Lateral visual pathway of giant barnacle

1. We have studied the responses to light, conduction down the axons, and anatomical projections of the photoreceptors of the lateral eye in the giant barnacle, Balanus nubilus. By recording intracellularly from ganglion cells that respond to visual input, we have described convergence of the lateral and median visual pathways. 2. Each lateral eye contains three photoreceptor cells, two large and one small. Cobalt filling of single large lateral receptor axons demonstrated that they end in a restricted ovoid bush on the ipsilateral side of the ganglion in approximately the same region in which the median receptors arborize. 3. The lateral receptors have dark resting potentials and responses to light similar to those previously described for the receptors of the median eye. Like the median receptors, the lateral receptors conduct visual signals decrementally, although their axons may be twice as long (14-25 mm). 4. Passing current of either polarity into either of the large receptors produced no detectable voltage change in the other cell. Action potentials elicited in either cell by stimulating it in the presence of tetraethylammonium ion were not detected in the other cell. Light-induced membrane noise in one cell did not correlate with noise in the other. Thus, like the receptors of the median eye, the large receptors of the lateral eye are not electrically coupled. 5. By shadowing each ocellus individually, we have shown that the signals from the median and lateral photoreceptors converge at the level of the second-order cells described for the median pathway. Shadowing the median or a lateral eye gave rise to synergistic responses in second-, third-, and all higher order ganglion cells studied. No cells were found that were driven solely by the lateral eyes. Thus, the lateral and median visual pathways are highly convergent.     

No evidence for transmission disequilibrium between a new marker at the myelin basic protein locus and multiple sclerosis in French patients

The myelin basic protein (MBP) gene is a candidate locus for susceptibility to multiple sclerosis. Several groups have tested a complex (TGGA)n repeat in the 5' region of this gene for association/linkage with multiple sclerosis, with divergent results. This region of tandem repetitive sequence has been subjected to complex rearrangements, and there is a possibility that alleles of the same size have different internal structures, which reduces the interest of this marker for linkage disequilibrium studies and may at least partly explain the conflicting results obtained so far. To overcome this problem, we isolated a new polymorphic (CA)n repeat within the Golli-MBP locus. The limited number of alleles identified makes this other marker suitable for transmission disequilibrium studies. We tested this marker for linkage with multiple sclerosis, using the transmission-disequilibrium test (TDT) on a sample of 196 nuclear families in which the genotypes of both parents could be unambiguously defined. We found no evidence of transmission disequilibrium between multiple sclerosis and any of the three alleles of this marker, even when the patients were subdivided according to their HLA-DRB1*1501 status. The present data thus provide no evidence for a contribution of the MBP gene to multiple sclerosis susceptibility in French patients.     

Reduced virulence of HWP1-deficient mutants of Candida albicans and their interactions with host cells

The Candida albicans gene HWP1 encodes a surface protein that is required for normal hyphal development in vitro. We used mutants lacking one or both alleles of HWP1 to investigate the role of this gene in virulence. Mice infected intravenously with the homozygous hwp1 null mutant, CAL3, survived a median of >14 days, whereas mice infected with a control strain containing two functional alleles of HWP1 survived only 3.5 days. After 1 day of infection, all strains produced similar levels of infection in the kidneys, spleen, and blood. However, after 2 and 3 days, there was a significant decrease in the number of organisms in the kidneys of the mice infected with CAL3. This finding suggests that the hwp1 homozygous null mutant is normal in its ability to initiate infection but deficient in its capacity to maintain infection. CAL3 also germinated minimally in the kidneys. The ability of the heterozygous null mutant to germinate and cause mortality in mice was intermediate to CAL3, suggesting a gene dosage effect. To investigate potential mechanisms for the diminished virulence of CAL3, we examined its interactions with endothelial cells and neutrophils in vitro. CAL3 caused less endothelial cell injury than the heterozygous hwp1 mutant. We conclude that the HWP1 gene product is important for both in vivo hyphal development and pathogenicity of C. albicans. Also, the ability to form filaments may be critical for candidal virulence by enabling the fungus to induce cellular injury and maintain a deep-seated infection.     

