Dopamine-mediated modulation of odour-evoked amygdala potentials during pavlovian conditioning

Pavlovian conditioning results when an innocuous stimulus, such as an odour, is paired with a behaviourally relevant stimulus, such as a foot-shock, so that eventually the former stimulus alone will elicit the behavioural response of the latter. The lateral nucleus of the amygdala (LAT) is necessary for the emotional memory formation in this paradigm. Enhanced neuronal firing in LAT to conditioned stimuli emerge in parallel with the behavioural changes and are dependent on local dopamine. To study the changes in neuronal excitability and synaptic drive that contribute to the pavlovian conditioning process, here we used in vivo intracellular recordings to examine LAT neurons during pavlovian conditioning in rats. We found that repeated pairings of an odour with a foot-shock resulted in enhanced post-synaptic potential (PSP) responses to the odour and increased neuronal excitability. However, a non-paired odour displayed PSP decrement. The dopamine antagonist haloperidol blocked the PSP enhancement and associated increased neuronal excitability, without reversing previous conditioning. These results demonstrate that conditioning and habituation processes produce opposite effects on LAT neurons and that dopamine is important in these events, consistent with its role in emotional memory formation.     

Possible thermal and chemical stabilization of body-centred-cubic iron in the Earth's core

The nature of the stable phase of iron in the Earth's solid inner core is still highly controversial. Laboratory experiments suggest the possibility of an uncharacterized phase transformation in iron at core conditions and seismological observations have indicated the possible presence of complex, inner-core layering. Theoretical studies currently suggest that the hexagonal close packed (h.c.p.) phase of iron is stable at core pressures and that the body centred cubic (b.c.c.) phase of iron becomes elastically unstable at high pressure. In other h.c.p. metals, however, a high-pressure b.c.c. form has been found to become stabilized at high temperature. We report here a quantum mechanical study of b.c.c.-iron able to model its behaviour at core temperatures as well as pressures, using ab initio molecular dynamics free-energy calculations. We find that b.c.c.-iron indeed becomes entropically stabilized at core temperatures, but in its pure state h.c.p.-iron still remains thermodynamically more favourable. The inner core, however, is not pure iron, and our calculations indicate that the b.c.c. phase will be stabilized with respect to the h.c.p. phase by sulphur or silicon impurities in the core. Consequently, a b.c.c.-structured alloy may be a strong candidate for explaining the observed seismic complexity of the inner core.     

Interaction of reelin signaling and Lis1 in brain development

Loss-of-function mutations in RELN (encoding reelin) or PAFAH1B1 (encoding LIS1) cause lissencephaly, a human neuronal migration disorder. In the mouse, homozygous mutations in Reln result in the reeler phenotype, characterized by ataxia and disrupted cortical layers. Pafah1b1(+/-) mice have hippocampal layering defects, whereas homozygous mutants are embryonic lethal. Reln encodes an extracellular protein that regulates layer formation by interacting with VLDLR and ApoER2 (Lrp8) receptors, thereby phosphorylating the Dab1 signaling molecule. Lis1 associates with microtubules and modulates neuronal migration. We investigated interactions between the reelin signaling pathway and Lis1 in brain development. Compound mutant mice with disruptions in the Reln pathway and heterozygous Pafah1b1 mutations had a higher incidence of hydrocephalus and enhanced cortical and hippocampal layering defects. Dab1 and Lis1 bound in a reelin-induced phosphorylation-dependent manner. These data indicate genetic and biochemical interaction between the reelin signaling pathway and Lis1.     

Black-tailed prairie dog populations one year after treatment with rodenticides

Three rodenticide treatments, zinc phosphide with prebait, strychnine with prebait, and strychnine without prebait, were applied to black-tailed prairie dog Cynomys ludovicianus colonies in west central South Dakota. Results were compared immediately posttreatment and for one year after application. Zinc phosphide was the most effective for reducing prairie dog numbers immediately. When burrow activity levels of prairie dogs were initially reduced by 45% with strychnine only, they returned to untreated levels within ten months. When initial reductions were 95% with zinc phosphide, however, the number of active burrows was still reduced 77% in September the following year. Strychnine with prebait treatment showed initial reductions of 83% in burrow activity. Bait consumption by prairie dogs was highest for zinc phosphide.     

Confirmational holism and its mathematical (w)holes

I critically examine confirmational holism as it pertains to the indispensability arguments for mathematical Platonism. I employ a distinction between pure and applied mathematics that grows out of the often overlooked symbiotic relationship between mathematics and science. I argue that this distinction undercuts the notion that (pure) mathematical theories fall under the holistic scope of the confirmation of our scientific theories.