Dynamics of the Development of Depressive-Like State in Rats Stressed by Chronic Exposure of Ultrasound of Variable Frequency.

We studied the effect of ultrasonic waves with a frequency of 20-45 kHz on behavioral reactions of rats after 7, 14 and 21 days of continuous exposure. A decrease in the number of social contacts in the social interest test was recorded in all groups, while lengthening of immobility time in Porsolt test was found only in the groups exposed to ultrasound for 2 and 3 weeks. Memory impairment in the new object recognition test was recorded only after 21 days of stressing. Chronic exposure to ultrasound of variable frequencies leads to the development of a depressive-like state in rats and the duration of exposure affects the specificity of the observed disorders. Different protocols of using of this model help to determine the stages of depressive-like condition in rats that can serve as a basis for the development of new methods of depressive disorders treatment.

Later Life Changes in Hippocampal Neurogenesis and Behavioral Functions After Low-Dose Prenatal Irradiation at Early Organogenesis Stage.

PURPOSE: To investigate long-term changes in behavioral functions of mice after exposure to low-dose prenatal radiation at an early organogenesis stage. METHODS AND MATERIALS: Pregnant C57BL/6J mice were irradiated (20 cGy) at postcoitus day 5.5. The male and female offspring were subjected to different behavioral assays for affective, motor, and cognitive functions at 3, 6, and 12 months of age. Behavioral functions were further correlated with the population of CA1 and CA3 pyramidal neurons and immature neurons in hippocampal dentate gyrus. RESULTS: Prenatally exposed mice of different age groups showed a sex-specific pattern of sustained changes in behavioral functions. Male mice showed significant changes in anxiety-like phenotypes, learning, and long-term memory at age 3 months. At 6 months of age such behavioral functions were recovered to a normal level but could not be sustained at age 12 months. Female mice showed an appreciable recovery in almost all behavioral functions at 12 months. Patterns of change in learning and long-term memory were comparable to the population of CA1 and CA3 pyramidal neurons and doublecortin-positive neurons in hippocampus. CONCLUSION: Our finding suggests that prenatal (early organogenesis stage) irradiation even at a lower dose level (20 cGy) is sufficient to cause potential changes in neurobehavioral function at later stages of life. Male mice showed relatively higher vulnerability to radiation-induced neurobehavioral changes as compared with female.

Nocturnal light exposure impairs affective responses in a wavelength-dependent manner.

Life on earth is entrained to a 24 h solar cycle that synchronizes circadian rhythms in physiology and behavior; light is the most potent entraining cue. In mammals, light is detected by (1) rods and cones, which mediate visual function, and (2) intrinsically photosensitive retinal ganglion cells (ipRGCs), which primarily project to the suprachiasmatic nucleus (SCN) in the hypothalamus to regulate circadian rhythms. Recent evidence, however, demonstrates that ipRGCs also project to limbic brain regions, suggesting that, through this pathway, light may have a role in cognition and mood. Therefore, it follows that unnatural exposure to light may have negative consequences for mood or behavior. Modern environmental lighting conditions have led to excessive exposure to light at night (LAN), and particularly to blue wavelength lights. We hypothesized that nocturnal light exposure (i.e., dim LAN) would induce depressive responses and alter neuronal structure in hamsters (Phodopus sungorus). If this effect is mediated by ipRGCs, which have reduced sensitivity to red wavelength light, then we predicted that red LAN would have limited effects on brain and behavior compared with shorter wavelengths. Additionally, red LAN would not induce c-Fos activation in the SCN. Our results demonstrate that exposure to LAN influences behavior and neuronal plasticity and that this effect is likely mediated by ipRGCs. Modern sources of LAN that contain blue wavelengths may be particularly disruptive to the circadian system, potentially contributing to altered mood regulation.

Antidepressant-like effects of echo-planar magnetic resonance imaging in mice determined using the forced swimming test.

Echo-planar magnetic resonance imaging (EP-MRI), which is novel variant of MRI, is thought to have antidepressant properties in humans and animal models. Using the forced swimming test (FST), we investigated which monoaminergic system in mice is affected by EP-MRI. The short- and long-term effects of EP-MRI on immobility time in the FST and motor activity within a locomotor activity cage were examined. Two groups of mice underwent 20 min of EP-MRI in an MR scanner (Siemens, 1.5 T Symphony) either 23.5 or 1 h before the start of the second session of the FST. In both groups, the immobility duration in the FST was reduced, similar to effective antidepressant drug treatments. Climbing behavior in the 1-h group and swimming behavior in the 23.5-h group increased significantly, similar to that seen after the administration of desipramine (a noradrenaline reuptake inhibitor) and sertraline (a selective serotonin reuptake inhibitor), respectively. The findings support the hypothesis that EP-MRI has an antidepressant-like effect. We suggest that the antidepressant-like effect begins in the early period with noradrenaline systems and is maintained in the late period with serotonin systems.

