bluuebunny/crossref_metadata_2025 huggingface dataset:
Localization of choline acetyltransferase‐like immunoreactivity in the embryonic chick retina
Authors: Spira Arthur W. , Millar Thomas J. , Ishimoto Ichiro , Epstein Miles L. , Johnson Carl D. , Dahl June L. , Morgan Ian G.
Published: January 2005

Putative sites of acetylcholine synthesis in the retina of the embryonic and posthatched chick were localized immunohistochemically with antisera to choline acetyltransferase; the resultant choline acetyltransferase‐like immunoreactivity (ChAT‐IR) was compared to demonstrated sites of acetyltransferase (AChE) activity, and changes were followed in localization during development. The results confirmed the early and rapid course of development of the chick's retinal cholinergic system described in previous biochemical and morphological studies. Immunoreactivity was first detected at embryonic day 6.5 in cells close to the retina's vitreal surface. By 8 days it was present in cells in two juxtaposed rows; by the ninth day the two rows were separated and Immunoreactivity was evident in two sublaminae of the inner plexiform layer. On the tenth day distribution was like that in the posthatched chicken, in type I cholinergic cells in the inner nuclear layer and in type II cells in the ganglion cell layer (Millar et al.: Neurosci. Lett. 61:311–316, '85.), and similar to that of most vertebrates. Three days before hatching, a third population of weakly immunoreactive cells (type III cells) appeared within the inner nuclear layer. The onset of localizable ChAT‐IR occurred in amacrine cells and in their processes, before the period of synaptogenesis. Acetylcholinesterase activity was localized at an earlier age than ChAT‐IR, and at all ages was present in more cells. The results obtained support the view that “displaced” cholinergic amacrine cells begin to differentiate at the same time and in the same retinal region as type I cholinergic cells. Separation of the two groups is a consequence of the ramification of processes of amacrine and ganglion cells rather than a result of the secondary migration of cells between layers.
Distribution of neurotensin‐like immunoreactivity in the diencephalon of the Japanese monkey (Macaca fuscata)
Authors: Makino Shigeru , Okamura Hitoshi , Morimoto Nobumitsu , Abe Jun , Yanaihara Noboru , Ibata Yasuhiko
Published: January 2005

The distribution of neurotensin‐like immunoreactive (NT‐LI) neurons was examined in the thalamus and hypothalamus of the Japanese monkey (Macaca fuscata) by using the peroxidase‐antiperoxidase immunocytochemistry technique. In the thalamus, NT‐LI neuronal perikarya were distributed mainly in the midline nuclear group and the dorsomedial nucleus, and partially in the intralaminar nucleus: Immunoreactive fibers were mainly distributed in the midline nucleus, particularly in the nucleus rhomboidalis. Numerous immunoreactive fibers were also detected in the regions that contain the pathways to extrathalamic areas such as the stratum zonale and inferior thalamic peduncle. In the hypothalamus, many immunoreactive neuronal perikarya were distributed in the lateral hypothalamic area and in the arcuate nucleus. Immunoreactive fibers were disseminated throughout the hypothalamus, but they were dense in the preoptic area and sparse in the ventromedial nucleus. An accumulation of dense immunoreactive endings was also observed in the external layer of the median eminence. NT‐LI fibers in the extenal layer of the median eminence were considered to represent nerve endings near portal vessels. Functional roles of neurotensin in the thalamus and hypothalamus are discussed from the anatomical point of view.
Morphology of corticotectal cells in the primary visual cortex of hooded rats
Authors: Schofield Brett R. , Hallman L. Eric , Lin Chia‐Sheng
Published: January 2005

In primary visual cortex of hooded rats, pyramidal cells in layer V may be classified as long, medium, or short, on the basis of the layer in which the apical dendrite terminates. The present study determines which of these types of pyramidal cells project to the superior colliculus. Two different strategies were used to label corticotectal cells with horseradish peroxidase (HRP). In the first set of experiments, a large number of corticotectal cells were labeled by retrograde transport following injection of HRP into the superior colliculus. In the second set of experiments, single unit recording was used to identify corticotectal cells physiologically by antidromic activation from the superior colliculus. These cells were then impaled and labeled by intracellular iontophoresis of HRP. The results from both techniques suggest that only long pyramidal cells send an axon to the superior colliculus. These cells are distinguished by an apical dendrite that extends into layer I. We conclude that in hooded rats corticotectal cells in primary visual cortex are the long pyramids in layer V.
Distribution of choline acetyltransferase‐, serotonin‐, dopamine‐β‐hydroxylase‐, tyrosine hydroxylase‐immunoreactive fibers in monkey primary auditory cortex
Authors: Campbell Michael J. , Lewis David A. , Foote Stephen L. , Morrison John H.
Published: January 2005

Immunohistochemical methods were used to visualize choline acetyl‐transferase (ChAT)‐, serotonin‐, dopamine‐β‐hydroxylase (DBH)‐, and tyrosine hydroxylase (TH)‐containing fibers in the primary auditory cortex of the cynomolgus monkey (Macaca fascicularis). Each antiserum revealed a subpopulation of axons with a distinct density and laminar distribution. ChAT‐immunoreactive fibers were very dense in superficial layers, particularly in layers I, deep III, and IV, and very sparse in layers V and VI. No immunoreactive cell bodies were evident. Serotonin‐immunoreactive fibers were very dense in all cortical layers but exhibited some subtle laminar differences in fiber size and orientation. The densities of DBH‐ and TH‐immunoreactive fibers were substantially lower than the densities of both ChAT‐ and serotonin‐immunoreactive fibers, particularly in layer IV. However, there were substantial differences between the distribution of TH‐immunoreactive fibers and that of DBH‐immunoreactive fibers. For example, the density of TH‐immunoreactive fibers was substantially greater than that of DBH–immunoreactive fibers in layer I. In addition, TH‐immunoreactive fibers differed from the other three systems in that TH‐immunoreactive fibers exhibited a rostral to caudal gradient of decreasing density.

