Interaction between pre-weaning undernutrition and post-weaning environmental enrichment on somatic development and behaviour in male and female rats

Male and female rats were undernourished from birth to 30 days by restricting access to the lactating mother, and then fed ad libitum. At weaning, underfed and normally suckled controls were permanently housed either in pairs in standard cages or in groups of 10 in 1 m(3) cages containing ladders, ropes etc. Severe undernutrition during suckling followed by 4 months of refeeding, produced some changes in sexual behaviour in adult males (increased ejaculation frequency) but had no effect on behaviour in open field, dark preference or passive avoidance. Differential post-weaning environment produced significant differences in behaviour, irrespective of previous feeding conditions. Enriched animals were more active and exploratory. Females differed from males in the same direction as enriched from standard, and were more responsive to social and housing conditions.

Psychoendocrinological assessment of the menstrual cycle: the relationship between hormones, sexuality, and mood

The role of sex hormones in sexuality and mood across the menstrual cycle was investigated. Twenty-one normal health women were followed for one menstrual cycle. Blood samples were taken frequently, and analyzed for estradiol, progesterone, testosterone, androstenedione, dehydroepiandrosterone sulfate, cortisol, and sex hormone-binding globulin. A diary concerning sexual interest and behavior, and different moods, was completed daily. Although the sample was not large, a clear effect of menstrual cycle phase on levels of testosterone and the free testosterone index was demonstrated. In a preliminary screening interview, 11 of the 21 women had reported that they suffered from premenstrual complaints (PC), the other 10 had reported no complaints in the premenstrual phase (NPC). Significant differences between the two groups were established in estradiol and the estradiol-progesterone ratio, with the NPC group having higher levels of both endocrine parameters across different menstrual samples. Psychologically, a cycle effect on tension and sexual interest was demonstrated. The NPC group reported a peak in sexual interest in the premenstrual phase, whereas the PC group reported a peak in the ovulatory phase. There was a difference between the two groups in feelings of fatigue but not in other moods across the menstrual cycle. The study provides further evidence of the importance of androgen levels in women's sexuality and shows again that the relationship between menstrual cycle phase and sexuality is much clearer than between phase and mood.

The premenstrual phase and reactions to aversive events: a study of hormonal influences on emotionality

Fifty-eight normal cycle, healthy women were confronted with an aversive, anger-provoking situation in the laboratory. Eighteen women were tested in their follicular phase. A further 40 women were tested in the premenstrual phase, half of whom reported suffering from complaints of premenstrual emotional lability and irritation, the other half reported being without premenstrual problems. Apart from a strong effect of emotion induction on cardiovascular arousal and anger-related moods in the follicular and premenstrual groups, a premenstrual phase effect was also demonstrated, with premenstrual women showing evidence of being more affected by the manipulations on systolic blood pressure and intensity of angry behaviour during anger provocation. Furthermore, some differences were found between those subjects who reported suffering from premenstrual complaints and those free of such complaints, among the most interesting ones being differences in cortisol level preceding the experimental session, in intensity of angry behaviour, and in report of anger intensity at debriefing. The study indicates that the premenstrual phase may have the effect of making women more susceptible to responding emotionally to negative life events.

Gender differences in behaviour: activating effects of cross-sex hormones

The relative contribution of organizing and activating effects of sex hormones to the establishment of gender differences in behaviour is still unclear. In a group of 35 female-to-male transsexuals and a group of 15 male-to-female transsexuals a large battery of tests on aggression, sexual motivation and cognitive functioning was administered twice: shortly before and three months after the start of cross-sex hormone treatment. The administration of androgens to females was clearly associated with an increase in aggression proneness, sexual arousability and spatial ability performance. In contrast, it had a deteriorating effect on verbal fluency tasks. The effects of cross-sex hormones were just as pronounced in the male-to-female group upon androgen deprivation: anger and aggression proneness, sexual arousability and spatial ability decreased, whereas verbal fluency improved. This study offers evidence that cross-sex hormones directly and quickly affect gender specific behaviours. If sex-specific organising effects of sex hormones do exist in the human, they do not prevent these effects of androgen administration to females and androgen deprivation of males to become manifest.

Activating effects of androgens on cognitive performance: causal evidence in a group of female-to-male transsexuals

It is still unclear whether sex differences in cognitive functioning are mainly due to perinatal organizing effects of sex hormones on the brain, or to activating effects in adulthood. In a group of 22 female-to-male transsexuals a battery of visuospatial and verbal ability tests was administered twice: shortly before and 3 months after the start of androgen treatment. The administering of androgens was clearly associated with an increase in spatial ability performance. In contrast, it had a deteriorating effect on verbal fluency tasks. This study offers preliminary evidence that androgens directly and quickly affect cognitive performance in females.

