Low prepulse inhibition predicts lower social interaction, impaired spatial working memory, reference memory and cognitive flexibility in genetically heterogeneous rats.

The "Genetically Heterogeneous National Institutes of Health (NIHHS)" stock rat (hereafter HS) shows a wide phenotypic variation, as a result of having been derived from eight inbred rat strains. Thus, these rats may be a conceivable parallel model of a healthy human sample. In order to evaluate whether HS rats have face validity as an animal model of schizophrenia-relevant features, it should be demonstrated that they present behavioural traits that may model negative and cognitive symptoms of the disorder. Previous studies on HS rats have shown that prepulse inhibition (PPI, a measure of sensorimotor gating processes), which is impaired in schizophrenic patients, is correlated with their working memory performance. In this study, we evaluated whether low PPI in the HS stock rat predicts impairments of spatial working memory (SWM), spatial reference memory and cognitive flexibility in the Morris water maze (MWM) test, and we evaluated HS rats for social interaction (SI) in a social investigation task. HS rats were stratified into 2 different groups according to their PPI scores, i.e. low- and high-PPI. In the SI task, low-PPI rats showed decreased social behaviour compared to high-PPI rats. In addition, relative to high-PPI HS rats, the low-PPI group displayed poorer SWM performance, impaired cognitive flexibility (in a reversal task) and worsened long-term spatial memory. Such differential behaviours in social and cognitive paradigms provide evidence on the face validity of low-PPI HS rats as a model of negative-like and cognitive schizophrenia-relevant traits.

c-Fos expression after neonatal handling in social brain regions: Distinctive profile of RHA-rat schizophrenia model on a social preference test.

Neonatal handling (NH) is an environmental manipulation that induces long-lasting changes in behavioural, neuroendocrine, and neuroanatomical processes in rodents. We have previously reported that NH treatment increases social interaction preference in an animal model of schizophrenia-relevant features, the Roman high-avoidance (RHA) rats. The present study was aimed at evaluating whether the increase of social behaviour/preference due to NH treatment in RHA rats is associated with differences in c-Fos expression levels in some of the brain areas that integrate the "social brain". To this aim, we evaluated the performance of adult male rats from both Roman rat strains (RHA vs. RLA -Roman low-avoidance- rats), either untreated (control) or treated with NH (administered during the first 21 days of life) in a social interaction task. For the analyses of c-Fos activation untreated and NH-treated animals were divided into three different experimental conditions: undisturbed home cage controls (HC); rats exposed to the testing set-up context (CTX); and rats exposed to a social interaction (SI) test. It was found that, compared with their RLA counterparts, NH treatment increased social behaviour in RHA rats, and also specifically enhanced c-Fos expression in RHA rats tested for SI in some brain areas related to social behaviour, i.e. the infralimbic cortex (IL) and the medial posterodorsal amygdala (MePD) regions.

Dissociation between schizophrenia-relevant behavioral profiles and volumetric brain measures after long-lasting social isolation in Roman rats.

Social isolation rearing of rodents is an environmental manipulation known to induce or potentiate psychotic-like symptoms and attentional and cognitive impairments relevant for schizophrenia. When subjected to a 28-week isolation rearing treatment, the Roman high-avoidance (RHA-I) rats display the common behavioral social isolation syndrome, with prepulse inhibition (PPI) deficits, hyperactivity, increased anxiety responses and learning/memory impairments when compared to their low-avoidance (RLA-I) counterparts. These results add face validity to the RHA-I rats as an animal model for schizophrenia-relevant behavioral and cognitive profiles and confirm previous results. The aim here was to further investigate the neuroanatomical effects of the isolation rearing, estimated through volume differences in medial prefrontal cortex (mPFC), dorsal striatum (dSt) and hippocampus (HPC). Results showed a global increase in volume in the mPFC in the isolated rats of both strains, as well as strain effects (RLA > RHA) in the three brain regions. These unexpected but robust results, might have unveiled some kind of compensatory mechanisms due to the particularly long-lasting isolation rearing period, much longer than those commonly used in the literature (which usually range from 4 to 12 weeks).

Synchronous fire activity in the tropical high Andes: an indication of regional climate forcing.

Global climate models suggest enhanced warming of the tropical mid and upper troposphere, with larger temperature rise rates at higher elevations. Changes in fire activity are amongst the most significant ecological consequences of rising temperatures and changing hydrological properties in mountainous ecosystems, and there is a global evidence of increased fire activity with elevation. Whilst fire research has become popular in the tropical lowlands, much less is known of the tropical high Andean region (>2000 masl, from Colombia to Bolivia). This study examines fire trends in the high Andes for three ecosystems, the Puna, the Paramo and the Yungas, for the period 1982-2006. We pose three questions: (i) is there an increased fire response with elevation? (ii) does the El Niño- Southern Oscillation control fire activity in this region? (iii) are the observed fire trends human driven (e.g., human practices and their effects on fuel build-up) or climate driven? We did not find evidence of increased fire activity with elevation but, instead, a quasicyclic and synchronous fire response in Ecuador, Peru and Bolivia, suggesting the influence of high-frequency climate forcing on fire responses on a subcontinental scale, in the high Andes. ENSO variability did not show a significant relation to fire activity for these three countries, partly because ENSO variability did not significantly relate to precipitation extremes, although it strongly did to temperature extremes. Whilst ENSO did not individually lead the observed regional fire trends, our results suggest a climate influence on fire activity, mainly through a sawtooth pattern of precipitation (increased rainfall before fire-peak seasons (t-1) followed by drought spells and unusual low temperatures (t0), which is particularly common where fire is carried by low fuel loads (e.g., grasslands and fine fuel). This climatic sawtooth appeared as the main driver of fire trends, above local human influences and fuel build-up cyclicity.

Medium-term sap flux monitoring in a Scots pine stand: analysis of the operability of the heat dissipation method for hydrological purposes.

The operability of Granier-type heat dissipation sap flow meters for the medium-term monitoring of Scots pine transpiration was tested. Three sensors that had been working for 3 years were duplicated by inserting new sensors in the same trees. The new sensors operated simultaneously with the old sensors for 18 months. Analysis of the temporal patterns of thermal dissipation of the sensors showed a slight, but significant decrease in all sensors, indicating the conservation of sapwood thermal properties. Although there was a high correlation between sap flux densities registered by the old and new sensors, significant differences in sap flux densities between the duplicated sensors were detected. Such differences could not be attributed to tissue injury around the sensors or to loss of sensitivity of the old sensors, because two of the old sensors registered higher flux rates than the new sensors. No instrumental error to explain the sap flux differences was found. Because the new sensors were installed at some angular distance from the old sap flow meters to avoid thermal interferences, it was inferred that the observed sap flux differences between duplicate sensors were the result of an azimuthal sap flow pattern.