Genetic analysis of schedule induced polydipsia

The relationship between adjunctive drinking, blood ethanol concentration and plasma corticosterone across fixed-time intervals of food delivery in two inbred mouse strains

Schedules of intermittent food delivery induce excessive fluid intake, termed schedule-induced polydipsia (SIP), and hypothalamic-pituitary-adrenal (HPA) axis activation is important for the expression and maintenance of this adjunctive behavior. Previous work has focused on examining the relationship between water intake and plasma corticosterone (CORT) in rats at a single or a limited range of fixed time (FT) intervals. However, little remains known regarding SIP and the corresponding stress response (1) across the bitonic function that epitomizes adjunctive behavior, (2) when ethanol is the available fluid, and (3) when a species other than rat or multiple strains are studied. Here we report the findings from ethanol-preferring C57BL/6J (B6) and non-preferring DBA/2J (D2) mice serially exposed to progressively larger FT intervals (0 → 60 min) and given access to either water or a 5% (v/v) ethanol solution. Following 2 weeks of experience with each schedule, blood samples were collected at the conclusion of the last 60-min session to evaluate CORT and the blood ethanol concentration (BEC) achieved. While both strains exhibited a bitonic function of ethanol intake and BEC that peaked at or near a 5-min interval, only D2 mice showed a similar response with water. In contrast, CORT levels rose monotonically with incremental increases in the FT interval regardless of the strain examined or fluid type offered, indicating that glucocorticoid release likely reflects the aversive aspects of increasing intervals between reinforcement rather than engagement in adjunctive behavior. These findings also caution against the use of a single intensity stressor to evaluate the relationship between stress and ethanol intake, as the magnitude of stress appears to affect ethanol consumption in a non-linear fashion.

Schedule-induced ethanol self-administration in DBA/2J and C57BL/6J mice

BACKGROUND

The purpose of these experiments was to provide an initial investigation into ethanol self-administration elicited in the schedule-induced polydipsia (SIP) paradigm.

METHODS

Mature male mice were food deprived to between 80 and 85% of their baseline weight and received 20 daily 1 hr SIP test sessions in which a food pellet (20 mg) was delivered on a fixed-time 60 sec schedule. In different groups, the acquisition of drinking 5% (v/v) ethanol solution (experiment 1) or water (experiment 2) was recorded along with other behaviors that occurred in the test chambers.

RESULTS

Results indicated that C57BL/6J mice drank significantly more ethanol than DBA/2J mice and that C57 mice achieved blood alcohol concentrations as high as 300 mg/dl. Blood alcohol concentrations were consistently correlated with g/kg ethanol intake. The groups did not differ in consumption of water. SIP test sessions using higher concentrations of ethanol (10-20% v/v, experiment 1) or sucrose solutions (0.1-2% w/v, experiment 2) then were performed. Group differences in ethanol consumption were maintained at all ethanol concentrations. Although DBAs drank more of a low concentration of sucrose (0.1%), when expressed as g/kg, sucrose intake was equivalent in the two strains at all concentrations. Analysis of the time course of drinking clearly showed that this behavior was adjunctive in nature.

CONCLUSION

These results demonstrate the effectiveness of this procedure in inducing ethanol self-administration and its utility for investigating the genetic bases of vulnerability toward excessive ethanol consumption.

Indication of a genetic basis of stereotypies in laboratory-bred bank voles (Clethrionomys glareolus)

The development of stereotypies was studied in two successive laboratory-bred generations of bank voles representing F1 (n=248) and F2 (n=270) of an originally wild caught stock. It was shown that the propensity to develop stereotypies under barren housing conditions strongly relates to the same propensity of the parents. Stereotypies were approximately seven times more frequent in the offspring of stereotyping parents than in the offspring of permanent non-stereotypers. This held true even when only one of the parents was stereotyper. The paternal and maternal contributions to stereotypies in the offspring appeared to be equal. Males showing stereotypies but prevented from any physical contact with the offspring were as potent as stereotyping females in producing stereotyping offspring. Moreover, the specific type of stereotypy appearing in the offspring after isolation was very much related to the type of stereotypy developed in the mothers. We found no support for the possible importance of social facilitation from littermates, in that the development of stereotypies was independent of the length of time the voles were kept socially with littermates before isolation. We suggest that the possible genetic basis of individual differences in the propensity to develop stereotypies in captivity may result from differences in genetic predispositions and their interactions with discrete frustrating stimuli early in life and/or to genetically different predispositions to cope with frustrating experiences later in life.