This is the first characterization of the innervation of a specific cortical region by all four of these systems and the first detailed description of the cholinergic innervation of a primate neocortical region utilizing a specific anti‐ChAT antiserum. These striking differences in density and laminar distribution suggest that the subcortical extrathalamic systems furnishing these axons differ significantly in their modulation of cortical auditory processing. These data extend observations of previous studies which revealed that the expansion and specialization of the primate neocortex is accompanied by a pronounced regional and laminar differentiation in the intracortical distribution of these highly divergent, extrathalamic afferents.
Vasopressin cells in the medial amygdala of the rat project to the lateral septum and ventral hippocampus
Authors: Caffé A. R. , van Leeuwen F. W. , Luiten P. G. M.
Published: January 2005

The rat brain contains a large number of vasopressin (VP) immunoreactive fibers, the sites of origin of which have not yet been established completely. For instance, the sources of VP fiber systems in the amygdala, ventral hippocampus (VH), mediodorsal thalamic nucleus, ventral tegmental area, and dorsal raphe yet remain obscure. These VP fibers may originate in any of the recently described extrahypothalamic VP cell groups, viz., medial amygdaloid nucleus (AME), dorsomedial hypothalamic nucleus, or locus coeruleus, since VP efferents from these cells still remain to be demonstrated. In search of AME VP efferents three approaches were followed: (1) the Phaseolus vulgaris anterograde tracing method, (2) immunocytochemistry after AME lesioning, and (3) retrograde transport of a fluorescent dye in combination with immunofluorescence. The results demonstrate that VP cells in the AME project to (1) the lateral septum (LS) by the ventral amygdalofugal pathway and (2) the VH via the amygdalohippocampal transition zone. In addition, the VP projection from the bed nucleus of the stria terminalis (BST) to the LS was confirmed. There was no indication that VP cells in the AME project through the amygdalotegmental pathway to the medulla oblongata and spinal cord. The results support the possibility that the BST and AME are an anatomical entity that may be part of the central loci controlling sexual processes in the rat.
Intrinsic circuitry involving the local axon collaterals of corticothalamic projection cells in mouse SmI cortex
Authors: White Edward L. , Keller Asaf
Published: January 2005

The objective of this study was to identify the components involved in a local synaptic circuit in the mouse cerebral cortex. The local axon collaterals of corticothalamic (CT) projection cells in the posteromedial barrel subfield area of primary somatosensory cortex were labeled by the retrograde transport of horseradish peroxidase injected into the ipsilateral thalamus. Thalamocortical (TC) axon terminals in the same region of cortex were labeled by lesion induced degeneration. CT axon terminals synapsed preferentially with dendritic shafts, whereas TC axon terminals synapsed mainly with dendritic spines. Some dendrites received both CT and TC synapses. Dendrites postsynaptic to CT axon terminals were reconstructed from serial thin sections; on the basis of their shapes and synaptic connections, these dendrites were interpreted to belong to nonspiny multipolar cells. These results indicate that a reciprocal synaptic relationship exists in the cortex between nonspiny multipolar cells and CT projection cells. Both CT projection cells and nonspiny multipolar neurons have been shown previously to receive TC synapses (White and Hersh: J. Neurocytol. 11:137–157, '82; White, Benshalom, and Hersch: J. Comp. Neurol 229:311–320, '84). These findings imply that a0 triadic relationship involving afferent input and populations of CT projection and intrinsic neurons is a basic feature of the synaptic organization of the cerebral cortex.
Distribution of acetylcholinesterase in the hippocampal region of the rabbit: II. Subiculum and hippocampus
Authors: Geneser Finn A.
Published: January 2005

The distribution of acetylcholinesterase (AChE) has been examined in two areas of the hippocampal region of the adult rabbit, viz., the subiculum and the hippocampus. AChE was demonstrated histochemically by using a modification of the Koelle copper thiocholine method. Moderate amounts of AChE were observed in the subiculum, whereas the hippocampus had a high content of this enzyme. In each area, the AChE staining displayed a distinctly stratified pattern which has been compared in detail with the fields and layers defined on the basis of cyto‐ and fibro‐architectonics. Most of the enzyme activity was confined to the neuropil, but a considerable number of nerve cell bodies were moderately or intensely stained in both the subiculum and the hippocampus.

