Long-term effects of an early-life exposure of fathead minnows to sediments containing bitumen. Part I: Survival, deformities, and growth.

The aim of this study was to investigate the long-term effects of a short exposure to natural sediments within the Athabasca oil sand formation to critical stages of embryo-larval development in fathead minnows (Pimephales promelas). Three different sediments were used: Ref sediment from the upper Steepbank River tested at 3 g/L (containing 12.2 ng/g ∑PAHs), and two bitumen-rich sediments tested at 1 and 3 g/L; one from the Ells River (Ells downstream, 6480 ng/g ∑PAHs) and one from the Steepbank River (Stp downstream, 4660 ng/g ∑PAHs). Eggs and larvae were exposed to sediments for 21 days, then transferred to clean water for a 5-month grow-out and recovery period. Larval fish had significantly decreased survival after exposure to 3 g/L sediment from Stp downstream, and decreased growth (length and weight at 16 days post hatch) in Ells and Stp downstream sediments at both 1 and 3 g/L. Decreased tail length was a sensitive endpoint in larval fish exposed to Ells and Stp downstream sediments for 21 days compared to Ref sediment. After the grow-out in clean water, all growth effects from the bitumen-containing sediments recovered, but adult fish from Stp downstream 3 g/L sediment had significant increases in jaw deformities. The study shows the potential for fish to recover from the decreased growth effects caused by sediments containing oil sands-related compounds, but that some effects of the early-life sediment exposure occur later on in adult fish.

The relationship between tetanus intensity and the magnitude of hippocampal long-term potentiation in vivo.

In this study, we assessed the effects of varying tetanus and test-pulse intensity on the magnitude of long-term potentiation (LTP) in the perforant path-dentate gyrus projection of urethane-anaesthetized rats. We developed a novel within-subjects procedure in which test-pulse-stimulation intensity (60-1000 µA) was varied quasi-randomly under computer control throughout the recording period. After a baseline period, we applied a high-frequency tetanus, the intensity of which was varied over the same range as test-pulse intensity, but between subjects. The time-course of LTP was thus monitored continuously across a range of test-pulse intensities in each rat. Intense high-frequency tetanization at 1000 µA resulted in a paradoxical depression of the dentate field excitatory post-synaptic potential (fEPSP) slope at the lowest test intensity used (60 µA), but caused a potentiation at higher test intensities in the same animal. Moreover, intense tetanization induced less LTP than a moderate tetanus over most of the test-intensity range. Explanations for this pattern of data include a potentiation of feed-forward inhibition in conjunction with LTP of excitatory neurotransmission, or local tissue damage at the stimulation site. To address this issue, we conducted an additional experiment in which a second stimulating electrode was placed in the perforant path at a site closer to the dentate, in order to activate a common population of afferents at a location 'downstream' of the original stimulation site. After 1000-µA tetanization of the original ('upstream') site, fEPSPs were again depressed in response to test stimulation of the upstream site, but only potentiation was observed in response to stimulation of the downstream site. This is consistent with the idea that the depression induced by intense tetanization results from local changes at the stimulation site. In conclusion, while tetanus intensity must exceed the LTP induction threshold, intensities above 500 µA should be avoided; in the present study, tetanization at 250-500 µA yielded maximal levels of LTP.

Synaptic tagging and capture in the living rat.

In isolated hippocampal slices, decaying long-term potentiation can be stabilized and converted to late long-term potentiation lasting many hours, by prior or subsequent strong high-frequency tetanization of an independent input to a common population of neurons-a phenomenon known as 'synaptic tagging and capture'. Here we show that the same phenomenon occurs in the intact rat. Late long-term potentiation can be induced in CA1 during the inhibition of protein synthesis if an independent input is strongly tetanized beforehand. Conversely, declining early long-term potentiation induced by weak tetanization can be converted into lasting late long-term potentiation by subsequent strong tetanization of a separate input. These findings indicate that synaptic tagging and capture is not limited to in vitro preparations; the past and future activity of neurons has a critical role in determining the persistence of synaptic changes in the living animal, thus providing a bridge between cellular studies of protein synthesis-dependent synaptic potentiation and behavioural studies of memory persistence.

Intersex and reproductive impairment of wild fish exposed to multiple municipal wastewater discharges.

