Capsaicin-Induced Changes in LTP in the Lateral Amygdala Are Mediated by TRPV1

The transient receptor potential vanilloid type 1 (TRPV1) channel is a well recognized polymodal signal detector that is activated by painful stimuli such as capsaicin. Here, we show that TRPV1 is expressed in the lateral nucleus of the amygdala (LA). Despite the fact that the central amygdala displays the highest neuronal density, the highest density of TRPV1 labeled neurons was found within the nuclei of the basolateral complex of the amygdala. Capsaicin specifically changed the magnitude of long-term potentiation (LTP) in the LA in brain slices of mice depending on the anesthetic (ether, isoflurane) used before euthanasia. After ether anesthesia, capsaicin had a suppressive effect on LA-LTP both in patch clamp and in extracellular recordings. The capsaicin-induced reduction of LTP was completely blocked by the nitric oxide synthase (NOS) inhibitor L-NAME and was absent in neuronal NOS as well as in TRPV1 deficient mice. The specific antagonist of cannabinoid receptor type 1 (CB1), AM 251, was also able to reduce the inhibitory effect of capsaicin on LA-LTP, suggesting that stimulation of TRPV1 provokes the generation of anandamide in the brain which seems to inhibit NO synthesis. After isoflurane anesthesia before euthanasia capsaicin caused a TRPV1-mediated increase in the magnitude of LA-LTP. Therefore, our results also indicate that the appropriate choice of the anesthetics used is an important consideration when brain plasticity and the action of endovanilloids will be evaluated. In summary, our results demonstrate that TRPV1 may be involved in the amygdala control of learning mechanisms

Heterotrophic fixation of CO2 in soil

The occurrence of heterotrophic CO2 fixation by soil microorganisms was tested in several mineral soils differing in pH and two artificial soils (a mixture of silica sand, alfalfa powder, and nutrient medium inoculated with a soil suspension). Soils were incubated at ambient (~0.05 vol%) and elevated (~5 vol%) CO2 concentrations under aerobic conditions for up to 21 days. CO2 fixation was detected using either a technique for determining the natural abundance of 13C or by measuring the distribution of labeled 14C-CO2 in soil and bacteria. The effects of elevated CO2 on microbial biomass (direct counts, chloroform fumigation extraction method), composition of microbial community (phospholipid fatty acids), microbial activity (respiration, dehydrogenase activity), and turnover rate were also measured. Heterotrophic CO2 fixation was proven in all soils under study, being higher in neutral soils. The main portion of the fixed CO2 (98–99%) was found in extracellular metabolites while only ~1% CO2 was incorporated into microbial cells. High CO2 concentration always induced an increase in microbial activity, changes in the composition of the microbial community, and a decrease in microbial turnover. The results suggest that heterotrophic CO2 fixation could be a widespread process in soils