bluuebunny/crossref_metadata_2025 huggingface dataset:
Pathology associated with a viral erythrocytic infection in turbot, Scophthalmus maximus (L.)
Authors: LAMAS J. , NOYA M. , FIGUERAS A. , TORANZO A. E.
Published: April 2006

Abstract. Since 1992, frequent erythrocytic viral infections have occurred in cultured turbot, Scophthalmus maximus (L.), on several fish farms in Galicia, Spain, causing important mortalities. Affected fish showed haemorrhages in the head, mouth and fins, exophthalmia and abdominal distension. The disease was also characterized by the presence of pale blue inclusions in affected erythrocytes. The examination of these erythrocytes by electron microscopy showed virus particles of 50–160 nm in size in the cytoplasm, budding av the cell membrane and extracellularly. The histopathological study revealed occasional necrosis of kidney haematopoietic tissue, an increase in the size and number of melanomacrophage centres of the spleen and kidney, and oedematous areas with hepatocytes containing eosinophilc bodies in the liver. Degeneration of muscle fibres was accompanied by an intense inflammatory oedema. Dermatitis as well as uveitis and corneal oedema were consistent lesions.
Bizarre organism from the skin of mahi mahi, Coryphaena hippurus L. (Teleostei: Coryphaenidae)
Authors: LANGDON J. S. , MASTERS A. , THORNE T. , WILTON S.
Published: April 2006

Abstract. Superficial stellate cells of an unknown origin were detected on the epidermis of juvenile mahi mahi, Coryphaena hippurus L., up to 60 days of age. The cells occurred in large numbers, and were detected in both wild and cultured fish. International authorities were unable to identify the organism and there was no pathology associated with the presence of the cells on the skin. Because of the fine cytoplasmic interdigitations between the organism and the host cell, and the close ecological association with both wild and cultured juveniles examined, it was thought that the cells could possibly be highly modified skin cells. We report here that the spinous cells possess DNA sequences encoding 16S subunit ribosomal RNA genes distinct from those of mahi mahi, and also that restriction enzyme digests of genomic DNA from the spinous cells and from mahi mahi produced distinct patterns after electrophoretic separation. This suggests that the spinous cells are a bizarre commensal organism displaying a close physical and ecological association with the fish host.
Effects of potassium aluminium sulphate (alum) used in an Aeromonas salmonicida bacterin on Atlantic salmon, Salmo salar L.
Authors: MULVEY B. , LANDOLT M. L. , BUSCH R. A.
Published: April 2006

Abstract. Potassium aluminium sulphate (alum) was tested for use as an adjuvant in an Aeromonas salmonicida bacterin injected into Atlantic salmon, Salmo salar L. Potential side‐effects of visceral adhesions, diminished growth and toxicity, as well as adjuvant effects, were examined. Both alum and the bacterin alone induced inflammation and adhesion formation when injected into the peritoneal cavity. When bacterin and alum were combined, these effects were compounded. Growth was not affected by any of the injected treatments. The acute toxicity of the bacterin was reduced from 33.7 to 0.3% mortality by the addition of alum. Alum appeared to enhance protection against challenge, but there were no statistically significant differences in protection between injecting bacterin alone or injecting bacterin with alum.
Identification of Gyrodactylus (Monogenea) species parasitizing salmonid fish using DNA probes
Authors: CUNNINGHAM C. O. , MCGILLIVRAY D. M. , MACKENZIE K. , MELVIN W. T.
Published: April 2006

Abstract. Oligonucleolides GsV4B, GdV4 and GtV4, complementary to sequences from Gyrodactylus Salaris, G. derjavini and G. truttae, respectively, were designed following examination of the sequence of the small subunit ribosomal RNA (srRNA) gene from each species. The oligonucleotides were end‐labelled with digoxigenin for use us species‐specific probes. The V4 region of the srRNA gene was amplified from individual gyrodactylids using the polymerase chain reaction (PCR) and aliquots of the PCR products werespotted onto nylon membrane. Optimum conditions for hybridization of the oligonucleotide probes to these samples were determined. The use of these three probes against aliquots of PCR product provides an objective, sensitive and specific method suitable for routine diagnostic use in identifyingGyrodactylus species found on salmonid fish, but cannot be used to distinguishG. salaris andG. thymulli.
Morphology of Ichthyophonus hoferi assessed by light and scanning electron microscopy
Authors: SPANGGAARD B. , HUSS H. H. , BRESCIANI J.
Published: April 2006

Abstract. The morphology of Ichthyophonus hoferi in vitro at pH 3.5 and 7.0 is described using light and scanning electron microscopy. Only vegetative growth was observed. At pH 3.5, hyphal growth was seen. The hyphae of I. hoferi are characterized by evacuated hyphal walls with the cytoplasm migrating to the apex and no septation. In contrast, the growth at pH 7.0 is mainly seen as spherical bodies which vary in size and are uni‐ to multinucleate. Amoeboid bodies showing slow movements were observed within 3–6 h of transfer to pH 7.0. We propose a life‐cycle involving the germination of thick‐walled multinucleate spores in the fish stomach as a response to the low pH. The hyphae then penetrate the digestive tract and rupture when they reach a blood vessel (neutral pH), whereby uni‐ and binucleate bodies and/or amoeboid bodies are released. The small cells are transported in the blood vessels and spread in the organs richly supplied with blood (heart, kidney, spleen, liver and muscle tissue) where they grow to form multinucleate spores.
Pathology of Enterococcus sp. infection in farmed turbot, Scophthalmus maximus L.
Authors: NIETO J. M. , DEVESA S. , QUIROGA I. , TORANZO A. E.
Published: April 2006

