Interfascicular Regions Research Articles

Deep brain stimulation targeted at lateral hypothalamus-medial forebrain bundle reverses depressive-like symptoms and related cognitive deficits in rat: Role of serotoninergic system

The aim of the study is to understand the rationale behind the application of deep brain stimulation (DBS) in the treatment of depression. Male Wistar rats, rendered depressive with chronic unpredictable mild stress (CUMS) were implanted with electrode in the lateral hypothalamus-medial forebrain bundle (LH-MFB) and subjected to deep brain stimulation (DBS) for 4 h each day for 14 days. DBS rats, as well as controls, were screened for a range of parameters indicative of depressive state. Symptomatic features noticed in CUMS rats like the memory deficit, anhedonia, reduction in body weight and 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) levels in mPFC and elevated plasma corticosterone were reversed in rats subjected to DBS. DBS arrested CUMS induced degeneration of 5-HT cells in interfascicular region of dorsal raphe nucleus (DRif) and fibers in LH-MFB and induced dendritic proliferation in mPFC neurons. MFB is known to serve as a major conduit for the DRif-mPFC serotoninergic pathway. While the density of serotonin fibers in the LH-MFB circuit was reduced in CUMS, it was upregulated in DBS-treated rats. Furthermore, microinjection of 5-HT1A receptor antagonist, WAY100635 into mPFC countered the positive effects of DBS like the antidepressant and memory-enhancing action. In this background, we suggest that DBS at LH-MFB may exercise positive effect in depressive rats via upregulation of the serotoninergic system. While these data drawn from the experiments on rat provide meaningful clues, we suggest that further studies aimed at understanding the usefulness of DBS at LH-MFB in humans may be rewarding.

Plant feeding by Nesidiocoris tenuis: Quantifying its behavioral and mechanical components

Zoophytophagous predators play an important, though sometimes controversial, role in pest management programs in different crops. In tomato crops, damage caused by phytophagy of the mirid Nesidiocoris tenuis has mainly been reported at high predator population levels or when prey is scarce. Previous research has focused on predator/prey ratios, stylet morphology and saliva composition to explain plant damage by N. tenuis. In this study, we investigated the behavioral and mechanical components of the damage. For this, we compared the feeding behaviors of males, females and fifth-instar nymphs ofN. tenuis. Additionally, we investigated the type of stylet activities performed by each stage while probing in plant tissue, using the electrical penetration graph technique (EPG). Furthermore, stylectomy was performed and plant histology studied with the aim to correlate the feeding activities observed in the EPG recordings with stylet tip positions in specific tissues of the leaf petioles. Behavioral observations during a 30-min period showed thatnymphs probed more frequently (38.6 ± 1.5 probes) than males and females (25.3 ± 1.1 and 24.3 ± 1.1 probes, respectively). Similarly, nymphs spent a higher proportion of time (656.0 ± 67.6 s) feeding on tomato apical sections compared to males and females (403.0 ± 48.8 s and 356.0 ± 43.7 s, respectively). The EPG recordings during 5 h indicated that cell-rupturing was the main stylet activity for all insect stages, and that fifth-instar nymphs spent a higher proportion of time on cell-rupturing events compared to adults. The histological studies revealed a trend ofN. tenuisfor the tissues within the vascular semi-ring. The stylet tips were found both in the vascular bundles and in the parenchyma of the interfascicular region. The findings of this study confirm an important role of fifth-instar nymphs feeding behavior in the damage potential of N. tenuis. Moreover, the increased time spent on cell rupturing behaviour suggests that stylet laceration and enzymatic maceration of the saliva occurring during this event might greatly contribute to the inflicted damage. A comprehensive understanding of the interactions of N. tenuis with the plant, at both the behavioral and mechanical levels, might shed light on new approaches to minimize its damage potential to tomato while maintaining its benefits as biocontrol agent.

