Double-stranded rna elements and virus-like particles in Aspergilli.

Mycoviruses with double-stranded RNA (dsRNA) genomes are frequently encountered in Aspergillus isolates. A detailed study of such dsRNA elements in black Aspergillus isolates collected worldwide was carried out, and the data were analysed. The results indicate that about 10% of black Aspergilli are infected. However, the geographic distribution of infected isolates exhibits large variations; 3-13% of the isolates collected from different continents were found to carry dsRNA elements. Hybridization experiments indicated that electrophoretic banding patterns are not reliable tools for estimating the diversity of these mycovirus genomes. Among strains representing other Aspergillus sections, dsRNA segments indicative of mycovirus infection were observed for the first time in 4 species (A. leporis, A. petrakii, A. fumigatus and A. primulinus). The latter species is able to reproduce sexually. This is the second report on the detection of naturally-occurring dsRNAs in sexually reproducing Aspergillus species. The presence of virus-like particles in these and other Aspergilli was also examined by electron microscopy. Most infected Aspergillus isolates examined were found to carry virus-like particles in the size range 36-40 nm.

Estrogen receptor immunoreactivity is present in the majority of central histaminergic neurons: evidence for a new neuroendocrine pathway associated with luteinizing hormone-releasing hormone-synthesizing neurons in rats and humans.

The central regulation of the preovulatory LH surge requires a complex sequence of interactions between neuronal systems that impinge on LH-releasing hormone (LHRH)-synthesizing neurons. The reported absence of estrogen receptors (ERs) in LHRH neurons indicates that estrogen-receptive neurons that are afferent to LHRH neurons are involved in mediating the effects of this steroid. We now present evidence indicating that central histaminergic neurons, exclusively located in the tuberomammillary complex of the caudal diencephalon, serve as an important relay in this system. Evaluation of this system revealed that 76% of histamine-synthesising neurons display ERalpha-immunoreactivity in their nucleus; furthermore histaminergic axons exhibit axo-dendritic and axo-somatic appositions onto LHRH neurons in both the rodent and the human brain. Our in vivo studies show that the intracerebroventricular administration of the histamine-1 (H1) receptor antagonist, mepyramine, but not the H2 receptor antagonist, ranitidine, can block the LH surge in ovariectomized estrogen-treated rats. These data are consistent with the hypothesis that the positive feedback effect of estrogen in the induction of the LH surge involves estrogen-receptive histamine-containing neurons in the tuberomammillary nucleus that relay the steroid signal to LHRH neurons via H1 receptors.