Abstract The lesions of an enterococcal septicaemia occurring in turbot, Scophthalmus maximus (L.), cultured in several farms in northwest Spain are described. The agent of this septicaemia was identified previously as an Enterococcus‐like bacterium. Two main patterns of lesions were observed in the diseased turbot: a focal form characterized by exophthalmia, muscular haemorrhages, acute branchitis, and suppurative inflammation of periorbital tissues, eyeball, meninges and brain; and another generalized form with similar lesions, but showing more extensive haemorrhages, ulceration and purulent inflammation of the skin, desquamative enteritis, and necrosis of spleen and kidney. Fatty changes of the liver were observed in all turbot examined (diseased and controls), which indicates that these alterations were not related to the infection. Experimentally inoculated turbot developed lesions corresponding to the generalized form of the natural disease. Although the Enterococcus strain was recovered in pure culture from all the organs, Gram‐positive bacteria could not be visualized histologically in the lesions of muscle and brain.
‘No‐mucus skin disease’ of rainbow trout, Oncorhynchus mykiss (Walbaum): a case report
Authors: FERGUSON H. W. , OSTLAND V. E. , MacPHEE D. D. , LUMSDEN J. S. , BYRNE P. J. , SPEARE D. J.
Published: April 2006

Abstract A skin disease of intensively reared salmonids in Ontario hatcheries, known to the farmers as‘no‐mucus skin disease’, is reported for the first time. It was characterized by erosive and ulcerative lesions found mainly on the flanks of fingerlings, which resulted in exposure of the tips of the scales. Associated with these lesions were colonies of bacteria seen in the SEM to be clustered round the mucous cell pores and under‐running the margins of epithelial cells. The cause of this condition is unknown, although the response of fish to formalin treatment, and the presence of bacilli seen in skin scrapings and in the SEM, suggest that bacteria are responsible.
Antigenic diversity of eastern Canadian isolates of infectious pancreatic necrosis virus
Authors: Tarrab E , Heppell J , Berthiaume L , Lecomte J
Published: April 2006

A collection of infectious pancreatic necrosis virus (IPNV) isolated in five provinces of eastern Canada was analysed by an antigen‐coated immunosorbent assay and by neutralization tests using selected monoclonal and polyclonal antibodies. Relevant antigenic sites of the two major capsid proteins, VP2 and VP3, were simultaneously compared. The A1 serotype was predominant and no significant variations of VP2 epitopes were observed. However, two subtypes could be distinguished on the basis of one or two epitopes on VP3. Other serotypes such as A6, A7 or A8 have been detected in piscicultures of New Brunswick and Nova Scotia. The antigenic characterization of IPNV strains appears of interest for epidemiological studies.
Comparative pathogenicity study on antigenically variant strains of Enterococcus seriolicida
Authors: Alim S R , Kawai K , Kusuda R
Published: April 2006

Enterococcus seriolicida strains were divided into two groups, agglutinating and nonagglutinating, by a slide agglutination test using antiserum against the YT‐3 strain. Intraperitoneal injection of agglutinating and nonagglutinating strains into yellowtail, Seriola quinqueradiata Temminck & Schlegel, revealed that nonagglutinating strains were more virulent than agglutinating strains. Two nonagglutinating and highly pathogenic strains SS91–014 and SS91–092 were subcultured 30 times in brain heart infusion broth, and the agglutination titres of 50 colonies from subcultures 1, 2, 3, 4, 5, 6, 11, 16, 21, 26 and 30 against anti‐YT‐3 serum were determined. Transformation from a nonagglutinating (1:<4) to an agglutinating (1: ≥4) pattern was first observed at the sixteenth subculture, and the ratio of agglutinating to nonagglutinating substrains rose until the thirtieth subculture. At this time, 70% of the SS91–014 population and 52% of the SS91–092 population were transformed to an agglutinating pattern. When the pathogenicity of four transformed substrains with different agglutination titres was tested in yellowtail, the nonagglutinating substrain showed higher pathogenicity than the agglutinating substrains, but no relationship between LD50 values and the agglutination titres of transformed substrains was observed. The pathogenicity of E. seriolicida appears to be related to the agglutination pattern, although it was not demonstrated that this property is solely responsible for pathogenicity.
Health status of two salmonid aquaculture facilities in North Portugal: characterization of the bacterial and viral pathogens causing notifiable diseases
Authors: Sousa J A , Romalde J L , Ledo A , Eiras J C , Barja J L , Toranzo A E
Published: April 2006