Anatomical investigations of the Turkish critically endangered species: Achillea sivasica Çelik et Akpulat (Asteraceae)

In this study, the root, stem, leaf midrib and leaf lamina anatomy and achene micromorphology of the Turkish critically endangered endemic Achillea sivasica were investigated for the first time. In this study, the root was found in late primary growth and in early secondary growth stage. It has a large cortex layer consisting of 12-16 cell rows beneath the periderm. Secretory ducts formed by 5-12 secretory cells embedded in the cortex and located near the vascular bundle were found at the root, which was in the early stage of secondary development. The stem was circular-pentagonal in cross-section. There was lamellar collenchyma beneath epidermis of pentagon corners, and cortex parenchyma between corners. Secretory ducts located near the phloem, between the cortex and endodermis on the interfascicular region, were also observed. An endodermis layer was evident and its cells have indentations and protrusions where they touch adjacent endodermis cells, which strengthens the connection between them. In addition, casparian strips were conspicuous in many endodermis cells. The leaf midrib area had a triangular cross section. There were secretory ducts, consisting of 4-5 secretory cells observed on both sides of the sclerenchymatous fibers that accompany the xylem. The leaf lamina was amphistomatic and stomata type was anomocytic. Mesophyll layer was equifacial. There was a large secretory duct and its diameter is bigger than the nearest main lamina vascular bundle. Achene shape of A. sivasica was lanceolate-oblong and its surface was ribbed and glabrous.

Profil Anatomi Batang Kacang Komak (Lablab purpureus (L.) Sweet) Lokal Pulau Lombok

Hyacinth bean (Lablab purpureus (L.) Sweet) is a member of Fabaceae which has high economic potential but is still treated as an underutilized crop. Research on Lombok’s hyacinth bean focused on stem anatomical profile has never been conducted. The aims of this research were to study stem anatomical profile of hyacinth bean in Lombok, West Nusa Tenggara. Young and mature stem were collected using exploration method. Anatomical sample preparation was done using free hand section method, stained with safranin, and mounted in a glycerine liquid. Sample was visualized and documented using binocular microscope connected to the digital camera integrated with ScopeImage 9 software. Data were analyzed by a triangulation method. The result showed that stem anatomical profile of hyacinth bean in Lombok by transversal section consists of one layer of an epidermal cell and unicellular glandular trichomes as it’s derivate. Parenchyma cell was found in the cortex, interfascicular region, and pith in shape of rounded, oval, up to polygonal and varied in size. Vascular tissue showed a unique structure and became the distinctive feature od hyacinth bean stem. There were 2 type of vascular bundles i.e big and small vascular bundles. The large vascular bundles contain xylem and phloem and the small vascular bundles may or may not contain both xylem and phloem.

Tendon extracellular matrix damage, degradation and inflammation in response to in vitro overload exercise.

ABSTRACTThe role of inflammation in tendon injury is uncertain and a topic of current interest. In vitro studies of tendon accelerated overload damage can serve as a valuable source of information on the early stages of tendinopathy. Viable fascicle bundles from bovine flexor tendons were subjected to cyclic uniaxial loading from 1–10% strain. Immuno‐staining for inflammatory markers and matrix degradation markers was performed on the samples after mechanical testing. Loaded samples exhibited visible extracellular matrix damage, with disrupted collagen fibers and fiber kinks, and notable damage to the interfascicular matrix. Inflammatory markers COX‐2 and IL‐6 were only expressed in the cyclically loaded samples. Collagen degradation markers MMP‐1 and C1,2C were colocalized in many areas, with staining occurring in the interfascicular matrix or the fascicular tenocytes. These markers were present in control samples, but staining became increasingly intense with loading. Little MMP‐3 or MMP‐13 was evident in control sections. In loaded samples, some sections showed intense staining of these markers, again localized to interfascicular regions. This study suggests that inflammatory markers may be expressed rapidly after tendon overload exercise. Interestingly, both inflammation and damage‐induced matrix remodeling seem to be concentrated in, or in the vicinity of, the highly cellular interfascicular matrix. © 2015 The Authors. Journal of Orthopaedic Research Published by Wiley Periodicals, Inc. J Orthop Res 33:889–897, 2015.

Anatomical response and infection of soybean during latent and pathogenic infection by type A and B of Phialophora gregata.

