2005

In order to determine cytological nature of the “small cells” found in the dorsal half of the bullfrog spinal cord at the electron microscopic level, the complete mapping of these elements was carried out, using both paraffin and thick sections. Asa result, these elements were demonstrated to have four main fine structural characteristics of an unequivocally neuronal nature: (1) synaptic contacts, (2) subsurface cisternae, (3) typical pattern of the rough‐surfaced endoplasmic reticulum, and (4) close contacts of astroglial proc‐esses with the somal surface.

The most prominent features in the bullfrog spinal cord can be summarized as follows: the microneurons occupy the dorsal region as well as the region around the central canal of the gray, and the most dorsal part of the gray in exclusively occupied by these microneurons. They show, furthermore, a tendency to separate grossly into medial and lateral groups. No microneurons are visible in the ventral horn. According to the results obtained from the cytoarchitectonic com‐parison of the bullfrog spinal cord and the rat spinal cord, it can be said that in the former no differentiated laminar structures can be recognized, while in the latter the gray matter is sufficiently differentiated to permit full percellation.
An electron microscope observation of the right and the two left portions of the habenular nuclei of the frog
Authors: Kemali Milena , Guglielmotti Vittorio
Published: January 2005

The right dorsal habenula (RDH), the left dorsal habenula, lateral portion(LDH‐LP) and the left dorsal habenula, medial portion (LDH‐MP) of the adult frog Rana esculenta have been studied by the electron microscope with the use of three types of fixatives: osmium tetroxide, aldehydes and potassium permanganate.

The study has demonstrated in the habenulae of both sides a variety of synaptic vesicles, special synaptic patterns (en passant, serial, axo‐somatic) containing small spherical transparent vesicles, never mixed with other types of vesicles, and large pale processes containing big granules. However, a particular type of synaptic vesicles characterized by small clear spherical vesicles with a tiny dark granule revealed by potassium permanganate fixation has been demonstrated only in the neuropil of the LDH and not in the RDH. Further, a peculiar type of intracytoplasmic inclusion appears in the form of myelin‐like and crystal‐like formations only in the LDH‐MP.

On the basis of these consistent ultrastructural differences, the dorsal habenular nuclei of the frog can be considered as composed of three individual nuclei, each with its own morphological characterization, dislocated, for some unknown reason, one on the right and two on the left side of the epithalamus.

The results suggest that the LDH‐MP is a nucleus metabolically different from the others and that the projections to the dorsal habenular nuclei are different on the right and left sides of the brain.
Neurophysiology of spastic, a behavior mutant of the mexican axolotl: Altered vestibular projection to cerebellar auricle and area acoustico‐lateralis
Authors: Ide Charles F.
Published: January 2005

The spastic mutant of Ambystoma mexicanum shows deficiencies in swimming coordination and equilibrium. Behavior “phenocopy” experiments done previously indicated that vestibular projections to cerebellum and hindbrain interneurons might be responsible for mutant behavior patterns. To test function in mutant vestibular projections, single unit recordings were carried out in the vestibulo‐cerebellum (auricle) and hindbrain area acousticolateralis (AAL) of wild‐type and mutant animals in response to natural vestibular stimulation. Vestibular unit types responding during longitudinal tilting or to sustained tilt were encountered in equal proportions in both animal types. However, mutants showed a significant increase in spontaneously active units in these areas indicating possible deficiencies in inhibitory circuitry. In addition, the topographic location of vestibular units changed under the influence of the spastic gene. In mutants, significant numbers of units were found “translocated” into a ventro‐caudal auricular zone abutting the AAL. Anatomical studies detailed in the following paper have shown this same area to contain grossly “translocated” cerebellar cells and afferent fiber tracts in mutants. These data are drawn together in a model in which deficiencies in the (form and) inhibitory function of the vestibulo‐cerebellum is postulated to underly the behavioral abnormalities of the spastic phenotype.
The cytoarchitecture of the torus semicircularis in the Tegu lizard, Tupinambis nigropunctatus
Authors: Browner Robert H. , Rubinson Kalman
Published: January 2005