In the subiculum, the plexiform layer showed a complex distribution of AChE, displaying four horizontal, differently stained subzones. In the cell layer, the staining was most intense in two narrow bands, one being immediately beneath the plexiform layer and the other bordering directly on the white matter. The remaining major part of the subicular cell layer generally had a low AChE content. In regio superior of the hippocampus, intense staining was observed in the deep part of the molecular layer, in a narrow suprapyramidal zone of the stratum radiatum, and in the stratum oriens. In regio inferior, very high AChE activity was present in the molecular layer, in two narrow bands bordering the mossy fiber layer superficially and at depth, and in the stratum oriens. The pyramidal cell bodies and the mossy fibers were unstained.

The distribution of AChE in the rabbit was compared with that in the rat and guinea pig; the latter two have been reported. The staining patterns of all three species share many conspicuous histochemical features, though notable species‐specific traits do exist.

Detailed consideration is given to possible structural correlates of the AChE observed in the two areas, in particular the relation to fiber systems known from either normal material or experimental investigations. A considerable portion of the enzyme is probably contained in afferents of septal origin, but it seems very likely that some of the AChE is associated with other fiber systems, the identity of which are unknown at present. A possible role of some of the AChE observed in the hippocampal region in the hydrolysis of substance P and enkephalin is discussed briefly.
The origins of cholinergic and other subcortical afferents to the thalamus in the rat
Authors: Hallanger Ann E. , Levey Allan I. , Lee Henry J. , Rye David B. , Wainer Bruce H.
Published: January 2005

The origins of the cholinergic and other afferents of several thalamic nuclei were investigated in the rat by using the retrograde transport of wheat germ agglutinin conjugated‐horseradish peroxidase in combination with the immunohistochemical localization of choline acetyltransferase immunoreactivity. Small injections placed into the reticular, ventral, laterodorsal, lateroposterior, posterior, mediodorsal, geniculate, and intralaminar nuclei resulted in several distinct patterns of retrograde labelling. As expected, the appropriate specific sensory and motor‐related subcortical structures were retrogradely labelled after injections into the principal thalamic nuclei. In addition, other basal forebrain and brainstem structures were also labelled, with their distribution dependent on the site of injection. A large percentage of these latter projections was cholinergic.

In the brainstem, the cholinergic pedunculopontine tegmental nucleus was retrogradely labelled after all thalamic injections, suggesting that it provides a widespread innervation to the thalamus. Neurons of the cholinergic laterodorsal tegmental nucleus were retrogradely labelled after injections into the anterior, laterodorsal, central medial, and mediodorsal nuclei, suggesting that it provides a projection to limbic components of the thalamus. Significant basal forebrain labelling occurred only with injections into the reticular and mediodorsal nuclei. Only injections into the reticular nucleus resulted in retrograde labelling of the cholinergic neurons in the nucleus basalis of Meynert.

The results provide evidence for an organized system of thalamic afferents arising from cholinergic and noncholinergic structures in the brainstem and basal forebrain. The brainstem structures, especially the cholinergic pedunculopontine tegmental nucleus, appear to project directly to principal thalamic nuclei, thereby providing a possible anatomical substrate for mediating the well‐known facilitory effects of brainstem stimulation upon thalamocortical transmission.
Comparative distribution of mRNAs for glutamic acid decatrboxylase, tyrosine hydroxylase, and tachykinins in the basal ganglia: An in situ hybridization study in the rodent brain
Authors: Chesselet Marie‐Francoise , Weiss Linda , Wuenschell Carol , Tobin Allan J. , Affolter Hans‐Urs
Published: January 2005

Neurotransmitter‐related messenger RNAs were detected by in situ hybridization in sections of rat and mouse brains by using 35S‐radiolabelled RNA probes transcribed from cDNAs cloned in SP6 promoter‐containing vectors. The distribution of messenger RNAs for glutamic acid decarboxylase, tachykinins (substance P and K), and tyrosine hydroxylase was examined in the striatum, pallidum, and substantia nigra. Dense clusters of silver grains were observed with the RNA probe complementary of the cellular messenger RNA for glutamic acid decarboxylase (antisense RNA) over most large neurons in the substantia nigra pars reticulata and medium‐sized to large neurons in all pallidal subdivisions. A few very densely and numerous lightly labelled medium‐sized neurons were present in the striatum. Among the areas examined, only the striatum contained neurons labelled with the antisense tachykinin RNA. Most of these neurons were of medium size, and a few were large. With the antisense tyrosine hydroxylase RNA, silver grains were found over neurons of the substantia nigra pars compacta and adjacent A10 and A8 dopaminergic cell groups. No signal was observed with RNAs identical to the cellular messenger RNA for glutamic acid decarboxylase or tachykinin (sense RNA). These results show a good correlation with immunohistochemical studies, suggesting that documented differences in the distribution and the level of glutamic acid decarboxylase, tyrosine hydroxylase, and substance P immunoreactivities in neurons of the basal ganglia are related to differences in the level of expression of the corresponding genes rather than to translation accessibility, stability, or transport of the gene products.
Spatiotemporal convergence and divergence in the rat S1 “Barrel” cortex
Authors: Armstrong‐James Michael , Fox Kevin
Published: January 2005

The size and response magnitude of receptive fields were evaluated for cells in the rat cortical barrel‐field by using standard vibrissal deflections of 1.14°. Such stimuli fell within the plateau region of stimulus‐response curves. The responses of all neurones to all vibrissae within and surrounding centre‐receptive fields were analysed for probability and latency of response. It was found that cells in supragranular layers had small centre‐receptive fields (average 1.6 vibrissae) with small excitatory surrounds (1.5 vibrissae) while cells in the granular layers had small, powerful centre‐receptive fields (1.4) with moderately large excitatory surrounds (2.6). Neurones in infragranular layers possessed large but weak centre‐receptive fields (2.6) with large surrounds (3.5).