A comparative bacteriological and virological survey was conducted in two fish farms in the North of Portugal. The fish species examined included cultured rainbow trout, Oncorhynchus mykiss (Walbaum), and brown trout, Salmo trutta L., as well as wild fish captured near both facilities. The microbial load in the internal organs of apparently healthy fish was nonitored over a year, an all the disease problems occurring during this period were investigated. Although both farms presented intermediate levels of infection(30–40% infected fish), farm B showed the poorest microbiological quality since constant but low mortalities were observed throughout the year. Flavobacterium and Psedomonas‐Xanthomonas were the predominant bacterial groups, comprising around 40–50% of the isolates from each farm. In farm B, members of the Enterobacteriaceae and mortile Aeromonas also showed significant prevalence (about 20%). The only outbreak of a notifiable disease was an occurrence of furunculosis, caused by Aeromonas salmonicida subsp. salmoncida, in farm A. However, Yersinia ruckeri was isolated not only from diseased fish, but also from asymptomatic fish, usually in mixed infections with motile Aeromonas or infections with motile Aeromonas or infectious pancreatic necrosis virus (IPNV). While Y. ruckeri isolates associated with mortalities belonged to the serotype O1 (subgroup a), those isolated from asymtomatic fish corresponded to serotype O3. Two strains of IPNV (serotype Ab) were isolated in farm B, which represents the first viral agent detected in Portuguese aquaculture. Qualitative and quantitative differences in microbial load were observed between cultured and wild fish. No notifiable bacterial or viral pathogens were detected in any of the feral species studied.
Retention of furunculosis vaccine components in Atlantic salmon, Salmo salar L., following different routes of vaccine administration
Authors: Press C McL , Evensen Ø , Reitan L J , Landsverk T
Published: April 2006

The retention of vaccine components was studied in Atlantic salmon, Salmo salar L., following different routes of vaccination against Aeromonas salmonicida. Frozen tissue was collected from the spleen, head kidney, hind gut and liver of fish that had been vaccinated by intraperitoneal injection (monovalent and trivalent vaccines), immersion and oral administration 2,6,8 and 16 weeks previously. The trivalent injection group showed the highest levels of specific antibodies and was the only group to show protection following challenge with virulent A. salmonicida. Following intraperitoneal injection, there was an initial widespread distribution of Aeromonas lipo‐polysaccharide, but by 16 weeks lipopolysaccharide was predominantly found in macrophage populations in the spleen, head kidney and abdominal granulomas. Only small amounts of lipopolysaccharide were retained in the head kidney of the immersion group and no lipopolysaccharide was retained in the oral group. Small and inconsistent amounts of A‐layer protein were present in the meianomacrophages of the head kidney of all groups. The relative prominence of A‐layer protein in the spleen of the trivalent injection group 8 weeks after vaccination was linked to the high levels of specific antibodies, and possible immune‐complex trapping and the enhancement of immunological memory.
Is the turbot, Scophthalmus maximus (L.), intestine a portal of entry for the fish pathogen Vibrio anguillarum?
Authors: Oisson J C , Jöborn A , Westerdahl A , Blomberg L , Kjelleberg S , Conway P L
Published: April 2006

The role of the intestinal tract in Vibrio anguillarum infection of turbot, Scophthalmus maximus (L.), fingerlings was investigated in two in vivo models and the possible mechanisms involved were studied in vitro. Viable V. anguillarum cells were detected in spleens from more than 50% of the fish administered the pathogen orally or rectally, suggesting that the intestinal tract is a portal of entry for V anguillarum. In transmission electron micrographs, V. anguillarum‐ like cells were seen close to the rectal epithelium, suggesting penetration of the mucus layer, but no epithelial cell penetration or endocytosis was evident. Attachment to intact turbot intestines was investigated, and 80% or more of the bacterial cells still remained attached after serial washings. A significantly higher number of cells attached to rectal segments than to the other intestinal segments. In vitro, V. anguillarum cells did not adhere specifically to intestinal mucus, but rather accumulated close to intestinal mucus interfaces and subsequently penetrated them. It is proposed that the intestinal ttact of tutbot is a portal of entry for V. anguillarum and that the cells penetrate the intestinal mucus overlaying the epithelial cells.
The effects of microcystins on the serum biochemistry of carp, Cyprinus carpio L., when the toxins are administered by gavage, immersion and intraperitoneal routes
Authors: Carbis C R , Mitchell G F , Anderson J W , McCauley I
Published: April 2006

Microcystins were administered to carp, Cyprinus carpio L., by intraperitoneal injection. Tests performed on the serum indicated liver and gill damage, and disturbances in hepatic and osmoregulatory functions. Exposure of carp to microcystins by gavage and inrimersion caused changes indicating mild liver damage and changes in the equilibrium of cationanion balance in some treatments. The results of gavage and immersion exposure indicate that acute roxicity is unlikely to occur in wild carp populations, but chronic poisoning may follow repeated sublethal exposure. A serum biochemical profile comprising alanine amino transferase, aspartate amino transferase, bile acids, bilirubin, sodium and chloride determinations may provide a useful diagnostic indication of microcystin poisoning in wild carp populations.
Morphological changes in carp epithelial cells infected with Aeromonas hydrophila
Authors: Leung K Y , Lim T M , Lam T J , Sin Y M
Published: April 2006