The torus semicircularis (TS) of the Tegu lizard extends from the superficial caudal mesencephalon, dorsal to the exiting trochlear nerve, to a position ventral to the middle part of the optic tectum and its ventricle. It has an oblique orientation with the caudal pole abutting the midline while the rostral end is lateral and slightly ventral. The TS consists of a central nucleus and several adjacent cell groups. The central nucleus and the laminar nucleus, situated medially, extend the entire length of the TS while the cortical nucleus, situated dorsally and laterally, is present only in the caudal superficial portion. The central nucleus is composed of ovoid neurons with branched, radiating dendrites. The dendrites are directed medially and laterally with spines on the distal portion of the dendritic tree. The laminar nucleus consists of three to five neuronal layers. It is mainly composed of fusiform neurons with one dendritic trunk from each extremity of the soma. There is little branching and few dendritic spines.

The cortical nucleus is a laminated region consisting of alternating layers of neurons and lateral lemniscal fibers. The neurons of the superficial layers are fusiform with their long axis perpendicular to the long axis of the brainstem. They possess two main dendritic trunks which parallel the laminae and are covered with dendritic spines. The deeper layers consist of pyramidal neurons with three dendritic trunks, secondary branches, and few spines. The long axis of these neurons extends from the center of the TS to the periphery. Two dendritic trunks extend dorsally or laterally towards the surface, while the third extends towards the central nucleus. The dendrites, thus, extend across the laminae. In addition, a cell‐free lateral zone is described.
Receptive field characteristics of superior colliculus neurons and visually guided behavior in dark‐reared hamsters
Authors: Rhoades Robert W. , Chalupa Leo M.
Published: January 2005

Visual response properties of single neurons in the superior colliculus of golden hamsters reared from birth to adulthood in total darkness were compared to those of normal hamsters. Directional selectivity, speed preferences, and receptive field organization in dark‐reared hamsters were essentially the same as those found in normally reared animals. Subtle neurophysiological effects of visual deprivation were indicated by the longer latencies of “on” responses to flashed spots of light in the dark‐reared animals. Also, in the visually deprived animals three cells were encountered which changed their responses from phasic to tonic as the size of the visual stimulus was increased. In normally reared animals all cells responding to stationary stimuli showed only phasic responses regardless of spot size. Behaviorally, dark‐reared animals could not be distinguished from normal animals on the basis of visual orienting and following tests. It was concluded that in the golden hamster visual experience during development has a minimal role in the induction or maintenance of the normal functional development of the superior colliculus.
Physiological and morphological changes in cells of the lateral geniculate nucleus in monocularly‐deprived andreverse‐sutured cats
Authors: Hoffman Klaus‐Peter , Holländer Horstmar
Published: January 2005

In the present study the size of large samples of cells and the relative frequency of Y‐cells were measured in the lateral geniculate nucleus of monocularly‐deprived and reverse‐sutured cats. Due to deprivation large cells shrink more than smaller cells. This shrinkage is irreversible even over two years of reverse suture although over the same time the animals showed a remarkable pattern discrimination ability, which, in these animals, depends on the integrity of the geniculo‐cortical system. Physiologically, a significant increase in the probability of recording Y‐cells in the early‐deprived laminae of the LGNd was found after a reverse suture. The relative frequency of Y‐cells in the earlydeprived layers and in the late‐deprived layers was almost equal and not different from normal, although after the early deprivation by itself only 20% Y‐cells were found in the deprived layers. The latter results confirm our previous observation (Sherman et al., '72). The increase in the number of recorded Y‐cells following a reverse suture after monocular deprivation is accompanied by only small changes in the distribution of cell sizes in the LGNd. The number of very large cells in the early‐deprived layers was increased but the mean cell size remained unaltered after long forced usage of the deprived eye.
Interlaminar connections of the visual cortex in the hedgehog (Paraechinus hypomelas)
Authors: Gould Harry J. , Ebner Ford F.
Published: January 2005

