Sex-dependent effects of restraint on nociception and pituitary-adrenal hormones in the rat.

The sex-dependent effects of acute restraint (RT) on nociceptive and pituitary-adrenal responses were investigated in the rat. In a first experiment, the effect of 30 min RT on pain sensitivity was evaluated through repeated use of the tail withdrawal test during and after treatment. RT induced an increase in the nociceptive threshold, i.e., analgesia, in males and females, but the duration and time-course of this effect varied between sexes. The latencies returned to approximately control values in females in the second half of RT, but in males they remained higher for the whole period of RT and immediately afterwards. Twenty-four hours later, males displayed longer latencies than controls in response to simple reexposure to the environment. In a second experiment, ACTH and corticosterone plasma levels were measured immediately after 15 or 30 min of RT. ACTH and corticosterone were higher in restrained animals than in controls after both periods of treatment, and in both sexes; however, females showed higher basal and stress corticosterone levels than males. The role played by corticosteroids in the nociceptive responses of the two sexes is discussed.

Sex differences in the behavioral consequences of inescapable footshocks depend on time since shock.

In two experiments, the effects of inescapable shock on subsequent shuttle-box escape performance were studied in male and female rats. Effects of treatment with short-duration shocks (2 s) were studied after 1- and 24-hour intervals (Experiment 1), and effects of long-duration shocks (6 s) were studied after 24- and 72-hour intervals (Experiment 2). Experience with inescapable shock resulted in a serious disruption of escape performance in both males and females. A large increment in escape latencies was found both during fixed ratio 1 and fixed ratio 2 escape training; however, effects of inescapable shock were more pronounced in males than in females. In Experiment 1, sex differences were most obvious after the short 1-hour interval whereas, in Experiment 2, sex differences were only present after 24 hours and not after 72 hours. Shuttle activity during 2-min adaptation prior to shock-escape training was reduced in both males and females treated with IS, and this effect was somewhat stronger in males than in females. The data of these experiments show that male rats are more sensitive to the consequences of exposure to inescapable aversive stimulation than female rats. It is proposed that the time-dependency of the sex differences in behavioral consequences of treatment with inescapable shock may be related to sex differences in transient neurochemical or hormonal changes induced by inescapable shock.

Sex-dependent effects of aversive stimulation on holeboard and elevated plus-maze behavior.

The behavioral effects of exposure to inescapable shocks (IS) were studied in both the holeboard and the elevated plus-maze, 24 and 72 h after IS in male and female Wistar rats. The following effects were observed at the 24-h interval. In both sexes, head-dipping in the holeboard was reduced by IS, whereas general activity (ambulation and rearing) was reduced in males and not in females. Furthermore, the results of a correlation analysis indicate that previous exposure to IS disrupts the dissociation observed in control groups between exploratory activity directed at the holes (head-dipping) and general activity in the holeboard (ambulation and rearing). Effects of IS on plus-maze behavior could be observed in a clear suppression of rearing in males and not in females. IS did not affect time spent on the open arms. At the 72-h interval, IS affected head-dipping in the holeboard only in males and not in females. The present findings show that the effect of IS on specified behavioral elements is sex-dependent, with stronger and longer-lasting effects in males than in females.

Sex-dependent effects of inescapable shock administration on shuttlebox-escape performance and elevated plus-maze behavior.

The present experiment investigated the effects of exposure to inescapable shocks (IS) on subsequent behavior in an elevated plus-maze and on shuttlebox-escape performance in male and female rats. In the elevated plus-maze, exposure to IS resulted in suppression of "total number of arm entries" and "rearings" in males but not in females. In addition "time on open arms" was reduced in both sexes after exposure to IS, but this effect seemed stronger in males than in females. Exposure to IS disrupted shuttlebox-escape performance of males, whereas escape performance of females was unaffected. Affected escape performance in males was transient and limited to the initial phase of escape training. A sex difference in emotional reaction to stress might contribute to the observed sex difference in the acquisition of an escape response. The strong passive avoidance tendency observed in males, which may be strengthened by IS, strongly interferes with the acquisition of the escape response by this sex, resulting in sex differences in susceptibility to behavioral disturbances induced by IS.

Sex-dependent effects of inescapable shock administration on behavior and subsequent escape performance in rats.

Stress-induced behavioral disturbances have widely been used as animal models of depression. Sex differences, however, have rarely been studied, even though evidence is available to show that males and females react differently after presentation of aversive stimuli. The present experiment investigated the behavioral effects of inescapable shocks on subsequent shuttlebox-escape performance in male and female rats. Exposure to inescapable shocks resulted in suppression of activity during shock administration, which was more severe when shock duration was increased. Females showed less behavioral suppression and they were also more active than males during the adaptation phase, prior to shuttlebox-escape training. Shuttlebox-escape performance was less affected in females than in males compared to that of nonshocked control subjects. Shock duration as a factor only affected efficiency of shuttlebox-escape performance in males.