Decrease In Amplitude Of Activity Research Articles

Blue light exposure-dependent improvement in robustness of circadian rest-activity rhythm in aged rats.

The aging effects on circadian rhythms have diverse implications including changes in the pattern of rhythmic expressions, such as a wide fragmentation of the rhythm of rest-activity and decrease in amplitude of activity regulated by the suprachiasmatic nucleus (SCN). The study of blue light on biological aspects has received great current interest due, among some aspects, to its positive effects on psychiatric disorders in humans. This study aims to evaluate the effect of blue light therapy on the SCN functional aspects, through the evaluation of the rest-activity rhythm, in aging rats. For this, 33 sixteen-months-old male Wistar rats underwent continuous records of locomotor activity and were exposed to periods of 6 hours of blue light during the first half of the light phase (Zeitgeber times 0-6) for 14 days. After this, the rats were maintained at 12h:12h light:dark cycle to check the long-term effect of blue light for 14 days. Blue light repeated exposure showed positive effects on the rhythmic variables of locomotor activity in aged rats, particularly the increase in amplitude, elevation of rhythmic robustness, phase advance in acrophase, and greater consolidation of the resting phase. This effect depends on the presence of daily blue light exposure. In conclusion, our results indicate that blue light is a reliable therapy to reduce circadian dysfunctions in aged rats, but other studies assessing how blue light modulates the neural components to modulate this response are still needed.

Effect of unilateral division of the septo-hippocampal tract on electrical activity of the dorsal hippocampus and behavior in rabbits.

1. Division of the septal input causes a decrease in amplitude of activity and in the number of theta-waves in the hippocampus, an increase in the representation of beta-frequencies, and disturbance of correlation between frequency bands of the hippocampal theta-rhythm and various forms of behavioral acts. 2. After unilateral division of the septo-hippocampal tract, despite the general decrease in amplitude of activity and increase in beta-frequencies in the opposite hippocampus the theta-waves are sufficiently abundant and the theta-rhythm correlates with behavior. 3. The results suggest that theta-activity and correlation of the theta-rhythm with different forms of behavioral acts arise in the hippocampus under the influence of the septal input, whereas the high-frequency waves, which increased after division of the septo-hippocampal tract, are organized under the influence of cortical afferents.