Structural plasticity can produce metaplasticity.

BACKGROUND: Synaptic plasticity underlies many aspect of learning memory and development. The properties of synaptic plasticity can change as a function of previous plasticity and previous activation of synapses, a phenomenon called metaplasticity. Synaptic plasticity not only changes the functional connectivity between neurons but in some cases produces a structural change in synaptic spines; a change thought to form a basis for this observed plasticity. Here we examine to what extent structural plasticity of spines can be a cause for metaplasticity. This study is motivated by the observation that structural changes in spines are likely to affect the calcium dynamics in spines. Since calcium dynamics determine the sign and magnitude of synaptic plasticity, it is likely that structural plasticity will alter the properties of synaptic plasticity. METHODOLOGY/PRINCIPAL FINDINGS: In this study we address the question how spine geometry and alterations of N-methyl-D-aspartic acid (NMDA) receptors conductance may affect plasticity. Based on a simplified model of the spine in combination with a calcium-dependent plasticity rule, we demonstrated that after the induction phase of plasticity a shift of the long term potentiation (LTP) or long term depression (LTD) threshold takes place. This induces a refractory period for further LTP induction and promotes depotentiation as observed experimentally. That resembles the BCM metaplasticity rule but specific for the individual synapse. In the second phase, alteration of the NMDA response may bring the synapse to a state such that further synaptic weight alterations are feasible. We show that if the enhancement of the NMDA response is proportional to the area of the post synaptic density (PSD) the plasticity curves most likely return to the initial state. CONCLUSIONS/SIGNIFICANCE: Using simulations of calcium dynamics in synaptic spines, coupled with a biophysically motivated calcium-dependent plasticity rule, we find under what conditions structural plasticity can form the basis of synapse specific metaplasticity.

A descriptive analysis of the consumers at farm stands outside WIC clinics

Because fruit and vegetable intake remains low in low-income populations, the attention of public health researchers has focused on different strategies to reach this population. One possible method of reaching low income populations is through government food assistance programs like the WIC's Farmers Market Nutrition Program (FMNP). This program provides vouchers to WIC recipients that are redeemable only at farmers' markets. In the summer of 2010, two farm stands near WIC clinics in Austin were surveyed in order to establish socio-demographic characteristics of the clientele of the markets. The overall purpose of this pilot study was to describe the clientele of the markets and to examine associations between food insecurity, acculturation, socio-demographic factors, and farmers' market participants' fruit and vegetable intake. The sample was a convenience sample of farmers' market customers. One hundred study participants completed self-administered surveys. Independent t-tests were used to explore the differences in means of fruit and vegetable intake according to acculturation and food insecurity levels. The overall mean (SD) of daily fruit and vegetable intake was 4.20±2.69 for customers of both markets. Significant differences were reported between the two markets in overall fruit and vegetable intake and specifically in the following: 100% juice (P=.023), fruit consumption (P=.028), green salad (P=.003), and salsa (P=.044). The differences showed that customers at the market in a more busy location were on average reporting eating more fruits and vegetables than customers at another market that was located in a more secluded location. When examined by level of food security, individuals who were more food secure consumed more fruit (P=.016). When examined by level of acculturation, the overall fruit and vegetable intake was not significantly different between levels of acculturation. The overall findings in this report suggest that the population at these markets consists of individuals who are food insecure and on government assistance programs. While there were no significant differences between fruit and vegetable intake, acculturation and food insecurity, this report suggests the need for culturally tailored interventions that serve the Hispanic population and would assist this population to become more food secure.^