Biological distribution and significance of brown adipose tissue

1. The structure, location, identification and thermogenic function of brown adipose tissue is discussed before describing its distribution in animals. 2. With a few interesting exceptions, brown fat occurs almost exclusively in mammals. 3. This tissue has been positively identified in thirteen orders, but more thorough investigations are required before its absence can be confirmed in the remaining eight mammalian orders. 4. Factors influencing the amount and activity of brown fat seen between and within species are numerous, but some of the most important are body size, diet, environmental temperature, age and reproductive state. 5. The role brown fat, and the effects of impairments in its function, are described in relation to thermoregulation and the control of energy balance and body composition.     

Utility of the white gene in estimating phylogenetic relationships among mosquitoes (Diptera: Culicidae)

The utility of a nuclear protein-coding gene for reconstructing phylogenetic relationships within the family Culicidae was explored. Relationships among 13 species representing three subfamilies and nine genera of Culicidae were analyzed using a 762-bp fragment of coding sequence from the eye color gene, white. Outgroups for the study were two species from the sister group Chaoboridae. Sequences were determined from clone PCR products amplified from genomic DNA, and aligned following conceptual intron splicing and amino acid translation. Third codon positions were characterized by high levels of divergence and biased nucleotide composition, the intensity and direction of which varied among taxa. Equal weighting of all characters resulted in parsimony and neighboring-joining trees at odds with the generally accepted phylogenetic hypothesis based on morphology and rDNA sequences. The application of differential weighting schemes recovered the traditional hypothesis, in which the subfamily Anophelinae formed the basal clade. The subfamily Toxorhynchitinae occupied an intermediate position, and was a sister group to the subfamily Culicinae. Within Culicinae, the genera Sabethes and Tripteroides formed an ancestral clade, while the Culex-Deinocerites and Aedes- Haemagogus clades occupied increasingly derived positions in the molecular phylogeny. An intron present in the Culicinae- Toxorhynchitinae lineage and one outgroup taxon was absent in the basal Anophelinae lineage and the second outgroup taxon, suggesting that intron insertions or deletions may not always be reliable systematic characters.      

Effects of an analogue of thyrotrophin-releasing hormone, RX77368, on infarct size and cerebral blood flow in focal cerebral ischaemia in the rat

Effects of a stable analogue of thyrotrophin-releasing hormone, RX77368, on cerebral blood flow and infarct size have been studied in an acute model of cerebral ischaemia in the rat. Two hours after electrocoagulation of the left middle cerebral artery (MCA), the mean area of ischaemia (+/- SEM), determined histochemically, was 11.5 +/- 2.2% of a single hemisphere and blood flow, determined using radiolabelled microspheres, was reduced by 40% in the left forebrain (p less than 0.001 compared with sham-operated animals). Administration of RX77368 (50 micrograms/kg, intracerebroventricularly) within 10 min of arterial occlusion caused a significant (p less than 0.01) reduction in mean lesion size to 3.7 +/- 1.8% and stimulation of blood flow to the left ischaemic forebrain (60% above saline treated). Peripheral administration of RX77368 (1 mg/kg intraperitoneally) also significantly stimulated blood flow to the ischaemic forebrain and caused an apparent decrease in frequency of large infarcted areas of brain tissue, although mean lesion size was not significantly affected. These findings indicate that RX77368 ameliorates tissue damage in acute focal cerebral ischaemia. Such effects may be related to stimulation of cerebral blood flow.     

Studies on the kinetics of expulsion by guinea-pigs of primary infections with the intestinal nematode parasite Trichostrongylus colubriformis

Heston strain guinea-pigs were infected with 1000 Trichostrongylus colubriformis infective larvae and the kinetics of parasite expulsion from the host studied. Expulsion began approximately 15 days after infection, after which log worm count declined from an initial level of approximately 2·77 at a rate of approximately 0·1 per day. There was no significant difference in worm counts in each sex.     

Spontaneous and experimental variations in body weight, food intake and metabolic rate in captive dormice (Glis glis)

Captive dormice (Glis glis) showed spontaneous cyclical fluctuations in body weight that were not synchronous between animals and not directly related to season. Presenting the animals with a varied and palatable (cafeteria) diet for short periods caused marked increases in energy intake and body weight, and higher levels of oxygen consumption (V02). The level of hyperphagia was fairly constant, but the rise in V02 during cafeteria feeding varied (20-80%) according to season, being greatest in the winter (Nov.-Jan.). Removal of the cafeteria foods caused weight loss, hypophagia and a fall in V02 to levels below that seen in either normally-fed or fasted dormice. This hypometabolism was associated with increased periods of sleep and torpor, and it is suggested that the excess fat deposition resulting from cafeteria feeding may have induced a transient "hibernation-like" state.     

Protein synthesis in liver,skeletal muscle,and brown adipose tissue of rats fed a protein-deficient diet

Feeding protein-deficient diets to rats is known to stimulate diet-induced thermogenesis and activate brown adipose tissue (BAT). The fact that BAT protein content, unlike that of other tissues, is unnaffected by protein deficiency prompted us to measure tissue protein synthesis in vivo in animals maintained on normal- (18.8%) and low- (7.6%) protein (LP) diets. Protein synthesis was depressed in the liver of the LP rats due to a fall in RNA activity, with no change in RNA content, and synthesis was also reduced in skeletal muscle from the LP group, but this was due to decreased RNA content with no change in RNA activity. Conversely, protein synthesis, RNA, DNA, and protein content of interscapular BAT were all unaltered in protein-restricted animals. These data indicate that, unlike liver, skeletal muscle, and whole carcass, BAT protein synthesis is not reduced in protein-restricted rats, and this may be related to activation of thermogenesis in the tissue.     

QUAESTORA AMPLECTA GEN. ET SP. N., A STRUCTURALLY SIMPLE MEDULLOSAN STEM FROM THE UPPER MISSISSIPPIAN OF ARKANSAS

A well preserved, permineralized seed fern stem is described from the Upper Mississippian Fayetteville Formation of north central Arkansas. Quaestora amplecta gen. et sp. n. is 41.6 cm long and exhibits six pairs of decussate, highly decurrent petiole bases. The stem has a cruciform, exarch protostele with prominent secondary xylem, vascular cambium and secondary phloem. Leaf traces are terete and occur as an outer ring with a small number of internal strands. The cauline vasculature, leaf-trace production, petiolar anatomy and several other features indicate that this specimen represents the most structurally simple and geologically ancient medullosan stem presently recognized.     

Conversion of DDT to DDD in flooded soil

Summary Anaerobic conditions obtained by flooding the soil caused reductive dechlorination of p,p-DDT and its conversion to p,p-DDD was enhanced under water-logged conditions creating or favouring anaerobiosis. The DDT showed recalcitrance in the soil kept at 15% moisture.More o,p-DDT was lost from the flooded soil. Similar amounts of p,p-DDE were detected in all of the three levels of technical DDT treatments and the concentrations were not significantly different under both aerobic and anaerobic conditions.