Testosterone as appetitive and discriminative stimulus in rats: sex- and dose-dependent effects

Stimulus properties of subcutaneously injected testosterone were studied in male and female rats. In a conditioned place preference procedure, dose-dependent effects (doses: 0, 0.5, and 1 mg/kg) were observed in males. In females, no place preference could be established (doses: 0, 1, and 3 mg/kg). In addition, 1 mg/kg testosterone acquired discriminative stimulus control in male rats in a taste aversion procedure. Animals injected with this hormone prior to saccharin-LiCl pairings and with its vehicle prior to saccharin-NaCl pairings suppressed fluid intake following the administration of testosterone and not following the administration of the vehicle. Subsequent generalization tests revealed dose-dependent stimulus control of this hormone (range of substitution doses: 0.125-2 mg/kg). It is concluded from the results that at least pharmacological (supraphysiological) doses of testosterone may act as appetitive stimuli in male rats, but not in female rats. Furthermore, in male rats (pharmacological doses of) testosterone also possess discriminative stimulus properties.

Changes in male copulatory behavior after sexual exciting stimuli: effects of medial amygdala lesions

A paradigm was developed to investigate how precoital sexual arousal affects parameters of sexual behavior in male rats. Estrous females in a wire mesh cage were used to induce sexual arousal before the sexual interaction test. In control procedures, males were presented in a wire mesh cage or else there was no stimuli at all. The results indicate that ejaculation latency is consistently reduced after preexposure to a female, but not after preexposure to a male, showing that the effect is specific for precoital sexual arousal. Other parameters were affected by precoital sexual arousal in some, but not in all experiments. Reductions in intromission latency moreover, were observed after both preexposure to a male and preexposure to a female, indicating that general social excitement affects this parameter. Preexposure to females for 10 minutes or 3 hours produced similar results. It was subsequently found that medial amygdala-lesioned (AME) animals differed from sham-lesioned (SHAM) controls with respect to their reaction to precoital sexual arousal. The results show that AME-lesioned animals, in contrast to SHAM-animals, do not show reduced ejaculation latencies after preexposure to an estrous female. The results are in line with the idea that AME-lesioned animals are deficient in the assimilation of information on sexual exciting stimuli.

Temporal characteristics of appetitive stimulus effects of luteinizing hormone-releasing hormone in male rats

Conditioned place preference, induced by intraperitoneal injections of 5 micrograms/kg luteinizing hormone-releasing hormone (LHRH), was studied by varying the interval between the injection of LHRH and the conditioning sessions. Place preference was investigated for five presession intervals (0, 15, 45, 75, and 120 min) in separate groups of gonadectomized male rats provided with a subcutaneous testosterone implant. It was shown that the presession interval is an important parameter in the development of LHRH-induced conditioned place preference. Place preference was not observed after conditioning with intervals of 0, 75, and 120 min. With 15 and 45 min, however, a reliable preference was induced by LHRH. This study provides insight into the onset and offset of the appetitive stimulus properties of LHRH in male rats.

Hypothalamic involvement in sexuality and hostility: comparative psychological aspects

Evidence presented in this article shows the representation of sexual and aggressive behaviors at the level of the hypothalamus to be more prominent than in all other brain areas involved. Indeed, there are good arguments to attribute a central position to the hypothalamus within larger structural systems encompassing the limbic system, where aspects of the behaviors involved can be influenced. So far, however, the arguments are purely descriptive and factual and do not contribute much to answering questions about hypothalamic function: the grounds for and consequences of this massive representation of apparently almost all emotionally relevant social behavioral complexes, so universally established in a diversity of species, still has to be detected. A second and equally important aspect of hypothalamic function obviously has to be related to its central position within various hormonal systems. The present article concentrated on the acute dynamics and behavioral significance of activation of the pituitary-adrenocortical and pituitary-gonadal axes. Evidence indicates that the unconditioned behavioral stimuli or the consequences of behavior, but also stimuli conditioned to emotionally relevant events, may drastically alter hypothalamic hormonal regulation. Most importantly, these hormonal consequences in themselves again seem to determine further behavior and responses in relevant situations. The evidence presented with respect to reward and aversion, associated with alterations of specific hormones of the gonadal axis, may add a new dimension to our understanding of psychoendocrine functions of the hypothalamus (see also Gary, 1975; Leshner et al., 1981; Carey, 1987). Psychologically, such data can be taken as an argument for a more thorough study of the relation between memory processes and emotion (Bower et al., 1981). However fragmentary and incomplete this review may be, it will be clear that hypothalamic substrates and directly related areas, as well as affiliated hormonal mechanisms, play a central role in many of the most complex motivational and emotional syndromes and disorders. The prime idea in this is that the psychological concomitants of hypothalamic (dys)function are as much output as input, and as much the consequences as the cause within related syndromes. Such a view places the hypothalamus at the core of psychological theories of emotion and motivation, which from their most early origin have been heavily set towards hormonal and humoral changes and their relationships with psychological experience.(ABSTRACT TRUNCATED AT 400 WORDS)

