Antennal sensory organs in the millipede Eurypauropus ornatus: Fine structure of the flagella and globulus

On the antennal tip of Eurypauropus ornatus are 3 threadlike sensilla—the flagella, and a single spheroid sensillum—the globulus. Each of the 3 flagella is innervated by 2 groups of sensory cells. One group contains 4 cells, the other, 5. All cells of the “four group” and 3 of the “five group” are comprised of single cilia and unbranched dendrites which extend along the lumen of the flagellum. Two cells of the “five group” have double cilia and pairs of unbranched dendrites. One pair also enters the flagellum and the other pair terminates beneath the flagellar base to form a concentric array of lamellae. No pores are present in the cuticular wall. Eight sensory cells innervate the globulus. They are arranged in 3 groups, one triplet and 2 pairs, in addition to a single cell. The single cell contains a pair of cilia whose unbranched dendrites differentiate into tubular bodies that are inserted into the base of the globulus. Each of the other 7 sensory cells has a single cilium. Their unbranched dendrites penetrate into the globulus in 3 groups as described for the sensory cells. The dendrites in each group terminate in an individual pore channel at the globulus tip and completely fuse with the electron-dense material that plugs the pore channel. Based on structural similarities to sensilla having known functions, it is probable that the flagella and the globulus are chemoreceptors, the former responding to odors, the latter sensitive to substances in aqueous solution.     

Selective Brain Cooling Reduces Water Turnover in Dehydrated Sheep

In artiodactyls, arterial blood destined for the brain can be cooled through counter-current heat exchange within the cavernous sinus via a process called selective brain cooling. We test the hypothesis that selective brain cooling, which results in lowered hypothalamic temperature, contributes to water conservation in sheep. Nine Dorper sheep, instrumented to provide measurements of carotid blood and brain temperature, were dosed with deuterium oxide (D₂O), exposed to heat for 8 days (40◦C for 6-h per day) and deprived of water for the last five days (days 3 to 8). Plasma osmolality increased and the body water fraction decreased over the five days of water deprivation, with the sheep losing 16.7% of their body mass. Following water deprivation, both the mean 24h carotid blood temperature and the mean 24h brain temperature increased, but carotid blood temperature increased more than did brain temperature resulting in increased selective brain cooling. There was considerable inter-individual variation in the degree to which individual sheep used selective brain cooling. In general, sheep spent more time using selective brain cooling, and it was of greater magnitude, when dehydrated compared to when they were euhydrated. We found a significant positive correlation between selective brain cooling magnitude and osmolality (an index of hydration state). Both the magnitude of selective brain cooling and the proportion of time that sheep spent selective brain cooling were negatively correlated with water turnover. Sheep that used selective brain cooling more frequently, and with greater magnitude, lost less water than did conspecifics using selective brain cooling less efficiently. Our results show that a 50kg sheep can save 2.6L of water per day (~60% of daily water intake) when it employs selective brain cooling for 50% of the day during heat exposure. We conclude that selective brain cooling has a water conservation function in artiodactyls.     

Sexual differentiation in Mucor: Trisporic acid response mutants and mutants blocked in zygospore development

Spores of a minus strain of Mucor mucedo (Bref.) were treated with 1-methyl-[3-nitro]-1-nitro-soguanidine and mutants were isolated either by testing for zygophore induction with externally supplied trisporic acids (TA) or by mating with wild type plus colonies. Mutants were found defective (Tar^?) or temperature-sensitive (Tar-Ts) in their reaction towards trisporic acids, blocked or temperature-sensitive in their mating with plus strain (Mat^? or Mat-Ts) or temperature-sensitive in zygospore development (Zyg-Ts). The inability to react against externally supplied trisporic acids was not necessarily coupled with an inability to mate with plus strain (phenotype Tar^? Mat⁺). This indicated that the diffusion and uptake of trisporic acids is not a necessary prerequisite to the sexual interaction of Mucor mating types.     

Inositol Phospholipid Hydrolysis by Rat Sciatic Nerve Phospholipase C

Rat sciatic nerve cytosol contains a phosphodiesterase of the phospholipase C type that catalyzes the hydrolysis of inositol phospholipids, with preferences of phosphatidylinositol 4'-phosphate (PIP) greater than phosphatidylinositol (PI) much greater than phosphatidylinositol 4',5'-bisphosphate (PIP2), at a pH optimum of 5.5-6.0 and at maximum rates of 55, 13, and 0.7 nmol/min/mg protein, respectively. Analysis of reaction products by TLC and formate exchange chromatography shows that inositol 1,2-cyclic phosphate (83%) and diacylglycerol are the major products of PI hydrolysis. [32P]-PIP hydrolysis yields inositol bisphosphate, inositol phosphate, and inorganic phosphate, indicating the presence of phosphodiesterase, phosphomonoesterase, and/or inositol phosphate phosphatase activities in nerve cytosol. Phosphodiesterase activity is Ca2+-dependent and completely inhibited by EGTA, but phosphomonoesterase activity is independent of divalent cations or chelating agents. Phosphatidylcholine (PC) and lysophosphatidylcholine (lysoPC) inhibit PI hydrolysis. They stimulate PIP and PIP2 hydrolysis up to equimolar concentrations, but are inhibitory at higher concentrations. Both diacylglycerols and free fatty acids stimulate PI hydrolysis and counteract its inhibition by PC and lysoPC. PIP2 is a poor substrate for the cytosolic phospholipase C and strongly inhibits hydrolysis of PI. However, it enhances PIP hydrolysis up to an equimolar concentration.