Social isolation during peri-adolescence or adulthood: effects on sexual motivation, testosterone and corticosterone response under conditions of sexual arousal in male rats.

Reproductive functions in adult organism are known to be affected by different factors. Effects of social environment at the postnatal ontogenesis attract particular attention since it has deep impact on the development of physiological and emotional state of an individual. Effects of chronic social isolation at different ages on male sexual motivation, testosterone and corticosterone response under conditions of sexual arousal were studied in Wistar rats. After weaning at the 21st [corrected] day of age, rats of one group were isolated for six weeks and after that they were housed in groups of five per cage for ten weeks (Iso3-9). Rats of the second group were housed in groups of five animals per cage till 13 weeks of age, and then they were isolated for six weeks (Iso13-19). Rats of the control group were housed in groups during the experiment. Adult 19 week- old male rats were tested under conditions of sexual arousal. The expression of sexual motivation was estimated as the behavioral activity of a male at the transparent perforated partition separating a receptive female. Isolation of adult male rats reduced the number of approaches to the partition, while the period of time a male spent at the partition was not changed and testosterone response was enhanced as compared to control rats. Chronic social isolation during peri-adolescence reduced sexual motivation and prevented arousal-induced elevation of testosterone. Plasma corticosterone increases at sexual arousal in the two groups of isolated rats did not differ from that in controls. Our results are evidence that social isolation during the post-maturity stage (Iso13-19) did not diminish the manifestation of sexual motivation and hormonal response to a receptive female, while isolation during peri-adolescence attenuated behavioral and hormonal expression of sexual arousal in adult males.

The genetic control of blood pressure and body composition in rats with stress-sensitive hypertension.

The genetic basis of the stress-sensitive arterial hypertension was investigated using the quantitative trait loci (QTL) approach. Two groups of F2 (inherited stress-induced arterial hypertension [ISIAH] × Wistar albino Glaxo [WAG]) hybrid males of different age (3-4 months old and 6 months old) were tested for blood pressure at rest and stressed conditions and for body composition traits. Several novel loci for the traits were determined. Some loci for blood pressure and organ weight were mapped to the same genetic region in rats of different age. The dynamic change of QTL effects in two rat groups of different age might reflect the process of stress-sensitive hypertension development.

Effects of the mitochondria-targeted antioxidant SkQ1 on sexually motivated behavior in male rats.

Ample research indicates that age-related neuronal-behavioral decrements are the result of oxidative stress and may be ameliorated by antioxidants. Here we examined effects of mitochondria-targeted antioxidant, SkQ1, on sexual motivation in 12-month-old Wistar and accelerated-senescent OXYS male rats. A change in behavioral activity of a male at a holed transparent partition with a receptive female on the other side was taken as an index of sexual motivation. The social behavior of male in same conditions with ovariectomised (OVXed) female and castrated male was investigated to differentiate sexually and socially motivated behavior. Behavioral response to social stimulus did not depend on age and genotype. No differences were found between 4- and 12-month-old Wistar males when sexual stimulus was presented; however, 12-month-old OXYS males demonstrated a lower propensity for sexual motivation as compared to 4-month-old OXYS rats and 12-month-old Wistar rats. We examined effects of SkQ1 on sexual motivation in 12-month-old male rats following prolonged supplementation begun at 1.5months of age (10, 50 or 250nmol/kg daily), a 45-day supplementation begun at 10.5months of age (50nmol/kg) and a 3-month supplementation begun at 9months of age (250nmol/kg). SkQ1 did not affect locomotor activity; however, it increased the time spent at the partition. A significantly higher measure of the motivational stage of sexual behavior was displayed following chronic preventive treatment at a dose of 50 and 250nmol/kg by OXYS rats. Chronic therapeutic treatment during 3months at a dose of 250nmol/kg was effective in age-accelerated OXYS rats too. These findings suggest an essential role for oxidative stress associated with mitochondrial dysfunction in the decline of sexually motivated behavior of male rats. Recovery from these impairments and/or their prevention enables a fully successful performance of the initial stage of male sexual behavior.

MAO A knockout attenuates adrenocortical response to various kinds of stress.

The effect of a lack of the gene encoding monoamine oxidase A (MAO A) in transgenic Tg 8 mice on the corticosterone response to restraint, cold, water deprivation-induced, or social acute stress as well as chronic variable stress was studied. It was found that Tg 8 mice with genetic MAO A knockout and wild-type C3H/HeJ (C3H) strain showed similar plasma corticosterone resting level. MAO A knockout mice differed from C3H mice by attenuated response to restraint (60 min), cold (4 degrees C, 60 min), and water deprivation (48 h) as well as to a chronic (15 days) variable stress. No difference between Tg 8 and C3H strains in the response to psychosocial stress (encounters for 30 min of six previously isolated mice) has been found. ACTH administration to dexamethasone-pretreated mice produced a similar corticosterone effect in Tg 8 and C3H mice, indicating that the decreased stress response in MAO A-deficient mice was due rather to the central mechanisms regulating stress-induced ACTH release than to adrenocortical responsiveness to ACTH.

Immediate and long-lasting effects of chronic stress in the prepubertal age on the startle reflex.

The immediate and long-lasting effects of two models of chronic stress during the prepubertal period of life (21-32 days) on the acoustic startle response (ASR) were studied in outbred Wistar normotensives and rats with inherited stress-induced arterial hypertension (ISIAH) derived from them. Chronic variable stress (CVS) and repeated handling were used as chronic treatment. The obtained data showed a significantly attenuated ASR and a greater magnitude of prepulse inhibition (PPI) in juvenile and adult ISIAH compared to Wistar rats. The immediate effects of prolonged stress on the ASR were genotype-dependent. Young ISIAH rats exposed to both types of prepubertal stimulation had higher ASR than the age-matched controls. No significant stress-induced changes in the ASR were found in young Wistar rats. The long-lasting consequences of prolonged prepubertal stress were similar in the two strains and were determined by the specificity of stress stimulation: chronic handling had no effect on the ASR, while CVS enhanced it. The long-lasting effect of CVS experienced in prepubertal life appears to produce ASR changes similar to those seen in patients with posttraumatic stress disorder (PTSD). The magnitude of PPI increased from early age to adulthood and it was tolerant to environmental influences. The two rat strains did not differ in the rate of short-term habituation to repeated acoustic stimuli, which was unaffected by prepubertal stress. Evidence was obtained indicating that genetic and environmental background in childhood may contribute to the truncation of the startle response.