The contribution of each cortical lamina to intracortical circuitry was studied in the visual neocortex of the Pakistani hedgehog. Punctate laminar lesions were made electrolytically within the visual cortex, and after five to seven days the brains were processed and stained with the Fink‐Heimer technique. The results of this study suggest that both horizontal and vertical connections are important to the organization of visual cortex in the hedgehog. The horizontal projections originate at three distinct cortical depths. Lesions in layer II reveal projections that traverse the inner one‐half of layer I; lesions in layers III and IV reveal projections that traverse layer IV and that enter the cortical white matter; lesions in layers V and VI reveal projections that traverse the outer one‐half of layer VI and that enter the cortical white matter. The vertical projections are oriented perpendicular to the pial surface. Layers II and III project to underlying layer V. Layers V and VI in turn contribute to a reciprocal projection back to all superficial cortical laminae. This anatomical data about intracortical circuitry is discussed with reference to the functional organization of visual cortex.
The neurons and the synaptic endings in the primate basilar pontine gray
Authors: Cooper Margaret H. , Beal John A.
Published: January 2005

Two types of neurons, projection and intrinsic, previously identified in Golgi preparations of the adult monkey (Macaca mulatta) basilar pontine gray (Cooper and Fox, 1976) were observed electronmicroscopically in Macaca mulatta and the squirrel monkey Saimiri sciureus. The cell body of the projection neuron measures up to 37 μ and its cytoplasm is rich in organelles. The Golgi apparatus, ribosomes, and mitochondria are disposed around the nucleus, while rough endoplasmic reticulum though abundant is usually confined to one half of the cell body. The cell body of the intrinsic neuron measures less than 20 μ and its cytoplasm displays prominent ribosomes, but a paucity of other organelles.

Five types of synaptic profiles have been identified in the neuropil of the basilar pons; one measures up to 5 μ and the rest 2 μ or less. They are: (1) a large profile (MSV) containing medium size vesicles (500 Å) and a central core of mitochondria and neurofilaments; (2) a profile (SSV) containing small round vesicles (250‐500 Å) which is the most abundant and ubiquitous; (3) a profile (F) containing flattened or pleomorphic vesicles; (4) a profile (LSV) containing large oval egg shaped vesicles (750 Å); and (5) a pale profile (PP) that contains oval and occasionally pleomorphic vesicles. MSV, SSV, and LSV terminals form asymmetrical contacts and F terminals form symmetrical contacts with both dendritic and vesicle‐containing, pale profiles. The vesicle‐containing, pale profile is both pre‐ and post‐synaptic and participates in serial synapses. Following unilateral cortical ablations both dark and filamentous degeneration were observed in the ipsilateral basilar pontine gray.
Converging projections from the mediodorsal thalamic nucleus and mesencephalic dopaminergic neurons to the neocortex in three species
Authors: Divac I. , Björklund A. , Lindvall O. , Passingham R. E.
Published: January 2005

Previous studies in the rat have shown that the neocortical dopaminergic afferents, originating in the mesencephalon, terminate in those areas of the forntal lobe which receive projections from the mediodorsal thalamic nucleus i.e., the prefrontal cortex. In order to clarify whether this overlap is accidental for the rat or a consistent feature of several species we have compared the projection areas of the ventral tegmental area and the mediodorsal thalamic nucleus in three species, rat, opossum and tree shrew, using HRP injections in combination with glyoxylic acid histofluorescence method. The results have shown, first, that the area innervated by the mediodorsal nucleus of the thalamus is localized in a different part of the frontal lobe in each species: dorsolateral in the opossum, anteromedial, polar and suprarhinal in the rat and frontopolar in the tree shrew. Secondly, this area alone in each species receives dense innervation in the deep cortical layers by fluorescent fibres probably containing dopamine. The neighbouring neocortical areas receive afferents neither from the mediodorsal nucleus of the thalamus nor from the ventral mesencephalic tegmentum; their catecholamine innervation is mainly confined to the superficial layers and appears to be of noradrenergic nature. Although the techniques used did not allow a precise determination of the borders of the two projection areas and, therefore, the exact degree of overlap, it appears that mesencephalic dopaminergic innervation is a characteristic feature of the prefrontal cortex in the mammalian brain.
Structure of the leech nerve cord: Distribution of neurons and organization of fiber pathways
Authors: Fernandez Juan
Published: January 2005