Growth and anatomical responses of plants during latent and pathogenic infection by fungal pathogens are not well understood. The interactions between soybean (Glycine max) and two types of the pathogen Phialophora gregata were investigated to determine how plants respond during latent and pathogenic infection. Stems of soybean cultivars with different or no genes for resistance to infection by P. gregata were inoculated with wildtype or GFP and RFP-labeled strains of types A or B of P. gregata. Plants were sectioned during latent and pathogenic infection, examined with transmitted light or fluorescent microscopy, and quantitative differences in vessels and qualitative differences in infection were assessed using captured images. During latent infection, the number of vessels was similar in resistant and susceptible plants infected with type A or B compared to the control, and fungal infection was rarely observed in vessels. During pathogenic infection, the resistant cultivars had 20 to 25% more vessels than the uninfected plants, and fungal hyphae were readily observed in the vessels. Furthermore, during the pathogenic phase in a resistant cultivar, P.gregata type A-GFP was limited to outside of the primary xylem, while P.gregata type B-RFP was observed in the primary xylem. The opposite occurred with the susceptible cultivar, where PgA-GFP was observed in the primary xylem and PgB-RFP was limited to the interfascicular region. In summary, soybean cultivars with resistance to BSR produced more vessels and can restrict or exclude P. gregata from the vascular system compared to susceptible cultivars. Structural resistance mechanisms potentially compensate for loss of vessel function and disrupted water movement.

Cellular events during interfascicular cambium ontogenesis in inflorescence stems of Arabidopsis

Development of cambium and its activity is important for our knowledge of the mechanism of secondary growth. Arabidopsis thaliana emerges as a good model plant for such a kind of study. Thus, this paper reports on cellular events taking place in the interfascicular regions of inflorescence stems of A. thaliana, leading to the development of interfascicular cambium from differentiated interfascicular parenchyma cells(IPC). These events are as follows: appearance of auxin accumulation, PIN1 gene expression, polar PIN1 protein localization in the basal plasma membrane and periclinal divisions. Distribution of auxin was observed to be higher in differentiating into cambium parenchyma cells compared to cells within the pith and cortex. Expression of PIN1 in IPC was always preceded by auxin accumulation. Basal localization of PIN1 was already established in the cells prior to their periclinal division. These cellular events initiated within parenchyma cells adjacent to the vascular bundles and successively extended from that point towards the middle region of the interfascicular area, located between neighboring vascular bundles. The final consequence of which was the closure of the cambial ring within the stem. Changes in the chemical composition of IPC walls were also detected and included changes of pectic epitopes, xyloglucans (XG) and extensins rich in hydroxyproline (HRGPs). In summary, results presented in this paper describe interfascicular cambium ontogenesis in terms of successive cellular events in the interfascicular regions of inflorescence stems of Arabidopsis.

Cell walls and the developmental anatomy of the Brachypodium distachyon stem internode.

While many aspects of plant cell wall polymer structure are known, their spatial and temporal distribution within the stem are not well understood. Here, we studied vascular system and fiber development, which has implication for both biofuel feedstock conversion efficiency and crop yield. The subject of this study, Brachypodium distachyon, has emerged as a grass model for food and energy crop research. Here, we conducted our investigation using B. distachyon by applying various histological approaches and Fourier transform infrared spectroscopy to the stem internode from three key developmental stages. While vascular bundle size and number did not change over time, the size of the interfascicular region increased dramatically, as did cell wall thickness. We also describe internal stem internode anatomy and demonstrate that lignin deposition continues after crystalline cellulose and xylan accumulation ceases. The vascular bundle anatomy of B. distachyon appears to be highly similar to domesticated grasses. While the arrangement of bundles within the stem is highly variable across grasses, B. distachyon appears to be a suitable model for the rind of large C4 grass crops. A better understanding of growth and various anatomical and cell wall features of B. distachyon will further our understanding of plant biomass accumulation processes.