The in vitro interaction of Aeromonas hydrophila with epithehoma papillosum cells of carp (EPC) was studied. All the virulent and type strains invaded and multiplied inside EPC cells. Morphological changes were induced by the virulent and type strains during the processes of invasion and intracellular replication. Among the virulent group, strain PPD134/91 required the shortest time (30 min post‐infection) to induce cytopathic effects in the EPC monolayers. The EPC cells infected with PPD 134/91 became retracted and condensed, lost their attachment abilities, and eventually disintegrated. Confocal microscopy revealed that tubular structures measuring 0.77 ± 0.19 μm appeared to connect the retracted EPC cells. The cytopathic effect was attributed to the growing and metabolically active bacteria. Avirulent strains such as L37 did not multiply nor induce cytopathic effects in the EPC monolayers.
Genogrouping of birnaviruses isolated from marine fish: a comparison of VP2/NS junction regions on genome segment A
Authors: Hosono N , Suzuki S , Kusuda R
Published: April 2006

Yellowtail ascites virus and related strains isolated from marine fish have been shown to be similar to infectious necrosis virus (IPNV) in terms of biological and serological characteristics. This paper explores the relationship of aquatic birnaviruses at the genetic level. The junction region on the genome segment A coding viral capsid protein VP2 and viral protease NS was amplified by PCR in six marine strains. Analysis of nucleotide and the deduced amino acid sequences revealed that the six marine strains have amino acid variations in the possible amino terminus of NS when compared to IPNV. The six marine strains form a new genogroup which is distinguished from three serotypes ofPNV.
Neurofibrillary tangles and deposition of oxidative products in the brain in cases of myotonic dystrophy
Authors: Oyamada Reiko , Hayashi Masaharu , Katoh Yuji , Tsuchiya Kuniaki , Mizutani Toshio , Tominaga Itaru , Kashima Haruo
Published: April 2006

Myotonic dystrophy (MyD) is a neuromuscular degenerative disorder that is neuropathologically characterized by minor changes, such as the presence of neurofibrillary tangles (NFT), thalamic inclusions and functional brainstem lesions. In the current study, we conducted an immunohistochemical analysis to examine the distribution of NFT and formation of oxidative products in the brain specimens of 12 patients with MyD. Neurofibrillary tangles were found in the limbic system and/or the brainstem of all the cases examined but there were no senile plaques. The density of distribution of the NFT was not significantly correlated with clinicopathological findings, although cases with fewer NFT in the brain frequently showed sleep disturbances and lack of spontaneity. Nuclear and cytoplasmic immunoreactivities for 8‐hydroxy‐2′‐deoxyguanosine and advanced glycation end products were observed in the glial cells and/or neurons in the brainstem, but not in the cerebral cortex. On the other hand, 10 out of the 12 cases showed cytoplasmic immunoreactivity for 4‐hydroxy‐2‐nonenal‐modified protein (4‐HNE) in neurons of the temporal cortex and raphe nucleus. Deposition of 4‐HNE was also recognized in the hippocampus and mesencephalic central gray matter, but not in the subiculum. The distribution pattern of the immunoreactivity for 4‐HNE showed no clear correlation with either the psychological disturbances or the distribution of the NFT. Altered expression of monoaminergic neurons in the brainstem of MyD patients has already been reported, and it is worth noting that most of our cases showed NFT in the brainstem. The selective deposition of 4‐HNE in the limbic system and brainstem suggests that lipid peroxidation may be involved in the neurodegenerative process in MyD. Using immunohistochemical analysis to determine the distribution of neurotransmitters in the mesencephalic central gray matter and/or pontine raphe nucleus may help elucidate the relationship between the clinical abnormalities, distribuion of NFT, and 4‐HNE deposition in the brain in patients with MyD.
Magnesium deficiency over generations in rats with special references to the pathogenesis of the parkinsonism–dementia complex and amyotrophic lateral sclerosis of Guam
Authors: Oyanagi Kiyomitsu , Kawakami Emiko , Kikuchi‐Horie Kae , Ohara Kazuhiko , Ogata Kentaro , Takahama Sachiko , Wada Manabu , Kihira Tameko , Yasui Masayuki
Published: April 2006

Parkinsonism–dementia complex (PDC) and amyotrophic lateral sclerosis (ALS) are fatal neurological diseases. The incidence on Guam was very high between 1950 and 1965 but decreased dramatically after 1965. It is thought that drinking water containing low levels of calcium (Ca) and magnesium (Mg), and high levels of aluminum and of a plant excitatory neurotoxin are involved in the pathogenesis of these diseases. The present experiment was performed in rats that were exposed to low Ca and/or Mg intake over two generations, thus simulating the conditions of human life on Guam, where several generations live continuously in the same environment. Significant loss of dopaminergic neurons was identified exclusively in the substantia nigra in 1‐year‐old rats that had been exposed continuously to low Mg intake (one‐fifth of the normal level) over generations. The present study suggests that low Mg intake over generations may be involved in the pathogenesis of substantia nigra degeneration in humans.
Neonatal Section of the Optic Chiasm Changes the Interhemispheric Transfer of Visual Information in Cats
Authors: Bisti Silvia , Biral Giampaolo , Trimarchi Carmela
Published: April 2006

