We present 12 CO 1 → 0 observations of eleven low luminosity (M B > −18), HI-rich dwarf galaxies. Only the three most metal-rich galaxies, with 12+log(O/H)≈ 8.2, are detected. Very deep CO spectra of six extremely metal-poor systems (12+log(O/H)≤7.5) yield only low upper limits on the CO surface brightness, I CO < 0.1 K km s −1 . Three of these six have never before been observed in a CO line, while the others now have much more stringent upper limits. For the very low metallicity galaxy Leo A, we do not confirm a previously reported detection in CO, and the limits are consistent with another recent nondetection.We combine these new observations with data from the literature to form a sample of dwarf galaxies which all have CO observations and measured oxygen abundances. No known galaxies with 12+log(O/H)<7.9 (Z < 0.1Z ⊙ ) have been detected in CO. Most of the star-forming galaxies with higher (12+log(O/H)>8.1) metallicities are detected at similar or higher I CO surface brightnesses. The data are consistent with a strong dependence of the I CO /M H 2 ≡ X CO conversion factor on ambient metallicity. The strikingly low upper limits on some metal-poor galaxies lead us to predict that the conversion factor is non-linear, increasing sharply below ∼1/10 of the solar metallicity (12+log(O/H)≤7.9).

Peptides structurally related to mammalian tachykinins have recently been isolated from the brain and intestine of several insect species, where they are believed to function as both neuromodulators and hormones. Further evidence for the signaling role of insect tachykinin-related peptides was provided by the cloning and characterization of cDNAs for two tachykinin receptors from Drosophila melanogaster. However, no endogenous ligand has been isolated for the Drosophila tachykinin receptors to date. Analysis of the Drosophila genome allowed us to identify a putative tachykininrelated peptide prohormone (prepro-DTK) gene. A 1.5-kilobase pair cDNA amplified from a Drosophila head cDNA library contained an 870-base pair open reading frame, which encodes five novel Drosophila tachykininrelated peptides (called DTK peptides) with conserved C-terminal FXGXR-amide motifs common to other insect tachykinin-related peptides. The tachykinin-related peptide prohormone gene (Dtk) is both expressed and post-translationally processed in larval and adult midgut endocrine cells and in the central nervous system, with midgut expression starting at stage 17 of embryogenesis. The predicted Drosophila tachykinin peptides have potent stimulatory effects on the contractions of insect gut. These data provide additional evidence for the conservation of both the structure and function of the tachykinin peptides in the brain and gut during the course of evolution.Substance P was the first peptide signaling molecule to be identified by virtue of its effects upon blood pressure and smooth muscle contraction (1) and is the archetypal member of the tachykinin family of peptides. Vertebrate tachykinins represent a large family of peptides that elicit a wide range of both central and peripheral responses (2-5). Although these peptides are structurally diverse, all contain a conserved C-terminal FXGLM-amide motif. Like other biologically active peptides, substance P is derived from a larger prohormone polypeptide (preprotachykinin A (PPT-A) 1 ) that also allows the production of several other biologically active peptides (neurokinin A, neuropeptide K, and neuropeptide ␥) (6). Three different isoforms of preprotachykinin can be produced as a result of alternative splicing of the PPT-A mRNA, which, in conjunction with alternative post-translational processing of the prohormone, allows the production of these peptides in a tissue-specific manner (7-9). A fifth mammalian tachykinin, neurokinin B, is derived from a separate gene product, preprotachykinin B (10).The tachykinin family is not confined to vertebrates, and a large number of tachykinins have now been isolated from a variety of invertebrate species such as the cockroach Leucophaea maderae (11, 12), the mosquito Culex salinarius (13), and the echiuroid worm Urechis unicinctus (14). In contrast to the vertebrate tachykinins, almost all of the invertebrate tachykinins contain a conserved C-terminal FXGXR-amide motif and, for this reason, have been termed tachykinin-related peptides (TRPs). Not...

Conscious patients with Grade III fourth ventricular compression should undergo urgent clot evacuation before deterioration. Surgical evacuation of the clot may not be required for large hematomas (>3 cm) if the fourth ventricle is not totally obliterated at the level of the clot.

Original article can be found at: http://adsabs.harvard.edu/ Copyright American Astronomical Society. DOI: 10.1086/192193 [Full text of this article is not available in the UHRA]We have conducted a directed search for intergalactic H I clouds, using H II galaxies as pointers to fields on the sky likely to contain such clouds. This extends our previous survey (Taylor et al. 1993) by using the VLA to map in the 21 cm line of H I a complete, volume-limited sample of H II galaxies. We detected 20 of the 21 galaxies in our sample and find that 14 have nearby H I companions. Some H II galaxies have multiple companions, and we have discovered a total of 19 companions, or a frequency of occurrence of companions of 0.67. This detection rate is statistically consistent with a lower limit of the companion frequency of 0.46, assuming that no companions are present outside of the spatial and velocity ranges searched by our VLA observations. The companion population is not a homogeneous one but is comprised of H II galaxies, cataloged and previously uncataloged dwarfs, and several objects for which there are no known optical counterparts. These latter objects may be intergalactic H I clouds. Here we present our H I maps and R-band optical images of the H II galaxy and companion systems, along with physical properties determined from these data. We compare our sample to samples of H II galaxies from the literature, finding that the literature samples over-represent the more massive, more luminous H II galaxies. Our total mass estimates imply that H II galaxies are dominated by dark matter, in agreement with observations of dwarf irregular galaxies. We also find a tendency for H II galaxies to be characterized by dense central H I concentrations surrounded by less dense envelopes. Detailed analysis of the H II galaxy/companion systems will appear in subsequent papers

Original article can be found at: http://adsabs.harvard.edu/abs/ Copyright American Astronomical Society. DOI: 10.1086/116910 [Full text of this article is not available in the UHRA]We present high resolution Very Large Array (VLA) 21 cm line observations of five H II galaxies combined with previous lower resolution data from Taylor et al. (1993) and optical broadband R and H-alpha Charge Coupled Device (CCD) images of the systems. Following Kennicutt (1989) we calculated the threshold H I surface density for star formation for the H II galaxies and compared the location and shape of this predicted threshold density contour with the optical shape of the galaxies. We find generally a good correlation between these two, although a constant density contour of 1021/sq cm fits the images of the optical galaxies equally as well. The H I synthesis observations have revealed that the H II galaxies have sharply peaked H I radial profiles, in contrast to the relatively flattened profiles of low surface brightness (LSB) galaxies, suggesting that large central concentrations of gas are a necessary condition for the occurrence of bursts of massive star formation seen in H II galaxies. These observations are consistent with the hypothesis that LSB galaxies represent the quiescent phase of H II galaxies, if a suitable mechanism exists (such as galaxy interactions) to cause H I to concentrate at the center of LSB galaxies prior to the onset of the burst of star formation. However, it is noted that the H II galaxies (and dwarf galaxies in general) span a relatively large range in mass. Since many properties correlate with mass (e.g., gas mass fraction), we point out that great care needs to be taken in choosing the proper comparison samples of LSB and H II galaxies