[The noradrenaline content and the alpha 2-adrenoreceptor count in the brain of brown rats selected for the absence of aggressive behavior in relation to man]

Artificial selection of gray rats by the domestic type of behaviour resulted in an increase of the noradrenaline content, but in a decrease of the alpha 2-adrenergic receptors number in the hypothalamus. The data suggest a significant difference in noradrenergic system between domesticated and aggressive animals associated with changes in aggressive behaviour towards man during selection.

Double insertion of homogeneously staining regions in chromosome 1 of wild Mus musculus musculus: effects on chromosome pairing and recombination

An examination of the meiotic pattern of chromosome 1 isolated from a feral mouse population and containing a double insertion (Is) of homogeneously staining regions (HSRs) was carried out. The region delineated by the proximal breakpoint of Is(HSR;1C5) 1Icg and the distal breakpoint of Is(HSR;1E3)2Icg is desynapsed during the early pachytene stage and heterosynapsed at the midpachytene, as shown by electron microscopic analysis of synaptonemal complexes. The HSRs have no effect on the segregation of chromosome 1 in heterozygous mice. The lack of homosynapsis in the region under study causes chiasmata redistribution in heteromorphic bivalents. In normal males, single chiasmata are located in the medial part of the chromosome. In heterozygotes, this segment is heterosynapsed and unavailable for recombination. This leads to a significant decrease in the frequency of bivalents bearing single chiasmata. The total number of chiasmata per bivalent is much higher in heterozygous males than in normal ones. The recombination frequency between proximal markers fz and In also is higher in heterozygous animals. The increase in the total chiasma number in the heteromorphic bivalent is due to the addition of double chiasmata located mostly at precentromeric and pretelomeric regions of the chromosome.

Behavior, adrenocortical activity, and brain monoamines in Norway rats selected for reduced aggressiveness towards man

Wild Norway rats were selected over 20 generations for reduced aggressiveness towards man. Selection for this characteristic was accompanied by many physiological changes. Although neophobia was significantly inhibited, and irritable aggression reduced by selection, no changes were revealed in mouse-killing behavior or in intermale aggression. The mean level of 5-hydroxyindole acetic acid in the hypothalamus as well as serotonin (5-HT) content in the hypothalamus, the midbrain and the cortices was higher in the 'domesticated' than in aggressive rats. Mean hypothalamic norepinephrine (NE) level also tended to be higher in the 'domesticated' animals. The resting corticosterone level and the response of the hypothalamic-pituitary-adrenocortical axis to an emotional stressor or intracerebroventricularly administered 5-HT or NE were decreased in domesticated rats compared to their aggressive counterparts. It is suggested that the diminution of the hypothalamic-pituitary-adrenocortical function as a result of selection for domesticated types of behavior depends, at least partly, on changes in brain monoaminergic systems.

Involvement of brain serotonin in regulation of sexual maturity in male rats

We have studied the effect of a reduction in the serotonin level at different times in the prepubertal period on the neuroendocrine and morphometric characteristics of sexual maturation of male rats. We established that injection of p-chlorophenylalanine, a blocker of serotonin synthesis, into male rats on the 30th and 34th day of life leads to activation of the endocrine function of the testes in 60-day-old animals. Injection of the preparation at later times, 40th and 44th day, produced a marked inhibiting effect on sexual maturation, expressed as inhibition of both the spermatogenic and the endocrine function of the testes of the animals investigated. The data obtained allow an assessment of the dual role of serotonin in the regulation of the rate of sexual maturation of male rats at different prepubertal periods.

[Role of brain serotonin in the regulation of sexual maturation in male rats]

The effect of decrease of the brain serotonin level in different periods of prepubertal development on sexual maturation of male rats, was studied. Injections of p-CPA on the 30th and 34th days of life activated the endocrine function of testis in 60-day old animals. Injections of p-CPA later in life, on the 40th and 44th days, delayed sexual maturation as revealed by a decrease of spermatogenesis and endocrine function of testis. The data obtained suggest that serotonin has a dual role in regulation of the rate of sexual maturation in different periods of prepubertal age.