Recent studies in adult split‐chiasm cats show that the contrast gain of the visual callosal pathway is considerably lower than the gain of the direct geniculocortical system and that high spatial and temporal frequencies are strongly attenuated in the process of callosal transfer. We recorded visual evoked potentials (VEPs) and single unit activities from visual cortical areas 17 and 18 in cats which had the optic chiasm sectioned at 3 weeks of age. Our results show that, unlike the animals sectioned as adults, the contrast gain and the spatial and temporal acuities of the callosal pathway of young split‐chiasm cats were as good as the direct retinogeniculocortical pathway. Thus, under the present experimental conditions all the spatial and temporal information processed in areas 17 and 18 of one hemicortex is transferred to the other hemicortex via the callosal connections. These animals have also been tested behaviourally for the interocular (interhemispheric) transfer of learning of patterns of high spatial frequency and low contrast. In agreement with the electrophysiological results, we find a complete interocular transfer for this behavioural task. We conclude that the functional development of the interhemispheric connections can be modified by an early section of the optic chiasm and therefore the loss in binocular convergence can be partially compensated.
Ultrastructural Double‐Labelling Study of Dopamine Terminals and GABA‐Containing Neurons in Rat Anteromedial Cerebral Cortex
Authors: Verney C. , Alvarez C. , Geffard M. , Berger B.
Published: April 2006

The aim of this study was to identify, at the ultrastructural level, the neuronal targets of dopamine afferents to the medial prefrontal and the anterior cingulate cortex of the adult rat. Since, in addition to pyramidal neurons, the cortical neuronal population mainly consists of GABAergic nonpyramidal intrinsic neurons, the simultaneous visualization of both dopamine‐ and GABA‐containing neurons should leave the pyramidal neurons as the only unlabelled dopamine postsynaptic target. In this context, we used a double labelling immunocytochemical procedure: a pre‐embedding PAP immunostaining to visualize monoclonal conjugated‐dopamine (DA) antibody, followed by postembedding immunogold staining with a polyclonal conjugated‐GABA antibody. In a single section sampling of 369 DA‐immunoreactive (DA‐IR) varicosities observed and the GABA‐containing elements, 75% of the DA‐IR terminals showed no indication of any contact with a GABA neuron. Twenty‐five per cent were found in nonsynaptic contiguity with a GABA‐immunoreactive neuronal element: axon, dendrite or cell body. When a DA varicosity was in nonsynaptic contiguity with a neuronal perikaryon (5% of cases), this cell was GABA positive. Ten per cent of the DA varicosities were contiguous to a GABA axon, but axoaxonic synapses in either direction were never observed. A symmetrical synapse between a DA varicosity and a GABA‐containing dendrite was observed only once. The other 13 DA‐IR terminals exhibiting a clear synaptic junction were apposed to nonGABA‐containing dendrites, spines and shafts. Triads were observed in which a DA varicosity, forming or not a symmetrical synapse, was apposed to an unlabelled dendrite already receiving a symmetrical junction from another unlabelled axon. These data confirm and extend previous results designating the pyramidal cell dendritic tree as the main synaptic target of DA cortical afferents in rat and primate cerebral cortex. However, a direct effect of dopamine on a subpopulation of intrinsic GABA neurons cannot be excluded.
Evidence for the Involvement of Rat Olfactory Bulb in Processes Supporting Long‐Term Olfactory Memory
Authors: Mouly A. M. , Gervais R. , Holley A.
Published: April 2006

Current advances in the neurobiology of learning and memory suggest the existence of experience‐induced plasticity in sensorial pathways conveying relevant information to higher integrative brain structures. For instance, olfactory learning is known to induce long‐lasting modifications of neural activity at the level of the first relay structure of the olfactory system, the olfactory bulb. The observed forms of plasticity depend on the action exerted during learning by ascending neuromodulatory systems, such as the noradrenergic (NA) system originating from the locus ceruleus. This study was aimed at investigating the importance of olfactory bulb plasticity in learning and retention of an olfactory task. In a daily training schedule animals had to learn to use multi‐site electrical stimulation patterns of the olfactory bulb as discriminative cues for choosing between a palatable and a nonpalatable solution. We first examined the effects of a continuous intrabulbar infusion of propranolol (a β‐NA receptor antagonist) carried out during the learning period. We found that this treatment neither impaired the retention of a previously learned task nor the learning of a new task. However, the animals presented a severe deficit in long‐term retention (>5 days) of the task learned under perfusion. Unexpectedly, this effect cannot be ascribed to a selective blockade of β‐NA receptors since infusion of the drug vehicle (saline‐ascorbate) produced exactly the same deficit while a saline solution remained without effect. A final experiment showed that the selective deficit in long‐term retention was not observed when the infusion of the saline‐ascorbate solution started on the day following completion of learning. Taken together, these results suggest that ascorbate‐sensitive neural processes occurring within the olfactory bulb during learning are of functional importance for long‐term storage of olfactory information.
Ibotenate Lesions of Hippocampus and/or Subiculum: Dissociating Components of Allocentric Spatial Learning
Authors: Morris R. G. M. , Schenk F. , Tweedie F. , Jarrard L. E.
Published: April 2006