Partial androgen insensitivity with phenotypic variation caused by androgen receptor mutations that disrupt activation function 2 and the NH(2)- and carboxyl-terminal interaction

Partial androgen insensitivity with sex phenotype variation in two unrelated families was associated with missense mutations in the androgen receptor (AR) gene that disrupted the AR NH(2)-terminal/carboxy terminal interaction. Each mutation caused a single amino acid change within the region of the ligand-binding domain that forms activation function 2 (AF2). In one family, the mutation I737T was in alpha helix 4 and in the other F725L was between helices 3 and 4. Neither mutation altered androgen binding as determined by assays of mutant AR in the patient's cultured genital skin fibroblasts or of recombinant mutant receptors transfected into COS cells. In transient cotransfection assays in CV1 cells, transactivation with the AR mutants at low concentrations of DHT was reduced several fold compared with wild-type AR but increased at higher concentrations. Defects in NH(2)-terminal/carboxy terminal interactions were identified in mammalian two hybrid assays. In similar assays, there was reduced binding of the p160 coactivators TIF2/SRC2 and SRC1 to the mutant AR ligand binding domains (LBD). In the family with AR I737T, sex phenotype varied from severely defective masculinization in the proband to a maternal great uncle whose only manifestation of AIS was severe gynecomastia. He was fertile and passed the mutation to two daughters. The proband of the F725L family was also incompletely masculinized but was raised as a male while his half-sibling by a different father was affected more severely and reared as a female. These studies indicate that the function of an AR AF2 mutant in male development can vary greatly depending on the genetic background.     

The effects of intrahippocampal ibotenic acid and their blockade by (−) 2-amino-7-phosphonoheptanoic acid: Morphological and electroencephalographical analysis

Intrahippocampal injections of the excitotoxin ibotenic acid caused a biphasic behavioral pattern in rats. Both the immediate induction of hyperactivity and stereotypical behaviors and a secondary phase of progressively decreasing behavioral activities beginning 15-20 min after ibotenate administration, were accompanied by characteristic seizures measured by bilateral recordings in hippocampus and cortex. Typically, EEG changes consisted of high voltage spiking in all leads. The phase of behavioral depression was accompanied by episodic, short (5-30 s) seizures. In addition, cortical slow waves very similar to those elicited by intrahippocampal muscimol were observed during this period. Attempts were made to correlate occurrence and severity of seizures with the extent of neuronal degeneration. While a trend in favor of such a correlation existed, a firm causal relationship could not be established; some animals could display seizure activity with only marginal concomitant nerve cell loss and vice versa. Intrahippocampal co- and post-administration of ibotenate with (-) 2-amino-7-phosphonoheptanoic acid entirely prevented or stopped the occurrence of both EEG changes and neuronal degeneration. Ibotenate-induced seizures and lesions and their specific blockade by a selective antagonist may constitute valuable experimental paradigms for the investigation of seizure disorders.     

Polymorphic MHC ancestral haplotypes affect the activity of tumour necrosis factor-alpha.

It remains unclear which MHC loci are involved in susceptibility to autoimmune diseases and immune deficiencies. We have chosen to evaluate whether different alleles of tumour necrosis factor-alpha (TNF-alpha) are important, as TNF has been implicated in the etiology of many immunological disorders. We have shown previously that a restriction fragment length polymorphism in the TNF region correlates with MHC ancestral haplotypes. We therefore examined the effect of ancestral haplotype on the activity of TNF-alpha in culture supernatants of lymphoblastoid cell lines. The results demonstrate that TNF-alpha activity in supernatants of 8.1 (A1, B8, DR3) cell lines was higher than that present in the supernatants from cells homozygous for eight different MHC ancestral haplotypes, and indicate that polymorphisms in TNF-alpha, or in other MHC genes that regulate TNF, may be responsible for the 8.1 phenotype.     

Relationship between fatty liver and subsequent development of necrosis, inflammation and fibrosis in experimental alcoholic liver disease

Rats fed a diet varying in the amount of fat, infused with ethanol, were studied to determine the relationship among diet, degree of fatty liver, and development of necrosis, inflammation, and fibrosis. Three groups of experimental animals, male Wistar rats, were fed diets containing 25% fat, 35% fat, and 32% fat with low protein. Morphologic assessment of liver injury was performed monthly by obtaining liver biopsies. The greatest degree of fatty infiltration at 1 month was seen in the high fat-low protein group, the mean fat score (3.8 +/- 0.37) was significantly higher than in the other two groups (P less than 0.05 and P less than 0.01). When the subsequent development of necrosis, inflammation, and fibrosis was related to the degree of fatty infiltration at 1 month, a significant relationship was seen between the number of animals developing these pathologic lesions and the severity of fatty liver. Our results show that the degree of fatty infiltration of the liver, influenced by the dietary intake of both fat and protein, is related to the subsequent development of necrosis, inflammation, and fibrosis in our intragastric feeding model for alcoholic liver disease.