Kindling of the lateral septum and the amygdala: effects on anxiety in rats

The presence of a conspecific induces risk-taking behaviour and enlargement of somata size of dopaminergic neurons in the brain of male medaka fish

Boldness and risk-taking behaviours in animals are important traits to obtain advantages such as habitation, food resources, reproductive success and social dominance. Risk-taking behaviour is influenced by physiological and environmental conditions; however, whether individual fish become bolder by the presence of conspecifics remains unknown. In this study, a light-dark preference test was conducted using medaka fish (Oryzias latipes) with or without a neighbouring conspecific. It was found that individual medaka male fish preferred a light environment and avoided a dark environment, whereas the display of a neighbouring conspecific enhanced the time the male spent in the dark environment (i.e., this condition encouraged risk-taking). The blood glucose level increased in fish confined to the dark condition but did not increase in light-preferring fish and risk-taking fish. Large somata expressing tyrosine hydroxylase, which is the rate-limiting enzyme in dopamine synthesis, were detected in the telencephalic and diencephalic brain regions in risk-taking medaka, whereas large somata were detected in the diencephalic region in medaka confined to the dark condition. These findings indicated that medaka is a good fish model to explore the central roles of dopaminergic neurons in the telencephalon and the diencephalon, which regulate risk-taking behaviour.

Behavioral effects of deep brain stimulation of the anterior nucleus of thalamus, entorhinal cortex and fornix in a rat model of Alzheimer's disease

Background:

Recent clinical and preclinical studies have suggested that deep brain stimulation (DBS) can be used as a tool to enhance cognitive functions. The aim of the present study was to investigate the impact of DBS at three separate targets in the Papez circuit, including the anterior nucleus of thalamus (ANT), the entorhinal cortex (EC), and the fornix (FX), on cognitive behaviors in an Alzheimer's disease (AD) rat model.

Methods:

Forty-eight rats were subjected to an intrahippocampal injection of amyloid peptides 1-42 to induce an AD model. Rats were divided into six groups: DBS and sham DBS groups of ANT, EC, and FX. Spatial learning and memory were assessed by the Morris water maze (MWM). Recognition memory was investigated by the novel object recognition memory test (NORM). Locomotor and anxiety-related behaviors were detected by the open field test (OF). By using two-way analysis of variance (ANOVA), behavior differences between the six groups were analyzed.

Results:

In the MWM, the ANT, EC, and FX DBS groups performed differently in terms of the time spent in the platform zone (F_(2,23) = 6.04, P < 0.01), the frequency of platform crossing (F_(2,23) = 11.53, P < 0.001), and the percent time spent within the platform quadrant (F_(2,23) = 6.29, P < 0.01). In the NORM, the EC and FX DBS groups spent more time with the novel object, although the ANT DBS group did not (F_(2,23) = 10.03, P < 0.001). In the OF, all of the groups showed a similar total distance moved (F_(1,42) = 1.14, P = 0.29) and relative time spent in the center (F_(2,42) = 0.56, P = 0.58).

Conclusions:

Our results demonstrated that DBS of the EC and FX facilitated hippocampus-dependent spatial memory more prominently than ANT DBS. In addition, hippocampus-independent recognition memory was enhanced by EC and FX DBS. None of the targets showed side-effects of anxiety or locomotor behaviors.

Anxiogenic- and antidepressant-like behavior in corneally kindled rats

BACKGROUND

Anxiety and depression affect epileptic patients much more often than individuals from the general population. We were interested in whether corneal kindling in rats, which is a model of complex partial seizures with secondary generalization, would influence animal behavior in models of anxiety and depression.

METHODS

Kindling was achieved by transcorneal electric stimulation and fully kindled rats were used in this study. Kindled and sham-stimulated rats were subjected to the elevated plus maze and forced swim test which are believed to be predictive models for anxiety and depression in humans, respectively.

RESULTS

Kindling significantly decreased the percentage of time spent by the rats in open arms relative to time spent in open plus closed arms and it reduced immobility time in the swim test as compared with sham-stimulated rats.

CONCLUSIONS

Our results suggest that corneal kindling produces antidepressant- and anxiety-like effects in rats and it may be a useful model to study epilepsy-associated anxiety.

Adolescent anabolic/androgenic steroids: Aggression and anxiety during exposure predict behavioral responding during withdrawal in Syrian hamsters (Mesocricetus auratus)

In the U.S. and worldwide anabolic/androgenic steroid use remains high in the adolescent population. This is concerning given that anabolic/androgenic steroid use is associated with a higher incidence of aggressive behavior during exposure and anxiety during withdrawal. This study uses pubertal Syrian hamsters (Mesocricetus auratus) to investigate the hypothesis that an inverse behavioral relationship exists between anabolic/androgenic steroid-induced aggression and anxiety across adolescent exposure and withdrawal. In the first experiment, we examined aggression and anxiety during adolescent anabolic/androgenic steroid exposure and withdrawal. Adolescent anabolic/androgenic steroid administration produced significant increases in aggression and decreases in anxiety during the exposure period followed by significant decreases in aggression and increases in anxiety during anabolic/androgenic steroid withdrawal. In a second experiment, anabolic/androgenic steroid exposed animals were separated into groups based on their aggressive response during the exposure period and then tested for anxiety during exposure and then for both aggression and anxiety during withdrawal. Data were analyzed using a within-subjects repeated measures predictive analysis. Linear regression analysis revealed that the difference in aggressive responding between the anabolic/androgenic steroid exposure and withdrawal periods was a significant predictor of differences in anxiety for both days of testing. Moreover, the combined data suggest that the decrease in aggressive behavior from exposure to withdrawal predicts an increase in anxiety-like responding within these same animals during this time span. Together these findings indicate that early anabolic/androgenic steroid exposure has potent aggression- and anxiety-eliciting effects and that these behavioral changes occur alongside a predictive relationship that exists between these two behaviors over time.

Age-dependent effects of environmental enrichment on brain networks and spatial memory in Wistar rats

We assessed the effect of 3h of environmental enrichment (EE) exposure per day started at different ages (3 and 18months old) on the performance in a spatial memory task and on brain regions involved in the spatial learning (SPL) process using the principal component analysis (PCA). The animals were tested in the four-arm radial water maze (4-RAWM) for 4days, with six daily trials. We used cytochrome c oxidase (COx) histochemistry to determine the brain oxidative metabolic changes related to age, SPL and EE. Behavioural results showed that the enriched groups, regardless of their age, achieved better performance in the spatial task. Interestingly, in the case of the distance travelled in the 4-RAWM, the effect of the EE was dependent on the age, so the young enriched group travelled a shorter distance compared to the aged enriched group. Respect to COx histochemistry results, we found that different brain mechanisms are triggered in aged rats to solve the spatial task, compared to young rats. PCA revealed the same brain functional network in both age groups, but the contribution of the brain regions involved in this network was slightly different depending on the age of the rats. Thus, in the aged group, brain regions involved in anxiety-like behaviour, such as the amygdala or the bed nucleus of the stria terminalis had more relevance; whereas in the young enriched group the frontal and the hippocampal subregions had more contribution.