bluuebunny/crossref_metadata_2025 huggingface dataset:
Abnormal pigmentation and unusual morphogenesis of the optic stalk may be correlated with retinal axon misguidance in embryonic siamese cats
Authors: Webster M. J. , Shatz C. J. , Kliot M. , Silver J.
Published: January 2005

Studies of albino rodents have shown that an absence of pigment in the developing optic stalk may alter the position of the first retinal fibers that grow toward the brain, thereby disrupting the gross topographic relationship of fibers in the nerve (Silver and Sapiro: J. Comp. Neurol. 202:521–538, ′81). The abnormalities associated with albinism are more extensive in the Siamese cat than in previously studied species. Therefore, any abnormalities in differentiation of the stalk and axon guidance may be more readily detected. To investigate the guidance and/or misguidance of optic axons, light and electron microscope analyses were made of serial sections through the optic stalk in normally pigmented and Siamese fetal cats.

On E20, before axons enter the optic stalk, the only clear morphological distinction between Siamese and normal cats is the distribution of pigment in the stalk. Pigment is found in the dorsal stalk cells of the normal cat for 200 μm from the optic disc. Although the retinal pigment epithelium of the Siamese cat embryo contains pigment, pigment could not be detected in the Siamese optic stalk. By E23 axons invade the ventral optic stalk in both strains. Concurrent with the early stages of axonal exit from the retina, there is complete separation of the stalk's dorsal and ventral tiers. As the cleavage occurs, basal lamina invaginates into the zone of separation following along the plane of the old lumen. The ventral stalk fills with axons while the dorsal tier is shed gradually. In contrast, in the Siamese cat, dorsal stalk cells are not sloughed off properly and instead are incorporated ectopically into the nerve. Basal lamina invagination is irregular. Axons do not fill the Siamese stalk symmetrically but enter the region of ectopic cells, which in turn disrupts gross fiber position. Usually, in the mutant, axons originating from the retina temporal to the optic fissure are those that invade the dorsal tier of ectopic cells. The altered position of optic axons in the mutant stalk may provide an explanation for the chiasmatic misrouting of optic axons in this species.
Visceral cortex: Integration of the mucosal senses with limbic information in the rat agranular insular cortex
Authors: Krushel Leslie A. , van Der Kooy Derek
Published: January 2005

The organization of the subcortical and cortical connections of the rat agranular insular cortex was examined. Retrogradely transported dyes were used to map the agranular insular cortex efferents to brainstem visceral nuclei (the nucleus of the solitary tract and the parabrachial nucleus), to gustatory‐visceral and limbic thalamic nuclei (medial ventrobasal and mediodorsal thalamus, respectively), and to association cortex (medial prefrontal and contralateral agranular insular cortex). The results revealed that a specific area within the ipsilateral agranular insular cortex projected to all of the subcortical and cortical areas listed above. This area of overlap in the agranular insular cortex stretched from the level of the genu of the corpus callosum rostrally to the crossing of the anterior commissure caudally.

Anterograde projections from the medial ventrobasal and mediodorsal thalamus and from the olfactory bulb to the agranular insular cortex were mapped with wheat germ agglutinin conjugated to horseradish peroxidase. The terminal cortical projections from these areas were generally separate, except in an area where they overlap immediately medial to the rhinal fissure in the agranular insular cortex. This overlap area matched the area in the agranular insular cortex where there was an overlap of cortical efferent cells projecting to the brainstem, thalamus, and association cortex, as revealed in the retrograde tracing studies. We refer to this region of convergence in the agranular insular cortex as the visceral cortex, and suggest its involvement in the efficient integration of specific visceral sensory stimuli with correlated limbic or motivational consequences. The visceral cortex may help regulate the organism's visceral response to stress.
Mammalian motoneuron development: Effect of peripheral deprivation on motoneuron numbers in a marsupial
Authors: Comans P. E. , McLennan I. S. , Mark R. F. , Hendry I. A.
Published: January 2005

In nonmammalian vertebrates, the survival of developing motoneurons is dependent on their contacting appropriate target cells. It is generally accepted that developing mammalian motoneurons have a similar dependency on their target, but as yet there is little experimental evidence to support this contention. This is mainly because of the difficulty of experimenting on eutherian embryos. We have, therefore, been studying neuronal development in the tammar (an Australian marsupial) as its nervous system is immature at birth. Radical or partial removal of hindlimb buds from newborn tammars resulted in an increased motoneuron cell death. The motoneurons which survived in the operated tammars did so by innervating muscle remnants. In the instances where a group of muscles was totally removed, the corresponding motonuclei appeared to be totally lost. This study supports the hypothesis that mammalian motoneurons must contact their appropriate muscle in order to survive through the period of natural neuronal cell death.
Immunocytochemical localization of peptides and other neurochemicals in the rat laterodorsal tegmental nucleus and adjacent area
Authors: Sutin Ellen L. , Jacobowitz David M.
Published: January 2005