Dietary control of pathogenesis in C57BL/KsJ db/db diabetes mice

Weanling C57BL/KsJ homozygous diabetic (db/db) and normal littermate (+/+ or +/db) mice were maintained for 5 mon on isocaloric diets containing either 60% sucrose, 23% casein, 8% corn oil (diet C) or 0% sucrose, 83% casein, 8% corn oil (diet B). Diabetic homozygotes consumed more diet C than normals, but ate control amounts of diet B. Diabetic mice fed diet C exhibited 57% mortality between 4 or 5 mo of age. All diabetic mutants fed the carbohydrate-free diet B appeared healthy at 6 mo of age; mutant females were normoglycemic and mutant males were only moderately hyperglycemic. Histological examination of pancreatic islets confirmed the absence of islet degeneration. In diet B maintained mutants, increased carcass fat composition, plasma and pancreatic content of insulin and glucagon, and thymidine incorporation into islets, all established that the db gene was being fully expressed. These results indicate that dietary protein stimulates islet growth and function in db/db mice, while high levels of refined carbohydrate in the diet predispose islet beta cells to undefined changes that culminate in necrosis. Restricting mutants' intake of a carbohydrate-containing diet to one-half the caloric intake of normal mice failed to block onset of beta cell necrosis. Thus, dietary composition rather than total caloric intake appears to be critical in the induction of islet necrosis and atrophy in this animal model of genetically transmitted diabetes.

Genetics in the analysis of behaviour

Behaviour genetics has developed rapidly in the last two decades and has now gone far beyond the stage of merely measuring the extent to which individual differences on a particular behaviour can be attributed to genetic factors. This paper discusses the uses to which genetics can be put in efficient experimental design, in determining the generality of results and, most importantly, in the simultaneous analysis of several behaviours and their relationship to each other and to physical and biochemical parameters. Because the principles of genetics apply to all organisms, the first animal discussed is Drosophila, the vinegar fly, which is a vital tool in genetics but which has met with scant attention among psychologists. Drosophila has some unique advantages such as the sex mosaic technique for studying sexual behaviour, but most of the discussion concerns learning and the extent to which parallels can be found between Drosophila and the vertebrates, both in terms of process and of genetic control. It is demonstrated how strain differences and the response to artificial selection can distinguish between learning and other components of behaviour. Drosophila are also used to explain how the type of genetic control can suggest the way in which natural selection acts upon the particular behaviour and further examples from rodents are discussed to show that this is a general result across species. There are many inbred strains and selection lines of mice and rats and examples from a wide range of behaviours illustrate the advantages of using such stocks. The concept of the 'behavioural phenotype' is explained, where genetic differences on a wide range of behaviours are considered, rather than just focusing on one behaviour or one response to a particular drug or environmental treatment. Many different aspects of open-field behaviour, learning and mother-infant interaction are used as examples of this concept. The extent of genotype-environmental interaction is considered, since the possibility that each genotype will have a unique response to a brief discussion of human behaviour genetics, since here again the concern is not just with the trivial question of measuring 'heritability', but rather with how such information can be used to understand behaviour. The final suggestion is that psychology may gain by having more contact not only with geneticists, but also with the ecologists concerned with the significance of behavioural differences in the wild.

Concurrent drinking by pigeons on fixed-interval reinforcement schedules

Three experienced pigeons were exposed to at least ten consecutive 100-min sessions on each of three food-reinforced fixed-interval (FI) schedules: FI 50-sec, FI 100-sec and FI 200-sec. Water was freely available. Drinking was largely confined to the first third of each fixed interval, and the mean sessional water intake was directly related to the food-reinforcement rate for each animal. The animals drank very quickly, i.e., 3--4 ml/sec, but the drinking bouts were brief, i.e., 0.8--1.4 sec, and infrequent, i.e., 2--5/hr. The parameters describing concurrent drinking in the pigeon are strikingly different from those describing rats' drinking under similar reinforcement schedules, which may contribute to the difficulty in demonstrating schedule-induced polydipsia in the pigeon.