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- and time-dependent changes in neurochemical and hormonal variables induced by predictable and unpredictable footshock

Previous experiments have revealed sex-dependent effects of inescapable shock in rats. Behavior of male rats was more severely disrupted by inescapable shock than behavior of female rats. These sex differences were found after 1- and 24-hour intervals but not after a 72-hour interval. The present experiment was designed to study various physiological parameters at 1-, 4- and 24-hour intervals after inescapable footshock. The predictability of shock was manipulated by adding a compound light and tone stimulus that preceded shock presentation for one group but was not correlated with shock presentation for another group of subjects. Noradrenaline, dopamine, serotonin, and metabolites of these 3 transmitters were measured in the frontal cortex. Transient shock-induced increments in dopamine and metabolites of dopamine and serotonin were found, but the sex of the animal did not differentially affect this neurotransmitter response. In addition to neurotransmitter concentrations in the frontal cortex, levels of corticosterone were measured in plasma. The pituitary-adrenal axis was activated for a longer period in females than males after shock. The present data do not provide evidence that behavioral sex differences induced by inescapable shock are paralleled by sex differences in neurotransmitter activity. In addition, sex-dependent effects of predictability of shock on neurotransmitter activity were not detected. The relevance of the observed sex-dependent responses in the pituitary-adrenal system is discussed.

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.

Testosterone fails to reverse spatial memory decline in aged rats and impairs retention in young and middle-aged animals

Recently, the vasopressin (AVP) innervation in the rat brain was shown to be restored in senescent rats following long-term testosterone administration. In order to investigate whether this restoration is accompanied by an improvement in learning and memory, both sham- and testosterone-treated young (4.5 months), middle-aged (20 months), and aged (31 months) male Brown-Norway rats were tested in a Morris water maze. All animals learned to localize a cued platform equally well, indicating that the ability to learn this task was not affected by sensory, motoric, or motivational changes with aging or testosterone treatment. There were no significant differences in retention following cue training. Subsequent training with a hidden platform in the opposite quadrant of the pool (place training) revealed impaired spatial learning in middle-aged and aged animals. Retention following place training was significantly impaired in the sham-treated aged rats as compared with sham-treated young rats. Testosterone treatment did not improve spatial learning nor retention of spatial information, but, on the contrary, impaired retention in young and middle-aged animals. The present results confirm earlier reports on an impairment of spatial learning and memory in senescent rats but fail to support a role of decreased plasma testosterone levels and central AVP innervation in this respect.

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.

Sex differences in passive avoidance depend on the integrity of the central serotonergic system

Effects of the neurotoxin para-chloroamphetamine (PCA) on sex differences in passive avoidance were studied. Seven days prior to passive avoidance training and testing, male and female rats were injected with PCA (5 mg/kg) or physiological saline (SAL). Treatment effects on brain monoamines levels were evaluated in brains collected shortly after the passive avoidance test. Compared to SAL-treated control groups PCA severely reduced both serotonin (5-HT) and 5-hydroxyindole-acetic acid (5-HIAA) in the frontal cortex of males and females. Levels of dopamine (DA) and homovanillic acid (HVA) in the frontal cortex were not affected. These data are indicative of a strong and selective depression of the central 5-HT activity. PCA- and SAL-treated male and female rats were trained and tested in a two-compartment step-through passive avoidance apparatus. Sex differences in passive avoidance were clearly observed in the SAL-treated control groups; a higher number of males did not enter either compartment within the maximum test duration. After PCA treatment sex differences in passive avoidance were abolished, mainly resulting from an increase in the number of PCA-males reentering. Irrespective of sex or treatment subjects seldom failed to choose the nonshock compartment when entering during the passive avoidance test, indicating that disturbance of memory or learning cannot explain for the present results. Rather, the data are discussed in terms of a sex-specific role of central 5-HT in punishment-induced behavioral suppression.