The laterodorsal tegmental nucleus (ntdl) contains a cluster of cells located just medial to the locus coeruleus in the pontine brainstem. The ntdl has been shown to project both rostrally to the forebrain and diencephalon and caudally to the spinal cord. In an effort to characterize this region neurochemically, the present study was conducted to identify a variety of neurochemicals localized within perikarya and fibers of the ntdl and surrounding nuclei. Rats were perfused with formalin, and brain sections were processed for fluorescence immunocytochemistry and acetylcholinesterase (AChE). Of the neurochemicals screened, atrial natriuretic factor (ANF), choline acetyltransferase (ChAT), cholecystokinin (CCK), calcitonin gene‐related peptide (CGRP), dynorphin B (Dyn B), galanin, somatostatin, substance P, neurotensin (NT), neuropeptide Y (NPY), vasopressin, vasoactive intestinal polypeptide (VIP), serotonin (5HT), glutamic acid decarboxylase (GAD), and tyrosine hydroxylase (TH) were studied. AChE and ChAT staining revealed that the ntdl contains mostly cholinergic neurons. In addition, brightly reactive substance P and galanin and paler staining CRF, ANF, CGRP, NT, VIP, and Dyn B cell bodies were found within the ntdl. Varicose fibers in this nucleus also contained these peptides in addition to CCK, GAD, TH, 5HT, and NPY. The dorsal tegmental nucleus, dorsal raphe nucleus, locus coeruleus, and the parabrachial region contained a dense and varied assortment of peptides with distinct positions and patterns. This multiplicity of neurochemicals within this area suggests a possible influence on a variety of functions modulated by the ntdl and other closely associated tegmental nuclei.
Circadian regulation of retinomotor movements: II. The role of gaba in the regulation of cone position
Authors: Pierce Mary E. , Besharse Joseph C.
Published: January 2005

Cone photoreceptor movements in lower vertebrates are regulated by the interaction of the light‐dark cycle and an endogenous circadian clock. We have suggested that melatonin and dopamine interact to regulate dark‐ and light‐adaptive movements, respectively, and that melatonin affects cones indirectly by inhibiting dopamine release. In fact, any factor modulating dopaminergic neurons in the retina may have effects on either cone elongation or contraction. We have utilized an in vitro eyecup preparation from the African clawed frog, Xenopus laevis, to evaluate a possible role of the neurotransmitter GABA, which is thought to tonically suppress dopamine release. GABA agonists mimic the effects of darkness and induce cone elongation; the effects of GABA agonists are blocked by dopamine. Muscimol‐induced cone elongation occurs at low light intensity but is inhibited by bright light in eyecups prepared from cyclic‐light‐maintained animals. Although neither melatonin nor muscimol stimulates cone elongation in bright light, simultaneous application of both drugs induces elongation. The GABA antagonist picrotoxin induces cone contraction which is blocked by the dopamine receptor antagonist spiroperidol, which suggests that GABA may affect cone movement in Xenopus by regulating dopamine neurons. Consistent with this, picrotoxin‐induced cone contraction is Ca+2 dependent and is blocked by high Mg+2 or the Ca+2 antagonist nifedipine. Pharmacological analysis suggests that the effects of GABA may result from its action at more than one receptor subtype. Our results support the hypothesis that dopamine is part of the light signal for cone contraction and that its suppression is part of the signal for cone elongation.
Neuropeptide Y‐immunoreactive amacrine cells in the retina of the turtle Pseudemys scripta elegans
Authors: Isayama Tomoki , Eldred William D.
Published: January 2005

Antiserum directed against neuropeptide Y selectively labeled certain amacrine cells in the turtle retina. The cell types, sizes, dendritic stratification, regional distribution, and degrees of immunolabeling were examined. The results indicated that three morphologically distinct cell types were labeled: types A, B, and C. Computer rotation of digitized data from camera lucida drawings was used to study dendritic stratification. The type A somata were large (11.5 μm in diameter), well‐stained, and located in the third tier of the inner nuclear layer. Type A somata gave rise to well‐stained processes which arborized within the inner plexiform layer in strata 1 and 3 and at the border between strata 4 and 5. Processes in stratum 1 were sparse and delicate with small boutons. Processes in stratum 3 were numerous and often coarse, with many large and small boutons. At the border between strata 4 and 5 the processes were frequently numerous but slender, with many small boutons. Occasional immunolabeled processes were found in the ganglion cell layer. The somata of the type B cells were smaller (9.0 μm in diameter) and gave rise to single labeled processes which descended into the inner plexiform layer and divided quickly into two secondary processes. These secondary processes gave rise to lightly labeled dendritic fields which arborized primarily in strata 2 and 4. The type C cells were usually observed at the periphery of the retina and had large somata (12.0 μm in diameter) with simple, but very elongated, dendritic arborizations in strata 1, 4, and 5. Observations also showed that type A and B cells were often found in close proximity to each other and suggested that dendrites of these cells made contact with each other. The labeled neurons were distributed relatively evenly throughout the retina except for the visual streak where they were sparse. This study indicates that neuropeptide Y–like immunoreactivity is found in more than one anatomically distinct class of amacrine cells in the turtle retina.
Somatostatin‐containing neuron systems in the rat hypothalamus: Retrograde tracing and immunohistochemical studies
Authors: Kawano Hitoshi , Daikoku Shigeo
Published: January 2005