The abdominal nerve cord of the leech Macrobdella decora was studied under the light and electron microscopes. The ganglionic cortex consists of six hemicone‐shaped packets of neuronal perikarya and apical processes regularly assembled in bilaterally symmetric rows. The orderly projection of the apical processes into the hilum of the packets is also followed by an orderly distribution of their branches across the neuropile. This part of the ganglion is made of two symmetrical halves or hemineuropiles enclosing two types of nerve tissue: coarse and fine neuropiles. The coarse neuropile has seven longitudinal and four commissural tracts of fibers and a distinctively segregated synaptic zone. Nerve processes in this neuropile mostly proceed from neurons in the ganglia and some are the branches of giant afferent axons. The fine neuropile includes several longitudinal tracts of fibers and a non‐segregated synaptic zone. Most nerve processes in this neuropile are small afferent axons and some come from neurons in the ganglia. Bundles of axons in the connectives result by the orderly projection of the neuropile longitudinal tracts and together form fiber pathways connecting the synaptic zones of successive ganglia. Pathways of through‐ganglia giant axons, linking the coarse neuropile synaptic zones, and of small axons, linking the fine neuropile synaptic zones, are described.
Characterization of various nervous tissues of the chick embryos through responses to chronic application and immunocytochemistry of β‐bungarotoxin
Authors: Hirokawa Nobutaka
Published: January 2005

β‐Bungarotoxin (β‐BT) was applied to chick embryos at 3‐day intervals beginning on the fourth day of incubation to investigate ultrastructurally the effects of chronically and massively applied β‐BT on various nervous tissues and muscles. On the twenty‐first day of incubation, spinal cords of β‐BT treated embryos were conspicuously decreased in size. Ventral root fibers, dorsal root fibers, white matter, and motor neurons disappeared. Although spinal ganglia and sympathetic trunk ganglia were completely absent, Auerbach's and Meissner's ganglia nerve cells in the small intestine and adrenal medullary cells were not affected. In retinas of β‐BT treated animals ganglion cells and optic nerve fibers disappeared, but photoreceptor cells, bipolar cells and horizontal cells remained intact. Furthermore, olfactory nerve cells and their unmyelinated nerve fibers ensheathed by Schwann cells were quite undamaged. Skeletal muscles degenerated, whereas cardiac muscles were unaffected. In the present study various nervous tissues of the twenty‐first day normal chick embryos were incubated with β‐BT and target cells of β‐BT were detected directly by the reaction with horseradish peroxidase labelled anti β‐BT guinea pig IgG. Motor nerve cells in the spinal cords, spinal and sympathetic ganglia nerve cells, ganglion cells and some nerve cells at the inner part of the inner nuclear layer in the retinas were positively stained, whereas Auerbach's and Meissner's ganglia nerve cells in the small intestine, adrenal medullary cells, photoreceptor cells, bipolar cells and horizontal cells in the retina and olfactory nerve cells were negative. Thus the present study shows that β‐BT has extensive destructive effects on various nerve cells which were revealed to be target neurons of β‐BT by immunocytochemistry. Those nerve cells, affected by β‐BT and positively stained with immunocytochemical reaction were supposed to have different characteristics from unaffected cells. One of the differences between these affected cells and unaffected cells may be whether there exist binding sites for β‐BT on the plasma membrane or not. The possibility of the use of β‐BT to characterize various nervous tissues is presented in the present study.
The organization of the hippocampus of the fence lizard: A light microscopic study
Authors: J. Lacey Daniel
Published: January 2005

