On-Farm Risikoanalysen zur Entwicklung von Kontrollmaßnahmen bei Kreuzkraut-Arten

Poisonous Senecio species occur in grasslands of various countries. Their further spread into farmland must be prevented, but efficient methods for their control are often lacking, especially under organic farming. We propose on-farm surveys designed as case-control studies to assess the risk for the occurrence of such species and present results of a study on S. aquaticus. Following a case-control design, 72 plots were evaluated for their botanical composition, half the plots contained S. aquaticus. For all the plots, the soil nutrients and the details of management practice, such as type and intensity of management and fertiliser application, were recorded from the farmer. There was a high risk for occurrence of S. aquaticus with low nitrogen fertilisation, with a decrease of management intensity in the preceding 15 years, high inclination, and gaps in the sward. For the long-term control of S. aquaticus, we suggest promoting dense swards and preventing sward damage as much as possible. This paper demonstrates the great power of case-control studies in on-farm research. The design allows thorough statistical testing using generalised linear models and provides reliable results in relatively short time. Various questions can be linked to the management practice on farms and over a wide range of environmental conditions. Such data can hardly be obtained from small plot experiments

Sortenvergleich von Lolium multiflorum unter Anbaubedingungen des ökologischen- und integrierten Landbaus

Forty-five varieties of Lolium multiflorum L. were examined in pure stands at three experimental sites over a three years period. One of these sites was on an organic farm, which was managed according to the “BIO SUISSE” guidelines. Due to the marked differences in management (weed control, N-fertilisation), the yield of the sown grass was clearly lower at the organic site. Nevertheless, there was an outstanding correspondence in terms of the yield of the different varieties among the experimental sites. The best varieties under integrated farming were also the best varieties in the organic system

GABA(B)-receptor subtypes assemble into functional heteromeric complexes

B-type receptors for the neurotransmitter GABA (gamma-aminobutyric acid) inhibit neuronal activity through G-protein-coupled second-messenger systems, which regulate the release of neurotransmitters and the activity of ion channels and adenylyl cyclase. Physiological and biochemical studies show that there are differences in drug efficiencies at different GABA(B) receptors, so it is expected that GABA(B)-receptor (GABA(B)R) subtypes exist. Two GABA(B)-receptor splice variants have been cloned (GABA(B)R1a and GABA(B)R1b), but native GABA(B) receptors and recombinant receptors showed unexplained differences in agonist-binding potencies. Moreover, the activation of presumed effector ion channels in heterologous cells expressing the recombinant receptors proved difficult. Here we describe a new GABA(B) receptor subtype, GABA(B)R2, which does not bind available GABA(B) antagonists with measurable potency. GABA(B)R1a, GABA(B)R1b and GABA(B)R2 alone do not activate Kir3-type potassium channels efficiently, but co-expression of these receptors yields a robust coupling to activation of Kir3 channels. We provide evidence for the assembly of heteromeric GABA(B) receptors in vivo and show that GABA(B)R2 and GABA(B)R1a/b proteins immunoprecipitate and localize together at dendritic spines. The heteromeric receptor complexes exhibit a significant increase in agonist- and partial-agonist-binding potencies as compared with individual receptors and probably represent the predominant native GABA(B) receptor. Heteromeric assembly among G-protein-coupled receptors has not, to our knowledge, been described before

Generalization of amygdala LTP and conditioned fear in the absence of presynaptic inhibition

Pavlovian fear conditioning, a simple form of associative learning, is thought to involve the induction of associative, NMDA receptor-dependent long-term potentiation (LTP) in the lateral amygdala. Using a combined genetic and electrophysiological approach, we show here that lack of a specific GABA(B) receptor subtype, GABA(B(1a,2)), unmasks a nonassociative, NMDA receptor-independent form of presynaptic LTP at cortico-amygdala afferents. Moreover, the level of presynaptic GABA(B(1a,2)) receptor activation, and hence the balance between associative and nonassociative forms of LTP, can be dynamically modulated by local inhibitory activity. At the behavioral level, genetic loss of GABA(B(1a)) results in a generalization of conditioned fear to nonconditioned stimuli. Our findings indicate that presynaptic inhibition through GABA(B(1a,2)) receptors serves as an activity-dependent constraint on the induction of homosynaptic plasticity, which may be important to prevent the generalization of conditioned fear