Behavioral despair is differentially affected by the length and timing of photic stimulation in the dark phase of an L/D cycle.

The effect of varying the length and timing of photic stimulation in the dark phase of an L/D lighting cycle on behavioral despair was investigated in female Wistar rats. Animals were kept in a vivarium on an L/D 12 h:12 h light cycle (lights on at 0700 h) except for a single day of light exposure in an insulated chamber in the dark phase of the L/D schedule. Light pulses provided by an incandescent lamp (15- and 25-W, for Exps. 1 and 2, respectively) either 2-h (Exp. 1) or 30-min in length (Exp. 2) were administered to independent groups of rats (n=8 each) either in the early, middle or late hours of the dark phase of the L/D cycle in the insulated chamber. Light pulses were delivered beginning 2 1/2, 5 1/2 or 7 1/2 h (Exp. 1) or 3 1/4, 6 1/4 and 8 1/4 h (Exp. 2) after dark onset. Control animals were treated similarly except for photic stimulation. In each experiment, an additional group received a light pulse of the appropriate length both in the early and late portion of the dark phase (double double-pulse groups): beginning 2 1/2 and 7 1/2 h (Exp. 1) or 3 1/4 and 8 1/4 h (Exp. 2) after dark onset. All animals then underwent two forced swim tests separated by 24 h with the first test occurring in the light (starting at 1500 h) following the dark phase when photic stimulation was administered. Total duration of immobility in the second swim test was measured to gauge behavioral despair. In Exp. 1, the 2-h double double-pulse group showed significantly shorter immobility compared to controls (p<0.05). In Exp. 2, 30-min light pulse delivered late in the dark phase reduced immobility significantly compared to controls and all the other light-treated groups (p<0.01). Results indicate that photic stimulation may have antidepressant effect on behavioral despair depending on the timing and the duration of photic stimulation.

Sex differences in antidepressant-like effect of chronic repetitive transcranial magnetic stimulation in rats.

Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive neurophysiological technique. Pre-clinical and clinical studies supported that rTMS might have antidepressant effects. However, whether antidepressant effect of chronic rTMS is gender-dependent is still unknown. In this study, male and female Wistar rats received 10-day rTMS (4 trains of 15 Hz; 200 stimuli/day; 1.0 T) or control condition, and then were subjected to the forced-swim test (FST). We found that female rats consistently showed higher activity levels than males in FST and revealed the significant effects of gender and rTMS as well as the interaction of gender and rTMS. The result suggested the antidepressant-like effects of chronic rTMS on behavioral components in FST are gender-dependent. The gender discrepancy related to rTMS should not be neglected in antidepressant treatment of rTMS.

Effect of lighting stress on fluctuating asymmetry, heterophil-to-lymphocyte ratio, and tonic immobility duration in eleven breeds of chickens.

The purpose of the present study was to analyze the effect of a lighting stress on the fluctuating asymmetry (FA), the heterophil-to-lymphocyte ratio, and the tonic immobility duration of chickens. The experiment (440 birds) measured the FA of several traits (outer, middle, inner, and hind toe lengths and leg, wing, second primary feather, and spur lengths), the heterophil-to-lymphocyte ratio, and the tonic immobility duration in 36-wk-old hens and cocks of 8 Spanish breeds of chickens (Black-Barred Andaluza, Black-Red Andaluza, Black Castellana, Buff Prat, Red-Barred Vasca, Red Villafranquina, Birchen Leonesa, and Blue Leonesa), a synthetic breed (Quail Castellana), a White Leghorn population, and the e(y) tester line, which had been housed in continuous light (24L:0D) or in a light-dark regimen (14L:10D) for 16 wk. There was a significant difference between lighting treatments in both females and males on the combined FA of the 4 toes (P < 0.01) and the combined FA of toe, leg, wing, feather, and spur (in males) lengths (P < 0.05), the FA of birds housed under continuous light being greater than that of control birds. There was a significant difference (P < 0.001) for the heterophil-to-lymphocyte ratio and the tonic immobility duration between lighting treatments, the ratio being higher and the duration being longer in the group of birds housed under continuous light. Thus, birds exposed to continuous light were more stressed and fearful than control hens. Results were consistent across the breeds and indicate that a continuous light regimen seriously negatively affects the welfare of birds.