The hippocampus of the fence lizard (Sceloporus undulatus) is composed of two laminated regions that are readily distinguishable on the basis of position and perikaryal size in Nissl preparations: the small‐celled (Hsc) and the large‐celled (Hlc) hippocampal divisions. Based upon cellular and fibrillar characteristics, the layers of the Hsc are: (1) the superficial plexiform layer; (2) the cellular layer; (3) the deep plexiform layer; (4) the layer of deep fibers, or alveus; and, (5) the ventricular ependyma. The layers of the Hlc are: (1) the tangential layer; (2) the molecular layer; (3) the pyramidal layer; (4) the deep plexiform layer; (5) the alveus; and, (6) the ventricular ependyma. The neurons of each hippocampal layer were grouped into classes based upon somal position and appearance, and dendritic and axonal arborization patterns in Golgi sections. Neurons of the Hsc are more numerous and pleomorphic than those of the Hlc. Data do not suggest an intrinsic organization that closely parallels that found in the mammalian hippocampus.
The organization of monoamine‐containing neurons in the brain of the sunfish (Lepomis gibbosus) as revealed by fluorescence microscopy
Authors: Parent A. , Dube L. , Braford M. R. , Northcutt R. G.
Published: January 2005

The morphological organization of the monoamine‐containing neurons in the brain of the sunfish (Lepomis gibbosus) was studied by means of the Falck‐Hillarp histofluorescence method. No attempt was made to distinguish between norepinephrine and dopamine, both primary catecholamines (CA) yielding a similar yellow‐green fluorescence after paraformaldehyde treatment. In the brain stem of this teleost fish, three groups of CA‐containing neuronal somata have been found. First, there is a small collection of CA perikarya located just caudal to the obex of the fourth ventricle. The neurons of this medullo‐spinal group give rise to numerous CA fibers many of which ascend within the central portion of the medulla. Intermingled with these CA fibers are some CA cells that constitute the central medullary group. The CA perikarya of this group are scattered between the levels of cranial nerves X and VIII. The tegmentum of the isthmus also contains a small group of very closely packed CA neurons. The large‐sized CA cells of the isthmal group are located dorsolateral to the medial longitudinal fasciculus, partly within the periventricular gray. High densities of CA varicosities were also disclosed in various brain stem structures such as the optic tectum, the torus semicircularis and the cerebellar valvula. In addition, numerous serotonin (5‐HT)‐type neuronal somata were found in the raphe region of the brain stem, particularly at caudal mesencephalic, isthmal and rostral medullar levels.

A large number of CA cell bodies were visualized in the sunfish hypothalamus. Most of them form two populations of small, round cells that are located along and partly within the ependymal walls of the posterior and lateral recesses of the third ventricle. These bipolar cells possess one short club‐like process protruding into the ventricle and their thin ependymofugal processes contribute to the CA innervation of numerous hypothalamic regions. Large CA neurons apparently without direct CSF contact also occur in the area of nucleus posterior tuberis, at the level of the mesodiencephalic junction. Although the hypothalamic inferior lobes are devoid of CA cell bodies they are heavily innervated by CA axons.

The sunfish telencephalon also receives a strikingly massive and complex monoaminergic innervation. Numerous CA fibers which are first observed at the level of the preoptic area, ascend through the central zone of the telencephalon and arborize profusely particularly within the medial zone of area dorsalis telencephali. Other CA fibers, as well as abundant fine 5‐HT varicosities were found in the lateral zone of area dorsalis. Although the exact origin of the telencephalic CA afferents in Lepomis is not known, part of it may arise from the isthmal CA cell group which appears similar to the locus coeruleus of reptiles, birds and mammals.
Topography of estrogen target cell in the forebrain of goldfish, Carassius auratus
Authors: Kim Ye Soon , Stumpf Walter E. , Sar Madhbananda
Published: January 2005

The topographical distribution of estradiol‐concentrating cells in the brain of male and female teleost, Carassis auratus, was determined by autoradiography, after injection of 3H estradiol‐17β. Radioactively labeled neurons and found in specific regions of the forebrain, with a similar topographical distribution both in males and females. Regions of accumulation of estrogen target cells include the supracommissural area of the telencephalon, the preoptic area, the central hypothalamic area and the thalamic area. Unlabeld estradiol injected prior to the administration of 3H estradiol reduces or eliminates nuclear uptake of radioactivity.

