Correlative secretion of protein, lactose and K + in milk of the goat

Rates of secretion of milk constituents (fat, protein, lactose, Na⁺ and K⁺) in the lactating goat were measured under normal circumstances and after injections of ouabain. In all experiments a close association was noted in the secretion rates for protein, lactose and K⁺. Under the influence of ouabain, the concentration of Na⁺ in the milk tended to rise and that of K⁺ to fall. The rate of milk fat secretion varied independently from the rates for the other constituents. It is reasonably assumed that the principal mechanism of milk protein secretion is by emptying of Golgi vesicles through the plasma membrane. The close correlation in rates for protein, lactose and K⁺ supports the contention that all three are assembled in Golgi vesicles and secreted by the same mechanism.     

Influence of lecithin acyl chain composition on the kinetics of exchange between chylomicrons and high density lipoproteins

The kinetics of lecithin exchange between native lipoproteins was characterized for individual molecular species of lecithins of rat mesenteric lymph chylomicrons and rat plasma HDL. Studies were performed in the absence of lipid transfer proteins. Donor (chylomicrons) and acceptor (HDL) particles were present in ratios of 1:1 and 1:10 with respect to total phospholipid. Biphasic exchange kinetics were observed for all major lecithins common to chylomicrons and HDL at both proportions of donor to acceptor particles. During the early rapid phase of exchange, complete in about 30 min, 40-60% of the total lecithin pool was exchanged. Initial exchange rates were most rapid for the more hydrophilic species of the major lecithins normally present in both lipoproteins. Calculated activation energies correspondingly were least for a diunsaturated lecithin (18:1-20:4), intermediate for lecithins were 16:0 in position-1 (16:0-18:2 and 16:0-20:4), and highest for analogous lecithins with 18:0 in position-1. A 10-fold increase in the ratio of acceptor to donor particles affected neither the biphasic nature of the exchange nor the rates of exchange of individual molecular species (consistent with exchange by diffusion rather than by particle collisions). Total equilibration of individual molecular lecithin species was achieved by 24 hr (37 degrees C, donor to acceptor ratio of 1:1) with only a small change in the relative mass of lecithins in chylomicrons and HDL. Novel lecithins containing 18:3, incorporated into chylomicrons, were found to exchange exceedingly rapidly.(ABSTRACT TRUNCATED AT 250 WORDS)     

STRUCTURAL AND BIOCHEMICAL MATURATION OF THE CEREBRAL PALLIUM IN RABBIT FETUSES: MORPHOGENESIS AND LIPIDS

Morphological parameters of maturation of the cerebral pallium in rabbit fetuses ranging between 20 days of gestation (d.g.) and the early neonatal stage are expressed semi-quantitatively and correlated with progressive changes in the brain lipids, glycolipids and nucleic acids. Dual expression of the chemical values, using as referents both the dry weight of the tissue and the DNA unit, reveal the crucial stage in brain development when rapid cell proliferation is replaced by rapid cell growth; this stage in rabbit fetuses occurred between 28 and 30 d.g. Between 20 d.g. and the early neonatal phase the RNA decreased moderately when expressed per unit of DNA. Even at the time of term birth the cortical nerve cells of the rabbit showed signs of immaturity including a relatively small nuclear volume. On the dry weight basis, the lipids of the cerebral pallium exhibited little change in composition during fetal development; however, cerebrosides rose substantially between 30 d.g. and the early neonatal phase. When expressed per unit of DNA, all lipids and glycolipids continued to increase progressively in a pattern characteristic of growth throughout the prenatal period studied. This increase was also apparent when the lipid constituents were expressed per total pallium at the progressive gestational stages. The molar ratios of phospholipids:cholesterol:cerebrosides in the pallium of rabbits of different ages were as follows: in adult rabbits-2.9: 2.6: 1.0, in the newborn-2.9: 1.3: 0.2 and in the 30 d.g. fetuses-3.0: 1.2:0.44. These values reflect the fact that during maturation the content of phospholipids changes little, whereas that of cholesterol and especially erebrosides increases markedly.     

Karyotypic variation following an elevational gradient in the pocket gopher,Thomomys bottae grahamensis Goldman

A system of non-Robertsonian chromosomal polymorphism is described for populations of the pocket gopher, Thomomys bottae grahamensis Goldman, from the Graham Mountains of southeastern Arizona. The polymorphism occurs in three of the four populations sampled, but the range of chromosomal variation within each population is less than for the whole sample. The diversity varies clinally with elevation and is strongly correlated with both habitat and moisture gradients. Each population is considered to be at an adaptive norm with respect to the occupied habitat, and the karyotypic changes are presumed to have played a role in this adaptability. Maintenance of the polymorphic conditions in each population is considered to be due to karyotypic stability (either frequency equilibrium or population monotypy) coupled with gene flow from adjacent populations.     

Lateral line stimulation patterns and prey orienting behavior in the Lake Michigan mottled sculpin (Cottus bairdi)

Information contained in the spatial excitation pattern along arrayed sensors in the lateral line system of Lake Michigan mottled sculpin, as well as other surface-feeding fish and amphibians, is thought to play a fundamental role in guiding prey-orienting behaviors. However, the way in which prey location is encoded by the excitation pattern and used by the nervous system to direct orienting behaviors is largely unknown. In this study, we test the hypothesis that mottled sculpin use excitation peaks (local ‘hot spots’) to determine the somatotopic location of an artificial prey (vibrating sphere/dipole source) along the body surface. Dipole orientation (axis of sphere vibration re: long axis of the fish) is manipulated to produce excitatory peaks in different body locations without changing the actual sphere location. Our results show that orienting accuracy is largely independent of source orientation, but not source distance and that turning directions are not guided by local hot spots in the somatotopic activation pattern of the lateral line.