This study examined the effects of ibotenic acid‐induced lesions of the hippocampus, subiculum and hippocampus ± subiculum upon the capacity of rats to learn and perform a series of allocentric spatial learning tasks in an open‐field water maze. The lesions were made by infusing small volumes of the neurotoxin at a total of 26 (hippocampus) or 20 (subiculum) sites intended to achieve complete target cell loss but minimal extratarget damage. The regional extent and axon‐sparing nature of these lesions was evaluated using both cresyl violet and Fink – Heimer stained sections. The behavioural findings indicated that both the hippocampus and subiculum lesions caused impairment to the initial postoperative acquisition of place navigation but did not prevent eventual learning to levels of performance almost as effective as those of controls. However, overtraining of the hippocampus + subiculum lesioned rats did not result in significant place learning. Qualitative observations of the paths taken to find a hidden escape platform indicated that different strategies were deployed by hippocampal and subiculum lesioned groups. Subsequent training on a delayed matching to place task revealed a deficit in all lesioned groups across a range of sample choice intervals, but the subiculum lesioned group was less impaired than the group with the hippocampal lesion. Finally, unoperated control rats given both the initial training and overtraining were later given either a hippocampal lesion or sham surgery. The hippocampal lesioned rats were impaired during a subsequent retention/relearning phase. Together, these findings suggest that total hippocampal cell loss may cause a dual deficit: a slower rate of place learning and a separate navigational impairment. The prospect of unravelling dissociable components of allocentric spatial learning is discussed.
Molecular Cloning of Forebrain mRNAs which are Modulated by Sleep Deprivation
Authors: Rhyner Thomas A. , Borbély Alexander A. , Mallet Jacques
Published: April 2006

Sleep deprivation (SD) experiments have suggested that specific endogenous substances mediate the control of sleep and waking. However, such ‘sleep substances’ have not yet been unambiguously identified. The isolation of specific molecular markers would make it possible to obtain new insights into the regulatory mechanisms underlying sleep and waking. For this purpose, we have used a molecular genetical approach based on subtractive cDNA cloning. Using these techniques, we were able to detect and isolate in rat forebrain four cDNA clones whose corresponding transcripts are expressed at a lower level after 24 h of SD, and six cDNA clones whose corresponding transcripts are expressed at a higher level. For two of the former transcripts, the level showed a significant reduction of approximately 50% after 24 h of SD and a non‐significant reduction after 12 h of SD. A significant reduction was also observed after 12 h of cold exposure. A regional analysis of their level under baseline conditions revealed variation during the 24‐h cycle. The highest levels tended to occur at the onset of darkness, the beginning of the rat's activity period. Our results are compatible with the hypothesis that the cloned transcripts are associated with the regulation of the sleep‐waking cycle. Analysis of their primary structure indicated that these mRNAs have not yet been characterized. The in vivo distribution of these transcripts in the forebrain shows some correspondence to that of receptors of excitatory amino acids, suggesting an association between the functional role of the cloned sequences and this neurotransmission system.
Spontaneous Saccades and Gaze‐Holding Ability in the Pigmented Rat. II. Effects of Localized Cerebellar Lesions
Authors: Chelazzi L. , Ghirardi M. , Rossi F. , Strata P. , Tempia F.
Published: April 2006

We have studied the effects of the ablation of the cerebellar vermal area corresponding to lobules VI – VIII and of the flocculus – paraflocculus of both sides on the spontaneous eye movements performed in the light and in the dark in head‐restrained pigmented rats. These effects have been compared with those already described for the inferior olive lesion. The cerebellar lesions were performed 1 week to 6 months in advance. Eye movements were recorded through a phase detection search coil apparatus. Following vermal topectomy, the main characteristics of the spontaneous saccades are unmodified. Following the ablation of the flocculus – paraflocculus there is no change in the saccadic main sequence. However, the spontaneous saccades in the dark present a postsaccadic drift made up of two components with different time courses, the first one being fast and the second one slow. The former is due in part to a mismatch between the phasic (the pulse) and the tonic (the step) components of the eye movements; the latter to the leakage of the neural integrator. In light only the first component is present and the eye maintains a steady position. The time constant of the neural integrator is considerably reduced to ∼600–900 ms from a value of ∼1600–4000 ms in the intact rats. The amplitude of the postsaccadic drift in the light depends on both the mismatch between the pulse and the step of innervation of the extraocular muscles and the increased leakiness of the neural integrator. The gain of the pulse to step transformation is reduced to ∼0.79 at all saccadic amplitudes and eccentricities and such a reduction is due to a decreased step amplitude, while the pulse amplitude remains unchanged. The contribution of the leakage of the neural integrator to the postsaccadic drift in the light is a function of the eccentricity with a slope of 0.23. The deficits described after flocculus–paraflocculus ablation are also very similar to those described following inferior olive lesion from a quantitative point of view. The possible mechanisms of the visually activated olivocerebellar system in the control of saccadic performance and in maintaining its calibration are discussed.
Both Astrocytes and Neurons Contribute to the Potentiation Mediated by α1‐Adrenoceptors of the β‐Adrenergic‐Stimulated Cyclic AMP Production in Brain
Authors: Marin P. , Delumeau J. C. , Cordier J. , Glowinski J. , Premont J.
Published: April 2006