The autoradiographic results demonstrate the existence of estrogen target neurons in the teleost forebrain at sites similar to those described in mammalian brains. However, under the conditions of the experiment, there exists no pallial representation of estrogen target cells.
A raphe dendrite bundle in the rabbit medulla
Authors: Cummings John P. , Felten David L.
Published: January 2005

A Golgi‐Cox, histofluorescence, and electron microscopic examination of the serotonergic raphe nuclei of the rabbit medulla has revealed a large, vertically‐oriented midline dendrite bundle extending from the floor of the fourth ventricle to the ventral boundary of nucleus raphe pallidus. The bundle was confined to the medulla, and averaged 150–200 μm in width in the adult. This dendrite bundle received contributions from four major sources: (1) Dendrites of midline and paramedian neurons of nucleus raphe obscurus; (2) Dendrites of midline and paramedian neurons of nucleus raphe pallidus; (3) Shafts from tanycytes located on the midline floor of the fourth ventricle; and (4) Dendrites from neurons of the medullary reticular formation. Perikarya and dendrites of serotonergic raphe neurons frequently abutted tanycyte shafts, midline blood vessels, and perikarya and dendrites of other raphe neurons. The tanycyte shafts extended from the floor of the fourth ventricle into the bundle, and often ran the entire length of the bundle, where they intertwined themselves among neurons and dendrites of the medullary raphe nuclei. This study suggests that neurons of the medullary raphe may be influenced by communication channels including dendro‐dendritic contacts within the midline bundle, fourth ventricular cerebrospinal fluid‐borne influences through tanycyte shafts, blood‐borne influences through the direct neuronal‐vascular relationship in the raphe, and traditionally described axonal contacts impinging upon raphe neurons. We suggest that the raphe neurons might act as both neurons and endocrine‐neural transducer cells.
The development of the septal region in the rat. II. Morphogenesis in normal and X‐irradiated embryos
Authors: Bayer Shirley A.
Published: January 2005

Morphogenesis of the septal region was examined in normal rat embryos from embryonic day (E) 10 to E22. The greater part of the septal region is postulated to form from two separate anlagen which can be clearly distinguished in the telencephalon by E13 and E14. One lies in the anterior ventromedial wall and presumably forms the nucleus of the diagonal band, medial, lateral, and triangular septal nuclei. The other lies in the posterior ventrolateral ridge and presumably forms the bed nuclei of the stria terminalis and the anterior commissure. On E15, the early differentiating cells in these anlagen fuse in the same region where the anterior commissure will cross on E17. With later embryonic development, differentiating cells of the strial bed nucleus accumulate rostral and caudal to the fused area. The same pattern is found in the medial and triangular septal nuclei and in the nucleus of the diagonal band. The differentiating cells of the lateral septal nucleus accumulate dorsal and lateral to the medial and triangular septal nuclei. On E16 and E17, a prominent subependymal zone develops in the anterior septal region and presumably gives rise to the nucleus accumbens.

A quantitative analysis was made of three cell zones (neuroepithelium, subependymal zone, differentiating cell zone) at coronal levels through the developing nucleus accumbens and the nucleus of the diagonal band (anterior level) and the medial and lateral septal nuclei (middle and posterior levels). At all levels, the area of the neuroepithelium continually declines, that of the differentiating cell zone continually increases, and that of the subependymal zone shows a rise and decline. On a proportional basis, both the neuroepithelium and subependymal zone occupy significantly more area anteriorly than posteriorly, while the differentiating cell zone shows the reverse gradient. To accurately locate regions of primitive mitotic and migratory cells within the zones at each level, the number of cells surviving a single exposure to 200 R X‐rays in embryonic brains (E15‐E22) were compared with controls. Each zone responded differently to X‐ray insult. The radiosensitivity of the neuroepithelium decreases significantly after E19; the subependymal zone is highly radiosensitive throughout; the differentiating cell zone is radioresistant throughout. The significance of these findings is discussed in the light of the autoradiographic determination of the time of formation of septal neurons (Bayer, '79).
The morphology of local non‐spiking interneurones in the metathoracic ganglion of the locust
Authors: Siegler M. V. S. , Burrows M.
Published: January 2005