By employing a combination of the immunohistochemistry for somatostatin (SRIF) and retrograde tracing with biotinylated wheat germ agglutinin (b‐WGA) injected into the posterior pituitary (group 1) or into the median eminence (group 2), functional topography of hypothalamic SRIF neurons was determined in the rat hypothalamus. In group 1, large numbers of WGA‐labeled neurons appeared in the rostral periventricular region and in the magnocellular division of the paraventricular and supraoptic nuclei; none of them were SRIF immunoreactive. In group 2, WGA‐labeled neurons were numerous in the rostral periventricular region, the parvicellular division of the paraventricular nucleus, and the arcuate nucleus; most of the WGA‐labeled neurons in the rostral periventricular region and some in the paraventricular nucleus were SRIF immunoreactive, but none in the arcuate nucleus showed immunoreactivity for SRIF. It is concluded that, in the rat hypothalamus, the locations of neurons containing hypophysiotrophic SRIF are confined within the rostral periventricular region and the parvicellular paraventricular nucleus. Our results do not support previous suggestions that SRIF immunoreactive axons innervate the posterior lobe of the pituitary.
Multiple pathways from the superior colliculus to the extrageniculate visual thalamus of the cat
Authors: Abramson Bruce P. , Chalupa Leo M.
Published: January 2005

The projections from the cat's superior colliculus to the extrageniculate visual thalamus were examined by the anterograde and retrograde transport of WGA‐HRP. An acetylthiocholinesterase (ATChE) stain was employed to facilitate the differentiation of regions within the posterior thalamus. On the basis of the distribution of terminal label as well as the laminar origin of projection neurons, four pathways were delineated. Cells in the stratum griseum superficiale (primarily sublaminae II and III) innervate two regions within the nucleus lateralis posterior (LP): the medial zone, which stains darkly for ATChE, and a restricted portion of the lateral zone, adjacent to the pulvinar. Both of these pathways were found to be topographically organized. By using the fluorescent retrograde tracers, fast blue and rhodamine labeled microspheres, it was determined that the inputs to the medial and lateral zones of LP originate primarily from separate cell populations since very few neurons were found to be double‐labeled. A third pathway originates principally from cells in the stratum opticum and terminates in an area just below the cholinesterase‐rich region of the LP, designated as the ventral division of the LP. The fourth projection is primarily from the stratum griseum intermedium to the suprageniculate complex. Each of these four pathways arises from a population of neurons with heterogeneous morphological characteristics, and for the most part, each pathway comprises morphologically similar cells. These results suggest that visual information from the superior colliculus is conveyed to the extrageniculate thalamus via multiple pathways that may subserve diverse functions.
Opioid peptide gene expression in rat trigeminal nucleus caudalis neurons: Normal distribution and effects of trigeminal deafferentation
Authors: Nishimori Toshikazu , Moskowitz Michael A. , Uhl George R.
Published: January 2005

Preproenkephalin (preproenkephalin A) and preprodynorphin (preproenkephalin B) are the opioid peptide genes expressed in neurons of the nucleus caudalis of the trigeminal nuclear complex. We have used recently developed techniques for quantitative in situ hybridization to identify the neurons in laminae I and II of the nucleus caudalis that display the mRNA products of each of these genes. The specificity of these hybridization patterns is supported by several biochemical features, and by qualitative and quantitative parallels with previous immunohistochemical results. In animals killed 4 days after unilateral lesions of the trigeminal ganglion, neuronal expression of both preproenkephalin and preprodynorphin is altered in the nucleus caudalis. Decreases in preproenkephalin mRNA are due to a decline in the number of neurons that appear to express this gene. Conversely, preprodynorphin mRNA increases by adding a significant population of expressing neurons. These deafferentation‐induced changes in gene expression may provide clues to the role of primary afferent information in modulating the functions of nucleus caudalis neurons containing opioid peptides.
GABA‐immunoreactive neurons and terminals in the lateral cervical nucleus of the cat
Authors: Broman Jonas , Westman Jan
Published: January 2005

Previous findings have indicated the presence of local circuit neurons in the lateral cervical nucleus (LCN). An immunohistochemical study with γ‐aminobutyric acid (GABA) antiserum was therefore performed both to investigate whether GABA‐immunoreactive neurons are present in the LCN, and if so, to compare their characteristics with those previously assigned to probable internuncial neurons in the nucleus. The fine structure and synaptology of GABA‐positive boutons in the LCN were also studied.

Transversely cut sections from the upper cervical spinal cord of three cats were processed for GABA immunohistochemistry with the free‐floating PAP technique. On light microscopic examination immunoreactive neurons were observed within the ventromedial half of the LCN. Their total number was estimated to be 42.5 ± 11.7 in the entire LCN on one side of the cervical spinal cord, but this may have been an underestimation, as the penetration by the antisera was limited. The labeled neurons were small and had a relatively large nucleus and a low bouton covering ratio. In their number, localization, and ultrastructural appearance the GABA‐positive neurons closely resembled the population of neurons previously suggested to be local circuit neurons.