Sixty‐four neurones in layer IV were studied, the precise locations of which were identified by using dye lesioning and cytochrome oxidase staining. There were no differences in receptive field size for cells within septa and barrel hollows, but the latter were twice as likely to produce two or more spikes per stimulus from the principal vibrissa (65% against 33%). Histological analysis showed that the principal vibrissa was synonymous with the appropriate vibrissa for the barrel on 86% (55 of 64) of occasions. A quantitative analysis of convergent input to three neighbouring barrels (E1, E2, and D1) showed considerable graded overlap of receptive field surrounds, although facial hair adjacent to the mystacial pad only influenced cells on the edge of the barrel‐field. Individual vibrissae exhibited significant divergent input to adjacent inappropriate barrels, being preferentially directed to distant septal rather than barrel hollow cells. An analysis of latencies showed that 40% of barrel hollow cells and 48% of barrel septal cells responded at short (< 10 ms) latencies to their appropriate vibrissa. In contrast, responses to inappropriate vibrissae were overwhelmingly of long latency (10‐ > 30 ms), only 2% of inappropriate responses from barrel hollow cells and 13% from septal cells being of short latency. These results suggest that direct inputs largely project to appropriate barrels. The possibility that divergent inputs are generated by intracortical mechanisms is discussed.
Ultrastructural observations of the development of the fourth ventricular roof in the mouse brain
Authors: Oda Yoshio , Nakanishi Isao
Published: January 2005

The developmental changes of the fourth ventricular roof of the brain in mouse fetuses and neonates were observed by scanning and transmission electron microscopy with particular attention to the caudal portion where a median foramen might be formed during the fetal period. The fourth ventricular roof was continuously paved with a single layer of cuboidal or squamous neuroepithelial cells with poorly developed basement membrane until the 12th intrauterine day when the primitive choroid plexus appeared at the middle portion of the roof. With development of the choroid plexus, the roof caudal to the choroid plexus (membranous roof) became thinner, and it was mostly lined with a single layer of flat ependymal cells having cilia and microvilli and resting on a continuous basement membrane. These ependymal cells were connected with one another by a gap junction or an intermediate junction for the entire period examined, except at the 13th to 14th intrauterine days, during which the interependymal clefts were transiently widened up to 2 μm in width, in places, without disruption of the continuous basement membrane. Neither a median aperture nor wide intercellular pores were formed in the membranous roof during the fetal or neonatal term.
Topographic organization of convergent projections to the thalamus from the inferior colliculus and spinal cord in the rat
Authors: Ledoux Joseph E. , Ruggiero David A. , Forest Ronni , Stornetta Ruth , Reis Donald J.
Published: January 2005

The purpose of this study was to identify thalamic areas receiving convergent sensory inputs from acoustic and spinal projection systems in the rat. The topographic distribution of afferents to the thalamus from the inferior colliculus and spinal cord was examined by using WGA‐HRP as an anterograde axonal tracer. Following injections in the inferior colliculus, terminal labeling was present in ventral, medial, and dorsal divisions of the medial genicuate body (MGB) and in adjacent areas of the posterior thalamus, including the posterior limitans nucleus, the posterior intralaminar nucleus, the marginal zone, the peripeduncular region, the lateral or parvicellular part of the subparafascicular nucleus, and a region intercalated between the posterior limitans nucleus and the suprageniculate nucleus. In the caudal thalamus spinal projections remained in the reticular formation medial to the collicular terminal field. At intermediate levels of the MG, however, the spinal projection began to overlap the collicular field, terminating in the medial division of the MG and in the posterior intralaminar nucleus, the marginal zone, the lateral subparafascicular nucleus, and the area between the suprageniculate and posterior limitans nuclei. More rostrally, the convergent field expanded to include aspects of the dorsal MG division. The extent to which afferent projections to the thalamus from the inferior colliculus and spinal cord converge is thus graded in the caudorostral plane, with the greatest overlap occurring at the level of the rostral third of the MGB. These observations identify potential areas of acoustic and somesthetic integration and may account for observations of neuronal plasticity in the thalamus in response to the pairing of acoustic and somesthetic inputs.
Topographic representation of the sensory and motor roots of the vagus nerve in the medulla of goldfish, Carassius auratus
Authors: Morita Yasuhiro , Finger Thomas E.
Published: January 2005

The coelomic root of the vagus nerve in goldfish is connected with sensory and motor nuclei of the medulla that are distinct from those serving the orobranchial roots of the same nerve. The primary sensory nucleus for coelomic sensation is itself divisible into medial and lateral subnuclei on the basis of afferent input and immunocytochemistry. The lateral subnucleus receives sensory input from the specialized chewing organ in the posterior pharynx and is poor in both substance P‐like and tyrosine‐hydroxylase‐like immunoreactivities. The medial subnucleus receives input from the subdiaphragmatic gastrointestinal tract and is rich in substance P‐like and tyrosine‐hydroxylase‐like immunoreactivities. The primary sensory fibers that innervate the gastrointestinal tract also project directly to the area postrema and to the vicinity of subdiaphragmatic visceral motor neurons.