The morphology is described of a number of non‐spiking interneurones in the metathoracic ganglion of the locust that control motor neurones innervating muscles in the coxa and femur of a hind leg. The nonspiking interneurones are penetrated with microelectrodes, physiologically characterized, injected with cobalt, and the stain subsequently intensified with silver. The interneurones have diverse shapes but all are local, intraganglionic interneurones. Their cell bodies are 10–20 μm in diameter and lie in either the ventral or dorsal layers of cell bodies that form a cortex around the ganglion. The branches of the interneurones are profuse and overlap those of the motor neurones that they affect. One interneurone may have branches in both the most ventral and the most dorsal areas of the neuropile. Most interneurones have branches only in one half of the ganglion, but one interneurone has extensive and asymmetrical regions of branches in both halves of the ganglion (fig. 4). Similar physiological effects can be mediated by interneurones with distinct morphologies. For example, the single slow extensor motor neurone is excited by six distinct morphological types of interneurones (figs. 10–13). It is suggested that as many as 65% of the neurones within a ganglion may be local interneurones, many of which in turn may be non‐spiking.
Organization of trigeminothalamic tracts and other thalamic afferent systems of the brainstem in the rat: Presence of gelatinosa neurons with thalamic connections
Authors: Fukushima Takanori , Kerr Frederick W. L.
Published: January 2005

Thalamic projections from trigeminal and certain other nuclei of the brainstem of the rat have been investigated using the technique of retrograde transport of horseradish peroxidase (HRP).

The pattern of trigeminothalamic projections is very specifically related to the individual subnuclei of the complex. The Main Sensory Nucleus (MSN) provides profuse crossed connections to the ventrobasal thalamus (VB); these arise exclusively from medium and small‐sized neurons, but never from the large cells. In addition to these crossed connections, a small ipsilateral dorsal trigeminothalamic tract arises from the dorsal third of the most rostral part of the MSN; this is the only ipsilateral connection to VB found in the trigeminal complex.

Subnucleus Oralis has no projections to the thalamus; it is suggested that it may be concerned primarily with reflex activation of the facial nucleus, with which it is co‐extensive in the rostro‐caudal axis.

Subnucleus Interpolaris has a well‐defined crossed projection of moderate size which arises from the large, medium and some of the small neurons.

Subnucleus Caudalis has a sparse output to the thalamus and differs in its projections from rostral to caudal. At the most rostral level, all layers (marginal, transitional gelatinosa and magnocellularis) contain neurons which project to the thalamus; particularly conspicuous in this respect are the marginal neurons, most of which are strongly labelled. The presence of gelatinosa neurons projecting to the thalamus emphasizes a point made in earlier reports, that these neurons do not form an homogeneous population. At caudal levels, the marginal neurons are the major source of thalamic projections, while connections to the thalamus form deeper lying neurons are infrequent.

With a single exception, the medullary reticular nuclei contained no neurons with thalamic connections; a small number of reticulo‐thalamic neurons were found in the ventral pontine area.

Marked labelling of the medial cuneate nucleus and moderate labelling of the gracilis and lateral cuneate nuclei occurred contralaterally to the injection site. A small number of medial cuneate and gracile neurons project to the ipsilateral thalamus. Projections from the solitary nucleus were always ipsilateral.

The boundaries of individual subnuclei of the lateral sensory trigeminal complex in the rat have been redefined on the basis of cytological criteria; these are in good accord with the corresponding thalamic projection patterns.
Evidence for a critical period of neuronal trophism late in the development of the chick visual system
Authors: Ostrach Louis H. , Mathers Lawrence H.
Published: January 2005

Chick embryos and young hatchling chicks have undergone unilateral retinal ablation and the brains were subsequently prepared for modified Fink‐Heimer staining to detect degenerating axoplasm. Additional animals have been injected with tritiated proline or combinations of tritiated proline and tritiated fucose. In examining the patterns of degeneration and labelling produced, it appears that during the stage 40–44 period of embryonic life there is a critical period during which damage to retinal axons produces degeneration not only in the direct targets of the optic tract (primary centers), but also in a number of nuclei not projected to by the optic tract (secondary centers). By examining various survival times following retinal ablation and animals of varying embryonic and post‐hatch age, we have concluded that retinal ablation during the critical period causes a rapid and fulminant degeneration in the secondary centers because they are all targets of the projection from the optic tectum, itself a prime target of the optic projection. Presumably, interruption of the retino‐tectal projection during the critical period disrupts some as yet undefined trophic relationship between these two sets of neurons. Our studies show that the observed degenerative reaction in the secondary centers occurs most strongly in chick embryos between stage 40 and stage 44. This period coincides with the onset of synaptogenesis in the retino‐tectal system (Rager, '76a,b). We therefore hypothesize that during this period some property or influence is passing from the retinal to the tectal neurons such that interruption of this process leads to death of the tectal neurons.
Proliferative and migratory activity of glial cells in the partially deafferented hippocampus
Authors: Gall Christine , Rose Greg , Lynch Gary
Published: January 2005