Immunoreactive bouton‐sized puncta were scattered throughout the LCN. Ultrastructural examination showed labeled terminals with a mean sectional area of 0.85 μm2 and a relatively high density of synaptic vesicles. The vast majority of GABA‐positive terminals were in contact with dendrites and only a minority had synaptic contact with cell bodies. No axoaxonal synapses were observed. The GABA‐positive boutons probably derive at least partly from the observed GABA‐positive neurons, but there is also a possibility of extrinsic GABAergic input.
Morphology and synaptic connections of HRP‐filled, axon‐bearing horizontal cells in the Xenopus retina
Authors: Witkovsky Paul , Stone Susan , MaCdonald E. Douglas
Published: January 2005

Axon‐bearing horizontal cells of the Xenopus retina were studied by intracellular injection of HRP following physiological characterization. The profile of the cell viewed in whole mount consisted of a round or oval perikaryon about 50 μm in diameter and an axon about 1 mm long which lacked a prominent terminal expansion. The axonal diameter was 0.5‐1.0 μm in its proximal third but 2‐4 μm in its distal portion. Along its course the axon emitted 25‐40 branchlets each 0.2 μm in diameter, up to 10 μm long and terminating in a cluster of two to six synaptic knobs. Electron microscopic examination revealed that both perikaryal dendrites and axon branchlets ended in both rod and cone synaptic bases; cone contacts outnumbered rod contacts by two‐ to threefold. We were unable to document synapses of presumed interplexiform cells onto identified horizontal cells. Horizontal cell axons are joined in their distal portions by numerous, small (0.2 μm long) gap junctions. Other gap junctions were noted between horizontal cell processes within the synaptic endings of photoreceptors. An hypothesis is advanced whereby the cluster of axon branchlet synaptic knobs permits dynamic interaction of rod and cone synaptic inputs to the horizontal cell.
Topographical and ultrastructural investigation of the habenulo‐interpeduncular pathway in the rat: A wheat germ agglutinin‐horseradish peroxidase anterograde study
Authors: Kawaja M. D. , Flumerfelt B. A. , Hrycyshyn A. W.
Published: January 2005

The topographical and ultrastructural organization of the habenular projection to the interpeduncular nucleus (IPN) of the rat was examined employing the anterogradely transported tracer wheat germ agglutininhorseradish peroxidase (WGA‐HRP) and the chromogen tetramethylbenzidine (TMB). Unilateral placements of WGA‐HRP in the habenular complex resulted in heavy terminal labelling in the rostral, central, and intermediate subnuclei bilaterally, and in the lateral subnuclei ipsilaterally. The apical subnucleus possessed only a sparse amount of label. Placements confined to the medial habenula (mH) produced similar results to those observed when the entire habenula was filled, suggesting that the afferent contribution made by the lateral habenula (lH) to the IPN is small.

Unilateral placements of WGA‐HRP in the dorsal portion of the mH resulted in heavy, predominantly ipsilateral labelling in the lateral subnucleus and the dorsal cap of the rostral subnucleus. In the lateral subnucleus labelled habenular terminals consistently contacted single dendritic processes shared by one or more other boutons, possibly of nonhabenular origin. Labelled habenular terminals in the rostral subnucleus normally contacted one or two dendrites. Labelled terminals in both subnuclei possessed clear, spherical vesicles and a variable number of dense‐core vesicles. Unilateral placements of WGA‐HRP in the ventral portion of the mH resulted in heavy labelling in the rostral half of the rostral subnucleus with a slight ipsilateral predominance, and in the central and intermediate subnuclei bilaterally. Terminal labelling was observed in crest and S synapses in the intermediate and central subnuclei respectively. Crest synapses, which consist of two parallel habenular terminals contacting an attenuated dendritic process, normally possessed label in only one of the two boutons. In the central subnucleus labelled horizontal axons formed several en passant S synapses with dendritic processes of small and medium diameter. These synaptic specializations of habenular axons contained numerous clear, spherical vesicles.

This study demonstrates that a major topographically organized projection to the IPN originates from two distinct subpopulations of habenular neurons which comprise a dorsal sector and a ventral sector of the mH. Ultrastructural examination demonstrated that axons originating from neurons in the ventral and dorsal mH form characteristic contacts in the various IPN subnuclei.
Sympathetic and afferent somata projecting in hindlimb nerves and the anatomical organization of the lumbar sympathetic nervous system of the rat
Authors: Baron Ralf , Jänig Wilfrid , Kollmann Wolfgang
Published: January 2005

The anatomy of the sympathetic pathways from the spinal cord to the lumbar sympathetic trunk and the inferior mesenteric ganglion was studied systematically in the rat. Details of the arrangements of white and gray rami communicantes, sympathetic trunk ganglia, the intermesenteric nerve, and the lumbar splanchnic nerves are summarized. A modified nomenclature for the segmental ganglia of the paravertebral sympathetic chain is proposed.

Cell bodies of sensory and sympathetic axons projecting to the skin and skeletal muscle of the rat hindlimb were labeled retrogradely with horseradish peroxidase (HRP) in order to study numbers, segmental distribution, and location of the somata of these neurons quantitatively. HRP was applied to the nerves supplying skeletal muscle (gastrocnemius‐soleus, GS), hairy skin (sural, SU; saphenous, SA) and to a mixed nerve (tibial, TI). All sensory somata and 96.4% of the sympathetic cell bodies were located ipsilaterally. Sensory somata were commonly restricted to two adjacent dorsal root ganglia (usually L3‐4 for SA; L4‐5 for GS, TI; L5‐6 for SU). Although the sympathetic somata were more widely distributed rostrocaudally (four to six segments), their maximum was always located one or two segments more cranially than the sensory outflow, i.e., corresponding to the rami communicantes grisei.