Populus biomass protein-protein interactions and their functions

Proteins are molecular machines that play roles in almost all biological activities through interactions with other molecules such as carbohydrates, lipids, nucleic acids and other proteins. We are mapping protein-protein interactions relevant to woody biomass production by focusing on proteins co-expressed in poplar secondary xylem. In addition to revealing novel regulatory mechanisms important to woody biomass production, mapping the poplar protein-protein interactome will provide fundamental information relevant to xylem differentiation and secondary growth. We have cloned a portion of the poplar biomass ORFeome, specifically 374 ORFs that are upregulated in xylem versus phloem, for use in protein-protein interaction research. Here we summarize the techniques we are using to discover and study protein-protein interactions and results to date. 1. Yeast two-hybrid (Y2H) binary assays: 108,205 Y2H binary assays involving over 300 biomass ORFeome members have been performed and 11 interaction pairs identified. The proportional yield from our binary screen is similar to that represented by the current preliminary binary screen data from the Arabidopsis interactome project. 2. Y2H cDNA library screening: We have used 40 bait proteins to screen our poplar xylem cDNA prey library, and a total of 60 biomass ORFeome members comprising putative regulators of lignocellulose synthesis will be screened in 2011. For the 26 ORFs that are completely through the library screen, we have identified 44 unique interacting sequences. Thus far, the proportional yield of interactors for proteins catalyzing metabolic reactions (such as cellulose synthase, PB138) is much lower than that for regulatory proteins (such as NIMA kinase, PB223). Results from these Y2H screens are available at our project website (http://xylome.vbi.vt.edu/index.html). Additional website information includes a project overview, project objectives, progress to date, sequences for all ORFs and primers, clone availability, and Y2H protocols. 3. Confirmation of selected protein-protein interactions identified by Y2H screens: Selected Y2H interactions are being confirmed by independent methods including bimolecular fluorescence complementation (BiFC) and co-immunoprecipitation/affinity purification using plant transient or stable expression systems. We have developed improved vectors and protocols for reducing background fluorescence during BiFC experiments. 4. Functional analysis: We are characterizing the functions of selected interacting pairs in both poplar and Arabidopsis by ectopically expressing or suppressing genes singly and in combination. For ectopic and/or over-expression experiments we are using 35S, SUC2 (phloem specific) and XCP2 (xylem specific) promoters. Co-expression of 35S::PB15 and 35S::PB129 in Arabidopsis resulted in expanded interfascicular regions containing enlarged fibers compared to fibers in wild-type plant interfascicular regions of the inflorescence stem. Importantly, this phenotype was not observed in transgenics overexpressing just one of these genes, showing the potential of novel interactome data to be translated into alteration of wood phenotypes.Arabidopsis mutants carrying T-DNA insertions within Arabidopsis orthologs of PB15 and PB129 are also being evaluated, and Populus RNA interference (RNAi) lines have been generated to study the effects of silencing PB15 and/or PB129 and their paralogs. 5. Transgenic poplar field trial: We prepared transgenic poplar overexpressing 11 biomass genes as tandem affinity purification-(TAPa)-tagged fusions and established these in a replicated field trial, which will be evaluated for overexpression phenotypes and serve as a source of xylem for identification of co-purified proteins.

Rays, intrusive growth, and storied cambium in the inflorescence stems of Arabidopsis thaliana (L.) Heynh

Arabidopsis thaliana is a model plant used in analysis of different aspects of plant growth and development. Under suitable conditions, secondary growth takes place in the hypocotyl of Arabidopsis plants, a finding which helps in understanding many aspects of xylogenesis. However, not all developmental processes of secondary tissue can be studied here, as no secondary rays and intrusive growth have been detected in hypocotyl. However, results presented here concerning the secondary growth in inflorescence stems of Arabidopsis shows that both secondary rays and intrusive growth of cambial cells can be detected, and that, in the interfascicular regions, a storied cambium can be developed.

Analysis of secondary growth in the Arabidopsis shoot reveals a positive role of jasmonate signalling in cambium formation.