The proliferative response of the glial cell population of the adult rat hippocampus deafferented by unilateral lesion of the entorhinal cortex was studied using 3H‐thymidine autoradiography. Two experimental paradigms were used, involving: (1) intraventricular 3H‐thymidine injection at a number of post‐lesion intervals with sacrifice six hours later and (2) intraventricular injection at 30 hours post‐lesion with sacrifice at 6, 96, or 192 hours later.

The first increase in the number of labeled glial cells was obtained at 20 hours post‐lesion and was confined to areas of degenerating axons. By 30 hours a large and uniformly dense proliferative response was observed throughout the ipsilateral, and medial aspects of the contralateral, hippocampus encompassing both deafferented and intact regions. Cell division continued through 50 and 65 hours post‐lesion particularly in directly deafferented regions, but diminished to control levels by 80 hours. Although oligodendroglia and astrocyte‐like cells were sometimes found to have incorporated the label the most common proliferative element within the hippocampus corresponded to previous light microscopic descriptions of “microglial” cells. The experiments using thymidine injection given at the peak proliferative period followed by survival periods of varying lengths indicated that a progressive redistribution of labeled nuclei occurred resulting in an accumulation of labeled cells in the zones of deafferentation. Multiple division of cells within these areas as well as the migration of nuclei from non‐deafferented regions was found to contribute to this effect. The possible involvement of glial proliferation with other morphological effects of deafferentation, including the sprouting response of intact afferents, is discussed.
Evidence for two organizational plans within the somatic sensory‐motor cortex of the rat
Authors: Donoghue John P. , Kerman Karen L. , Ebner Ford F.
Published: January 2005

Previous electrophysiological mapping of somatic sensory (SI) and motor (MI) cortex in the rat has shown that these functional regions are completely overlapping in the hindlimb (HL) area. Partially separate in the forelimb area, and completel separate in the face area. The present studies were designed to show how the sensory and motor thalamic relay nuclei priject onto separate or overlapping subdivisions of SI and MI cortex. The experimental sequence involved physiological mapping of one subdivision of SI or MI cortex and then injecting horseradish peroxidase (HRP) as a retrograde cell marker to back‐fill the thalamic neurons that project to the identified area of cortex. The central issue was to compare the projection of the lemniscal‐recipient ventrobasal nucleus (VB) and the cerebellar‐recipient ventrolateral nucleus (VL) to the hindlimb and face subdivision of SI and MI cortex. Various authors, however have divided the ventral nucleus differently using Nisslstained transverse sections through the thalamus. Therefore, tritiated amino acids were also injected into the deep cerebellar nuclei and the distribution of cerebellar fiber terminals in the ventral nucleus was used as another criterion to identify the border between VB and VL.

Following HRP injections in physiologically identified HL cortex, labelled neurons were present in both VB an VL. Face area SI injections back‐filled cells in VB (but not VL), while face area MI injections back‐filled cells in VL (but not VB). Neurons in the intralminar nuclei and the posterior nuclear complex were labelled after all injections.

These results demonstrate that SI and MI cortex in the rat shows a combiation of overlapping and separated plans of organization. Other species, in which both the anatomical an physiological information is available, show other organizational plans. In the Virginia opssum, for example, overlap is present in all subregions of SI and MI cortex. While the Rhesus monkey shows separation of these areas. The result suggest that different mammals have evolved different degrees of separation of SI and MI cortex. Our results predict that in every case where there is evidence of sensory and motor overlap, there will be anatomical convergence of VB and VL projections to htat single cortical area.