The effects of oestrous condition and familiarity on the sexual behaviour of polecats (Mustela putorius and M. fur × M. putorius hybrids)

The effects of two factors on the sexual behaviour of polecats ( Mustela furo and M. putorius × M. furo hybrids) were investigated, in an indoor arena of 16 m², firstly the oestrous condition of the female and secondly the familiarity of the two individuals.
The initial approaches of a male polecat are similar irrespective of the oestrous condition of the female but his subsequent behaviour is dependent upon the female's response. Whereas males copulated with oestrous females they showed a wider repertoire of social acts and a greater number of changes of behaviour towards females which were not in oestrous. Unreceptive females elicited both sexual and aggressive behaviour from males.
Unfamiliar females provide a more powerful eliciting stimulus for the male's copulatory behaviour than do familiar females.     

Direct observations on the sublittoral marine algae of Argyll,Scotland

Summary The distribution with depth of sublittoral marine algae has been investigated at 11 sites on the west coast of Scotland. More than half of the species found were confined to the sublittoral zone. The greatest variety of species was found in shallow water at sites sheltered from excessive turbulence. With increasing depth the number of species found steadily decreased. There was no evidence of a specifically distinct algal flora confined to deeper water. No algae were found deeper than 36 m below ELWS at any site, but the lower limit of algal growth was reduced to 9 m in a turbid water loch and to 3 m at a site where the herbivorous echinoderm Ophiocomina nigra was abundant. Fairly distinct algal communities were found on different substrates. The major communities recognised underwater were algae attached to stable substrata, algae attached to unstable substrata and epiphytic on other algae, especially on the stipes of Laminaria hyperborea. On stable rock in areas subject to water movement L. hyperborea forest was the dominant vegetation whereas on unstable substrata and in sheltered localities L. saccharina was dominant.     

SODIUM AND THE FLUX OF CALCIUM IONS IN ELECTRICALLY-STIMULATED CEREBRAL TISSUE

Abstract— The rate of efflux of ⁴⁵Ca²⁺ from slices of rat cerebral cortex was resolved into two exponential curves which were attributed to an extracellular component and an intracellular or bound component. Electrical stimulation increased efflux of ⁴⁵Ca²⁺ from the more stable pool and the time course for the redistribution of Na⁺ and K⁺ paralleled that for the increased efflux of Ca²⁺. This effect of stimulationwas dependent on the presence of Na⁺ in the incubation medium. Lack of Na⁺ in the medium during loading of the slices with ⁴⁵Ca²⁺ increased uptake but on subsequent transfer to a medium containing Na⁺, electrical pulses failed to increase the rate of efflux of ⁴⁵Ca²⁺. In unstimulated slices, the rate of efflux of ⁴⁵Ca²⁺ was dependent upon the concentration ratio of Na⁺ to Ca²⁺ in the incubation medium. Saxitoxin and tetrodotoxin inhibited the increased efflux of ⁴⁵Ca²⁺ that occurred during electrical stimulation but exerted no effect on Ca²⁺-Ca²⁺ exchange. Our results suggest that there is a Na⁺-dependent turnover of Ca²⁺ in brain slices which may involve changes in affinity at a common binding site. The possible involvement of such a Na⁺-Ca²⁺ interaction in the regulation of neurotransmitter function is discussed.     

New Mutant Types at the ade3 Locus of Saccharomyces cerevisiae

Six mutants, allelic to ade3, were isolated after mutagenic treatment of a prototrophic strain of yeast. All six grow on medium supplemented with adenine alone and four respond to histidine. Supplementation with adenine plus histidine or methionine inhibits growth, but a mixture of these three is stimulatory. Heteroallelic diploids formed by the new mutants with the standard ade3 can resemble either parent or show an intermediate phenotype. The new mutants, unlike standard ade3, are not fully epistatic to ade2. The activities of three enzymes concerned in tetrahydrofolate metabolism have been assayed in the new and standard ade3 mutants and wild type. The only difference detected between the new and standard ade3 was in the levels of 10-formyltetrahydrofolate synthetase. Activity in the new mutants ranged from 36 to 109% of wild type compared with 10 to 12% in the standard ade3. Possible mechanisms to account for the varied phenotypes at the ade3 locus are discussed.     

Light-independent accumulation of chlorophyll a and b and protochlorophyllide in green barley (Hordeum vulgare)

Barley ( Hordeum vulgare L. cvs Clipper, Procter, Astrix) seedlings were transferred from daylight to darkness and changes in chlorophyll a , chlorophyll b , protochlorophyllide and chlorophyllide (μ leaf⁻¹) in either the first or second leaf determined spectrophotometrically after separating the esterified from unesterified pigments by partitioning between ammoniacal acetone and light petroleum ether. Chlorophyll a and b as well as protochlorophyllide accumulated in the dark. The ratio of chlorophyll to protochlorophyllide formed in the absence of light was 18:1. 5-aminolevulinic acid (10 m M ) promoted the synthesis of chlorophyll a and b and protochlorophyllide. Pigment synthesis and response to 5-aminolevulinic acid addition was related to tissue age. Mature tissue in the apical third of the leaf accumulated most chlorophyll, but per μg chlorophyll present at the time of transfer to darkness, was less efficient than immature tissue towards the base of the leaf. Immature tissue was also most responsive to added 5-aminolevulinic acid. Chlorophyll synthesis in the dark was accompanied by chloroplast development. Chloroplasts in immature leaf tissue increased in size and extent of thylakoid development when transferred from daylight to darkness. The results indicate that chlorophyll synthesis and chloroplast membrane development in light-grown barley continue into the dark phase of the diurnal cycle. A light-independent protochlorophyllide reductase in light-grown barley seedlings is postulated.     