After primary growth, most dicotyledonous plants undergo secondary growth. Secondary growth involves an increase in the diameter of shoots and roots through formation of secondary vascular tissue. A hallmark of secondary growth initiation in shoots of dicotyledonous plants is the initiation of meristematic activity between primary vascular bundles, i.e. in the interfascicular regions. This results in establishment of a cylindrical meristem, namely the vascular cambium. Surprisingly, despite its major implications for plant growth and the accumulation of biomass, the molecular regulation of secondary growth is only poorly understood. Here, we combine histological, molecular and genetic approaches to characterize interfascicular cambium initiation in the Arabidopsis thaliana inflorescence shoot. Using genome-wide transcriptional profiling, we show that stress-related and touch-inducible genes are up-regulated in stem regions where secondary growth takes place. Furthermore, we show that the products of COI1, MYC2, JAZ7 and the touch-inducible gene JAZ10, which are components of the JA signalling pathway, are cambium regulators. The positive effect of JA application on cambium activity confirmed a stimulatory role of JA in secondary growth, and suggests that JA signalling triggers cell divisions in this particular context.

An NAC transcription factor orchestrates multiple features of cell wall development in Medicago truncatula

To identify genes controlling secondary cell wall biosynthesis in the model legume Medicago truncatula, we screened a Tnt1 retrotransposon insertion mutant population for plants with altered patterns of lignin autofluorescence. From more than 9000 R1 plants screened, four independent lines were identified with a total lack of lignin in the interfascicular region. The mutants also showed loss of lignin in phloem fibers, reduced lignin in vascular elements, failure in anther dehiscence and absence of phenolic autofluorescence in stomatal guard cell walls. Microarray and PCR analyses confirmed that the mutations were caused by the insertion of Tnt1 in a gene annotated as encoding a NAM (no apical meristem)-like protein (here designated Medicago truncatula NAC SECONDARY WALL THICKENING PROMOTING FACTOR 1, MtNST1). MtNST1 is the only family member in Medicago, but has three homologs (AtNST1-AtNST3) in Arabidopsis thaliana, which function in different combinations to control cell wall composition in stems and anthers. Loss of MtNST1 function resulted in reduced lignin content, associated with reduced expression of most lignin biosynthetic genes, and a smaller reduction in cell wall polysaccharide content, associated with reduced expression of putative cellulose and hemicellulose biosynthetic genes. Acid pre-treatment and cellulase digestion released significantly more sugars from cell walls of nst1 mutants compared with the wild type. We discuss the implications of these findings for the development of alfalfa (Medicago sativa) as a dedicated bioenergy crop.

Intramedullary neuroma of the cervicomedullary junction

Neuromas typically arise in the peripheral nervous system in response to traumatic injury at the site of partial or complete nerve transection as new axons from the proximal nerve stump sprout to reinnervate the distal segment. In rare cases neuromas have also been described as intramedullary spinal cord lesions. These lesions have been identified as incidental autopsy findings in association with prior trauma and cervical spondylosis, multiple sclerosis, spinal tumors, and syringomyelia. The authors report the case of a 50-year-old man who had been involved in a motor vehicle accident, during which his car was struck from behind as it was stationary at an intersection, more than 5 years before presentation. A workup for syncopal and presyncopal episodes involved magnetic resonance imaging that revealed a 1.1-cm lesion at the cervicomedullary junction (CMJ). The imaging features of the lesion raised the question of an ependymoma or subependymoma. The lesion was excised, and examination of the tissue demonstrated a neuroma with haphazardly arranged interlacing bundles of axons ensheathed by Schwann cells with interfascicular regions of reactive glial cells and Rosenthal fibers, consistent with those present after traumatic injury. This case may represent the first true traumatic intramedullary neuroma of the CMJ diagnosed in a living patient and treated surgically.