The vagal motor neuronal pool is divisible into three columns: paramedian (cardiac), medial, and lateral. The paramedian group innervates the heart and is situated in a loosely aggregated column at the boundary zone between the ventricular ependyma and the underlying brainstem. The medial vagal motor neurons innervate the subdiaphragmatic viscera, while the lateral column motor neurons innervate the posterior pharynx and muscles of the chewing organ. The motor neurons in this motor column are arranged in a topographic rostrocaudal order within the motor column according to the muscle of innervation.

Thus both the general visceral sensory and general visceral motor nuclei of the medulla are organized into functional domains. Furthermore, in the goldfish, the special visceral (gustatory) and general visceral sensory nuclei form a continuous series in the medulla with the external and oral systems represented anteriorly and the pharyngeal and digestive systems represented posteriorly.
Cellular and synaptic morphology of a feeding motor circuit in Aplysia californica
Authors: Kreiner Thane , Kirk Mark D. , Scheller Richard H.
Published: January 2005

The cellular and synaptic morphology of a component of the feeding motor circuit in Aplysia californica was examined with light and electron microscopic techniques. The circuit consists of a pair of inhibitory premotor interneurons, B4 and B5, as well as two motoneurons, B15 and B16, which innervate the accessory radula closer muscle. The neurons have wide, varicose arborizations in the buccal ganglion neuropil. All four of these neurons are cholinergic, and in addition, B15 contains immunoreactivity to sera raised against small cardioactive peptide B. Varicose processes in the accessory radula closer muscle are immunoreactive with antisera against several neuropeptides. We identified specific neuromuscular junctions by visualizing horseradish peroxidase uptake in recycled synaptic vesicles. Direct innervation of the accessory radula closer muscle by B15 and B16 is demonstrated by experiments in which horseradish peroxidase is transported from motoneuronal soma to the terminals on muscle fibers. In addition, specific synaptic contacts between B4 and B5 and each of the motoneurons are observed in the buccal ganglion neuropil. Finally, multiple contacts consistent with peptidergic, serotoninergic, and cholinergic synapses are made onto the neurons, suggesting that a variety of transmitters modulate motor output at each level of the hierarchical circuit. These results support the physiological evidence suggesting the involvement of neuropeptides as well as “classical” transmitters in the modulation of circuitry governing feeding behavior in Aplysia.
Anatomical and physiological characteristics of vestibular neurons mediating the horizontal vestibulo‐ocular reflex of the squirrel monkey
Authors: McCrea R. A. , Strassman A. , May E. , Highstein S. M.
Published: January 2005

The anatomical characteristics of vestibular neurons, which are involved in controlling the horizontal vestibulo‐ocular reflex, were studied by injecting horseradish peroxidase (HRP) into neurons whose response during spontaneous eye movements had been characterized in alert squirrel monkeys. Most of the vestibular neurons injected with HRP that had axons projecting to the abducens nucleus or the medial rectus subdivision of the oculomotor nucleus had discharge rates related to eye position and eye velocity.

Three morphological types of cells were injected whose firing rates were related to horizontal eye movements. Two of the cell types were located in the ventral lateral vestibular nucleus and the ventral part of the medial vestibular nucleus (MV). These vestibular neurons could be activated at monosynaptic latencies following electrical stimulation of the vestibular nerve; increased their firing rate when the eye moved in the direction contralateral to the soma; had tonic firing rates that increased when the eye was held in contralateral positions; and had a pause in their firing rate during saccadic eye movements in the ipsilateral or vertical directions. Eleven of the above cells had axons that arborized exclusively on the contralateral side of the brainstem, terminating in the contralateral abducens nucleus, the dorsal paramedian pontine reticular formation, the prepositus nucleus, medial vestibular nucleus, dorsal medullary reticular formation, caudal interstitial nucleus of the medial longitudinal fasciculus, and raphé obscurus. Eight of the cells had axons that projected rostrally in the ascending tract of Deiters and arborized exclusively on the ipsilateral side of the brainstem, terminating in the ipsilateral medial rectus subdivision of the oculomotor nucleus and, in some cases, the dorsal paramedian pontine reticular formation or the caudal interstitial nucleus of the medial longitudinal fasciculus.

Two MV neurons were injected that had discharge rates related to ipsilateral eye position, generated bursts of spikes during saccades in the ipsilateral direction, and paused during saccades in the contralateral direction. The axons of those cells arborized ipsilaterally, and terminated in the ipsilateral abducens nucleus, MV, prepositus nucleus, and the dorsal medullary reticular formation. The morphology of vestibular neurons that projected to the abducens nucleus whose discharge rate was not related to eye movements, or was related primarily to vertical eye movements, is also briefly presented.
Development of the preoptic area: Time and site of origin, migratory routes, and settling patterns of its neurons
Authors: Bayer Shirley A. , Altman Joseph
Published: January 2005

