Immobility reaction or catalepsy is a natural passive defensive (cryptic) behavioral response to the appearance of a predator. Selection for high predisposition to catalepsy has been performed in a population of (CBA × (CBA × AKR)) backcrosses of the crossing between mouse lines prone and resistant to catalepsy (CBA and AKR, respectively). A rapid increase in the number of animals with catalepsy has been observed: from 23% in backcrosses to 71% in the S 3 generation. Selection for catalepsy does not affect mouse anxiety in the open field and plus-maze tests. However, S 8 and S 9 mice are characterized by a decreased motor activity in the open-field test and an increased immobility in the forced swim and tail suspension tests, which is interpreted as an increase in "depressiveness." The results indicate that genetically determined catalepsy is related to depressive-like characteristics of defensive behavior.
GENERAL GENETICS
The effects of water deprivation and hydration on plasma corticosterone concentration and the activity of tryptophan hydroxylase (TPH), the rate-limiting enzyme in serotonin (5-HT) biosynthesis, in the hypothalamus of vasopressin- (AVP-) deficient homozygous Brattleboro and normal Wistar rats were studied. In the Wistar rats, water deprivation caused an increase in the TPH activity in the anterior and middle (infundibular) parts of the hypothalamus, while hydration did not affect the activity of the enzyme in the anterior hypothalamus but produced an increase in its middle part. In contrast, in the Brattleboro rats, water deprivation had no effect on TPH activity in the anterior and middle parts of the hypothalamus but hydration produced a decrease in TPH activity in the anterior hypothalamus. After 48 h of water deprivation, the plasma corticosterone concentration significantly increased in water-deprived and decreased in hydrated Wistar rats. Under water deprivation, the rise in corticosterone concentration in the homozygous Brattleboro rats was significantly greater than that in the Wistar rats. The data provide evidence that the CRH-like activity of AVP is not necessary for activation of the hypothalamic-pituitary-adrenal system induced by water deprivation. The observations show that AVP is involved in the activation of TPH induced by water deprivation. This suggests that AVP modulates the metabolism of 5-HT and the response of the 5-HT-ergic system to water deprivation.
Rats selected by predisposition to catalepsy showed decreased level of 2A-serotonin receptor mRNA in the frontal cortex in comparison with Wistar rats (p<0.05). Chronic administration of tricyclic antidepressant imipramine hydrochloride 2-fold increased the content of receptor mRNA in genetically cataleptic rats (p<0.001) and did not change this parameter in Wistar rats. These results prompted us to revise current notion on the mechanisms of chronic effect of imipramine on 2A-serotonin receptors.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.