Older rats show slow modulation of hippocampal theta rhythm during voluntary running.

Aging causes brain function degeneration and slows many motor and behavioural responses. The hippocampal theta rhythm (4-12 Hz) is related to cognition and locomotion. However, the findings on aging-related changes in the frequency and amplitude of hippocampal theta oscillations have been inconsistent. We hypothesized that older rats have slower responses in terms of hippocampal theta rhythm during voluntary wheel running than do young adult rats. By simultaneously recording electroencephalography and physical activity (PA), we evaluated theta oscillations in 8-week-old (young adult) and 60-week-old (middle-aged) rats before and during wheel running, which was conducted only during the rats' 12-h dark period. To test the alterations of hippocampal theta rhythm in voluntary wheel running, we analyzed the signals without (8-s) or with (2-s) chronological order. No significant difference was observed in total frequency (TP, 4-12 Hz), low-frequency (LT, 4-6.5 Hz), or high-frequency (9.5-12 Hz) theta activity between active waking and overall running in either group. The theta oscillations were slower in the middle-aged rats than in the young adult rats during wheel running but increased during running for both age groups. During wheel running, the middle-aged rats exhibited an increased LT, which was related to PA. On the basis of the chronological order of running, the young adult rats exhibited increased TP, and the middle-aged rats exhibited significant increases in middle-frequency (MT, 6.5-9.5 Hz) theta activity. The dominant modulations of MT in the middle-aged rats may have caused nonsignificant changes in total activity. These between-group differences in theta rhythm characteristics during voluntary running provide insights into age-related brain function decline.

Behavioural consistency and hippocampal theta rhythm can reflect age-related anxiety during the behaviour test.

It is known that anxiety has a lot of comorbidity such as depression and may cause older subjects to be more prone to anxiety. Animal studies have also observed that older rats have lower movement in different situations, somewhat like anxiety symptoms (avoidance and freezing). The anxiety level of rodents is commonly evaluated using the elevated plus maze test, and videos are often used to record and quantify the activities of animals during the test. Furthermore, aging can reduce the frequency and activity of locomotion-induced hippocampal theta rhythm, and these reductions are also reflected in sensory-motor integration and cognition. Thus, directly analyzing the hippocampal theta rhythm and the quantity and quality of physical activity (PA) during the anxiety test can help elucidate the mechanisms underlying the anxiety-like behaviour. We explored alterations in the hippocampal theta rhythm, PA, and behavioural consistency (cross-correlation with 8-s window length) from triaxial acceleration vectors and subsequently examined the effects of age during the elevated plus maze test. We hypothesized that middle-aged rats would exhibit more anxiety, which is correlated with a reduction in behavioural consistency and hippocampal theta frequency during the elevated plus maze test. The middle-aged rats had a lower open-arm frequency and more low-frequency theta oscillations. The middle-aged rats had a lower mean power frequency (Frq) of the hippocampal theta rhythm, PA, and behavioural consistency. The Frq of the middle-aged rats was positively correlated with behavioural consistency. The results indicated that behavioural consistency could distinguish age-related anxiety-like behaviour. Behavioural consistency can serve as an index for the quality of movement and be used to distinguish age-related anxiety.

Judicious use of transthoracic echocardiography in infective endocarditis screening.

BACKGROUND: Patients with a very low probability of infective endocarditis (IE) do not benefit from transthoracic echocardiography (TTE). Because the term 'very low probability' has not yet been defined, the present prospective study sought to identify the population with a 'very low probability'. METHODS: TTE was performed between July 2005 and October 2006 in consecutive patients clinically suspected of having IE. Clinical parameters suggestive of IE and presence of infectious focus were recorded. RESULTS: Twenty-four (15.5%) of 155 patients studied had positive findings on TTE. Significant positive predictors were embolic events, intravenous drug use, the presence of a prosthetic valve, positive blood cultures and immunological phenomena. The significant negative predictor was confirmed infection sites other than endocardium. Sixty-three (40.6%) of 155 patients without positive predictors were found to have no vegetation. Thus, the collective absence of these predictors indicated a zero probability of TTE showing evidence of IE. A significant negative predictor was a definite etiology of infection other than IE. Only one in 76 patients was diagnosed with both IE and infection at another site. CONCLUSIONS: The absence of positive predictors or the presence of a negative predictor indicate a near-zero probability of IE being detected by TTE. Use of clinical parameters may avoid up to 41% of unnecessary TTE examinations, increasing the likelihood that such a diagnosis will be correct.