Neurogenesis and morphogenesis in the rat preoptic area were examined with [3H] thymidine autoradiography. For neurogenesis, the experimental animals were the offspring of pregnant females given an injection of [3H]thymidine on two consecutive gestational days. Nine groups were exposed to [3H]thymidine on embryonic days E13–E14, E14–E15, E21–E22, respectively. On postnatal day P5, the percentage of labeled cells and the proportion of cells originating during 24‐hr periods were quantified at four anteroposterior levels in the preoptic area. Throughout most of the preoptic area there is a lateral to medial neurogenetic gradient. Neurons originate between E12–E15 in the lateral preoptic area, between E13–E16 in the medial preoptic area, between E14–E17 in the medial preoptic nucleus, and between E15–E18 in the periventricular nucleus. These structures also have intrinsic dorsal to ventral neurogenetic gradients. There are two atypical structures: (1) the sexually dimorphic nucleus originates exceptionally late (E15–E19) and is located more lateral to the ventricle than older neurons; (2) in the median preoptic nucleus, where older neurons (E13–E14) are located closer to the third ventricle than younger neurons (E14–E17).

For an autoradiographic study of morphogenesis, pregnant females were given a single injection of [3H] thymidine during gestation, and their embryos were removed either two hrs later (short survival) or in successive 24‐hr periods (sequential survival). Short‐survival autoradiography was used to locate the putative neuroepithelial sources of preoptic nuclei, and sequential survival autoradiography was used to trace the migratory waves of young neurons and their final settling locations. The preoptic neuroepithelium is located anterior to and in the front wall of the optic recess. The neuroepithelium lining the third ventricle is postulated to contain a mosaic of spatiotemporally defined neuroepithelial zones, each containing precursor cells for a specific structure. The neuroepithelial zones and the migratory waves originating from them are illustrated. Throughout most of the preoptic area, neurons migrate predominantly laterally. The older neurons in the lateral preoptic area migrate earlier and settle adjacent to the telencephalon. Younger neurons migrate in successively later waves and accumulate medially. The sexually dimorphic neurons are exceptional since they migrate past older cells to settle in the core of the medial preoptic nucleus. The median preoptic nucleus originates from a midline neuroepithelial zone that is continuous with the neuroepithelium in the midline basal telencephalon, and is, therefore, considered to represent a transitional area between the telencephalon and the diencephalon.
Dual control by targets and afferents of developmental neuronal death in the mammalian central nervous system: A study in the parabigeminal nucleus of the rat
Authors: Linden Rafael , Piñon Luzia G. P.
Published: January 2005

Natural and induced cell degeneration were studied in the mesencephalic parabigeminal nucleus of postnatally developing rats. Natural cell death in the normal parabigeminal nucleus had already started at birth, was maximal at 3 days, and proceeded with a declining rate until postnatal days 8–10 in the dorsal, middle, and ventral divisions that compose the nucleus. The number of neurons declined by approximately one‐third between birth and postnatal day 15. A unilateral lesion of the superior colliculus made at birth modified this pattern. In the deafferented ipsilateral middle division, the rate of cell death was above normal from day 1 to day 10, and the number of neurons at day 15 was 60% less than in unoperated controls. In the contralateral middle division, in which at least some of the neurons were axotomized by the lesion, the rate of cell death increased at days 1–2 and decreased below normal at days 3–5. Induced changes in the number of neurons were consistent with this pattern, and at day 15 the number was similar to the control value. In the ipsilateral dorsal and ventral divisions, which suffered simultaneous axotmy and deafferentation, the rate of cell death increased in 2 peaks at days 1–2 and 4–6, and the numbers of neurons dropped to negligible values at day 15. The frequency curves of degenerating cells were poor predictors of the absolute changes in neuron numbers, and evidence was found of continued postnatal migration of neurons into the developing parabigeminal nucleus. This study indicated that retrograde and anterograde degeneration cotemporal with natural cell death in the developing parabigeminal nucleus proceed with distinct time courses and interact when induced simultaneously. The nucleus regulates through a reduction in the rate of cell death after an early depletion of neurons caused by axotomy, as long as the tectal input remains intact. The results support the hypothesis that the afferent supply, as well as the integrity of axons, have major roles in the control of neuronal survival in the developing brain.
Retinal ganglion cell morphology in the frog, Rana pipiens
Authors: Frank Bennett D. , Hollyfield Joe G.
Published: January 2005