Potential bioactivation pathways for the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)

The metabolism of the selective nigrostriatal toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) has been studied in rat brain mitochondrial incubation mixtures. The 1-methyl-4-phenylpyridinium species MPP+ has been characterized by chemical ionization mass spectral and 1H NMR analysis. Evidence also was obtained for the formation of an intermediate product which, with the aid of deuterium incorporation studies, was tentatively identified as the alpha-carbon oxidation product, the 1-methyl-4-phenyl-2,3-dihydropyridinium species MPDP+. Comparison of the diode array UV spectrum of this metabolite with that of the synthetic perchlorate salt of MPDP+ confirmed this assignment. The oxidation of MPTP to MPDP+ but not of MPDP+ to MPP+ is completely inhibited by 10(-7) M pargyline. MPDP+, on the other hand, is unstable and rapidly undergoes disproportionation to MPTP and MPP+. Based on these results, we speculate that the neurotoxicity of MPTP is mediated by its intraneuronal oxidation to MPDP+, a reaction which appears to be catalyzed by MAO. The interactions of MPDP+ and/or MPP+ with dopamine, a readily oxidizable compound present in high concentration in the nigrostriatum, to form neurotoxic species may account for the selective toxic properties of the parent drug.     

Effect of sodium sulfate on in vitro organogenesis of tobacco callus

Callus of tobacco (Nicotiana tabacum L. cv. Wisconsin 38) was grown on callus-proliferating (CP) and shoot-forming (SF) media with elevated sodium sulfate (Na₂SO₄) concentrations either in the light or dark for more than one year. An increase in Na₂SO₄ concentration resulted in a decrease in callus growth index, an increase in percent dry weight of callus tissues grown on both media, and a decrease in both number of calli forming shoots and number of shoots per callus in SF medium. The CP callus grown in the light spontaneously began to form shoots after the 5th monthly transfer, and spontaneous root formation occured after the 16th transfer in the presence of 0.75 and 1.0% Na₂SO₄. Both water () and osmotic (_s) potentials of the callus increased with increasing Na₂SO₄ concentration; and callus exhibited greater and _s in the light than dark for both CP and SF media.     

Active uptake of MPP+, a metabolite of MPTP, by brain synaptosomes

Mouse brain synaptosomal preparations were used to study uptake of N-methyl-4-phenylpyridine (MPP+), a metabolite of the neurotoxin MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine). The uptake of [3H]-MPP+ by striatal synaptosomes was approximately 25 X greater than that of [3H]-MPTP, with a KM of 0.48 microM and a Vmax of 5.3 nmoles/g tissue/min. Uptake was Na+ dependent and inhibited by ouabain, cocaine and dopamine (Ki 0.12 microM). Synaptosomes prepared from the corpus striatum accumulated [3H]-MPP+ at a rate 5-10 times higher than preparations from other brain regions. This selective uptake of MPP+ may contribute to the specificity of the toxic effects of MPTP on nigrostriatal dopaminergic neurons.     

Oestrogen-induced cholesterol and fatty acid biosynthesis in Xenopus laevis liver during vitellogenic response

1. Oestradiol-17β induces livers of Xenopus laevis (South African clawed toad) to synthesize and secrete into the serum large quantities of the egg-yolk-protein precursor, vitellogenin. The peak of this response occurs 9–16 days after hormone treatment [Dolphin, Ansari, Lazier, Munday & Akhtar (1971) Biochem. J. 124, 751–758]. It is now shown that 6 days after hormone treatment a 120–160-fold stimulation of the synthesis of cholesterol and fatty acid compared with control values occurred. 2. A cell-free system, derived from Xenopus liver, which synthesizes squalene and fatty acid is described. By using this system, several hundredfold stimulation of incorporation of [¹⁴C]acetate into squalene was recorded 6 days after the administration of oestradiol-17β, compared with a 3–4-fold stimulation of incorporation of [³H]mevalonate compared with control values. It is argued that oestradiol-17β must affect enzyme(s) catalysing step(s) between acetate and mevalonate in the biosynthetic pathway to cholesterol. 3. In incubation of liver slices in vitro, most of the lipid and cholesterol synthesized in response to the steroid hormone was associated with those subcellular fractions that contained membranes. Moreover, pulse-labelling experiments in vivo showed that 70% of this lipid and cholesterol was retained in the liver. The remainder appeared in the serum, where it was equally distributed between vitellogenin and vitellogenin-free serum. 4. G.l.c. analyses of the cholesterol content of liver microsomal fractions of Xenopus laevis indicated that the cholesterol content was at least 50% higher in microsomal fractions obtained from livers that had been exposed to oestradiol-17β. Meanwhile, g.l.c. analysis of the lipid moiety of secreted vitellogenin showed that up to 35% of its lipid was cholesterol.