Assignment of the gene for adenine phosphoribosyltransferase on the genetic map of mouse chromosome 8

Two electrophoretic variants of adenine phosphoribosyltransferase (APRT) were identified in a population of wild mice (Mus musculus bactrianus). Breeding tests demonstrated that the APRT variants are under the control of two alleles at an autosomal locus designated Aprt. We have examined the linkage relationships between Aprt and the markers of chromosome 8 including esterase-1 and the centromere. The recombination distance between the centromere and Aprt is 44 +/- 7 cM, and that between Es-1 and Aprt is 25 +/- 2 cM, i.e., the probable order of the markers examined is cen-Es-1-Aprt on chromosome 8.

[Rate of sexual maturation of tame and aggressive gray rats]

The sexual maturation of female and male rats selected for domestic behaviour, occur much earlier than in aggressive animals as revealed by an earlier vagina opening in females and start of spermiogenesis in males. Hormonal activity of ovaries and testicles is also more obvious in the prepubertal period in domesticated male and female rats.

[Effect of selection for behavior on the seasonal characteristics of the reproductive function in brown rats]

Artificial selection of grey rats by the domestic type of behaviour resulted in the decrease of the dependence of reproductive function on the effect of photoperiod. Domesticated animals exhibited a significantly lower decrease of the intensity of reproduction in autumn and winter as compared to aggressive ones. One of the causes of this difference is probably the observed shift in the seasonal changes in the level of sex steroids in the blood.

[Change in certain forms of aggressive behavior and the concentration of monoamines in the brain during selection of wild rats for taming]

Norway rats have been selected during 20 generations by the absence of aggressive reaction to man (tamed rats). From 7 up to 20th generations of selection, different forms of aggressive behaviour (reaction to glove, intermale, shock-induced aggression and predatory aggression) were studied, and the level of noradrenaline, serotonin and its metabolite 5-hydroxyindoleacetic acid was determined in the brain. In the absence of aggressive reaction to glove in tamed rats, the shock-induced aggression considerably decreased while the predatory aggressiveness (mouse-killing behaviour) and intermale aggressiveness did not change. Beginning from 15-16th generation of selection, a higher level of the 5-hydroxyindoleacetic acid in the hypothalamus was established, in the 20th generation an increased content of serotonin was revealed in the hypothalamus and the midbrain. In some generations of selection an increased level of noradrenaline in the hypothalamus in comparison to wild rats was observed. A conclusion is made that the selection of animals by taming unequally influences different kinds of aggressiveness and is accompanied by inherited consolidated reorganization of the monoamine brain systems.

[Role of the brain neurochemical systems in altering the reactivity of the hypophyseal-adrenal system in the gray rat selected for behavior]

Studies have been made of the interrelationship between brain monoaminergic system and pituitary-adrenal function in two groups of the grey rat Rattus norvegicus Berk. One group consisted of non-aggressive rats selected for lack of agonism towards experimentator, the other one included aggressive animals. Domesticated animals exhibited the decreased reaction of the pituitary-adrenocortical complex to emotional stress as well as the decreased response of the endocrine system during stimulation of noradrenaline or serotonin mechanisms of the brain. In addition, noradrenaline and serotonin content of the brain decreased in domesticated rats during emotional stress to a lower extent, as compared to that in aggressive ones. Therefore, one of the sources of correlational changes in the activity of the pituitary-adrenocortical complex during selection for domesticated behaviour is the effect of selection on neurochemical, in particular monoaminergic systems of the brain.

[Genetic problems of stress. V. The genetics of adrenal cortical reactivity in emotional stress in rats]

Genetic analysis of adrenocortical reactivity (the level of plasma corticosterone and secretion of the adrenal gland in vitro) was carried out under conditions of emotional stress in three inbred strains of rats (Wistar, August, Sprague-Dawley) and in their F1 reciprocal hybrids. The basal adrenocortical function was similar in genotypes studied. However, significant genotype-dependent variability was demonstrated under conditions of stress stimulation. The variability of adrenal secretion in vitro was mediated by genes displaying an additive action, while variability in the level of plasma corticosterone included components both of general combining ability and of specific combining ability. Also, the role of a reciprocal effect was noted. The peculiarities of genetic determination of adrenocortical reactivity to emotional stress are discussed.

Inheritance of alternative states of the fused gene in mice

The genetics of the fused (Fu) gene in the house mouse, Mus musculus, was studied by use of the closely linked recessive marker, tufted (tf). Evidence was obtained indicating that Fu passes from a phenotypically active state to inactive: Fu in equilibrium with [Fu]. These alternative states may be genetically transmitted. It is suggested that the activation of a "dormant" Fu gene may underlie this passage.