From the data, it is estimated that 420 sympathetic and 530 afferent neurons project into GS, 590 and 3,610 into SU, 920 and 3,750 into SA, and 1,070 and 5,760 into TI. These absolute neuron numbers are compared with electron microscopic fiber counts from the literature.
Substance P‐like immunoreactive amacrine cells in the cat retina
Authors: Pourcho Roberta G. , Goebel Dennis J.
Published: January 2005

Substance P‐like immunoreactivity was localized by immunocytochemical techniques to two subpopulations of amacrine cells in the cat retina. One cell was a unistratified amacrine with processes ramifying within stratum 4 of the inner plexiform layer. The other cell type was a bistratified cell with processes in both stratum 1 (s1) and stratum 4 (s4). Both cell types were seen with their somas displaced to the ganglion cell layer as well as in the conventional amacrine location in the inner nuclear layer. Substance P cells were present in the greatest density within the area centralis and decreased in number toward the periphery. The ratio of amacrine to displaced amacrine cells also decreased peripherally. However, the coverage by immunoreactive fibers in s4 remained three times that seen in s1. Computer‐assisted analysis confirmed the location of substance P‐containing processes at 5‐15% (s1) and 50‐70% (s4) depth levels in the inner plexiform layer. A comparison of substance P‐like immunoreactivity in light‐ and dark‐adapted cat retinas showed no apparent differences in the distribution of immunoreactivity due to lighting conditions.
Local circuit neurons of macaque monkey striate cortex: II. Neurons of laminae 5B and 6
Authors: Lund Jennifer S. , Hawken Michael J. , Parker Andrew J.
Published: January 2005

This study investigates the intrinsic organization of axons and dendrites of aspinous, local circuit neurons of the macaque monkey visual striate cortex. These investigations use Golgi Rapid preparations of cortical tissue from monkeys aged 3 weeks postnatal to adult. We have earlier (Lund, '87) described local circuit neurons found within laminae 5A and 4C; this present account is of neurons found in the infragranular laminae 5B and 6. Since the majority of such neurons are GABAergic and therefore believed to be inhibitory, their role in laminae 5B and 6, the principal sources of efferent projections to subcortical regions, is of considerable importance. We find laminae 5B and 6 to have in common at least one general class of local circuit neuron–the “basket” neuron. However, a major difference is seen in the axonal projections to the superficial layers made by these and other local circuit neurons in the two laminae; lamina 5B has local circuit neurons with principal rising axon projections to lamina 2/3A, areas whereas lamina 6 has local circuit neurons with principal rising axon projections to divisions of 4C, 4A, and 3B. These local circuit neuron axon projections mimic the different patterns of apical dendritic and recurrent axon projections of pyramidal neurons lying within laminae 5B and 6, which are linked together by both dendritic and axonal arbors of local circuit neurons in their neuropils extending between the two laminae. The border zone between 5B and 6 is a specialized region with its own variety of horizontally oriented local circuit neurons, and it also serves as a special focus for pericellular axon arrays from a particular variety of local circuit neuron lying within lamina 6. These pericellular axon “baskets” surround the somata and initial dendritic segments of the largest pyramidal neurons of layer 6, which are known to project both to cortical area MT (V5) and to the superior colliculus (Fries et al., '85). Many of the local circuit neurons of layer 5B send axon trunks into the white matter, and we therefore, suspect them of providing efferent projections. The axons of lamina 6 local circuit neurons have not been found to make such clear‐cut contributions to the white matter.
Ultrastructural features of functionally identified primary afferent neurons with C (unmyelinated) fibers of the guinea pig: Classification of dorsal root ganglion cell type with reference to sensory modality
Authors: Sugiura Yasuo , Hosoya Yasuhiko , Ito Ryuzo , Kohno Kunio
Published: January 2005

Intracellular labeling of neurons permitted a direct correlation of neuronal profiles with sensory modality of cutaneous receptors. In the guinea pig, 47 neurons in the dorsal root ganglion (displaying C‐fiber conduction velocities) were labeled with horseradish peroxidase (HRP) by iontophoresis after determining the sensory modality. Receptive fields were explored with systematic “natural” stimuli. Cell areas of all C‐fiber units were measured by tracing the cellular contour in light microscopy. The mean cellular diamter calculated from cell areas was 21.8 μm in the second cervical ganglion of the guinea pig. Mean cell diameter for high‐threshold mechanoreceptors was 20.9 μm, 24.6 μm for polymodal nociceptors, and 25.7 μm for mechanicalcold nociceptors. Electron microscopic observations showed that all labeled neurons of C‐fiber units had profiles of small, dark type‐B neurons. Neurons representative of each sensory modality exhibited different cell features, each belonging to a distinct subtype of small B neurons. High‐threshold mechanoreceptor and mechanical‐cold nociceptor displayed a peripheral lamellar arrangement of cisternae of endoplasmic reticulum (ER), corresponding to the B1 subtype. Polymodal nociceptor units were characteristically of the B2 subtype, in which stacks of long and short cisternae of ER were distributed randomly throughout the cytoplasm, and the arrangement of Golgi bodies varied among these cells. Cooling receptors displayed poorly developed, flattened cisternae of ER and numerous vesicles, typical of the B3 subtype. These results imply that all C‐fiber cells belong to the small B‐type cell category and that the ultrastructural features of the neuron in the dorsal root ganglion may reflect the sensory modality of the receptive field.
Distribution of opioid peptides in the preoptic region: Immunohistochemical evidence for a steroid‐sensitive enkephalin sexual dimorphism
Authors: Simerly R. B. , McCall L. D. , Watson S. J.
Published: January 2005