Ontogeny of the interfascicular cambium in the petiole ofTabebuia rosea DC. (Bignoniaceae)

In order to elucidate the origin of interfascicular cambium in the petiole ofTabebuia rosea, transverse and tangential views of the cells in the interfascicular region during the different developmental stages of the petiole have been traced. Interfascicular cambium originates from the interfascicular parenchyma, which has been differentiated from interfascicular vascular meristem cells. Interfascicular parenchyma cells divide periclinally differentiating into the interfascicular metacambial cells and then into the cambium. Tangentially the homogenous structure of interfascicular parenchyma cells in the early stage gradually changes into a heterogenous structure with long and short cells from which fusiform and ray initials are derived, respectively. Ontogenetic pattern of the interfascicular cambium is similar to that of the fascicular one with interfascicular metacambium as an intermediate stage.

Cambial Variant in the Stem of Serjania Corrugata (Sapindaceae)

The establishment of the cambial variant and the development of the stem of Serjania corrugata Radlk. (Sapindaceae) was analyzed. In the early stages of development, the stem is lobed, with five lobes and five furrows in cross section. Around the fourth internode, each lobe has a vascular arc with one or two more developed central vascular bundles, two lateral bundles and phloem in the interfascicular regions. Procambial strands are also found in perimedullary position, producing only phloem elements. At this stage, the beginning of the cambial activity can be seen in the central vascular bundle in each lobe. This activity then extends to the lateral vascular bundles and to the perimedullary phloem. Parenchymatic cells, located between the vascular ring of the lobe and the perimedullary phloem, dedifferentiate and initiate meristematic activity, uniting these two regions. The development of xylem masses (one in each lobe) that characterizes the adult stem results from this cambial activity. The development of the cambial variant in S. corrugata is quite similar to that previously described in S. elegans Cambess.

Hca: an Arabidopsis mutant exhibiting unusual cambial activity and altered vascular patterning

By screening a T-DNA population of Arabidopsis mutants for alterations in inflorescence stem vasculature, we have isolated a mutant with a dramatic increase in vascular tissue development, characterized by a continuous ring of xylem/phloem. This phenotype is the consequence of premature and numerous cambial cell divisions in both the fascicular and interfascicular regions that result in the loss of the alternate vascular bundle/fiber organization typically observed in Arabidopsis stems. The mutant was therefore designated high cambial activity (hca). The hca mutation also resulted in pleiotropic effects including stunting and a delay in developmental events such as flowering and senescence. The physiological characterization of hca seedlings in vitro revealed an altered auxin and cytokinin response and, most strikingly, an enhanced sensitivity to cytokinin. These results were substantiated by comparative microarray analysis between hca and wild-type plants. The genetic analysis of hca indicated that the mutant phenotype was not tagged by the T-DNA and that the hca mutation segregated as a single recessive locus, mapping to the long arm of chromosome 4. We propose that hca is involved in mechanisms controlling the arrangement of vascular bundles throughout the plant by regulating the auxin-cytokinin sensitivity of vascular cambial cells. Thus, the hca mutant is a useful model for examining the genetic and hormonal control of cambial growth and differentiation.

MicroRNA-directed cleavage of ATHB15 mRNA regulates vascular development in Arabidopsis inflorescence stems.

Class III homeodomain-leucine zipper proteins regulate critical aspects of plant development, including lateral organ polarity, apical and lateral meristem formation, and vascular development. ATHB15, a member of this transcription factor family, is exclusively expressed in vascular tissues. Recently, a microRNA (miRNA) binding sequence has been identified in ATHB15 mRNA, suggesting that a molecular mechanism governed by miRNA binding may direct vascular development through ATHB15. Here, we show that miR166-mediated ATHB15 mRNA cleavage is a principal mechanism for the regulation of vascular development. In a gain-of-function MIR166a mutant, the decreased transcript level of ATHB15 was accompanied by an altered vascular system with expanded xylem tissue and interfascicular region, indicative of accelerated vascular cell differentiation from cambial/procambial cells. A similar phenotype was observed in Arabidopsis plants with reduced ATHB15 expression but reversed in transgenic plants overexpressing an miR166-resistant ATHB15. ATHB15 mRNA cleavage occurred in standard wheat germ extracts and in Arabidopsis and was mediated by miR166 in Nicotiana benthamiana cells. miR166-assisted ATHB15 repression is likely to be a conserved mechanism that regulates vascular development in all vascular plants.