Using primary neuronal or astrocyte cultures from the striatum of the embryonic mouse, we have observed that the β‐adrenergic agonist isoprenaline (10−5 M) induced a more pronounced accumulation of cAMP in astrocytes than in neurons. In both cell types, the α‐adrenergic selective agonist methoxamine (10−4 M), which alone did not affect the production of cAMP, potentiated the isoprenaline‐evoked response. In support of these observations, when associated α2‐noradrenergic and D1‐dopaminergic responses were prevented, the mixed α1‐ and β‐adrenergic agonist noradrenaline (10−5 M) induced a production of cAMP which was totally blocked by propranolol (10−6 M) and partially abolished by prazosin (10−6 M). Since experiments were made in the presence of 3‐isobutyl‐1‐methylxanthine (1 mM), the observed effects on cAMP accumulation were not related to a modulation of phosphodiesterase activities. In addition, both in astrocytes and in neurons, the potentiation by α1‐adrenergic agonists of the β‐adrenergic‐evoked response required external calcium. Using INDO 1 as a fluorescent probe, methoxamine (25 μM) was shown to induce in astrocytes an increase in cytosolic calcium concentration which was prolonged by isoprenaline (10−5 M) only in the presence of external calcium. These results suggest that the prolonged increase in cytosolic calcium concentration linked to the activation of α1‐ and β‐adrenergic receptors is responsible for the potentiation of the β‐adrenergic‐induced production of cAMP, which is partially dependent on external calcium.
Calbindin D‐28k Protein and mRNA Localization in the Rat Brain
Authors: Séquier J. M. , Hunziker W. , Andressen C. , Celio M. R.
Published: April 2006

After the discovery of calretinin, a protein with high sequence homology to calbindin D‐28k, the validity of immunohistochemical results obtained using polyclonal antibodies for this protein, was in question. In order to validate the previous results on the localization of calbindin D‐28k in the brain, we localized the protein by highly specific monoclonal antibodies and revealed its mRNA histochemically by in situ hybridization. In general there was good agreement between the results obtained using these two different techniques and those reported in previous publications. The concordance was particularly impressive for the cerebral cortex, basal ganglia, basal nucleus of Meynert, hippocampus, thalamus, cerebellum and superior colliculus. In the amygdala and hypothalamus the low spatial resolution of in situ hybridization did not allow precise definition of some nuclei displaying a positive reaction for the protein. In the rhombencephalon, cells of the parabrachial nuclei and the dorsal raphe nucleus expressed calbindin D‐28k. Neurons in the dorsal horn of the spinal cord and some horizontal cells of the retina were tagged with both methods. The only discrepancy was the presence of immunoreactive ependymal cells, whereas mRNA never occurred in cells lining the ventricles. Thus, the combined approach has established the widespread distribution of cells expressing calbindin D‐28k in the rat brain.
Some Actions of 9‐Amino‐1,2,3,4‐Tetrahydroacridine (THA) on Cholinergic Transmission and Membrane Currents in Rat Sympathetic Ganglia
Authors: Marsh S. J. , Hubbard A. , Brown D. A.
Published: April 2006

THA (Tacrine) is an anticholinesterase drug reported to alleviate cognitive deficit in Alzheimer's disease. We have used rat isolated superior cervical sympathetic ganglia as a model mammalian cholinergic neural system to study effects of THA on cholinergic synaptic transmission and postsynaptic membrane currents. At 0.1 −3 μM, THA augmented the postsynaptic depolarizations and inward clamp currents produced by acetylcholine but not by the cholinesterase‐resistant analogue, DMPP. Higher concentrations depressed these responses to both acetylcholine and DMPP, and reduced the acetylcholine‐induced increase in membrane current noise. At 1 μM, THA did not affect the amplitude or time‐course of fast (nicotinic) excitatory postsynaptic currents (epscs) evoked by single orthodromic volleys, but higher concentrations induced a biphasic epsc decay. In contrast, low concentrations of THA (1–3 μM) greatly augmented and prolonged the muscarinic slow epsc evoked by repetitive orthodromic volleys: this effect was blocked by 1 μM atropine. Concentrations above 0.1 mM produced a membrane depolarization and inhibited a variety of membrane ionic currents, including voltage‐gated Ca current and subsequent Ca‐activated K currents, and voltage‐gated M‐ and A‐type K currents. It is concluded that the principal effect of THA is to inhibit cholinesterase, and that the main consequence of this is to augment and prolong the muscarinic slow epsc. In contrast, the nicotinic fast epsc is not increased but instead may be reduced through a nicotinic channel‐blocking action. Although THA could also block several other ion channels the concentrations required were too high to contribute significantly to its principal pharmacological actions on ganglionic transmission.
The Study of Passive Membrane Properties and Morphology Reveals Neuronal Differences Along the Sagittal Axis of the Ventral Periaqueductal Grey Matter
Authors: Sánchez D. , Armengol J. A. , Ribas J.
Published: April 2006

The membrane properties of the neurons located in the ventral part of the periaqueductal grey (PAG) of the guinea‐pig were studied using an in vitro slice preparation. Cells had low values of resting membrane potential (−53.3 ± 1.3 mV, mean ± standard error), high input resistance (195.5 ± 16.2 MΩ) and moderate values of membrane time constant (12.6 ± 0.7 ms). The last two parameters changed as recordings were made along the sagittal axis, higher values corresponding to the more rostral cells. Three main neuronal types—fusiform, triangular and stellate—were found in the ventral PAG using intracellular injection of Lucifer yellow. A study of the cell number and cell density was carried out in coronal and sagittal sections of the ventral PAG. This analysis showed a clear gradient of size in this region arising from the gradual disappearance of large (17 to 40 μm) neurons in the caudorostral direction. The neuronal density also increased in this direction. Therefore, some electrotonic and morphological parameters differ along the sagittal axis. These findings suggest a larger neuronal heterogeneity of the caudal part of the PAG, and might contribute to a functional segregation of this region.
Direct Immunohistochemical Evidence of the Existence of 5‐HT1A Autoreceptors on Serotoninergic Neurons in the Midbrain Raphe Nuclei
Authors: Sotelo Constantino , Cholley Béatrice , El Mestikawy Salah , Gozlan Henri , Hamon Michel
Published: April 2006