Gonadal steroid influence upon sexual and aggressive behavior of female rats

The present experiment investigates the activation of aggressive and sexual behaviors by gonadal hormones in female rats of the S3-strain. In the first experiment three doses of testosterone propionate (TP) were chronically injected. In the second experiment effects of TP were compared to those of estradiol benzoate (EB) and methyltrienelone (R1881), a synthetic, unaromatizable androgen. Females of the S3-strain were tested against TP-treated female Wistar rats as opponents, and masculine and feminine sexual responses were assessed in the test for aggression as well as in separate tests with sexually active stimulus animals. The results of the first experiment indicate that TP in all doses, increased aggressive as well as sexual behavior equally, although plasma testosterone levels differed significantly between the groups. In the second experiment, EB significantly decreased overall aggression as compared to control-treatment. TP- and R1881-stimulated fighting, particularly, as the most offensive parameter of aggression, but did not increase overall levels of aggression. Tests for sexual preference in which the choice between a sexually active male or female was given, indicated that TP-treated females stayed near males with longer durations. Scentmarking frequencies, measured in the semiopenfield test, were effectively activated by TP-treatment. EB- and R1881-treatment resulted in intermediate levels of marking behavior.

Acute effects of sex steroids on lordosis behaviour of the female rat

In the present series of experiments, dose-response and time-response relationships between single injections of sex steroids and the display of lordosis behaviour in the female rat, were investigated. When injected 48 h prior to testing, increasing doses of estradiol benzoate (EB) or testosterone propionate (TP) resulted in increasing levels of lordosis behaviour. TP was much less effective than EB in facilitating lordosis behaviour in the female rat. The optimum time interval between hormonal treatment and testing was 48-72 h for TP, but 48 h for EB. Single injections of dihydrotestosterone propionate (DHTP), also injected 48 h prior to testing, inhibited lordosis behaviour in EB-primed female rats. DHTP-inhibition of lordosis behaviour in EB-primed female rats was most effective when given prior to and least effective when given after EB-treatment. Progesterone, injected 4 h prior to testing, facilitated lordosis in EB-, TP- or EB + DHTP-treated female rats.

Variable mounting levels in the female rat: the influence of experience and acute effects of testosterone

Ovariectomized female rats were tested for mounting behaviour along 4 different procedures in order to investigate which factors may contribute to the variability of this behaviour observed in different experiments. Mounting behaviour was facilitated by repeated testing (group A). Estradiol-benzoate, when given for a short period of time (group B), induced a dramatic and long-lasting increase in mounting in females which were repeatedly tested according to the procedure of group A. Prolonged adaptation to the test environment (group C) did not facilitate mounting in repeatedly tested females. The 3 procedures used did not reduce inter-individual variability. Highly significant, positive, inter-test correlation coefficients indicated that relative individual differences in mounting remained highly stable throughout testing. Facilitatory effects of testosterone propionate (TP, 500 micrograms, injected once 48 h prior to testing) on mounting behaviour appeared to stimulate existing behavioural tendencies, rather than activating new patterns of behaviour: TP facilitated mounting in groups A and B, but not in group C. Neither did TP facilitate mounting in a group which had been left sexually naive (group D) until the time of TP-injection. It is concluded that highly stable inter-individual differences in mounting behaviour are present in the adult female rat. Differences in sensitivity for gonadal hormones are not likely to underly these individual differences.

Delayed spatial response alternation: effects of delay-interval duration and lesions of the medial prefrontal cortex on response accuracy of male and female Wistar rats

A delayed spatial response alternation procedure was used to assess behavioural differences between male and female Wistar rats, assumed to involve memory functioning. In Expt. I, subjects were required to alternate responses between two levers in an operant environment. The delay between response opportunities was varied between 1, 3, 7.5 and 15 s in different experimental conditions. Incorrect responses produced a time-out from experimental contingencies for the duration of the currently active delay interval. Response accuracy decreased for males as well as females as the duration of the delay interval was increased. Performance improved as subjects were exposed to the different delay interval durations during consecutive trials. Sex differences in behavioural accuracy were not observed. In Expt. II, some subjects who participated in Expt. I received lesions of the medial prefrontal cortex, while others were control-operated. When re-exposed to the 1 and 7.5 s delay conditions of the first experiment, lesioned subjects at first behaved less accurately than control-operated subjects. Accuracy, however, improved after prolonged exposure to the experimental conditions. Sex differences in behaviour after surgery could not be observed.

Sexual behavior in female rats born in all-female litters

Females born in all-female litters and females stemming from predominantly male litters were compared for masculine (mounting) and feminine sexual behavior (lordosis) under various dosages of estradiol followed by progesterone and under testosterone stimulation. Estradiol did not affect mounting levels in these groups. A critical dose level was established at 0.25 mg/animal of estradiol for both groups with respect to receptive behavior. Testosterone treatment reliably stimulated mounting in these females, but no differences were determined with respect to the litter composition in utero. The results are considered as a critical and negative finding with regard to the possibility that testosterone stemming from male littermates in utero affects the female's sexual development.