Isolation ofCOV1, a gene involved in the regulation of vascular patterning in the stem ofArabidopsis

The molecular mechanisms that control the ordered patterning of vascular tissue development in plants are not well understood. Several models propose a two-component system for vascular differentiation. These components include an inducer of vascular tissue development and an inhibitor that prevents the formation of vascular bundles near pre-existing bundles. We have identified two recessive allelic mutants in Arabidopsis, designated continuous vascular ring (cov1), that display a dramatic increase in vascular tissue development in the stem in place of the interfascicular region that normally separates the vascular bundles. The mutant plants exhibited relatively normal vascular patterning in leaves and cotyledons. Analysis of the interaction of cov1 with a known auxin signalling mutant and direct analysis of auxin concentrations suggests that cov1 affects vascular pattering by some mechanism that is independent of auxin. The COV1 protein is predicted to be an integral membrane protein of unknown function, highly conserved between plants and bacteria. In plants, COV1 is likely to be involved in a mechanism that negatively regulates the differentiation of vascular tissue in the stem.

Stem anatomy of Amaranthaceae: Rayless nature of xylem

Summary Secondary xylem of seventeen species from nine genera of Amaranthaceae was studied anatomically. In all these species radial growth in the main stem was achieved by the formation of cambial variants. After cessation of cell divisions in the previous cambium, a new ring of cambium was developed from axial parenchyma cells at a distance of about three to six cell layers outside the phloem produced by the previous cambium. Among all these species, alternating segments of cambium in each ring led to variation in the differentiation of their derivatives i.e. the segment of cambium producing conducting elements of xylem and phloem (i.e. fascicular segment) and another segment of cambium exclusively producing axial parenchyma cells/conjunctive tissues (interfascicular segment), staggered according to the different cambium rings. In Amaranthus, Celosia and Digera arvensis formation of thick walled xylem derivatives was restricted to the fascicular segment; the interfascicular regions exclusively differentiated into thin walled axial parenchyma cells on both xylem and the phloem side. This variation in the formation of xylem derivatives gives an impression that vascular bundles were embedded in parenchymatous groundmass. In all the other species, the interfascicular regions of the cambium differentiated into thick-walled conjunctive tissues on xylem side and thin walled parenchyma on phloem side. All these species accumulated scanty secondary xylem, which was composed of vessel elements, tracheids, fibres and axial parenchyma while xylem rays were absent at least in the early stages of secondary growth. In the later part of secondary growth, species of Amaranthus, Celosia and Digera arvensis produced axially elongated upright ray cells in the region of cambium that differentiates only into thin walled parenchyma. In the rest of the species xylem was devoid of rays even at the senescent stage of the life cycle. Occurrence of nucleated xylem fibres is an interesting feature of all the species and is correlated with the rayless nature of xylem.

Projections from the prefrontal cortex to the dorsal raphe nucleus of the rat

Projections from the prefrontal cortex to subdivisions of the dorsal raphe nucleus were investigated in the rat using retrograde and anterograde tracing methods. A retrograde tracer, gold‐conjugated horseradish peroxi‐dase (WGA‐apo‐HRP‐gold), was injected into each subdivision of the dorsal raphe including lateral wing, dorsomedial, and ventromedial areas. The majority of retrogradely labeled cells were located in the prelimbic, infralim‐bic, and dorsal peduncular areas of the medial prefrontal cortex. A few cells were also identified in the cingulate, various regions of the orbital, and agranular insular cortices. Secondly, an anterograde tracer, Phaseolus vulgaris leucoagglutinin (PHA‐L), was injected into the medial prefrontal cortex involving the prelimbic or infralimbic areas. Axonal fibers with vari‐cosities were identified in all subdivisions of the DR including the lateral wing, dorsomedial, and ventromedial areas. Projections were bilateral, with ipsilateral predominance. Axonal fibers were observed at the lateral border of medial longitudinal fasciculus or in the interfascicular region at the midline. The present findings demonstrate that both the midline and lateral wing regions of the dorsal raphe nucleus receive excitatory input from cognitive and emotional centers of the cerebral cortex.