The distribution of cells and fibers that contain opioid peptides within the preoptic region of the rat was examined immunohistochemically. Cells and/or fibers that contain peptides derived from each of the three major opioid peptide families were differentially stained by using antisera that recognize unique derivatives of each precursor molecule and do not crossreact with members of the other opioid peptide families. A beta‐endorphin (ßE) antiserum was used to stain fibers that contain peptides derived from the proopiomelanocortin molecule, and dynorphin‐containing cells were identified by using an antiserum directed toward dynorphin B (Dyn B) that does not show detectable cross‐reactivity with enkephalin‐related peptides. An antiserum raised against peptide E (PE), which does not appear to cross‐react significantly with dynorphin peptides, was used to localize enkephalin cells and fibers. Each family of opioid peptides showed a unique distribution in the preoptic region. ßE‐immunoreactive fibers were primarily localized to the preoptic part of the periventricular nucleus, with moderate densities of fibers contained in the anteroventral periventricular nucleus (AVPv) and medial preoptic nucleus (MPN). Dyn B‐immunoreactive fibers showed a somewhat more uniform distribution throughout the region, and only a few Dyn B‐stained cells bodies were found within the medial preoptic area. In contrast, the preoptic region contained hundreds of PE‐immunoreactive cells, which were particularly numerous within the AVPv, MPN, and anterodorsal preoptic nucleus. The AVPv and MPN also contained discretely localized plexuses of PE‐stained fibers.

Although the overall distributions of opioid peptide‐containing fibers within the preoptic region were quite similar in male and female rats, differential distributions of fibers were found in certain nuclei such as the AVPv and MPN, and they were correlated with previously identified cytoarchitectonic sexual dimorphisms. Such differential distributions were particularly distinct for enkephalin‐containing fibers. Although the AVPv is larger in female rats, it contained more PE‐immunoreactive cell bodies in male rats, and we have shown here that this sexual dimorphism appears to be at least partially dependent on perinatal levels of gonadal steroids. In contrast, no difference in the number of PE‐stained cells was found within the anterodorsal preoptic nucleus of male and female animals, indicating that sexual differences are not a general characteristic of enkephalinergic cells in the preoptic region of the rat. These findings suggest that gonadal steroids act during development to organize opiate‐containing pathways within the preoptic region, which may contribute to the expression of sexually differentiated physiological and behavioral responses.
Brainstem origin of serotonin‐ and enkephalin‐immunoreactive afferents to the opossum's cerebellum
Authors: Walker James J. , Bishop Georgia A. , Ho Raymond H. , King James S.
Published: January 2005

Previous studies have described the distribution of serotonin‐ and enkephalin‐immunoreactive elements in the posterior lobe vermis of the oposum's cerebellum. In the present study we have used a double labeling paradigm which combines the retrograde transport of horseradish peroxidase (HRP) with serotonin and enkephalin immunohistochemistry to determine the brainstem origin of serotoninergic and enkephalinergic neurons that project to the opossum's cerebellar cortex.

Subsequent to HRP injections into the posterior lobe vermis, widespread areas of the medulla and pons were found to contain retrogradely labeled neurons. Serotonin‐immunoreactive somata are present primarily in the raphe nuclei and the adjacent reticular formation. Enkephalinergic neurons were numerous in the raphe nuclei, medial accessory olive, gigantocellular reticular formation, locus coeruleus, and the nucleus of the trapezoid body. However, serotoninergic neurons that project to the cerebellum were located only in the medullary pyramids and the reticular formation adjacent to the raphe. Double‐labeled enkephalinergic neurons were located 1) within the medullary pyramids, 2) throughout the extent of the caudal medial accessory olive, 3) in the rostral subnucleus a of the medial accessory olive, 4) in the nucleus reticularis gigantocellularis pars ventralis, 5) in the nucleus reticularis lateralis, and 6) in the nucleus reticularis ventralis lateral to the inferior olivary complex.