The Grand River watershed in Ontario, Canada, receives and assimilates the outflow of 29 Municipal Wastewater Effluent (MWWE) discharges which is a mixture of domestic and industrial wastes. The purpose of this study was to investigate the cumulative impact of multiple sewage discharges on populations of wild fish. In field studies, responses of fish populations and individual fish responses in terms of growth (condition factor), reproduction (in vitro sex steroid production, gonadosomatic indices, histology [cellular development and intersex]) were assessed upstream and downstream of two municipal discharges. Fish [Greenside Darters Etheostoma blennioides and Rainbow Darters E. caeruleum] collected downstream of two municipal wastewater plants had the potential to have greater growth (longer and heavier) when compared to reference fish collections regardless of sex. Fish were not assimilating additional anthropogenic resources into energy storage (increased condition, liver somatic index). Impacts on ovarian development appeared to be minor with no differences in growth, steroid production or cellular development. Sewage exposed male fish were experiencing impairment in the capacity to produce testosterone and 11-ketotestosterone in vitro, and in cellular development (GSI, intersex). Male darters of both species collected in the upstream agricultural region demonstrated no evidence of intersex whereas our urban reference sites had incidence of intersex of up to 20%. Rates of intersex were elevated downstream of both sewage discharges studied (33% and>60%, respectively). Lower rates of intersex at the intermediate sites, and then increases downstream of second sewage discharge suggests that fish populations have to potential to recover prior to exposure to the second sewage effluent. Pre-spawning darters demonstrated dramatically higher incidence of intersex in the spring at both urban reference sites (33% and 50%, respectively), and increased more so downstream of the near-field and far-field exposure sites (60% and 100%, respectively). These findings suggest that the compounds released in STP effluents have a tendency to act on the male reproductive system. These effects may become more pronounced as projected human population growth will require the aquatic environment to assimilate an increasing amount of sewage waste.

Mapping immediate-early gene activity in the rat after place learning in a water-maze: the importance of matched control conditions.

The expression of two immediate-early genes (IEGs), Zif268 and c-Fos, was quantified in hippocampal subregions and related structures following spatial learning in the Morris water-maze. A critical feature was the novel control protocol alongside more standard controls, the purpose of which was to test whether hippocampal activity is set automatically when traversing an environment or whether it is dependent on reaching a specific goal using learning that requires the hippocampus (i.e. task dependent). The new control protocol (Procedural Task) made it possible to match swim time, swim distance and learning to escape from water with that of the experimental (Working Memory) group. Unlike the Working Memory group, the Procedural Task animals showed no evidence of learning the absolute platform location during the test session. While the Working Memory rats showed c-Fos increases relative to the Procedural Task controls in the frontal and parahippocampal cortices, hippocampal levels did not differ. Again, for Zif268 there was no evidence of a relative increase of hippocampal activity in the Working Memory group. In fact, hippocampal Zif268 showed evidence of a relative decrease, even though the spatial working memory task is hippocampal dependent. The study not only highlighted the shortcomings of other control procedures used in water-maze studies (free-swimming or home cage control), but also indicated that the expression of these IEGs in the hippocampus is not a direct predictor of explicit spatial location learning. Rather, the activity in combinations of regions, including prefrontal cortex, provides a stronger correlate of water-maze learning.

Anterior thalamic lesions produce chronic and profuse transcriptional de-regulation in retrosplenial cortex: A model of retrosplenial hypoactivity and covert pathology.

Anterior thalamic lesions are thought to produce 'covert pathology' in retrosplenial cortex, but the causes are unknown. Microarray analyses tested the hypothesis that thalamic damage causes a chronic, hypo-function of metabolic and plasticity-related pathways (Experiment 1). Rats with unilateral, anterior thalamic lesions were exposed to a novel environment for 20 minutes, and granular retrosplenial tissue sampled from both hemispheres 30 minutes, 2h, or 8h later. Complementary statistical approaches (analyses of variance, predictive patterning and gene set enrichment analysis) revealed pervasive gene expression differences between retrosplenial cortex ipsilateral to the thalamic lesion and contralateral to the lesion. Selected gene differences were validated by QPCR, immunohistochemistry (Experiment 1), and in situ hybridisation (Experiment 2). Following thalamic lesions, the retrosplenial cortex undergoes profuse cellular transcriptome changes including lower relative levels of specific mRNAs involved in energy metabolism and neuronal plasticity. These changes in functional gene expression may be largely driven by decreases in the expression of multiple transcription factors, including brd8, c-fos, fra-2, klf5, nfix, nr4a1, smad3, smarcc2, and zfp9, with a much smaller number (nfat5, neuroD1, RXRγ) showing increases. These findings have implications for conditions such as diencephalic amnesia and Alzheimer's disease, where both anterior thalamic pathology and retrosplenial cortex hypometabolism are prominent.

The cold-shock stress response in Mycobacterium smegmatis induces the expression of a histone-like protein.

The response of Mycobacterium smegmatis to a cold shock was investigated by monitoring changes in both growth and cellular protein composition of the organism. The nature of the cellular response was influenced by the magnitude of the temperature reduction, with the shock from 37 degrees C to 10 degrees C having the most widespread effect on growth, metabolism and protein composition. This 27 degrees C temperature reduction was associated with a lag period of 21-24 h before increases were seen in all the measured cellular activities. The response to cold shock was adaptive, with growth resuming after this period, albeit at a 50-fold slower rate. The synthesis of at least 15 proteins was induced during the lag period. Two distinct patterns of cold-induced synthesis were apparent, namely transient and continuous, indicating the production of both cold-induced and cold-acclimation proteins. One of these cold-shock proteins, CipMa, was identified as the histone-like protein, Hlp, of M. smegmatis, which is also induced during anaerobic-induced dormancy. The corresponding gene demonstrated transient, cold-inducible expression with a five- to sevenfold increase in mRNA occurring 9-12 h after temperature shift. Although bacterial survival was unaffected, CipMa/Hlp knock-out mutants were unable to adapt metabolically to the cold shock and resume growth, thus indicating a key role for CipMa in the cold-shock response.