Male and female immediate fear reaction to white noise in a semi-natural environment: A detailed behavioural analysis of the role of sex and oestrogen receptors.

In classical rodent anxiety models, females usually display lower anxiety than males, whereas anxiety disorders are more prevalent in women. Perhaps this contradiction is caused by the use of behavioural models with low external validity. Therefore, we analysed immediate reactions to a sudden 90-dB white noise in a semi-natural environment. We observed mixed-sex groups of rats for the 60 seconds preceding noise onset and the first 60 seconds of exposure. White noise elicited fear-specific behaviours hiding alone and huddling. It also increased exploratory and ambulatory behaviours, although only in the burrow zone farthest from the open area. Thus, in a semi-natural environment, white noise enhanced motor activity as a product of fear-induced general arousal. Then, we compared male and female sexual, social, exploratory and anxiety-related behaviour, and found little sex difference. This absence of behavioural effect, also observed in other studies, might be a result of our study design, a familiar environment with an ecologically relevant social context. Fear and anxiety responses are modulated by oestrogens through the activation of oestrogen receptors α and ß. Thus, in a third part of out study, we analysed how treatment with either oil, oestradiol benzoate (EB), an agonist to the oestrogen receptor α (propylpyrazoletriol [PPT]) or ß (diarylpropionitrile [DPN]) influenced female behaviour. The effect of treatment was limited, both EB and PPT stimulated motor activity in the open area before white noise, probably because of sexual activity. PPT increased the probability of fleeing from the noise, and decreased the latency to do so, which is consistent with a pattern of anxiogenic properties found in previous studies. Contrary to reports in classical procedures, we failed to detect any effect of DPN on immediate fear reactions in a semi-natural environment.

Annual changes in the copulatory behavior of male rats maintained under constant laboratory conditions.

The objective of the present study was to evaluate the sexual behavior of male rats kept under constant laboratory conditions for one entire year. A total of 213 sexually-inexperienced, male Wistar rats were maintained in controlled environmental conditions from birth. Depending the month in which they reached the age 3-month-old, the male rats were divided into 12 groups, one for each month of the year, and their sexual behavior was evaluated. Records of their sexual behavior were made from 09:00 to 11:00 hrs am. The following parameters were recorded: mount (latency and number), intromission (latency and number), ejaculation latency, and intromission rate. During the months of March, June, July and September, the rats showed lower mount and intromission latencies than in January, February, April, May and October-to-December. Similarly, in March, June, July and August they had higher copulatory efficiency than in January, February, April and December. Results suggest that male rats exposed to controlled environmental conditions could have endogenous mechanisms that regulate sexual behavior but are independent of seasonal environmental signals. The annual variability in the sexual behavior of male rats maintained under constant laboratory conditions should be considered when planning research and experiments.

Prenatal stress suppresses the prefrontal and amygdaline EEG changes associated with a sexually-motivated state in male rats.

The medial prefrontal cortex (mPFC) and basolateral amygdala (BLA) participate in the modulation of several motivated behaviors, such as the sexual behavior. Both structures are sensitive to stress when it is experienced mainly in critical periods of the life-cycle, such as the prenatal period. This study evaluated the effects of prenatal stress on electroencephalographic activity (EEG) of the mPFC and BLA during sexual motivation. EEG was recorded in the mPFC and BLA of male rats assigned to either a prenatally-stressed group (SG, dam immobilized from days 14 to 21of pregnancy), or a control group (CG), during the following conditions: awake-quiet state without sexual motivation, and awake-quiet state with sexual motivation. Compared to CG, fewer SG subjects presented copulatory responses and their levels of sexual motivation were lower. The CG subjects with sexual motivation showed a higher absolute power (AP) of the 14-30Hz band in the left mPFC and BLA than those without sexual motivation. The SG showed a lower AP of the 4-7 and 8-13Hz bands in the left BLA. Thus, prenatal stress suppressed the prefrontal and amygdaline EEG changes associated with a sexually-motivated state. EEG data show that stress affects the functioning of these two brain structures and so could interfere with the adequate processing of sexual stimuli. These findings contribute to understanding the brain mechanisms that underlie the effect of prenatal stress on the processing of sexual stimuli in male rats.