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We investigated the role of the septo-hippocampal cholinergic projection in anxiety, spatial novelty preference, and differential reward for low rates of responding (DRL) performance. Cholinergic neurons of the rat medial septum (MS) and the vertical limb of the diagonal band of Broca (VDB) were lesioned using the selective immunotoxin, 192 IgG-saporin. Rats were then tested on several behavioral tests previously shown to be sensitive to either (a) hippocampal lesions or (b) nonselective MS/VDB lesions which target both cholinergic and y-aminobutyric acid (GABA)-ergic projections, or both. Saporin lesions substantially reduced hippocampal cholinergic innervation, resulting in an absence of acetyl cholinesterase staining and markedly reduced choline acetyltransferase activity (mean reduction: 80 ± 5%; range: 50-97%). However, the saporin-lesioned rats did not differ from control rats in any of the behavioral tests. Thus we found no evidence from these lesion studies that the septo-hippocampal cholinergic projection plays an essential role in anxiety, spatial novelty preference, or DRL. [ABSTRACT FROM AUTHOR]

Studies of the effects of aging on decision making suggest that choices can be altered in a variety of ways depending on the situation, the nature of the outcome and risk, or certainty levels. To better characterize how aging impacts decision making in rodents, young and aged Fischer 344 rats underwent a series of probabilistic discounting tasks in which reward magnitude and probabilities were manipulated. Young rats tended to choose 1 of 2 different strategies: (a) to press for the large/uncertain reward, regardless of the reward probability; or (b) to continually adapt their behavior according to the odds of winning. The first strategy was adopted by about half of the younger rats, the second by the remaining young animals and the entire group of aged rats. Additionally, we found that when the odds of winning were varied from uncertain to certain during a session, aged rats chose most often the lever associated with the small/ certain reward. This is consistent with an interpretation of increased risk aversion. When this behavior was further characterized using a lose-shift analysis, it appears that older rats exhibited an increased sensitivity to negative feedback. In contrast, sensitivity to wins was unaltered in aged rats compared with young, suggesting that aging selectively impacts rat's behavior following losses. In line with some human aging studies, it appears that aged rats are either more risk averse or have a greater certainty bias, which may result from age differences in emotion regulation. [ABSTRACT FROM AUTHOR]

The consequences of traumatic brain injury (TBI) sustained during late adolescence (7 weeks old) on spontaneous object recognition memory and on anxiety-like behaviors in the elevated plus maze were tested in rats during adulthood. Testing took place at 2 different postinjury times, in separate groups: 3 and 6 weeks, when animals were 10 and 13 weeks old, respectively. The rats were either submitted to controlled cortical impact injury, an experimental model of focal TBI with contusion, or were shamoperated. TBI animals failed to remember the familiar object and had a significantly lower performance than sham-operated animals, indicating memory disruption, when the retention delay was 24 hr, but not when it was 3 hr. TBI did not have any significant effect on the main anxiety-related behaviors, but it reduced time in the central platform of the elevated plus maze. The effects of TBI on memory and on anxiety-like behaviors were similar at the 2 postinjury times. In both TBI and sham-operated groups, animals tested 6 weeks after surgery had lower anxiety-related indices than those tested at 3 weeks, an effect that might be indicative of reduced anxiety levels with increasing age. In summary, focal TBI with contusion sustained during late adolescence led to object recognition memory deficits in a 24-hr test during adulthood but did not have a major impact on anxiety-like behaviors. Memory deficits persisted for at least 6 weeks after injury, indicating that spontaneous modifications of these functional disturbances did not take place along this time span. [ABSTRACT FROM AUTHOR]