Physiological, pharmacological and radioautographic binding studies have suggested the presence of the 5‐HT1A autoreceptors on midbrain serotoninergic neurons. The recent production of specific anti‐rat 5‐HT1A receptor antibodies in rabbits injected with a synthetic peptide has provided a tool to examine this problem directly. Using the immunoperoxidase method to localize the receptor protein, neurons of all the sizes and forms characterizing the neuronal populations in the dorsal and median raphe nuclei were stained. Reaction product was distributed along the neuronal surface, outlining the contours of perikarya and dendrites in a continuous but uneven manner. Intracellular staining was scarce and confined to the perinuclear region. Double immunohistochemical staining using the anti‐5‐HT1A receptor antibodies and an anti‐serotonin (5‐HT) antiserum showed that all the 5‐HT1A receptor immunoreactive neurons in the dorsal raphe, and the vast majority of them in the median raphe, are serotoninergic neurons. These data provide the first direct demonstration of the existence of 5‐HT1A autoreceptors on the perikarya and dendrites of serotoninergic neurons in the anterior raphe nuclei.
Active and Passive Membrane Properties of Spinal Cord Neurons that Are Rhythmically Active during Swimming in Xenopus Embryos
Authors: Soffe S. R.
Published: April 2006

Cellular properties have been examined in ventrally located Xenopus spinal cord neurons that are rhythmically active during fictive swimming and presumed to be motoneurons. Resting potentials and input resistances of such neurons are ‐75 ± 2 mV (mean ± standard error) and 118 ± 17 MΩ respectively. Most cells fire a single impulse, 0.5 to 2.0 ms in duration and 48.5 ± 1.8 mV in amplitude, in response to a depolarizing current step. A minority fire several spikes of diminishing amplitude to more strongly depolarizing current. Cells held above spike, threshold fire on rebound from brief hyperpolarizing pulses. Spikes are blocked by 0.1 to 1.0 μM tetrodotoxin (TTX) and are therefore Na+‐dependent. Current/voltage (I/V) plots to injected current are approximately linear near the resting potential but become non‐linear at more depolarized levels. Cells recorded in TTX with CsCl‐filled microelectrodes show a linearized I/V plot at depolarized membrane potentials suggesting the normal presence of a voltage‐dependent K+ conductance activated at relatively depolarized levels. Most cells recorded in this way but without TTX fire long trains of spikes of near constant amplitude, pointing to a role of the K+ conductance in limiting firing in normal cells. Spike blockage with TTX reveals, in some cells, a transient depolarizing Cd2+‐sensitive and therefore presumably Ca2+‐dependent potential that increases in amplitude with depolarization. Cells in TTX, Cd2+, and strychnine, and recorded with CsCl‐filled microelectrodes to block active conductances respond to hyperpolarizing current steps with a two component exponential response. The cell time constant (τ0) obtained from the longer of these by exponential peeling is relatively long (mean 15.7 ms). These findings contribute to an increased understanding of the cellular properties involved in spinal rhythm generation in this simple vertebrate.
The Course of Fibre Diameter Classes Through the Chiasmatic Region in the Ferret
Authors: Reese B. E. , Baker G. E.
Published: April 2006

The present study has examined the transition of fibre order from the optic nerve through the optic chiasm and into the optic tract in the ferret's retinofugal pathway. Semi‐thin sections through the chiasmatic region were examined in normal and in monocularly enucleated ferrets in order to display the segregation of the different axon diameter classes as the fibres pass from the optic nerve into the optic tract, and to determine, for each diameter class, where the crossed and uncrossed components become separated in the chiasmatic region.

As demonstrated in the preceding manuscript, fine and coarse optic axons begin to segregate from the medium optic axons rostral to the fusion of the two optic nerves. This segregation continues in the chiasmatic region where the different axon diameter classes decussate at different rostro‐caudal levels: the fine and coarse diameter axons decussate rostrally, accumulating along the ventral, superficial surface of the contralateral half‐chiasm, while the medium diameter axons continue caudally before crossing the midline. These two populations, a ventral, crossed (fine and coarse) population and a dorsal, yet‐to‐cross (medium) population are discriminable not only by their size in the chiasmatic region, but also by a thin invagination of hypothalamic neuropil separating them at their lateral extreme. The population of ipsilaterally projecting fibres is composed of both fine and medium optic axons. No coarse optic axons project ipsilaterally in the ferret: these fibres all decussate rostrally in the optic chiasm, intermingled with many of the decussating fine fibres.

The fibre ordering in the adult ferret's optic chiasm is interpreted as reflecting a gradient of axonal arrival during development, with successively later arriving optic axons entering one of the two optic tracts at a progressively more superficial, rostral and ventral, location in the chiasmatic region. A fibre's position and time of arrival may influence its subsequent crossed or uncrossed course during the period of axonal ingrowth in development.