The morphology of retinal ganglion cells in the frog, Rana pipiens, has been examined in retinal flatmounts following backfilling of axons with horseradish peroxidase (HRP). Size and shape of the cell body and of the dendritic arbor, the dendritic branching pattern, and the depth of dendritic arborization within the inner plexiform layer (IPL) were all used to classify these cells. All of the ganglion cells so visualized can be grouped into one of 7 distinct cell classes. Class 1 contains the largest ganglion cells, with a soma size of 323 ± 5.3 μm2 and dendritic fields of 86,819 ± 11,817 μm2; the dendrites branch within strata 1 and 2 of the IPL. The second largest cells are class 2, with somas of 245 ± 19.7 μm2 and dendritic fields of 55,983 ± 7,392 μm2; the dendrites also branch within strata 1 and 2 of the IPL. Class 3 cells are the next largest class with somas of 211 ± 11.8 μm2 and dendritic fields of 18,186 ± 1,394 μm2; there are three varieties of class 3 cells based on the depth of branching of the dendrites: some cells are bistratified, others are tristratified, while still other cells arborize diffusely within the IPL. Class 4 cells are intermediate in size, with somas of 113 ± 7.4 μm2 and dendrites of 4800 ± 759 μm2; the dendrites arborize within strata 4 and 5 of the IPL. Class 5 cells have not been quantititively analyzed because they are heterogeneous in soma and dendritic size. However, class 5 cells all have cell bodies displaced in location into the inner nuclear layer and all have a unique dendritic specialization: they send from 1 to 3 processes into the outer plexiform layer. Class 6 cells are the second smallest cell class with somas of 68.1 ± 5.13 μm2 and dendritic fields of 888 ± 182 μm2; the dendrites arborize within strata 3, 4, and 5 of the IP. Class 7 contains the smallest ganglion cells with somas of 62.1 ± 2.86 μm2; and dendritic fields of 831 ± 74.2 μm2; the dendrites arborize within strata 3, 4, and 5 of the IPL. The frequency of each cell class is inversely proportional to the size of the dendritic field. Thus, class 7 cells are the most frequent; class 1 cells are the least frequent. Furthermore, each of these 7 classes of ganglion cells has representative cells located in the inner nuclear layer. The majority of these displaced ganglion cells are located in the central retina, within a horizontal streak just dorsal to the optic nerve head. The various morphological types of ganglion cells we observe may provide the structural basis for the diversity of frog ganglion cell receptive field types.
Trajectories of regenerating retinal axons in the goldfish tectum: II. Exploratory branches and growth cones on axons at early regeneration stages
Authors: Stuermer Claudia A. O.
Published: January 2005

HRP was applied to small sites in the dorsotemporal or dorsonasal retina in fish at 10–36 days after optic nerve section. The anterogradely labeled axons were visualized in tectal whole mounts.

Axons traveled through all regions of the tectum in various abnormal routes. Misrouted axons were also seen to alter their orientation and to direct their course toward their target. At all regeneration stages the majority of dorsotemporal axons coursed and achieved target‐related orientations preferentially within the rostral tectal half whereas dorsonasal axons proceeded into the caudal tectum.

The growing axons exhibited various morphologies. All axons in the superficial fascicle layer stratum opticum (SO) and some in the synaptic layer stratum fibrosum et griseum superficiale (SFGS) were unbranched and tipped with a leading growth cone. Other axons in the synaptic layer carried one to several growth cones at their ends and often filopodia proximal to the growth cone, or they had sprouted numerous side branches with growth cones and filopodia on the shaft and on branches. Some axons at retinotopic or ectopic sites gave rise to several long branches of several hundred microns in length, with growth cones and filopodia. From 32 days onward axons ending in terminal arbors at retinotopic sites became apparent. Thus, numerous axons at early regeneration stages go through a phase of exploratory growth on their way toward their target sites.
The process of reinnervation in the dentate gyrus of adult rats: An ultrastructural study of changes in presynaptic terminals as a result of sprouting
Authors: Steward Oswald , Vinsant Sharon L. , Davis Lauren
Published: January 2005

The present study was undertaken to define the ultrastructure of synapses of the crossed temporodentate pathway after they had sprouted to reinnervate the dentate gyrus following the destruction of the normal ipsilateral temporodentate pathway. The synapses of the sprouted crossed temporodentate pathway were identified at the EM level by using autoradiographic techniques and by evaluating the degeneration of the pathway following secondary lesions. Both EM autoradiography and EM degeneration revealed that the terminals of the sprouted crossed temporodentate pathway formed asymmetric synapses on spines; individual terminals appeared to make more synaptic contacts per terminal (multiple synapses) than in the case of the normal crossed pathway. In the two lesioned animals exhibiting the best labeling, labeled terminals made an average of 3.0 ± 2.2 and 2.0 ± 1.3 contacts per terminal. In contrast, labeled terminals in normal animals exhibited only one contact per terminal. The terminals of the sprouted pathway were also larger than those of the normal crossed pathway. The synapses of the crossed temporodentate pathway that degenerated after a secondary lesion of the entorhinal cortex exhibited both electron‐lucent and electron‐dense forms of degeneration at 2 days postlesion. In two animals that were quantitatively analyzed, the density of degenerating synaptic terminals was 281 and 218/10,000 μm2 in the terminal field of the sprouted crossed pathway. These values are much higher than in normal animals, where the density of degenerating synaptic terminals was only 2.12/10,000 μm2 at 2 days postlesion. Because degenerating terminals were evident at 2 days postlesion, the sprouted crossed pathway does not appear to exhibit the very rapid degeneration that is characteristic of the normal crossed pathway. We conclude that sprouting in this pathway involves terminal proliferation (an increase in the number of presynaptic elements), and terminal hypertrophy (an increase in the size of presynaptic terminals, together with an increase in the number of synaptic contacts formed by individual terminals).
Morphology of physiologically identified mitral cells in the carp olfactory bulb: A light microscopic study after intracellular staining with horseradish peroxidase
Authors: Fujita Ichiro , Satou Masahiko , Ueda Kazuo
Published: January 2005

Physiologically identified mitral cells in the carp olfactory bulb were stained by intracellular injection of horseradish peroxidase in order to study the morphology in detail.

