Effects of lipopolysaccharide and interleukin-6 on cataleptic immobility and locomotor activity in mice.

Catalepsy (animal hypnosis, tonic immobility) is a type of passive defensive behavior. Its exaggerated form is a syndrome of some psychopathological disorders. Numerous neurotransmitters have impact on the regulation of catalepsy. In this paper we demonstrated the involvement of interleukin-6 (IL-6) in the mechanism of cataleptic immobility. Effects of exogenous IL-6 treatment (7.5 and 10µg/kg, i.p) or stimulation of endogenous IL-6 secretion with lipopolysaccharide (LPS) administration (50, 100 and 200µg/kg, i.p.) on catalepsy and locomotor activity were studied in adult C57BL/6 male mice. IL-6 induced catalepsy in 70% (7.5µg/kg) or 72.7% (10µg/kg) of animals with no effect on locomotor activity. LPS administration reduced distance travelled and number of rears in the open field at any dose used, however, only high doses (100 or 200µg/kg) of the toxin induced catalepsy in 50% of mice. This result indicates that IL-6 is involved in the regulation of catalepsy, this effect is specific and does not arise from inhibition of locomotor activity. The study provides a new evidence on participation of IL-6 in mechanisms of abnormal behavior.

Serotonin transporter, 5-HT1A receptor, and behavior in DBA/2J mice in comparison with four inbred mouse strains.

Prepulse inhibition (PPI), the reduction in acoustic startle produced when it is preceded by a weak prepulse stimulus, is impaired in schizophrenic patients. The DBA/2J mouse strain displayed deficient PPI and is therefore suggested as an experimental animal model for the loss of sensorimotor gating in schizophrenia. Brain serotonin (5-HT) has been implicated in the pathophysiology of several psychiatric disorders, including major depressive disorder and schizophrenia. In the present study, behavior, 5-HT transporter (5-HTT) mRNA level, 5-HT(1A) receptor mRNA level, and 5-HT(1A) receptor density in the brain regions were studied in DBA/2J mice in comparison with four inbred mouse strains (CBA/Lac, C57BL/6, BALB/c, and ICR). A decrease in 5-HTT mRNA level in the midbrain and a reduced density of 5-HT(1A) receptors in the frontal cortex without significant changes in 5-HT(1A) receptor mRNA level in DBA/2J mice were found. It was shown that, along with decreased PPI, DBA/2J mice demonstrated considerably reduced immobility in the tail suspension test and in the forced swim test. No significant interstrain differences in intermale aggression, or in light-dark box and elevated plus-maze tests, were found. The results suggested the involvement of decreased 5-HTT gene expression and 5-HT(1A) receptor density in genetically defined PPI deficiency and showed a lack of any association between PPI deficiency and predisposition to aggressive, anxiety, and depressive-like behaviors.

Cross-fostering effects on weight, exploratory activity, acoustic startle reflex and corticosterone stress response in Norway gray rats selected for elimination and for enhancement of aggressiveness towards human.

Two rat lines, one tame, the other aggressive, differing by many behavioral features and stress reactivity were developed by long-term selection of wild gray rats for elimination and enhancement of aggressiveness towards humans. The aim of this work was to study the role of the maternal environment in the expression of these differences between the two rat lines using the cross-fostering paradigm. Fostering of tame rats of both sexes by aggressive mothers and aggressive females by tame mothers was without effect on behavior score towards humans, but the cross-fostered aggressive males had a small, yet significant, increase in aggressiveness score. Cross-fostering revealed that exploratory behavior in the hole-board test and the acoustic startle amplitude were weakly affected by maternal interactions, although there was an effect on body weight and on the stress corticosterone response. Body weight was decreased in tame males fostered by aggressive mothers only and it was increased in cross-fostered aggressive rats of both sexes. Fostering of tame males and females by an aggressive mother enhanced almost twofold the corticosterone response immediately after stress, while fostering of aggressive ratlings of both sexes by a tame mother was without effect. The current results demonstrated that the maternal postnatal environment had no substantial effect on the behavioral responses of both tame and aggressive rats, but it possibly contributed to the development of the corticosterone response to restraint stress in the tame, and not the aggressive rats, i.e. these effects of cross-fostering were dependent on ratling genotype.

Reproductive abnormalities in adult male mice following preimplantation exposures to estradiol or pesticide methoxychlor.

Adult females of ICR strain of mice were bred, separated into different experimental groups, and treated as follows. On Days 2-4 of pregnancy, the mice received daily subcutaneous injections of either 0.05 ml sesame oil (vehicle) or same volume of 5.0mg of purified methoxychlor (MXC) suspended in the vehicle. Another group received a single subcutaneous injection of 1.0 microg of estradiol-17beta (E) on Day 2 of pregnancy only. Male offspring were tested at 3 and 6 months of age. At 3 months, E or MXC did not alter the weights of seminal vesicles, preputial glands, or testes, although after exposure for 30 min to a female in estrus behind a partition, testosterone levels were significantly reduced in treated males in comparison to control males exposed to the same partition test. At 6 months, the preputial glands and testes weight remained unchanged, while the seminal vesicles were significantly heavier in E- and MXC-treated males. Same partition tests again revealed that in E and MXC groups, testosterone levels remained significantly lower in comparison to control males. MXC or E exposures during preimplantation appear to induce long-term effects on the sexual development in 3 and 6 month-old-males by compromising their sexual arousal and altering seminal vesicles weights in the older group.