These results indicate that although neurons containing serotonin and enkephalin immunoreactivity may be present in some of the same pontine and medullary nuclei, those serotoninergic and enkephalinergic neurons that project to the cerebellum are present primarily in restricted and spatially separate regions of the caudal medulla.
Relationship between synaptogenesis and cytochrome oxidase activity in Purkinje cells of the developing rat cerebellum
Authors: Mjaatvedt A. E. , Wong‐Riley M. T. T.
Published: January 2005

In the adult CNS, the level of oxidative metabolism, as indicated by cytochrome oxidase cytochemistry, can be correlated with the level of neuronal activity. Specifically, heightened cytochrome oxidase activity in postsynaptic neurons can often be correlated with a greater proportion of excitatory inputs, whereas inhibitory inputs often result in a low level of cytochrome oxidase activity. This relationship has not been explored in developing neurons. To this end, cytochrome oxidase cytochemistry was used to compare the levels of oxidative metabolism in rat cerebellar Purkinje cells at various stages of their development. The results indicated that the level of cytochrome oxidase activity in Purkinje cell somata and dendrites correlated closely with the type of synaptic input (excitatory or inhibitory) received by the different segments of the cell. When the cell somata received predominantly excitatory input from climbing fibers, their mitochondria were evenly distributed between the three reactive classes: dark, moderate, and lightly reactive for cytochrome oxidase. When the cell somata received predominantly inhibitory input from basket cell terminals, lightly reactive mitochondria were the prevailing type. Further support for the correlation of excitatory synaptic input with high levels of cytochrome oxidase activity was found in the quantitation of mitochondria within Purkinje cell dendrites. These dendrites received largely excitatory input at all ages and had high levels of cytochrome oxidase activity throughout development and adulthood. There was also a relationship between the level of cytochrome oxidase activity and mitochondrial size within Purkinje cell somata and dendrites from birth to adult. Darkly reactive mitochondria had a greater mean area than moderately reactive mitochondria which, in turn, had a greater mean area than lightly reactive mitochondria. In addition, the packing density of mitochondria within the cytoplasm varied with age in both somata and dendrites. In the somata, the packing density peaked at postnatal day 7, and in dendrites, the peak occurred at postnatal day 10. These data indicate that in a developing system, postsynaptic neurons respond to sequential excitatory and inhibitory inputs by sequential heightening and lowering of their energy metabolism. Thus, cytochrome oxidase activity in a postsynaptic neuron can be correlated with the predominant type of synaptic input that it receives.
Ultrastructure of taste cells and synapses in the mudpuppy Necturus maculosus
Authors: Delay Rona J. , Roper Stephen D.
Published: January 2005

Taste buds in the mudpuppy Necturus maculosus were examined with electron microscopy. Three cell types (dark, light, and basal) were identified and reconstructed from serial thick sections. Dark and light cells extend from the basal lamina to the surface of the tongue. The apical process of the dark cells was usually quite lamellar when viewed in cross section, in contrast to light cells, whose apical process appeared more cylindrical. Basal cells are situated at the base of the bud and do not extend processes to the surface of the tongue. The cytoplasm of basal cells contains numerous clear and dense‐cored vesicles. Small, spinelike processes (2–3 μm in length) project outward from the basal cells into the cytoplasm of the surrounding taste receptor cells. Morphologically, basal cells in mudpuppy taste buds resemble Merkel cells. Unmyelinated afferent nerve fibers enter the taste bud at the base and course through the lower portion of the bud. Synapses were found between taste receptor cells and nerve fibers, between basal cells and nerve fibers, and between basal cells and taste receptor cells. Over 65% of the synapses observed in the mudpuppy taste bud involved the basal cell. These findings suggest that basal cells play some role in chemosensory signal processing or integration of the taste response.
Time course of neocortical graft innvervation by AChE‐positive fibers
Authors: Clinton Robert J. , Ebner Ford F.
Published: January 2005

Acetylcholinesterase (AChE)‐containing axons are the only extrinsic fibers projecting to the adult cortex that readily innervate embryonic cortical grafts up to normal densities without prior manipulation of the host brain. In the present paper we compare the time course of AChE‐positive fiber innervation in the normal mouse cortex with that seen in neocortical grafts by using AChE histochemistry as a marker for presumed cholinergic fibers. Donor tissue was taken at two different stages of gestation; before (embryonic days 12–14, or El2–14) and after (El7–19) the cortical plate is formed. Three features are analyzed: (1) the distribution and density of AChE‐containing fibers, (2) the presence of AChE‐positive cells, and (3) the distribution of butyrylcholinesterase (BuChE)‐positive elements.

The modification of Koelle's method used for AChE localization showed AChE‐positive fibers in developing parietal neocortex as early as El8–19. The distribution of AChE‐labeled fibers in the normal cortex achieves the mature pattern by the end of the third postnatal week. The rate of innervation of transplants takes longer and depends on the age of the donor tissue. Tissue from both donor ages first showed AChE‐positive fibers crossing the host‐transplant interface by 7 days postsurgery. El7–19 tissue approaches the density of AChE‐positive fibers in the normal adult cortex by 15 weeks after grafting, whereas the El2–14 donor tissue does not approach normal innervation densities until after 20 weeks. While the degree of innervation in the El2–14 donor tissue never equalled the surrounding adult cortex within our range of survival times, a few of the El7–19 transplants did develop densities equal to that of the host cortex.

AChE‐positive cells are first detectable in the normal parietal cortex on the day of birth, peak by the end of the first postnatal week, and then decline in number to the low levels of the mature cortex after the second postnatal week. Grafted cells in El2–14 tissue stain lightly for AChE by 7 days postsurgery, achieve maximal densities by 3 weeks, and become markedly reduced in number and density by 10 weeks. Cells in El7–19 tissue are lightly reactive by 7 days postsurgery, reach maximal numbers by 2 weeks postsurgery, and become similar in number and density to those seen in the mature cortex after 4 weeks. The appearance of BuChE‐reactive blood vessels, neurons, and glia in both normal development and in the transplants is described and discussed.