The somata were fusiform, elongated, oval, triangular, or irregular. The mean diameters of the somata were 30 μm × 14 μm. Two to five thick dendrites arose from the somata and frequently gave off branches to form glomerular tufts. The dendrites extended less than 400 μm; the dendritic field of single mitral cells in the medial or lateral part of the olfactory bulb was confined within the respective part of the bulb. The axons arose from either the somata or the dendrites and had a conical initial portion, usually with a smooth contour. Some cells had poorly developed intrabulbar axon collaterals. No difference between the mitral cells in the medial part of the olfactory bulb and those in the lateral part was found in the soma diameter, the dendritic diameter at the base, or the number of first‐order dendrites. However, there was a difference in the site of the origin of the axon between them: most of the axons of the mitral cells in the medial part arose from the dendrites, while most of the axons of the mitral cells in the lateral part arose from the somata.

The morphology of physiologically identified mitral cells is basically consistent with that reported in the Golgi studies of teleosts. The limited dendritic fields of mitral cells may underlie the previously reported functional separation of the olfactory bulb into medial and lateral parts. The results also indicate that the two parts of the teleost olfactory bulb are differentiated not only functionally but also morphologically.
Identification of synaptic terminals of thalamic or cortical origin in contact with distinct medium‐size spiny neurons in the rat neostriatum
Authors: Dubé Lorraine , Smith A. David , Bolam J. Paul
Published: January 2005

In order to determine what types of neurons in the striatum receive direct synaptic input from corticostriatal and thalamostriatal fibres and whether these afferents converge on individual striatal neurons, double anterograde labelling of axon terminals was combined with Golgi impregnation at both the light and electron microscopic levels.

The area of the central neostriatum that receives input from both the parafascicular nucleus of the thalamus and the somatosensory cortex was identified by retrograde transport of a conjugate of horseradish peroxidase and wheat germ agglutinin (HRP‐WGA). The same region of the neostriatum was studied in rats that had received multiple electrolytic lesions in the somatosensory cortex and also an injection of HRP‐WGA in different parts of the parafascicular nucleus. Sections of this part of the neostriatum were impregnated by the single‐section Golgi procedure after revealing anterogradely transported HRP‐WGA. Twelve Golgi‐impregnated spiny neurons were recovered and examined in the light and electron microscope after gold‐toning. Ten of these neurons were typical very densely spiny medium‐size neurons and they were all found to receive asymmetric synaptic input on dendritic spines from degenerating corticostriatal boutons. However, even though numerous boutons labelled anterogradely by HRP‐WGA from the parafascicular nucleus were found within the dendritic fields of neurons that received cortical input, none of the terminals from the thalamus made synaptic contact with these neurons. Instead, all 96 thalamostriatal boutons studied were found in asymmetric synaptic contact with dendritic shafts of other neurons. Two such neurons that received input from the parafascicular nucleus were Golgi‐impregnated and appeared to be medium‐size spiny neurons, but they had a lower density of spines than the typical very densely spiny neurons. An independent confirmation that the targets of thalamostriatal neurons originating in the parafascicular nucleus are dendritic shafts was provided by studying the boutons labelled following electrolytic lesioning or injection of the lectin Phaseolus vulgaris‐leucoagglutinin (PHA‐L) into this nucleus: these boutons were also found to form asymmetric synaptic contacts with dendritic shafts within the neostriatum.

It is concluded that although afferents from the somatosensory cortex and from the parafascicular nucleus converge upon the same part of the neostriatum, they probably do not converge upon the same spiny neurons. The afferents from the neocortex form synapses on the spines of densely spiny medium‐size neurons, whereas terminals originating from neurons in the parafascicular nucleus are in synaptic contact with the dendritic shafts of what appears to be a morphologically distinct type of medium‐size spiny neuron. The integration of the inputs from these two areas probably involves the local axon collaterals of these two types of spiny neuron.
Cell death in the inner and outer nuclear layers of the developing cat retina
Authors: Robinson Stephen R.
Published: January 2005

The occurrence and distribution of pyknotic profiles (dying cells) in the inner (INL) and outer nuclear layers (ONL) were mapped from radial sections through 13 kitten retinae aged from the 30th postconceptional day (30PCD) to the 81PCD (17th postnatal day). Cell death in the INL occurs in two consecutive waves, each beginning at the area centralis and proceeding toward the retinal edge. The first wave involves cells located in the inner part of the INL, adjacent to the inner plexiform layer. It begins on the 50PCD and lasts until the 66PCD, with a peak of 72,000 profiles on the 58PCD. This wave of cell death seems to be associated with the formation of the inner plexiform layer and may be due to the elimination of amacrine cells which have failed to establish sustaining connections with their appropriate target cells. The second wave involves cells located in the outer part of the INL, adjacent to the outer plexiform layer. It begins on the 60PCD and lasts until after the 81PCD, with a peak of 65,000 on the 71PCD. This wave appears to be due to the elimination of ectopic photoreceptor cells displaced by the formation of the OPL and presumably prevented from establishing sustaining connections with their appropriate target cells. A phase of cell death in the ONL begins on about the 42PCD and lasts until after the 81PCD, with a peak of 10,300 pyknotic profiles on the 60PCD. Pyknotic profiles in the ONL were always distributed fairly uniformly across the retina, and did not reflect the centropheripheral maturation of the outer plexiform layer, suggesting that cell death in this layer is not target‐related. The findings of the present study indicate that naturally occurring cell death can be as extensive in populations of intrinsic neurons as it is in populations of extrinsic neurons.