These findings indicate that embryonic neocortical tissue implanted into adult neocortex becomes innervated by AChE‐positive fibers from the host brain at different rates depending on the age of the donor tissue. Cells within the transplants express AChE transiently, similar to cortical neurons during normal development. Possible roles for the cholinergic inputs to normal and transplanted cortex are discussed.
Cortical organization after treatment of a peripheral nerve with ricin: An evaluation of the relationship between sensory neuron death and cortical adjustments after nerve injury
Authors: Wall J. T. , Cusick C. G. , Migani‐Wall S. A. , Wiley R. G.
Published: January 2005

The present study was designed to assess whether cortical changes after peripheral nerve damage are related to the degree of death of primary sensory neurons in the damaged nerve. The cytotoxin ricin was injected into the sciatic nerves of adult rats to kill primary sensory neurons with axons through the injection site. Following periods of 6–101 days, the S‐I hindpaw map was evaluated with neurophysiological techniques and compared with the hindpaw maps of previously studied normal adult rats and adult rats that had undergone adult or neonatal sciatic section at a comparable level of the nerve. These comparisons allowed evaluation of cortical functional organization following different degrees of sensory neuron loss after sciatic nerve injury.

There were three main results. 1) The comparison of ricin‐treated and normal adult rats indicated that ricin treatment interrupted inputs from the sciatic skin territory on the hindpaw and caused a limited increase in the size of the cortical area that was activated by stimulation of hindpaw skin innervated by the remaining saphenous nerve. 2) The cortical maps of rats that had undergone adult ricin treatment (relatively large primary neuron loss) or section during adulthood (small to moderate primary neuron loss) were similar. In both groups, only the saphenous hindpaw skin was represented in cortex, and the cortical area that was activated by stimulation of the saphenous hindpaw skin had undergone a comparable limited enlargement. 3) The comparison of ricin‐treated adult rats (relatively large primary neuron loss) and adult rats that had undergone neonatal section (relatively large primary neuron loss) indicated that cortical organization differed after these treatments. In particular, after ricin treatment the cortical area that was activated by stimulation of the saphenous hindpaw skin was larger than the comparable area in neonatal denervates, and the topographical progressions between the hindpaw and adjacent body representations were not as variable as after neonatal section.

These findings indicate that cortical maps are altered after injection of ricin into a nerve. The similarity in cortical organization after ricin treatment (relatively large sensory neuron loss) and nerve section in adults (relatively small sensory neuron loss) and the differences in cortical organization after ricin treatment and nerve section in neonates (both relatively large sensory neuron loss) indicate cortical changes do not covary as a simple function of the degree of peripheral neuron death.
Organization of the association cortical afferent connections of area 5: A retrograde tracer study in the cat
Authors: Avendaño C. , Rausell E. , Perez‐Aguilar D. , Isorna S.
Published: January 2005

The association (intrahemispheric) cortico‐cortical afferent connections of area 5 were studied in the cat by means of retrograde tracing techniques involving horseradish peroxidase (HRP) free or wheat germ agglutininconjugated (WGA‐HRP) or fluorochrome injections. Single or multiple injections were placed in different parts of areas 5a and 5b, the medial division of area 5 (5m), or in the anterior suprasylvian area (SsA). Labeled cells were plotted on projection drawings of the coronal sections and on two‐dimensional “maps” of the cerebral cortex, which were produced according to an accurate and consistent procedure.

The major findings of this study are:

All divisions of the anterior parietal cortex (areas 3a, 3b, 1, and 2) project to area 5 and to SsA. These projections, however, show marked differences in amount and topographical distribution, depending on the mediolateral and rostrocaudal location of the injections.

The motor cortex (areas 4 and 6) also projects heavily to area 5 and to SsA in a well‐organized topographic fashion: Area 4 projects mainly upon areas 5a, 5m, SsA, and the medial part of 5b; area 6 projects mainly upon the lateral part of 5b and SsA. Moreover, the upper bank of the cruciate sulcus (areas 4 and 4aα) projects to medial parts of area 5, and the lower bank (areas 4&6aδ, and 6aß) projects to lateral parts of area 5.

The somatosensory areas in the anterior ectosylvian gyrus and surrounding cortices (SIIm, SII, and SIV) are connected primarily with medial parts of area 5 (particularly 5a), and SsA.

Areas 7 and 7m and a number of visual areas (19, SVA, AmLS, PmLS, 21, 20, 18, ALS, and PLS) project in varying degrees to lateral parts of area 5b. Some of these areas also send weak to moderate projections to the medial part of 5b and the lateral part of 5a.

Sparse projections arising from the dorsolateral prefrontal, cingular, retrosplenial, granular insular, and suprasylvian fringe cortices were found to distribute in area 5 and SsA, particularly in lateral portions of 5b.

Quite abundant intrinsic connections also were found, which were loosely organized according to a complex topographic pattern.

On the basis of these and previous results (Avendaño et al., 1985), the identity of area 5 in the cat is discussed, and comparisons are made between this area and sectors of adjoining cortex of cat and primates.